U.S. patent application number 12/761240 was filed with the patent office on 2010-10-21 for reel-to-reel plating of conductive grids for flexible thin film solar cells.
This patent application is currently assigned to SOLOPOWER, INC.. Invention is credited to Bulent M. Basol.
Application Number | 20100264035 12/761240 |
Document ID | / |
Family ID | 42980185 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100264035 |
Kind Code |
A1 |
Basol; Bulent M. |
October 21, 2010 |
REEL-TO-REEL PLATING OF CONDUCTIVE GRIDS FOR FLEXIBLE THIN FILM
SOLAR CELLS
Abstract
The present inventions provide structures and methods for
manufacturing high electrical conductivity grid patterns having
minimum shadowing effect on the illuminated side of the solar
cells. In a particular aspect, a width of an effective channel
region is greater than a spacing that exists between conductive
elements in adjacent grid patterns that exist along a lengthwise
direction of a continuous workpiece.
Inventors: |
Basol; Bulent M.; (Manhattan
Beach, CA) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
SOLOPOWER, INC.
San Jose
CA
|
Family ID: |
42980185 |
Appl. No.: |
12/761240 |
Filed: |
April 15, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61169673 |
Apr 15, 2009 |
|
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|
Current U.S.
Class: |
205/122 |
Current CPC
Class: |
H01L 31/0749 20130101;
Y02P 70/50 20151101; Y02P 70/521 20151101; Y02E 10/541 20130101;
H01L 31/022425 20130101; H01L 31/03928 20130101; C25D 17/001
20130101; C25D 7/0657 20130101; C25D 5/02 20130101; C25D 5/06
20130101; H01L 31/206 20130101 |
Class at
Publication: |
205/122 |
International
Class: |
C25D 5/02 20060101
C25D005/02; C25D 7/00 20060101 C25D007/00 |
Claims
1. A method of roll to roll manufacturing low electrical
resistivity conductive grids having reduced shading effect for
solar cells, comprising: providing a flexible continuous workpiece,
the flexible continuous workpiece comprising a continuous flexible
substrate, a bottom contact layer disposed atop the continuous
flexible substrate, an absorber layer disposed atop the bottom
contact layer, a transparent conductive layer disposed atop the
absorber layer, and a first conductive film having a first
resistivity disposed atop predetermined areas of a top surface of
the transparent conductive layer and in electrical communication
with the transparent conductive layer to form a raised grid pattern
along a length of the flexible continuous workpiece, wherein the
raised grid pattern includes a plurality of adjacent grids, with
each grid having a predetermined grid width, a predetermined grid
length, and a predetermined spacing between adjacent grids along
the length direction of the flexible continuous workpiece, wherein
a sheet resistance of the first conductive film is less than the
sheet resistance of the transparent conductive layer, and wherein
the top surface of the transparent conductive layer and the raised
grid pattern disposed thereon form a front surface of the flexible
continuous workpiece; applying an electrodeposition solution onto
an effective plating region established on a portion of the front
surface, including a part of the first conductive film, and onto an
anode placed across from the portion of the front surface, the
effective plating region having a length that is substantially the
same as a width of the workpiece and a predetermined width that is
at least longer than the predetermined spacing between adjacent
grids; applying a voltage between the anode and the part of the
first conductive film; selectively electrodepositing a conductive
material from the electrodeposition solution onto the first
conductive film and not the transparent conductive layer to form a
second conductive film having a second resistivity atop the first
conductive film, thereby forming the low electrical resistivity
conductive grids having reduced shading effect, wherein the first
resistivity is greater than the second resistivity; and moving the
front surface, including the part of the first conductive film,
through the effective plating region, during the steps of applying
the electrodeposition solution, applying the voltage, and
selectively electrodepositing.
2. The method of claim 1, wherein each grid includes fingers
disposed parallel to the flexible continuous workpiece edges
extending along the length of the flexible continuous
workpiece.
3. The method of claim 2, wherein in the step of moving, portions
of the flexible continuous workpiece are continuously advanced into
a front side of the effective plating region and through the
effective plating region to form the second conductive film and
then continuously advanced out of the effective plating region
through a back side of the effective plating region after forming
the second conductive film.
4. The method of claim 3 wherein the step of selectively
electrodepositing includes applying a first electrical contact
adjacent the front side of the effective plating region and a
second electrical contact adjacent the back side of the effective
plating region, wherein a distance between the first and second
contacts is less than or equal to the length of each of the
fingers.
