U.S. patent application number 12/922583 was filed with the patent office on 2011-03-17 for photovoltaic cell module and method of forming same.
Invention is credited to Kevin Houle, Malinda Howell, David Johnson, Donnie Juen, Barry Ketola, Nick Evan Shephard.
Application Number | 20110061724 12/922583 |
Document ID | / |
Family ID | 41065733 |
Filed Date | 2011-03-17 |
United States Patent
Application |
20110061724 |
Kind Code |
A1 |
Houle; Kevin ; et
al. |
March 17, 2011 |
Photovoltaic Cell Module And Method Of Forming Same
Abstract
A photovoltaic cell module, a photovoltaic array including at
least two modules, and a method of forming the module are provided.
The photovoltaic cell module includes a substrate and a tie layer
disposed on the substrate. The tie layer has a depth of penetration
of from 1.1 to 100 mm and a tack value of less than -0.6 gsec. The
photovoltaic cell module also includes a photovoltaic cell disposed
on the tie layer. The method of forming the photovoltaic cell
module includes the steps of disposing the tie layer on the
substrate and disposing the photovoltaic cell on the tie layer to
form the photovoltaic cell module.
Inventors: |
Houle; Kevin; (Midland,
MI) ; Howell; Malinda; (Midland, MI) ;
Johnson; David; (Midland, MI) ; Juen; Donnie;
(Sanford, MI) ; Ketola; Barry; (Freeland, MI)
; Shephard; Nick Evan; (Midland, MI) |
Family ID: |
41065733 |
Appl. No.: |
12/922583 |
Filed: |
March 13, 2009 |
PCT Filed: |
March 13, 2009 |
PCT NO: |
PCT/US09/01623 |
371 Date: |
November 10, 2010 |
Current U.S.
Class: |
136/252 ;
204/192.25; 257/E31.11; 438/73 |
Current CPC
Class: |
H01L 31/048 20130101;
H01L 21/67092 20130101; Y02E 10/50 20130101; H01L 31/1876 20130101;
Y10T 29/49115 20150115; Y02P 20/582 20151101; Y02P 70/50 20151101;
B32B 37/1009 20130101; B32B 2309/62 20130101; B32B 2309/68
20130101; Y02P 70/521 20151101; B32B 38/1858 20130101; B32B 2457/12
20130101; B32B 37/003 20130101; Y10T 29/49108 20150115; B32B 37/10
20130101 |
Class at
Publication: |
136/252 ;
204/192.25; 438/73; 257/E31.11 |
International
Class: |
H01L 31/048 20060101
H01L031/048; C23C 14/34 20060101 C23C014/34; H01L 31/18 20060101
H01L031/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2008 |
US |
61036748 |
Mar 14, 2008 |
US |
61036752 |
Jan 22, 2009 |
US |
61146551 |
Mar 13, 2009 |
US |
PCT/US2009/001623 |
Claims
1. A photovoltaic cell module comprising: A. a substrate; B. a tie
layer disposed on said substrate having a depth of penetration of
from 1.1 to 100 mm and a tack value of less than -0.6 gsec; and C.
a photovoltaic cell disposed on said tie layer.
2. A photovoltaic cell as set forth in claim 1 wherein said tie
layer has a thickness that varies across said substrate from 1 to
25 mils or from 5 to 25 mils.
3. (canceled)
4. (canceled)
5. A photovoltaic cell module as set forth in claim 1 further
comprising first and second electrical leads each spaced apart from
one another, disposed on a first side of said photovoltaic cell,
and sandwiched between said photovoltaic cell and said tie layer
and wherein said tie layer has a thickness of from 10 to 30 mils
between said first electrical lead and said substrate, a thickness
of from 10 to 30 mils between said second electrical lead and said
substrate, and a thickness of from 5 to 25 mils across a remainder
of said substrate.
6. A photovoltaic cell module as set forth in claim 5 wherein said
thickness across the remainder of said substrate is further defined
as from 5 to 7 mils and/or said thicknesses between said first and
second electrical leads and said substrate are each independently
further defined as from 12 to 15 mils.
7. (canceled)
8. A photovoltaic cell module as set forth in claim 1 further
comprising a second tie layer that is the same or different than
said tie layer and that is disposed on said photovoltaic cell.
9. (canceled)
10. A photovoltaic cell module as set forth in claim 1 wherein said
cell module further comprises third and fourth electrical leads
each spaced apart from one another and disposed on a second side of
said photovoltaic cell opposite said first side, wherein said third
and fourth electrical leads are sandwiched between said
photovoltaic cell and said second tie layer and wherein said second
tie layer has a thickness of from 5 to 25 mils.
11. (canceled)
12. (canceled)
13. A photovoltaic cell module as set forth in claim 5 wherein said
cell module further comprises a second substrate that is the same
or different than said substrate, and the photovoltaic cell is
further disposed on the second substrate via chemical vapor
deposition or physical sputtering.
14. (canceled)
15. (canceled)
16. (canceled)
17. A photovoltaic cell module as set forth in claim 16 wherein
said curable composition comprises carbon atoms and is
substantially free of compounds including silicon atoms.
18. (canceled)
19. (canceled)
20. A photovoltaic cell module as set forth in claim 1 wherein said
tie layer is formed from a curable composition and said curable
composition comprises a cross-linking agent having silicon-bonded
hydrogen atoms and a diorganopolysiloxane having alkenyl groups and
a mole ratio of silicon-bonded hydrogen atoms in said cross-linking
agent to alkenyl groups in said diorganopolysiloxane is less than
0.9.
21. A photovoltaic cell module as set forth in claim 15 wherein
said tie layer is formed from a curable composition and said
curable composition comprises a diorganopolysiloxane having the
average unit formula:
(R'.sub.3SiO.sub.1/2).sub.x(R'.sub.2SiO.sub.2/2).sub.y(R'SiO.sub.3/2).sub-
.z wherein x and y are positive numbers, z is greater than or equal
to zero, and each R' is independently a monovalent radical.
22. A photovoltaic cell module as set forth in claim 1 wherein said
tie layer is formed from a curable composition and said curable
composition comprises at least one of an ethylene-vinyl acetate
copolymer, a polyurethane, an ethylene tetrafluoroethylene, a
polyvinylfluoride, a polyethylene terephthalate, and combinations
thereof.
23. A photovoltaic cell module as set forth in claim 1 wherein said
tie layer is further defined as a film.
24. (canceled)
25. (canceled)
26. A method of forming a photovoltaic cell module comprising a
substrate, a tie layer formed from a curable composition, and a
photovoltaic cell, said method comprising the steps of: A.
disposing, on the substrate, the tie layer having a depth of
penetration of from 1.1 to 100 mm and a tack value of less than
-0.6 gsec; and B. disposing the photovoltaic cell on the tie layer
to form the photovoltaic cell module.
27. (canceled)
28. A method as set forth in claim 26 wherein the photovoltaic cell
module further comprises first and second electrical leads each
spaced apart from one another, disposed on a first side of the
photovoltaic cell, and sandwiched between the photovoltaic cell and
the tie layer and wherein the step of disposing the tie layer is
further defined as: A. applying a base amount of the curable
composition on the substrate resulting in a first thickness of from
5 to 25 mils on the substrate; B. applying a first supplemental
amount of the curable composition between the first electrical lead
and the substrate resulting in a second thickness of from 10 to 30
mils about the first electrical lead; C. applying a second
supplemental amount of the curable composition between the second
electrical lead and the substrate resulting in a third thickness of
from 10 to 30 mils about the second electrical lead; and D. curing
the curable composition after the amounts have been applied to form
the tie layer.
29. A method as set forth in claim 28 wherein the first thickness
is further defined as across an entirety of the substrate, the step
of applying the first supplemental amount is further defined as
applying the first supplemental amount on the first thickness, and
the step of applying the second supplemental amount is further
defined as applying the second supplemental amount on the first
thickness.
30. A method as set forth in claim 29 wherein the first thickness
is further defined as from 5 to 7 mils.
31. A method as set forth in claim 30 wherein the second and third
thicknesses are each independently further defined as from 12 to 15
mils.
32. A method as set forth in claim 28 wherein said steps of
applying the first and second supplemental amounts of the curable
composition occur sequentially.
33. A method as set forth in claim 28 wherein said steps of
applying the first and second supplemental amounts of the curable
composition occur simultaneously.
34. A method as set forth in claim 28 wherein said steps of
applying the first and second supplemental amounts of the curable
composition occur after the step of applying the base amount of the
curable composition.
35. A method as set forth in claim 28 wherein said steps of
applying the first and second supplemental amounts of the curable
composition occur before the step of applying the base amount of
the curable composition.
36. A method as set forth in claim 28 wherein the cell module
further comprises a second tie layer that is the same or different
than the tie layer and that is disposed on the photovoltaic cell, a
second substrate disposed on the second tie layer, and third and
fourth electrical leads each spaced apart from one another and
disposed on a second side of the photovoltaic cell opposite the
first side, wherein the third and fourth electrical leads are
sandwiched between the photovoltaic cell and the second tie layer,
and wherein the method further comprises the step of applying a
second base amount of the curable composition across the second
substrate wherein the second base amount of the curable composition
has a thickness of from 5 to 25 mils.
37. (canceled)
38. A method as set forth in claim 36 wherein the second base
amount of the curable composition has a thickness of from 5 to 25
mils.
39. (canceled)
40. (canceled)
41. A method as set forth in claim 26 wherein the step of disposing
the tie layer on the substrate is further defined as disposing the
curable composition on the substrate and curing the curable
composition on the substrate to form the tie layer.
42. (canceled)
43. A method as set forth in claim 26 wherein the method further
comprises the step of curing the curable composition to form the
tie layer prior to the step of disposing the tie layer on the
substrate.
44. A method as set forth in claim 26 wherein the method further
comprises the steps of applying the curable composition to the
photovoltaic cell and curing the curable composition on the
photovoltaic cell to form the tie layer prior to the step of
disposing the tie layer on the substrate.
45. A method as set forth in claim 26 wherein the tie layer is
further defined as a film and the step of disposing the tie layer
is further defined as melting the film on the substrate.
46. (canceled)
47. A method as set forth in claim 41 further comprising the step
of applying the photovoltaic cell to the substrate by chemical
vapor deposition or physical sputtering.
48. (canceled)
49. (canceled)
50. (canceled)
51. (canceled)
52. A method as set forth in claim 26 wherein the curable
composition comprises a cross-linking agent having silicon-bonded
hydrogen atoms and a diorganopolysiloxane having alkenyl groups and
a mole ratio of silicon-bonded hydrogen atoms in the cross-linking
agent to alkenyl groups in the diorganopolysiloxane is less than
0.9.
53. (canceled)
54. A method as set forth in claim 26 wherein the curable
composition comprises carbon atoms and is substantially free of
compounds including silicon atoms.
55. (canceled)
56. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The subject patent application claims priority to, and all
the benefits of, U.S. Provisional Patent Application Ser. Nos.
61/036,748 and 61/036,752, both filed on Mar. 14, 2008, and U.S.
Provisional Patent Application Ser. No. 61/146,551 filed on Jan.
22, 2009. The entirety of these provisional patent applications is
expressly incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention generally relates to a photovoltaic
cell module and method of forming the same. More specifically, the
photovoltaic cell module includes a substrate and a tie layer
having particular properties that is disposed on the substrate.
DESCRIPTION OF THE RELATED ART
[0003] Solar or photovoltaic cells are semiconductor devices used
to convert light into electricity. There are two general types of
photovoltaic cells, wafers and thin films. Wafers are thin sheets
of semiconductor material that are typically formed from casting or
mechanically sawing the wafer from a single crystal or multicrystal
ingot. Thin film photovoltaic cells usually include continuous
layers of semi-conducting materials deposited on a substrate using
sputtering or chemical vapor deposition.
[0004] In many applications, the photovoltaic cells are
encapsulated to provide additional protection from environmental
factors such as wind and rain. However, encapsulants and
encapsulation methods known in the art are expensive and time
consuming and typically ineffective.
[0005] One known encapsulant is ethyl vinyl acetate (EVA). EVA is
used because it is able to harvest light for the photovoltaic
cells. However, EVA is degraded by wavelengths of light below 400
nm. Hence, photovoltaic cells including EVA are limited to
harvesting light at wavelengths above 400 nm. More specifically,
EVA has low UV resistance, has a tendency to discolor, and has a
tendency to chemically and physically degrade upon exposure to
light.
[0006] EVA is also known to exhibit poor adhesive properties
relative to glass substrates and have a high modulus. These poor
adhesive properties and high modulus tend to cause high stress
conditions around the photovoltaic cells resulting in gradual
delamination of the encapsulant from the substrate. This
delamination leads to water accumulation in the encapsulant and
photovoltaic cell corrosion.
[0007] Consequently, the industry has used increased amounts of EVA
to reduce delamination and discoloring. However, this reduces a
total amount of available light impinging on the photovoltaic cell,
thereby reducing cell efficiency. Additionally, glass doped with
cerium and antimony has been used as a substrate or superstrate to
protect the EVA from UV damage. Further, UV stabilizing packages
including UV absorbers and/or hindered amine light stabilizers have
been added to the EVA. However, use of the doped glass or UV
absorbers typically causes a 1% to 5% loss in photovoltaic cell
efficiency.
[0008] Use of EVA to encapsulate photovoltaic cells is described in
EP 0658943, WO 94/29106, EP 0528566 and EP 0755080. Typically, EVA
is applied as one or more thermosetting sheets sandwiched between a
substrate and a superstrate and subjected to heat, vacuum and
pressure. These conditions cause the EVA to flow, wet the substrate
and the superstrate, and encapsulate the photovoltaic cell.
Production of photovoltaic cells in this way is relatively
expensive and time consuming.
[0009] Alternatively, the EVA may be cured through use of peroxides
to initiate a radical cure. This method tends to promote side
reactions that reduce overall durability. If peroxides are used,
curing temperatures typically range from 150.degree. C. to
160.degree. C. These temperatures typically cause excessive stress
in the photovoltaic cells and result in mechanical breakdown and/or
increased production time and a number of steps needed to
strengthen the photovoltaic cells.
