U.S. patent application number 17/142084 was filed with the patent office on 2021-04-29 for high efficiency multijunction photovoltaic cells.
The applicant listed for this patent is Array Photonics, Inc.. Invention is credited to David Taner BILIR, Jordan LANG, Ting LIU, Ferran SUAREZ, Arsen SUKIASYAN, Homan B. YUEN.
Application Number | 20210126148 17/142084 |
Document ID | / |
Family ID | 1000005326533 |
Filed Date | 2021-04-29 |
![](/patent/app/20210126148/US20210126148A1-20210429\US20210126148A1-2021042)
United States Patent
Application |
20210126148 |
Kind Code |
A1 |
SUAREZ; Ferran ; et
al. |
April 29, 2021 |
HIGH EFFICIENCY MULTIJUNCTION PHOTOVOLTAIC CELLS
Abstract
Multijunction photovoltaic cells having at least three subcells
are disclosed, in which at least one of the subcells comprises a
base layer formed of GaInNAsSb. The GaInNAsSb subcells exhibit high
internal quantum efficiencies over a broad range of irradiance
energies.
Inventors: |
SUAREZ; Ferran; (Chandler,
AZ) ; LIU; Ting; (San Jose, CA) ; YUEN; Homan
B.; (Santa Clara, CA) ; BILIR; David Taner;
(Redwood City, CA) ; SUKIASYAN; Arsen;
(Plainsboro, NJ) ; LANG; Jordan; (Sunnyvale,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Array Photonics, Inc. |
Tempe |
AZ |
US |
|
|
Family ID: |
1000005326533 |
Appl. No.: |
17/142084 |
Filed: |
January 5, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16282762 |
Feb 22, 2019 |
10916675 |
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17142084 |
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14887021 |
Oct 19, 2015 |
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16282762 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 31/0735 20130101;
H01L 31/0725 20130101; H01L 31/03048 20130101; Y02E 10/544
20130101; H01L 31/0687 20130101 |
International
Class: |
H01L 31/0725 20060101
H01L031/0725; H01L 31/0735 20060101 H01L031/0735; H01L 31/0304
20060101 H01L031/0304; H01L 31/0687 20060101 H01L031/0687 |
Claims
1. A multijunction photovoltaic cell comprising: a (Si,Sn) Ge
substrate; at least three subcells overlying the (Si,Sn)Ge
substrate, wherein: each of the at least three subcells is lattice
matched to each of the other subcells and to the (Si,Sn)Ge
substrate; at least one of the subcells comprises a GaInNAsSb
subcell comprising a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
base layer, wherein the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z base layer includes:
0.075.ltoreq.x.ltoreq.0.081, 0.040.ltoreq.y.ltoreq.0.051, and
0.010.ltoreq.z.ltoreq.0.018, a band gap from 1.111 eV to 1.117 eV,
a thickness from 1 .mu.m to 4 .mu.m, a short circuit current
density Jsc greater than 9 mA/cm.sup.2, and an open circuit voltage
Voc greater than 0.4 V, wherein the Jsc and the Voc are measured
using a 1 sun AM1.5D spectrum at a junction temperature of
25.degree. C.
2. The multijunction photovoltaic cell of claim 1, wherein the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z base layer has an
internal quantum efficiency greater than 70% at irradiance energies
from about 1.27 eV to about 1.38 eV.
3. The multijunction photovoltaic cell of claim 1, wherein the
GaInNAsSb subcell is characterized by a Eg/q-Voc equal to or
greater than 0.55 V measured using a 1 sun AM1.5D spectrum at a
junction temperature of 25.degree. C.
4. The multijunction photovoltaic cell of claim 1, wherein the
GaInNAsSb subcell is characterized by a Eg/q-Voc from 0.4 V to 0.7
V measured using a 1 sun AM1.5D spectrum at a junction temperature
of 25.degree. C.
5. The multijunction photovoltaic cell of claim 1, wherein the
GaInNAsSb subcell is characterized by a compressive strain less
than 0.6%.
6. The multijunction photovoltaic cell of claim 1, wherein the
GaInNAsSb subcell is characterized by a compressive strain from
0.1% to 0.6%.
