U.S. patent application number 12/566555 was filed with the patent office on 2010-02-25 for interconnect assembly.
This patent application is currently assigned to MIASOLE. Invention is credited to Jason Stephen Corneille, Steven Thomas Croft, Steven Douglas Flanders, William James McColl, Mulugeta Zerfu Wudu.
Application Number | 20100043863 12/566555 |
Document ID | / |
Family ID | 41695192 |
Filed Date | 2010-02-25 |
United States Patent
Application |
20100043863 |
Kind Code |
A1 |
Wudu; Mulugeta Zerfu ; et
al. |
February 25, 2010 |
INTERCONNECT ASSEMBLY
Abstract
An interconnect assembly. The interconnect assembly includes a
trace that includes a plurality of electrically conductive
portions. The plurality of electrically conductive portions is
configured both to collect current from a first solar cell and to
interconnect electrically to a second solar cell. In addition, the
plurality of electrically conductive portions is configured such
that solar-cell efficiency is substantially undiminished in an
event that any one of the plurality of electrically conductive
portions is conductively impaired.
Inventors: |
Wudu; Mulugeta Zerfu; (San
Jose, CA) ; Corneille; Jason Stephen; (San Jose,
CA) ; Croft; Steven Thomas; (Menlo Park, CA) ;
Flanders; Steven Douglas; (San Jose, CA) ; McColl;
William James; (Palo Alto, CA) |
Correspondence
Address: |
Weaver Austin Villeneuve & Sampson LLP
P.O. BOX 70250
OAKLAND
CA
94612-0250
US
|
Assignee: |
MIASOLE
Santa Clara
CA
|
Family ID: |
41695192 |
Appl. No.: |
12/566555 |
Filed: |
September 24, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12052476 |
Mar 20, 2008 |
|
|
|
12566555 |
|
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|
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Current U.S.
Class: |
136/244 ;
136/256; 174/126.1 |
Current CPC
Class: |
H01L 31/0445 20141201;
H01L 31/0512 20130101; H01L 31/0201 20130101; H01L 31/0504
20130101; Y02E 10/50 20130101 |
Class at
Publication: |
136/244 ;
136/256; 174/126.1 |
International
Class: |
H01L 31/042 20060101
H01L031/042; H01L 31/00 20060101 H01L031/00; H01B 5/00 20060101
H01B005/00 |
Claims
1. An interconnect assembly comprising: a trace comprising a
plurality of electrically conductive portions, said plurality of
electrically conductive portions configured both to collect current
from a first solar cell and to interconnect electrically to a
second solar cell; a top carrier film, wherein said top carrier
film comprises a first substantially transparent, electrically
insulating layer coupled to said trace and disposed above a top
portion of said trace; and a bottom carrier film, wherein said
bottom carrier film comprises a carrier film selected from a group
consisting of a second electrically insulating layer, a structural
plastic layer, and a metallic layer, said bottom carrier film
coupled to said trace and disposed below a bottom portion of said
trace; and wherein said plurality of electrically conductive
portions is configured such that solar-cell efficiency is
substantially undiminished in an event that any one of said
plurality of electrically conductive portions is conductively
impaired.
2. The interconnect assembly of claim 1, wherein said plurality of
electrically conductive portions further comprises: a first portion
of said plurality of electrically conductive portions configured
both to collect current from said first solar cell and to
interconnect electrically to said second solar cell, said first
portion comprising a first end distal from said second solar cell;
and a second portion of said plurality of electrically conductive
portions configured both to collect current from said first solar
cell and to interconnect electrically to said second solar cell,
said second portion comprising a second end distal from said second
solar cell; wherein said second portion is disposed proximately to
said first portion and electrically connected to said first portion
such that said first distal end is electrically connected to said
second distal end such that said second portion is configured
electrically in parallel to said first portion when configured to
interconnect to said second solar cell.
3. The interconnect assembly of claim 2, wherein said plurality of
electrically conductive portions further comprises: said second
portion comprising a third end distal from said first solar cell;
and a third portion of said plurality of electrically conductive
portions configured both to collect current from said first solar
cell and to interconnect electrically to said second solar cell,
said third portion comprising a fourth end distal from said first
solar cell; wherein said third portion is disposed proximately to
said second portion and electrically connected to said second
portion such that said third distal end is electrically connected
to said fourth distal end such that said third portion is
configured electrically in parallel to said second portion when
configured to interconnect with said first solar cell.
4. The interconnect assembly of claim 1, wherein said plurality of
electrically conductive portions further comprises: a second
portion of said plurality of electrically conductive portions
configured both to collect current from said first solar cell and
to interconnect electrically to said second solar cell, said second
portion comprising a third end distal from said first solar cell;
and a third portion of said plurality of electrically conductive
portions configured both to collect current from said first solar
cell and to interconnect electrically to said second solar cell,
said third portion comprising a fourth end distal from said first
solar cell; wherein said third portion is disposed proximately to
said second portion and electrically connected to said second
portion such that said third distal end is electrically connected
to said fourth distal end such that said third portion is
configured electrically in parallel to said second portion when
configured to interconnect with said first solar cell.
5. The interconnect assembly of claim 1, wherein said top carrier
film further comprises a first adhesive medium coupling said trace
to said first substantially transparent, electrically insulating
layer, and wherein said first adhesive medium allows for coupling
said trace to said first solar cell without requiring solder.
6. The interconnect assembly of claim 1, wherein the top carrier
film is configured to terminate short of an edge of the first solar
cell closest to the second solar cell.
7. The interconnect assembly of claim 1, wherein the top carrier
film is configured such that it does not form part of a portion of
the interconnect bridging a gap between closest edges of the first
and second solar cells.
8. The interconnect assembly of claim 1, wherein said bottom
carrier film further comprises a second adhesive medium coupling
said trace to said second electrically insulating layer, and
wherein said second adhesive medium allows for coupling said trace
to said second solar cell without requiring solder.
9. The interconnect assembly of claim 1, wherein said plurality of
electrically conductive portions is connected electrically in
series to form a single continuous electrically conductive
line.
10. The interconnect assembly of claim 1, wherein said trace is
disposed in a serpentine pattern such that said interconnect
assembly is configured to collect current from said first solar
cell and to interconnect electrically to said second solar
cell.
11. A combined solar-cell, interconnect assembly comprising: a
first solar cell; and an interconnect assembly comprising: a trace
disposed above a light-facing side of said first solar cell, said
trace further comprising: a plurality of electrically conductive
portions, all electrically conductive portions of said plurality of
electrically conductive portions configured to collect current from
said first solar cell and to interconnect electrically to a second
solar cell; wherein said plurality of electrically conductive
portions is configured such that solar-cell efficiency is
substantially undiminished in an event that any one of said
plurality of electrically conductive portions is conductively
impaired; a top carrier film, wherein said top carrier film
comprises a first substantially transparent, electrically
insulating layer coupled to said trace and disposed above a top
portion of said trace; and a bottom carrier film, wherein said
bottom carrier film comprises a carrier film selected from a group
consisting of a second electrically insulating layer, a structural
plastic layer, and a metallic layer, said bottom carrier film
coupled to said trace and disposed below a bottom portion of said
trace.
12. The combined solar-cell, interconnect assembly of claim 11,
further comprising a second solar cell.
13. The combined solar-cell, interconnect assembly of claim 12,
wherein a gap between closest edges of the first and second solar
cells is no more than about 2 mm.
14. The combined solar-cell, interconnect assembly of claim 13,
wherein the top carrier film is configured to terminate short of
the edge of the first solar cell closest to the second solar
cell.
15. The combined solar-cell, interconnect assembly of claim 13,
wherein the top carrier film is configured such that it does not
form part of a portion of the interconnect bridging the gap between
closest edges of the first and second solar cells.
16. The combined solar-cell, interconnect assembly of claim 14,
wherein the top carrier film is configured such that it does not
form part of a portion of the interconnect bridging the gap between
closest edges of the first and second solar cells.
17. A solar-cell module, comprising: a first solar cell; at least a
second solar cell; and an interconnect assembly disposed above a
light-facing side of an absorber layer of said first solar cell
comprising: a trace comprising a plurality of electrically
conductive portions, said plurality of electrically conductive
portions configured both to collect current from said first solar
cell and to interconnect electrically to said second solar cell; a
top carrier film, wherein said top carrier film comprises a first
substantially transparent, electrically insulating layer coupled to
said trace and disposed above a top portion of said trace; and a
bottom carrier film, wherein said bottom carrier film comprises a
carrier film selected from a group consisting of a second
electrically insulating layer, a structural plastic layer, and a
metallic layer, said bottom carrier film coupled to said trace and
disposed below a bottom portion of said trace; and wherein said
plurality of electrically conductive portions is configured such
that solar-cell efficiency is substantially undiminished in an
event that any one of said plurality of electrically conductive
portions is conductively impaired.
18. The solar-cell module of claim 17, wherein the top carrier film
is configured to terminate short of an edge of the first solar cell
closest to the second solar cell.
19. The solar-cell module of claim 17, wherein the top carrier film
is configured such that it does not form part of a portion of the
interconnect bridging a gap between closest edges of the first and
second solar cells.
20. The solar-cell module of claim 18, wherein the top carrier film
is configured such that it does not form part of a portion of the
interconnect bridging a gap between closest edges of the first and
second solar cells.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/052,476 titled INTERCONNECT ASSEMBLY, filed
Mar. 20, 2008, incorporated herein by reference in its entirety for
all purposes.
TECHNICAL FIELD
[0002] Embodiments of the present invention relate generally to the
field of photovoltaic technology.
BACKGROUND
[0003] In the drive for renewable sources of energy, photovoltaic
technology has assumed a preeminent position as a cheap renewable
source of clean energy. In particular, solar cells based on the
compound semiconductor copper indium gallium diselenide (CIGS) used
as an absorber layer offer great promise for thin-film solar cells
having high efficiency and low cost. Of comparable importance to
the technology used to fabricate thin-film solar cells themselves,
is the technology used to collect current from the solar cells and
to interconnect one solar cell to another to form a solar-cell
module.
[0004] Just as the efficiency of thin-film solar cells is affected
by parasitic series resistances, solar-cell modules fabricated from
arrays of such thin-film solar cells are also impacted by parasitic
series resistances. A significant challenge is the development of
solar-cell, current collection and interconnection schemes that
minimize the effects of such parasitic resistances. Moreover, the
reliability of solar-cell modules based on such schemes is equally
important as it determines the useful life of the solar-cell module
and therefore its cost effectiveness and viability as a reliable
alternative source of energy.
SUMMARY
[0005] Embodiments of the present invention include an interconnect
assembly. The interconnect assembly includes a trace that includes
a plurality of electrically conductive portions. The plurality of
electrically conductive portions is configured both to collect
current from a first solar cell and to interconnect electrically to
a second solar cell. In addition, the plurality of electrically
conductive portions is configured such that solar-cell efficiency
is substantially undiminished in an event that any one of the
plurality of electrically conductive portions is conductively
impaired.
DESCRIPTION OF THE DRAWINGS
[0006] The accompanying drawings, which are incorporated in and
form a part of this specification, illustrate embodiments of the
invention and, together with the description, serve to explain the
embodiments of the invention:
[0007] FIG. 1A is a cross-sectional elevation view of a layer
structure of a solar cell, in accordance with an embodiment of the
present invention.
[0008] FIG. 1B is a schematic diagram of a model circuit of a solar
cell, electrically connected to a load, in accordance with an
embodiment of the present invention.
[0009] FIG. 2 is a schematic diagram of a model circuit of a
solar-cell module, electrically connected to a load, that shows the
interconnection of solar cells in the solar-cell module, in
accordance with an embodiment of the present invention.
[0010] FIG. 3 is a schematic diagram of a model circuit of a
solar-cell module, electrically connected to a load, that details
model circuits of interconnect assemblies, in accordance with an
embodiment of the present invention.
[0011] FIG. 4A is a schematic diagram of a model circuit of an
interconnect assembly for connecting two solar cells of a
solar-cell module, in accordance with an embodiment of the present
invention.
[0012] FIG. 4B is a plan view of the interconnect assembly of FIG.
4A that shows the physical interconnection of two solar cells in
the solar-cell module, in accordance with an embodiment of the
present invention.
[0013] FIG. 4C is a cross-sectional, elevation view of the
interconnect assembly of FIG. 4B that shows the physical
interconnection of two solar cells in the solar-cell module, in
accordance with an embodiment of the present invention.
[0014] FIG. 4D is a cross-sectional, elevation view of an
alternative interconnect assembly for FIG. 4B that shows an
edge-conforming interconnect assembly for the physical
interconnection of two solar cells in the solar-cell module, in
accordance with an embodiment of the present invention.
[0015] FIG. 4E is a cross-sectional, elevation view of an
alternative interconnect assembly for FIG. 4B that shows a
shingled-solar-cell arrangement for the physical interconnection of
two solar cells in the solar-cell module, in accordance with an
embodiment of the present invention.
[0016] FIG. 4F is a plan view of an alternative interconnect
assembly for FIG. 4A that shows the physical interconnection of two
solar cells in the solar-cell module, in accordance with an
embodiment of the present invention.
[0017] FIG. 4G is a plan view of the interconnect assembly of FIG.
4A that shows the physical interconnection of two solar cells in
the solar-cell module, in accordance with an embodiment of the
present invention.
[0018] FIG. 4H is a cross-sectional, elevation view of the
interconnect assembly of FIG. 4G that shows the physical
interconnection of two solar cells in the solar-cell module, in
accordance with an embodiment of the present invention.
[0019] FIG. 5A is a plan view of the combined applicable carrier
film, interconnect assembly that shows the physical arrangement of
a trace with respect to a top carrier film and a bottom carrier
film in the combined applicable carrier film, interconnect
assembly, in accordance with an embodiment of the present
invention.
[0020] FIG. 5B is a plan view of the combined applicable carrier
film, interconnect assembly that shows the physical arrangement of
a trace with respect to a top carrier film and a bottom carrier
film in the combined applicable carrier film, interconnect
assembly, in accordance with another embodiment of the present
invention.
[0021] FIG. 5C is a cross-sectional schematic view of the physical
arrangement of elements of an interconnect assembly connecting two
solar cells in accordance with an embodiment of the present
invention such as described and illustrated with reference to FIG.
5B.
[0022] FIG. 5D is a cross-sectional, elevation view of the combined
applicable carrier film, interconnect assembly of FIG. 5A or 5B
that shows the physical arrangement of a trace with respect to a
top carrier film in the combined applicable carrier film,
interconnect assembly prior to disposition on a solar cell, in
accordance with embodiments of the present invention.
[0023] FIG. 5E is a cross-sectional, elevation view of the
interconnect assembly of FIG. 5D that shows the physical
arrangement of a trace with respect to a top carrier film in the
combined applicable carrier film, interconnect assembly after
disposition on a solar cell, in accordance with an embodiment of
the present invention.
[0024] FIG. 6A is a plan view of an integrated
busbar-solar-cell-current collector that shows the physical
interconnection of a terminating solar cell with a terminating
busbar in the integrated busbar-solar-cell-current collector, in
accordance with an embodiment of the present invention.
[0025] FIG. 6B is a cross-sectional, elevation view of the
integrated busbar-solar-cell-current collector of FIG. 6A that
shows the physical interconnection of the terminating solar cell
with the terminating busbar in the integrated
busbar-solar-cell-current collector, in accordance with an
embodiment of the present invention.
[0026] FIG. 7A is a combined cross-sectional elevation and
perspective view of a roll-to-roll, interconnect-assembly
fabricator for fabricating the interconnect assembly from a first
roll of top carrier film and from a dispenser of conductive-trace
material, in accordance with an embodiment of the present
invention.
[0027] FIG. 7B is a combined cross-sectional elevation and
perspective view of a roll-to-roll, laminated-interconnect-assembly
for fabricating a laminated-interconnect assembly from the first
roll of top carrier film, from a second roll of bottom carrier film
and from the dispenser of conductive-trace material, in accordance
with an embodiment of the present invention.
