U.S. patent application number 12/910681 was filed with the patent office on 2011-10-27 for fabrication process for photovoltaic cell.
This patent application is currently assigned to Solaria Corporation. Invention is credited to Alelie Funcell.
Application Number | 20110260733 12/910681 |
Document ID | / |
Family ID | 43741751 |
Filed Date | 2011-10-27 |
United States Patent
Application |
20110260733 |
Kind Code |
A1 |
Funcell; Alelie |
October 27, 2011 |
FABRICATION PROCESS FOR PHOTOVOLTAIC CELL
Abstract
A photovoltaic strip is physically separated from a
semiconductor wafer utilizing physical sawing or other techniques.
In accordance with one embodiment, a type of semiconductor wafer is
first determined by interrogating the wafer to identify one or more
of its optical, thermal, or electrical characteristics. This
information regarding substrate type is then communicated to a
separation apparatus, which then accomplishes precise physical
separation of the substrate into discrete strips. Electrical
performance of the strips may be tested prior to their
incorporation into an assembled solar cell, where they are coupled
to a concentrating element utilizing an elastomer encapsulant.
Inventors: |
Funcell; Alelie; (Milpitas,
CA) |
Assignee: |
Solaria Corporation
Fremont
CA
|
Family ID: |
43741751 |
Appl. No.: |
12/910681 |
Filed: |
October 22, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11253182 |
Oct 17, 2005 |
7910822 |
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12910681 |
|
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Current U.S.
Class: |
324/501 ;
257/E21.521; 324/756.01; 438/17 |
Current CPC
Class: |
Y02E 10/52 20130101;
H01L 31/18 20130101; H01L 31/0547 20141201 |
Class at
Publication: |
324/501 ; 438/17;
324/756.01; 257/E21.521 |
International
Class: |
G01R 31/26 20060101
G01R031/26; H01L 21/66 20060101 H01L021/66 |
Claims
1. A method for creating a photovoltaic strip for incorporation
into a solar cell, the method comprising: providing a semiconductor
wafer having a PN junction and a first electrical contact and a
second electrical contact, the semiconductor wafer further
comprising a photovoltaic strip; interrogating the semiconductor
wafer to identify its type; and physically separating the
photovoltaic strip from the semiconductor wafer based upon the
wafer type.
2. The method of claim 1 wherein the semiconductor wafer is
interrogated utilizing at least one of optical, electrical, and
thermal techniques.
3. The method of claim 1 further comprising incorporating the
semiconductor strip into an assembled solar cell.
4. The method of claim 3 further comprising testing electrical
characteristics of the photovoltaic strip prior to its
incorporation into the solar cell.
5. The method of claim 4 wherein testing the photovoltaic strip
comprises testing at least one of current/voltage curve (IV-curve),
short-circuit current (Isc), open circuit voltage (Voc),
efficiency, and fill factor.
6. The method of claim 1 wherein the photovoltaic strip is
physically separated by sawing.
7. The method of claim 6 wherein the sawing creates a scribe line,
and the photovoltaic stripe is physical separated by fracturing
along an axis of a unit cell.
8. The method of claim 6 wherein the first and second electrical
contacts are present on a back side of the semiconductor wafer,
wherein a front side of the wafer is sawed.
9-13. (canceled)
14. An apparatus for testing a photovoltaic strip, the apparatus
comprising: a jig comprising a surface; a first electrical contact
located on a first side of the jig surface, the first electrical
contact in electrical communication with a first terminal of a
power supply; a second electrical contact located on a second side
of the jig surface opposite to the first side, the second
electrical contact in electrical communication a second terminal of
the power supply; and a member for securing a photovoltaic strip
onto the surface, such that a region of a first conductivity type
in the substrate is in electrical communication with the first
electrical contact, and a region of the second conductivity type in
the substrate is in electrical communication with the second
electrical contact.
15. The apparatus of claim 14 wherein the first and second
electrical contacts are configured to be in electrical
communication with a variable power supply in order to evaluate at
least one of current/voltage curve (IV-curve), short-circuit
current (Isc), open circuit voltage (Voc), efficiency, and fill
factor of a supported photovoltaic strip.
16. An apparatus for identifying a type of semiconductor substrate,
the apparatus comprising: a member configured to support a
substrate thereon; a first conducting pin configured to be in
electrical communication with a first electrical contact located on
a back side of the supported substrate; and a second conducting pin
configured to be in electrical communication with a second
electrical contact located on front side of the supported
substrate.
17. The apparatus of claim 16 further comprising a light source
configured to illuminate a front surface of the substrate in order
to provoke electrical output therefrom detected by at least one of
the first and second pins.
18. The apparatus of claim 16 further comprising a detector
configured to detect ohmic heating on the substrate resulting from
application of a potential difference applied between the first and
second pins.
19. The apparatus of claim 16 further comprising an optical scanner
configured to detect a pattern of conducting lines on a surface of
the substrate.
20. The apparatus of claim 16 further comprising a processor in
electrical communication with a database storing information
regarding characteristics of a plurality of semiconductor types.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to solar energy
techniques. In particular, the present invention provides a method
and resulting device fabricated from a plurality of photovoltaic
regions provided within one or more substrate members. More
particularly, the present invention provides a method and resulting
device for manufacturing the photovoltaic regions within the
substrate member, which is coupled to a plurality of concentrating
elements, using a coupling technique between the photovoltaic
regions and respective concentrating elements. Merely by way of
example, the invention has been applied to solar panels, commonly
termed modules, but it would be recognized that the invention has a
much broader range of applicability.
[0002] As the population of the world increases, industrial
expansion has lead to an equally large consumption of energy.
