U.S. patent application number 09/891752 was filed with the patent office on 2002-01-31 for partially transparent photovoltaic modules.
Invention is credited to Liu, Shengzhong, Oswald, Robert S..
Application Number | 20020011641 09/891752 |
Document ID | / |
Family ID | 27396278 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020011641 |
Kind Code |
A1 |
Oswald, Robert S. ; et
al. |
January 31, 2002 |
Partially transparent photovoltaic modules
Abstract
A photovoltaic cell comprising a supporting substrate, a front
contact layer on the substrate, a layer or layers of semiconductor
material and a back contact layer comprising a metal, the back
contact having areas without metal thereby permitting the passage
of light through the cell.
Inventors: |
Oswald, Robert S.;
(Mechanicsville, VA) ; Liu, Shengzhong;
(Mechanicsville, VA) |
Correspondence
Address: |
BP America Inc.
Docket Clerk, BP Legal, M.C. 2207A
200 East Randolph Drive
Chicago
IL
60601
US
|
Family ID: |
27396278 |
Appl. No.: |
09/891752 |
Filed: |
June 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60216415 |
Jul 6, 2000 |
|
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60220346 |
Jul 24, 2000 |
|
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60221627 |
Jul 28, 2000 |
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Current U.S.
Class: |
257/447 ;
257/448; 438/96 |
Current CPC
Class: |
H01L 31/0468 20141201;
Y02E 10/50 20130101; H02S 20/10 20141201; H01L 31/046 20141201;
H01L 31/0463 20141201 |
Class at
Publication: |
257/447 ; 438/96;
257/448 |
International
Class: |
H01L 021/00; H01L
031/00 |
Claims
That which is claimed is:
1. A method for making a thin film partially transparent
photovoltaic module comprising series connected cells, at least one
amorphous semiconductor layer, a metal contact layer, and
interconnects connecting the series connected cells, the method
comprising laser scribing a plurality of laser scribes at least
through the metal contact and positioning the scribes in a
direction that crosses the direction of the interconnects.
2. The method of claim 1 further comprising bus bars located
adjacent the first and last cell in the module and wherein the
scribes extend across the surface of the photovoltaic module but
not including the bus bars.
3. The method of claim 1 wherein the laser scribes are formed by
using a laser to ablate semiconductor material which bursts through
the metal contact layer to form the scribes.
4. The method of claim 1 wherein the laser used to ablate the
semiconductor material is selected from the group consisting of
Nd-YAG, Nd:YFL and Nd:YVO.sub.4 lasers.
5. The method of claim 1 wherein each scribe has a width of about
0.01 to about 0.5 mm and the scribes are spaced from each other
about 0.5 to about 5 mm.
6. The method of claim 5 wherein each scribe has a width of about
0.05 to about 0.2 mm.
7. The method of claim 6 wherein the scribes are spaced from each
other about 0.5 to about 2 mm.
8. The method of claim 6 wherein no more than about 50 percent of
the area of the metal contact layer comprises the laser
scribes.
9. The method of claim 6 wherein no more than about 20 percent of
the area of the metal contact layer comprises the laser
scribes.
10. The method of claim 1 wherein the laser scribes are positioned
in a direction that is perpendicular to the direction of the
interconnects.
11. The method of claim 1 wherein the scribes are in the form of a
series of interconnected holdes.
12. The method of claim 11 wherein the holes are round and have a
diameter of about 0.1 to about 0.2 mm.
13. The method of claim 1 wherein the scribes are parallel to each
other.
14. The method of claim 1 wherein the scribes are grouped in bands
of closely spaced scribes separated by bonds having few or no
scribes.
15. The method of claim 14 wherein each scribe has a width of about
0.05 to about 0.2 mm and are spaced from each other about 0.5 to
about 2 mm.
16. The method of claim 1 wherein the laser scribes are spaced from
each other and the spacing is graded in at least a portion of the
module.
17. A method of making a partially transparent photovoltaic module
comprising series connected cells, at least one amorphous
semiconductor layer, a metal contact layer, and interconnects
connecting the series-connected cells, the method comprising at
least one selected from the group consisting of (a) laser scribing
a plurality of scribes at least through the metal contact in a
direction that crosses the direction of the interconnects and (b)
selectively removing at least portions of the metal contact in a
preselected pattern to impart a design, lettering, logo or other
descriptive pattern on the photovoltaic module.
18. The method of claim 17 wherein the method comprises selectively
removing at least portions of the metal contact in a preselected
pattern to impart a design, lettering, logo or other descriptive
pattern on the photovoltaic module.
19. The method of claim 18 wherein the metal contact is removed by
laser scribing a pattern of holes.
20. The method of claim 19 wherein the holes are connected.
21. The method of claim 20 wherein the holes are round and have a
diameter of about 0.1 to about 0.2 mm.
22. A method of making a photovoltaic module comprising series
connected cells, at least one amorphous semiconductor layer, a
metal contact layer, and interconnects connecting the series
connected cells comprising selectively removing portions of the
metal contact using a laser for the purpose of permitting light to
pass through the module where the metal is selectively removed.
23. The method of claim 22 wherein the portions of metal removed
are in the form of a plurality of holes.
24. The method of claim 23 wherein at least some of the holes are
connected.
25. The method of claim 26 wherein the holes are round in
shape.
26. The method of claim 22 wherein the metal is removed by using
the laser to ablate semiconductor material which bursts through the
metal contact layer to remove the metal.
27. The method of claim 22 wherein the module has a transmission of
at least about 5 percent.
28. A thin film partially transparent photovoltaic module
comprising series connected cells, at least one amorphous
semiconductor layer, a metal contact layer, and interconnects
connecting the series-connected cells, the module comprising a
plurality of scribes at least through the metal contact layer
positioned in a direction that crosses the direction of the
interconnects.
29. The module of claim 28 wherein each scribe has a width of about
0.01 to about 0.5 mm.
30. The module of claim 29 wherein each scribe has a width of about
0.05 to about 0.2 mm.
31. The module of claim 30 wherein the scribes are spaced from each
other about 0.5 to about 5 mm.
32. The module of claim 28 having a transmission of at least about
10 percent.
33. The module of claim 28 having a transmission of least about 20
percent.
34. The module of claim 28 wherein the scribes are in the form of
connected holes.
35. The module of claim 34 wherein the holes are round and have a
diameter of about 0.01 to about 0.2 mm.
36. The module of claim 28 further comprising bus bars located
adjacent to the first and last cell in the module and wherein the
laser scribes extend across the surface of the photovoltaic module
but not including the bus bars.
37. A photovoltaic module comprising series connected cells, at
least one amorphous semiconductor layer, a metal contact layer, and
interconnects connecting the series-connected cells, the module
comprising lettering, a logo or other descriptive pattern formed in
and extending through the metal contact layer.
38. The photovoltaic module of claim 37 wherein the descriptive
pattern is formed by laser scribing a pattern of holes.
