Document:

ASSIGNMENT OF PATENT

     WHEREAS, the undersigned (the "Patentee") did obtain a United States Patent
for Transparent  Solar Cell and Method of Fabrication  (Method of  Fabrication),
No. 6,320,117, dated November 20, 2001 (the "Patent");

     WHEREAS, the Patentee is the sole owner of the Patent;

     WHEREAS,  XsunX,  Inc., a Colorado  corporation  previously named Sun River
Mining,  Inc.  (the  "Assignee")  whose  mailing  address is 7609 Ralston  Road,
Arvada,  CO 80002,  desires to acquire the entire right,  title, and interest in
and to the Patent.

     NOW THEREFORE,  in consideration for the sum of one dollar ($1.00),  shares
of the common stock of the  Assignee and other good and valuable  consideration,
the receipt and sufficiency of which are hereby acknowledged,  the Patentee does
hereby sell, assign,  and transfer to the Assignee the entire right,  title, and
interest in and to the Patent to be held and enjoyed by the Assignee for its own
use and on its own behalf, and for its legal representatives and assigns, to the
full end of the term for  which  the  Patent  has  been  granted,  as fully  and
entirely as the Patent would have been held by the Patentee had this  assignment
and sale not been made.

         Executed this 25th day of September 2003 at Camarillo
California.

                                                     XOPTIX, INC.

                            By:
                              --------------------------------------------------
                              Douglas O'Rear, President

State of                                             )
         --------------------------------------------

County of                                            )
          -------------------------------------------

Before me personally appeared said
                                  -------------------------------------

and acknowledge that the foregoing instrument to be his free act and deed this
25th day of September, 2003

                                  (Notary Public)
         SealASSIGNMENT OF PATENT

     WHEREAS, the undersigned (the "Patentee") did obtain a United States Patent
for  Transparent  Solar Cell and Method of  Fabrication  (formed with a Schottky
barrier diode and method of its manufacture),  No. 6,509,204,  dated January 21,
2003 (the "Patent");

     WHEREAS, the Patentee is the sole owner of the Patent;

     WHEREAS,  XsunX,  Inc., a Colorado  corporation  previously named Sun River
Mining,  Inc.  (the  "Assignee")  whose  mailing  address is 7609 Ralston  Road,
Arvada,  CO 80002,  desires to acquire the entire right,  title, and interest in
and to the Patent.

     NOW THEREFORE,  in consideration for the sum of one dollar ($1.00),  shares
of the common stock of the  Assignee and other good and valuable  consideration,
the receipt and sufficiency of which are hereby acknowledged,  the Patentee does
hereby sell, assign,  and transfer to the Assignee the entire right,  title, and
interest in and to the Patent to be held and enjoyed by the Assignee for its own
use and on its own behalf, and for its legal representatives and assigns, to the
full end of the term for  which  the  Patent  has  been  granted,  as fully  and
entirely as the Patent would have been held by the Patentee had this  assignment
and sale not been made.

         Executed this 25th day of September 2003 at Camarillo
California.

                                                     XOPTIX, INC.

                   By:
                        --------------------------------------------------
                                    Douglas O'Rear, President

State of                                             )
         --------------------------------------------

County of                                            )
          -------------------------------------------

Before me personally appeared said
                                  -------------------------------------

and acknowledge that the foregoing instrument to be his free act and deed this
25th day of September, 2003

                                             (Notary Public)
SealUnited States Patent                                                  6,320,117
Campbell ,   et al.                                            November 20, 2001
Transparent solar cell and method of fabrication

                                    Abstract

A transparent solar cell and method of manufacture. The method includes steps of
providing a transparent substrate. The method also includes forming a first
conductive layer overlying the substrate. The method also includes forming a
first amorphous silicon layer of a first dopant type overlying the first
conductive layer. A step of annealing the first amorphous silicon layer is
included. The method also forms a second amorphous silicon layer of a second
dopant type, and also anneals the second amorphous silicon layer. A second
conductive layer is formed overlying the second amorphous silicon layer. A
combination of these steps forms a transparent solar cell structure.

