U.S. patent application number 12/290896 was filed with the patent office on 2009-04-30 for collector grid, electrode structures and interrconnect structures for photovoltaic arrays and methods of manufacture.
Invention is credited to Daniel Luch.
Application Number | 20090111206 12/290896 |
Document ID | / |
Family ID | 46332042 |
Filed Date | 2009-04-30 |
United States Patent
Application |
20090111206 |
Kind Code |
A1 |
Luch; Daniel |
April 30, 2009 |
Collector grid, electrode structures and interrconnect structures
for photovoltaic arrays and methods of manufacture
Abstract
The invention teaches novel structure and methods for producing
electrical current collectors and electrical interconnection
structure. Such articles find particular use in facile production
of modular arrays of photovoltaic cells. The current collector and
interconnecting structures may be initially produced separately
from the photovoltaic cells thereby allowing the use of unique
materials and manufacture. Subsequent combination of the structures
with photovoltaic cells allows facile and efficient completion of
modular arrays. Methods for combining the collector and
interconnection structures with cells and final interconnecting
into modular arrays are taught
Inventors: |
Luch; Daniel; (Morgan Hill,
CA) |
Correspondence
Address: |
Daniel Luch
17161 Copper Hill Drive
Morgan Hill
CA
95037
US
|
Family ID: |
46332042 |
Appl. No.: |
12/290896 |
Filed: |
November 5, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11824047 |
Jun 30, 2007 |
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12290896 |
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11404168 |
Apr 13, 2006 |
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11824047 |
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10776480 |
Feb 11, 2004 |
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11404168 |
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10682093 |
Oct 8, 2003 |
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10776480 |
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10186546 |
Jul 1, 2002 |
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10682093 |
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09528086 |
Mar 17, 2000 |
6414235 |
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10186546 |
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09281656 |
Mar 30, 1999 |
6239352 |
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09528086 |
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Current U.S.
Class: |
438/59 ;
257/E21.514 |
Current CPC
Class: |
H01L 31/0463 20141201;
H01L 31/0465 20141201; H01L 31/0504 20130101; H01L 31/022425
20130101; H01L 31/046 20141201; H01L 31/02008 20130101; Y02E 10/50
20130101 |
Class at
Publication: |
438/59 ;
257/E21.514 |
International
Class: |
H01L 21/04 20060101
H01L021/04 |
Claims
1. A method of manufacture of an article combining a photovoltaic
cell structure and a current collector structure suitable for
collecting current from light incident surfaces of photovoltaic
cells, said method comprising the steps of, providing a
photovoltaic cell structure having semiconductor material
positioned between a top light incident cell surface and bottom
cell surface, providing current collector structure, said current
collector structure comprising a flexible, polymer based sheetlike
substrate having a first surface and a second surface and
comprising a pattern of electrically conductive material supported
by said substrate and positioned over said first surface, said
current collector structure being manufactured separately and
distinctly from said cell structure, combining a portion of said
current collector structure and said cell structure such that said
first substrate surface of said collector structure portion and
said top light incident surface of said cell structure face each
other and said pattern of conductive material associated with said
collector structure portion extends over and is in electrical
contact with a preponderance of said top light incident cell
surface.
2. The method of claim 1 wherein said current collector structure
is supplied to said combining step in a form wherein said substrate
is characterized as continuous.
3. The method of claim 2 wherein said photovoltaic cell structure
is supplied to said combining step as a continuous form.
4. The method of claim 1 wherein said combining step comprises
lamination of said current collector structure portion to said
light incident cell surface.
5. The method of claim 2 wherein said combining step is
characterized as roll-to-roll processing.
6. A method of manufacture of an article combining a photovoltaic
cell structure and a current collector structure suitable for
collecting current from light incident surfaces of photovoltaic
cells, said method comprising the steps of, providing a
photovoltaic cell structure having a light incident surface,
providing a separately prepared current collector structure, said
current collector structure comprising a sheetlike substrate having
a first surface and a pattern of electrically conductive material
extending over said first surface, said current collector structure
being initially separate and distinct from said photovoltaic cell
structure, combining said photovoltaic cell structure and a portion
of said current collector structure such that said light incident
surface of said cell structure and said first substrate surface of
said collector structure portion not covered by said conductive
material face each other and are adhesively bonded to each other,
and said pattern of electrically conductive material associated
with said collector structure portion is in electrical contact with
said light incident surface.
7. The method of claim 6 wherein said light incident surface of
said cell portion has substantially uniform composition.
9. The method of claim 6 wherein said first surface is formed by a
polymer based adhesive.
10. The method of claim 6 wherein said pattern of electrically
conductive material associated with said collector structure
portion extends over a preponderance of said light incident surface
of said cell structure.
11. The method of claim 6 wherein said sheetlike substrate
comprises multiple layers.
12. The method of claim 6 wherein said sheetlike substrate
comprises a layer of glass.
13. The method of claim 11 wherein said sheetlike substrate
comprises multiple polymer based layers.
14. The method of claim 6 wherein said sheetlike substrate is
flexible.
15. The method of claim 6 wherein said photovoltaic cell structure
comprises thin film semiconductor material.
16. The method of claim 6 wherein said pattern of electrically
conductive material comprises an electrically conductive adhesive
to adhesively bond portions of said material to said light incident
surface.
17. The method of claim 6 wherein said pattern of electrically
conductive material has surface portions formed by a low melting
point metal-based material.
18. The method of claim 17 wherein said low melting point
metal-based material comprises Indium.
19. A method of manufacture of an article combining a photovoltaic
cell structure and a current collector structure suitable for
collecting current from light incident surfaces of photovoltaic
cells, said method comprising the steps of, providing a separately
prepared current collector structure, said current collector
structure comprising a flexible polymer based sheetlike substrate
having a first surface and comprising a pattern of electrically
conductive material extending over said first surface, said current
collector structure being initially separate and distinct from said
photovoltaic cell structure, applying photovoltaic cell structure
over at least a portion of said current collector structure, said
cell structure comprising a light incident surface, a back surface
and semiconductor material positioned between said light incident
and back surfaces, said application being such that a preponderance
of said light incident surface faces and is in electrical
communication with said pattern of conductive material associated
with said portion of current collector structure.
20. The method according to claim 19 wherein said current collector
structure provided has a form wherein said substrate is
characterized as continuous.
21. A method of manufacture of an article combining a photovoltaic
cell structure and a current collector structure suitable for
collecting current from light incident surfaces of photovoltaic
cells, said method comprising the steps of, providing a separately
prepared current collector structure, said current collector
structure comprising a transparent or translucent substrate having
a length dimension and having a first surface, said current
collector structure further comprising multiple distinctly
separated patterns of electrically conductive material supported on
said first surface, each of said patterns being elongate in said
length dimension and having a width dimension perpendicular to said
length dimension, said multiple patterns being repetitive in said
width dimension, said patterns being distinctly separated from each
other by a region of substrate absent conductive material extending
in said length dimension, positioning photovoltaic cell structures
over at least a portions of each of said patterns of conductive
material, each of said cell structures comprising a light incident
surface, a back surface and semiconductor material positioned
between said light incident and back surfaces, said positioning
being such that a preponderance of said light incident surface of
each of said cell structures faces and is in electrical contact
with a said pattern of conductive material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation-in-Part of U.S. patent
application Ser. No. 11/824,047 filed Jun. 30, 2007, entitled
Collector Grid, Electrode Structures and Interconnect Structures
for Photovoltaic Arrays and other Optoelectric Devices, which is a
Continuation-in-Part of U.S. application Ser. No. 11/404,168 filed
Apr. 13, 2006, entitled Substrate and Collector Grid Structures for
Integrated Photovoltaic Arrays and Process of Manufacture of Such
Arrays, which is a Continuation-in-Part of U.S. application Ser.
No. 10/776,480 filed Feb. 11, 2004, entitled Methods and Structures
for the Continuous Production of Metallized or Electrically Treated
Articles, now abandoned, which is a Continuation-in-Part of U.S.
patent application Ser. No. 10/682,093 filed Oct. 8, 2003 entitled
Substrate and Collector Grid Structures for Integrated Series
Connected Photovoltaic Arrays and Process of Manufacture of Such
Arrays, which is a Continuation-in-Part of U.S. patent application
Ser. No. 10/186,546 filed Jul. 1, 2002, entitled Substrate and
Collector Grid Structures for Integrated Series Connected
Photovoltaic Arrays and Process of Manufacture of Such Arrays, now
abandoned, which is a Continuation-in-Part of U.S. patent
application Ser. No. 09/528,086, filed Mar. 17, 2000, entitled
Substrate and Collector Grid Structures for Integrated Series
Connected Photovoltaic Arrays and Process of Manufacture of Such
Arrays, and now U.S. Pat. No. 6,414,235, which is a
Continuation-in-Part of U.S. patent application Ser. No.
09/281,656, filed Mar. 30, 1999, entitled Substrate and Collector
Grid Structures for Electrically Interconnecting Photovoltaic
Arrays and Process of Manufacture of Such Arrays, and now U.S. Pat.
No. 6,239,352. The entire contents of the above identified
applications are incorporated herein by this reference.
BACKGROUND OF THE INVENTION
[0002] This invention teaches novel structure and methods for
achieving efficient collection and conveyance of power from
photovoltaic power generating devices.
[0003] Photovoltaic cells have developed according to two distinct
methods. The initial operational cells employed a matrix of single
crystal silicon appropriately doped to produce a planar p-n
junction. An intrinsic electric field established at the p-n
junction produces a voltage by directing solar photon produced
holes and free electrons in opposite directions. Despite good
conversion efficiencies and long-term reliability, widespread
energy collection using single-crystal silicon cells is thwarted by
the high cost of single crystal silicon material and
interconnection processing.
[0004] A second approach to produce photovoltaic cells is by
depositing thin photovoltaic semiconductor films on a supporting
substrate. Material requirements are minimized and technologies can
be proposed for mass production. Thin film photovoltaic cells
employing amorphous silicon, cadmium telluride, copper indium
gallium diselenide, dye sensitized solar cells (DSSC), printed
silicon inks and the like have received increasing attention in
recent years.
[0005] Despite significant improvements in individual cell
conversion efficiencies for both single crystal and thin film
approaches, photovoltaic energy collection has been generally
restricted to applications having low power requirements. One
factor characteristic of many optoelectric devices and photovoltaic
cells in particular is that electrical energy is produced over a
relatively expansive surface area. Thus a challenge to implementing
bulk power systems is the problem of economically collecting the
photogenerated power from an expansive surface. In particular,
photovoltaic cells can be described as high current, low voltage
devices. Typically individual cell voltage is less than about two
volts, and often less than 0.6 volt. The current component is a
substantial characteristic of the power generated. Efficient power
collection from expansive photovoltaic cell surfaces must minimize
resistive losses associated with the high current characteristic.
In the specific case of most photovoltaic cells, the upper surface
is normally formed by a transparent conductive oxide (TCO).
However, these TCO layers are relatively resistive compared to pure
metals and have a surface resistivity on the order of 10 to 100
ohms per square. Thus the conductive surface itself is limited in
its ability to collect and transport current and efforts must be
made to minimize resistive losses in transport of current through
the TCO layer. This problem increases in severity as individual
cell sizes increase. One solution is to simply reduce individual
cell size (and thus accumulated current from an individual cell) to
a point where the transparent conductive oxide alone can handle the
current. Where larger individual cell sizes are the norm, it is
common practice to augment the transparent conductive oxide with a
current collector structure comprising a pattern of highly
conductive traces extending over substantially the entire surface
from which current is to be collected. Often the structure is in
the form of a grid or lattice pattern. The current collector
structure reduces the distance that current must be transported by
the transparent conductive oxide before it reaches a highly
conductive conveyance path off the surface. Thus the current
collector structure collects current from a surface having
relatively low surface conductivity. Many current collector
structures or grids are conventionally prepared by first applying
metal wires, fused silver filled pastes or silver filled ink traces
to the cell surface and then covering the surface with a sealing
material in a subsequent operation. These highly conductive traces
may lead to a collection buss such as a copper foil strip which
also functions as a tab extending to the back electrode of an
adjacent cell. The wire approach requires positioning and fixing of
multiple fine fragile wires which makes mass production difficult
and expensive. Silver pastes are expensive and require high fusion
temperatures which not all photovoltaic semiconductors can
tolerate. A silver filled ink, as compared to a fuseable paste, is
simply dried or cured at mild temperatures which do not adversely
affect the cell. However, this ink approach requires the use of
relatively expensive inks because of the high loading of finely
divided silver particles. In addition, batch printing on the
individual cells is laborious and expensive. Finally, the silver
filled ink is relatively resistive compared to a fuseable silver
paste or metal wire. Typical silver filled inks have intrinsic
resistivities in the range 0.00002 to 0.01 ohm-cm.
[0006] Thus there remains a need for improved materials and
structure for collecting the current from the top light incident
surface of photovoltaic cells.
[0007] Normally one envisions a photovoltaic power collection
device much larger than the size of an individual cell. Therefore,
an arrangement must be supplied to collect power from multiple
cells. This is normally accomplished by interconnecting multiple
cells in series. In this way, voltage is stepped through each cell
while current and associated resistive losses are minimized. Such
interconnected multi-cell arrangements are commonly referred to as
"modules" or "arrays". However, it is readily recognized that
making effective, durable series connections among multiple small
cells can be laborious, difficult and expensive. Regarding
traditional crystalline silicon cells, the individual cells are
normally discrete and comprise rigid wafers approximately 200
micrometers thick and approximately 230 square centimeters in area.
A common way to convert multiple such cells into modules is to use
a conventional "string and tab" arrangement. In this process
multiple discrete cells are arranged in "strings" and the topside
current collector electrodes of cells are connected to backside
electrodes of adjacent cells using "tabs" or ribbons of conductive
material. The cell connections often involve tedious manual
operations such as soldering and handling of multiple
interconnected cells. Next, unwieldy flexible leads from the
terminal cells must be directed and secured in position for outside
connections, again a tedious operation. Finally, weight and
assembly concerns limit the ultimate size of the module. These
limitations impede adoption of the modules for large scale power
generation.
[0008] In order to approach economical mass production of modules
of series connected individual cells, a number of factors must be
considered in addition to the type of photovoltaic materials
chosen. These include the substrate employed and the process
envisioned. Since thin films can be deposited over expansive areas,
thin film technologies offer additional opportunities for mass
production of interconnected modules compared to inherently small,
discrete single crystal silicon cells. Thus a number of U.S.
patents have issued proposing designs and processes to achieve
series interconnections among thin film photovoltaic cells. Many of
these technologies comprise deposition of photovoltaic thin films
on glass substrates followed by scribing to form smaller area
individual cells. Multiple steps then follow to electrically
connect the individual cells in series while maintaining the
original common glass substrate. These "common" substrate
approaches have come to be known as "monolithic integration".
Examples of these proposed processes are presented in U.S. Pat.
Nos. 4,443,651, 4,724,011, and 4,769,086 to Swartz, Turner et al.
and Tanner et al. respectively. While expanding the opportunities
for mass production of interconnected cell modules compared with
inherently discrete approaches for crystal silicon cells,
monolithic integration employing common glass substrates must
inherently be performed on an individual batch basis. In addition,
many monolithic approaches are not compatible with the use of a
current collector grid and therefore cell sizes (in the direction
of current flow) are constrained. Typically, cell widths for
monolithic integration between 0.5 cm. and 1.0 cm. are taught in
the art. However, as cell widths decrease, the width of the area
between individual cells (interconnect area) should also decrease
so that the relative portion of inactive surface of the
interconnect area does not become excessive. These small cell
widths demand very fine interconnect area widths, which dictate
delicate and sensitive techniques to be used to electrically
connect the top TCO surface of one cell to the bottom electrode of
an adjacent series connected cell. Furthermore, achieving good
stable ohmic contact to the TCO cell surface has proven difficult,
especially when one employs those sensitive techniques available
when using the TCO only as the top collector electrode.
[0009] More recently, developers have explored depositing wide area
films using continuous roll-to-roll processing. This technology
generally involves depositing thin films of photovoltaic material
onto a continuously moving web. However, a challenge still remains
regarding subdividing the expansive films into individual cells
followed by interconnecting into a series connected array. For
example, U.S. Pat. No. 4,965,655 to Grimmer et. al. and U.S. Pat.
No. 4,697,041 to Okamiwa teach processes requiring expensive laser
scribing and interconnections achieved with laser heat staking. In
addition, these two references teach a substrate of thin vacuum
deposited metal on films of relatively expensive polymers. The
electrical resistance of thin vacuum metallized layers may
significantly limit the active area of the individual
interconnected cells.
[0010] It has become well known in the art that the efficiencies of
certain promising thin film photovoltaic junctions can be
substantially increased by high temperature treatments. These
treatments involve temperatures at which even the most heat
resistant plastics suffer rapid deterioration. Use of a metal foil
as a substrate allows high temperature treatments and continuous
roll-to-roll processing. However, the subsequent conversion to an
interconnected module of multiple cells has proven difficult, in
part because the metal foil substrate is electrically
conducting.
[0011] U.S. Pat. No. 4,746,618 to Nath et al. teaches a design and
process to achieve interconnected arrays using roll-to-roll
processing of a metal web substrate such as stainless steel. The
process includes multiple operations of cutting, selective
deposition, and riveting. These operations add considerably to the
final interconnected array cost.
[0012] U.S. Pat. No. 5,385,848 to Grimmer teaches roll-to-roll
methods to achieve integrated series connections of adjacent thin
film photovoltaic cells supported on an electrically conductive
metal substrate. The process includes mechanical or chemical etch
removal of a portion of the photovoltaic semiconductor and
transparent top electrode to expose a portion of the electrically
conductive metal substrate. The exposed metal serves as a contact
area for interconnecting adjacent cells. These material removal
techniques are troublesome for a number of reasons. First, many of
the chemical elements involved in the best photovoltaic
semiconductors are expensive and environmentally unfriendly. This
removal subsequent to controlled deposition involves containment,
dust and dirt collection and disposal, and possible cell
contamination. This is not only wasteful but considerably adds to
expense. Secondly, the removal processes are difficult to control
dimensionally. Thus a significant amount of the valuable
photovoltaic semiconductor is lost to the removal process. Ultimate
module efficiencies are further compromised in that the spacing
between adjacent cells grows, thereby reducing the effective active
collector area for a given module area.
[0013] Thus there remains a need for acceptable mass manufacturing
processes and articles to achieve effective integrated
interconnections among photovoltaic cells.
[0014] A further issue that has impeded adoption of photovoltaic
technology, especially for bulk power collection in the form of
solar farms, involves installation of multiple modules over
expansive regions of surface. Traditionally, modules have been
mounted individually on supporting mounts, normally at an incline
to horizontal appropriate to the latitude of the site. Conducting
leads from each module are then physically coupled with leads from
an adjacent module in order to interconnect multiple modules. This
arrangement results in a string of modules each of which is coupled
to an adjacent module. At one end of the string, the power is
transferred from the end module to be conveyed to a separate site
for further treatment such as voltage adjustment. This arrangement
avoids having to run conductive cabling from each individual module
to the separate treatment site.
[0015] The traditional solar farm installation described in the
above paragraph has some drawbacks. First, traditional modules are
limited in size due to weight and manufacturing constraints. This
fact increases the number of individual modules required to cover a
desired surface area. Next, the module itself comprises a string of
individual cells. In the conventional module lead conductors in the
form of flexible wires or ribbons are attached to an electrode on
the two cells positioned at each end of the string in order to
convey the power from the module. After mounting the individual
modules on their support at the installation site, the respective
leads from adjacent modules must be connected in order to couple
adjacent modules, and the connection must be protected to avoid
environmental deterioration or separation. These are intrinsically
tedious manual operations. Finally, since the module leads and cell
interconnections are not of high current carrying capacity, the
adjacent cells are normally connected in series arrangement. Thus
voltage builds up to high levels even at relatively short strings
of modules. While not an overriding problem security and insulation
must be appropriate to eliminate a shock hazard.
[0016] Thus there remains a need for improved module form factors
and complimentary installation structure to reduce the cost and
complexity of achieving large area "utility" scale photovoltaic
installations.
