U.S. patent application number 13/533800 was filed with the patent office on 2012-11-08 for method of manufacturing photovoltaic modules with improved reliability.
Invention is credited to Bulent M. Basol.
Application Number | 20120282727 13/533800 |
Document ID | / |
Family ID | 41651792 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120282727 |
Kind Code |
A1 |
Basol; Bulent M. |
November 8, 2012 |
METHOD OF MANUFACTURING PHOTOVOLTAIC MODULES WITH IMPROVED
RELIABILITY
Abstract
A solar module includes a protective shell with at least two
sealed sections formed by moisture barrier sealants. Each sealed
section is separated from the adjacent sections and includes at
least a portion of a solar cell. In this sectioned configuration,
any local defect through the protective shell will only affect the
performance of the portions of the solar cells within a particular
section that contains this defect and will not affect the portions
of the solar cells that are in other sections.
Inventors: |
Basol; Bulent M.; (Manhattan
Beach, CA) |
Family ID: |
41651792 |
Appl. No.: |
13/533800 |
Filed: |
June 26, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12189627 |
Aug 11, 2008 |
8207440 |
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13533800 |
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Current U.S.
Class: |
438/73 ;
257/E31.001 |
Current CPC
Class: |
H01L 31/046 20141201;
Y02P 70/50 20151101; Y02P 70/521 20151101; H01L 31/048 20130101;
H01L 31/03928 20130101; B32B 17/10302 20130101; B32B 17/10036
20130101; Y02E 10/541 20130101 |
Class at
Publication: |
438/73 ;
257/E31.001 |
International
Class: |
H01L 31/18 20060101
H01L031/18 |
Claims
1-19. (canceled)
20. A method of manufacturing a solar cell module comprising the
steps of: disposing at least one solar cell over a first protective
sheet, the at least one solar cell including a front light
receiving side and a back substrate side; disposing an edge sealant
along the edges of the first protective sheet, thereby forming a
cavity holding the at least one solar cell; at least partially
covering the at least one solar cell with a support material on
both the front light receiving side and the back substrate side of
the solar cell; disposing a divider sealant to divide the cavity
into at least two cavity sections; and placing a second protective
sheet over the support material, the edge sealant and the divider
sealant to enclose the at least two cavity sections, wherein the
moisture transmission rate through the edge sealant and the divider
sealant is less than 0.001 gm/m.sup.2/day.
21. The method of claim 20 further comprising applying heat and
pressure to a resulting assembly of the protective sheets, at least
one solar cell, sealant and the support material so as to laminate
the solar cell units between the two protective sheets.
22. The method of claim 21 further comprising cooling the resulting
assembly so as to cause the support material to bond to the first
and second protective sheets and to the at least one solar
cell.
23. The method of claim 20, wherein the at least one solar cell
includes a first solar cell and a second solar cell that is
electrically interconnected to the first solar cell.
24. The method of claim 23, wherein each of the at least two cavity
sections contains one of the first solar cell and the second solar
cell that is electrically interconnected to the first solar
cell.
25. The method of claim 24, wherein the step of at least partially
covering the at least one solar cell with the support material
comprises sandwiching the first solar cell between a first set of
layers of the support material, and sandwiching the second solar
cell between a second set of layers of the support material.
26. The method of claim 25, wherein the divider sealant is aligned
with a busbar of the at least one of the first and second solar
cells.
27. The method of claim 23, wherein a divider sealant space is
located on at least one of the first and second solar cells.
28. The method of claim 27, wherein the step of at least partially
covering the at least one solar cell with the support material
comprises sandwiching the first solar cell between a first set of
layers of the support material, and sandwiching the second solar
cell between a second set of layers of the support material,
wherein the divider sealant space is free of and excludes the
support material.
29. The method of claim 28, wherein the step of disposing the
divider sealant comprises disposing at least a portion of the
divider sealant on the divider sealant space located on at least
one of the first and second solar cells.
30. The method of claim 29, wherein the portion of the divider
sealant is disposed on at least one of the front light receiving
side and the back substrate side of at least one the first solar
cell and the second solar cells.