7. The multijunction photovoltaic cell of claim 1, wherein the
GaInNAsSb subcell has a thickness from 2 .mu.m to 3 .mu.m.
8. The multijunction photovoltaic cell of claim 1, wherein at least
two of the subcells comprises a GaInNAsSb subcell.
9. The multijunction photovoltaic cell of claim 1, wherein the
GaInNAsSb subcell comprises a window, wherein the window includes
(Al)InGaP or (In)GaAs having a thickness from 0 nm to 300 nm.
10. The multijunction photovoltaic cell of claim 1, wherein the
GaInNAsSb subcell comprises an emitter, wherein the emitter
includes (In)GaAs or a GaInNAsSb alloy having a thickness from 100
nm to 200 nm.
11. The multijunction photovoltaic cell of claim 1, wherein the
GaInNAsSb subcell comprises an emitter, wherein the emitter
includes InGaAs or a III-AsNV alloy having a thickness from 100 nm
to 150 nm.
12. The multijunction photovoltaic cell of claim 1, wherein
GaInNAsSb subcell comprises a back surface field (BSF) layer,
wherein the BSF layer includes (In)GaAs having a thickness from 50
nm to 300 nm.
13. The multijunction photovoltaic cell of claim 12, wherein the
(In)GaAs has a thickness from 50 nm to 200 nm.
14. The multijunction photovoltaic cell of claim 1, further
comprising: a plurality of tunnel junctions disposed between each
of the at least three subcells.
15. The multijunction photovoltaic cell of claim 14, wherein each
of the plurality of tunnel junctions includes an n-type (Al,In)GaAs
layer, an n-type (Al)InGaP(As) layer, or a p-type (Al,In)GaAs
layer.
16. The multijunction photovoltaic cell of claim 14, wherein each
of the plurality of tunnel junctions has a thickness less than 100
nm.
17. A method of fabricating a multijunction photovoltaic cell, the
method comprising: depositing from at least three subcells
overlying a (Si,Sn)Ge substrate, wherein: each of the at least
three subcells is lattice matched to each of the other subcells and
to the (Si,Sn) Ge substrate; at least one of the subcells comprises
a GaInNAsSb subcell comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z base layer, wherein
the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.x-y-zSb.sub.z base layer
includes: 0.075.ltoreq.x.ltoreq.0.081, 0.040.ltoreq.y.ltoreq.0.051,
and 0.010.ltoreq.z.ltoreq.0.018, a band gap from 1.111 eV to 1.117
eV, a thickness from 1 .mu.m to 4 .mu.m, a short circuit current
density Jsc greater than 9 mA/cm.sup.2, and an open circuit voltage
Voc greater than 0.4 V, wherein the Jsc and the Voc are measured
using a 1 sun AM1.5D spectrum at a junction temperature of
25.degree. C.
18. The method of claim 17, wherein depositing the GaInNAsSb
subcell comprises depositing using molecular beam epitaxy.
19. The method of claim 17, wherein depositing a subcell other than
the GaInNAsSb subcell comprises depositing using metal organic
chemical vapor deposition.
20. The method of claim 17, further comprising after depositing the
at least three subcells, annealing the at least three subcells at a
temperature from 400.degree. C. to 1000.degree. C. for between 10
seconds to 10 hours.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of Ser. No.
16/282,762, filed on Feb. 22, 2019, now U.S. Publication No.:
2019/0189826, which is a divisional of U.S. application Ser. No.
14/887,021, filed on Oct. 19, 2015, now abandoned, which is
incorporated by reference in its entirety.
FIELD
[0002] The present invention relates to multijunction photovoltaic
cells having at least three subcells, in which at least one of the
subcells comprises a base layer formed of GaInNAsSb. The GaInNAsSb
subcells exhibit high internal quantum efficiencies over a broad
range of irradiance energies.
BACKGROUND
[0003] The present invention relates to photovoltaic cells, and in
particular to high efficiency, multijunction photovoltaic cells
comprising at least one GaInNAsSb subcell.
[0004] High efficiency photovoltaic cell efficiencies have been
produced by multijunction photovoltaic cells comprising GaInNAsSb.