Inventors:     Campbell; James P. (Atherton, CA); Galyean; Eric W. (Los Altos
               Hills, CA); Spreckman;
               Harvey R. (Thousand Oaks, CA)
Assignee:      Xoptix, Inc. (Woodland Hills, CA)
Appl. No.:     692366
Filed:         October 18, 2000
Current U.S. Class:  136/258; 136/245; 136/256; 136/261; 257/51; 257/74; 257/75;
                                                 257/461; 438/96; 438/97; 438/98
Intern'l Class:                                       H01L 031/109; H01L 031/045
Field of Search:     136/258 AM,261,258 PC,256,245 257/51,75,461,74 438/97,96,98
[GRAPHIC OMITTED]
                        References Cited [Referenced By]
<TABLE>
<CAPTION>

                                             U.S. Patent Documents
<S>                         <C>                        <C>                                         <C>

4059461                     Nov., 1977                 Fan et al.                                   438/92.
-------
4214918                     Jul., 1980                 Gat et al.                                  438/618.
-------
4400577                     Aug., 1983                 Spear                                       136/259.
-------
4663495                     May., 1987                 Berman et al.                               136/248.
-------
4824489                     Apr., 1989                 Cogan et al.                                136/256.
-------
5192991                     Mar., 1993                 Hosokawa                                    136/258.
-------
5413959                     May., 1995                 Yamamoto et al.                              438/98.
-------
5667597                     Sep., 1997                 Ishihara                                    136/258.
-------
5714404                     Feb., 1998                 Mitlitsky et al.                             439/97.
-------
5886688                     Mar., 1999                 Fifield et al.                              345/206.
-------
6180871                     Jan., 2001                 Campbell et al.                             136/258.
-------

</TABLE>

<PAGE>

Primary Examiner: Diamond; Alan
Attorney, Agent or Firm: Townsend and Townsend and Crew LLP

                                Parent Case Text

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. application Ser. No. 09/343,069, filed Jun. 29, 1999,
now U.S. Pat. No. 6,180,871 the specification of which is incorporated herein by
reference for all purposes.

                                     Claims

What is claimed is:

1. A method of forming a solar cell comprising:

providing a substrate;

forming a first layer of conductive material overlying the substrate;

forming a second layer of amorphous silicon of a first dopant type overlying the
first layer;

annealing the second layer to convert the amorphous  silicon of the second layer
into polycrystalline silicon;

forming a third layer of amorphous silicon of a second dopant type overlying the
second layer forming a p-n junction between the second layer and the third
layer;

annealing  the third layer to convert the  amorphous  silicon of the third layer
into polycrystalline silicon; and

forming a fourth layer of conductive material overlying the third layer.

2. The method of claim 1 wherein the first dopant type is p+.

3. The method of claim 2 wherein the second dopant type is n-.

4. The method of claim 1 wherein the melting point of the substrate is less than
450.degree. C.

5. The method of claim 1 wherein the first layer is formed by an annealing step.

6. The method of claim 1 wherein the  annealing  of the second  layer is done by
applying thermal energy while maintaining the substrate at a temperature of less
than 450.degree. C.

<PAGE>

7. The method of claim 1 wherein the annealing of the second layer comprises
application of thermal energy with a laser.

8. The method of claim 7 wherein the laser is a pulsed Excimer laser.

9. The method of claim 1 wherein the first layer is Indium Tin Oxide.

10. A method for  fabricating a structure  comprising a  transparent  solar cell
structure, the method comprising:

forming a first layer overlying a transparent substrate;

forming a second layer of amorphous silicon overlying the first layer, the
second layer being of a first impurity type;

converting the second layer into polycrystalline silicon;

forming a third layer of amorphous silicon overlying the second layer, the third
layer being of a second dopant type forming a p-n junction between the second
layer and the third layer;

converting the third layer into polycrystalline silicon; and

forming a fourth layer of conductive material overlying the third layer.

11. The method of claim 10 wherein the first layer, the second layer, the third
layer, and the fourth layer define a solar cell device.

12. The method of claim 10 wherein the second layer includes a thickness of 1000
..ANG. and less, which provides a transparent structure.

13. The method of claim 10 wherein the third layer  includes a thickness of 1000
..ANG. and less, which provides a transparent structure.

14.  The  method of claim 10  wherein  the  converting  of the  second  layer is
provided using a rapid thermal anneal process,  the rapid thermal anneal process
maintaining a temperature of less than about  450.degree.  C. at the transparent
substrate.

15. The method of claim 10 wherein the converting of the third layer is provided
using  a  rapid  thermal  anneal  process,  the  rapid  thermal  anneal  process
maintaining a temperature of less than about  450.degree.  C. at the transparent
substrate.