5. The method of claim 4, wherein in the step of moving the
portions of the flexible continuous workpiece are released from a
supply roll of the flexible continuous workpiece and wound as a
receiving roll when advanced out of the -effective plating
region.
6. The method of claim 4, wherein the first and the second contacts
are conductive roll contacts rolling on the front surface as the
flexible continuous workpiece is advanced.
7. The method of claim 4, wherein the first and the second contacts
are conductive brush contacts sweeping the front surface as the
flexible continuous workpiece is advanced.
8. The method of claim 1, wherein the first resistivity of the
first conductive film is in the range of 10-30 micro ohm-cm, the
second resistivity of the second conductor is in the range of 2-10
micro ohm-cm, and the resistivity of the transparent conductive
layer is in the range of 200-500 micro ohm-cm.
9. The method of claim 1, wherein the first conductive film
includes a silver (Ag) based conductive material formed using one
of a screen printing process and an ink jet printing process.
10. The method of claim 1, wherein the second conductive film
includes one of copper, silver, a copper alloy and a silver
alloy.
11. The method of claim 1, wherein the transparent conductive layer
includes a stack including a transparent buffer layer deposited
over the absorber layer and a transparent conductive oxide (TCO)
layer deposited over the transparent buffer layer, and wherein the
transparent buffer layer includes one of CdS and ZnS, and the TCO
layer includes one of ZnO and indium tin oxide (ITO).
12. The method of claim 1, wherein the absorber layer includes a
group IBIIIAVIA compound semiconductor.
13. The method of claim 1, wherein the substrate includes one of a
stainless steel foil and an aluminum foil.
14. The method of claim 1, wherein the bottom contact layer
includes at least one of Mo, W, Ta, Ti, Cr and Ru materials.
15. The method of claim 1, wherein the effective plating region is
defined by an enclosure including a front wall and a back wall
extending along the length of the effective plating region and two
side walls extending along the width of the effective plating
region.
16. The method of claim 15, wherein the flexible continuous
workpiece enters the effective plating region through an entrance
opening the in the front wall and exits the effective plating
region through an exit opening in the back wall.
17. The method of claim 16, wherein the electrodeposition solution
is delivered through a top opening of the enclosure and used
electrodeposition solution flows out of the enclosure through at
least one of the entrance and exit openings.
18. The method of claim 5, wherein the effective plating region is
defined by an enclosure including a front wall and a back wall
extending along the length of the effective plating region and two
side walls extending along the width of the effective plating
region, wherein the front and the back walls forms the front and
back sides of the effective plating region, respectively.
19. The method of claim 18, wherein the electrodeposition solution
is delivered through a top opening of the enclosure and used
electrodeposition solution flows out of the enclosure through at
least one of the entrance and exit openings.
20. The method of claim 19, wherein the first and the second
contacts are conductive roll contacts rolling on the front surface
as the flexible continuous workpiece is advanced.
21. The method of claim 19, wherein the first and the second
contacts are conductive brush contacts sweeping the front surface
as the flexible continuous workpiece is advanced.
22. The method of claim 1, wherein the thickness of the first
conductive film is in the range of 1-10 microns.
23. The method of claim 1, wherein the thickness of the second
conductive film is in the range of 1-5 microns.
24. The method of claim 1, wherein the thickness of the transparent
conductive layer is in the range of 0.1-0.5 microns.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Application No: 61/169673 filed Apr. 15, 2009 entitled "Reel to
Reel Plating of Conductive Grids for Flexible Thin Film Solar
Cells", the entirety of which is incorporated herein by
reference.
BACKGROUND
[0002] 1. Field of the Inventions
[0003] The present inventions generally relate to solar cell
fabrication and, more particularly, to fabrication of flexible thin
film solar cells.
[0004] 2. Description of the Related Art
[0005] Solar cells are photovoltaic devices that convert sunlight
directly into electrical power. The most common solar cell material
is silicon, which is in the form of single or polycrystalline
wafers. However, the cost of electricity generated using
silicon-based solar cells is higher than the cost of electricity
generated by the more traditional methods. Therefore, since early
1970's there has been an effort to reduce cost of solar cells for
terrestrial use. One way of reducing the cost of solar cells is to
develop low-cost thin film growth techniques that can deposit
solar-cell-quality absorber materials on large area substrates and
to fabricate these devices using high-throughput, low-cost
methods.