[0028] FIG. 8 is flow chart illustrating a method for roll-to-roll
fabrication of an interconnect assembly, in accordance with an
embodiment of the present invention.
[0029] FIG. 9 is flow chart illustrating a method for
interconnecting two solar cells, in accordance with an embodiment
of the present invention.
[0030] The drawings referred to in this description should not be
understood as being drawn to scale except if specifically
noted.
DESCRIPTION OF EMBODIMENTS
[0031] Reference will now be made in detail to the various
embodiments of the present invention. While the invention will be
described in conjunction with the various embodiments, it will be
understood that they are not intended to limit the invention to
these embodiments. On the contrary, the invention is intended to
cover alternatives, modifications and equivalents, which may be
included within the spirit and scope of the invention as defined by
the appended claims.
[0032] Furthermore, in the following description of embodiments of
the present invention, numerous specific details are set forth in
order to provide a thorough understanding of the present invention.
However, it should be appreciated that embodiments of the present
invention may be practiced without these specific details. In other
instances, well known methods, procedures, and components have not
been described in detail as not to unnecessarily obscure
embodiments of the present invention.
Physical Description of Embodiments of the Present Invention for an
Interconnect Assembly
[0033] With reference to FIG. 1A, in accordance with an embodiment
of the present invention, a cross-sectional elevation view of a
layer structure of a solar cell 100A is shown. The solar cell 100A
includes a metallic substrate 104. In accordance with an embodiment
of the present invention, an absorber layer 112 is disposed on the
metallic substrate 104; the absorber layer 112 may include a layer
of the material copper indium gallium diselenide (CIGS) having the
chemical formula Cu(In.sub.1-xGa.sub.x)Se.sub.2, where x may be a
decimal less than one but greater than zero that determines the
relative amounts of the constituents, indium, In, and gallium, Ga.
Alternatively, semiconductors having the chalcopyrite crystal
structure, for example, chemically homologous compounds with the
compound CIGS having the chalcopyrite crystal structure, in which
alternative elemental constituents are substituted for Cu, In, Ga,
and/or Se, may be used as the absorber layer 112. Moreover, in
embodiments of the present invention, it should be noted that
semiconductors, such as silicon and cadmium telluride, as well as
other semiconductors, may be used as the absorber layer 112.
[0034] As shown, the absorber layer 112 includes a p-type portion
112a and an n-type portion 112b. As a result, a pn homojunction
112c is produced in the absorber layer 112 that serves to separate
charge carriers that are created by light incident on the absorber
layer 112. To facilitate the efficient conversion of light energy
to charge carriers in the absorber layer 112, the composition of
the p-type portion 112a of the absorber layer 112 may vary with
depth to produce a graded band gap of the absorber layer 112.
Alternatively, the absorber layer 112 may include only a p-type
chalcopyrite semiconductor layer, such as a CIGS material layer,
and a pn heterojunction may be produced between the absorber layer
112 and an n-type layer, such as a metal oxide, metal sulfide or
metal selenide, disposed on its top surface in place of the n-type
portion 112b shown in FIG. 1A. However, embodiments of the present
invention are not limited to pn junctions fabricated in the manner
described above, but rather a generic pn junction produced either
as a homojunction in a single semiconductor material, or
alternatively a heterojunction between two different semiconductor
materials, is within the spirit and scope of embodiments of the
present invention. Moreover, in embodiments of the present
invention, it should be noted that semiconductors, such as silicon
and cadmium telluride, as well as other semiconductors, may be used
as the absorber layer 112.
[0035] In accordance with an embodiment of the present invention,
on the surface of the n-type portion 112b of the absorber layer
112, one or more transparent electrically conductive oxide (TCO)
layers 116 are disposed, for example, to provide a means for
collection of current from the absorber layer 112 for conduction to
an external load. As used herein, it should be noted that the
phrase "collection of current" refers to collecting current
carriers of either sign, whether they be positively charged holes
or negatively charged electrons; for the structure shown in FIG. 1A
in which the TCO layer is disposed on the n-type portion 112b, the
current carriers collected under normal operating conditions are
negatively charged electrons; but, embodiments of the present
invention apply, without limitation thereto, to solar cell
configurations where a p-type layer is disposed on an n-type
absorber layer, in which case the current carriers collected may be
positively charged holes. The TCO layer 116 may include zinc oxide,
ZnO, or alternatively a doped conductive oxide, such as aluminum
zinc oxide (AZO), Al.sub.xZn.sub.1-xO.sub.y, and indium tin oxide
(ITO), In.sub.xSn.sub.1-xO.sub.y, where the subscripts x and y
indicate that the relative amount of the constituents may be
varied. Alternatively, the TCO layer 116 may be composed of a
plurality of conductive oxide layers. These TCO layer materials may
be sputtered directly from an oxide target, or alternatively the
TCO layer may be reactively sputtered in an oxygen atmosphere from
a metallic target, such as zinc, Zn, Al--Zn alloy, or In--Sn alloy
targets. For example, the zinc oxide may be deposited on the
absorber layer 112 by sputtering from a zinc-oxide-containing
target; alternatively, the zinc oxide may be deposited from a
zinc-containing target in a reactive oxygen atmosphere in a
reactive-sputtering process. The reactive-sputtering process may
provide a means for doping the absorber layer 112 with an n-type
dopant, such as zinc, Zn, or indium, In, to create a thin n-type
portion 112b, if the partial pressure of oxygen is initially
reduced during the initial stages of sputtering a metallic target,
such as zinc, Zn, or indium, In, and the layer structure of the
solar cell 100A is subsequently annealed to allow interdiffusion of
the zinc, Zn, or indium, In, with CIGS material used as the
absorber layer 112. Alternatively, sputtering a compound target,
such as a metal oxide, metal sulfide or metal selenide, may also be
used to provide the n-type layer, as described above, on the p-type
portion 112a of the absorber layer 112.
[0036] With further reference to FIG. 1A, in accordance with the
embodiment of the present invention, a conductive backing layer 108
may be disposed between the absorber layer 112 and the metallic
substrate 104 to provide a diffusion barrier between the absorber
layer 112 and the metallic substrate 104. The conductive backing
layer 108 may include molybdenum, Mo, or other suitable metallic
layer having a low propensity for interdiffusion with an absorber
layer 112, such as one composed of CIGS material, as well as a low
diffusion coefficient for constituents of the substrate. Moreover,
the conductive backing layer 108 may provide other functions in
addition to, or independent of, the diffusion-barrier function, for
example, a light-reflecting function, for example, as a
light-reflecting layer, to enhance the efficiency of the solar
cell, as well as other functions. The embodiments recited above for
the conductive backing layer 108 should not be construed as
limiting the function of the conductive backing layer 108 to only
those recited, as other functions of the conductive backing layer
108 are within the spirit and scope of embodiments of the present
invention, as well.
[0037] With reference now to FIG. 1B, in accordance with an
embodiment of the present invention, a schematic diagram of a model
circuit 100B of a solar cell that is electrically connected to a
load is shown. The model circuit 100B of the solar cell includes a
current source 158 that generates a photocurrent, i.sub.L. As shown
in FIG. 1A, the current source 158 is such as to produce
counterclockwise electrical current, or equivalently an clockwise
electron-flow, flowing around each of the loops of the circuit
shown; embodiments of the present invention also apply, without
limitation thereto, to solar-cell circuits in which the electrical
current flows in a clockwise direction, or equivalently electrons
flow in a counterclockwise direction. The photocurrent, i.sub.L, is
produced when a plurality of incident photons, light particles, of
which one example photon 154 with energy, hv, is shown, produce
electron-hole pairs in the absorber layer 112 and these
electron-hole pairs are separated by the pn homojunction 112c, or
in the alternative, by a pn heterojunction as described above. It
should be appreciated that the energy, hv, of each incident photon
of the plurality of photons should exceed the band-gap energy,
E.sub.g, that separates the valence band from the conduction band
of the absorber layer 112 to produce such electron-hole pairs,
which result in the photocurrent, i.sub.L.
[0038] The model circuit 100B of the solar cell further includes a
diode 162, which corresponds to recombination currents, primarily
at the pn homojunction 112c, that are shunted away from the
connected load. As shown in FIG. 1B, the diode is shown having a
polarity consistent with electrical current flowing
counterclockwise, or equivalently electron-flow clockwise, around
the loops of the circuit shown; embodiments of the present
invention apply, without limitation thereto, to a solar cell in
which the diode of the model circuit has the opposite polarity in
which electrical current flows clockwise, or equivalently
electron-flow flows counterclockwise, around the loops of the
circuit shown. In addition, the model circuit 100B of the solar
cell includes two parasitic resistances corresponding to a shunt
resistor 166 with shunt resistance, R.sub.Sh, and to a series
resistor 170 with series resistance, R.sub.S. The solar cell may be
connected to a load represented by a load resistor 180 with load
resistance, R.sub.L. Thus, the circuit elements of the solar cell
include the current source 158, the diode 162 and the shunt
resistor 166 connected across the current source 158, and the
series resistor 170 connected in series with the load resistor 180
across the current source 158, as shown. As the shunt resistor 166,
like the diode 162, are connected across the current source 158,
these two circuit elements are associated with internal electrical
currents within the solar cell shunted away from useful application
to the load. As the series resistor 170 connected in series with
the load resistor 180 are connected across the current source 158,
the series resistor 170 is associated with internal resistance of
the solar cell that limits the electrical current to the load.
[0039] With further reference to FIG. 1B, it should be recognized
that the shunt resistance may be associated with surface leakage
currents that follow paths at free surfaces that cross the pn
homojunction 112c; free surfaces are usually found at the edges of
the solar cell along the side walls of the device that define its
lateral dimensions; such free surfaces may also be found at
discontinuities in the absorber layer 112 that extend past the pn
homojunction 112c. The shunt resistance may also be associated with
shunt defects which may be present that shunt electrical current
away from the load. A small value of the shunt resistance,
R.sub.Sh, is undesirable as it lowers the open circuit voltage,
V.sub.OC, of the solar cell, which directly affects the efficiency
of the solar cell. Moreover, it should also be recognized that the
series resistance, R.sub.S, is associated with: the contact
resistance between the p-type portion 112a and the conductive
backing layer 108, the bulk resistance of the p-type portion 112a,
the bulk resistance of the n-type portion 112b, the contact
resistance between the n-type portion 112b and TCO layer 116, and
other components, such as conductive leads, and connections in
series with the load. These latter sources of series resistance,
conductive leads, and connections in series with the load, are
germane to embodiments of the present invention as interconnect
assemblies, which is subsequently described. A large value of the
series resistance, R.sub.S, is undesirable as it lowers the short
circuit current, I.sub.SC, of the solar cell, which also directly
affects the efficiency of the solar cell.
[0040] With reference now to FIG. 2, in accordance with an
embodiment of the present invention, a schematic diagram of a model
circuit 200 of a solar-cell module 204 that is coupled to a load is
shown. The load is represented by a load resistor 208 with load
resistance, R.sub.L, as shown. The solar-cell module 204 of the
model circuit 200 includes a plurality of solar cells: a first
solar cell 210 including a current source 210a that generates a
photocurrent, i.sub.L1, produced by example photon 214 with energy,
hv.sub.1, a diode 210b and a shunt resistor 210c with shunt
resistance, R.sub.Sh1; a second solar cell 230 including a current
source 230a that generates a photocurrent, i.sub.L2, produced by
example photon 234 with energy, hv.sub.2, a diode 230b and a shunt
resistor 230c with shunt resistance, R.sub.Sh2; and, a terminating
solar cell 260 including a current source 260a that generates a
photocurrent, i.sub.L3, produced by example photon 264 with energy,
hv.sub.n, a diode 260b and a shunt resistor 260c with shunt
resistance, R.sub.Shn. Parasitic series internal resistances of the
respective solar cells 210, 230 and 260 have been omitted from the
schematic diagram to simplify the discussion. Instead, series
resistors with series resistances, R.sub.S1, R.sub.S2 and R.sub.Sn
are shown disposed in the solar-cell module 204 of the model
circuit 200 connected in series with the solar cells 210, 230 and
260 and the load resistor 208.
[0041] As shown in FIGS. 2 and 3, the current sources are such as
to produce counterclockwise electrical current, or equivalently an
clockwise electron-flow, flowing around each of the loops of the
circuit shown; embodiments of the present invention also apply,
without limitation thereto, to solar-cell circuits in which the
electrical current flows in a clockwise direction, or equivalently
electrons flow in a counterclockwise direction. Similarly, as shown
in FIGS. 2 and 3, the diode is shown having a polarity consistent
with electrical current flowing counterclockwise, or equivalently
electron-flow clockwise, around the loops of the circuit shown;
embodiments of the present invention apply, without limitation
thereto, to a solar cell in which the diode of the model circuit
has the opposite polarity in which electrical current flows
clockwise, or equivalently electron-flow flows counterclockwise,
around the loops of the circuit shown.
[0042] With further reference to FIG. 2, in accordance with an
embodiment of the present invention, the series resistors with
series resistances R.sub.S1 and R.sub.S2 correspond to interconnect
assemblies 220 and 240, respectively. Series resistor with series
resistance, R.sub.S1, corresponding to interconnect assembly 220 is
shown configured both to collect current from the first solar cell
210 and to interconnect electrically to the second solar cell 230.
Series resistor with series resistance, R.sub.Sn, corresponds to an
integrated solar-cell, current collector 270. The ellipsis 250
indicates additional solar cells and interconnect assemblies (not
shown) coupled in alternating pairs in series in model circuit 200
that make up the solar-cell module 204. Also, in series with the
solar cells 210, 230 and 260 are a first busbar 284 and a
terminating busbar 280 with series resistances R.sub.B1 and
R.sub.B2, respectively, that carry the electrical current generated
by solar-cell module 204 to the load resistor 208. The series
resistor with resistance R.sub.Sn, corresponding to the integrated
solar-cell, current collector 270, and R.sub.B2, corresponding to
the terminating busbar 280, in combination correspond to a
integrated busbar-solar-cell-current collector 290 coupling the
terminating solar cell 260 with the load resistor 208. In addition,
series resistor with resistance R.sub.S1, corresponding to
interconnect assembly 220, and first solar cell 210 in combination
correspond to a combined solar-cell, interconnect assembly 294.
[0043] As shown in FIG. 2 and as used herein, it should be noted
that the phrases "to collect current," "collecting current" and
"current collector" refer to collecting, transferring, and/or
transmitting current carriers of either sign, whether they be
positively charged holes or negatively charged electrons; for the
structures shown in FIGS. 1A-B, 2, 3, 4A-F, 5A-C and 6A-B, in which
an interconnect assembly is disposed above and electrically coupled
to an n-type portion of the solar cell, the current carriers
collected under normal operating conditions are negatively charged
electrons. Moreover, embodiments of the present invention apply,
without limitation thereto, to solar cell configurations where a
p-type layer is disposed on an n-type absorber layer, in which case
the current carriers collected may be positively charged holes, as
would be the case for solar cells modeled by diodes and current
sources of opposite polarity to those of FIGS. 1A-B, 2, 3, 4A-F,
5A-C and 6A-B. Therefore, in accordance with embodiments of the
present invention, a current collector and associated interconnect
assembly that collects current may, without limitation thereto,
collect, transfer, and/or transmit charges associated with an
electrical current, and/or charges associated with an
electron-flow, as for either polarity of the diodes and current
sources described herein, and thus for either configuration of a
solar cell with an n-type layer disposed on and electrically
coupled to a p-type absorber layer or a p-type layer disposed on
and electrically coupled to an n-type absorber layer, as well as
other solar cell configurations.
