U.S. patent application number 12/738392 was filed with the patent office on 2010-12-02 for solution deposition assembly.
Invention is credited to Geoffrey T. Green, Yann Roussillon, Jeremy H. Scholz, Addison Shelton, Piyaphant Utthachoo.
Application Number | 20100300352 12/738392 |
Document ID | / |
Family ID | 40756054 |
Filed Date | 2010-12-02 |
United States Patent
Application |
20100300352 |
Kind Code |
A1 |
Roussillon; Yann ; et
al. |
December 2, 2010 |
SOLUTION DEPOSITION ASSEMBLY
Abstract
Methods and devices are provided for improved deposition
systems. In one embodiment of the present invention, a deposition
system is provided for use with a solution and a substrate. The
system comprises of a solution deposition apparatus; at least one
heating chamber; at least one assembly for holding a solution over
the substrate; and a substrate curling apparatus for curling at
least one edge of the substrate to define a zone capable of
containing a volume of the solution over the substrate. In another
embodiment of the present invention, a deposition system for use
with a substrate, the system comprising a solution deposition
apparatus; at heating chamber; and at least assembly for holding
solution over the substrate to allow for a depth of at least about
0.5 microns to 10 mm.
Inventors: |
Roussillon; Yann;
(Sunnyvale, CA) ; Utthachoo; Piyaphant; (San Jose,
CA) ; Green; Geoffrey T.; (Belmont, CA) ;
Shelton; Addison; (Sunnyvale, CA) ; Scholz; Jeremy
H.; (Sunnyvale, CA) |
Correspondence
Address: |
Director of IP
5521 Hellyer Avenue
San Jose
CA
95138
US
|
Family ID: |
40756054 |
Appl. No.: |
12/738392 |
Filed: |
October 17, 2008 |
PCT Filed: |
October 17, 2008 |
PCT NO: |
PCT/US08/80391 |
371 Date: |
August 3, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60980757 |
Oct 17, 2007 |
|
|
|
61027817 |
Feb 11, 2008 |
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Current U.S.
Class: |
118/415 |
Current CPC
Class: |
Y02E 10/543 20130101;
H01L 21/02628 20130101; H01L 21/02568 20130101; C23C 18/1279
20130101; C25D 17/00 20130101; C25D 17/001 20130101; B65H
2301/51214 20130101; H01L 21/02551 20130101; B65H 20/00 20130101;
H01L 31/03928 20130101; Y02E 10/541 20130101; C23C 18/06 20130101;
H01L 31/1828 20130101; C23C 18/1245 20130101; C23C 18/1275
20130101; C23C 18/1204 20130101; H01L 31/0749 20130101; C25D 5/50
20130101; C23C 18/1283 20130101; C23C 18/1291 20130101 |
Class at
Publication: |
118/415 |
International
Class: |
B05C 3/02 20060101
B05C003/02 |
Goverment Interests
[0001] This invention was made with Government support under
Contract No. DE-FC36-07GO17047 awarded by the Department of Energy.
The Government has certain rights in this invention.
Claims
1. A deposition system for use with a solution and a substrate.
2. The system of claim 1 wherein the system comprises: a solution
deposition apparatus; at least one heating chamber; at least one
assembly for holding a solution over the substrate; and a substrate
curling apparatus for curling at least one edge of the substrate to
define a zone capable of containing a volume of the solution over
the substrate.
3. The system of claim 2 wherein the assembly curls at least two
edges of the substrate.
4. The system of claim 2 wherein the assembly for holding solution
over the substrate to allow for a depth of at least about 0.5
microns to about 10 mm.
5. The system of claim 2 wherein the assembly for holding solution
over the substrate to allow for a depth of at least about 1 mm to
about 5 mm.
6. The system of claim 2 wherein the curling apparatus curls
opposing edges of the substrate.
7. The system of claim 6 wherein the curling apparatus is
configured to transition a planar substrate to a substrate with
curls along two edges, wherein the transition occurs over a
distance sufficient prevent permanent deformation of the substrate
when the substrate is uncurled.
8. The system of claim 6 wherein the curling apparatus is
configured to transition a planar substrate to a substrate with
curls along two edges over a distance of at least 4 inches.
9. The system of claim 6 wherein the curling apparatus is
configured to transition a planar substrate to a substrate with
curls along two edges over a distance of at least 6 inches.
10. The system of claim 6 wherein the curling apparatus creates
curls of sufficient height to contain the volume of solution
therein without allowing the solution to spill over an upper of the
curl.
11. The system of claim 6 wherein the assembly for holding solution
further comprises of an uncurling apparatus for uncurling at least
two edges of the substrate to return the substrate to a
substantially planar configuration.
12. The system of claim 6 wherein the curling apparatus comprise of
a web guide.
13. The system of claim 6 wherein the curling apparatus comprise of
a shaped web guide.
14. The system of claim 2 wherein the solution deposition apparatus
comprises of a spray deposition system to deposit the solution over
the substrate.
15. The system of claim 2 wherein the solution deposition apparatus
comprises of an ultrasonic spray deposition system to deposit the
solution over the substrate.
16. The system of claim 2 wherein the substrate comprises of a
flexible material.
17. The system of claim 2 wherein the substrate comprises of a
metal foil.
18. The system of claim 2 wherein the solution comprises a
precursor for forming a junction partner for a group IB-IIIA-VIA
absorber layer.
19. The system of claim 2 wherein the solution comprises a
precursor for forming a Group IIB-VIA junction partner.
20. The system of claim 2 wherein the solution comprises a
precursor for forming a junction partner selected from the group
consisting of: cadmium sulfide (CdS), zinc sulfide (ZnS), zinc
hydroxide, zinc selenide (ZnSe).
21. The system of claim 2 wherein the solution comprises of a Group
IIB ionic species is obtained from an aqueous solution of one or
more of the following: sulfate, acetate, bromide, fluoride,
chloride, iodide, hydroxide, nitrate, oxalate, citrate, phosphate,
tungstate, or hydrates of the Group IIB species.
22. The system of claim 2 wherein the solution comprises of a Group
VIA ionic species is obtained from an aqueous solution of one or
more of the following: oxides, halides, sulfates, nitrates, or
ureates of the Group VIA species.
23. The system of claim 2 wherein the solution has a pH of from
about 9 to about 14.
24. The system of claim 2 wherein the solution has a pH of from
about 11 to about 12.
25. The system of claim 2 wherein the assembly for holding solution
is at least partially contained in the heating chamber.
Description
FIELD OF THE INVENTION
[0002] This invention relates generally to deposition systems, and
more specifically, solution deposition systems for use in forming
photovoltaic devices.
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-di-(sulfo-selenide, 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) typically
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] High throughput production methods are in development to
manufacture this type of thin-film photovoltaic device. As
improvements are made for high throughput production of the
absorber layer in such thin-film devices, similar advances need to
be made with regards the deposition or formation of the junction
partner layer to prevent bottlenecking of the production
process.
[0005] It should be understood, however, that the materials used
for forming the junction partner can contain toxic material and
difficulties are encountered in improving the manufacturing system.
One process for forming the junction partner involves using Group
II-VI compounds such as CdS. The CdS used in the formation process
may create hazardous waste by-products, thus increasing processing
costs. Known processes are also inefficient or unreliable in
creating a system with high throughput and high yield. Some known
systems either use too much starting material, much of which is
wasted during production. Others use systems that may be
susceptible to imperfections in the underlying substrate that may
cause non-uniform deposition of the junction partner material over
a wide web. Therefore, a need exists in the art for an improved
junction partner deposition system.
SUMMARY OF THE INVENTION
[0006] Embodiments of the present invention address at least some
of the drawbacks set forth above. The present invention provides
for the improved deposition system for group IIB-VIA materials.
Although not limited to the following, these improved module
designs are well suited for roll-to-roll, in-line processing
equipment. It should be understood that at least some embodiments
of the present invention may be applicable to any type of solar
cell, whether they are rigid or flexible in nature or the type of
material used in the absorber layer. Embodiments of the present
invention may be adaptable for roll-to-roll and/or batch
manufacturing processes. At least some of these and other
objectives described herein will be met by various embodiments of
the present invention.
[0007] In one embodiment of the present invention, a deposition
system is provided for use with a solution and a substrate. The
system comprises of a solution deposition apparatus; at least one
heating chamber; at least one assembly for holding a solution over
the substrate; and a substrate curling apparatus for curling at
least one edge of the substrate to define a zone capable of
containing a volume of the solution over the substrate.
[0008] In another embodiment of the present invention, \a
deposition system for use with a substrate, the system comprising a
solution deposition apparatus; at heating chamber; and at least
assembly for holding solution over the substrate to allow for a
depth of at least about 0.5 microns to 10 mm.
[0009] In yet another embodiment of the present invention, a
deposition system is provided for use with a solution and a
substrate. The system comprises of a solution deposition apparatus;
at least one heating chamber; at least one assembly for holding a
solution over the substrate; and a substrate curling apparatus for
curling at least one edge of the substrate to define a zone capable
of containing a volume of the solution over the substrate.