31. The method of claim 27, wherein the at least two cavity
sections each contain at least a portion of at least one of the
first solar cell and the second solar cell that is electrically
interconnected to the first solar cell.
32. The method of claim 20, wherein the step of disposing the
divider sealant comprises disposing at least a portion of the
divider sealant on the at least one solar cell so that at least one
of the cavity sections contain at least one portion of the at least
one solar cell and the support material covering the at least one
portion of the at least one solar cell.
33. The method of claim 32, wherein the portion of the divider
sealant is disposed on at least one of the front light receiving
side and the back substrate side of the at least one solar
cell.
34. The method of claim 32, wherein the portion of the divider
sealant is aligned with a busbar of the at least one solar
cell.
35. The method of claim 20, wherein the support material is a
transparent polymeric material.
36. The method of claim 20, wherein the first protective sheet
includes one of a moisture barrier flexible polymeric film and
glass.
37. The method of claim 36, wherein the second protective sheet
includes one of a moisture barrier flexible polymeric film and
glass.
38. The method of claim 20, wherein the solar cells are Group
IBIIIAVIA thin film solar cells with stainless steel substrate.
39. The method of claim 38 wherein the solar cells, the front
protective sheet and the back protective sheet are flexible.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/189,627 filed Aug. 11, 2008, and is hereby incorporated
by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The aspects and advantages of the present inventions
generally relate to apparatus and methods of photovoltaic or solar
module design and fabrication and, more particularly, to packaging
techniques for solar modules such as solar modules employing thin
film solar cells.
[0004] 2. Description of the Related Art
[0005] Solar cells are photovoltaic devices that convert sunlight
directly into electrical power. The most common solar cell material
is silicon, which is in the form of single or polycrystalline
wafers. However, the cost of electricity generated using
silicon-based solar cells is higher than the cost of electricity
generated by the more traditional methods. Therefore, since early
1970's there has been an effort to reduce cost of solar cells for
terrestrial use. One way of reducing the cost of solar cells is to
develop low-cost thin film growth techniques that can deposit
solar-cell-quality absorber materials on large area substrates and
to fabricate these devices using high-throughput, low-cost
methods.
[0006] Group IBIIIAVIA compound semiconductors comprising some of
the Group IB (Cu, Ag, Au), Group IIIA (B, Al, Ga, In, Tl) and Group
VIA (O, S, Se, Te, Po) materials or elements of the periodic table
are excellent absorber materials for thin film solar cell
structures. Especially, compounds of Cu, In, Ga, Se and S which are
generally referred to as CIGS(S), or Cu(In,Ga)(S,Se).sub.2 or
CuIn.sub.1-xGa.sub.x(S.sub.ySe.sub.1-y).sub.k, where
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1 and k is approximately 2,
have already been employed in solar cell structures that yielded
conversion efficiencies approaching 20%. Absorbers containing Group
IIIA element Al and/or Group VIA element Te also showed promise.
Therefore, in summary, compounds containing: i) Cu from Group IB,
ii) at least one of In, Ga, and Al from Group IIIA, and iii) at
least one of S, Se, and Te from Group VIA, are of great interest
for solar cell applications. It should be noted that although the
chemical formula for CIGS(S) is often written as
Cu(In,Ga)(S,Se).sub.2, a more accurate formula for the compound is
Cu(In,Ga)(S,Se).sub.k, where k is typically close to 2 but may not
be exactly 2. For simplicity we will continue to use the value of k
as 2. It should be further noted that the notation "Cu(X,Y)" in the
chemical formula means all chemical compositions of X and Y from
(X=0% and Y=100%) to (X=100% and Y=0%). For example, Cu(In,Ga)
means all compositions from CuIn to CuGa. Similarly,
Cu(In,Ga)(S,Se).sub.2 means the whole family of compounds with
Ga/(Ga+In) molar ratio varying from 0 to 1, and Se/(Se+S) molar
ratio varying from 0 to 1.
