U.S. patent application number 13/074390 was filed with the patent office on 2011-07-21 for spectrally adaptive multijunction photovoltaic thin film device and method of producing same.
This patent application is currently assigned to SUNLIGHT PHOTONICS INC.. Invention is credited to Allan James Bruce, Sergey Frolov, Joseph Shmulovich.
Application Number | 20110174366 13/074390 |
Document ID | / |
Family ID | 39738581 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110174366 |
Kind Code |
A1 |
Frolov; Sergey ; et
al. |
July 21, 2011 |
SPECTRALLY ADAPTIVE MULTIJUNCTION PHOTOVOLTAIC THIN FILM DEVICE AND
METHOD OF PRODUCING SAME
Abstract
A method is provided for converting optical energy to electrical
energy in a spectrally adaptive manner. The method begins by
directing optical energy into a first photovoltaic module that
includes non-single crystalline semiconductor layers defining a
junction such that a first spectral portion of the optical energy
is converted into a first quantity of electrical energy. A second
spectral portion of the optical energy unabsorbed by the first
module is absorbed by a second photovoltaic module that includes
non-single crystalline semiconductor layers defining a junction and
converted into a second quantity of electrical energy. The first
quantity of electrical energy is conducted from the first module to
a first external electrical circuit along a first path. The second
quantity of electrical energy is conducted from the second module
to a second external electrical circuit along a second path that is
in parallel with the first path.
Inventors: |
Frolov; Sergey; (Murray
Hill, NJ) ; Bruce; Allan James; (Scotch Plains,
NJ) ; Shmulovich; Joseph; (New Providence,
NJ) |
Assignee: |
SUNLIGHT PHOTONICS INC.
South Plainfield
NJ
|
Family ID: |
39738581 |
Appl. No.: |
13/074390 |
Filed: |
March 29, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11714681 |
Mar 6, 2007 |
|
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13074390 |
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Current U.S.
Class: |
136/255 ;
257/E31.001; 438/73 |
Current CPC
Class: |
H01L 31/042 20130101;
H01L 31/078 20130101; H01L 31/076 20130101; Y02E 10/548 20130101;
H01L 31/0322 20130101; H01L 31/043 20141201; H01L 31/0725
20130101 |
Class at
Publication: |
136/255 ; 438/73;
257/E31.001 |
International
Class: |
H01L 31/06 20060101
H01L031/06; H01L 31/18 20060101 H01L031/18 |
Claims
1. A spectrally adaptive photovoltaic device, comprising: a
plurality of photovoltaic modules disposed one on top of another,
each of the modules including first and second conductive layers
and at least first and second semiconductor layers disposed between
the conductive layers, said first and second semiconductor layers
defining a junction at an interface therebetween; said first and
second semiconductor layers of at least one of the modules being
non-single crystalline, thin-film layers; a substrate on which the
plurality of photovoltaic modules are stacked; an insulating layer
disposed between adjacent photovoltaic modules; and wherein at
least one of the junctions is configured to convert a first
spectral portion of optical energy into an electrical voltage and
transmit a second spectral portion of optical energy to another of
the junctions that is configured to convert the second spectral
portion of optical energy into an electrical voltage.
2. A device of claim 1 wherein the plurality of modules includes at
least three modules.
3. A device of claim 1 wherein the plurality of junctions
collectively have a solar energy conversion efficiency of greater
than about 20%.
4. A device of claim 1 where at least two of the junctions have
semiconductor bandgaps that are different from each other.
5. A device of claim 4 where said junction with a smaller bandgap
is disposed below another of junction with a larger bandgap and
absorbs said second part of optical energy.
6. A device of claim 1 where said modules are laterally displaced
from one another in part to thereby expose a portion of each of the
conductive layers.
7. A device of claim 1 where said semiconductor layers comprise
CIGS-based semiconductor materials.
8. A device of claim 1 where said semiconductor layers comprise
Cd-based semiconductor materials.
9. A device of claim 1 where said semiconductor layers comprise
semiconducting polymers.
10. A device of claim 1 where said semiconductor layers comprise
nanoparticle composite materials.
11. A device of claim 1 where said semiconductor layers comprise
organic composite materials.
