U.S. patent application number 13/470287 was filed with the patent office on 2012-12-20 for solid group iiia particles formed via quenching.
This patent application is currently assigned to NANOSOLAR, INC.. Invention is credited to Chris Eberspacher, Matthew R. Robinson, Jeroen K. J. Van Duren.
Application Number | 20120322197 13/470287 |
Document ID | / |
Family ID | 38832801 |
Filed Date | 2012-12-20 |
United States Patent
Application |
20120322197 |
Kind Code |
A1 |
Robinson; Matthew R. ; et
al. |
December 20, 2012 |
Solid Group IIIA Particles Formed Via Quenching
Abstract
Methods and devices are provided for forming thin-films from
solid group IIIA-based particles. In one embodiment, a process for
forming solid particles is provided. The method includes providing
a first suspension of solid and/or liquid particles containing at
least one group IIIA element. A material may be added to
substantially increase the melting point of at least one set of
group IIIA-containing particles in the suspension into
higher-melting solid particles comprising an alloy of the group
IIIA element and at least a part of the added material. The
suspension may be deposited onto a substrate to form a precursor
layer on the substrate and the precursor layer is reacted in a
suitable atmosphere to form a film.
Inventors: |
Robinson; Matthew R.; (East
Palo Alto, CA) ; Eberspacher; Chris; (Palo Alto,
CA) ; Van Duren; Jeroen K. J.; (Menlo Park,
CA) |
Assignee: |
NANOSOLAR, INC.
San Jose
CA
|
Family ID: |
38832801 |
Appl. No.: |
13/470287 |
Filed: |
May 12, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11762058 |
Jun 12, 2007 |
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13470287 |
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60804565 |
Jun 12, 2006 |
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60804566 |
Jun 12, 2006 |
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60804567 |
Jun 12, 2006 |
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60804569 |
Jun 12, 2006 |
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60804649 |
Jun 13, 2006 |
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60804647 |
Jun 13, 2006 |
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Current U.S.
Class: |
438/95 ;
257/E31.004 |
Current CPC
Class: |
H01L 31/0322 20130101;
Y02E 10/541 20130101 |
Class at
Publication: |
438/95 ;
257/E31.004 |
International
Class: |
H01L 31/0264 20060101
H01L031/0264 |
Claims
1. A process comprising: providing a first suspension of liquid
particles containing at least one group III element; adding a
liquid group IA material to the first suspension to solidify a
binary alloy of group IIIA and IA material out of at least part of
an original material in the first suspension to form nanoparticles
of group IA-IIIA of a size smaller than the liquid particles of
group IIIA element in the first suspension; depositing the
suspension of solid group IA-IIIA nanoparticles with group IB and
IIIA material onto a substrate to form a precursor layer on the
substrate; and reacting the precursor layer in a suitable
atmosphere to form a film.
2. The process of claim 1 wherein the alloy has a higher melting
temperature than a melting temperature of the IIIA element.
3. The process of claim 1 wherein the solid and/or liquid particles
contain at least one element from the group consisting of: group
IB, IIIA, VIA element, alloys containing any of the foregoing
elements, or combinations.
4. The process of claim 1 further comprising providing a second
suspension of solid and/or liquid particles containing at least one
element from the group consisting of: group IB, IIIA, VIA element,
alloys containing any of the foregoing elements, or
combinations
5. The process of claim 1 wherein adding the material creates solid
particles of the material and the group IIIA element.
6. The process of claim 1 further comprising separately preparing
the first suspension before mixing it with a second suspension.
7. The process of claim 1 further comprising separately preparing a
IIIA-alloy-solid-particles-based suspension before mixing it with
other IB and/or IIIA and/or VIA elements.
8. The process of claim 1 comprising separate emulsion/suspension
creation step before adding it to a mixed final suspension and
depositing the suspension onto a substrate to form a precursor
layer on the substrate.
9. The process of claim 1 wherein at least one set of the solid
particles are group IIIA-Na alloy containing particles, wherein Na
in the group IIIA-Na alloy containing particles is at an amount
sufficient so that no liquid phase of a group IIIA-Na alloy is
present within the group IIIA-Na alloy containing particles in a
temperature range between room temperature and a process
temperature higher than room temperature, wherein the group IIIA
based material is otherwise liquid in that temperature range.
10. The process of claim 1 wherein at least one set of the solid
particles are group IIIA-Na alloy containing particles, wherein Na
in the group IIIA-Na alloy containing particles is at an amount
sufficient so that no liquid phase of a group MA-Na alloy is
present within the group IIIA-Na alloy containing particles in a
temperature range between about 15 C and about 500 C, wherein the
group IIIA-based material is otherwise liquid in that temperature
range.
11. The process of claim 1 wherein at least one set of the solid
particles are group IIIA-Na alloy containing particles, wherein Na
in the group IIIA-Na alloy containing particles is at an amount
sufficient so that no liquid phase of a group IIIA-Na alloy is
present within the group IIIA-Na alloy containing particles at a
deposition and/or dispersion temperature.
12. The process of claim 1 wherein depositing comprises solution
depositing the suspension.
13. The process of claim 1 wherein the material comprises elemental
sodium.
14. The process of claim 1 wherein the material comprises a
sodium-based material.
15. The process of claim 1 wherein the material comprises a
sodium-based material.
16. The process of claim 1 wherein the adding step comprises adding
an emulsion of the material to an emulsion containing a liquid
group IIIA element to create the solid particles.
17. The process of claim 1 wherein the adding step comprises adding
an emulsion of the material to dispersion of solid group IIIA
element to create the solid particles.
18. The process of claim 1 wherein the adding step comprises adding
a dispersion of solid particles of the material to an emulsion
containing a liquid group IIIA element to create the solid
particles.
19. The process of claim 1 wherein the adding step comprises adding
a dispersion of solid particles of the material to a dispersion of
solid particle containing a group IIIA element for a solid-solid
reaction to create solid particles.
20. The process of claim 1 further comprising milling the material
and the one set of group IIIA-containing liquid particles in the
suspension to more thoroughly mix solids with the liquid.
21. The process of claim 1 further comprising mechanically alloying
the material and the one set of group IIIA-containing particles in
the suspension to more thoroughly mix solids.
22. The process of claim 1 wherein adding the material creates
particles of sizes smaller than the size of the group
IIIA-containing particles found in the suspension prior to
introduction of the material.
23. The process of claim 1 further comprising agitating the
suspension to mix and size reduce the particles.
24. The process of claim 1 further comprising sonicating the
suspension to mix and size reduce the particles.
25. The process of claim 1 further comprising using electromagnetic
size-reduction/control to mix and size reduce the particles.
26. The process of claim 1 further comprising adding any sodium
containing particles during emulsification to solidify droplets of
Ga to form solid Ga--Na particles.
27. The process of claim 1 further comprising adding sodium in
elemental form prior to, during, or after emulsification to
solidify droplets of Ga to form solid Ga--Na particles.
28. The process of claim 1 further comprising adding liquid sodium
in elemental form prior to, during, or after emulsification to
solidify droplets of Ga to form solid Ga--Na particles.
29. The process of claim 1 further comprising combining a sodium
emulsion with a gallium emulsion to solidify droplets of Ga to form
solid Ga--Na particles.
30. The process of claim 1 further comprising combining a sodium
emulsion with a gallium emulsion by milling to solidify droplets of
Ga to form solid Ga--Na particles.
31. The process of claim 1 further comprising combining a sodium
emulsion with a solid gallium particles by mechanical alloying at
temperatures below the melting point of gallium to form solid.
Ga--Na particles.
32. The process of claim 1 further comprising combining a sodium
dispersion with a gallium dispersion by mechanical alloying to
solidify droplets of Ga to form solid Ga--Na particles.
33. The process of claim 1 wherein the film includes a group
IB-IIIA-VIA compound.
34. The process of claim 1 wherein reacting comprises heating the
layer in a suitable atmosphere.
35. The process of claim 1 wherein at least one set of the
particles in the suspension is in the form of nanoglobules.
36. The process of claim 1 wherein at least one set of the
particles in the suspension are in the form of nanoglobules and
contain at least one group IIIA element.
37. The process of claim 1 wherein at least one set of the
particles in the suspension is in the form of nanoglobules
comprising of a group IIIA element in elemental form.
38. The process of claim 1 wherein at least some of the particles
have a platelet shape.
39. The process of claim 1 wherein a majority of the particles have
a platelet shape.
40. The process of claim 1 wherein all of the particles have a
platelet shape.
41. The process of claim 1 wherein the depositing step comprises
coating the substrate with the suspension.
42. The process of claim 1 wherein the suspension comprises an
emulsion.
43. The process of claim 1 wherein gallium is incorporated as a
group IIIA element in the form of a suspension of nanoglobules.
44. The process of claim 43 wherein nanoglobules of gallium are
formed by creating an emulsion of liquid gallium in a solution.
45. The process of claim 43 further comprising maintaining or
enhancing a suspension of liquid gallium in solution by stirring,
mechanical means, electromagnetic means, ultrasonic means, and/or
the addition of dispersants and/or emulsifiers.
46. The process of claim 1 further comprising adding a mixture of
one or more elemental particles selected from: aluminum, tellurium,
or sulfur.
47. The process of claim 1 wherein the suitable atmosphere contains
at least one of the following: selenium, sulfur, tellurium,
H.sub.2, CO, H.sub.2Se, H.sub.2S, Ar, N.sub.2 or combinations or
mixture thereof.
48. The process of claim 1 wherein one or more classes of the
particles are doped with one or more inorganic materials.
49. The process of claim 1, wherein one or more classes of the
particles are doped with one or more inorganic materials chosen
from the group consisting of: aluminum (Al), sulfur (S), sodium
(Na), potassium (K), lithium (Li), alloys containing the foregoing
elements, or combinations thereof.
50. The process of claim 1 wherein the particles are
nanoparticles.
51. The process of claim 1 further comprising forming the particles
from a feedstock by one of the following processes: milling,
electroexplosive wire (EEW) processing, evaporation condensation
(EC), pulsed plasma processing, or combinations thereof.
52. The process of claim 1 wherein the material does negatively
impact the resulting absorber layer and does not need to be removed
from the resulting absorber layer.
53. The process of claim 1 wherein the material comprises Al to
make solid Al--Ga particles.
54. The process of claim 1 wherein the material comprises Al;
wherein Ga dissolves in Al to make solid Al--Ga particles for use
in forming a film of CAGS and/or CAIGS.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/762,058 filed Jun. 12, 2007, which claims
the benefit of priority to U.S. Provisional Applications No.
60/804,565 filed Jun. 12, 2006, No. 60/804,566 filed Jun. 12, 2006,
No. 60/804,567 filed Jun. 12, 2006, No. 60/804,569 filed Jun. 12,
2006, No. 60/804,649 filed Jun. 13, 2006 and No. 60/804,647 filed
Jun. 13, 2006, all fully incorporated herein by reference for all
purposes.
FIELD OF THE INVENTION
[0002] This invention relates generally to semiconductor films, and
more specifically, to semiconductor films containing a group
IB-IIIA-VIA compound and formed in part from solid group IIIA-based
materials.
BACKGROUND OF THE INVENTION
[0003] Solar cells and solar modules convert sunlight into
electricity. These electronic devices have been traditionally
fabricated using silicon (Si) as a light-absorbing, semiconducting
material in a relatively expensive production process. To make
solar cells more economically viable, solar cell device
architectures have been developed that can inexpensively make use
of thin-film, light-absorbing semiconductor materials such as
copper-indium-gallium-sulfo-diselenide, Cu(In, Ga)(S, Se).sub.2,
also termed CI(G)S(S). This class of solar cells typically has a
p-type absorber layer sandwiched between a back electrode layer and
an n-type junction partner layer. The back electrode layer is often
Mo, while the junction partner is often CdS. A transparent
conductive oxide (TCO) such as zinc oxide (ZnO.sub.x) doped with
aluminum is formed on the junction partner layer and is typically
used as a transparent electrode. CIS-based solar cells have been
demonstrated to have power conversion efficiencies exceeding
19%.
[0004] A central challenge in cost-effectively constructing a
large-area copper-indium-gallium-di-selenide (CIGS) based solar
cell or module is that the elements of the CIGS layer must be
within a narrow stoichiometric ratio on nano-, meso-, and
macroscopic length scale in all three dimensions in order for the
resulting cell or module to be highly efficient. Achieving precise
stoichiometric composition over relatively large substrate areas
is, however, difficult using traditional vacuum-based deposition
processes. For example, it is difficult to deposit compounds and/or
alloys containing more than one element by sputtering or
evaporation. Both techniques rely on deposition approaches that are
limited to line-of-sight and limited-area sources, tending to
result in poor surface coverage. Line-of-sight trajectories and
limited-area sources can result in non-uniform three-dimensional
distribution of the elements in all three dimensions and/or poor
film-thickness uniformity over large areas. These non-uniformities
can occur over the nano-, meso-, and/or macroscopic scales. Such
non-uniformity also alters the local stoichiometric ratios of the
absorber layer, decreasing the potential power conversion
efficiency of the complete cell or module.
[0005] Alternatives to traditional vacuum-based deposition
techniques have been developed. In particular, production of solar
cells on flexible substrates using non-vacuum, semiconductor
printing technologies provides a highly cost-efficient alternative
to conventional vacuum-deposited solar cells. For example, T. Arita
and coworkers [20th IEEE PV Specialists Conference, 1988, page
1650] described a non-vacuum, screen printing technique that
involved mixing and milling pure Cu, In and Se powders in the
compositional ratio of 1:1:2 and forming a screen printable paste,
screen printing the paste on a substrate, and sintering this film
to form the compound layer. They reported that although they had
started with elemental Cu, In and Se powders, after the milling
step the paste contained the Cu--In--Se.sub.2 phase. However, solar
cells fabricated from the sintered layers had very low efficiencies
because the structural and electronic quality of these absorbers
was poor.
[0006] Screen-printed Cu--In--Se.sub.2 deposited in a thin-film was
also reported by A. Vervaet et al. [9th European Communities PV
Solar Energy Conference, 1989, page 480], where a micron-sized
Cu--In--Se.sub.2 powder was used along with micron-sized Se powder
to prepare a screen printable paste. Layers formed by non-vacuum,
screen printing were sintered at high temperature. A difficulty in
this approach was finding an appropriate fluxing agent for dense
Cu--In--Se.sub.2 film formation. Even though solar cells made in
this manner had poor conversion efficiencies, the use of printing
and other non-vacuum techniques to create solar cells remains
promising.
[0007] It should be understood that some precursor materials used
in non-vacuum manufacturing of thin-films suitable for
semiconductor devices may be in liquid form, with these precursor
materials serving as source material for the thin-film, whereas
most other precursor materials in the ink are in solid form and
desirably so, this in contrast to materials added to the ink to
allow for reliable, fast and uniform deposition, like solvents and
organic additives. These solvents and organic additives are
typically unwanted in the final thin-film and require facile
removal during or after the deposition process. Unfortunately,
sometimes these preferably solid components can become liquid at
the handling and/or particle size reduction temperatures typically
associated with non-vacuum techniques for solar cell production.
This may be a disadvantageous feature as premature and/or undesired
liquification or coalescence increases the difficulty in handling
these materials during processing, during ink storage, and may
require more involved techniques. For example, elemental gallium is
a liquid above 30.degree. C., which is very close to room
temperature and below the processing temperature associated with
deposition and/or ink preparation. It may also be disadvantageous
during processing since the liquid form may change the kinetics of
the conversion of the particulate layer to the final semiconductor
film. For example, if too much liquid is present at or near the
onset of a reaction, liquid may group together at certain areas and
not be evenly distributed throughout the reaction area. This can
result in thickness non-uniformity and/or lateral composition
non-uniformity. Furthermore, if material in liquid form leaches out
from an alloy or compound containing that material, this may change
the local stoichiometry at the start of the reaction resulting in
different compound(s) in the final thin-film if the leaching occurs
prior to or during processing of the materials.
[0008] For example for the preferably solid components, liquid form
might be present and undesirable before/during the synthesis of the
particles. Such components in liquid form increases the difficulty
in controlling and maintaining the particle (droplet) size during
ink preparation and solution deposition. In one example, elemental
gallium used in thin-film solar cell production is a liquid above
30.degree. C., which is very close to room temperature and below
the processing temperature typically used during ink deposition.
Lowering the processing temperature far below the melting point of
gallium complicates the ink preparation and solution deposition.
Additionally, difficulty in controlling the particle (droplet) size
during deposition complicates controlling and maintaining the
target thickness uniformity of the resulting film on micro-, and
macroscopic length scales.
[0009] Additionally for the preferably solid components, liquid
might be present and undesirable when annealing the coatings of
ink. It may also be disadvantageous during single and/or multi-step
conversion of the solution-deposited coating or layer into the
resulting semiconductor film since the premature presence of liquid
may change the kinetics of the reactions involved and therefore the
quality and uniformity of the semiconductor film. For example, if
too much liquid is present at or near the onset of a reaction,
liquid may dewet from the surface and ball up resulting in a
non-uniform material distribution throughout the layer, both in
thickness and composition.
[0010] Due to the aforementioned issues, there are significant
opportunities for improving non-vacuum CIGS manufacturing
processes. Improvements may be made to increase the throughput of
existing CIGS manufacturing process and decrease the cost
associated with CIGS based solar devices. The decreased cost and
increased production throughput should increase market penetration
and commercial adoption of such products.
SUMMARY OF THE INVENTION
[0011] Embodiments of the present invention address at least some
of the drawbacks set forth above. The present invention provides
for the use of solid particles in the formation of high quality
precursor layers which are processed into dense films,
semiconductor films, and/or semiconductor dense films. The
resulting films may be useful in a variety of industries and
applications, including but not limited to, the manufacture of
photovoltaic devices and solar cells. More specifically, the
present invention has particular application in the formation of
precursor layers for thin film solar cells. The present invention
provides for more efficient and simplified creation of a
dispersion, and the resulting coating thereof. It should be
understood that this invention is generally applicable to any
processes involving the deposition of a material from dispersion.
At least some of these and other objectives described herein will
be met by various embodiments of the present invention.
[0012] In one embodiment of the present invention, a method is
described comprising of providing a first material comprising an
alloy of: a) a group IIIA-based material and b) at least one other
material. The material may be included in an amount sufficient so
that no liquid phase of the alloy is present within the first
material in a temperature range between room temperature and a
deposition or pre-deposition temperature higher than room
temperature, wherein the group IIIA-based material is otherwise
liquid in that temperature range. The other material may be a group
IA material. A precursor material may be formulated comprising: a)
particles of the first material and b) particles containing at
least one element from the group consisting of: group IB, IIIA, VIA
element, alloys containing any of the foregoing elements, or
combinations thereof. The temperature range described above may be
between about 20.degree. C. and about 200.degree. C. It should be
understood that the alloy may have a higher melting temperature
than a melting temperature of the IIIA-based material in elemental
form.
[0013] For any of the embodiments described herein, the following
may also apply. The group IA-based material may be a Na-based
material. The group IA-based material may be comprised of NaF. The
group IA-based material may contain an element chosen from the
group consisting of: sodium (Na), potassium (K), lithium (Li),
Rubidium (Rb), Cesium (Cs), Francium (Fr), an alloy containing any
of the foregoing, or combinations thereof. The group IA-based
material may be comprised of an elemental material. The group
IA-based material may be comprised of a binary alloy. The group
IA-based material may be comprised of a multinary alloy. The group
IIIA-based material of the first material may be Indium. The group
IIIA-based material of the first material may be Gallium. The alloy
may be a binary alloy and/or a multinary alloy. The alloy may be
comprised of a Ga--Na based alloy. The alloy may be Ga.sub.4Na
and/or Ga.sub.29Na.sub.32. Optionally, the alloy contains at least
about 0.6 weight percent Na. The alloy may contain at least about 8
weight percent Na. The alloy may contain at least about 11 weight
percent Na. The alloy may include an In--Na based alloy. The alloy
may be comprised of In.sub.8Na.sub.5. The precursor material may
contain particles comprised of Cu-based particles. The precursor
material may contain particles comprised of Cu-based alloy
particles. The precursor material may contain particles comprised
of Cu-IIIA based alloy particles. The precursor material may
contain particles comprised of Cu-VIA based alloy particles.
Optionally, the particles may be nanoparticles. The particles may
be spherical nanoparticles and/or non-spherical, planar flakes. The
alloy may be formed by at least one method selected from the group
consisting of: atomization, pyrometallurgy, mechanical alloying, or
combinations thereof.
[0014] In a still further embodiment of the present invention, a
composition is provided having a precursor material comprising of:
a) solid particles of a first material comprising an alloy of a
group IIIA-based material and at least one group IA-based material
and b) particles containing at least one element from the group
consisting of: group IB, IIIA, VIA element, alloys containing any
of the foregoing elements, or combinations thereof. The group
IA-based material is included in an amount sufficient so that no
liquid phase of the alloy is present within the first material in a
temperature range between room temperature and a deposition or
pre-deposition temperature higher than room temperature, wherein
the group IIIA-based material is otherwise liquid in that
temperature range. It should be understood that the group IA-based
material comprises of Na.
[0015] For any of the embodiments described herein, the following
may also apply. Optionally, the method may include formulating an
ink including the precursor material; solution depositing the ink
onto a substrate to form a precursor layer on the substrate; and
reacting the precursor layer in a suitable atmosphere to form a
group IB-IIIA based film. This may be a two step process where the
group IB-IIIA film may not include a group VIA material and is
further treated in a second step to form a group IB-IIIA-VIA
compound. The first film may be a dense film that includes a group
IB-IIIA compound. The method may comprise of heating the film in a
group VIA based atmosphere to form a group IB-IIIA-VIA compound
film. The film may comprise of a semiconductor film suitable for
use as an absorber layer in a photovoltaic device. The film may be
comprised of an absorber layer for a solar cell. The reacting step
may be comprised of heating the precursor layer. In other
embodiments, the reacting step comprises of heating the precursor
layer in a group VIA-based atmosphere. Optionally, the suitable
atmosphere may contain at least one of the following: selenium,
sulfur, tellurium, H.sub.2, CO, H.sub.2Se, H.sub.2S, Ar, N.sub.2 or
combinations or mixtures thereof. The method may include adding a
mixture of one or more elemental or alloy particles containing at
least one element selected from the group consisting of: aluminum,
tellurium, or sulfur. One or more classes of the particles may be
doped with one or more inorganic materials. One or more classes of
the particles may be doped with one or more inorganic materials
chosen from the group consisting of: aluminum (Al) and sulfur (S).
One or more classes of the particles may be doped with one or more
inorganic materials chosen from the group consisting of: sodium
(Na), potassium (K), or lithium (Li). The alloy containing
particles may be a sole source of group IIIA elements in the ink.
In terms of composition, the film may have a Cu/(In+Ga)
compositional range of about 0.01 to about 1.0 and a Ga/(In+Ga)
compositional range of about 0.01 to about 1.0. The film may have a
Cu/(In +Ga) compositional range of about >1.0 for Cu/(In+Ga) and
a Ga/(In+Ga) compositional range of about 0.01 to about 1.0. The
film may have a Cu/(In+Ga) compositional range of about 0.01 to
about 1.0 and a Ga/(In+Ga) compositional range of about 0.01 to
about 1.0. Optionally, the film has a desired Cu/(In+Ga) molar
ratio is in the range of about 0.7 to about 1.0 and a desired
Ga/(Ga+In) molar ratio in the range of about 0.1 to about 0.8.
Optionally, there is the possibility of having a ratio of
Cu/(In+Ga)>1.0 and using subsequent post-treatment (KCN, etc.)
to change Cu/(In+Ga)<1.0.
[0016] For any of the embodiments described herein, the following
may also apply. In some embodiments, the ink includes a carrier
liquid. The depositing step may include using at least one of the
following techniques: wet coating, spray coating, spin coating,
doctor blade coating, contact printing, top feed reverse printing,
bottom feed reverse printing, nozzle feed reverse printing, gravure
printing, microgravure printing, reverse microgravure printing,
comma direct printing, roller coating, slot die coating, meyerbar
coating, lip direct coating, dual lip direct coating, capillary
coating, ink-jet printing, jet deposition, spray deposition, or
combinations thereof.
[0017] For any of the embodiments described herein, the following
may also apply. The material may increase the melting temperature
and does not contain contaminants that require further heating to
remove contaminants added by the material. The material may be
included in an amount sufficient so that no liquid phase of the
alloy is present within the first material in a temperature range
between room temperature and a deposition or pre-deposition
temperature higher than room temperature, wherein the material is
otherwise liquid in that temperature range and does not require
further heating to remove any materials added by the additive.
[0018] In yet another embodiment of the present invention, the
method includes providing a first material comprising an alloy of
a) a group IIIA-based material and b) a second material, wherein
the second material is included in an amount sufficient so that no
liquid phase of the alloy is present within the first material in a
temperature range between room temperature and a deposition or
pre-deposition temperature higher than room temperature, wherein
the group IIIA-based material is otherwise liquid in that
temperature range. A precursor material may be formulated
comprising of a) particles of the first material and b) particles
containing at least one element from the group consisting of: group
IB, IIIA, VIA element, alloys containing any of the foregoing
elements, or combinations thereof. The second material comprises of
F. Optionally, the second material comprises of NO.sub.3. The
second material comprises of any melting-point increasing material,
relative to a melting point of the group IIIA-based material. The
alloy may be comprised of GaF.sub.3. The alloy may also be
comprised of Ga(NO.sub.3).sub.3. The alloy may be comprised of a
group IIIA-based salt. The alloy may be comprised of an
organo-gallium compound. The method may include heating the
precursor material to form a layer without C, N, O, or F elements
in the layer. The second material may contain aluminum (Al) and/or
aluminum compounds. The second material may contain sulfur (S)
and/or sulfur compounds.
[0019] Alloys
[0020] In one embodiment of the present invention, a method is
provided for creating solid alloy particles. The method may include
providing a first material containing at least one alloy comprising
of: a) a group IIIA element, b) at least one group IB, IIIA, and/or
VIA element different from the group IIIA element of a), and c) a
group IA-based material. The group IA-based material may be
included in an amount sufficient so that no liquid phase of the
alloy is present in a temperature range between room temperature
and a deposition or pre-deposition temperature higher than room
temperature, wherein the group IIIA element is otherwise liquid in
that temperature range. The method may involve formulating a
precursor material comprising of: a) particles of the first
material and b) particles containing at least one element from one
of the following: a group IB element, a group IIIA element, a group
VIA element, alloys containing any of the foregoing elements, or
combinations thereof.
