U.S. patent application number 15/018398 was filed with the patent office on 2016-06-02 for pressure transfer process for thin film solar cell fabrication.
The applicant listed for this patent is GLOBALFOUNDRIES INC.. Invention is credited to Shafaat Ahmed, Hariklia Deligianni, Qiang Huang, Lubomyr T. Romankiw, Raman Vaidyanathan.
Application Number | 20160155889 15/018398 |
Document ID | / |
Family ID | 52668297 |
Filed Date | 2016-06-02 |
United States Patent
Application |
20160155889 |
Kind Code |
A1 |
Ahmed; Shafaat ; et
al. |
June 2, 2016 |
PRESSURE TRANSFER PROCESS FOR THIN FILM SOLAR CELL FABRICATION
Abstract
In one aspect, a method for fabricating a thin film solar cell
includes the following steps. A first absorber material is
deposited as a layer A on a substrate while applying pressure to
the substrate/layer A. A second absorber material is deposited as a
layer B on layer A while applying pressure to the substrate/layer
B. A third absorber material is deposited as a layer C on layer B
while applying pressure to the substrate/layer C. A fourth absorber
material is deposited as a layer D on layer C while applying
pressure to the substrate/layer D. The first absorber material
comprises copper, the second absorber material comprises indium,
the third absorber material comprises gallium, and the fourth
absorber material comprises one or more of sulfur and selenium, and
wherein by way of performing the steps of claim 1 a chalcogenide
absorber layer is formed on the substrate.
Inventors: |
Ahmed; Shafaat; (Ballston
Lake, NY) ; Deligianni; Hariklia; (Alpine, NJ)
; Huang; Qiang; (Tuscaloosa, AL) ; Romankiw;
Lubomyr T.; (Briarcliff Manor, NY) ; Vaidyanathan;
Raman; (Whiteplains, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GLOBALFOUNDRIES INC. |
Grand Cayman |
|
KY |
|
|
Family ID: |
52668297 |
Appl. No.: |
15/018398 |
Filed: |
February 8, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14030019 |
Sep 18, 2013 |
9293632 |
|
|
15018398 |
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Current U.S.
Class: |
204/203 ;
204/298.24 |
Current CPC
Class: |
Y02P 70/50 20151101;
H01L 21/02568 20130101; H01L 21/02614 20130101; Y02E 10/541
20130101; H01L 21/02491 20130101; H01L 31/206 20130101; H01L 31/18
20130101; H01L 31/0749 20130101; H01L 21/02425 20130101; H01L
31/0322 20130101; H01L 31/1876 20130101; Y02P 70/521 20151101; H01L
21/02521 20130101; C25D 17/001 20130101 |
International
Class: |
H01L 31/18 20060101
H01L031/18; C25D 17/00 20060101 C25D017/00; H01L 31/0749 20060101
H01L031/0749 |
Claims
1. An apparatus for fabricating a thin film solar cell, the
apparatus comprising: a set of rollers (a) configured to, when a
substrate passes between the set of rollers (a), deposit a first
absorber material as a layer A on the substrate while applying
pressure to both the substrate and the layer A; a set of rollers
(b) configured to, when the substrate with the layer A thereon
passes through the set of rollers (b), deposit a second absorber
material as a layer B on the layer A while applying pressure to
both the substrate and the layer B; a set of rollers (c) configured
to, when the substrate with the layers A and B thereon passes
through the set of rollers (c), deposit a third absorber material
as a layer C on the layer B while applying pressure to both the
substrate and the layer C; a set of rollers (d) configured to, when
the substrate with the layers A-C thereon passes through the set of
rollers (d), deposit a fourth absorber material as a layer D on the
layer C while applying pressure to both the substrate and the layer
D; and a set of rollers (e) configured to, when the substrate with
the layers A-D thereon passes through the set of rollers (e),
anneal the layers A-D while applying pressure to both the substrate
and the layer D, wherein the first absorber material comprises
copper, the second absorber material comprises indium, the third
absorber material comprises gallium, and the fourth absorber
material comprises one or more of sulfur and selenium, and wherein
the apparatus is configured to form a chalcogenide absorber layer
on the substrate.
2. The apparatus of claim 1, further comprising: a set of rollers
(f) configured to, when the substrate with the layers A-C thereon
passes through the set of rollers (f), soft anneal the layers A-C
while applying pressure to both the substrate and the layer C.
3. The apparatus of claim 1, wherein the set of rollers (a) are
configured to deposit the layer A from a chemical or
electrochemical solution, the apparatus further comprising: a set
of rollers (g) which following deposition of the first absorber
material on the substrate is configured to, when the substrate with
the layer A thereon passes through the set of rollers (g), heat the
layer A while applying pressure to both the substrate and the layer
A.
4. The apparatus of claim 1, wherein the set of rollers (b) are
configured to deposit the layer B from a chemical or
electrochemical solution, the apparatus further comprising: a set
of rollers (h) which following deposition of the layer B on the
layer A is configured to, when the substrate with the layers A and
B thereon passes through the set of rollers (h), heat the layer B
while applying pressure to both the substrate and the layer B.
5. The apparatus of claim 1, wherein the set of rollers (b) are
configured to deposit the layer B from a molten bath, the apparatus
further comprising: a set of rollers (h) which following deposition
of the layer B on the layer A is configured to, when the substrate
with the layers A and B thereon passes through the set of rollers
(h), cool the layer B while applying pressure to both the substrate
and the layer B.
6. The apparatus of claim 1, wherein the set of rollers (c) are
configured to deposit the layer C from a chemical or
electrochemical solution, the apparatus further comprising: a set
of rollers (i) which following deposition of the layer C on the
layer B is configured to, when the substrate with the layers A-C
thereon passes through the set of rollers (i), heat the layer C
while applying pressure to both the substrate and the layer C.
7. The apparatus of claim 1, wherein the set of rollers (c) are
configured to deposit the layer C from a molten bath, the apparatus
further comprising: a set of rollers (i) which following deposition
of the layer C on the layer B is configured to, when the substrate
with the layers A-C thereon passes through the set of rollers (i),
cool the layer C while applying pressure to both the substrate and
the layer C.
8. The apparatus of claim 1, wherein the set of rollers (d) are
configured to deposit the layer D from a chemical or
electrochemical solution, the apparatus further comprising: a set
of rollers G) which following deposition of the layer D on the
layer C is configured to, when the substrate with the layers A-D
thereon passes through the set of rollers G), heat the layer D
while applying pressure to both the substrate and the layer D.
9. The apparatus of claim 1, wherein the set of rollers (d) are
configured to deposit the layer D from a molten bath, the apparatus
further comprising: a set of rollers G) which following deposition
of the layer D on the layer C is configured to, when the substrate
with the layers A-D thereon passes through the set of rollers G),
cool the layer D while applying pressure to both the substrate and
the layer D.
Description
FIELD
[0001] The present invention relates to the fabrication of
copper-indium-gallium-sulfur/selenium (CIGS)-based thin film solar
cells and more particularly, to techniques for fabricating
CIGS-based thin film solar cells that employ a pressure transfer
process to control volume expansion and stresses on the CIGS layers
that occur during the fabrication process and thereby prevent loss
of adhesion between the layers.
BACKGROUND
[0002] Copper-indium-gallium-sulfur/selenium (CIGS) materials are
commonly used as the absorber in thin film solar cells. One
approach to producing a CIGS absorber in thin film solar cell
technology is to successively deposit elemental layers of the
copper, indium, gallium and sulfur, followed by an annealing step
(for example in a selenium environment).
[0003] One challenge in this fabrication process is to maintain
adhesion between the deposited layers. Namely, the layers being
formed from different materials will have different coefficients of
thermal expansion. During the heating and cooling cycles of
absorber fabrication, the differing amounts of volume expansion can
cause the layers to delaminate. This delamination problem is a
significant roadblock to large-scale implementation of CIGS thin
film solar cell production.
[0004] Thus, techniques for fabricating CIGS thin film solar cells
that minimize or eliminate such adhesion problems would be
desirable.
BRIEF SUMMARY
[0005] The present invention provides techniques for fabricating
CIGS-based thin film solar cells that employ a pressure transfer
process to control volume expansion and stresses on the CIGS layers
that occur during the fabrication process and thereby prevent loss
of adhesion between the layers. In one aspect of the invention, a
method for fabricating a thin film solar cell is provided. The
method includes the following steps. A substrate is provided. A
first absorber material is deposited as a layer A on the substrate
while applying pressure to both the substrate and the layer A. A
second absorber material is deposited as a layer B on the layer A
while applying pressure to both the substrate and the layer B. A
third absorber material is deposited as a layer C on the layer B
while applying pressure to both the substrate and the layer C. A
fourth absorber material is deposited as a layer D on the layer C
while applying pressure to both the substrate and the layer D. The
layers A-D are annealed while applying pressure to both the
substrate and the layer D, wherein the first absorber material
comprises copper, the second absorber material comprises indium,
the third absorber material comprises gallium, and the fourth
absorber material comprises one or more of sulfur and selenium, and
wherein by way of performing the steps of the method a chalcogenide
absorber layer is formed on the substrate.
[0006] In another aspect of the invention, an apparatus for
fabricating a thin film solar cell is provided. The apparatus
includes a set of rollers (a) configured to, when a substrate
passes between the set of rollers (a), deposit a first absorber
material as a layer A on the substrate while applying pressure to
both the substrate and the layer A; a set of rollers (b) configured
to, when the substrate with the layer A thereon passes through the
set of rollers (b), deposit a second absorber material as a layer B
on the layer A while applying pressure to both the substrate and
the layer B; a set of rollers (c) configured to, when the substrate
with the layers A and B thereon passes through the set of rollers
(c), deposit a third absorber material as a layer C on the layer B
while applying pressure to both the substrate and the layer C; a
set of rollers (d) configured to, when the substrate with the
layers A-C thereon passes through the set of rollers (d), deposit a
fourth absorber material as a layer D on the layer C while applying
pressure to both the substrate and the layer D; and a set of
rollers (e) configured to, when the substrate with the layers A-D
thereon passes through the set of rollers (e), anneal the layers
A-D while applying pressure to both the substrate and the layer D,
wherein the first absorber material comprises copper, the second
absorber material comprises indium, the third absorber material
comprises gallium, and the fourth absorber material comprises one
or more of sulfur and selenium, and wherein the apparatus is
configured to form a chalcogenide absorber layer on the
substrate.
[0007] A more complete understanding of the present invention, as
well as further features and advantages of the present invention,
will be obtained by reference to the following detailed description
and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a diagram illustrating an exemplary methodology
for fabrication of thin film solar cells according to an embodiment
of the present invention;
[0009] FIG. 2 is a diagram illustrating another exemplary
methodology for fabrication of thin film solar cells according to
an embodiment of the present invention;
[0010] FIGS. 3A-B are diagrams illustrating a continuous line
processing apparatus for fabricating thin film solar cells
according to the method of FIG. 1 according to an embodiment of the
present invention;
[0011] FIGS. 4A-B are diagrams illustrating another continuous line
processing apparatus for fabricating thin film solar cells
according to the method of FIG. 1 according to an embodiment of the
present invention;
[0012] FIGS. 5A-B are diagrams illustrating a continuous line
processing apparatus for fabricating thin film solar cells
according to the method of FIG. 2 according to an embodiment of the
present invention;
[0013] FIG. 6 is an exemplary drive system that may be employed
with any of the continuous-line apparatuses presented herein
according to an embodiment of the present invention;
[0014] FIG. 7 is a diagram illustrating an alternate embodiment
wherein material is deposited onto the rollers using, e.g., a
sputtering process, and then transferred to the substrate according
to an embodiment of the present invention; and
[0015] FIG. 8 is a diagram illustrating another alternate
embodiment wherein material is deposited directly onto the
substrate using, e.g., a sputtering process, and the rollers are
used to apply pressure and/or heat according to an embodiment of
the present invention.
DETAILED DESCRIPTION
[0016] As provided above, the fabrication of
copper-indium-gallium-sulfur/selenium (CIGS) absorbers for thin
film solar cell production can be accomplished by successive
deposition of elemental layers of the copper (Cu), indium (In),
gallium (Ga) and sulfur (S), followed by an anneal in a selenium
(Se) environment. However due to the differences in material
composition, adhesion problems can occur during the fabrication
process as the layers are heated and cooled. Advantageously,
provided herein are techniques for fabricating chalcogenide (e.g.,
CIGS) thin film solar cells that employ a pressure transfer
process, for example by way of rollers that apply pressure to both
sides of the solar cell workpiece, to control volume expansion and
stresses on the CIGS layers that occur during the fabrication
process and thereby prevent loss of adhesion between the
layers.