[0007] The structure of a conventional Group IBIIIAVIA compound
photovoltaic cell such as a Cu(In,Ga,Al)(S,Se,Te).sub.2 thin film
solar cell is shown in FIG. 1. A photovoltaic cell 10 is fabricated
on a substrate 11, such as a sheet of glass, a sheet of metal, an
insulating foil or web, or a conductive foil or web. An absorber
film 12, which includes a material in the family of
Cu(In,Ga,Al)(S,Se,Te).sub.2, is grown over a conductive layer 13 or
contact layer, which is previously deposited on the substrate 11
and which acts as the electrical contact to the device. The
substrate 11 and the conductive layer 13 form a base 20 on which
the absorber film 12 is formed. Various conductive layers
comprising Mo, Ta, W, Ti, and their nitrides have been used in the
solar cell structure of FIG. 1. If the substrate itself is a
properly selected conductive material, it is possible not to use
the conductive layer 13, since the substrate 11 may then be used as
the ohmic contact to the device. After the absorber film 12 is
grown, a transparent layer 14 such as a CdS, ZnO, CdS/ZnO or
CdS/ZnO/ITO stack is formed on the absorber film 12. Radiation 15
enters the device through the transparent layer 14. Metallic grids
(not shown) may also be deposited over the transparent layer 14 to
reduce the effective series resistance of the device. The preferred
electrical type of the absorber film 12 is p-type, and the
preferred electrical type of the transparent layer 14 is n-type.
However, an n-type absorber and a p-type window layer can also be
utilized. The preferred device structure of FIG. 1 is called a
"substrate-type" structure. A "superstrate-type" structure can also
be constructed by depositing a transparent conductive layer on a
transparent superstrate such as glass or transparent polymeric
foil, and then depositing the Cu(In,Ga,Al)(S,Se,Te).sub.2 absorber
film, and finally forming an ohmic contact to the device by a
conductive layer. In this superstrate structure light enters the
device from the transparent superstrate side.
[0008] There are two different approaches for manufacturing PV
modules. In one approach that is applicable to thin film CdTe,
amorphous Si and CIGS technologies, the solar cells are deposited
or formed on an insulating substrate such as glass that also serves
as a front protective sheet or a back protective sheet. In this
case the solar cells are electrically interconnected as they are
deposited on the substrate. In other words, the solar cells are
monolithically integrated on the substrate as they are formed.
These modules are monolithically integrated structures. For CdTe
thin film technology the substrate is glass which also is the front
protective sheet for the monolithically integrated module. In CIGS
technology the substrate is glass or polyimide and serves as the
back protective sheet for the monolithically integrated module. In
monolithically integrated module structures, after the formation of
solar cells which are already integrated and interconnected in
series on the substrate, an encapsulant is placed over the
integrated module structure and a protective sheet is attached to
the encapsulant. An edge seal may also be formed along the edge of
the module to prevent water vapor or liquid transmission through
the edge into the monolithically integrated module structure.
[0009] In standard Si module technologies and for CIGS and
amorphous Si cells that are fabricated on conductive substrates
such as aluminum or stainless steel foils the solar cells are not
deposited or formed on the protective sheet. They are separately
manufactured and then the, manufactured solar cells are
electrically interconnected by stringing them or shingling them to
form solar cell strings. In shingling, individual cells are placed
in a staggered manner so that a bottom surface of one cell makes
direct physical and electrical contact to a top surface of an
adjacent cell. Therefore, there is no gap between two shingled
cells. Stringing is typically done by placing the cells side by
side with a small gap between them and using conductive wires or
ribbons that connect an electrical terminal of one cell to an
electrical terminal of an adjacent cell. Strings obtained by
stringing or shingling are then interconnected to form circuits.
Circuits may then be packaged in protective packages to form
modules. Each module typically includes a plurality of strings of
solar cells which are electrically connected to one another. The
solar modules are constructed using various packaging materials to
mechanically support and protect the solar cells in them against
mechanical damage. The most common packaging technology involves
lamination of circuits in transparent encapsulants. In a lamination
process, in general, the electrically interconnected solar cells
are covered with a transparent and flexible encapsulant layer which
fills any hollow space among the cells and tightly seals them into
a module structure, preferably covering both of their surfaces. A
variety of materials are used as encapsulants, for packaging solar
cell modules, such as ethylene vinyl acetate copolymer (EVA) and
thermoplastic polyurethanes (TPU). However, in general, such
encapsulant materials are moisture permeable; therefore, they must
be further sealed from the environment by a protective shell, which
forms a barrier to moisture transmission into the module package.