[0021] For any of the embodiments described herein, the following
may also apply. The temperature range where the alloy is solid may
be between about 20.degree. C. and about 200.degree. C. The alloy
may have a higher melting temperature than a melting temperature of
the group IIIA element of a). The precursor material may further
include a second material containing a group IB, IIIA, and/or VIA
based material. There may further include particles containing the
precursor material. The group IIIA element of the first material
may be indium. The group IIIA element of the first material may be
Ga. The group IA-based material may be at least partially included
in the particles. The group IA-based material may be comprised of
elemental sodium. The group IA-based material may be comprised of a
sodium-based compound. The group IA-based material may contain an
element chosen from the group consisting of sodium (Na), potassium
(K), lithium (Li), compounds containing any of the foregoing, or
combinations thereof. The alloy may be comprised of In--Ga--Na,
In--Ga--Se--Na, and/or Ga--Se--Na. Optionally, the alloy may be
comprised of one of the following: In--Se--Na, Cu--In--Na, or
Cu--Ga--Na. The alloy may be comprised of a sulfide. The alloy may
be comprised of Cu--In--Ga--Na. The precursor material contains
particles comprising of Cu-based particles. The precursor material
may contain particles comprising of Cu-based alloy particles. The
precursor material may contain particles comprising of Cu-IIIA
based alloy particles. The precursor material may contain particles
comprising of Cu-VIA based alloy particles. The particles may
include nanoparticles. Optionally, the particles may include
spherical nanoparticles. The particles include non-spherical,
planar flakes.
[0022] In one embodiment, the material may solidify substantially
all of the particle. Optionally, the alloy may solidify at least an
outer portion of the particles to prevent leaching or phase
separation of liquid group IIIA element from the particles. The
alloy may create a solid outer shell on the particles to prevent
leaching of liquid group IIIA element from the particles. The
particles may be formed by using at least one of the following
methods: grinding, milling, electroexplosive wire (EEW) processing,
evaporation condensation (EC), pulsed plasma processing, or
combinations thereof. The particles may be formed using at least
one of the following methods: sonification, agitation,
electromagnetically mixing of a liquid metal or liquid alloy. The
particles may be formed using at least one of the following
methods: spray-pyrolysis, laser pyrolysis, or a bottom-up technique
like wet chemical approaches.
[0023] For any of the embodiments described herein, the following
may also apply. The particles may be nanoparticles. The particles
may be spherical nanoparticles. Optionally, at least some of the
particles are non-spherical, planar flakes. The method may include
using the precursor material in a solution coatable ink for forming
a film on a substrate. The method may include formulating an ink
including the precursor material; solution depositing the ink onto
a substrate to form a precursor layer on the substrate; and
reacting the precursor layer in a suitable atmosphere to form a
group IB-IIIA-VIA based film. In other embodiments, the method may
include formulating an ink including the precursor material;
solution depositing the ink onto a substrate to form a precursor
layer on the substrate; and reacting the precursor layer in a
suitable atmosphere to form a IB-IIIA film. The film may include a
group IB-IIIA-VIA compound. The film may be a dense film that
includes a group IB-IIIA compound. The film may be heated in a
group VIA based atmosphere to form a group IB-IIIA-VIA compound
film. The film may be comprised of a semiconductor film suitable
for use in a photovoltaic device. The film may be comprised of an
absorber layer for a solar cell. The reacting step may be comprised
of heating the layer in the suitable atmosphere. The method may
include adding a mixture of one or more elemental particles
selected from: aluminum, tellurium, sulfur, copper, indium,
gallium, alloys containing any of the foregoing, and combinations
thereof. The suitable atmosphere may contain at least one of the
following: selenium, sulfur, tellurium, H2, CO, H2Se, H2S, Ar, N2
or combinations or mixtures thereof. Optionally, one or more
classes of the particles may be doped with one or more inorganic
materials. One or more classes of the particles may be doped with
one or more inorganic materials containing at least one element
from the group of aluminum (Al), sulfur (S), sodium (Na), potassium
(K), or lithium (Li).
[0024] For any of the embodiments described herein, the following
may also apply. Optionally, the alloy containing particles may be a
sole source of group IIIA elements in the ink. The film may have a
Cu/(In+Ga) compositional range of about 0.01 to about 1.0 and a
Ga/(In+Ga) compositional range of about 0.01 to about 1.0. The film
may have a Cu/(In+Ga) compositional range >1.0 and a Ga/(In+Ga)
compositional range of about 0.01 to about 1.0. The film may have a
desired Cu/(In+Ga) molar ratio is in the range of about 0.7 to
about 1.0 and a desired Ga/(Ga+In) molar ratio in the range of
about 0.1 to about 0.8. The ink may include a carrier liquid.
Depositing the material may be comprised of using at least one of
the following techniques: wet coating, spray coating, spin coating,
doctor blade coating, contact printing, top feed reverse printing,
bottom feed reverse printing, nozzle feed reverse printing, gravure
printing, microgravure printing, reverse microgravure printing,
comma direct printing, roller coating, slot die coating, meyerbar
coating, lip direct coating, dual lip direct coating, capillary
coating, ink jet printing, jet deposition, spray deposition, or
combinations thereof.
[0025] In yet another embodiment of the present invention, a
composition is provided that comprises of a precursor material
comprising of: a) solid particles of a first material and b)
particles containing at least one element from the group consisting
of: group IB, IIIA, VIA element, alloys containing any of the
foregoing elements, or combinations thereof. The first material may
contain at least one alloy comprised of: a) a group IIIA element,
b) at least one group IB, IIIA, and/or VIA element different from
the group IIIA element of a), and c) a group IA-based material. The
group IA-based material is included in an amount sufficient so that
no liquid phase of the alloy is present in a temperature range
between room temperature and a deposition or pre-deposition
temperature higher than room temperature, wherein the group IIIA
element is otherwise liquid in that temperature range. The group
IA-based material may be comprised of Na. The composition may
include any of features previously discussed in the foregoing
paragraphs.
[0026] In a still further embodiment of the present invention, a
method includes providing a first material containing at least one
alloy comprising: a) a group IIIA element, b) at least one group
IB, IIIA, and/or VIA element different from the group IIIA element
of a), and c) a second material. The second material is included in
an amount sufficient so that no liquid phase of the alloy is
present in a temperature range between room temperature and a
deposition or pre-deposition temperature higher than room
temperature, wherein the group IIIA element is otherwise liquid in
that temperature range. The method may include formulating a
precursor material comprising a) particles of the first material
and b) particles containing at least one element from the group
consisting of: group IB, IIIA, VIA element, alloys containing any
of the foregoing elements, or combinations thereof.
[0027] For any of the embodiments described herein, the following
may also apply. The second material may be comprised of F.
Optionally, the second material may be comprised of NO.sub.3. The
second material may include any melting-point increasing material
for increasing the melting point relative to a melting point of the
group IIIA-based material. The alloy may be comprised of GaF.sub.3
and/or Ga(NO.sub.3).sub.3. Optionally, the alloy may be comprised
of a group IIIA-based salt. The alloy may be comprised of an
organo-gallium compound. The precursor material may be heated to
form a layer without C, N, O, or F elements in the layer. The
second material may contain aluminum (Al) and/or aluminum
compounds. The second material may contain sulfur (S) and/or sulfur
compounds.
[0028] Quenching
[0029] In one embodiment of the present invention, a process for
forming solid particles is provided. The method includes providing
a first suspension of solid and/or liquid particles containing at
least one group IIIA element. A material may be added to
substantially increase the melting point of at least one set of
group IIIA-containing particles in the suspension into
higher-melting solid particles comprising an alloy of the group
IIIA element and at least a part of the added material. The
suspension may be deposited onto a substrate to form a precursor
layer on the substrate and the precursor layer is reacted in a
suitable atmosphere to form a film.
[0030] For any of the embodiments described herein, the following
may also apply. The alloy may have a higher melting temperature
than a melting temperature of the IIIA element. The solid and/or
liquid particles contain at least one element from the group
consisting of: group IB, IIIA, VIA element, alloys containing any
of the foregoing elements, or combinations. A second suspension may
be provided, wherein the second suspension includes solid and/or
liquid particles containing at least one element from the group
consisting of: group IB, IIIA, VIA element, alloys containing any
of the foregoing elements, or combinations. The material may be
added to create solid particles of the material and the group IIIA
element. The first suspension may be separately prepared before
mixing it with a second suspension. A
IIIA-alloy-solid-particles-based suspension may be separately
prepared before mixing it with the other IB and/or IIIA and/or VIA
elements. The method may involve separate emulsion/suspension
creation step before adding it to the mixed final suspension and
depositing the suspension onto a substrate to form a precursor
layer on the substrate. Optionally, at least one set of the solid
particles are group IIIA-Na alloy containing particles, wherein Na
in the group IIIA-Na alloy containing particles is at an amount
sufficient so that no liquid phase of a group IIIA-Na alloy is
present within the group IIIA-Na alloy containing particles in a
temperature range between room temperature and a deposition or
pre-deposition temperature higher than room temperature, wherein
the group IIIA-based material is otherwise liquid in that
temperature range. Optionally, at least one set of the solid
particles are group IIIA-Na alloy containing particles, wherein Na
in the group IIIA-Na alloy containing particles is at an amount
sufficient so that no liquid phase of a group IIIA-Na alloy is
present within the group IIIA-Na alloy containing particles in a
temperature range between about 15 C and about 200 C, wherein the
group IIIA-based material is otherwise liquid in that temperature
range. Optionally, at least one set of the solid particles are
group IIIA-Na alloy containing particles, wherein Na in the group
IIIA-Na alloy containing particles is at an amount sufficient so
that no liquid phase of a group IIIA-Na alloy is present within the
group IIIA-Na alloy containing particles at a deposition and/or
dispersion temperature. The suspension may be cooled to solidify
the particles. The depositing step may be comprised of solution
depositing the suspension.
[0031] For any of the embodiments described herein, the following
may also apply. The material may be comprised of elemental sodium
and/or a sodium-based material. The material may be comprised of
the aforementioned in liquid and/or solid form. The adding step may
be comprised of adding an emulsion of the material to an emulsion
containing a liquid group IIIA element to create the solid
particles. The adding step may be comprised of adding an emulsion
of the material to dispersion of solid group IIIA element to create
the solid particles. Optionally, the adding step comprises of
adding a dispersion of solid material particles of the material to
an emulsion containing a liquid group IIIA element to create the
solid particles. The adding step may be comprised of adding a
dispersion of solid material particles of the material to a
dispersion of solid particle containing a group IIIA element for a
solid-solid reaction to create solid particles. The method may
include milling the material and the one set of group
IIIA-containing liquid particles in the suspension to more
thoroughly mix solids with the liquid. Optionally, the method may
include mechanically alloying the material and the one set of group
IIIA-containing particles in the suspension to more thoroughly mix
solids. Adding the material may create particles of sizes smaller
than the size of the group IIIA-containing particles found in the
suspension prior to introduction of the material. The method may
include agitating the suspension to mix and size reduce the
particles. The suspension may be sonicated to mix and size reduce
the particles. Electromagnetic size-reduction/control may be used
to mix and size reduce the particles. Any sodium containing
particles may be added during emulsification to solidify droplets
of Ga to form solid Ga--Na particles. Sodium in elemental form may
be added prior to, during, or after emulsification to solidify
droplets of Ga to form solid Ga--Na particles. Liquid sodium may be
added in elemental form prior to, during, or after emulsification
to solidify droplets of Ga to form solid Ga--Na particles. A sodium
emulsion may be combined with a gallium emulsion to solidify
droplets of Ga to form solid Ga--Na particles. A sodium emulsion
may be combined with a gallium emulsion by milling to solidify
droplets of Ga to form solid Ga--Na particles. A sodium emulsion
may be combined with a solid gallium particles by mechanical
alloying at temperatures below the melting point of gallium to form
solid Ga--Na particles. A sodium dispersion may be combined with a
gallium dispersion by mechanical alloying to solidify droplets of
Ga to form solid Ga--Na particles. The film may include a group
IB-IIIA-VIA compound. The reacting step may be comprised of heating
the layer in a suitable atmosphere.
[0032] For any of the embodiments described herein, the following
may also apply. Optionally, at least one set of the particles in
the suspension is in the form of nanoglobules. In other
embodiments, at least one set of the particles in the suspension
are in the form of nanoglobules and contain at least one group IIIA
element. At least one set of the particles in the suspension may be
in the form of nanoglobules comprising of a group IIIA element in
elemental form. At least some of the particles may have a platelet
shape. Optionally, a majority of the particles may have a platelet
shape. All of the particles may have a platelet shape. The
particles may have a substantially flat, planar shape. A majority
of the particles may have a flat, planar shape. All of the
particles may have a flat, planar shape. The depositing step may
include coating the substrate with the suspension. The suspension
may be comprised of an emulsion. Gallium may be incorporated as a
group IIIA element in the form of a suspension of nanoglobules.
Nanoglobules of gallium may be formed by creating an emulsion of
liquid gallium in a solution. A suspension of liquid gallium in
solution may be maintained or enhanced by stirring, mechanical
means, electromagnetic means, ultrasonic means, and/or the addition
of dispersants and/or emulsifiers.
[0033] For any of the embodiments described herein, the following
may also apply. A mixture of one or more elemental particles may be
added, wherein the particles are selected from: aluminum,
tellurium, and/or sulfur. The suitable atmosphere may contain at
least one of the following: selenium, sulfur, tellurium, H.sub.2,
CO, H.sub.2Se, H.sub.2S, Ar, N.sub.2 or combinations or mixture
thereof. One or more classes of the particles may include one or
more inorganic materials. The particles may be contain one or more
inorganic materials chosen from the group consisting of: aluminum
(Al), sulfur (S), sodium (Na), potassium (K), lithium (Li), alloys
containing the foregoing elements, or combinations thereof. The
particles may be nanoparticles. Particles may be formed from a
feedstock by one of the following processes: milling,
electroexplosive wire (EEW) processing, evaporation condensation
(EC), pulsed plasma processing, or combinations thereof.
Optionally, the material does negatively impact the resulting
absorber layer and not need to be removed from the resulting
absorber layer. The material may be comprised of Al to make solid
Al--Ga particles. Optionally, the process may be comprised of a
material comprising of Al, wherein Ga dissolves in Al to make solid
Al--Ga particles for use in forming a film of CAGS and/or
CAIGS.
[0034] Bandgap
[0035] In one embodiment, a method is provided for bandgap grading
in a thin-film device using such particles. The method may be
comprised of providing a bandgap grading material comprising of an
alloy having: a) a IIIA material and b) a group IA-based material,
wherein the alloy has a higher melting temperature than a melting
temperature of the IIIA material in elemental form. A precursor
material may be deposited on a substrate to form a precursor layer.
The precursor material comprising group IB, IIIA, and/or VIA based
particles. The bandgap grading material of the alloy may be
deposited after depositing the precursor material. The alloy in the
grading material may react after the precursor layer has begun to
sinter and thus maintains a higher concentration of IIIA material
in a portion of the compound film that forms above a portion that
sinters first.
[0036] For any of the embodiments described herein, the following
may also apply. The bandgap grading material may melt above
450.degree. C. Optionally, the bandgap grading material melts above
500.degree. C. In another embodiment, the bandgap grading material
melts above 550.degree. C. The method may include at least
partially sintering the precursor material to form a dense film
prior to depositing the bandgap grading material. The precursor
material may be completely sintered to form a dense film prior to
depositing the bandgap grading material. The precursor material may
be reacted in a suitable atmosphere to form a CIS-based film prior
to depositing the bandgap grading material. The precursor material
and the bandgap grading material may be reacted in a suitable
atmosphere to form a CIGS film. The alloy may have a higher
reacting temperature than a maximum sintering temperature of the
precursor material. The depositing step may be comprised of
solution depositing the precursor material. Optionally, the
depositing step may be comprised of dry powder depositing the
precursor material. The reacting step comprises of using a
solid-state reaction. The reacting step comprises of heating the
precursor material at a first temperature profile, wherein the
precursor layer at least partially sinters at the first temperature
profile where a maximum temperature is lower than a reacting
temperature of the alloy; and increasing processing temperature to
a second temperature sufficient to melt react the particles of the
alloy, wherein the alloy reacts after the precursor layer has begun
to at least partially sinter. The bandgap grading material may be
solution deposited over the precursor layer. The bandgap grading
material may be deposited over the precursor layer using a
vacuum-based technique. The bandgap grading material may be
deposited over the precursor layer by sputtering. The bandgap
grading material may be deposited over the precursor layer by at
least one of the following techniques: ALD, CVD, PVD, or
combinations thereof electrodeposition, solution-deposition of
`moleculary` soluble Ga-compounds in contrast to
particles=aggregates). The precursor material may be comprised of a
material that forms a Cu--In--Se based alloy when sintered at the
first temperature profile. The precursor material may be comprised
of a precursor material that forms a Cu--In--Se based alloy when
sintered at the first temperature profile and combines with the
alloy to form a Cu--In--Ga--Se based alloy when processed with the
second temperature profile.
[0037] For any of the embodiments described herein, the following
may also apply. The precursor material may be comprised of a
material that forms a Cu--In--Ga--Se based alloy when sintered at
the first temperature profile and combines with the alloy to form a
Cu--In--Ga--Se based alloy when processed with the second
temperature profile with increase Ga content near a top surface of
the layer. The alloy may be comprised of a Ga--Na based material, a
Ga--Na--Se based material, a Ga--Na--S based material, and/or a
Ga--Na--Te based material. The group IA-based material may be
comprised of elemental sodium-based material. The group IA-based
material may be comprised of a sodium-based compound. The group
IA-based material may be chosen from the group of sodium (Na),
potassium (K), lithium (Li), alloys containing any of the
foregoing, or combinations thereof. The precursor material may
contain particles comprised of Cu-based alloy particles. The
precursor material contains particles comprised of Cu-IIIA based
alloy particles. The precursor material may contain particles
comprised of Cu-VIA based alloy particles. The precursor material
may be comprised of a selenide-based alloy. The particles may be
nanoparticles. The particles may be spherical nanoparticles. The
particles may include non-spherical, planar flakes. The compound
film may include a group IB-IIIA-VIA compound. The compound film
may be comprised of a semiconductor film suitable for use in a
photovoltaic device. The compound film may be comprised of an
absorber layer for a solar cell. A mixture of one or more elemental
particles may be added and selected from: aluminum, tellurium, or
sulfur. The suitable atmosphere may contain at least one of the
following: selenium, sulfur, tellurium, H2, CO, H2Se, H2S, Ar, N2
or combinations or mixtures thereof. One or more classes of the
particles may be doped with one or more inorganic materials. One or
more classes of the particles may be doped with one or more
inorganic materials chosen from the group of aluminum (Al), sulfur
(S), sodium (Na), potassium (K), or lithium (Li). The film may have
a Cu/(In+Ga) compositional range of about 0.01 to about 1.0 and a
Ga/(In+Ga) compositional range of about 0.01 to about 1.0. The film
may have a desired Cu/(In+Ga) molar ratio in the range of about 0.7
to about 1.0 and a desired Ga/(Ga+In) molar ratio in the range of
about 0.1 to about 0.8. The film may optionally have a desired
Cu/(In+Ga) molar ratio in the range of greater than about 1.0 and a
desired Ga/(Ga+In) molar ratio in the range of about 0.1 to about
0.8. The film may be reacted in a post-reacting step to change
Cu/(In+Ga) to be in a range less than about 1.0. Solution
deposition comprises using at least one of the following
techniques: wet coating, spray coating, spin coating, doctor blade
coating, contact printing, top feed reverse printing, bottom feed
reverse printing, nozzle feed reverse printing, gravure printing,
microgravure printing, reverse microgravure printing, comma direct
printing, roller coating, slot die coating, meyerbar coating, lip
direct coating, dual lip direct coating, capillary coating, ink-jet
printing, jet deposition, spray deposition, or combinations
thereof.
[0038] In yet another embodiment of the present invention, a method
is provided for bandgap grading. The method may be comprised of
providing a bandgap grading material having an alloy of a) an group
IA-based material and b) Ga. The particles of the alloy may be
deposited over a previously formed Cu--In--Ga--Se based layer. The
particles with the previously formed Cu--In--Ga--Se based layer may
be reacted in a suitable atmosphere at a processing temperature,
wherein the bandgap grading material is reacted to form a
gallium-rich portion of the Cu--In--Ga--Se based layer over at
least a portion of the previously formed Cu--In--Ga--Se based
layer.
[0039] For any of the embodiments described herein, the following
may also apply. The group IA-based material may be comprised of an
Na-based material. The group IA-based material may be comprised of
elemental Na. The alloy may be comprised of a Ga--Na based
material. The alloy may be comprised of a Ga--Na--Se based
material. It should be understood that any of the materials used
herein are not limited to solution deposition but may also be
suitable for deposition using vacuum-based techniques.
[0040] Inter-Metallics
[0041] In one embodiment, the method comprises forming a precursor
layer on a substrate, wherein the precursor layer comprises one or
more discrete layers. The layers may include at least a first layer
containing one or more group IB elements and two or more different
group IIIA elements and at least a second layer containing
elemental chalcogen particles. The precursor layer may be heated to
a temperature sufficient to melt the chalcogen particles and to
react the chalcogen particles with the one or more group IB
elements and group IIIA elements in the precursor layer to form a
film of a group IB-IIIA-chalcogenide compound. The method may also
include making a film of group IB-IIIA-chalcogenide compound that
includes mixing the nanoparticles and/or nanoglobules and/or
nanodroplets to form an ink, depositing the ink on a substrate,
heating to melt the extra chalcogen and to react the chalcogen with
the group IB and group IIIA elements and/or chalcogenides to form a
dense film. In some embodiments, densification of the precursor
layer is not used since the absorber layer may be formed without
first sintering the precursor layer to a temperature where
densification occurs. At least one set of the particles in the
precursor layer are inter-metallic particles containing at least
one group IB-IIIA inter-metallic alloy phase. Alternatively, at
least one set of the particles in the precursor layer are formed
from a feedstock of inter-metallic particles containing at least
one group IB-IIIA inter-metallic alloy phase.
[0042] For any of the embodiments described herein, the following
may also apply. Optionally, the first layer may be formed over the
second layer. In another embodiment, the second layer may be formed
over the first layer. The first layer may also contain elemental
chalcogen particles. The first layer may have group IB elements in
the form of a group IB-chalcogenide. The first layer may have group
IIIA elements in the form of a group IIIA-chalcogenide. There may
be a third layer containing elemental chalcogen particles. The two
or more different group IIIA elements may include indium and
gallium. The group IB element may be copper. The chalcogen
particles may be particles of selenium, sulfur, and/or tellurium.
The precursor layer may be substantially oxygen-free. Forming the
precursor layer may include forming a dispersion including
nanoparticles containing one or more group IB elements and
nanoparticles containing two or more group IIIA elements, spreading
a film of the dispersion onto the substrate. Forming the precursor
layer may include sintering the film to form the precursor layer.
Sintering the precursor layer may take place before the step of
disposing the layer containing elemental chalcogen particles over
the precursor layer. The substrate may be a flexible substrate and
wherein forming the precursor layer and/or disposing the layer
containing elemental chalcogen particles over the precursor layer,
and/or heating the precursor layer and chalcogen particles includes
the use of roll-to-roll manufacturing on the flexible substrate.
The substrate may be an aluminum foil substrate. The group
IB-IIIA-chalcogenide compound may be of the form
CuzIn(1-x)GaxS2(1-y)Se2y, where 0.5.ltoreq.z.ltoreq.1.5,
0.ltoreq.x.ltoreq.1.0 and 0.ltoreq.y.ltoreq.1.0. In another
embodiment of the present invention, heating of precursor layer and
chalcogen particles may include heating the substrate and precursor
layer from an ambient temperature to a plateau temperature range of
between about 200.degree. C. and about 600.degree. C., maintaining
a temperature of the substrate and precursor layer in the plateau
range for a period of time ranging between about a fraction of a
second to about 60 minutes, and subsequently reducing the
temperature of the substrate and precursor layer.
[0043] In a still further embodiment of the present invention, a
method is provided for forming a film of a group
IB-IIIA-chalcogenide compound. The method includes forming a
precursor layer on a substrate, wherein the precursor layer
contains one or more group IB elements and one or more group IIIA
elements. The method may include sintering the precursor layer.
After sintering the precursor layer, the method may include forming
a layer containing elemental chalcogen particles over the precursor
layer. The method may also include heating the precursor layer and
chalcogen particles to a temperature sufficient to melt the
chalcogen particles and to react the chalcogen particles with the
group IB element and group IIIA elements in the precursor layer to
form a film of a group IB-IIIA-chalcogenide compound. The one or
more group IIIA elements may include indium and gallium. The
chalcogen particles may be particles of selenium, sulfur or
tellurium. The precursor layer may be substantially oxygen-free.
The method may include forming the precursor layer which includes
forming a dispersion containing nanoparticles containing one or
more group IB elements and nanoparticles containing two or more
group IIIA elements, spreading a film of the dispersion onto a
substrate. The method may include forming the precursor layer
and/or sintering the precursor layer and/or disposing the layer
containing elemental chalcogen particles over the precursor layer
and/or heating the precursor layer and chalcogen particles to a
temperature sufficient to melt the chalcogen particles includes the
use of roll-to-roll manufacturing on the flexible substrate. The
group IB-IIIA-chalcogenide compound may be of the form
CuzIn(1-x)GaxS2(1-y)Se2y, where 0.5.ltoreq.z.ltoreq.1.5,
0.ltoreq.x.ltoreq.1.0 and 0.ltoreq.y.ltoreq.1.0.
[0044] For any of the embodiments described herein, the following
may also apply. Sintering the precursor layer may include heating
the substrate and precursor layer from an ambient temperature to a
plateau temperature range of between about 200.degree. C. and about
600.degree. C., maintaining a temperature of the substrate and
precursor layer in the plateau range for a period of time ranging
between about a fraction of a second to about 60 minutes, and
subsequently reducing the temperature of the substrate and
precursor layer. Heating the precursor layer and chalcogen
particles may include heating the substrate, precursor layer, and
chalcogen particles from an ambient temperature to a plateau
temperature range of between about 200.degree. C. and about
600.degree. C., maintaining a temperature of the substrate and
precursor layer in the plateau range for a period of time ranging
between about a fraction of a second to about 60 minutes, and
subsequently reducing the temperature of the substrate and
precursor layer. It should also be understood that the substrate
may be an aluminum foil substrate.
[0045] In a still further embodiment of the present invention, a
method is provided that is comprised of forming a precursor layer
containing particles having one or more group IB elements and two
or more different group IIIA elements and forming a layer
containing surplus chalcogen particles providing a source of excess
chalcogen, wherein the precursor layer and the surplus chalcogen
layer are adjacent to one another. The precursor layer and the
surplus chalcogen layer are heated to a temperature sufficient to
melt the particles providing the source of excess chalcogen and to
react the particles with the one or more group IB elements and
group IIIA elements in the precursor layer to form a film of a
group IB-IIIA-chalcogenide compound on a substrate. The surplus
chalcogen layer may be formed over the precursor layer. The surplus
chalcogen layer may be formed under the precursor layer. The
particles providing the source of excess chalcogen may be comprised
of elemental chalcogen particles. The particles providing the
source of excess chalcogen may be comprised of chalcogenide
particles. The particles providing the source of excess chalcogen
may be comprised of chalcogen-rich chalcogenide particles. The
precursor layer may also contain elemental chalcogen particles. The
precursor layer may have group IB elements in the form of a group
IB-chalcogenide. The precursor layer may have group IIIA elements
in the form of a group IIIA-chalcogenide. A third layer may be
provided that contains elemental chalcogen particles. The film may
be formed from the precursor layer of the particles and a layer of
a sodium-containing material in contact with the precursor
layer.