[0010] It should be understood that any of the embodiments herein
may be adapted to have one or more of the following features. In
one embodiment, the assembly curls at least two edges of the
substrate. Optionally, the assembly for holding solution over the
substrate to allow for a depth of at least about 0.5 microns to
about 10 mm. Optionally, the assembly for holding solution over the
substrate to allow for a depth of at least about 1 mm to about 5
mm. Optionally, the curling apparatus curls opposing edges of the
substrate. Optionally, the curling apparatus is configured to
transition a planar substrate to a substrate with curls along two
edges, wherein the transition occurs over a distance sufficient
prevent permanent deformation of the substrate when the substrate
is uncurled. Optionally, the curling apparatus is configured to
transition a planar substrate to a substrate with curls along two
edges over a distance of at least 4 inches. Optionally, the curling
apparatus is configured to transition a planar substrate to a
substrate with curls along two edges over a distance of at least 6
inches. Optionally, the curling apparatus creates curls of
sufficient height to contain the volume of solution therein without
allowing the solution to spill over an upper of the curl.
Optionally, the assembly for holding solution further comprises of
an uncurling apparatus for uncurling at least two edges of the
substrate to return the substrate to a substantially planar
configuration. Optionally, the curling apparatus comprise of a web
guide. Optionally, the curling apparatus comprise of a shaped web
guide. Optionally, the solution deposition apparatus comprises of a
spray deposition system to deposit the solution over the substrate.
Optionally, the solution deposition apparatus comprises of an
ultrasonic spray deposition system to deposit the solution over the
substrate. Optionally, the substrate comprises of a flexible
material. Optionally, the substrate comprises of a metal foil.
Optionally, the solution comprises a precursor for forming a
junction partner for a group IB-IIIA-VIA absorber layer.
Optionally, the solution comprises a precursor for forming a Group
IIB-VIA junction partner. Optionally, the solution comprises a
precursor for forming a junction partner selected from the group
consisting of: cadmium sulfide (CdS), zinc sulfide (ZnS), zinc
hydroxide, zinc selenide (ZnSe). Optionally, the solution comprises
of a Group IIB ionic species is obtained from an aqueous solution
of one or more of the following: sulfate, acetate, bromide,
fluoride, chloride, iodide, hydroxide, nitrate, oxalate, citrate,
phosphate, tungstate, or hydrates of the Group IIB species.
Optionally, the solution comprises of a Group VIA ionic species is
obtained from an aqueous solution of one or more of the following:
oxides, halides, sulfates, nitrates, or ureates of the Group VIA
species. Optionally, the solution has a pH of from about 9 to about
14. Optionally, the solution has a pH of from about 11 to about 12.
Optionally, the assembly for holding solution is at least partially
contained in the heating chamber.
[0011] 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
[0012] FIG. 1 is a cross-sectional view of a photovoltaic device
according to one embodiment of the present invention.
[0013] FIG. 2 shows a processing system according to one embodiment
of the present invention.
[0014] FIG. 3 shows a processing system according to another
embodiment of the present invention.
[0015] FIG. 4 shows top down view of a processing system according
to another embodiment of the present invention.
[0016] FIG. 5 shows cross-sectional view of a processing system
according to one embodiment of the present invention.
[0017] FIG. 6 shows a processing system according to another
embodiment of the present invention.
[0018] FIG. 7 shows a processing system according to another
embodiment of the present invention.
[0019] FIG. 8 shows a cross-sectional view showing deposition of
material embodiment of the present invention.
[0020] FIG. 9 shows a cross-sectional view of one embodiment of a
processing system configured to curl one or more edges of a
substrate.
[0021] FIG. 10 through 11B show various mechanisms for use for
curling one or more edges of a substrate.
[0022] FIGS. 12A-12C show various configurations for a substrate
with upwardly shaped edges.
[0023] FIGS. 13 and 14 are top down views of a processing system
showing locations of the substrate shaping assemblies according to
embodiments of the present invention.
[0024] FIGS. 15 through 19 are side views of processing systems
according to various embodiments of the present invention.
[0025] FIG. 20 shows a top down view of one portion of a substrate
according to the present invention.
[0026] FIGS. 21 and 22 show a cross-web view of the substrate
according to embodiments of the present invention.
[0027] FIGS. 23A and 23B show a cross-web view of the substrate
according to embodiments of the present invention.
[0028] FIGS. 24 through 28 show various methods for edge sealing
against the lateral edges of the substrate according to embodiments
of the present invention.
[0029] FIGS. 29 and 30 show embodiments of the present invention
with stirring mechanisms along the substrate path.
[0030] FIGS. 31 shows one embodiment of a vacuum belt suitable for
use with an embodiment of the present invention.
[0031] FIGS. 32 shows one embodiment of a vacuum guide suitable for
use with an embodiment of the present invention.
[0032] FIG. 33 shows a web path through one embodiment of
processing system according to the present invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0033] 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.
[0034] 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:
[0035] "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 roller optionally
contains a feature for a thermally conductive film, this means that
the conductive film feature may or may not be present, and, thus,
the description includes both structures wherein a roller possesses
the conductive film feature and structures wherein the film feature
is not present.
Photovoltaic Device Structure
[0036] Referring now to FIG. 1, one embodiment of such a
photovoltaic device 10 will now be described. Although the present
embodiment is described in the context of a thin-film group
IB-IIIA-VIA device, it should be understood that other types of
photovoltaic devices may also be produced using the junction
partner formation techniques described herein.
[0037] As seen in FIG. 1, the structure of a photovoltaic device 10
according to the present invention includes a base substrate 12, an
optional intermediate layer 13, a base or back electrode 14, a
p-type absorber layer 16 incorporating a film of the type described
above, a n-type junction partner semiconductor thin film 18, and a
transparent electrode 20. By way of example, the base substrate 12
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, or a metallized plastic. By way of
nonlimiting example, related polymers include those with similar
structural and/or functional properties and/or material attributes.
The base electrode 14 is made of an electrically conductive
material. By way of example, the base electrode 14 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 13
may be incorporated between the electrode 14 and the substrate 12.
The transparent electrode 20 may include a transparent conductive
layer 19 and a layer of metal (e.g., Al, Ag, Cu, or Ni) fingers 21
to reduce sheet resistance.
[0038] In one embodiment, the base substrate 12 may be a metal foil
made of a material such as but not limited to stainless steel,
copper, aluminum, nickel, molybdenum, or the like. In one
embodiment, aluminum is used with a molybdenum base electrode.
Aluminum and molybdenum, however, 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 10. Furthermore aluminum can
diffuse though molybdenum into layers beyond e.g. CIG(S). To
inhibit such inter-diffusion, an intermediate, interfacial layer 13
may be incorporated between the aluminum foil substrate 12 and
molybdenum base electrode 14. 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 13 is
at least 100 nm or more. In another embodiment, the thickness of
the layer 13 is at least 150 nm or more. In one embodiment, the
thickness of the layer 13 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 13 and below the base electrode layer 14. 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 13 and below the base electrode layer 14.
This layer may be thicker than the layer 13. Optionally, it may be
the same thickness or thinner than the layer 13. This layer 13 may
be placed on one or optionally both sides of the aluminum foil
(shown as layer 15 in phantom in FIG. 5). Some embodiments may use
an electrically conductive barrier on side and a non-electrically
conductive barrier on the other side. Other embodiments use the
same type of conductivity material on both sides.
[0039] If barrier layers are on both sides of the substrate 12, 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
[0040] In the present embodiment, the structure of the photovoltaic
device 10 may include a semiconductor thin film 18 of a
complementary charge type that serves as a junction partner between
the compound film and the transparent conducting layer 19. By way
of example, the n-type semiconductor thin film 18 (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.
Other types of junction partner material such as
poly(benzimidazobenzophenanthroline ladder) (BBL) may also be used
as a junction partner material according to the present invention.
Details about BBL is provided in copending U.S. patent application
Ser. No. 11/409,503 filed Apr. 21, 2006, fully incorporated herein
by reference for all purposes. 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 optionally from about 5 nm
to about 500 nm, and most optionally from about 10 nm to about 300
nm. In some embodiments, the thickness may be in the range of about
10 to about 100 nm. In other embodiments, the thickness may be in
the range of about 15 to about 80 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.
[0041] The transparent conductive layer 19 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 18 and transparent conductive layer
19. Combinations of inorganic and organic materials can also be
used to form a hybrid transparent conductive layer. Thus, the layer
19 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.
[0042] 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.
Junction Partner Deposition System
[0043] Referring now to FIG. 2, one embodiment of a junction
partner deposition system will now be described. In this embodiment
of the invention, the deposition system may be a solution
deposition system that occurs in an environment at atmospheric
pressures. Optionally, it should be understood that the deposition
system may also be used with vacuum, low vacuum, and/or
sub-atmospheric pressures. Some embodiments may also use
environments at pressures higher than atmospheric pressure.