[0017] In a somewhat removed segment of technology, a number of
electrically conductive fillers have been used to produce
electrically conductive polymeric materials. This technology
generally involves mixing of a conductive filler such as silver
particles with the polymer resin prior to fabrication of the
material into its final shape. Conductive fillers may have high
aspect ratio structure such as metal fibers, metal flakes or
powder, or highly structured carbon blacks, with the choice based
on a number of cost/performance considerations. More recently, fine
particles of intrinsically conductive polymers have been employed
as conductive fillers within a resin binder. Electrically
conductive polymers have been used as bulk thermoplastic
compositions, or formulated into paints and inks. Their development
has been spurred in large part by electromagnetic radiation
shielding and static discharge requirements for plastic components
used in the electronics industry. Other known applications include
resistive heating fibers and battery components and production of
conductive patterns and traces. The characterization "electrically
conductive polymer" covers a very wide range of intrinsic
resistivities depending on the filler, the filler loading and the
methods of manufacture of the filler/polymer blend. Resistivities
for filled electrically conductive polymers may be as low as
0.00001 ohm-cm. for very heavily filled silver inks, yet may be as
high as 10,000 ohm-cm or even more for lightly filled carbon black
materials or other "anti-static" materials. "Electrically
conductive polymer" has become a broad industry term to
characterize all such materials. In addition, it has been reported
that recently developed intrinsically conducting polymers (absent
conductive filler) may exhibit resistivities comparable to pure
metals.
[0018] In yet another separate technological segment, coating
plastic substrates with metal electrodeposits has been employed to
achieve decorative effects on items such as knobs, cosmetic
closures, faucets, and automotive trim. The normal conventional
process actually combines two primary deposition technologies. The
first is to deposit an adherent metal coating using chemical
(electroless) deposition to first coat the nonconductive plastic
and thereby render its surface highly conductive. This electroless
step is then followed by conventional electroplating. ABS
(acrylonitrile-butadiene-styrene) plastic dominates as the
substrate of choice for most applications because of a blend of
mechanical and process properties and ability to be uniformly
etched. The overall plating process comprises many steps. First,
the plastic substrate is chemically etched to microscopically
roughen the surface. This is followed by depositing an initial
metal layer by chemical reduction (typically referred to as
"electroless plating"). This initial metal layer is normally copper
or nickel of thickness typically one-half micrometer. The object is
then electroplated with metals such as bright nickel and chromium
to achieve the desired thickness and decorative effects. The
process is very sensitive to processing variables used to fabricate
the plastic substrate, limiting applications to carefully prepared
parts and designs. In addition, the many steps employing harsh
chemicals make the process intrinsically costly and environmentally
difficult. Finally, the sensitivity of ABS plastic to liquid
hydrocarbons has prevented certain applications. ABS and other such
polymers have been referred to as "electroplateable" polymers or
resins. This is a misnomer in the strict sense, since ABS (and
other nonconductive polymers) are incapable of accepting an
electrodeposit directly and must be first metallized by other means
before being finally coated with an electrodeposit. The
conventional technology for electroplating on plastic (etching,
chemical reduction, electroplating) has been extensively documented
and discussed in the public and commercial literature. See, for
example, Saubestre, Transactions of the Institute of Metal
Finishing, 1969, Vol. 47, or Arcilesi et al., Products Finishing,
March 1984.
[0019] Many attempts have been made to simplify the process of
electroplating on plastic substrates. Some involve special chemical
techniques to produce an electrically conductive film on the
surface. Typical examples of this approach are taught by U.S. Pat.
No. 3,523,875 to Minklei, U.S. Pat. No. 3,682,786 to Brown et. al.,
and U.S. Pat. No. 3,619,382 to Lupinski. The electrically
conductive film produced was then electroplated. None of these
attempts at simplification have achieved any recognizable
commercial application.
[0020] A number of proposals have been made to make the plastic
itself conductive enough to allow it to be electroplated directly
thereby avoiding the "electroless plating" process. As noted above,
it is common to produce electrically conductive polymers by
incorporating conductive or semiconductive fillers into a polymeric
binder. Investigators have attempted to produce electrically
conductive polymers capable of accepting an electrodeposited metal
coating by loading polymers with relatively small conductive
particulate fillers such as graphite, carbon black, and silver or
nickel powder or flake. Heavy such loadings are sufficient to
reduce volume resistivity to a level where electroplating may be
considered. However, attempts to make an acceptable
electroplateable polymer using the relatively small metal
containing fillers alone encounter a number of barriers. First, the
most conductive fine metal containing fillers such as silver are
relatively expensive. The loadings required to achieve the
particle-to-particle proximity to achieve acceptable conductivity
increases the cost of the polymer/filler blend dramatically. The
metal containing fillers are accompanied by further problems. They
tend to cause deterioration of the mechanical properties and
processing characteristics of many resins. This significantly
limits options in resin selection. All polymer processing is best
achieved by formulating resins with processing characteristics
specifically tailored to the specific process (injection molding,
extrusion, blow molding, printing etc.). A required heavy loading
of metal filler severely restricts ability to manipulate processing
properties in this way. A further problem is that metal fillers can
be abrasive to processing machinery and may require specialized
screws, barrels, and the like.
[0021] Another major obstacle involved in the electroplating of
electrically conductive polymers is a consideration of adhesion
between the electrodeposited metal and polymeric substrate
(metal/polymer adhesion). In most cases sufficient adhesion is
required to prevent metal/polymer separation during extended
environmental and use cycles. Despite being electrically
conductive, a simple metal-filled polymer offers no assured bonding
mechanism to produce adhesion of an electrodeposit since the metal
particles may be encapsulated by the resin binder, often resulting
in a resin-rich "skin".
[0022] A number of methods to enhance electrodeposit adhesion to
electrically conductive polymers have been proposed. For example,
etching of the surface prior to plating can be considered. Etching
can be achieved by immersion in vigorous solutions such as
chromic/sulfuric acid. Alternatively, or in addition, an etchable
species can be incorporated into the conductive polymeric compound.
The etchable species at exposed surfaces is removed by immersion in
an etchant prior to electroplating. Oxidizing surface treatments
can also be considered to improve metal/plastic adhesion. These
include processes such as flame or plasma treatments or immersion
in oxidizing acids. In the case of conductive polymers containing
finely divided metal, one can propose achieving direct
metal-to-metal adhesion between electrodeposit and filler. However,
here the metal particles are generally encapsulated by the resin
binder, often resulting in a resin rich "skin". To overcome this
effect, one could propose methods to remove the "skin", exposing
active metal filler to bond to subsequently electrodeposited
metal.
[0023] Another approach to impart adhesion between conductive resin
substrates and electrodeposits is incorporation of an "adhesion
promoter" at the surface of the electrically conductive resin
substrate. This approach was taught by Chien et al. in U.S. Pat.
No. 4,278,510 where maleic anhydride modified propylene polymers
were taught as an adhesion promoter. Luch, in U.S. Pat. No.
3,865,699 taught that certain sulfur bearing chemicals could
function to improve adhesion of initially electrodeposited Group
VIII metals.
[0024] For the above reasons, electrically conductive polymers
employing metal fillers have not been widely used as bulk
substrates for electroplateable articles. Such metal containing
polymers have found use as inks or pastes in production of printed
circuitry. Revived efforts and advances have been made in the past
few years to accomplish electroplating onto printed conductive
patterns formed by silver filled inks and pastes.
[0025] An additional physical obstacle confronting practical
electroplating onto electrically conductive polymers is the initial
"bridge" of electrodeposit onto the surface of the electrically
conductive polymer. In electrodeposition, the substrate to be
plated is often made cathodic through a pressure contact to a metal
rack tip, itself under cathodic potential. However, if the contact
resistance is excessive or the substrate is insufficiently
conductive, the electrodeposit current favors the rack tip to the
point where the electrodeposit will not bridge to the
substrate.
[0026] Moreover, a further problem is encountered even if
specialized racking or cathodic contact successfully achieves
electrodeposit bridging to the substrate. Many of the electrically
conductive polymers have resistivities far higher than those of
typical metal substrates. Also, many applications involve
electroplating onto a thin (less than 25 micrometer) printed
substrate. The conductive polymeric substrate may be relatively
limited in the amount of electrodeposition current which it alone
can convey. Thus, the conductive polymeric substrate does not cover
almost instantly with electrodeposit as is typical with metallic
substrates. Except for the most heavily loaded and highly
conductive polymer substrates, a large portion of the
electrodeposition current must pass back through the previously
electrodeposited metal growing laterally over the surface of the
conductive plastic substrate. In a fashion similar to the bridging
problem discussed above, the electrodeposition current favors the
electrodeposited metal and the lateral growth can be extremely slow
and erratic. This restricts the size and "growth length" of the
substrate conductive pattern, increases plating costs, and can also
result in large non-uniformities in electrodeposit integrity and
thickness over the pattern.
[0027] This lateral growth is dependent on the ability of the
substrate to convey current. Thus, the thickness and resistivity of
the conductive polymeric substrate can be defining factors in the
ability to achieve satisfactory electrodeposit coverage rates. When
dealing with selectively electroplated patterns long thin metal
traces are often desired. Electrodeposited metal thicknesses of
from 1 to 25 micrometer are often typical. The metal traces must
normally be of relatively uniform thickness and have a minimum of
internal stress. Further, an electrically conductive polymer "seed"
pattern defining the traces is often relatively thin, less than
about 25 micrometers, and therefore may have relatively low current
carrying capacity. These factors of course often work against
achieving the desired result.
[0028] This coverage rate problem likely can be characterized by a
continuum, being dependent on many factors such as the nature of
the initially electrodeposited metal, electroplating bath
chemistry, the nature of the polymeric binder and the resistivity
of the electrically conductive polymeric substrate. As a "rule of
thumb", the instant inventor estimates that coverage rate issue
would demand attention if the resistivity of a bulk conductive
polymeric substrate rose above about 0.001 ohm-cm. Alternatively, a
"rule of thumb" appropriate for thin film substrates would be that
attention is appropriate if the substrate film to be plated had a
surface "sheet" resistance of greater than about 0.075 ohm per
square.
[0029] The least expensive (and least conductive) of the readily
available conductive fillers for plastics are carbon blacks.
Attempts have been made to electroplate electrically conductive
polymers using carbon black loadings. Examples of this approach are
the teachings of U.S. Pat. Nos. 4,038,042, 3,865,699, and 4,278,510
to Adelman, Luch, and Chien et al. respectively. These earlier
efforts were directed primarily at achieving decorative
electroplated articles with the substrate fully encapsulated with
electrodeposit.
[0030] Adelman taught incorporation of conductive carbon black into
a polymeric matrix to achieve electrical conductivity required for
electroplating. The substrate was pre-etched in chromic/sulfuric
acid to achieve adhesion of the subsequently electroplated metal. A
fundamental problem remaining unresolved by the Adelman teaching is
the relatively high resistivity of carbon loaded polymers. The
lowest "microscopic resistivity" generally achievable with carbon
black loaded polymers is about 1 ohm-cm. This is about five to six
orders of magnitude higher than typical electrodeposited metals
such as copper or nickel. Thus, the electrodeposit bridging and
coverage rate problems described above remained unresolved by the
Adelman teachings.
[0031] Luch in U.S. Pat. No. 3,865,699 and Chien et al. in U.S.
Pat. No. 4,278,510 also chose carbon black as a filler to provide
an electrically conductive surface for the polymeric compounds to
be electroplated. The Luch U.S. Pat. No. 3,865,699 and the Chien
U.S. Pat. No. 4,278,510 are hereby incorporated in their entirety
by this reference. However, these inventors further taught
inclusion of materials to increase the rate of metal coverage or
the rate of metal deposition on the polymer. These materials can be
described herein as "electrodeposit growth rate accelerators" or
"electrodeposit coverage rate accelerators". An electrodeposit
coverage rate accelerator is a material functioning to increase the
electrodeposition coverage rate over the surface of an electrically
conductive polymer independent of any incidental affect it may have
on the conductivity of an electrically conductive polymer. In the
embodiments, examples and teachings of U.S. Pat. Nos. 3,865,699 and
4,278,510, it was shown that certain sulfur bearing materials,
including elemental sulfur, can function as electrodeposit coverage
or growth rate accelerators to overcome problems in achieving
electrodeposit coverage of electrically conductive polymeric
surfaces having relatively high resistivity or thin electrically
conductive polymeric substrates having limited current carrying
capacity.
[0032] In addition to elemental sulfur, sulfur in the form of
sulfur donors such as sulfur chloride, 2-mercapto-benzothiazole,
N-cyclohexyle-2-benzothiaozole sulfonomide, dibutyl xanthogen
disulfide, and tetramethyl thiuram disulfide or combinations of
these and sulfur were identified. Those skilled in the art will
recognize that these sulfur donors are the materials which have
been used or have been proposed for use as vulcanizing agents or
accelerators. Since the polymer-based compositions taught by Luch
and Chien et al. could be electroplated directly they could be
accurately defined as directly electroplateable resins (DER). These
directly electroplateable resins (DER) can be generally described
as electrically conductive polymers with the inclusion of a growth
rate accelerator.
[0033] Specifically for the present invention, specification, and
claims, directly electroplateable resins, (DER), are characterized
by the following features: [0034] (a) presence of an electrically
conductive polymer; [0035] (b) presence of an electrodeposit
coverage rate accelerator; [0036] (c) presence of the electrically
conductive polymer and the electrodeposit coverage rate accelerator
in the directly electroplateable composition in cooperative amounts
required to achieve direct coverage of the composition with an
electrodeposited metal or metal-based alloy.
[0037] In his Patents, Luch specifically identified unsaturated
elastomers such as natural rubber, polychloroprene, butyl rubber,
chlorinated butyl rubber, polybutadiene rubber,
acrylonitrile-butadiene rubber, styrene-butadiene rubber etc. as
suitable for the matrix polymer of a directly electroplateable
resin. Other polymers identified by Luch as useful included
polyvinyls, polyolefins, polystyrenes, polyamides, polyesters and
polyurethanes.
[0038] Using the materials and loadings reported, the carbon
black/polymer formulations of Adelman, Luch and Chien referenced
above would be expected to have intrinsic "microscopic"
resistivities of less than about 1000 ohm-cm. (i.e. 1 ohm-cm., 10
ohm-cm., 100 ohm-cm., 1000 ohm-cm.). When used alone, the minimum
workable level of carbon black required to achieve "microscopic"
electrical resistivities of less than 1000 ohm-cm. for a
polymer/carbon black mix appears to be about 8 weight percent based
on the combined weight of polymer plus carbon black. The
"microscopic" material resistivity generally is not reduced below
about 1 ohm-cm. by using conductive carbon black alone. This is
several orders of magnitude larger than typical metal resistivities
or resistivities associated with common silver filled inks.
[0039] It is understood that in addition to carbon blacks, other
well known, highly conductive fillers can be considered to decrease
the "microscopic" resistivity of DER compositions. Examples include
but are not limited to metallic fillers or flake such as silver. In
these cases the more highly conductive fillers can be used to
augment or even replace the conductive carbon black. Furthermore,
one may consider using intrinsically conductive polymers to supply
the required conductivity. For example, an intrinsically conductive
polymer in particulate form may be considered as a conductive
filler.
[0040] The "bulk, macroscopic" resistivity of conductive carbon
black filled polymers can be further reduced by augmenting the
carbon black filler with additional highly conductive, high aspect
ratio fillers such as metal containing fibers. This can be an
important consideration in the success of certain applications.
Furthermore, one should realize that incorporation of
non-conductive fillers may increase the "bulk, macroscopic"
resistivity of conductive polymers loaded with finely divided
conductive fillers without significantly altering the "microscopic
resistivity" of the conductive polymer "matrix" encapsulating the
non-conductive filler particles. It has been found that DER
formulations can include substantial quantities of non-conductive
fillers. In particular, loading of DER formulations with glass
fibers has been shown to dramatically reduce mold shrinkage and
increase stiffness of these formulations.
[0041] Regarding electrodeposit coverage rate accelerators, both
Luch and Chien et al. in the above discussed U.S. patents
demonstrated that sulfur and other sulfur bearing materials such as
sulfur donors and vulcanization accelerators function as
electrodeposit coverage rate accelerators when using an initial
Group VIII metal electrodeposit "strike" layer. Thus, an
electrodeposit coverage rate accelerator need not be electrically
conductive, but may be a material that is normally characterized as
a non-conductor. The coverage rate accelerator need not appreciably
affect the conductivity of the polymeric substrate. As an aid in
understanding the function of an electrodeposit coverage rate
accelerator the following is offered: [0042] a. A specific
conductive polymeric structure is identified as having insufficient
current carrying capacity to be directly electroplated in a
practical manner. [0043] b. A material is added to the conductive
polymeric material forming said structure. Said material addition
may have insignificant affect on the current carrying capacity of
the structure (i.e. it does not appreciably reduce resistivity or
increase thickness). The material need only be present at the
substrate surface. [0044] c. Nevertheless, inclusion of said
material greatly increases the speed at which an electrodeposited
metal laterally covers the electrically conductive surface. It is
contemplated that a coverage rate accelerator may be present as an
additive, as a species absorbed on a filler surface, or even as a
functional group attached to the polymer chain. One or more growth
rate accelerators may be present in a directly electroplateable
resin (DER) to achieve combined, often synergistic results.
[0045] A hypothetical example might be an extended trace of
conductive ink having a dry thickness of 1 micrometer. Such inks
typically include a conductive filler such as silver, nickel,
copper, conductive carbon etc. The limited thickness of the ink
reduces the current carrying capacity of this trace thus preventing
direct electroplating in a practical manner. However, inclusion of
an appropriate quantity of a coverage rate accelerator may allow
the conductive trace to be directly electroplated in a practical
manner.
[0046] One might expect that other Group 6A elements, such as
oxygen, selenium and tellurium, could function in a way similar to
sulfur. In addition, other combinations of electrodeposited metals,
such as copper and appropriate coverage rate accelerators may be
identified. It is important to recognize that such an
electrodeposit coverage rate accelerator is important in order to
achieve direct electrodeposition in a practical way onto polymeric
substrates having low conductivity or very thin electrically
conductive polymeric substrates having restricted current carrying
ability.
[0047] It has also been found that the inclusion of an
electrodeposit coverage rate accelerator promotes electrodeposit
bridging from a discrete cathodic metal contact to a DER surface.
This greatly reduces the bridging problems described above.
[0048] Due to multiple performance problems associated with their
intended end use, the instant inventor is unaware of any
recognizable commercial success for attempts to directly
electroplate electrically conductive polymers in applications
intended to produce decorative "bright" electroplated objects.
Nevertheless, electroplating in a selective manner onto insulating
substrates for functional applications remains an intriguing
possibility for many applications. This is because electroplating
is selective between conductive and insulating surfaces and is
inexpensive. Further, a wide variety of metals and alloys can be
deposited by electroplating and the deposition rates are relatively
rapid. There are a number of techniques available to achieve
selective electrodeposited patterns on insulating substrates. Most
involve initial formation of a "seed" pattern. The "seed" pattern
is formed from a material that has the ability to assist in
subsequent metal electrodeposition. Typical "seed" patterns
comprise metals, polymers containing electroless plating catalysts,
and electrically conductive polymers. Examples of such processes
follow in subparagraphs 1 through 3.
[0049] (1) An electrically conductive polymer is formed into a
"seed" pattern by printing from an ink formulation onto the surface
of an insulating substrate. This electrically conductive polymer
"seed layer" pattern, when dried, is then subjected to a metal
electroplating process to cover the pattern with a conductive
metal.
[0050] (2) A polymeric composition containing a catalyst suitable
for initiating chemical metal deposition is printed into a "seed
layer" pattern. After appropriate activation, the article is
subjected to a chemical metal deposition "electroless" plating
bath. Following coverage with electroless metal, the "seed
pattern", now comprising a layered structure of polymer and
chemically deposited metal, is subjected to an electroplating
process to cover the pattern with electrodeposited metal.
[0051] (3) An insulating substrate is coated in its entirety with a
thin film of metal. This uniform coating may be achieved, for
example, using vacuum metallizing, sputtering, chemical metal
deposition processing. As a next step, a mask is applied having a
pattern the reverse of the eventual desired selective metal
pattern. The remaining exposed pattern (reverse of the mask
pattern) retains its conductive surface and thereby forms a "seed"
pattern for subsequent further metal electrodeposition. This
subsequent electrodeposition increases metal thickness and also may
apply a final coat resistant to an eventual etch. The mask is then
removed and the article etched to completely remove the metal that
had been covered by the mask.
[0052] As previously noted, the current inventor is unaware of any
recognizable success in attempts to use DER technology to produce
decorative "bright" electroplated objects. Nevertheless, the
current inventor has persisted in personal efforts to overcome
certain performance deficiencies associated with the initial DER
technology. Along with these efforts has come a recognition of
unique and eminently suitable applications employing the DER
technology for functional applications. These functional
applications often have requirements, such as selectivity, fine
patterning and relatively thin electrodeposits, which differ
substantially from the requirements of purely decorative
electroplating. Some examples of these unique applications for
electroplated articles include solar cell electrical current
collection grids and interconnect structures, electrodes,
electrical circuits, electrical traces, circuit boards, antennas,
capacitors, induction heaters, connectors, switches, and resistors.
One readily recognizes that the demand for such functional
applications for electroplated articles is relatively recent and
has been particularly explosive during the past decade.