[0017] In one exemplary embodiment which will be described in
detail below, the present techniques are applied to a continuous
line chalcogenide (e.g., CIGS) thin film solar cell fabrication
process wherein the elemental layers of the CIGS absorber are
successively applied to a substrate (e.g., molybdenum (Mo)-coated
glass or metal substrate) material that is being continuously fed
through the production line. The thin film layers of the absorber
are applied at different stages of the continuous line process. In
some exemplary embodiments, described below, sets of rollers are
employed throughout the fabrication stages to deposit the CIGS
layers onto the workpiece and/or heat/cool the workpiece while at
the same time applying pressure to both sides of the workpiece.
Applying pressure to both sides of the workpiece during the thin
film fabrication process serves to passivate the stresses caused by
the volume expansion of the layers. Thus, the above-described
adhesion problems commonly associated with conventional thin film
solar cell fabrication can be avoided.
[0018] According to the present techniques, deposition of the CIGS
layers onto the workpiece can be carried out in several different
ways. For example, in one scenario an electrodeposition process is
used to deposit the CIGS layers using separate electroplating
cells. As will be described in detail below, the rollers can be
used during this electrodeposition process to simultaneously apply
pressure to both sides of the workpiece while serving to deposit
the CIGS material onto the workpiece (and at some stages of the
process heat or cool the workpiece). In another exemplary scenario,
one or more of the CIGS components are deposited onto the workpiece
from a molten bath. Again, the rollers can be used during this
molten deposition process to simultaneously apply pressure to both
sides of the workpiece while serving to deposit the CIGS material
onto the workpiece (and at some stages of the process heat or cool
the workpiece).
[0019] An overview of the first exemplary scenario wherein the CIGS
materials are deposited onto the workpiece via electrodeposition is
provided by way of reference to FIG. 1. Then an overview of the
exemplary scenario wherein one or more of the CIGS materials are
deposited from a molten bath is provided by way of reference to
FIG. 2. Exemplary continuous line thin film production apparatuses
which may be employed to implement the present techniques will then
be shown and described by way of reference to FIGS. 3-5.
[0020] FIG. 1 is a diagram illustrating an exemplary methodology
100 for fabrication of CIGS thin film solar cells employing
electrodeposition. While the present techniques are being described
in the context of fabricating a solar cell, in theory the same
techniques may be applied in any continuous line thin film
fabrication process. In step 102, a substrate material is provided.
Suitable substrate materials for solar cell applications include,
but are not limited to, glass substrates having a back contact
layer formed thereon such as a molybdenum (Mo)-coated glass
substrate, and a flexible metal substrate, such as a stainless
steel foil substrate. In the exemplary embodiments described below,
the substrate material is fed continuously from a roll, the CIGS
absorber material is formed on the substrate material, and the
output is spooled onto a second roll. This process is also referred
to herein as a roll-to-roll process.
[0021] Next, in step 104 a Cu layer is deposited onto the substrate
material. It is notable that in the case of a Mo-coated glass
substrate, in this step the Cu is deposited onto the Mo layer. In
order to control volume expansion and stresses on the layers of the
cell, pressure is applied to both sides (i.e., to a top and
bottom-to the substrate and Cu layer, respectively) of the
workpiece during this Cu deposition step. By way of example only, a
linear pressure applied to the workpiece during this step is from
about 10 N/mm to about 700 N/mm.
[0022] As will be described in detail below, in some exemplary
embodiments, the Cu deposition and simultaneous application of
pressure to the workpiece is performed via a set of two rollers
that are in contact with opposing sides (i.e., one roller is in
contact with the top and one roller is in contact with the bottom)
of the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the set of rollers.
[0023] According to an exemplary embodiment, the rollers are
configured to deposit the Cu onto the workpiece from a
Cu-containing electrochemical electrolyte solution through which
one of the rollers passes. Namely, the Cu (which is
electrodeposited onto the roller from the electrolyte solution) is
transferred from the roller onto the workpiece. The transfer of the
Cu from the roller to the workpiece can be facilitated by cooling
the roller, see below. Namely, as will be described in detail
below, the rollers may be made of a metal such as stainless steel.
The material (in this case Cu) will be deposited via the rollers
onto the substrate under pressure--as provided above. Cooling the
rollers will facilitate cladding the Cu to the workpiece, rather
than to the (metal) roller. Further, due to this being a continuous
line process, as the workpiece passes through each stage, the
material already deposited and cladded onto the workpiece will aid
in removing the material from the roller (similar to when any sort
of material is unwound from a roll) and cooling the rollers
facilitates removal of the material from the roll. Thus, in one
exemplary embodiment, the rollers are in this step cooled to a
temperature of from about -5.degree. C. to about 10.degree. C.
Thus, in this exemplary embodiment, the rollers are configured to
simultaneously 1) apply Cu to the workpiece and 2) apply pressure
to both sides of the workpiece. Pressure is defined herein as a
physical force being exerted on a first object (in this case the
workpiece) by one or more other objects (in this case the rollers)
in contact with the first object. As the CIGS absorber layers are
successively deposited onto the substrate, pressure is applied to
the workpiece via the rollers which are in contact with the
substrate and the layer currently being deposited. Thus, during the
Cu deposition step, pressure from the rollers is exerted
simultaneously on the Cu layer and on the substrate. During the In
deposition step, pressure from the rollers is exerted
simultaneously on the In layer and on the substrate. And so on.
[0024] As will be described in detail below, electrodeposition is
only one possible process that may be implemented to deposit the
thin film materials onto the substrate. For instance, the Cu can be
deposited onto the rollers using for example a sputtering (or other
suitable process) and then transferred from the rollers to the
substrate in the manner described above. Alternatively, the Cu can
be deposited directly onto the substrate and pressure/heat would be
applied via the rollers in the manner described above. These
alternative embodiments are described in detail below.
[0025] In order to bond the Cu deposited onto the substrate
material in step 104, pressure and heat are applied to the
workpiece in step 106. This process of bonding dissimilar metals
(e.g., the Cu with the metal substrate or with the Mo-coated
substrate) is also referred to herein by the term "cladding."
Linear pressure (e.g., from about 10 N/mm to about 700 N/mm) is
applied to both sides (i.e., to a top and bottom-to the Cu layer
and substrate, respectively) of the workpiece during this step
which, as provided above, also serves to control volume expansion
and stresses on the layers of the cell. By way of example only, the
workpiece may be heated at this step to a temperature of from about
50.degree. C. to about 250.degree. C.
[0026] As will be described in detail below, in some exemplary
embodiments, the heating and simultaneous application of pressure
to the workpiece is performed in step 106 via a set of two rollers
that are in contact with opposing sides (i.e., one roller is in
contact with the top and one roller is in contact with the bottom)
of the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the set of rollers. The rollers can be heated to thereby heat the
workpiece as the workpiece passes between the rollers. Thus, in
this exemplary embodiment, the rollers at this stage of the
continuous line process are configured to simultaneously 1) heat
the workpiece and 2) apply pressure to both sides of the
workpiece.
[0027] Next, in step 108 an In layer is deposited onto the
substrate material on top of the Cu layer. In order to control
volume expansion and stresses on the layers of the cell, pressure
is applied to both sides (i.e., to a top and bottom-to the
substrate and In layer, respectively) of the workpiece during this
In deposition step. Exemplary pressure values that may be employed
during this metal deposition step were provided above.
[0028] As will be described in detail below, in some exemplary
embodiments, the In deposition and simultaneous application of
pressure to the workpiece is performed via another set of rollers
that are in contact with opposing sides (i.e., one roller is in
contact with the top and one roller is in contact with the bottom)
of the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the set of rollers. The rollers can be configured to deposit the In
onto the workpiece from a In-containing electrochemical electrolyte
solution through which one of the rollers passes. Namely, the In
(which is electrodeposited onto the roller from the electrolyte
solution) is transferred from the roller onto the workpiece. As
with the case of the Cu deposition above, the transfer of the In
from the roller to the workpiece can be facilitated by cooling the
roller, see below. Exemplary temperature values were provided above
regarding cooling the workpiece to facilitate material transfer
from the rollers to the workpiece. Thus, in this exemplary
embodiment, the rollers are configured to simultaneously 1) apply
In to the workpiece, and 2) apply pressure to both sides of the
workpiece.
[0029] Cladding of the In deposited onto the Cu layer (in step 108)
is achieved by applying pressure and heat to the workpiece in step
110. Exemplary temperature and pressure values for this cladding
process were provided above.
[0030] Alternatively, as provided above, electrodeposition is only
one exemplary process that may be employed herein for depositing
the material onto the substrate. For instance, another suitable
deposition process (such as sputtering) may be used to deposit the
material onto the rollers, which then apply the material to the
substrate in the manner described above. Alternatively, the
material may be deposited directly onto the substrate with pressure
and/or heat being supplied via the rollers as described above.
These alternative embodiments are described in detail below.
[0031] As will be described in detail below, in some exemplary
embodiments, the heating and simultaneous application of pressure
to the workpiece is performed in step 110 via another set of
rollers that are in contact with opposing sides (i.e., one roller
is in contact with the top and one roller is in contact with the
bottom) of the workpiece such that as the workpiece is fed through
the continuous line fabrication process, the workpiece passes
between the set of rollers. The rollers can be heated to thereby
heat the workpiece as the workpiece passes between the rollers.
Thus, in this exemplary embodiment, the rollers at this stage of
the continuous line process are configured to simultaneously 1)
heat the workpiece and 2) apply pressure to both sides of the
workpiece.
[0032] Next, in step 112 a Ga layer is deposited onto the substrate
material on top of the In layer. In order to control volume
expansion and stresses on the layers of the cell, pressure is
applied to both sides (i.e., to a top and bottom-to the substrate
and Ga layer, respectively) of the workpiece during this Ga
deposition step. Exemplary pressure values that may be employed
during this metal deposition step were provided above.
[0033] As will be described in detail below, in some exemplary
embodiments, the Ga deposition and simultaneous application of
pressure to the workpiece is performed via another set of rollers
that are in contact with opposing sides (i.e., one roller is in
contact with the top and one roller is in contact with the bottom)
of the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the set of rollers. The rollers can be configured to deposit the Ga
onto the workpiece from a Ga-containing electrochemical electrolyte
solution through which one of the rollers passes. Namely, the Ga
(which is electrodeposited onto the roller from the electrolyte
solution) is transferred from the roller onto the workpiece. As
with the materials above, the transfer of the Ga from the roller to
the workpiece can be facilitated by cooling the roller, see below.
Thus, in one exemplary embodiment, the rollers are in this step are
cooled. Exemplary temperature values were provided above regarding
cooling the workpiece to facilitate material transfer from the
rollers to the workpiece. Thus, in this exemplary embodiment, the
rollers are configured to simultaneously 1) apply Ga to the
workpiece, and 2) apply pressure to both sides of the
workpiece.
[0034] Cladding of the Ga deposited onto the In layer (in step 112)
is achieved by applying pressure and heat to the workpiece in step
114. Exemplary temperature and pressure values for this cladding
process were provided above.
[0035] Alternatively, as provided above, electrodeposition is only
one exemplary process that may be employed herein for depositing
the material onto the substrate. For instance, another suitable
deposition process (such as sputtering) may be used to deposit the
material onto the rollers, which then apply the material to the
substrate in the manner described above. Alternatively, the
material may be deposited directly onto the substrate with pressure
and/or heat being supplied via the rollers as described above.
These alternative embodiments are described in detail below.
[0036] As will be described in detail below, in some exemplary
embodiments, the heating and simultaneous application of pressure
to the workpiece is performed in step 114 via another set of
rollers that are in contact with opposing sides (i.e., one roller
is in contact with the top and one roller is in contact with the
bottom) of the workpiece such that as the workpiece is fed through
the continuous line fabrication process, the workpiece passes
between the set of rollers. The rollers can be heated to thereby
heat the workpiece as the workpiece passes between the rollers.
Thus, in this exemplary embodiment, the rollers at this stage of
the continuous line process are configured to simultaneously 1)
heat the workpiece and 2) apply pressure to both sides of the
workpiece.
[0037] In step 116, the workpiece is subjected to an intermediate
or soft anneal. As with the heating steps described above, pressure
is applied to the workpiece while the workpiece is heated during
step 116. While the soft anneal performed in step 116 is optional,
uniformity of the final CIGS material will be enhanced by
performing this soft/intermediate anneal. According to an exemplary
embodiment, in step 116 the workpiece is annealed at a temperature
of from about 100.degree. C. to about 300.degree. C., e.g., at a
temperature of about 155.degree. C., while a linear pressure of
from about 10 N/mm to about 700 N/mm is simultaneously applied to
both sides (i.e., to a top and bottom) of the workpiece which, as
provided above, also serves to control volume expansion and
stresses on the layers of the cell. As will be described below, a
final anneal will be performed in an S-containing environment to
complete the CIGS absorber.
[0038] As will be described in detail below, in some exemplary
embodiments, the heating and simultaneous application of pressure
to the workpiece is performed in step 116 via another set of
rollers that are in contact with opposing sides (i.e., one roller
is in contact with the top and one roller is in contact with the
bottom) of the workpiece such that as the workpiece is fed through
the continuous line fabrication process, the workpiece passes
between the set of rollers. The rollers can be heated to thereby
heat the workpiece as the workpiece passes between the rollers.