[0044] FIG. 2 shows a system with a substrate 50 configured for use
in an in-line, roll-to-roll configuration. The substrate 50 may be
a coated metal, coated polymer, coated metallized polymer
substrate, or any other substrate previous described herein. The
coating may be a photovoltaic absorber layer such as but not
limited to Cu--In--Ga--Se, Cu--In--Se, Cu--In--Ga--S,
Cu--In--Ga--Se--S, other group IB-IIIA-VIA absorbers, CdTe,
sulfo-salt, group IIB-VIA absorber, or other photovoltaic absorbers
that use a junction partner layer. The photovoltaic absorber layer
or other coating formed on the substrate 50 may be formed from one
or more precursors deposited by any of a variety methods including
but not limited to sputtering, electrodeposition, electroplating,
solution deposition, ALD, evaporation, CVD, PVD, and/or the like.
When the term substrate 50 is discussed herein, it may be a bare
substrate or it may be the substrate with the coating thereon. By
way of nonlimiting example, these absorber layers may also be
formed on rigid substrates or flexible substrates.
[0045] In one embodiment, the substrate 50 is a flexible elongate
substrate such as but not limited to an absorber coated metal foil.
In another embodiment, the substrate 50 is a multi-layered flexible
substrate such as that shown in FIG. 1. Optionally, there may be a
carrier on which discrete or pre-cut substrates comprising the
precursor layers may be placed. The carrier may then carry these
discrete or pre-cut substrates through the processing station(s).
As part of the initial setup, the surface of the substrate to be
processed may be cleaned prior to solution deposition.
[0046] By way of example and not limitation, the junction partner
used with the substrate 50 may be a Group IIB-VIA material. In one
embodiment, the Group IIB ionic species may be comprised of one or
more of the following: cadmium, mercury, zinc, cadmium, mercury or
zinc which may be provided by one or more solutions of the
following: sulfate, acetate, bromide, fluoride, chloride, iodide,
hydroxide, nitrate, oxalate, citrate, phosphate, tungstate,
hydrates or combinations thereof. The Group VIA ionic species
comprises oxygen, sulfur, selenium, tellurium, polonium, or
combinations thereof. The Group VIA ionic species is optionally
obtained from an aqueous solution of oxides, halides, sulfates,
nitrates, or ureates of the Group VIA species. The liquid coating
composition optionally further comprises a solvent such as water,
optionally deionized water. The liquid coating composition
optionally has a pH of from about 9 to about 14, more optionally
from about 10 to about 13 and most optionally from about 11 to
about 12.
[0047] In one embodiment, a CdS layer is formed on substrate 50 by
a solution deposition process. More specifically, in this
embodiment, a solution containing cadmium acetate (Cd(CH.sub.3
COO).sub.2), thiourea (NH.sub.2 CSNH.sub.2), ammonium acetate
(CH.sub.3 COONH.sub.4) and ammonia is prepared. In this present
embodiment, the concentration of the cadmium acetate in the
solution was 0.001M, the concentration of the thiourea was 0.005M,
the concentration of the ammonium acetate was 0.01M and the
concentration of the ammonia was 0.4M. The substrate coated in this
solution to form a CdS layer on the substrate. This is purely
exemplary and is non-limiting.
[0048] A variety of solution-based coating techniques may be used
to apply the above liquids 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, ultrasonic spray
deposition, and the like, as well as combinations of the above
and/or related technologies. The surface of the substrate 50 can be
modified by the addition of a wetting agent to the solution, such
as but not limited to glycerine. The liquid may also be a
dispersion or ink containing the aforementioned materials.
Depending on such surface tension, application of the liquid onto
the substrate may optionally be conducted upside down.
[0049] Referring still to FIG. 2, this embodiment shows that a
spray technique is used to apply the liquid coating to the
substrate 50. In this embodiment, the solution may be a mixture of
0.005-0.01M CdSO4 solution with 2M of NH4OH to pH of about 12.
Optionally, the solution may be a mixture of cadmium sulfate is
between about 0.001 to about 0.008 mole/liter. Optionally, the
solution may be a mixture of cadmium sulfate is between about 0.002
to about 0.005 mole/liter. Optionally, a 0.3-0.5M thiourea solution
is included. Optionally, the thiourea concentration is between
0.1-0.6 mole/liter. Optionally, the thiourea concentration is
between 0.2-0.5 mole/liter. FIG. 2 shows that this embodiment uses
a spraying assembly 60 configured to spray material onto the
substrate 50. By way of example and not limitation, the spray
assembly 60 may use a single nozzle, two nozzles, or multiple
nozzles to spray liquid across the width of the substrate 50. One
or more of the nozzles may be ultrasonic nozzles. Ultrasonic
nozzles are commercially available from manufacturers such as J D
Ultrasonics of the United Kingdom. Optionally, the nozzles may be
dual jet nozzles that are configured for atomizing liquid across a
wide web such as that available from Wilson Spray Nozzle of
Singapore. There may be one or more these wide web nozzles in
assembly 60. Optionally, one or more of the nozzles may be a vortex
nozzle, wherein the flow from the nozzle is such that a vortexing
flow exits the nozzle to define a cone-shaped spray. Optionally,
wide web and vortex nozzles may be used in combination. The spray
assembly 60 may be sufficient to spray across a substrate 50 that
may have a width of greater than 0.5 meters. Optionally, the spray
assembly 60 may be sufficient to spray across a substrate 50 that
may have a width of greater than 1.0 meters. Optionally, the spray
assembly 60 may be sufficient to spray across a substrate 50 that
may have a width of greater than 2.0 meters. Optionally, the spray
assembly 60 may be sufficient to spray across a substrate 50 that
may have a width of greater than 3.0 meters.
[0050] It should also be understood that the temperature of the
solution or dispersion being deposited and/or that of the substrate
may also be controlled. In one embodiment, the container containing
this solution was put in a hot water bath kept at about 85 degree.
C prior to deposition and is deposited on a substrate at a lower
temperature. In some embodiments, the substrate is at ambient
temperature, or heated but to a temperature less than or equal to
the temperature of the solution or dispersion to be deposited.
Optionally, both the solution and the substrate 50 are at
substantially the same temperature. In one embodiment, neither the
solution or the substrate 50 are heated and both are at ambient
temperatures. In other embodiments, the substrate 50 may be heated
from ambient to about 60 to about 90.degree. C. In other
embodiments, the substrate 50 may be heated from ambient to about
50 to about 90.degree. C. In other embodiments, the substrate 50
may be heated from ambient to about 40 to about 100.degree. C. In
other embodiments, the solution or dispersion may actually be
chilled or cooled to be below ambient temperature.
[0051] In another aspect, the amount of solution applied may be
either a thin layer or it may be sufficient to create a bath of a
depth of about 0.5 mm to about 5 mm in depth. Optionally, the bath
may be about 0.5 microns to about 10 mm in depth. A shallow bath
allows for sufficient coverage of the entire target surface of the
substrate 50 while not substantially under-utilizing the raw
material. The bath above the substrate 50 may be contained above
the substrate 50 against a slidable seal and/or a movable seal.
Optionally, the substrate 50 passes through a bath of the solution,
wherein the substrate 50 may have a backside layer that can be
removed.
[0052] Referring still to FIG. 2, a second deposition assembly 70
(shown in phantom) may also be used. This may be the same type of
ultrasonic nozzle used in the solution deposition assembly 60.
Optionally, it may one of the other types of deposition system such
as but not limited to a vortex, wide-web, or other nozzle type
different from the nozzle used in the solution deposition assembly
60. Optionally, the second deposition assembly 70 may include one
or more of the following: 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 solution from assembly 70 may be the same as that
from assembly 60 or it may be a component used in the process such
as the thiourea solution or the like.
[0053] It should be understood that in some embodiments, there may
be more than two deposition sources 60 and 70. Some embodiments may
have three or more. Each may be depositing just one component of
the material in the processing solution. Some may be depositing
mixtures. Some embodiments may use a combination (some sources
depositing just one component, while another source depositions
mixtures of one or more). It should also be understood that in some
embodiments, the solutions, components, or other material from
deposition sources 60 and 70 may all be at temperatures higher than
that of the substrate, the same as the temperature of the
substrate, or at temperatures lower than that of the substrate.
Optionally, only one of the deposition sources is depositing at
temperatures higher than that of the substrate. Optionally, only
one of the deposition sources is depositing at temperatures the
same as that of the substrate. Optionally, only one of the
deposition sources is depositing at temperatures lower than that of
the substrate. The sequence may also be varied such as but not
limited to a cadmium salt solution first and then thiourea or other
S solution later. Some embodiments may add one or more other
complexing agents. The sequence may be varied with the S solution
deposited first and then followed by the cadmium salt solution and
any other components. Some may involve a combination of wet
deposition and dry deposition processes such as a liquid S solution
with cadmium salt nanoparticles added at a different station. Of
course, the type of deposition may also be varied such as but not
limited to slot die deposition followed by a predefined time delay
of a spray deposition of another component or vice versa. Any of
the multi-deposition source systems may be adapted for use with any
of the embodiment of the processing system described herein.