[0053] It is important to recognize a number of important
characteristics of directly electroplateable resins (DER's) which
may facilitate certain embodiments of the current invention. One
such characteristic of the DER technology is its ability to employ
polymer resins and formulations generally chosen in recognition of
the fabrication process envisioned and the intended end use
requirements. In order to provide clarity, examples of some such
fabrication processes are presented immediately below in
subparagraphs 1 through 9. [0054] (1) Should it be desired to
electroplate an ink, paint, coating, or paste which may be printed
or formed on a substrate, a good film forming polymer, for example
a soluble resin such as an elastomer, can be chosen to fabricate a
DER ink (paint, coating, paste etc.). For example, in some
embodiments thermoplastic elastomers having an olefin base, a
urethane base, a block copolymer base or a random copolymer base
may be appropriate. In some embodiments the coating may comprise a
water based latex. Other embodiments may employ more rigid film
forming polymers. The DER ink composition can be tailored for a
specific process such flexographic printing, rotary silk screening,
gravure printing, ink jet printing, flow coating, spraying etc.
Furthermore, additives such as tackifiers or curatives can be
employed to improve the adhesion of the DER ink to various
substrates. [0055] (2) Very thin DER traces often associated with
collector grid structures can be printed and then electroplated due
to the inclusion of the electrodeposit growth rate accelerator.
Traces as thin as 1.5 micrometer have been demonstrated as
practical. Silk screening has produced trace widths as little as
150 micrometers. [0056] (3) Should it be desired to cure the DER
substrate to a 3 dimensional matrix, an unsaturated elastomer or
other "curable" resin may be chosen. [0057] (4) DER inks can be
formulated to form electrical traces on a variety of flexible
substrates. For example, should it be desired to form electrical
structure on a laminating film, a DER ink adherent to the sealing
surface of the laminating film can be effectively electroplated
with metal and subsequently laminated to a separate surface. [0058]
(5) Should it be desired to electroplate a fabric, a DER ink can be
used to coat all or selected portion of the fabric intended to be
electroplated. Furthermore, since DER's can be fabricated out of
the thermoplastic materials commonly used to create fabrics, the
fabric itself could completely or partially comprise a DER. This
would eliminate the need to coat the fabric. [0059] (6) Should one
desire to electroplate a thermoformed article or structure, DER's
would represent an eminently suitable material choice. DER's can be
easily formulated using olefinic materials which are often a
preferred material for the thermoforming process. Furthermore,
DER's can be easily and inexpensively extruded into the sheet like
structure necessary for the thermoforming process. [0060] (7)
Should one desire to electroplate an extruded article or structure,
for example a sheet or film, DER's can be formulated to possess the
necessary melt strength advantageous for the extrusion process.
[0061] (8) Should one desire to injection mold an article or
structure having thin walls, broad surface areas etc. a DER
composition comprising a high flow polymer can be chosen. [0062]
(9) Should one desire to vary adhesion between an electrodeposited
DER structure supported by a substrate the DER material can be
formulated to supply the required adhesive characteristics to the
substrate. For example, the polymer chosen to fabricate a DER ink
can be chosen to cooperate with an "ink adhesion promoting" surface
treatment such as a material primer or corona treatment. In this
regard, it has been observed that it may be advantageous to limit
such adhesion promoting treatments to a single side of the
substrate. Treatment of both sides of the substrate in a roll to
roll process may adversely affect the surface of the DER material
and may lead to deterioration in plateability. For example, it has
been observed that primers on both sides of a roll of PET film have
adversely affected plateability of DER inks printed on the PET. It
is believed that this is due to primer being transferred to the
surface of the DER ink when the PET is rolled up.
[0063] All polymer fabrication processes require specific resin
processing characteristics for success. The ability to "custom
formulate" DER's to comply with these changing processing and end
use requirements while still allowing facile, quality
electroplating is unique among methods to electroplate onto
polymeric forms.
[0064] Another important recognition regarding the suitability of
DER's for the teachings of the current invention is the simplicity
of the electroplating process. Unlike many conventional
electroplated plastics, DER's do not require a significant number
of process steps prior to actual electroplating. This allows for
simplified manufacturing and improved process control. It also
reduces the risk of cross contamination such as solution dragout
from one process bath being transported to another process bath.
The simplified manufacturing process will also result in reduced
manufacturing costs.
[0065] Yet another recognition of the benefit of DER's for the
teachings of the current invention is the ability they offer to
selectively electroplate metal onto an article or structure. The
desired metal structures of the invention often involve long yet
fine metal traces. Further, the articles of the invention often
consist of such metal patterns selectively positioned in
conjunction with flexible insulating materials. Such selective
positioning of metals can often be expensive and difficult. As
discussed previously, the coverage rate accelerators included in
DER formulations allow for such extended surfaces to be covered
with electrodeposit in a relatively rapid and simple manner.
[0066] Yet another recognition of the benefit of DER's is their
ability they to be continuously electroplated. As will be shown in
later embodiments, it is often desired to continuously electroplate
metal onto "seed" patterns defining specific structure. DER's are
eminently suitable as "seed" patterns for such continuous
electroplating.
[0067] Yet another recognition of the benefit of DER's for the
teachings of the current invention is their ability to withstand
the pre-treatments often required to prepare other materials for
plating. For example, were a DER to be combined with a metal, the
DER material would be resistant to many of the pre-treatments such
as cleaning which may be necessary to electroplate the metal.
[0068] Another important recognition is the suitability of metal
electrodeposition for producing articles of the current invention.
Electroplating is a rapid and inexpensive metal deposition process.
Electroplating allows selective deposition of a wide variety of
metals and alloys. Single or multi-layered deposits may be chosen
for specific attributes. Examples may include copper for
conductivity and nickel, silver or gold for corrosion resistance.
Electrodeposition further allows a wide range of appropriate
deposit thickness to be achieved relatively quickly. The articles
of the invention may require metal traces varying from about 0.1
micrometer to greater than about 100 micrometer (i.e. 0.1
micrometer, 1 micrometer, 10 micrometer 25 micrometer, 100
micrometer etc.). Such thicknesses may be readily achieved in
reasonable time using metal electrodeposition.
[0069] These and other attributes of DER's and electroplating may
contribute to successful articles and processing of the instant
invention. However, it is emphasized that the DER technology, and
more broadly electroplating onto conductive polymeric "seed"
layers, is but one of a number of alternative metal deposition or
positioning processes suitable to produce many of the embodiments
of the instant invention. Other approaches, such as electroless
metal deposition, selective metal etching, placement of metal forms
such as wires or strips, stamping metal patterns and selective
vacuum or chemical deposition may be suitable alternatives for
producing the selectively positioned metal structures of the
invention. These choices will become clear to the skilled artisan
in light of the teachings to follow in the remaining specification,
accompanying figures and claims.
[0070] Another important aspect of the embodiments of the current
invention is the inclusion of web processing to achieve structure
and combinations in a facile and economic fashion. A web is a
generally planar or sheet-like structure, normally flexible, having
thickness much smaller than its length or width. This sheet-like
structure may also have a length far greater than its width. A web
of extended length may be conveyed through one or more processing
steps in a way that can be described as "continuous", thereby
achieving the advantages of continuous processing. "Continuous" web
processing is well known in the paper and packaging industries. It
is normally accomplished by supplying web material from a feed roll
of extended length to the process steps. The product resulting from
the process is often continuously retrieved onto a takeup roll
following processing, in which case the process may be termed
roll-to-roll or reel-to-reel processing.
[0071] An advantage of web processing is that the web can comprise
many different materials, surface characteristics and forms. The
web may comprise layers for packaging material options such as
pressure sensitive or hot melt adhesive layers, environmental
barriers, and as support for printing and other features. The web
can constitute a nonporous film or may be a fabric and may be
transparent or opaque. Combinations of such differences over the
expansive surface of the web can be achieved. Indeed, as will be
shown, the web itself can comprise materials such as conductive
polymers or even metal fibers which will allow the web itself to
perform electrical function. The web material may remain as part of
the final article of manufacture or may be removed after
processing, in which case it would serve as a surrogate or
temporary support during processing.
[0072] In order to eliminate ambiguity in terminology, for the
present invention the following definitions are supplied:
[0073] While not precisely definable, for the purposes of this
specification, electrically insulating materials may generally be
characterized as having electrical resistivities greater than
10,000 ohm-cm. Also, electrically conductive materials may
generally be characterized as having electrical resistivities less
than 0.001 ohm-cm. Also electrically resistive or semi-conductive
materials may generally be characterized as having electrical
resistivities in the range of about 0.01 ohm-cm to about 10,000
ohm-cm. The characterization "electrically conductive polymer"
covers a very wide range of intrinsic resistivities depending on
the filler, the filler loading and the methods of manufacture of
the filler/polymer blend. Resistivities for electrically conductive
polymers may be as low as 0.00001 ohm-cm. for very heavily filled
silver inks, yet may be as high as 10,000 ohm-cm or even more for
lightly filled carbon black materials or other "anti-static"
materials. "Electrically conductive polymer" has become a broad
industry term to characterize all such materials. Thus, the term
"electrically conductive polymer" as used in the art and in this
specification and claims extends to materials of a very wide range
of resistivities from about 0.00001 ohm-cm. to about 10,000 ohm-cm
and higher.
[0074] An "electroplateable material" is a material having suitable
attributes that allow it to be coated with a layer of
electrodeposited material.
[0075] A "metallizable material" is a material suitable to be
coated with a metal deposited by any one or more of the available
metallizing process, including chemical deposition, vacuum
metallizing, sputtering, metal spraying, sintering and
electrodeposition.
[0076] "Metal-based" refers to a material or structure having at
least one metallic property and comprising one or more components
at least one of which is a metal or metal-containing alloy.
[0077] "Alloy" refers to a substance composed of two or more
intimately mixed materials.
[0078] "Group VIII metal-based" refers to a substance containing by
weight 50% to 100% metal from Group VIII of the Periodic Table of
Elements.
[0079] A "bulk metal foil" refers to a thin structure of metal or
metal-based material that may maintain its integrity absent a
supporting structure. Generally, metal films of thickness greater
than about 2 micrometers may have this characteristic. Thus, in
most cases a "bulk metal foil" will have a thickness between about
2 micrometers and 250 micrometers (i.e. 2 micrometer, 5 micrometer,
10 micrometer, 25 micrometer, 100 micrometer, 250 micrometer) and
may comprise a laminate of multiple layers.
[0080] The term "monolithic" or "monolithic structure" is used in
this specification and claims as is common in industry to describe
an object that is made or formed into or from a single item or
material.
[0081] The term "continuous form" refers to a material structure
having one dimension of sufficient size such that it can be fed to
or retrieved from a process over an extended time period without
interruption of the material structure.
[0082] The term "continuous process" refers to a process or method
in which at least one of the material feed components or a product
of the process has a continuous form.
[0083] A web is a generally planar or sheet-like structure,
normally flexible, having thickness much smaller than its length or
width.
[0084] "Web processing" is a process wherein a web itself is
altered by the process or wherein structure supported by the web is
added, altered or otherwise modified by the process.
[0085] A "reel to reel" or "roll to roll" process is one wherein at
least one of the feed components to a process is supplied in a
continuous roll form and the product of the process is retrieved on
a takeup roll.
OBJECTS OF THE INVENTION
[0086] An object of the invention is to eliminate the deficiencies
in the prior art methods of producing expansive area, series or
parallel interconnected photovoltaic modules and arrays.
[0087] A further object of the present invention is to provide
improved substrates to achieve series or parallel interconnections
among photovoltaic cells.
[0088] A further object of the invention is to provide structures
useful for collecting current from an electrically conductive
surface.
[0089] A further object of the invention is to provide structures
useful in collecting current from a surface of limited current
carrying capacity such as those of many optoelectric devices
including photovoltaic cells. The current collector structure
comprising a pattern of highly conductive traces normally extends
over a preponderance of the surface from which current is to be
collected.
[0090] A further object of the present invention is to provide
improved processes whereby interconnected photovoltaic modules can
be economically mass produced.
[0091] A further object of the invention is to provide a process
and means to accomplish interconnection of photovoltaic cells into
an integrated array through continuous processing.
[0092] Other objects and advantages will become apparent in light
of the following description taken in conjunction with the drawings
and embodiments.
SUMMARY OF THE INVENTION
[0093] The current invention provides a solution to the stated
needs by producing the active photovoltaic cells and
interconnecting structures separately and subsequently combining
them to produce the desired interconnected array or module. One
embodiment of the invention contemplates deposition of thin film
photovoltaic junctions on metal foil substrates which may be heat
treated following deposition if required in a continuous fashion
without deterioration of the metal support structure. In a separate
operation, interconnection structures are produced. In an
embodiment, interconnection structures are produced in a continuous
roll-to-roll fashion. In an embodiment, the interconnecting
structure is laminated to the foil supported photovoltaic cell and
conductive connections are applied to complete the array.
Application of a separate interconnection structure subsequent to
cell manufacture allows the interconnection structures to be
uniquely formulated using polymer-based materials. Interconnections
are achieved without the need to use the expensive and intricate
material removal operations currently taught in the art to achieve
interconnections.
[0094] In another embodiment, a separately prepared current
collector grid structure is taught. In an embodiment the current
collector structure is produced in a continuous roll-to-roll
fashion. The current collector structure comprises conductive
material pattern positioned on a first surface of a laminating
sheet or positioning carrier sheet. This combination is prepared
such that a first surface of the laminating or positioning sheet
and the conductive material can be positioned in abutting contact
with a conductive surface. In one embodiment the conductive surface
is the light incident surface of a photovoltaic cell. In another
embodiment the conductive surface is the rear conductive surface of
a photovoltaic cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0095] The various factors and details of the structures and
manufacturing methods of the present invention are hereinafter more
fully set forth with reference to the accompanying drawings
wherein:
[0096] FIG. 1 is a top plan view of a thin film photovoltaic
structure including its support structure.
[0097] FIG. 1A is a top plan view of the article of FIG. 1
following an optional processing step of subdividing the article of
FIG. 1 into cells of smaller dimension.
[0098] FIG. 2 is a sectional view taken substantially along the
line 2-2 of FIG. 1.
[0099] FIG. 2A is a sectional view taken substantially along the
line 2A-2A of FIG. 1A.
[0100] FIG. 2B is a simplified sectional depiction of the structure
embodied in FIG. 2A.
[0101] FIG. 3 is an expanded sectional view showing a form of the
structure of semiconductor 11 of FIGS. 2 and 2A.
[0102] FIG. 4 illustrates a possible process for producing the
structure shown in FIGS. 1-3.
[0103] FIG. 5 is a sectional view illustrating the problems
associated with making series connections among thin film
photovoltaic cells shown in FIGS. 1-3.
[0104] FIG. 6 is a top plan view of a starting structure for an
embodiment of the instant invention.
[0105] FIG. 7 is a sectional view, taken substantially along the
lines 7-7 of FIG. 6, illustrating a possible laminate structure of
the embodiment.
[0106] FIG. 8 is a simplified sectional depiction of the FIG. 7
structure suitable for ease of presentation of additional
embodiments.
[0107] FIG. 9 is a top plan view of the structure embodied in FIGS.
6 through 8 following an additional processing step.
[0108] FIG. 10 is a sectional view taken substantially from the
perspective of lines 10-10 of FIG. 9.
[0109] FIG. 11 is a sectional view taken substantially from the
perspective of lines 11-11 of FIG. 9.
[0110] FIG. 12 is a top plan view of an article resulting from
exposing the FIG. 9 article to an additional processing step.
[0111] FIG. 13 is a sectional view taken substantially from the
perspective of lines 13-13 of FIG. 12.
[0112] FIG. 14 is a sectional view taken substantially from the
perspective of lines 14-14 of FIG. 12.
[0113] FIG. 15 is a sectional view taken substantially from the
perspective of lines 15-15 of FIG. 12.
[0114] FIG. 16 is a top plan of an alternate embodiment similar in
structure to the embodiment of FIG. 9.
[0115] FIG. 17 is a sectional view taken substantially from the
perspective of lines 17-17 of FIG. 16.
[0116] FIG. 18 is a sectional view taken substantially from the
perspective of lines 18-18 of FIG. 16.
[0117] FIG. 19 is a simplified sectional view of the article
embodied in FIGS. 16-18 suitable for ease of clarity of
presentation of additional embodiments.
[0118] FIG. 20 is a sectional view showing the article of FIGS. 16
through 19 following an additional optional processing step.
[0119] FIG. 21 is a simplified depiction of a process useful in
producing objects of the instant invention.
[0120] FIG. 22 is a sectional view taken substantially from the
perspective of lines 22-22 of FIG. 21 showing an arrangement of
three components just prior to the Process 92 depicted in FIG.
21.
[0121] FIG. 23 is a sectional view showing the result of combining
the components of FIG. 22 using the process of FIG. 21.
[0122] FIG. 24 is a sectional view embodying a series
interconnection of multiple articles as depicted in FIG. 23
[0123] FIG. 25 is an exploded sectional view of the region within
the box "K" of FIG. 24.
[0124] FIG. 26 is a top plan view of a starting article in the
production of another embodiment of the instant invention.
[0125] FIG. 27 is a sectional view taken from the perspective of
lines 27-27 of FIG. 26.
[0126] FIG. 28 is a simplified sectional depiction of the article
of FIGS. 26 and 27 useful in preserving clarity of presentation of
additional embodiments.
[0127] FIG. 29 is a top plan view of the original article of FIGS.
26-28 following an additional processing step.
[0128] FIG. 30 is a sectional view taken substantially from the
perspective of lines 30-30 of FIG. 29.
[0129] FIG. 31 is a sectional view of the article of FIGS. 29 and
30 following an additional optional processing step.
[0130] FIG. 32 is a sectional view, similar to FIG. 22, showing an
arrangement of articles just prior to combination using a process
such as depicted in FIG. 21.
[0131] FIG. 33 is a sectional view showing the result of combining
the arrangement depicted in FIG. 32 using a process as depicted in
FIG. 21.
[0132] FIG. 34 is a sectional view a series interconnection of a
multiple of articles such as depicted in FIG. 33.
[0133] FIG. 35 is a top plan view of a starting article used to
produce another embodiment of the instant invention.
[0134] FIG. 36 is a simplified sectional view taken substantially
from the perspective of lines 36-36 of FIG. 35.
[0135] FIG. 37 is a expanded sectional view of the article embodied
in FIGS. 35 and 36 showing a possible multi-layered structure of
the article.
[0136] FIG. 38 is a sectional view showing a structure combining
repetitive units of the article embodied in FIGS. 35 and 36.
[0137] FIG. 39 is a top plan view of the article of FIGS. 35 and 36
following an additional processing step.
[0138] FIG. 40 is a sectional view taken from the perspective of
lines 40-40 of FIG. 39.
[0139] FIG. 41 is a sectional view similar to that of FIG. 40
following an additional optional processing step.
[0140] FIG. 42 is a sectional view showing a possible combining of
the article of FIG. 41 with a photovoltaic cell.
[0141] FIG. 43 is a sectional view showing multiple articles as in
FIG. 42 arranged in a series interconnected array.
[0142] FIG. 44 is a top plan view of a starting article in the
production of yet another embodiment of the instant invention.
[0143] FIG. 45 is a sectional view taken substantially from the
perspective of lines 45-45 of FIG. 44 showing a possible layered
structure for the article.
[0144] FIG. 46 is a sectional view similar to FIG. 45 but showing
an alternate structural embodiment.
[0145] FIG. 47 is a simplified sectional view of the articles
embodied in FIGS. 44-46 useful in maintaining clarity and
simplicity for subsequent embodiments.
[0146] FIG. 48 is a top plan view of the articles of FIGS. 44-47
following an additional processing step.
[0147] FIG. 49 is a sectional view taken substantially from the
perspective of lines 49-49 of FIG. 48.
[0148] FIG. 50 is a top plan view of the article of FIGS. 48 and 49
following an additional processing step.
[0149] FIG. 51 is a sectional view taken substantially from the
perspective of lines 51-51 of FIG. 50.
[0150] FIG. 52 is a sectional view of the article of FIGS. 50 and
51 following an additional optional processing step.
[0151] FIG. 53 is a top plan view of an article similar to that of
FIG. 50 but embodying an alternate structure.
[0152] FIG. 54 is a sectional view taken substantially from the
perspective of lines 54-54 of FIG. 53.
[0153] FIG. 55 is a sectional view showing an article combining the
article of FIG. 52 with a photovoltaic cell.
[0154] FIG. 56 is a sectional view embodying series interconnection
of multiple articles as depicted in FIG. 55.
[0155] FIG. 57 is a sectional view embodying a possible condition
when using a circular form in a lamination process.
[0156] FIG. 58 is a sectional view embodying a possible condition
resulting from choosing a low profile form in a lamination
process.
[0157] FIG. 59 is a top plan view embodying a possible process to
achieve positioning and combining of photovoltaic cells into a
series interconnected array.