[0006] Group IBIIIAVIA compound semiconductors comprising some of
the Group IB (Cu, Ag, Au), Group IIIA (B, Al, Ga, In, Tl) and Group
VIA (O, S, Se, Te, Po) materials or elements of the periodic table
are excellent absorber materials for thin film solar cell
structures. Especially, compounds of Cu, In, Ga, Se and S which are
generally referred to as CIGS(S), or Cu(In,Ga)(S,Se).sub.2 or
CuIn.sub.1-xGa.sub.x (S.sub.ySe.sub.1-y).sub.k, where
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1 and k is approximately 2,
have already been employed in solar cell structures that yielded
conversion efficiencies approaching 20%. It should be noted that
the notation "Cu(X,Y)" in the chemical formula means all chemical
compositions of X and Y from (X=0% and Y=100%) to (X=100% and
Y=0%). For example, Cu(In,Ga) means all compositions from CuIn to
CuGa. Similarly, Cu(In,Ga)(S,Se).sub.2 means the whole family of
compounds with Ga/(Ga+In) molar ratio varying from 0 to 1, and
Se/(Se+S) molar ratio varying from 0 to 1.
[0007] The structure of a conventional Group IBIIIAVIA compound
photovoltaic cell such as a Cu(In,Ga,Al)(S,Se,Te).sub.2 thin film
solar cell is shown in FIG. 1A. A photovoltaic cell 10 is
fabricated on a substrate 11, such as a sheet of glass, a sheet of
metal, an insulating foil or web, or a conductive foil or web. An
absorber film 12, which comprises a material in the family of
Cu(In,Ga,Al)(S,Se,Te).sub.2, is grown over a conductive layer 13 or
contact layer, which is previously deposited on the substrate 11
and which acts as the electrical contact to the device. The
substrate 11 and the conductive layer 13 form a base 20 on which
the absorber film 12 is formed. Various conductive layers
comprising Mo, Ta, W, Ti, and their nitrides have been used in the
solar cell structure of FIG. 1A. If the substrate itself is a
properly selected conductive material, it is possible not to use
the conductive layer 13, since the substrate 11 may then be used as
the ohmic contact to the device. After the absorber film 12 is
grown, a transparent conductive layer 14 such as a CdS, ZnO,
CdS/ZnO or CdS/ZnO/ITO stack is formed on the absorber film 12.
Radiation 15 enters the device through the transparent conductive
layer 14. As shown in FIG. 1B in top view, metallic grids 30 may
also be deposited over top surface 16 of the transparent layer 14
to reduce the effective series resistance of the device. The top
surface 16 forms the illuminated surface of the solar cell 10. The
preferred electrical type of the absorber film 12 is p-type, and
the preferred electrical type of the transparent conductive layer
14 is n-type. However, an n-type absorber and a p-type window layer
can also be utilized. The preferred device structure of FIG. 1A is
called a "substrate-type" structure. A "superstrate-type" structure
can also be constructed by depositing a transparent conductive
layer on a transparent superstrate such as glass or transparent
polymeric foil, and then depositing the Cu(In,Ga,Al)(S,Se,Te).sub.2
absorber film, and finally forming an ohmic contact to the device
by a conductive layer. In this superstrate structure light enters
the device from the transparent superstrate side.
[0008] If the substrate 11 of the CIGS(S) type cell shown in FIG.
1A is a metallic foil, then under illumination, a positive voltage
develops on the substrate 11 with respect to the transparent layer
14. In other words, an electrical wire (not shown) that may be
attached to the substrate 11 would constitute the (+) terminal of
the solar cell 10 and a lead (not shown) that may be connected to
the metallic grid 30 would constitute the (-) terminal of the solar
cell.
[0009] After fabrication, individual solar cells are typically
assembled into solar cell strings or circuits by interconnecting
them in series electrically, i.e. by connecting the (+) terminal of
one cell to the (-) terminal of a neighboring cell. This way the
total voltage of the solar cell circuit is increased. The solar
cell circuit is then laminated into a protective package to form a
photovoltaic module.
[0010] As shown in FIG. 1B the metallic grid 30 or the grid pattern
is deposited on the illuminated side of the solar cell device and
includes one or more busbars 32 and multiple fingers 34 to carry
the current from various parts of the device to the busbars 32.