12. A device of claim 1 where said semiconductor layers comprise
amorphous semiconductor materials.
13. A device of claim 1 wherein the semiconductor layers of at
least one of the modules comprise a compound semiconductor
material.
14. A device of claim 1 where said first and second conductive
layers comprise transparent conducting layers.
15. A device of claim 1 where said insulating layer comprises a
transparent insulating layer.
16. A device of claim 1 further comprising a reflecting coating
located between a bottommost junction and the substrate.
17. A device of claim 1 further comprising a textured surface for
scattering unabsorbed part of said optical energy.
18. A device of claim 1 wherein a fill factor of a module remote
from the substrate is largely independent of a fill factor of a
module closer to the substrate.
19. A device of claim 1 where said modules are hybridly attached to
each other.
20. A device of claim 1 where said modules are laminated to each
other.
21. A device of claim 1 where said modules are bonded to each
other.
22. A device of claim 1 wherein each module has an area larger than
about 400 cm.sup.2.
23. A device of claim 1 further comprising a plurality of
electrical voltage converters coupled to the conductive layers for
converting different voltages from different junctions to a single
common voltage.
24. A device of claim 1 wherein a conversion efficiency of the
device is less dependent on the spectral content of said optical
energy than a corresponding device in which current matching is
applicable.
25. A method of forming a spectrally adaptive photovoltaic device,
comprising: forming on a substrate a first photovoltaic module that
includes first and second conductive layers and at least first and
second semiconductor layers disposed between the first and second
conductive layers, said first and second semiconductor layers
defining a first junction at an interface therebetween such that
the first junction converts a first spectral portion of optical
energy into an electrical voltage; forming an insulating layer over
the first photovoltaic module; and forming on the insulating layer
a second photovoltaic module that includes third and fourth
conductive layers and at least third and fourth semiconductor
layers disposed between the third and fourth conductive layers,
said third and fourth semiconductor layers defining a second
junction at an interface therebetween such that the second junction
converts a second spectral portion of optical energy into an
electrical voltage.
26. The method of claim 25 wherein said modules are initially
produced on different sacrificial substrates.
27. The method of claim 25 further comprising independently
selecting values of output voltages and currents for each of said
photovoltaic modules to enhance their respective individual fill
factors, wherein said values of output voltages and currents depend
at least on part on a spectral profile of said optical energy.
28. The method device of claim 25 where said modules are hybridly
attached to each other.
29. The method of claim 25 where said modules are laminated to each
other.
30. The method of claim 25 where said modules are bonded to each
other.
31. The method of claim 25 wherein each module has an area larger
than about 400 cm.sup.2.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of co-pending U.S.
patent application Ser. No. 11/714,681, filed Mar. 6, 2007, which
is incorporated herein by reference in its entirety.
BACKGROUND
[0002] 1. Field
[0003] The following relates to photovoltaic devices and methods of
producing such devices. More particularly, the following relates to
photovoltaic devices that have substantially improved optical
spectral responsivity and efficiency, and that can be produced by
laminating or otherwise integrating multiples of discrete
photovoltaic devices.
[0004] 2. Related Art
[0005] Photovoltaic devices represent one of the major sources of
environmentally clean and renewable energy. They are frequently
used to convert optical energy into electrical energy. Typically, a
photovoltaic device is made of one semiconducting material with
p-doped and n-doped regions. The conversion efficiency of solar
power into electricity of this device is limited to a maximum of
about 37%, since photon energy in excess of the semiconductor's
bandgap is wasted as heat. A photovoltaic device with multiple
semiconductor layers of different bandgaps is more efficient: an
optimized two-bandgap photovoltaic device has the maximum solar
conversion efficiency of 50%, whereas a three-bandgap photovoltaic
device has the maximum solar conversion efficiency of 56%. Realized
efficiencies are typically less than theoretical values in all
cases.