39. The photovoltaic module of claim 38 wherein at least a portion
of the holes are connected.
40. The photovoltaic module of claim 38 wherein the holes are round
and have a diameter of about 0.01 to about 0.2 mm.
41. A window comprising the photovoltaic module of claim 28.
42. Sun screens and canopies comprising the photovoltaic modules of
claim 28.
43. The photovoltaic module of claim 28 wherein the scribes are
grouped in bands of closely spaced scribe lines separated by bands
having few or no scribes.
44. The photovoltaic module of claim 28 wherein the distance
between at least a portion of the scribes is graded.
45. A method of manufacturing a photovoltaic device on a substrate,
comprising the steps of: (a) depositing a transparent conductive
oxide film on a substrate to form a front contact layer; (b) laser
scribing substantially parallel first grooves in the front contact
layer with a laser beam to form front electrode segments on the
substrate; (c) depositing and forming a layer or layers of a
semiconductor material on said front electrode segments, and
filling the first grooves with the semiconductor material; (d)
laser scribing second grooves in the layer or layers of
semiconductor material at positions substantially parallel to the
first grooves; (e) depositing and forming a back contact layer
comprising a metal on the layer or layers of semiconductor
material, and filling the second grooves with the metal to form a
series connection to connect the front electrode segments and the
back contact layer; (f) laser scribing third grooves in the back
contact layer at positions substantially parallel to the second
grooves with a laser beam; and (g) laser scribing grooves in the
back contact layer at a direction which crosses the direction of
the second groove.
46. A method of manufacturing a photovoltaic device on a substrate,
comprising the steps of: (a) depositing a transparent conductive
oxide film on a substrate to form a front contact layer; (b) laser
scribing substantially parallel first grooves in the front contact
layer with a laser beam to form front electrode segments on the
substrate; (c) depositing and forming a layer or layers of a
semiconductor material on the front electrode segments, and filling
the first grooves with the semiconductor material; (d) laser
scribing second grooves in the layer or layers of semiconductor
material at positions substantially parallel to the first grooves;
(e) depositing and forming a back contact layer comprising a metal
on the layer of semiconductor material, and filling the second
grooves with the metal to form a series connection to connect the
front electrode segments and the back contact layer; (f) laser
scribing third grooves in the back contact layer at positions
substantially parallel to the second grooves with a laser beam; and
(g) selectively removing sections of the back contact using a laser
to impart a desired design, lettering, logo or other feature to the
photovoltaic device.
47. The method of claim 1 further comprising annealing the module
after laser scribing the plurality of laser scribes.
48. The method of claim 1 further comprising ultrasonically
cleaning the module after laser scribing the plurality of laser
scribes.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/216,415 filed Jul. 6, 2000, 60/220,346 filed
Jul. 24, 2000 and 60/221,627 filed Jul. 28, 2000.
FIELD OF THE INVENTION
[0002] The present invention relates to partially transparent
photovoltaic cells and modules and methods for their manufacture.
More particularly, the present invention relates to partially
transparent amorphous silicon photovoltaic cells and modules
wherein the transparency is provided by removing at least part of
the back contact layer of the photovoltaic cell. This invention
also relates to photovoltaic modules where the removal of the back
contact can be used to form a design or logo on the photovoltaic
modules so that when viewed from the front or back the design or
logo is apparent.
[0003] A conventional thin film photovoltaic cell typically
includes a front contact disposed on a substrate wherein the front
contact is made of, for example, a metal oxide such as tin oxide, a
p-i-n or PIN junction and a back or rear contact made of, for
example, a metal such as aluminum. The p-i-n or PIN junction
includes a layer of a semiconductor material doped with a p-type
dopant to form a p-layer, an undoped layer of a semiconductor
material that forms an intrinsic or i-layer, and a layer of a
semiconductor material doped with an n-type dopant to form an
n-layer. Light incident on the substrate passes through the
substrate, the front contact, and the p-i-n junction. The light is
reflected by the rear contact back into the p-i-n junction.
However, since the back contact generally covers the entire surface
of the photovoltaic cell, the cell is opaque when the back contact
is made of a metal such as aluminum and does not transmit or allow
any light to pass through. In certain applications, however, it
would be desirable to have a photovoltaic cell that is efficient
for converting light energy into electrical energy yet provides for
the transmission of light through the cell. It would also be
desirable to have an efficient method to manufacture such
photovoltaic cells. Photovoltaic cells with such capability would
be very desirable in applications of the photovoltaic cell such as
windows, sun screens, canopies and other uses where it is desirable
to see through the photovoltaic cell or to have a certain amount of
the light incident on the cell pass through the cell. The present
invention provides for such a photovoltaic cell, modules comprising
such cells, and an efficient method for their manufacture.
SUMMARY OF THE INVENTION
[0004] This invention is a method of manufacturing a photovoltaic
device on a monolithic substrate, comprising the steps of:
[0005] (a) depositing a transparent conductive oxide film on a
monolithic substrate to form a front contact layer;
[0006] (b) laser scribing substantially parallel first grooves in
the front contact layer with a laser beam to form front electrode
segments on the monolithic substrate;
[0007] (c) depositing and forming a layer or layers of a
semiconductor material on said front electrode segments, and
filling the first grooves with the semiconductor material;
[0008] (d) laser scribing second grooves in the layer or layers of
semiconductor material at positions substantially parallel to the
first grooves;
[0009] (e) depositing and forming a back contact layer comprising a
metal on the layer or layers of semiconductor material, and filling
the second grooves with the metal to form a series connection to
connect the front electrode segments and the back contact
layer;
[0010] (f) laser scribing third grooves in the back contact layer
at positions substantially parallel to said second grooves with a
laser beam;
[0011] (g) laser scribing grooves in the back contact layer at a
direction which crosses the direction of the second groove.
[0012] This invention is also a method of manufacturing a
photovoltaic device on a monolithic substrate, comprising the steps
of:
[0013] (a) depositing a transparent conductive oxide film on a
monolithic substrate to form a front contact layer;
[0014] (b) laser scribing substantially parallel first grooves in
the front contact layer with a laser beam to form front electrode
segments on the monolithic substrate;
[0015] (c) depositing and forming a layer or layers of a
semiconductor material on the front electrode segments, and filling
the first grooves with the semiconductor material;
[0016] (d) laser scribing second grooves in the layer or layers of
semiconductor material at positions substantially parallel to the
first grooves;
[0017] (e) depositing and forming a back contact layer comprising a
metal on the layer of semiconductor material, and filling the
second grooves with the metal to form a series connection to
connect the front electrode segments and the back contact
layer;
[0018] (f) laser scribing third grooves in the back contact layer
at positions substantially parallel to the second grooves with a
laser beam;
[0019] (g) selectively removing sections of the back contact using
a laser to impart a desired design, lettering, logo or other
feature to the photovoltaic device.