Busbars 32 and fingers 30 generally comprise metals with low
electrical resistivity such as silver or silver alloys, which can
be ink-deposited or screen printed over the illuminated surfaces
using silver-based inks or pastes.
[0011] Although the low electrical resistivity of such materials
plays an important role in their choice, in operation, there is a
trade off relationship between their size, i.e. height and width,
and their electrical resistance, which critically depends on the
cross sectional area of the fingers and the busbars. Since the
fingers are spread over the illuminated surface, in order to reduce
the shadowing effect caused by their presence on the illuminated
surface, their width needs to be minimized while their height needs
to be maximized to keep the cross sectional area high and therefore
the resistance low. However, in ink deposition or screen printing
approaches, when the width of the finger is reduced to minimize the
shadowing loss, the height of the finger also gets reduced due to
the nature of these processes and the nature of the inks and pastes
used. Therefore, for narrow fingers the cross sectional area gets
reduced and the resistance of the finger increases causing the
overall efficiency of the solar cell to go down despite the fact
that more light enters the device. It should be noted that
resistivity and bulk resistivity mean the same in this application
and they have the units of "ohm-cm". Sheet resistance of a layer is
defined as the resistivity of the material making up the layer
divided by the thickness of the layer and has the units of "ohms
per square". The resistance of a conductive line, which has the
units of "ohms" is equal to the resistivity of the material making
up the line times the length divided by the cross sectional area of
the line.
[0012] From the foregoing, there is a need in the thin film solar
cell industry for improved grid structures and manufacturing
methods that allows fabrication of narrow fingers with low
resistance so that the conversion efficiency of the solar cells may
be improved.
SUMMARY
[0013] The present inventions provide structures and methods for
manufacturing high electrical conductivity grid patterns having
minimum shadowing effect on the illuminated side of the solar
cells.
[0014] In a particular aspect, a width of an effective channel
region is greater than a spacing that exists between conductive
elements in a adjacent grid patterns that exist along a lengthwise
direction of a continuous workpiece.
[0015] In a preferred aspect there is described a method of roll to
roll manufacturing low electrical resistivity conductive grids
having reduced shading effect for solar cells, comprising:
providing a flexible continuous workpiece, the flexible continuous
workpiece comprising a continuous flexible substrate, a bottom
contact layer disposed atop the continuous flexible substrate, an
absorber layer disposed atop the bottom contact layer, a
transparent conductive layer disposed atop the absorber layer, and
a first conductive film having a first resistivity disposed atop
predetermined areas of a top surface of the transparent conductive
layer and in electrical communication with the transparent
conductive layer to form a raised grid pattern along a length of
the flexible continuous workpiece, wherein the raised grid pattern
includes a plurality of adjacent grids, with each grid having a
predetermined grid width, a predetermined grid length, and a
predetermined spacing between adjacent grids along the length
direction of the flexible continuous workpiece, wherein a sheet
resistance of the first conductive film is less than the sheet
resistance of the transparent conductive layer, and wherein the top
surface of the transparent conductive layer and the raised grid
pattern disposed thereon form a front surface of the flexible
continuous workpiece; applying an electrodeposition solution onto
an effective plating region established on a portion of the front
surface, including a part of the first conductive film, and onto an
anode placed across from the portion of the front surface, the
effective plating region having a length that is substantially the
same as a width of the workpiece and a predetermined width that is
at least longer than the predetermined spacing between adjacent
grids; applying a voltage between the anode and the part of the
first conductive film; selectively electrodepositing a conductive
material from the electrodeposition solution onto the first
conductive film and not the transparent conductive layer to form a
second conductive film having a second resistivity atop the first
conductive film, thereby forming the low electrical resistivity
conductive grids having reduced shading effect, wherein the first
resistivity is greater than the second resistivity; and moving the
front surface, including the part of the first conductive film,
through the effective plating region, during the steps of applying
the electrodeposition solution, applying the voltage, and
selectively electrodepositing.