[0158] FIG. 60 is a perspective view of the process embodied in
FIG. 59.
[0159] FIG. 61 is a top plan view showing a simplified depiction of
structure useful to explain a concept of the invention.
[0160] FIG. 62 is a sectional view taken substantially from the
perspective of lines 62-62 of FIG. 61.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0161] Reference will now be made in detail to the preferred
embodiments of the invention, examples of which are illustrated in
the accompanying drawings. In the drawings, like reference numerals
designate identical, equivalent or corresponding parts throughout
several views and an additional letter designation is
characteristic of a particular embodiment.
[0162] Referring to FIGS. 1 and 2, an embodiment of a thin film
photovoltaic structure is generally indicated by numeral 1. It is
noted here that "thin film" has become commonplace in the industry
to designate certain types of semiconductor materials in
photovoltaic applications. These include amorphous silicon, cadmium
telluride, copper-indium-gallium diselenide, dye sensitized
polymers, so-called "Graetzel" electrolyte cells and the like.
While the characterization "thin film" may be used to describe many
of the embodiments of the instant invention, principles of the
invention may extend to photovoltaic devices not normally
considered "thin film" such as single crystal or polysilicon
devices, as those skilled in the art will readily appreciate. The
article 1 embodiment has a light-incident top surface 59 and a
bottom surface 66. Structure 1 has a width X-1 and length Y-1. It
is contemplated that length Y-1 may be considerably greater than
width X-1 such that length Y-1 can generally be described as
"continuous" or being able to be processed in a roll-to-roll
fashion. FIG. 2 shows that embodiment 1 structure comprises a thin
film semiconductor structure 11 supported by "bulk" metal-based
foil 12. "Bulk" foil 12 is often self supporting to allow
continuous processing. Foil 12 has a top surface 65, bottom surface
66, and thickness "Z". In the embodiment, bottom surface 66 of foil
12 also forms the bottom surface of photovoltaic structure 1.
Metal-based foil 12 may be of uniform composition or may comprise a
laminate of multiple layers. For example, foil 12 may comprise a
base layer of inexpensive and processable metal 13 with an
additional metal-based layer 14 disposed between base layer 13 and
semiconductor structure 11. The additional metal-based layer 14 may
be chosen to ensure good ohmic contact between the top surface 65
of foil 12 and photovoltaic semiconductor structure 11. Bottom
surface 66 of foil 12 may comprise a material 75 chosen to achieve
good electrical and mechanical joining characteristics as will be
shown. The thickness "Z" of foil 12 is often between 2 micrometers
and 250 micrometers (i.e. 5 micrometers, 10 micrometers, 25
micrometers, 50 micrometers, 100 micrometers, 250 micrometers), and
most often in the range of 10 micrometer to 125 micrometer although
thicknesses outside this range may be functional in certain
applications. One notes for example that should additional support
be possible, such as that supplied by a supporting plastic film,
metal foil thickness may be far less (0.1 to 1 micrometer) than
those characteristic of a "bulk" foil. Nevertheless, a foil
thickness between 2 micrometers and 250 micrometers may be self
supporting and provide adequate handling strength and integrity
while still allowing flexibility for certain processing as further
taught hereinafter.
[0163] In its simplest form, a photovoltaic structure combines an
n-type semiconductor with a p-type semiconductor to from a p-n
junction. Often an optically transparent "window electrode", such
as a thin film of zinc oxide, tin oxide indium tin oxide or the
like is employed to minimize resistive losses involved in current
collection. FIG. 3 illustrates an example of a typical photovoltaic
structure in section. In FIGS. 2 and 3 and other figures, an arrow
labeled "hv" is used to indicate the light incident side of the
structure. In FIG. 3, 15 represents a thin film of a p-type
semiconductor, 16 a thin film of n-type semiconductor and 17 the
resulting photovoltaic junction. Window electrode 18 completes a
typical photovoltaic structure. Various photovoltaic structures are
known. For example, cells can be multiple junction or single
junction and comprise homo or hetero junctions. Semiconductor
structure 11 may comprise any of the thin film structures known in
the art, including but not limited to CIS, CIGS, CdTe, Cu2S,
amorphous silicon, so-called "Graetzel" electrolyte cells, organic
solar cells such as dye sensitized cells, polymer based
semiconductors, cells based on silicon inks and the like. Further,
semiconductor structure 11 may also represent characteristically
"non-thin film" cells such as those based on single crystal or
polycrystal silicon since many embodiments of the invention may
encompass such cells, as will be evident to those skilled in the
art in light of the teachings to follow.
[0164] "Window electrode" 18 normally comprises a conductive metal
oxide. These materials are applied as a thin layer, normally having
a thickness less than about 1 micrometer. In addition, these
materials have much higher intrinsic resistivity (in the range
0.001 ohm-cm.) than metals such as copper. Thus the light incident
surface of the cell, despite being characterized as conductive, has
limited current carrying capacity.
[0165] In the following, photovoltaic cells having a "bulk" metal
based support foil will be used to illustrate many of the
embodiments and teachings of the invention. The metal based foil
may often serve as the back electrode of the cell. However, those
skilled in the art will recognize that many of the applications of
the instant invention may not use a "bulk" foil as represented in
FIGS. 1 and 2. In many embodiments, other substrate structures,
such as a metallized polymer film or glass, or a thin conductive
polymer layer, may be employed as a back electrode rather than a
"bulk" metal foil.
[0166] FIG. 4 refers to a method of manufacture of bulk thin film
photovoltaic structures generally illustrated in FIGS. 1 and 2. In
the FIG. 4 embodiment, a metal-based support foil 12 is moved in
the direction of its length Y through a deposition process,
generally indicated as 19. Often foil 12 possesses structural
characteristics such that it may be characterized as self
supporting. Process 19 accomplishes deposition of the active
photovoltaic structure onto foil 12. Foil 12 is unwound from supply
roll 20a, passed through deposition process 19 and rewound onto
takeup roll 20b. Process 19 can comprise any of the processes
well-known in the art for depositing thin film photovoltaic
structures. These processes include electroplating, vacuum
evaporation and sputtering, chemical deposition, and printing of
nanoparticle precursors. Process 19 may also include treatments,
such as heat treatments, intended to enhance photovoltaic cell
performance.
[0167] Those skilled in the art will readily realize that the
deposition process 19 of FIG. 4 may often most efficiently produce
photovoltaic structure 1 having dimensions far greater than those
suitable for individual cells in an interconnected array. Thus, the
photovoltaic structure 1 may be subdivided into cells 10 having
dimensions X-10 and Y-10 as indicated in FIGS. 1A and 2A for
further fabrication. In FIG. 1A, width X-10 defines a first
photovoltaic cell terminal edge 45 and second photovoltaic cell
terminal edge 46. In one embodiment, for example, X-10 of FIG. 1A
may be from 0.02 inches to 12 inches and Y10 of FIG. 1A may be
characterized as "continuous". In other embodiments the final form
of cell 10 may be rectangular, such as 6 inch by 6 inch, 4 inch by
3 inch or 8 inch by 2 inch. In other embodiments, the photovoltaic
structure 1 of FIG. 1 may be subdivided in the "X" dimension only
thereby retaining the option of further processing in a
"continuous" fashion in the "Y" direction. In the following, cell
structure 10 in a form having dimensions suitable for
interconnection into a multi-cell array may be referred to as "cell
stock" or simply as cells. "Cell stock" can be characterized as
being either continuous or discreet.
[0168] FIG. 2B is a simplified depiction of cell 10 shown in FIG.
2A. In order to facilitate presentation of the aspects of the
instant invention, the simplified depiction of cell 10 shown in
FIG. 2B will normally be used.
[0169] Referring now to FIG. 5, there are illustrated cells 10 as
shown in FIG. 2A. The cells have been positioned to achieve spatial
positioning on the support substrate 21. Support structure 21 is by
necessity non-conductive at least in a space indicated by numeral
27 separating the adjacent cells 10. This insulating space prevents
short circuiting from metal foil electrode 12 of one cell to foil
electrode 12 of an adjacent cell. In order to achieve series
connection, electrical communication must be made from the top
surface of window electrode 18 to the foil electrode 12 of an
adjacent cell. This communication is shown in the FIG. 5 as a metal
wire or tab 41. The direction of the net current flow for the
arrangement shown in FIG. 5 is indicated by the double pointed
arrow "i". It should be noted that foil electrode 12 is normally
relatively thin, on the order of 5 micrometer to 250 micrometer.
Moreover, in order to have the flexibility and physical integrity
required for processing such as the roll-to-roll process 19 as
embodied in FIG. 4, a foil thickness of between 10 micrometers and
250 micrometer may be appropriate. Therefore, connecting to the
foil edge as indicated in FIG. 5 would be impractical. Thus, such
connections are normally made to the top surface 65 or the bottom
surface 66 of foil 12. One readily recognizes that connecting metal
wire or tab 41 is laborious, making inexpensive production
difficult.
[0170] FIG. 6 is a top plan view of a starting article in
production of a laminating current collector grid or electrode
according to the instant invention. FIG. 6 embodies a polymer based
film or glass substrate 70. Substrate 70 has width X-70 and length
Y-70. When substrate 70 comprises glass, it would typically be
processed as discrete articles having defined width and length
dimensions. In other embodiments involving, for example, flexible
films or webs and taught in detail below, Y-70 may be much greater
than width X-70, whereby substrate film 70 can generally be
described as "continuous" in length and able to be processed in
length direction Y-70 in a continuous fashion. FIG. 7 is a
sectional view taken substantially from the view 7-7 of FIG. 6.
Thickness dimension Z-70 is small in comparison to dimensions Y-70,
X-70. In a preferred embodiment substrate 70 may have a flexible
sheetlike, or web structure. However, substrate flexibility is not
a requirement for all embodiments of the invention. As shown in
FIG. 7, substrate 70 may be a laminate of multiple layers 72, 74,
76 etc. or may comprise a single layer of material. Any number of
layers 72, 74, 76 etc. may be employed. The layers 72, 74, 76 etc.
may comprise inorganic or organic components such as
thermoplastics, thermosets or silicon containing glass-like layers.
The various layers are intended to supply functional attributes
such as environmental barrier protection or adhesive
characteristics. Such functional layering is well-known and widely
practiced in the plastic packaging art. Sheetlike substrate 70 has
first surface 80 and second surface 82. In particular, in light of
the teachings to follow, one will recognize that it may be
advantageous to have layer 72 forming surface 80 comprise a
polymeric adhesive sealing material such as an ethylene vinyl
acetate (EVA), ethylene ethyl acetate (EEA), an ionomer, or a
polyolefin based adhesive to impart adhesive characteristics during
a possible subsequent lamination process. It may be advantageous
for the adhesive layer to have elastomeric characteristics to
insure flexibility and stress relief for the composite. Other
sealing materials useful in certain embodiments include those
comprising silicones, silicone gels, epoxies, polydimethyl siloxane
(PDMS), RTV rubbers, polyvinyl butyral (PVB), thermoplastic
polyurethanes (TPU), acrylics and urethanes. An adhesive layer 72
forming surface 80 may further comprise a curing component which
would activate to produce a cross linked structure. Such cross
linking may improve adhesion of surface 80 to a mating surface or
also function to resist permanent deformation during thermal
cycling. Suitable curatives may be activated by heat and/or
radiation such as ultraviolet (UV) radiation.
[0171] Lamination of such sheetlike films employing such sealing
materials is a common practice in the packaging industry. In the
packaging industry lamination is known and understood as applying a
film, normally polymer based and normally having a surface
comprising a sealing material, to a second surface and sealing them
together with heat and/or pressure. However, while a combination of
heat and pressure is often used in the lamination process, the
instant invention is applicable to laminating materials, such as
pressure sensitive adhesives, which may be applied using pressure
alone. Suitable sealing materials may be made tacky and flowable,
often under heated conditions, and retain their adhesive bond to
many surfaces upon cooling and/or release of pressure. A wide
variety of laminating films with associated sealing materials is
possible, depending on the surface to which the adhesive seal or
bond is to be made. Sealing materials such as olefin copolymers or
atactic polyolefins may be advantageous, since these materials
allow for the minimizing of materials which may be detrimental to
the longevity of a solar cell with which it is in contact.
Additional layers 74, 76 etc. may comprise materials which assist
in support or processing such as polypropylene, polyethylene
terepthalate and polycarbonate. Additional layers 74, 76 may
comprise barrier materials such as fluorinated polymers, biaxially
oriented polypropylene (BOPP), Saran, and thin compound layers such
as Siox. Saran is a tradename for poly (vinylidene chloride)
manufactured by Dow Chemical Corporation. Siox refers to a thin
film of silicon oxide often vapor deposited on a polymer support.
Additional layers 74, 76 etc. may also comprise materials intended
to afford protection against ultraviolet radiation and may also
comprise materials to promote curing. The instant invention does
not depend on the presence of any specific material for layers 72,
74, or 76. In many embodiments substrate 70 may be generally be
characterized as a laminating material. For example, the invention
has been successfully demonstrated using standard laminating films
sold by GBC Corp., Northbrook, Ill., 60062.
[0172] FIG. 8 depicts the structure of substrate 70 (possibly
laminate) as a single layer for purposes of presentation
simplicity. Substrate 70 will be represented as this single layer
in the subsequent embodiments, but it will be understood that
structure 70 may be a laminate of any number of layers. In
addition, substrate 70 is shown in FIGS. 6 through 8 as a uniform,
unvarying monolithic sheet. In this specification and claims, the
term "monolithic" or "monolithic structure" is used as is common in
industry to describe an object that is made or formed into or from
a single item. However, it is understood that various regions of
substrate 70 may differ in composition through thickness Z-70. For
example, selected regions of substrate 70 may comprise differing
sheetlike structures patched together using appropriate seaming
techniques. A purpose for such a "patchwork" structure will become
clear in light of the teachings to follow.
[0173] FIG. 9 is a plan view of the structure following an
additional manufacturing step.
[0174] FIG. 10 is a sectional view taken along line 10-10 of FIG.
9.
[0175] FIG. 11 is a sectional view taken along line 11-11 of FIG.
9.
[0176] In the embodiment of FIGS. 9, 10, and 11, a structure is now
designated 71 to reflect the additional processing. It is seen in
these embodiments that a repetitive pattern of multiple
repetitively spaced "fingers" or "traces", designated 84, extends
from "buss" or "tab" structures, designated 86. In the embodiments
of FIGS. 9, 10, and 11, both "fingers" 84 and "busses" 86 are
positioned on supporting substrate 70 in a grid pattern. In this
embodiment, "fingers" 84 extend in the width X-71 direction of
article 71 and "busses" ("tabs") extend in the Y-71 direction
substantially perpendicular to the "fingers". Dimensions and
structure for the "fingers" and "busses" may vary with application.
For example, if the article 71 is intended for collecting current
from a top light incident surface of a photovoltaic cell, one will
understand that shading by "fingers" 84 is of concern. Thus, the
surface area of the fingers may normally be minimized consistent
with adequate current carrying characteristics. Dimensions may also
be dictated somewhat by the materials and fabrication process used
to create the fingers and busses, and the dimensions of the
individual cell. For example, should the fingers be formed by a
process such as silk screening of an ink, a minimum practical width
of about 100 micrometer is typical. Should the fingers be formed by
other techniques such as selective metal etching or metal wire
placement, widths less than 100 micrometers may be suitable.
Spacing between the fingers may also vary depending on factors such
as current carrying capacity and surface conductivity of a mating
conductive surface.
[0177] While a pattern of "fingers" and "busses" is shown in the
FIG. 9 embodiment, one will readily understand that other patterns
appropriate to the eventual application of the article are possible
and that the pattern of "fingers"/"busses" is but one of many
structural patterns possible within the scope of the instant
invention. Specifically, the invention allows design flexibility
associated with the process used to establish the material pattern
of "fingers" and "busses". "Design flexible" processing includes
printing of conductive inks or "seed" layers, foil etching or
stamping, masked deposition using paint or vacuum deposition, and
the like. As an example, the conductive paths can have triangular
type surface structures increasing in width (and thus cross
section) in the direction of current flow. Thus the resistance
decreases as net current accumulates to reduce power losses.
Various structural features, such as radiused connections between
fingers and busses may be employed to improve structural robustness
Further, the invention permits a variety of structural forms to
create the pattern. For example, while the embodiments of FIGS. 9
through 11 show the "fingers" and "busses" as essentially planar
rectangular structures, the fingers or traces may be wires of
circular cross section.
[0178] As indicated, structure 71 may be produced and processed
extending continuously in the length "Y-71" direction. Repetitive
multiple "finger/buss" arrangements are shown in the FIG. 9
embodiment with a repeat dimension "F" as indicted. As will be
seen, dimension "F" is associated with the repeat distance among
adjacent interconnected photovoltaic cells. When structure 71 is
intended for eventual use as a current collector structure for the
light incident surface of a photovoltaic cell, portions of
substrate 70 not overlayed by "fingers" 84 and "busses" 86 remain
transparent or translucent to visible light. In the embodiment of
FIGS. 9 through 11, the "fingers" 84 and "busses" 86 are shown to
be a single layer for simplicity of presentation. However, the
"fingers" and "busses" can comprise multiple layers of differing
materials chosen to support various functional attributes. For
example the material in direct contact with substrate 70 defining
the "buss" or "finger" patterns may be chosen for its adhesive
affinity to surface 80 of substrate 70 and also to a subsequently
applied constituent of the buss or finger structure. Further, it
may be advantageous to have the first visible material component of
the fingers and busses be of dark color or black. As will be shown,
the light incident side (outside surface) of the substrate 70 will
eventually be surface 82. By having the first visible component of
the fingers and busses be dark, they will aesthetically blend with
the generally dark color of the photovoltaic cell. This eliminates
the often objectionable appearance of a metal colored grid
pattern.
[0179] "Fingers" 84 and "busses" 86 may comprise electrically
conductive material. Examples of such materials are metal wires and
foils, stamped or die cut metal patterns, conductive metal
containing inks and pastes such as those having a conductive filler
comprising silver or stainless steel, patterned deposited metals
such as etched metal patterns or masked vacuum deposited metals,
intrinsically conductive polymers and DER formulations. In a
preferred embodiment, the pattern of "fingers and "busses" comprise
electroplateable material such as DER or an electrically conductive
ink which will enhance or allow subsequent metal electrodeposition.
"Fingers" 84 and "busses" 86 may also comprise non-conductive
material which would assist accomplishing a subsequent deposition
of conductive material in the pattern defined by the "fingers" and
"busses". For example, "fingers" 84 or "busses" 86 could comprise a
polymer which may be seeded to catalyze chemical deposition of a
metal in a subsequent step. An example of such a material is seeded
ABS. Patterns comprising electroplateable materials or materials
facilitating subsequent electrodeposition are often referred to as
"seed" patterns or layers. "Fingers" 84 and "busses" 86 may also
comprise materials selected to promote adhesion of a subsequently
applied conductive material. "Fingers" 84 and "busses" 86 may
differ in actual composition and be applied separately. For
example, "fingers" 84 may comprise a conductive ink while
"buss/tab" 86 may comprise a conductive metal foil strip.
Alternatively, fingers and busses may comprise a continuous
unvarying monolithic material structure forming portions of both
fingers and busses. Fingers and busses need not both be present in
certain embodiments of the invention.
[0180] One will recognize that while shown in the embodiments as a
continuous void free surface, "buss" 86 could be selectively
structured. Such selective structuring may be appropriate to
enhance functionality, such as flexibility, of article 71 or any
article produced there from. Furthermore, regions of substrate 70
supporting the "buss" regions 86 may be different than those
regions supporting "fingers" 84. For example, substrate 70
associated with "buss region" 86 may comprise a fabric while
substrate 70 may comprise a solid transparent film in the region
associated with "fingers" 84. A "holey" structure in the "buss
region" would provide increased flexibility, increased surface area
and increased structural characteristic for an adhesive to
grip.
[0181] The embodiment of FIG. 9 shows multiple "busses" 86
extending in the direction Y-71 with "fingers" extending from one
side of the "busses" in the X-71 direction. Many different such
structural arrangements of the laminating current collector
structures are possible within the scope and purview of the instant
invention. It is important to note however that the laminating
current collector structures of the instant invention may be
manufactured utilizing continuous, bulk processing, including roll
to roll processing. While the collector grid embodiments of the
current invention may advantageously be produced using continuous
processing, one will recognize that combining of grids or
electrodes so produced with mating conductive surfaces may be
accomplished using either continuous or batch processing. In one
case it may be desired to produce photovoltaic cells having
discrete defined dimensions. For example, single crystal silicon
cells are often produced having X-Y dimensions of about 6 inches by
6 inches. In this case the collector grids of the instant
invention, which may be produced continuously, may then be
subdivided to dimensions appropriate for combining with such cells.
