U.S. patent application number 17/019964 was filed with the patent office on 2020-12-31 for monolithic integration of microinverters on solar cells.
The applicant listed for this patent is The Regents of the University of Michigan. Invention is credited to Stephen R. Forrest, Kyusang Lee.
Application Number | 20200412297 17/019964 |
Document ID | / |
Family ID | 1000005086829 |
Filed Date | 2020-12-31 |
United States Patent
Application |
20200412297 |
Kind Code |
A1 |
Forrest; Stephen R. ; et
al. |
December 31, 2020 |
MONOLITHIC INTEGRATION OF MICROINVERTERS ON SOLAR CELLS
Abstract
A method of fabricating a photovoltaic cell having a
microinverter is provided. The method may include fabricating a
monolithic microinverter layer through epitaxy and operably
connecting the at least one microinverter layer to at least one
photovoltaic cell formed on a photovoltaic layer. A photovoltaic
device is also provided. The device may have a photovoltaic layer
comprising at least one photovoltaic cell and a microinverter layer
comprising at least one microinverter, wherein the microinverter
layer was fabricated through epitaxy, the at least one
microinverter is configured to be operably connected to at least
one photovoltaic cell.
Inventors: |
Forrest; Stephen R.; (Ann
Arbor, MI) ; Lee; Kyusang; (Ann Arbor, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Regents of the University of Michigan |
Ann Arbor |
MI |
US |
|
|
Family ID: |
1000005086829 |
Appl. No.: |
17/019964 |
Filed: |
September 14, 2020 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15534504 |
Jun 9, 2017 |
10778141 |
|
|
PCT/US2015/065167 |
Dec 11, 2015 |
|
|
|
17019964 |
|
|
|
|
62090661 |
Dec 11, 2014 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 31/0693 20130101;
H01L 31/1844 20130101; H01L 31/1896 20130101; H01L 31/0735
20130101; Y02E 10/544 20130101; H01L 31/184 20130101; H02S 40/32
20141201 |
International
Class: |
H02S 40/32 20060101
H02S040/32; H01L 31/0735 20060101 H01L031/0735; H01L 31/18 20060101
H01L031/18; H01L 31/0693 20060101 H01L031/0693 |
Claims
1. A photovoltaic device comprising: a photovoltaic layer of at
least one photovoltaic cell; and a microinverter layer of at least
one microinverter; wherein the photovoltaic layer and the
microinverter layer are epitaxial layers such that the at least one
microinverter is operably connected to the at least one
photovoltaic cell.
2. The photovoltaic device of claim 1, further comprising an
insulating layer between the photovoltaic layer and the
microinverter layer.
3. The photovoltaic device of claim 2, wherein the insulating layer
comprises a wide band bandgap semiconductor material.
4. The photovoltaic device of claim 1, wherein the microinverter
layer is atop the photovoltaic layer such that the at least one
microinverter is on top of the at least one photovoltaic cell.
5. The photovoltaic device of claim 1, further comprising a
substrate, wherein the at least one photovoltaic cell is between
the substrate and the at least one microinverter.
6. The photovoltaic device of claim 5, further comprising a metal
contact between the photovoltaic layer and the substrate such that
the at least one photovoltaic cell and the at least one
microinverter are connected to the substrate via the metal
contact.
7. The photovoltaic device of claim 5, wherein the substrate is
flexible.
8. The photovoltaic device of claim 5, wherein the at least one
photovoltaic cell is cold weld bonded to a metallized surface of
the substrate.
9. The photovoltaic device of claim 1, wherein the at least one
microinverter comprises an H-bridge DC/AC inverter circuit
monolithically integrated on top of the at least one photovoltaic
cell.
10. A photovoltaic device comprising: a substrate; and a stack of
active device layers disposed on the substrate; wherein the stack
of active device layers comprises a photovoltaic layer of a
photovoltaic cell, and further comprises a transistor layer of a
microinverter, such that the photovoltaic cell and the
microinverter are integrated.
11. The photovoltaic device of claim 10, further comprising an
insulating layer between the photovoltaic layer and the transistor
layer.
12. The photovoltaic device of claim 11, wherein the insulating
layer comprises a wide band bandgap semiconductor material.
13. The photovoltaic device of claim 10, wherein the photovoltaic
layer is disposed between the substrate and the transistor
layer.
14. The photovoltaic device of claim 10, wherein the transistor
layer is atop the photovoltaic layer such that the microinverter is
on top of the photovoltaic cell.
15. The photovoltaic device of claim 10, further comprising a metal
contact between the photovoltaic layer and the substrate such that
the photovoltaic cell and the microinverter are connected to the
substrate via the metal contact.
16. The photovoltaic device of claim 10, wherein the substrate is
flexible.