[0044] With further reference to FIG. 2, in accordance with an
embodiment of the present invention, the series resistances of the
interconnect assemblies 220 and 240, integrated solar-cell, current
collector 270, and the interconnect assemblies included in ellipsis
250 can have a substantial net series resistance in the model
circuit 200 of the solar-cell module 204, unless the series
resistances of the interconnect assemblies 220 and 240, integrated
solar-cell, current collector 270, and the interconnect assemblies
included in ellipsis 250 are made small. If a large plurality of
solar cells are connected in series, the short circuit current of
the solar-cell module, I.sub.SCM, may be reduced, which also
directly affects the solar-cell-module efficiency analogous to the
manner in which solar-cell efficiency is reduced by a parasitic
series resistance, R.sub.S, as described above with reference to
FIG. 1. Embodiments of the present invention provide for
diminishing the series resistances of the interconnect assemblies
220 and 240, integrated solar-cell, current collector 270, and the
interconnect assemblies included in ellipsis 250.
[0045] With reference now to FIG. 3, in accordance with embodiments
of the present invention, a schematic diagram of a model circuit
300 of a solar-cell module 304 is shown that illustrates
embodiments of the present invention such that the series
resistances of the interconnect assemblies 320 and 340, integrated
solar-cell, current collector 370, and the interconnect assemblies
included in ellipsis 350 are made small. The solar-cell module 304
is coupled to a load represented by a load resistor 308 with load
resistance, R.sub.L, as shown. The solar-cell module 304 of the
model circuit 300 includes a plurality of solar cells: a first
solar cell 310 including a current source 310a that generates a
photocurrent, i.sub.L1, produced by example photon 314 with energy,
hv.sub.1, a diode 310b and a shunt resistor 310c with shunt
resistance, R.sub.Sh1; a second solar cell 330 including a current
source 330a that generates a photocurrent, i.sub.L2, produced by
example photon 334 with energy, hv.sub.2, a diode 330b and a shunt
resistor 330c with shunt resistance, R.sub.Sh2; and, a terminating
solar cell 360 including a current source 360a that generates a
photocurrent, i.sub.L3, produced by example photon 364 with energy,
hv.sub.n, a diode 360b and a shunt resistor 360c with shunt
resistance, R.sub.Shn.
[0046] With further reference to FIG. 3, in accordance with an
embodiment of the present invention, the interconnect assemblies
320 and 340 and the integrated solar-cell, current collector 370,
with respective equivalent series resistances R.sub.S1, R.sub.S2
and R.sub.Sn are shown disposed in the solar-cell module 304 of the
model circuit 300 connected in series with the solar cells 310, 330
and 360 and the load resistor 308. The ellipsis 350 indicates
additional solar cells and interconnect assemblies (not shown)
coupled in alternating pairs in series in model circuit 300 that
make up the solar-cell module 304. Also, in series with the solar
cells 310, 330 and 360 are a first busbar 384 and a terminating
busbar 380 with series resistances R.sub.B1 and R.sub.B2,
respectively, that carry the electrical current generated by
solar-cell module 304 to the load resistor 308. The integrated
solar-cell, current collector 370 with resistance R.sub.Sn, and the
series resistor with series resistance R.sub.B2, corresponding to
the terminating busbar 380, in combination correspond to an
integrated busbar-solar-cell-current collector 390 coupling the
terminating solar cell 360 with the load resistor 308. In addition,
interconnect assembly 320 with resistance, R.sub.S2, and solar cell
310 in combination correspond to a combined solar-cell,
interconnect assembly 394.
[0047] With further reference to FIG. 3, in accordance with
embodiments of the present invention, the interconnect assembly 320
includes a trace including a plurality of electrically conductive
portions, identified with resistors 320a, 320b, 320c, and 320m with
respective resistances, r.sub.P11, r.sub.P12, r.sub.P13 and
r.sub.P1m, and the ellipsis 320i indicating additional resistors
(not shown). It should be noted that although the plurality of
electrically conductive portions of the trace are modeled here as
discrete resistors the interconnection with solar cell 330 is
considerably more complicated involving the distributed resistance
in the TCO layer of the solar cell, which has been omitted for the
sake of elucidating functional features of embodiments of the
present invention. Therefore, it should be understood that
embodiments of the present invention may also include, without
limitation thereto, the effects of such distributed resistances on
the trace. The plurality of electrically conductive portions,
without limitation thereto, identified with resistors 320a, 320b,
320c, 320i, and 320m, are configured both to collect current from
the first solar cell 310 and to interconnect electrically to the
second solar cell 330. The plurality of electrically conductive
portions, identified with resistors 320a, 320b, 320c, 320i, and
320m, are configured such that upon interconnecting the first solar
cell 310 and the second solar cell 330 the plurality of
electrically conductive portions are connected electrically in
parallel between the first solar cell 310 and the second solar cell
330.
[0048] Thus, in accordance with embodiments of the present
invention, the plurality of electrically conductive portions is
configured such that equivalent series resistance, R.sub.S1, of the
interconnect assembly 320 including the parallel network of
resistors 320a, 320b, 320c, 320i, and 320m, is less than the
resistance of any one resistor in the parallel network. Therefore,
upon interconnecting the first solar cell 310 with the second solar
cell 330, the equivalent series resistance, R.sub.S1, of the
interconnect assembly 320, is given approximately, omitting the
effects of distributed resistances at the interconnects with the
first and second solar cells 310 and 330, by the formula for a
plurality of resistors connected electrically in parallel, viz.
R.sub.S1=1/[.SIGMA.(1/r.sub.P1i)], where r.sub.P1i is the
resistance of the ith resistor in the parallel-resistor network,
and the sum, .SIGMA., is taken over all of the resistors in the
network from i=1 to m. Hence, by connecting the first solar cell
310 to the second solar cell 330, with the interconnect assembly
320, the series resistance, R.sub.S1, of the interconnect assembly
320 can be reduced lowering the effective series resistance between
solar cells in the solar-cell module 304 improving the
solar-cell-module efficiency.
[0049] Moreover, in accordance with embodiments of the present
invention, the configuration of the plurality of electrically
conductive portions due to this parallel arrangement of
electrically conductive portions between the first solar cell 310
and the second solar cell 330 provides a redundancy of electrical
current carrying capacity between interconnected solar cells should
one of the plurality of electrically conductive portions become
damaged, or its reliability become impaired. Thus, embodiments of
the present invention provide that the plurality of electrically
conductive portions is configured such that solar-cell efficiency
is substantially undiminished in an event that any one of the
plurality of electrically conductive portions is conductively
impaired, because the loss of electrical current through any one
electrically conductive portion will be compensated for by the
plurality of other parallel electrically conductive portions
coupling the first solar cell 310 with the second solar cell 330.
It should be noted that as used herein the phrase, "substantially
undiminished," with respect to solar-cell efficiency means that the
solar-cell efficiency is not reduced below an acceptable level of
productive performance.
[0050] With further reference to FIG. 3, in accordance with
embodiments of the present invention, the interconnect assembly 340
includes a trace including a plurality of electrically conductive
portions identified with resistors 340a, 340b, 340c, and 340m with
respective resistances, r.sub.P21, r.sub.P22, r.sub.P23 and
r.sub.P2m, and the ellipsis 340i indicating additional resistors
(not shown). The plurality of electrically conductive portions,
without limitation thereto, identified with resistors 340a, 340b,
340c, 340i, and 340m, are configured both to collect current from a
first solar cell 330 and to interconnect electrically to a second
solar cell, in this case a next adjacent one of the plurality of
solar cells represented by ellipsis 350. From this example, it
should be clear that for embodiments of the present invention a
first solar cell and a second solar cell refer, without limitation
thereto, to just two adjacent solar cells configured in series in
the solar-cell module, and need not be limited to a solar cell
located first in line of a series of solar cells in a solar-cell
module, nor a solar cell located second in line of a series of
solar cells in a solar-cell module. The resistors 340a, 340b, 340c,
340i, and 340m, are configured such that upon interconnecting the
first solar cell 330 and the second solar cell, in this case the
next adjacent solar cell of the plurality of solar cells
represented by ellipsis 350, the resistors 340a, 340b, 340c, 340i,
and 340m, are coupled electrically in parallel between the first
solar cell 330 and the second solar cell, the next adjacent solar
cell of the plurality of solar cells represented by ellipsis
350.
[0051] Thus, in accordance with embodiments of the present
invention, the plurality of electrically conductive portions is
configured such that series resistance, R.sub.S2, of the
interconnect assembly 340 including the parallel network of
resistors 340a, 340b, 340c, 340i, and 340m, is less than the
resistance of any one resistor in the network. Hence, the series
resistance, R.sub.S2, of the interconnect assembly 340 can be
reduced lowering the effective series resistance between solar
cells in the solar-cell module improving the solar-cell-module
efficiency of the solar-cell module 304. Moreover, the plurality of
electrically conductive portions, identified with resistors 340a,
340b, 340c, 340i, and 340m, may be configured such that solar-cell
efficiency is substantially undiminished in an event that any one
of the plurality of electrically conductive portions is
conductively impaired.
[0052] With further reference to FIG. 3, in accordance with
embodiments of the present invention, the combined solar-cell,
interconnect assembly 394 includes the first solar cell 310 and the
interconnect assembly 320; the interconnect assembly 320 includes a
trace disposed above a light-facing side of the first solar cell
310, the trace further including a plurality of electrically
conductive portions, identified with resistors 320a, 320b, 320c,
and 320m with respective resistances, r.sub.P21, r.sub.P22,
r.sub.P23 and r.sub.P2m, and the ellipsis 320i indicating
additional resistors (not shown). All electrically conductive
portions of the plurality of electrically conductive portions,
without limitation thereto, identified with resistors 320a, 320b,
320c, 320i, and 320m, are configured to collect current from the
first solar cell 310 and to interconnect electrically to the second
solar cell 330. In addition, the plurality of electrically
conductive portions, identified with resistors 320a, 320b, 320c,
320i, and 320m, may be configured such that solar-cell efficiency
is substantially undiminished in an event that any one of the
plurality of electrically conductive portions is conductively
impaired. Also, any of the plurality of electrically conductive
portions, identified with resistors 320a, 320b, 320c, 320i, and
320m, may be configured to interconnect electrically to the second
solar cell 330.
[0053] With further reference to FIG. 3, in accordance with
embodiments of the present invention, the integrated
busbar-solar-cell-current collector 390 includes the terminating
busbar 380 and the integrated solar-cell, current collector 370.
The integrated solar-cell, current collector 370 includes a trace
including a plurality of electrically conductive portions,
identified with resistors 370a, 370b, 3701, and 370m with
respective resistances, r.sub.Pn1, r.sub.Pn2, r.sub.Pnl and
r.sub.Pnm, and the ellipsis 370i indicating additional resistors
(not shown). The plurality of electrically conductive portions,
without limitation thereto, identified with resistors 370a, 370b,
370i, 370l and 370m, are configured both to collect current from
the first solar cell 310 and to interconnect electrically to the
terminating busbar 380. The resistors 370a, 370b, 370i, 370l and
370m, are coupled electrically in parallel between the terminating
solar cell 360 and the terminating busbar 380 series resistor with
series resistance, R.sub.B2. Thus, the plurality of electrically
conductive portions is configured such that series resistance,
R.sub.Sn, of the interconnect assembly 340 including the parallel
network of resistors 370a, 370b, 370i, 370l and 370m, is less than
the resistance of any one resistor in the network.
[0054] In accordance with embodiments of the present invention, the
integrated solar-cell, current collector 370 includes a plurality
of integrated pairs of electrically conductive, electrically
parallel trace portions. Resistors 370a, 370b, 370l and 370m with
respective resistances, r.sub.Pn1, r.sub.Pn2, r.sub.Pnl and
r.sub.Pnm, and the ellipsis 370i indicating additional resistors
(not shown) form such a plurality of integrated pairs of
electrically conductive, electrically parallel trace portions when
suitably paired as adjacent pair units connected electrically
together as an integral unit over the terminating solar cell 360.
For example, one such pair of the plurality of integrated pairs of
electrically conductive, electrically parallel trace portions is
pair of resistors 370a and 370b connected electrically together as
an integral unit over the terminating solar cell 360, as shown. The
plurality of integrated pairs of electrically conductive,
electrically parallel trace portions are configured both to collect
current from the terminating solar cell 360 and to interconnect
electrically to the terminating busbar 380. Moreover, the plurality
of integrated pairs of electrically conductive, electrically
parallel trace portions is configured such that solar-cell
efficiency is substantially undiminished in an event that any one
electrically conductive, electrically parallel trace portion, for
example, either one, but not both, of the resistors 370a and 370b
of the integral pair, of the plurality of integrated pairs of
electrically conductive, electrically parallel trace portions is
conductively impaired.
[0055] With further reference to FIG. 3, in accordance with
embodiments of the present invention, the solar-cell module 304
includes the first solar cell 310, at least the second solar cell
330 and the interconnect assembly 320 disposed above a light-facing
side of an absorber layer of the first solar cell 310. The
interconnect assembly 320 includes a trace comprising a plurality
of electrically conductive portions, identified with resistors
320a, 320b, 320c, and 320m with respective resistances, r.sub.P11,
r.sub.P12, r.sub.P13 and r.sub.P1m, and the ellipsis 320i
indicating additional resistors (not shown). The plurality of
electrically conductive portions is configured both to collect
current from the first solar cell 310 and to interconnect
electrically to the second solar cell 330. The plurality of
electrically conductive portions is configured such that solar-cell
efficiency is substantially undiminished in an event that any one
of the plurality of electrically conductive portions is
conductively impaired.
[0056] With reference now to FIGS. 4A, 4B and 4C, in accordance
with embodiments of the present invention, a schematic diagram of a
model circuit 400A of an interconnect assembly 420 connecting a
first solar cell 410 to a second solar cell 430 of a solar-cell
module 404 is shown. The interconnect assembly 420 includes a trace
including a plurality of electrically conductive portions,
identified with resistors 420a, 420b, 420c, and 420m with
respective resistances, r.sub.P11, r.sub.P12, r.sub.P13 and
r.sub.P1m, and the ellipsis 420i indicating additional resistors
(not shown). The plurality of electrically conductive portions,
without limitation thereto, identified with resistors 420a, 420b,
420c, 420i, and 420m, are configured both to collect current from
the first solar cell 410 and to interconnect electrically to the
second solar cell 430. The plurality of electrically conductive
portions, identified with resistors 420a, 420b, 420c, 420i, and
420m, are configured such that, upon interconnecting the first
solar cell 410 and the second solar cell 430, the plurality of
electrically conductive portions are connected electrically in
parallel between the first solar cell 410 and the second solar cell
430. The plurality of electrically conductive portions is
configured such that equivalent series resistance, R.sub.S1, of the
interconnect assembly 420 including the parallel network of
resistors 420a, 420b, 420c, 420i, and 420m, is less than the
resistance of any one resistor in the parallel network. Therefore,
by connecting the first solar cell 410 to the second solar cell
430, with the interconnect assembly 420, the series resistance,
R.sub.S1, of the interconnect assembly 420 can be reduced lowering
the effective series resistance between solar cells in the
solar-cell module 404 improving the solar-cell-module
efficiency.