16.  The  method of claim 10  wherein  the  converting  of the  second  layer is
provided using a laser.

17. A method for  fabricating a structure  comprising a  transparent  solar cell
structure, the method comprising:

<PAGE>

providing a substrate;

forming a first layer of conductive material overlying the substrate;

forming a second layer of amorphous silicon overlying the first layer, the
second layer being of a first impurity type;

converting the second layer into polycrystalline silicon;

forming a third layer of amorphous silicon overlying the second layer, the third
layer being of a second dopant type;

converting the third layer into polycrystalline silicon;

forming a fourth layer of conductive material overlying the third layer;

forming a fifth layer of amorphous silicon overlying the fourth layer;

converting the fifth layer into polycrystalline silicon;

forming a sixth layer of amorphous silicon overlying the fifth layer;

converting the sixth layer into polycrystalline silicon; and

forming a seventh layer of conductive material overlying the sixth layer.

18. The method of claim 17 wherein the converting of at least one of the second,
third,  fifth and sixth  layers is done while  maintaining  the  substrate  at a
temperature of less than 450.degree. C.

19. The method of claim 17 wherein the converting of each of the second,  third,
fifth and sixth layers is done while  maintaining the substrate at a temperature
of less than 450.degree. C.

20. The method of claim 17 wherein the converting of at least one of the second,
third, fifth and sixth layers is done using an Excimer laser.

21. The method of claim 17 wherein the third layer directly overlies the second
layer with no intervening layers.

22. A solar cell structure comprising:

a substrate with a melting temperature of less than 450.degree. C.;

a first conductive layer overlying the substrate;

a first polycrystalline film overlying the first conductive layer;

a second polycrystalline film overlying the first polycrystalline film;

<PAGE>

a second conductive layer overlying the second polycrystalline film;

a third polycrystalline film overlying the second conductive layer;

a fourth polycrystalline film overlying the third polycrystalline film; and

a third conductive layer overlying the fourth polycrystalline film.

23. The solar cell structure of claim 22 wherein the second polycrystalline film
directly overlies the first polycrystalline film with no intervening layer.

                                   Description

BACKGROUND OF THE INVENTION

The present invention relates, in general, to electronic devices. More
particularly, the present invention provides a transparent solar cell and method
of its manufacture.

Solar energy provides many advantages over traditional energy sources. For
example, energy from the sun is virtually unlimited and easily accessible
throughout the world. It does not require the extraction of a natural resource
from the ground to obtain the energy and it can be converted to electricity in a
manner that is not harmful to the environment. Solar energy is available
whenever the sun is shining and can be collected and stored for use when no
light source is available. Therefore, if it can be harnessed economically, it
provides an environmentally friendly source of energy that does not deplete or
destroy precious natural resources. This is in stark contrast to the use of
fossil fuels that are of limited supply and which cause environmental damage
with both their use and extraction processes. The use of fossil fuel also
requires a constant source of raw materials that may be difficult obtain in many
circumstances.

Many different applications benefit greatly from the use of solar energy. For
example, buildings and automobiles, with their broad surfaces that are exposed
to the sun's energy for much of the day, can use that energy to provide some or
all of their energy needs. Various solar cells have been developed using
different fabrication techniques to take advantage of this energy source.

One type of solar cell is formed with crystalline silicon. For these solar
cells, crystalline silicon is formed by melting silicon and drawing an ingot of
crystalline silicon of the size desired. Alternatively, a ribbon of crystalline
silicon can be pulled from molton silicon to form a crystalline silicon solar
cell. A conductor is placed on either side of the crystalline silicon to form
the solar cell. These processes use high temperatures and the solar cells are
expensive to manufacture. Packaging is also difficult and expensive and creates
a rigid structure. Their maximum size is limited by the manufacturing process.
It is difficult to slice the resulting crystalline silicon thin enough to
provide a transparent or flexible solar cell. However, these structures are very
efficient (relative to other types of presently available commercial solar
cells). As such, crystalline solar cells are used primarily for applications
where efficiency is more important than cost and where the structures do not
need to be flexible. For example, these are commonly used on satellites.

Another type of solar cell is formed with polycrystalline silicon. These may be
formed as thin layers on wafers and can thus be made thinner than crystalline
silicon solar cells. As is well known in the art, polycrystalline silicon can be
formed by heating amorphous silicon. Typically, amorphous silicon begins to
crystallize at temperatures greater than about 1400.degree. C. Because of these
high temperatures, known processes can only use substrates with high melting
points. These processes are not appropriate for substrates made of plastics or
other materials that melt at lower temperatures. In the manufacture of flat
panel displays, it is known to use

<PAGE>

lasers to form polycrystalline silicon thin film transistors (TFTs). Such use
has not included the formation of P-N junctions or solar cells which presents
its own set of challenges. Moreover, these manufacturing processes generally
formed single transistors and were not used to form large sheets or areas of
polycrystalline silicon. Further, lasers have been used in the manufacture of
solar cells, but only as a tool to mechanically form (slice, pattern, etch,
etc.) the solar cells.