17. The photovoltaic device of claim 10, wherein the photovoltaic
cell is cold weld bonded to a metallized surface of the
substrate.
18. The photovoltaic device of claim 10, further comprising an
H-bridge DC/AC inverter circuit monolithically integrated on top of
the photovoltaic cell, the H-bridge DC/AC inverter circuit
comprising the transistor layer.
19. A solar power system comprising a plurality of solar cell
modules, wherein each solar cell module of the plurality of solar
cell modules comprises a respective photovoltaic device in
accordance with claim 10.
20. The solar power system of claim 19, wherein the plurality of
solar cell modules are connected in parallel.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. non-provisional
application Ser. No. 15/534,504, entitled "Device and Method of
Monolithic Integration of Microinverters on Solar Cells," and filed
Jun. 9, 2017, which was a national phase application based on
International Application No. PCT/US2015/065167, filed Dec. 11,
2015, which, in turn, claimed the benefit of U.S. provisional
application Ser. No. 62/090,661, filed Dec. 11, 2014, the entire
disclosures of which are hereby expressly incorporated by
reference.
BACKGROUND OF THE DISCLOSURE
Field of the Disclosure
[0002] The present disclosure is directed to monolithic
microinverter devices and methods of fabricating, and more
particularly, monolithic microinverter devices for photovoltaic
cells.
Brief Description of Related Technology
[0003] Photovoltaic cells generate a direct current (DC) output;
therefore, DC-AC inverters are generally needed to convert the DC
output into a utility frequency alternating current (AC) which can
be fed into a commercial AC electrical grid or AC off-grid
electrical systems. The inverter is usually a primary component in
a photovoltaic panel and also usually makes up a considerable
portion of the balance of system (BOS) cost. Some photovoltaic
panels have an array of solar cells that use a single common
inverter to convert the current from DC to AC. One disadvantage for
this configuration is that an array of solar cells using a single
inverter operates at lower power generation in shaded conditions
even if the entire array is not shaded. The use of more than one
inverter has been pursued, but installation costs and other
concerns associated with redundant components in the solar cell
have limited this option.
SUMMARY OF THE DISCLOSURE
[0004] In one aspect, the present disclosure is directed to a
method of fabricating a photovoltaic cell having a microinverter.
The method may include fabricating a monolithic microinverter layer
through epitaxy and operably connecting the at least one
microinverter layer to at least one photovoltaic cell formed on a
photovoltaic layer.
[0005] In some embodiments, the method may further include
depositing an insulating layer between the photovoltaic layer and
the microinverter layer. In some embodiments, the microinverter
layer may include a layer of transistors chosen from high electron
mobility transistors, metal semiconductor field effect transistors,
junction field effect transistors, and heterojunction bipolar
transistors. In some embodiments, the microinverter layer may
further include an H-bridge DC/AC inverter circuit. In some
embodiments, the photovoltaic layer may include III V
semiconductors. In some embodiments, the method may be applied to
substrate based devices. In some embodiments, the method may be
applied to thin film based devices. In some embodiments, a growth
order may be normal and may be combined with transfer printing
techniques.
[0006] In some embodiments, fabricating the microinverter layer
through epitaxy may include depositing at least one sacrificial
layer on a growth substrate, depositing the microinverter layer on
the at least one sacrificial layer, depositing at least one
insulator layer on the at least one microinverter layer, and
etching the sacrificial layer with one or more etch steps that
remove at least the photovoltaic layer from the growth substrate to
form integrated thin film solar cells.
[0007] In some embodiments, operably connecting the at least one
microinverter layer to at least one photovoltaic cell formed on a
photovoltaic layer may include depositing a photovoltaic layer on
the at least one insulator layer and forming a patterned metal
layer on the photovoltaic layer by a photolithography method. In
some embodiments, the photovoltaic layer may be inverted. In some
embodiments, the method may further include cold weld bonding the
photovoltaic cell to a metallized surface of a substrate.
[0008] In another aspect, the present disclosure is directed to a
photovoltaic device. The device may include a photovoltaic layer
and a microinverter layer.
[0009] In some embodiments, the photovoltaic layer may include at
least one photovoltaic cell. In some embodiments, the microinverter
layer may include at least one microinverter. In some embodiments,
the microinverter layer may be fabricated through epitaxy. In some
embodiments, the at least one microinverter is configured to be
operably connected to at least one photovoltaic cell. In some
embodiments, such a photovoltaic device may further include an
insulating layer between the photovoltaic layer and microinverter
layer.
[0010] In some embodiments, the microinverter layer may include a
layer of transistors chosen from high electron mobility
transistors, metal semiconductor field effect transistors, junction
field effect transistors, and heterojunction bipolar transistors.