[0057] Moreover, in accordance with embodiments of the present
invention, the configuration of the plurality of electrically
conductive portions due to this parallel arrangement of
electrically conductive portions between the first solar cell 410
and the second solar cell 430 provides a redundancy of electrical
current carrying capacity between interconnected solar cells should
any one of the plurality of electrically conductive portions become
damaged, or its reliability become impaired. Thus, embodiments of
the present invention provide that the plurality of electrically
conductive portions is configured such that solar-cell efficiency
is substantially undiminished in an event that any one of the
plurality of electrically conductive portions is conductively
impaired, because the loss of electrical current through any one
electrically conductive portion will be compensated for by the
plurality of the unimpaired parallel electrically conductive
portions coupling the first solar cell 410 with the second solar
cell 430. It should be noted that as used herein the phrase,
"substantially undiminished," with respect to solar-cell efficiency
means that the solar-cell efficiency is not reduced below an
acceptable level of productive performance. In addition, in
accordance with embodiments of the present invention, the plurality
of electrically conductive portions may be configured in pairs of
electrically conductive portions, for example, identified with
resistors 420a and 420b. Thus, the plurality of electrically
conductive portions may be configured such that solar-cell
efficiency is substantially undiminished even in an event that, in
every pair of electrically conductive portions of the plurality of
electrically conductive portions, one electrically conductive
portion of the pair is conductively impaired. In accordance with
embodiments of the present invention, each member of a pair of
electrically conductive portions may be electrically equivalent to
the other member of the pair, but need not be electrically
equivalent to the other member of the pair, it only being necessary
that in an event one member, a first member, of the pair becomes
conductively impaired the other member, a second member, is
configured such that solar-cell efficiency is substantially
undiminished.
[0058] With further reference to FIGS. 4B and 4C, in accordance
with embodiments of the present invention, a plan view 400B of the
interconnect assembly 420 of FIG. 4A is shown that details the
physical interconnection of two solar cells 410 and 430 in the
solar-cell module 404. The solar-cell module 404 includes the first
solar cell 410, at least the second solar cell 430 and the
interconnect assembly 420 disposed above a light-facing side 416 of
the absorber layer of the first solar cell 410. The interconnect
assembly 420 includes a trace comprising a plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m,
previously identified herein with the resistors 420a, 420b, 420c,
420i and 420m described in FIG. 400A, where the ellipsis of 420i
indicates additional electrically conductive portions (not shown).
The plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m is configured both to collect current from the first
solar cell 410 and to interconnect electrically to the second solar
cell 430. The plurality of electrically conductive portions 420a,
420b, 420c, 420i and 420m is configured such that solar-cell
efficiency is substantially undiminished in an event that any one
of the plurality of electrically conductive portions 420a, 420b,
420c, 420i and 420m is conductively impaired.
[0059] With further reference to FIG. 4B, in accordance with
embodiments of the present invention, the detailed configuration of
the plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m is shown. The plurality of electrically conductive
portions 420a, 420b, 420c, 420i and 420m further includes a first
portion 420a of the plurality of electrically conductive portions
420a, 420b, 420c, 420i and 420m configured both to collect current
from the first solar cell 410 and to interconnect electrically to
the second solar cell 430 and a second portion 420b of the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m configured both to collect current from the first
solar cell 410 and to interconnect electrically to the second solar
cell 430. The first portion 420a includes a first end 420p distal
from the second solar cell 430. Also, the second portion 420b
includes a second end 420q distal from the second solar cell 430.
The second portion 420b is disposed proximately to the first
portion 420a and electrically connected to the first portion 420a
such that the first distal end 420p is electrically connected to
the second distal end 420q, for example, at first junction 420r, or
by a linking portion, such that the second portion 420b is
configured electrically in parallel to the first portion 420a when
configured to interconnect to the second solar cell 430.
[0060] With further reference to FIG. 4B, in accordance with
embodiments of the present invention, the plurality of electrically
conductive portions 420a, 420b, 420c, 420i and 420m may further
include the second portion 420b including a third end 420s distal
from the first solar cell 410 and a third portion 420c of the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m configured both to collect current from the first
solar cell 410 and to interconnect electrically to the second solar
cell 430. The third portion 420c includes a fourth end 420t distal
from the first solar cell 410. The third portion 420c is disposed
proximately to the second portion 420b and electrically connected
to the second portion 420b such that the third distal end 420s is
electrically connected to the fourth distal end 420t, for example,
at second junction 420u, or by a linking portion, such that the
third portion 420c is configured electrically in parallel to the
second portion 420b when configured to interconnect with the first
solar cell 430.
[0061] With further reference to FIGS. 4B and 4C, in accordance
with embodiments of the present invention, it should be noted that
the nature of the parallel connection between electrically
conductive portions interconnecting a first solar cell and a second
solar cell is such that, for distal ends of electrically conductive
portions not directly joined together, without limitation thereto,
the metallic substrate of a second solar cell and a TCO layer of
the first solar cell may provide the necessary electrical coupling.
For example, distal ends 420v and 420s are electrically coupled
through a low resistance connection through a metallic substrate
430c of second solar cell 430. Similarly, for example, distal ends
420w and 420q are electrically coupled through the low resistance
connection through the TCO layer 410b of first solar cell 410.
[0062] With further reference to FIG. 4B, in accordance with
embodiments of the present invention, an open-circuit defect 440 is
shown such that second portion 420b is conductively impaired. FIG.
4B illustrates the manner in which the plurality of electrically
conductive portions 420a, 420b, 420c, 420i and 420m is configured
such that solar-cell efficiency is substantially undiminished in an
event that any one of the plurality of electrically conductive
portions 420a, 420b, 420c, 420i and 420m is conductively impaired,
for example, second portion 420b. An arrow 448 indicates the
nominal electron-flow through a third portion 420c of the plurality
of electrically conductive portions 420a, 420b, 420c, 420i and 420m
essentially unaffected by open-circuit defect 440. In the absence
of open-circuit defect 440, an electron-flow indicated by arrow 448
would normally flow through any one electrically conductive portion
of the plurality of electrically conductive portions 420a, 420b,
420c, 420i and 420m, in particular, second portion 420b. However,
when the open-circuit defect 440 is present, this electron-flow
divides into two portions shown by arrows 442 and 444: arrow 442
corresponding to that portion of the normal electron-flow flowing
to the right along the second portion 420b to the second solar cell
430, and arrow 444 corresponding to that portion of the normal
electron-flow flowing to the left along the second portion 420b to
the first portion 420a and then to the right along the first
portion 420a to the second solar cell 430. Thus, the net
electron-flow represented by arrow 446 flowing to the right along
the first portion 420a is consequently larger than what would
normally flow to the right along the first portion 420a to the
second solar cell 430 in the absence of the open-circuit defect
440.
[0063] It should be noted that open-circuit defect 440 is for
illustration purposes only and that embodiments of the present
invention compensate for other types of defects in an electrically
conductive portion, in general, such as, without limitation to: a
delamination of an electrically conductive portion from the first
solar cell 410, corrosion of an electrically conductive portion,
and even complete loss of an electrically conductive portion. In
accordance with embodiments of the present invention, in the event
a defect completely conductively impairs an electrically conductive
portion, the physical spacing between adjacent electrically
conductive portions, identified with double-headed arrow 449, may
be chosen such that solar-cell efficiency is substantially
undiminished. Nevertheless, embodiments of the present invention
embrace, without limitation thereto, other physical spacings
between adjacent electrically conductive portions in the event
defects are less severe than those causing a complete loss of one
of the electrically conductive portions.
[0064] With further reference to FIG. 4B, in accordance with
embodiments of the present invention, the plurality of electrically
conductive portions 420a, 420b, 420c, 420i and 420m may be
connected electrically in series to form a single continuous
electrically conductive line. Moreover, the trace that includes the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m may be disposed in a serpentine pattern such that the
interconnect assembly 420 is configured to collect current from the
first solar cell 410 and to interconnect electrically to the second
solar cell 430, as shown.
[0065] With further reference to FIG. 4C, in accordance with
embodiments of the present invention, a cross-sectional, elevation
view 400C of the interconnect assembly 420 is shown that further
details the physical interconnection of two solar cells 410 and 430
in the solar-cell module 404. Projections 474 and 478 of planes
orthogonal to both of the views in FIGS. 4B and 4C, and coincident
with the ends of the plurality of electrically conductive portions
420a, 420b, 420c, 420i and 420m show the correspondence between
features of the plan view 400B of FIG. 4B and features in the
cross-sectional, elevation view 400C of FIG. 4C. Also, it should be
noted that although the solar-cell module 404 is shown with
separation 472 between the first solar cell 410 and the second
solar cell 430, there need not be such separation 472 between the
first solar cell 410 and the second solar cell 430. As shown in
FIGS. 4B and 4C, a combined solar-cell, interconnect assembly 494
includes the first solar cell 410 and the interconnect assembly
420. The interconnect assembly 420 includes the trace disposed
above the light-facing side 416 of the first solar cell 410, the
trace further including the plurality of electrically conductive
portions 420a, 420b, 420c, 420i and 420m. All electrically
conductive portions of the plurality of electrically conductive
portions 420a, 420b, 420c, 420i and 420m are configured to collect
current from the first solar cell 410 and to interconnect
electrically to the second solar cell 430. In addition, the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m may be configured such that solar-cell efficiency is
substantially undiminished in an event that any one of the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m is conductively impaired. Also, any of the plurality
of electrically conductive portions 420a, 420b, 420c, 420i and 420m
may be configured to interconnect electrically to the second solar
cell 430. The first solar cell 410 of the combined solar-cell,
interconnect assembly 494 may include a metallic substrate 410c and
an absorber layer 410a. The absorber layer 410a of the first solar
cell 410 may include copper indium gallium diselenide (CIGS).
Alternatively, other semiconductors having the chalcopyrite crystal
structure, for example, chemically homologous compounds with the
compound CIGS having the chalcopyrite crystal structure, in which
alternative elemental constituents are substituted for Cu, In, Ga,
and/or Se, may be used as the absorber layer 410a. Moreover, in
embodiments of the present invention, it should be noted that
semiconductors, such as silicon and cadmium telluride, as well as
other semiconductors, may be used as the absorber layer 410a.
[0066] With further reference to FIG. 4C, in accordance with
embodiments of the present invention, the plurality of electrically
conductive portions 420a, 420b, 420c, 420i and 420m of the combined
solar-cell, interconnect assembly 494 further includes the first
portion 420a of the plurality of electrically conductive portions
420a, 420b, 420c, 420i and 420m configured to collect current from
the first solar cell 410 and the second portion 420b of the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m configured to collect current from the first solar
cell 410. The first portion 420a includes the first end 420p distal
from an edge 414 of the first solar cell 410. The second portion
420b includes the second end 420q distal from the edge 414 of the
first solar cell 410. The second portion 420b is disposed
proximately to the first portion 420a and electrically connected to
the first portion 420a such that the first distal end 420p is
electrically connected to the second distal end 420q such that the
second portion 420b is configured electrically in parallel to the
first portion 420a when configured to interconnect to the second
solar cell 430.
[0067] With further reference to FIG. 4C, in accordance with
embodiments of the present invention, the interconnect assembly 420
further includes a top carrier film 450. The top carrier film 450
includes a first substantially transparent, electrically insulating
layer coupled to the trace and disposed above a top portion of the
trace. The first substantially transparent, electrically insulating
layer allows for forming a short-circuit-preventing portion 454 at
an edge 434 of the second solar cell 430. The first substantially
transparent, electrically insulating layer allows for forming the
short-circuit-preventing portion 454 at the edge 434 of the second
solar cell 430 to prevent the first portion 420a from short
circuiting an absorber layer 430a of the second solar cell 430 in
the event that the first portion 420a buckles and rides up a side
432 of second solar cell 430. The edge 434 is located at the
intersection of the side 432 of the second solar cell 430 and a
back side 438 of the second solar cell 430 that couples with the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m, for example, first portion 420a as shown. The second
solar cell 430 may include the absorber layer 430a, a TCO layer
430b, and the metallic substrate 430c; a backing layer (not shown)
may also be disposed between the absorber layer 430a and the
metallic substrate 430c. Above a light-facing side 436 of the
second solar cell 430, an integrated busbar-solar-cell-current
collector (not shown in FIG. 4C, but which is shown in FIGS. 6A and
6B) may be disposed and coupled to the second solar cell 430 to
provide interconnection with a load (not shown). Alternatively,
above the light-facing side 436 of the second solar cell 430,
another interconnect assembly (not shown) may be disposed and
coupled to the second solar cell 430 to provide interconnection
with additional solar-cells (not shown) in the solar-cell module
404.
[0068] With further reference to FIG. 4C, in accordance with
embodiments of the present invention, the interconnect assembly 420
further includes a bottom carrier film 460. The bottom carrier film
460 may include a second electrically insulating layer coupled to
the trace and disposed below a bottom portion of the trace.
Alternatively, The bottom carrier film 460 may include a carrier
film selected from a group consisting of a second electrically
insulating layer, a structural plastic layer, and a metallic layer,
and is coupled to the trace and is disposed below a bottom portion
of the trace. The second electrically insulating layer allows for
forming an edge-protecting portion 464 at the edge 414 of the first
solar cell 410. Alternatively, a supplementary isolation strip (not
shown) of a third electrically insulating layer may be disposed
between the bottom carrier film 460 and the first portion 420a of
the plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m, or alternatively between the bottom carrier film 460
and the edge 414, to provide additional protection at the edge 414.
The supplementary isolation strip may be as wide as 5 millimeters
(mm) in the direction of the double-headed arrow showing the
separation 472, and may extend along the full length of a side 412
of the first solar cell 410. The edge 414 is located at the
intersection of the side 412 of the first solar cell 410 and a
light-facing side 416 of the first solar cell 410 that couples with
the plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m, for example, first portion 420a as shown. The first
solar cell 410 may include the absorber layer 410a, the TCO layer
410b, and the metallic substrate 410c; a backing layer (not shown)
may also be disposed between the absorber layer 410a and the
metallic substrate 410c. Below a back side 418 of the first solar
cell 410, a first busbar (not shown) may be disposed and coupled to
the first solar cell 410 to provide interconnection with a load
(not shown). Alternatively, below the back side 418 of the first
solar cell 410, another interconnect assembly (not shown) may be
disposed and coupled to the first solar cell 410 to provide
interconnection with additional solar-cells (not shown) in the
solar-cell module 404.
[0069] With reference now to FIGS. 4D and 4E, in accordance with
embodiments of the present invention, cross-sectional, elevation
views 400D and 400E, respectively, of two alternative interconnect
assemblies that minimize the separation 472 (see FIG. 4B) between
the first solar cell 410 and the second solar cell 430 to improve
the solar-cell-module efficiency of the solar-cell module 404 are
shown. In both examples shown in FIGS. 4D and 4E, the side 412 of
the first solar cell 410 essentially coincides with the side 432 of
the second solar cell 430. It should be noted that as used herein
the phrase, "essentially coincides," with respect to the side 412
of the first solar cell 410 and the side 432 of the second solar
cell 430 means that there is little or no separation 472 between
the first solar cell 410 and the second solar cell 430, and little
or no overlap of the first solar cell 410 with the second solar
cell 430 so that there is less wasted space and open area between
the solar cells 410 and 430, which improves the solar-collection
efficiency of the solar-cell module 404 resulting in improved
solar-cell-module efficiency. FIG. 4D shows an edge-conforming
interconnect assembly for the physical interconnection of the two
solar cells 410 and 430 in the solar-cell module 404. FIG. 4E shows
a shingled-solar-cell arrangement for the physical interconnection
of the two solar cells 410 and 430 in the solar-cell module 404.
For both the edge-conforming interconnect assembly of FIG. 4D and
the shingled-solar-cell arrangement of FIG. 4E, the interconnect
assembly 420 further includes the bottom carrier film 460. The
bottom carrier film 460 includes a second electrically insulating
layer coupled to the trace and disposed below a bottom portion of
the trace. Alternatively, The bottom carrier film 460 may include a
carrier film selected from a group consisting of a second
electrically insulating layer, a structural plastic layer, and a
metallic layer, and is coupled to the trace and is disposed below a
bottom portion of the trace. The second electrically insulating
layer allows for forming the edge-protecting portion 464 at the
edge 414 of the first solar cell 410. In the case of the
edge-conforming interconnect assembly shown in FIG. 4D, the bottom
carrier film 460 and the first portion 420a of the interconnect
assembly 420 may be relatively flexible and compliant allowing them
to wrap around the edge 414 and down the side 412 of the first
solar cell 410, as shown. The edge 414 is located at the
intersection of the side 412 of the first solar cell 410 and the
light-facing side 416 of the first solar cell 410 that couples with
the plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m, for example, first portion 420a as shown. The first
solar cell 410 may include the absorber layer 410a, a TCO layer
410b, and the metallic substrate 410c; a backing layer (not shown)
may also be disposed between the absorber layer 410a and the
metallic substrate 410c. Below the back side 418 of the first solar
cell 410, another interconnect assembly (not shown) or first busbar
(not shown) may be disposed and coupled to the first solar cell 410
as described above for FIG. 4C. If an additional solar cell (not
shown) is interconnected to the back side 418 of the first solar
cell 410 as in the shingled-solar-cell arrangement of FIG. 4E, the
first solar cell 410 would be pitched upward at its left-hand side
and interconnected to another interconnect assembly similar to the
manner in which the second solar cell 430 is shown interconnected
with solar cell 410 at side 412 in FIG. 4E.