[0010] Some photovoltaic cell modules include multiple sheets of
EVA as hot melt thermoset adhesives. As set forth in FIG. 1, which
represents the prior art, photovoltaic cell modules include
multiple sheets of EVA (B) as hot melt thermoset adhesives to bond
and encapsulate photovoltaic cells (C) to a glass superstrate (D)
and a Tedlar or PET/SiOx-PET/Al substrate (A). The glass
superstrate (D), whilst transparent to light, is typically doped
with cerium and antimony to filter UV light thereby increasing
production costs and complexities.
[0011] In addition, silicones have been investigated for use as
encapsulants but are not typically used due to numerous drawbacks
resulting from production methods. WO 2005/006451 describes a
continuous method for the encapsulation of photovoltaic cells using
heat cured liquid silicone. Whilst this method provides significant
advantages over other encapsulation methods, the method tends to
trap air bubbles underneath the photovoltaic cells which causes the
photovoltaic cells to exhibit inferior properties. Additional
drawbacks include a difficulty in controlling thickness of the
encapsulant, increased expense, increased processing times, and
increased processing complexity. These all result in increased cost
for the end purchaser.
[0012] The prior art does not account for differing thicknesses of
electrical leads that are included on photovoltaic cells in
relation to detrimental exposure of such leads due to long term use
of the photovoltaic cells, weathering, and general wear and tear.
The exposure of the leads results in decreased performance and
decreased conversion of light into electricity. Furthermore, the
prior art does not account for the use of differing amounts of
encapsulants to protect the electrical leads while maintaining
performance and decreasing production costs.
[0013] Accordingly, there remains an opportunity to develop
photovoltaic cell modules that are effective and durable. There
also remains an opportunity to develop a method of forming the
photovoltaic cell modules that minimizes processing complexities,
trapped air underneath photovoltaic cells, and an amount of a tie
layer that is used, thus maximizing production efficiency, cost
savings, and repeatability.
SUMMARY OF THE INVENTION AND ADVANTAGES
[0014] The instant invention provides a photovoltaic cell module
and a method of forming. The photovoltaic cell module includes a
substrate and a tie layer disposed on the substrate. The tie layer
has a depth of penetration of from 1.1 to 100 mm and a tack value
of less than -0.6 gsec. The photovoltaic cell module also includes
a photovoltaic cell disposed on the tie layer. The method of
forming the photovoltaic cell module includes the steps of
disposing the tie layer on the substrate and disposing the
photovoltaic cell on the tie layer to form the photovoltaic cell
module.
[0015] The tie layer allows light to enter the photovoltaic cell
and be efficiently converted to electricity. The tie layer also
allows the photovoltaic cell to be secured within the photovoltaic
cell module while simultaneously allowing for trapped air to be
evacuated from underneath thereby leading to increased durability
and weatherability. The tie layer further allows for cost effective
and repeatable production of the photovoltaic cell module because
of efficient evacuation of the trapped air.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0016] Other advantages of the present invention will be readily
appreciated, as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying drawings wherein:
[0017] FIG. 1 is a cross-sectional view of a photovoltaic cell
module of the prior art including EVA sheets;
[0018] FIG. 2 is a cross-sectional view of one embodiment of a
photovoltaic cell module of this invention including a substrate, a
tie layer disposed on the substrate, and a photovoltaic cell
disposed on the tie layer;
[0019] FIG. 3 is a cross-sectional view of the photovoltaic cell
module of FIG. 2 including a second tie layer disposed on the
photovoltaic cell;
[0020] FIG. 4 is a cross-sectional view of the photovoltaic cell
module of FIG. 3 including a second substrate disposed on the
second tie layer;
[0021] FIG. 5 is a cross-sectional view of another embodiment of a
photovoltaic cell module of this invention including a substrate, a
photovoltaic cell disposed directly on the substrate via chemical
vapor deposition or physical sputtering, a tie layer disposed
directly on the photovoltaic cell, and a second substrate disposed
directly on the tie layer;
[0022] FIG. 6A is a cross-sectional view of a series of
photovoltaic cell modules of FIG. 4 that are electrically connected
and arranged as a photovoltaic array;
[0023] FIG. 6B is a magnified cross-sectional view of the series of
photovoltaic cell modules of FIG. 4 that are electrically connected
and arranged as a photovoltaic array.
[0024] FIG. 7A is an exploded cross-sectional view of yet another
embodiment of a photovoltaic cell module of this invention
including a substrate and a tie layer disposed on the substrate and
having thicknesses (T.sub.1, T.sub.2, T.sub.3) that vary across the
substrate. The photovoltaic cell module also includes a
photovoltaic cell and first and second electrical leads each spaced
apart from one another, disposed on a first side of the
photovoltaic cell, and sandwiched between the photovoltaic cell and
the tie layer;
[0025] FIG. 7B is a cross-sectional view of the photovoltaic cell
module of FIG. 7A formed according to this invention;
[0026] FIG. 8A is an exploded cross-sectional view of the
photovoltaic cell module of FIG. 7A further including a second tie
layer that is the same or different than the tie layer and that is
also disposed on the photovoltaic cell, and a second substrate
disposed on the second tie layer;
[0027] FIG. 8B is a cross-sectional view of the photovoltaic cell
module of FIG. 8A formed according to this invention;
[0028] FIG. 9A is an exploded cross-sectional view of the
photovoltaic cell module of FIG. 8A further including third and
fourth electrical leads each spaced apart from one another,
disposed on a second side of the photovoltaic cell opposite the
first side, and sandwiched between the photovoltaic cell and the
second tie layer; and
[0029] FIG. 9B is a cross-sectional view of the photovoltaic cell
module of FIG. 9A formed according to this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The present invention provides a photovoltaic cell module
(10) (hereinafter referred to as "module") generally shown in FIGS.
2-9 and a method of forming the module (10). The module (10)
includes a substrate (12), a tie layer (14) disposed on the
substrate (12), and a photovoltaic cell (16) disposed on the tie
layer (12), as shown in FIG. 2. The substrate (12), tie layer (14),
and photovoltaic cell (16) are described in greater detail
below.
[0031] Modules (10) convert light energy into electrical energy due
to a photovoltaic effect and perform two primary functions. A first
function is photogeneration of charge carriers such as electrons
and holes in light absorbing materials. The second function is
direction of the charge carriers to a conductive contact to
transmit electricity.
[0032] The module (10) includes the substrate (12) which may
include any suitable material known in the art. Typically, the
substrate (12) provides protection to a rear surface (22) of the
module (10). Similarly, the substrate (12) may provide protection
to a front surface (24) of the module (10). The substrate (12) may
be soft and flexible but is typically rigid and stiff.
Alternatively, the substrate (12) may include rigid and stiff
segments while simultaneously including soft and flexible segments.
The substrate (12) is typically transparent to light, may be
opaque, or may not transmit light (i.e., be impervious to light).
The substrate (12) may include glass, stainless steel, metal foils,
polyimides, ethylene-vinyl acetate copolymers, and/or organic
fluoropolymers including, but not limited to, ethylene
tetrafluoroethylene (ETFE), Tedlar.RTM. (polyvinylfluoride),
polyester/Tedlar.RTM., Tedlar.RTM./polyester/Tedlar.RTM.,
polyethylene terephthalate (PET) alone or coated with silicon and
oxygen based materials (SiO.sub.x), and combinations thereof. In
one embodiment, the substrate (12) is selected from the group of
polyvinylfluoride and polyethylene. The substrate (12) may
alternatively be further defined as a PET/SiO.sub.x-PET/Al
substrate, wherein x has a value of from 1 to 4. Still further, the
substrate (12) may include silicone, may consist essentially of
silicone and not include organic monomers or polymers, or may
consist of silicone. It is to be understood that the substrate (12)
is not limited to the aforementioned compounds.
[0033] The substrate (12) may be load bearing or non-load bearing
and may be included in any portion of the module (10). Typically,
the substrate (12) is load bearing. The substrate (12) may be a
"top layer," also known as a superstrate, or a "bottom layer" of
the module (10). Bottom layers are typically positioned behind the
photovoltaic cells (16) and serve as mechanical support, as shown
in the Figures. In various embodiments, the module (10) includes
the substrate (12) and a second substrate (20), which may be the
same or different from each other. In other words, the substrate
(12) and the second substrate (20) may be formed from the same
material or from different materials. The substrate (12) is
typically the bottom layer while the second substrate (20) is
typically the top layer and functions as a superstrate, as shown in
FIGS. 4-6, 8, and 9. Typically, the second substrate (20) (e.g. a
second substrate functioning as a superstrate) is transparent to
sunlight and is positioned on top of the substrate (12) and in
front of a light source. The second substrate (20) is typically
used to protect the module (10) from environmental conditions such
as rain, snow, and heat. Most typically, the second substrate (20)
functions as a superstrate and is a rigid glass panel that is
transparent to sunlight and is used to protect the front surface of
the module (10), as also shown in FIGS. 4-6, 8 and 9.
[0034] The substrate (12) and/or the second substrate (20)
typically have a thickness of from 50 to 500, of from 100 to 225,
or of from 175 to 225, micrometers. The substrate (12) and/or the
second substrate (20) may have a length and width of 125 mm each or
a length and width of 156 mm each. Of course, the instant invention
is not limited to these dimensions.
[0035] In addition, the module (10) also includes the tie layer
(14). The tie layer (14) is disposed on the substrate (12) and
usually functions to adhere the photovoltaic cell (16) to the
substrate (12). The module (10) typically includes multiple tie
layers, e.g. a second (18) and/or a third tie layer. Any second
(18), third, or additional tie layer may be the same or different
from the tie layer (14). Thus, any second (18), third or additional
tie layer may be formed from the same material or from a different
material than the tie layer (14). In one embodiment, the module
(10) includes the tie layer (14) and a second tie layer (18), as
shown in FIGS. 3, 4, 6, 8 and 9. The second tie layer (18) may also
be disposed on the substrate (12). Alternatively, the second tie
layer (18) may be disposed on the first tie layer (14) and/or may
be disposed on a photovoltaic cell (16) as described in greater
detail below and as set forth in FIGS. 3, 4, 6, 8 and 9. Further,
the tie layer (14) is typically transparent to UV and/or visible
light and the second (or additional) tie layers (18) may be
impermeable to light or opaque. In one embodiment, the second tie
layer (18) has high transmission across visible wavelengths, long
term stability to UV and provides long term protection to the
photovoltaic cell (16). In this embodiment, there is no need to
dope the substrate (12) with cerium due to the UV stability of the
tie layer (14)
[0036] The tie layer (14) has a depth of penetration (value) of
from 1.1 to 100 mm. It is understood by those of skill in the
silicone arts that the terminology "depth of penetration" is also
referred to as "penetration" or "penetration value." In various
embodiments, the tie layer (14) has a depth of penetration of from
1.3 to 100 mm and more typically of from 2 to 55 mm. Without
intending to be bound by any particular theory, it is believed that
as temperature rises, the depth of penetration values also rise. It
is contemplated that the tie layer (14) may have a depth of
penetration of from 1.1 to 100 mm, of from 1.3 to 100 mm, or of
from 2 to 55 mm, as determined at room temperature or at any other
temperature. Typically, depth of penetration is determined at room
temperature.
[0037] The depth of penetration is determined by first calculating
hardness and then calculating depth of penetration. Thus, the tie
layer (14) typically has a hardness in grams (g) of Force of from 5
to 500, more typically of from 5 to 400, and most typically of from
10 to 300. More specifically, hardness is determined using a TA-XT2
Texture Analyzer commercially available from Stable Micro Systems
using a 0.5 inch (1.27 cm) diameter steel probe. Test samples of
the tie layer having a mass of 12 g are heated at 100.degree. C.
for 10 minutes and are analyzed for hardness using the following
testing parameters, as known in the art: 2 mm/sec pre-test and
post-test speed; 1 mm/s test speed; 4 mm target distance; 60 second
hold; and a 5 g force trigger value. The maximum grams force is
measured at 4 mm distance into the tie layer (14).
[0038] Depth of penetration measurements are typically calculated
using the hardness (grams of force) obtained using the TA-XT2
Texture Analyzer and the following equation: Depth of penetration
(mm.times.10)=5,350/grams force. This relationship is determined
using a universal penetrometer, commercially available from
Precision Scientific of Chicago, Ill., and by measuring hardness
with the texture analyzer of the tie layer (14). There typically
are seventy nine sample measurements taken for the tie layer (14).
The 5,350 constant is determined by multiplying the depth of
penetration by the grams of force from the texture analyzer for
each of the seventy nine samples and then averaging the
results.
[0039] The tie layer (14) also has a tack value of less than -0.6
gsec. In various embodiments, the tie layer (14) has a tack value
of from -0.7 to -300 gsec and more typically of from -1 to -100
gsec. In one embodiment, the tie layer (14) has a tack value of
about -27 gsec. Without intending to be bound by any particular
theory, it is believed that as temperature rises, the tack value
decreases. It is contemplated that the tie layer (14) may have a
tack value of less than -0.6 gsec., of from -0.7 to -300 gsec., or
of from -1 to -100 gsec., as determined at room temperature or at
any other temperature. Typically, tack value is determined at room
temperature.
[0040] The tack value is determined using the TA-XT2 Texture
Analyzer using a 0.5 inch (1.27 cm) diameter steel probe. The probe
is inserted into the tie layer (14) to a depth of 4 mm and then
withdrawn at a rate of 2 mm/sec. The tack value is calculated as a
total area (Force-Time) during withdrawal of the probe from the tie
layer (14). The tack value is expressed in gramsec. wherein the
time is measured as a time difference between a time when the force
is equal to zero and a time when the probe separates from the tie
layer (14). It is believed that the depth of penetration and the
tack values do not substantially change with varying thicknesses of
the tie layer (14). However, methods of determining the depth of
penetration and the tack values may be modified depending on the
thickness of the tie layer (14).
[0041] The tie layer (14) is typically tacky and may be a gel, gum,
liquid, paste, resin, or solid. In one embodiment, the tie layer
(14) is a film. In another embodiment, the tie layer (14) is a gel.