Another type of solar cell has been formed using doped layers of amorphous
silicon. These are not subject to some of the problems inherent in the
previously described crystalline silicon or polycrystalline solar cells. First,
amorphous silicon can be formed using low temperature processes. Thus, it can be
formed on plastic and other flexible substrates. They can also be formed over
large surfaces. Second, the processing techniques are less expensive.
Nevertheless, amorphous solar cells introduce other significant limitations not
found in crystalline silicon or polycrystalline silicon solar cells. For
example, hydrogen is generally added during the manufacturing to increase the
efficiency of the cell. Amorphous silicon solar cells tend however to lose this
hydrogen over time, causing reduced efficiency and reduced usable life.
Moreover, amorphous silicon solar cells are not transparent. Thus, they are not
appropriate for many applications. For example, buildings and cars with solar
cells can be unsightly, and the solar panels may block the view of the outdoors
or access to outside light indoors. Also, portable electronics often place a
premium on size and surface area. Some devices have displays that cover most--if
not all--of the exposed surface of the device. Therefore, it is often
undesirable or impossible to mount a traditional amorphous silicon solar cell on
the device.

Attempts have been made to solve this transparency problem by making transparent
panels from existing solar cell processes. One method has been to take advantage
of the "window shade effect" whereby solar cells are formed on a transparent
substrate with gaps between adjacent solar cells. This allows some light to pass
through to create a transparent effect. The larger the gaps, the more
transparency the device has. A disadvantage of this technique is that much of
the space is unused, therefore the efficiency of the device is less than it
would be if all of the surface area were used for solar cells. Of course,
devices of this type also suffer from the problems inherent to the type of cell
used. For example, if based on amorphous silicon, these devices suffer from the
hydrogen loss exhibited in other amorphous silicon devices.

Other work has been done at making transparent solar cells using materials other
than silicon (for example, cadmium telluride (CdTe)). These cells suffer from
the challenges inherit to using materials other than silicon.

Thus, a new solar cell and method of fabrication that will avoid these problems
is desirable.

SUMMARY OF THE INVENTION

The present invention provides a solar cell and method of its manufacture. It
combines the following advantages: 1) is transparent and therefore can be used
in places not applicable to existing solar cells 2) is cost effective because it
uses thin film amorphous silicon 3) may be readily manufactured because the
method for manufacture uses commercially available CVD and laser annealing
equipment and 4) can be used on a wide variety of substrates including low
temperature substrates.

According to the present invention, a technique including a method and device
for fabricating a solar cell is provided. In an exemplary embodiment, the
present invention provides a method and structure which forms a substantially
transparent solar cell. The solar cell is thin, flexible, and easy to make and
use with conventional semiconductor processes. The solar cell also operates
effectively as an optical filter.

<PAGE>

In a specific embodiment, the present invention includes a method of forming a
solar cell. The method includes steps of providing a substrate, e.g., glass,
plastic, Mylar and other substrates, including those with low melting points.
The method also includes forming a first conductive layer overlying the
substrate. The method also includes forming a first amorphous silicon layer of a
first dopant type overlying the first conductive layer. A step of annealing the
first amorphous silicon layer is included. The method also forms a second
amorphous silicon layer of a second dopant type, and also anneals the second
amorphous silicon layer. A second conductive layer is formed overlying the
second amorphous silicon layer. A combination of these steps forms a transparent
solar cell structure.

In an alternative aspect, the present invention provides a solar cell structure,
which is transparent. The structure includes a transparent substrate, which can
be selected from glass, crystal, plastic, Mylar, and other substrates, including
those that have low melting points. A conductive layer is formed overlying the
transparent substrate. A first polycrystalline silicon layer from a first
amorphous silicon layer of a first dopant type is formed overlying the first
conductive layer. The structure also includes a second polycrystalline silicon
layer from a second amorphous silicon layer of a second dopant type overlying
the first polycrystalline silicon layer, and a second conductive layer overlying
the second polycrystalline silicon layer. The combination of these layers forms
a transparent structure.

In a further aspect, the present invention provides a method for fabricating a
structure comprising a transparent solar cell structure. The method includes
forming a first conductive layer overlying a transparent substrate, and forming
a first amorphous silicon layer overlying the first conductive layer. The method
also includes converting the first amorphous silicon layer into a first
polycrystalline silicon; and forming a second amorphous silicon layer overlying
the first amorphous silicon layer. A step of converting the second amorphous
silicon layer into a second polycrystalline silicon is included. The method also
includes forming a second conductive layer overlying the second amorphous
silicon layer. The combination of these steps forms a transparent solar cell
structure overlying the substrate.