[0006] Multi-layered or multi junction devices are currently
manufactured as monolithic wafers, where each semiconductor layer
is crystal-grown on top of the previous one. As a result, the
semiconductor layers are electrically connected in series and have
to be current-matched, in order to obtain maximum conversion
efficiency. This current-matching procedure complicates the design
and decreases the efficiency of the device. The latter becomes
particularly evident when considering the effect of spectral
filtering on the device efficiency. If a part of the solar spectrum
is absorbed or scattered, e.g. by water vapors, the resulting
disproportional decrease of photocurrent in one of junctions will
limit the current through the whole device and thus decrease its
conversion efficiency.
SUMMARY
[0007] An apparatus for spectrally adaptive photovoltaic energy
conversion device, insensitive to current matching effects, and a
method for producing the same are provided. The apparatus includes
a substrate, a plurality of thin-film single junction photovoltaic
layers disposed on said substrate and a plurality of electrical
contacts to each of said layers. The plurality of photovoltaic
layers may be semi-conducting and have different respective
bandgaps so as to increase the conversion efficiency of the device.
The said layers may further be at least partially transparent in
the spectral energy range below their respective bandgaps. The said
layers may further be electrically isolated from each other. The
plurality of electrical contacts is arranged to receive independent
electrical currents from each of the photovoltaic layers, so as to
further increase conversion efficiency and provide spectrally
adaptive capabilities of a device with respect color and intensity
variations in incident or absorbed light.
[0008] In accordance with another aspect of the invention, a method
is provided for converting optical energy to electrical energy in a
spectrally adaptive manner. The method begins by directing optical
energy into a first photovoltaic module that includes non-single
crystalline semiconductor layers defining a junction such that a
first spectral portion of the optical energy is converted into a
first quantity of electrical energy. A second spectral portion of
the optical energy unabsorbed by the first module is absorbed by a
second photovoltaic module that includes non-single crystalline
semiconductor layers defining a junction and converted into a
second quantity of electrical energy. The first quantity of
electrical energy is conducted from the first module to a first
external electrical circuit along a first path. The second quantity
of electrical energy is conducted from the second module to a
second external electrical circuit along a second path that is in
parallel with the first path.
[0009] In accordance with another aspect of the invention, a method
is provided for converting optical energy with a given spectral
profile to electrical energy. The method begins by receiving
optical energy on an uppermost module of a photovoltaic device that
includes a plurality of modules stacked one on top of another. A
first spectral portion of the optical energy is converted to
electrical energy. The uppermost module has a first fill factor
determined in part by the given spectral profile of the first
spectral portion of the optical energy. A remaining portion of the
optical energy is transferred to a second module located below the
uppermost module. At least a fraction of the remaining portion of
the optical energy is converted to electrical energy. The second
module has a second fill factor largely independent of the first
fill factor of the uppermost module and determined in part by the
given spectral profile of the remaining spectral portion of the
optical energy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic diagram of a thin-film multi junction
photovoltaic device with spectrally adaptive capabilities.
[0011] FIG. 2 is a cross-section of a multi-layered multi junction
photovoltaic thin film stack.
[0012] FIG. 3 is a schematic diagram for external electrical
connections providing a single voltage electrical terminal.
DETAILED DESCRIPTION
Overview
[0013] In the following detailed description, numerous specific
details are set forth in order to provide a thorough understanding
of exemplary embodiments or other examples described herein.
However, it will be understood that these embodiments and examples
may be practiced without the specific details. In other instances,
well-known methods, procedures, components and circuits have not
been described in detail, so as not to obscure the following
description. Further, the embodiments disclosed are for exemplary
purposes only and other embodiments may be employed in lieu of, or
in combination with, the embodiments disclosed.
[0014] As summarized above and described in more detail below, the
apparatus for spectrally adaptive photovoltaic energy conversion
device and the method for producing the same is provided.
Embodiments of this apparatus and method may facilitate the ability
to efficiently and economically convert electro-magnetic energy in
the form of light into electrical energy in the form of electrical
current. Embodiments of this apparatus and method may also
facilitate large volume production and widespread usage of
photovoltaic devices.
[0015] This invention utilizes thin-film technology as an
alternative method of producing a multi junction photovoltaic
device. As well known in the art, multi junction devices in general
are a more efficient means for conversion solar energy into
electricity. However, the development of these devices is currently
hindered by the complexity of semiconductor manufacturing processes
and their high cost. On the other hand, thin-film processing is
substantially less complex and expensive. Using new design
approaches and thin-film technology, a new efficient photovoltaic
device with expanded capabilities and application range can be
produced.