[0020] This invention is also a photovoltaic cell comprising a
supporting substrate, a front contact layer on the substrate, a
layer or layers of semiconductor material and a back contact layer
comprising a metal, the back contact having areas without metal
thereby permitting the passage of light through the cell.
[0021] This invention is also a method for making a partially
transparent photovoltaic module comprising series connected cells,
at least one amorphous semiconductor layer, a metal contact layer,
and interconnects connecting the series-connected cells, the method
comprising laser scribing a plurality of laser scribes at least
through the metal contact and positioning the scribes in a
direction that crosses the direction of the interconnects.
[0022] This invention is also a method of making a photovoltaic
module comprising series connected cells, at least one amorphous
semiconductor layer, a metal contact layer, and interconnects
connecting the series-connected cells comprising selectively
removing portions of the metal contact using a laser for the
purpose of permitting light to pass through the module where the
metal is selectively removed.
[0023] This invention is also a partially transparent photovoltaic
module comprising series connected cells, at least one amorphous
semiconductor layer, a metal contact layer, and interconnects
connecting the series-connected cells, the module comprising a
plurality of scribes at least through the metal contact layer
positioned in a direction that crosses the direction of the
interconnects.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Photovoltaic cells that convert radiation and particularly
solar radiation into usable electrical energy can be fabricated by
sandwiching certain semiconductor structures, such as, for example,
the amorphous silicon PIN structure disclosed in U.S. Pat. No.
4,064,521, between two electrodes. One of the electrodes typically
is transparent to permit solar radiation to reach the semiconductor
material. This "front" electrode (or contact) can be comprised of a
thin film, for example, less than 10 micrometers in thickness of
transparent conductive oxide material, such as tin oxide, and
usually is formed between a transparent supporting substrate made
of glass or plastic and the photovoltaic semiconductor material.
The "back" or "rear" electrode (or contact), which is formed on the
surface of the semiconductor material opposite the front electrode,
generally comprises a thin film of metal such as, for example,
aluminum or silver, or the like, or a thin film of metal and a thin
film of a metal oxide such as zinc oxide between the semiconductor
material and the metal thin film. The metal oxide can be doped with
boron or aluminum and is typically deposited by low pressure
chemical vapor deposition.
[0025] FIG. 1 shows thin film photovoltaic module 10 comprised of a
plurality of series-connected photovoltaic cells 12 formed on a
transparent substrate 14, e.g., glass, and subjected to solar
radiation or other light 16 passing through substrate 14. (A series
of photovoltaic cells is a module.) Each photovoltaic cell 12
includes a front electrode 18 of transparent conductive oxide, a
transparent photovoltaic element 20 made of a semiconductor
material, such as, for example, hydrogenated amorphous silicon, and
a back or rear electrode 22 of a metal such as aluminum.
Photovoltaic element 20 can comprise, for example, a PIN structure.
Adjacent front electrodes 18 are separated by first grooves 24,
which are filled with the semiconductor material of photovoltaic
elements 20. The dielectric semiconductor material in first grooves
24 electrically insulates adjacent front electrodes 18. Adjacent
photovoltaic elements 20 are separated by second grooves 26, which
are filled with the metal of back electrodes 22 to provide a series
connection between the front electrode of one cell and the back
electrode of an adjacent cell. These connections are referred to
herein as "interconnects." Adjacent back electrodes 22 are
electrically isolated from one another by third grooves 28.
[0026] We discovered that the transmission of light through the
photovoltaic cell and module can be accomplished by removing metal
from the rear contact, preferably by a laser scribing process. We
also discovered that the removal of metal from the back contact by
the laser scribing method of this invention can be accomplished in
a manner to impart a descriptive pattern or logo on the
photovoltaic module. Additionally, we discovered partially
transparent photovoltaic modules having exceptional photovoltaic
performance can be manufactured by forming grooves in the back
contact where the grooves run from one side of the photovoltaic
module to the other and are disposed so they cross the
interconnects, and preferably, cross perpendicular to the direction
of the interconnects.
[0027] The thin-film photovoltaic module of FIG. 1 typically is
manufactured by a deposition and patterning method. One example of
a suitable technique for depositing a semiconductor material on a
substrate is glow discharge in silane, as described, for example,
in U.S. Pat. No. 4,064,521. Several patterning techniques are
conventionally known for forming the grooves separating adjacent
photovoltaic cells, including silkscreening with resist masks,
etching with positive or negative photoresists, mechanical
scribing, electrical discharge scribing, and laser scribing.
Silkscreening and particularly laser scribing methods have emerged
as practical, cost-effective, high-volume processes for
manufacturing thin-film semiconductor devices, including thin-film
amorphous silicon photovoltaic modules. Laser scribing has an
additional advantage over silkscreening because it can separate
adjacent cells in a multi-cell device by forming separation grooves
having a width less than 25 micrometers, compared to the typical
silkscreened groove width of approximately 300-500 micrometers. A
photovoltaic module fabricated with laser scribing thus has a large
percentage of its surface area actively engaged in producing
electricity and, consequently, has a higher efficiency than a
module fabricated by silkscreening. A method of laser scribing the
layers of a photovoltaic module is disclosed in U.S. Pat. No.
4,292,092.
[0028] Referring to FIG. 1, a method of fabricating a multi-cell
photovoltaic module using laser scribing comprises; depositing a
continuous film of transparent conductive oxide on a transparent
substrate 14, scribing first grooves 24 to separate the transparent
conductive oxide film into front electrodes 18, fabricating a
continuous film of semiconductor material on top of front
electrodes 18 and in first grooves 24, scribing second grooves 26
parallel and adjacent to first grooves 24 to separate the
semiconductor material into individual photovoltaic elements 20 (or
"segments") and expose portions of front electrodes 18 at the
bottoms of the second grooves, forming a continuous film of metal
on segments 20 and in second grooves 26 SO that the metal forms
electrical connections with front electrodes 18, i.e., the
interconnects, and then scribing third grooves 28 parallel and
adjacent to second grooves 26 to separate and electrically isolate
adjacent back electrodes 22. As shown in FIG. 1, the third grooves
28 are scribed in the metallic back electrode from the back contact
side or face of the photovoltaic cell. The first and last cell of a
module generally have bus bars which provide for a means to connect
the module to wires or other electrically conductive elements. The
bus bars generally run along the length of the outer, long portion
of the first and last cell.
[0029] We discovered that the photovoltaic cells and modules such
as the one described in FIG. 1 can be made partially transparent by
scribing the back contact. We also discovered that the back contact
can be removed in a specified pattern on the photovoltaic cell or
module using a laser, and preferably a computer-controlled laser,
such that the cell or module can have a logo or other sign such
that when the photovoltaic cell or module is viewed the logo or
sign is highly noticeable. The photovoltaic cell or module
therefore functions both as a means for generating electric current
and as a source of information such as an advertisement or means of
identification. We also discovered that if it is desirable to have
a photovoltaic module that transmits light without regard to the
need to have a logo or other design or information on the
photovoltaic cell, a highly efficient means for making such a
module comprises scribing with a laser, or otherwise forming lines
or interconnecting holes through the back contact and in a
direction that crosses the direction of the interconnects of the
photovoltaic module. Preferably, such scribe lines are
perpendicular or nearly so to the direction of the interconnects.