[0016] These and other aspects and advantages are described further
herein
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1A is a side schematic view of a solar cell of the
prior art;
[0018] FIG. 1B is a top schematic view of the solar cell with a
conductive grid over the top surface;
[0019] FIG. 2 is a perspective depiction of a reel to reel
electroplating system processing a workpiece to form a raised
conductive grid according to a preferred embodiment;
[0020] FIG. 3 is a schematic side view of a portion of a solar cell
structure including a raised conductive grid formed on the
transparent conductive layer;
[0021] FIG. 4 is a schematic view of a top portion of the
workpiece; and
[0022] FIG. 5A is schematic side view of an electroplating
apparatus of the electroplating system;
[0023] FIG. 5B is schematic frontal view of the electroplating
apparatus; and
[0024] FIG. 5C is schematic top view of the electroplating
apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Described herein are methods and apparatus to form low
electrical resistance grid patterns over illuminated side of
photovoltaic cells or solar cells. In one embodiment, initially a
conductive grid pattern is formed, preferably by a screen printing
or ink deposition technique, over a transparent conductive layer of
a solar cell structure. In the following step, a conductive
material is selectively electroplated over the conductive grid
pattern using the electroplating apparatus. The electroplated
conductive material increases the height of the conductive grid
pattern and reduces its electrical resistance. It should be noted
that the resistivity of an electroplated conductor such as
electroplated Cu or Ag is lower than the resistivity of screen
printed or ink deposited conductors such as Ag pastes.
[0026] FIG. 2 shows a depiction of a roll to roll or reel to reel
electrodeposition system 100 to selectively deposit a conductor
onto a first conductive film 102 shaped as a plurality of grid
patterns formed on a front surface 104A at a front side 101A of a
workpiece 105, with only those components necessary of this
description to be understood illustrated, and it being understood
that the actual roll to roll or reel to reel electrodeposition
system 100 will have additional components therein. The conductor
material may include silver or silver alloy or another low
electrical resistance material. Each grid pattern may form a top
terminal of a solar cell after the electroplating step and after
cutting individual solar cells out of the workpiece. The first
conductive film includes a conductive metal such as silver or a
silver alloy or compound which may be deposited by techniques such
as screen printing and ink jet printing. During the process, the
work piece 105 is advanced from a supply spool 106A in a process
direction `P`, passed through a deposition unit 108 and wrapped
around a receiving spool 106B. The conductor is electrodeposited on
the first conductive film 102 as the workpiece 105 is passed
through the deposition unit 108. Both the electrodeposited
conductive material and the first conductive film 102 underneath,
form a raised conductive film 110 having the shape of the grid
patterns, which will be called final grid patterns hereinafter.
During the process a back side 101B of the workpiece 105 of the
workpiece is supported by various support means such as support
plates or rollers.
[0027] FIG. 3 shows a detailed cross sectional view of an exemplary
portion of the workpiece 105 (FIG. 2) after the electrodeposition
process. As shown in FIG. 3, the conductor deposited by the
electrodeposition process forms a second conductive film 103 on the
first conductive film 102. Therefore, the raised conductive film
110 comprises the first conductive film 102 deposited on the front
surface 104A of the workpiece 105 and the second conductive film
103 selectively deposited on the first conductive film 102. As
mentioned above, each grid pattern on the front side 101A of the
workpiece 105 forms a top terminal for the future solar cells.
Accordingly, the layers under each grid pattern form the structural
components of the future solar cells as well. In this respect, the
front surface 104A includes the surface of a transparent conductive
layer 112, such as a buffer-layer/TCO stack, formed on an absorber
layer 114 which may be a Group IBIIIAVIA absorber layer such as a
CIGS absorber layer. TCO stands for transparent conductive oxide
such as a ZnO layer, an indium tin oxide (ITO) layer or a stack
comprising both ZnO and ITO. An exemplary buffer layer may be a
(Cd, Zn)S layer. The absorber layer 114 is formed on a base 115
including a flexible substrate 118 and contact layer 116 formed on
the flexible substrate 118. A preferred flexible substrate material
may be a metallic material such as stainless steel, aluminum (Al)
or the like. An exemplary contact layer material may comprise
molybdenum (Mo).
[0028] FIG. 4 shows a portion of the front side 101A of the
workpiece 105 during an instant of the electroplating process. The
portion of the front side 101A includes the grid patterns of the
first conductive film 102 and a final grid pattern of the raised
conductive film 110 located at both sides of an effective plating
region 120 in which the workpiece 105 is advanced so that the grid
patterns of first conductive film 102 are selectively electroplated
with the conductor to form the grid patterns of raised conductive
film 110 or the final grid patterns. As will be described below the
effective plating region 120 is an area that an electrodeposition
device (see FIGS. 5A-5C) in a preferred embodiment can deposit the
conductor on the grid patterns of the first conductive film 102 as
they moved through the effective area 120, thus forming the final
grid patterns.