In some embodiments, the microinverter layer may further include an
H-bridge DC/AC inverter circuit. In some embodiments, the
photovoltaic layer may include III V semiconductors. In some
embodiments, the photovoltaic device may be a substrate based
device. In some embodiments, the photovoltaic device may be a thin
film based device. In some embodiments, the photovoltaic cell may
be cold weld bonded to a metallized surface of a substrate.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0011] FIG. 1A is a schematic illustration of a generalized
structure for epitaxial growth, according to an exemplary
embodiment.
[0012] FIG. 1B is a schematic illustration of the transferred
active device layers of FIG. 1A onto a host substrate, according to
an exemplary embodiment.
[0013] FIG. 2 is a schematic of an H-bridge DC/AC inverter circuit
plus solar cell array, according to an exemplary embodiment.
[0014] FIG. 3 is a monolithic integration schematic of a GaAs HEMT
transistor plus solar cell cold-weld bonded to a flexible
substrate, according to an exemplary embodiment.
[0015] FIG. 4A is a schematic illustration of a solar power system
with a large number of panels connected to a single inverter.
[0016] FIG. 4B is a schematic illustration of a solar power system
where each solar cell or module incorporates its own inverters,
according to an exemplary embodiment.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0017] The present disclosure is directed to monolithic
microinverter devices and methods of fabricating, and more
particularly, monolithic microinverter devices for photovoltaic
cells. The term monolithic as used herein may describe systems or
devices wherein the functionally distinguishable aspects are not
separate components by design, rather the functionally
distinguishable aspects are configured to be integrated components.
Herein the terms photovoltaic layer and solar cell are used
interchangeably.
[0018] FIGS. 1A and 1B show an exemplary embodiment of the
fabrication method. FIG. 1A shows a schematic of a growth structure
100. To integrate a DC/AC inverter with thin-film solar cells on a
host substrate using an epitaxial lift-off (ELO) process, an
inverted (as opposed to a normal growth order) photovoltaic
structure can be grown on the wafer (GaAs or InP) using epitaxial
growth. For reference, an ELO process is described by Yablonovitch
et al. in Extreme selectivity in the lift-off of epitaxial GaAs
films (Yablonovitch, E., Gmitter, T., Harbison, J. P. & Bhat,
R. Extreme selectivity in the lift-off of epitaxial GaAs films.
Appl. Phys. Len. 51, 2222 (1987). In an inverted solar cell, the
photoexcited charges flow through the device in the opposite
direction as in a normal device because the positive and negative
electrodes are reversed relative to the direction of
photoexcitation. In some embodiments the normal growth order can be
employed and further combined with an additional transferring
process, such as transfer printing method. A transfer printing
method, for reference, is described by Yoon et al. in GaAs
photovoltaics and optoelectronics using releasable multilayer
epitaxial assemblies (Yoon, J., Jo, S., Chun, I. S., Jung, I., Kim,
H.-S., Meitl, M., Menard, E., Li. X, Coleman, J. J, Paik, U. &
Rogers, J. A. GaAs photovoltaics and optoelectronics using
releasable multilayer epitaxial assemblies. Nature 465, 329-333
(2010)). In some embodiments, un-doped wide-bandgap semiconductor
materials (such as InGaP, AlGaInP and AlGaAs) can be inserted
between transistor and solar cell epi-layers to electrically
isolate the solar cells and transistors active layers. In some
embodiments the transistor structure can be chosen from high
electron mobility transistors (HEMTs), metal semiconductor field
effect transistors (MESFETs), junction field effect transistors
(JFETs) and heterojunction bipolar transistors (JBTs).
[0019] Growth structure 100 may be grown in an inverted growth
order and may be configured to undergo an ELO process. In this
particular embodiment, which is configured to undergo the ELO
process, a sacrificial layer 108 is grown on a substrate 110. The
following layers may be deposited above the sacrificial layer 108:
a transistor layer 106, an insulating layer 104 and a solar cell
layer 102. The order of layers 102-106 in this embodiment represent
an inverted growth structure so the solar cell layer may be
deposited last, which allows for etching of the sacrificial layer,
turning over the device architecture, and placing the transistor
layer atop the solar cell layer.
[0020] FIG. 1B shows an exemplary embodiment of a device structure
200, transferred from the parent wafer, on a host substrate after
the completion of an ELO process. According to this embodiment, the
device structure 200 may include transistor layer 106, insulating
layer 104, and solar cell layer 102, which may be fabricated
through the process described herein with reference to FIG. 1A.
Layers 102-106 fabricated as shown in FIG. 1A, may be operably
connected to a host substrate 210, through a metal contact 208, as
shown in FIG. 1B. To bond the sample to the host substrate,
cold-weld bonding can be employed. For reference, cold-weld bonding
is described by Lee et al. in Multiple growths of epitaxial
lift-off solar cells from a single InP substrate (Lee, K., Shiu,
K.-T., Zimmerman, J. D., Renshaw, C. K. & Forrest, S. R.