[0016] Typically, single-crystal semiconductors are grown
epitaxially, layer-by-layer on a monolithic wafer. Thin-film
materials, in contrast, depending on their chemical origin can be
deposited and layered by a variety of different methods, using for
example evaporation, sputtering, spraying, inkjet printing etc.,
some of which could be very inexpensive. Furthermore, some
thin-film layers can be produced separately and then integrated
hybridly using bonding, lamination and other similar methods.
Alternatively, in some cases the entire structure may be
sequentially grown without the need for any mechanical integration
of the individual layers. This flexibility in a manufacturing
method makes it possible to implement new design approaches in
producing a better photovoltaic device.
[0017] Specifically, a multi-layered and multi junction
photovoltaic device 100 may be produced as shown in FIG. 1, in
which each junction layer (111, 112 and 113) includes a single
junction with an optically active semiconductor having a specific
bandgap. Of course, each so-called junction layer includes at least
two sublayers that define a junction at their interface. The
junction may be a heterojunction in which the sublayers are formed
of dissimilar materials. Alternatively, the junction may be of any
type known in the art such as, but not limited to, p-i-n junctions,
MIS junctions and the like. The number of junction layers, n, may
be larger than two. Also, the semiconductor material may be, for
example, a compound semiconductor formed from an inorganic,
polymer-based material, an organic dye-based material, a
nanoparticle composite material, a quantum dot composite material,
or a mixture of the above materials. Said junction layers are
situated in a stack one above another in said multi-layered device.
When this photovoltaic device is illuminated by light 101, each one
of its junction layers may absorb a part of light with photon
energies above a corresponding bandgap and transmit a part of light
with photon energies below a corresponding bandgap (102 and 103).
These junction layers may be arranged so that the bandgaps of lower
lying junctions are smaller than the bandgaps of higher lying
junctions; this condition improves the conversion efficiency of the
device. Furthermore, these junction layers may be electrically
isolated from each other and provided with at least two individual
electrical contacts 130 of opposite polarity for producing
electrical current. All the junction layers may be attached to a
common substrate that may be sturdy yet flexible. The substrate
also may be coated with a reflective layer. One or more surfaces in
this device could be textured to provide a relief pattern for
multiple light reflections and scattering, which increase
absorption length and improve conversion efficiency.
[0018] Thin-film technology greatly simplifies the production of a
multi-junction, non-single crystalline (e.g., polycrystalline,
amorphous) photovoltaic device. Furthermore, it enables the
production of large area, single-sheet, photovoltaic multi junction
devices. The latter is not possible using a standard single-crystal
semiconductor technology due to the typically limited and small
size of semiconductor wafers. Thin-film layers formed from various
compound semiconductors may be manufactured as large sheets and
laminated, or otherwise joined, together to form a single large
area, low-cost device. Moreover, one may define a figure-of-merit
for a photovoltaic device as the ratio of its conversion efficiency
to the manufacturing cost per unit area:
a. FOM=Efficiency/Cost (1)
[0019] One may also see using Eq.1, that thin-film non-single
crystalline multi junction devices will provide the highest
attainable FOM. Indeed, their conversion efficiency is estimated to
be in the range of 30% to 50% and comparable to that of a single
crystal multi junction device, whereas a single junction thin-film
photovoltaic device has efficiency of less than 20%. Yet at the
same time, their manufacturing cost is estimated to be two orders
of magnitude lower than that of a single crystal multi junction
device. Thus, it is estimated that FOM of thin-film multi junction
devices could be about 100 times larger than that of a single
crystal multi junction device and 3-5 times larger than that of a
single junction thin-film device.