In other cases, such as production of many thin film photovoltaic
structures, a continuous roll-to-roll production of an expansive
surface article can be accomplished in the "Y" direction as
identified in FIG. 1. Such a continuous expansive photovoltaic
structure may be combined with a continuous arrangement of
collector grids of the instant invention in a semicontinuous or
continuous manner. Alternatively the expansive semiconductor
structure may be subdivided into continuous strips of cell stock.
In this case, combining a continuous strip of cell stock with a
continuous strip of collector grid of the instant invention may be
accomplished in a continuous or semi-continuous manner.
[0182] FIGS. 12, 13 and 14 correspond to the views of FIGS. 9, 10
and 11 respectively following an additional optional processing
step. FIG. 15 is a sectional view taken substantially along line
15-15 of FIG. 12. FIGS. 12 through 15 show additional conductive
material deposited onto the "fingers" 84 and "busses" 86 of FIGS. 9
through 11. In this embodiment additional conductive material is
designated by one or more layers 88, 90 and the fingers and busses
project above surface 80 as shown by dimension "H". In some cases
it may be desirable to reduce the height of projection "H" prior to
eventual combination with a conductive surface such as 59 or 66 of
photovoltaic cell 10. This reduction may be accomplished by passing
the structures as depicted in FIGS. 12-15 through a pressurized
and/or heated roller or the like to embed "fingers" 84 and/or
"busses" 86 into layer 72 of substrate 70.
[0183] While shown as two layers 88, 90, it is understood that this
conductive material could comprise more than two layers or be a
single layer. In addition, while each additional conductive layer
is shown in the embodiment as having the same continuous monolithic
material extending over both the buss and finger patterns, one will
realize that selective deposition techniques would allow the
additional "finger" layers to differ from additional "buss" layers.
For example, as best shown in FIG. 14, "fingers" 84 have top free
surface 98 and "busses" 86 have top free surface 100. As noted,
selective deposition techniques such as brush electroplating or
masked deposition would allow different materials to be considered
for the "buss" surface 100 and "finger" surface 98. In a preferred
embodiment, at least one of the additional layers 88, 90 etc. are
deposited by electrodeposition, taking advantage of the deposition
speed, compositional choice, low cost and selectivity of the
electrodeposition process. Many various metals, including highly
conductive silver, copper and gold, nickel, tin, indium and alloys
of these can be readily electrodeposited. In these embodiments, it
may be advantageous to utilize electrodeposition technology giving
an electrodeposit of low tensile stress to prevent curling and
promote flatness of the metal deposits. In particular, use of
nickel deposited from a nickel sulfamate bath, nickel deposited
from a bath containing stress reducing additives such as
brighteners, or copper from a standard acid copper bath have been
found particularly suitable. Electrodeposition also permits precise
control of thickness and composition to permit optimization of
other requirements of the overall manufacturing process for
interconnected arrays. Thus, the electrodeposited metal may
significantly increase the current carrying capacity of the "buss"
and "finger" structure and may be the dominant current carrying
material for these structures. In general, electrodeposit
thicknesses characterized as "low profile", less than about 50
micrometer (i.e. 1 micrometer, 10 micrometer, 25 micrometer, 50
micrometer), supply adequate current carrying capacity for the grid
"fingers" of the instant invention. Thus electrodeposited metal
offers a very appropriate material to achieve the dominant current
carrying capacity for the "buss" and "finger" structure.
Alternatively, these additional conductive layers may be deposited
by selective chemical deposition or registered masked vapor
deposition. These additional layers 88, 90 may also comprise
conductive inks or adhesives applied by registered printing.
[0184] It has been found very advantageous to form surface 98 of
"fingers" 84 or top surface 100 of "busses" 86 with a material
compatible with the conductive surface with which eventual contact
is made. In preferred embodiments, electroless deposition or
electrodeposition is used to form a suitable metallic surface.
Specifically electrodeposition offers a wide choice of potentially
suitable materials to form the top surface. Corrosion resistant
materials such as nickel, chromium, tin, indium, silver, gold and
platinum are readily electrodeposited. These functional top
coatings, sometimes referred to as "flash" coatings, are often
thin, less than about two micrometer (i.e. 0.1 micrometer, 1
micrometer, 2 micrometer). The "flash" coatings normally need not
exhibit exceptional current carrying capacity since the bulk of the
current may be carried by the underlying material such as the above
described electroplated metals such as copper. When compatible, of
course, surfaces comprising metals such as copper or zinc or alloys
of copper or zinc may be considered. Alternatively, surfaces 98 and
100 may comprise a conversion coating, such as a chromate coating,
of a material such as copper or zinc. Further, as will be discussed
below, it may be highly advantageous to choose a material to form
surfaces 98 or 100 which exhibits adhesive or bonding ability to a
subsequently positioned abutting conductive surface. For example,
it may be advantageous to form surfaces 98 and 100 using an
electrically conductive adhesive. Such an adhesive could be applied
intermittently, for example as a series of "dots" over the
underlying conductive surface. Alternatively, it may be
advantageous to form surfaces 98 of "fingers" 84 or 100 of "busses"
86 with a conductive material such as a low melting point metal
such as tin, tin containing alloys, indium, lead etc. in order to
facilitate electrical joining to a complimentary conductive
surface. Such low melting point materials can be caused to melt at
temperatures below that of many polymer processing operations such
as lamination. These processes are normally carried out at
temperatures below about 325 degree C. (i.e. 100 degree C., 150
degree C., 250 degree C.). One will note that materials forming
"fingers" surface 98 and "buss" surface 100 need not be the same.
It is emphasized that many of the principles taught in detail with
reference to FIGS. 6 through 15 extend to additional embodiments of
the invention taught in subsequent Figures.
[0185] FIG. 16 is a top plan view of an article 102 embodying
another form of the electrodes of the current invention. FIG. 16
shows article 102 having structure comprising "fingers" 84a
extending from "buss/tab" 86a arranged on a substrate 70a. The
structure of FIG. 16 is similar to that shown in FIG. 9. However,
whereas FIG. 9 depicted multiple finger and buss/tab structures
arranged in a substantially repetitive pattern in direction "X-71",
the FIG. 16 embodiment consists of one finger/buss pattern. Thus,
the dimension "X-102" of FIG. 16 may be roughly equivalent to the
repeat dimension "F" shown in FIG. 9. Indeed, it is contemplated
that article 102 of FIG. 16 may be produced by subdividing the FIG.
9 structure 71 according to repeat dimension "F" shown in FIG. 9.
Dimension "Y-102" may be chosen appropriate to the particular
processing scheme envisioned for the eventual lamination to a
conductive surface such as a photovoltaic cell. However, it is
envisioned that "Y-102" may be much greater than "X-102" such that
article 102 may be characterized as continuous or capable of being
processed in a continuous, possibly roll-to-roll fashion. Article
102 has a first terminal edge 104 and second terminal edge 106. In
the FIG. 16 embodiment "fingers" 84a are seen to terminate prior to
intersection with terminal edge 106. One will understand that this
is not a requirement.
[0186] "Fingers" 84a and "buss/tab" 86a of FIG. 16 have the same
characterization as "fingers" 84 and "busses" 86 of FIGS. 9 through
11. Like the "fingers" 84 and "busses" 86 of FIGS. 9 through 11,
"fingers" 84a and "buss" 86a of FIG. 16 may comprise materials that
are either conductive, assist in a subsequent deposition of
conductive material or promote adhesion of a subsequently applied
conductive material to substrate 70a. While shown as a single
layer, one appreciates that "fingers" 84a and "buss" 86a may
comprise multiple layers. The materials forming "fingers" 84a and
"buss" 86a may be different or the same. In addition, the substrate
70a may comprise different materials or structures in those regions
associated with "fingers" 84a and "buss region" 86a. For example,
substrate 70a associated with "buss region" 86a may comprise a
fabric to provide thru-hole communication and enhance flexibility,
while substrate 70a in the region associated with "fingers" 84a may
comprise a film devoid of thru-holes such as depicted in FIGS. 6-8.
A "holey" structure in the "buss region" would provide increased
flexibility, surface area and structural characteristic for an
adhesive to grip.
[0187] FIGS. 17 and 18 are sectional embodiments taken
substantially from the perspective of lines 17-17 and 18-18
respectively of FIG. 16. FIGS. 17 and 18 show that article 102 has
thickness Z-102 which may be much smaller than the X and Y
dimensions, thereby allowing article 102 to be flexible and
processable in roll form. Also, flexible sheet-like article 102 may
comprise any number of discrete layers (three layers 72a, 74a, 76a
are shown in FIGS. 17 and 18). These layers contribute to
functionality as previously pointed out in the discussion of FIG.
7. As will be understood in light of the following discussion, it
is normally helpful for layer 72a forming free surface 80a to
exhibit adhesive characteristics to the eventual abutting
conductive surface.
[0188] FIG. 19 is an alternate representation of the sectional view
of FIG. 18. FIG. 19 depicts substrate 70a as a single layer for
ease of presentation. The single layer representation will be used
in many following embodiments, but one will understand that
substrate 70a may comprise multiple layers.
[0189] FIG. 20 is a sectional view of the article now identified as
110, similar to FIG. 19, after an additional optional processing
step. In a fashion like that described above for production of the
current collector structure of FIGS. 12 through 15, additional
conductive material (88a/90a) has been deposited by optional
processing to produce the article 110 of FIG. 20. The discussion
involving processing to produce the article of FIGS. 12 through 15
is proper to describe production of the article of FIG. 20. Thus,
while additional conductive material has been designated as a
single layer (88a/90a) in the FIG. 20 embodiment, one will
understand that layer (88a/90a) of FIG. 20 may represent any number
of multiple additional layers. In subsequent embodiments,
additional conductive material (88a/90a) will be represented as a
single layer for ease of presentation. In its form prior to
combination with a conductive surface (such as surface 59 of cells
10), the structures such as shown in FIGS. 9-15, and 16-20 can be
referred to as "current collector stock". For the purposes of this
specification and claims a current collector in its form prior to
combination with a conductive surface can be referred to as
"current collector stock". "Current collector stock" can be
characterized as being either continuous or discrete.
[0190] The invention contemplates a particularly attractive
conductive joining that may be achieved through a technique
described herein as a laminated contact. In light of the teachings
to follow one will recognize that the structures shown in FIGS.
9-15 and 16-20 may function and be further characterized as
electrodes employing a laminated contact (laminating electrodes).
One structure involved in the laminated contact is a first portion
of conductive structure which is to be electrically joined to a
second conductive surface. The first portion comprises a conductive
pattern positioned over or embedded in a surface of an adhesive. In
a preferred embodiment, the adhesive is characterized as a
polymeric hot melt adhesive. A hot melt adhesive is a material,
substantially solid at room temperature, whose full adhesive
affinity is activated by heating, normally to a temperature where
the material softens or melts sufficiently for it to flow under
simultaneously applied pressure. Many various hot melt materials,
such as ethylene vinyl acetate (EVA), are well known in the art. It
is noted that while the invention is described herein regarding the
use of hot melt laminating adhesives, the invention contemplates
use of laminating adhesives such as pressure sensitive adhesives
not requiring heat for function.
[0191] In the process of producing a laminated contact, the exposed
surface of a conductive material pattern positioned on or embedded
in the surface of an adhesive is brought into facing relationship
with a second conductive surface to which electrical joining is
intended. Heat and/or pressure are applied to soften the adhesive
which then may flow around edges or through openings in the
conductive pattern to also contact and adhesively "grab" the
exposed second surface portions adjacent the conductive pattern.
When heat and pressure are removed, the adhesive adjacent edges of
the conductive pattern firmly fixes features of conductive pattern
in secure mechanical contact with the second surface.
[0192] The laminated contact is particularly suitable for the
electrical joining requirements of many embodiments of the instant
invention. A simplified depiction of structure to assist
understanding the concept of a laminated contact is embodied in
FIGS. 61 and 62. FIG. 61 shows a top plan view of an article 350.
Article 350 comprises a conductive mesh 352 positioned on the
surface of or partially embedded in adhesive 351. Mesh 352 may be
in the form of a metal screen, a metallized fabric or a fabric
comprising conductive fibers and the like. Adhesive 351 possesses
adhesive affinity to the conductive surface to which electrical
joining is intended. Numeral 354 indicates holes through the mesh
or fabric. One will realize that many different patterns and
conductive materials may be suitable for the conductive material
represented by conductive mesh 352, including conductive comb-like
patterns, serpentine traces, monolithic metal mesh patterns,
metallized fabric, wires, etched or die cut metal forms, forms
comprising vacuum deposited, chemically deposited and
electrodeposited metals, etc.
[0193] FIG. 62 shows a sectional view of article 350 juxtaposed
such that the free surface of adhesive 351 and metal 352 are in
facing relationship to a mating conductive surface 360 of article
362 to which electrical joining is desired. In the embodiment,
article 350 is seen to be a composite of the conductive material
pattern 352 positioned on a top surface of hot melt adhesive film
351. In the embodiment, an additional support film 366 is included
for structural and process integrity, and possibly barrier
properties. Additional film 366 may be a polymer film of a material
such as polyethylene terephthalate, polypropylene, polycarbonate,
etc. Film 366 may be multilayered and comprise layers intended to
achieve functional attributes such as moisture barrier, UV
protection etc. Film 366 may also comprise a structure such as
glass. Article 350 can include additional layered materials (not
shown) to achieve desired functional characteristics similar to
article 70 discussed above. Also depicted in FIG. 62 is article 362
having a bottom surface 360. Surface 360 may represent, for
example, the top or bottom surfaces 59 or 66 respectively of solar
cell structure 10 (FIG. 2A).
[0194] In order to achieve the laminated contact, articles 350 and
362 are brought together in the facing relationship depicted and
heat and pressure are applied. The adhesive layer 351 softens and
flows to contact surface 360. In the case of the FIG. 62
embodiment, flow occurs through the holes 354 in the mesh 352. Upon
cooling and removal of the pressure, the metal mesh 352 overlays
and is held in secure and firm electrical contact with surface 360
by virtue of the adhesive bond between adhesive 351 and surface
360. Thus mesh may function as a laminated electrode or current
collector in combination with surface 360.
[0195] Figures illustrates a process 92 by which the current
collector grids of FIGS. 16 through 20 may be combined with the
structure illustrated in FIG. 1A, 2A or 2B to accomplish lamination
of current collecting electrodes of top and bottom surfaces
photovoltaic cell stock. The combining process envisioned in FIG.
21 has been demonstrated using standard lamination processing such
as roll lamination and vacuum lamination. In a preferred
embodiment, roll lamination allows continuous lamination processing
and a wide choice of application temperatures and pressure.
Temperatures employed are typical for lamination of standard
polymeric materials used in the high volume plastics packaging
industry, normally less than about 325 degree Centigrade. Process
92 is but one of many processes possible to achieve such
application. In FIG. 21 rolls 94 and 97 represent "continuous" feed
rolls of grid/buss structure on a flexible sheetlike substrate
(current collector stock) as depicted in FIGS. 16 through 20. Roll
96 represents a "continuous" feed roll of the sheetlike cell stock
as depicted in FIGS. 1A, 2A and 2B. FIG. 22 is a sectional view
taken substantially from the perspective of line 22-22 of FIG. 21.
FIG. 22 shows a photovoltaic cell 10 such as embodied in FIGS. 2A
and 2B disposed between two current collecting electrodes 110a and
110b such as article 110 embodied in FIG. 20. It is understood that
suitable insulating materials (not shown) may be applied to
terminal edges 45 and 46 of cell 10 to prevent shorting by the
conductive materials of articles 110a and 110b in crossing the
terminal edges.
[0196] FIG. 23 is a sectional view showing the article 112
resulting from using process 92 to laminate the three individual
structures of FIG. 22 while substantially maintaining the relative
positioning depicted in FIG. 22. FIG. 23 shows that a laminating
current collector electrode 110a has now been applied to the top
conductive surface 59 of cell 10. Portions of surface 80a of
electrode 110a not covered with "fingers" 84a face and are
adhesively bonded to surface 59 of cell 10. Similarly, laminating
current collector electrode 110b mates with and contacts the bottom
conductive surface 66 of cell 10. Grid "fingers" 84a of a top
current collector electrode 110a project laterally across the top
surface 59 of cell stock 10 and extend to a "buss" region 86a
located outside terminal edge 45 of cell stock 10. The grid
"fingers" 84a of a bottom current collector electrode 110b project
laterally across the bottom surface 66 of cell stock 10 and extend
to a "buss" region 86a located outside terminal edge 46 of cell
stock 10. Thus article 112 is characterized as having readily
accessible conductive surface portions 114 and 116 in the form of
tabs in electrical communication with both top cell surface 59 and
bottom cell surface 66 respectively. Article 112 can be described
as a "tabbed cell stock". In the present specification and claims,
a "tabbed cell stock" is defined as a photovoltaic cell structure
combined with electrically conducting material in electrical
communication with a conductive surface of the cell structure, and
further wherein the electrically conducting material extends
outside a terminal edge of the cell structure to present a readily
accessible contact surface. In light of the present teachings, one
will understand that "tabbed cell stock" can be characterized as
being either continuous or discrete. One will also recognize that
electrodes 110a and 110b can be used independently of each other.
For example, 110b could be employed as a back side electrode while
a current collector structurally or materially different than 110b
is employed on the top side of cell 10. Also, one will understand
that while electrodes 110a and 110b are shown in the embodiment to
be the same structure, different structures and materials may be
chosen for electrodes 110a and 110b.
[0197] A "tabbed cell stock" combination 112 has a number of
fundamental advantageous attributes. First, the laminated current
collector electrodes protect the surfaces of the cell from defects
possibly introduced by the further handing associated with final
interconnections. Moreover, "tabbed cell stock" can be produced as
a continuous form using a continuous cell "strip" originally
produced in the "machine" direction ("Y" direction of FIG. 1 or
1A). Such a continuous raw cell "strip" would be anticipated to
have more uniform performance characteristics than portions chosen
transverse to the "machine" direction ("X" direction of FIG. 1).
Next, the "tabbed cell stock" combination 112 may be produced in a
continuous fashion in the Y direction (direction normal to the
paper in the sectional view of FIG. 23) using either roll
lamination or intermittent vacuum lamination. Following the
envisioned lamination, the "tabbed cell stock" strip can be
continuously monitored for quality since there is ready access to
the conductive, exposed free surfaces 114 and 116 in electrical
communication with top cell surface 59 and the cell bottom surface
66 respectively. Alternative "sorting" options exist at this
point.
[0198] a. It would be anticipated that since the raw cell "strip"
is continuous in the "machine" direction, performance variation
would be minimized and the "tabbed cell stock" could be accumulated
in takeup roll form.
[0199] b. Should there be excessive performance variation along the
length of the raw cell "strip", the "tabbed cell stock" combination
may be continuously characterized, cut to standard lengths and
automatically sorted prior to assembly into a module. Excessively
defective cell material could be readily identified and discarded
prior to final interconnection into a module. Acceptable lengths
could be automatically sorted according to defined parameters and
placed in appropriate cassette feeders prior to assembly into final
modules.
[0200] The lamination process 92 of FIG. 21 normally involves
application of heat and pressure. Temperatures will vary depending
on materials and exposure time. Typical temperatures less than
about 325 degree Centigrade are envisioned. Lamination temperatures
of less than 325 degree centigrade would be more than sufficient to
melt and activate not only typical polymeric sealing materials but
also many low melting point metals, alloys and metallic solders.
For example, tin melts at about 230 degree Centigrade and its
alloys even lower. Tin alloys with for example bismuth, lead and
indium are common industrial materials. Many conductive "hot melt"
adhesives can be activated at even lower temperatures such as 200
degree Centigrade. Typical thermal curing temperatures for polymers
are in the range 95 to 200 degree Centigrade. Thus, typical
lamination practice widespread in the packaging industry is
normally appropriate to simultaneously accomplish many conductive
joining possibilities.
[0201] It will be understood that while the process 92 of FIG. 21
envisions a roll type lamination, other forms of laminating process
are appropriate in practice of the invention. For example, a
semi-continuous or indexed feed lamination process, perhaps
augmented by vacuum, may be employed. Moreover, should the
substrate 70a comprise a rigid or discrete component such as glass,
a semi-continuous or discrete batch lamination process may be
envisioned.
[0202] The sectional drawings of FIGS. 24 and 25 show the result of
joining multiple articles 112a, 112b. Each article has a readily
accessible downward facing pattern 114 (in the drawing perspective)
with a conductive surface 100a in communication with the cell top
surface 59. A readily accessible upward facing pattern 116 having
another conductive surface 100a communicates with the cell bottom
surfaces 66. One will appreciate that in this embodiment, current
collector 110b functions as an interconnecting substrate unit.