In yet another embodiment, the tie layer (14) is a liquid that is
cured (e.g. pre-cured) to form a gel. Alternatively, the tie layer
(14) may include multiple segments, with each segment including a
different composition and/or different form (e.g., gel and liquid),
so long as the segments and the overall tie layer (14) have the
appropriate depth of penetration and tack values, set forth above.
Examples of suitable gels for use as the tie layer (14) are
described in U.S. Pat. Nos. 5,145,933, 4,340,709, and 6,020,409,
each of which is expressly incorporated herein by reference
relative to these gels. It is to be understood that the tie layer
(14) can have any form so long as the tie layer (14) has a depth of
penetration of from 1.1 to 100 mm and a tack value of less than
-0.6 gsec. The tie layer (14) also typically has an elastic modulus
(G' at cure) of from 7.times.10.sup.2 to 6.times.10.sup.5,
dynes/cm.sup.2.
[0042] The tie layer (14) may be formed from and/or include any
suitable compound known in the art. These compounds may or may not
require curing. In one embodiment, the curable composition includes
at least one of an ethylene-vinyl acetate copolymer, a
polyurethane, an ethylene tetrafluoroethylene, a polyvinylfluoride,
a polyethylene terephthalate, and combinations thereof. In another
embodiment, the curable composition includes carbon atoms and is
substantially free of compounds including silicon atoms. The
terminology "substantially free," as used immediately above, refers
to less than 0.1 weight percent of compounds including silicon
atoms present in the curable composition. The curable composition
may include organic compounds and less than 0.1 weight percent of
compounds including silicon atoms.
[0043] In a further embodiment, the tie layer (14) is formed from a
curable composition including silicon atoms. The tie layer may be
formed completely from a curable silicone composition such as those
disclosed in U.S. Pat. Nos. 6,020,409 and 6,169,155, herein
expressly incorporated by reference relative to these curable
silicone compositions. In an alternative embodiment, the tie layer
(14) may be formed from a cured or curable composition that
includes a silicone fluid such as those commercially available from
Dow Corning Corporation of Midland, Mich. One non-limiting example
of a particularly suitable silicone fluid is trimethylsilyl
terminated polydimethylsiloxane having a viscosity of 100 mPas.
[0044] In one embodiment, the curable silicone composition is
further defined as hydrosilylation-curable and includes an
organosilicon compound having at least one unsaturated moiety per
molecule, an organohydrogensilicon compound having at least one
silicon-bonded hydrogen atom per molecule, and a hydrosilylation
catalyst used to accelerate a hydrosilylation reaction between the
organosilicon compound and the organohydrogensilicon compound. In
this embodiment, a ratio of silicon-bonded hydrogen atoms per
molecule of the organohydrogensilicon compound to unsaturated
moieties per molecule of the organosilicon compound is typically of
from 0.05 to 100.
[0045] In an alternative embodiment, the organosilicon compound is
further defined as an alkenyldialkylsilyl end-blocked
polydialkylsiloxane which may itself be further defined as
vinyldimethylsilyl end-blocked polydimethylsiloxane. The
organohydrogensilicon compound may also be further defined as a
mixture of a dialkylhydrogensilyl terminated polydialkylsiloxane
and a trialkylsilyl terminated
polydialkylsiloxane-alkylhydrogensiloxane co-polymer. The
dialkylhydrogensilyl terminated polydialkylsiloxane itself may be
further defined as dimethylhydrogensilyl terminated
polydimethylsiloxane while the trialkylsilyl terminated
polydialkylsiloxane-alkylhydrogensiloxane co-polymer may be further
defined as a trimethylsilyl terminated
polydimethylsiloxane-methylhydrogensiloxane co-polymer.
[0046] Alternatively, the tie layer (14) may be formed from a
curable composition including one or more of components (A)-(E) and
combinations thereof. Each of components (A)-(E) is optional for
use in this invention and is not required. One or more of
components (A)-(E) may be silicon containing or may be organic. If
the curable composition is further defined as a curable silicone
composition, component (A) is typically utilized along with
component (B). Component (A) may include a mixture of compounds.
Similarly, each of components (B)-(E) may independently include
mixtures of compounds.
[0047] Component (A) may include any organic and/or inorganic
compounds known in the art and may include both carbon and silicon
atoms. Typically, component (A) includes a diorganopolysiloxane
containing polymer. The diorganopolysiloxane containing polymer may
have high or low number (M.sub.n) and/or weight average (M.sub.w)
molecular weights and may be a silicone gum having at least two
reactive groups per molecule that are designed to cure with
component (B), described in greater detail below. Alternatively,
the diorganopolysiloxane containing polymer may be a resin, a gel
and/or a gum or may include a gum, a gel and/or a gum. In another
embodiment, the diorganopolysiloxane containing polymer has a low
molecular weight. However, the diorganopolysiloxane containing
polymer is not limited to the description above and may have any
number average or weight average molecular weight.
[0048] The diorganopolysiloxane containing polymer typically has a
molecular structure which is substantially linear. However, this
structure may be partially branched. In one embodiment, the
diorganopolysiloxane containing polymer has the average unit
formula:
(R'.sub.3SiO.sub.1/2).sub.x(R'.sub.2SiO.sub.2/2).sub.y(R'SiO.sub.3/2).su-
b.z
wherein x and y are positive numbers, z is greater than or equal to
zero, and each R' is independently a monovalent radical. In this
formula, x+y+z is typically at least 100 and is more typically
greater than 700. Also, y/(x+y+z) is typically greater than or
equal to 0.8 and more typically greater than or equal to 0.95.
Non-limiting examples of monovalent radicals include alkyl groups
such as methyl, ethyl, propyl, isopropyl, butyl, and tertiary butyl
groups, phenyl groups, alkylphenyl groups, hydrogen atoms, hydroxyl
groups, alkenyl groups, oximo groups, alkoxy groups, epoxide
groups, carboxyl groups, alkyl amino radicals, and combinations
thereof. Typically all non-reactive R' groups are alkyl groups
having from 1 to 6 carbon atoms and/or phenyl groups. Most
typically, all non-reactive R' groups are methyl groups. Typically
at least two R' groups per molecule are reactive groups which may
be unsaturated and may be alkenyl and/or alkynyl groups. Most
typically, these reactive groups are alkenyl groups such as vinyl
or hexenyl groups. Suitable non-limiting examples of reactive
groups include alkenyl groups that are linear or branched and have
from 2 to 10 carbon atoms, such as vinyl groups, propenyl groups,
butenyl groups, hexenyl groups, isopropenyl groups, tertiary
butenyl groups and combinations thereof. The diorganopolysiloxane
may also include reactive groups other than unsaturated groups to
enhance adhesion properties of the curable composition.
[0049] Additional suitable examples of component (A) include, but
are not limited to, dimethylalkenylsiloxy-terminated
dimethylpolysiloxanes, dimethylalkenylsiloxy-terminated copolymers
of methylalkenylsiloxane and dimethylsiloxane,
dimethylalkenylsiloxy-terminated copolymers of methylphenylsiloxane
and dimethylsiloxane, dimethylalkenylsiloxy-terminated copolymers
of methylphenylsiloxane, methylalkenylsiloxane, and
dimethylsiloxane, dimethylalkenylsiloxy-terminated copolymers of
diphenylsiloxane and dimethylsiloxane,
dimethylalkenylsiloxy-terminated copolymers of diphenylsiloxane,
methylalkenylsiloxane, and dimethylsiloxane, and combinations
thereof.
[0050] Alternatively, component (A) may include a compound having
hydroxyl or hydrolysable groups X and X.sup.1 which may be the same
or different. These groups may or may not be terminal groups and
are typically not sterically hindered. For example, this compound
may have the general formula:
X-A-X.sup.1
wherein X and/or X.sup.1 may include and/or terminate with any of
the following groups: --Si(OH).sub.3, --(R.sup.a)Si(OH).sub.2,
--(R.sup.a).sub.2SiOH, --R.sup.aSi(OR.sup.b).sub.2,
--Si(OR.sup.b).sub.3, --R.sup.a.sub.2SiOR.sup.b or
--R.sup.a.sub.2Si--R.sup.c--SiR.sup.d.sub.p(OR.sup.b).sub.3-p where
each R.sup.a may independently include a monovalent hydrocarbyl
group such as an alkyl group having from 1 to 8 carbon atoms.
Typically, R.sup.a is a methyl group. Each R.sup.b and R.sup.d may
independently be an alkyl group having up to 6 carbon atoms or
alkoxy group. R.sup.c is typically a divalent hydrocarbon group
which may include one or more siloxane spacers having up to six
silicon atoms. Typically, p has a value 0, 1 or 2. In one
embodiment, X and/or X.sup.1 include functional groups which are
hydrolysable in the presence of moisture.
[0051] Additionally, in this formula, (A) typically includes a
siloxane molecular chain. In one embodiment, (A) includes a
polydiorgano-siloxane chain having siloxane units of the following
formula
--(R.sup.5.sub.sSiO.sub.(4-s)/2)--
wherein each R.sup.5 is independently an organic group such as a
hydrocarbyl group having from 1 to 10 carbon atoms that is
optionally substituted with one or more halogen group such as
chlorine or fluorine, and s is 0, 1 or 2. More specifically,
R.sup.5 may include methyl, ethyl, propyl, butyl, vinyl,
cyclohexyl, phenyl, and/or tolyl groups, propyl groups substituted
with chlorine or fluorine such as 3,3,3-trifluoropropyl,
chlorophenyl, beta-(perfluorobutyl)ethyl or chlorocyclohexyl
groups, and combinations thereof. Typically at least some of the
groups R.sup.5 are methyl groups. Most typically, all of the
R.sup.5 groups are methyl groups. Typically there are at least
approximately 700 units of the above formula per molecule.
[0052] Typically, component (A) has a viscosity of greater than 50
mPas. In one embodiment, component (A) has a viscosity of greater
than 1,000,000 mPas. In another embodiment, component (A) has a
viscosity of 50 to 1,000,000, more typically of from 100 to
250,000, and most typically of from 100 to 100,000, mPas. Each of
the aforementioned viscosities are measured at 25.degree. C.
according to ASTM D4287 using a Brookfield DVIII Cone and Plate
Viscometer. Component (A) is typically present in the curable
composition in an amount of from 25 to 99.5 parts by weight, per
100 parts by weight of the curable composition.
[0053] In some embodiments, component (A) has a degree of
polymerization (dp) of above 1500 and a Williams plasticity number,
as determined using ASTM D926, of from 95 to 125. In other
embodiments, component (A) has a dp of greater than 100 or even
greater than 700. The plasticity number, as used herein, is defined
as a thickness in millimeters.times.100 of a cylindrical test
specimen 2 cm.sup.3 in volume and approximately 10 mm in height
after the specimen has been subjected to a compressive load of 49
Newtons for three minutes at 25.degree. C.
[0054] Referring now to component (B), this component typically
includes a silicone resin (M, D, T, and/or Q) or mixture of resins.
The resin(s) may or may not include functional groups that could
react with component (A). Component (B) may be combined with
component (A) with or without solvent. More specifically, component
(B) may include an organosiloxane resin such as an MQ resin
including R.sup.5.sub.3SiO.sub.1/2 units and SiO.sub.4/2 units, a
TD resin including R.sup.5SiO.sub.3/2 units and
R.sup.5.sub.2SiO.sub.2/2 units, an MT resin including
R.sup.5.sub.3SiO.sub.1/2 units and R.sup.5SiO.sub.3/2 units, an MTD
resins including R.sup.5.sub.3SiO.sub.1/2 units, R.sup.5SiO.sub.3/2
units, and R.sup.5.sub.2SiO.sub.2/2 units, and combinations
thereof. In these formulas, R.sup.5 is as described above.
[0055] The symbols M, D, T, and Q used above represent the
functionality of structural units of polyorganosiloxanes including
organosilicon fluids, rubbers (elastomers) and resins. The symbols
are used in accordance with established understanding in the art.
Thus, M represents the monofunctional unit
R.sup.5.sub.3SiO.sub.1/2. D represents the difunctional unit
R.sup.5.sub.2SiO.sub.2/2. T represents the trifunctional unit
R.sup.5SiO.sub.3/2. Q represents the tetrafunctional unit
SiO.sub.4/2. Generic structural formulas of these units are shown
below:
##STR00001##
Typically, the number average molecular weight of component (B) is
at least 5,000 and typically greater than 10,000 g/mol. Component
(B) is typically present in the curable composition in an amount of
from 0.5 to 75 parts by weight per 100 parts by weight per 100
parts by weight of the curable composition.
[0056] Without intending to be bound by any particular theory, it
is believed that the aforementioned silicones impart outstanding UV
resistance to the curable compound and tie layer (14). Use of these
silicones may reduce or eliminate a need to include a UV additive
or cerium doped glass in the module (10). These silicones may also
exhibit long term UV and visual light transmission thereby
maximizing an efficiency of the module (10).
[0057] Referring now to component (C), this component typically
includes a curing catalyst. The catalyst may be of any type known
in the art and typically is selected from the group of condensation
catalysts, hydrosilylation catalysts, radical catalysts, UV
catalysts, thermal catalysts, and combinations thereof. Choice of
this catalyst may reduce production and processing times by >20%
and may eliminate certain production steps altogether, thereby
leading to decreased production costs and purchasing costs for the
end user.