The high efficiencies of these photovoltaic cells make them
attractive for terrestrial concentrating photovoltaic systems and
for systems designed to operate in space.
[0005] High efficiency photovoltaic cells have consisted of a
monolithic stack of three subcells, which are equivalently referred
to as junctions, grown on germanium (Ge) or gallium arsenide (GaAs)
substrates. The subcells contain the regions of the photovoltaic
cell where light energy in a range of wavelengths is absorbed and
converted into electrical energy that may be collected externally.
The subcells may be interconnected to one another by tunnel
junctions. Other layers, such as buffer layers, may also be present
between the subcells. In certain photovoltaic cells, the top
subcell has one or more absorbing layers made of (Al)InGaP, the
intermediate subcell has one or more absorbing layers made of
(In)GaAs, and the bottom subcell includes a Ge substrate or has
absorbing layers made of a III-V material. The foregoing
nomenclature for a III-V alloy, wherein a constituent element is
shown parenthetically, such as Al in (Al)InGaP, denotes a condition
of variability in which the element in parenthesis can be zero.
[0006] Each subcell can comprise several associated layers, such as
a window (front surface field, FSF), emitter, base, and back
surface field (BSF). Each of the foregoing layers may itself
include one or more sublayers. The emitter and the base of a
subcell are either formed of the same material, or the emitter is
formed of a material with a different band gap than that of the
base. Emitter-base pairs that are formed of the same material (such
as InGaP emitter/InGaP base or AlInGaP emitter/AlInGaP base) are
referred to as homojunctions. Emitter-base formed of different
materials are either heterojunctions (such as InGaP emitter/AlInGaP
base) which can improve voltage, or reverse heterojunctions (such
as InGaP emitter/AlInGaP base) which can reduce resistivity in the
emitter). The window and emitter can be of one doping polarity
(e.g., n-type) and the base and back surface field can be of the
opposite polarity (e.g., p-type), with a p-n or n-p junction formed
between the base and the emitter. If the base contains an intrinsic
region in addition to an intentionally doped region, then it may be
considered a p-i-n or n-i-p junction. By convention, the specific
alloy and the band gap of a given subcell are considered to be the
name and the band gap, respectively, of the material forming the
base. The material used for the base may or may not also be used
for the window, emitter and back surface field of a subcell. For
example, a subcell comprising an AlInP window, an InGaP emitter, a
GaAs base and an AlGaAs back surface field would be denoted a GaAs
subcell and the associated band gap would be the GaAs band gap of
1.4 eV. A subcell comprising an AlInP window, an InGaP emitter, an
InGaP base and an InGaP back surface field would be denoted an
InGaP subcell, and the associated band gap would be that of the
InGaP base. Ae subcell may include layers in addition to those
listed above. Those skilled in the art will also recognize that
subcells may also be constructed without one or more of the
foregoing layers. For example, subcells may be constructed without
a window or without a back surface field.
[0007] Specific elements within an alloy are sometimes expressed
with parenthesis, indicating that the element may be included in
the composition. For example, a subcell comprising (Al)InGaP may
include any amount of Al or none at all, covering all ranges of
compositions In, Ga and P, however, are present. Those skilled in
the art will recognize that (Al)InGaP is different than AlInGaP.
The latter indicates that the composition must include some amount
of Al. Similarly, (Si,Sn)Ge indicates Si and Sn may be present or
absent in the alloy composition while Ge is required; SiSnGe
indicates that all three elements are present.
[0008] When discussing the stacking order of the subcells from top
to bottom, the top subcell is defined to be the subcell closest to
the light source during operation of the multijunction photovoltaic
cell, and the bottom subcell is furthest from the light source.
Relative terms like "above," "below," "upper," and "lower" also
refer to position in the stack with respect to the light source.
The order in which the subcells are grown is not relevant to this
definition. The top subcell can also be denoted "J1," with "J2"
being the second subcell from the top, "J3" being third from the
top, and the highest number going to the bottom subcell.