Thus, in this exemplary embodiment, the rollers at this stage of
the continuous line process are configured to simultaneously 1)
heat the workpiece and 2) apply pressure to both sides of the
workpiece.
[0039] Next, in step 118 a S, Se, or S+Se layer (abbreviated herein
as S/Se layer) is deposited onto the substrate material on top of
the Ga layer. In order to control volume expansion and stresses on
the layers of the cell, pressure is applied to both sides (i.e., to
a top and bottom-to the substrate and S/Se layer, respectively) of
the workpiece during this S/Se deposition step. Exemplary pressure
values that may be employed during this metal deposition step were
provided above.
[0040] As will be described in detail below, in some exemplary
embodiments, the S/Se deposition and simultaneous application of
pressure to the workpiece is performed via another set of rollers
that are in contact with opposing sides (i.e., one roller is in
contact with the top and one roller is in contact with the bottom)
of the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the set of rollers. The rollers can be configured to deposit the
S/Se onto the workpiece from a S/Se-containing electrochemical
electrolyte solution through which one of the rollers passes.
Namely, the S/Se (which is electrodeposited onto the roller from
the electrolyte solution) is transferred from the roller onto the
workpiece. As with the materials above, the transfer of the S/Se
from the roller to the workpiece can be facilitated by cooling the
roller, see below. Thus, in one exemplary embodiment, the rollers
are in this step cooled. Exemplary temperature values were provided
above regarding cooling the workpiece to facilitate material
transfer from the rollers to the workpiece. Thus, in this exemplary
embodiment, the rollers are configured to simultaneously 1) apply
S/Se to the workpiece, and 2) apply pressure to both sides of the
workpiece.
[0041] Cladding of the S/Se deposited onto the Ga layer (in step
118) is achieved by applying pressure and heat to the workpiece in
step 120. Exemplary temperature and pressure values for this
cladding process were provided above.
[0042] As provided above, electrodeposition is only one exemplary
process that may be employed herein for depositing the material
onto the substrate. For instance, another suitable deposition
process (such as sputtering) may be used to deposit the material
onto the rollers, which then apply the material to the substrate in
the manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above. These
alternative embodiments are described in detail below.
[0043] As will be described in detail below, in some exemplary
embodiments, the heating and simultaneous application of pressure
to the workpiece is performed in step 120 via another set of
rollers that are in contact with opposing sides (i.e., one roller
is in contact with the top and one roller is in contact with the
bottom) of the workpiece such that as the workpiece is fed through
the continuous line fabrication process, the workpiece passes
between the set of rollers. The rollers can be heated to thereby
heat the workpiece as the workpiece passes between the rollers.
Thus, in this exemplary embodiment, the rollers at this stage of
the continuous line process are configured to simultaneously 1)
heat the workpiece and 2) apply pressure to both sides of the
workpiece.
[0044] Finally, in step 122, the workpiece is subjected to a final
anneal in a S environment. As with the heating steps described
above, pressure is applied to the workpiece while the workpiece is
heated during step 122. According to an exemplary embodiment, in
step 122 the workpiece is annealed at a temperature of from about
500.degree. C. to about 600.degree. C., e.g., at a temperature of
about 500.degree. C., while a linear pressure of from about 10 N/mm
to about 700 N/mm is simultaneously applied to both sides (i.e., to
a top and bottom) of the workpiece which, as provided above, also
serves to control volume expansion and stresses on the layers of
the cell.
[0045] As will be described in detail below, in some exemplary
embodiments, the heating and simultaneous application of pressure
to the workpiece is performed in step 122 via another set of
rollers that are in contact with opposing sides (i.e., one roller
is in contact with the top and one roller is in contact with the
bottom) of the workpiece such that as the workpiece is fed through
the continuous line fabrication process, the workpiece passes
between the set of rollers. The rollers can be heated to thereby
heat the workpiece as the workpiece passes between the rollers.
Thus, in this exemplary embodiment, the rollers at this stage of
the continuous line process are configured to simultaneously 1)
heat the workpiece and 2) apply pressure to both sides of the
workpiece.
[0046] The CIGS absorber is now complete. Any further processing of
the cell can be carried out using conventional techniques to form a
buffer layer, top electrode, etc. to complete the solar cell.
[0047] It is notable that the thin film compositions described
above, and elsewhere herein are merely examples intended to
illustrate the present techniques, and a variety of other film
compositions can be achieved in the manner described herein. One
would need only to vary the composition of the materials deposited
in one or more of the steps and/or the order in which the materials
are deposited in order to achieve different thin film compositions.
In addition to the CIGS example provided above, by way of example
only, one may adapt the present techniques to produce any of the
following thin film solar cell compositions: CZTS
(Cu.sub.2ZnSn(Se,S).sub.4), FeS.sub.2, Zn.sub.2P.sub.3, CdSe, CdS,
ZnSe, WSe.sub.2, MoSe.sub.2, Bi.sub.2S.sub.3, Ag.sub.2S,
Cu.sub.2Zn(Fe,Sn)(Se,S).sub.4, CuxS, CdTe, ZnTe, PbSe, PdS, NiS,
NiSeS, InP, ZnO, GaAs. An example involving a I-III-IV.sub.2
material is provided below.
[0048] As provided above, according to another exemplary scenario,
one or more of the CIGS components are deposited onto the workpiece
from a molten bath. An overview of this process is now provided by
way of reference to FIG. 2. FIG. 2 is a diagram illustrating an
exemplary methodology 200 for fabrication of CIGS thin film solar
cells wherein one or more of the CIGS materials are deposited from
a molten bath. While the present techniques are being described in
the context of fabricating a solar cell, in theory the same
techniques may be applied in any continuous line thin film
fabrication process.
[0049] In step 202, a substrate material is provided. Suitable
substrate materials for solar cell applications include, but are
not limited to, glass substrates having a back contact layer formed
thereon such as a Mo-coated glass substrate, and a flexible metal
substrate, such as a stainless steel foil substrate. In the
exemplary embodiments described below, the substrate material is
fed continuously from a roll, the CIGS absorber material is formed
on the substrate material, and the output is spooled onto a second
roll. This process is also referred to herein as a roll-to-roll
process.
[0050] Next, in step 204 a Cu layer is deposited onto the substrate
material. It is notable that in the case of a Mo-coated glass
substrate, in this step the Cu is deposited onto the Mo layer. In
order to control volume expansion and stresses on the layers of the
cell, pressure is applied to both sides (i.e., to a top and
bottom-to the substrate and Cu layer, respectively) of the
workpiece during this Cu deposition step. By way of example only, a
linear pressure applied to the workpiece during this step is from
about 10 N/mm to about 700 N/mm. In this example, the Cu will be
deposited in step 204 by electrodeposition from an electrolyte,
whereas the In, Ga and S will be deposited from a molten bath.
[0051] As will be described in detail below, in some exemplary
embodiments, the Cu deposition and simultaneous application of
pressure to the workpiece is performed via a set of two rollers
that are in contact with opposing sides (i.e., one roller is in
contact with the top and one roller is in contact with the bottom)
of the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the set of rollers. The rollers can be configured to deposit the Cu
onto the workpiece from a Cu-containing electrolyte solution
through which one of the rollers passes. Namely, the Cu (which is
electrodeposited onto the roller from the electrochemical
electrolyte solution) is transferred from the roller onto the
workpiece. As described above, the transfer of the Cu from the
roller to the workpiece can be facilitated by cooling the roller.
Exemplary temperature values for cooling the rollers to facilitate
material transfer from the roller to the workpiece were provided
above. Thus, in this exemplary embodiment, the rollers are
configured to simultaneously 1) apply Cu to the workpiece, and 2)
apply pressure to both sides of the workpiece.
[0052] As provided above, electrodeposition is only one exemplary
process that may be employed herein for depositing the material
onto the substrate. For instance, another suitable deposition
process (such as sputtering) may be used to deposit the material
onto the rollers, which then apply the material to the substrate in
the manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above. These
alternative embodiments are described in detail below.
[0053] In order to bond the Cu deposited onto the substrate
material in step 204, pressure and heat are applied to the
workpiece in step 206. This process of bonding dissimilar metals
(e.g., the Cu with the metal substrate or with the Mo-coated
substrate) is also referred to herein by the term "cladding."
Linear pressure (e.g., from about 10 N/mm to about 700 N/mm) is
applied to both sides (i.e., to a top and bottom) of the workpiece
during this step which, as provided above, also serves to control
volume expansion and stresses on the layers of the cell. By way of
example only, the workpiece may be heated at this step to a
temperature of from about 50.degree. C. to about 250.degree. C.
[0054] As will be described in detail below, in some exemplary
embodiments, the heating and simultaneous application of pressure
to the workpiece is performed in step 206 via a set of two rollers
that are in contact with opposing sides (i.e., one roller is in
contact with the top and one roller is in contact with the bottom)
of the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the set of rollers. The rollers can be heated to thereby heat the
workpiece as the workpiece passes between the rollers. Thus, in
this exemplary embodiment, the rollers at this stage of the
continuous line process are configured to simultaneously 1) heat
the workpiece and 2) apply pressure to both sides of the
workpiece.
[0055] Next, in step 208 an In layer is deposited onto the
substrate material on top of the Cu layer. In order to control
volume expansion and stresses on the layers of the cell, pressure
is applied to both sides (i.e., to a top and bottom-to the
substrate and In layer, respectively) of the workpiece during this
In deposition step. Exemplary pressure values that may be employed
during this metal deposition step were provided above.
[0056] As will be described in detail below, in some exemplary
embodiments, the In deposition and simultaneous application of
pressure to the workpiece is performed via another set of rollers
that are in contact with opposing sides (i.e., one roller is in
contact with the top and one roller is in contact with the bottom)
of the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the set of rollers. The rollers can be configured to deposit the In
onto the workpiece from a bath of molten In through which one of
the rollers passes. Namely, as the roller passes through the bath,
some of the molten In is picked up by the roller and transferred to
the workpiece. Thus, in this exemplary embodiment, the rollers are
configured to simultaneously 1) apply In to the workpiece, 2) apply
pressure to both sides of the workpiece.
[0057] The In material deposited in step 208 will still be (at
least to some extent) molten after it is transferred to the
workpiece. Thus, in step 210 the workpiece is cooled. In order to
control volume expansion and stresses on the layers of the cell,
pressure is applied to both sides (i.e., to a top and bottom) of
the workpiece during this cooling step. By way of example only, the
workpiece is cooled in this step to a temperature of from about
-5.degree. C. to about 10.degree. C. and the linear pressure
applied to the workpiece during this step is from about 10 N/mm to
about 700 N/mm.
[0058] As will be described in detail below, m some exemplary
embodiments, the cooling and simultaneous application of pressure
to the workpiece is performed in step 210 via another set of
rollers that are in contact with opposing sides (i.e., one roller
is in contact with the top and one roller is in contact with the
bottom) of the workpiece such that as the workpiece is fed through
the continuous line fabrication process, the workpiece passes
between the set of rollers. The rollers can be cooled to thereby
cool the workpiece as the workpiece passes between the rollers.
Thus, in this exemplary embodiment, the rollers at this stage of
the continuous line process are configured to simultaneously 1)
cool the workpiece and 2) apply pressure to both sides of the
workpiece.
[0059] Next, in step 212 a Ga layer is deposited onto the substrate
material on top of the In layer. In order to control volume
expansion and stresses on the layers of the cell, pressure is
applied to both sides (i.e., to a top and bottom-to the substrate
and Ga layer, respectively) of the workpiece during this Ga
deposition step. Exemplary pressure values that may be employed
during this metal deposition step were provided above.
[0060] As will be described in detail below, in some exemplary
embodiments, the Ga deposition and simultaneous application of
pressure to the workpiece is performed via another set of rollers
that are in contact with opposing sides (i.e., one roller is in
contact with the top and one roller is in contact with the bottom)
of the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the set of rollers. The rollers can be configured to deposit the Ga
onto the workpiece from a bath of molten Ga through which one of
the rollers passes. Namely, as the roller passes through the bath,
some of the molten Ga is picked up by the roller and transferred to
the workpiece. Thus, in this exemplary embodiment, the rollers are
configured to simultaneously 1) apply Ga to the workpiece, 2) apply
pressure to both sides of the workpiece.
[0061] The Ga material deposited in step 212 will still be (at
least to some extent) molten after it is transferred to the
workpiece. Thus, in step 214 the workpiece is cooled. In order to
control volume expansion and stresses on the layers of the cell,
pressure is applied to both sides (i.e., to a top and bottom) of
the workpiece during this cooling step. Exemplary temperature and
pressure values for this stage of the process were provided
above.