The protective shell generally includes a front protective sheet, a
back protective sheet and an edge sealant that is at the periphery
of the module structure (see for example, published application
WO/2003/050891, "Sealed Thin Film PV Modules"). The top protective
sheet is typically glass, but may also be a transparent flexible
polymer film such as TEFZEL.RTM. (a product of DuPont),
polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
and the like. The top polymeric film may have a moisture barrier
coating on it. The back protective sheet may be a sheet of glass or
a polymeric sheet such as TEDLAR.RTM. (a product of DuPont). The
back protective polymeric sheet may also have a moisture barrier
layer in its structure such as a metallic film like an aluminum
film. Light enters the module through the front protective sheet.
The edge sealant is a moisture barrier material that may be in the
form of a viscous fluid which may be dispensed from a nozzle to the
peripheral edge of the module structure or it may be in the form of
a tape which may be applied to the peripheral edge of the module
structure. There are a variety of such edge sealants provided to
solar module manufacturers. It should be appreciated that in the
above described non-monolithic module structure where separate
pieces of solar cells are interconnected and then encapsulated on
both surfaces by an encapsulant, the encapsulant becomes a conduit
through which moisture may travel to all regions of the solar cell,
front and back.
[0010] FIG. 2A shows a prior art solar module 50 including a first
string 52A of solar cells and a second string 52B of solar cells.
The first string 52A includes solar cells A1, A2 and A3, the second
string 52B includes solar cells B1, B2 and B3. The solar cells in
each string are electrically interconnected with one another. The
strings 52A and 52B are also electrically connected with one
another. The interconnections between cells and strings are not
shown in the figure to simplify the drawing. As shown in FIG. 2B in
cross section, the solar cells are encapsulated by encapsulant
material 54 and sandwiched between a top or front protective sheet
56, typically glass, through which the light enters and a back
protective sheet 58, and a bottom or back protective sheet 58,
which may be glass or a polymeric sheet. An edge sealant 60 seals
the edges of the protective sheets. The protective sheets and the
edge sealant 60 form a protective shell of the solar module 50,
which protects the solar cells encapsulated by the encapsulant
material from outside conditions such as moisture. Although the
exemplary prior art solar module design shown in FIG. 2A has six
solar cells, many more electrically connected solar cells can be
packed into the protective shell. However, one disadvantage
associated with this design is the fact that any defect in the
protective shell that causes moisture to get inside the module
structure causes complete failure of the whole module. Once
moisture gets into the protective shell it diffuses fast through
the encapsulant material which is a poor moisture barrier. Such
moisture diffusion through substantially the whole inside volume of
the protective shell results in corrosion and malfunction of the
entire solar cell population within the protective shell. Defects
in the protective shell may occur in the edge sealant or in the
front or back protective sheets. For the newly developed flexible
module structures such as flexible modules employing flexible CIGS
or amorphous Si solar cells fabricated on metal foil substrates,
this concern of defectivity is even more important compared to the
module structures employing glass protective sheets. Since the
flexible module structures employ thin polymeric materials as the
front and back protective sheets, preferably with moisture barrier
coatings or layers, any defects in the polymeric sheets and/or the
moisture barrier coatings or layers would cause moisture to enter
the module structure through the front or back protective sheets
and cause failure as described above. Since the total area of the
front and back protective sheets is much larger than the cross
sectional area of the edge sealant through which moisture may
enter, the probability of defect formation in the large area front
and back protective sheets is high in flexible and large module
structures.