It is also preferable that such scribe lines run completely across
the photovoltaic module up to but not crossing the bus bars of the
first and last cells of the series of cells in a module. The number
of such scribes which are made on the back contact will determine
the degree of transparency. Of course, for each scribe, that amount
of area of the cell becomes photovoltaically inactive. However, we
determined that the scribes made in the manner described above,
particularly where the scribe comprises a series of connected holes
to form a line, provides for the least amount of loss of
photovoltaic activity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The accompanying drawings, which are incorporated in and
which constitute a part of the specification, illustrate at least
one embodiment of the invention and, together with the description,
explain the principles of the invention.
[0031] FIG. 1 is a schematic perspective view of a typical thin
film photovoltaic module fabricated according to a known
method;
[0032] FIGS. 2(a)-2(g) are schematic cross sectional views
depicting the steps in a method for fabricating another type of
thin film photovoltaic module;
[0033] FIG. 3 is a schematic perspective view of one embodiment of
this invention where a single laser scribe is positioned on the
back contact of the photovoltaic module of FIG. 1 to provide for
partial transparency of the photovoltaic cells and module.
[0034] FIG. 4 is a schematic perspective view of the module of FIG.
2(g).
[0035] FIG. 5 is a schematic perspective view of one embodiment of
this invention showing only a single laser scribe positioned on the
back contact of the photovoltaic module of FIG. 4 to provide for
partial transparency and where the scribe was formed by a laser
directed from the substrate side of the photovoltaic module.
[0036] FIG. 6 is a view of a section of a thin film photovoltaic
device of this invention having a "logo" formed in metal rear or
back contact layer of the photovoltaic device.
[0037] FIG. 7 is a view of canopies that can be constructed using
photovoltaic devices of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Reference now will be made in detail to the presently
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings.
[0039] FIG. 2(g) is a schematic cross sectional view of a portion
of a multi-cell thin-film photovoltaic module, designated generally
by reference numeral 110. Photovoltaic module 110 is comprised of a
plurality of series-connected photovoltaic cells 112 formed on a
flat, transparent substrate 114. In operation, photovoltaic module
110 generates electricity in response to light, particularly solar
radiation, 116, passing through substrate 114, which preferably is
formed of glass. Each photovoltaic cell 112 includes a front
electrode segment 118 of transparent conductive oxide, a
photovoltaic element 120 made of semiconductor material, such as,
for example, hydrogenated amorphous silicon, and a back electrode
122 comprising a metal, preferably aluminum, and optionally a metal
oxide such as zinc oxide. Adjacent front electrode segments 118 are
separated by first grooves 124, which are filled with the
semiconductor material of photovoltaic elements 120. Adjacent
photovoltaic elements 120 are separated by second grooves 126 and
also by third grooves 128. An inactive portion 130 of semiconductor
material is positioned between second groove 126 and third groove
128. Portions 130 are "inactive" in the sense that they do not
contribute to the conversion of light 116 into electricity. Second
grooves 126 are filled with the material of back electrodes 122 to
provide a series connection between the front electrode of one cell
and the back electrode of an adjacent cell. These connections are
referred to as interconnects. Gaps 129, located at the tops of
third grooves 128, separate and electrically isolate adjacent back
electrodes 122. A series of photovoltaic cells, 112 as shown in
FIG. 2(g) comprise a module. The module can have a large number of
individual cells. Two or more modules can be connected in parallel
to increase the current of the photovoltaic device. If a series of
photovoltaic cells 112 are used, the contact of the first and last
cell must be available for attaching a wire or other conductive
element in order to connect the module to a device that will use
the electric current generated by the module. Generally, a
conductive strip or "bus bar" is added to the outside of the first
and last cell in the module (i.e., parallel to the grooves). These
bus bars are used to make the electrical connection to the device
that will utilize the electrical current generated when the module
is exposed to light.
[0040] In the preferred method of this invention a portion of the
back contact is selectively removed or ablated by lasers to form a
design on the back contact, or is scribed to produce a partially
transparent photoelectric module. The scribing can be done by any
means such as masking and etching or by mechanical scribing.
However, we discovered that the preferred method for removing part
of the rear contact is to use a laser. As described above, the
selective removal of the metal of the rear contact can be
accomplished in such a manner as to impart a design, lettering or
logo to the photovoltaic module. This can be done to achieve
shading, textures or three dimensional effects. The particular
design or lettering or other feature to be added to the
photovoltaic module can be stored in a computer or other memory
system and such stored information can be recalled during the
manufacturing process to quickly and accurately reproduce the
desired design, lettering, logo or other feature on the
photovoltaic module by directing the laser to scribe the pattern on
the module by selectively removing the appropriate portions of the
back contact.
[0041] If only transparency and not a design is desired, the rear
contact can be scribed, again by one or more of the techniques
mentioned above, to remove at least some of the back contact.
Preferably a laser scribing process is used for this procedure as
well. Preferably, such scribing is accomplished by scribing lines
or grooves across the module in a pattern that crosses the
interconnects, i.e., the scribe lines to produce partial
transparency cross rather than run parallel to the interconnects.
Preferably the scribe lines or grooves that are used to produce
partial transparency of the photovoltaic module run perpendicular
to the direction of the interconnects. Preferably the scribe lines
for producing partial transparency are parallel to each other. The
number of scribes that are added to the photovoltaic module to
produce partial transparency of the module can vary depending on
the desired transparency. Also the width of each scribe can vary
depending on the desired transparency. Generally, the amount of
back contact removed by the scribing is no more than about 50
percent of the area of the back contact, more preferably no more
than about 20 percent of the back contact and most preferably no
more than about 10 percent of the back contact. As stated above,
the greater amount of the back contact removed, the more
transparent the photovoltaic module will be. However, the more
contact removed the less effective the module will be in generating
electrical current when exposed to sunlight or other light sources.
Generally, the spacing of the scribe lines is about 0.5 to about 5
millimeters (mm). More preferably about 0.5 to about 2 mm and most
preferably about 0.5 to about 1.0 mm. The width of each scribe line
is preferably about 0.5 to about 0.01 mm. More preferably about 0.2
to about 0.05 mm. The scribe line can be a solid line if, for
example a laser scribing technique is used to form the line where
the laser beam is projected as a linear beam. The scribe lines can
also be in the form of a series or row of holes. The shape of the
holes can be of any shape such as circles, squares or rectangles.
Preferably, if the scribe lines are a series of small holes, and
the holes are preferably connected or overlap so as to form a
continuous scribe across all or a part of the surface of the
photovoltaic module but not including the bus bars. Most
preferably, the scribing is in the form of circular holes having a
diameter of at least about 0.01 mm, preferably about 0.1 to about
0.2 mm. We have determined that circular holes, particularly when
they are interconnected, lead to minimized power loss and maximized
light transmission for the photovoltaic device.