[0062] As will be described m detail below, in some exemplary
embodiments, the cooling and simultaneous application of pressure
to the workpiece is performed in step 212 via another set of
rollers that are in contact with opposing sides (i.e., one roller
is in contact with the top and one roller is in contact with the
bottom) of the workpiece such that as the workpiece is fed through
the continuous line fabrication process, the workpiece passes
between the set of rollers. The rollers can be cooled to thereby
cool the workpiece as the workpiece passes between the rollers.
Thus, in this exemplary embodiment, the rollers at this stage of
the continuous line process are configured to simultaneously 1)
cool the workpiece and 2) apply pressure to both sides of the
workpiece.
[0063] In step 216, the workpiece is subjected to an intermediate
or soft anneal. As with the heating steps described above, pressure
is applied to the workpiece while the workpiece is heated during
step 216. While the soft anneal performed in step 216 is optional,
uniformity of the final CIGS material will be enhanced by
performing this soft/intermediate anneal. According to an exemplary
embodiment, in step 216 the workpiece is annealed at a temperature
of from about 100.degree. C. to about 300.degree. C., e.g., at a
temperature of about 155.degree. C., while a linear pressure of
from about 10 N/mm to about 700 N/mm is simultaneously applied to
both sides (i.e., to a top and bottom) of the workpiece which, as
provided above, also serves to control volume expansion and
stresses on the layers of the cell. As will be described below, a
final anneal will be performed in an S-containing environment to
complete the CIGS absorber.
[0064] As will be described in detail below, in some exemplary
embodiments, the heating and simultaneous application of pressure
to the workpiece is performed in step 216 via another set of
rollers that are in contact with opposing sides (i.e., one roller
is in contact with the top and one roller is in contact with the
bottom) of the workpiece such that as the workpiece is fed through
the continuous line fabrication process, the workpiece passes
between the set of rollers. The rollers can be heated to thereby
heat the workpiece as the workpiece passes between the rollers.
Thus, in this exemplary embodiment, the rollers at this stage of
the continuous line process are configured to simultaneously 1)
heat the workpiece and 2) apply pressure to both sides of the
workpiece.
[0065] Next, in step 218 a S/Se layer is deposited onto the
substrate material on top of the Ga layer. In order to control
volume expansion and stresses on the layers of the cell, pressure
is applied to both sides (i.e., to a top and bottom-to the
substrate and S/Se layer, respectively) of the workpiece during
this S/Se deposition step. Exemplary pressure values that may be
employed during this metal deposition step were provided above.
[0066] As will be described in detail below, in some exemplary
embodiments, the S/Se deposition and simultaneous application of
pressure to the workpiece is performed via another set of rollers
that are in contact with opposing sides (i.e., one roller is in
contact with the top and one roller is in contact with the bottom)
of the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the set of rollers. The rollers can be configured to deposit the
S/Se onto the workpiece from a bath of molten S/Se through which
one of the rollers passes. Namely, as the roller passes through the
bath, some of the molten S/Se is picked up by the roller and
transferred to the workpiece. Thus, in this exemplary embodiment,
the rollers are configured to simultaneously 1) apply S/Se to the
workpiece, 2) apply pressure to both sides of the workpiece.
[0067] The S/Se material deposited in step 218 will still be (at
least to some extent) molten after it is transferred to the
workpiece. Thus, in step 220 the workpiece is cooled. In order to
control volume expansion and stresses on the layers of the cell,
pressure is applied to both sides (i.e., to a top and bottom) of
the workpiece during this cooling step. Exemplary temperature and
pressure values for this stage of the process were provided
above.
[0068] As will be described in detail below, in some exemplary
embodiments, the cooling and simultaneous application of pressure
to the workpiece is performed in step 220 via another set of
rollers that are in contact with opposing sides (i.e., one roller
is in contact with the top and one roller is in contact with the
bottom) of the workpiece such that as the workpiece is fed through
the continuous line fabrication process, the workpiece passes
between the set of rollers. The rollers can be cooled to thereby
cool the workpiece as the workpiece passes between the rollers.
Thus, in this exemplary embodiment, the rollers at this stage of
the continuous line process are configured to simultaneously 1)
cool the workpiece and 2) apply pressure to both sides of the
workpiece.
[0069] Finally, in step 222, the workpiece is subjected to a final
anneal in a S environment. As with the heating steps described
above, pressure is applied to the workpiece while the workpiece is
heated during step 222. According to an exemplary embodiment, in
step 222 the workpiece is annealed at a temperature of from about
500.degree. C. to about 600.degree. C., e.g., at a temperature of
about 500.degree. C., while a linear pressure of from about 10 N/mm
to about 700 N/mm is simultaneously applied to both sides (i.e., to
a top and bottom) of the workpiece which, as provided above, also
serves to control volume expansion and stresses on the layers of
the cell.
[0070] As will be described in detail below, in some exemplary
embodiments, the heating and simultaneous application of pressure
to the workpiece is performed in step 222 via another set of
rollers that are in contact with opposing sides (i.e., one roller
is in contact with the top and one roller is in contact with the
bottom) of the workpiece such that as the workpiece is fed through
the continuous line fabrication process, the workpiece passes
between the set of rollers. The rollers can be heated to thereby
heat the workpiece as the workpiece passes between the rollers.
Thus, in this exemplary embodiment, the rollers at this stage of
the continuous line process are configured to simultaneously 1)
heat the workpiece and 2) apply pressure to both sides of the
workpiece.
[0071] The CIGS absorber is now complete. Any further processing of
the cell can be carried out using conventional techniques to form a
buffer layer, top electrode, etc. to complete the solar cell.
[0072] It is notable that the above sequence of processing steps is
merely exemplary, and depending on the desired final composition of
the thin film solar cell the sequence of steps performed and/or the
materials deposited at each of the stages may vary. Thus, the
present process is configurable to a variety of different thin film
configurations. What is notable here is that the present techniques
provide means to apply pressure to both sides of the workpiece
while simultaneously depositing a thin film material (and
potentially also simultaneously heating or cooling the workpiece).
The exact thin film material being deposited and/or the order in
which the materials are deposited, heated/cooled, etc. can be
varied yet still remain within the confines of the present
techniques.
[0073] Further, as is apparent from the description above, in
accordance with the present techniques, the materials may be
deposited from an electrochemical solution (via an
electrodeposition process) and/or from another chemical solution
(e.g., via deposition from a molten bath, sputtering, etc.). The
term "electrochemical solution" as used herein will generally refer
to the solutions described herein for use in an electrodeposition
process. All other solutions used for depositing the present
materials onto the substrate (e.g., molten metal bath) will
generally be referred to herein as "chemical solutions."
[0074] Exemplary embodiments implementing the present techniques
for continuous-line fabrication of thin film solar cells are now
described by way of reference to FIGS. 3-5. In FIGS. 3A-B a
continuous line processing apparatus is depicted performing the
method described in FIG. 1, above (i.e., wherein deposition of the
various CIGS layers occurs via electrodeposition) on a Mo-coated
glass substrate. It is to be understood that FIGS. 3A-B illustrate
a single, continuous-line apparatus/process, however, for ease and
clarity of depiction, the figure is broken into two parts (FIG. 3A
and FIG. 3B).
[0075] As shown in FIG. 3A, a Mo-coated glass substrate is fed into
the apparatus between a first set of rollers 302. As described in
conjunction with the description of step 104 of FIG. 1, above, a Cu
layer is deposited onto the substrate (i.e., onto the Mo layer of
the Mo-coated substrate) while at the same time pressure is applied
to both sides (i.e., to a top and bottom) of the workpiece in order
to control volume expansion and stresses on the layers of the cell.
In the embodiment shown in FIG. 3A, this Cu deposition and
simultaneous application of pressure to the workpiece is performed
via rollers 302 which as shown in FIG. 3A are in contact with
opposing sides (i.e., one of rollers 302 is in contact with the top
and one of rollers 302 is in contact with the bottom) of the
workpiece such that as the workpiece is fed through the continuous
line fabrication process, the workpiece passes between rollers 302.
Further, as shown in FIG. 3A, the rollers 302 are configured to
deposit the Cu onto the workpiece from a Cu-containing electrolyte
solution through which one of the rollers 302 passes. Namely,
according to an exemplary embodiment, rollers 302 are made of a
metal such as stainless steel. As the bottom roller 302 passes
through the Cu-containing electrolyte solution, the Cu is
electrodeposited onto the roller from the electrolyte solution. In
this example, there is an anode in the electrolyte solution and the
bottom (e.g., metal) roller 302 acts as a cathode for the
electrodeposition process. The Cu electrodeposited on the bottom
roller 302 is then transferred (from the bottom roller 302) onto
the workpiece. As described above, the transfer of the Cu from the
bottom roller 302 to the workpiece can be facilitated by cooling
the rollers 302. Namely, cooling the rollers will facilitate
cladding the Cu to the workpiece, rather than to the (metal) roller
itself. Further, due to this being a continuous line process, as
the workpiece passes through each stage, the material already
deposited and cladded onto the workpiece will aid in removing the
material from the roller (similar to when any sort of material is
unwound from a roll) and cooling the rollers facilitates removal of
the material from the roll. Temperature and pressure parameters for
this step were provided above. Thus, in this exemplary embodiment,
the rollers 302 are configured to simultaneously 1) apply Cu to the
workpiece and 2) apply pressure to both sides of the workpiece.
[0076] The pressure applied to the workpiece by the rollers 302 may
be based on the weight of the top roller 302 pressing down on the
workpiece against the bottom roller 302. Thus, as shown in FIG. 3A,
the top roller 302 might have a size (wherein the size of a roller
is determined based on its cross-sectional diameter) that equates
with a certain weight of the top roller 302 to achieve a desired
amount of pressure when the weight of the top roller 302 is applied
to the workpiece against the bottom roller 302. Accordingly the top
roller 302 and the bottom roller 302 are not shown to be the same
size as one another.
[0077] As shown in FIG. 3A, a (e.g., nitrogen (N.sub.2)) air knife
present in the direction of rotation between the plating cell and
the workpiece serves to direct plating solution from the roller 302
back into the Cu plating cell. A water jet may also be implemented
in the line following the Cu deposition, to clean the workpiece,
followed by an air drying step to remove the water.
[0078] As described in conjunction with the description of step 106
of FIG. 1, above, in order to bond the Cu deposited onto the
substrate material, pressure and heat are applied to the workpiece
in step 106. The pressure serves to control volume expansion and
stresses on the layers of the cell. In the exemplary embodiments
shown in FIG. 3A, this heating and simultaneous application of
pressure to the workpiece is performed via rollers 304 that are in
contact with opposing sides (i.e., one of the rollers 304 is in
contact with the top and one of the rollers 304 is in contact with
the bottom) of the workpiece such that as the workpiece is fed
through the continuous line fabrication process, the workpiece
passes between the rollers 304. The rollers 304 can be heated to
thereby heat the workpiece as the workpiece passes between the
rollers 304. Temperature and pressure parameters for this step were
provided above. Thus, in this exemplary embodiment, the rollers 304
at this stage of the continuous line process are configured to
simultaneously 1) heat the workpiece and 2) apply pressure to both
sides of the workpiece.
[0079] As provided above, electrodeposition is only one exemplary
process that may be employed herein for depositing the material
onto the substrate. For instance, another suitable deposition
process (such as sputtering) may be used to deposit the material
onto the rollers, which then apply the material to the substrate in
the manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above. These
alternative embodiments are described in detail below.
[0080] As described in conjunction with the description of step 108
of FIG. 1, above, a In layer is deposited onto the substrate on top
of the Cu layer while at the same time pressure is applied to both
sides (i.e., to a top and bottom) of the workpiece in order to
control volume expansion and stresses on the layers of the cell. In
the embodiment shown in FIG. 3A, this In deposition and
simultaneous application of pressure to the workpiece is performed
via rollers 306 which as shown in FIG. 3A are in contact with
opposing sides (i.e., one of rollers 306 is in contact with the top
and one of rollers 306 is in contact with the bottom) of the
workpiece such that as the workpiece is fed through the continuous
line fabrication process, the workpiece passes between rollers 306.
Further, as shown in FIG. 3A, the rollers 306 are configured to
deposit the In onto the workpiece from an In-containing electrolyte
solution through which one of the rollers 306 passes. Namely, as
described above, the rollers 302 can be made of a metal such as
stainless steel and as the bottom roller 306 passes through the
In-containing electrolyte solution, the In is electrodeposited onto
the roller from the electrolyte solution (i.e., the bottom roller
306 acts as a cathode for the electrodeposition process). The In
electrodeposited on the bottom roller 306 is then transferred (from
the bottom roller 306) onto the workpiece. As described above, the
transfer of the In from the bottom roller 306 to the workpiece can
be facilitated by cooling the rollers 306--to insure cladding of
the In onto the workpiece rather than onto the rollers. Temperature
and pressure parameters for this step were provided above. Thus, in
this exemplary embodiment, the rollers 306 are configured to
simultaneously 1) apply In to the workpiece and 2) apply pressure
to both sides of the workpiece.