[0058] More specifically, component (C) may include any suitable
hydrosilylation catalyst, such as the hydrosilylation catalyst
introduced and described above. The hydrosilylation catalyst can be
any of the well known hydrosilylation catalysts including a
platinum group metal, a compound containing a platinum group metal,
or a microencapsulated platinum group metal or compound containing
same. These metals typically include platinum, rhodium, ruthenium,
palladium, osmium and iridium. More specifically, component (C) may
include any suitable hydrosilylation catalyst, such as the
hydrosilylation catalyst introduced and described above. The
hydrosilylation catalyst can be any of the well known
hydrosilylation catalysts including a platinum group metal, a
compound containing a platinum group metal, or a microencapsulated
platinum group metal or compound containing same. These metals
typically include platinum, rhodium, ruthenium, palladium, osmium
and iridium. Platinum and platinum compounds are most typically
used based on their high activity level in hydrosilylation
reactions. Most typically, the catalyst is a hydrosilylation
catalyst and includes platinum. This catalyst may be a Karstedt
based platinum catalyst and/or may include fine platinum powder,
platinum black, chloroplatinic acid, an alcoholic solution of
chloroplatinic acid, an olefin complex of chloroplatinic acid, a
complex of chloroplatinic acid and alkenylsiloxane, a thermoplastic
resin including platinum, and combinations thereof. In various
embodiments, the catalyst is typically present in the curable
composition in an amount of from 0.01 to 1, more typically in an
amount of from 0.01 to 0.5, and most typically in an amount of from
0.01 to 0.3, parts by weight per one hundred parts by weight of the
curable composition. If the catalyst includes a metal, the metal
itself is typically present in the curable composition in an amount
of from 1 to 500, more typically of from 1 to 100, and most
typically of from 1 to 50, parts by weight per one million parts by
weight of the curable composition. Resins may be used in
conjunction with microencapsulated catalysts and may include, but
are not limited to, organosilicon resins and organic resins derived
from ethylenically unsaturated hydrocarbons and/or esters of
ethylenically unsaturated carboxylic acids, such as acrylic and
methacrylic acids.
[0059] In another embodiment, component (C) includes a peroxide
catalyst which is used for free-radical based reactions between
siloxanes including, but not limited to, .dbd.Si--CH.sub.3 groups
and other .dbd.Si--CH.sub.3 groups or .dbd.Si--CH.sub.3 groups and
.dbd.Si-alkenyl groups (typically vinyl), or .dbd.Si-alkenyl groups
and .dbd.Si-alkenyl groups. Suitable peroxide catalysts may
include, but are not restricted to, 2,4-dichlorobenzoyl peroxide,
benzoyl peroxide, dicumyl peroxide, tert-butyl perbenzoate.
1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane (TMCH)
(2,5-bis(t-butylperoxy)-2,5-dimethylhexane) catalyst,
1,1-bis(tert-amylperoxy)cyclohexane, ethyl
3,3-bis(tert-amylperoxy)butyrate,
1,1-bis(tert-butylperoxy)cyclohexane, and combinations thereof.
These catalysts may be utilized as a neat compound or in an inert
matrix (liquid or solid).
[0060] Typically, when one or more peroxide catalysts are used, a
temperature at which curing is initiated is generally
determined/controlled on a basis of a half-life of the catalyst.
However, a rate of cure and ultimate physical properties of the
curable compound and the tie layer (14) are controlled by a level
of unsaturation of compounds used to form the tie layer (14).
Additionally, reaction kinetics and physical properties can be
tuned by blending linear non-reactively endblocked polymers with
differing degrees of polymerization (dp) with
dimethylmethylvinyl-copolymers with or without vinyl
endblocking.
[0061] In yet another embodiment, component (C) includes a
condensation catalyst and may also include a combination of the
condensation catalyst with one or more silanes or siloxane based
cross-linking agents which include silicon bonded hydrolysable
groups such as acyloxy groups (for example, acetoxy, octanoyloxy,
and benzoyloxy groups), ketoximino groups (for example dimethyl
ketoxime and isobutylketoximino groups), alkoxy groups (for example
methoxy, ethoxy, and propoxy groups), alkenyloxy groups (for
example isopropenyloxy and 1-ethyl-2-methylvinyloxy groups), and
combinations thereof. It is also contemplated that condensation
catalysts may be used in component (C) when the curable composition
includes resin polymer blends that are prepared such that they form
a sheeting material that, on exposure to a moist atmosphere, reacts
to form a permanent network. Alternatively, condensation catalysts
may be used in component (C) when the curable composition includes
alkoxy-functional silicone polymers that are capable of co-reacting
with the moisture triggered polymers.
[0062] Component (C) may include any suitable condensation catalyst
known in the art. More specifically, the condensation catalyst may
include, but is not limited to, tin, lead, antimony, iron, cadmium,
barium, manganese, zinc, chromium, cobalt, nickel, aluminum,
gallium, germanium, zirconium, and combinations thereof.
Non-limiting particularly suitable condensation catalysts include
alkyltin ester compounds such as dibutyltin dioctoate, dibutyltin
diacetate, dibutyltin dimaleate, dibutyltin dilaurate, butyltin
2-ethylhexoate, 2-ethylhexoates of iron, cobalt, manganese, lead
and zinc, and combinations thereof.
[0063] Alternatively, the condensation catalyst may include
titanates and/or zirconates having the general formula Ti[OR].sub.4
or Zr[OR].sub.4 respectively, wherein each R may be the same or
different and represents a monovalent, primary, secondary or
tertiary aliphatic hydrocarbon group which may be linear or
branched and have from 1 to 10 carbon atoms. In one embodiment, the
condensation catalyst includes a titanate including partially
unsaturated groups. In another embodiment, the condensation
catalyst includes titanates and/or zirconates wherein R includes
methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl, and/or
branched secondary alkyl groups such as 2,4-dimethyl-3-pentyl, and
combinations thereof. Typically, when each R is the same, R is an
isopropyl group, branched secondary alkyl group or a tertiary alkyl
group, and, in particular, a tertiary butyl group. Alternatively,
the titanate may be chelated. Chelation may be accomplished with
any suitable chelating agent such as an alkyl acetylacetonate such
as methyl or ethylacetylacetonate. Examples of suitable titanium
and/or zirconium based catalysts are described in EP 1254192 which
is expressly incorporated herein by reference relative to these
catalysts. Typically, the condensation catalyst, if utilized, is
present in an amount of from 0.01 to 3% by weight of the total
curable composition.
[0064] Component (C) may alternatively include a cationic initiator
which can be used when the curable composition includes
cycloaliphatic epoxy functionality. Typically, the cationic
initiators are suitable for thermal and/or UV cure and may be used
when the curable composition includes iodonium or sulfonium salts
that will produce a cured network upon heating. In one embodiment,
the cationic initiator is used in combination with a radical
initiator. This combination can be cured by UV-visible irradiation
when sensitized with suitable UV-visible radical initiators such
those described above.
[0065] Referring now to component (D), this component typically
includes a cross-linking agent, chain extender, or a combinations
thereof. Each of the cross-linking agent and/or chain extender may
independently have a linear, partially branched linear, cyclic, or
a net-like structure. Component (D) may be included independently
of, or in combination with, the catalyst described above. Component
(D) may be any known in the art and typically includes a
polyorganosiloxane having at least two silicon-bonded hydrogen
atoms per molecule. Component (D) may promote a hydrosilylation or
addition cure reaction between an Si--H group (typically of the
cross-linking agent) and an Si-alkenyl group, e.g. a vinyl group of
the diorganopolysiloxane, to form an alkylene group between
adjacent silicon atoms (.dbd.Si--CH.sub.2--CH.sub.2--Si.dbd.).
Typical examples of component (D) are described in U.S. Pat. Nos.
6,020,409 and 6,169,155, which are hereby expressly incorporated by
reference relative to these cross-linking agents.
[0066] In various embodiments, component (D) includes a
polyorganosiloxane having at least two silicon-bonded hydrogen
atoms per molecule and the following average unit formula:
R.sup.i.sub.bSiO.sub.(4-b)/2
wherein each R.sup.i may be the same or different and may be a
hydrogen atom, an alkyl group such as methyl, ethyl, propyl, and
isopropyl groups, or an aryl group such as phenyl and tolyl groups,
and b is from 0 to 2. Particularly suitable examples of
polyorganosiloxanes include, but are not limited to, a
trimethylsiloxy-terminated polymethylhydrogensiloxane, a
trimethylsiloxy-terminated copolymer of methylhydrogensiloxane and
dimethylsiloxane, a dimethylhydrogensiloxy-terminated copolymer of
methylhydrogensiloxane and dimethylsiloxane, a cyclic polymer of
methylhydrogensiloxane, a cyclic copolymer of
methylhydrogensiloxane and dimethylsiloxane, an organopolysiloxane
composed of siloxane units expressed by the formula
(CH.sub.3).sub.3SiO.sub.1/2, siloxane units expressed by the
formula (CH.sub.3).sub.2HSiO.sub.1/2, and/or siloxane units
expressed by the formula SiO.sub.4/2, an organopolysiloxane
including siloxane units expressed by the formula
(CH.sub.3).sub.2HSiO.sub.1/2 or siloxane units expressed by the
formula CH.sub.3SiO.sub.3/2, an organopolysiloxane including
siloxane units expressed by the formula
(CH.sub.3).sub.2HSiO.sub.1/2, siloxane units expressed by the
formula (CH.sub.3).sub.2SiO.sub.2/2, and/or siloxane units
expressed by the formula CH.sub.3SiO.sub.3/2, a
dimethylhydrogensiloxy-terminated polydimethylsiloxane, a
dimethylhydrogensiloxy-terminated copolymer of methylphenylsiloxane
and dimethylsiloxane, a dimethylhydrogensiloxy-terminated copolymer
of a methyl (3,3,3-trifluoropropyl) siloxane and dimethylsiloxane,
a product formed from cyclic silicone hydride cross-linkers as
outlined in WO 2003/093349 or WO 2003/093369, each of which are
expressly incorporated herein by reference relative to these
cross-linkers, and combinations thereof. In one embodiment,
component (D) is further defined as a (poly)dialkylhydrogensilyl
terminated polymer such as a (poly)dimethylhydrogensilyl terminated
polydimethylsiloxane. Typically, this polymer acts as a chain
extender.
[0067] In another embodiment, component (D) is selected from the
group of silanes, siloxanes, and combinations thereof. Suitable
non-limiting examples of silanes and siloxanes include
alkyltrialkoxysilanes such as methyltrimethoxysilane (MTM) and
methyltriethoxysilane, alkenyltrialkoxy silanes such as
vinyltrimethoxysilane and vinyltriethoxysilane,
isobutyltrimethoxysilane (iBTM), ethyltrimethoxysilane,
vinyltriethoxysilane, phenyltrimethoxysilane, alkenyl alkyl
dialkoxysilanes such as vinyl methyl dimethoxysilane, vinyl
ethyldimethoxysilane, vinyl methyldiethoxysilane,
vinylethyldiethoxysilane, alkenylalkyldioximosilanes such as vinyl
methyl dioximosilane, vinyl ethyldioximosilane, vinyl
methyldioximosilane, vinylethyldioximosilane, alkoxytrioximosilane,
alkenyltrioximosilane, alkenylalkyldiacetoxysilanes such as vinyl
methyl diacetoxysilane, vinyl ethyldiacetoxysilane, vinyl
methyldiacetoxysilane, vinylethyldiacetoxysilane and
alkenylalkyldihydroxysilanes such as vinyl methyl dihydroxysilane,
vinyl ethyldihydroxysilane, vinyl methyldihydroxysilane,
vinylethyldihydroxysilane, methylphenyl-dimethoxysilane,
3,3,3-trifluoropropyltrimethoxysilane, methyltriacetoxysilane,
vinyltriacetoxysilane, ethyl triacetoxysilane, di-butoxy
diacetoxysilane, phenyl-tripropionoxysilane,
methyltris(methylethylketoximo)silane,
vinyl-tris-methylethylketoximo)silane,
methyltris(methylethylketoximino)silane,
methyltris(isopropenoxy)silane, vinyltris(isopropenoxy)silane,
ethylpolysilicate, n-propylorthosilicate, ethylorthosilicate,
dimethyltetraacetoxydisiloxane, alkylalkenylbis(N-alkylacetamido)
silanes such as methylvinyldi-(N-methylacetamido)silane, and
methylvinyldi-(N-ethylacetamido)silane, dialkylbis(N-arylacetamido)
silanes such as dimethyldi-(N-methylacetamido)silane,
dimethyldi-(N-ethylacetamido)silane,
alkylalkenylbis(N-arylacetamido) silanes such as
methylvinyldi(N-phenylacetamido)silane, dialkylbis(N-arylacetamido)
silanes such as dimethyldi-(N-phenylacetamido)silane, and
combinations thereof.
[0068] Alternatively, component (D) may have two but typically has
three or more silicon-bonded hydrolysable groups per molecule. If
component (D) is a silane and has three silicon-bonded hydrolysable
groups per molecule, component (D) may also include a
non-hydrolysable silicon-bonded organic group. These silicon-bonded
organic groups are typically hydrocarbyl groups which are
optionally substituted by halogen such as fluorine and chlorine.
Examples of suitable groups include, but are not limited to, alkyl
groups such as methyl, ethyl, propyl, and butyl groups, cycloalkyl
groups such as cyclopentyl and cyclohexyl groups, alkenyl groups
such as vinyl and allyl groups, aryl groups such as phenyl and
tolyl groups, aralkyl groups such as 2-phenylethyl groups, and
halogenated derivatives thereof. Most typically, the
non-hydrolysable silicon-bonded organic group is a methyl
group.
[0069] In another embodiment, component (D) includes one or more
silanes including hydrolysable groups such as acyloxy groups (e.g.
acetoxy, octanoyloxy, and benzoyloxy groups), ketoximino groups
(e.g. dimethyl ketoximo and isobutylketoximino groups), alkoxy
groups (e.g. methoxy, ethoxy, and propoxy groups), alkenyloxy
groups (e.g. isopropenyloxy and 1-ethyl-2-methylvinyloxy groups),
and combinations thereof. These siloxanes may be straight chained,
branched, or cyclic.
[0070] In one embodiment, component (D) has silicon-bonded hydrogen
atoms (Si--H moieties) and the diorganopolysiloxane has alkenyl
groups (e.g. vinyl groups) such that a mole ratio of silicon-bonded
hydrogen atoms in the cross-linking agent to alkenyl groups in the
diorganopolysiloxane is less than 0.9. In another embodiment,
component (D) is added to the curable composition in an amount such
that a mole number of silicon-bonded hydrogen atoms in component
(D) to a mole number of alkenyl groups in the diorganopolysiloxane
(Si-vinyl moieties), for example, is in the range of from 0.1:1.5
to 1:1.5, more typically of from 0.1:1 to 0.8:1, and most typically
of from 0.1:1 to 0.6:1. Alternatively, the ratio may be less than 1
or 0.4. If this ratio is too low, the density of cross-linking will
be too low and the tie layer (14) will be excessively fluid.