[0042] When a laser is used to remove parts of the back contact to
form the photovoltaic modules of this invention having the design
or other such feature imparted to the photovoltaic module, or to
form the photovoltaic module of this invention which is partially
transparent, the laser used to remove the desired sections of the
back contact is preferably a continuous wave laser or more
preferably a pulsed laser. The laser can be an ultraviolet laser
such as Excimer laser such as an KrF or ArCl laser and the like, or
a third or forth harmonic of Nd:YAG, Nd:YLF and Nd:YVO.sub.4
lasers. The laser can also be a visible or infrared laser. Most
preferably, the laser used is a visible laser, preferably a green
laser, for example, a frequency doubled Nd-YAG, Nd-YLF or
Nd-YVO.sub.4 laser. The laser can be directed to the top of the
back contact so that the back contact is directly ablated or
removed by the laser. In a preferred technique the laser beam is
directed through the transparent substrate and through the
transparent PIN component layers to ablate the rear contact. In a
preferred method of operation, the laser is used to generate shock
waves by using short pulses of high laser beam energy. We have
determined that this enhances the removal of the back contact and
reduces shunting. After the removal of the back contact,
particularly after using the laser method, the photovoltaic cell is
preferably cleaned, preferably using an ultrasonic bath. The
cleaning process removes dust particles and melted materials along
the edges of the scribe patterns thereby reducing shunting. We have
determined that the cleaning, particularly high power ultrasonic
cleaning, results in the recovery of as much as 3 percent of the
cells power that would otherwise be lost if such cleaning was not
conducted. The method for forming photovoltaic module 110 now will
be described with reference to FIGS. 2(a) through 2(g).
[0043] In a method in accordance with the present invention,
conductive transparent oxide, such as, for example,
indium-tin-oxide, zinc oxide, cadmium stannate or preferably tin
oxide (CTO), preferably a fluorinated tin oxide, is deposited on a
substrate, such as glass, to form a front contact layer 132, or
glass having the conductive tin oxide already deposited thereon can
be obtained from suitable glass suppliers. The conductive
transparent oxide layer is preferably less than about 10,000 .ANG.
in thickness. The tin oxide layer can have a smooth or textured
surface. The textured surface is preferred for application of the
photoelectric device of this invention where the greatest electric
generating efficiency is desired. However, where the least amount
of distortion of light coming through the partially transparent
photovoltaic cell or module is desired, a smooth tin oxide surface
is preferred. Such lower distortion, partially transparent
photovoltaic cells and modules are particularly useful as windows
or in other applications where minimizing distortion of the
transmitted light is desired. Next a strip of conductive material,
preferably silver (Ag) containing materials, is deposited on the
outside edges of two opposite sides of CTO layer 132 to form bus
bars.
[0044] Following thermal cure, if required, of the conductive
material, the front contact layer 132 is laser scribed to form
scribe lines 124. Following laser scribing of scribe lines 124, the
remaining steps in the fabrication of the photovoltaic module as
shown in FIGS. 2(c) to 2(g) as described herein are performed as
described below.
[0045] It should be noted that in FIGS. 2(a) to 2(g), the front
contact layer 132 is shown but the bus means are not. It should be
understood, however, that bus means are disposed on front contact
layer 132 in the manner described above following which the steps
shown in FIGS. 2(c) to 2(g) are performed.
[0046] A photovoltaic region comprised of a substantially
continuous thin film 134 of semiconductor material is fabricated
over front electrodes 118 and in first grooves 124, as shown in
FIG. 2(c). The semiconductor material filling first grooves 124
provides electrical insulation between adjacent front electrodes
118. Preferably, the photovoltaic region is made of hydrogenated
amorphous silicon in a conventional PIN structure (not shown) and
is typically up to about 5000 .ANG. in thickness, being typically
comprised of a p-layer suitably having a thickness of about 30
.ANG. to about 250 .ANG., preferably less than about 150 .ANG., and
typically of about 100 .ANG., an i-layer of 2000-4500 .ANG., and an
n-layer of about 200-400 .ANG.. Deposition preferably is by glow
discharge in silane or a mixture of silane and hydrogen, as
described, for example, in U.S. Pat. No. 4,064,521. Alternatively,
the semiconductor material may be CdS/CulnSe.sub.2 and CdTe. The
semiconductor layer can comprise a single PIN type layer. However,
the photovoltaic devices of this invention can have other
semiconductor layers, for example, it can be a tandem or
triple-junction structure. Suitable semiconductor layers useful in
the photovoltaic devices of this invention and methods for their
manufacture are described, for example, in United Kingdom Patent
Application No. 9916531.8 (Publication No. 2339963, Feb. 9, 2000)
which is incorporated herein by reference.
[0047] The semiconductor film 134 then is scribed with a laser to
ablate the semiconductor material along a second predetermined
pattern of lines and form second grooves 126, which divide
semiconductor film 134 into a plurality of photovoltaic elements
120, as shown in FIG. 2(d). Front electrodes 118 are exposed at the
bottoms of second grooves 126. Scribing may be performed with the
same laser used to scribe transparent conductive oxide layer 132,
except that power density is typically reduced to a level that will
ablate the semiconductor material without affecting the conductive
oxide of front electrodes 118. The laser scribing of semiconductor
film 134 can be performed from either side of substrate 114. Second
grooves 126 preferably are scribed adjacent and parallel to first
grooves 124 and preferably are approximately about 20 to about 1000
micrometer in width.
[0048] A thin film of metal 136, such as one or more of silver,
molybdenum, platinum, steel, iron, niobium, titanium, chromium,
bismuth, antimony or preferably aluminum, is fabricated over
photovoltaic elements 120 and in second grooves 126, as shown in
FIG. 2(e). The conductive material filling second grooves 126
provides electrical connections between film 136 and the portions
of front electrodes 118 exposed at the bottoms of second grooves
126. Conductive film 136 is formed, for example, by sputtering or
other well known techniques. The thickness of film 136 depends on
the intended application of the module. As an example, for modules
intended to generate sufficient power to charge a 12-volt storage
battery, metal film 136 typically is formed of aluminum and is
about 2000-6000 .ANG. thick.
[0049] The next step is to scribe metal film 136 with a laser to
ablate the metal along a pattern of lines and form a series of
grooves dividing film 136 into a plurality of back electrodes. In
one such method, as taught, for example, in U.S. Pat. No.
4,292,092, because of the high reflectivity of aluminum and other
metals conventionally used to form the back electrodes, the laser
used to scribe the back electrode usually is operated at a
significantly higher power density than those used to scribe second
grooves 126 in semiconductor film 134, often 10 to 20 times
higher.