[0054] As seen in FIG. 2, after solution deposition by assembly 60
and/or 70, the substrate 50 enters an oven 80 for heating the
solution to enable film growth or formation. In one embodiment, the
over 80 is used to heat the substrate to between about 65 to about
90 C. Optionally, some embodiments, may heat to higher temperatures
such as about 90 to about 130 C. A variety of ovens may work. In
one embodiment, the oven 80 comprises of an infrared oven is used
to heat the substrate 50 and the solution over the substrate 50.
Infrared ovens are available from a variety of manufacturers
including Glenro Inc. of Paterson, N.J. Other embodiments may use
muffles wherein the heating elements are located outside the tube
furnace or muffle through which the substrate passes. The heating
elements heat the muffle, which in turn heats the substrate. Some
embodiments may only include heating element on one side of the
oven 80 (e.g. top) or only on the other side (e.g. bottom). In one
embodiment, the group IIB-VIA material over the substrate 50 may
have a cured thickness of about 20 to about 100 nanometers.
Optionally, the thickness may be between about 100 to about 150
nanometers.
[0055] After passing through the oven 80, the substrate 50 reaches
a cleaning station 90. This cleaning system 90 may use a pressure
spray of liquid such as but not limited to deionized water to
remove unused or uncured solution applied to the substrate 50. The
wash off from the pressure spray is collected and the waste liquid
contained or processed for proper removal.
[0056] Optionally, a second cleaning station 100 is included. This
may be an additional washing station similar to the cleaning
station 90, it may be an air knife or other source to dry the
substrate 50, or it may be cleaning system using some other type of
cleaning solution. The cleaning and/or drying may occur on only one
side of the substrate 50 or it may be from the underside or other
directions as indicted by stations 92 and 102 in phantom.
Optionally, it may be a combined heating and air dry station to
remove un-wanted material from the surface of the substrate and to
prepare the substrate for the next stage of processing. In some
embodiments, the heating may occur after the air drying and may use
an infrared heating to increase the substrate temperature and to
prepare it for the next layer to be deposited on the photovoltaic
device. In one embodiment, the substrate 50 after the various
processes above, is heated to about 100 C or higher at 2 meters per
minute to dry the web or substrate 50 and to prepare it for the
next layer.
[0057] Referring now to FIG. 3, another embodiment of the present
invention will now be described. This embodiment shows a junction
partner deposition system 130 with a solution deposition by
assembly 60 and/or 70. The oven 80 is used to heat the solution
deposited on the substrate 50 to from the assembly 60 and/or 70.
This embodiment of the junction partner deposition system includes
a vacuum pull belt system 140 which will help flatten the substrate
50 during the processing. This is particularly helpful as some
wider flexible substrates 50 after deposition of semiconductor or
other absorber material will curl and assume non-planar
configurations without force or substrate guides to help flatten
the substrate 50. Vacuum pull belt systems are available from
manufacturers such as Kliklok-Woodman of Decatur Ga. Some systems
may use an articulated floating vacuum pull belt arrangement as
described in U.S. Pat. No. 5,715,656 and fully incorporated herein
by reference for all purposes.
[0058] In this embodiment, the vacuum pull belt system 140 extends
outside the oven 80. Optionally, in other embodiments, the vacuum
pull belt system 140 may extend only within the boundaries of the
oven 80. As seen in FIG. 3, the spray of the solution may occur
over the system 140 by way of the spray assembly 60 or it may occur
at a location of the substrate 50 spaced away from the belt system
140 as indicated by a spray assembly located at position 70.
[0059] FIG. 4 shows yet another embodiment wherein a moving seal
systems 160 and 162 which may be alongside the areas where the
solution is deposited on the substrate 50. FIG. 4 is a top down
view of the substrate 50 and the seals of the systems 160 and 162
will form side walls against the substrate 50 that allows the bath
to be formed over the substrate 50. In one embodiment, the seals of
the systems 160 and 162 will also keep the bath or layer of
solution on only one side of the substrate 50. The systems 160 and
162 may also be configured to have seals that move with the
substrate 50. Other embodiments may have stationary seals that
allow the substrate to slide along against it. Some embodiments may
also include a dip in the substrate path (see FIG. 33) to help
prevent the fluid or solution from flowing too far downweb or
upweb. Scrubbing units 170 and 172 may also be included to clean
the surface of the seal to remove and undesired build up that may
prevent a good seal against the substrate 50. Other embodiments may
use the units 170 and 172 to apply sealant to help the seal against
the substrate 50.
[0060] Still further embodiments may use two back-to-back
substrates 50 to allow for higher utilization. To avoid waste or
undesired processing, two substrates may be attached together
"back-to-back" to form a dual substrate having, in effect, two
front sides with the back sides protected against undesired
treatment. Preferably, the substrates are attached in a manner that
allows them to be separated from each other after processing. By
way of example the substrates may be attached with a low-strength
adhesive or electrostatic film applied to the back side of one or
both substrates. Alternatively, an edge where the two substrates
join may be sealed, e.g., with a tape, so that reactants cannot
reach the back sides during processing. The dual substrate may then
be wound into a coil and coated such that both front surfaces are
treated while the back surfaces are not. Processing the substrate
in this fashion may reduce the waste of reactants and may increase
the area of the substrate that can be processed at one time.
Optionally, other embodiments may use a sacrificial backside that
is removed after processing to reveal a backside that is not
processed. These systems are particularly suited for a bath-type
system wherein the substrate is passed through a solution that
exposes both sides of the substrate.
[0061] Referring now to FIG. 5, it should be understood that the
environment inside the oven may be different from the ambient
atmosphere. Although some embodiments may used an ambient air
environment inside the oven 180, other embodiments may use non-air
atmospheres. By way of example and non-limiting example, the
atmosphere in the muffle 182 may be comprised of ammonia or ammonia
based material to prevent loss of ammonia or similar material from
the solution. The loss of material may create a change in pH that
changes the reaction dynamics. Other embodiments may use other
atmospheres that create an overpressure of the material that may be
volatile and escape from the solution during processing. The
material in the gas environment of muffle 182 is based on what type
of reaction is occurring and what materials may be vaporized or
lost during processing.
[0062] By way of example and not limitation, the muffle 182 may be
designed with openings sized to handle foils of wide widths. In one
nonlimiting example, the substrate 50 may be at least 1 meter in
width. In another embodiment, the substrate 50 may be at least 2
meters in width. In another embodiment, the substrate 50 may be at
least 3 meter in width.
[0063] In one embodiment, the openings in muffle 182 are sized so
as to provide minimal clearance above the substrate to reduce the
amount of gas escaping. In one embodiment, the interior height of
the muffle is less than about 3 inches. In one embodiment, the
interior height of the muffle is less than about 2 inches. In one
embodiment, the interior height of the muffle is less than about 1
inch. In one embodiment, the interior height of the muffle is less
than about 0.5 inches. Although not limited to the following, the
ratio of the interior width to the interior height at the narrow
points in the chamber or muffle may be at least about 10:1.
Although not limited to the following, the ratio of the interior
width to the interior height at the narrow points in the chamber or
muffle may be greater than about 10:1. Optionally in other
embodiments of the invention, the ratio of the interior width to
the interior height at the narrow points in the chamber or muffle
may be greater than about 14:1. Although a muffle is used in this
example, it should be understood that other designs using a cover
over a U cross-sectional shaped web guide may also be sufficient to
create the desired covered tunnel environment. In one embodiment,
the height of the head space above the substrate is predetermined
based on the processing gas and/or fluid used in that particular
zone or area of the processing system.
[0064] In some embodiments herein, the muffle 182 may be
multi-zoned with separate chambers in the muffle. These zones may
be integrated into one structure or they may be separated detached
structures each defining at least one zone. The zones may be
separated from each other by a small gap, or alternately all zones
may structurally be connected to each other, however they may be
internally separated through use of seals or spacers.
[0065] FIG. 5 also shows in phantom that a second muffle 190 may be
used around the inner muffler 182. The atmosphere in outer muffle
190 may be the same as that in the inner muffle 182. Optionally,
the muffle 190 has an atmosphere different from that in the muffle
182. In one embodiment, the muffle 190 includes an inert atmosphere
such as but not limited to nitrogen, argon, or the like. The muffle
190 may be the same length as the muffle 182. Optionally, the
muffle 190 may be longer than the inner muffle 182 to prevent
escape of gas into the outside environment. It would instead escape
into the outer muffle 190. Optionally, each muffle may be inert gas
zones near the inlet and outlet of each muffle to help prevent
escape of the interior processing gas. FIG. 5 also shows how heater
elements 192 and 194 may be located outside, above and/or below the
muffle.