[0046] For any of the embodiments described herein, the following
may also apply. Optionally, the film may be formed from a precursor
layer of the particles and a layer in contact with the precursor
layer and containing at least one of the following materials: a
group IB element, a group IIIA element, a group VIA element, a
group IA element, a binary and/or multinary alloy of any of the
preceding elements, a solid solution of any of the preceding
elements, copper, indium, gallium, selenium, copper indium, copper
gallium, indium gallium, sodium, a sodium compound, sodium
fluoride, sodium indium sulfide, copper selenide, copper sulfide,
indium selenide, indium sulfide, gallium selenide, gallium sulfide,
copper indium selenide, copper indium sulfide, copper gallium
selenide, copper gallium sulfide, indium gallium selenide, indium
gallium sulfide, copper indium gallium selenide, and/or copper
indium gallium sulfide. In one embodiment, the particles contain
sodium at about 1 at. % or less. The particles may contain at least
one of the following materials: Cu--Na, In--Na, Ga--Na, Cu--In--Na,
Cu--Ga--Na, In--Ga--Na, Na--Se, Cu--Se--Na, In--Se--Na, Ga--Se--Na,
Cu--In--Se--Na, Cu--Ga--Se--Na, In--Ga--Se--Na, Cu--In--Ga--Se--Na,
Na--S, Cu--S--Na, In--S--Na, Ga--S--Na, Cu--In--S--Na,
Cu--Ga--S--Na, In--Ga--S--Na, or Cu--In--Ga--S--Na. The film may be
formed from a precursor layer of the particles and an ink
containing a sodium compound with an organic counter-ion or a
sodium compound with an inorganic counter-ion. Optionally, the film
may be formed from a precursor layer of the particles and a layer
of a sodium containing material in contact with the precursor layer
and/or particles containing at least one of the following
materials: Cu--Na, In--Na, Ga--Na, Cu--In--Na, Cu--Ga--Na,
In--Ga--Na, Na--Se, Cu--Se--Na, In--Se--Na, Ga--Se--Na,
Cu--In--Se--Na, Cu--Ga--Se--Na, In--Ga--Se--Na, Cu--In--Ga--Se--Na,
Na--S, Cu--S--Na, In--S--Na, Ga--S--Na, Cu--In--S--Na,
Cu--Ga--S--Na, In--Ga--S--Na, or Cu--In--Ga--S--Na; and/or an ink
containing the particles and a sodium compound with an organic
counter-ion or a sodium compound with an inorganic counter-ion. The
method may also include adding a sodium containing material to the
film after the heating step.
[0047] For any of the embodiments described herein, the following
may also apply. A liquid ink may be made using one or more liquid
metals. For example, an ink may be made starting with a liquid
and/or molten mixture of Gallium and/or Indium. Copper
nanoparticles may then be added to the mixture, which may then be
used as the ink/paste. Copper nanoparticles are available
commercially. Alternatively, the temperature of the Cu--Ga--In
mixture may be adjusted (e.g. cooled) until a solid forms. The
solid may be ground at that temperature until small nanoparticles
(e.g., less than 5 nm) are present. Selenium may be added to the
ink and/or a film formed from the ink by exposure to selenium
vapor, e.g., before, during, or after annealing.
[0048] In another embodiment, a liquid ink may be made using one or
more liquid metals. For example, an ink may be made starting with a
liquid and/or molten mixture of Gallium and/or Indium. Copper
nanoparticles may then be added to the mixture, which may then be
used as the ink/paste. Copper nanoparticles are available
commercially. Alternatively, the temperature of the Cu--Ga--In
mixture may be adjusted (e.g. cooled) until a solid forms. The
solid may be ground at that temperature until small nanoparticles
(e.g., less than 5 nm) are present. Selenium may be added to the
ink and/or a film formed from the ink by exposure to selenium
vapor, e.g., before, during, or after annealing.
[0049] In yet another embodiment of the present invention, a
process is described comprising of formulating a dispersion of
solid and/or liquid particles comprising group IB and/or IIIA
elements, and, optionally, at least one group VIA element. The
process includes depositing the dispersion onto a substrate to form
a layer on the substrate and reacting the layer in a suitable
atmosphere to form a film. In this process, at least one set of the
particles are inter-metallic particles containing at least one
group IB-IIIA inter-metallic phase.
[0050] In yet another embodiment of the present invention, a
composition is provided comprised of a plurality of particles
comprising group IB and/or IIIA elements, and, optionally, at least
one group VIA element. At least one set of the particles contains
at least one group IB-IIIA inter-metallic alloy phase.
[0051] For any of the embodiments described herein, the following
may also apply. The method may include formulating a dispersion of
particles comprising group IB and/or IIIA elements, and,
optionally, at least one group VIA element. The method may include
depositing the dispersion onto a substrate to form a layer on the
substrate and reacting the layer in a suitable atmosphere to form a
film. At least one set of the particles contain a group IB-poor,
group IB-IIIA alloy phase. In some embodiments, group IB-poor
particles contribute less than about 50 molar percent of group IB
elements found in all of the particles. The group IB-poor, group
IB-IIIA alloy phase particles may be a sole source of one of the
group IIIA elements. The group IB-poor, group IB-IIIA alloy phase
particles may contain an inter-metallic phase and may be a sole
source of one of the group IIIA elements. The group IB-poor, group
IB-IIIA alloy phase particles may contain an inter-metallic phase
and are a sole source of one of the group IIIA elements. The group
IB-poor, group IB-IIIA alloy phase particles may be
Cu.sub.1In.sub.2 particles and are a sole source of indium in the
material.
[0052] For any of the embodiments described herein, the following
may also apply. It should be understood that for any of the
foregoing, the film and/or final compound may include a group
IB-IIIA-VIA compound. The reacting step may comprise of heating the
layer in the suitable atmosphere. The depositing step may include
coating the substrate with the dispersion. At least one set of the
particles in the dispersion may be in the form of nanoglobules. At
least one set of the particles in the dispersion may be in the form
of nanoglobules and contain at least one group IIIA element. At
least one set of the particles in the dispersion may be in the form
of nanoglobules comprising of a group IIIA element in elemental
form. In some embodiments of the present invention, the
inter-metallic phase is not a terminal solid solution phase. In
some embodiments of the present invention, the inter-metallic phase
is not a solid solution phase. The inter-metallic particles may
contribute less than about 50 molar percent of group IB elements
found in all of the particles. The inter-metallic particles may
contribute less than about 50 molar percent of group IIIA elements
found in all of the particles. The inter-metallic particles may
contribute less than about 50 molar percent of the group IB
elements and less than about 50 molar percent of the group IIIA
elements in the dispersion deposited on the substrate. The
inter-metallic particles may contribute less than about 50 molar
percent of the group IB elements and more than about 50 molar
percent of the group IIIA elements in the dispersion deposited on
the substrate. The inter-metallic particles may contribute more
than about 50 molar percent of the group IB elements and less than
about 50 molar percent of the group IIIA elements in the dispersion
deposited on the substrate. The molar percent for any of the
foregoing may be based on a total molar mass of the elements in all
particles present in the dispersion. In some embodiments, at least
some of the particles have a platelet shape. In some embodiments, a
majority of the particles have a platelet shape. In other
embodiments, substantially all of the particles have a platelet
shape.
[0053] For any of the embodiments described herein, the following
may also apply. For any of the foregoing embodiments, an
inter-metallic material for use with the present invention is a
binary material. The inter-metallic material may be a ternary
material. It may be a copper rich (or group IB rich) ternary or
binary. It may be a copper poor (or group IB poor) ternary or
copper poor binary, wherein additional copper (or group IB
material) may be added from a different source. The copper poor (or
group IB poor) ternary or binary may contribute less than about 50%
of the total group IB material in the precursor and/or final film.
The copper poor (or group IB poor) ternary or binary may contribute
less than about 40% of the total group IB material in the precursor
and/or final film. The copper poor (or group IB poor) ternary or
binary may contribute less than about 30% of the total group IB
material in the precursor and/or final film. The copper poor (or
group IB poor) ternary or binary may contribute less than about 20%
of the total group IB material in the precursor and/or final film.
The copper poor (or group IB poor) ternary or binary may contribute
less than about 10% of the total group IB material in the precursor
and/or final film. The inter-metallic material may comprise of
Cu.sub.1In.sub.2. The inter-metallic material may be comprised of a
composition in a .delta. phase of Cu.sub.1In.sub.2. The
inter-metallic material may be comprised of a composition in
between a .delta. phase of Cu.sub.1In.sub.2 and a phase defined by
Cu16In9. The inter-metallic material may be comprised of
Cu.sub.1Ga.sub.2. The inter-metallic material may be comprised of
an intermediate solid-solution of Cu.sub.1Ga.sub.2. The
inter-metallic material may be comprised of Cu.sub.68Ga.sub.38. The
inter-metallic material may be comprised of Cu.sub.70Ga.sub.30. The
inter-metallic material may be comprised of Cu.sub.75Ga.sub.25. The
inter-metallic material may be comprised of a composition of Cu--Ga
of a phase in between the terminal solid-solution and an
intermediate solid-solution next to it. The inter-metallic may be
comprised of a composition of Cu--Ga in a .gamma.1 phase (about
31.8 to about 39.8 wt % Ga). The inter-metallic may be comprised of
a composition of Cu--Ga in a .gamma.2 phase (about 36.0 to about
39.9 wt % Ga). The inter-metallic may be comprised of a composition
of Cu--Ga in a .gamma.3 phase (about 39.7 to about -44.9 wt % Ga).
The inter-metallic may be comprised of a composition of Cu--Ga in a
phase between .gamma.2 and .gamma.3. The inter-metallic may be
comprised of a composition of Cu--Ga in a phase between the
terminal solid solution and .gamma.1. The inter-metallic may be
comprised of a composition of Cu--Ga in a .theta. phase (about 66.7
to about 68.7 wt % Ga). The inter-metallic material may be
comprised of Cu-rich Cu--Ga. Gallium may be incorporated as a group
IIIA element in the form of a suspension of nanoglobules.
Nanoglobules of gallium may be formed by creating an emulsion of
liquid gallium in a solution. Gallium nanoglobules may be created
by being quenched below room temperature.
[0054] For any of the embodiments described herein, the following
may also apply. A process according to the any of the foregoing
embodiments of the present invention may include maintaining or
enhancing a dispersion of liquid gallium in solution by stirring,
mechanical means, electromagnetic means, ultrasonic means, and/or
the addition of dispersants and/or emulsifiers. The process may
include adding a mixture of one or more elemental particles
selected from: aluminum, tellurium, or sulfur. The suitable
atmosphere may contain selenium, sulfur, tellurium, H.sub.2, CO,
H.sub.2Se, H.sub.2S, Ar, N.sub.2 or combinations or mixture
thereof. The suitable atmosphere may contain at least one of the
following: H.sub.2, CO, Ar, and N.sub.2. One or more classes of the
particles may be doped with one or more inorganic materials.
Optionally, one or more classes of the particles are doped with one
or more inorganic materials chosen from the group of aluminum (Al),
sulfur (S), sodium (Na), potassium (K), or lithium (Li).
Optionally, embodiments of the present invention may include having
a copper source that does not immediately alloy with In, and/or Ga.
One option would be to use (slightly) oxidized copper. The other
option would be to use CuxSey. Note that for the (slightly)
oxidized copper approach, a reducing step may be desired.
Basically, if elemental copper is used in liquid In and/or Ga,
speed of the process between ink preparation and coating should be
sufficient so that the particles have not grown to a size that will
result in thickness non-uniform coatings. It should be understood
that the temperature range may that of the substrate only since
that is typically the only one that should not be heated above its
melting point. This holds for the lowest melting material in the
substrate, being A1 and other suitable substrates.
[0055] Vapor
[0056] For any of the embodiments described herein, the following
may also apply. In one embodiment of the present invention, the
method comprises forming a precursor material comprising group IB
and/or group IIIA particles of any shape. The method may include
forming a precursor layer of the precursor material over a surface
of a substrate. The method may further include heating the particle
precursor material in a substantially oxygen-free chalcogen
atmosphere to a processing temperature sufficient to react the
particles and to release chalcogen from the chalcogenide particles,
wherein the chalcogen assumes a liquid form and acts as a flux to
improve intermixing of elements to form a group
IB-IIIA-chalcogenide film at a desired stoichiometric ratio. The
chalcogen atmosphere may provide a partial pressure greater than or
equal to the vapor pressure of liquid chalcogen in the precursor
layer at the processing temperature. This may be used in a one
stage process or a two stage process.
[0057] For any of the embodiments described herein, the following
may also apply. In one embodiment of the present invention, the
method comprises forming a precursor material comprising group IB
and/or group IIIA and/or group VIA particles of any shape. The
method may include forming a precursor layer of the precursor
material over a surface of a substrate. The method may further
include heating the particle precursor material in a substantially
oxygen-free chalcogen atmosphere to a processing temperature
sufficient to react the particles and to release chalcogen from the
chalcogenide particles, wherein the chalcogen assumes a liquid form
and acts as a flux to improve intermixing of elements to form a
group IB-IIIA-chalcogenide film at a desired stoichiometric ratio.
The suitable atmosphere may be a selenium atmosphere. The suitable
atmosphere may comprise of a selenium atmosphere providing a
partial pressure greater than or equal to vapor pressure of
selenium in the precursor layer. The suitable atmosphere may
comprise of a non-oxygen atmosphere containing chalcogen vapor at a
partial pressure of the chalcogen greater than or equal to a vapor
pressure of the chalcogen at the processing temperature and
processing pressure to minimize loss of chalcogen from the
precursor layer, wherein the processing pressure is a non-vacuum
pressure. The suitable atmosphere may comprises of a non-oxygen
atmosphere containing chalcogen vapor at a partial pressure of the
chalcogen greater than or equal to a vapor pressure of the
chalcogen at the processing temperature and processing pressure to
minimize loss of chalcogen from the precursor layer, wherein the
processing pressure is a non-vacuum pressure and wherein the
particles are one or more types of binary chalcogenides.
[0058] For any of the embodiments described herein, the following
may also apply. In one embodiment of the present invention, the
method comprises forming a precursor material comprising group
IB-chalcogenide and/or group IIIA-chalcogenide particles, wherein
an overall amount of chalcogen in the particles relative to an
overall amount of chalcogen in a group IB-IIIA-chalcogenide film
created from the precursor material, is at a ratio that provides an
excess amount of chalcogen in the precursor material. The method
also includes using the precursor material to form a precursor
layer over a surface of a substrate. The particle precursor
material is heated in a suitable atmosphere to a temperature
sufficient to melt the particles and to release at least the excess
amount of chalcogen from the chalcogenide particles, wherein the
excess amount of chalcogen assumes a liquid form and acts as a flux
to improve intermixing of elements to form the group
IB-IIIA-chalcogenide film at a desired stoichiometric ratio. The
overall amount of chalcogen in the precursor material is an amount
greater than or equal to a stoichiometric amount found in the
IB-IIIA-chalcogenide film.
[0059] For any of the embodiments described herein, the following
may also apply. It should be understood that, optionally, the
overall amount of chalcogen may be greater than a minimum amount
necessary to form the final IB-IIIA-chalcogenide at the desired
stoichiometric ratio. The overall amount of chalcogen in the
precursor material may be an amount greater than or equal to the
sum of: 1) the stoichiometric amount found in the
IB-IIIA-chalcogenide film and 2) a minimum amount of chalcogen
necessary to account for chalcogen lost during processing to form
the group IB-IIIA-chalcogenide film having the desired
stoichiometric ratio. Optionally, the overall amount may be about 2
times greater than a minimum amount necessary to form the
IB-IIIA-chalcogenide film at the desired stoichiometric ratio. The
particles may be chalcogen-rich particles and/or selenium-rich
particles and/or sulfur-rich particles and/or tellurium-rich
particles. In one embodiment, the overall amount of chalcogen in
the group IB-chalcogenide particles is greater than an overall
amount of chalcogen in the group IIIA particles. The overall amount
of chalcogen in the group IB-chalcogenide particles may be less
than an overall amount of chalcogen in the group IIIA
particles.
[0060] For any of the embodiments described herein, the following
may also apply. Optionally, the group IB-chalcogenide particles may
include a mix of particles, wherein some particles are
chalcogen-rich and some are not, and wherein the chalcogen-rich
particles outnumber the particles that are not. The group
IIIA-chalcogenide particles may include a mix of particles, wherein
some particles are chalcogen-rich and some are not, and wherein the
chalcogen-rich particles outnumber the particles that are not. The
particles may be IBxVIAy and/or IIIAaVIAb particles, wherein x<y
and a<b. The resulting group IB-IIIA-chalcogenide film may be
CuzIn(1-x)GaxSe 2, wherein 0.5.ltoreq.z.ltoreq.1.5 and
0.ltoreq.x.ltoreq.1. The amount of chalcogen in the particles may
be above the stoichiometric ratio required to form the film. The
particles may be substantially oxygen-free particles. The particles
may be particles that do not contain oxygen above about 5.0
weight-percentage. The group IB element may be copper. The group
IIIA element may be comprised of gallium and/or indium and/or
aluminum. The chalcogen may be selenium or sulfur or tellurium. The
particles may be alloy particles. The particles may be binary alloy
particles and/or ternary alloy particles and/or multi-nary alloy
particles and/or compound particles and/or solid-solution
particles.
[0061] For any of the embodiments described herein, the following
may also apply. Optionally, the precursor material may include
group IB-chalcogenide particles containing a chalcogenide material
in the form of an alloy of a chalcogen and an element of group IB
and/or wherein the particle precursor material includes group
IIIA-chalcogenide particles containing a chalcogenide material in
the form of an alloy of a chalcogen and one or more elements of
group IIIA. The group IB-chalcogenide may be comprised of CGS and
the group IIIA-chalcogenide may be comprised of CIS. The method may
include adding an additional source of chalcogen prior to heating
the precursor material. The method may include adding an additional
source of chalcogen during heating of the precursor material. The
method may further include adding an additional source of chalcogen
before, simultaneously with, or after forming the precursor layer.
The method may include adding an additional source of chalcogen by
forming a layer of the additional source over the precursor layer.
The method may include adding an additional source of chalcogen on
the substrate prior to forming the precursor layer. A vacuum-based
process may be used to add an additional source of chalcogen in
contact with the precursor layer. The amounts of the group IB
element and amounts of chalcogen in the particles may be selected
to be at a stoichiometric ratio for the group IB chalcogenide that
provides a melting temperature less than a highest melting
temperature found on a phase diagram for any stoichiometric ratio
of elements for the group IB chalcogenide. The method may include
using a source of extra chalcogen that includes particles of an
elemental chalcogen. The extra source of chalcogen may be a
chalcogenide. The amounts of the group IIIA element and amounts of
chalcogen in the particles may be selected to be at a
stoichiometric ratio for the group IIIA chalcogenide that provides
a melting temperature less than a highest melting temperature found
on a phase diagram for any stoichiometric ratio of elements for the
group IIIA chalcogenide.
[0062] For any of the embodiments described herein, the following
may also apply. Optionally, the group IB-chalcogenide particles may
be CuxSey, wherein the values for x and y are selected to create a
material with a reduced melting temperature as determined by
reference to the highest melting temperature on a phase diagram for
Cu--Se. The group IB-chalcogenide particles may be CuxSey, wherein
x is in the range of about 2 to about 1 and y is in the range of
about 1 to about 2. The group IIIA-chalcogenide particles may be
InxSey, wherein the values for x and y are selected to create a
material with a reduced melting temperature as determined by
reference to the highest melting temperature on a phase diagram for
In--Se. The group IIIA-chalcogenide particles may be InxSey,
wherein x is in the range of about 1 to about 6 and y is in the
range of about 0 to about 7. The group IIIA-chalcogenide particles
may be GaxSey, wherein the values for x and y are selected to
create a material with a reduced melting temperature as determined
by reference to the highest melting temperature on a phase diagram
for Ga--Se. The group IIIA-chalcogenide particles may be GaxSey,
wherein x is in the range of about 1 to about 2 and y is in the
range of about 1 to about 3. The melting temperature may be at a
eutectic temperature for the material as indicated on the phase
diagram. The group IB or IIIA chalcogenide may have a
stoichiometric ratio that results in the group IB or IIIA
chalcogenide being less thermodynamically stable than the group
IB-IIIA-chalcogenide compound.
[0063] In yet another embodiment of the present invention, a
precursor material is provided that is comprised of group
IB-chalcogenide particles containing a substantially oxygen-free
chalcogenide material in the form of an alloy of a chalcogen with
an element of group IB; and/or group IIIA-chalcogenide particles
containing a substantially oxygen-free chalcogenide material in the
form of an alloy of a chalcogen with one or more elements of group
IIIA. The group IB-chalcogenide particles and/or the group
IIIA-chalcogenide particles may have a stoichiometric ratio that
provides a source of surplus chalcogen, wherein the overall amount
of chalcogen in the precursor material is an amount greater than or
equal to a stoichiometric amount found in the IB-IIIA-chalcogenide
film. The overall amount of chalcogen in the precursor material is
an amount greater than or equal to the sum of: 1) the
stoichiometric amount found in the IB-IIIA-chalcogenide film and 2)
a minimum amount of chalcogen necessary to account for chalcogen
lost during processing to form the group IB-IIIA-chalcogenide film
having the desired stoichiometric ratio. The overall amount may be
greater than a minimum amount necessary to form the
IB-IIIA-chalcogenide film at the desired stoichiometric ratio. The
overall amount may be about 2 times greater than a minimum amount
necessary to form the IB-IIIA-chalcogenide film at the desired
stoichiometric ratio.
[0064] The material may be solid at the processing temperature used
in deposition and around the ink preparation temperature
complicating controlling particle size. If too much liquid is
present at or near the onset of a reaction, liquid may group
together at certain areas and not be evenly distributed throughout
the reaction area. This can result in thickness non-uniformity
and/or lateral composition non-uniformity. Furthermore, if material
in liquid form leaches out from an alloy or compound containing
that material, this may change the local stoichiometry at the start
of the reaction resulting in different compound(s) in the final
thin-film if the leaching occurs prior to or during processing of
the materials. Some embodiments may have a composition where there
is a mixture of elemental Ga and solid Ga4Na. This can be
generalized to a composition where there is elemental group IIIA
material and group IA-IIIA material.
[0065] A further understanding of the nature and advantages of the
invention will become apparent by reference to the remaining
portions of the specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0066] FIGS. 1A-1D are schematic cross-sectional diagrams
illustrating fabrication of a film according to an embodiment of
the present invention.
[0067] FIG. 2 shows the binary phase diagram for a Gallium-Sodium
alloy.
[0068] FIG. 3 shows the binary phase diagram for an Indium-Sodium
alloy.
[0069] FIGS. 4A and 4B show particles being processed in accordance
with an embodiment of the present invention.
[0070] FIG. 5 shows a process flow schematic for creating solid
particles using a dispersion and/or suspension method according to
one embodiment of the present invention.
[0071] FIGS. 6A and 6B show another method of forming solid
particles according to an embodiment of the present invention.
[0072] FIGS. 7A through 7C show one method of bandgap grading
according to an embodiment of the present invention.
[0073] FIGS. 8A through 8C show another method of bandgap grading
according to an embodiment of the present invention.
[0074] FIGS. 9A and 9B show another method of bandgap grading
according to an embodiment of the present invention.
[0075] FIGS. 10A and 10B show yet another method of bandgap grading
according to an embodiment of the present invention.
[0076] FIG. 11 shows the use of spherical particles and
non-spherical particles according to an embodiment of the present
invention.
[0077] FIG. 12 shows the use of spherical particles and planar
according to an embodiment of the present invention.
[0078] FIGS. 13A through 13E cross-sectional schematics showing
that layers of material may be deposited above and/or below the
precursor layer according to embodiments of the present
invention.
[0079] FIG. 14 shows roll-to-roll process according to an
embodiment of the present invention.
[0080] FIG. 15A shows a cross-sectional view of a photovoltaic
device according to an embodiment of the present invention.
[0081] FIG. 15B shows one embodiment of a module according to the
present invention.
[0082] FIG. 16A shows one embodiment of a system for use with rigid
substrates according to one embodiment of the present
invention.
[0083] FIG. 16B shows one embodiment of a system for use with rigid
substrates according to one embodiment of the present
invention.
[0084] FIGS. 17-19 show the use of inter-metallic material to form
a film according to embodiments of the present invention.
[0085] FIG. 20 is a cross-sectional view showing the use of
multiple layers to form a film according to embodiments of the
present invention.
[0086] FIG. 21 shows feedstock material being processed according
to embodiments of the present invention.
[0087] FIGS. 22A and 22B show features of flakes according to
embodiments of the present invention.
[0088] FIGS. 23A and 23B show features of platelets.
[0089] FIG. 24 shows the use of spherical inter-metallic material
to form a film according to embodiments of the present
invention.
[0090] FIG. 25 shows feedstock material being processed according
to embodiments of the present invention.
[0091] FIG. 26A-26D show cross-sectional view of depositing
additional chalcogen according to one embodiment of the present
invention.
[0092] FIG. 27A shows a schematic of a system using a chalcogen
vapor environment according to one embodiment of the present
invention.
[0093] FIG. 27B shows a schematic of a system using a chalcogen
vapor environment according to one embodiment of the present
invention.
[0094] FIG. 27C shows a schematic of a system using a chalcogen
vapor environment according to one embodiment of the present
invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0095] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the invention, as
claimed. It may be noted that, as used in the specification and the
appended claims, the singular forms "a", "an" and "the" include
plural referents unless the context clearly dictates otherwise.
Thus, for example, reference to "a material" may include mixtures
of materials, reference to "a compound" may include multiple
compounds, and the like. References cited herein are hereby
incorporated by reference in their entirety, except to the extent
that they conflict with teachings explicitly set forth in this
specification.
[0096] In this specification and in the claims which follow,
reference will be made to a number of terms which shall be defined
to have the following meanings:
[0097] "Optional" or "optionally" means that the subsequently
described circumstance may or may not occur, so that the
description includes instances where the circumstance occurs and
instances where it does not. For example, if a device optionally
contains a feature for a barrier film, this means that the barrier
film feature may or may not be present, and, thus, the description
includes both structures wherein a device possesses the barrier
film feature and structures wherein the barrier film feature is not
present.