[0070] With further reference to FIGS. 4D and 4E, in accordance
with embodiments of the present invention, the interconnect
assembly 420 further includes the top carrier film 450. The top
carrier film 450 includes a first substantially transparent,
electrically insulating layer coupled to the trace and disposed
above a top portion of the trace. The first substantially
transparent, electrically insulating layer allows for forming the
short-circuit-preventing portion 454 at the edge 434 of the second
solar cell 430 to prevent the first portion 420a from short
circuiting the absorber layer 430a of the second solar cell 430 in
the event that the first portion 420a rides up the side 432 of
second solar cell 430. The edge 434 is located at the intersection
of the side 432 of the second solar cell 430 and the back side 438
of the second solar cell 430 that couples with the plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m,
for example, first portion 420a as shown. In the case of the
edge-conforming interconnect assembly shown in FIG. 4D, the top
carrier film 450 may be relatively flexible and compliant allowing
it to follow the conformation of the bottom carrier film 460 and
the first portion 420a of the interconnect assembly 420 underlying
it that wrap around the edge 414 and down the side 412 of the first
solar cell 410, as shown. The second solar cell 430 may include the
absorber layer 430a, the TCO layer 430b, and the metallic substrate
430c; a backing layer (not shown) may also be disposed between the
absorber layer 430a and the metallic substrate 430c. Also, in the
case of the edge-conforming interconnect assembly, the absorber
layer 430a, TCO layer 430b, and metallic substrate 430c of the
second solar cell 430 may be relatively flexible and compliant
allowing them to follow the conformation of the underlying
interconnect assembly 420 that wraps around the edge 414 and down
the side 412 of the first solar cell 410. Above the light-facing
side 436 of the second solar cell 430, an integrated
busbar-solar-cell-current collector (not shown in FIG. 4C, but
which is shown in FIGS. 6A and 6B), or alternatively another
interconnect assembly (not shown), may be disposed on and coupled
to the second solar cell 430, as described above for FIG. 4C.
[0071] With reference now to FIG. 4F, in accordance with
embodiments of the present invention, a plan view 400F of an
alternative interconnect assembly for the interconnect assembly 420
of FIG. 4A is shown that details the physical interconnection of
two solar cells 410 and 430 in the solar-cell module 404. The
solar-cell module 404 includes the first solar cell 410, at least
the second solar cell 430 and the interconnect assembly 420
disposed above the light-facing side 416 of the absorber layer of
the first solar cell 410. The edges 414 and 434 of the solar cells
410 and 430 may be separated by the separation 472 as shown in FIG.
4F; or alternatively, the edges 414 and 434 of the solar cells 410
and 430 may essentially coincide as discussed above for FIGS. 4D
and 4E. The interconnect assembly 420 includes a trace comprising a
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m, previously identified herein with the resistors
420a, 420b, 420c, 420i and 420m described in FIG. 400A, where the
ellipsis of 420i indicates additional electrically conductive
portions (not shown). The plurality of electrically conductive
portions 420a, 420b, 420c, 420i and 420m is configured both to
collect current from the first solar cell 410 and to interconnect
electrically to the second solar cell 430. The plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m is
configured such that solar-cell efficiency is substantially
undiminished in an event that any one of the plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m is
conductively impaired.
[0072] With further reference to FIG. 4F, in accordance with
embodiments of the present invention, the detailed configuration of
the plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m is shown without electrically connecting trace
portions, for example, junctions formed in the trace or linking
portions of the trace. For example, in the case where electrically
connecting trace portions of the trace have been cut away, removed,
or are otherwise absent, from the distal ends of the plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m,
as shown in FIG. 4F. The plurality of electrically conductive
portions 420a, 420b, 420c, 420i and 420m may be linked together
instead indirectly by the TCO layer 410b of the first solar cell
410 at distal ends of the trace disposed over the first solar cell
410, for example, first distal end 420p of first portion 420a and
second distal end 420q of second portion 420b by portions of the
TCO layer 410b of the first solar cell 410 that lie in between the
distal ends 420p and 420q. In like fashion, the distal ends 420w
and 420q are electrically coupled through the low resistance
connection through the TCO layer 410b of first solar cell 410.
Similarly, the plurality of electrically conductive portions 420a,
420b, 420c, 420i and 420m may be linked together instead indirectly
by the metallic substrate 430c, or intervening backing layer (not
shown), of the first solar cell 430 at distal ends of the trace
disposed under the second solar cell 430, for example, third distal
end 420s of second portion 420b and fourth distal end 420t of third
portion 420c by portions of the metallic substrate 430c of the
second solar cell 430 that lie in between the distal ends 420s and
420t. In like fashion, the distal ends 420v and 420s are
electrically coupled through a low resistance connection through
the metallic substrate 430c of second solar cell 430.
[0073] With further reference to FIG. 4F, in accordance with
embodiments of the present invention, the open-circuit defect 440
is shown such that second portion 420b is conductively impaired.
FIG. 4F illustrates the manner in which the plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m is
configured such that solar-cell efficiency is substantially
undiminished in an event that any one of the plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m is
conductively impaired, for example, second portion 420b. An arrow
480 indicates the nominal electron-flow through an m-th portion
420m of the plurality of electrically conductive portions 420a,
420b, 420c, 420i and 420m essentially unaffected by open-circuit
defect 440. In the absence of open-circuit defect 440, an
electron-flow indicated by arrow 480 would normally flow through
any one electrically conductive portion of the plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m,
in particular, second portion 420b. However, when the open-circuit
defect 440 is present, portions of this electron-flow are lost to
adjacent electrically conductive portions 420a and 420c shown by
arrows 484a and 484c; arrow 482 corresponds to that portion of the
normal electron-flow flowing to the right along the second portion
420b to the second solar cell 430, and arrow 484b corresponds to
that portion of the normal electron-flow that would bridge the
open-circuit defect 440 by flowing through the higher resistance
path of the TCO layer 410b bridging across the two portions of
second portion 420b on either side of the open-circuit defect 440.
Thus, the net electron-flow represented by arrow 486 flowing to the
right along the first portion 420a is consequently larger than what
would normally flow to the right along the first portion 420a to
the second solar cell 430 in the absence of the open-circuit defect
440; and, the net electron-flow represented by arrow 488 flowing to
the right along the third portion 420c is consequently larger than
what would normally flow to the right along the third portion 420c
to the second solar cell 430 in the absence of the open-circuit
defect 440.
[0074] Moreover, in the case of the alternative interconnect
assembly depicted in FIG. 4F, as stated before for the interconnect
assembly depicted in FIG. 4B, it should again be noted that
open-circuit defect 440 is for illustration purposes only and that
embodiments of the present invention compensate for other types of
defects in an electrically conductive portion, in general, such as,
without limitation to: a delamination of an electrically conductive
portion from the first solar cell 410, corrosion of an electrically
conductive portion, and even complete loss of an electrically
conductive portion. In accordance with embodiments of the present
invention, in the event a defect completely conductively impairs an
electrically conductive portion, the physical spacing between
adjacent electrically conductive portions, identified with
double-headed arrow 449, may be chosen such that solar-cell
efficiency is substantially undiminished. Nevertheless, embodiments
of the present invention embrace, without limitation thereto, other
physical spacings between adjacent electrically conductive portions
in the event defects are less severe than those causing a complete
loss of one of the electrically conductive portions.
[0075] With further reference to FIGS. 4G and 4H, in accordance
with embodiments of the present invention, a plan view 400G of the
interconnect assembly 420 of FIG. 4A is shown that details the
physical interconnection of two solar cells 410 and 430 in the
solar-cell module 404. The solar-cell module 404 includes the first
solar cell 410, at least the second solar cell 430 and the
interconnect assembly 420 disposed above a light-facing side 416 of
the absorber layer of the first solar cell 410. The interconnect
assembly 420 includes a trace comprising a plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m,
previously identified herein with the resistors 420a, 420b, 420c,
420i and 420m described in FIG. 400A, where the ellipsis of 420i
indicates additional electrically conductive portions (not shown).
The plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m is configured both to collect current from the first
solar cell 410 and to interconnect electrically to the second solar
cell 430. The plurality of electrically conductive portions 420a,
420b, 420c, 420i and 420m is configured such that solar-cell
efficiency is substantially undiminished in an event that any one
of the plurality of electrically conductive portions 420a, 420b,
420c, 420i and 420m is conductively impaired.
[0076] With further reference to FIG. 4G, in accordance with
embodiments of the present invention, the detailed configuration of
the plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m is shown. The plurality of electrically conductive
portions 420a, 420b, 420c, 420i and 420m further includes a first
portion 420a of the plurality of electrically conductive portions
420a, 420b, 420c, 420i and 420m configured both to collect current
from the first solar cell 410 and to interconnect electrically to
the second solar cell 430 and a second portion 420b of the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m configured both to collect current from the first
solar cell 410 and to interconnect electrically to the second solar
cell 430. The first portion 420a includes a first end 420p distal
from the second solar cell 430. Also, the second portion 420b
includes a second end 420q distal from the second solar cell 430.
The second portion 420b is disposed proximately to the first
portion 420a and electrically connected to the first portion 420a
such that the first distal end 420p is electrically connected to
the second distal end 420q, for example, at first junction 420r, or
by a linking portion, such that the second portion 420b is
configured electrically in parallel to the first portion 420a when
configured to interconnect to the second solar cell 430.
[0077] With further reference to FIG. 4G, in accordance with
embodiments of the present invention, the plurality of electrically
conductive portions 420a, 420b, 420c, 420i and 420m may further
include the second portion 420b including a third end 420s distal
from the first solar cell 410 and a third portion 420c of the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m configured both to collect current from the first
solar cell 410 and to interconnect electrically to the second solar
cell 430. The third portion 420c includes a fourth end 420t distal
from the first solar cell 410. The third portion 420c is disposed
proximately to the second portion 420b and electrically connected
to the second portion 420b such that the third distal end 420s is
electrically connected to the fourth distal end 420t, for example,
at second junction 420u, or by a linking portion, such that the
third portion 420c is configured electrically in parallel to the
second portion 420b when configured to interconnect with the first
solar cell 430.
[0078] With further reference to FIGS. 4G and 4H, in accordance
with embodiments of the present invention, it should be noted that
the nature of the parallel connection between electrically
conductive portions interconnecting a first solar cell and a second
solar cell is such that, for distal ends of electrically conductive
portions not directly joined together, without limitation thereto,
the metallic substrate of a second solar cell and a TCO layer of
the first solar cell may provide the necessary electrical coupling.
For example, distal ends 420v and 420s are electrically coupled
through a low resistance connection through a metallic substrate
430c of second solar cell 430. Similarly, for example, distal ends
420w and 420q are electrically coupled through the low resistance
connection through the TCO layer 410b of first solar cell 410.
[0079] With further reference to FIG. 4G, in accordance with
embodiments of the present invention, an open-circuit defect 440 is
shown such that second portion 420b is conductively impaired. FIG.
4G illustrates the manner in which the plurality of electrically
conductive portions 420a, 420b, 420c, 420i and 420m is configured
such that solar-cell efficiency is substantially undiminished in an
event that any one of the plurality of electrically conductive
portions 420a, 420b, 420c, 420i and 420m is conductively impaired,
for example, second portion 420b. An arrow 448 indicates the
nominal electron-flow through a third portion 420c of the plurality
of electrically conductive portions 420a, 420b, 420c, 420i and 420m
essentially unaffected by open-circuit defect 440. In the absence
of open-circuit defect 440, an electron-flow indicated by arrow 448
would normally flow through any one electrically conductive portion
of the plurality of electrically conductive portions 420a, 420b,
420c, 420i and 420m, in particular, second portion 420b. However,
when the open-circuit defect 440 is present, this electron-flow
divides into two portions shown by arrows 442 and 444: arrow 442
corresponding to that portion of the normal electron-flow flowing
to the right along the second portion 420b to the second solar cell
430, and arrow 444 corresponding to that portion of the normal
electron-flow flowing to the left along the second portion 420b to
the first portion 420a and then to the right along the first
portion 420a to the second solar cell 430. Thus, the net
electron-flow represented by arrow 446 flowing to the right along
the first portion 420a is consequently larger than what would
normally flow to the right along the first portion 420a to the
second solar cell 430 in the absence of the open-circuit defect
440.
[0080] It should be noted that open-circuit defect 440 is for
illustration purposes only and that embodiments of the present
invention compensate for other types of defects in an electrically
conductive portion, in general, such as, without limitation to: a
delamination of an electrically conductive portion from the first
solar cell 410, corrosion of an electrically conductive portion,
and even complete loss of an electrically conductive portion. In
accordance with embodiments of the present invention, in the event
a defect completely conductively impairs an electrically conductive
portion, the physical spacing between adjacent electrically
conductive portions, identified with double-headed arrow 449, may
be chosen such that solar-cell efficiency is substantially
undiminished. Nevertheless, embodiments of the present invention
embrace, without limitation thereto, other physical spacings
between adjacent electrically conductive portions in the event
defects are less severe than those causing a complete loss of one
of the electrically conductive portions.
[0081] With further reference to FIG. 4G, in accordance with
embodiments of the present invention, the plurality of electrically
conductive portions 420a, 420b, 420c, 420i and 420m may be
connected electrically in series to form a single continuous
electrically conductive line. Moreover, the trace that includes the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m may be disposed in a serpentine pattern such that the
interconnect assembly 420 is configured to collect current from the
first solar cell 410 and to interconnect electrically to the second
solar cell 430, as shown.
[0082] With further reference to FIG. 4H, in accordance with
embodiments of the present invention, a cross-sectional, elevation
view 400H of the interconnect assembly 420 is shown that further
details the physical interconnection of two solar cells 410 and 430
in the solar-cell module 404. Projections 474 and 478 of planes
orthogonal to both of the views in FIGS. 4G and 4H, and coincident
with the ends of the plurality of electrically conductive portions
420a, 420b, 420c, 420i and 420m show the correspondence between
features of the plan view 400G of FIG. 4G and features in the
cross-sectional, elevation view 400H of FIG. 4H. Also, it should be
noted that although the solar-cell module 404 is shown with
separation 472 between the first solar cell 410 and the second
solar cell 430, there need not be such separation 472 between the
first solar cell 410 and the second solar cell 430. In some
embodiments, the separation will be less than that depicted in the
figures. In some embodiments, the cells may overlap.
[0083] As shown in FIGS. 4G and 4H, a combined solar-cell,
interconnect assembly 494 includes the first solar cell 410 and the
interconnect assembly 420. The interconnect assembly 420 includes
the trace disposed above the light-facing side 416 of the first
solar cell 410, the trace further including the plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m.