Energy often comes from fossil fuels, including coal and oil,
hydroelectric plants, nuclear sources, and others. As merely an
example, the International Energy Agency projects further increases
in oil consumption, with developing nations such as China and India
accounting for most of the increase. Almost every element of our
daily lives depends, in part, on oil, which is becoming
increasingly scarce. As time further progresses, an era of "cheap"
and plentiful oil is coming to an end. Accordingly, other and
alternative sources of energy have been developed.
[0003] Concurrent with oil, we have also relied upon other very
useful sources of energy such as hydroelectric, nuclear, and the
like to provide our electricity needs. As an example, most of our
conventional electricity requirements for home and business use
comes from turbines run on coal or other forms of fossil fuel,
nuclear power generation plants, and hydroelectric plants, as well
as other forms of renewable energy. Often times, home and business
use of electrical power has been stable and widespread.
[0004] Most importantly, much if not all of the useful energy found
on the Earth comes from our sun. Generally all common plant life on
the Earth achieves life using photosynthesis processes from sun
light. Fossil fuels such as oil were also developed from biological
materials derived from energy associated with the sun. For human
beings including "sun worshipers," sunlight has been essential. For
life on the planet Earth, the sun has been our most important
energy source and fuel for modern day solar energy.
[0005] Solar energy possesses many characteristics that arc very
desirable! Solar energy is renewable, clean, abundant, and often
widespread. Certain technologies developed often capture solar
energy, concentrate it, store it, and convert it into other useful
forms of energy.
[0006] Solar panels have been developed to convert sunlight into
energy. As merely an example, solar thermal panels often convert
electromagnetic radiation from the sun into thermal energy for
heating homes, running certain industrial processes, or driving
high grade turbines to generate electricity. As another example,
solar photovoltaic panels convert sunlight directly into
electricity for a variety of applications. Solar panels are
generally composed of an array of solar cells, which are
interconnected to each other. The cells are often arranged in
series and/or parallel groups of cells in series. Accordingly,
solar panels have great potential to benefit our nation, security,
and human users. They can even diversify our energy requirements
and reduce the world's dependence on oil and other potentially
detrimental sources of energy.
[0007] Although solar panels have been used successful for certain
applications, there are still certain limitations. For example,
solar cells are often costly. Depending upon the geographic region,
there are often financial subsidies from governmental entities for
purchasing solar panels, which often cannot compete with the direct
purchase of electricity from public power companies.
[0008] Moreover, the conventional panels are often composed of
silicon bearing wafer materials. Such wafer materials are often
costly and difficult to manufacture efficiently on a large scale.
Availability of solar panels is also somewhat scarce. That is,
solar panels are often difficult to find and purchase from limited
sources of photovoltaic silicon bearing materials.
[0009] In addition, conventional silicon bearing semiconductor
wafer materials exhibit substantial variation in design. For
example, some solar cell semiconductor wafer designs exhibit
electrical contacts on both the front and back side of the wafer,
while other solar cell semiconductor wafer designs exhibit
electrical contacts only on one side. This nonuniformity in design
makes it difficult to adapt these conventional semiconductor wafer
designs for use in a common solar panel.
[0010] From the above, it is seen that techniques for improving
solar devices is highly desirable.
BRIEF SUMMARY OF THE INVENTION
[0011] According to the present invention, techniques related to
solar energy are provided. In particular, the present invention
provides a method and resulting device fabricated from a plurality
of photovoltaic regions provided within one or more substrate
members. More particularly, the present invention provides a method
and resulting device for manufacturing the photovoltaic regions
within the substrate member, which is coupled to a plurality of
concentrating elements, using a coupling technique between the
photovoltaic regions and respective concentrating elements Merely
by way of example, the invention has been applied to solar panels,
commonly termed modules, but it would be recognized that the
invention has a much broader range of applicability.
[0012] According to embodiments of the present invention, a
photovoltaic strip is physically separated from a semiconductor
wafer utilizing physical sawing or other techniques. In accordance
with one embodiment, an identity/source of the semiconductor wafer
is first determined by interrogating the wafer to identify one or
more of its optical, thermal, or electrical characteristics. This
information regarding substrate type is then communicated to a
separation apparatus, which then accomplishes precise physical
separation of the substrate into discrete strips. The electrical
performance of the strips is then tested prior to their
incorporation into an assembled solar cell, where they are coupled
to a concentrating element utilizing an elastomer encapsulant.
[0013] An embodiment of a method for creating a photovoltaic strip
in accordance with an embodiment of the present invention for
incorporation into a solar cell, comprises, providing a
semiconductor wafer having a PN junction and a first electrical
contact and a second electrical contact, the semiconductor wafer
further comprising a photovoltaic strip. The semiconductor wafer is
interrogated to identify its type, and the photovoltaic strip is
physically separated from the semiconductor wafer based upon wafer
type.
[0014] An embodiment of a method in accordance with the present
invention for fabricating a solar cell, comprises, interrogating a
semiconductor substrate with at least one of optical, thermal, and
electrical techniques to detect at least one characteristic of the
substrate. The characteristic is compared to information stored in
a database regarding a plurality of substrate types, in order to
determine a type of the substrate, and the semiconductor substrate
is separated into one or more photovoltaic strips based upon the
substrate type determined.
[0015] An embodiment of an apparatus in accordance with the present
invention for testing a photovoltaic strip, comprises, a jig
comprising a surface, a first electrical contact located on a first
side of the jig surface, the first electrical contact in electrical
communication with a first terminal of a power supply, and a second
electrical contact located on a second side of the jig surface
opposite to the first side, the second electrical contact in
electrical communication a second terminal of the power supply. The
apparatus further comprises a member for securing a photovoltaic
strip onto the surface, such that a region of a first conductivity
type in the substrate is in electrical communication with the first
electrical contact, and a region of the second conductivity type in
the substrate is in electrical communication with the second
electrical contact.