Series connections are easily achieved by overlapping the top
surface extension 114 of one article 112b and a bottom surface
extension 116 of a second article 112a and electrically connecting
these extensions with electrically conductive joining means such as
conductive adhesive 42 shown in FIGS. 24 and 25. Other electrically
conductive joining means including those defined above may be
selected in place of conductive adhesive 42. For example, surfaces
114 and 116 could comprise solderable material which would fuse
during a lamination process. Alternatively, surfaces 114 and 116
could overlap and be electrically joined to top and bottom surfaces
of a metal foil member. Finally, since the articles 112 of FIG. 23
can be produced in a continuous form (in the direction normal to
the paper in FIG. 23) the series connections and array production
embodied in FIGS. 24 and 25 may also be accomplished in a
continuous manner by using continuous feed rolls of "tabbed cell
stock" 112. However, while continuous assembly may be possible,
other processing may be envisioned to produce the interconnection
embodied in FIGS. 24 and 25. For example, defined lengths of
"tabbed cell stock" 112 could be produced by subdividing a
continuous strip of "tabbed cell stock" 112 in the Y dimension and
the individual articles thereby produced could be arranged as shown
in FIGS. 24 and 25 using, for example, standard pick and place
positioning.
[0203] FIG. 26 is a top plan view of an article in production of
another embodiment of a laminating current collector grid or
electrode according to the instant invention. FIG. 26 embodies a
polymer based film or glass substrate 120. Substrate 120 has width
X-120 and length Y120. In embodiments, taught in detail below,
Y-120 may be much greater than width X-120, whereby film 120 can
generally be described as "continuous" in length and able to be
processed in length direction Y-120 in a continuous roll-to-roll
fashion. FIG. 27 is a sectional view taken substantially from the
view 27-27 of FIG. 26. Thickness dimension Z-120 is small in
comparison to dimensions Y-120, X-120 and thus substrate 120 may
have a flexible sheetlike, or web structure contributing to
possible roll-to-roll processing. As shown in FIG. 27, substrate
120 may be a laminate of multiple layers 72b, 74b, 76b etc. or may
comprise a single layer of material. Thus substrate 120 may have
structure similar to that of the FIGS. 6 through 8 embodiments, and
the discussion of the characteristics of article 70 of FIGS. 6
through 8 is proper to characterize article 120 as well. As with
the representation of the article 70 of FIGS. 6 through 8, and as
shown in FIG. 28, article 120 (possibly multilayered) will be
embodied as a single layer in the following for simplicity of
presentation.
[0204] FIG. 29 is a top plan view of an article 124 following an
additional processing step using article 120. FIG. 30 is a
sectional view substantially from the perspective of lines 30-30 of
FIG. 29. The structure depicted in FIGS. 29 and 30 is similar to
that embodied in FIGS. 16 and 18. It is seen that article 124
comprises a pattern of "fingers" or "traces", designated 84b,
extending from "buss" or "tab" structures, designated 86b. In the
embodiments of FIGS. 29 and 30, both "fingers" 84b and "busses" 86b
are positioned on supporting substrate 120 in a grid pattern.
"Fingers" 84b extend in the width X-124 direction of article 124
and "busses" ("tabs") 86b extend in the Y-124 direction
substantially perpendicular to the "fingers". In the FIG. 29
embodiment, it is seen that the ends of the fingers opposite the
"buss" 86b are joined by connecting trace of material 128 extending
in the "Y-124" direction. In the embodiment of FIGS. 29 and 30, the
buss 86b region is characterized as having multiple regions 126
devoid of material forming "buss" pattern 86b. In the FIG. 29
embodiment, the voided regions 126 are presented as circular
regions periodically spaced in the "Y-124" direction. One will
understand in light of the teachings to follow that the circular
forms 126 depicted in FIG. 29 is but one of many different patterns
possible for the voided regions 126. The sectional view of FIG. 30
shows the voided regions 126 leave regions of the top surface 80b
of substrate 120 exposed. Surface 80b of substrate 120 remains
exposed in those regions not covered by the finger/buss pattern.
These exposed regions are further indicated by numeral 127 in FIG.
29.
[0205] Structure 124 may be produced, processed and extend
continuously in the length "Y-124" direction.
[0206] The embodiment of FIGS. 29 and 30 show substrate 120 as a
uniform monolithic structure. As discussed for the embodiments of
FIGS. 9-15 and 16-20, regions of substrate 120 associated with
fingers 84b may differ from regions supporting buss 86b. However,
it is understood that should article 124 be intended to mate with a
light incident surface 59 of a photovoltaic cell, portions of
substrate 120 not overlayed by material forming "fingers" 84b will
remain transparent or translucent to visible light. Such regions
are generally identified by numeral 127 in FIG. 29. In the
embodiment of FIGS. 29 and 30, the "fingers" 84b and "busses" 86b
are shown to be a single layer for simplicity of presentation.
However, the "fingers" and "busses" can comprise multiple layers of
differing materials chosen to support various functional
attributes. For example the material defining the "buss" or
"finger" patterns which is in direct contact with substrate 120 may
be chosen for its adhesive affinity to surface 80b of substrate 120
and also to a subsequently applied constituent of the buss or
finger structure. Further, it may be advantageous to have the first
visible material component of the fingers and busses be of dark
color or black. As will be shown, the light incident side (outside
surface) of the substrate 120 will eventually be surface 82b. By
having the first visible component of the fingers and busses be
dark, they will aesthetically blend with the generally dark color
of the photovoltaic cell. This eliminates the often objectionable
appearance of a metal colored grid pattern. As previously discussed
permissible dimensions and structure for the "fingers" and "busses"
will vary somewhat depending on materials and fabrication process
used for the fingers and busses, and the dimensions of the
individual cell.
[0207] "Fingers" 84b and "busses" 86b may comprise electrically
conductive material. Examples of such materials are metal wires and
foils, stamped metal patterns, conductive metal containing inks and
pastes such as those having a conductive filler comprising silver
or stainless steel, patterned deposited metals such as etched metal
patterns or masked vacuum deposited metals, intrinsically
conductive polymers and DER formulations. In a preferred
embodiment, the "fingers and "busses" comprise electroplateable
material such as DER or an electrically conductive ink which will
enhance or allow subsequent metal electrodeposition. "Fingers" 84b
and "busses" 86b may also comprise non-conductive material which
would assist accomplishing a subsequent deposition of conductive
material in the pattern defined by the "fingers" and "busses". For
example, "fingers" 84b or "busses" 86b could comprise a polymer
which may be seeded to catalyze chemical deposition of a metal in a
subsequent step. An example of such a material is seeded ABS.
Patterns comprising electroplateable materials or materials
facilitating subsequent electrodeposition are often referred to as
"seed" patterns or layers. "Fingers" 84b and "busses" 86b may also
comprise materials selected to promote adhesion of a subsequently
applied conductive material. "Fingers" 84b and "busses" 86b may
differ in actual composition and be applied separately. For
example, "fingers" 84b may comprise a conductive ink while
"buss/tab" 86b may comprise a conductive metal foil strip.
Alternatively, fingers and busses may comprise a continuous
unvarying monolithic material structure forming portions of both
fingers and busses. Fingers and busses need not both be present in
certain embodiments of the invention.
[0208] The embodiments of FIGS. 29 and 30 show the "fingers" 84b,
"busses" 86b, and connecting trace 128 as essentially planar
rectangular structures. Other geometrical forms are clearly
possible, especially when design flexibility is associated with the
process used to establish the material pattern of "fingers" and
"busses". "Design flexible" processing includes printing of
conductive inks or "seed" layers, foil etching or stamping, masked
deposition using paint or vacuum deposition, and the like. For
example, these conductive paths can have triangular type surface
structures increasing in width (and thus cross section) in the
direction of current flow. Thus the resistance decreases as net
current accumulates to reduce power losses. Alternatively, one may
select more intricate patterns, such as a "watershed" pattern as
described in U.S. Patent Application Publication 2006/0157103 A1
which is hereby incorporated in its entirety by reference. Various
structural features, such as radiused connections between fingers
and busses may be employed to improve structural robustness.
[0209] It is important to note however that the laminating current
collector structures of the instant invention may be manufactured
utilizing continuous, bulk roll to roll processing. While the
collector grid embodiments of the current invention may
advantageously be produced using continuous processing, one will
recognize that combining of grids or electrodes so produced with
mating conductive surfaces may be accomplished using either
continuous or batch processing. In one case it may be desired to
produce photovoltaic cells having discrete defined dimensions. For
example, single crystal silicon cells are often produced having X-Y
dimensions of 6 inches by 6 inches. In this case the collector
grids of the instant invention, which may be produced continuously,
may then be subdivided to dimensions appropriate for combining with
such cells. In other cases, such as production of many thin film
photovoltaic structures, a continuous roll-to-roll production of an
expansive surface article can be accomplished in the "Y" direction
as identified in FIG. 1. Such a continuous expansive photovoltaic
structure may be combined with a continuous arrangement of
collector grids of the instant invention in a semicontinuous or
continuous manner. Alternatively the expansive semiconductor
structure may be subdivided into continuous strips of cell stock.
In this case, combining a continuous strip of cell stock with a
continuous strip of collector grid of the instant invention may be
accomplished in a continuous or semi-continuous manner.
[0210] FIG. 31 corresponds to the view of FIG. 30 following an
additional optional processing step. The FIG. 31 article is now
designated by numeral 125 to reflect this additional processing.
FIG. 31 shows additional conductive material deposited onto the
"fingers" 84b and "buss" 86b. In this embodiment additional
conductive material is designated by one or more layers (88b/90b)
and the fingers and busses project above surface 80b as shown by
dimension "H". It is understood that conductive material could
comprise more than two layers or be a single layer. Conductive
material (88b/90b) is shown as a single layer in the FIG. 31
embodiment for ease of presentation. Article 125 is another
embodiment of a "current collector stock". Dimension "H" is
normally smaller than about 50 micrometers and thus the structure
of fingers and busses depicted in FIG. 31 can be considered as a
"low profile" structure. In some cases it may be desirable to
reduce the height of projection "H" prior to eventual combination
with a conductive surface such as 59 or 66 of photovoltaic cell 10.
This reduction may be accomplished by passing the structures as
depicted in FIGS. 29-31 through a pressurized and/or heated roller
or the like to partially embed "fingers" 84b and/or "busses" 86b
into layer 72b of substrate 120.
[0211] While each additional conductive material is shown the FIG.
31 embodiment as having the same continuous monolithic material
extending over both the buss and finger patterns, one will realize
that selective deposition techniques would allow the additional
"finger" layers to differ from additional "buss" layers. For
example, as shown in FIG. 31, "fingers" 84b have top free surface
98b and "busses" 86b have top free surface 100b. As noted,
selective deposition techniques such as brush electroplating or
masked deposition would allow different materials to be considered
for the "buss" surface 100b and "finger" surface 98b. In a
preferred embodiment, at least one of the additional layers
(88b/90b) etc. are deposited by electrodeposition, taking advantage
of the deposition speed, compositional choice, low cost and
selectivity of the electrodeposition process. Many various metals,
including highly conductive silver, copper and gold, nickel, tin
and alloys can be readily electrodeposited. In these embodiments,
it may be advantageous to utilize electrodeposition technology
giving an electrodeposit of low tensile stress to prevent curling
and promote flatness of the metal deposits. In particular, use of
nickel deposited from a nickel sulfamate bath, nickel deposited
from a bath containing stress reducing additives such as
brighteners, or copper from a standard acid copper bath have been
found particularly suitable. Electrodeposition also permits precise
control of thickness and composition to permit optimization of
other requirements of the overall manufacturing process for
interconnected arrays. Alternatively, these additional conductive
layers may be deposited by selective chemical deposition or
registered masked vapor deposition. These additional layers (88/90)
may also comprise conductive inks applied by registered
printing.
[0212] It has been found very advantageous to form surface 98b of
"fingers" 84b or top surface 100b of "busses" 86b with a material
compatible with the conductive surface with which eventual contact
is made. In preferred embodiments, electroless deposition or
electrodeposition is used to form a suitable surface 98b or 100b.
Specifically electrodeposition offers a wide choice of potentially
suitable materials to form these top surfaces. Corrosion resistant
materials such as nickel, chromium, tin, indium, silver, gold and
platinum are readily electrodeposited. When compatible, of course,
surfaces comprising metals such as copper or zinc or alloys of
copper or zinc may be considered. Alternatively, the surface 98b or
100b may comprise a conductive conversion coating, such as a
chromate coating, of a material such as copper or zinc. Further, as
will be discussed below, it may be highly advantageous to choose a
material to form surfaces 98b or 100b which exhibits adhesive or
bonding ability to a subsequently positioned abutting conductive
surface. For example, it may be advantageous to form surfaces 98b
and 100b using an electrically conductive adhesive or low melting
point metal or solder. For example, forming surfaces 98b or 100b
with a conductive hot melt adhesive or with materials such as tin
or tin alloyed with element such as lead, bismuth or indium could
result in a surface material having a melting point less than the
temperature of a subsequent lamination process. This would
facilitate electrical joining during the subsequent lamination
steps. One will note that materials forming "fingers" surface 98b
and "buss" surface 100b need not be the same.
[0213] FIG. 32 depicts an arrangement of 3 articles just prior to a
laminating process according to a process embodiment such as that
of FIG. 21. In the FIG. 32 embodiment, "current collector stock"
125 is positioned above a photovoltaic cell 10. A second article of
laminating "current collector stock", identified by numeral 129, is
positioned beneath cell 10. Article 129 may be similar in structure
to article 110 of FIG. 20.
[0214] FIG. 33 shows the article 130 resulting from passing the
FIG. 32 arrangement through a lamination process as depicted in
FIG. 21. The lamination process has applied article 125 over the
top surface 59 of cell 10. Thus, the conductive surfaces 98b of
grid "fingers" 84b of article 125 are fixed by the lamination in
intimate contact with conductive top surface 59 of cell 10. The
lamination process has similarly positioned the conductive surface
98a of "fingers" 84a of article 129 in intimate contact with the
bottom surface 66 of cell 10. The conductive material associated
with current collector stock 125 extends past a first terminal edge
46 of cell 10. The conductive material associated with current
collector stock 129 extends past second terminal edge 45 of cell
10. These extensions, identified by numerals 134 and 136 in FIG.
33, form convenient "tab" surfaces to facilitate electrical
connections to and from the actual cell. Thus article 130 can be
properly characterized as a form or embodiment of a "tabbed cell
stock".
[0215] FIG. 34 embodies the combination of multiple portions of
"tabbed cell stock" 130. In the FIG. 34 embodiment, an extension
134a associated with a first unit of "tabbed cell stock" 130a
overlaps extension 136b of an adjacent unit of "tabbed cell stock"
130b. The same spatial arrangement exists between "tabbed cell
stock" units 130b and 130c. The conductive surfaces associated with
the mating extensions are positioned and held in secure contact as
a result of an adhesive material forming surface 80b of the
substrate 120 melting and filling holes shown at 126. The mating
contact is additionally secured by adhesive bonding produced by
additional originally exposed portions of the substrates, shown at
127, in the region of the mechanical and pressure induced
electrical joining between adjacent units of "tabbed cell stock".
These originally exposed regions of substrate surface in the region
of the mechanical and pressure induced electrical joining between
adjacent units of "tabbed cell stock" are identified by the numeral
127 in the FIG. 34. It is clear that in the FIG. 34 embodiment a
secure and robust series electrical connection is achieved between
adjacent units of "tabbed cell stock" by virtue of the lamination
process taught herein.
[0216] Referring now to FIGS. 35 through 38, there are shown
embodiments of a starting structure for another grid/interconnect
article of the invention. FIG. 35 is a top plan view of an article
198. Article 198 comprises a polymeric film or glass sheet
substrate generally identified by numeral 200. Substrate 200 has
width X-200 and length Y-200. Length Y-200 is sometimes much
greater the width X-200 such that film 200 can be processed in
essentially a "roll-to-roll" fashion. However, this is not
necessarily the case. Dimension "Y" can be chosen according to the
application and process envisioned. FIG. 36 is a sectional view
taken substantially from the perspective of lines 36-36 of FIG. 35.
Thickness dimension Z-200 is normally small in comparison to
dimensions Y-200 and X-200 and thus substrate 200 has a sheetlike
structure and is often flexible. Substrate 200 is further
characterized by having regions of essentially solid structure
combined with regions having holes 202 extending through the
thickness Z-200. In the FIG. 35 embodiment, a substantially solid
region is generally defined by a width Wcc, representing a current
collection portion. Another portion with through-holes (holey
region) is generally defined by width Win, representing an
interconnection region. Imaginary line 201 separates the two
portions. Holes 202 may be formed by simple punching, laser
drilling and the like. Alternatively, holey region Win may comprise
a fabric joined to region Wcc along imaginary line 201, whereby the
fabric structure comprises through-holes. The reason for these
distinctions and definitions will become clear in light of the
following teachings.
[0217] Referring now to FIG. 36, region Wcc of substrate 200 has a
first surface 210 and second surface 212. The sectional view of
substrate 200 shown in FIG. 36 shows a single layer structure. This
depiction is suitable for simplicity and clarity of presentation.
Often, however, film 200 will comprise a laminate of multiple
layers as depicted in FIG. 37. In the FIG. 37 embodiment, substrate
200 is seen to comprise multiple layers 204, 206, 208, etc. As
previously taught herein, the multiple layers may comprise
inorganic or organic components such as thermoplastics, thermosets,
or silicon containing glass-like layers. The various layers are
intended to supply functional attributes such as environmental
barrier protection or adhesive characteristics. In particular, in
light of the teachings herein, one will recognize that it may be
advantageous to have layer 204 forming surface 210 comprise a
sealing material such as ethylene vinyl acetate (EVA), an ionomer,
an olefin based adhesive, atactic polyolefin, or a polymer
containing polar functional groups for adhesive characteristics
during a possible subsequent lamination process. For example, the
invention has been successfully demonstrated using a standard
laminating material sold by GBC Corp., Northbrook, Ill., 60062.
Additional layers 206, 208 etc. may comprise materials which assist
in support or processing such as polypropylene and polyethylene
terepthalate, barrier materials such as fluorinated polymers and
biaxially oriented polypropylene, and materials offering protection
against ultraviolet radiation as previously taught in
characterizing substrate 70 of FIG. 6.
[0218] As embodied in FIGS. 35 and 36, the solid regions Wcc and
"holey" regions Win of substrate 200 may comprise the same
material. This is not necessarily the case. For example, the
"holey" regions Win of substrate 200 could comprise a fabric, woven
or non-woven, joined to an adjacent substantially solid region
along imaginary line 201. However, should substrate 200 be used for
current collection from a light incident surface of a photovoltaic
cell, the materials forming the solid region Wcc should be
relatively transparent or translucent to visible light, as will be
understood in light of the teachings to follow.
[0219] FIG. 38 depicts an embodiment wherein multiple widths 200-1,
200-2 etc. of the general structure of FIGS. 35 and 36 are joined
together in a generally repetitive pattern in the width direction.
Such a structure allows simultaneous production of multiple repeat
structures corresponding to widths 200-1, 200-2 in a fashion
similar to that taught in conjunction with the embodiments of FIGS.
6 through 15.
[0220] FIG. 39 is a plan view of the FIG. 35 substrate 200
following an additional processing step, and FIG. 40 is a sectional
view taken along line 40-40 of FIG. 39. In FIGS. 39 and 40, the
article is now designated by the numeral 214 to reflect this
additional processing. In FIGS. 39 and 40, it is seen that a
pattern of "fingers" 216 has been formed by material 218 positioned
in a pattern over surface 210 of original sheetlike substrate 200.
"Fingers" 216 extend over the width Wcc of the solid portion of
sheetlike structure 214. The "fingers" 216 extend to the "holey"
interconnection region generally defined by Win. Portions of the
Wcc region not overlayed by "fingers" 216 remain transparent or
translucent to visible light. The "fingers" may comprise
electrically conductive material. Examples of such materials are
metal containing inks, patterned deposited metals such as etched
metal patterns, stamped metal patterns, masked vacuum deposited
metal patterns, fine metal wires, intrinsically conductive polymers
and DER formulations. In other embodiments the "fingers" may
comprise materials intended to facilitate subsequent deposition of
conductive material in the pattern defined by the fingers. An
example of such a material would be ABS, catalyzed to constitute a
"seed" layer to initiate chemical "electroless" metal deposition.
Another example would be a material functioning to promote adhesion
of a subsequently applied conductive material to the film 200. In a
preferred embodiment, the "fingers" comprise material which will
enhance or allow subsequent metal electrodeposition such as a DER
or electrically conductive ink. In the embodiment of FIGS. 39 and
40, the "fingers" 216 are shown to be a single layer of material
218 for simplicity of presentation. However, the "fingers" can
comprise multiple layers of differing materials chosen to support
various functional attributes as has previously been taught.