All electrically conductive portions of the plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m
are configured to collect current from the first solar cell 410 and
to interconnect electrically to the second solar cell 430. In
addition, the plurality of electrically conductive portions 420a,
420b, 420c, 420i and 420m may be configured such that solar-cell
efficiency is substantially undiminished in an event that any one
of the plurality of electrically conductive portions 420a, 420b,
420c, 420i and 420m is conductively impaired. Also, any of the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m may be configured to interconnect electrically to the
second solar cell 430. The first solar cell 410 of the combined
solar-cell, interconnect assembly 494 may include a metallic
substrate 410c and an absorber layer 410a. The absorber layer 410a
of the first solar cell 410 may include copper indium gallium
diselenide (CIGS). Alternatively, other semiconductors having the
chalcopyrite crystal structure, for example, chemically homologous
compounds with the compound CIGS having the chalcopyrite crystal
structure, in which alternative elemental constituents are
substituted for Cu, In, Ga, and/or Se, may be used as the absorber
layer 410a. Moreover, in embodiments of the present invention, it
should be noted that semiconductors, such as silicon and cadmium
telluride, as well as other semiconductors, may be used as the
absorber layer 410a.
[0084] With further reference to FIG. 4H, in accordance with
embodiments of the present invention, the plurality of electrically
conductive portions 420a, 420b, 420c, 420i and 420m of the combined
solar-cell, interconnect assembly 494 further includes the first
portion 420a of the plurality of electrically conductive portions
420a, 420b, 420c, 420i and 420m configured to collect current from
the first solar cell 410 and the second portion 420b of the
plurality of electrically conductive portions 420a, 420b, 420c,
420i and 420m configured to collect current from the first solar
cell 410. The first portion 420a includes the first end 420p distal
from an edge 414 of the first solar cell 410. The second portion
420b includes the second end 420q distal from the edge 414 of the
first solar cell 410. The second portion 420b is disposed
proximately to the first portion 420a and electrically connected to
the first portion 420a such that the first distal end 420p is
electrically connected to the second distal end 420q such that the
second portion 420b is configured electrically in parallel to the
first portion 420a when configured to interconnect to the second
solar cell 430.
[0085] With further reference to FIG. 4H, in accordance with
embodiments of the present invention, the interconnect assembly 420
further includes top and bottom carrier films 450 and 460,
respectively. The top carrier film 450 includes a first
substantially transparent, electrically insulating layer coupled to
the trace 420 and disposed above a top portion 420x of the trace
420. The first substantially transparent, electrically insulating
layer terminates a small distance short of the edge 412 of the
first cell 410. The bottom carrier film 460 may include a second
electrically insulating layer coupled to the trace 420 and disposed
below a bottom portion of the trace 420a. Alternatively, the bottom
carrier film 460 may include a carrier film selected from a group
consisting of a second electrically insulating layer, a structural
plastic layer, and a metallic layer, and is coupled to the trace
and is disposed below a bottom portion of the trace. The second
electrically insulating layer allows for forming an edge-protecting
portion 464 at the edge 414 of the first solar cell 410.
Alternatively, a supplementary isolation strip (not shown) of a
third electrically insulating layer may be disposed between the
bottom carrier film 460 and the first portion 420a of the plurality
of electrically conductive portions 420a, 420b, 420c, 420i and
420m, or alternatively between the bottom carrier film 460 and the
edge 414, to provide additional protection at the edge 414. The
supplementary isolation strip may be as wide as 5 millimeters (mm)
in the direction of the double-headed arrow showing the separation
472, and may extend along the full length of a side 412 of the
first solar cell 410. The edge 414 is located at the intersection
of the side 412 of the first solar cell 410 and a light-facing side
416 of the first solar cell 410 that couples with the plurality of
electrically conductive portions 420a, 420b, 420c, 420i and 420m,
for example, first portion 420a as shown.
[0086] The first solar cell 410 may include the absorber layer
410a, the TCO layer 410b, and the metallic substrate 410c; a
backing layer (not shown) may also be disposed between the absorber
layer 410a and the metallic substrate 410c. Below a back side 418
of the first solar cell 410, a first busbar (not shown) may be
disposed and coupled to the first solar cell 410 to provide
interconnection with a load (not shown). Alternatively, below the
back side 418 of the first solar cell 410, another interconnect
assembly (not shown) may be disposed and coupled to the first solar
cell 410 to provide interconnection with additional solar-cells
(not shown) in the solar-cell module 404.
[0087] The second solar cell 430 may include the absorber layer
430a, a TCO layer 430b, and the metallic substrate 430c; a backing
layer (not shown) may also be disposed between the absorber layer
430a and the metallic substrate 430c. Above a light-facing side 436
of the second solar cell 430, an integrated
busbar-solar-cell-current collector (not shown in FIG. 4H, but
which is shown in FIGS. 6A and 6B) may be disposed and coupled to
the second solar cell 430 to provide interconnection with a load
(not shown). Alternatively, above the light-facing side 436 of the
second solar cell 430, another interconnect assembly (not shown)
may be disposed and coupled to the second solar cell 430 to provide
interconnection with additional solar-cells (not shown) in the
solar-cell module 404.
[0088] With reference now to FIG. 5A, in accordance with
embodiments of the present invention, a plan view 500A of the
combined applicable carrier film, interconnect assembly 504 is
shown. FIG. 5A shows the physical arrangement of a trace 520 with
respect to a top carrier film 550 and a bottom carrier film 560 in
the combined applicable carrier film, interconnect assembly 504.
The combined applicable carrier film, interconnect assembly 504
includes the top carrier film 550 and the trace 520 including a
plurality of electrically conductive portions 520a, 520b, 520c,
520d, 520e, 520f, 520g, 520m and 520i, the latter corresponding to
the ellipsis indicating additional electrically conductive portions
(not shown). The plurality of electrically conductive portions 520a
through 520m is configured both to collect current from a first
solar cell 510 (shown in FIG. 5D) and to interconnect electrically
to a second solar cell (not shown). As shown in FIG. 5A, the
plurality of electrically conductive portions 520a through 520m run
over the top of the first solar cell 510 on the left and over an
edge 514 of the first solar cell 510 to the right under an edge 534
of, and underneath, the second solar cell (not shown). The top
carrier film 550 includes a first substantially transparent,
electrically insulating layer 550A (shown in FIG. 5B). The
plurality of electrically conductive portions 520a through 520m is
configured such that solar-cell efficiency is substantially
undiminished in an event that any one of the plurality of
electrically conductive portions 520a through 520m is conductively
impaired. It should be noted that as used herein the phrase,
"substantially transparent," with respect to a substantially
transparent, electrically insulating layer means that light passes
through the substantially transparent, electrically insulating
layer with negligible absorption. The first substantially
transparent, electrically insulating layer 550a is coupled to the
trace 520 and disposed above a top portion of the trace 520 (shown
in FIG. 5B) as indicated by the dashed portions of the trace 520 on
the left of FIG. 5A.
[0089] With reference now to FIG. 5B, in accordance with
embodiments of the present invention, a plan view 500B of the
combined applicable carrier film, interconnect assembly 504 is
shown. FIG. 5B shows the physical arrangement of a trace 520 with
respect to a top carrier film 550 and a bottom carrier film 560 in
the combined applicable carrier film, interconnect assembly 504.
The combined applicable carrier film, interconnect assembly 504
includes the top carrier film 550 and the trace 520 including a
plurality of electrically conductive portions 520a, 520b, 520c,
520d, 520e, 520f, 520g, 520m and 520i, the latter corresponding to
the ellipsis indicating additional electrically conductive portions
(not shown). The plurality of electrically conductive portions 520a
through 520m is configured both to collect current from a first
solar cell 510 (shown in FIG. 5E) and to interconnect electrically
to a second solar cell (not shown). As shown in FIG. 5B, the
plurality of electrically conductive portions 520a through 520m run
over the top of the first solar cell 510 on the left and over an
edge 514 of the first solar cell 510 to the right under an edge 534
of, and underneath, the second solar cell (not shown). The top
carrier film 550 includes a first substantially transparent,
electrically insulating layer 550a (shown in FIG. 5D). The
plurality of electrically conductive portions 520a through 520m is
configured such that solar-cell efficiency is substantially
undiminished in an event that any one of the plurality of
electrically conductive portions 520a through 520m is conductively
impaired. It should be noted that as used herein the phrase,
"substantially transparent," with respect to a substantially
transparent, electrically insulating layer means that light passes
through the substantially transparent, electrically insulating
layer with negligible absorption. The first substantially
transparent, electrically insulating layer 550a is coupled to the
trace 520 and disposed above a top portion of the trace 520 (shown
in FIG. 5D) as indicated by the dashed portions of the trace 520 on
the left of FIG. 5B.
[0090] FIG. 5C provides a further illustration, in cross-section,
of a specific embodiment of the present invention in accordance
with that described with reference to FIG. 5B. The figure shows
aspects of the interconnection arrangement of two solar cells. The
first solar cell 570 can be constructed as previously described
herein and include a CIGS thin film 572 on a stainless steel
substrate 574. The second solar cell 580 can have the same
construction as the first cell 570, again including a CIGS thin
film 582 on a stainless steel substrate 584. The two cells 570 and
580 are arranged so that there is a small gap 599, generally as
small a gap as possible, for example about 1-2 mm, between their
respective closest edges 575 and 585. As noted above, in
alternative embodiments, the gap may be wider or the cells may even
slightly overlap.
[0091] The cells are interconnected by an interconnect 590 that
includes top and bottom carrier films (polymer decals) 592 and 594
and a conductive wire 596. In specific embodiments, the wire can be
about 34 gauge and the decals can be composed of a layer of about 2
mil thick PET between layers of about 2 mil thick Surlyn adhesive.
The decals 592, 594 and wire 596 are arranged so that a portion of
the wire 596 is exposed for electrical contact with a top side 573
of the first cell 570 and the bottom side 583 of the second solar
cell 580. The top decal 592 covers the top of the wire 596 and
extends from a first end 597 of the wire 596 over the first solar
cell 570 almost to the edge 575 of the first solar cell 570. The
bottom decal 594 covers the bottom of the wire 596, slightly
overlaps the first decal 592 in extent, and extends to a second end
598 of the wire 596 under the second solar cell 580.
[0092] With reference now to FIGS. 5D and 5E, in accordance with
embodiments of the present invention, a cross-sectional, elevation
view of the combined applicable carrier film, interconnect assembly
504 of FIG. 5A or 5B is shown. As shown in FIGS. 5D and 5E, the
cross-section of the view is taken along a cut parallel to the edge
514 of the first solar cell 510. The cross-sectional, elevation
view of FIG. 5D shows the physical arrangement of the trace 520
with respect to the top carrier film 550 in the combined applicable
carrier film, interconnect assembly 504 prior to disposition on the
first solar cell 510. On the other hand, the cross-sectional,
elevation view of FIG. 5E shows the physical arrangement of the
trace 520 with respect to the top carrier film 550 and the first
solar cell 510 of the combined applicable carrier film,
interconnect assembly 504 after it couples with the first solar
cell 510. The top carrier film 550 and the trace 520 are configured
for applying to a light-facing side of the first solar cell 510
both to collect current from the first solar cell 510 and to
interconnect electrically to the second solar cell (not shown). The
first solar cell 510 may include an absorber layer 510a, a TCO
layer 510b, and a metallic substrate 510c; the backing layer (not
shown) may also be disposed between the absorber layer 510a and the
metallic substrate 510c. The first substantially transparent,
electrically insulating layer 550a holds the trace 520 down in
contact with the first solar cell 510 and allows for forming a
short-circuit-preventing portion at an edge of the second solar
cell (not shown). The top carrier film 550 further includes a first
substantially transparent, adhesive medium 550b coupling the trace
520 to the substantially transparent, electrically insulating layer
550a. As shown in FIG. 5D, prior to disposition on the first solar
cell 510, the top carrier film 550 lies relatively flat across the
top portion of the trace 520, for example, as for the
conformational state of the top carrier film 550 immediately after
roll-to-roll fabrication of the combined applicable carrier film,
interconnect assembly 504. In contrast, after disposition on the
first solar cell 510, the top carrier film 550 conforms to the top
portion of the trace 520, as shown in FIG. 5D. The first
substantially transparent, adhesive medium 550b allows for coupling
the trace 520 to the first solar cell 510 without requiring solder.
The first substantially transparent, electrically insulating layer
550a may include a structural plastic material, such as
polyethylene terephthalate (PET). In accordance with embodiments of
the present invention, a first substantially transparent, adhesive
medium such as first substantially transparent, adhesive medium
550b may be included, without limitation thereto, in a top carrier
film of: the combined applicable carrier film, interconnect
assembly 504, the interconnect assembly 320, the integrated
busbar-solar-cell-current collector 690 (see FIG. 6B), the combined
solar-cell, interconnect assembly 494, or the interconnect assembly
420 of the solar-cell module 404.
[0093] With further reference to FIGS. 5A, 5B and 5D, in accordance
with embodiments of the present invention, the combined applicable
carrier film, interconnect assembly 504 further includes the bottom
carrier film 560. The bottom carrier film 560 includes a second
electrically insulating layer, like 550a, coupled to the trace 520
and disposed below a bottom portion of the trace 520, as indicated
by the solid-line portions of the trace 520 on the right of FIG.
5A. Alternatively, the bottom carrier film 560 may include a
carrier film selected from a group consisting of a second
electrically insulating layer, a structural plastic layer, and a
metallic layer, and is coupled to the trace 520 and is disposed
below a bottom portion of the trace 520. The second electrically
insulating layer, like 550a, holds the trace 520 down in contact
with a back side of the second solar cell (not shown) and allows
for forming an edge-protecting portion at the edge 514 of the first
solar cell 510. The bottom carrier film 560 further includes a
second adhesive medium, like 550b, coupling the trace to the second
electrically insulating layer, like 550a. The second adhesive
medium, like 550b, allows for coupling the trace 520 to the back
side of the second solar cell (not shown) without requiring solder.
The second electrically insulating layer, like 550a, includes a
structural plastic material, such as PET. In accordance with
embodiments of the present invention, a second adhesive medium,
like 550b, may be included, without limitation thereto, in a bottom
carrier film of: the combined applicable carrier film, interconnect
assembly 504, the interconnect assembly 320, the combined
solar-cell, interconnect assembly 494, or the interconnect assembly
420 of the solar-cell module 404.
[0094] With further reference to FIGS. 5A and 5B, in accordance
with embodiments of the present invention, the trace 520 may be
disposed in a serpentine pattern that allows for collecting current
from the first solar cell 510 (shown in FIG. 5D) and electrically
interconnecting to the second solar cell (not shown). It should be
noted that neither the first solar cell 510 nor the second solar
cell (not shown) are shown in FIG. 5A or 5B so as not to obscure
the structure of the combined applicable carrier film, interconnect
assembly 504. As shown in FIG. 5A, the combined applicable carrier
film, interconnect assembly 504 includes the trace 520 including
the plurality of electrically conductive portions 520a through 520m
that may run in a serpentine pattern back and forth between the
first solar cell 510 and the second solar cell (not shown). The
serpentine pattern is such that adjacent electrically conductive
portions of the plurality of electrically conductive portions 520a
through 520m are configured in pairs of adjacent electrically
conductive portions: 520a and 520b, 520c and 520d, 520e and 520f,
etc. The pairs of adjacent electrically conductive portions may be
configured in a regular repeating pattern of equally spaced
adjacent electrically conductive portions. The trace 520 including
the plurality of electrically conductive portions 520a through 520m
is disposed between the top carrier film 550 disposed above a top
portion of the trace 520 and the bottom carrier film 560 disposed
below a bottom portion of the trace 520. The first substantially
transparent, electrically insulating layer 550a of top carrier film
550 and the second electrically insulating layer, or alternatively,
structural plastic layer or metallic layer, of bottom carrier film
560 are coupled to the trace 520 with a first substantially
transparent, adhesive medium 550b and second adhesive medium which
also serve to couple the trace 520 to the first solar cell 510,
which may be located on the left, and the second solar cell, which
may be located on the right.