[0081] As described above, the pressure applied to the workpiece by
the rollers 306 may be based on the weight of the top roller 306
pressing down on the workpiece against the bottom roller 306.
Accordingly, as provided above, the rollers 306 may not be the same
size as one another.
[0082] While not explicitly shown in FIG. 3A, a (e.g., nitrogen
(N.sub.2)) air knife may be present in the direction of rotation
between the plating cell and the workpiece to direct plating
solution from the rollers 306 back into the In plating cell. A
water jet may also be implemented in the line following the In
deposition, to clean the workpiece, followed by an air drying step
to remove the water. The air knife, water jet and air drying would
be implemented in the same manner as described above in conjunction
with the Cu deposition electroplating stage.
[0083] As described in conjunction with the description of step 110
of FIG. 1, above, in order to bond the In deposited onto the
substrate material, pressure and heat are applied to the workpiece.
The pressure serves to control volume expansion and stresses on the
layers of the cell. In the exemplary embodiments shown in FIG. 3A,
this heating and simultaneous application of pressure to the
workpiece is performed via rollers 308 that are in contact with
opposing sides (i.e., one of the rollers 308 is in contact with the
top and one of the rollers 308 is in contact with the bottom) of
the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the rollers 308. The rollers 308 can be heated to thereby heat the
workpiece as the workpiece passes between the rollers 308.
Temperature and pressure parameters for this step were provided
above. Thus, in this exemplary embodiment, the rollers 308 at this
stage of the continuous line process are configured to
simultaneously 1) heat the workpiece and 2) apply pressure to both
sides of the workpiece.
[0084] Again, electrodeposition is only one exemplary process that
may be employed herein for depositing the material onto the
substrate. For instance, another suitable deposition process (such
as sputtering) may be used to deposit the material onto the
rollers, which then apply the material to the substrate in the
manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above.
[0085] As described in conjunction with the description of step 112
of FIG. 1, above, a Ga layer is deposited onto the substrate on top
of the In layer while at the same time pressure is applied to both
sides (i.e., to a top and bottom) of the workpiece in order to
control volume expansion and stresses on the layers of the cell. In
the embodiment shown in FIG. 3A, this Ga deposition and
simultaneous application of pressure to the workpiece is performed
via rollers 310 which as shown in FIG. 3A are in contact with
opposing sides (i.e., one of rollers 310 is in contact with the top
and one of rollers 310 is in contact with the bottom) of the
workpiece such that as the workpiece is fed through the continuous
line fabrication process, the workpiece passes between rollers 310.
Further, as shown in FIG. 3A, the rollers 310 are configured to
deposit the Ga onto the workpiece from a Ga-containing electrolyte
solution through which one of the rollers 310 passes. Namely, as
described above, the rollers 310 can be made of a metal such as
stainless steel and as the bottom roller 310 passes through the
Ga-containing electrolyte solution, the Ga is electrodeposited onto
the roller from the electrolyte solution (i.e., the bottom roller
310 acts as a cathode for the electrodeposition process). The Ga
electrodeposited on the bottom roller 310 is then transferred (from
the bottom roller 310) onto the workpiece. As described above, the
transfer of the Ga from the bottom roller 310 to the workpiece can
be facilitated by cooling the rollers 310--to insure cladding of
the Ga onto the workpiece rather than onto the rollers. Temperature
and pressure parameters for this step were provided above. Thus, in
this exemplary embodiment, the rollers 310 are configured to
simultaneously 1) apply Ga to the workpiece and 2) apply pressure
to both sides of the workpiece.
[0086] As described above, the pressure applied to the workpiece by
the rollers 310 may be based on the weight of the top roller 310
pressing down on the workpiece against the bottom roller 310.
Accordingly, as provided above, the rollers 310 may not be the same
size as one another.
[0087] While not explicitly shown in FIG. 3A, a (e.g., nitrogen
(N.sub.2)) air knife may be present in the direction of rotation
between the plating cell and the workpiece to direct plating
solution from the rollers 310 back into the Ga plating cell. A
water jet may also be implemented in the line following the Ga
deposition, to clean the workpiece, followed by an air drying step
to remove the water. The air knife, water jet and air drying would
be implemented in the same manner as described above in conjunction
with the Cu deposition electroplating stage.
[0088] As described in conjunction with the description of step 114
of FIG. 1, above, in order to bond the Ga deposited onto the
substrate material, pressure and heat are applied to the workpiece.
The pressure serves to control volume expansion and stresses on the
layers of the cell. In the exemplary embodiment shown in FIG. 3A,
this heating and simultaneous application of pressure to the
workpiece is performed via rollers 312 that are in contact with
opposing sides (i.e., one of the rollers 312 is in contact with the
top and one of the rollers 312 is in contact with the bottom) of
the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the rollers 312. The rollers 312 can be heated to thereby heat the
workpiece as the workpiece passes between the rollers 312.
Temperature and pressure parameters for this step were provided
above. Thus, in this exemplary embodiment, the rollers 312 at this
stage of the continuous line process are configured to
simultaneously 1) heat the workpiece and 2) apply pressure to both
sides of the workpiece.
[0089] As described in conjunction with the description of step 116
of FIG. 1, above, following deposition of the Ga onto the workpiece
an optional soft/intermediate anneal may be performed to enhance
the uniformity of the final CIGS material. Temperature and pressure
parameters for this step were provided above. As with the heating
steps described above, pressure is applied to the workpiece while
the workpiece is heated during this soft annealing step. In the
exemplary embodiment shown in FIG. 3B, this heating and
simultaneous application of pressure to the workpiece is performed
via rollers 314 that are in contact with opposing sides (i.e., one
of the rollers 314 is in contact with the top and one of the
rollers 314 is in contact with the bottom) of the workpiece such
that as the workpiece is fed through the continuous line
fabrication process, the workpiece passes between the rollers 314.
The rollers 314 can be heated to thereby heat the workpiece as the
workpiece passes between the rollers 314. Temperature and pressure
parameters for this step were provided above. Thus, in this
exemplary embodiment, the rollers 314 at this stage of the
continuous line process are configured to simultaneously 1) heat
the workpiece and 2) apply pressure to both sides of the
workpiece.
[0090] Again, electrodeposition is only one exemplary process that
may be employed herein for depositing the material onto the
substrate. For instance, another suitable deposition process (such
as sputtering) may be used to deposit the material onto the
rollers, which then apply the material to the substrate in the
manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above.
[0091] As described in conjunction with the description of step 118
of FIG. 1, above, a S and/or Se layer is deposited onto the
substrate on top of the Ga layer while at the same time pressure is
applied to both sides (i.e., to a top and bottom) of the workpiece
in order to control volume expansion and stresses on the layers of
the cell. In the embodiment shown in FIG. 3B, this S/Se deposition
and simultaneous application of pressure to the workpiece is
performed via rollers 316 which as shown in FIG. 3B are in contact
with opposing sides (i.e., one of rollers 316 is in contact with
the top and one of rollers 316 is in contact with the bottom) of
the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
rollers 316. Further, as shown in FIG. 3B, the rollers 316 are
configured to deposit the S/Se onto the workpiece from a
S/Se-containing electrolyte solution through which one of the
rollers 316 passes. Namely, as described above, the rollers 316 can
be made of a metal such as stainless steel and as the bottom roller
316 passes through the S/Se-containing electrolyte solution, the
S/Se is electrodeposited onto the roller from the electrolyte
solution (i.e., the bottom roller 316 acts as a cathode for the
electrodeposition process). The S/Se electrodeposited on the bottom
roller 316 is then transferred (from the bottom roller 316) onto
the workpiece. As described above, the transfer of the S/Se from
the bottom roller 316 to the workpiece can be facilitated by
cooling the rollers 316--to insure cladding of the S/Se onto the
workpiece rather than onto the rollers. Temperature and pressure
parameters for this step were provided above. Thus, in this
exemplary embodiment, the rollers 316 are configured to
simultaneously 1) apply S/Se to the workpiece and 2) apply pressure
to both sides of the workpiece. As described above, the pressure
applied to the workpiece by the rollers 316 may be based on the
weight of the top roller 316 pressing down on the workpiece against
the bottom roller 316. Accordingly, as provided above, the rollers
316 may not be the same size as one another.
[0092] While not explicitly shown in FIG. 3B, a (e.g., nitrogen
(N.sub.2)) air knife may be present in the direction of rotation
between the plating cell and the workpiece to direct plating
solution from the rollers 316 back into the S/Se plating cell. A
water jet may also be implemented in the line following the S/Se
deposition, to clean the workpiece, followed by an air drying step
to remove the water. The air knife, water jet and air drying would
be implemented in the same manner as described above in conjunction
with the Cu deposition electroplating stage.
[0093] Again, electrodeposition is only one exemplary process that
may be employed herein for depositing the material onto the
substrate. For instance, another suitable deposition process (such
as sputtering) may be used to deposit the material onto the
rollers, which then apply the material to the substrate in the
manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above.
[0094] As described in conjunction with the description of step 120
of FIG. 1, above, in order to bond the S/Se deposited onto the
substrate material, pressure and heat are applied to the workpiece.
The pressure serves to control volume expansion and stresses on the
layers of the cell. In the exemplary embodiment shown in FIG. 3B,
this heating and simultaneous application of pressure to the
workpiece is performed via rollers 318 that are in contact with
opposing sides (i.e., one of the rollers 318 is in contact with the
top and one of the rollers 318 is in contact with the bottom) of
the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the rollers 318. The rollers 318 can be heated to thereby heat the
workpiece as the workpiece passes between the rollers 318.
Temperature and pressure parameters for this step were provided
above. Thus, in this exemplary embodiment, the rollers 318 at this
stage of the continuous line process are configured to
simultaneously 1) heat the workpiece and 2) apply pressure to both
sides of the workpiece.
[0095] As described in conjunction with the description of step 122
of FIG. 1, above, following deposition of the S/Se onto the
workpiece a final anneal is performed. Temperature and pressure
parameters for this step were provided above. As with the heating
steps described above, pressure is applied to the workpiece while
the workpiece is heated during this final annealing step. In the
exemplary embodiment shown in FIG. 3B, this heating and
simultaneous application of pressure to the workpiece is performed
via rollers 320 that are in contact with opposing sides (i.e., one
of the roller 320 is in contact with the top and one of the roller
320 is in contact with the bottom) of the workpiece such that as
the workpiece is fed through the continuous line fabrication
process, the workpiece passes between the rollers 320. The rollers
320 can be heated to thereby heat the workpiece as the workpiece
passes between the rollers 320. Thus, in this exemplary embodiment,
the rollers 320 at this stage of the continuous line process are
configured to simultaneously 1) heat the workpiece and 2) apply
pressure to both sides of the workpiece.
[0096] As shown in FIG. 3B, this final anneal is conducted in a S
environment. By way of example only, the workpiece may be fed (in a
continuous line fashion) into a sulfurization annealing chamber.
The final output is a CIGS panel.
[0097] It is notable that the thin film compositions described
above, and elsewhere herein are merely examples intended to
illustrate the present techniques, and a variety of other film
compositions can be achieved in the manner described herein. One
would need only to vary the composition of the materials deposited
in one or more of the steps and/or the order in which the materials
are deposited in order to achieve different thin film compositions.
In addition to the CIGS example provided above, by way of example
only, one may adapt the present techniques to produce any of the
following thin film solar cell compositions: CZTS
(Cu.sub.2ZnSn(Se,S).sub.4), FeS.sub.2, Zn.sub.2P.sub.3, CdSe, CdS,
ZnSe, WSe.sub.2, MoSe.sub.2, BhS.sub.3, Ag.sub.2S,
Cu.sub.2Zn(Fe,Sn)(Se,S).sub.4, CuxS, CdTe, ZnTe, PbSe, PdS, NiS,
NiSeS, InP, ZnO, GaAs. An example involving a I-III-IV.sub.2
material is provided below.
[0098] Another exemplary embodiment implementing the present
techniques for continuous-line fabrication of thin film solar cells
is now described by way of reference to FIGS. 4A-B. In FIGS. 4A-B a
continuous line processing apparatus is depicted performing the
method described in FIG. 1, above (i.e., wherein deposition of the
various CIGS layers occurs via electrodeposition) on a metal (e.g.,
stainless steel (SS) sheet) substrate. It is to be understood that
FIGS. 4A-B illustrate a single, continuous-line apparatus/process,
however, for ease and clarity of depiction, the figure is broken
into two parts (FIG. 4A and FIG. 4B).
[0099] As shown in FIG. 4A, a stainless steel substrate is fed into
the apparatus between a first set of rollers 402. As compared to
the glass substrate illustrated in FIGS. 3A-B, a stainless steel
metal substrate is more flexible and can be fed through the
continuous line apparatus/process from a roll (as shown in FIG.