[0016] An embodiment of an apparatus in accordance with the present
invention for identifying a type of semiconductor substrate,
comprises, a member configured to support a substrate thereon, a
first conducting pin configured to be in electrical communication
with a first electrical contact located on a back side of the
supported substrate, and a second conducting pin configured to be
in electrical communication with a second electrical contact
located on front side of the supported substrate.
[0017] Various additional objects, features and advantages of the
present invention can be more fully appreciated with reference to
the detailed description and accompanying drawings that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a simplified diagram illustrating an expanded view
of a solar cell structure according to an embodiment of the present
invention;
[0019] FIG. 2 is a simplified top-view diagram of a solar cell
according to an embodiment of the present invention;
[0020] FIG. 3 is a detailed cross-sectional view diagram of a
photovoltaic region coupled to a concentrating element of a solar
cell according to an embodiment of the present invention;
[0021] FIG. 4 is a detailed alternative cross-sectional view
diagram of a photovoltaic region coupled to a concentrating element
of a solar cell according to an embodiment of the present
invention;
[0022] FIG. 5 is a detailed cross-sectional view diagram of a
photovoltaic region coupled to a concentrating element of a solar
cell according to an embodiment of the present invention; and
[0023] FIG. 5A is a larger detailed cross-sectional view diagram of
the photovoltaic region coupled to the concentrating element of the
solar cell of FIG. 5 according to an embodiment of the present
invention.
[0024] FIG. 6 is a simplified top plan view of one type of a
conventional semiconductor wafer configured to generate electrical
current in response to incident light.
[0025] FIG. 6A is a simplified cross-sectional view of the
conventional semiconductor wafer shown in FIG. 6.
[0026] FIG. 7 is a simplified underside plan view of an alternative
type of a conventional semiconductor wafer configured to generate
electrical current in response to incident light.
[0027] FIG. 7A is a simplified cross-sectional view of the
conventional semiconductor wafer shown in FIG. 7.
[0028] FIG. 7B is a simplified underside plan view of the
conventional semiconductor wafer of FIG. 7, showing the location of
a photovoltaic strip.
[0029] FIG. 7C is a simplified enlarged view of a photovoltaic
strip.
[0030] FIG. 7D is a simplified cross-sectional view of the
conventional semiconductor wafer of FIG. 7B, taken along line
D-D'.
[0031] FIG. 7E is a simplified cross-sectional view of the
conventional semiconductor wafer of FIG. 7B, showing partial sawing
from the front side of the wafer.
[0032] FIG. 7F is a simplified cross-sectional view of the
conventional semiconductor wafer of FIG. 7E, showing completion of
physical separation of an edge of the photovoltaic strip by
fracturing along an axis of the unit cell.
[0033] FIG. 8 is a simplified flow diagram illustrating steps of
one embodiment of a method in accordance with the present invention
for forming photovoltaic strips.
[0034] FIG. 9 shows a simplified perspective view of an embodiment
of an apparatus for identifying semiconductor wafer type.
[0035] FIG. 10 shows a simplified perspective view of an embodiment
of a testing jig for photovoltaic strips.
DETAILED DESCRIPTION OF THE INVENTION
[0036] According to the present invention, techniques related to
solar energy are provided. In particular, the present invention
provides a method and resulting device fabricated from a plurality
of photovoltaic regions provided within one or more substrate
members. More particularly, the present invention provides a method
and resulting device for manufacturing the photovoltaic regions
within the substrate member, which is coupled to a plurality of
concentrating elements. Merely by way of example, the invention has
been applied to solar panels, commonly termed modules, but it would
be recognized that the invention has a much broader range of
applicability.
[0037] According to embodiments of the present invention, a
photovoltaic strip is physically separated from a semiconductor
wafer utilizing physical sawing or other techniques. In accordance
with one embodiment, an identity/source of the semiconductor wafer
is first determined by interrogating the wafer to identify one or
more of its optical, thermal, or electrical characteristics. This
information regarding substrate type is then communicated to a
separation apparatus, which then accomplishes precise physical
separation of the substrate into discrete strips. The electrical
performance of the strips is then tested prior to their
incorporation into an assembled solar cell, where they are coupled
to a concentrating element utilizing an elastomer encapsulant.
[0038] A method for fabricating a solar cell structure according to
an embodiment of the present invention may be outlined as follows:
[0039] 1. Provide a semiconductor wafer having photovoltaic regions
thereon; [0040] 2. Identify the specific configuration of the
photovoltaic regions on the semiconductor wafer; [0041] 3.
Physically separate the semiconductor wafer into photovoltaic
strips; [0042] 4. Test the photovoltaic strips; [0043] 5. Provide
the at least one photovoltaic strip on a lead frame member; [0044]
6. Provide an optical elastomer material having a first thickness;
[0045] 7. Provide a second substrate member comprising at least one
optical concentrating element thereon; [0046] 8. Couple the optical
concentrating element such that the optical elastomer material is
in between the surface region of the photovoltaic strip and the
second side of the optical concentrating element; [0047] 9. Form a
first interface within a vicinity of the surface region and the
thickness of the optical elastomer material; [0048] 10. Form a
second interface within a vicinity of the second side and the
optical elastomer material; [0049] 11. Maintain a spacing between
the second side of the optical concentrating element and the
surface region of the photovoltaic strip using a plurality of
particles having a predetermined dimension spatially disposed
overlying the surface region of the photovoltaic strip and within a
second thickness of the optical elastomer material; [0050] 12. Cure
the optical elastomer material between the surface region and the
second side; [0051] 13. Provide the first interface substantially
free from one or more gaps (e.g., air gaps and/or pockets, bubbles,
vapor) and the second interface substantially free from one or more
gaps to form a substantially continuous optical interface from the
first side of the optical concentrating element, through the first
interface, and through the second interface to the photovoltaic
strip; and
[0052] 14. Perform other steps, as desired.