[0050] For example, if metal film 136 is formed of aluminum and is
about 7000 .ANG. thick, and if the aluminum is to be directly
ablated by a frequency-doubled neodymium:YAG laser emitting light
having a wavelength of about 0.53 micrometers and operated in a
TEM.sub.00 (spherical) mode, the laser typically would be focused
to about 0.25 micrometers and operated at about 300 mW. Shorter
pulse duration may reduce average laser power requirements. When
the same laser is used to ablate semiconductor film 134 and form
second grooves 126, it preferably is defocused to 100 micrometers
and is operated at about 360 mW. Although the laser would be
operated at a slightly lower power level for direct ablation of
aluminum, the number of photons per second per unit area, that is,
the power density of the laser, also is a function of the spot size
of the laser beam. For a given power level, power density varies
inversely with the square of the radius of the spot. Thus, in the
example described above, the laser power density required for
direct ablation of the aluminum film is about 13 times the power
density required to ablate the amorphous silicon film.
[0051] It is difficult to prevent a laser operating at the power
density necessary for direct ablation of aluminum from damaging the
underlying semiconductor material. Specifically, the photovoltaic
cell may become shorted due to molten metal flowing into the
scribed groove and electrically connecting adjacent back
electrodes, or due to molten metal diffusing into the underlying
semiconductor material and producing a short across a photovoltaic
element. In addition, where the underlying semiconductor material
is comprised of amorphous silicon, the underlying amorphous silicon
material may recrystallize. Moreover, in an amorphous silicon PIN
structure dopants from the n-layer or p-layer may diffuse into the
recrystallized amorphous silicon of the i-layer.
[0052] Therefore, after fabrication of metal film 136, the
photovoltaic regions 120 underlying metal film 136 are preferably
scribed with a laser operated at a power density sufficient to
ablate the semiconductor material along a predetermined pattern of
third lines parallel to and adjacent second grooves 126 but
insufficient to ablate the conductive oxide of front electrodes 118
or the metal of film 136. More specifically, the laser must be
operated at a power level that will ablate the semiconductor
material and produce particulates that structurally weaken and
burst through the portions of the metal film positioned along the
third lines to form substantially continuous gaps in the metal film
along the third lines and separate the metal film into a plurality
of back electrodes. As shown in FIG. 2(e), where the laser beams
are shown schematically and designated by reference numerals 138,
laser patterning of metal film 136 by ablation of the underlying
semiconductor material is performed through substrate 114.
[0053] Ablating the semiconductor material of photovoltaic regions
120 along the pattern of third lines forms third grooves or scribes
128 in the semiconductor material, as seen in FIG. 2(f). Third
grooves 128 preferably are about 100 micrometers wide and are
spaced apart from second grooves 126 by inactive portions 130 of
semiconductor material. As described above, the ablation of the
semiconductor material formerly in third grooves 128 produces
particulates, for example, particulate silicon from the ablation of
amorphous silicon, which structurally weaken and burst through the
portions of metal film 136 overlying the ablated semiconductor
material to form gaps 129 that separate film 136 into a plurality
of back electrodes 122.
[0054] Gaps 129 preferably are substantially continuous as viewed
along a line orthogonal to the plane of FIG. 2(f). The laser
parameters required to produce continuous gaps 129 in metal film
136 will, of course, depend on a number of factors, such as the
thickness and material of the metal film, the characteristic
wavelength of the laser, the power density of the laser, the pulse
rate and pulse duration of the laser, and the scribing feed rate.
To pattern a film of aluminum having a thickness of about 2000-6000
.ANG. by ablation of an underlying amorphous silicon film
approximately 6000 .ANG. in thickness with a frequency-doubled
neodymium:YAG laser emitting light having a wavelength of about
0.53 micrometers, when the pulse rate of the laser is about 5 kHz,
and the feed rate is about 13 cm/sec, the laser can be focused to
about 100 micrometers in a TEM.sub.00 (spherical) mode and operated
at about 320-370 mW. Under the above conditions, when the laser is
operated at less than about 320 mW, portions of metal film 136 may
remain as bridges across third grooves 128 and produce shorts
between adjacent cells. When the laser is operated above about 370
mW, continuous gaps 129 may be produced, but the performance of the
resulting module, as measured by the fill factor, may be degraded.
Although the precise cause of degraded performance presently is
unknown, we believe that the higher laser power levels may cause
melting of portions of the amorphous silicon photovoltaic elements
that remain after third grooves 128 are ablated. In addition, the
increased power densities may cause the laser to cut into front
electrodes 118, which would increase series resistance and, if the
power density is sufficiently high, might render the module
inoperable by cutting off the series connections between adjacent
cells.
[0055] The next step to form the photovoltaic cells of this
invention is to remove additional metal from the back contact. As
described above, this metal can be removed in a preselected pattern
to form lettering, a logo, or other visible feature on the
photovoltaic cell. Additional metal of the back contact can also be
removed to increase the transparency of the photovoltaic cell. The
metal of the back contact is preferably removed by laser. If
lettering, logo or other feature is desired, the metal is removed
in the desired pattern using, for example, a pattern of holes on
the back contact. The holes can be round, square or other shape.
They can be connected or not connected to each other, or only some
connected. If transparency is desired, the metal is preferably
removed or ablated in grooves or scribes running across the
photovoltaic cell relative to the direction of the interconnects,
preferably perpendicular to the direction of the interconnects.
FIGS. 3 and 5 show a three dimensional representation of one
transparency scribe or groove 140 in the photovoltaic module. FIG.
3 is the same as FIG. 1 except for the added scribe 140. FIG. 5 is
the same as FIG. 4 except for the added scribe 140. The numerals in
FIGS. 1 and 3 refer to the same elements. The numerals in FIGS.
2(g), 4 and 5 refer to the same elements. In the actual module, the
number of such grooves would be increased and spaced, shaped and
sized as described hereinabove, in order to provide for the desired
level of transparency. As shown in FIG. 3, the groove 140 extends
only through the metal layer 22 to semiconductor layer 20. As shown
in FIG. 5 the groove 140 extends from the metal back contact layer
122 down to the first contact 118. In FIG. 5 the groove is
represented as a straight sided groove. However, as described
above, this groove can be a series of connected holes.
[0056] Although removal of the back contact layer by laser scribing
to form the partially transparent photovoltaic modules and cells of
this invention, or to form the photovoltaic modules of this
invention having designs, logos, lettering or other features can be
accomplished using the techniques described hereinabove for
producing gaps or grooves 128 and 129 in FIGS. 2, 4 and 5, a
preferred method is to use a high repeating rate, high power laser
such as Nd:YVO.sub.4 laser, preferably, at about 20-100 kHz at a
rapid scribing speed of, for example, about 10-20 meters per second
with a spot size of, for example, 0.1 to about 0.2 mm. Such
conditions can be used to form a partially transparent photovoltaic
module 48 inches by 26 inches having, for example, a 5%
transmission in less than about one minute. The laser beam passes
through a telescope and is directed to XY scanning mirrors
controlled by galvanometers. The XY scanning mirrors deflect the
laser beam in the X and Y axes. The telescope focuses the beam on
to the photovoltaic module and scribing rates of about 5 to 20
meters per second are achieved by this method. In another method,
using a high power Eximer laser and cylindrical optics, an entire
scribe line can be made in a single laser pulse. Such a laser
scanning or single laser pulse technique can be used to form the
interconnect and other scribe lines to form the series arranged
photovoltaic cells or modules described herein, i.e., scribes or
grooves 124, 126 and 128 as shown in FIGS. 4 and 5.