4A--labeled "roll of SS-sheet"). Accordingly, additional rollers
may be employed in the production line prior to rollers 402 in
order to guide the substrate from the roll. The particular number
and positioning of these `guide` rollers will of course vary
depending on the particular set-up at hand, and their use is
optional.
[0100] As described in conjunction with the description of step 104
of FIG. 1, above, a Cu layer is deposited onto the substrate while
at the same time pressure is applied to both sides (i.e., to a top
and bottom) of the workpiece in order to control volume expansion
and stresses on the layers of the cell. In the embodiment shown in
FIG. 4A, this Cu deposition and simultaneous application of
pressure to the workpiece is performed via rollers 402 which as
shown in FIG. 4A are in contact with opposing sides (i.e., one of
rollers 402 is in contact with the top and one of rollers 402 is in
contact with the bottom) of the workpiece such that as the
workpiece is fed through the continuous line fabrication process,
the workpiece passes between rollers 402. Further, as shown in FIG.
4A, the rollers 402 are configured to deposit the Cu onto the
workpiece from a Cu-containing electrolyte solution through which
one of the rollers 402 passes. Namely, according to an exemplary
embodiment, rollers 402 are made of a metal such as stainless
steel. As the bottom roller 402 passes through the Cu-containing
electrolyte solution, the Cu is electrodeposited onto the roller
from the electrolyte solution. In this example, there is an anode
in the electrolyte solution and the bottom (e.g., metal) roller 402
acts as a cathode for the electrodeposition process. The Cu
electrodeposited on the bottom roller 402 is then transferred (from
the bottom roller 402) onto the workpiece. As described above, the
transfer of the Cu from the bottom roller 402 to the workpiece can
be facilitated by cooling the rollers 402. Namely, cooling the
rollers will facilitate cladding the Cu to the workpiece, rather
than to the (metal) roller itself. Further, due to this being a
continuous line process, as the workpiece passes through each
stage, the material already deposited and cladded onto the
workpiece will aid in removing the material from the roller
(similar to when any sort of material is unwound from a roll) and
cooling the rollers facilitates removal of the material from the
roll. Thus, in this exemplary embodiment, the rollers 402 are
configured to simultaneously 1) apply Cu to the workpiece and 2)
apply pressure to both sides of the workpiece. As described above,
the pressure applied to the workpiece by the rollers 402 may be
based on the weight of the top roller 402 pressing down on the
workpiece against the bottom roller 402, and accordingly the top
roller 402 and the bottom roller 402 may not be the same size as
one another.
[0101] As shown in FIG. 4A, a (e.g., nitrogen (N.sub.2)) air knife
present in the direction of rotation between the plating cell and
the workpiece serves to direct plating solution from the rollers
402 back into the Cu plating cell. A water jet may also be
implemented in the line following the Cu deposition, to clean the
workpiece, followed by an air drying step to remove the water.
[0102] As described in conjunction with the description of step 106
of FIG. 1, above, in order to bond the Cu deposited onto the
substrate material, pressure and heat are applied to the workpiece
in step 106. The pressure serves to control volume expansion and
stresses on the layers of the cell. In the exemplary embodiment
shown in FIG. 4A, this heating and simultaneous application of
pressure to the workpiece is performed via rollers 404 that are in
contact with opposing sides (i.e., one of the roller 404 is in
contact with the top and one of the roller 404 is in contact with
the bottom) of the workpiece such that as the workpiece is fed
through the continuous line fabrication process, the workpiece
passes between the rollers 404. The rollers 404 can be heated to
thereby heat the workpiece as the workpiece passes between the
rollers 404. Temperature and pressure parameters for this step were
provided above. Thus, in this exemplary embodiment, the rollers 404
at this stage of the continuous line process are configured to
simultaneously 1) heat the workpiece and 2) apply pressure to both
sides of the workpiece.
[0103] As provided above, electrodeposition is only one exemplary
process that may be employed herein for depositing the material
onto the substrate. For instance, another suitable deposition
process (such as sputtering) may be used to deposit the material
onto the rollers, which then apply the material to the substrate in
the manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above.
[0104] As described in conjunction with the description of step 108
of FIG. 1, above, a In layer is deposited onto the substrate on top
of the Cu layer while at the same time pressure is applied to both
sides (i.e., to a top and bottom) of the workpiece in order to
control volume expansion and stresses on the layers of the cell. In
the embodiment shown in FIG. 4A, this In deposition and
simultaneous application of pressure to the workpiece is performed
via rollers 406 which as shown in FIG. 4A are in contact with
opposing sides (i.e., one of rollers 406 is in contact with the top
and one of rollers 406 is in contact with the bottom) of the
workpiece such that as the workpiece is fed through the continuous
line fabrication process, the workpiece passes between rollers 406.
Further, as shown in FIG. 4A, the rollers 406 are configured to
deposit the In onto the workpiece from an In-containing electrolyte
solution through which one of the rollers 406 passes. Namely, as
described above, the rollers 402 can be made of a metal such as
stainless steel and as the bottom roller 406 passes through the
In-containing electrolyte solution, the In is electrodeposited onto
the roller from the electrolyte solution (i.e., the bottom roller
406 acts as a cathode for the electrodeposition process). The In
electrodeposited on the bottom roller 406 is then transferred (from
the bottom roller 406) onto the workpiece. As described above, the
transfer of the In from the bottom roller 406 to the workpiece can
be facilitated by cooling the rollers 406--to insure cladding of
the In onto the workpiece rather than onto the rollers. Temperature
and pressure parameters for this step were provided above. Thus, in
this exemplary embodiment, the rollers 406 are configured to
simultaneously 1) apply Cu to the workpiece and 2) apply pressure
to both sides of the workpiece.
[0105] As described above, the pressure applied to the workpiece by
the rollers 406 may be based on the weight of the top roller 406
pressing down on the workpiece against the bottom roller 406.
Accordingly, as provided above, the rollers 406 may not be the same
size as one another.
[0106] While not explicitly shown in FIG. 4A, a (e.g., nitrogen
(N.sub.2)) air knife may be present in the direction of rotation
between the plating cell and the workpiece to direct plating
solution from the rollers 406 back into the In plating cell. A
water jet may also be implemented in the line following the In
deposition, to clean the workpiece, followed by an air drying step
to remove the water. The air knife, water jet and air drying would
be implemented in the same manner as described above in conjunction
with the Cu deposition electroplating stage.
[0107] Again, electrodeposition is only one exemplary process that
may be employed herein for depositing the material onto the
substrate. For instance, another suitable deposition process (such
as sputtering) may be used to deposit the material onto the
rollers, which then apply the material to the substrate in the
manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above.
[0108] As described in conjunction with the description of step 110
of FIG. 1, above, in order to bond the In deposited onto the
substrate material, pressure and heat are applied to the workpiece.
The pressure serves to control volume expansion and stresses on the
layers of the cell. In the exemplary embodiments shown in FIG. 4A,
this heating and simultaneous application of pressure to the
workpiece is performed via rollers 408 that are in contact with
opposing sides (i.e., one of the rollers 408 is in contact with the
top and one of the rollers 408 is in contact with the bottom) of
the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the rollers 408. The rollers 408 can be heated to thereby heat the
workpiece as the workpiece passes between the rollers 408.
Temperature and pressure parameters for this step were provided
above. Thus, in this exemplary embodiment, the rollers 408 at this
stage of the continuous line process are configured to
simultaneously 1) heat the workpiece and 2) apply pressure to both
sides of the workpiece.
[0109] As described in conjunction with the description of step 112
of FIG. 1, above, a Ga layer is deposited onto the substrate on top
of the In layer while at the same time pressure is applied to both
sides (i.e., to a top and bottom) of the workpiece in order to
control volume expansion and stresses on the layers of the cell. In
the embodiment shown in FIG. 4A, this Ga deposition and
simultaneous application of pressure to the workpiece is performed
via rollers 410 which as shown in FIG. 4A are in contact with
opposing sides (i.e., one of rollers 410 is in contact with the top
and one of rollers 410 is in contact with the bottom) of the
workpiece such that as the workpiece is fed through the continuous
line fabrication process, the workpiece passes between rollers 410.
Further, as shown in FIG. 4A, the rollers 410 are configured to
deposit the Ga onto the workpiece from a Ga-containing electrolyte
solution through which one of the rollers 410 passes. Namely, as
described above, the rollers 410 can be made of a metal such as
stainless steel and as the bottom roller 410 passes through the
Ga-containing electrolyte solution, the Ga is electrodeposited onto
the roller from the electrolyte solution (i.e., the bottom roller
410 acts as a cathode for the electrodeposition process). The Ga
electrodeposited on the bottom roller 410 is then transferred (from
the bottom roller 410) onto the workpiece. As described above, the
transfer of the Ga from the bottom roller 410 to the workpiece can
be facilitated by cooling the rollers 410--to insure cladding of
the Ga onto the workpiece rather than onto the rollers. Temperature
and pressure parameters for this step were provided above. Thus, in
this exemplary embodiment, the rollers 410 are configured to
simultaneously 1) apply Ga to the workpiece and 2) apply pressure
to both sides of the workpiece.
[0110] As described above, the pressure applied to the workpiece by
the rollers 410 may be based on the weight of the top roller 410
pressing down on the workpiece against the bottom roller 410.
Accordingly, as provided above, the rollers 410 may not be the same
size as one another.
[0111] While not explicitly shown in FIG. 4A, a (e.g., nitrogen
(N.sub.2)) air knife may be present in the direction of rotation
between the plating cell and the workpiece to direct plating
solution from the rollers 410 back into the Ga plating cell. A
water jet may also be implemented in the line following the Ga
deposition, to clean the workpiece, followed by an air drying step
to remove the water. The air knife, water jet and air drying would
be implemented in the same manner as described above in conjunction
with the Cu deposition electroplating stage.
[0112] Again, electrodeposition is only one exemplary process that
may be employed herein for depositing the material onto the
substrate. For instance, another suitable deposition process (such
as sputtering) may be used to deposit the material onto the
rollers, which then apply the material to the substrate in the
manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above.
[0113] As described in conjunction with the description of step 114
of FIG. 1, above, in order to bond the Ga deposited onto the
substrate material, pressure and heat are applied to the workpiece.
The pressure serves to control volume expansion and stresses on the
layers of the cell. In the exemplary embodiment shown in FIG. 4A,
this heating and simultaneous application of pressure to the
workpiece is performed via rollers 412 that are in contact with
opposing sides (i.e., one of the rollers 412 is in contact with the
top and one of the rollers 412 is in contact with the bottom) of
the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the rollers 412. The rollers 412 can be heated to thereby heat the
workpiece as the workpiece passes between the rollers 412.
Temperature and pressure parameters for this step were provided
above. Thus, in this exemplary embodiment, the rollers 412 at this
stage of the continuous line process are configured to
simultaneously 1) heat the workpiece and 2) apply pressure to both
sides of the workpiece.
[0114] As described in conjunction with the description of step 116
of FIG. 1, above, following deposition of the Ga onto the workpiece
an optional soft/intermediate anneal may be performed to enhance
the uniformity of the final CIGS material. Temperature and pressure
parameters for this step were provided above. As with the heating
steps described above, pressure is applied to the workpiece while
the workpiece is heated during this soft annealing step. In the
exemplary embodiment shown in FIG. 4B, this heating and
simultaneous application of pressure to the workpiece is performed
via rollers 414 that are in contact with opposing sides (i.e., one
of the rollers 414 is in contact with the top and one of the
rollers 414 is in contact with the bottom) of the workpiece such
that as the workpiece is fed through the continuous line
fabrication process, the workpiece passes between the rollers 414.
The rollers 414 can be heated to thereby heat the workpiece as the
workpiece passes between the rollers 414. Temperature and pressure
parameters for this step were provided above. Thus, in this
exemplary embodiment, the rollers 414 at this stage of the
continuous line process are configured to simultaneously 1) heat
the workpiece and 2) apply pressure to both sides of the
workpiece.
[0115] As described in conjunction with the description of step 118
of FIG. 1, above, a S and/or Se layer is deposited onto the
substrate on top of the Ga layer while at the same time pressure is
applied to both sides (i.e., to a top and bottom) of the workpiece
in order to control volume expansion and stresses on the layers of
the cell. In the embodiment shown in FIG. 4B, this S/Se deposition
and simultaneous application of pressure to the workpiece is
performed via rollers 416 which as shown in FIG. 4B are in contact
with opposing sides (i.e., one of rollers 416 is in contact with
the top and one of rollers 416 is in contact with the bottom) of
the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
rollers 416. Further, as shown in FIG. 4B, the rollers 416 are
configured to deposit the S/Se onto the workpiece from a
S/Se-containing electrolyte solution through which one of the
rollers 416 passes. Namely, as described above, the rollers 416 can
be made of a metal such as stainless steel and as the bottom roller
416 passes through the S/Se-containing electrolyte solution, the
S/Se is electrodeposited onto the roller from the electrolyte
solution (i.e., the bottom roller 316 acts as a cathode for the
electrodeposition process). The S/Se electrodeposited on the bottom
roller 416 is then transferred (from the bottom roller 416) onto
the workpiece. As described above, the transfer of the S/Se from
the bottom roller 416 to the workpiece can be facilitated by
cooling the rollers 416--to insure cladding of the S/Se onto the
workpiece rather than onto the rollers. Temperature and pressure
parameters for this step were provided above. Thus, in this
exemplary embodiment, the rollers 416 are configured to
simultaneously 1) apply S/Se to the workpiece and 2) apply pressure
to both sides of the workpiece.