[0053] The above sequence of steps provides a method according to
an embodiment of the present invention. As shown, the method uses a
combination of steps including a way of forming a solar cell for a
solar panel, which has a plurality of solar cells. Other
alternatives can also be provided where steps are added, one or
more steps are removed, or one or more steps are provided in a
different sequence without departing from the scope of the claims
herein. Further details of the present method and resulting
structures can be found throughout the present specification and
more particularly below.
[0054] Referring now to FIG. 1, an expanded view 10 of a solar cell
structure according to an embodiment of the present invention is
illustrated. This diagram is merely an example, which should not
unduly limit the scope of the claims herein. One of ordinary skill
in the art would recognize many variations, modifications, and
alternatives. As shown is an expanded view of the present solar
cell device structure, which includes various elements. The device
has a back cover member 101, which includes a surface area and a
back area. The back cover member also has a plurality of sites,
which are spatially disposed, for electrical members, such as bus
bars, and a plurality of photovoltaic regions. In a specific
embodiment, the bus bars can be provided on a lead frame structure,
which will be described in more detail throughout the present
specification and more particularly below. Of course, there can be
other variations, modifications, and alternatives.
[0055] In a preferred embodiment, the device has a plurality of
photovoltaic strips 105, each of which is disposed overlying the
surface area of the back cover member. In a preferred embodiment,
the plurality of photovoltaic strips correspond to a cumulative
area occupying a total photovoltaic spatial region, which is active
and converts sunlight into electrical energy. Of course, there can
be other variations, modifications, and alternatives.
[0056] Photovoltaic strips 105 are typically formed by physical
separation from a semiconductor wafer having photovoltaic regions.
Typically, this physical separation is accomplished by sawing
through the semiconductor wafer, although this physical separation
can alternatively be accomplished by other methods, such as a
combination of sawing and snapping along a axis of the lattice cell
structure. Formation of the photovoltaic strips is discussed in
detail below in connection with FIGS. 6-10.
[0057] An encapsulating material 115 is overlying a portion of the
back cover member. That is, an encapsulating material forms
overlying the plurality of strips, and exposed regions of the back
cover, and electrical members. In a preferred embodiment, the
encapsulating material can be a single layer, multiple layers, or
portions of layers, depending upon the application. Of course,
there can be other variations, modifications, and alternatives.
[0058] In a specific embodiment, a front cover member 121 is
coupled to the encapsulating material. That is, the front cover
member is formed overlying the encapsulant to form a multilayered
structure including at least the back cover, bus bars, plurality of
photovoltaic strips, encapsulant, and front cover. In a preferred
embodiment, the front cover includes one or more concentrating
elements, which concentrate (e.g., intensify per unit area)
sunlight onto the plurality of photovoltaic strips. That is, each
of the concentrating elements can be associated respectively with
each of or at least one of the photovoltaic strips.
[0059] Upon assembly of the back cover, bus bars, photovoltaic
strips, encapsulant, and front cover, an interface region is
provided along at least a peripheral region of the back cover
member and the front cover member. The interface region may also be
provided surrounding each of the strips or certain groups of the
strips depending upon the embodiment. The device has a sealed
region and is formed on at least the interface region to form an
individual solar cell from the back cover member and the front
cover member. The sealed region maintains the active regions,
including photovoltaic strips, in a controlled environment free
from external effects, such as weather, mechanical handling,
environmental conditions, and other influences that may degrade the
quality of the solar cell. Additionally, the sealed region and/or
sealed member (e.g., two substrates) protect certain optical
characteristics associated with the solar cell and also protects
and maintains any of the electrical conductive members, such as bus
bars, interconnects, and the like. Of course, there can be other
benefits achieved using the sealed member structure according to
other embodiments.
[0060] In a preferred embodiment, the total photovoltaic spatial
region occupies a smaller spatial region than the surface area of
the back cover. That is, the total photovoltaic spatial region uses
less silicon than conventional solar cells for a given solar cell
size. In a preferred embodiment, the total photovoltaic spatial
region occupies about 80% and less of the surface area of the back
cover for the individual solar cell. Depending upon the embodiment,
the photovoltaic spatial region may also occupy about 70% and less
or 60% and less or preferably 50% and less of the surface area of
the back cover or given area of a solar cell. Of course, there can
be other percentages that have not been expressly recited according
to other embodiments. Here, the terms "back cover member" and
"front cover member" are provided for illustrative purposes, and
not intended to limit the scope of the claims to a particular
configuration relative to a spatial orientation according to a
specific embodiment. Further details of various elements in the
solar cell can be found throughout the present specification and
more particularly below. More particularly, certain details on
coupling each of the photovoltaic regions to the concentrating
elements can be found throughout the present specification and more
particularly below.
[0061] FIG. 2 is a simplified top-view diagram 200 of a solar cell
according to an embodiment of the present invention. This diagram
is merely an example, which should not unduly limit the scope of
the claims herein. One of ordinary skill in the art would recognize
many variations, modifications, and alternatives. In an alternative
specific embodiment, the present invention provides a solar cell
device. The device has a housing member, which is a back cover
member 203. The device also has a lead frame member 201 coupled to
the housing member. In a specific embodiment, the lead frame member
can be selected from a copper member and/or an Alloy 42 member. Of
course, there can be other variations, modifications, and
alternatives.