[0057] FIG. 6 shows an embodiment of the invention having the word
"logo" as a representative design or logo as part of the
photovoltaic module. In FIG. 6, 1 is a section of a photovoltaic
module of this invention. In FIG. 6, 2 is part of one cell in the
module and there are eleven such sections of cells shown, although
a module can have a smaller or greater number of cells. Although
not shown in FIG. 6, each cell can have a layered structure as
shown in FIG. 4. That is, each cell 2 in FIG. 6 can correspond to a
cell 112 in FIG. 4. In FIG. 6, the dark lines 3 and the "dots"
forming the letters "L", "o", "g", and "o", represent regions of
the module where the metal back or rear contact is not present.
Thus, these regions of the module would transmit light and when the
module is viewed with a source of light from behind the module.
Lines 3 and the letters spelling "logo" would be visible to a
viewer of the module. Lines 3 in FIG. 6 represent the scribes or
grooves that separate the back or rear contact so that there is one
back or rear contact per cell in the module. Scribe lines or
grooves 3 can correspond to grooves 128 in FIG. 4. Letters 4, 5, 6
and 7 in FIG. 6 are a pattern of holes in the back or rear contact
formed, for example, by selective removal of the metal layer in the
back or rear contact by a laser scribing process such as one or
more of the processes described herein. In FIG. 6, the letter "L"
identified as 4 in FIG. 6 is a pattern of round holes, some of
which are connected or overlap with each other. The letter "o"
identified as 5 in FIG. 6 is similarly formed by a pattern of round
holes. The letter "g" identified as 6 in FIG. 6 is formed by rows
of round holes where some of the holes are connected. The letter
"o" identified as 7 in FIG. 6 is also formed by a row of holes in
the metal back contact layer where all the holes are connected or
overlap. The holes which form the letters in FIG. 6 can have, for
example, a diameter of about 0.1 to about 0.2 mm. In FIG. 6, the
section of the module is viewed from the substrate side of the
module. That is, in FIG. 6, the module is being viewed from the
same side light would enter the module for conversion of the light
to electrical current.
[0058] In another embodiment of this invention, rather than space
the grooves or scribe lines evenly across the surface of the
photovoltaic cells and module to form a partially transparent
photovoltaic cell and module of this invention, the scribes or
grooves to produce the partial transparency can be grouped in bands
where, in each band, each scribe line is closely spaced. Bands of
closely spaced scribe lines can alternate with bands having no or
very few scribes or grooves for partial transparency. A
photovoltaic module made in such a manner with alternating bands
has a "Venetian Blind-like" appearance. Such a photovoltaic module
is aesthetically appealing. In one such embodiment, high
transmission bands, for example bands about 0.5 to 2 cm wide with
transmission of 20-40% are alternated with opaque bands, for
example, having a transmission of less than about 5%, more
preferably less than about 1%, having a width of about 0.5 to about
1.0 cm. A Venetian Blind-like photovoltaic device can also be made
by mounting strips of a photovoltaic panel, for example, strips of
a photovoltaic device made on plastic or metal as a substrate, onto
glass or some other transparent substrate.
[0059] In other embodiments of the invention, the partially
transparent photovoltaic cells and modules of this invention can
have other arrangements or configurations for the scribes or
grooves used to impart partial transparency. The modules of this
invention can have scribes or groves that impart partial
transparency where the distance between the scribes within a module
is graded either for the entire module or only a portion therof.
For example, proceeding from one end of the module to the other end
of the module the distances or spaces between the scribes used to
provide partial transparency as described herein above can increase
or decrease in a graded manner. For example, in a linear grading, a
square root grading or by a logarithmic grading or other suitable
grading. Thus, the resulting module has a graded level of
transmission of light proceeding from one end of the module to the
other, such as, for example, 1 to about 5% transmission of light at
one end of the module and 10 to about 50% transmission at the other
end of the module. The first two scribes on one end of the module
can be separated by about 0.2 to about 1 mm and the last two on the
other end of the module can be separated by about 0.5 to about 5 mm
with the distance between the intervening scribes increasing
gradually and, preferably, in a linear grading, a square root
grading or by a logarithmic grading. In a logarithmitic type of
grading, for example, the first scribe would be separated from the
second scribe by log(2) mm, the spacing between the second and the
third scribe would be log(3) mm, the spacing between the third and
the fourth scribe would be log(4) mm, and so forth. In another
embodiment, the scribes or groves used to impart partial
transparency can, as described herein above, be grouped in bands
having a plurality of scribes separated by bands of few or no
scribes where, within the bands having the plurality of scribes,
the distance between each scribe is graded as described above. In
yet another embodiment, the modules of this invention have bands
having a plurality of scribes either spaced from each other with
the regular spacing as described herein above or with the graded
spacing as described hereinabove, where such bands are separated by
bands having few or no scribes, and where the bands having few or
no scribes have a width which is graded from one end of the module
to the other end. Such grading can be, for example, linear, square
root grading or logarithmic grading, or other suitable grading. The
bands as described herein above either with a plurality of scribes
or with few or no scribes can have any desired width. However, the
width of such bands generally is about 0.2 to about 5 cm. As used
herein, with respect to describing a band, having few scribes
preferably means that the band has a transparency of no more than
about 5%, preferably no more than about 1%. As used herein,
transmission means the percentage of light incident on the modules
or region of the module that passes through the module or region of
the module.
[0060] Following the laser scribing to form the photovoltaic
modules of this invention, it is preferable to anneal the module.
We have discovered that annealing the module improves performance
of the module, for example, by decreasing shunting loss. For
example, the scribed module can be annealed in air at a temperature
of 150 to about 175.degree. C. for 0.5 to about 1.0 hour.