[0221] Continuing reference to FIGS. 39 and 40 also shows
additional material 220 applied to the "holey" region Win of
article 214 and extending through holes 202 from surface 210 to
surface 212. As with the material comprising the "fingers" 216, the
material 220 applied to the "holey" region Win is either conductive
or material intended to facilitate subsequent deposition of
conductive material. One will understand that "holey" region Win
may comprise a fabric which may further comprise conductive
material extending through the natural holes of the fabric.
Further, such a fabric may comprise fibrils formed from conductive
materials such as metals or conductive polymers. Such a fabric
structure can be expected to increase and retain flexibility after
subsequent processing such as metal electroplating and perhaps
bonding ability of the ultimate interconnected cells. Alternatively
one may choose to establish electrical communication between
surface 210 and 212 by using an electrically conductive polymer or
metal foil to form portions of the substrate associated with
interconnection region Win as will be understood in light of the
teachings contained hereafter. In the embodiment of FIGS. 39 and
40, the "holey" region takes the general form of a "buss" 221
extending in the Y-214 direction in communication with the
individual fingers. However, as one will understand through the
subsequent teachings, the invention requires only that conductive
communication extend from the fingers to a region Win intended to
be electrically joined to the bottom conductive surface of an
adjacent cell. The "holey" region Win thus does not require overall
electrical continuity in the "Y" direction as is characteristic of
a "buss" form depicted in the embodiment of FIGS. 39 and 40.
[0222] Reference to FIG. 40 shows that the material 220 applied to
the "holey" interconnection region Win is shown as the same as that
applied to form the fingers 216. However, these materials 218 and
220 need not be identical. In this embodiment material 220 applied
to the "holey" region extends through holes 202 and onto the
opposite second surface 212 of article 214. The extension of
material 220 through the holes 202 can be readily accomplished as a
result of the relatively small thickness (Z dimension) of the
sheetlike substrate 200. Techniques include two sided printing of
material 220, through hole spray application, masked metallization
or selective chemical deposition or mechanical means such as
stapling, wire sewing or riveting.
[0223] FIG. 41 is a view similar to that of FIG. 40 following an
additional optional processing step. The article embodied in FIG.
41 is designated by numeral 226 to reflect this additional
processing. It is seen in FIG. 41 that the additional processing
has deposited highly conductive material 222 over the originally
free surfaces of materials 218 and 220. Material 222 normally
comprises metal-based material such as copper or nickel, tin or a
conductive metal containing paste or ink. Typical deposition
techniques such as printing, chemical or electrochemical metal
deposition and masked deposition can be used for this additional
optional process to produce the article 226. In a preferred
embodiment, electrodeposition is chosen for its speed, ease, and
cost effectiveness as taught above. It is understood that article
226 is another embodiment of "current collector stock".
[0224] It is seen in FIG. 41 that highly conductive material 222
extends through holes to electrically join and form electrically
conductive surfaces on opposite sides of article 226. While shown
as a single layer in the FIG. 41 embodiment, the highly conductive
material can comprise multiple layers to achieve functional value.
In particular, a layer of copper is often desirable for its high
conductivity. Nickel is often desired for its adhesion
characteristics, plateability and corrosion resistance. The exposed
surface 229 of material 222 can be selected for corrosion
resistance and bonding ability. It has been found very advantageous
to form surface 229 with a material compatible with the conductive
surface with which eventual contact is made. In preferred
embodiments, electroless deposition or electrodeposition is used to
form a suitable metallic surface. Specifically electrodeposition
offers a wide choice of potentially suitable materials to form the
top surface 229. Corrosion resistant materials such as nickel,
chromium, tin, indium, silver, gold and platinum are readily
electrodeposited may be chosen to form surface 229. When
compatible, of course, surfaces comprising metals such as copper or
zinc or alloys of copper or zinc may be considered. Alternatively,
the surface 229 may comprise a conductive conversion coating, such
as a chromate coating, of a material such as copper or zinc.
Further, it may be highly advantageous to choose a material, such
as a conductive adhesive or metallic solder to form surface 229
which exhibits adhesive or bonding ability to a subsequently
positioned abutting conductive surface. In this regard,
electrodeposition offers a wide choice of materials to form surface
229. In particular, indium, tin or tin containing alloys are a
possible choice of material to form the exposed surface 229 of
material 222. These metals melt at relatively low temperatures less
than about 275 degree Centigrade. Thus these metals may be
desirable to promote ohmic joining, through soldering, to other
components in subsequent processing such as lamination.
Alternatively, exposed surface 229 may comprise an electrically
conductive adhesive. Selective deposition techniques such as brush
plating or printing would allow the conductive materials of region
Win to differ from those of fingers 216. In addition to supplying
electrical communication from surfaces 210 to 212, holes 202 also
function to increase flexibility of "buss" 221 by relieving the
"sandwiching" effect of continuous oppositely disposed layers.
Holes 202 can clearly be the holes naturally present should
substrate 200 in the region Win be a fabric. One realizes that an
important attribute of the embodied structure is that electrical
communication is achieved between opposing surfaces 210 and 212 of
substrate 200 in the interconnection region Win. One further
realizes that this communication may be achieved using structure
other than using the holes shown. For example, similar
communication by be achieved by using a conductive fabric, metal
mesh, an electrically conductive polymer or metal foil to form a
portion of the substrate 200 associated with region Win. These
alternate materials would be patched to the remaining transparent
current collector portion Wcc of substrate 200. In all these ways
electrical communication is achieved from surface 200 to opposite
surface 210 within region Win.
[0225] One method of combining the current collector stock 226
embodied in FIG. 41 with a cell stock 10 as embodied in FIGS. 1A
and 2A is illustrated in FIGS. 42 and 43. In the FIG. 43 structure,
individual current collector stocks 226 are combined with cells
10a, 10b, 10c respectively to produce a series interconnected
array. This may be accomplished via a process generally described
as follows.
[0226] As embodied in FIG. 42, individual current collector stock,
such as 226, is combined with cells such as 10 by positioning of
surface region "Wcc" of current collector stock 226 having free
surface 210 in registration with the light incident surface 59 of
cell 10. The article so produced is identified as article 227.
Adhesion joining the two surfaces is accomplished by a suitable
process. In particular, the material forming the remaining free
surface 210 of article 226 (that portion of surface 210 not covered
with conductive material 222) may be a sealing material chosen for
adhesive affinity to surface 59 of cell 10 thereby promoting good
adhesion between the collector stock 226 and cell surface 59
resulting from a laminating process such as that depicted in FIG.
21. Such a laminating process brings the conductive material of
fingers 216 into firm and effective contact with the window
electrode 18 forming surface 59 of cell 10. This contact is ensured
by the blanketing "hold down" afforded by the adhesive bonding
adjacent the conductive fingers 216. Also, as mentioned above, the
nature of the free surface of conductive material 222 may
optionally be manipulated and chosen to further enhance ohmic
joining and adhesion. It is envisioned that batch or continuous
laminating would be suitable. The invention has been demonstrated
using both roll laminators and batch vacuum laminators. Should the
articles 226 and 10 be in a continuous form it will be understood
that article 227 could be formed as a continuous "tabbed cell
stock. The subsequent series arrangement of articles 227a, 227b,
depicted in FIG. 43 may employ strip portions of "tabbed cell
stock" having a defined length. Alternatively continuous series
interconnection of multiple strips of tabbed cell stock supplied
from corresponding multiple rolls of tabbed cell stock is
possible.
[0227] Referring to FIG. 43, it is seen that proper positioning
allows the conductive material 222 extending over the second
surface 212 of article 227b to be ohmicly adhered to the bottom
surface 66 of cell 10a. This joining is accomplished by suitable
electrical joining techniques such as soldering, riveting, spot
welding or conductive adhesive application. The particular ohmic
joining technique embodied in FIG. 43 is through electrically
conductive adhesive 42. A particularly suitable conductive adhesive
is one comprising a carbon black filler in a polymer matrix
possibly augmented with a more highly conductive metal filler. Such
adhesive formulations are relatively inexpensive and can be
produced as hot melt formulations. Despite the fact that adhesive
formulations employing carbon black alone have relatively high
intrinsic resistivities (of the order 1 ohm-cm.), the bonding in
this embodiment is accomplished through a relatively thin adhesive
layer and over a broad surface. Thus the resulting resistance
losses are relatively limited. A hot melt conductive adhesive is
very suitable for establishing the ohmic connection using a
straightforward lamination process.
[0228] FIG. 43 embodies multiple cells assembled in a series
arrangement using the teachings of the instant invention. In FIG.
43, "i" indicates the direction of net current flow and "hv"
indicates the light incidence for the arrangement. It is noted that
the arrangement of FIG. 43 resembles a shingling arrangement of
cells, but with an important distinction. The prior art shingling
arrangements have included an overlapping of cells at a sacrifice
of portions of very valuable cell surface. In the FIG. 43 teaching,
the benefits of the shingling interconnection concept are achieved
without any loss of photovoltaic surface from shading by an
overlapping cell. In addition, the FIG. 43 arrangement retains a
high degree of flexibility because there is no immediate overlap of
the metal foil cell substrate. Conversely, inspection of the FIG.
43 embodiment shows that interconnection may also be achieved
without any substantial separation between adjacent connected cells
(except for a very slight, vertical displacement). In this way
active collection area is maximized, since no "dead area" exists
between cells.
[0229] Yet another form of the instant invention is embodied in
FIGS. 44 through 56. FIG. 44 is a top plan view of an article
designated 230. Article 230 has width "X-230" and length "Y-230".
It is contemplated that "Y-230" may be considerably greater than
"X-230" such that article 230 may be processed in continuous
roll-to-roll fashion. However, such continuous processing is not a
requirement.
[0230] FIG. 45 is a sectional view taken substantially from the
perspective of lines 45-45 of FIG. 44. It is shown in FIG. 45 that
article 230 may comprise any number of layers such as those
designated by numerals 232, 234, 236. The layers are intended to
supply functional attributes to article 230 as has been discussed
for prior embodiments. Article 230 is also shown to have thickness
"Z-230". "Z-230" is much smaller than "X-230" of "Y-230" and thus
article 230 may be generally characterized as being flexible and
sheetlike. Article 230 is shown to have a first surface 238 and
second surface 240. As will become clear in subsequent embodiments,
it may be advantageous to form layer 232 forming surface 238 using
a material having adhesive affinity to the bottom surface 66 of
cell 10. In addition, it may be advantageous to have surface 240
formed by a material having adhesive affinity to surface 59 of cell
10.
[0231] FIG. 46 is an alternate sectional embodiment depicting an
article 230a. The layers forming article 230a do not necessarily
have to cover the entire expanse of article 230a.
[0232] FIG. 47 is a simplified sectional view of the article 230
which will be used to simplify presentation of embodiments to
follow. While FIG. 47 presents article 230 as a single layer, it is
emphasized that article 230 may comprise any number of layers.
[0233] FIG. 48 is a top plan view of the initial article 230
following an additional processing step. The article embodied in
FIG. 48 is designated 244 to reflect this additional processing
step. FIG. 49 is a sectional view taken substantially from the
perspective of lines 49-49 of FIG. 48. Reference to FIGS. 48 and 49
show that the additional processing has produced holes 242 in the
direction of "Y-244". The holes extend from the top surface 238 to
the bottom surface 240 of article 244. Holes 242 may be produced by
any number of techniques such as laser drilling or simple
punching.
[0234] FIG. 50 is a top plan view of the article 244 following an
additional processing step. The article of FIG. 50 is designated
250 to reflect this additional processing. FIG. 51 is a sectional
view taken substantially from the perspective of lines 51-51 of
FIG. 50. Reference to FIGS. 50 and 51 shows that material 251 has
been applied to the first surface 238 in the form of "fingers" 252.
Further, material 253 has been applied to second surface 240 in the
form of "fingers" 254. In the embodiment, "fingers" 252 and 254
extend substantially perpendicular from a "buss-like" structure 256
extending in the direction "Y-250". As seen in FIG. 51, additional
materials 251 and 253 extend through the holes 242. In the FIG. 51
embodiment, materials 251 and 253 are shown as being the same. This
is not necessarily a requirement and they may be different. Also,
in the embodiment of FIGS. 50 and 51, the buss-like structure 256
is shown as being formed by materials 251/253. This is not
necessarily a requirement. Materials forming the "fingers" 252 and
254 and "buss" 256 may all be the same or they may differ in actual
composition and be applied separately. Alternatively, fingers and
busses may comprise a continuous monolithic material structure
forming portions of both fingers and busses. Fingers and busses
need not both be present in certain embodiments of the
invention.
[0235] As in prior embodiments, "fingers" 252 and 254 and "buss"
256 may comprise electrically conductive material. Examples of such
materials are metal wires and metal foils, conductive metal
containing inks and pastes, patterned metals such as etched metal
patterns or masked vacuum deposited metals, intrinsically
conductive polymers, conductive inks and DER formulations. In a
preferred embodiment, the "fingers and "busses" comprise material
such as DER or an electrically conductive ink such as silver
containing ink which will enhance or allow subsequent metal
electrodeposition. "Fingers" 252 and 254 and "buss" 256 may also
comprise non-conductive material which would assist accomplishing a
subsequent deposition of conductive material in the pattern defined
by the "fingers" and "busses". For example, "fingers" 252 and 254
or "buss" 256 could comprise a polymer which may be seeded to
catalyze chemical deposition of a metal in a subsequent step. An
example of such a material is "seeded" ABS. "Fingers" 252 and 254
and "buss" 256 may also comprise materials selected to promote
adhesion of a subsequently applied conductive material.
[0236] FIG. 52 is a sectional view showing the article 250
following an additional optional processing step. The article of
FIG. 52 is designated 260 to reflect this additional processing. In
a fashion like that described above for production of prior
embodiments of current collector structures, additional conductive
material 266 has been deposited by optional processing to produce
the article 260 of FIG. 52. The discussion involving processing to
produce the articles of FIGS. 12-15, 20, 31, and 41 is proper to
describe the additional processing to produce the article 260 of
FIG. 52. In a preferred embodiment, conductive material 266
comprises material applied by chemical metal deposition or metal
electrodeposition. In addition, while shown in FIG. 52 as a single
continuous, monolithic layer, the additional conductive material
may comprise multiple layers. As in prior embodiments, it may be
advantageous to use a material such as a low melting point alloy or
conductive adhesive to form exterior surface 268 of additional
conductive material 266. Additional conductive material overlaying
"fingers" 252 need not be the same as the additional conductive
material overlaying "fingers" 254.
[0237] The sectional views of FIGS. 55 and 56 embody the use of
article 250 or 260 to achieve a series connected structural array
of photovoltaic cells 10. In FIG. 55, an article designated as 270
has been formed by combining article 260 with cell 10 by laminating
the bottom surface 240 of article 260 to the top conductive surface
59 of cell 10. In a preferred embodiment, exposed surface 240
(those regions not covered with "fingers" 254) is formed by a
material having adhesive affinity to surface 59 and a secure and
extensive adhesive bond forms between surfaces 240 and 59 during
the heat and pressure exposure of the lamination process. Thus an
adhesive "blanket" holds conductive material 266 of "fingers" 254
in secure ohmic contact with surface 59. As previously pointed out,
low melting point alloys or conductive adhesives may also be
considered to enhance this contact. It is understood that article
270 of FIG. 55 is yet another embodiment of a "tabbed cell
stock".
[0238] The sectional view of FIG. 56 embodies multiple articles 270
arranged in a series interconnected array. The series connected
array is designated by numeral 290 in FIG. 56. In the FIG. 56
embodiment, it is seen that "fingers" 252 positioned on surface 238
of article 270b have been brought into contact with the bottom
surface 66 of cell 10 associated with article 270a. This contact is
achieved by choosing material 232 forming free surface 238 of
article 270b to have adhesive affinity for bottom conductive
surface 66 of cell 10 of article 270a. Secure adhesive bonding is
achieved during the heat and pressure exposure of a laminating
process thereby resulting in a hold down of the "fingers" 252. The
ohmic contact thus achieved can be enhanced using low melting point
alloys or conductive adhesives as previously taught herein.
[0239] Thus, it is seen in the FIG. 56 embodiment that continuous
communication is achieved between the top surface of one cell and
the bottom or rear surface of an adjacent cell. Importantly; the
communication is achieved with a continuous, monolithic conductive
structure. This avoids added resistances and potential degradation
of contacts sometimes associated with multiple contact surfaces
when using other techniques, such as conductive adhesives and
solders, to conductively join a multiple component conductive path.
In addition, the FIG. 56 embodiment clearly shows an advantageous
"shingling" type structure that avoids any shielding of valuable
photovoltaic cell surface. Conversely, the FIG. 56 structure avoids
any substantial separation between adjacent cells. Finally, it is
seen that the structural embodiment of FIG. 56 includes complete
encapsulation of cells 10.
[0240] The embodiments of FIGS. 50 through 52 show the "fingers"
and "busses" as essentially planar rectangular structures. Other
geometrical forms are clearly possible. This is especially the case
when considering structure for contacting the rear or bottom
surface 66 of a photovoltaic cell 10. One embodiment of an
alternate structure is depicted in FIGS. 53 and 54. FIG. 53 is a
top plan view while FIG. 54 is a sectional view taken substantially
from the perspective of lines 54-54 of FIG. 53. In FIGS. 53 and 54,
there is depicted an article 275 analogous to article 250 of FIG.
50. The article 275 in FIGS. 53 and 54 comprises "fingers" 280
similar to "fingers" 254 of the FIG. 50 embodiment. However, the
pattern of material 251 forming the structure on the top surface
238a of article 275 is considerably different than the "fingers"
252 and "buss" 256 of the FIG. 50 embodiment. In FIG. 53, material
251a is deposited in a mesh-like pattern having voids 276 leaving
multiple regions of surface 238a exposed. Lamination of such a
structure may result in improved surface area contact of the
pattern compared to the finger structure of FIG. 50. It is
emphasized that since surface 238a of article 275 eventually
contacts rear surface 66 of the photovoltaic cell, potential
shading is not an issue and thus geometrical design of the exposed
contacting surfaces 238a relative to the mating conductive surfaces
66 can be optimized without consideration to shading issues.
[0241] In the present specification lamination has been shown as a
means of combining the collector grid or electrode structures with
a conductive surface. However, one will recognize that other
application methods to combine the grid or electrode with a
conductive surface may be appropriate such as transfer application
processing. For example, in the embodiments such as those of FIG.
23 or 33, the substrate is shown to remain in its entirety as a
component of the "tabbed cell stock" and final interconnected
array. However, this is not a requirement. In other embodiments,
all or a portion of the substrate may be removed prior to or after
a laminating process accomplishing positioning and attachment of
"fingers" 84 and "busses" 86 to a conductive cell surface. In this
case, a suitable release material (not shown) may be used to
facilitate separation of the conductive collector electrode
structure from a removed portion of substrate 70 during or
following an application such as the lamination process depicted in
FIG. 21. Thus, in this case the removed portion of substrate 70
would serve as a surrogate or temporary support to initially
manufacture and transfer the grid or electrode structure to the
desired conductive surface. One example would be that situation
where layer 72 of FIG. 7 would remain with the final interconnected
array while layers 74 and/or 76 would be removed.
[0242] Using a laminating approach to secure the conductive grid
materials to a conductive surface involves some design and
performance "tradeoffs". For example, if the electrical trace or
path "finger" 84 comprises a wire form, it has the advantage of
potentially reducing light shading of the surface (at equivalent
current carrying capacity) in comparison to a substantially flat
electrodeposited, printed, etched or die cut foil member. However,
the relatively higher profile for the wire form must be addressed.
It has been taught in the art that wire diameters as small as 50
micrometers (0.002 inch) can be assembled into grid like
arrangements onto photovoltaic cell surfaces prior to applying
sealing materials. Thus when laid on a flat surface such a wire
would project above the surface 50 micrometers (0.002 inches). For
purposes of this instant specification and claims, a structure
projecting above a surface less than 50 micrometers (0.002 inches),
i.e. 1 micrometer, 5 micrometer, 10 micrometer 25 micrometer, 50
micrometer, will be defined as a low profile structure. Often a low
profile structure may be further characterized as having a
substantially flat surface.
[0243] A potential cross sectional view of a wire form 84d after
being laminated to a surface is depicted in FIG. 57. FIG. 58
depicts a typical cross sectional view of an electrical trace 84e
formed by printing, electrodeposition, chemical "electroless"
plating, foil etching or stamping, masked vacuum deposition etc. It
is seen in FIG. 57 that being round the wire itself contacts the
surface essentially along a line (normal to the paper in FIG. 57).
In addition, the wire form is embedded in the sealing material, but
the sealing material forming surface 80d of film 70 may have
difficulty flowing completely around the wire, leaving voids as
shown in FIG. 57 at 99, possibly leading to insecure contact. Thus,
the thickness of the sealing layer and lamination parameters and
material choice become very important when using a round wire form.