[0116] As described above, the pressure applied to the workpiece by
the rollers 416 may be based on the weight of the top roller 416
pressing down on the workpiece against the bottom roller 416.
Accordingly, as provided above, the rollers 416 may not be the same
size as one another.
[0117] While not explicitly shown in FIG. 4B, a (e.g., nitrogen
(N.sub.2)) air knife may be present in the direction of rotation
between the plating cell and the workpiece to direct plating
solution from the rollers 416 back into the S/Se plating cell. A
water jet may also be implemented in the line following the S/Se
deposition, to clean the workpiece, followed by an air drying step
to remove the water. The air knife, water jet and air drying would
be implemented in the same manner as described above in conjunction
with the Cu deposition electroplating stage.
[0118] Again, electrodeposition is only one exemplary process that
may be employed herein for depositing the material onto the
substrate. For instance, another suitable deposition process (such
as sputtering) may be used to deposit the material onto the
rollers, which then apply the material to the substrate in the
manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above.
[0119] As described in conjunction with the description of step 120
of FIG. 1, above, in order to bond the S/Se deposited onto the
substrate material, pressure and heat are applied to the workpiece.
The pressure serves to control volume expansion and stresses on the
layers of the cell. In the exemplary embodiment shown in FIG. 4B,
this heating and simultaneous application of pressure to the
workpiece is performed via rollers 418 that are in contact with
opposing sides (i.e., one of the rollers 418 is in contact with the
top and one of the rollers 418 is in contact with the bottom) of
the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
the rollers 418. The rollers 418 can be heated to thereby heat the
workpiece as the workpiece passes between the rollers 418.
Temperature and pressure parameters for this step were provided
above. Thus, in this exemplary embodiment, the rollers 418 at this
stage of the continuous line process are configured to
simultaneously 1) heat the workpiece and 2) apply pressure to both
sides of the workpiece.
[0120] As described in conjunction with the description of step 122
of FIG. 1, above, following deposition of the S/Se onto the
workpiece final anneal is performed. Temperature and pressure
parameters for this step were provided above. As with the heating
steps described above, pressure is applied to the workpiece while
the workpiece is heated during this final annealing step. In the
exemplary embodiment shown in FIG. 4B, this heating and
simultaneous application of pressure to the workpiece is performed
via rollers 420 that are in contact with opposing sides (i.e., one
of the rollers 420 is in contact with the top and one of the
rollers 420 is in contact with the bottom) of the workpiece such
that as the workpiece is fed through the continuous line
fabrication process, the workpiece passes between the rollers 420.
The rollers 420 can be heated to thereby heat the workpiece as the
workpiece passes between the rollers 420. Thus, in this exemplary
embodiment, the rollers 420 at this stage of the continuous line
process are configured to simultaneously 1) heat the workpiece and
2) apply pressure to both sides of the workpiece.
[0121] As shown in FIG. 4B, this final anneal is conducted in a
S/Se environment. By way of example only, the workpiece may be fed
(in a continuous line fashion) into a sulfurization annealing
chamber. The final output is a CIGS panel.
[0122] Yet another exemplary embodiment implementing the present
techniques for continuous-line fabrication of thin film solar cells
is now described by way of reference to FIGS. 5A-B. In FIGS. 5A-B a
continuous line processing apparatus is depicted performing the
method described in FIG. 2, above (i.e., wherein deposition of the
various CIGS layers occurs via electrodeposition and/or via
deposition from a molten bath) on a metal (e.g., stainless steel
(SS) sheet) substrate. It is to be understood that FIGS. 5A-B
illustrate a single, continuous-line apparatus/process, however,
for ease and clarity of depiction, the figure is broken into two
parts (FIG. 5A and FIG. 5B). By contrast with the embodiments shown
illustrated in FIGS. 3A-B and 4A-B, in FIGS. 5A-B some of the CIGS
layers are deposited onto the workpiece from a molten bath rather
than via an electroplating cell.
[0123] As shown in FIG. 5A, a stainless steel substrate is fed into
the apparatus between a first set of rollers 502. As compared to
the glass substrate illustrated in FIGS. 3A-B, a stainless steel
metal substrate is more flexible and can be fed through the
continuous line apparatus/process from a roll (as shown in FIG.
5A--labeled "roll of SS-sheet"). Accordingly, additional rollers
may be employed in the production line prior to rollers 502 in
order to guide the substrate from the roll. The particular number
and positioning of these `guide` rollers will of course vary
depending on the particular set-up at hand, and their use is
optional.
[0124] As described in conjunction with the description of step 204
of FIG. 2, above, a Cu layer is deposited onto the substrate while
at the same time pressure is applied to both sides (i.e., to a top
and bottom) of the workpiece in order to control volume expansion
and stresses on the layers of the cell. In the embodiment shown in
FIG. 5A, this Cu deposition and simultaneous application of
pressure to the workpiece is performed via rollers 502 which as
shown in FIG. 5A are in contact with opposing sides (i.e., one of
rollers 502 is in contact with the top and one of rollers 502 is in
contact with the bottom) of the workpiece such that as the
workpiece is fed through the continuous line fabrication process,
the workpiece passes between rollers 502. Further, as shown in FIG.
5A, the rollers 502 are configured to deposit the Cu onto the
workpiece from a Cu-containing electrolyte solution through which
one of the rollers 502 passes. Namely, according to an exemplary
embodiment, rollers 502 are made of a metal such as stainless
steel. As the bottom roller 502 passes through the Cu-containing
electrolyte solution, the Cu is electrodeposited onto the roller
from the electrolyte solution. In this example, there is an anode
in the electrolyte solution and the bottom (e.g., metal) roller 502
acts as a cathode for the electrodeposition process. The Cu
electrodeposited on the bottom roller 502 is then transferred (from
the bottom roller 502) onto the workpiece. As described above, the
transfer of the Cu from the bottom roller 502 to the workpiece can
be facilitated by cooling the rollers 502. Namely, cooling the
rollers will facilitate cladding the Cu to the workpiece, rather
than to the (metal) roller itself. Further, due to this being a
continuous line process, as the workpiece passes through each
stage, the material already deposited and cladded onto the
workpiece will aid in removing the material from the roller
(similar to when any sort of material is unwound from a roll) and
cooling the rollers facilitates removal of the material from the
roll. Temperature and pressure parameters for this step were
provided above. Thus, in this exemplary embodiment, the rollers 502
are configured to simultaneously 1) apply Cu to the workpiece and
2) apply pressure to both sides of the workpiece. As described
above, the pressure applied to the workpiece by the rollers 502 may
be based on the weight of the top roller 502 pressing down on the
workpiece against the bottom roller 502, and accordingly the top
roller 502 and the bottom roller 502 may not be the same size as
one another.
[0125] As shown in FIG. 5A, a (e.g., nitrogen (N.sub.2)) air knife
present in the direction of rotation between the plating cell and
the workpiece serves to direct plating solution from the rollers
502 back into the cu plating cell. A water jet may also be
implemented in the line following the Cu deposition, to clean the
workpiece, followed by an air drying step to remove the water.
[0126] As provided above, electrodeposition is only one exemplary
process that may be employed herein for depositing the material
onto the substrate. For instance, another suitable deposition
process (such as sputtering) may be used to deposit the material
onto the rollers, which then apply the material to the substrate in
the manner described above. Alternatively, the material may be
deposited directly onto the substrate with pressure and/or heat
being supplied via the rollers as described above.
[0127] As described in conjunction with the description of step 206
of FIG. 2, above, in order to bond the Cu deposited onto the
substrate material, pressure and heat are applied to the workpiece
in step 206. The pressure serves to control volume expansion and
stresses on the layers of the cell. In the exemplary embodiment
shown in FIG. 5A, this heating and simultaneous application of
pressure to the workpiece is performed via rollers 504 that are in
contact with opposing sides (i.e., one of the roller 504 is in
contact with the top and one of the roller 504 is in contact with
the bottom) of the workpiece such that as the workpiece is fed
through the continuous line fabrication process, the workpiece
passes between the rollers 504. The rollers 504 can be heated to
thereby heat the workpiece as the workpiece passes between the
rollers 504. Temperature and pressure parameters for this step were
provided above. Thus, in this exemplary embodiment, the rollers 504
at this stage of the continuous line process are configured to
simultaneously 1) heat the workpiece and 2) apply pressure to both
sides of the workpiece.
[0128] As described in conjunction with the description of step 208
of FIG. 2, above, a In layer is deposited onto the substrate on top
of the Cu layer while at the same time pressure is applied to both
sides (i.e., to a top and bottom) of the workpiece in order to
control volume expansion and stresses on the layers of the cell. In
the embodiment shown in FIG. 5A, this In deposition and
simultaneous application of pressure to the workpiece is performed
via rollers 506 which as shown in FIG. 5A are in contact with
opposing sides (i.e., one of rollers 506 is in contact with the top
and one of rollers 506 is in contact with the bottom) of the
workpiece such that as the workpiece is fed through the continuous
line fabrication process, the workpiece passes between rollers 506.
Further, as shown in FIG. 5A, the rollers 506 are configured to
deposit the In onto the workpiece from a bath of molten In through
which one of the rollers 506 passes. Namely, as the bottom roller
506 passes through the bath, some of the molten In is picked up by
the roller and transferred to the workpiece. As described above,
the transfer of the In from the bottom roller 506 to the workpiece
can be facilitated by cooling the rollers 506. Temperature and
pressure parameters for this step were provided above. Thus, in
this exemplary embodiment, the rollers 506 are configured to
simultaneously 1) apply In to the workpiece and 2) apply pressure
to both sides of the workpiece.
[0129] As described above, the pressure applied to the workpiece by
the rollers 506 may be based on the weight of the top roller 506
pressing down on the workpiece against the bottom roller 506.
Accordingly, as provided above, the rollers 506 may not be the same
size as one another. As shown in FIG. 5A, a doctor blade may be
present in the direction of rotation between the molten In bath and
the workpiece to direct molten In from the rollers 506 back into
the molten In bath.
[0130] As described in conjunction with the description of step 210
of FIG. 2, above, the In material deposited on the workpiece from
the molten bath will still be (at least to some extent) molten
after it is transferred to the workpiece. Thus, the workpiece is
cooled. In order to control volume expansion and stresses on the
layers of the cell, pressure is applied to both sides (i.e., to a
top and bottom) of the workpiece during this cooling step. In the
exemplary embodiment shown in FIG. 5A, this cooling and
simultaneous application of pressure to the workpiece is performed
via rollers 508 that are in contact with opposing sides (i.e., one
of the rollers 508 is in contact with the top and one of the
rollers 508 is in contact with the bottom) of the workpiece such
that as the workpiece is fed through the continuous line
fabrication process, the workpiece passes between the rollers 508.
The rollers 508 can be cooled to thereby cool the workpiece as the
workpiece passes between the rollers 508. Temperature and pressure
parameters for this step were provided above. Thus, in this
exemplary embodiment, the rollers 508 at this stage of the
continuous line process are configured to simultaneously 1) cool
the workpiece and 2) apply pressure to both sides of the
workpiece.
[0131] As described in conjunction with the description of step 212
of FIG. 2, above, a Ga layer is deposited onto the substrate on top
of the In layer while at the same time pressure is applied to both
sides (i.e., to a top and bottom) of the workpiece in order to
control volume expansion and stresses on the layers of the cell. In
the embodiment shown in FIG. 5A, this Ga deposition and
simultaneous application of pressure to the workpiece is performed
via rollers 510 which as shown in FIG. 5A are in contact with
opposing sides (i.e., one of rollers 510 is in contact with the top
and one of rollers 510 is in contact with the bottom) of the
workpiece such that as the workpiece is fed through the continuous
line fabrication process, the workpiece passes between rollers 510.
Further, as shown in FIG. 5A, the rollers 510 are configured to
deposit the Ga onto the workpiece from a bath of molten Ga through
which one of the rollers 510 passes. Namely, as the bottom roller
510 passes through the bath, some of the molten Ga is picked up by
the roller and transferred to the workpiece. As described above,
the transfer of the Ga from the bottom roller 510 to the workpiece
can be facilitated by cooling the rollers 510--to insure cladding
of the Ga onto the workpiece rather than onto the rollers.
Temperature and pressure parameters for this step were provided
above. Thus, in this exemplary embodiment, the rollers 510 are
configured to simultaneously 1) apply Ga to the workpiece and 2)
apply pressure to both sides of the workpiece.