[0011] From the foregoing, there is a need in the solar cell
manufacturing industry, especially in thin film photovoltaics, for
better packaging techniques that can provide reliable performance
at reduced cost. For example, CIGS solar cells are being developed
for their low cost and high efficiency. However, the long term
reliability of CIGS modules depends on the ability of the module
package to keep the moisture away from the solar cells for over 20
years. It should be noted that CIGS solar cells are sensitive to
moisture and they need to be protected, especially in
non-monolithic module structures where individual CIGS cells are
interconnected and then encapsulated in an encapsulant.
SUMMARY
[0012] The aspects and advantages of the present inventions
generally relate to apparatus and methods of photovoltaic or solar
module design and fabrication and, more particularly, to packaging
techniques for solar modules such as solar modules employing thin
film solar cells.
[0013] In one aspect, an embodiment provides a method of
manufacturing a solar cell module that includes disposing at least
one solar cell over a first protective sheet, the at least one
solar cell including a front light receiving side and a back
substrate side; disposing an edge sealant along the edges of the
first protective sheet, thereby forming a cavity holding the at
least one solar cell; at least partially covering the at least one
solar cell with a support material on both the front light
receiving side and the back substrate side of the solar cell;
disposing a divider sealant to divide the cavity into at least two
cavity sections; and placing a second protective sheet over the
support material, the edge sealant and the divider sealant to
enclose the at least two cavity sections, wherein the moisture
transmission rate through the edge sealant and the divider sealant
is less than 0.001 gm/m.sup.2/day.
[0014] These and other aspects and advantages are described further
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic view a solar cell;
[0016] FIG. 2A is a schematic view of a prior art solar cell
module;
[0017] FIG. 2B is a schematic cross sectional view of the solar
cell module shown in
[0018] FIG. 2A taken along the line 2B-2B;
[0019] FIG. 3 is a schematic view of a solar cell module according
to one embodiment;
[0020] FIG. 3A is a schematic view of an embodiment of a solar cell
module;
[0021] FIG. 3B is a schematic cross sectional view of the solar
cell module shown in FIG. 3A taken along the line 3B-3B;
[0022] FIG. 3C is a schematic cross sectional view of the solar
cell module shown in FIG. 3 taken along the line F1-F2;
[0023] FIG. 4 is a schematic view showing the components of the
solar cell module during manufacturing;
[0024] FIGS. 5 and 6 are schematic views of various embodiments of
the solar cell module;
[0025] FIG. 7 is a module design; and
[0026] FIG. 7A is a solar cell used in the module design of FIG.
7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The preferred embodiments described herein provide methods
of manufacturing solar cell modules that include a protective shell
having two or more sealed sections. Each sealed section is isolated
from the adjacent section by a sealant that is a moisture barrier.
Each section includes a cell unit. Each cell unit comprises at
least one solar cell or a portion of a solar cell. If more than one
solar cell is included in a cell unit, the cell unit may be called
a string. Each sealed section may contain one or more strings
having a plurality of solar cells. The solar cells in each string
are electrically interconnected. Light receiving front surface of
the solar cells are configured to form a front side of each string
while the substrates of the solar cells are configured to form a
back side of each string. A support material or encapsulant such as
EVA may cover at least one of a front side and the back side of
each cell or cell string. The support material may be used to fully
encapsulate each solar cell and each string, top and bottom.
[0028] In one embodiment, the protective shell comprises top and
bottom protective sheets, and an edge sealant to seal the edges at
the perimeter of the protective sheets, and one or more divider
sealants to divide the interior volume or space of the protective
shell into sections, each section comprising at least a portion of
a solar cell and an encapsulant encapsulating the front and back
surfaces of the portion. The edge and divider sealants are disposed
between the top and the bottom protective sheets. In this sectioned
module configuration, any local defect through the protective shell
will affect the solar cell(s) or solar cell portions within a
particular section that may be in contact with this defect and will
not affect the solar cell(s) or solar cell portions that are in
other sections which are separated from the particular section by
the divider sealants. Therefore, the solar cells or solar cell
portions in the sections that are not affected by the defect will
continue functioning and producing power.
[0029] FIG. 3 shows a top or front view of a module 500. FIG. 3C
shows a cross sectional view along the line F1-F2. It should be
noted that the module 500 may not be the exact design of a module
that one may manufacture. Rather, it is exemplary and demonstrative
and is drawn for the purpose of demonstrating or showing various
aspects of the present inventions in a general way in a single
module structure.