Photovoltaic Device Chemistry
[0098] The solid particles for use with the present invention may
be used with a variety of different chemistries to arrive at a
desired semiconductor film. Although not limited to the following,
an active layer for a photovoltaic device may be fabricated by
first formulating an ink of spherical and/or non-spherical
particles each containing at least one element from groups IB, IIIA
and/or VIA, coating a substrate with the ink to form a precursor
layer, and heating the precursor layer to form a dense film. In a
two step process, the dense film may then be processed in a
suitable atmosphere to form a group IB-IIIA-VIA compound. In other
embodiments, the precursor layer forms a layer with a group
IB-IIIA-VIA compound in a one step process. Optionally, others may
take one or more steps. It should be understood that reduction
and/or densification of the precursor layer may not be needed in
some embodiments, particularly if the precursor materials are
oxygen-free or substantially oxygen free. Thus, the heating step
may optionally be skipped if the particles are processed air-free
and are oxygen-free. The resulting group IB-IIIA-VIA compound for
either a one step or a two step process may be a compound of Cu,
In, Ga and selenium (Se) and/or sulfur S of the form
CuIn.sub.(1-x)Ga.sub.xS.sub.2(1-y)Se.sub.2y, where
0.ltoreq.x.ltoreq.1 and 0.ltoreq.y.ltoreq.1. Optionally, it should
also be understood that the resulting group IB-IIIA-VIA compound
may be a compound of Cu, In, Ga and selenium (Se) and/or sulfur S
of the form Cu.sub.2In.sub.(1-x)Ga.sub.xS.sub.2(1-y)Se.sub.2y,
where 0.5.ltoreq.z.ltoreq.1.5, 0.ltoreq.x.ltoreq.1.0 and
0.ltoreq.y.ltoreq.1.0. Some embodiments may also form the desired
semiconductor film in a one step process.
[0099] It should be understood that group IB, IIIA, and VIA
elements other than Cu, In, Ga, Se, and S may be included in the
description of the IB-IIIA-VIA materials described herein, and that
the use of a hyphen ("-" e.g., in Cu--Se or Cu--In--Se) does not
indicate a compound, but rather indicates a coexisting mixture of
the elements joined by the hyphen. It is also understood that group
IB is sometimes referred to as group 11, group IIIA is sometimes
referred to as group 13 and group VIA is sometimes referred to as
group 16. Furthermore, elements of group VIA (16) are sometimes
referred to as chalcogens. Where several elements can be combined
with or substituted for each other, such as In and Ga, or Se, and
S, in embodiments of the present invention, it is not uncommon in
this art to include in a set of parentheses those elements that can
be combined or interchanged, such as (In, Ga) or (Se, S). The
descriptions in this specification sometimes use this convenience.
Finally, also for convenience, the elements are discussed with
their commonly accepted chemical symbols. Group IB elements
suitable for use in the method of this invention include copper
(Cu), silver (Ag), and gold (Au). Preferably the group IB element
is copper (Cu). Group IIIA elements suitable for use in the method
of this invention include gallium (Ga), indium (In), aluminum (Al),
and thallium (Tl). Preferably the group IIIA element is gallium
(Ga) and/or indium (In). Group VIA elements of interest include
selenium (Se), sulfur (S), and tellurium (Te), and preferably the
group VIA element is either Se and/or S. It should be understood
that mixtures such as, but not limited to, alloys, solid solutions,
and compounds of any of the above can also be used. The shapes of
the solid particles may be any of those described herein.
Method of Forming a Film
[0100] Referring now to FIG. 1, one method of forming a
semiconductor film from solid particles according to the present
invention will now be described. It should be understood that the
present embodiment of the invention uses non-vacuum techniques to
form the semiconductor film. Other embodiments of the invention,
however, may optionally form the film under a vacuum environment in
one or more steps, and the use of solid particles (non-spherical
and/or spherical) is not limited to only non-vacuum coating
techniques.
[0101] As seen in FIG. 1, a substrate 102 is provided. By way of
non-limiting example, the substrate 102 may be made of a metal such
as aluminum. In other embodiments, metals such as, but not limited
to, stainless steel, molybdenum, titanium, copper, metallized
plastic films, coated metal foils, or combinations of the foregoing
may be used as the substrate 102. Alternative substrates include
but are not limited to ceramics, glasses, and the like. Any of
these substrates may be in the form of foils, sheets, rolls, the
like, or combinations thereof. Depending on the material of the
substrate 102, it may be useful to form or apply a contact layer
104 to the surface of substrate 102 to promote electrical contact
between the substrate 102 and the absorber layer that is to be
formed on it. As a nonlimiting example, when the substrate 102 is
made of aluminum, the contact layer 104 may be but is not limited
to a layer of molybdenum. For the purposes of the present
discussion, the contact layer 104 may be regarded as being part of
the substrate. As such, any discussion of forming or disposing a
material or layer of material on the substrate 102 includes
disposing or forming such material or layer on the contact layer
104, if one is used. Optionally, other layers of materials may also
be used with the contact layer 104 for insulation or other purposes
and still considered part of the substrate 102. It should be
understood that the contact layer 104 may comprise of more than one
type or more than one discrete layer of material. Optionally, some
embodiments may use any one and/or combinations of the following
for the contact layer: a copper, aluminum, chromium, molybdenum,
vanadium, etc. and/or iron-cobalt alloys.
[0102] Aluminum and molybdenum can and often do inter-diffuse into
one another, especially upon heating to elevated temperatures as
used for absorber growth, with deleterious electronic and/or
optoelectronic effects on the device 100. Furthermore aluminum can
diffuse though molybdenum into layers beyond e.g. CIG(S). To
inhibit such inter-diffusion, an intermediate, interfacial layer
103 may be incorporated between the aluminum foil substrate 102 and
molybdenum base electrode 104. The interfacial layer may be
composed of any of a variety of materials, including but not
limited to chromium, vanadium, tungsten, and glass, or compounds
such as nitrides (including but not limited to titanium nitride,
tantalum nitride, tungsten nitride, hafnium nitride, niobium
nitride, zirconium nitride, vanadium nitride, silicon nitride, or
molybdenum nitride), oxynitrides (including but not limited to
oxynitrides of Ti, Ta, V, W, Si, Zr, Nb, Hf, or Mo), oxides, and/or
carbides. The material may be selected to be an electrically
conductive material. In one embodiment, the materials selected from
the aforementioned may be those that are electrically conductive
diffusion barriers. The thickness of this layer can range from 10
nm to 50 nm or from 10 nm to 30 nm. Optionally, the thickness may
be in the range of about 50 nm to about 1000 nm. Optionally, the
thickness may be in the range of about 100 nm to about 750 nm.
Optionally, the thickness may be in the range of about 100 nm to
about 500 nm. Optionally, the thickness may be in the range of
about 110 nm to about 300 nm. In one embodiment, the thickness of
the layer 103 is at least 100 nm or more. In another embodiment,
the thickness of the layer 103 is at least 150 nm or more. In one
embodiment, the thickness of the layer 103 is at least 200 nm or
more. Optionally, some embodiments may include another layer such
as but not limited to a copper layer, a titanium layer, or other
metal layer above the layer 103 and below the base electrode layer
104. Optionally, some embodiments may include another layer such as
but not limited to a copper layer, a titanium layer, an aluminum
layer, or other metal layer below the layer 103 and below the base
electrode layer 104. This layer may be thicker than the layer 103.
Optionally, it may be the same thickness or thinner than the layer
103. This layer 103 may be placed on one or optionally both sides
of the aluminum foil (shown as layer 105 in phantom in FIG. 1).
[0103] If barrier layers are on both sides of the aluminum foil, it
should be understood that the protective layers may be of the same
material or they may optionally be different materials from the
aforementioned materials. The bottom protective layer 105 may be
any of the materials. Optionally, some embodiments may include
another layer 107 such as but not limited to an aluminum layer
above the layer 105 and below the aluminum foil 102. This layer 107
may be thicker than the layer 103 (or the layer 104). Optionally,
it may be the same thickness or thinner than the layer 103 (or the
layer 104). Although not limited to the following, this layer 107
may be comprised of one or more of the following: Mo, Cu, Ag, Al,
Ta, Ni, Cr, NiCr, or steel. Some embodiments may optionally have
more than one layer between the protective layer 105 and the
aluminum foil 102. Optionally, the material for the layer 105 may
be an electrically insulating material such as but not limited to
an oxide, alumina, or similar materials. For any of the embodiments
herein, the layer 105 may be used with or without the layer
107.
[0104] Referring now to FIG. 1B, a precursor layer 106 is formed
over the substrate 102 by coating the substrate 102 with a
dispersion such as but not limited to an ink. As one nonlimiting
example, the ink may be comprised of a carrier liquid mixed with
the microflakes 108 and has a rheology that allows the ink to be
coatable over the substrate 102. In one embodiment, the present
invention may use dry powder mixed with the vehicle and sonicated
before coating. Optionally, the inks may be already formulated as
the precursor materials are formed in the mill. In the case of
mixing a plurality of flake compositions, the product may be mixed
from various mills. This mixing could be sonicated but other forms
of mechanical agitation and/or another mill may also be used. The
ink used to form the precursor layer 106 may contain non-spherical
particles 108 such as but not limited to microflakes and/or
nanoflakes. It should also be understood that the ink may
optionally use both non-spherical and spherical particles in any of
a variety of relative proportions.
[0105] FIG. 1B includes a close-up view of the microflakes 108 in
the precursor layer 106, as seen in the enlarged image. Microflakes
have non-spherical shapes and are substantially planar on at least
one side. A more detailed view of one embodiment of the microflakes
108 can be found in FIGS. 2A and 2B of U.S. patent application Ser.
No. 11/362,266 filed Feb. 23, 2006 and fully incorporated herein by
reference. Microflakes may be defined as particles having at least
one substantially planar surface with a length and/or largest
lateral dimension of about 500 nm or more and the particles have an
aspect ratio of about 2 or more. In other embodiments, the
microflake is a substantially planar structure with thickness of
between about 10 and about 250 nm and lengths between about 500 nm
and about 5 microns. It should be understood that in other
embodiments of the invention, microflakes may have lengths as large
as 10 microns. Optionally, other microflakes may be those with a
thickness dimension substantially less than its length and width.
In such other embodiments, flakes may be curved or undulating, or
other non-planar shape, but still have a high aspect ratio between
thickness and length-to-width. Although not limited to the
following, at least some of the solid group IIIA-particles may be
processed into planar particles and adapted for use during solution
deposition.
[0106] It should be understood that different types of particles
such as microflakes 108 may be used to form the precursor layer
106. In one nonlimiting example, the microflakes are elemental
microflakes, i.e., microflakes having only a single atomic species.
The microflakes may be single metal particles of Cu, Ga, In, or Se.
Some inks may have only one type of microflake. Other inks may have
two or more types of microflakes which may differ in material
composition and/or other quality such as but not limited to shape,
size, interior architecture (e.g. a central core surrounded by one
or more shell layers) exterior coating, or the like. In one
embodiment, the ink used for precursor layer 106 may contain
microflakes comprising one or more group IB elements and
microflakes comprising one or more different group IIIA elements.
Optionally, the precursor layer 106 contains copper, indium and
gallium. In another embodiment, the precursor layer 106 may be an
oxygen-free layer containing copper, indium and gallium.
Optionally, the ratio of elements in the precursor layer may be
such that the layer, when processed, forms one or more compounds of
a compound of CuIn.sub.xGa.sub.1-x, where 0.ltoreq.x.ltoreq.1.
Those of skill in the art will recognize that other group IB
elements may be partially or completely substituted for Cu and
other group IIIA elements may be partially or completely
substituted for In and Ga. Optionally, the precursor may contain Se
as well, such as but not limited to Cu--In--Ga--Se flakes. This is
feasible if the precursor is oxygen-free and densification is not
needed. Optionally, this is also feasible when the precursor layer
is not oxygen-free or when densification prior to absorber-growth
is desired. Two nonlimiting examples are provided. One nonlimiting
example would be to densify a precursor layer that is Se-poor,
where the Se is mainly added to limit undesired oxidation of the
particles, and in a subsequent step form the absorber layer.
Another nonlimiting example would be to form the absorber layer
from a Se-poor precursor layer in one step without the need for a
separate densification step. In still further embodiments, the
precursor material may contain microflakes of group IB, IIIA, and
VIA elements. In one nonlimiting example, the precursor may contain
Cu--In--Ga--Se microflakes, which would be particularly
advantageous if the microflakes are formed air free and
densification prior to film formation is not needed.
[0107] Optionally, the microflakes 108 in the ink may be of alloy
material. In one nonlimiting example, the alloy microflakes may be
binary alloy microflakes such as but not limited to Cu--In, In--Ga,
or Cu--Ga. Alternatively, the microflakes may be a binary alloy of
group IB, IIIA elements, a binary alloy of Group IB, VIA elements,
and/or a binary alloy of group IIIA, VIA elements. In other
embodiments, the particles may be a ternary alloy of group IB,
IIIA, and/or VIA elements. For example, the particles may be
ternary alloy particles of any of the above elements such as but
not limited to Cu--In--Ga. In other embodiments, the ink may
contain particles that are a quaternary alloy of group IB, IIIA,
and/or VIA elements. Some embodiments may have quaternary or
multi-nary microflakes. The ink may also combine microflakes of
different classes such as but not limited to elemental microflakes
with alloy microflakes or the like. In one embodiment of the
present invention, the microflakes used to form the precursor layer
106 contain no oxygen other than those amounts unavoidably present
as impurities. Optionally, the microflakes contain less than about
0.1 wt % of oxygen. In other embodiments, the microflakes contain
less than about 0.5 wt % of oxygen. In still further embodiments,
the microflakes contain less than about 1.0 wt % of oxygen. In yet
another embodiment, the microflakes contain less than about 3.0 wt
% of oxygen. In other embodiments, the microflakes contain less
than about 5.0 wt % of oxygen. Some embodiments may have a shell
layer that contains 0 to 5 wt % of oxygen. Optionally, the shell
may have 5-25 wt % of oxygen. Optionally, the shell may be a full
oxide. Any of the foregoing may optionally be applied to any
particles used with the present invention, regardless of shape or
size. It should also be understood that the source of group VIA
material may be added as discussed in commonly assigned, co-pending
U.S. patent application Ser. No. 11/243,522 (Attorney Docket No.
NSL-046) filed on Feb. 23, 2006 and fully incorporated herein by
reference.
[0108] Optionally, the microflakes 108 in the ink may be
chalcogenide particles, such as but not limited to, a group IB or
group IIIA selenide. In one nonlimiting example, the microflakes
may be a group IB-chalcogenide formed with one or more elements of
group IB (new-style: group 11), e.g., copper (Cu), silver (Ag), and
gold (Au). Examples include, but are not limited to,
Cu.sub.xSe.sub.y, wherein x is in the range of about 1 to 10 and y
is in the range of about 1 to 10. In some embodiments of the
present invention, x<y. Alternatively, some embodiments may have
selenides that are more selenium rich, such as but not limited to,
Cu.sub.1Se.sub.x (where x>1). This may provide an increased
source of selenium as discussed in commonly assigned, co-pending
U.S. patent application Ser. No. 11/243,522 (Attorney Docket No.
NSL-046) filed on Feb. 23, 2006 and fully incorporated herein by
reference. Alternatively, some embodiments may have selenides that
are selenium poor, such as but not limited to, Cu.sub.1Se.sub.x
(where x<1). In another nonlimiting example, the microflakes may
be a group IIIA-chalcogenide formed with one or more elements of
group IIIA (new style: group 16), e.g., aluminum (Al), indium (In),
gallium (Ga), and thallium (Tl). Examples include In.sub.xSe.sub.y
and Ga.sub.xSe.sub.y wherein x is in the range of about 1 to about
10 and y is in the range of about 1 to about 10. Still further, the
microflakes may be a Group IB-IIIA-chalcogenide compound of one or
more group IB elements, one or more group IIIA elements and one or
more chalcogens. Examples include CuInGa--Se.sub.2. Other
embodiments may replace the selenide component with another group
VIA element such as but not limited to sulfur, or combinations of
multiple group VIA elements such as both sulfur and selenium. Any
of the foregoing may optionally apply to any particles used with
the present invention, regardless of shape or size.
[0109] It should be understood that the ink used in the present
invention may include more than one type of chalcogenide
microflakes. For example, some may include microflakes from both
group IB-chalcogenide(s) and group IIIA-chalcogenide(s). Others may
include microflakes from different group IB-chalcogenides with
different stoichiometric ratios. Others may include microflakes
from different group IIIA-chalcogenides with different
stoichiometric ratios.
[0110] Optionally, the microflakes 108 in the ink may also be
particles of at least one solid solution. In one nonlimiting
example, the nano-powder may contain copper-gallium solid solution
particles, and at least one of indium particles, indium-gallium
solid-solution particles, copper-indium solid solution particles,
and copper particles. Alternatively, the nano-powder may contain
copper particles and indium-gallium solid-solution particles. Yet
in another nonlimiting example, the nano-powder may contain both
copper particles and copper-indium-gallium solid-solution
particles
[0111] Generally, an ink may be formed by dispersing the
microflakes (and/or other particles) in a vehicle containing a
dispersant (e.g., a surfactant or polymer) along with (optionally)
some combination of other components commonly used in making inks.
In some embodiments of the present invention, the ink is formulated
without a dispersant or other additives. The carrier liquid may be
an aqueous (water-based) or non-aqueous (organic) solvent. Other
components include, without limitation, dispersing agents, binders,
emulsifiers, anti-foaming agents, dryers, solvents, fillers,
extenders, thickening agents, film conditioners, anti-oxidants,
flow and leveling agents, plasticizers and preservatives. These
components can be added in various combinations to improve the film
quality and optimize the coating properties of the microflake
dispersion. An alternative method to mixing microflakes and
subsequently preparing a dispersion from these mixed microflakes
would be to prepare separate dispersions for each individual type
of microflake and subsequently mixing these dispersions. It should
be understood that, due to favorable interaction of the planar
shape of the microflakes with the carrier liquid, some embodiments
of the ink may be formulated by use of a carrier liquid and without
a dispersing agent.
[0112] The precursor layer 106 from the dispersion may be formed on
the substrate 102 by any of a variety of solution-based coating
techniques including but not limited to wet coating, spray coating,
spin coating, doctor blade coating, contact printing, top feed
reverse printing, bottom feed reverse printing, nozzle feed reverse
printing, gravure printing, microgravure printing, reverse
microgravure printing, comma direct printing, roller coating, slot
die coating, meyerbar coating, lip direct coating, dual lip direct
coating, capillary coating, ink-jet printing, jet deposition, spray
deposition, and the like, as well as combinations of the above
and/or related technologies. The foregoing may apply to any
embodiments herein, regardless of particle size or shape.
[0113] In some embodiments, extra chalcogen, alloys particles, or
elemental particles, e.g., micron- or sub-micron-sized chalcogen
powder may be mixed into the dispersion containing the microflakes
so that the microflakes and extra chalcogen are deposited at the
same time. Alternatively the chalcogen powder may be deposited on
the substrate in a separate solution-based coating step before or
after depositing the dispersion containing the particles. In other
embodiment, group IIIA elemental material such as but not limited
to gallium droplets may be mixed with the flakes. This is more
fully described in commonly assigned, copending U.S. patent
application Ser. No. 11/243,522 (Attorney Docket No. NSL-046) filed
on Feb. 23, 2006 and fully incorporated herein by reference. This
may create an additional layer 107 (shown in phantom in FIG. 1C).
Optionally, additional chalcogen may be added by any combination of
(1) any chalcogen source that can be solution-deposited, e.g. a Se,
S, or calcogen-containing alloy nano- or micron-sized powder mixed
into the precursor layers or deposited as a separate layer, (2)
chalcogen (e.g., Se or S) evaporation, (3) an H.sub.2Se (H.sub.2S)
atmosphere, (4) a chalcogen (e.g., Se or S) atmosphere, (5) an
H.sub.2 atmosphere, (6) an organo-selenium atmosphere, e.g.
diethylselenide or another organo-metallic material, (7) another
reducing atmosphere, e.g. CO, (8) a wet chemical reduction step,
and a (9) heat treatment. The stoichiometric ratio of microflakes
to extra chalcogen, given as Se/(Cu+In+Ga+Se) may be in the range
of about 0 to about 1000. This is purely exemplary and nonlimiting.
Any of the foregoing may optionally apply to any particles used
with the present invention, regardless of shape or size.
[0114] Note that the solution-based deposition of the proposed
mixtures of microflakes does not necessarily have to be performed
by depositing these mixtures in a single step. In some embodiments
of the present invention, the coating step may be performed by
sequentially depositing microflake dispersions having different
compositions of IB-, IIIA- and chalcogen-based particulates in two
or more steps. For example, the method may be to first deposit a
dispersion containing an indium selenide microflake (e.g. with an
In-to-Se ratio of .about.1), and subsequently deposit a dispersion
of a copper selenide microflake (e.g. with a Cu-to-Se ratio of
.about.1) and a gallium selenide microflake (e.g. with a Ga-to-Se
ratio of .about.1) followed optionally by depositing a dispersion
of Se. This would result in a stack of three solution-based
deposited layers, which may be heated together. Alternatively, each
layer may be heated before depositing the next layer. A number of
different sequences are possible. For example, a layer of
In.sub.xGa.sub.ySe.sub.z with x.gtoreq.0 (larger than or equal to
zero), y.gtoreq.0 (larger than or equal to zero), and z.gtoreq.0
(larger than or equal to zero), may be formed as described above on
top of a uniform, dense layer of Cu.sub.wIn.sub.xGa.sub.y with
w.gtoreq.0 (larger than or equal to zero), x.gtoreq.0 (larger than
or equal to zero), and y.gtoreq.0 (larger than or equal to zero),
and subsequently converting the two layers into CIGS. Alternatively
a layer of Cu.sub.wIn.sub.xGa.sub.y may be formed on top of a
uniform, dense layer of In.sub.xGa.sub.ySe.sub.z and subsequently
converting the two layers into CIGS.
[0115] In alternative embodiments, microflake-based dispersions as
described above may further include elemental IB, and/or IIIA
nanoparticles (e.g., in metallic form). These nanoparticles may be
in flake form, or optionally, take other shapes such as but not
limited to spherical, spheroidal, oblong, cubic, or other
non-planar shapes. These particles may also include but is not
limited to emulsions, molten materials, mixtures, and the like, in
addition to solids. For example Cu.sub.xIn.sub.yGa.sub.zSe.sub.u
materials, with u>0 (larger than zero), with x.gtoreq.0 (larger
than or equal to zero), y.gtoreq.0 (larger than or equal to zero),
and z.gtoreq.0 (larger than or equal to zero), may be combined with
an additional source of selenium (or other chalcogen) and metallic
gallium into a dispersion that is formed into a film on the
substrate by heating. Metallic gallium nanoparticles and/or
nanoglobules and/or nanodroplets may be formed, e.g., by initially
creating an emulsion of liquid gallium in a solution. Gallium metal
or gallium metal in a solvent with or without emulsifier may be
heated to liquefy the metal, which is then sonicated and/or
otherwise mechanically agitated in the presence of a solvent.
Agitation may be carried out either mechanically,
electromagnetically, or acoustically in the presence of a solvent
with or without a surfactant, dispersant, and/or emulsifier. The
gallium nanoglobules and/or nanodroplets can then be manipulated in
the form of a solid-particulate, by quenching in an environment
either at or below room temperature to convert the liquid gallium
nanoglobules into solid gallium nanoparticles. This technique is
described in detail in commonly-assigned U.S. patent application
Ser. No. 11/081,163 to Matthew R. Robinson and Martin R. Roscheisen
entitled "Metallic Dispersion", the entire disclosures of which are
incorporated herein by reference.
[0116] Referring now to FIG. 1C, the precursor layer 106 may then
be processed in a suitable atmosphere to form a film. The film may
be a dense film. In one embodiment, this involves heating the
precursor layer 106 to a temperature sufficient to convert the ink
(as-deposited ink. Note that solvent and possibly dispersant have
been removed by drying) to a film. The temperature may be between
about 375.degree. C. and about 525.degree. C. (a safe temperature
range for processing on aluminum foil or high-melting-temperature
polymer substrates). The processing may occur at various
temperatures in the range, such as but not limited to 450.degree.
C. In other embodiments, the temperature at the substrate may be
between about 400.degree. C. and about 600.degree. C. at the level
of the precursor layer, but optionally cooler at the substrate. The
time duration of the processing may also be reduced by at least
about 20% if certain steps are removed. In one embodiment, the
heating may occur over a range between about two minutes to about
ten minutes. In one embodiment, the processing comprises heating
the precursor layer to a temperature greater than about 375.degree.
C. but less than a melting temperature of the substrate for a
period of less than about 15 minutes. In another embodiment, the
processing comprises heating the precursor layer to a temperature
greater than about 375.degree. C. but less than a melting
temperature of the substrate for a period of about 1 minute or
less. In a still further embodiment, the processing comprises
heating the precursor layer to an annealing temperature but less
than a melting temperature of the substrate for a period of about 1
minute or less. The processing step may also be heated and/or
accelerated via thermal processing techniques using at least one of
the following processes: pulsed thermal processing, exposure to
laser beams, or heating via IR lamps, and/or similar or related
processes. Although not limited by the following, one-step
processes typically occur in a reactive atmosphere, while
multi-step processes may include one or steps in non-reactive
atmosphere(s) while the remaining steps are in an reactive
atmosphere.
[0117] Although pulsed thermal processing remains generally
promising, certain implementations of the pulsed thermal processing
such as a directed plasma arc system, face numerous challenges. In
this particular example, a directed plasma arc system sufficient to
provide pulsed thermal processing is an inherently cumbersome
system with high operational costs. The direct plasma arc system
requires power at a level that makes the entire system
energetically expensive and adds significant cost to the
manufacturing process. The directed plasma arc also exhibits long
lag time between pulses and thus makes the system difficult to mate
and synchronize with a continuous, roll-to-roll system. The time it
takes for such a system to recharge between pulses also creates a
very slow system or one that uses more than one directed plasma
arc, which rapidly increase system costs.
[0118] In some embodiments of the present invention, other devices
suitable for rapid thermal processing may be used and they include
pulsed lasers used in adiabatic mode for annealing (Shtyrokov E I,
Sov. Phys.--Semicond. 9 1309), continuous wave lasers (10-30W
typically) (Ferris S D 1979 Laser-Solid Interactions and Laser
Processing (New York: AIP)), pulsed electron beam devices (Kamins T
I 1979 Appl. Phys. Leti. 35 282-5), scanning electron beam systems
(McMahon R A 1979 J. Vac. Sci. Techno. 16 1840-2) (Regolini J L
1979 Appl. Phys. Lett. 34 410), other beam systems (Hodgson R T
1980 Appl. Phys. Lett. 37 187-9), graphite plate heaters (Fan J C C
1983 Mater. Res. Soc. Proc. 4 751-8) (M W Geis 1980 Appl. Phys.
Lett. 37 454), lamp systems (Cohen R L 1978 Appl. Phys. Lett. 33
751-3), and scanned hydrogen flame systems (Downey D F 1982 Solid
State Technol. 25 87-93). In some embodiments of the present
invention, a non-directed, low density system may be used.