[0029] As shown in FIG. 4, each grid pattern of the first
conductive layer 102 includes busbars 122 and fingers 124. After
electrodepositing the conductor within the effective plating region
120, the busbars 122 become raised busbars 123 and the fingers 124
become raised fingers 125, both the raised busbars and fingers
forming the final grid pattern. As will be appreciated, the raised
busbars 123 and the raised fingers 125 comprise the first
conductive film 102 and the second conductive film 103. It is
critical that, in order to electrodeposit the conductor onto the
first conductive film 102, the sheet resistance of the first
conductive film 102 must be less than the sheet resistance of the
front surface 104A which is the surface of the transparent
conductive layer 112. The sheet resistance of the first conductive
film 102 deposited in the form of a finger pattern on the
transparent conductive layer 112 is less than about one tenth,
preferably less than about one hundredth of the sheet resistance of
the transparent conductive layer, which is typically in the range
of 5-20 ohms per square.
[0030] The width `W` of the effective plating region is greater
than the distance `d` between the grid patterns of the first
conductive film 102. This way it is assured that a portion of the
first conductive film 102 or a portion of the already plated grid
pattern is always in the effective plating region 120. Since the
resistances of the first and second conductive films 102 and 103
are much lower than that of the transparent conductive layer 112,
the plating current preferentially passes through the fingers 124
and/or the raised fingers 125, depositing material there rather
than on the transparent conductive layer. It should be noted that
the bulk resistivity of the Ag-based material forming the first
conductive film 102 is in the range of 10-30 micro-ohm-cm, whereas
the resistivity of materials forming the transparent conductive
layer 112 (FIG. 3) is in the range of 200-500 micro-ohm-cm.
Furthermore the thickness of the first conductive film 102 is in
the range of 1-10 microns, whereas the thickness of the transparent
conductive layer 112 is typically in the range of 0.1-0.5 microns.
As a result, the sheet resistance of the transparent conductive
layer 112 is typically 100-5000 times larger than the sheet
resistance of the first conductive layer. This differential
facilitates the preferential plating on the first conductive layer
102 if there is, at all times, a section of the grid pattern within
the effective plating region 120 and there is at least one
electrical contact made to that grid pattern as will be further
described. It should also be noted that the electroplated conductor
or the second conductive film 103 typically has a very low
resistivity in the range of 2-10 micro-ohm-cm, and therefore its
thickness can be lower than the thickness of the first conductive
film 102. For example, the thickness of the second conductive film
103 may be in the range of 1-5 microns.
[0031] FIGS. 5A, 5B and 5C show in side, top and front view,
respectively, an electrodeposition apparatus 130 through which the
workpiece 105 is advanced in the process direction `P`, during the
electrodeposition process. A support member 131, such as a plate or
a series of rollers, mechanically supports the workpiece portion
that is being processed by the apparatus 130. As shown in FIG. 5A,
the electrodeposition process applied by the apparatus 130 forms
the raised fingers 125 from the fingers 124 by electrodepositing
the conductive material onto the fingers 124, and thereby
increasing its thickness and conductivity, while the workpiece 105
is advanced. The electrodeposition apparatus 130 is located in the
deposition unit 108 of the electrodeposition system 100 shown in
FIG. 2. As its components shown in FIGS. 5A and 5C, the
electrodeposition apparatus 130 includes an electrodeposition cell
132, surface contacts 134 and a power supply 138. The
electrodeposition cell 132 includes a substantially rectangular
chamber 140 (see FIG. 5C) including long side walls 142A and 142B
and short side walls 142C and 142D. The long side walls 142A and
142B extend along the width of the workpiece 105 and are separated
by the distance `W` which is also the width of effective plating
region 120 shown in FIG. 5C and also in FIG. 4 in this embodiment.