Conversely, if this ratio is too high, the tie layer (14) will be
excessively viscous. In one embodiment, component (D) is added in
an amount such that a mole ratio of silicon-bonded hydrogen atoms
in the cross-linking agent to the mole number of alkenyl groups in
components (A) and (B) is in the range of from 0.8:1 to 4:1. In
this embodiment, there is an excess of Si--H moieties (i.e. the
ratio is >1:1) which enhances adhesion between the substrate
(12) and the tie layer (14). In another embodiment, the ratio is
also >1:1 which enhances adhesion between the tie layer (14) and
the second tie layer (18). In a further embodiment, the ratio in
the tie layer (14) is <1 while the ratio in the second tie layer
(18) is >1 which increases adhesion and allows for efficient
encapsulation of the photovoltaic cell (16) between the tie layer
(14) and the second tie layer (18).
[0071] As described above, component (D) may be combined with the
aforementioned catalyst of component (C). In one embodiment,
component (D) includes oximosilanes and/or acetoxysilanes and is
combined with a tin catalyst such as diorganotin dicarboxylate,
dibutyltin dilaurate, dibutyltin diacetate, dimethyltin
bisneodecanoate, and combinations thereof. In another embodiment,
component (D) includes alkoxysilanes combined with titanate and/or
zirconate catalysts such as tetrabutyl titanate, tetraisopropyl
titanate, chelated titanates or zirconates such as diisopropyl
bis(acetylacetonyl)titanate, diisopropyl
bis(ethylacetoacetonyl)titanate, diisopropoxytitanium
bis(Ethylacetoacetate), and combinations thereof. Alternatively,
component (D) may include one or more silanes or siloxanes which
may include silicon bonded hydrolysable groups such as acyloxy
groups (for example, acetoxy, octanoyloxy, and benzoyloxy groups),
ketoximino groups (for example dimethyl ketoximo and
isobutylketoximino groups), alkoxy groups (for example methoxy,
ethoxy, and propoxy groups) and alkenyloxy groups (for example
isopropenyloxy and 1-ethyl-2-methylvinyloxy groups). In the case of
siloxanes, the molecular structure can be straight chained,
branched, or cyclic.
[0072] The curable composition may also include component (E). This
component typically includes a highly functional modifier. Suitable
modifiers include, but are not limited to, methyl vinyl cyclic
organopolysiloxane structures (E.sup.Vi.sub.x) and branched
structures such as (M.sup.ViE.sub.x).sub.4Q structures, which are
described in EP 1070734 which is expressly incorporated herein by
reference relative to these structures. If included, component (E)
is may be used in amounts determined by those of skill in the
art.
[0073] In addition to components (A-E), the curable composition may
further include a block copolymer and/or a mixture of a block
copolymer and a silicone resin. The block copolymer may be used
alone but is typically cured using one of the catalysts described
above. The block copolymer may include a thermoplastic elastomer
having a "hard" segment (i.e., having a glass transition point
T.sub.g.gtoreq.the operating temperature of the module (10)) and a
"soft" segment (i.e., having a glass transition point
T.sub.g.ltoreq.the operating temperature of the module (10)).
Typically, the soft segment is an organopolysiloxane segment. It is
contemplated that the block copolymer may be an AB, an ABA, or
(AB).sub.n block copolymer.
[0074] More specifically, these block co-polymers may be prepared
from a hard segment polymer prepared from an organic monomer or
oligomer or combination of organic monomers and/or oligomers
including, but not limited to, styrene, methylmethacrylate,
butylacrylate, acrylonitrile, alkenyl monomers, isocyanate monomers
and combinations thereof. Typically, the hard segment polymer is
combined or reacted with a soft segment polymer prepared from a
compound having at least one silicon atom such as an
organopolysiloxane polymer. Each of the aforementioned hard and
soft segments can be linear or branched polymer networks or
combination thereof.
[0075] Preferred block-copolymers for use in the present invention
include silicone-urethane and silicone-urea copolymers.
Silicone-urethane and silicone-urea copolymers, described in U.S.
Pat. Nos. 4,840,796 and 4,686,137, expressly incorporated herein by
reference relative to these copolymers, typically form materials
with good mechanical properties such as being elastomeric at room
temperature. Desired properties of these silicone-urea/urethane
copolymers can be optimized by varying a level of
polydimethylsiloxane (PDMS), a type of chain extender used, and a
type of isocyanate used. If included, the block copolymers are
typically present in the curable composition in an amount of from 1
to 100 parts by weight per 100 parts by weight of the curable
composition.
[0076] The curable composition may also include a curing inhibitor
to improve handling conditions and storage properties. The curing
inhibitor may be any known in the art and may include, but is not
limited to, methyl-vinyl cyclics, acetylene-type compounds, such as
2-methyl-3-butyn-2-ol, 2-phenyl-3-butyn-2-ol,
3,5-dimethyl-1-hexyn-3-ol, 1-ethynyl-1-cyclohexanol, 1,5-hexadiene,
1,6-heptadiene, 3,5-dimethyl-1-hexen-1-yne, 3-ethyl-3-buten-1-yne
and/or 3-phenyl-3-buten-1-yne, an alkenylsiloxane oligomer such as
1,3-divinyltetramethyldisiloxane, 1,3,5,7-tetravinyltetramethyl
cyclotetrasiloxane, or 1,3-divinyl-1,3-diphenyldimethyldisiloxane,
a silicon compound including an ethynyl group such as methyltris
(3-methyl-1-butyn-3-oxy) silane, a nitrogen compound such as
tributylamine, tetramethylethylenediamine, benzotriazole, a
phosphorus compound such as triphenylphosphine, sulphur compounds,
hydroperoxy compounds, maleic-acid derivatives thereof, and
combinations thereof. Alternatively, the curing inhibitor may be
selected from the curing inhibitors disclosed in U.S. Pat. Nos.
6,020,409 and 6,169,155, expressly incorporated herein by reference
relative to the curing inhibitors. If included, the curing
inhibitors are and is typically included in an amount of less than
3 parts by weight, more typically of from 0.001 to 3 parts by
weight, and most typically of from 0.01 to 1 part by weight, per
100 parts by weight of component (A). In one embodiment, the curing
inhibitor is further defined as methylvinylcyclosiloxane having a
viscosity of 3 mPas. with an average dp of 4, an average number
average molecular weight of 344 g/mol, and 31.4 weight percent of
Si-Vinyl bonds.
[0077] Each of the components (A-E) may be pre-reacted (or
tethered) together, also known in the art as bodying. In one
embodiment, silanol functional polymers are tethered to silanol
functional resins. This tethering typically involves condensation
and re-organization and can be carried out using base or acid
catalysis. Tethering can be further refined by the inclusion of
reactive or non-reactive organo-silane species.
[0078] Still further, the curable composition may include additives
such as fillers, extending fillers, reinforcing particulate
fillers, pigments, adhesion promoters, corrosion inhibitors, dyes,
diluents, anti-soiling additives, and combinations thereof.
Inclusion of such additives may be based on shelf-life, cure
kinetics and optical properties of the final tie layer (14) or
second tie layer (18). More specifically, the reinforcing
particulate fillers may include one or more finely divided
reinforcing particulate fillers such as high surface area fumed and
precipitated silicas, calcium carbonate, and/or additional
extending fillers such as crushed quartz, diatomaceous earths,
barium sulphate, iron oxide, titanium dioxide and carbon black,
talc, wollastonite, aluminite, calcium sulphate (anhydrite),
gypsum, calcium sulphate, magnesium carbonate, clays such as
kaolin, aluminum trihydroxide, magnesium hydroxide (brucite),
graphite, copper carbonate such as malachite, nickel carbonate such
as zarachite, barium carbonate such as witherite, strontium
carbonate such as strontianite, aluminum oxide, silicates
including, but not limited to, olivine groups, garnet groups,
aluminosilicates, ring silicates, chain silicates, and sheet
silicates, and combinations thereof. The olivine groups may
include, but are not limited to, forsterite, Mg.sub.2SiO.sub.4, and
combinations thereof. Non-limiting examples of the garnet groups
may include pyrope, Mg.sub.3Al.sub.2Si.sub.3O.sub.12, grossular,
Ca.sub.2Al.sub.2Si.sub.3O.sub.12, and combinations thereof. The
aluminosilicates may include, but are not limited to, sillimanite,
Al.sub.2SiO.sub.5, mullite, 3Al.sub.2O.sub.3.2SiO.sub.2, kyanite,
Al.sub.2SiO.sub.5 and combinations thereof. The ring silicates may
include, but are not limited to, cordierite,
Al.sub.3(MgFe).sub.2[Si.sub.4AlO.sub.18], and combinations thereof.
The chain silicates may include, but are not limited to,
wollastonite, Ca[SiO.sub.3], and combinations thereof. Suitable
examples of the sheet silicates that are not limiting may include
mica, K.sub.2Al.sub.14[Si.sub.6Al.sub.2O.sub.20](OH).sub.4,
pyrophyllite, Al.sub.4[Si.sub.8O.sub.20](OH).sub.4, talc,
Mg.sub.6[Si.sub.8O.sub.20](OH).sub.4, serpentine, asbestos,
Kaolinite, Al.sub.4[Si.sub.4O.sub.10](OH).sub.8, vermiculite, and
combinations thereof. Low density fillers may also be included to
reduce weight and cost per volume. Typically, the fillers are
transparent to light and substantially match a refractive index of
the silicone. The reinforcing particulate fillers also typically
include particles that are smaller than 1/4 of the wavelength of
light to avoid scattering. Thus, reinforcing particulate fillers
such as wollastonite, silica, quartz, titanium dioxide, hollow
glass spheres and clays, e.g. kaolin, are particularly preferred.
In one embodiment, the curable composition is not a gel if it
includes reinforcing particulate fillers.
[0079] When included in the curable composition, an amount of
filler depends on properties desired in tie layer (14) and/or
second tie layer (18). In one embodiment, the filler is typically
included in the curable composition in an amount of from 1 to 150
parts by weight per 100 parts by weight of the curable composition.
The aforementioned fillers may be surface treated with fatty acids
or fatty acid esters to make the fillers easier to handle and
obtain a homogeneous mixture with the other components of the
curable composition. In one embodiment, the filler is further
defined as a quartz filler having an average particle size of 5
.mu.m. In another embodiment, the second tie layer (18) does not
need to be transparent to light and includes a reinforcing
particulate filler which provides added strength to the second tie
layer (18) such that a second substrate is not required in the
module (10).
[0080] The curable composition may also include co-catalysts for
accelerating curing, optical brighteners, rheological modifiers,
adhesion promoters, pigments, heat stabilizers, flame retardants,
UV stabilizers, chain extenders, plasticizers, extenders,
fungicides and/or biocides, water scavengers, pre-cured silicone
and/or organic rubber particles to improve ductility and maintain
low surface tack, and combinations thereof. Each of these
components may be included in amounts as determined by one of skill
in the art.
[0081] Particularly preferred examples of suitable adhesion
promoters may include, but are not limited to,
vinyltriethoxysilane, acrylopropyltrimethoxysilane,
alkylacrylopropyltrimethoxysilane, allyltriethoxysilane,
glycidopropyltrimethoxysilane, allylglycidylether, hydroxydialkyl
silyl terminated methylvinylsiloxane-dimethylsiloxane copolymer, a
reaction product of hydroxydialkyl silyl terminated
methylvinylsiloxane-dimethylsiloxane copolymer with
glycidopropyltrimethoxysilane, bis-triethoxysilyl ethylene glycol,
hydroxydialkyl silyl terminated
methylvinylsiloxane-dimethylsiloxane copolymer, a reaction product
of hydroxydialkyl silyl terminated
methylvinylsiloxane-dimethylsiloxane copolymer with
glycidopropyltrimethoxysilane and bis-triethoxysilyl ethylene
glycol, a 0.5:1 to 1:2, and more typically a 1:1 mixture of the
hydroxydialkyl silyl terminated
methylvinylsiloxane-dimethylsiloxane copolymer and a
methacrylopropyltrimethoxysilane, and combinations thereof.
[0082] Suitable examples of the fire retardants include alumina
powder or wollastonite as described in WO 00/46817, which is
expressly incorporated herein by reference relative to these fire
retardants. The fire retardant may be used alone or in combination
with other fire retardants or a pigment such as titanium
dioxide.
[0083] In one embodiment, the curable composition is substantially
free of silicone resins. In another embodiment, the curable
composition is substantially free of thermoplastic resins. The
terminology "substantially free," as used immediately above, refers
to an amount of the silicone resins and/or thermoplastic resins in
the curable composition of less than 1,000, more typically of less
than 500, and most typically of less than 100, parts by weight per
one million parts by weight of the curable composition. In a
further embodiment, the curable composition does not have suitable
physical properties such that it could be classified as a hot melt
composition, i.e., as an optionally curable thermoset product that
is inherently high in strength and resistant to flow (i.e. high
viscosity) at room temperature.
[0084] The curable composition may be cured by any mechanism known
in the art. These mechanisms include, but are not limited to, a
hydrosilylation cure, a condensation cure, a radical cure, a heat
cure, a UV light cure, and combinations thereof. The curable
composition may be completely cured, partially cured, or
"pre-cured," as described in greater detail below.
[0085] In one embodiment, the curable composition is cured at a
temperature of from 25.degree. C. to 200.degree. C. Alternatively,
the curable composition may be cured at a temperature of from
50.degree. C. to 150.degree. C. or at a temperature of
approximately 100.degree. C. However, other temperatures may be
used, as selected by one of skill in the art. If the curable
composition is cured with heat, heating may occur in any suitable
oven or the like in either a batch or continuous mode. A continuous
mode is most preferred. Additionally, the curable composition may
be cured for a time of from 1 to 600 seconds. However, the curable
composition may be cured for a longer time, as selected by one of
skill in the art depending on application.