[0030] The exemplary module 500 comprises twelve solar cells that
are labeled as 501A, 501B, 501C, 501D, 501E, 501F, 501G, 501H,
5011, 501J, 501K, and 501L. These solar cells are electrically
interconnected. The interconnections are not shown in the figure to
simplify the drawing. In FIG. 3 there are gaps between the solar
cells. However, as explained before, it is possible that these
solar cells may be shingled and therefore, there may not be gaps
between them. Cells may also be shaped differently. For example,
they may be elongated with one dimension being 2-100 times larger
than the other dimension. The module 500 has a top protective sheet
550 and a bottom protective sheet 551 and an edge sealant 502
between the top protective sheet 550 and the bottom protective
sheet 551. The edge sealant 502 is placed at the edge of the module
structure and is rectangular in shape in this example. For other
module structures with different shapes, the edge sealant may also
be shaped differently, following the circumference of the different
shape modules. The top protective sheet 550, the bottom protective
sheet 551 and the edge sealant 502 forms a protective shell.
[0031] The module 500 further comprises divider sealants 503 that
are formed within the protective shell, i.e. within the volume or
space created by the top protective sheet 550, the bottom
protective sheet 551 and the edge sealant 502. The divider sealants
503 form a sealant pattern 504 that divides the protective shell
into sealed sections 505. There are fifteen sections 505 in the
exemplary module of FIG. 3. Some of the sections 505 in the middle
region of the module 500 are bordered by only the divider sealants
503. Sections close to the edge of the module 500, on the other
hand are bordered by divider sealants 503 as well as portions of
the edge sealant 502. As can be seen from FIG. 3, each section may
contain a solar cell, a portion of a solar cell, portions of more
than one solar cell or more than one solar cell. For example,
sections labeled as 505A and 505B each contain a different portion
of the solar cell 501A, whereas the section labeled as 505C
contains the single solar cell 501B. The section labeled as 505D,
on the other hand, contains the solar cells 501H and 501L, as well
as a portion of the solar cell 501K. The sealant pattern 504 of the
divider sealants 503 may be shaped in many different ways, such as
rectangular, curved, circular, etc. Portions of the divider
sealants 503 may be placed in the gap between the solar cells, on
the solar cells and even under the solar cells. If the divider
sealants 503 or their portions are placed on the solar cells, it is
preferable that they are lined up with the busbars (not shown in
the figure to simplify the drawing) of the solar cells so that any
possible extra shadowing of the cells by the divider sealants 503
is avoided.
[0032] As shown in FIGS. 3 and 3C, the portions of the divider
sealants may be placed on divider sealant spaces 520 on the solar
cells. The divider sealant spaces 520 are designated locations on
the front surface or the back surface of the solar cells. The
divider sealant spaces 520 do not contain any support material so
that the divider sealant can be attached to the front or back side
of the solar cell. It should be noted that busbars on solar cells
already shadow the cell portions right under them and therefore,
placing the divider sealants 503 over the busbars would not cause
additional loss of area in the devices: As can be seen in the cross
sectional view of the module 500 in FIG. 3C a portion 503A of the
sealant pattern 504 is placed over the solar cell 501J. Another
sealant portion 503B may also be present under the solar cell 501J.
In other words, a bottom sealant pattern (not shown) may be
employed under the solar cells. The bottom sealant pattern may or
may not match the shape of the sealant pattern 504. The solar cells
in the module 500 are encapsulated within an encapsulant 560 that
surrounds and supports them. After this general description of a
general module structure employing various teachings of the present
inventions, more simplified module structures will now be described
to explain its unique features and benefits.
[0033] FIGS. 3A and 3B show a solar cell module 100 including at
least two solar cell units, a first solar cell unit 102 and a
second solar cell unit 104. The units 102 and 104 may be strings of
solar cells. The unit 102 may include solar cells 102A, 102B and
102C, and the unit 104 may include solar cells 104A, 104B and 104C.