[0061] As mentioned above, partially transparent photovoltaic cells
and modules, and particularly the partially transparent
photovoltaic cells and modules of this invention, or cells or
modules comprising a logo, design, descriptive pattern, sign or
other feature, particularly such cells and modules made according
to this invention, or a combination thereof either separately or on
the same cell or module (i.e., a module having scribes imparting
partial-transparency as well as the logo, design, descriptive
pattern, sign, etc. on the same cell or module) are suitable for
forming canopies. In one particular preferred use these cells and
modules form or are part of a canopy over a fuel filling station
such as a station used by consumers to fuel their automobiles or
trucks or other vehicles with gasoline, diesel or other fuel. The
partially transparent photovoltaic cells and modules are
particularly useful for this purpose because they allow for the
partial transmission of light, particularly sunlight, thereby
providing natural light for the consumer or other user of the fuel
to perform the desired operation under the canopy, and at the same
time the canopy can be used to generate electric current from, for
example, sunlight, thereby providing electrical power for the fuel
filling station or for other uses. For example, the electric
current generated can be distributed to the local electric power
grid if either all or part of the electric is not utilized by the
fuel filling station. Thus, the canopies of this invention can
provide for protection from rain, snow and other elements, as well
as from the full heat and radiation of the sun, yet provide for the
transmission of light to allow the consumer or other person beneath
the canopy to have natural light to proceed with their intended
operations such as fueling a vehicle, and/or to provide for a logo,
design, descriptive pattern, sign (letters etc.) and the like
overhead of the consumer or other person beneath the canopy.
[0062] The canopy of this invention useful for a fuel filling
station can have only a percentage of the surface of the canopy
containing the partially transparent cells or modules, preferably
the partially transparent cells and modules of this invention
and/or cell and modules having a logo, design, descriptive pattern,
sign and the like. For example, from about 10% of the total surface
area of the canopy to about 99% of the surface area. However, the
amount of area of the canopy containing the photovoltaic cells or
modules is not limited and can be greater than 50% of the total
surface area of the canopy. For example it can cover at least 70%,
or at least 75% or even at least 80% or 90%. In some applications,
at least 95% of the surface area of the canopy is one or more of
the partially transparent photovoltaic cells or modules, preferably
the partially transparent photovoltaic cells or modules of this
invention. As described herein, the amount of light transmitted by
each cell or module can also vary depending on the desired amount
of light to be transmitted through the canopy.
[0063] The canopy over the fuel filling station containing the
partially transparent photovoltaic cells and modules, particularly
the partially transparent photovoltaic cells of this invention
and/or cells or modules comprising a logo, design, descriptive
pattern, sign, and the like, can have any shape. For example it can
be flat, or curved upward or downward. It can be a flat canopy, but
on an incline. The incline can be adjustable to account for
different elevations of the sun so as to maximize the conversion of
sunlight to electricity. It can also be in the shape of a
pitched-roof type of canopy.
[0064] The photovoltaic cells and modules can, for example, be
mounted on the canopy in one or more frames made from, for example,
metal, plastic or other suitable material. Or they can, for
example, be mounted on a transparent substrate such as glass or
plastic which is attached to and part of the canopy.
[0065] FIG. 7 is a drawing of an example of a curve-shaped canopy
with the curve extending in an up direction, a flat canopy, and a
flat canopy that is tilted or at an angle. In FIG. 7, 1 is the
canopy, 2 are preferably partially transparent photovoltaic cells
or preferably modules, preferably the partially transparent
photovoltaic cells or modules of this invention and/or the cells or
modules having a logo, design, descriptive pattern, sign( letters
etc.) and the like either separately from or on the same cell or
module as the cell or module with the partial transparency scribes,
3 is a frame for holding the cells or modules, and 4 are columns
for supporting the canopy over the fuel filling station. The
canopies described herein are particularly useful for canopies over
fuel filling stations. They are also useful for covering other
operations where it is desirable to have the combination of light
transmission through the canopy and a canopy that can generate
electric power.
[0066] Provisional Patent Application Nos. 60/216,415 filed Jul. 6,
200, 60/220,346 filed Jul. 24, 2000 and 60/221,627 filed Jul. 28,
2000, and the patents referred to herein by number are incorporated
herein by reference in their entirety.
EXAMPLES
Example 1
[0067] A partially transparent photovoltaic (PV) module with 5%
transmission line pattern was made from what was otherwise a
thin-film, amorphous silicon BP Solar production PV module
(26.times.48 inches, MV) as follows.
[0068] The apparatus used was a high power Nd:YVO4 laser capable of
working at 100 kHz and output about 10 W; an XY scanner with
mirrors coated for high power laser applications; a laser focusing
lens; a beam expander and two mirrors. The XY scanner was a
combination of X and Y axis mirrors each controlled by a
galvanometer. The focusing lens was mounted on a micrometer that
allowed adjustment of the laser focus accurately. The laser beam
from the laser was collimated by the beam expander and then
directed to the focusing lens by two mirrors. The focused laser
beam was projected to the work surface by the XY scanning mirrors.
The galvanometers positioned the beam to the desired location on
the PV module. The laser beam was directed from the glass substrate
side of the module. The micrometer controlled focusing lens was
used to adjust the lens position to make sure the entire module was
processed uniformly. The XY scanner was controlled by a computer.
By controlling the X and Y mirror positions, the laser beam
location on the PV plate was accurately controlled. For the 5% line
pattern, the beam was scanned along the X direction which is
perpendicular to the direction of the interconnects. The scribe
lines were about 2 mm apart and extended from one buss bar to the
other buss bar on the PV module. The laser scribe lines removed the
back aluminum contact and the semiconductor material of the PV
module but left the front contact intact. The distance between the
focusing lens (also XY mirrors) and the surface of the PV module
was about 1800 mm, the average laser power used was about 8 W and
the laser pulse repetition rate was 50 kHz. The spot size of the
laser at the surface of the PV module was about 0.15 mm in
diameter. The scan rate was about 7.5 meters per second and the
entire PV module was completed in less than 1 minute to produce a
PV module having 5% transmission (about 5% of the incident light
passing through the module.)
[0069] After laser scribing the partially transparent PV module was
washed in a high power ultrasonic tank using water, and then it was
dried and annealed at 175 C for one hour. The operations above were
performed prior to sealing a second glass plate to the thin-film
module formed on the glass substrate.
Example 2
[0070] A partially transparent photovoltaic (PV) module with 10%
transmission line pattern was laser prepared as follows.
[0071] Same as Example 1, except the scribe line spacing was
reduced to about 1 mm.
Example 3
[0072] A dynamic focusing unit was used to replace the focusing
lens in Example 1. The dynamic focusing ensured the laser focused
on the working surface at all times during the laser scanning,
leading to more uniform coverage across the PV module.
Example 4
[0073] Examples 1 and 3 were repeated except, for more robust
production, two laser mirrors were removed and the laser beam, beam
expander, focusing system (focus lens or dynamic focusing unit) and
the entrance of the XY scanner were made coaxial.
Example 5
[0074] To produce a logo, design, or other pattern on the PV module
(either a partially transparent module containing scribe lines
perpendicular to the interconnects or a non-transparent module) the
logo, design or other pattern was transformed into a vector format
using HP graphics language (hpgl). Using the apparatus described in
Example 1, a computer directed the laser beam to the location on
the module according to the vector file. The laser ablated
(removed) the back contact where directed by the vector file and
the computer making that portion of the PV module transparent and
thereby forming the module having the logo, design or other pattern
featured on the module.
* * * * *