In still a further aspect, the present invention provides a solar cell
comprising a substrate with a melting temperature of less than 450.degree. C., a
first conductive layer overlying the substrate, a first polycrystalline film
overlying the first conductive layer, a second polycrystalline film overlying
the first polycrystalline film, and a second conductive layer overlying the
second polycrystalline film.

Numerous advantages are achieved over conventional techniques for forming solar
cells. For example, the present method uses conventional equipment and processes
from semiconductor operations to manufacture the solar cells. In one aspect of
the present invention, an Excimer laser is used to anneal the amorphous silicon
layers. Use of this--or a similar laser--allows the forming of polycrystalline
silicon without exposing the substrate to high temperature that will distort or
destroy it. Therefore, low melting point materials such as plastic may be used.
The present solar cells can be transparent, which makes them desirable for
placing over glass and other see-through structures. In other aspects, the
present invention is easy to implement and control. The present cell structure
is extremely thin and efficient and can be implemented on a variety of
applications. For example, it can be formed on a flexible substrate and
substantially maintain the flexibility of the substrate. Depending upon the
embodiment, one or more of these advantages may exist. Other advantages may also
exist depending upon the embodiment.

A further understanding of the nature and advantages of the inventions presented
herein may be realized by reference to the remaining portions of the
specification and the attached drawings.

<PAGE>

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram of a transparent solar cell according to the
present invention;

FIG. 2 is a flow diagram  showing a method of fabricating  solar cells according
to the present invention;

FIGS.  3-8  are  cross-sectional  diagrams  of the  solar  cell  of the  present
invention at various steps of fabrication;

FIG.  9A shows a cross  section  of the  solar  cell  during  an  embodiment  of
annealing process;

FIG. 9B shows a thermal graph of the solar cell's temperature  through its depth
during the annealing process; and

FIG.  10 is a  cross-sectional  diagram  of a multiple  layer  solar cell of the
present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 is a cross-sectional diagram of an embodiment of a solar cell 100
according to the present invention. While referred to generically herein as a
solar cell, solar cell 100 also may operate efficiently as an optical filter. It
may be used as a solar cell exclusively, an optical filter exclusively, or as a
combination solar cell and optical filter.

Solar cell 100 may be fabricated in sheets of a size appropriate for its
intended use. It may also be fabricated on small substrates or in configurations
other than sheets. For example, solar cell 100 may be fabricated as a small
device for a hand-held electronic device or on large sheets to be applied to
large areas such as windows, buildings and automobiles. In contrast to existing
amorphous silicon solar cells, solar cell 100 is transparent. In this context,
transparency is defined as having the property of transmitting light without
appreciable scattering so that bodies lying beyond are seen clearly. In the
specific embodiment, the reflective component is very low; however, the amount
of reflection is controllable as will be discussed in more detail below.

Solar cell 100 has a substrate layer 110 providing a base structure for the
device. Substrate layer 110 may be a flexible material or a rigid material
depending on its intended use. A first conductive layer 120 overlies substrate
110. A P-N junction overlies first conductive layer 120. The P-N junction is
formed by a p+doped transparent polycrystalline silicon layer 135 and an n-doped
transparent polycrystalline silicon layer 145. In other embodiments (not shown),
the order is reversed and p+ polycrystalline silicon layer 135 is formed above
n- polycrystalline layer 145. The p+ doped polycrystalline silicon layer 135 and
the n- doped polycrystalline silicon layer 145 may obtain their transparency by
virtue of their method of fabrication as will be described in detail below. A
second conductive layer 150 resides above the P-N junction.

Because of its transparent nature, solar cell 100 can be placed unobtrusively
over a variety of surfaces for generating electricity. For example, it can be
used as window covering on buildings or automobiles, while maintaining the
aesthetics and functionality of the window. Such a window covering can absorb
some of the photons from sunlight or other light sources to produce electricity,
while allowing those photons not absorbed to pass through to the other side.
Thus, the view through the covered window is not completely blocked. Similarly,
solar cell 100 can cover a display from a laptop computer or other electronic
device such that it can gather light and generate electricity whether the device
is in operation or not. Such electronic devices may include portable telephones,
laptop computers, palm top computers, electronic watches, etc. While this is a
list of some of its applications, it is of course not exhaustive. One can
readily identify many applications in which transparent solar cell 100 might be
used to generate electricity while not obscuring in any significant degree, the
view of the user.