[0020] Current approaches to the design of multi junction devices
usually result in production of serially connected junctions. As a
result, an electrical current through each junction must be the
same; this is a condition called current matching and it is
accomplished by careful selection of semiconductor bandgaps and
layer thicknesses given a predetermined shape of the light
spectrum. This current matching unduly complicates the design of
the device, reduces its fault tolerance and may also reduce its
conversion efficiency. For example, a failure of one junction will
result in a failure of the whole device. Furthermore, under
changing environmental conditions the spectrum of light used for
energy conversion may change substantially. This effect may in turn
lead to disproportionately different changes of current in
different junctions, thus breaking the current matching condition
and reducing conversion efficiency. For example, if an increase of
moisture content in terrestrial atmosphere leads to 50% reduction
of infrared portion of sunlight optical energy due to optical
filtering effect, then a typical single crystal multi junction
device with Ge as a bottom layer active material may experience an
overall 50% reduction in its output current. In this situation the
bottom-most junction will limit the current provided by the whole
device because the current in the upper junction or junctions
cannot exceed this value even though they would be able to do so
otherwise. As a result, the fill factor of the upper junction or
junctions will be substantially reduced and the overall conversion
efficiency of the device will decrease.
[0021] To overcome the problems arising from serially connected
junctions, this invention further improves photovoltaic conversion
technology by providing separate contact layers 130 and electrical
contacts 140 for each junction layer in thin-film multijunction
device. Each contact pair 140 acts as a separate, independent
photovoltaic source, thus producing n sets of currents and
voltages: from I.sub.1 and V.sub.1, I.sub.2 and V.sub.2, to I.sub.n
and V.sub.n, where n is the number of junctions. This provision
eliminates the need for the current matching condition, which in
turn results in a simpler design and manufacturing process, a more
robust and fault tolerant performance, higher conversion efficiency
and an adaptive capability with respect to changes in the spectral
content of light used for conversion. More specifically, the latter
property of the multijunction photovoltaic device, referred to as
spectral adaptation, allows the photovoltaic device to operate at
its maximum possible efficiency regardless of any optical filtering
effects that may occur during its operation. That is, with spectral
adaptation, if the spectral content or profile of the optical
energy changes, the conversion efficiency of the device will not
decrease to as large an extent as it would if the junctions in the
device were required to be current matched. This is because the
fill factor of each junction can be largely tailored to the
spectral content of the optical energy independent of the other
junctions in the device. Also, a failure of any of the thin-film
junction layers will not result in failure of the whole device,
since they are electrically isolated.
[0022] An additional benefit of this modular manufacturing approach
is that a toolbox of individual cell components with different
bandgaps could be separately developed and that the set of such
cells used in a multijunction device may be specifically selected
to maximize the performance for different illumination conditions
including AM0 (Space) without any significant change to the
manufacturing approach or processing. It is further conceived that
a single manufacturing line could be used for a family of
products.
Examples
[0023] FIG. 2 shows an exemplary embodiment of this invention, in
which three different junction layers 111, 112 and 113 are
utilized. Maximum sunlight power conversion efficiency of this
architecture is about 56% for highly concentrated sunbeam and about
50% for regular sunlight intensity (so called condition AM1.5). All
three layers contain active polycrystalline semiconductor materials
based, for example, on a CIGS (Copper Indium Gallium Selenide)
material system or a related alloy, and the corresponding junctions
are produced using single junction designs known in the art. By
varying the In and Ga relative concentrations the bandgaps in layer
111 may be adjusted to about 1.7 eV, in layer 112--to about 1.4 eV
and in layer 113--to about 1.1 eV. The thickness of each layer may
be in the range of 1 to 10 microns. Each junction layer may also
contain buffer layers, such as, for example, a thin CdSe layer with
a thickness in the range of 10 to 1000 nm. Each junction layer may
be located between appropriately matched transparent conducting
layers 130. The conducting layers 130 may be formed from thin
layers of ITO or ZnO with a thickness in the range of 0.1 to 5
.quadrature.m. Adjacent conducting layers may be separated by an
electrical insulator layer 220, which is optically transparent in
the appropriate spectral range. For example, electrically
insulating layers may comprise thin films of polymer coating with a
thickness in the range of 0.5 to 10 microns. For purposes of
clarity in what follows, each junction layer (e.g., junction layers
111,112 and 113) along with its associated conducting layer from
time to time may be referred to as a single module. That is, the
photovoltaic device shown in FIG. 2 is formed from three such
modules.