Adjacent the lower ends of the long side walls 142A and 142B, an
entrance opening 149A and an exit opening 149B are located
respectively. The short side walls 142C and 142D which are parallel
to the edges of the workpiece 105 complete the rectangular chamber
140 which retains an electrodeposition electrolyte 146 and an
electrode 148 or anode immersed into the electrolyte 146. FIG. 5B
shows in front view the long side wall 142A, the entrance opening
149A and the position of the workpiece 105 entering through the
entrance opening 149A of the electrodeposition cell 132 as the
workpiece is advanced in the process direction `P`. As shown in
FIGS. 5A and 5C, during the process the workpiece 105 enters the
electrodeposition cell 132 through the entrance opening 149A and
leaves the electrodeposition cell through the exit opening 149B
while being supported by the support 131. In a preferred
embodiment, a sufficient amount of the electrolyte 146 is
maintained in the chamber 140 by being continuously or periodically
filled from the top of the chamber 140 at an overall rate that
accounts for the removal of the electrolyte 146 through the
entrance and exit slits 147A and 149A, although it will be
understood that other arrangements could be used to maintain the
environment necessary for the electrodeposition to occur.
[0032] As the workpiece 105 is advanced through the
electrodeposition cell 132, the electrodeposition electrolyte 146
flows towards the front side 101A of the workpiece 105, contacts it
and flows out of both the entrance opening 149A and the exit
opening 149B. The electrolyte 146 is pumped into the chamber 140
from an electrolyte supply tank (not shown) and the used
electrolyte leaves the cell through the entrance opening 149A and
the exit opening 149B. This used electrolyte may be flowed into a
recycling tank (not shown) to filter and replenish it. The
replenished electrolyte is then redirected into the
electrodeposition cell 132 or the electrolyte supply tank (not
shown). In this embodiment, the side walls 142A and 142B of the
rectangular chamber 140 and the edges of workpiece as they pass
through the plating chamber define the effective plating region
120.
[0033] The surface contacts 134 may be made of conductive rollers
or brushes which negatively polarize the surface 104A and the first
conductive film 102 which is shown as the finger 124 in FIG. 5. As
shown in FIGS. 5A and 5C, there may be at least two surface
contacts positioned at both sides of the cell 132 and they may
extend along the width of the workpiece 105. If the surface
contacts are made of conductive rollers, they roll on the surface
as the workpiece travels. The anode electrode 148 and the surface
contacts 134 are electrically connected to a positive and negative
terminals of the power supply 130, respectively.
[0034] As can be seen in FIGS. 5A and 5C, the effective plating
region 120 defined by the distance `W` between the long side walls
142A, 142B and the edges of the workpiece within the
electrodeposition cell 132 and thus the electrodeposition occurs in
this region. As shown, the distance W is kept greater than the
distance `d` between the grids of the first conductive layer so as
to leave at least a portion of the finger 124 or the raised finger
125 within the effective plating region. Since the sheet resistance
of the finger 124 is lower than the sheet resistance of the surface
104A, the conductive material only deposits onto the fingers.
Referring to FIG. 4 and FIGS. 5A and 5C, position of the surface
contacts 134 is also predetermined depending on the length `L` of
the grid pattern so that at least one of the surface contacts 134
stays on the grid patterns. Further, the distance between the
surface contacts should be less than or equal to the length of the
fingers so that when a portion of a finger is in the effective
plating region that particular finger is always contacted at least
one surface contact outside the effective plating region.
[0035] Therefore, in one embodiment a finger plating or grid
plating method comprises the steps of: i) providing a continuous
flexible workpiece with two edges and a width, the workpiece
comprising multiple solar cell structures on its front surface,
each solar cell structure having a conductive grid pattern with
fingers which are parallel to the two edges of the workpiece, ii)
applying an electrodeposition solution onto an effective plating
region on the front surface of the workpiece and onto an anode
placed across from the front surface of the workpiece, the
effective plating region having a length that is substantially the
same as the width of the workpiece and a predetermined width that
is larger than a distance between the grid patterns of adjacent
solar cell structures, iii) applying a voltage between the anode
and two contacts that touch the front surface of the workpiece
while moving the workpiece and the effective plating region with
respect to each other and in a direction that is substantially
parallel to the fingers of the grid patterns thus causing
electrodeposition of a conductive material from the
electrodeposition solution onto the conductive grid patterns of
solar cell structures, wherein the two contacts are provided on two
sides of the effective plating region and a distance between the
two contacts is less than or equal to the total length of each of
the fingers of the grid patterns.
[0036] Although the present inventions are described with respect
to certain preferred embodiments, modifications thereto will be
apparent to those skilled in the art.
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