[0132] As described above, the pressure applied to the workpiece by
the rollers 510 may be based on the weight of the top roller 510
pressing down on the workpiece against the bottom roller 510.
Accordingly, as provided above, the rollers 510 may not be the same
size as one another. As shown in FIG. 5A, a doctor blade may be
present in the direction of rotation between the molten Ga bath and
the workpiece to direct molten Ga from the rollers 510 back into
the molten Ga bath.
[0133] As described in conjunction with the description of step 214
of FIG. 2, above, the Ga material deposited on the workpiece from
the molten bath will still be (at least to some extent) molten
after it is transferred to the workpiece. Thus, the workpiece is
cooled. In order to control volume expansion and stresses on the
layers of the cell, pressure is applied to both sides (i.e., to a
top and bottom) of the workpiece during this cooling step. In the
exemplary embodiment shown in FIG. 5A, this cooling and
simultaneous application of pressure to the workpiece is performed
via rollers 512 that are in contact with opposing sides (i.e., one
of the rollers S12 is in contact with the top and one of the
rollers 512 is in contact with the bottom) of the workpiece such
that as the workpiece is fed through the continuous line
fabrication process, the workpiece passes between the rollers 512.
The rollers 512 can be cooled to thereby cool the workpiece as the
workpiece passes between the rollers 512. Temperature and pressure
parameters for this step were provided above. Thus, in this
exemplary embodiment, the rollers 512 at this stage of the
continuous line process are configured to simultaneously 1) cool
the workpiece and 2) apply pressure to both sides of the
workpiece.
[0134] As described in conjunction with the description of step 216
of FIG. 2, above, following deposition of the Ga onto the workpiece
an optional soft/intermediate anneal may be performed to enhance
the uniformity of the final CIGS material. Temperature and pressure
parameters for this step were provided above. As with the heating
steps described above, pressure is applied to the workpiece while
the workpiece is heated during this soft annealing step. In the
exemplary embodiment shown in FIG. 5B, this heating and
simultaneous application of pressure to the workpiece is performed
via rollers 514 that are in contact with opposing sides (i.e., one
of the rollers 514 is in contact with the top and one of the
rollers 514 is in contact with the bottom) of the workpiece such
that as the workpiece is fed through the continuous line
fabrication process, the workpiece passes between the rollers 514.
The rollers 514 can be heated to thereby heat the workpiece as the
workpiece passes between the rollers 514. Temperature and pressure
parameters for this step were provided above. Thus, in this
exemplary embodiment, the rollers 514 at this stage of the
continuous line process are configured to simultaneously 1) heat
the workpiece and 2) apply pressure to both sides of the
workpiece.
[0135] As described in conjunction with the description of step 218
of FIG. 2, above, a S and/or Se layer is deposited onto the
substrate on top of the Ga layer while at the same time pressure is
applied to both sides (i.e., to a top and bottom) of the workpiece
in order to control volume expansion and stresses on the layers of
the cell. In the embodiment shown in FIG. 5B, this S/Se deposition
and simultaneous application of pressure to the workpiece is
performed via rollers 516 which as shown in FIG. 5B are in contact
with opposing sides (i.e., one of rollers 516 is in contact with
the top and one of rollers 516 is in contact with the bottom) of
the workpiece such that as the workpiece is fed through the
continuous line fabrication process, the workpiece passes between
rollers 516. Further, as shown in FIG. 5B, the rollers 516 are
configured to deposit the S/Se onto the workpiece from a bath of
molten S/Se through which one of the rollers 516 passes. Namely, as
the bottom roller 516 passes through the bath, some of the molten
S/Se is picked up by the roller and transferred to the workpiece.
As described above, the transfer of the S/Se from the bottom roller
516 to the workpiece can be facilitated by cooling the rollers
516--to insure cladding of the S onto the workpiece rather than
onto the rollers. Temperature and pressure parameters for this step
were provided above. Thus, in this exemplary embodiment, the
rollers 516 are configured to simultaneously 1) apply S/Se to the
workpiece and 2) apply pressure to both sides of the workpiece.
[0136] As described above, the pressure applied to the workpiece by
the rollers 516 may be based on the weight of the top roller S16
pressing down on the workpiece against the bottom roller 516.
Accordingly, as provided above, the rollers 516 may not be the same
size as one another. As shown in FIG. 5B, a doctor blade may be
present in the direction of rotation between the molten S/Se bath
and the workpiece to direct molten S/Se from the rollers 516 back
into the molten S/Se bath.
[0137] As described in conjunction with the description of step 220
of FIG. 2, above, the S/Se material deposited on the workpiece from
the molten bath will still be (at least to some extent) molten
after it is transferred to the workpiece. Thus, the workpiece is
cooled. In order to control volume expansion and stresses on the
layers of the cell, pressure is applied to both sides (i.e., to a
top and bottom) of the workpiece during this cooling step. In the
exemplary embodiment shown in FIG. 5B, this cooling and
simultaneous application of pressure to the workpiece is performed
via rollers 518 that are in contact with opposing sides (i.e., one
of the rollers 518 is in contact with the top and one of the
rollers 518 is in contact with the bottom) of the workpiece such
that as the workpiece is fed through the continuous line
fabrication process, the workpiece passes between the rollers 518.
The rollers 518 can be cooled to thereby cool the workpiece as the
workpiece passes between the rollers 518. Temperature and pressure
parameters for this step were provided above. Thus, in this
exemplary embodiment, the rollers 518 at this stage of the
continuous line process are configured to simultaneously 1) cool
the workpiece and 2) apply pressure to both sides of the
workpiece.
[0138] As described in conjunction with the description of step 222
of FIG. 2, above, following deposition of the S/Se onto the
workpiece final anneal is performed. Temperature and pressure
parameters for this step were provided above. As with the heating
steps described above, pressure is applied to the workpiece while
the workpiece is heated during this final annealing step. In the
exemplary embodiment shown in FIG. 5B, this heating and
simultaneous application of pressure to the workpiece is performed
via rollers 520 that are in contact with opposing sides (i.e., one
of the rollers 520 is in contact with the top and one of the
rollers 520 is in contact with the bottom) of the workpiece such
that as the workpiece is fed through the continuous line
fabrication process, the workpiece passes between the rollers 520.
The rollers 520 can be heated to thereby heat the workpiece as the
workpiece passes between the rollers 520. Thus, in this exemplary
embodiment, the rollers 520 at this stage of the continuous line
process are configured to simultaneously 1) heat the workpiece and
2) apply pressure to both sides of the workpiece.
[0139] As shown in FIG. 5B, this final anneal is conducted in a S
environment. By way of example only, the workpiece may be fed (in a
continuous line fashion) into a sulfurization annealing chamber.
The final output is a CIGS panel.
[0140] FIG. 6 is an exemplary drive system for turning the rollers
and thereby advancing the workpiece throughout the present
continuous-line processing apparatus. As provided above, this drive
system may be implemented in any of the apparatus embodiments shown
and described above. As shown in FIG. 6, the drive system includes
a first roller 602 that is motor-driven. For illustrative purposes,
the first roller 602 is shown to be turning in a clockwise
direction. The first roller 602 is in physical contact with one
(i.e., roller 604) of a set of rollers. By turning in a clockwise
direction, the roller 602 turns the roller 604 in a
counterclockwise direction. Both of the sets of rollers 604 and 606
are in physical contact with the workpiece 608. In having the
roller 604 turn in a counterclockwise direction, the workpiece 608
is advanced (from left to right in the depiction shown). Movement
of the workpiece turns the roller 606 in a clockwise direction. As
provided above, the sets of rollers (in this case roller 604 and
roller 606, also serve to apply pressure to the workpiece,
heat/cool the workpiece, and apply film material to the workpiece.
The function of applying pressure (also termed "roll-to-roll
pressure--since the pressure is being applied by the two rollers
between which the workpiece passes) is now described.
[0141] According to one exemplary embodiment, the rollers are
constructed of metal and the pressure applied to the workpiece is
supplied based on the weight of the roller on the workpiece. For
instance, in the example shown in FIG. 6, the top roller 604 can be
configured to have a weight such that the force of roller 604 on
the workpiece against roller 606 provides the specified amount of
pressure (see above) on the workpiece. Accordingly, the size (i.e.,
diameter) of the top roller can be configured such that the roller
has a certain weight and thus applies the desired amount of
pressure to the workpiece. This is illustrated in FIG. 6 where the
size (i.e., diameter) of roller 604 is less than that of roller
606.
[0142] It is notable that while the drive system shown in FIG. 6
may be fitted to each set of rollers in the apparatus, this might
not be necessary as driving (e.g., only one or two sets of rollers)
may be sufficient to feed the workpiece through the apparatus.
According to an exemplary embodiment, only the first set of rollers
in the apparatus is powered (motor-driven).
[0143] In the examples provided above, deposition of the thin film
materials (e.g., Cu, In, Ga, S/Se, etc.) onto the rollers occurs
via electrodeposition and/or passage through a molten bath. Other
deposition processes may however be employed in accordance with the
present techniques. For instance, as shown in FIG. 7, a deposition
process, such as spraying, sputtering, and chemical vapor
deposition, may be used to deposit the thin film material 706 onto
roller 702, which in turn then transfers the material to a
substrate 708 under pressure and/or heating/cooling in the manner
described above. The rollers 702 and 704 depicted in FIG. 7
generally represent any of the above-described rollers used to
apply pressure and/or heat/cool the substrate during thin film
deposition. Similarly, the material 706 shown being deposited onto
the roller 702 in FIG. 7 generally represents any of the materials
described herein for use in the thin film solar cell fabrication
process according to the present techniques. The substrate 708
shown in FIG. 7 generally represents any of the (e.g., Mo-coated
glass, metal, etc.) substrates described herein which, depending on
the particular stage of production, may have one or more layers of
thin films already deposited thereon. It is further noted, that
combinations of the teachings provided herein can be implemented,
if so desired. For instance, one or more of the materials can be
deposited via the rollers using electrodeposition and/or transfer
from a molten bath (as provided above), and one or more other
materials can be deposited via the materials being sprayed, etc. on
the rollers (as shown in FIG. 7).
[0144] Alternatively, as shown in FIG. 8, one or more of the thin
film materials (e.g., Cu, In, Ga, S/Se, etc.--see above) can be
deposited directly onto a substrate and the above-described
pressure and/or heating/cooling applied via the rollers. The
rollers 802 and 804 depicted in FIG. 8 generally represent any of
the above-described rollers used to apply pressure and/or heat/cool
the substrate during thin film deposition. Similarly, the material
806 shown being deposited onto the substrate 808 in FIG. 8
generally represents any of the materials described herein for use
in the thin film solar cell fabrication process according to the
present techniques. The substrate 808 shown in FIG. 8 generally
represents any of the (e.g., Mo-coated glass, metal, etc.)
substrates described herein which, depending on the particular
stage of production, may have one or more layers of thin films
already deposited thereon. In this example, any suitable deposition
process can be used to deposit the material onto the substrate,
including but not limited to spraying, sputtering, and chemical
vapor deposition. Further, as shown in FIG. 8, since the rollers
will be used to apply pressure, heat, etc., then the material
should be deposited onto the substrate prior to the substrate
passing between the rollers.
[0145] The thin film materials described above are examples
provided merely to illustrate the present techniques, and a variety
of other film compositions can be achieved in the same manner
described herein. One would need only to vary the composition of
the materials deposited in one or more of the steps and/or the
order in which the materials are deposited in order to achieve
different solar cell (or any other device) configurations. By way
of example only, one may adapt the present techniques to produce
any of the following thin film solar cell compositions: CIGS, CZTS
(Cu.sub.2ZnSn(Se,S).sub.4), FeS.sub.2, Zn.sub.2P.sub.3, CdSe, CdS,
ZnSe, WSe.sub.2, MoSe.sub.2, Bi.sub.2S.sub.3, Ag.sub.2S,
Cu.sub.2Zn(Fe,Sn)(Se,S).sub.4, CuxS, CdTe, ZnTe, PbSe, PdS, NiS,
NiSeS, InP, ZnO, GaAs.
[0146] For instance, in one exemplary implementation of the present
techniques, a I-III-IV2 thin film solar cell is produced. As is
known in the art, a I-III-IV2 material includes at least one from
group I element, at least one group III element, and at least one
group IV element. By way of example only, some I-III-IV.sub.2
materials include, but are not limited to, CuAlGe.sub.2,
CuGaGe.sub.2, CuAlSn.sub.2, and CuGaSn.sub.2. Using CuGaSn.sub.2 as
an example, the present techniques can be employed to deposit Cu to
the substrate, followed by Ga, and finally tin (Sn) all while
pressure is applied via the rollers in the manner described
above.
[0147] Although illustrative embodiments of the present invention
have been described herein, it is to be understood that the
invention is not limited to those precise embodiments, and that
various other changes and modifications may be made by one skilled
in the art without departing from the scope of the invention.
* * * * *