[0086] Relative to compositions including silicon atoms that are
cured via hydrosilylation mechanisms, and without intending to be
bound by any particular theory, it is believed that the depth of
penetration and the tack values depend, at least in part, on a
ratio of Si:H groups to vinyl groups in the compositions. Relative
to all types of compositions (such as those including silicon atoms
and those free of silicon atoms), it is also believed that the tack
values, and to a lesser extent the depth of penetration, depend, at
least in part, on a presence of chain extenders and/or
cross-linkers which increase density and complexity of the
compositions. Still further, it is believed that the presence of
long chain polymers, such as those having a viscosity of 450 mPas
at 25.degree. C., in the compositions, contributes to the tack
values and, to a lesser extent, the depth of penetration.
[0087] It is also contemplated that the curable composition may
include silicone-organic compounds, also known as silicone-organic
"hybrids." Suitable, non-limiting examples of silicone-organic
"hybrids" are described above and also include organosilicones,
organosiloxanes, compounds that have organic backbones and pendant
silicon-containing groups, and compounds that have silicone
backbones and pendant organic groups.
[0088] Referring back to the tie layer (14), the tie layer (14) is
disposed on the substrate (12). In one embodiment, the substrate
(12) is in direct contact with the tie layer (14), as shown in
FIGS. 2-4 and 6-9. However, the invention is not limited to such an
embodiment, i.e., the tie layer (14) may be physically separated
from the substrate (12) and remain "disposed on" the substrate
(12), as set forth in FIG. 5.
[0089] In one embodiment, the tie layer (14) has a thickness that
varies across the substrate (12). The thickness of the tie layer
(14) may be varied to minimize an amount of the tie layer that is
used, thereby reducing production costs of the module (10), and
also to simultaneously minimize or prevent "bottoming out" of
electrical leads (28, 30, 32, 34). The electrical leads (28, 30,
32, 34) are described in greater detail below. The terminology
"bottoming-out" refers to when the electrical leads (28, 30, 32,
34) contact the substrate (12) or second substrate (20) during
compression, such as during a step of compressing the photovoltaic
cell (16), the tie layer (14), and the substrate (12) which is also
described in greater detail below. This phenomenon is undesirable,
and is preferably minimized or eliminated. The tie layer (14)
typically may have a varying thickness of from 1 to 30, or
alternatively of from 1 to 25, 1 to 20, 3 to 17, 5 to 10, 5 to 25,
or 10 to 30, mils. In one embodiment, the tie layer (14) has a
varying thickness of from 10 to 15 mils. In another embodiment, the
tie layer (14) has a varying thickness of from 10 to 17 mils. In
still another embodiment, the tie layer (14) has a varying
thickness of from 12 to 15 mils. It is to be understood that the
tie layer (14) is not limited to these varying thicknesses. In one
embodiment, the tie layer (14) has a varying thickness and is
thicker across some portions of the substrate (12) and thinner
across other portions. In another embodiment, the tie layer (14)
has a thickness of from 1 to 10 mils across some portions of the
substrate (12) and has a thickness of from 10 to 30 mils across
other portions. In a further embodiment, the tie layer (14) has a
thickness of from 5 to 7 mils across some portions of the substrate
(12) and a thickness of from 12 to 15 mils across other
portions.
[0090] In one embodiment, the tie layer (14) is substantially free
of entrapped air (bubbles). The terminology "substantially free of
entrapped air" means that the tie layer (14) has no visible air
bubbles. In another embodiment, the tie layer (14) is totally free
of entrapped air including both visible and microscopic air
bubbles. The second tie layer (18), like the tie layer (14)
described immediately above, can also be substantially free or
totally free of entrapped air.
[0091] Referring back to the second tie layer (18), the second tie
layer (18) can be the same or different from the tie layer (14), as
described above. In one embodiment, the module (10) includes the
second tie layer (18) but does not include the second substrate
(20). In another embodiment, the second tie layer (18) is formed
from the curable silicone composition that is
hydrosilylation-curable. In this embodiment, the curable silicone
composition includes the organosilicon compound having the at least
one unsaturated moiety per molecule, the organohydrogensilicon
compound having the at least one silicon-bonded hydrogen atom per
molecule, and the hydrosilylation catalyst, described above. The
curable composition, the organosilicon compound, and/or the
organohydrogen silicon compound may be any known in the art.
[0092] When included in the module (10), the second tie layer (18)
is typically the same size as the substrate (12) and the
photovoltaic cell (16). However, in one embodiment, the second tie
layer (18) is smaller than the photovoltaic cell (16). Of course,
the instant invention is not limited to these dimensions.
[0093] In addition, the second tie layer (18) typically has a
thickness of from 1 to 50, more typically of from 3 to 30, and most
typically of from 4 to 15, mils. In various embodiments, the second
tie layer (18) has a thickness of from 1 to 30, 1 to 25, 1 to 20, 3
to 17, 5 to 10, 5 to 25, 10 to 15, 10 to 17, 12 to 15, or 10 to 30,
mils. In an additional embodiment, the second tie layer (18) has a
thickness of about 9 mils. Of course, the invention is not limited
to these thicknesses.
[0094] In one embodiment, the second tie layer (18) has high
transmission across visible wavelengths, long term stability to UV
light and provides long term protection to the photovoltaic cell
(16). Thus, in this embodiment, there is no need to dope the
substrate (12) with cerium due to the UV stability of the tie layer
(14).
[0095] In an alternative embodiment, the second tie layer (18) may
be any silicone encapsulant or any organic encapsulant, such as
ethyl vinyl acetate (EVA). In another embodiment, the second tie
layer (18) is further defined as an EVA film and/or a UV curable
urethane. In various other embodiments, the second tie layer (18)
is further defined as the silicone encapsulant that is a silicone
liquid or gel and/or a hot melt silicone sheet of the type
described in the applicant's co-pending application
PCT/US06/043073. EVA is a thermoplastic which melts at temperatures
above 80.degree. C. However, at temperatures of from about
25.degree. C. to less than about 80.degree. C., the EVA can be a
gel or can be gel-like. Organic encapsulants such as EVA can be
reformulated to form a gel or be gel-like at any temperature
including temperatures above 80.degree. C.
[0096] In addition to the substrate (12) and the tie layer (14)
disposed thereon, the module (10) also includes the photovoltaic
cell (16) disposed on the tie layer (14). The photovoltaic cell
(16) is typically in direct contact with the tie layer (14) but may
be spaced apart from the tie layer (14). The photovoltaic cell (16)
is also typically sandwiched between the tie layer (14) and the
second tie layer (18), as shown in FIGS. 3, 4, 6, 8 and 9. In
another embodiment, the photovoltaic cell (16) is sandwiched
between the tie layer (14) and the second tie layer (18) in
addition to being sandwiched between the substrate (12) and the
second substrate (20), as also shown in FIGS. 4, 6, 8 and 9. The
photovoltaic cell (16) typically has a thickness of from 50 to 250,
more typically of from 100 to 225, and most typically of from 175
to 225, micrometers. The photovoltaic cell (16) also typically has
a length and width of from 100.times.100 cm to 200.times.200 cm. In
one embodiment, the photovoltaic cell (16) has a length and width
of 125 cm each. In another embodiment, the photovoltaic cell (16)
has a length and width of 156 cm each. It is to be understood that
the instant invention is not limited to these dimensions.
[0097] The photovoltaic cell (16) may include large-area,
single-crystal, single layer p-n junction diodes. These
photovoltaic cells (16) are typically made using a diffusion
process with silicon wafers, also commonly referred to as sliced
wafers. Alternatively, the photovoltaic cell (16) may include thin
epitaxial deposits of (silicon) semiconductors on lattice-matched
wafers. In this embodiment, photovoltaic cells (16) including the
thin epitaxial deposits may be classified as either space or
terrestrial and typically have AM0 efficiencies of from 7 to 40%.
Further, the photovoltaic cell (16) may include quantum well
devices such as quantum dots, quantum ropes, and the like, and also
include carbon nanotubes. Without intending to be limited by any
particular theory, it is believed that these types of photovoltaic
cells (16) can have up to a 45% AM0 production efficiency. Still
further, the photovoltaic cell (16) may include mixtures of
polymers and nano particles that form a single multispectrum layer
which can be stacked to make multispectrum photovoltaic cells more
efficient and less expensive.
[0098] The photovoltaic cell (16) may include amorphous silicon,
monocrystalline silicon, polycrystalline silicon, microcrystalline
silicon, nanocrystalline silica, cadmium telluride, copper
indium/gallium selenide/sulfide, gallium arsenide, polyphenylene
vinylene, copper phthalocyanine, carbon fullerenes, and
combinations thereof in ingots, ribbons, thin films, and/or wafers.
The photovoltaic cell (16) may also include light absorbing dyes
such as ruthenium organometallic dyes. Most typically, the
photovoltaic cell (16) includes monocrystalline and polycrystalline
silicon.
[0099] The photovoltaic cell (16) also has a first side and a
second side. Typically the first side is opposite the second side.
However, the first and second sides may be adjacent each other.
Typically, one or more of the electrical leads (28, 30, 32, 34) are
attached to one or both of the first and second sides to connect a
series of modules (10) together and form a photovoltaic array. The
electrical leads (28, 30, 32, 34) may be of any size and shape and
typically are rectangular-shaped and have dimensions of
approximately 0.005 to 0.080 inches in length and/or width. In
various embodiments, the electrical leads (28, 30, 32, 34) have a
thickness of from 0.005 to 0.015, from 0.005 to 0.010, or from
0.007 to 0.010, inches. The electrical leads (28, 30, 32, 34) may
be of any type known in the art and may be disposed on any portion
of the module (10).
[0100] Typically, one electrical lead acts as an anode while
another electrical lead typically acts as a cathode. As described
in greater detail below, the module (10) of this invention may
include first, second, third, and fourth electrical leads (28, 30,
32, 34) disposed on the photovoltaic cell (16). These electrical
leads (28, 30, 32, 34) may be the same or may be different from
each other (i.e., made from the same material or from different
materials) and may include metals, conducting polymers, and
combinations thereof. In one embodiment, the first, second, third,
and fourth electrical leads (28, 30, 32, 34) include tin-silver
solder coated copper. In another embodiment, the first, second,
third, and fourth electrical leads (28, 30, 32, 34) include
tin-lead solder coated copper.
[0101] In one embodiment, as shown in FIGS. 7-9, the module (10)
includes first and second electrical leads (28, 30) spaced apart
from each other, disposed on the first side the photovoltaic cell
(16), and sandwiched between the photovoltaic cell (16) and the tie
layer (14). In this embodiment, the tie layer (14) typically has a
thickness of from 1 to 30 mils between the first electrical lead
(28) and the substrate (12). Also in this embodiment, the tie layer
(14) also typically has a thickness of from 1 to 30 mils between
the second electrical lead (30) and the substrate (12). In
addition, the tie layer typically has a different thickness across
a remainder of the substrate (12), e.g. of from 1 to 30 mils. In
various other embodiments, the thicknesses of the tie layers
described immediately above are further defined as from 1 to 30, 1
to 25, 1 to 20, 3 to 17, 5 to 10, 5 to 25, 10 to 15, 10 to 17, 12
to 15, or 10 to 30, mils. Typically, the thickness of the tie
layers is related to, or a function of, the thickness of the
electrical leads.
[0102] In another embodiment, the module (10) includes the second
tie layer (18) and the second substrate (20), and the first and
second electrical leads (28, 30) are spaced apart from one another
and disposed on opposite sides of the photovoltaic cell (16). In
addition, the first electrical lead (28) may be sandwiched between
the photovoltaic cell (16) and the tie layer (14), the second
electrical lead (30) is sandwiched between the photovoltaic cell
(16) and the second tie layer (18). In this embodiment, the tie
layer (14) has a thickness of from 1 to 30 mils between the first
electrical lead (28) and the substrate (12). Also in this
embodiment, the second tie layer (18) also has a thickness of from
1 to 30 mils between the second electrical lead (30) and the second
substrate (20). In addition, the tie layer (14) and/or the second
tie layer (18) typically have different thicknesses across a
remainder of the substrate (12) and/or the second substrate (20),
respectively, e.g. of from 1 to 30 mils. In various other
embodiments, the thicknesses of the tie layers described
immediately above are further defined as from 1 to 30, 1 to 25, 1
to 20, 3 to 17, 5 to 10, 5 to 25, 10 to 15, 10 to 17, 12 to 15, or
from 10 to 30, mils.
[0103] In yet another embodiment, as shown in FIG. 9, the module
(10) includes the second tie layer (18), the second substrate (20),
and third and fourth electrical leads (32, 34) each spaced apart
from one another and disposed on the second side of the
photovoltaic cell opposite the first side. The third and fourth
electrical leads (32, 34) may be the same or different from the
first and/or second electrical leads (28, 30). In other words, the
third and fourth electrical leads (32, 34) may be formed from the
same material or from different materials than the first and/or
second electrical leads (28, 30). In this embodiment, the third and
fourth electrical leads (32, 34) are sandwiched between the
photovoltaic cell (16) and the second tie layer (18). The second
tie layer (18) typically has a thickness of from 1 to 3 mils
between the third electrical lead (32) and the second substrate
(20) The second tie layer (18) typically also has a thickness of
from 1 to 30 mils between the fourth electrical lead (34) and the
second substrate (20). In addition, the second tie layer (18) has a
different thickness across a remainder of the second substrate
(20). In various embodiments, the thicknesses of the tie layers
described immediately above are further defined as from 1 to 30, 1
to 25, 1 to 20, 3 to 17, 5 to 10, 5 to 25, 10 to 15, to 17, 12 to
15, or from 10 to 30, mils. In a further embodiment, the second tie
layer (18) has a thickness at least equal to a thickness of said
third and fourth electrical leads (32, 34). In still another
embodiment, the module (10) includes the second substrate (20) that
is the same or different than the substrate (12), as described
above, and the photovoltaic cell (16) is further disposed on the
second substrate (20) via chemical vapor deposition or sputtering.