[0009] Three junction photovoltaic cells are capable of achieving
efficiencies of about 45% under concentrated light with a AM1.5D
STD terrestrial spectrum and about 31% under a one sun AM0 STD
space spectrum. To reach significantly higher efficiencies,
additional junctions or subcells are needed. With additional
subcells, photons can be absorbed more efficiently by materials
with band gaps closer to incident photon energies, which are then
able to convert more light energy into electrical energy rather
than heat. In addition, the total photovoltaic cell current with
additional subcells may be lower for a given amount of incident
light, which may reduce series resistance losses. Another mechanism
for increasing efficiency is to absorb a larger fraction of the
photovoltaic spectrum with additional subcell(s). For many years,
there has been widespread recognition of the need for higher
numbers of junctions, such as photovoltaic cells having four, five
or six junctions. There are additional challenges related to the
increased number of tunnel junctions required to interconnect the
additional subcells, including the loss of light by tunnel junction
absorption.
[0010] There has long been interest in high efficiency,
lattice-matched multijunction photovoltaic cells with four or more
subcells, but suitable materials for creating high efficiencies
while maintaining lattice matching among the subcells and to a
substrate have previously been elusive. For example, U.S. Pat. No.
7,807,921 discusses the possibility of a four junction,
lattice-matched photovoltaic cell with GaIn.sub.xNAs as the
material for a 1.0 eV subcell. To overcome problems associated with
finding feasible, lattice-matched structures, the patent teaches
the use of metamorphic materials including a graded metamorphic
layer of GaIn.sub.xNAs that is not lattice matched.
[0011] What is needed to continue the progress toward higher
efficiency photovoltaic cells are designs for multijunction
photovoltaic cells with four or more subcells that can reach higher
efficiencies than can be practically attained with three junction
photovoltaic cells. Substantially lattice-matched designs are
desirable because they have proven reliability and because
lattice-matched photovoltaic cells use less semiconductor material
than do metamorphic photovoltaic cells, which require relatively
thick buffer layers to accommodate differences in the lattice
constants of the various materials. It is to be noted that the
general understanding of "substantially lattice matched" is that
the in-plane lattice constants of the materials in their fully
relaxed states differ by less than 0.6% when the materials are
present in thicknesses greater than 100 nm. Further, subcells that
are substantially lattice matched to each other means that all
materials in the subcells that are present in thicknesses greater
than 100 nm have in-plane lattice constants in their fully relaxed
states that differ by less than 0.6%. In an alternative meaning,
substantially lattice matched refers to the strain. As such, base
layers can have a strain from 0.1% to 6%, from 0.1% to 5%, from
0.1% to 4%, from 0.1 to 3%, from 0.1% to 2%, or from 0.1% to 1%; or
can have strain less than 6%, less than 5%, less than 4%, less than
3%, less than 2%, or less than 1%. Strain refers to compressive
strain and/or to tensile strain.
[0012] Three junction photovoltaic cells comprising a lattice
matched GaInNAsSb subcell are disclosed in U.S. Application
Publication No. 2010/0319764, which is incorporated by reference in
its entirety. These and other data on single junctions and three
junction photovoltaic cells comprising a GaInNAsSb subcell have
been extrapolated using a validated computational model to four-,
five-, and six-junction lattice matched GaInNAsSb photovoltaic
cells. The composition of these GaInNAsSb photovoltaic cells is
disclosed in U.S. Application Publication No. 2013/0118546, which
is incorporated by reference in its entirety.
SUMMARY
[0013] Three, four, five or more junction photovoltaic cells
comprising at least one GaInNAsSb subcell exhibiting a high
internal quantum efficiency throughout a broad range of irradiance
energies and exhibiting a short circuit current density Jsc and
open circuit voltage Voc suitable for use in high efficiency
multijunction photovoltaic cells are disclosed.
[0014] The invention includes multijunction photovoltaic cells
comprising four, five or more subcells having efficiencies that can
exceed those of known photovoltaic cells. The multijunction
photovoltaic cells incorporate at least one subcell that has a base
comprising a GaInNAsSb semiconductor material wherein the
composition of the material is tailored for band gap and lattice
constant. The GaInNAsSb subcells can comprise the bottom subcell
and/or the subcell immediately adjacent to the bottom subcell in
each of the multijunction photovoltaic cells provided by the
present disclosure. Each of the subcells of the multijunction
photovoltaic cells are substantially lattice-matched to each other.