In another embodiment of the present invention, solar cell 100 may operate
effectively as an optical filter. In yet another embodiment, it may operate as
both a solar cell and an optical filter. It filters out light in undesirable
frequencies, while allowing light in the visible frequencies to pass through.
Because of its low reflectivity, it may also be used in applications that
benefit from anti-reflective coatings. While it is referred to herein
generically as solar cell 100, it is specifically intended that the term include
its usage as an optical filter as well.

<PAGE>

FIG. 2 shows a flow diagram of a method of fabricating solar cell 100 according
to the present invention. While FIG. 2 shows a specific embodiment, it is not
intended that this be the only way such a transparent solar cell may be
fabricated. One of skill in the art will recognize that other variations of the
invention are readily apparent from the specific embodiment described herein.

Referring to the flow diagram of FIG. 2, in step 210 a suitable substrate 110 is
provided upon which solar cell 100 may be fabricated. FIG. 3 shows a
cross-section of the device at step 210 of the fabrication. Substrate 110 may be
a rigid or flexible material. For example, flexible substrates such as plastic,
Mylar or Polyolifin may be used. Rigid substrates such as glass, crystal,
acrylic, or ceramic may also be used. Significantly, substrate 110 need not be a
material with a high melting point compared to the temperature at which
amorphous silicon crystallizes. Instead, it may include plastics and other
materials that have relatively low melting temperatures. This is in stark
contrast to previously known crystalline solar cells that required the use of a
substrate of a high melting point to withstand the fabrication process. One of
skill in the art will recognize many acceptable material for substrate 110 and
any may be used without departing from the present invention. The selection of a
rigid or flexible substrate 110 is arbitrary except to the extent that a rigid
or flexible structure is more appropriate for the end use of solar cell 100.
Depending upon the embodiment, substrate 110 may also be coated with a variety
of materials. The substrate can also be dyed.

In step 220, a first conductive layer 120 is formed on substrate 110 as depicted
in FIG. 4. In the specific embodiment, conductive layer 120 is indium tin oxide
(ITO) that is deposited by chemical vapor deposition (CVD). Other materials for
conductive layer 120 include magnesium fluoride, aluminum, tungsten, titanium
nitride, gold, silver, etc. In an embodiment of the present invention, a flash
of silver, aluminum, titanium or other reflective coating may be used to provide
a more reflective solar cell. The specific embodiment has an ITO thickness of
approximately one half micron over the area of interest; however, other
thicknesses may be appropriate for different applications and materials. Its
thickness is a function of the desired amount of transparency, conductivity, and
flexibility. It may be desirable for conductive layer 120 to be annealed after
it has been deposited. Such annealing improves mobility of electrons and holes
in conductive layer 120. Conductive layer 120 may also be deposited or formed in
other ways besides CVD. First conductive layer 120 may be a single layer or
multiple layers, depending upon the embodiment.

In step 225, first conductive layer 120 is optionally cleaned using any of a
variety of techniques well known in the art. Such techniques include metal
etching, laser scan, etc.

In step 230, a first doped amorphous silicon layer 130 is formed overlying the
region of interest of conductive layer 120. The resulting structure is shown in
FIG. 5. In the specific embodiment, amorphous silicon layer 130 is a p+ type
material. It is in-situ doped using CVD with boron at concentration such as are
commonly used for producing solar cells. In other embodiments, amorphous silicon
layer 130 may be formed by implantation or diffusion processes. First amorphous
silicon layer 130 preferably has a thickness of at least 300 .ANG. at its
thinnest points and a nominal thickness of at least 500 .ANG. across its
surface. Its maximum thickness is about 1,000 .ANG. in the specific embodiment
due to limits on the effectiveness of the Excimer laser to convert amorphous
silicon to polycrystalline silicon (see step 240 below). Of course, it will be
recognized that new techniques, processes and materials may be developed that
will have different minimum and maximum specifications.

Next, in step 240, first amorphous silicon layer 130 is annealed at high
temperature by applying rapid thermal energy to the region, thereby converting
amorphous silicon layer 130 to transparent polycrystalline silicon layer 135. In
this context, annealing is defined as the process of converting amorphous
silicon to polycrystalline silicon. The resulting structure is depicted in FIG.
6. In the specific embodiment, this annealing is accomplished with a pulsed
Excimer laser, which is a gas laser using xenon chloride. The Excimer laser
heats up the material at approximately 1,000,000 degrees per second allowing
first amorphous silicon layer 130 to be rapidly annealed. Other types of lasers
or other rapid thermal energy devices may also be preferably used to perform
this annealing. For example, a diode laser that has been frequency

<PAGE>

converted to ultraviolet frequencies, a diode crystal laser that has been
frequency converted to ultraviolet frequencies, and a diode pumped crystal (YAG
or YELF) laser that has been frequency converted to ultraviolet frequencies are
examples of lasers that may be used, although the present invention is not
limited to only these types of lasers.