[0066] Referring now to FIG. 6, yet another embodiment of the
present invention is shown wherein multiple spray and heating
locations are shown. In this embodiment, a spray section 200 is
used to deposit the solution, followed by an oven section 202 to
heat the liquid. This system may be followed by spray section 204,
oven 206, spray section 208, and oven 210. The spray and oven
sections may be repeated as desired to create the layer on the
substrate 50 of the desired thickness. In this embodiment, each
spray and oven section creates about 25 to about 35 nanometer
thickness of the junction partner. Other embodiments may use
deposition sections that create thicker or thinner layers. Some may
also use sections to deposit different materials or different
components used for the junction partner. Still other embodiments
may use ovens that run at different temperatures. Some may have
heat in about 70 to about 90 C. Optionally, others may heat higher
to about 40 to about 90 C. Optionally, others may heat higher to
about 90 to about 130 C. Optionally, others may use lower
temperatures of about 55 to about 75 C. The ovens may be arranged
to go high heat to low heat. Optionally, they may go from low heat
to high heat. Others may use a heat profile with high heat in the
middle oven, but lower heat at the beginning or end ovens. This
heating may be followed up by wash and dry units 90 and 100. An
oven 220 may be included to further dry the substrate and/or
prepare it for the next layer of processing. Some embodiment may
roll directly to the next deposition section which may be a TCO
sputtering or other deposition device. The substrate 50 may also
come directly from CIGS or other absorber layer deposition and
processing in a complete roll-to-roll process. It should also be
understood that in alternative embodiments, there may be an
alternative embodiment with a delayed processing, e.g. not direct
and not step repeat. In these alternative embodiments, there may be
non-continuous processing of the substrate.
[0067] Referring now to FIG. 7, a still further embodiment of the
present invention will now be described. This embodiment uses a
frame 250 that is raised and lowered over the substrate 50. In a
step-repeat function, the substrate 50 may be advanced to place an
unprocessed portion below the frame 250. The frame 250 is lowered
to contact the substrate 50 or close enough to prevent significant
loss (more than 10%) of the fluid over the substrate during
processing. Again, any solution deposition may be used. A variety
of solution-based coating techniques may be used to apply the
liquid 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, ultrasonic spray deposition, and the like, as well as
combinations of the above and/or related technologies. The surface
of the substrate 50 can be modified by the addition of a wetting
agent to the solution, such as glycerine. The liquid may also be a
dispersion or ink containing the aforementioned materials.
Depending on such surface tension, application of the liquid onto
the substrate may optionally be conducted upside down.
[0068] The oven 80 is heated during, before, or after deposition of
fluid into the frame 250. After processing and heating, the frame
250 is raised and the substrate 50 is advanced to place a new,
untreated section below the frame 250. Again, the oven 80 may have
an ammonia or other atmosphere as described above. The frame 250
maybe filled multiple times over one section of the substrate 50 to
build up the desired amount of thickness. Other embodiments may use
a frame 250 that moves with the substrate to allow for a moving
process where the substrate is not complete stopped. The frame 250
may be lowered down over an area of the substrate while it is
outside the oven 80.
[0069] Referring now to FIG. 8, yet another embodiment of the
present invention will now be described. This embodiment shows that
instead of using seals, frames or other elements to help contain a
fluid over the substrate 50, the edges 53 and 55 of a flexible
substrate 50 may be curved, curled, or angled upward. This defines
a cupped or bowl-type cross-sectional shape that allows fluid to be
filled therebetween as indicated by line 57 shown in phantom. The
depth of the fluid between the upwardly curled edges 53 and 55 may
be filled to a level below the upper edges, below the upper edges,
and/or optionally over the upper edges. By way of example and not
limitation, the depth of fluid over the substrate 50 may be in
range from about 0.1 mm to about 20 mm. Optionally, in another
embodiment, the depth of fluid over the substrate 50 may be in
range from about 0.5 mm to about 10 mm. In the present embodiment,
a fluid deposition assembly 259 may be used to form a covering of
fluid over the substrate 50. Optionally, the assembly 259 and any
other of the deposition systems such as but not limited to drip,
spray, or other fluid coating devices may be mounted to move in
manner such as but noted limited to that as indicated by arrows 257
to improve coverage of the fluid deposition over substrate 50.
Optionally, this may be achieved by mechanical motion laterally
and/or by angulation of deposition nozzle, hose, or other
deposition device/assembly.
[0070] It should be understood that the fluid may be deposited by
any of a variety of solution deposition 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,
ultrasonic spray deposition, and the like, as well as combinations
of the above and/or related technologies. FIG. 8 shows one
embodiment wherein the fluid is sprayed onto the substrate 50. The
fluid may being deposited may be at a temperature that is
substantially the same as that of the substrate 50. Optionally, in
other embodiments, the fluid may be cooler than the substrate 50 or
hotter than the substrate 50. Some embodiments may heat the fluid
so that it is warmer than the ambient temperature. Some embodiments
may use an air knife to cool and/or clean the substrate prior to
deposition of the fluid.
[0071] FIG. 9 shows that in one embodiment, the substrate 50 with
or without curls 53 and 55 may be moved into a closely spaced
muffle, covered oven, or other structure to minimize the amount of
open space above the substrate 50. These embodiments reduce the
amount of evaporation of the fluid covering the substrate 50. In
the current embodiment, the muffle 260 is used to define the
covered oven through which the substrate 50 passes. The muffle 260
is shown to have curved wall surfaces to maintain the curved
configuration of the substrate 50. Some embodiments may optionally
have slots or grooves defined by guides 262 and 264 (shown in
phantom).
[0072] FIG. 9 also shows that an optional external oven 270 may be
used around the muffle 260. This embodiment allows for convective
heating to be used outside the muffle 260 to heat the muffle 260,
the substrate 50, and the fluid over the substrate 50. The oven 270
may be filled with the same atmosphere as that inside the muffle
260. Optionally, the muffle 260 may be filled with an inert gas
such as but not limited to nitrogen, argon, other inert gas, or
other gas suitable for use with the atmosphere in the muffle 260.
The over 270 may be the same length as muffle 260, shorter than
muffle 260, or longer than muffle 260.
[0073] Referring now to FIG. 10, a cross-section of a guide is
shown for curling the substrate 50 to have the formed edges 53 and
55. This cross-section shows that substrate 50 may be transformed
from a substantially planar configuration to one with a
configuration sufficient to hold fluid therebetween. Again, guides
280 and 282 may be provided to help curl the substrate upward. The
surface 281 may be a low friction surface such as but not limited
to Teflon.RTM. or similar material. The surfaces of guides 280 and
282 may be similarly treated. Optionally, a low friction surface
281 may comprise of a covering, tiles, plates, or other overlayers
that are placed on top of a surface that may have a higher
coefficient or friction. Some embodiments may have a low friction
surface along all portions of the substrate path wherein the
backside of the substrate contacts or slides against any portion of
the processing system.
[0074] FIG. 11A shows that the surface 284 of guide 280 may be a
gradually curving surface to transition the planar edge of the
substrate to a curved configuration. By way of example and not
limitation, the length of surface 284 as indicated by arrow 286 may
be in the range from about 1 inch to about 10 inches. The greater
length eases the transition from planar configuration to curved
configuration. Optionally, the transition length may be in the
range of about 2 to about 6 inches. Optionally, the transition
length may be a percentage based on the width of the web. In one
embodiment it may be between 10% to 120% of the width of the web.
Optionally, in another embodiment, the transition length is
selected to be between 25% to 75% of the width of the web or
substrate. Optionally, some embodiments also factor the height of
the bent portion into the amount of length desired for the
transition. In one embodiment, the length for transition is about
8.times. to 24.times. the height of the desired bend. Optionally,
the transition length is about 4.times. to 40.times. the height of
the desired bend.
[0075] FIG. 11B shows yet another embodiment of the invention
wherein the guide 290 comprises of a plurality of discrete elements
292 that are oriented to provide the same curving the substrate 50
to achieve the same functionality as that of guide 280. By way of
example and not limitation, the discrete element 292 may be a
roller, bearing, drum, or fixed roller. Other rotatable, fixed, or
other shaped discrete elements may be used to guide the substrate
50. The guides may be any of a series of smooth surfaces, angled
surfaces, rounded surfaces, the like, or combinations of the
foregoing to achieved the desired configuration for substrate 50.
Again, any of the surfaces of the elements in FIGS. 11A and 11B may
also be coated or made of a low-friction material as described for
surface 281.
[0076] Referring now to FIGS. 12A-12C, it should be understood that
the guides herein may be configured provide a variety of different
geometries. FIG. 12A shows that the substrate 50 may have angled
but substantially straight upward extending edge 293. FIG. 12B
shows that the substrate 50 may have a vertical but substantially
straight upward extending edge 295. FIG. 12C shows that the
substrate 50 may have a multi-bend upward extending edge 297. It
should be understood that other geometries of straight or curved
sections may be combined in any order to create the desired
cross-sectional profile for the substrate 50. The upward extending
portion of the substrate 50 may be at any angle so long as it is
sufficient to contain or constrain the fluid over the substrate 50.
It should be understood that the amount of upward bending portion
(on each side) may be described as a percentage of the cross-web
width of the substrate such as but not limited to between 1% to 7%
of the web width, with a minimum in this embodiment of at least 1
mm. Optionally, it may be between 2% to 6% of the web width, with a
minimum in this embodiment of at least 2 mm. Optionally, it may be
between 3% to 6% of the web width, with a minimum in this
embodiment of at least 3 mm.