[0062] In a preferred embodiment, the lead frame member has at
least one photovoltaic strip 205 thereon, which has a surface
region and a back side region. In a specific embodiment, each of
the photovoltaic strips is made of a silicon bearing material,
which includes a photo energy conversion device therein. That is,
each of the strips is made of single crystal and/or poly
crystalline silicon that have suitable characteristics to cause it
to convert applied sunlight or electromagnetic radiation into
electric current energy according to a specific embodiment. An
example of such a strip is called the Sliver Cell.RTM. product
manufactured by Origin Energy of Australia, but can be others. In
other examples, the strips or regions of photovoltaic material can
be made of other suitable materials such as other semiconductor
materials, including semiconductor elements listed in the Periodic
Table of Elements, polymeric materials that have photovoltaic
properties, or any combination of these, and the like. In a
specific embodiment, the photovoltaic region is provided on the
lead frame using a conductive epoxy paste and/or solder adhesive,
including paste and/or other bonding techniques. Of course, there
can be other variations, modifications, and alternatives.
[0063] In a specific embodiment, the device has an optical
elastomer material having a first thickness overlying the surface
region of the photovoltaic surface. The elastomer material is an
optical elastomer material, which begins as a liquid (e.g., paste,
soft paste) and cures to form a solid material, e.g., pliable. The
elastomer material has suitable thermal and optical
characteristics. That is, a refractive index of the elastomer
material is substantially matched to a overlying concentrating
element according to a specific embodiment. In a specific
embodiment, the encapsulant material adapts for a first coefficient
of thermal expansion of the plurality of photovoltaic strips on the
lead frame member and a second coefficient of thermal expansion
associated with the concentrating element. In a specific
embodiment, the encapsulant material facilitates transfer of one of
more photons between one of the concentrating elements and one of
the plurality of photovoltaic strips. The encapsulant material can
act as a barrier material, an electrical isolating structure, a
glue layer, and other desirable features. The encapsulating
material can also be a tape and/or film according to a specific
embodiment. Depending upon the embodiment, the encapsulant material
can be cured using a thermal, ultraviolet, and/or other process
according to a specific embodiment. Of course, there can be other
variations, modifications, and alternatives. In a specific
embodiment, the device has a second substrate member comprising at
least one optical concentrating element thereon. Further details of
the concentrating element and other features can be found in the
figures described below.
[0064] FIG. 3 is a detailed cross-sectional view diagram 300 of a
photovoltaic region coupled to a concentrating element of a solar
cell according to an embodiment of the present invention. This
diagram is merely an example, which should not unduly limit the
scope of the claims herein. One of ordinary skill in the art would
recognize many variations, modifications, and alternatives. As
shown, FIG. 3 is a cross section of "SECTION A-A" illustrated in
FIG. 2. As shown, the device has an optical concentrating element
301, which has a first side and a second side. The device also has
other element including the back cover, photovoltaic region, lead
frame, and others. Specific details of other views of the device
are provided throughout the present specification and more
particularly below.
[0065] FIG. 4 is a detailed alternative cross-sectional view
diagram 400 of a photovoltaic region coupled to a concentrating
element of a solar cell according to an embodiment of the present
invention. This diagram is merely an example, which should not
unduly limit the scope of the claims herein. One of ordinary skill
in the art would recognize many variations, modifications, and
alternatives. As shown, FIG. 4 is a cross section of "SECTION B-B"
illustrated in FIG. 2. As shown, the device has an optical
concentrating element 301, which has a first side and a second
side. The device also has other element including the back cover,
photovoltaic region, lead frame, and others. Specific details of
other views of the device are provided throughout the present
specification and more particularly below.
[0066] FIG. 5 is a detailed cross-sectional view diagram of a
photovoltaic region coupled to a concentrating element of a solar
cell according to an embodiment of the present invention. This
diagram is merely an example, which should not unduly limit the
scope of the claims herein. One of ordinary skill in the art would
recognize many variations, modifications, and alternatives. As
shown, FIG. 5 is a cross section of "SECTION C-C" illustrated in
FIG. 2. More specifically, FIG. 5A is a larger detailed
cross-sectional view diagram of the photovoltaic region coupled to
the concentrating element of the solar cell of
[0067] FIG. 5 according to an embodiment of the present invention.
This diagram is merely an example, which should not unduly limit
the scope of the claims herein. One of ordinary skill in the art
would recognize many variations, modifications, and alternatives.
As shown, the device has an optical concentrating element 301,
which has a first side 503 and a second side 501. The device also
has other element including the back cover, photovoltaic region,
lead frame, and others.
[0068] In a specific embodiment, the device has a first interface
within a vicinity of the surface region and the first thickness of
the optical elastomer material. The device also has a second
interface within a vicinity of the second side and the optical
elastomer material. In a specific embodiment, the optical
concentrating element 301 is coupled to the surface region of the
photovoltaic strip 205 such that the optical elastomer material is
in between the surface region of the photovoltaic strip and the
second side of the optical concentrating element. In a specific
embodiment, the device has a spacing comprising essentially the
optical elastomer material between the second side of the optical
concentrating element and the surface region of the photovoltaic
strip. The device has a plurality of particles 505 having a
predetermined dimension (e.g., non-compressible and substantially
non-deformable particles, spherical glass particles, which are
substantially transparent) spatially disposed overlying the surface
region of the photovoltaic strip and within a second thickness of
the optical elastomer material to define the spacing between the
surface region and the second side of the optical concentrating
element. In a specific embodiment, the second thickness is the same
as the first thickness, although they can differ in other
embodiments. In a specific embodiment, the first interface is
substantially free from one or more gaps (e.g., air gaps and/or
pockets) and the second interface substantially free from one or
more gaps to form a substantially continuous optical interface from
the first side of the optical concentrating element, through the
first interface, and through the second interface to the
photovoltaic strip. Of course, there can be other variations,
modifications, and alternatives.