[0024] The various modules shown in FIG. 2 may be laminated
together on a common carrier substrate 110, such as a thin
polyimide film with a thickness in the range of 25 to 500 microns.
The substrate may be coated with metal such as Al to reflect
unabsorbed light back into the individual junction modules. The
junction modules may be staggered or laterally offset from one
another so that each conducting layer 130 has an exposed region
230. The exposed regions 230, which may be covered with metal to
provide better conductivity, serve as surfaces that can connect the
modules to external electrical circuits. As a result, the three
modules shown in the device of FIG. 2 may have up to six electrical
output connectors.
[0025] In another embodiment, the apparatus and method described
above and shown in FIG. 2 may be modified, so that the bandgaps of
junction layers 111, 112 and 113 are 1.8 eV, 1.2 eV and 0.8 eV,
respectively. This bandgaps selection is close to the optimum set
of three bandgaps for a multijunction photovoltaic device with
optimized conversion efficiency.
[0026] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that the
active semiconducting material used in producing one or more
junction layers is other than the CIGS-based material. This
material may be for example CdTe. In another version of this
embodiment this material may be a semiconducting polymer material,
such as for example poly-phenylene-vinylene and its derivatives. A
variety of other known and previously mentioned semiconducting
materials may be chosen without departing from the scope of the
invention.
[0027] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that the
substrate is transparent and is attached on the top of the first
junction layer 111.
[0028] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that said
junction layers are attached to individual insulating and
transparent substrates providing mechanical support such that the
common substrate is not necessary.
[0029] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that three
of electrical output connectors may be shorted or connected to the
ground without loss of device functionality.
[0030] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that
additional junction layers with different bandgaps may be laminated
with additional individual electrical contacts. In this embodiment
the total number of junctions and bandgaps may be greater than
four, and the bandgap values are chosen to maximize device
conversion efficiency for a given number of junctions.
[0031] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that said
junction layers may be produced on separate sacrificial substrates
and detached from these substrate before or during the lamination
process.
[0032] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that said
junction layers may be bonded together to produce a single
multi-layered photovoltaic film.
[0033] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that said
junction layers may be glued together to produce a single
multi-layered photovoltaic film.
[0034] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that
intermediate insulating material may have a refractive index
matched to the surrounding layers, in order to minimize light
reflections at layer interfaces in appropriate regions of the
optical spectrum.
[0035] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that said
conducting layers 130 may be covered with a patterned grid of
highly conductive metal, such as Cu or Al, to decrease electrical
resistance of the corresponding contact layers without substantial
decrease in optical transmissivity of the corresponding contact
layers.
[0036] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that the
reflective surface of the bottom substrate may be textured so that
reflected light is scattered and absorbed by junction layers more
efficiently.
[0037] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that the
bottom substrate may be textured and non-uniform so as to provide a
textured and non-uniform pattern for all junction layers in order
to increase light absorption by junction layers.
[0038] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that the
bottom substrate may be transparent and its bottom surface may be
reflective and textured in order to increase light scattering and
absorption.
[0039] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that the
multi-layered multijunction film has an area larger than 400
cm.sup.2.
[0040] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that at
least one electrical contact pair from a junction layer is
connected to an individual electrical grid which improves
conversion efficiency of the whole photovoltaic film.
[0041] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that each
electrical contact pair from corresponding junction layers is
connected to an individual electrical grid which improves
conversion efficiency of the whole photovoltaic film.
[0042] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that each
electrical contact pair from corresponding junction layers is
connected to a DC-to-DC voltage converter.
[0043] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that each
electrical contact pair from corresponding junction layers is
connected to a DC-to-AC voltage converter.
[0044] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that each
electrical contact pair from corresponding junction layers is
connected to a voltage converter. Each voltage converter 301 may
convert a different junction voltage to a common voltage, so that
all junction layers may be connected in parallel without loss of
functionality as shown in FIG. 3 thus providing only two output
terminals.
[0045] In yet another embodiment, the apparatus and method
described above and shown in FIG. 2 may be modified, so that said
junction layers are subdivided into different sections and
electrically connected in series to provide a higher output
voltage.
[0046] Variations of the apparatus and method described above are
possible without departing from the scope of the invention.
* * * * *