[0077] FIG. 13 shows that the guides 280 and 282 may be positioned
to narrow the substrate 50 to achieve the curved configuration with
the curved edges 53 and 55. Guides 284 and 286 are similar to the
guides 280 and 282, except that the configuration is reversed to
gradually uncurl the curved portions 53 and 55 and return the
substrate 50 to a substantially planar configuration. By way of
example and not limitation, it is desirable that the curling and
uncurling occur in a manner that does not cause substantially
permanent deformation that causes warping or damage to substantial
portions of the substrate 50.
[0078] FIG. 13 also shows that when the edges of the substrate 50
is configured to have curved portions 53 and 55, the width 283 of
the substrate 50 is less than the width 285 of the substrate 50
when planar. The movement of the substrate 50 is in the direction
as indicated by arrow 294.
[0079] FIG. 14 shows that a cascade of one or more guides may be
used to gradually curve the substrate 50. In this embodiment of the
invention, the guides 280 and 282 are included. Additionally, a
second set of guides 300 and 302 are included to further curl the
substrate 50. This decreases the width to that indicated by arrows
304. FIG. 14 also shows the multiple guides 306, 308, 284, and 286
are used to uncurl, unbend, and/or uncurve a selected portion of
the substrate 50.
[0080] Referring now to FIG. 15, one embodiment of a deposition
system 320 according to the present invention is shown. The
deposition system 320 includes a deposition zone 322, a heated zone
324, a cleaning zone 326, and a drying zone 328. A belt system 330
is used to transport the substrate 50 through the heated zone 324.
The deposition zone 322 may be located in an unheated zone.
Optionally, it may be included in the heated zone 324.
[0081] FIG. 15 shows that in this embodiment an air knife or other
gas source 340 may be used to clean off the surface of the
substrate 50. The air knife or cleaning mechanism 340 may also be
used to cool or temperature regulate the substrate 50 before fluid
is deposited onto the substrate 50. This may be particularly useful
as the belt system 330 may carry some heat from the heated zone
324. Optionally, in other embodiments, the belt system 330 may be
sized such that the system 330 is housed mainly in the heated zone
324 and does not extend into the deposition zone 322 in manner that
causes the substrate 50 to be heated prior to deposition of the
fluid thereon. By way of example, the substrate 50 may be moved
over a low-friction surface, free spanned in the deposition zone
322, transported by a separate conveyor system, or otherwise
transported through the deposition zone 322. Some may have sections
of the processing system that are without any conveyor system while
other sections are conveyored. Some embodiments are entirely
without conveyors. Some systems may have the non-conveyored system
with a base have a pre-defined cross-section so as to curve or bend
the substrate upward when the substrate is laid on or pulled to
conform to the base.
[0082] In the present embodiment, the deposition assembly 350 used
in the deposition zone 322 may be a variety of solution deposition
devices. It should be understood that the fluid may be deposited by
any of a variety of solution deposition 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,
ultrasonic spray deposition, and the like, as well as combinations
of the above and/or related technologies. In one embodiment, a
ultrasonic spray system such as but not limited to the Prism
Ultra-Coat system available from Ultrasonic Systems, Inc. of
Haverhill, Mass. may be used in the deposition assembly 350. Some
embodiments may use more than one fluid deposition zone. They may
use the same deposition technique or different techniques. Some
embodiments may combine more than one deposition technique in the
same deposition zone. It should also be understood that the fluid
may be deposited at a temperature that is substantially the same as
that of the substrate 50. Optionally, in other embodiments, the
fluid may be cooler than the substrate 50 or hotter than the
substrate 50. Some embodiments may heat the fluid so that it is
warmer than the ambient temperature. Some embodiments may use an
air knife to cool and/or clean the substrate prior to deposition of
the fluid.
[0083] By way of example and not limitation, it should be
understood that the heating zone 324 may use a variety of heating
techniques. Some may use convection heating, infrared (IR) heating,
or electromagnetic heating. Some embodiments may use chilled
rollers or surfaces (not shown) on the underside of the substrate
50 to keep a lower portion of the substrate 50 cool while the upper
portion is at a processing temperature. As seen in FIG. 15, there
may be one or more separate zones in the heating zone 324. This
allows for different temperature profiles during processing. In one
embodiment, the heating elements may be positioned to heat all
components in the heating zone to the same temperature. This
includes the cover over the substrate, a muffle, or other elements
used inside the heating enclosure. Again, heating may occur by
convection heating, infrared (IR) heating, and/or electromagnetic
heating.
[0084] Referring still to FIG. 15, after the substrate 50 passes
through the heating zone 324, the cleaning zone 326 may use a
combination of washing, blowing, rinsing, suction, cooling,
shaping, heating, and/or other assemblies to post-treat the
substrate 50 after the heating zone 324. In the present embodiment,
a water sprayer 360 is used with an air knife 362. A second water
sprayer 364 is used with a second air knife 366. This combination
is designed to remove any excess fluid that is not reacted as the
substrate 50 leaves the heating zone 324. The fluid and waste
liquid being washed off will be collected by one or more liquid
waste containers 370 and 372. The waste container 370 may be viewed
as the primary waste container as it will contain a more
concentrated waste fluid than the waste fluid filling the waste
container 372. It should also be understood that in some
embodiments, the fluid from containers 370 or 372 may be
reconditioned in reservoir 373 for use again in the system. In one
non-limiting example, used solution is cooled, and replenished in a
solution container 373 and redirected into the deposition
chamber.
[0085] There may be additional components such as filters on the
return line 325, filters (not shown) on the feed line 327, or
filters in fluid communication with reservoir 373 that may
circulate the solution within the solution container 22 for the
purpose of particle elimination, cooling, mixing etc. There may be
a cooling loop with a cooling coil within the solution container
373. A cooling liquid may be circulated through the cooling coil to
lower the temperature of the bath within the solution container
373. The temperature of the solution within the solution container
373 may be in the range of 5-40 C, preferably in the 15-20 C range.
In effect the deposition section becomes a cold-wall reactor where
only the wall carrying the structure to be coated with CdS is
heated.
[0086] FIG. 15 also shows that in this embodiment of the invention,
the substrate 50 is dried after passing through the cleaning zone
326. Drying zone 328 is positioned over the substrate 50 and will
cure the material on the substrate 50. In one embodiment, the
drying zone 328 uses a plurality of ultraviolet curing lamps to
remove any residual moisture that may be on the substrate.
Optionally, in another embodiment of the invention, heated gases
may be circulated over the substrate 50 to remove any residual
moisture from the substrate 50. Some embodiment may circulate
heated inert gas such as but not limited to nitrogen. Optionally,
some embodiments may merely circulate heated ambient air that is
drawn into the drying zone 328.
[0087] It should also be understood that a variety of sensors may
also be installed along the path that the substrate 50 travels
through the deposition system 320. By way of nonlimiting example,
this may include a thickness sensor 380 positioned to detect the
thickness of the coated substrate. Optionally, other embodiments
may use an optical sensor to detect surface imperfection on the
coated substrate 50. FIG. 15 also shows that exhausts 390, 392, and
394 are positioned along the path of the substrate 50 to draw off
waste gases that may be created during processing. Sensors may also
be optionally present to optionally detect chemical composition
either on surface and/or through depth of coating. Some embodiments
may have optional sensor system to assess spatial uniformity (not
just aberrations but also standard uniformity).
[0088] It should also be understood that some embodiments may have
multiple heating zones 324. Some embodiments may have alternating
zones 322 and 324. The zones may be combined various orders such as
that shown in FIG. 6. Cleaning zones 326 may also be included after
one or more of the heating zones 324.
[0089] Referring now to FIG. 16, yet another embodiment of the
present invention is now described. The deposition system 400 in
FIG. 16 is similar in some aspect to the system 320 shown in FIG.
15. By way of example and not limitation, the heating zone 324
includes additional convention chambers therein. The exhaust 394 is
connected to its own chamber 410. Deposition system 400 includes a
substrate guide or contour device 420 located upstream of the
heating chamber. This substrate contour device 420 will shape the
edges of the substrate 50 to define an area over the substrate 50
to hold fluid thereon. A second substrate contour device 430 will
uncurl the edges of the substrate 50 to return the substrate 50 to
a substantially planar configuration. One other area of difference
in the deposition system 400 involves the cleaning zone 326. The
cleaning zone 326 in system 400 includes a suction element 440 for
removing excess fluid from the substrate 50 after processing
through the heating zone 324. This suction element 440 provides for
increased control of fluid being removed from substrate 50 prior
the washing and blowing elements similar to that of system 320.
[0090] Optionally, it should be understood that any of the
embodiments herein may be equipped with thermally conductive
coverplate(s) 351 which may include a plurality of fins or other
heat transfer improving shapes or features to improve the heat
transfer from the convection system to the substrate 50. The plates
351 may be made of a thermally conductive material such as but not
limited to steel, aluminum, titanium, or the like. Optionally,
in-line heating elements 353 may be also be included below and/or
above the substrate to improve heat transfer to the substrate. They
may be integrated to be part of the coverplates 351 or separate
discrete elements. Some embodiment may also use free-spanning
substrate 50 that is move without the use of a conveyor belt.