[0095] In the space between the two solar cells in the embodiment
depicted in FIG. 5A, between the edge 514 of the first solar cell
and the edge 534 of the second solar cell, the trace is sandwiched
between the two carrier films 550 and 560; the overlapping region
of the two carrier films 550 and 560 extends somewhat beyond the
respective edges 514 and 534 of the first and second solar cells so
as to form, respectively, an edge-protecting portion at the edge
514 of the first solar cell, and a short-circuit-preventing portion
at the edge 534 of the second solar cell, from the trace 520 that
crosses the edges 514 and 534.
[0096] In the space between the two solar cells in the embodiment
depicted in FIG. 5B, between the edge 514 of the first solar cell
and the edge 534 of the second solar cell, the trace is carried by
bottom carrier film 560; the top carrier film terminates just short
of the edge 514 of the first solar cell 510. In this way, the
bottom carrier film 560 prevents contact between the trace 520 and
the edge 514 of the first solar cell. In this embodiment, there is
no need to prevent contact between the trace 520 and the edge 534
of the second solar cell, since the edge is not electrically
conductive.
[0097] With further reference to FIGS. 5B and 5E, in accordance
with embodiments of the present invention, the trace 520 may
further include an electrically conductive line including a
conductive core 520A with at least one overlying layer 520B. In one
embodiment of the present invention, the electrically conductive
line may include the conductive core 520A including a material
having greater conductivity than nickel, for example, copper, with
an overlying nickel layer 520B. In another embodiment of the
present invention, electrically conductive line may include the
conductive core 520A including nickel without the overlying layer
520B. The electrically conductive line may also be selected from a
group consisting of a copper conductive core clad with a silver
cladding, a copper conductive core clad with a nickel coating
further clad with a silver cladding and an aluminum conductive core
clad with a silver cladding.
[0098] With further reference to FIGS. 5B and 5E, in accordance
with embodiments of the present invention, the trace 520 for
collecting current from a solar cell, for example the first solar
cell 510, may include an electrically conductive line including the
conductive core 520A, and the overlying layer 520B that limits
current flow to a proximate shunt defect (not shown) in the solar
cell. The proximate shunt defect may be proximately located in the
vicinity of an electrical contact between the overlying layer 520B
of the electrically conductive line and the TCO layer 510b of the
solar cell, for example, first solar cell 510. The overlying layer
520B of the electrically conductive line of the trace 520 may
further include an overlying layer 520B composed of nickel. The
conductive core 520A of the electrically conductive line of the
trace 520 may further include nickel. The conductive core 520A may
also include a material selected from a group consisting of copper,
silver, aluminum, and elemental constituents and alloys having high
electrical conductivity, which may be greater than the electrical
conductivity of nickel. The TCO layer 510b of the solar cell, for
example first solar cell 510, may include a conductive oxide
selected from a group consisting of zinc oxide, aluminum zinc oxide
and indium tin oxide. In addition, the absorber layer 510a, for
example, absorber layer 112 of FIG. 1A, of the solar cell, for
example, first solar cell 510, may include copper indium gallium
diselenide (CIGS). Alternatively, in embodiments of the present
invention, it should be noted that semiconductors, such as silicon,
cadmium telluride, and chalcopyrite semiconductors, as well as
other semiconductors, may be used as the absorber layer 510a.
Moreover, an n-type layer, for example, n-type portion 112b of
absorber layer 112 of FIG. 1A, of the solar cell, for example,
first solar cell 510, may be disposed on and electrically coupled
to a p-type absorber layer, for example, absorber layer 112 of FIG.
1A, of the solar cell, for example, first solar cell 510, and the
n-type layer, for example, n-type portion 112b of absorber layer
112 of FIG. 1A, may be selected from a group consisting of a metal
oxide, a metal sulfide and a metal selenide.
[0099] Although the trace 520 is shown as having a circular
cross-section having a point-like contact with a solar cell, for
example, with the TCO layer 510b, or, without limitation thereto,
to a top surface, of the first solar cell 510, embodiments of the
present inventions include, without limitation thereto, other
cross-sectional profiles of the trace 520, such as a profile
including a flattened top portion and a flattened bottom portion,
so as to increase the contact area between the trace 520 and a
solar cell with which it makes contact. For example, a flattened
bottom portion of trace 520 increases the contact area with the
light-facing side of the first solar cell 510; on the other hand, a
flattened top portion of trace 520 increases the contact area with
a back side of an adjacent solar cell to which the plurality of
electrically conductive portions 520a through 520m of the trace 520
interconnects. In accordance with embodiments of the present
invention, a trace, such as trace 520, may be included, without
limitation thereto, in: the combined applicable carrier film,
interconnect assembly 504, the interconnect assembly 320, the
integrated busbar-solar-cell-current collector 690 (see FIG. 6B),
the combined solar-cell, interconnect assembly 494, or the
interconnect assembly 420 of the solar-cell module 404.
[0100] With reference now to FIG. 6A, in accordance with
embodiments of the present invention, a plan view 600A of an
integrated busbar-solar-cell-current collector 690 is shown. FIG.
6A shows the physical interconnection of a terminating solar cell
660 with a terminating busbar 680 of the integrated
busbar-solar-cell-current collector 690. The integrated
busbar-solar-cell-current collector 690 includes the terminating
busbar 680 and an integrated solar-cell, current collector 670. The
integrated solar-cell, current collector 670 includes a plurality
of integrated pairs 670a&b, 670c&d, 670e&f, 670g&h,
and 670l&m and 670i, the ellipsis indicating additional
integrated pairs (not shown), of electrically conductive,
electrically parallel trace portions 670a-m. Throughout the
following, the respective integrated pairs: 670a and 670b, 670c and
670d, 670e and 670f, 670g and 670h, and 670l and 670m, are referred
to respectively as: 670a&b, 670c&d, 670e&f, 670g&h,
and 670l&m; and the electrically conductive, electrically
parallel trace portions: 670a, 670b, 670c, 670d, 670e, 670f, 670g,
670h, 670l and 670m, are referred to as 670a-m. The plurality of
integrated pairs 670a&b, 670c&c, 670e&f, 670g&h,
670i and 670l&m of electrically conductive, electrically
parallel trace portions 670a-m is configured both to collect
current from the terminating solar cell 660 and to interconnect
electrically to the terminating busbar 680. The plurality of
integrated pairs 670a&b, 670c&c, 670e&f, 670g&h,
670i and 670l&m of electrically conductive, electrically
parallel trace portions 670a-m is configured such that solar-cell
efficiency is substantially undiminished in an event that any one
electrically conductive, electrically parallel trace portion, for
example, 670h, of the plurality of integrated pairs 670a&b,
670c&c, 670e&f, 670g&h, 670i and 670l&m of
electrically conductive, electrically parallel trace portions
670a-m is conductively impaired.
[0101] With further reference to FIGS. 6A and 6B, in accordance
with embodiments of the present invention, the plurality of
integrated pairs 670a&b, 670c&c, 670e&f, 670g&h,
670i and 670l&m of electrically conductive, electrically
parallel trace portions 670a-m further includes a first
electrically conductive, electrically parallel trace portion 670a
of a first integrated pair 670a&b of the electrically
conductive, electrically parallel trace portions 670a-m configured
both to collect current from the terminating solar cell 660 and to
interconnect electrically to the terminating busbar 680, and a
second electrically conductive, electrically parallel trace portion
670b of the first integrated pair 670a&b of the electrically
conductive, electrically parallel trace portions 670a-m configured
both to collect current from the terminating solar cell 660 and to
interconnect electrically to the terminating busbar 680. The first
electrically conductive, electrically parallel trace portion 670a
includes a first end 670p distal from the terminating busbar 680
located parallel to a side 662 of the terminating solar cell 660.
The second electrically conductive, electrically parallel trace
portion 670b includes a second end 670q distal from the terminating
busbar 680. The second electrically conductive, electrically
parallel trace portion 670b is disposed proximately to the first
electrically conductive, electrically parallel trace portion 670a
and electrically connected to the first electrically conductive,
electrically parallel trace portion 670a such that the first distal
end 670p is electrically connected to the second distal end 670q,
for example, at first junction 670r, or by a linking portion, such
that the second electrically conductive, electrically parallel
trace portion 670b is configured electrically in parallel to the
first electrically conductive, electrically parallel trace portion
670a when configured to interconnect to the terminating busbar 680.
In addition, in accordance with embodiments of the present
invention, the terminating busbar 680 may be disposed above and
connected electrically to extended portions, for example, 670x and
670y, of the plurality of integrated pairs 670a&b, 670c&c,
670e&f, 670g&h, 670i and 670l&m of electrically
conductive, electrically parallel trace portions 670a-m configured
such that the terminating busbar 680 is configured to reduce
shadowing of the terminating solar cell 660.
[0102] With further reference to FIG. 6A, in accordance with
embodiments of the present invention, an open-circuit defect 640 is
shown such that eighth electrically conductive, electrically
parallel trace portion 670h is conductively impaired. FIG. 6A
illustrates the manner in which the plurality of integrated pairs
670a&b, 670c&c, 670e&f, 670g&h and 670l&m of
electrically conductive, electrically parallel trace portions
670a-m is configured such that solar-cell efficiency is
substantially undiminished in an event that any one electrically
conductive, electrically parallel trace portion, for example,
eighth electrically conductive, electrically parallel trace portion
670h, of the plurality of integrated pairs 670a&b, 670c&c,
670e&f, 670g&h and 670l&m of electrically conductive,
electrically parallel trace portions 670a-m is conductively
impaired. The arrow 648 indicates the nominal electron-flow through
a sixth electrically conductive, electrically parallel trace
portion 670f of the plurality of integrated pairs 670a&b,
670c&c, 670e&f, 670g&h and 670l&m of electrically
conductive, electrically parallel trace portions 670a-m essentially
unaffected by open-circuit defect 640. In the absence of
open-circuit defect 640, an electron-flow indicated by arrow 648
would normally flow through any one electrically conductive,
electrically parallel trace portion of the plurality of integrated
pairs 670a&b, 670c&c, 670e&f, 670g&h and 670l&m
of electrically conductive, electrically parallel trace portions
670a-m, in particular, eighth electrically conductive, electrically
parallel trace portion 670h. However, when the open-circuit defect
640 is present, this electron-flow divides into two portions shown
by arrows 642 and 644: arrow 642 corresponding to that portion of
the normal electron-flow flowing to the right along the eighth
electrically conductive, electrically parallel trace portion 670h
to the terminating busbar 680, and arrow 644 corresponding to that
portion of the normal electron-flow flowing to the left along the
eighth electrically conductive, electrically parallel trace portion
670h to the seventh electrically conductive, electrically parallel
trace portion 670g and then to the right along the seventh
electrically conductive, electrically parallel trace portion 670g
to the terminating busbar 680. Thus, the net electron-flow
represented by arrow 646 flowing to the right along the seventh
electrically conductive, electrically parallel trace portion 670g
is consequently larger than what would normally flow to the right
along the seventh electrically conductive, electrically parallel
trace portion 670g to the terminating busbar 680 in the absence of
the open-circuit defect 640. It should be noted that open-circuit
defect 640 is for illustration purposes only and that embodiments
of the present invention compensate for other types of defects in
an electrically conductive, electrically parallel trace portion, in
general, such as, without limitation to: a delamination of an
electrically conductive, electrically parallel trace portion from
the terminating solar cell 660, corrosion of an electrically
conductive, electrically parallel trace portion, and even complete
loss of an electrically conductive, electrically parallel trace
portion. In accordance with embodiments of the present invention,
in the event a defect completely conductively impairs an
electrically conductive, electrically parallel trace portion, the
physical spacing between adjacent electrically conductive,
electrically parallel trace portions, identified with double-headed
arrow 649, may be chosen such that solar-cell efficiency is
substantially undiminished. Nevertheless, embodiments of the
present invention embrace, without limitation thereto, other
physical spacings between adjacent electrically conductive,
electrically parallel trace portions in the event defects are less
severe than those causing a complete loss of one of the
electrically conductive, electrically parallel trace portions.
[0103] With reference now to FIG. 6B and further reference to FIG.
6A, in accordance with embodiments of the present invention, a
cross-sectional, elevation view 600B of the integrated
busbar-solar-cell-current collector 690 of FIG. 6A is shown. FIG.
6B shows the physical interconnection of the terminating solar cell
660 with the terminating busbar 680 in the integrated
busbar-solar-cell-current collector 690. In accordance with
embodiments of the present invention, the interconnection approach
employing a carrier film is also conducive to coupling the
integrated busbar-solar-cell-current collector 690 directly to the
terminating busbar 680 without requiring solder. Thus, the
integrated busbar-solar-cell-current collector 690 further includes
a top carrier film 650. The top carrier film 650 includes a first
substantially transparent, electrically insulating layer (not
shown, but like 550a of FIG. 5B) coupled to the plurality of
integrated pairs 670a&b, 670c&c, 670e&f, 670g&h,
670i and 670l&m of electrically conductive, electrically
parallel trace portions 670a-m, for example, electrically
conductive, electrically parallel trace portion 670a, and disposed
above a top portion of the plurality of integrated pairs
670a&b, 670c&c, 670e&f, 670g&h, 670i and 670l&m
of electrically conductive, electrically parallel trace portions
670a-m.
[0104] With further reference to FIGS. 6A and 6B, in accordance
with embodiments of the present invention, the top carrier film 650
further includes a first adhesive medium (not shown, but like 550b
of FIGS. 5B and 5E) coupling the plurality of integrated pairs
670a&b, 670c&c, 670e&f, 670g&h, 670i and 670l&m
of electrically conductive, electrically parallel trace portions
670a-m to the electrically insulating layer (like 550a of FIG. 5B).
The first adhesive medium (like 550b of FIGS. 5B and 5E) allows for
coupling the plurality of integrated pairs 670a&b, 670c&c,
670e&f, 670g&h, 670i and 670l&m of electrically
conductive, electrically parallel trace portions 670a-m to the
terminating solar cell 660 without requiring solder. The
terminating solar cell 660 may include an absorber layer 660a, a
TCO layer 660b, and a metallic substrate 660c; a backing layer (not
shown) may also be disposed between the absorber layer 660a and the
metallic substrate 660c. The plurality of integrated pairs of
electrically conductive, electrically parallel trace portions
670a-m may be connected electrically in series to form a single
continuous electrically conductive line (not shown). The single
continuous electrically conductive line may be disposed in a
serpentine pattern (not shown, but like the pattern of trace 520 in
FIG. 5A) such that the integrated busbar-solar-cell-current
collector 690 is configured to collect current from the terminating
solar cell 660 and to interconnect electrically to the terminating
busbar 680. The plurality of integrated pairs 670a&b,
670c&c, 670e&f, 670g&h, 670i and 670l&m of
electrically conductive, electrically parallel trace portions
670a-m may further include a plurality of electrically conductive
lines (not shown, but like trace 520 of FIGS. 5B and 5E), any
electrically conductive line of the plurality of electrically
conductive lines selected from a group consisting of a copper
conductive core clad with a silver cladding, a copper conductive
core clad with a nickel coating further clad with a silver cladding
and an aluminum conductive core clad with a silver cladding.