Alternatively, other known pulsed heating processes are also
described in U.S. Pat. Nos. 4,350,537 and 4,356,384. Additionally,
it should be understood that methods and apparatus involving pulsed
electron beam processing and rapid thermal processing of solar
cells as described in expired U.S. Pat. Nos. 3,950,187 ("Method and
apparatus involving pulsed electron beam processing of
semiconductor devices") and 4,082,958 ("Apparatus involving pulsed
electron beam processing of semiconductor devices") are in the
public domain and well known. U.S. Pat. No. 4,729,962 also
describes another known method for rapid thermal processing of
solar cells. The above may be applied singly or in single or
multiple combinations with the above or other similar processing
techniques with various embodiments of the present invention.
[0119] It should be noted that using microflakes typically results
in precursor layers that heat into a solid layer at temperatures as
much as 50.degree. C. lower than a corresponding layer of spherical
nanoparticles. This is due in part because of the greater surface
area contact between particles. Of course, it should be understood
that the use of solid group IIIA-based particles is not limited to
only planar particles such as microflakes, and those solid group
IIIA-based particles may be suitable for particles of various
shapes.
[0120] In certain embodiments of the invention, the precursor layer
106 (or any of its sub-layers) may be annealed, either sequentially
or simultaneously. Such annealing may be accomplished by rapid
heating of the substrate 102 and precursor layer 106 from an
ambient temperature to a plateau temperature range of between about
200.degree. C. and about 600.degree. C. In this embodiment of the
invention, the temperature is maintained in the plateau range for a
period of time ranging between about a fraction of a second to
about 60 minutes, and subsequently reduced. Alternatively, the
annealing temperature could be modulated to oscillate within a
temperature range without being maintained at a particular plateau
temperature. This technique (referred to herein as rapid thermal
annealing or RTA) is particularly suitable for forming photovoltaic
active layers (sometimes called "absorber" layers) on metal foil
substrates, such as but not limited to aluminum foil. Other
suitable substrates include but are not limited to other metals
such as Stainless Steel, Copper, Titanium, or Molybdenum,
metallized plastic foils, glass, ceramic films, and mixtures,
alloys, and blends of these and similar or related materials. The
substrate may be flexible, such as the form of a foil, or rigid,
such as the form of a plate, or combinations of these forms.
Additional details of this technique are described in U.S. patent
application Ser. No. 10/943,685, which is incorporated herein by
reference.
[0121] The atmosphere associated with the annealing step may also
be varied. In one embodiment, the suitable atmosphere comprises a
hydrogen atmosphere. In another embodiment the suitable atmosphere
comprises a carbon monoxide atmosphere. However, in other
embodiments where very low or no amounts of oxygen are found in the
microflakes and/or other particles, the suitable atmosphere may be
comprised of a nitrogen atmosphere, an argon atmosphere, a carbon
monoxide atmosphere, or an atmosphere having less than about 10%
hydrogen. These other atmospheres may be advantageous to enable and
improve material handling during production.
[0122] Referring now to FIG. 1D, the precursor layer 106 is
processed to form the dense film 110. The dense film 110 may
actually have a reduced thickness compared to the thickness of the
wet precursor layer 106 since the carrier liquid and other
materials have been removed during processing. In one embodiment,
the film 110 may have a thickness in the range of about 0.5 microns
to about 2.5 microns. In other embodiments, the thickness of film
110 may be between about 1.5 microns and about 2.25 microns. In one
embodiment, the resulting dense film 110 may be substantially void
free. In some embodiments, the dense film 110 has a void volume of
about 5% or less. In other embodiments, the void volume is about
10% or less. In another embodiment, the void volume is about 20% or
less. In still other embodiments, the void volume is about 24% or
less. In still other embodiments, the void volume is about 30% or
less. The processing of the precursor layer 106 will fuse the
microflakes together and in most instances, remove void space and
thus reduce the thickness of the resulting dense film.
[0123] Depending on the type of materials used to form the film
110, the film 110 may be a film for use in a one step process, or a
two step process, or a multi-step process. In a one step process,
the film 110 is formed to include group IB-IIIA-VIA compounds and
the film 110 may be an absorber film suitable for use in a
photovoltaic device. In a two step process, the film 110 may be a
solid and/or densified film that will have further processing to be
suitable for use as an absorber film for use in a photovoltaic
device. As a nonlimiting example, the film 110 in a two step
process may not contain any and/or sufficient amounts of a group
VIA element to function as an absorber layer. Adding a group VIA
element or other material may be the second step of the two-step
process. Either a mixture of two or more VIA elements can be used,
or a third step can be added with another VIA element as used in
the second step. A variety of methods of adding that material
include printing of group VIA element, using VIA element vapor,
and/or other techniques. It should also be understood that in a two
step process, the process atmospheres may be different. By way of
nonlimiting example, one atmosphere may optionally be a group
VIA-based atmosphere. As another nonlimiting example, one
atmosphere may be an inert atmosphere as described herein. It
should be understood that this further processing may actually
react the densified film into a layer with increased thickness.
[0124] Optionally, the present invention may comprise of adding a
material to solidify micron-sized or larger feedstock (to be used
to prepare sub-micron or nano-sized particles), that otherwise
would be all or partially liquid at particle preparation, handling,
or deposition or pre-deposition temperature. In another embodiment,
the present invention may comprise of adding material to solidify
sub-micron or nano-sized globules/droplets, that otherwise would be
all or partially liquid at particle preparation, handling, or
deposition or pre-deposition temperature. All combinations of size
(large feedstock and sub-micron), process temperature (particle
preparation, ink and web handling, and deposition), and timing
(before size reduction, after size reduction) are considered
herein.
Solid Group IIIA Particles
[0125] Referring now to FIG. 2, various methods of forming the
solid particles such as but not limited to solid group IIIA
particles will now be described. For some of the embodiments
described herein, it may be desirable to have particles that are in
solid form. This may be particularly useful for processing group
IIIA-based materials in preparation for introduction into the
precursor layer and/or resulting semiconductor film. Solid
particles may allow for the use of known processing techniques for
size reduction and/or shape alteration on the group IIIA-based
material prior to dispersing the material in a carrier liquid. This
may simplify processing and increase process robustness.
[0126] Obtaining solid particles is generally not an issue for many
of the elements used in forming CIGS based solar cells because they
are solid at/or near room temperature. However, some materials,
particularly group IIIA-based materials, may be in liquid form
at/or near room temperature, and the liquid form may increase the
difficulty of handling the material or reducing the material to
sufficiently small particle and/or droplet sizes. For example,
elemental gallium (Ga) may be liquid at temperatures higher than
30.degree. C., and elemental indium (In) may be liquid at
temperatures above 156.degree. C. Certainly, there are many
possible ways for including these Group IIIA elements into printed
CIGS solar cells including, but not limited to using a liquid
metallic dispersion of liquid group IIIA elements. One such method
is described in commonly assigned copending U.S. patent application
Ser. No. 11/081,163, filed Mar. 16, 2005 and in copending U.S.
patent application Ser. No. 10/782,017, filed Feb. 19, 2004, both
fully incorporated herein by reference for all purposes.
[0127] It is possible, however, to solidify Group IIIA based
materials and increase their melting temperatures. This may
advantageously increase the robustness of the thin-film
manufacturing process. A variety of materials may be introduced in
appropriate amounts to change the characteristics of elemental
gallium or indium and create solid particles of Group IIIA-based
materials. The resulting solid materials may be, but are not
limited to, metallic alloys, chalcogen-based alloys, and/or salts.
In one embodiment of the present invention, sodium may be the
material introduced to increase the melting temperature of the
resulting alloy. Advantageously, sodium is not a contaminant that
needs to be removed from the resulting Group IB-IIIA-VIA film.
Concurrently, sodium may improve the performance of the
photovoltaic device. Furthermore, an alloy of a Group IIIA element
and an added material such as, but not limited to, sodium or other
group IA elements will be in solid state well above room
temperature and above all size reduction/shape altering/particle
formation processes used with the materials. This allows spherical
and/or non-spherical particles to be made via processes such as but
not limited to milling, evaporation condensation (EC),
electroexplosive wire (EEW), plasma pulse processing, or other
methods to create particles desired for use in the present
invention.
[0128] Referring now to FIG. 2, a phase diagram of gallium and
sodium (Ga--Na) is shown. As seen in FIG. 2, the phase diagram of
Ga--Na indicates that the melting point of the binary alloy steady
rises from about 30.degree. C. to about 499.degree. C. as the
weight percent of sodium is increased from about 0% to about 8% the
amount of solid material increases and stays solid at higher
temperature compared to pure gallium (30.degree. C.), up to about
499.degree. C. at about 8%. (as seen along the top axis). Hence,
the addition of sodium will substantially increase the range of
temperatures where at least part of the Ga--Na is a solid and can
be handled or sized-reduced while in solid form. At about 7.6
weight percent, the alloy may be stable as Ga.sub.4Na), the Ga--Na
alloy turns into a line-compound and is all solid up to 499.degree.
C. Compounds containing lower amounts of sodium may contain
portions that separate out into elemental Gallium. At higher weight
percentages such as about 15.7% Na, the alloy may be stable as
Ga.sub.39Na.sub.22. The melting temperature of such an alloy of
Ga.sub.39Na.sub.22 may be as high as about 556.degree. C. This is
substantially higher than the handling and processing temperature
associated with preparing the particles for deposition and is one
method of introducing Gallium using a stable, solid particle.
[0129] Referring now to FIG. 3, a similar result can also be found
for other group IIIA based alloys such as indium and sodium
(In--Na). At about 11.1 weight percent of sodium, the In--Na alloy
turns into a line-compound, is In.sub.8Na.sub.5 and may have a
melting temperature as high as 441.degree. C. At about 16.7 weight
percent of sodium, the In--Na alloy turns into the line-compound is
InNa and may have a melting temperature as high as 345.degree. C.
Again, the addition of a second material, which in this case is
sodium to indium, increases the range of temperatures where the
group IIIA-based particle is a solid particle and can be handled
and processed in the same manner as other solid particles.
[0130] As a nonlimiting example, the range of materials suitable
for use in increasing the temperature where liquid is formed
Accordingly, as seen with regards to FIGS. 2 and 3, material such
as a Group IA element may be added to a Group IIIA element to
solidify the Group IIIA element that otherwise would be all or
partially liquid at particle preparation, handling, or deposition
or pre-deposition temperature. This material may be added to
micron-sized or larger Group IIIA feedstock to be used to prepare
sub-micron or nano-sized particles. Optionally, the material may be
added to solidify sub-micron or nano-sized globules/droplets that
otherwise would be all or partially liquid at particle preparation,
handling, or deposition or pre-deposition temperature. The amount
of group IA material may be adjusted to account for any
combinations of size (large feedstock and sub-micron), process
temperature (particle preparation, ink and web handling, and
deposition), and timing (before size reduction, after size
reduction) to reduce premature presence of liquid.
[0131] In addition to Group IA elements mentioned above, another
embodiment of the invention may use other materials that can
maintain a substantially all solid material. As a nonlimiting
example, the range of material suitable for use in increasing the
melting and/or reacting temperature of a group IIIA-based material
may include: sodium, lithium, potassium, rubidium, cesium, sulfur,
selenium, rare-earth elements, and/or aluminum. This suitable
material may include one or more group IA-based material (in
elemental, alloy, or compound form). By way of example and not
detract from semiconductor film quality include, but are not
limited to: lithium, potassium, rubidium, cesium, sulfur, aluminum,
and/or combinations thereof.
[0132] As a nonlimiting example, the range of materials suitable
for use in increasing the temperature where liquid is formed in a
group IIIA-based material may include one or more group IA-based
materials (in elemental, alloy, or compound form). By way of
example and without limitation, Table I shows some of the possible
combinations.
TABLE-US-00001 TABLE I Na Li K Rb Cs S Al In In--Na In--Li In--K
In--Rb In--Cs In--S In--Al Ga Ga--Na Ga--Li Ga--K Ga--Rb Ga--Cs
Ga--S Ga--Al In--Ga In--Ga--Na In--Ga--Li In--Ga--K In--Ga--Rb
In--Ga--Cs In--Ga--S In--Ga--Al Cu--In--Ga Cu--In--Ga--
Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga--
Cu--In--Ga-- Na Li K Rb Cs S Al Al--Ga Al--Ga--Na Al--Ga--Li
Al--Ga--K Al--Ga--Rb Al--Ga--Cs Al--Ga--S Al--Ga Al--In Al--In--Na
Al--In--Li Al--In--K Al--In--Rb Al--In--Cs Al--In--S Al--In
Cu--Al--Ga Cu--Al--Ga-- Cu--Al--Ga-- Cu--Al--Ga-- Cu--Al--Ga--
Cu--Al--Ga-- Cu--Al--Ga-- Cu--Al--Ga Na Li K Rb Cs S Cu--Al--In
Cu--Al--In-- Cu--Al--In-- Cu--Al--In-- Cu--Al--In-- Cu--Al--In--
Cu--Al--In-- Cu--Al--In Na Li K Rb Cs S Cu--In--Se Cu--In--Se--
Cu--In--Se-- Cu--In--Se-- Cu--In--Se-- Cu--In--Se-- Cu--In--Se--
Cu--In--Se-- Na Li K Rb Cs S Al Cu--Ga--Se Cu--Ga--Se--
Cu--Ga--Se-- Cu--Ga--Se-- Cu--Ga--Se-- Cu--Ga--Se-- Cu--Ga--Se--
Cu--Ga--Se-- Na Li K Rb Cs S Al In--Ga--Se In--Ga--Se--
In--Ga--Se-- In--Ga--Se-- In--Ga--Se-- In--Ga--Se-- In--Ga--Se--
In--Ga--Se-- Na Li K Rb Cs S Al Cu--In--Ga-- Cu--In--Ga--
Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga--
Cu--In--Ga-- Se Se--Na Se--Li Se--K Se--Rb Se--Cs Se--S Se--Al
[0133] As a nonlimiting example, the range of materials suitable
for use in increasing the temperature where liquid is formed in a
group IIIA-based material may include one or more group IA-based
materials (in elemental, alloy, or compound form). By way of
example and without limitation, Table I shows some of the possible
combinations. Various sodium salts and other salt compounds may
added to Gallium or other group IIIA elements to form solid
compounds. Although not limited to the following, some examples of
Gallium-based compounds include: Ga--Na--F (better leave out
stoichiometry), GaF.sub.3, and or Ga(NO.sub.3).sub.3. Similar
Indium based compounds may also be used. Basically, any Ga, In, or
Ga--In-salt could be included, e.g. any halide as counter-anion
(although Cl less optimal as it may decrease performance of CIGS
cells), sulfates, sulfites, nitrates, phosphates, hydroxides,
selenites, borates, acetate, butyrate, hexanoate, etc. . . .
Although not limited to the following, the salts may be selected to
NOT be soluble in the solvent. The salt counter-ion may easily be
decomposed with the counterion decomposing into volatiles, either
by heating in an inert atmosphere, heating in a reducing
atmosphere, heating in a selenizing (sulfurizing) atmosphere, or
any combination of the previous. Additionally, any other
conceivable method of replacing the counter-ion by Se and/or S
(e.g. wet chemically) would allow counter-ions that do not
decompose under heat, H2, and/or a selenizing or sulfurizing
atmosphere.
[0134] Apart from alloys of IIIA and sodium, sodium can be added in
different ways as well. Other suitable sodium containing compounds
include any deprotonated organic and inorganic acid, deprotonated
alcohol where the proton is replaced by sodium. The list may also
include deprotonated acids, being the sodium salt of the
(deprotonated) acid, sodium hydroxide, sodium acetate, and the
sodium salts of e.g. the following acids: Butyric acid, Caproic
Acid, Caprylic Acid, Capric Acid, Laurie Acid, Myristic Acid,
Palmitic Acid, Palmitoleic Acid, Stearic Acid, Oleic Acid, Vaccenic
Acid, Linoleic Acid, Alpha-Linolenic Acid, Gamma-Linolenic Acid.
Other possibilities include deprotonated alcohols such as sodium
ethoxide. Other inorganic compounds include sodium nitrate, sodium
selenite, sodium sulphate, sodium sulphite, sodium phosphate,
and/or sodium phospite.
[0135] In another embodiment of the present invention, the
technique of using a group IIIA-based alloy to introduce a group
IIIA element into the semiconductor film may be optimized if the
material alloyed with the group IIIA element is a material that
does not need to be subsequently removed from the semiconductor
film. Sodium may be advantageous in this regard. Other materials
that may be used in amounts that will not detract from
semiconductor film quality include, but are not limited to: sodium,
lithium, potassium, rubidium, cesium, sulfur, aluminum, and/or
combinations thereof. Materials containing high amounts of carbon
(C), nitrogen (N), or oxygen (O), or fluoride (F) would leave
residuals that may need to be removed to maximize performance of
the resulting semiconductor film.
[0136] As further example of solid Group IIIA-based materials,
solid Ga particles can optionally also be created via temperature
control (Ga <29.degree. C.) or when combined to form Cu--Ga,
Cu--Ga--In, Ga--Se, Ga--S, In--Ga--S, In--Ga--Se, etc., Ga--IA
(e.g. with Group IA e.g. Na, K, Li), Ga-salts (e.g. GaF.sub.3,
Ga(NO.sub.3).sub.3). For certain embodiments of the present
invention using salts and even for more exotic organo-gallium
compounds, the element and/or materials added to Ga are preferably
removed prior to, during, or after the formation of CIGS to
minimize the amount of C, N, O, F, etc. in the CIGS film as
previously mentioned.
[0137] The alloy may be formed by a variety of methods such as, but
not limited to, atomization, pyrometallurgy, mechanical alloying,
or combinations thereof. Bulk materials of the alloy may be treated
by the following to form particles using at least one of the
following methods: grinding, milling, electroexplosive wire (EEW)
processing, evaporation condensation (EC), pulsed plasma
processing, or combinations thereof. Optionally, the particles may
be formed using at least one of the following methods:
spray-pyrolysis, laser pyrolysis, or a bottom-up technique like wet
chemical approaches. It should be understood that in some
embodiments, further processing may be used to refine the material
created as described above. For example, mechanical alloying may be
used to combine a material such as Ga--Na with Cu--In or other
materials. This may be particularly useful if a ternary or
multi-nary alloy is too hard to mill into smaller pieces or
different shapes. In some embodiments, instead of starting with an
atomically homogeneously mixed feedstock, a mixture of two or more
start materials each having a different composition may be using
during mechanical milling.
[0138] The particles created above may be used in a precursor
material in a variety of substances including a solution coatable
ink for forming a film on a substrate. The method may include
formulating an ink containing the precursor material and then
solution depositing the ink onto a substrate to form a precursor
layer on the substrate. Of course as previously described, the
precursor layer may be reacted in a suitable atmosphere to form a
group IB-IIIA-VIA based film in a one step process or it may become
a group IB-IIIA-VIA based film via a two-step or multi-step
process.
[0139] The solid IIIA-based particles may optionally be a sole
source of group IIIA elements in the ink. In terms of composition,
the resulting film may have a Cu/(In+Ga) compositional range of
about 0.01 to about 1.0 and a Ga/(In+Ga) compositional range of
about 0.01 to about 1.0. The film may have a Cu/(In+Ga)
compositional range of about >1.0 for Cu/(In+Ga) and a
Ga/(In+Ga) compositional range of about 0.01 to about 1.0. The film
may have a Cu/(In+Ga) compositional range of about 0.01 to about
1.0 and a Ga/(In+Ga) compositional range of about 0.01 to about
1.0. Optionally, the film has a desired Cu/(In+Ga) molar ratio is
in the range of about 0.7 to about 1.0 and a desired Ga/(Ga+In)
molar ratio in the range of about 0.1 to about 0.8. Optionally,
there is the possibility of having a ratio of Cu/(In+Ga)>1.0 and
using subsequent post-treatment (KCN, etc.) to change
Cu/(In+Ga)<1.0.
Adding Material to Solidify an Alloy
[0140] Referring now to FIGS. 4A and 4B, another embodiment of the
present invention adds a material 130 such as but not limited to
sodium to metal alloys 132 that might ordinarily be characterized
by leaching or phase separation of a component element from the
alloy particle contains regions that are liquid and other regions
that are solid (i.e. phase separation of a group IIIA component
such as liquid gallium). In one such example involving a group
IIIA-based alloy, a group IIIA alloy such as copper gallium may
have gallium leach from the alloy as the temperature increases
and/or during mechanical alloying. This leaching is generally
undesirable since this may change the stoichiometry of the
resulting reaction if the leached material is lost and the leeching
occurs prior to processing of the materials. It may also be
disadvantageous during processing since the liquid form may change
the kinetics of the reaction. For example, if too much liquid is
present at or near the onset of a reaction, liquid may group
together at certain areas and not be evenly distributed throughout
the reaction area. In other situations, the leached material may
gum-up or clog equipment used in milling.
[0141] To solidify elements which may leach in liquid form at
particle preparation, handling, or deposition or pre-deposition
temperature, a material as described previously may be combined
with the alloy. This may include adding a group IA element or
IA-based material such as sodium to metal alloys such as In--Ga,
Cu--In--Ga, In--Ga--Se, Ga--Se and other metal alloys as described
in Table I. The methods used to make this solid alloy 134 may
include any of those described previously herein. The addition of
this material overcomes gallium leaching which may occur during
milling and/or mechanical alloying of the bulk materials.
[0142] It should be understood that a binary or multinary alloy
(such as but not limited to IB-IIIA-VIA-IA) in a broad range of
compositions hardly ever consists of one (solid) line-compound, but
typically is a combination of two or more line-compounds and
solid-solutions, where one or more compounds might be present as a
liquid at processing temperature. As a non-limiting example, Ga--Na
at 300.degree. C. with a composition of 15 atomic percent Na
consists mainly of solid Ga.sub.4Na (at thermodynamic equilibrium,
see phase diagram) and some, almost pure, liquid gallium. Another
nonlimiting example, Ga--Na at 200.degree. C. with a composition of
28 atomic percent sodium consists of a mixture of two different
solids, being Ga.sub.4Na and Ga.sub.39Na.sub.22. In other words, a
material with a formula like e.g. Cu--In--Ga (with or without
details on the actual stoichiometry of the bulk material) might
consist of one, but more commonly, a mixture of two or more
different compounds of different compositions.
[0143] The material 130 to be added to the alloy may be prepared
using a variety of methods such as but not limited to atomization,
pyrometallurgy, mechanical alloying, or combinations thereof. The
resulting material may then be treated using the previously
mentioned methods of grinding, milling, electroexplosive wire (EEW)
processing, evaporation condensation (EC), pulsed plasma
processing, or combinations thereof.
[0144] FIG. 4B shows that the particles need not be spherical and
may have a material represented in a non-spherical particle 140 and
the alloy represented by non-spherical particle 142. The resulting
alloy may also be non-spherical particles 144. Of course,
combinations of spherical and non-spherical particles are also
combinable. It should also be understood that the group IIIA
elements may be introduced where one or more are introduced as a
liquid (or as liquid droplets/nanoglobules) in combination with
solid particles.
[0145] The amount of material added may be in trace or dopant
amounts or it may be in sufficient amounts to alter the composition
of the resulting film. In one embodiment, the final film may
include 1) a group IB-IIIA-VIA-IA compound and/or 2) at least a
mixture of one or more IB-IIIA-VIA compounds and one or more
IA-containing compounds. Of course, other embodiments may use other
materials such as but not limited to rare earth elements in place
of IA material. Because the atomic concentration of group IA
material may be much lower than the concentration of the IB, IIIA,
and VIA elements, the IA elements are typically not mentioned and
are seen as dopants.
Quenching Group IIIA Droplets Via Addition of Group IA Material
[0146] Referring now to FIG. 5, it should be understood that the
formation of solid group IIIA-based alloy particles may be achieved
by a variety of methods many of which were discussed above. The
present embodiment describes a still further process that uses an
emulsion-based process wherein a material such as sodium is added
to an emulsion of a group IIIA-based material to solidify droplets
and/or nanoparticles in the emulsion. The formed solid material may
be Ga.sub.4Na or other similar materials that are solid at or near
room temperature. The sodium may be added in the form of elemental
sodium and/or a sodium-based compound, either to a group IIIA-based
emulsion (of droplets) or dispersion (of solid particles). Other
embodiments may add liquid sodium (melting point 100.degree. C.),
either to a group IIIA-based emulsion (of droplets) or dispersion
(of solid particles). Still further embodiments may add a
sodium-based emulsion, either to a group IIIA-based emulsion (of
droplets), or to a group IIIA-based dispersion (of solid
particles)). Still further embodiments may add a sodium-based
emulsion to a gallium-based emulsion.
[0147] As seen in the example of FIG. 5, an emulsion of gallium is
created by adding gallium shot 150 into a carrier liquid 152. The
carrier liquid 152 may be a solvent and/or include a surfactant.
Optionally, the carrier liquid 152 may be a non-organic solvent. In
some embodiments, the carrier liquid 152 is water. The combined
gallium shot 150 and carrier liquid 152 may then be heated, prior
to or during agitation, to a temperature within a desired range.
The temperature range in this particular example may be between
about 40.degree. C. to about 110.degree. C. Preferably, the
temperature will be 100.degree. C. or greater. The heated material
154 may then be agitated to create the gallium emulsion 156. The
agitation may be by sonication, vibration, stirring, manipulation
of fluid flow, and/or combinations thereof, or any other
combination of mechanical, electromagnetic, or acoustic means.
[0148] Referring still to FIG. 5, the group IA-based material added
to the gallium emulsion 156 may be prepared by adding the group IA
shots 160 into a carrier liquid 162. The carrier liquid 162 may be
a solvent and/or include a surfactant. Optionally, the carrier
liquid 162 may be a non-organic solvent. In some embodiments, the
carrier liquid 162 is water. The combined group IA shots 160 and
carrier liquid 162 may then be heated to a temperature sufficient
to liquefy the group IA shots 160. The temperature will preferably
be 100.degree. C. or greater. The heated material 164 may then be
agitated to create the group IA-based emulsion 166. The agitation
may be sonication, stirring, manipulating of fluid flow, mechanical
churning, and combinations thereof, or any other combination of
mechanical, electromagnetic, or acoustic means.