Multiple growths of epitaxial lift-off solar cells from a single
InP substrate. Appl. Phys. Lett. 97, 101107 (2010)). For reference,
cold-weld bonding is further described by Kim et al. in
"Micropatterning of organic electronic devices by cold-welding"
(Kim, C., Burrows, P. & Forrest, S. Micropatterning of organic
electronic devices by cold-welding. Science 288, 831-3 (2000)). For
reference, cold-weld bonding is further described by Ferguson et
al. in Contact adhesion of thin gold films on elastomeric supports:
cold welding under ambient conditions (Ferguson, G. S., Chaudhury,
M. K., Sigal, G. B. & Whitesides, G. M. Contact adhesion of
thin gold films on elastomeric supports: cold welding under ambient
conditions. Science 253, 776-778 (1991)). For the cold-welding
process, the surfaces of the epi-layer and the host substrate are
pre-coated with layers of a similar noble metal (Au, Ni etc.), then
appropriate pressure is applied between two metal interfaces. Once
the GaAs substrate is bonded to the plastic substrate, the active
device region is lifted-off from the parent wafer by immersion in
hydrofluoric acid. After the bonding and the ELO process, the
structure may be inverted, leaving the transistor layers on top.
The transistor layer, which may also be referred to as the
transistor mesa may then be etched, and metal interconnects may be
deposited.
[0021] FIG. 2 shows a schematic of an exemplary embodiment wherein
a H-bridge DC/AC inverter circuit 300 may be integrated with solar
cells. In this embodiment DC/AC inversion can be achieved, in some
embodiments further using an external transformer, by switching
contacts G1/G4 and the associated transistors T1/T4, on/off while
switching G2/G3 off/on.
[0022] FIG. 3 shows a schematic of a H-bridge DC/AC inverter
circuit 400 according to an exemplary embodiment. According to this
embodiment, the contacts G1-G4 and transistors T1-T4 in FIG. 3
correspond to the schematic of FIG. 2. As shown in FIG. 3, the
H-bridge DC/AC inverter circuit may be monolithically integrated on
top of thin-film solar cells 418 where the H-bridge DC/AC inverter
circuit comprises a thin-film HEMT structure (T1-T4, 402-414),
which may include a source 402, a gate 404, a drain 406, a n+ GaAs
layer 408, an AlGaAs layer 410, a AlGaAs spacer layer 412, and an
undoped GaAs layer 414. In this exemplary embodiment, the H-bridge
DC/AC inverter circuit 400 may be grown on top of the solar cell
active layer 418 and wide-bandgap isolation layer 416. Due to the
fact that the area of the microinverter layer is toughly 10.sup.-4
times smaller than the solar cells, the loss of active area in this
exemplary embodiment may be negligible. In some embodiments, an
integrated microinverter on each solar cell may allow for the
parallel connection of individual cells in a modular way, for
example, as shown in FIG. 4B. This may provide enhanced power
generation especially under the shaded condition compared with the
photovoltaic system using a single inverter, for example, as shown
in FIG. 4A. In some embodiments, the microinverter embedded with a
power optimizer provides a maximum power point tracking
functionality by pinpointing individual cell's ideal voltage and
producing at its maximum power.
[0023] The disclosed method and devices are not limited to
integrating of H-bridge inverter, but also can employ monolithic
integration of various inverter circuits and photovoltaic
optimizer, such as maximum power point tracking circuit and
real-time monitoring circuits. Additional circuits would be
apparent to one of ordinary skill in the art.
[0024] In some embodiments, a single photovoltaic cell may be
connected to a single microinverter. In some embodiments, several
photovoltaic cells may be connected to a single microinverter.
Further it will be apparent to those skilled in the art that
various modifications and variations can be made to the disclosed
method and devices. Other embodiments will be apparent to those
skilled in the art from consideration of the specification and
practice of the disclosed method. It is intended that the
specification and examples be considered as exemplary only, with a
true scope being indicated by the claims included with this
specification and their equivalents
[0025] The exemplary disclosed method may be applicable in
fabricating solar devices. Photovoltaic cells generate a direct
current (DC) output; therefore, DC-AC inverters are generally
needed to convert the DC output into a utility frequency
alternating current (AC) which can be fed into a commercial
electrical grid or off-grid electrical systems. An inverter is an
essential component in a photovoltaic panel, but at the same time,
it takes a considerable portion of balance of system cost.
Therefore, the integration of microinverters with photovoltaic
cells provides a potential to reduce the cost of photovoltaic
system. In addition, integrated microinverters on each solar cell
may allow for the parallel connection of individual cells in a
modular way thus providing enhanced power generation especially
under the shaded conditions compared with the photovoltaic system
using single inverter.
* * * * *