The Excimer laser outputs a beam that effectively converts amorphous silicon to
polycrystalline silicon for a depth of approximately 1,000 .ANG.. Because it
heats up only such a relatively short distance into the structure, the
underlying substrate is not subjected to the high temperatures to which the
amorphous silicon layer is subjected. Therefore, in contrast to other
methodologies, the substrate may be of a low melting point material such as
plastic. In the specific embodiment, the Excimer laser is operated at 248-308 nm
at, typically, 600 mJ/cm.sup.2, with a pulse duration of no more than 50
nanoseconds, but typically 45 nanoseconds.

In applications in which the substrate can be processed at moderately high
temperatures (for example, glass at 550 degrees C.,) rapid thermal annealing of
amorphous silicon into polycrystalline silicon could alternatively be done using
flash lamps or similar devices (e.g. pulsed CO.sub.2 lasers).

This annealing step also serves to activate the p-type dopant. In the specific
embodiment, the underlying substrate may be preheated to a temperature below the
melting point of the substrate before applying the laser. In the specific
embodiment, this preheating is approximately 300 to 350 degrees. Other
embodiments may not use any preheating at all.

The amorphous silicon deposition process of step 230 and the thermal annealing
process of step 240 results in a particular grain size for polycrystalline
silicon layer 135. In the specific embodiment, the root mean square (RMS) of
grain sizes is between 0.25 microns and 0.50 microns. The grain size is
preferably between 0.1 micron and 2.0 microns.

In step 245, a temporary barrier (not shown) is formed overlying polycrystalline
silicon layer 135. This step is optional and may be skipped in some embodiments.
The barrier is preferably a 50 .ANG. thick layer of SiO.sub.2, a nitride, or
other dielectric material. Its purpose is to seal polycrystalline silicon layer
135 from a subsequent oppositely doped layer. The barrier is intended to be
temporary and may be removed in later processing.

In steps 250, second doped amorphous silicon layer 140 is formed overlying
polycrystalline silicon layer 135. Amorphous silicon layer 140 is oppositely
doped from amorphous silicon layer 130. The resulting structure is shown in FIG.
7. In the specific embodiment, amorphous silicon layer 140 is doped with an
n-type material such as phosphene or other n-type dopant. It may be formed with
in-situ doping and CVD deposition. Other embodiments may reverse the order of
the different dopant types in amorphous silicon layers 130 and 140 so that the
p-type layer overlies the n-type layer. Amorphous silicon layer 140 may
alternatively be doped by implantation or diffusion.

In step 260, amorphous silicon layer 140 is annealed using the Excimer laser or
other rapid thermal energy process as described in step 240. This results in a
transparent polycrystalline silicon layer 145. The resulting structure is shown
in FIG. 8. Step 260 also activates the dopant. The barrier formed in step 245
may be removed during the annealing process leaving a P-N junction between
layers 135 and 145.

In step 270, a second conductive layer 150 is formed above the P-N junction
resulting in solar cell 100 as shown in FIG. 1. In the specific embodiment, the
second conductive layer is also ITO that is deposited with CVD at a thickness of
about one-half micron over the area of interest. Again, its maximum thickness is
dependent upon the desired transparency, conductivity, and flexibility. Second
conductive layer 150 may also be optionally annealed to improve the mobility of
the electrons and holes.

<PAGE>

Steps 220-270 may be performed using a roll-to-roll coater. Such roll-to-roll
coaters are well known in the art. Using this technique, large sheets of solar
cells 100 may be formed on large rolls of a substrate such as plastic.
Processing steps 220-270 are performed with equipment located between the two
rolls of the roll-to-roll coater. The Excimer laser is one of these pieces of
equipment. It typically outputs a beam that is 0.6 mm wide and extends across
the substrate. Multiple lasers may be also be used together to increase the rate
of processing over large surface areas. The rolls of plastic may be moved so the
entire substrate is exposed to the laser. Alternatively, the laser may be moved
over the substrate instead of moving the substrate.