[0149] In one embodiment of the present invention, the gallium
emulsion 156 and the group IA emulsion 166, e.g. a Na emulsion, may
be combined to form the Ga.sub.4Na dispersion 170 which may be
dried to obtain dry Ga.sub.4Na particles. In other embodiments, it
should be understood that dry Na or group IA element powder may be
used in place of and/or in combination with the group IA emulsion
166. This may provide sufficient amounts of sodium or group IA
element to reach the desired stoichiometry to form the desired
group IIIA-IA based particles. Note that it might be advantageous
to make the Ga-emulsion at rt (or 40.degree. C.), make the
Na-emulsion >100.degree. C., subsequently, cool-down one or both
to have either one or both as solid particles during the alloying
in case the alloying is extremely exothermic (lot of heat
generated, possibly causing an uncontrollable reaction). If the
reaction is easily controlled, than in view of time, having both
>100.degree. C. would be the best (liquid-liquid chemistry
typically faster than liquid-solid or solid-solid).
[0150] Referring now to FIGS. 6A and 6B, the emulsion technique may
lead to smaller particles than the gallium droplets 180 in the
initial Ga-emulsion 156. This may be the result of the slow
addition of the sodium emulsion into the emulsion of gallium, or
vice versa. The gallium will diffuse into the (smaller) sodium
droplets in emulsion 166 or Ga.sub.4Na shells or cores will be
found on or inside the gallium droplets 182 (see FIG. 6B) which
will then be broken up by sonication or other processes while
exposing new un-reacted gallium in smaller droplets 184. The
portions broken off will likely be smaller particles and the
continued exposure of unreacted gallium will continue to create
other small particles. Furthermore, it is possible that milling be
used as the agitation source in this case since any coating from
liquid gallium on mill part will come off when solidified. As seen
in FIG. 6B, some of the solidified particles 186 of Ga.sub.4Na will
settle to the bottom of the container if unagitated. Of course,
other techniques besides sonication may also be used to size reduce
and/agitate the globules in the emulsion. Other such techniques
include but are not limited to: mechanical agitation, high pressure
homogenization using a device such as an Emulsiflex.TM., available
from Avestin, Inc., agitation via stirring, and emulsification via
(horizontal) bead-milling, manipulation of fluid flow, stirring,
combinations of the foregoing, or the like.
[0151] Note that forming solid In particles by quenching an
emulsion of In is possible as well, from a particle synthesis and
size control point of view. The process may involve making an
In-emulsion and quenching the emulsion by adding a compound that
acts as a seed to solidify it into smaller particles than the
In-nanoglobules.
Bandgap Grading Using IIIA-Based Materials
[0152] Referring now to FIGS. 7A-7C, a still further embodiment of
the present invention will now be described. This embodiment
describes a method of selecting materials that have different
reaction rates, due to e.g. a higher thermodynamic stability
compared to the other materials used, to achieve a desired
distribution of material in the photovoltaic device. This may allow
for fine tuning of the resulting photovoltaic device by controlling
where materials are located in the device layers. By way of
nonlimiting example, the reaction rate of the group IIIA-IA based
alloy may be sufficiently high such that it does not react until
other portions of the precursor material have begun to react. For
Ga.sub.4Na and Ga.sub.39Na.sub.22, they melt at the selenization
temperature and above the anneal temperature for other materials
used for CIGS formation via RTP. For example, the melting point of
Ga.sub.4Na and Ga.sub.39Na.sub.22 is much higher than the typical
decomposition, melting, and reaction temperatures of most of the
intermetallic alloys and chalcogenides present, formed, and
consumed during the absorber growth process(es). This
advantageously keeps these materials at or near the locations where
these materials were deposited and not letting them migrate as they
tend to do when they react at the same time as the other
materials.
[0153] As seen in FIG. 7A, one embodiment of the present invention
involves coating a dispersion 200 of the solid group IIIA-IA based
particles over the precursor layer 202. In this example, the
precursor layer 202 may be a layer of un-annealed material over a
conductive layer 204 and a substrate 206. Although not limited to
the following, the particles in layer 202 may be all spherical
particles, all non-spherical particles, and/or mixtures of
particles of various shapes. When heated as shown in FIG. 7B, the
precursor layer 202 fuses into the annealed layer 208. FIG. 7B
continues to show that the coating of the dispersion 200 continues
to have particles of solid group IIIA-IA based material. The
dispersion 200 with the solid particles of group IIIA-IA based
material has not reached a sufficient temperature to react the
particles therein significantly, or at least not to the same extent
as the particles in 202. The layers of materials continues to be
heated from the configuration of FIG. 7B to that of 7C. FIG. 7C
shows that continued heating at a higher temperature or for a
longer time results in the reacting of the coating of the
dispersion 200 and formation of a layer 210 similar to the layer
208, except that the layer 210 has an increased group IIIA and
group IA concentration. The annealed layers 208 and 210 may be part
of a two-step or multi-step processing technique where further
processing is required to turn the layers into an absorber layer.
Thus for a CIGS absorber layer, the layers 208 and 210 may require
further selenization to become a CIGS absorber layer. Due to the
differing compositions of the layers 208 and 210 (i.e. higher group
IIIA content in layer 210), a desired bandgap grading will be
retained in the resulting absorber layer. The stoichiometry will be
such that there is a higher ratio of a group IIIA element such as
but not limited to gallium in the layer 210 than in layer 208 to
obtain the desired performance and/or bandgap. In one embodiment,
the desired stoichiometric ratio in layer 208 for band gap grading
may include but is not limited to a Ga/(In+Ga) at the back of 208
(and 210) in the range of 0.3-0.7, close to the top surface of 210
a Ga/(In+Ga) of 0.1-0.4, and at the top surface of 210 a Ga/(In+Ga)
in the range of 0.15-0.45. Regarding Cu/(In+Ga); in the bulk
<1.0.
[0154] Referring now to FIGS. 8A-8C, yet another embodiment of the
present invention will now be described. This embodiment of the
present invention involves coating a dispersion 220 of the solid
group IIIA-IA based particles over a precursor layer 222. In this
example, the precursor layer 222 may be a layer of unannealed
material over a conductive layer 204 and a substrate 206, or may
contain one or more evaporated layers including selenium. The
conductive layer 204 may be conductive electrically, thermally, or
both. When heated as shown in FIG. 8B, the precursor layer 222
fuses into the annealed layer 228. In the example shown in FIG. 8B,
the layer 228 may be a CIS layer. The layer 220 has not reached a
sufficient temperature to react significantly or at least not to
the same extent as the particles in 222. The embodiment of FIG. 8B
is heated to a higher temperature or for a longer time, where it
then reacts with the layer 228 to form layer 230 in FIG. 8C. As
seen in FIG. 8C, the layer 230 may be a CIGS absorber layer. It may
have a higher concentration of group IIIA elements near the top
surface formerly occupied by layer 220. The difference between
layer 228 of FIG. 8B and layer 208 of FIG. 7B is the inclusion of a
group VIA element in layer 228. The layer 228 may be part of a
one-step processing technique where further processing is not
required to turn the resulting layer 230 into an absorber layer
after annealing of layers 220 and 228.
[0155] Referring now to FIGS. 9A and 9B, bandgap grading may also
be applied on top of a fully formed absorber layer 230. FIG. 9A
shows that the present invention involves coating a dispersion 200
of the solid group IIIA-IA based particles over a CIGS absorber
layer 230. An extra layer 240 of group VIA material such as but not
limited to selenium may be used with the dispersion 200, especially
if the group IIIA-IA based material does not contain any or
sufficient amounts of group VIA material in coating of the
dispersion 200. If the coating of the dispersion 200 is a solid
group IIIA-IA-VIA based material, then this layer 240 may or may
not be necessary depending on the content therein. FIG. 9B shows
that upon sufficient heating, the resulting layer 250 may be formed
as a CIGS layer with a graded bandgap.
[0156] FIGS. 10A-10B shows yet another variation similar to that of
FIGS. 9A-9B. Instead of using a group IIIA-IA based material, layer
260 uses a group IIIA-IA-VIA based material and thus a separate
layer 240 of group VIA material is not used. The resulting layer
250 will have the desired bandgap grading and is similar to formed
in FIG. 9B.
[0157] As seen from the foregoing, a variety of methods may be used
to obtain bandgap grading using materials that will react after the
sub-layers have begun to at least partially anneal. As nonlimiting
examples, Ga--Na (any Na concentration if thin enough) or
Ga--Se--Na may be used on top of either precursor CIG, CIGS, CI,
annealed CIG, CI (from elements or alloys), or on top of a
selenized layer which could even be copper rich for crystal growth
or other purposes. In another embodiment, coating of a Ga--Na or
similar layer on top of a selenized layer is not very different
from a process point of view from solution deposition of a gallium
emulsion, except that thin coatings from Ga--Na are likely easier
to coat than a gallium emulsion containing larger droplets and/or
sensitive to coalescence. The dewetting risk is low since liquid is
not formed until the temperature where the gallium is likely to
incorporate into the film, which is higher than the anneal
temperature. In a still further embodiment, coating this material
on top of a precursor layer (prior to selenization or anneal) is
likely to have an advantage in that gallium is less likely to
diffuse into the bulk because it will be in the solid state at low
temperatures. Then at the melting temperature, the temperature is
high enough for good CIGS formation which is likely to freeze the
gallium at the top. Optionally, it should be understood that other
embodiments may also mix the bandgap grading material in the
precursor layer, in addition to or in place of additional bandgap
material above the precursor layer.
[0158] Additionally, some embodiments may use Ga--Na particles that
are not completely solid particles. At about 7.6 weight percent,
the alloy can be stable as Ga.sub.4Na and be fully solid. Compounds
containing lower amounts of sodium may contain portions that
separate out from the composition into elemental gallium and
Ga.sub.4Na. At higher weight percentages such as about 15.7% Na,
the alloy may be stable as Ga.sub.39Na.sub.22. Some embodiments may
use Na at weight percentages greater than about 15.7%. These may
have some separation but still provide the desired band gap
grading. Optionally, elements of other group IA-IIIA material may
also be incorporated into the particle to prevent separation of
undesired elemental materials. These group IA-IIIA materials may be
deposited above, with, and/or below the precursor material.
[0159] It should be understood that a binary or multi-nary alloy
(IB-IIIA-VIA-IA) in a broad range of compositions may be a
combination of two or more line-compounds and solid-solutions,
where one or more compounds might be present as a liquid at
processing temperature. As a non-limiting example, Ga--Na at 300 C
with a composition of 15 atomic percent Na consists mainly of solid
Ga.sub.4Na (at thermodynamic equilibrium, see phase diagram) and
some, almost pure, liquid gallium. Another nonlimiting example,
Ga--Na at 200 C with a composition of 28 atomic percent sodium
consists of a mixture of two different solids, being Ga.sub.4Na and
Ga.sub.39Na.sub.22. In other words, a material with a formula like
e.g. Cu--In--Ga (with or without details on the actual
stoichiometry of the bulk material) might consist of one, but more
commonly, a mixture of two or more different compounds of different
compositions.
[0160] It should be understood that in some embodiments, part of
the precursor material is allowed to liquefy, meaning starting with
a composition of Ga--Na that will result in both nanodroplets of
elemental-Ga and solid Ga.sub.4Na particles. The same holds for
In--Na (although, liquefying elemental-In occurs at 156.degree.
C.). In other words in some embodiments of the present invention,
the precursor material containing the solid IIIA-alloy may contain
liquid material next to the solid IIIA-alloy prior to, during, or
after particle synthesis. In some embodiments of the present
invention, the same holds for ink preparation, ink deposition, and
conversion to a compound layer.
Particle Shapes
[0161] It should be understood that any of solid particles as
discussed herein may be used in spherical and/or non-spherical
particle shapes. FIG. 1A shows that the particles may all be
non-spherical, planar flake particles. By way of example and not
limitation, it should be understood that the solid Group IIIA-based
particles may be particles of various shapes used with any of the
combinations shown below in Table II. Flakes may be considered to
be one type of non-spherical particles.
TABLE-US-00002 TABLE II Spherical Non-Spherical Flake Nanoglobules
Spherical Spherical Non-spherical + Flake + Nanoglobules +
Spherical Spherical Spherical Non-Spherical Spherical +
Non-spherical Flake + Nanoglobules + Non-spherical Non-spherical
Non-spherical Flake Spherical + Non-spherical + Flake Nanoglobules
+ Flake Flake Flake Nanoglobules Spherical + Non-spherical + Flake
+ Nanoglobules Nanoglobules Nanoglobules Nanoglobules Spherical +
Spherical + Spherical + Spherical + Spherical + Non-spherical
Non-spherical Non-spherical Non-spherical + Non-spherical + Flake
Nanoglobules Spherical + Spherical + Spherical + Spherical +
Spherical + Flake Flake Flake + Flake Flake + Non-spherical
Nanoglobules Spherical + Spherical + Spherical + Spherical +
Spherical + Nanoglobules Nanoglobules Nanoglobules + Nanoglobules +
Nanoglobules Non-spherical Flake Flake + Flake + Flake + Flake +
Flake + Non-spherical Non-spherical + Non-spherical Non-spherical
Non-spherical + Spherical Nanoglobules Flake + Flake + Flake +
Flake + Flake + Nanoglobules Nanoglobules + Nanoglobules +
Nanoglobules Nanoglobules Spherical Non-spherical Non-spherical +
Non-spherical + Non-spherical + Non-spherical + Non-spherical +
Nanoglobules Nanoglobules + Nanoglobules Nanoglobules +
Nanoglobules Spherical Flake
[0162] FIG. 11 shows one embodiment of the present invention where
spherical particles 280 and oblong particles 282 (i.e. one type of
non-spherical particles) are shown in combination. They may be
deposited together or sequentially to form precursor layer 284.
[0163] FIG. 12 shows yet another embodiment of the present
invention where particles of one time are used in combination with
particles of another type. FIG. 12 shows that planar, flake
particles 290 maybe used with spherical particles 292 to form the
precursor layer 294.
Additional Sodium
[0164] Referring now to FIGS. 13A-13E, it should be understood that
even with solid group IIIA-based particles, more sodium may be
desired in certain embodiments of the present invention to provide
improved performance. This embodiment of the invention shows that
layers of material may be deposited above and/or below the
precursor layer. Some layers may be deposited after the precursor
layer has been processed. Although not limited to the following,
these layers may provide one technique for adding additional
sodium.
[0165] Referring now to FIG. 13A, the absorber layer may be formed
on a substrate 312, as shown in FIG. 13A. A surface of the
substrate 312 may be coated with a contact layer 314 to promote
electrical contact between the substrate 312 and the absorber layer
that is to be formed on it. By way of example, an aluminum
substrate 312 may be coated with a contact layer 314 of molybdenum.
As discussed herein, forming or disposing a material or layer of
material on the substrate 312 includes disposing or forming such
material or layer on the contact layer 314, if one is used.
Optionally, it should also be understood that a layer 315 may also
be formed on top of contact layer 314 and/or directly on substrate
312. An interlayer may also be incorporated as previously
described. This layer may be solution coated, evaporated, and/or
deposited using vacuum based techniques. Although not limited to
the following, the layer 315 may have a thickness less than that of
the precursor layer 316. In one nonlimiting example, the layer may
be between about 1 nm to about 100 nm in thickness. The layer 315
may be comprised of various materials including but not limited to
at least one of the following: a group IB element, a group IIIA
element, a group VIA element, a group IA element (new style: group
1), a binary and/or multinary alloy of any of the preceding
elements, a solid solution of any of the preceding elements,
copper, indium, gallium, selenium, copper indium, copper gallium,
indium gallium, sodium, a sodium compound, sodium fluoride, sodium
indium sulfide, copper selenide, copper sulfide, indium selenide,
indium sulfide, gallium selenide, gallium sulfide, copper indium
selenide, copper indium sulfide, copper gallium selenide, copper
gallium sulfide, indium gallium selenide, indium gallium sulfide,
copper indium gallium selenide, and/or copper indium gallium
sulfide.
[0166] As shown in FIG. 13B, a precursor layer 316 is formed on the
substrate. The precursor layer 316 contains one or more group IB
elements and one or more group IIIA elements. Preferably, the one
or more group IB elements include copper. The one or more group
IIIA elements may include indium and/or gallium. The precursor
layer may be formed using any of the techniques described above. In
one embodiment, the precursor layer contains no oxygen other than
those unavoidably present as impurities or incidentally present in
components of the film other than the nano- or microflakes
themselves. Although the precursor layer 316 is preferably formed
using non-vacuum methods, it should be understood that it may
optionally be formed by other means, such as but not limited to,
evaporation, sputtering, chemical vapor deposition, physical vapor
deposition, atomic layer deposition (ALD), etc. By way of example,
the precursor layer 316 may be an oxygen-free compound containing
copper, indium and gallium. In one embodiment, the non-vacuum
system operates at pressures above about 3.2 kPa (24 Torr).
Optionally, it should also be understood that a layer 317 may also
be formed on top of precursor layer 316. It should be understood
that the stack may have both layers 315 and 317, only one of the
layers, or none of the layers. Although not limited to the
following, the layer 317 may have a thickness less than that of the
precursor layer 316. In one nonlimiting example, the layer may be
between about 1 to about 100 nm in thickness. The layer 317 may be
comprised of various materials including but not limited to at
least one of the following: a group IB element, a group IIIA
element, a group VIA element, a group IA element (new style: group
1), a binary and/or multinary alloy of any of the preceding
elements, a solid solution of any of the preceding elements,
copper, indium, gallium, selenium, copper indium, copper gallium,
indium gallium, sodium, a sodium compound, sodium fluoride, sodium
indium sulfide, copper selenide, copper sulfide, indium selenide,
indium sulfide, gallium selenide, gallium sulfide, copper indium
selenide, copper indium sulfide, copper gallium selenide, copper
gallium sulfide, indium gallium selenide, indium gallium sulfide,
copper indium gallium selenide, and/or copper indium gallium
sulfide.
[0167] Referring now to FIG. 13C, heat 320 is applied to anneal the
first precursor layer 316 into a group IB-IIIA compound film 318.
It should be understood that this may also include some amounts of
IA material, but the IA material is typically at a level that does
not change the main IB-IIIA material. In one nonlimiting example,
the group IA material is less than about 3% at. of the composition
in the precursor material and less than 0.1% of the final
semiconductor material that contains group IA material. Optionally,
some may have less than about 2% at. of the composition in the
precursor material. Optionally, some may have less than about 1%
at. of the composition in the precursor material. In many
embodiments, most of the excess IA material is not in the final
film but can be found along the boundaries. Optionally, the IA
material is included as a dopant. Optionally, some embodiments may
have significant amounts of Na and thus create a group IA-IB-IIIA
compound film which in the final embodiment may be a
IA-IB-IIIA-VIA. Optionally, the IA material may be such that it
helps crystal growth for the IB-IIIA-VIA material, but the IA
material is mainly gone in the final semiconductor film.
[0168] Referring still to the embodiment of FIG. 13C, the heat 320
may be supplied in a rapid thermal annealing process, e.g., as
described above. As a nonlimiting example, the substrate 312 and
precursor layer(s) 316 may be heated from an ambient temperature to
a plateau temperature range of between about 200.degree. C. and
about 600.degree. C. The heat 320 may be supplied in a rapid
thermal annealing process, e.g., as described above. As a
non-limiting example, the substrate 312 and precursor layer(s) 316
may be heated from an ambient temperature to a plateau temperature
range of between about 200.degree. C. and about 600.degree. C.
Processing comprises annealing with a ramp-rate of about
1-5.degree. C./sec, optionally over about 5.degree. C./sec, to a
temperature of about 200.degree. C. and about 600.degree. C. The
temperature is maintained in the plateau range for a period of time
ranging between about a fraction of a second to about 60 minutes,
and subsequently reduced. Optionally in some embodiments, there are
embodiments contemplated wherein the ramp-down and ramp-up between
the H2-anneal and selenization is avoided. In one such embodiment,
there does not include a step where temperature is reduced to room
temperature and/or temperatures less than 100 C. In addition, some
embodiments of the present invention may use heating of the
as-coated CIG (IB-IIIA) and/or as-annealed CIG (IB-IIIA) without
heating the substrate by using a laser. Optionally, processing
further comprise selenizing this annealed layer with a ramp-rate of
about 1-5.degree. C./sec, optionally over about 5.degree. C./sec,
to a temperature of about 225 to about 600.degree. C. for a time
period of about 60 seconds to about 10 minutes in Se vapor, where
the plateau temperature is not necessarily kept constant in time,
to form the thin-film containing one or more chalcogenide compounds
containing Cu, In, Ga, and Se. Optionally, processing comprises
selenizing without the separate annealing step in an atmosphere
containing hydrogen gas, but may be densified and selenized in one
step with a ramp-rate of 1-5.degree. C./sec, preferably over
5.degree. C./sec, to a temperature of 225 to 600.degree. C. for a
time period of about 120 seconds to about 20 minutes in an
atmosphere containing either H.sub.2Se or a mixture of H.sub.2 and
Se vapor. The heat turns the precursor layer into a film 322.
Optionally, this may be a dense, metallic film as shown in FIG.
13D. The heating may remove voids and create a denser film than the
precursor layer. In other embodiments, where the precursor layer is
already dense, there may be little to no densification.
[0169] Optionally, as shown in FIG. 13D, a layer 326 containing an
additional chalcogen source, and/or an atmosphere containing a
chalcogen source, may optionally be applied to layer 322. Heat 328
may optionally be applied to layer 322 and the layer 326 and/or
atmosphere containing the chalcogen source to heat them to a
temperature sufficient to melt the chalcogen source and to react
the chalcogen source with the group IB element and group IIIA
elements in the precursor layer 322. The heat 328 may be applied in
a rapid thermal annealing process, e.g., as described above. The
reaction of the chalcogen source with the group IB and IIIA
elements forms a compound film 330 of a group IB-IIIA-chalcogenide
compound as shown in FIG. 13E. Preferably, the group
IB-IIIA-chalcogenide compound is of the form
Cu.sub.zIn.sub.1-x-Ga.sub.xSe.sub.2(1-y)S.sub.2y, where
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, and
0.5.ltoreq.y.ltoreq.1.5. Although not limited to the following, the
compound film 330 may be thicker than the film 322 due to the
reaction with group VIA elements.
[0170] Referring now to FIGS. 13A-13E, it should be understood that
sodium may also be used with the precursor material to improve the
qualities of the resulting film. This may be particularly useful in
the situation where solid Group IIIA particles are formed without
using a sodium based material and additional sodium is desired. In
a first method, as discussed in regards to FIGS. 13A and 13B, one
or more layers of a sodium containing material may be formed above
and/or below the precursor layer 316. The formation may occur by
solution coating and/or other techniques such as but not limited to
sputtering, evaporation, chemical bath deposition (CBD,
electroplating, sol-gel based coating, spray coating, chemical
vapor deposition (CVD), physical vapor deposition (PVD), atomic
layer deposition (ALD), and the like.
[0171] Optionally, in a second method, sodium may also be
introduced into the stack by sodium doping the nanoflakes
microflakes and/or particles in the precursor layer 316. As a
nonlimiting example, the nanoflakes and/or other particles in the
precursor layer 316 may be a sodium containing material such as,
but not limited to, Cu--Na, In--Na, Ga--Na, Cu--In--Na, Cu--Ga--Na,
In--Ga--Na, Na--Se, Cu--Se--Na, In--Se--Na, Ga--Se--Na,
Cu--In--Se--Na, Cu--Ga--Se--Na, In--Ga--Se--Na, Cu--In--Ga--Se--Na,
Na--S, Cu--In--Ga--Na, Cu--S--Na, In--S--Na, Ga--S--Na,
Cu--In--S--Na, Cu--Ga--S--Na, In--Ga--S--Na, and/or
Cu--In--Ga--S--Na. In one embodiment of the present invention, the
amount of sodium in the nanoflakes or microflakes and/or other
particles may be about 1 atomic percent (at. %) or less. In another
embodiment, the amount of sodium may be about 0.5 at. % or less. In
yet another embodiment, the amount of sodium may be about 0.1 at. %
or less. It should be understood that the doped particles and/or
flakes may be made by a variety of methods including milling
feedstock material with the sodium containing material and/or
elemental sodium.
[0172] Optionally, in a third method, sodium may be incorporated
into the ink itself, regardless of the type of particle,
nanoparticle, microflake, and/or nanoflakes dispersed in the ink.
As a nonlimiting example, the ink may include nanoflakes (Na doped
or undoped) and a sodium compound with an organic counter-ion (such
as but not limited to sodium acetate) and/or a sodium compound with
an inorganic counter-ion (such as but not limited to sodium
sulfide). It should be understood that sodium compounds added into
the ink (as a separate compound), might be present as particles
(e.g. nanoparticles), or dissolved and/or in (reverse) micelles.
The sodium may be in "aggregate" form of the sodium compound (e.g.
dispersed particles), and the "molecularly dissolved" form. Finally
this added sodium may incorporate into the particles by the milling
process or by any number of alloying processes described above.
[0173] None of the three aforementioned methods are mutually
exclusive and may be applied singly or in any single or multiple
combination(s) to provide the desired amount of sodium to the stack
containing the precursor material. Additionally, sodium and/or a
sodium containing compound may also be added to the substrate (e.g.
into the molybdenum target). Also, sodium-containing layers may be
formed in between one or more precursor layers if multiple
precursor layers (using the same or different materials) are used.
It should also be understood that the source of the sodium is not
limited to those materials previously listed. Some may include
other sodium compounds such as NaBF4, NaPF6, and/or sodium
tetraphenlborate. As a nonlimiting example, basically, any
deprotonated alcohol where the proton is replaced by sodium, any
deprotonated organic and/or inorganic acid being, the sodium salt
of the (deprotonated) acid can be used,
Na.sub.xH.sub.ySe.sub.zS.sub.uTe.sub.vO.sub.w where x, y, z, u, v,
and w.gtoreq.0, Na.sub.xCu.sub.yIn.sub.zGa.sub.uO.sub.v where x, y,
z, u, and v.gtoreq.0 sodium hydroxide, sodium acetate, and the
sodium salts of the following acids: butanoic acid, hexanoic acid,
octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid,
hexadecanoic acid, 9-hexadecenoic acid, octadecanoic acid,
9-octadecenoic acid, 11-octadecenoic acid, 9,12-octadecadienoic
acid, 9,12,15-octadecatrienoic acid, and/or 6,9,12-octadecatrienoic
acid.
[0174] Optionally, as seen in FIG. 13E, it should also be
understood that sodium and/or a sodium compound may be added to the
processed chalcogenide film after the precursor layer has been
annealed or otherwise processed. This embodiment of the present
invention thus modifies the film after CIGS formation. With sodium,
carrier trap levels associated with the grain boundaries are
reduced, permitting improved electronic properties in the film. A
variety of sodium containing materials such as those listed above
may be deposited as layer 432 onto the processed film and then
annealed to treat the CIGS film.