Each solar cell includes a light receiving front portion 105A and a
back portion 105B or base. The light receiving front portions of
the solar cells form the front side of the solar cell units 102 and
104, while the back portions form the back side of the solar cell
units. Solar cells in each unit or string are electrically
interconnected to one another using conductive interconnects (not
shown for clarity) by utilizing processes, such as soldering or
gluing, that are well known in the field. As shown in FIGS. 3A-3B
the module 100 has a multi-section structure with a first section
106A and a second section 106B. The first section 106A includes the
first string 102 and the second section 106B includes the second
string 104. The sections are formed between a top protective sheet
107 and a back protective sheet 108 of the module 100. A first
sealant 112 or an edge sealant seals the edges of the protective
sheets at their perimeter thereby forming a protective shell 110. A
second sealant 114 or a divider sealant separates the strings 102
and 104 thereby forming the sections 106A and 106B. Both the edge
sealant 112 and the divider sealant are disposed between and
attached to the front and back protective sheets 107 and 108 as in
the manner shown in FIGS. 3A and 3B. The edge and the divider
sealants may be two parts of a single piece sealant.
[0034] In this embodiment, each solar cell string is encapsulated
with a support material layer 116. The support material 116 such as
EVA may fully fill the sections 106A and 106B which are sealed by
the edge sealant 112 and the divider sealant 114 and the first and
second protective sheets 107 and 108. Separately sealed sections
independently protect the solar cell strings encapsulated within
them by the support material 116. This provides extra protection to
the solar cell strings. For example, even if a defect in the edge
sealant 112 near the first section 106A allows moisture to leak
into the first section 106A and causes malfunction of the first
string 102, the second string 104 in the second section 106 B,
which is sealed, can still function and produce power. It should be
noted that as the number of individually sealed sections within a
module structure increases, probability of solar cell failure due
to a defect in the protective shell decreases. The defects may be
in the edge sealant or even in either one of the front protective
sheet and the back protective sheet. If a defect in the protective
shell brings moisture into a sealed section, the moisture gets
trapped in that sealed section without ability to diffuse through
the rest of the module structure. The solar cell module 100 of FIG.
3A may, for example, have six sections instead of the two that is
shown. In this case, each of the solar cells 102A, 102B, 102C,
104A, 104B and 104C may be in a section of its own.
[0035] A four section module design is shown in FIG. 7. The module
600 of FIG. 7 comprises six cells, 601A, 601B, 601C, 601D, 601E,
and 601F, all of which may be similar in design. The solar cell
design is shown in FIG. 7A. The solar cell 601A comprises a busbar
650 and fingers 651. These design details of the solar cells are
not shown in FIG. 7 to simplify the drawing. The module 600 has a
four-section structure, each of the four sections 602A, 602B, 602C
and 602D containing one half portion of three cells. For example,
section 602 A contains a portion of cell 601A, a portion of cell
601B and a portion of cell 601C. Sections 602A, 602B, 602C and 602D
are formed by the edge sealant 605 and the divider sealants 606
which comprises three divider sealant portions 606A, 606B and 606C.
The divider sealant portions 606A and 606C are substantially
aligned with the busbars 650 of the solar cells 601A, 601B, 601C,
601D, 601E, and 601F, so that shadowing losses due to the divider
sealant portions 606A, 606B and 606C are minimized.
[0036] As depicted in FIG. 3 and FIG. 7, there is merit for forming
sealed sections in the module structure where each section contains
only a portion of a solar cell. This way, if moisture or other
vapors enter into a section and damages a portion of a solar cell,
other portions of the solar cell contained in other sections that
are not affected by the moisture would continue producing power
efficiently. This way, the overall performance of the module
structure would be enhanced compared to a module without the
sections. The edge sealant and divider sealants are materials that
are highly resistive to moisture penetration. The water vapor
transmission rate of the edge and divider sealants is preferably
below 0.001 gm/m.sup.2/day, more preferably below 0.0001
gm/m.sup.2/day.