FIG.  9A  shows a cross  section  of solar  cell 100  during  an  embodiment  of
annealing process of step 240. A sheet of substrate 110 has already been layered
with  transparent  conductor 120 and amorphous  silicon 130. A laser 300 resides
above the  sheet  and  transmits  thermal  energy  into  amorphous  silicon  130
converting it to polycrystalline  silicon 135 as the sheet moves past laser 300.
As described  above,  laser 300 may be an Excimer  laser or other type of laser.
The thermal energy output of laser 300 is such that amorphous  silicon layer 130
is heated above approximately  1400.degree.  C. to convert it to polycrystalline
silicon, but substrate 110 remains below 450.degree.  C. FIG. 9B shows a thermal
graph of the temperature of the sheet through its depth. At the top of amorphous
silicon 130, the temperature  may be  1450.degree.  C. while at the bottom it is
approximately 1400.degree.  C. Through transparent conductor 120 the temperature
declines rapidly until it is less than  450.degree.  C. at substrate 110. In the
specific  embodiment,  the laser  moves  across the sheet slow  enough that each
pulse of the laser overlaps the portion that was previously exposed to the beam.
Preferably  the overlap is two thirds the width of the beam. A typical scan rate
is 60 mm per second.

In operation, electrodes are provided to each of the p+ and n- polycrystalline
silicon layers 135 and 145 to form an electrical circuit. In the presence of
optical radiation, the P-N junction of the specific embodiment develops a
typical 0.46 volt potential at approximately 7 mA/cm.sup.2 in sunlight. However,
it can be constructed such that a wide range of power output is provided. Such
outputs can vary by orders of magnitude. The size of the area, the quantum
efficiency of the cell (electron-hole mobility/absorptivity) and the energy
level of the instant optical energy determines the amount of optical energy
converted to electrical current. A typical design efficiency is about 2-3% or
better, as compared with an opaque crystalline solar cell with an efficiency of
13%. An advantage of solar cell 100 is that it does not depend on hydrogen as a
carrier, so it does not suffer from the efficiency loss that amorphous silicon
does. Thus, its lifetime is extended over that of amorphous solar cells.

In another embodiment of the present invention, multiple layers of P-N junctions
may be formed by repeating steps 220-270. The resulting multiple layer solar
cell may increase the efficiency to more closely resemble that of crystalline
solar cells. FIG. 9 is a cross-sectional diagram of a resulting multiple layer
solar cell 900. Although solar cell 900 shows only two levels of solar cells,
any number may be formed. Since these layers are transparent, the resulting
solar cells in the lower levels are exposed to the light even though they are
underneath other solar cells. This may be desirable for some applications to
increase the efficiency and extend the life of the resulting structure.

Referring to FIG. 10, a single layer solar cell such as solar cell 100 is formed
and an additional solar cell is formed above it to form a multiple layer solar
cell 900. In some embodiments, second transparent conductor 150 is thicker than
first transparent conductor 120. In other embodiments it is the same thickness.
In still other embodiments, a dielectric layer (not shown) is formed on another
conductive layer (not shown) is formed above the dielectric layer.

A second p+ polycrystalline layer 910 is formed by forming a p+ amorphous
silicon layer and annealing it as described above. A second n- polycrystalline
layer 910 is formed above second p+ polycrystalline layer 910 by forming an n-
amorphous silicon layer and annealing it. A third transparent conductor 930 is
formed above that. This process may be repeated to form as many layers as is
desirable.

<PAGE>

As described briefly above, the reflectivity of solar cell 100 may be varied
depending on the application. In some embodiments, it is desirable that the
outer conductive layer (i.e., second conductive layer 150) be as anti-reflective
as possible, while the inner conductive layer (i.e., first conductive layer 120)
is reflective. Such a design will allow the maximum amount of sunlight to be
absorbed since it passes through solar cell 100 as it enters and as it is
reflected back. Other embodiments may make use of various reflective qualities
for functional or aesthetic reasons.

To provide the reflectivity, an embodiment substitutes a flash of silver,
aluminum, titanium or other reflective conductor instead of a transparent
conductor such as ITO. This substitution can be made on any or all of the
conductive layers, depending on the desired reflectivity.

In other embodiments of the present invention, solar cell 100 may also be used
as an optical filter. Using the above-described methodology, solar cell 100
provides a photopic response that is very similar to that of the human eye. That
is, it absorbs about 20-80% of those light frequencies which are visible to the
human eye, while allowing the rest of the visible light to pass through. It can
be used as an optical filter alone, or in combination with its use as a solar
cell.

While a specific embodiment has been described herein, it will be recognized
that the present invention is not limited to the specific embodiment described.
For example, the p+ and n- layers 135 and 145 may be reversed. Also, different
or new fabrication techniques may be used or other changes made that do not
depart from this spirit and scope of the present invention. The invention is
intended to be limited only by the attached claims.

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