[0175] Additionally, the sodium material may be combined with other
elements that can provide a bandgap widening effect. Two elements
which would achieve this include gallium and sulfur. The use of one
or more of these elements, in addition to sodium, may further
improve the quality of the absorber layer. The use of a sodium
compound such as but not limited to Na.sub.2S, NaInS.sub.2, or the
like provides both Na and S to the film and could be driven in with
an anneal such as but not limited to an RTA step to provide a layer
with a bandgap different from the bandgap of the unmodified CIGS
layer or film.
Roll-to-Roll Manufacturing
[0176] Referring now to FIG. 14, a roll-to-roll manufacturing
process according to the present invention will now be described.
Embodiments of the invention using the solid group IIIA-based
materials are well suited for use with roll-to-roll manufacturing.
Specifically, in a roll-to-roll manufacturing system 400 a flexible
substrate 401, e.g., aluminum foil travels from a supply roll 402
to a take-up roll 404. The width of the row may vary depending on
the application. Some embodiments have a roll(s) with a width
greater than 0.5 m, greater than 1.0 m, greater than 2.0 m, and/or
greater than 3.0 m or more. These substrates may be high aspect
ratio with lengths substantially greater than the width such as but
not limited to aspect ratios of 50:1, 100:1, or more. In between
the supply and take-up rolls, the substrate 401 passes a number of
applicators 406A, 406B, 406C, e.g. microgravure rollers and heater
units 408A, 408B, 408C. Each applicator deposits a different layer
or sub-layer of a precursor layer, e.g., as described above. The
heater units are used to anneal the different layers and/or
sub-layers to form dense films. In the example depicted in FIG. 14,
applicators 406A and 406B may apply different sub-layers of a
precursor layer. Heater units 408A and 408B may anneal each
sub-layer before the next sub-layer is deposited. Alternatively,
both sub-layers may be annealed at the same time. Applicator 406C
may optionally apply an extra layer of material containing
chalcogen or alloy or elemental particles as described above.
Heater unit 408C heats the optional layer and precursor layer as
described above. Note that it is also possible to deposit the
precursor layer (or sub-layers) then deposit any additional layer
and then heat all three layers together to form the
IB-IIIA-chalcogenide compound film used for the photovoltaic
absorber layer. The roll-to-roll system may be a continuous
roll-to-roll and/or segmented roll-to-roll, and/or batch mode
processing.
[0177] Photovoltaic Device
[0178] Referring now to FIG. 15A, the films fabricated as described
above using solid group IIIA-based materials may serve as an
absorber layer in a photovoltaic device, module, or solar panel. An
example of such a photovoltaic device 450 is shown in FIG. 14. The
device 450 includes a base substrate 452, an optional adhesion
layer 453, a base or back electrode 454, a p-type absorber layer
456 incorporating a film of the type described above, a n-type
semiconductor thin film 458 and a transparent electrode 460. By way
of example, the base substrate 452 may be made of a metal foil, a
polymer such as polyimides (PI), polyamides, polyetheretherketone
(PEEK), Polyethersulfone (PES), polyetherimide (PEI), polyethylene
naphtalate (PEN), Polyester (PET), related polymers, a metallized
plastic, and/or combination of the above and/or similar materials.
By way of nonlimiting example, related polymers include those with
similar structural and/or functional properties and/or material
attributes. The base electrode 454 is made of an electrically
conductive material. By way of example, the base electrode 454 may
be of a metal layer whose thickness may be selected from the range
of about 0.1 micron to about 25 microns. An optional intermediate
layer 453 may be incorporated between the electrode 454 and the
substrate 452. The transparent electrode 460 may include a
transparent conductive layer 459 and a layer of metal (e.g., Al,
Ag, Cu, or Ni) fingers 461 to reduce sheet resistance. Optionally,
the layer 453 may be a diffusion barrier layer to prevent diffusion
of material between the substrate 452 and the electrode 454. The
diffusion barrier layer 453 may be a conductive layer or it may be
an electrically nonconductive layer. As nonlimiting examples, the
layer 453 may be composed of any of a variety of materials,
including but not limited to chromium, vanadium, tungsten, and
glass, or compounds such as nitrides (including tantalum nitride,
tungsten nitride, titanium nitride, silicon nitride, zirconium
nitride, and/or hafnium nitride), oxides, carbides, and/or any
single or multiple combination of the foregoing. As nonlimiting
examples, the layer 453 may be composed of any of a variety of
materials, including but not limited to chromium, vanadium,
tungsten, and glass, or compounds such as nitrides (including
tantalum nitride, tungsten nitride, titanium nitride, silicon
nitride, zirconium nitride, and/or hafnium nitride), oxides,
carbides, and/or any single or multiple combination of the
foregoing. Although not limited to the following, the thickness of
this layer can range from 10 nm to 500 nm. In some embodiments, the
layer may be from 100 nm to 300 nm. Optionally, the thickness may
be in the range of about 150 nm to about 250 nm. Optionally, the
thickness may be about 200 nm. In some embodiments, two barrier
layers may be used, one on each side of the substrate 452.
Optionally, an interfacial layer may be located above the electrode
454 and be comprised of a material such as including but not
limited to chromium, vanadium, tungsten, and glass, or compounds
such as nitrides (including tantalum nitride, tungsten nitride,
titanium nitride, silicon nitride, zirconium nitride, and/or
hafnium nitride), oxides, carbides, and/or any single or multiple
combination of the foregoing.
[0179] The n-type semiconductor thin film 458 serves as a junction
partner between the compound film and the transparent conducting
layer 459. By way of example, the n-type semiconductor thin film
458 (sometimes referred to as a junction partner layer) may include
inorganic materials such as cadmium sulfide (CdS), zinc sulfide
(ZnS), zinc hydroxide, zinc selenide (ZnSe), n-type organic
materials, or some combination of two or more of these or similar
materials, or organic materials such as n-type polymers and/or
small molecules. Layers of these materials may be deposited, e.g.,
by chemical bath deposition (CBD) and/or chemical surface
deposition (and/or related methods), to a thickness ranging from
about 2 nm to about 1000 nm, more preferably from about 5 nm to
about 500 nm, and most preferably from about 10 nm to about 300 nm.
This may also configured for use in a continuous roll-to-roll
and/or segmented roll-to-roll and/or a batch mode system.
[0180] The transparent conductive layer 459 may be inorganic, e.g.,
a transparent conductive oxide (TCO) such as but not limited to
indium tin oxide (ITO), fluorinated indium tin oxide, zinc oxide
(ZnO) or zinc oxide (ZnO.sub.x) doped with aluminum, or a related
material, which can be deposited using any of a variety of means
including but not limited to sputtering, evaporation, chemical bath
deposition (CBD, electroplating, sol-gel based coating, spray
coating, chemical vapor deposition (CVD), physical vapor deposition
(PVD), atomic layer deposition (ALD), and the like. Alternatively,
the transparent conductive layer may include a transparent
conductive polymeric layer, e.g. a transparent layer of doped PEDOT
(Poly-3,4-Ethylenedioxythiophene), carbon nanotubes or related
structures, or other transparent organic materials, either singly
or in combination, which can be deposited using spin, dip, or spray
coating, and the like or using any of various vapor deposition
techniques. Optionally, it should be understood that a
non-conductive layer such as intrinsic ZnO (i-ZnO) may be used
between CdS and Al-doped ZnO. Optionally, an insulating layer may
be included between the layer 458 and transparent conductive layer
459. Combinations of inorganic and organic materials can also be
used to form a hybrid transparent conductive layer. Thus, the layer
459 may optionally be an organic (polymeric or a mixed
polymeric-molecular) or a hybrid (organic-inorganic) material.
Examples of such a transparent conductive layer are described e.g.,
in commonly-assigned US Patent Application Publication Number
20040187317, which is incorporated herein by reference.
[0181] Those of skill in the art will be able to devise variations
on the above embodiments that are within the scope of these
teachings. For example, it is noted that in embodiments of the
present invention, portions of the IB-IIIA precursor layers (or
certain sub-layers of the precursor layers or other layers in the
stack) may be deposited using techniques other than
microflake-based inks. For example precursor layers or constituent
sub-layers may be deposited using any of a variety of alternative
deposition techniques including but not limited to
solution-deposition of spherical nanopowder-based inks, vapor
deposition techniques such as ALD, evaporation, sputtering, CVD,
PVD, electroplating and the like.
[0182] Referring now to FIG. 15B, it should also be understood that
a plurality of devices 450 may be incorporated into a module 500 to
form a solar module that includes various packaging, durability,
and environmental protection features to enable the devices 450 to
be installed in an outdoor environment. In one embodiment, the
module 500 may include a frame 502 that supports a substrate 504 on
which the devices 450 may be mounted. This module 500 simplifies
the installation process by allowing a plurality of devices 450 to
be installed at one time. Alternatively, flexible form factors may
also be employed. It should also be understood that an
encapsulating device and/or layers may be used to protect from
environmental influences. As a nonlimiting example, the
encapsulating device and/or layers may block the ingress of
moisture and/or oxygen and/or acidic rain into the device,
especially over extended environmental exposure.
[0183] Referring now to FIG. 16A, it should also be understood that
the embodiments of the present invention may also be used on a
rigid substrate 600. By way of nonlimiting example, the rigid
substrate 600 may be glass, soda-lime glass, steel, stainless
steel, aluminum, polymer, ceramic, coated polymer, or other rigid
material suitable for use as a solar cell or solar module
substrate. A high speed pick-and-place robot 602 may be used to
move rigid substrates 600 onto a processing area from a stack or
other storage area. In FIG. 17A, the substrates 600 are placed on a
conveyor belt which then moves them through the various processing
chambers. Optionally, the substrates 600 may have already undergone
some processing by the time and may already include a precursor
layer on the substrate 600. Other embodiments of the invention may
form the precursor layer as the substrate 600 passes through the
chamber 606.
[0184] FIG. 16B shows another embodiment of the present system
where a pick-and-place robot 610 is used to position a plurality of
rigid substrates on a carrier device 612 which may then be moved to
a processing area as indicated by arrow 614. This allows for
multiple substrates 600 to be loaded before they are all moved
together to undergo processing. Source 662 may provide a source of
processing gas to provide a suitable atmosphere to create the
desired semiconductor film. In one embodiment, chalcogen vapor may
be provided by using a partially or fully enclosed chamber with a
chalcogen source 662 therein or coupled to the chamber.
Inter-Metallic Material
[0185] Referring now to FIG. 17, any of the foregoing solid
particles, including solid group IIIA-based particles may be used
with the following inter-metallic materials. By way of example and
not limitation, the present invention also includes the possibility
of using solid particles, emulsions of liquid materials,
inter-metallic materials, and/or any single or multiple
combinations of the foregoing.
[0186] In one embodiment, the particles used to form a precursor
layer 1500 may include particles that are inter-metallic particles
1502. In one embodiment, an inter-metallic material is a material
containing at least two elements, wherein the amount of one element
in the inter-metallic material is less than about 50 molar percent
of the total molar amount of the inter-metallic material and/or the
total molar amount of that one element in a precursor material. The
amount of the second element is variable and may range from less
than about 50 molar percent to about 50 or more molar percent of
the inter-metallic material and/or the total molar amount of that
one element in a precursor material. Alternatively, inter-metallic
phase materials may be comprised of two or more metals where the
materials are admixed in a ratio between the upper bound of the
terminal solid solution and an alloy comprised of about 50% of one
of the elements in the inter-metallic material. The particle
distribution shown in the enlarged view of FIG. 17 is purely
exemplary and is nonlimiting. It should be understood that some
embodiments may have particles that all contain inter-metallic
materials, mixture of metallic and inter-metallic materials,
metallic particles and inter-metallic particles, or combinations
thereof.
[0187] It should be understood that inter-metallic phase materials
are compounds and/or intermediate solid solutions containing two or
more metals, which have characteristic properties and crystal
structures different from those of either the pure metals or the
terminal solid solutions. Inter-metallic phase materials arise from
the diffusion of one material into another via crystal lattice
vacancies made available by defects, contamination, impurities,
grain boundaries, and mechanical stress. Upon two or more metals
diffusing into one another, intermediate metallic species are
created that are combinations of the two materials. Sub-types of
inter-metallic compounds include both electron and interstitial
compounds.
[0188] Electron compounds arise if two or more mixed metals are of
different crystal structure, valency, or electropositivity relative
to one another; examples include but are not limited to copper
selenide, gallium selenide, indium selenide, copper telluride,
gallium telluride, indium telluride, and similar and/or related
materials and/or blends or mixtures of these materials.
[0189] Interstitial compounds arise from the admixture of metals or
metals and non-metallic elements, with atomic sizes that are
similar enough to allow the formation of interstitial crystal
structures, where the atoms of one material fit into the spaces
between the atoms of another material. For inter-metallic materials
where each material is of a single crystal phase, two materials
typically exhibit two diffraction peaks, each representative of
each individual material, superimposed onto the same spectra. Thus
inter-metallic compounds typically contain the crystal structures
of both materials contained within the same volume. Examples
include but are not limited to Cu--Ga, Cu--In, and similar and/or
related materials and/or blends or mixtures of these materials,
where the compositional ratio of each element to the other places
that material in a region of its phase diagram other than that of
the terminal solid solution.
[0190] Inter-metallic materials are useful in the formation of
precursor materials for CIGS photovoltaic devices in that metals
interspersed in a highly homogenous and uniform manner amongst one
another, and where each material is present in a substantially
similar amount relative to the other, thus allowing for rapid
reaction kinetics leading to high quality absorber films that are
substantially uniform in all three dimensions and at the nano-,
micro, and meso-scales.
[0191] In the absence of the addition of indium nanoparticles,
which are difficult to synthesize and handle, terminal solid
solutions do not readily allow a sufficiently large range of
precursor materials to be incorporated into a precursor film in the
correct ratio (e.g. Cu/(In+Ga)=0.85) to provide for the formation
of a highly light absorbing, photoactive absorber layer.
Furthermore, terminal solid solutions may have mechanical
properties that differ from those of inter-metallic materials
and/or intermediate solid solutions (solid solutions between a
terminal solid solution and/or element). As a nonlimiting example,
some terminal solid solutions are not brittle enough to be milled
for size reduction. Other embodiments may be too hard to be milled.
The use of inter-metallic materials and/or intermediate solid
solutions can address some of these drawbacks.
[0192] The advantages of particles 1502 having an inter-metallic
phase are multi-fold. As a nonlimiting example, a precursor
material suitable for use in a thin film solar cell may contain
group IB and group IIIA elements such as copper and indium,
respectively. If an inter-metallic phase of Cu--In is used such as
Cu.sub.1In.sub.2, then Indium is part of an In-rich Cu material and
not added as pure indium. Adding pure indium as a metallic particle
is challenging due to the difficulty in achieving In particle
synthesis with high yield, small and narrow nanoparticle size
distribution, and requiring particle size discrimination, which
adds further cost. Using inter-metallic In-rich Cu particles avoids
pure elemental In as a precursor material. Additionally, because
the inter-metallic material is Cu poor, this also advantageously
allows Cu to be added separately to achieve precisely the amount of
Cu desired in the precursor material. The Cu is not tied to the
ratio fixed in alloys or solid solutions that can be created by Cu
and In. The inter-metallic material and the amount of Cu can be
fine tuned as desired to reach a desired stoichiometric ratio. Ball
milling of these particles results in no need for particle size
discrimination, which decreases cost and improves the throughput of
the material production process.
[0193] In some specific embodiments of the present invention,
having an inter-metallic material provides a broader range of
flexibility. Since economically manufacturing elemental indium
particles is difficult, it would be advantageous to have an
indium-source that is more economically interesting. Additionally,
it would be advantageous if this indium source still allows varying
both the Cu/(In+Ga) and Ga/(In+Ga) in the layer independently of
each other. As one nonlimiting example, a distinction can be made
between Cu.sub.11In.sub.9 and Cu.sub.1In.sub.2 with an
inter-metallic phase. This particularly true if only one layer of
precursor material is used. If, for this particular example, if
indium is only provided by Cu.sub.11In.sub.9, there is more
restriction what stoichiometric ratio can be created in a final
group IB-IIIA-VIA compound. With Cu.sub.1In.sub.2 as the only
indium source, however, there is much greater range of ratio can be
created in a final group IB-IIIA-VIA compound. Cu.sub.1In.sub.2
allows you to vary both the Cu/(In+Ga) and Ga/(In+Ga) independently
in a broad range, whereas Cu11In9 does not. For instance, Cu11In9
does only allow for Ga/(In+Ga)=0.25 with Cu/(In+Ga)>0.92. Yet
another example, Cu11In9 does only allow for Ga/(In+Ga)=0.20 with
Cu/(In+Ga)>0.98. Yet another example, Cu11In9 does only allow
for Ga/(In+Ga)=0.15 with Cu/(In+Ga)>1.04. Thus for an
intermetallic material, particularly when the intermetallic
material is a sole source of one of the elements in the final
compound, the final compound may be created with stoichiometric
ratios that more broadly explore the bounds of Cu/(In+Ga) with a
compositional range of about 0.7 to about 1.0, and Ga/(In+Ga) with
a compositional range of about 0.05 to about 0.3 In other
embodiments, Cu/(In+Ga) compositional range may be about 0.01 to
about 1.0. In other embodiments, the Cu/(In+Ga) compositional range
may be about 0.01 to about 1.1. In other embodiments, the
Cu/(In+Ga) compositional range may be about 0.01 to about 1.5. This
typically results in additional Cu.sub.xSe.sub.y which we might be
able to remove afterwards if it is at the top surface. It should be
understood that these ratios may apply to any of the above
embodiments described herein.
[0194] Furthermore, it should be understood that during processing,
an intermetallic material may create more liquid than other
compounds. As a nonlimiting example, Cu.sub.11In.sub.2 will form
more liquid when heated during processing than Cu11In9. More liquid
promotes more atomic intermixing since it easier for material to
move and mix while in a liquid stage.
[0195] Additionally, there are specific advantages for particular
types of inter-metallic particles such as, but not limited to,
Cu.sub.1In.sub.2. Cu.sub.1In.sub.2 is a material that is
metastable. The material is more prone to decomposition, which
advantageously for the present invention, will increase the rate of
reaction (kinetically). Further, the material is less prone to
oxidation (e.g. compared to pure In) and this further simplifies
processing. This material may also be single-phase, which would
make it more uniform as a precursor material, resulting in better
yield.
[0196] As seen in FIGS. 18 and 19, after the layer 1500 is
deposited over the substrate 1506, it may then be heated in a
suitable atmosphere to react the layer 1500 in FIG. 18 and form
film 1510 shown in FIG. 19. It should be understood that the layer
1500 may be used in conjunction with layers 915 and 917 as
described above with regards to FIG. 13A-13B. The layer 915 may be
comprised of various materials including but not limited at least
one of the following: a group IB element, a group IIIA element, a
group VIA element, a group IA element (new style: group 1), a
binary and/or multinary alloy of any of the preceding elements, a
solid solution of any of the preceding elements. It should be
understood that sodium or a sodium-based material such as but not
limited to sodium, a sodium compound, sodium fluoride, and/or
sodium indium sulfide, may also be used in layer 915 with the
precursor material to improve the qualities of the resulting film.
FIG. 19 shows that a layer 932 may also be used as described with
regards to FIG. 13F. Any of the method suggested previously with
regards to sodium content may also be adapted for use with the
embodiments shown in FIGS. 17-19.
[0197] It should be understood that other embodiments of the
present invention also disclose material comprised of at least two
elements wherein the amount of at least one element in the material
is less than about 50 molar percent of the total molar amount of
that element in the precursor material. This includes embodiments
where the amount of group IB element is less than the amount of
group IIIA element in inter-metallic material. As a nonlimiting
example, this may include other group IB poor, group IB-IIIA
materials such as Cu-poor Cu.sub.xIn.sub.y particles (where
x<y). The amount of group IIIA material may be in any range as
desired (more than about 50 molar percent of the element in the
precursor material or less than 50 molar percent). In another
nonlimiting example, Cu.sub.1Ga.sub.2 may be used with elemental Cu
and elemental In. Although this material is not an inter-metallic
material, this material is a intermediate solid solution and is
different from a terminal solid solution. All solid particles are
created based on a Cu.sub.1Ga.sub.2 precursor. In this embodiment,
no emulsions are used.
[0198] In still other embodiments of the present invention, other
viable precursor materials may be formed using a group IB rich,
group IB-IIIA material. As a nonlimiting example, a variety of
intermediate solid-solutions may be used. Cu--Ga (38 at % Ga) may
be used in precursor layer 1500 with elemental indium and elemental
copper. In yet another embodiment, Cu--Ga (30 at % Ga) may be used
in precursor layer 1500 with elemental copper and elemental indium.
Both of these embodiments describe Cu-rich materials with the Group
IIIA element being less than about 50 molar percent of that element
in the precursor material. In still further embodiments, Cu--Ga
(multiphasic, 25 at % Ga) may be used with elemental copper and
indium to form the desired precursor layer. It should be understood
that nanoparticles of these materials may be created by mechanical
milling or other size reduction methods. In other embodiments,
these particles may be made by electroexplosive wire (EEW)
processing, evaporation condensation (EC), pulsed plasma
processing, or other methods. Although not limited to the
following, the particles sizes may be in the range of about 10 nm
to about 1 micron. They may be of any shape as described
herein.
[0199] Referring now to FIG. 20, in a still further embodiment of
the present invention, two or more layers of materials may be
coated, printed, or otherwise formed to provide a precursor layer
with the desired stoichiometric ratio. As a nonlimiting example,
layer 1530 may contain a precursor material having
Cu.sub.11In.sub.9 and a Ga source such as elemental Ga and/or
Ga.sub.xSe.sub.y. A copper rich precursor layer 1532 containing
Cu.sub.78In.sub.28 (solid-solution) and elemental indium or
In.sub.xSe.sub.y may be printed over layer 1530. In such an
embodiment, the resulting overall ratios may have Cu/(In+Ga)=0.85
and Ga/(In+Ga) 0.19. In one embodiment of the resulting film, the
film may have a stoichiometric ratio of Cu/(In+Ga) with a
compositional range of about 0.7 to about 1.0 and Ga/(In+Ga) with a
compositional range of about 0.05 to about 0.3.
[0200] Referring now to FIG. 21, it should be understood that in
some embodiments of the present invention, the inter-metallic
material is used as a feedstock or starting material from which
particles and/or nanoparticles may be formed. As a nonlimiting
example, FIG. 21 shows one inter-metallic feedstock particle 1550
being processed to form other particles. Any method used for size
reduction and/or shape change may be suitable including but not
limited to milling, EEW, EC, pulsed plasma processing, or
combinations thereof. Particles 552, 554, 556, and 558 may be
formed. These particles may be of varying shapes and some may
contain only the inter-metallic phase while others may contain that
phase and other material phases.
[0201] Referring now to FIGS. 22A and 22B, flakes 1600 (microflakes
and/or nanoflakes) provide certain advantages over other
non-spherical shapes such as but not limited to platelets. The
flakes 1600 provide for highly efficient stacking (due to uniform
thickness in Z-axis) and high surface area (in X and Y axes). This
leads to faster reactions, better kinetics, and more uniform
products/films/compounds (with fewer side propagations). Platelet
1602 as seen in FIGS. 23A and 23B fail to have all of the above
advantages.
[0202] Referring now to FIG. 24, shows that the foregoing
discussion on intermetallics also applies to spherical particles.
These spherical intermetallic particles may be used with other
spherical particles, non-spherical particles, particles of various
shapes, and/or any single or multiple combination of the
foregoing.
[0203] In one embodiment, the particles used to form a precursor
layer 1700 may include particles that are inter-metallic particles
1702. In one embodiment, an inter-metallic material is a material
containing at least two elements, wherein the amount of one element
in the inter-metallic material is less than about 50 molar percent
of the total molar amount of the inter-metallic material and/or the
total molar amount of that one element in a precursor material. The
amount of the second element is variable and may range from less
than about 50 molar percent to about 50 or more molar percent of
the inter-metallic material and/or the total molar amount of that
one element in a precursor material. Alternatively, inter-metallic
phase materials may be comprised of two or more metals where the
materials are admixed in a ratio between the upper bound of the
terminal solid solution and an alloy comprised of about 50% of one
of the elements in the inter-metallic material. The particle
distribution shown in the enlarged view of FIG. 24 is purely
exemplary and is nonlimiting. It should be understood that some
embodiments may have particles that all contain inter-metallic
materials, mixture of metallic and inter-metallic materials,
metallic particles and inter-metallic particles, or combinations
thereof.
[0204] It should be understood that inter-metallic phase materials
are compounds and/or intermediate solid solutions containing two or
more metals, which have characteristic properties and crystal
structures different from those of either the pure metals or the
terminal solid solutions. Inter-metallic phase materials arise from
the diffusion of one material into another via crystal lattice
vacancies made available by defects, contamination, impurities,
grain boundaries, and mechanical stress. Upon two or more metals
diffusing into one another, intermediate metallic species are
created that are combinations of the two materials. Sub-types of
inter-metallic compounds include both electron and interstitial
compounds.
[0205] Electron compounds arise if two or more mixed metals are of
different crystal structure, valency, or electropositivity relative
to one another; examples include but are not limited to copper
selenide, gallium selenide, indium selenide, copper telluride,
gallium telluride, indium telluride, and similar and/or related
materials and/or blends or mixtures of these materials.
[0206] Interstitial compounds arise from the admixture of metals or
metals and non-metallic elements, with atomic sizes that are
similar enough to allow the formation of interstitial crystal
structures, where the atoms of one material fit into the spaces
between the atoms of another material. For inter-metallic materials
where each material is of a single crystal phase, two materials
typically exhibit two diffraction peaks, each representative of
each individual material, superimposed onto the same spectra. Thus
inter-metallic compounds typically contain the crystal structures
of both materials contained within the same volume. Examples
include but are not limited to Cu--Ga, Cu--In, and similar and/or
related materials and/or blends or mixtures of these materials,
where the compositional ratio of each element to the other places
that material in a region of its phase diagram other than that of
the terminal solid solution.
[0207] Inter-metallic materials are useful in the formation of
precursor materials for CIGS photovoltaic devices in that metals
interspersed in a highly homogenous and uniform manner amongst one
another, and where each material is present in a substantially
similar amount relative to the other, thus allowing for rapid
reaction kinetics leading to high quality absorber films that are
substantially uniform in all three dimensions and at the nano-,
micro, and meso-scales.
[0208] In the absence of the addition of indium nanoparticles,
which are difficult to synthesize and handle, terminal solid
solutions do not readily allow a sufficiently large range of
precursor materials to be incorporated into a precursor film in the
correct ratio (e.g. Cu/(In+Ga)=0.85) to provide for the formation
of a highly light absorbing, photoactive absorber layer.
Furthermore, terminal solid solutions may have mechanical
properties that differ from those of inter-metallic materials
and/or intermediate solid solutions (solid solutions between a
terminal solid solution and/or element). As a nonlimiting example,
some terminal solid solutions are not brittle enough to be milled
for size reduction. Other embodiments may be too hard to be milled.