[0091] FIG. 17 shows a still further embodiment wherein a bath type
deposition system 500 is used with moving seals 502 and 504. The
moving seals 502 and 504 may cover the side, top, and/or bottom
surfaces of the substrate 50 as seen more clearly in FIGS. 24-28.
The path of the substrate 50 through the system 500 may be lowered
to create a bath inside the system 500 without spillage downweb or
upweb. Again, any solution deposition technique may be used. A
variety of solution-based coating techniques may be used to apply
the liquid 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, ultrasonic spray deposition, and the like, as well as
combinations of the above and/or related technologies. The surface
of the substrate 50 can be modified by the addition of a wetting
agent to the solution, such as glycerine. The liquid may also be a
dispersion or ink containing the aforementioned materials.
Depending on such surface tension, application of the liquid onto
the substrate may optionally be conducted upside down. Heating of
the web may occur after the deposition has occurred and/or at the
same time. Optionally, the solution may itself be heated to a
temperature above that of the substrate.
[0092] Referring now to FIG. 18, this embodiment shows that the
substrate 50 may be passed through a bath 550 of Group
IIB-VIA-based solution as shown. The rollers 552 are positioned so
as to prevent contact the coated surface 554 of the substrate 50.
Alternatively, some embodiments may allow the rollers 554 to
contact the coated surface. FIG. 18 shows that this embodiment may
optionally include a stirrer 560 to keep fluid moving around the
surfaces of the container. FIG. 18 also shows that a reservoir 570
may be included to create fluid flow in the bath. Conduits 572 and
574 may be used to couple the bath 550 to the reservoir 570.
[0093] Referring now to FIG. 19, yet another embodiment of the
present invention will now be described. FIG. 19 shows a shaped
container 580 that contains a bath 582 therein. There may be
movable surfaces 584 and/or 586 (shown in phantom) along the sides
of the shaped container 580 to allow for deposits on those surfaces
to be cleaned. Optionally, some embodiments may have normal wall
surfaces, but the container 580 is frequently cleaned to remove and
deposits formed thereon. Some embodiments may also be fitted with a
reservoir similar to reservoir 570 to allow for constant fluid flow
in the container 570 and more specifically along the walls of
container 570 to minimize deposits thereon. Similar to FIG. 18, the
rollers 588 may be configured not contact the coated surface 552 of
the substrate 50. The shaped container also prevents fluid from
escaping. Heating elements may be included in the bath or outside
the container 580 to heat the bath 582 therein to the desired
processing temperature. Some embodiments may have the same
temperature throughout the bath 582. Optionally, other embodiments
may have different heating zones that may include barriers 589 in
the bath that separate different fluid zones that may have
different temperatures. These embodiments may or may not use the
substrate edge bending techniques previously described herein.
[0094] FIG. 20 shows a still further embodiment wherein an
additional material 600 is coupled to the edges of the substrate
50. This allows for the material 600 to define the curved portion
that allows a bath to be defined thereon. The material 600 may be a
disposable material or reusable material. This minimizes the risk
that the curling may scratch or damage the coating on the substrate
50. The material 600 may comprise of a variety of materials such as
but not limited to Teflon, polymer, silicone, or other material.
The material 600 may be coupled to the substrate 50 by adhesives or
by heating.
[0095] As seen in FIG. 21, the material 600 may be in the form a
sheet that covers the entire backside of the substrate 50 and
extends beyond the edges of the substrate 50. This may be
particularly useful when the substrate 50 is a plurality of
pre-formed, discrete, or pre-cut rigid substrates and the material
600 is a pliable material to allow for curving to define a zone
over the substrate for holding the fluid. The material 600 may act
as a carrier on which pre-formed, discrete, or pre-cut substrates
may be placed. The carrier may then carry these pre-formed,
discrete, or pre-cut substrates through the processing station(s).
In some embodiments, the edges of the material 600 may be
pre-shaped to have the upward bending configuration and not
separate curling apparatus is need to help transform the material
600 from a planar configuration to one with upwardly pointing
edges.
[0096] FIG. 22 shows that another embodiment of the invention may
use the substrate 50 with strips of material 602 and 604 instead of
an entire backside sheet of material 600. The material 602 and 604
may be similar to that used for material 600. The material 602 and
604 may be sufficiently flexible to allow the upward extending
portion to be formed and allow a bath to be contained therein. This
edge material may optionally be disposable so that the materials
602 and 604 may be handled more aggressively to get the desired
throughput or shape. The same may also be said of material 600 in
embodiments where it is designed to be disposable.
[0097] Referring now to FIG. 23A, it should be understood that some
embodiments may use a separate layer 610 that is attached to the
backside of the substrate 50. This provides backside protection of
the substrate 50, may also prevent unwanted formation of junction
partner material on the backside, to act as a thermal mass to cool
the backside, or to protect the backside during the curling or
uncurling process. This backside material may be permanently
attached to the substrate 50 or it may be a disposable material
that is removed. Some embodiments may have the material dissolve
away during processing.
[0098] FIG. 23B shows that two substrates 50 and 51 may be joined
together. Coating or otherwise treating both sides of one substrate
can result in waste of valuable reactants or may lead to extra
processing steps such as removing unwanted coatings. To avoid such
waste or undesired processing, two substrates may be attached
together "back-to-back" to form a dual substrate having, in effect,
two front sides with the back sides protected against undesired
treatment. Optionally, the substrates are attached in a manner that
allows them to be separated from each other after processing. By
way of example the substrates may be attached with a low-strength
adhesive or electrostatic film applied to the back side of one or
both substrates. Alternatively, an edge where the two substrates
join may be sealed, e.g., with a tape, so that reactants cannot
reach the back sides during processing. The dual substrate 50 and
51 may then be introduced into the bath and coated such that both
front surfaces are treated while the back surfaces are not.
Processing the substrate in this fashion may reduce the waste of
reactants and may increase the area of the substrate that can be
processed at one time. The substrates may be joined directly
together or may have an adhesive layer 612 therebetween.
[0099] FIGS. 24 through 28 show some of the various types of edge
seals that may be used with the substrate 50 or with substrate 50
and a disposable edge material to allow for a bath to be formed
over the substrate 50. FIG. 24 shows that seal material 620 may be
slidably or fixably attached to an upper surface 622 of the edge of
the substrate 50. FIG. 25 shows that seal material 624 may be
slidably or fixably attached to a side surface 626 of the edge of
the substrate 50.
[0100] FIG. 26 shows that shaped seals 630 formed against a side
surface 626 and/or a bottom surface 632 of the substrate 50. The
seals 630 may be slidably or fixably attached to the substrate 50.
FIG. 27 shows that a shaped seal 640 may be formed against a side
surface 626 and/or a top surface 622 of the substrate 50. The seals
640 may be slidably or fixably attached to the substrate 50. FIG.
28 shows that a shaped seal 650 may be formed against a side
surface 626, and/or a top surface 622, and/or a bottom surface 632
of the substrate 50. The seals 640 may be slidably or fixably
attached to the various surfaces of substrate 50. Optionally, the
surfaces of shaped seal 650 engaging the surfaces of substrate 50
may be angled and not necessary parallel to the surfaces against
which they engage. This may created a pinched contact if a tighter
engagement is desired.
[0101] Referring now to FIG. 29, yet another embodiment of the
present invention will now be described. FIG. 29 shows a top-down
view of the substrate 50 as it is being processed for formation of
the junction partner layer. This embodiment has a single fluid
deposition source 700 that directs fluid onto the substrate 50. The
source 700 may be oriented to direct fluid downstream. This may be
as a result of a slight angle of the deposition system as seen in
FIG. 3 and may help to prevent flow of fluid upstream to
un-contained areas where fluid may flow off the sides of the
substrate 50. The fluid deposition source 700 may also be designed
to have a reciprocating feature wherein the direction of the
deposition will move through a series of angles 702 to more evenly
distribute fluid over the substrate 50.
[0102] FIG. 29 also shows that one or more rotational stirring
elements 710 and 712 may also be included in the present invention.
The stirring elements 710 and 712 may be the same or different
size. They may be positioned to create gas or air flow over the
bath of fluid covering substrate 50. This may be helpful in
creating convection or flow to more evenly distribute heat
uniformly over the substrate 50. Optionally, the stirring elements
710 and 712 may be fully in or at least partially stirring the
fluid over the substrate 50. They may be configured to rotate in
the same or different directions. Other, non-rotation devices may
also be used to create liquid flow or gas flow.
[0103] FIG. 30 shows a still further embodiment wherein there is
more than one fluid deposition assembly 720 and 722 which are
positioned at locations along the length and/or width of substrate
50. This may achieve a desired even distribution of fluid over the
substrate 50. Some embodiments may have two or more fluid
depositions assemblies. One or more the fluid deposition assembly
720 and 722 may be movable across different angles 702, similar to
that as shown in the embodiment of FIG. 30. For any of the
embodiments herein, a static or active mixer may be used upstream
of the deposition assemblies to mix the fluids together prior to
deposition onto substrate 50.