Typically, in this embodiment, no second tie layer (18) is
required.
[0104] This embodiment is typically referred to as a "thin-film"
application. Typically, after the photovoltaic cell (16) is
disposed on the second substrate (20) using sputtering or chemical
vapor deposition processing techniques, one or more of the
electrical leads (28, 30, 32, 34) are attached to the photovoltaic
cell (16). The curable composition may then be applied over the
electrical leads (28, 30, 32, 34) and cured to form the tie layer
(14).
[0105] As described above, the module (10) includes the substrate
(12), the tie layer (14), and the photovoltaic cell (16). These may
be present in the module (10) in any order. In one embodiment, as
shown in FIG. 2, the module (10) includes the following, in order:
the substrate (12), the tie layer (14) disposed directly on the
substrate (12), and the photovoltaic cell (16) disposed directly on
the tie layer (14). In another embodiment, as shown in FIG. 3, the
module (10) includes the following, in order: the substrate (12),
the tie layer (14) disposed directly on the substrate (12), the
photovoltaic cell (16) disposed directly on the tie layer (14), and
the second tie layer (18) disposed directly on the photovoltaic
cell (16). In a further embodiment, as shown in FIG. 4, the module
(10) includes the following, in order: the substrate (12), the tie
layer (14) disposed directly on the substrate (12), the
photovoltaic cell (16) disposed directly on the tie layer (14), a
second tie layer (18) disposed directly on the photovoltaic cell
(16), and the second substrate (20) disposed directly on the second
tie layer (18).
[0106] In addition, the module (10) may include a protective seal
(not shown in the Figures) disposed along each edge of the module
(10) to cover the edges. The module (10) may also be partially or
totally enclosed within a perimeter frame that typically includes
aluminum and/or plastic (also not shown in the Figures).
[0107] The module (10) of the instant invention can be used in any
industry. In one embodiment, a series of module (10) are
electrically connected and form a photovoltaic array (26), as set
forth in FIGS. 6A and 6B. More specifically, in FIG. 6, the
photovoltaic array (26) includes a series of modules of the type
shown in FIG. 4 that are electrically connected together. The
photovoltaic array (26) of the instant invention may be planar or
non-planar and typically functions as a single electricity
producing unit wherein the modules (10) are interconnected in such
a way as to generate voltage.
[0108] The present invention also provides a method of forming the
module (10). The method includes the step of disposing the tie
layer (14) on the substrate (12). This step may include any
suitable application method known in the art. In various
embodiments, the tie layer (14) is a liquid or a gel and the liquid
or gel is disposed on the substrate (12) using an application
method including, but not limited to, spray coating, flow coating,
curtain coating, dip coating, extrusion coating, knife coating,
screen coating, laminating, melting, pouring, and combinations
thereof. In an alternative embodiment, the curable composition is
applied to the substrate (12) by one or more of the aforementioned
methods and is then cured or pre-cured on the substrate (12) to
form the tie layer (14). Typically, the tie layer (14) is formed
from the curable composition and the method further includes the
step of partially curing, e.g. "pre-curing," the curable
composition to form the tie layer (14). As set forth herein, the
terminology "pre-curing" includes curing the curable composition
such that it forms the tie layer (14) having a depth of penetration
of from 1.1 to 100 mm and a tack value of less than -0.6 gsec. It
is to be understood that the terminology "pre-curing" can be used
interchangeably with "curing" throughout. In another embodiment,
the method further includes the steps of applying the curable
composition to the photovoltaic cell (16) and curing the curable
composition on the photovoltaic cell (16) to form the tie layer
(14). In this embodiment, the curable composition is typically
cured prior to the step of disposing the tie layer (14) on the
substrate (12). In other words, the curable composition may be
cured and the tie layer (14) may be formed completely independent
from the substrate (12). In this embodiment, the tie layer (14) may
be a pre-formed film, sheet, laminate, or the like or may be formed
into a film, sheet, laminate or the like. The method may also
include the step of curing the curable composition on the substrate
(12) prior to the step of disposing the photovoltaic cell (16) on
the tie layer (14). As set forth above, the curable composition is
typically cured at a temperature of from 25 to 200.degree. C. The
curable composition is also typically cured for a time of from 1 to
600 seconds. Alternatively, the curable composition may be cured in
a time of greater than 600 seconds, as determined by one of skill
in the art.
[0109] In one embodiment, the curable composition is a liquid and
the step(s) of applying is further defined as applying a liquid. In
another embodiment, the curable composition is supplied to a user
as a multi-part system. A first part may include components (A),
(B), and/or (D), as described above. A second part may include
components (A), (B), and/or (C), as also described above. The first
and second parts are typically mixed immediately prior to the
step(s) of applying. Alternatively, each component and/or a mixture
of components of the curable composition may be applied
individually and then react to form the tie layer (14).
[0110] In one embodiment, the method includes the step of applying
a base amount of the curable composition on the substrate (12)
resulting in a first thickness (T.sub.1) of from 5 to 25 mils
across the substrate (12), as set forth in FIGS. 7-9. The method
also includes the step of applying a first supplemental amount of
the curable composition between the first electrical lead (28) and
the substrate (12) resulting in a second thickness (T.sub.2) of
from 10 to 30 mils about the first electrical lead (28), as also
set forth in FIGS. 7-9. The method further includes the step of
applying a second supplemental amount of the curable composition
between the second electrical lead (30) and the substrate (12)
resulting in a third thickness (T.sub.3) of from 10 to 30 mils
about the second electrical lead (30), as further set forth in
FIGS. 7-9. Still further, the curable composition is cured after
the amounts have been applied to form the tie layer (14). In other
words, in this embodiment, the base amount of the curable
composition is not cured before the first and second supplemental
amounts are applied. In addition, the method includes the step of
disposing the photovoltaic cell (16) on the tie layer (14) to form
the module (10).
[0111] Typically, the first and/or second supplemental amounts are
applied on the first thickness (T.sub.1). However, the first and/or
second supplements amounts may be applied only on one portion of
the substrate (12) or, in the alternative, across an entirety of
the substrate (12), and may be applied directly on the substrate as
opposed to on the first thickness (T.sub.1). The first thickness
(T.sub.1) is typically further defined as from 5 to 7 mils, while
the second and/or third thicknesses (T.sub.2, T.sub.3) are
typically each independently be further defined as from 12 to 15
mils.
[0112] The step(s) of applying the first and/or second supplemental
amounts of the curable composition may occur sequentially or
simultaneously. In one embodiment, the steps of applying the first
and second supplemental amounts of the curable composition occur
after the step of applying the base amount. Alternatively, the
steps of applying the first and second supplemental amounts of the
curable composition may occur before the step of applying the base
amount.
[0113] The method also includes the step of disposing the
photovoltaic cell (16) on the tie layer (14) to form the module
(10). Typically, the photovoltaic cell (16) is disposed on the tie
layer (14) after the curable composition is cured. However, the
invention is not limited to this embodiment. The photovoltaic cell
(16) can be disposed (e.g. applied) by any suitable mechanisms
known in the art but is typically applied using an applicator in a
continuous mode. Other suitable mechanisms of application include
applying a force to the photovoltaic cell (16) to more completely
contact the photovoltaic cell (16) and the tie layer (14). In one
embodiment, the method includes the step of compressing the
photovoltaic cell (16) and the tie layer (14). Compressing the
photovoltaic cell (16) and the tie layer (14) is believed to
maximize contact between the two and maximize encapsulation, if
desired. As set forth above, it is to be understood that even if
the method includes the step of compressing, the photovoltaic cell
(16) and the tie layer (14) do not need to be in direct contact.
The step of compressing is typically further defined as applying a
vacuum to the photovoltaic cell (16) and the tie layer (14).
Alternatively, a mechanical weight, press, or roller (e.g. a pinch
roller) may be used for compression. In one embodiment, the step of
compressing is further defined as compressing using the cell press
described in U.S. Provisional Patent Application No. 61/036,748,
which is expressly incorporated herein by reference. The tie layer
(14) and/or curable composition may be applied to the substrate
(12) and/or to the photovoltaic cell (16) outside of the cell press
or within the cell press. Similarly, the curable composition may be
cured or pre-cured on or apart from the substrate (12) and/or the
photovoltaic cell (16) to form the tie layer (14) either outside of
the cell press or within the cell press. Further, the step of
compressing may be further defined as laminating. Still further,
the method may include the step of applying heat to the module (10)
or any or all of the substrate (12), the tie layer (14), the
photovoltaic cell (16), the second (18) (or multiple) tie layers,
and/or the second substrate (20). Heat may be applied in
combination with any other step or may be applied in a discrete
step. The entire method may be continuous or batch-wise or may
include a combination of continuous and batch-wise steps.
[0114] The step of disposing the photovoltaic cell (16) on the tie
layer (14) may be further defined as encapsulating at least part of
the photovoltaic cell (16) with the tie layer (14) and/or the
second tie layer (18). More specifically, the tie layer (14) and/or
second tie layer (18) may partially or totally encapsulate the
photovoltaic cell (16). Alternatively, the photovoltaic cell (16)
may simply be disposed on the tie layer (14) without any
encapsulation. Without intending to be limited by any particular
theory, it is believed that at least partial encapsulation
encourages more efficient manufacturing and better utilization of
the solar spectrum, thereby resulting in greater efficiency. Use of
the tie layer (14) of the instant invention allows for production
of a module (10) with the optical and chemical advantages of
silicone. Additionally, use of silicone allows for formation of UV
transparent tie layers (14) and may increase cell efficiency by at
least 1-5%. Use of peroxide catalysts, as described above, may also
provide better transparency and increased cure speeds. Sheets of
the curable composition including silicone may be used to assemble
the module (10).
[0115] In an additional embodiment, the method also includes the
step of applying a second base amount of the curable composition
across the second substrate (20). Typically, the second base amount
of the curable composition has a thickness at least equal to that
of the third and fourth electrical leads (32, 34). In various
embodiments, the second base amount of the curable composition has
a thickness of from 1 to 30, 1 to 25, 1 to 20, 3 to 17, 5 to 10, 5
to 25, 10 to 15, 10 to 17, 12 to 15, or to 30, mils.
[0116] In yet another embodiment of the instant method, the curable
composition may be further defined as a film and the step(s) of
applying may be further defined as applying the film. In this
embodiment, the step of applying the film may be further defined as
melting the film. Alternatively, the film may be laminated. In
still another embodiment, the method includes the steps of applying
the protective seal and/or the frame to the module (10), as first
introduced above.
[0117] In an alternative embodiment, the method includes the step
of applying the photovoltaic cell (16) to the substrate (12) by
chemical vapor deposition or physical sputtering. This step may be
performed by any mechanisms known in the art.
[0118] The method may also include the step of applying the second
tie layer (18). The second tie layer (18) may be applied to the
photovoltaic cell (16), the first tie layer (14), the substrate
(12), and/or the second substrate (20). The method may further
include the step of applying the second substrate (20). The second
substrate (20) may be applied to the photovoltaic cell (16), the
first tie layer (14), the substrate (12), and/or the second tie
layer (18).
[0119] This invention also provides a method of forming the module
(10), wherein the module is commonly known as a "thin-film" module.
In this embodiment of the method, the module (10) includes the
substrate (12), the tie layer (14) disposed on the substrate (12),
the photovoltaic cell (16), the first and second electrical leads
(22, 24) each spaced apart from one another, disposed on the first
side of the photovoltaic cell (16), and sandwiched between the
photovoltaic cell (16) and the tie layer (14), and the second
substrate (20) that is the same or different than the substrate
(12), as described above. Typically, in this embodiment, no second
tie layer (18) is required. This method typically includes the
steps of applying the base amount of the curable composition on the
substrate (12) resulting in the first thickness of from 5 to 25
mils on the substrate (12) and applying the first supplemental
amount of the curable composition between the first electrical lead
(22) and the substrate (12) resulting in the second thickness of
from 10 to 30 mils about the first electrical lead (22). This
method also typically includes the steps of applying the second
supplemental amount of the curable composition between the second
electrical lead (24) and the substrate (12) resulting in the third
thickness of from 10 to 30 mils about the second electrical lead
(24) and curing the curable composition after the amounts have been
applied to form the tie layer (12). Still further, this method
typically includes the steps of disposing the photovoltaic cell
(14) on the second substrate (20) via chemical vapor deposition or
physical sputtering and then disposing the photovoltaic cell (16)
on the tie layer (12) to form the module (10). In one embodiment,
the method also includes the steps of disposing the first and
second electrical leads (22, 24) on the first side of the
photovoltaic cell (16) after the photovoltaic cell (16) is disposed
on the second substrate (20) via chemical vapor deposition or
physical sputtering.
EXAMPLES
[0120] Two tie layers (Layers 1 and 2) are formed according to the
instant invention. In addition, two comparative tie layers
(Comparative Layers 1 and 2) are also formed but not according to
the instant invention. During and after formation, each of the
Layers 1 and 2 and the Comparative Layers 1 and 2 are evaluated to
determine viscosity, Shore 00 durometer hardness, hardness, depth
of penetration, and tack value. The formulations used to form
Layers 1 and 2 and the Comparative Layers 1 and 2, in addition to
the measurements of viscosity, Shore 00 durometer hardness,
hardness, depth of penetration, and tack value are set forth in
Table 1 below wherein all parts are in parts by weight, unless
otherwise indicated.