The use of inter-metallic materials and/or intermediate solid
solutions can address some of these drawbacks.
[0209] Referring now to FIG. 25, it should be understood that in
some embodiments of the present invention, the inter-metallic
material is used as a feedstock or starting material from which
particles and/or nanoparticles may be formed. As a nonlimiting
example, FIG. 25 shows one inter-metallic feedstock particle 1750
being processed to form other particles. Any method used for size
reduction and/or shape change may be suitable including but not
limited to milling, EEW, EC, pulsed plasma processing, or
combinations thereof. Particles 1752, 1754, 1756, and 1758 may be
formed. These particles may be of varying shapes and some may
contain only the inter-metallic phase while others may contain that
phase and other material phases.
[0210] Again, any of the solid particles, including solid group
IIIA-based particles may be used with the foregoing inter-metallic
materials. By way of example and not limitation, the present
invention also includes the possibility of using solid particles,
emulsions of liquid materials, intermetallic materials, and/or any
single or multiple combinations of the foregoing.
Chalcogenides
[0211] It should be understood that a variety of chalcogen and/or
chalcogenide particles may also be combined with non-chalcogenide
particles to arrive at the desired excess supply of chalcogen in
the precursor layer. The following table (Table IV) provides a
non-limiting matrix of some of the possible combinations between
chalcogenide particles listed in the rows and the non-chalcogenide
particles listed in the columns. It should also be understood that
two more materials from the columns may be combined. As a
nonlimiting example, Cu--Ga+In+Se may also be combined even though
the are from different columns. Another possibility involves,
Cu--Ga+In--Ga+Se (or some other chalcogen source).
TABLE-US-00003 TABLE IV Cu In Ga Cu--In Cu--Ga In--Ga Cu--In--Ga Se
Se + Cu Se + In Se + Ga Se + Cu--In Se + Cu--Ga Se + In--Ga Se +
Cu--In-- Ga Cu--Se Cu--Se + Cu Cu--Se + In Cu--Se + Ga Cu--Se +
Cu-- Cu--Se + Cu-- Cu--Se + In-- Cu--Se + Cu-- In Ga Ga In--Ga
In--Se In--Se + Cu In--Se + In In--Se + Ga In--Se + Cu-- In--Se +
Cu-- In--Se + In-- In--Se + Cu-- In Ga Ga In--Ga Ga--Se Ga--Se + Cu
Ga--Se + In Ga--Se + Ga Ga--Se + Cu-- Ga--Se + Cu-- Ga--Se + In--
Ga--Se + Cu-- In Ga Ga In--Ga Cu--In--Se Cu--In--Se + Cu--In--Se +
Cu--In--Se + Cu--In--Se + Cu--In--Se + Cu--In--Se + Cu--In--Se + Cu
In Ga Cu--In Cu--Ga In--Ga Cu--In--Ga Cu--Ga--Se Cu--Ga--Se +
Cu--Ga--Se + Cu--Ga--Se + Cu--Ga--Se + Cu--Ga--Se + Cu--Ga--Se +
Cu--Ga--Se + Cu In Ga Cu--In Cu--Ga In--Ga Cu--In--Ga In--Ga--Se
In--Ga--Se + In--Ga--Se + In--Ga--Se + In--Ga--Se + In--Ga--Se +
In--Ga--Se + In--Ga--Se + Cu In Ga Cu--In Cu--Ga In--Ga Cu--In--Ga
Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga--
Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga--Se + Se Se + Cu Se + In Se +
Ga Se + Cu--In Se + Cu--Ga Se + In--Ga Cu--In--Ga
[0212] In yet another embodiment, the present invention may combine
a variety of chalcogenide particles with other chalcogenide
particles. The following table (Table V) provides a non-limiting
matrix of some of the possible combinations between chalcogenide
particles listed for the rows and chalcogenide particles listed for
the columns.
TABLE-US-00004 TABLE V Cu--In--Ga-- Cu--Se In--Se Ga--Se Cu--In--Se
Cu--Ga--Se In--Ga--Se Se Se Se + Cu--Se Se + In--Se Se + Ga--Se Se
+ Cu--In-- Se + Cu--Ga-- Se + In--Ga-- Se + Cu--In-- Se Se Se
Ga--Se Cu--Se Cu--Se Cu--Se + In-- Cu--Se + Ga-- Cu--Se + Cu--
Cu--Se + Cu-- Cu--Se + In-- Cu--Se + Cu-- Se Se In--Se Ga--Se
Ga--Se In--Ga--Se In--Se In--Se + Cu-- In--Se In--Se + Ga-- In--Se
+ Cu-- In--Se + Cu-- In--Se + In-- In--Se + Cu-- Se Se In--Se
Ga--Se Ga--Se In--Ga--Se Ga--Se Ga--Se + Cu-- Ga--Se + In-- Ga--Se
Ga--Se + Cu-- Ga--Se + Cu-- Ga--Se + In-- Ga--Se + Cu-- Se Se
In--Se Ga--Se Ga--Se In--Ga--Se Cu--In--Se Cu--In--Se + Cu--In--Se
+ Cu--In--Se + Cu--In--Se Cu--In--Se + Cu--In--Se + Cu--In--Se +
Cu--Se In--Se Ga--Se Cu--Ga--Se In--Ga--Se Cu--In--Ga-- Se
Cu--Ga--Se Cu--Ga--Se + Cu--Ga--Se + Cu--Ga--Se + Cu--Ga--Se +
Cu--Ga--Se Cu--Ga--Se + Cu--Ga--Se + Cu--Se In--Se Ga--Se
Cu--In--Se In--Ga--Se Cu--In--Ga-- Se In--Ga--Se In--Ga--Se +
In--Ga--Se + In--Ga--Se + In--Ga--Se + In--Ga--Se + In--Ga--Se
In--Ga--Se + Cu--Se In--Se Ga--Se Cu--In--Se Cu--Ga--Se
Cu--In--Ga-- Se Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga--
Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga-- Cu--In--Ga-- Se Se + Cu--Se
Se + In--Se Se + Ga--Se Se + Cu--In-- Se + Cu--Ga-- Se + In--Ga--
Se Se Se Se
[0213] Additionally, it should be understood that any number of
combinations of flake and non-flake particles may be used according
to the present invention in the various layers. As a nonlimiting
example, the combinations may include but are not limited to:
TABLE-US-00005 TABLE VI Combination 1 1) chalcogenide (flake) +
non-chalcogenide (flake) Combination 2 2) chalcogenide (flake) +
non-chalcogenide (non-flake) Combination 3 3) chalcogenide
(non-flake) + non-chalcogenide (flake) Combination 4 4)
chalcogenide (non-flake) + non-chalcogenide (non-flake) Combination
5 5) chalcogenide (flake) + chalcogenide (flake) Combination 6 6)
chalcogenide (flake) + chalcogenide (non-flake) Combination 7 7)
chalcogenide (non-flake) + chalcogenide (non-flake) Combination 8
8) non-chalcogenide (flake) + non-chalcogenide (flake) Combination
9 9) non-chalcogenide (flake) + non-chalcogenide (non-flake)
Combination 10 10) non-chalcogenide (non-flake) + non-chalcogenide
(non-flake)
Additional Chalcogen
[0214] Any of the methods described herein may be further optimized
by using, prior to, during, or after the solution deposition and/or
heating of one or more of the precursor layers, any combination of
(1) any chalcogen source that can be solution-deposited, e.g. a Se
or S nano- or micron-sized powder mixed into the precursor layers
or deposited as a separate layer, (2) chalcogen (e.g., Se or S)
evaporation, (3) an H.sub.2Se (H.sub.2S) atmosphere, (4) a
chalcogen (e.g., Se or S) atmosphere, (5) an H.sub.2 atmosphere,
(6) an organo-selenium atmosphere, e.g. diethylselenide or another
organo-metallic material, (7) another reducing atmosphere, e.g. CO,
and a (8) heat treatment. The stoichiometric ratio of microflakes
to extra chalcogen, given as Se/(Cu+In+Ga+Se) may be in the range
of about 0 to about 1000.
[0215] For example as shown in FIG. 26A, a layer 1808 containing
elemental chalcogen particles 1807 over the precursor layer 1806.
By way of example, and without loss of generality, the chalcogen
particles may be particles of selenium, sulfur or tellurium. As
shown in FIG. 26B, heat 1809 is applied to the precursor layer 1806
and the layer 1808 containing the chalcogen particles to heat them
to a temperature sufficient to melt the chalcogen particles 1807
and to react the chalcogen particles 1807 with the group IB element
and group IIIA elements in the precursor layer 1806. The reaction
of the chalcogen particles 1807 with the group IB and IIIA elements
forms a compound film 1810 of a group IB-IIIA-chalcogenide compound
as shown in FIG. 26C. Optionally, the group IB-IIIA-chalcogenide
compound is of the form
Cu.sub.zIn.sub.1-xGa.sub.xSe.sub.2(1-y)S.sub.y, where 0<x<1,
0.ltoreq.y.ltoreq.1, and 0.5.ltoreq.z.ltoreq.1.5.
[0216] If the chalcogen particles 1807 melt at a relatively low
temperature (e.g., 220.degree. C. for Se, 120.degree. C. for S) the
chalcogen is already in a liquid state and makes good contact with
the group IB and IIIA nanoparticles in the precursor layer 1806. If
the precursor layer 1806 and molten chalcogen are then heated
sufficiently (e.g., at about 375.degree. C.) the chalcogen reacts
with the group IB and IIIA elements in the precursor layer 1806 to
form the desired IB-IIIA-chalcogenide material in the compound film
1810. As one nonlimiting example, the precursor layer is between
about 10 nm and about 5000 nm thick. In other embodiments, the
precursor layer may be between about 4.0 to about 0.5 microns
thick.
[0217] There are a number of different techniques for forming the
IB-IIIA precursor layer 1806. For example, the precursor layer 1806
may be formed from a nanoparticulate film including nanoparticles
containing the desired group IB and IIIA elements. The
nanoparticles may be a mixture elemental nanoparticles, i.e.,
nanoparticles having only a single atomic species. Alternatively,
the nanoparticles may be binary nanoparticles, e.g., Cu--In,
In--Ga, or Cu--Ga or ternary particles, such as, but not limited
to, Cu--In--Ga, or quaternary particles. Such nanoparticles may be
obtained, e.g., by ball milling a commercially available powder of
the desired elemental, binary or ternary material. These
nanoparticles may be between about 0.1 nanometer and about 500
nanometers in size.
[0218] One of the advantages of the use of nanoparticle-based
dispersions is that it is possible to vary the concentration of the
elements within the compound film 1810 either by building the
precursor layer in a sequence of sub-layers or by directly varying
the relative concentrations in the precursor layer 1806. The
relative elemental concentration of the nanoparticles that make up
the ink for each sub-layer may be varied. Thus, for example, the
concentration of gallium within the absorber layer may be varied as
a function of depth within the absorber layer.
[0219] The layer 1808 containing the chalcogen particles 1807 may
be disposed over the nanoparticulate film and the nanoparticulate
film (or one or more of its constituent sub-layers) may be
subsequently sintered in conjunction with heating the chalcogen
particles 1807. Alternatively, the nanoparticulate film may be
heated to form the precursor layer 1806 before disposing the layer
1808 containing elemental chalcogen particles 1807 over precursor
layer 1806. Additional disclosure on depositing chalcogen material
may be found in co-pending U.S. patent application Ser. No.
11/361,522 filed Feb. 23, 2006 and fully incorporated herein by
reference for all purposes.
[0220] Referring now to FIG. 27A, it should be understood that any
of the foregoing may also be used in a chalcogen vapor environment.
It should be understood that this may be used in a one stage
process, a two stage process, or a multi-stage process. In two
stage and/or multi-stage process, different atmospheres may
optionally be used for each stage and some may be inert atmospheres
as described previously.
[0221] In another embodiment for use with a particle and/or
microflake precursor material, it should be understood that
overpressure from chalcogen vapor is used to provide a chalcogen
atmosphere to improve processing of the film and crystal growth.
FIG. 27A shows a chamber 1050 with a substrate 1052 having a
contact layer 1054 and a precursor layer 1056. Extra sources 1058
of chalcogen are included in the chamber and are brought to a
temperature to generate chalcogen vapor as indicated by lines 1060.
In one embodiment of the present invention, the chalcogen vapor is
provided to have a partial pressure of the chalcogen present in the
atmosphere greater than or equal to the vapor pressure of chalcogen
that would be required to maintain a partial chalcogen pressure at
the processing temperature and processing pressure to minimize loss
of chalcogen from the precursor layer, and if desired, provide the
precursor layer with additional chalcogen. The partial pressure is
determined in part on the temperature that the chamber 1050 or the
precursor layer 1056 is at. It should also be understood that the
chalcogen vapor is used in the chamber 1050 at a non-vacuum
pressure. In one embodiment, the pressure in the chamber is at
about atmospheric pressure. Per the ideal gas law PV=nRT, it should
be understood that the temperature influences the vapor pressure.
In one embodiment, this chalcogen vapor may be provided by using a
partially or fully enclosed chamber with a chalcogen source 1062
therein or coupled to the chamber. In another embodiment using a
more open chamber, the chalcogen atmosphere may be provided by
supplying a source producing a chalcogen vapor. The chalcogen vapor
may serve to help keep the chalcogen in the film or to provide the
chalcogen to covert the precursor layer. Thus, the chalcogen vapor
may or may not be used to provide excess chalcogen. In some
embodiments, this may serve more to keep the chalcogen present in
the film than to provide more chalcogen into the film.
[0222] Optionally, this vapor or atmosphere maybe used as a
chalcogen that is introduced into an otherwise chalcogen free or
selenium free precursor layer. It should be understood that the
exposure to chalcogen vapor may occur in a non-vacuum environment.
The exposure to chalcogen vapor may occur at or near atmospheric
pressure. These conditions may be applicable to any of the
embodiments described herein. The chalcogen may be carried into the
chamber by a carrier gas. The carrier gas may be an inert gas such
as nitrogen, argon, or the like. This chalcogen atmosphere system
may be adapted for use in a roll-to-roll system.
[0223] Referring now to FIG. 27B, it shown that the present
invention may be adopted for use with a roll-to-roll system where
the substrate 1070 carrying the precursor layer may be flexible and
configured as rolls 1072 and 1074. The chamber 1076 may be at
vacuum or non-vacuum pressures. The chamber 1076 may be designed to
incorporate a differential valve design to minimize the loss of
chalcogen vapor at the chamber entry and chamber exit points of the
roll-to-roll substrate 1070.
[0224] Referring now to FIG. 27C, yet another embodiment of the
present invention uses a chamber 1090 of sufficient size to hold
the entire substrate, including any rolls 1072 or 1074 associated
with using a roll-to-roll configuration.
[0225] While the invention has been described and illustrated with
reference to certain particular embodiments thereof, those skilled
in the art will appreciate that various adaptations, changes,
modifications, substitutions, deletions, or additions of procedures
and protocols may be made without departing from the spirit and
scope of the invention. For example, with any of the above
embodiments, particles of various shapes and sizes may be used
separately or in combination with one another. Although the
examples provided herein describe microflakes, it should be
understood that flakes of other sizes may also be used in some
embodiments of the invention. By way of nonlimiting example,
microflakes (of solid group IIIA particles or particles of other
compositions) may be replaced by and/or mixed with nanoflakes
wherein the lengths of the planar nanoflakes are about 500 nm to
about 1 nm. They may also be mixed with spherical particles of the
same or different composition. As a nonlimiting example, the
nanoflakes may have lengths and/or largest lateral dimension of
about 300 nm to about 10 nm. In other embodiments, the nanoflakes
may be of thickness in the range of about 200 nm to about 20 nm. In
another embodiment, these nanoflakes may be of thickness in the
range of about 100 nm to about 10 nm. In one embodiment, these
nanoflakes may be of thickness in the range of about 200 nm to
about 20 nm. As mentioned, some embodiments of the invention may
include both microflakes and nanoflakes. Other may include flakes
that are exclusively in the size range of microflakes or the size
range of nanoflakes. With any of the above embodiments, the
microflakes may be replaced and/or combined with microrods which
are substantially linear, elongate members. Still further
embodiments may combine nanorods with microflakes in the precursor
layer. The microrods may have lengths between about 500 nm to about
1 nm. In another embodiment, the nanorods may have lengths between
about 500 nm and 20 nm. In yet another embodiment, the nanorods may
have lengths between about 300 nm and 30 nm. Any of the above
embodiments may be used on rigid substrate, flexible substrate, or
a combinations of the two such as but not limited to a flexible
substrate that become rigid during processing due to its material
properties. In one embodiment of the present invention, the
particles may be plates and/or discs and/or flakes and/or wires
and/or rods of micro-sized proportions. In another embodiment of
the present invention, the particles may be nanoplates and/or
nanodiscs and/or nanoflakes and/or nanowires and/or nanorods of
nano-sized proportions. Again, any of the foregoing may also be
combined with spherical particles in a suspension. Some embodiments
may have all spherical particles, all non-spherical particles,
and/or mixtures of particles of various shapes. It should be
understood that the solid group IIIA-based particles may be used in
single or multiple combination with particles of other shapes
and/or composition. This may include shapes such as but not limited
to spherical, planar, flake, platelet, other non-spherical, and/or
single or multiple combinations of the foregoing. As for materials,
this may include alloys, elementals, chalcogenides,
inter-metallics, solid-solutions and/or single or multiple
combinations of the foregoing in any shape or form. Use of solid
particles with dispersions and/or emulsions of the foregoing is
also envisioned. The solid solutions are described in pending U.S.
patent application Ser. No. 10/474,259 and published as
US20040219730, fully incorporated herein by reference for all
purposes. The following applications are also fully incorporated
herein by reference: Ser. No. 11/395,438, Ser. No. 11/395,668, and
Ser. No. 11/395,426 both filed Mar. 30, 2006. Any of the
embodiments described in those applications may be adapted for use
with the solid IIIA-based particles described herein.
[0226] For any of the above embodiments, it should be understood
that in addition to the aforementioned, the temperature used during
annealing may also vary over different time periods of precursor
layer processing. As a nonlimiting example, the heating may occur
at a first temperature over an initial processing time period and
proceed to other temperatures for subsequent time periods of the
processing. Optionally, the method may include intentionally
creating one or more temperature dips so that, as a nonlimiting
example, the method comprises heating, cooling, heating, and
subsequent cooling. For any of the above embodiments, it is also
possible to have two or more elements of IB elements in the
chalcogenide particle and/or the resulting film. Although the
description herein uses an ink, it should be understood that in
some embodiments, the ink may have the consistency of a paste or
slurry.
[0227] Additionally, concentrations, amounts, and other numerical
data may be presented herein in a range format. It is to be
understood that such range format is used merely for convenience
and brevity and should be interpreted flexibly to include not only
the numerical values explicitly recited as the limits of the range,
but also to include all the individual numerical values or
sub-ranges encompassed within that range as if each numerical value
and sub-range is explicitly recited. For example, a size range of
about 1 nm to about 200 nm should be interpreted to include not
only the explicitly recited limits of about 1 nm and about 200 nm,
but also to include individual sizes such as 2 nm, 3 nm, 4 nm, and
sub-ranges such as 10 nm to 50 nm, 20 nm to 100 nm, etc. . . .
[0228] For example, still other embodiments of the present
invention may use a Cu--In precursor material wherein Cu--In
contributes less than about 50 percent of both Cu and In found in
the precursor material. The remaining amount is incorporated by
elemental form or by non IB-IIIA alloys. Thus, a Cu.sub.11In.sub.9
may be used with elemental Cu, In, and Ga to form a resulting film.
In another embodiment, instead of elemental Cu, In, and Ga, other
materials such as Cu--Se, In--Se, and/or Ga--Se may be substituted
as source of the group IB or IIIA material. Optionally, in another
embodiment, the IB source may be any particle that contains Cu
without being alloyed with In and Ga (Cu, Cu--Se). The IIIA source
may be any particle that contains In without Cu (In--Se,
In--Ga--Se) or any particle that contains Ga without Cu (Ga,
Ga--Se, or In--Ga--Se). Other embodiments may have these
combinations of the IB material in a nitride or oxide form. Still
other embodiments may have these combinations of the IIIA material
in a nitride or oxide form. The present invention may use any
combination of elements and/or selenides (binary, ternary, or
multinary) may be used. Optionally, some other embodiments may use
oxides such as In.sub.2O.sub.3 to add the desired amounts of
materials. It should be understood for any of the above embodiments
that more than one solid solution may be used, multi-phasic alloys,
and/or more general alloys may also be used. For any of the above
embodiments, the annealing process may also involve exposure of the
compound film to a gas such as H.sub.2, CO, N.sub.2, Ar, H.sub.2Se,
Se vapor, S vapor, or other group VIA containing vapor. There may
be a two stage process where there is an initial anneal in a non
group-VIA based atmosphere and then a second or more heating in
group VIA-based atmosphere. There may be a two stage process where
there is an initial anneal in a non group-VIA based atmosphere and
then a second heating in a non-group VIA based atmosphere, wherein
VIA material is placed directly on the stack for the second heating
and additional is the VIA-containing vapor is not used.
Alternatively, some may use a one stage process to create a final
film, or a multi-stage process where each heating step use a
different atmosphere.
[0229] It should also be understood that several intermediate solid
solutions may also be suitable for use according to the present
invention. As nonlimiting examples, a composition in the .delta.
phase for Cu--In (about 42.52 to about 44.3 wt % In) and/or a
composition between the .delta. phase for Cu--In and
Cu.sub.16In.sub.9 may be suitable inter-metallic materials for use
with the present invention to form a group IB-IIIA-VIA compound. It
should be understood that these inter-metallic materials may be
mixed with elemental or other materials such as Cu--Se, In--Se,
and/or Ga--Se to provide sources of the group IB or IIIA material
to reach the desired stoichiometric ratios in the final compound.
Other nonlimiting examples of inter-metallic material include
compositions of Cu--Ga containing the following phases:
.gamma..sub.1 (about 31.8 to about 39.8 wt % Ga), .gamma..sub.2
(about 36.0 to about 39.9 wt % Ga), .gamma..sub.3 (about 39.7 to
about -44.9 wt % Ga), the phase between .gamma..sub.2 and
.gamma..sub.3, the phase between the terminal solid solution and
.gamma..sub.1, and .theta. (about 66.7 to about 68.7 wt % Ga). For
Cu--Ga, a suitable composition is also found in the range in
between the terminal solid-solution of and the intermediate
solid-solution next to it. Advantageously, some of these
inter-metallic materials may be multi-phasic which are more likely
to lead to brittle materials that can be mechanically milled. Phase
diagrams for the following materials may be found in ASM Handbook,
Volume 3 Alloy Phase Diagrams (1992) by ASM International and fully
incorporated herein by reference for all purposes. Some specific
examples (fully incorporated herein by reference) may be found on
pages 2-168, 2-170, 2-176, 2-178, 2-208, 2-214, 2-257, and/or
2-259. It should also be understood that a particle may have
portions that are of a solid alloy and portions that are phase
separated into individual elements or other alloys that are
liquid.
[0230] It should be understood that any of the embodiments herein
may be adapted for use in a one step process, or a two step
process, or a multi-step process for forming a photovoltaic
absorber layer. One step processes do not require a second
follow-up process to convert the film into an absorber layer. A two
step process typically creates a film that uses a second process to
convert the film into an absorber layer. Additionally, some
embodiments may have anywhere from about 0 to about 5 wt % oxygen
in the shell.
[0231] It should be understood that the solid IIIA particles as
described herein may be used with solids, solid solutions,
intermetallics, nanoglobules, emulsions, nanoglobule, emulsion, or
other types of particles.
[0232] The publications discussed or cited herein are provided
solely for their disclosure prior to the filing date of the present
application. Nothing herein is to be construed as an admission that
the present invention is not entitled to antedate such publication
by virtue of prior invention. Further, the dates of publication
provided may be different from the actual publication dates which
may need to be independently confirmed. All publications mentioned
herein are incorporated herein by reference to disclose and
describe the structures and/or methods in connection with which the
publications are cited. The following related applications are
fully incorporated herein by reference for all purposes: U.S.
patent application Ser. No. 11/290,633 entitled "CHALCOGENIDE SOLAR
CELLS" filed Nov. 29, 2005, U.S. patent application Ser. No.
10/782,017, entitled "SOLUTION-BASED FABRICATION OF PHOTOVOLTAIC
CELL" filed Feb. 19, 2004, U.S. patent application Ser. No.
10/943,657, entitled "COATED NANOPARTICLES AND QUANTUM DOTS FOR
SOLUTION-BASED FABRICATION OF PHOTOVOLTAIC CELLS" filed Sep. 18,
2004, U.S. patent application Ser. No. 11/081,163, entitled
"METALLIC DISPERSION", filed Mar. 16, 2005, and U.S. patent
application Ser. No. 10/943,685, entitled "FORMATION OF CIGS
ABSORBER LAYERS ON FOIL SUBSTRATES", filed Sep. 18, 2004, Ser. No.
60/804,649 filed Jun. 13, 2006, and Ser. No. 60/804,565 filed Jun.
12, 2006, the entire disclosures of which are incorporated herein
by reference. The following applications are also incorporated
herein by reference for all purposes: Ser. No. 11/361,498 entitled
"HIGH-THROUGHPUT PRINTING OF SEMICONDUCTOR PRECURSOR LAYER FROM
MICROFLAKE PARTICLES" filed Feb. 23, 2006 and commonly-assigned,
co-pending application Ser. No. 11/361,433 entitled
"HIGH-THROUGHPUT PRINTING OF SEMICONDUCTOR PRECURSOR LAYER FROM
NANOFLAKE PARTICLES" filed Feb. 23, 2006, Ser. No. 60/804,565 filed
Jun. 12, 2006, Ser. No. 60/804,566 filed Jun. 12, 2006, Ser. No.
60/804,567 filed Jun. 12, 2006, Ser. No. 60/804,569 filed Jun. 12,
2006, Ser. No. 60/804,649 filed Jun. 13, 2006, and Ser. No.
60/804,647 filed Jun. 13, 2006.
[0233] While the above is a complete description of the preferred
embodiment of the present invention, it is possible to use various
alternatives, modifications and equivalents. Therefore, the scope
of the present invention should be determined not with reference to
the above description but should, instead, be determined with
reference to the appended claims, along with their full scope of
equivalents. Any feature, whether preferred or not, may be combined
with any other feature, whether preferred or not. In the claims
that follow, the indefinite article "A", or "An" refers to a
quantity of one or more of the item following the article, except
where expressly stated otherwise. The appended claims are not to be
interpreted as including means-plus-function limitations, unless
such a limitation is explicitly recited in a given claim using the
phrase "means for."
* * * * *