[0104] Referring now to FIG. 31, yet another aspect of the present
invention will now be described. FIG. 31 shows a conveyor belt 730
with vacuum holes 732 therein to allow for suction of a substrate
50 thereon. This is useful to facilitate transport of the substrate
50 without scratching the underside. The vacuum holes 732 in the
belt are suctioned by way of a vacuum source 734. The conveyor belt
730 may be sized to be the same as or almost the same width as the
substrate 50. Optionally, it may be wider than the substrate 50.
Optionally, belts 730 that are less wide may also be used. The
thinner belts 730 may be used to suction down the substrate 50 at
various strategic locations. Some embodiments may also use shaped
conveyors which provide the desired contour at the edges of the
substrate 50. Such shaped conveyors may have a lip 733 (shown in
phantom) that may help to maintain the contour of the substrate 50
being transported by the conveyor. In some embodiments, the
conveyor may be made of a thermally conductive material such as but
not limited to a metal belt of titanium, stainless steel or the
like. Optionally, the conveyor may be made of a polymer or
thermally insulating material.
[0105] Optionally as seen in FIG. 32, on some very low surface
transport surfaces, instead of using vacuum holes on the belts, the
vacuum holes 732 may optionally be formed onto the low-friction
surface 738. In one embodiment, the low-friction surface may be a
Teflon.RTM. surface. Optionally, it may a surface with a static
coefficient of friction between about 0.12 to about 0.20.
Optionally, it may a surface with a static coefficient of friction
between about 0.10 to about 0.30. This may allow the substrate to
be held flat as it is pulled across the transport surface. This may
be of particular use since the substrate 50 may be somewhat
non-flat after processing.
[0106] Referring now to FIG. 33, a still further aspect of the
present invention will now be described. This shows that a
substrate 50 may be taken along a path that dips to allow for a
bath to be created at recessed area to minimize the loss of process
fluid either upstream or downstream. This dip 740 in the path may
be achieved through the use of rollers or other web guiding devices
to direct the substrate 50 to a lower pathway. The substrate 50 may
remain at this lower level and the rise upward vertically or at an
angle to rise out of the lower path.
[0107] 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, the present invention may be adapted for use with
superstrate or substrate designs. The tool designs of this
invention may be used for continuous, in-line processing of
substrates which may be in the form of a web or in the form of
large sheets such as glass sheets. The substrate may be a
continuous web or sheet of a metal or an insulator comprising a
precursor layer that has been reacted to form a compound film
absorber layer. The present invention is not limited to deposition
of junction partner material. By way of nonlimiting example, it may
also be used to deposit precursor materials for photovoltaic
absorber layers. Optionally, it may be used to deposit materials
for use as or precursor materials that form: anti-reflective
coatings on cells or modules, moisture barriers on such modules or
devices, encapsulant materials, adhesive materials, conductive
materials, insulating materials, and/or semiconducting
material.
[0108] For any of the embodiment herein, the substrate may be an
elongate material suitable for use in a continuous, roll-to-roll
process. Optionally, there may be a carrier on which discrete or
pre-cut substrates comprising the precursor layers may be placed.
The carrier may then carry these discrete or pre-cut substrates
through the processing station(s). The carrier may be the same or a
different material from the discrete, pre-cut, or individual
substrate. The carrier may be sufficiently pliable to be shaped to
create the zone to hold sufficient fluid on the carrier to submerge
the discrete or pre-cut substrates in processing fluid. In any of
these embodiments, the substrate may be moved continuously at the
same or different rate, or optionally in sequential stop and go
steps.
[0109] The heating steps and cooling steps may be repeated either
for depositing thicker CdS on the same surface or for depositing
CdS on surfaces of new structures introduced into the deposition
section in a cyclic or continuous manner. Optionally, some
embodiments may use continuous recycling of the solution between
the solution container collecting used solution and the deposition
section, although intermittent flow of the solution between the
deposition section and the solution container may also be utilized.
Once the solution is in the recirculating solution container it may
be analyzed for its composition and ingredients that may be reduced
due to reactions may be added to the solution. Such ingredients
include but are not limited to water, ammonia, Cd salt, S source,
complexing agent etc. By controlling the solution composition this
way, the same solution may be used for coating a large number of
structures with CdS without replacing the base solution. This
reduces waste and thus cost of the process. The base solution may
be occasionally replaced with a fresh one if its impurity content
increases to a level that may affect the quality of the deposited
CdS film. Removal of particles from the solution may be achieved
through filtration using various approaches including centrifuging
the solution. The CdS particles thus removed may be re-cycled later
to form a Cd source for the process.
[0110] With regards to the type of various junction partner
suitable for use with the present invention, various chemical
compositions have been evaluated in solar cell structures. CdS,
ZnS, Zn--S--OH, Zn--S--O--OH, ZnO, Zn--Mg--O, Cd--Zn--S, ZnSe,
In--Se, In--Ga--Se, In--S, In--Ga--S, In--O--OH, In--S--O,
In--S--OH, etc. are some non-limiting examples of possible
materials. Such layer maybe in the thickness range of about 5-200
nm thick and may be deposited by various techniques such as
evaporation, sputtering, atomic layer deposition (ALD),
electrodeposition and chemical bath deposition (CBD), etc
[0111] In one example, a suitable solution for growing a cadmium
sulfide (CdS) layer employs a chemical bath comprising cadmium (Cd)
species (from a Cd salt source such as Cd-chloride, Cd-sulfate,
Cd-acetate, etc.), sulfur (S) species (from a S source such as
thiourea) and a complexing agent (such as ammonia, triethanolamine
(TEA), diethanolamine (DEA), ethlene diamine tetra-acetic acid
(EDTA), etc) that regulates the reaction rate between the Cd and S
species. In one example, the deposition bath may be formed by
mixing in water 1-50 ml of 1 M cadmium salt solution, such as
Cd-chloride, Cd-sulfate, Cd-acetate, or the like, 1-50 ml of 14.53
M ammonium hydroxide solution as complexing agent, and 1-50 ml of
1M thiourea as S solution. Another complexing agent solution such
as 0.5M Triethanolamine (TEA) may also be added in an amount that
is in the range of 1-20 ml. A typical bath may contain (by volume)
5-15% cadmium solution, 5-15% complexing agent (ammonium
hydroxide), 5-15% S solution (thiourea) and optionally 5-10% of the
additional complexing agent solution (TEA), the balance being the
solvent, i.e. water.
[0112] Furthermore, those of skill in the art will recognize that
any of the embodiments of the present invention can be applied to
almost any type of solar cell material and/or architecture. For
example, the absorber layer in solar cell 10 may be an absorber
layer comprised of silicon, amorphous silicon, organic oligomers or
polymers (for organic solar cells), bi-layers or interpenetrating
layers or inorganic and organic materials (for hybrid
organic/inorganic solar cells), dye-sensitized titania
nanoparticles in a liquid or gel-based electrolyte (for Graetzel
cells in which an optically transparent film comprised of titanium
dioxide particles a few nanometers in size is coated with a
monolayer of charge transfer dye to sensitize the film for light
harvesting), copper-indium-gallium-selenium (for CIGS solar cells),
CdSe, CdTe, Cu(In,Ga)(S,Se).sub.2, Cu(In,Ga,Al)(S,Se,Te).sub.2,
other absorber materials, IB-IIB-IVA-VIA absorber solar cells,
other thing film solar cells, and/or combinations of the above,
where the active materials are present in any of several forms
including but not limited to bulk materials, micro-particles,
nano-particles, or quantum dots. The CIGS cells may be formed by
vacuum or non-vacuum processes. The processes may be one stage, two
stage, or multi-stage CIGS processing techniques. Additionally,
other possible absorber layers may be based on amorphous silicon
(doped or undoped), a nanostructured layer having an inorganic
porous semiconductor template with pores filled by an organic
semiconductor material (see e.g., US Patent Application Publication
US 2005-0121068 A1, which is incorporated herein by reference), a
polymer/blend cell architecture, organic dyes, and/or C.sub.60
molecules, and/or other small molecules, micro-crystalline silicon
cell architecture, randomly placed nanorods and/or tetrapods of
inorganic materials dispersed in an organic matrix, quantum
dot-based cells, or combinations of the above. Many of these types
of cells can be fabricated on flexible substrates.
[0113] 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 thickness 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 but not limited to 2
nm, 3 nm, 4 nm, and sub-ranges such as 10 nm to 50 nm, 20 nm to 100
nm, etc. . . .
[0114] 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. For example, U.S. patent application Ser.
No. 12/203,117 filed Sep. 2, 2008 is fully incorporated herein by
reference for all purposes. Additionally, U.S. Provisional
Application Ser. No. 60/980,757 filed Oct. 17, 2007 and U.S.
Provisional Application Ser. No. 61/027,817 filed Feb. 11, 2008 are
both fully incorporated herein by reference for all purposes.
[0115] 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."
* * * * *