[0037] A method of manufacturing an embodiment of the solar module
100 will be described in connection to FIG. 4. Initially, a pair of
front support layers 116A is placed on an inner surface 107B of the
front protective sheet 107 which is pre-cleaned. Sealant spaces 118
are left between the edge of the protective sheet 107 and between
the front support layers 116A to accommodate the edge sealant and
the divider sealant described above. In the following step, the
front portion 105A of the solar cell strings 102 and 104 may be
placed on the front support layers 116A. Then, the back support
layers 116B are placed on the back sides 105B of the solar cell
strings 102 and 104. The edge sealant 112 and the divider sealant
114 are attached to the sealant spaces 118. Finally, an inner
surface 108B of the back protective sheet 108 is placed over the
back support layers 116B and over the edge and divider sealants.
The front protective sheet 107 is typically a glass, but may also
be a transparent flexible polymer film such as TEFZEL.RTM., or
another polymeric film with moisture barrier coatings. TEDLAR.RTM.
and TEFZEL.RTM. are brand names of fluoropolymer materials from
DuPont. TEDLAR.RTM. is polyvinyl fluoride (PVF), and TEFZEL.RTM. is
ethylene tetrafluoroethylene (ETFE) fluoropolymer. The back
protective sheet 108 may be a sheet of glass or a polymeric sheet
such as TEDLAR.RTM., or another polymeric material which may or may
not be transparent. The back protective sheet 108 may comprise
stacked sheets comprising various material combinations such as
metallic films as moisture barrier. The front and back support
layer materials may preferably include EVA or thermoplastic
polyurethane (TPU) material or both. It should be noted that the
thicknesses of the components shown in the figures are not to
scale. The module 100 may have a rectangular or any other
geometrical shape, and thus the size of the sections and the
distribution of the solar cell strings may be arranged accordingly.
It is also possible that either one or both of the front support
layer and the back support layer may be eliminated from the module
structures.
[0038] The stacked components of the solar cell module depicted in
FIG. 4 are placed in a laminator and heat treated for about 10-20
minutes in a temperature range of 120.degree.-160.degree. C. under
pressure. This can alternatively be achieved through roll-to-roll
lamination. As shown in FIGS. 3B and 4, each solar cell includes a
front portion and a back portion or base. The base 105B includes a
substrate and a contact layer formed on the substrate. A preferred
substrate material may be a metallic material such as stainless
steel, aluminum or the like. An exemplary contact layer material
may be molybdenum. The front portion 105A may include an absorber
layer, such as a CIGS absorber layer which is formed on the contact
layer, and a transparent layer, such as a buffer-layer/ZnO stack,
formed on the absorber layer. An exemplary buffer layer may be a
(Cd,Zn)S layer. Conductive fingers (not shown) may be formed over
the transparent layer. Each interconnect electrically connects the
substrate or the contact layer of one of the cells to the
transparent layer of the next cell. However, the solar cells may be
interconnected using any other method known in the field.
[0039] FIG. 5 shows another embodiment of the module 100 in side
view. In this embodiment, the strings 102 and 104 are supported by
the edge and divider sealants 112 and 114. Gaps 122 are left
between the back side of the strings and the back protective sheet
108 and between the front side of the strings and the front
protective sheet 107. Within the sections 106A and 106B, the edges
of the strings 102 and 104 are held in place and sealed by the edge
and divider sealants 112 and 114 as in the manner shown in FIG. 5.
It is possible to fill any of the gaps 122 with a support layer
(not shown) identified as support layer 116A or 116B in FIG. 4.
[0040] FIG. 6 shows yet another embodiment of the module 100 in
side view. In this embodiment, a gap 122A is present over the front
side of the strings 102 and 104. The gap 122A may optionally be
filled with a front support layer (not shown but similar to the
front support layer 116A of FIG. 4). The back sides of the strings
102 and 104 are placed on the back sheet 108. The edges of the
strings 102 and 104 are held in place and sealed by the edge and
the divider sealants 112 and 114 as in the manner shown in FIG.
6.
[0041] Although aspects and advantages of the present inventions
are described herein with respect to certain preferred embodiments,
modifications of the preferred embodiments will be apparent to
those skilled in the art.
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