[0069] As described above in connection with FIGS. 2-5, embodiments
of solar devices in accordance with the present invention feature a
plurality of photovoltaic elements in the form of silicon strips
205. These strips 205 are obtained by cutting sections of an
existing semiconductor wafer which has been patterned to exhibit
specific photovoltaic regions.
[0070] For example, FIGS. 6 and 6A show simplified top plan and
cross-sectional views taken along line A-A', respectively, of a
conventional semiconductor wafer 600 having a photovoltaic region
in the form of junction 601 between N-type silicon 602 and P-type
silicon 604. Top surface 600a of wafer 600 bears broader conducting
lines in the form of a pair of bus bars 604, and a plurality of
narrower conducting lines 606 orthogonal to the bus bars.
Conducting lines 604 and 606 are typically formed from a conducting
materials such as Ag solder. The particular pattern of conducting
lines 604 and 606 varies according to the manufacturer of the
substrate, but these lines serve as a first electrode of the solar
cell.
[0071] The cross-sectional view of FIG. 6A also shows the presence
of conducting material 608 on the backside 600b of wafer 600. This
backside conducting material 608 serves as a second electrode for
the solar cell. Application of a bias potential between the first
electrode (lines 604 and 606 on the wafer front side), and the
second electrode (conducting material 608 present on the back side
600b of the wafer 600), allows a flow of electrons generated at
junction 601 by incident light from source 650, to be collected as
an output current.
[0072] FIGS. 7 and 7A show simplified top plan and cross-sectional
views, respectively, of another type of conventional semiconductor
wafer 700 having both the first and second electrodes 705 and 707
present on the same (back) side of the wafer. As shown in FIGS.
7-7A, wafer 700 bears an anti-reflective coating 706 on its front
side. Anti-reflective coating 706 typically comprises silicon
nitride that is formed by chemical vapor deposition.
Anti-reflective coating 706 promotes absorption by the wafer of
optical energy from source 750.
[0073] The photovoltaic region of the conventional semiconductor
wafer of FIGS. 7 and 7A is in the form of junction 701 between
N-type silicon regions 702 interdigitated with P-type silicon
regions 704. This interdigitated arrangement of N- and P-type
regions 702 and 704 may be created, for example, by masked ion
implantation. First contact 705 is in electrical communication with
N-type silicon region 702, and second contact 707 is in electrical
communication with P-type silicon region 704. Application of a bias
potential between first contact 705 and second contact 707 allows a
flow of electrons generated at junction 701 by incident light from
source 750, to be collected as an output current.
[0074] As described in detail above, the photovoltaic strips
utilized in fabricating solar cells in accordance with embodiments
of the present invention, are typically formed by physically
separating portions of an existing semiconductor wafer, for example
a conventional wafer having the structure shown in FIGS. 6-6A or
7-7A. As is apparent from these Figures, however, the pattern of
conducting and semiconducting material is different between these
wafer designs.
[0075] Therefore, as shown in the simplified flow chart of FIG. 8,
a first step 802 of a method 800 in accordance with an embodiment
of the present invention, causes a semiconductor wafer to be
interrogated to identify the configuration of photovoltaic regions
present therein. Such interrogation may take the form of one or
more techniques, employed alone or in combination.
[0076] For example, the back side of a semiconductor wafer may be
exposed to optical scanning, in order to identify features
characteristic of a typical configuration of photovoltaic regions.
Thus in relation to the specific convention semiconductor wafer
designs described above, such back side optical scanning would
allow a user to rapidly and reliably distinguish the presence of
the interdigitated conducting lines characteristic of the
semiconductor wafer design of FIGS. 7-7A.
[0077] Alternatively or in combination with the optical scanning
technique just described, the configuration of photovoltaic regions
of a semiconductor wafer may determined through electrical
techniques. In one particular embodiment, a front side of a
semiconductor wafer could be illuminated with light, and the
location of voltages/currents on the back side of the wafer
detected. The location of such voltages/currents would reveal the
arrangement of conducting lines present on the back side of the
wafer, again rapidly and reliably allowing conventional wafers of
the first type (FIGS. 6-6A) to be distinguished from wafers of the
second type (FIGS. 7-7A).
[0078] Still further alternatively, the configuration of
photovoltaic regions of a semiconductor wafer my be determined by
thermal techniques. In one particular embodiment, the location of
contacts on the wafer could first be identified, and then a
potential difference of known magnitude intentionally applied
across these contacts. The resulting ohmic heating of conducting
elements on the wafer could be thermally detected and mapped to
reveal the characteristic configuration of photovoltaic regions on
the wafer.
[0079] FIG. 9 shows a simplified schematic diagram of an apparatus
for identifying a type of semiconductor wafer. Apparatus 900
includes rotatable support 902 that is configured to support wafer
904. Optical scanner devices 906 and 908 are configured to
illuminate the top and bottom surfaces, respectively, of supported
wafer 904. Based upon this optical interrogation, the nature of the
semiconductor wafer can be determined.
[0080] Apparatus 900 of FIG. 9 also includes light source 910 that
is configured to illuminate the front side of the substrate with
radiation of a plurality of wavelengths, mimicking sunlight
incident to the solar cell in order to provoke electrical output
from the wafer. Apparatus 900 further includes conducting pins 912
that can be configured to detect current/voltage generated the
front and back surfaces of the wafer in response to light received
from source 910. The location and character of electrical activity
in the form of current/voltages detected by pins 912 on one or both
surfaces of the substrate, can be analyzed to reveal the type of
semiconductor wafer.