TABLE-US-00001 TABLE 1 Comparative Comparative Layer 1 Layer 2
Layer 1 Layer 2 Formulation Polymer 1 98.98 48.81 35.1 80.49
Polymer 2 -- 41.87 -- -- Polymer 3 -- -- -- 11.04 Polymer 4 -- 4.06
-- 7.73 Polymer 5 0.9 0.13 1.44 0.49 Polymer 6 -- 5.38 -- -- Cure
0.04 0.01 0.19 0.17 Inhibitor Catalyst 1 0.08 -- 0.09 -- Catalyst 2
-- 0.14 -- 0.08 Filler -- -- 55.38 -- Pigment -- -- 7.57 --
Adhesion -- -- 0.23 -- Promoter Total Weight 100.00 100.00 100.00
100.00 percent SiH:SiVi 0.39 0.87 1.12 0.94 Ratio Pt 4.7 12.5 5.4
6.6 Concentration (ppm) Viscosity 403 296 3750 392 (mPa s) Shore 00
0 0 75 58 Durometer Hardness Hardness 11.5 72.4 6066 501 (grams of
force) Depth of 46.5 7.4 0.09 1.07 Penetration (mm) Elastic 7.75
.times. 10.sup.3 4.6 .times. 10.sup.4 4.5 .times. 10.sup.6 6.9
.times. 10.sup.5 Modulus G' at Cure (dynes/cm.sup.2) Tack Value
Area F-T 3:4 -27.4 -27.8 0 -0.56 (g.sec) Time 1 (sec) 67.0 64.90 0
65.74 Time 2 (sec) 73.0 66.78 0 65.98 Time 2 - 1 6.0 1.88 0 0.24
(sec)
[0121] Polymer 1 is a vinyldimethylsilyl end-blocked
polydimethylsiloxane having a viscosity of 450 mPas at 25.degree.
C. and including 0.46 weight percent Si-Vinyl bonds.
[0122] Polymer 2 is a trimethylsilyl terminated
polydimethylsiloxane that has a viscosity of 100 mPas and that is
commercially available from Dow Corning Corporation of Midland,
Mich.
[0123] Polymer 3 is a polymer/filler blend of 80% by weight of
Polymer 1 and 20% by weight of (CH.sub.3).sub.3SiO.sub.3/2 treated
fumed silica, has a viscosity of 120,000 mPas and has 0.37 weight
percent of Si-Vinyl bonds.
[0124] Polymer 4 is a dimethylhydrogensilyl terminated
polydimethylsiloxane that has a viscosity of 10 mPas and 0.16
weight percent of Si--H bonds.
[0125] Polymer 5 is a trimethylsilyl terminated
polydimethylsiloxane-methylhydrogensiloxane co-polymer having a
viscosity of 5 mPas and including 0.76 weight percent of Si--H
bonds.
[0126] Polymer 6 is a vinyldimethylsilyl endblocked
polydimethylsiloxane having a viscosity of 55,000 mPas. and
including 0.09 weight percent of Si-Vinyl bonds.
[0127] Cure Inhibitor is methylvinylcyclosiloxane having a
viscosity of 3 mPas. with an average dp of 4, an average number
average molecular weight of 344 g/mol, and 31.4 weight percent of
Si-Vinyl bonds.
[0128] Catalysts 1 and 2 are platinum catalysts including platinum
complexes of 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane.
[0129] Filler is a quartz filler having an average particle size of
5 .mu.m.
[0130] Pigment is a blend of 82 weight percent of Polymer 1, 12
weight percent of ZnO powder, and 6 weight percent of carbon black
powder, has a viscosity of 20,000 mPas., and has 0.38 weight
percent of Si-Vinyl bonds.
[0131] Adhesion Promoter is a reaction product of trimethylsilyl-
and dimethylvinylsilyl-treated silica and an organofunctional
silane and has a viscosity of 25 mPas.
[0132] The viscosity measurements of the Layers 1 and 2 and the
Comparative Layers 1 and 2 are taken using a Brookfield DVIII Cone
and Plate Viscometer at 25.degree. C. according to ASTM D4287. More
specifically, a 0.5 g sample of each of the Layers is tested using
a CPE 51 spindle and a speed of the spindle is varied to keep
torque in the required range.
[0133] Durometer hardness measurements are taken by placing 12 g of
each of the Layers in a 44 ml aluminum weigh dish and curing each
of the Layers 100.degree. C. for 10 minutes, according to ASTM
D2240. 1 inch (2.54 cm) diameter circular discs are then punched
out from each of the cured layers and analyzed using a Shore 00
Durometer.
[0134] Hardness measurements are taken using a TA-XT2 Texture
Analyzer commercially available from Stable Micro Systems using a
0.5 inch (1.27 cm) diameter steel probe. Test samples of 12 g of
each of the uncured layers are cured in a 2 ounce (oz) glass vial
at 100.degree. C. for 10 minutes. Samples are analyzed using the
following Texture Analyzer test method: 2 mm/s pre-test and
post-test probe speed; 1 mm/s test probe speed; 4 mm target
distance; 60 sec hold; and a 5 g Force trigger value. The maximum
grams force hardness is determined at a 4 mm distance.
[0135] Depth of Penetration measurements are calculated using the
hardness measurements (grams of force) obtained using the TA-XT2
Texture Analyzer and the following equation: Depth of Penetration
(mm.times.10)=5,350/grams force. This relationship is determined
using a universal penetrometer, commercially available from
Precision Scientific of Chicago, Ill., and by measuring hardness
with the texture analyzer of each Layer. There are seventy nine
sample measurements taken for each layer. The 5,350 constant is
determined by multiplying the depth of penetration by the grams of
force from the texture analyzer for each of the seventy nine
samples and then averaging the results.
[0136] Tack values are determined using a Stable Micro Systems TA
XT2 Texture Analyzer. A 0.5 inch diameter stainless steel probe is
inserted into 12 gram samples of each of the Layers to a depth of 4
mm and then withdrawn at a rate of 2 mm/s. The tack values are
determined as a total area under a Force-Time curve during probe
separation from the Layers. The results in Force-Time are expressed
in gramsec. wherein the time is measured as a time difference
between a time when the force is equal to zero and a time when the
probe separates from the layers.
[0137] After formation, both of the Layers 1 and 2 are used to
assemble modules (Modules 1-6) of the instant invention. The
Comparative Layers 1 and 2 are used to form Comparative Modules 1
and 2 but not via the method of the instant invention. The
terminology "front contact" and "back contact" are well known in
the art and refer to a side of the photovoltaic cell (16) upon
which one of the Layers 1 and 2 or Comparative Layers 1 and 2 are
disposed.
Module 1:
[0138] Module 1 includes a Substrate (12) including glass; 15 mils
of Layer 1 disposed on the Substrate (12), and a "front contact"
polycrystalline Photovoltaic Cell (16) disposed on Layer 1.
Module 2:
[0139] Module 2 includes a Substrate (12) including glass; 15 mils
of Layer 1 disposed on the Substrate (12), and a "front contact"
monocrystalline Photovoltaic Cell (16) disposed on Layer 1.
Module 3:
[0140] Module 3 includes a Substrate (12) including glass; 10 mils
of Layer 1 disposed on the Substrate (12), and a "back contact"
monocrystalline Photovoltaic Cell (16) disposed on Layer 1.
Module 4:
[0141] Module 4 includes a Substrate (12) including glass; 15 mils
of Layer 2 disposed on the Substrate (12), and a "front contact"
polycrystalline Photovoltaic Cell (16) disposed on Layer 1.
Module 5:
[0142] Module 5 includes a Substrate (12) including glass; 15 mils
of Layer 2 disposed on the Substrate (12), and a "front contact"
monocrystalline Photovoltaic Cell (16) disposed on Layer 1.
Module 6:
[0143] Module 6 includes a Substrate (12) including glass; 10 mils
of Layer 2 disposed on the Substrate (12), and a "back contact"
monocrystalline Photovoltaic Cell (16) disposed on Layer 1.
Comparative Module 1:
[0144] Comparative Module 1 includes a Substrate (12) including
glass; 15 mils of Comparative Layer 1 disposed on the Substrate
(12), and a "front contact" monocrystalline Photovoltaic Cell (16)
disposed on Layer 1.
Comparative Module 2:
[0145] Comparative Module 2 includes a Substrate (12) including
glass; 15 mils of Comparative Layer 2 disposed on the Substrate
(12), and a "front contact" monocrystalline Photovoltaic Cell (16)
disposed on Layer 1.
[0146] After formation, each of the Modules 1-6 and the Comparative
Modules 1 and 2 are evaluated to determine an amount of air
entrapped in the Layers 1 or 2 or the Comparative Layers 1 or 2,
respectively. The Modules are also evaluated to determine Adhesion
of the Substrate (12), the Layers, and the Photovoltaic Cells (16).
Both of these determinations are set forth in Table 2 below and
both are based on visual evaluations.
TABLE-US-00002 TABLE 2 Comp. Comp. Mod. 1 Mod. 2 Mod. 3 Mod. 4 Mod.
5 Mod. 6 Mod. 1 Mod. 2 Amount 0 0 0 0 0 0 Visible Visible of
Trapped Air Adhesion Yes Yes Yes Yes Yes Yes No No
[0147] In addition, both of the Layers 1 and 2 are used to assemble
additional modules (Modules 7 and 8) according to the method of
this invention. Further, Comparative Modules 3 and 4 are formed
using the Comparative Layers 1 and 2.
Module 7:
[0148] Module 7 includes a Substrate (12) including glass, Layer 1
disposed on the substrate, a monocrystalline Photovoltaic Cell
(16), and First and Second Electrical Leads (28, 30) each spaced
apart from one another, disposed on a first side of the
Photovoltaic Cell (16) and sandwiched between the Photovoltaic Cell
(16) and Layer 1. More specifically, Module 7 includes 5-10 mils of
Layer 1 formed from the composition described above and disposed
across the Substrate (12), 10 to 17 mils of Layer 1 between the
First Electrical Lead (28) and the Substrate (12) resulting in a
thickness of from 10 to 17 mils of Layer 1 about the First
Electrical Lead (28) and 10 to 17 mils of Layer 1 between the
Second Electrical Lead (30) and the Substrate (12) resulting in a
thickness of from 10 to 17 mils of Layer 1 about the Second
Electrical Lead (30).
Module 8:
[0149] Module 8 includes a Substrate (12) including glass, Layer 2
disposed on the substrate, a monocrystalline Photovoltaic Cell
(16), and First and Second Electrical Leads (28, 30) each spaced
apart from one another, disposed on a first side of the
Photovoltaic Cell (16) and sandwiched between the Photovoltaic Cell
(16) and Layer 2. More specifically, Module 8 includes 5-10 mils of
Layer 2 formed from the composition described above and disposed
across the Substrate (12), 10 to 17 mils of Layer 2 between the
First Electrical Lead (28) and the Substrate (12) resulting in a
thickness of from 10 to 17 mils of Layer 2 about the First
Electrical Lead (28) and 10 to 17 mils of Layer 2 between the
Second Electrical Lead (30) and the Substrate (12) resulting in a
thickness of from 10 to 17 mils of Layer 2 about the Second
Electrical Lead (30).
Comparative Module 3:
[0150] Comparative Module 3 includes a Substrate (12) including
glass; 15 mils of Comparative Layer 1 disposed across an entirety
of Substrate (12), a monocrystalline Photovoltaic Cell (16)
disposed on Layer 1, and first and second electrical leads (22, 24)
disposed on the photovoltaic cell (16).
Comparative Module 4:
[0151] Comparative Module 4 includes a Substrate (12) including
glass; 15 mils of Comparative Layer 2 disposed across an entirety
of Substrate (12), a monocrystalline Photovoltaic Cell (16)
disposed on Layer 1, and first and second electrical leads (22, 24)
disposed on the photovoltaic cell (16).
[0152] After formation, each of the Modules 7 and 8 and the
Comparative Modules 3 and 4 are also evaluated to determine an
amount of air entrapped in the Layers 1 and 2 and Comparative
Layers 1 and 2 and evaluated to determine Adhesion of the Substrate
(12), the Layers, and the Photovoltaic Cells (16) and whether the
Photovoltaic Cell (16) is securely disposed within the Modules.
These determinations are set forth in Table 3 below and are based
on visual evaluations.
TABLE-US-00003 TABLE 3 Comparative Comparative Module 7 Module 8
Module 3 Module 4 Amount of 0 0 Visible Visible Trapped Air
Adhesion Yes Yes No No Photovoltaic Cell Yes Yes No No Securely
Disposed Within Module
[0153] As shown above in Tables 2 and 3 above, the Modules 1-8 of
the instant invention do not include visible air bubbles trapped in
the Layers. This increases adhesion and overall stability of the
Modules, provides better aesthetic performance, reduces potential
erosion due to condensation, and prevents degradation of efficiency
due to light reflection off of air bubbles. The Modules of the
instant invention also exhibit adhesion, i.e., structural
stability, between the Substrate (12), the Layers, and the
Photovoltaic Cell (16). Conversely, the Comparative Modules 1-4 do
not exhibit adequate adhesion to form a unified and functioning
module. Without intending to be limited by any particular theory,
it is believed that this is due to the presence of the air bubbles
and the inability of the Comparative Layers 1 and 2 to adequately
"wet" the Substrates (12) and bond the Substrates (12) to the
Photovoltaic Cells (16).
[0154] In addition, the Modules of the instant invention allow the
Photovoltaic Cell to be securely disposed therein, while the
Comparative Modules 1 and 2 do not. The determination of whether
the Photovoltaic Cells are securely disposed within the Modules is
determined visually on a "pass/fail" basis. Without intending to be
limited by any particular theory, it is believed that the poor
adhesion and the lack security of the Photovoltaic Cells in the
modules is due to the presence of the air bubbles and the inability
of the Comparative Layers 1 and 2 to adequately "wet" the
Substrates (12) and bond the Substrates (12) to the Photovoltaic
Cells (16).
[0155] Further, the minimized amount of the Layers 1 and 2 used in
the Modules 7 and 8 and the strategic deposition of the Layers 1
and 2 around the first and second electrical leads, not only
provide superior Modules but also allow the Modules to be produced
faster and with less cost than the Comparative Modules 1-4 which
are formed using excess amounts of the Comparative Layers 1 and 2.
In addition, the strategic deposition of the Layers 1 and 2 around
the first and second electrical leads allows the Modules to be
formed with minimized deformation of the photovoltaic cell and
without cracking the photovoltaic cell upon compression.
[0156] The invention has been described in an illustrative manner,
and it is to be understood that the terminology which has been used
is intended to be in the nature of words of description rather than
of limitation. Many modifications and variations of the present
invention are possible in light of the above teachings, and the
invention may be practiced otherwise than as specifically
described.
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