[0105] With further reference to FIGS. 6A and 6B, in accordance
with embodiments of the present invention, integrated
busbar-solar-cell-current collector 690 may include a supplementary
isolation strip (not shown) at an edge 664 of the terminating solar
cell 660 and running along the length of the side 662 to provide
additional protection at the edge 664 and side 662 of the
terminating solar cell 660 from the extended portions, for example,
670x and 670y, of the plurality of integrated pairs 670a&b,
670c&c, 670e&f, 670g&h, 670i and 670l&m of
electrically conductive, electrically parallel trace portions
670a-m. In another embodiment of the present invention, the
extended portions, for example, 670x and 670y, may be configured
(not shown) to provide stress relief and to allow folding the
terminating busbar 680 along edge 664 under a back side 668 and at
the side 662 of terminating solar cell 660, so that there is less
wasted space and open area between the terminating solar cell 660
of one module and the initial solar cell (not shown) of an adjacent
module. Moreover, integrated busbar-solar-cell-current collector
690 may include a supplementary carrier-film strip (not shown) at
the edge 664 of the terminating solar cell 660 and running along
the length of the side 662 disposed above and coupled to top
carrier film 650 and the terminating busbar 680 to affix the
terminating busbar 680 to the extended portions, for example, 670x
and 670y. Alternatively, the integrated busbar-solar-cell-current
collector 690 may include the top carrier film 650 extending over
the top of the terminating busbar 680 and extended portions, for
example, 670x and 670y, to affix the terminating busbar 680 to
these extended portions. Thus, these latter two embodiments of the
present invention provide a laminate including the terminating
busbar 680 disposed between top carrier film 650, or alternatively
the supplementary carrier-film strip, and the supplementary
isolation strip (not shown) along the edge 664 and side 662 of the
terminating solar cell 660. Moreover, the top carrier film 650, or
the supplementary carrier-film strip, is conducive to connecting
the terminating busbar 680 without requiring solder to the
plurality, itself, or to the extended portions, for example, 670x
and 670y, of the plurality of integrated pairs 670a&b,
670c&c, 670e&f, 670g&h, 670i and 670l&m of
electrically conductive, electrically parallel trace portions
670a-m
[0106] With reference now to FIG. 7A, in accordance with
embodiments of the present invention, a combined cross-sectional
elevation and perspective view of a roll-to-roll,
interconnect-assembly fabricator 700A is shown. FIG. 7A shows the
roll-to-roll, interconnect-assembly fabricator 700A operationally
configured to fabricate an interconnect assembly 720. A top carrier
film 716 including an electrically insulating layer, for example a
first substantially transparent, electrically insulating layer, is
provided to roll-to-roll, interconnect-assembly fabricator 700A in
roll form from a first roll of material 714. The roll-to-roll,
interconnect-assembly fabricator 700A includes an first unwinding
spool 710 upon which the first roll of material 714 of the top
carrier film 716 including the electrically insulating layer is
mounted. As shown, a portion of the first roll of material 714 is
unrolled. The unrolled portion of the top carrier film 716
including the electrically insulating layer passes to the right and
is taken up on a take-up spool 718 upon which it is rewound as a
third roll 722 of interconnect assembly 720, after conductive-trace
material 750 is provided from a dispenser 754 and is laid down onto
the unrolled portion of the top carrier film 716 including the
electrically insulating layer. The dispenser 754 of
conductive-trace material 750 may be a spool of wire, or some other
container providing conductive-trace material. The conductive-trace
material 750 may be laid down onto the unrolled portion of the top
carrier film 716 including the electrically insulating layer in an
oscillatory motion, but without limitation to a strictly
oscillatory motion, indicated by double-headed arrow 758, to create
a first plurality of electrically conductive portions configured
both to collect current from a first solar cell and to interconnect
electrically to a second solar cell such that solar-cell efficiency
is substantially undiminished in an event that any one of the first
plurality of electrically conductive portions is conductively
impaired. As shown in FIG. 7A, a portion of the electrically
conductive portions overhang one side of the top carrier film 716
to allow the electrically conductive portions of the trace to
interconnect electrically to the second solar cell on the exposed
top side of the trace, while the exposed bottom side of the trace,
here shown as facing upward on the top carrier film 716, allows the
electrically conductive portions of the trace in contact with the
top carrier film 716 to interconnect electrically to the first
solar cell. Moreover, the conductive-trace material 750 may be
disposed in a serpentine pattern to create the plurality of
electrically conductive portions configured both to collect current
from the first solar cell and to interconnect electrically to the
second solar cell. The arrows adjacent to the first unwinding spool
710, and the take-up spool 718 indicate that these are rotating
components of the roll-to-roll, interconnect-assembly fabricator
700A; the first unwinding spool 710, and the take-up spool 718 are
shown rotating in clockwise direction, as indicated by the
arrow-heads on the respective arrows adjacent to these components,
to transport the unrolled portion of the first roll of material 714
from the first unwinding spool 710 on the left to the take-up spool
718 on the right.
[0107] With reference now to FIG. 7B, in accordance with
embodiments of the present invention, a combined cross-sectional
elevation and perspective view of a roll-to-roll,
laminated-interconnect-assembly fabricator 700B is shown. FIG. 7A
shows the roll-to-roll, laminated-interconnect-assembly fabricator
700B operationally configured to fabricate a laminated-interconnect
assembly 740. The roll-to-roll, laminated-interconnect-assembly
fabricator 700B first fabricates the interconnect assembly 720
shown on the left-hand side of FIG. 7B from the first roll of
material 714 of the top carrier film 716 including the electrically
insulating layer and from conductive-trace material 750 provided
from dispenser 754. Then, the roll-to-roll,
laminated-interconnect-assembly fabricator 700B continues
fabrication of the laminated-interconnect assembly 740 by applying
a bottom carrier film 736 from a second roll 734. The bottom
carrier film 736 includes a carrier film selected from a group
consisting of a second electrically insulating layer, a structural
plastic layer, and a metallic layer, and is coupled to the
conductive-trace material 750 and is disposed below a bottom
portion of the conductive-trace material 750. If a metallic layer
is used for the bottom carrier film 736, a supplementary isolation
strip (not shown) of a third electrically insulating layer is added
to the laminated-interconnect assembly 740 configured to allow
interposition of the third electrically insulating layer between
the bottom carrier film 736 and a top surface of the first solar
cell to provide additional protection at an edge of the first solar
cell and to prevent shorting out the solar cell in the event that
the bottom carrier film 736 including the metallic layer should
ride down the side of the first solar cell. The
laminated-interconnect assembly 740 passes to the right-hand side
of FIG. 7B and is taken up on the take-up spool 718 upon which it
is wound as a fourth roll 742 of laminated-interconnect assembly
740. The arrows adjacent to the first unwinding spool 710, a second
unwinding spool 730 and the take-up spool 718 indicate that these
are rotating components of the roll-to-roll,
laminated-interconnect-assembly fabricator 700B; the first
unwinding spool 710, and the take-up spool 718 are shown rotating
in clockwise direction, as indicated by the arrow-heads on the
respective arrows adjacent to these components, to transport the
unrolled portion of the first roll of material 714 from the first
unwinding spool 710 on the left to the take-up spool 718 on the
right. The second unwinding spool 730, and the dispenser 754 are
shown rotating in a counterclockwise direction and a clockwise
direction, respectively, as indicated by the arrow-heads on the
respective arrows adjacent to these components, as they release the
bottom carrier layer 736 and the conductive-trace material 750,
respectively, in fabrication of the laminated-interconnect assembly
740. The double-headed arrow 758 indicates the motion imparted to
the conductive trace material by the roll-to-roll,
laminated-interconnect-assembly fabricator 700B creates a first
plurality of electrically conductive portions configured both to
collect current from a first solar cell and to interconnect
electrically to a second solar cell such that solar-cell efficiency
is substantially undiminished in an event that any one of the first
plurality of electrically conductive portions is conductively
impaired.
Description of Embodiments of the Present Invention for a Method
for Roll-To-Roll Fabrication of an Interconnect Assembly
[0108] With reference now to FIG. 8, a flow chart illustrates an
embodiment of the present invention for a method for roll-to-roll
fabrication of an interconnect assembly. At 810, a first carrier
film including a first substantially transparent, electrically
insulating layer is provided in roll form. At 820, a trace is
provided from a dispenser of conductive-trace material. The
dispenser may be a spool of wire or other container of
conductive-trace material. At 830, a portion of the first carrier
film including the first substantially transparent, electrically
insulating layer is unrolled. At 840, the trace from the dispenser
of conductive-trace material is laid down onto the portion of the
first carrier film including the first substantially transparent,
electrically insulating layer. At 850, the trace is configured as a
first plurality of electrically conductive portions such that
solar-cell efficiency is substantially undiminished in an event
that any one of the first plurality of electrically conductive
portions is conductively impaired. At 860, the portion of the first
said first carrier film including the substantially transparent,
electrically insulating layer is coupled to a top portion of the
trace to provide an interconnect assembly.
[0109] In an embodiment of the present invention, configuring the
trace also includes: configuring the trace as a second plurality of
paired trace portions; configuring a first portion of a paired
portion of the second plurality of paired trace portions to allow
both collecting current from a first solar cell and electrically
interconnecting the first solar cell with a second solar cell;
disposing proximately to the first portion, a second portion of the
paired portion; and configuring the second portion to allow both
collecting current from the first solar cell and electrically
interconnecting the first solar cell with the second solar cell.
Alternatively, configuring the trace may include disposing the
trace in a serpentine pattern that allows for collecting current
from the first solar cell and electrically interconnecting to the
second solar cell. In an embodiment of the present invention, the
method may also include: providing a second carrier film including
a second electrically insulating layer; coupling the second carrier
film including the second electrically insulating layer to a bottom
portion of the trace; and configuring the second electrically
insulating layer to allow forming an edge-protecting portion at an
edge of the first solar cell. Moreover, the method may include
configuring the first substantially transparent, electrically
insulating layer to allow forming a short-circuit-preventing
portion at an edge of the second solar cell.
Description of Embodiments of the Present Invention for a Method of
Interconnecting Two Solar Cells
[0110] With reference now to FIG. 9, a flow chart illustrates an
embodiment of the present invention for a method of interconnecting
two solar cells. At 910, a first solar cell and at least a second
solar cell are provided. At 920, a combined applicable carrier
film, interconnect assembly including a trace including a plurality
of electrically conductive portions is provided. At 930, the
plurality of electrically conductive portions of the trace is
configured both to collect current from the first solar cell and to
interconnect electrically with the second solar cell such that
solar-cell efficiency is substantially undiminished in an event
that any one of the plurality of electrically conductive portions
is conductively impaired. At 940, the combined applicable carrier
film, interconnect assembly is applied and coupled to a
light-facing side of the first solar cell. At 950, the combined
applicable carrier film, interconnect assembly is applied and
coupled to a back side of the second solar cell.
[0111] In an embodiment of the present invention, the method also
includes applying and coupling the combined applicable carrier
film, interconnect assembly to the light-facing side of the first
solar cell without requiring solder. In addition, the method may
include applying and coupling the combined applicable carrier film,
interconnect assembly to the back side of the second solar cell
without requiring solder. Moreover, the method includes applying
and coupling the combined applicable carrier film, interconnect
assembly to the light-facing side of the first solar cell such that
a second electrically insulating layer of the applicable carrier
film, interconnect assembly forms an edge-protecting portion at an
edge of the first solar cell. The method also includes applying and
coupling the combined applicable carrier film, interconnect
assembly to the back side of the second solar cell such that a
first substantially transparent, electrically insulating layer of
the applicable carrier film, interconnect assembly forms a
short-circuit-preventing portion at an edge of the second solar
cell. The method may also include configuring the trace in a
serpentine pattern that allows for collecting current from the
first solar cell and electrically interconnecting to the second
solar cell.
Physical Description of Embodiments of the Present Invention for a
Trace
[0112] In accordance with other embodiments of the present
invention, the trace does not need to be used in conjunction with
the afore-mentioned serpentine interconnect assembly approach, but
could be used for other current collection and/or interconnection
approaches used in solar cell technology. A trace including a
conductive core with an overlying layer of nickel provides the
unexpected result that when placed in contact with the TCO layer of
a solar cell it suppresses current in the vicinity of short-circuit
defects in the solar cell that might occur in the vicinity of the
contact of the nickel layer of the trace with the TCO layer. The
nickel increases local contact resistance which improves the
ability of the solar cell to survive in the event of the formation
of a defect, such as a shunt or a near shunt, located in the
adjacent vicinity of the contact of the nickel layer of the trace
with the TCO layer. If there is such a defect in the vicinity of
the contact of the nickel layer of the trace with the TCO layer,
the nickel reduces the tendency of the solar cell to pass increased
current through the site of the defect, such as a shunt or a near
shunt. Thus, the nickel acts as a localized resistor preventing
run-away currents and high current densities in the small localized
area associated with the site of the defect, such as a shunt or a
near shunt. The current-limiting ability of nickel is in contrast,
for example, to a low resistivity material such as silver, where
the current density becomes so high at the location of the defect
due to the high conductivity of silver that nearly almost all the
current of the cell would be passed at the location of the defect
causing a hot spot that would result in the melting of the silver
with the formation of a hole in the solar cell filling with the
silver migrating to the site of the defect to form a super-shunt.
In contrast, nickel does not readily migrate nor melt in the
presence of elevated localized temperatures associated with the
site of increased currents attending formation of the defect, such
as a shunt or a near shunt. Moreover, in contrast to silver, copper
and tin, which tend to electromigrate, migrate or diffuse at
elevated temperatures, nickel tends to stay put so that if the site
of a shunt occurs in the vicinity of a nickel coated or nickel
trace, the nickel has less tendency to move to the location of the
shunt thereby further exacerbating the drop of resistance at the
shunt site. In addition, experimental results of the present
invention indicate that a nickel trace, or a trace including a
nickel layer, may actually increase its resistance due the possible
formation of a nickel oxide such that the nickel trace, or the
trace including the nickel layer, acts like a localized fuse
limiting the current flow in the vicinity of the shunt site. In
some cases, the efficiency of the solar cell has actually been
observed to increase after formation of the shunt defect when the
nickel trace, or the trace including the nickel layer, is used in
contact with the TCO layer.
[0113] With further reference to FIGS. 5B and 5E, in accordance
with other embodiments of the present invention, the trace 520 for
collecting current from a solar cell, for example, first solar cell
510, includes an electrically conductive line including the
conductive core 520A, and the overlying layer 520B that limits
current flow to a proximate shunt defect (not shown) in the solar
cell, for example, first solar cell 510. The proximate shunt defect
may be proximately located in the vicinity of an electrical contact
between the overlying layer 520B of the electrically conductive
line and the TCO layer 510b of the solar cell, for example, first
solar cell 510. The overlying layer 520B of the electrically
conductive line of the trace 520 may further include an overlying
layer 520B composed of nickel. The conductive core 520A of the
electrically conductive line of the trace 520 may further include
nickel. The conductive core 520A may also include a material
selected from a group consisting of copper, silver, aluminum, and
elemental constituents and alloys having high electrical
conductivity, which may be greater than the electrical conductivity
of nickel. The TCO layer 510b of the solar cell, for example, first
solar cell 510, may include a conductive oxide selected from a
group consisting of zinc oxide, aluminum zinc oxide and indium tin
oxide. In addition, the absorber layer 510a, for example, absorber
layer 112 of FIG. 1A, of the solar cell, for example, first solar
cell 510, may include copper indium gallium diselenide (CIGS).
Alternatively, in embodiments of the present invention, it should
be noted that semiconductors, such as silicon, cadmium telluride,
and chalcopyrite semiconductors, as well as other semiconductors,
may be used as the absorber layer 510a. Moreover, an n-type layer,
for example, n-type portion 112b of absorber layer 112 of FIG. 1A,
of the solar cell, for example, first solar cell 510, may be
disposed on and electrically coupled to a p-type absorber layer,
for example, absorber layer 112 of FIG. 1A, of the solar cell, for
example, first solar cell 510, and the n-type layer, for example,
n-type portion 112b of absorber layer 112 of FIG. 1A, may be
selected from a group consisting of a metal oxide, a metal sulfide
and a metal selenide.
[0114] The foregoing descriptions of specific embodiments of the
present invention have been presented for purposes of illustration
and description. They are not intended to be exhaustive or to limit
the invention to the precise forms disclosed, and many
modifications and variations are possible in light of the above
teaching. The embodiments described herein were chosen and
described in order to best explain the principles of the invention
and its practical application, to thereby enable others skilled in
the art to best utilize the invention and various embodiments with
various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be
defined by the claims appended hereto and their equivalents.
* * * * *