On the other hand, using a lower profile substantially flat
conductive trace such as depicted in FIG. 58 increases contact
surface area compared to the line contact associated with a wire.
The low profile form of FIG. 58 is easily embedded into the sealing
layer promoting broad surface contact and secure lamination but
comes at the expense of increased light shading for equivalent
current carrying capacity. The low profile, flat structure does
require consideration of the thickness of the "flowable" sealing
layer forming surface 80e relative to the thickness of the
conductive trace. Excessive thickness of certain sealing layer
materials might allow relaxation of the "blanket" pressure
promoting contact of the surfaces 98 with a mating conductive
surface such as 59. Insufficient thickness may lead to voids
similar to those depicted for the wire forms of FIG. 57. However,
testing has indicated that sealing layer thicknesses for low
profile traces such as embodied in FIG. 58 ranging from 0.5 mil
(0.0005 inch) to 10 mil (0.01 inch) all perform satisfactorily.
Thus a wide range of thickness is possible, and the invention is
not limited to sealing layer thicknesses within the stated tested
range.
[0244] A low profile structure such as depicted in FIG. 58 may be
advantageous because it may allow minimizing sealing layer
thickness and consequently reducing the total amount of functional
groups present in the sealing layer. Such functional groups may
adversely affect solar cell performance or integrity. For example,
it may be advantageous to limit the thickness of a sealing layer
such as EVA to 3 mils or less when using a CIS or CIGS photovoltaic
material.
[0245] Electrical contact between conductive grid "fingers" or
"traces" 84 and a conductive surface (such as cell surface 59) may
be further enhanced by coating a conductive adhesive formulation
onto "fingers" 84 and possibly "busses" 86 prior to or during the
lamination process such as taught in the embodiment of FIG. 21. In
a preferred embodiment, the conductive adhesive would be a "hot
melt" material. A "hot melt" conductive adhesive would melt and
flow at the temperatures involved in the laminating process 92 of
FIG. 21. In this way surface 98 (see FIGS. 14 and 15) is formed by
a conductive adhesive resulting in secure adhesive and electrical
joining of grid "fingers" 84 to a conductive surface such as top
surface 59 following the lamination process. In addition, such a
"flowable" conductive material may assist in reducing voids such as
depicted in FIG. 57 for a wire form. In addition, a "flowable"
conductive adhesive may increase the contact area for a wire form
84d.
[0246] In the case of a low profile form such as depicted in FIG.
58, the conductive adhesive may be applied by standard registered
printing techniques. However, it is noted that a conductive
adhesive coating for a low profile conductive trace may be very
thin, of the order of 0.1 to 10 micrometer thick. Thus, the
intrinsic resistivity of the conductive adhesive can be relatively
high, perhaps up to or even exceeding about 100 ohm-cm. This fact
allows reduced loading and increased choices for a conductive
filler. Since the conductive adhesive does not require heavy filler
loading (i.e. it may have a relatively high intrinsic resistivity
as noted above) other unique application options exist.
[0247] For example, a suitable conductive "hot melt" adhesive may
be deposited from solution onto the surface of the "fingers" and
"busses" by conventional paint electrodeposition techniques.
Alternatively, should a condition be present wherein the exposed
surface of fingers and busses be pristine (no oxide or tarnished
surface), the well known characteristic of such a surface to "wet"
with water based formulations may be employed to advantage. A
freshly activated or freshly electroplated metal surface will be
readily "wetted" by dipping in a water-based polymer containing
fluid such as a latex emulsion containing a conductive filler such
as carbon black. Application selectivity would be achieved because
the exposed polymeric sealing surface 80 would not wet with the
water based latex emulsion. The water based material would simply
run off or could be blown off the sealing material using a
conventional air knife. However, the water based film forming
emulsion would cling to the freshly activated or electroplated
metal surface. This approach is similar to applying an anti-tarnish
or conversion dip coating to freshly electroplated metals such as
copper and zinc.
[0248] Alternatively, one may employ a low melting point
metal-based material as a constituent of the material forming
either or both surfaces 98 and 100 of "fingers" and "busses". In
this case the low melting point metal-based material, or alloy,
melts during the temperature exposure of the process 92 of FIG. 21
(typically less than 325 degrees Centigrade) thereby increasing the
contact area between the mating surfaces 98, 100 and a conductive
surface such as 59. Alternatively, induction heating may be
suitable to sufficiently heat the conductive metallic pattern. Such
low melting point metal-based materials may be applied by
electrodeposition or simple dipping to wet the underlying
conductive trace. Suitable low melting point metals may be based on
tin, such as tin-bismuth and tin-lead alloys. Such alloys are
commonly referred to as "solders". In another preferred embodiment
indium or indium containing alloys are chosen as the low melting
point contact material at surfaces 98, 100. Indium melts at a low
temperature, considerably below possible lamination temperatures.
In addition, indium is known to bond to glass and ceramic materials
when melted in contact with them. Given sufficient lamination
pressures, only a very thin layer of indium or indium alloy would
be required to take advantage of this bonding ability.
[0249] In yet another embodiment, one or more of the layers 84, 86,
88, 90 etc. may comprise a material having magnetic
characteristics. Magnetic materials include nickel and iron. In
this embodiment, either a magnetic material in the cell substrate
or the material present in the finger/grid collector structure is
caused to be permanently magnetized. The magnetic attraction
between the "grid pattern" and magnetic component of the foil
substrate of the photovoltaic cell (or visa versa) creates a
permanent "pressure" contact.
[0250] In yet another embodiment, the "fingers" 84 and/or "busses"
86 comprise a magnetic component such as iron or nickel and a
external magnetic field is used to maintain positioning of the
fingers or busses during the lamination process depicted in FIG.
21.
[0251] A number of methods are available to employ the current
collecting and interconnection structures taught hereinabove with
photovoltaic cell stock to achieve effective interconnection of
multiple cells into arrays. A brief description of some possible
methods follows. A first method envisions combining photovoltaic
cell structure with current collecting electrodes while both
components are in their originally prepared "bulk" form prior to
subdivision to dimensions appropriate for individual cells. An
expansive surface area of photovoltaic structure such as embodied
in FIGS. 1 and 2 of the instant specification representing the
cumulative area of multiple unit cells is produced. As a separate
and distinct operation, an array comprising multiple current
collector electrodes arranged on a common substrate, such as the
array of electrodes taught in FIGS. 9 through 15 is produced. The
bulk array of electrodes is then combined with the expansive
surface of photovoltaic structure in a process such as the
laminating process embodied in FIG. 21. This process results in a
bulk combination of photovoltaic structure and collector electrode.
Appropriate subdividing of the bulk combination results in
individual cells having a pre-attached current collector structure.
Electrical access to the collector structure of individual cells
may be achieved using through holes, as taught in conjunction with
the embodiments of FIGS. 35 through 42. Alternatively, one may
simply lift the collector structure away from the cell surface 59
at the edge of the unit photovoltaic cell to expose the collector
electrode.
[0252] Another method of combining the collector electrodes and
interconnect structures taught herein with photovoltaic cells
involves a first step of manufacture of multiple individual current
collecting structures or electrodes. A suitable method of
manufacture is to produce a bulk continuous roll of electrodes
using roll to roll processing. Examples of such manufacture are the
processes and structures embodied in the discussion of FIGS. 9
through 15 of the instant specification. The bulk roll is then
subdivided into individual current collector electrodes for
combination with discrete units of cell stock. The combination
produces discrete individual units of "tabbed" cell stock. In
concept, this approach is appropriate for individual cells having
known and defined surface dimensions, such as 6''.times.6'',
4''.times.3'', 2''.times.8'' and 2''.times.16''. Cells of such
defined dimensions may be produced directly; such as with
conventional crystal silicon manufacture. Alternatively, cells of
such dimension are produced by subdividing an expansive cell
structure into smaller dimensions. The "tabbed" cell stock thereby
produced could be packaged in cassette packaging. The discrete
"tabbed" cells are then electrically interconnected into an array,
optionally using automatic dispensing, positioning and electrical
joining of multiple cells. The overhanging tabs of the individual
"tabbed" cells facilitate such joining into an array as was taught
in the embodiments of FIGS. 24, 34, 43, and 56 above.
[0253] Alternate methods to achieve interconnected arrays according
to the instant invention comprise first manufacturing multiple
current collector structures in bulk roll to roll fashion. In this
case the "current collector stock" would comprise electrically
conductive current collecting structure on a supporting sheetlike
web essentially continuous in the "Y" or "machine" direction.
Furthermore, the conductive structure is possibly repetitive in the
"X" direction, such as the arrangement depicted in FIGS. 9, 12 and
38 of the instant specification. In a separate operation,
individual rolls of unit "cell stock" are produced, possibly by
subdividing an expansive web of cell structure. The individual
rolls of unit "cell stock" are envisioned to be continuous in the
"Y" direction and having a defined width corresponding to the
defined width of cells to be eventually arranged in interconnected
array.
[0254] Having separately prepared rolls of "current collector
stock" and unit "cell stock", multiple assembly processes may be
considered to assemble modules as follows. In one form of array
assembly process, a roll of unit "current collector stock" is
produced, possibly by subdividing a bulk roll of "current collector
stock" to appropriate width for the unit roll. The rolls of unit
"current collector stock" and unit "cell stock" are then combined
in a continuous process to produce a roll of unit "tabbed stock".
The "tabbed" stock therefore comprises cells, which may be
extensive in the "Y" dimension, equipped with readily accessible
contacting surfaces for either or both the top and bottom surfaces
of the cell. The "tabbed" stock may be assembled into an
interconnected array using a multiple of different processes. As
examples, two such process paths are discussed according to (A) and
(B) following.
Process Example (A)
[0255] Multiple strips of "tabbed" stock are fed to a process such
that an interconnected array of multiple cells is achieved
continuously in the machine (original "Y") direction. This process
would produce an interconnected array having series connections of
cells whose number would correspond to the number of rolls of
"tabbed" stock being fed. In this case the individual strips of
"tabbed" stock would be arranged in appropriate overlapping fashion
as dictated by the particular embodiment of "tabbed" stock. The
multiple overlapping tabbed cells would be electrically joined
appropriately using electrical joining means, surface mating
through laminating or combinations thereof as has been taught
above. Both the feed and exit of such an assembly process would be
substantially in the original "Y" direction and the output of such
a process would be essentially continuous in the original "Y"
direction. The multiple interconnected cells could be rewound onto
a roll for further processing.
Process Example (B)
[0256] An alternative process is taught in conjunction with FIGS.
59 and 60. FIG. 59 is a top view of the process and FIG. 60 is a
perspective view. The process is embodied in FIGS. 59 and 60 using
the "tabbed cell stock" 270 as shown in FIG. 55. One will recognize
that other forms of "tabbed cell stock" such as those shown in
FIGS. 23, 33, 42, are also suitable. A single strip of "tabbed"
cell stock 270 is unwound from roll 300 and cut to a predetermined
length "Y-59". "Y-59" represents the width of the form factor of
the eventual interconnected array. The strip of "tabbed cell stock"
cut to length "Y-59" is then positioned. In the embodiment of FIGS.
59 and 60 the strip is securely positioned on vacuum belt 302. The
strip is then "shuttled" in the original "x" direction of the
"tabbed cell stock" a distance substantially the length of a repeat
dimension among adjacent series connected cells. This repeat
distance is indicated in FIGS. 56 and 59 as "X-10". A second strip
of "tabbed cell stock" 270 is then unwound and appropriately
positioned to properly overlap the first strip, as best shown in
FIG. 56. This second strip is cut to length "Y-59". The second
strip is then slightly tacked to the first strip of "tabbed cell
stock" using exposed substrate material, as that indicated at
numeral 306 in FIG. 56. The tacking may be accomplished quickly and
simply at points spaced in the "Y-59" direction using heated probes
to melt small regions of the sealing material forming the surface
of the exposed substrate. This process of positioning and tacking
is repeated multiple times. It is understood that methods other
than tacking may be chosen to maintain positioning of the adjacent
cells prior to lamination. Eventually, the repetitive structures
are passed through a lamination step. In the embodiment of FIGS. 59
and 60, the lamination is accomplished using roll laminator 310.
Thus the series connected structure 290 depicted in FIG. 56 is
achieved. The electrical joining may take many forms, depending
somewhat on the structure of the individual "tabbed cell stock".
For example, in the embodiment of FIGS. 24 and 25, joining may take
the form of an electrically conductive adhesive, solder, etc. as
previously taught. In the case of "tabbed" cell stock such as FIG.
55, electrical joining may comprise a simple adhesive "blanket hold
down" lamination such as embodied in FIG. 56, but may also include
additional conductive adhesives. It is seen that in the process
depicted in FIGS. 59 and 60 the interconnected cell stock would
exit the basic lamination assembly process in a fashion
substantially perpendicular to the original "Y" direction of the
"tabbed cell stock". The interconnected cells produced would
therefore have a new predetermined width "Y-59" and the new length
(in the original "X" direction) may be of extended dimension. The
output in the new length dimension may be described as essentially
continuous and thus the output of interconnected cells may be
gathered on roll 320 as shown.
[0257] While the feed material in the process embodiment of FIGS.
59 and 60 is shown as a continuous strip of "tabbed cell stock"
270, one will understand that the process may alternatively be
practiced using defined lengths (Y-59) of "tabbed cell stock" fed
from, for example, a cassette of lengths sorted according to
performance characteristics.
[0258] It will be appreciated that using the processing as embodied
in FIGS. 59 and 60, a large choice of final form factors for the
interconnected array is possible. For example, dimension "Y-59"
could conceivably and reasonably be quite large, for example 8 feet
while dimension "X-59" may be virtually any desired dimension. To
date, module sizes have been restricted by the practical problems
of handling and interconnecting large numbers of small individual
cells. The largest commercially available module known to the
instant inventor is about 60 square feet. Using the instant
invention, module sizes far in excess of 60 square feet are
reasonable. Large modules suitable for combination with standard
construction materials may be produced. For example, a module
surface area of 4 ft. by 8 ft. (a standard dimension for plywood
and other sheetlike construction materials) is readily produced
using the processing of the instant invention. Alternatively, since
the final modular array can be accumulated in roll form as shown in
FIGS. 59 and 60, installation could be facilitated by the ability
to simply "roll out" the array at the installation site. The
ability to easily make modular arrays of very expansive surface and
having wide choice of form factor greatly facilitates eventual
installation and is a substantial improvement over existing options
for modular array manufacture.
[0259] It is further pointed out that additional optional
operations may be achieved after or during the formation of modular
arrays such as those of FIGS. 24, 34, 43, and 56 are formed. For
example, additional film structure such as barrier layers can be
added just prior to the lamination step depicted at rolls 310 in
FIG. 60 or in an additional lamination step. Alternatively, the
continuous output 290 of the FIG. 59 process may be fed to
additional process steps. For example, the modular structure 290 of
FIG. 59 may be cut to predetermined lengths in the "X-59" dimension
for positioning into a casing of predetermined dimensions and/or
further protected with a layer such as glass. This would of course
eliminate the delicate and careful handling associated with
placements multiple cells interconnected with conventional "string
and tab" structure.
[0260] Finally, the modularization processes described by way of
example above in paragraphs 245 through 249 are very scaleable
since they adopt laminating processing firmly established in the
packaging industry.
Example 1
[0261] A standard plastic laminating sheet from GBC Corp. 75
micrometer (0.003 inch) thick was coated with DER in a pattern of
repetitive fingers joined along one end with a busslike structure
resulting in an article as embodied in FIGS. 16 through 19. The
fingers were 0.020 inch wide, 1.625 inch long and were repetitively
separated by 0.150 inch. The buss-like structure which contacted
the fingers extended in a direction perpendicular to the fingers as
shown in FIG. 16. The buss-like structure had a width of 0.25 inch.
Both the finger pattern and buss-like structure were printed
simultaneously using the same DER ink and using silk screen
printing. The DER printing pattern was applied to the laminating
sheet surface formed by the sealing layer (i.e. that surface facing
to the inside of the standard sealing pouch).
[0262] The finger/buss pattern thus produced on the lamination
sheet was then electroplated with nickel in a standard Watts nickel
bath at a current density of 50 amps. per sq. ft. Approximately 4
micrometers of nickel thickness was deposited to the overall
pattern.
[0263] A photovoltaic cell having surface dimensions of 1.75 inch
wide by 2.0625 inch long was used. This cell was a CIGS
semiconductor type deposited on a 0.001 inch stainless steel
substrate. A section of the laminating sheet containing the
electroplated buss/finger pattern was then applied to the top,
light incident side of the cell, with the electroplated grid finger
extending in the width direction (1.75 inch dimension) of the cell.
Care was taken to ensure that the buss region of the conductive
electroplated metal did not overlap the cell surface. This resulted
in a total cell surface of 3.61 sq. inch. (2.0625''.times.1.75'')
with about 12% shading from the grid, (i.e. about 88% open area for
the cell).
[0264] The electroplated "finger/buss" on the lamination film was
applied to the photovoltaic cell using a standard Xerox office
laminator. The resulting completed cell showed good appearance and
connection.
[0265] The cell prepared as above was tested in direct sunlight for
photovoltaic response. Testing was done at noon, Morgan Hill,
Calif. on Apr. 8, 2006 in full sunlight. The cell recorded an open
circuit voltage of 0.52 Volts. Also recorded was a "short circuit"
current of 0.65 Amps. This indicates excellent power collection
from the cell at high efficiency of collection.
Example 2
[0266] Individual thin film CIGS semiconductor cells comprising a
stainless steel supporting substrate 0.001 inch thick were cut to
dimensions of 7.5 inch length and 1.75 inch width.
[0267] In a separate operation, multiple laminating collector grids
were prepared as follows. A 0.002 inch thick film of Surlyn
material was applied to both sides of a 0.003 inch thick PET film
to produce a starting laminating substrate as embodied in FIG. 44.
Holes having a 0.125 inch diameter were punched through the
laminate to produce a structure as in FIG. 48. A DER ink was then
printed on opposite surfaces and through the holes to form a
pattern of DER traces. The resulting structure resembled that
depicted in FIG. 51. The grid fingers 254 depicted in FIGS. 50 and
51 were 0.012 inch wide and 1.625 inch long and were spaced on
centers 0.120 inch apart in the length direction. The grid fingers
252 were 0.062 inch wide and extended 1 inch and were spaced on
centers 0.5 inch apart. The printed film was then electroplated to
deposit approximately 2 micrometers nickel strike, 5 micrometers
copper and a top flash coating of 1 micrometer nickel. This
operation produced multiple sheets of laminating current collector
stock having overall dimension of 7.5 inch length ("Y" dimension)
and 4.25 in width ("X" dimension) as indicated in FIG. 50. These
individual current collector sheets were laminated to cells having
dimension of 7.25 inches in length and 1.75 inches in width to
produce tabbed cell stock as depicted in FIG. 55. A standard Xerox
office roll laminator was used to produce the tabbed cell stock.
Six pieces of the tabbed cell stock were laminated together as
depicted in FIG. 56. A standard Xerox office roll laminator was
used to produce the FIG. 56 embodiment. The combined series
interconnected array had a total surface area of 76.1 square
inches. In full noon sunlight the 6 cell array had an open circuit
voltage of 3.2 Volts and a short circuit current of 2.3
amperes.
[0268] While many of the embodiments of the invention refer to
"current collector" structure, one will appreciate that similar
articles could be employed to collect and convey other electrical
characteristics such as voltage.
[0269] One application of the modules made practical by the
teachings above is expansive area photovoltaic energy farms or
expansive area rooftop applications. The instant invention
envisions facile manufacture and installation of large sheetlike
modules having area dimensions suitable for covering expansive
surface areas. Practical module widths may be 2 ft., 4 ft., 8 ft
etc. Practical module lengths may be 2 ft., 4 ft., 10 ft., 50 ft,
100 ft., 500 ft., or larger. The "sheetlike" modules may be
produced in a wide range of forms. The longer lengths can be
characterized as "continuous" and be shipped and installed in a
roll format. In another application, the sheetlike modules may be
adhered to a rigid supporting member such as plywood, polymeric
sheet or a honeycomb structure. The sheetlike modules may be
produced having terminal bars at two opposite terminal ends of the
module. These terminal bars are easily incorporated into the
modules using the same continuous processes used in assembly of the
bulk module. It is noted that in the hereinbefore teachings, the
terminal bars may have oppositely facing conductive surface regions
with electrical communication between them. This is an advantage
for certain embodiments of the instant invention, in that an upward
facing conductive surface for the terminal bars may facilitate
electrical connections.
[0270] Although the present invention has been described in
conjunction with preferred embodiments, it is to be understood that
modifications, alternatives and equivalents may be included without
departing from the spirit and scope of the inventions, as those
skilled in the art will readily understand. Such modifications,
alternatives and equivalents are considered to be within the
purview and scope of the invention and appended claims.
* * * * *