[0081] Apparatus 900 of FIG. 9 also includes a radiation detector
914 that is configured to detect infrared or other radiation
emitted from the substrate. Specifically, application of a
potential difference by pins 912 in communication with terminals
980a-b of power supply 980, across contacts located on the wafer
back side and/or wafer front side, may result in ohmic heating of
conductive elements present on the wafer. Radiation detector 914
may be configured to sense the location/intensity of infrared
emissions from the wafer that are characteristic of such heating,
allowing corresponding identification of the wafer type.
[0082] As indicated in FIG. 9, pins 912, source 910, detector 914,
and scanners 906 and 908 are all in selective electronic
communication with processor 916. Processor 916 is configured to
operate these various elements to interrogate the wafer. Processor
916 may also be configured to reference database 918 containing
stored attributes representative of different wafer types.
[0083] Once the identity of the semiconductor wafer has been
identified utilizing one or more of the above-referenced
techniques, this information may be communicated to configure an
apparatus to physically separate the semiconductor wafer into one
or more photovoltaic strips, as shown in second step 804 of method
800 of FIG. 8. Specifically, the apparatus for physically
separating the wafer into strips may be in knowledge communication
with the apparatus utilized to identify the substrate type. On the
basis of information received from the wafer identification
apparatus, the wafer apparatus is configured to select specific
locations of lines at which the wafer/substrate is optimally
separated into individual photovoltaic strips. For example, as
described below, receipt of information indicating a substrate has
electrical contacts exclusively on its back side, may indicate that
physical separation is best achieved by sawing through a front side
of the substrate.
[0084] Physical separation of the wafer into photovoltaic strips in
accordance with embodiments of the present invention can be
achieved utilizing a number of different techniques, employed alone
or in combination. In accordance with one embodiment of the present
invention, this physical separation of the semiconductor wafer into
strips may be accomplished by physical sawing. Conventionally,
cutting or sawing a silicon wafer is performed in the semiconductor
industry to separate a wafer into individual die. Typically in such
a conventional sawing process, the silicon wafers are designed with
pre-determined scribe streets. The kerf width (cut area) will
normally have rugged, rough, and uneven edges, and most of the
material along the width of the street will be cut and removed
without any negative impact to the performance of the semiconductor
device.
[0085] In a photovoltaic cell application, however, such a rough,
uneven, and rugged cut may give rise to an edge effect which
undesirably lowers the efficiency of the device. Specifically,
roughness at the edge of a sawn strip may promote recombination of
hole-electron pairs, rather than the separation of such pairs which
leads to the generation of current.
[0086] Moreover, as indicated above many solar cell wafer designs
are not pre-designed to be cut/sawed or scribed. Finding the
"sweet-spot" or the correct or optimum location for a cut between
strips, is vital to minimize or prevent loss in efficiency rate or
maximize current voltage curve (IV curve) performance. Of course,
one of ordinary skill in the art would recognize other variations,
modifications, and alternatives.
[0087] For example, FIG. 7B again shows a plan underside view of
the back side of a conventional semiconductor wafer 700 of FIGS.
7-7A. Dashed line 760 shows the outline of a photovoltaic strip 762
that is to be prepared from wafer 700. FIG. 7C shows an enlarged
view of this photovoltaic strip 762, which comprises P-type region
704 flanked by adjacent N-type regions 702. In order to maintain
optimum efficiency of the photovoltaic strip, strip 762 is cut in
order to maintain the same ratio of area of P- and N-type regions
present on the original substrate. Therefore, exact positioning of
the location of physical separation of adjacent strips is of
paramount concern.
[0088] Accordingly, in one embodiment of a method in accordance
with the present invention, photovoltaic strips having very clean,
even and kerf free edges were fabricated with a saw equipped with a
very thin diamond blade. In accordance with one particular
embodiment, the saw having a blade width equal or less than 0.001''
was used to separate photovoltaic strips with less than a 0.001''
scribe width, thereby reducing to the greatest extent possible the
amount of silicon area cut away and lost during solar cell
fabrication. The saw speed was set at 1''-3''/sec, and a spray of
deionized water was focused directly on the blade during sawing.
After sawing, the wafer is washed and cleaned using a high pressure
wash and spin dryer system to remove silicon dust and other loose
foreign materials.
[0089] In order to minimize cell area lost during a cutting
process, it is important to minimize the amount of silicon that is
cut away. However, as shown and described above in connection with
FIGS. 7-7A, with backside-only contact photovoltaic semiconductor
wafers, conducting material is present on only one (the back) side
of the wafer, and the front side of the photovoltaic element is
normally uniformly blue in color. This makes the precise physical
separation of photovoltaic strips extremely difficult to achieve by
sawing the wafer from the front side.
[0090] Despite this, in accordance with other embodiments of the
present invention, a clean, even edge cut in a photovoltaic cell
having back side contacts, is achieved by cutting/sawing on the
front side of the semiconductor wafer, rather than on the back side
bearing electrically conducting lines. This cutting of the front
side of the wafer avoids loading the saw blade with cut metal
debris, that can result in a rough, uneven cut, and short blade
life.
[0091] In such embodiments, accurate positioning of the saw blade
is achieved based upon the prior, wafer identification step.
Specifically, once a wafer type has been recognized, the location
of conducting and other elements on the wafer backside can be known
with a high degree of specificity, allowing cutting to occur from
the featureless front-side of the wafer.
[0092] Other embodiments in accordance with the present invention
may utilize the above-referenced techniques in combination, for
example etching with a small diamond blade the front side of a
substrate having only back side contacts.
[0093] Various different kinds of apparatuses my be utilized for
sawing. One apparatus may utilize a single saw blade whose
positioning is determined by a microprocessor based upon
information regarding wafer type obtained from the interrogation.
Other apparatuses may employ a gang of spaced apart blades
operating at the same time in order to accomplish physical
separation of multiple strips.
[0094] Moreover, still other embodiments in accordance with the
present invention may utilize techniques other than sawing, for
physical separation of a substrate into strips. For example,
turning again to the conventional wafer having only back side
contacts that is shown in FIG. 7A, junction 701 between N- and
P-type regions does not extend through the entire thickness of the
silicon.
[0095] Therefore, in accordance with an alternative embodiment of
the present invention, an initial saw cut through only a portion of
the substrate to form a scribe line, may be followed by fracturing
along this scribe line to complete physical separation of the
strips. This is shown in FIGS. 7D-F. FIG. 7D shows a simplified
cross-sectional view of the wafer taken along line D-D' of FIG. 7B,
showing a portion of the wafer containing the strip that is to be
physically separated therefrom. FIG. 7E shows that in a first strip
separation step, wafer 700 is sawn from the front side only
partially through the thickness of the substrate, halting just
prior to entering the doped region. Having created scribe lines 764
by sawing to define adjacent photovoltaic strips, in the second
step separation step shown in FIG. 7F, physical separation between
the strips could then be completed by snapping the wafer along
these scribe lines, which are positioned to correspond with axes of
unit cells of the crystal lattice. Fracture along such axes of the
unit cell results in an extremely smooth and even break, with
minimal edge loss effect.
[0096] Still other techniques may alternatively be employed to form
the photovoltaic strips from the wafer. In accordance with one such
alternative embodiment, masking and etching techniques may be used
to define and expose inter-strip regions to plasma etching
conditions resulting in removal of material. Again, identification
of semiconductor substrate type and the location of corresponding
conducting regions would be important to determine the optimal
location of the patterned mask. And as described above, such
etching could be utilized in combination with stress-induced
fracture along the axes of the unit cell, to achieve strip edges
that are extremely even and smooth.
[0097] Once individual photovoltaic strips have been created from a
semiconductor wafer according to embodiments of the present
invention, in accordance with step 806 of method 800 or FIG. 8,
each photovoltaic strip may be electrically tested to initially
determine its electrical performance. Based on this testing,
electrical characteristics such as the current/voltage curve
(IV-curve), short-circuit current (Isc), open circuit voltage
(Voc), efficiency, and fill factor can be determined. Such testing
of the photovoltaic strips is helpful in order to allow them to be
evaluated prior to the laborious and time-consuming step of
incorporating them into the assembled solar cell.
[0098] FIG. 10 shows a simplified perspective view of an example of
a jig for use in testing the electrical properties of photovoltaic
strips. Jig 1000 comprises body 1002 having upper surface 1002a.
Clamp(s) 1004 are configured to physically secure the photovoltaic
strip 1006 in place on surface 1002a of jig 1000.
[0099] In particular, upper surface 1002a of testing jig 1000 also
bears spaced-apart test contacts 1008a and 1008b that are in
electrical communication with opposite poles 1010a and 1010b,
respectively, of variable power supply 1012. Application of a
potential bias across different portions of the photovoltaic strip
1006 through contacts 1008a and 1008b allows investigation of
different electrical properties of the strip. For example,
electrical characteristics such as current/voltage curve
(IV-curve), short-circuit current (Isc), and open circuit voltage
(Voc) can be determined by applying a potential across contacts
1008a-b.
[0100] In a final step 808 of method 800 shown in FIG. 8, the
photovoltaic strip that has been formed, is incorporated into a
solar cell design as described above. In accordance with one
particular embodiment, the photovoltaic strip is coupled with a
concentrator element utilizing an elastomer encapsulant.
[0101] Many benefits are achieved by way of the present invention
over conventional techniques. For example, the present technique
provides an easy to use process that relies upon conventional
technology such as silicon materials, although other materials can
also be used. Additionally, the method provides a process that is
compatible with conventional process technology without substantial
modifications to conventional equipment and processes. Furthermore,
embodiments in accordance with the present invention are flexible,
in that they allow semiconductor wafers from a plurality of
different suppliers to be used to form the photovoltaic strips.
[0102] In general, embodiments in accordance with the present
invention provide for an improved solar cell, which is less costly
and easy to handle. Such solar cell uses a plurality of
photovoltaic regions, which are coupled to concentrating elements
according to a preferred embodiment. In a preferred embodiment, the
invention provides a method and completed solar cell structure
using a plurality of photovoltaic strips free and clear from a
module or panel assembly, which are provided during a later
assembly process. Also in a preferred embodiment, one or more of
the solar cells have less silicon per area (e.g., 80% or less, 50%
or less) than conventional solar cells. In preferred embodiments,
the present method and cell structures are also light weight and
not detrimental to building structures and the like. That is, the
weight is about the same or slightly more than conventional solar
cells at a module level according to a specific embodiment. In a
preferred embodiment, the present solar cell using the plurality of
photovoltaic strips can be used as a "drop in" replacement of
conventional solar cell structures. As a drop in replacement, the
present solar cell can be used with conventional solar cell
technologies for efficient implementation according to a preferred
embodiment. In a preferred embodiment, the present invention
provides a resulting structure that is reliable and can withstand
environmental conditions overtime. Depending upon the embodiment,
one or more of these benefits may be achieved.
[0103] Although the above has been described in terms of a specific
cutting technique, there can be other variations, modifications,
and alternatives. For example, the cutting technique can be laser
cut, water jet cut, high water jet pressure cut, scribe and break,
chemical etch, including reactive ion etch, ion milling, any
combination of these, and the like. Of course, there can be other
variations, modifications, and alternatives.
[0104] It is also understood that the examples and embodiments
described herein are for illustrative purposes only and that
various modifications or changes in light thereof will be suggested
to persons skilled in the art and are to be included within the
spirit and purview of this application and scope of the appended
claims.
* * * * *