In certain embodiments, the subcells of the multijunction
photovoltaic cells are substantially lattice-matched to a
substrate, such as a Ge substrate or a GaAs substrate. A Ge
substrate can also function as a sub-cell of a multijunction
photovoltaic cell. In a specific embodiment two GaInNAsSb subcells
of differing band gaps are fabricated in a single multijunction
photovoltaic cell.
[0015] According to the invention,
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell, wherein the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell is
characterized by: an internal quantum efficiency of at least 70% at
an irradiance energy from 1.38 eV to 1.27 eV, and an internal
quantum efficiency of at least 80% at an irradiance energy from
1.38 eV to 1.30 eV; an internal quantum efficiency of at least 70%
at an irradiance energy from 1.38 eV to 1.18 eV, and an internal
quantum efficiency of at least 80% at an irradiance energy from
1.38 eV to 1.30 eV; an internal quantum efficiency of at least 70%
at an irradiance energy from 1.38 eV to 1.10 eV, and an internal
quantum efficiency of at least 80% at an irradiance energy from
1.38 eV to 1.18 eV; an internal quantum efficiency of at least 70%
at an irradiance energy from 1.38 eV to 1.03 eV, and an internal
quantum efficiency of at least 80% at an irradiance energy from
1.38 eV to 1.13 eV; or an internal quantum efficiency of at least
60% at an irradiance energy from 1.38 eV to 0.92 eV, an internal
quantum efficiency of at least 70% at an irradiance energy from
1.38 eV to 1.03 eV, and an internal quantum efficiency of at least
80% at an irradiance energy from 1.38 eV to 1.08 eV; wherein the
internal quantum efficiency is measured at a junction temperature
of 25.degree. C.
[0016] According to the invention, multijunction photovoltaic cells
comprise from three to five subcells, wherein at least one of the
subcells comprises the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z semiconductor
material or subcell provided by the present disclosure; and each of
the subcells is lattice matched to each of the other subcells.
[0017] According to the invention, multijunction photovoltaic cells
comprise a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell
characterized by a bandgap from 0.9 eV to 1.1 eV; an (Al, In)GaAs
subcell overlying the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcell, wherein the (Al In)GaAs subcell is characterized by a
bandgap from 1.3 eV to 1.5 eV; and an (Al)InGaP subcell overlying
the (Al, In)GaAs subcell, wherein the (Al)InGaP subcell is
characterized by a bandgap from 1.8 eV to 2.10 eV; wherein, each of
the subcells is lattice matched to each of the other subcells; and
the multijunction photovoltaic cell is characterized by, an open
circuit voltage Voc equal to or greater than 2.5 V; a short circuit
current density Jsc equal to or greater than 12 mA/cm.sup.2; a fill
factor equal to or greater than 75%; and an efficiency of at least
28%, measured using a 1 sun AM1.5D or AM0 spectrum at a junction
temperature of 25.degree. C.
[0018] According to the invention, multijunction photovoltaic cells
comprise a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell
characterized by a bandgap from 0.9 eV to 1.05 eV; a (Al,In)GaAs
subcell overlying the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcell, wherein the (Al,In)GaAs subcell is characterized by a
bandgap from 1.3 eV to 1.5 eV; and an (Al)InGaP subcell overlying
the(Al,In)GaAs subcell, wherein the (Al)InGaP subcell is
characterized by a bandgap from 1.85 eV to 2.05 eV; wherein, each
of the subcells is lattice matched to each of the other subcells;
and the multijunction photovoltaic cell is characterized by an open
circuit voltage Voc equal to or greater than 2.5 V; a short circuit
current density Jsc equal to or greater than 12 mA/cm.sup.2; a fill
factor equal to or greater than 70%; and an efficiency equal to or
greater than 28%, measured using a 1 sun AM1.5D spectrum at a
junction temperature of 25.degree. C.
[0019] According to the invention, multijunction photovoltaic cells
comprise a first subcell comprising (Al)InGaP; a second subcell
comprising (Al,In)GaAs underlying the first subcell; a third
subcell comprising Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
underlying the second subcell; and a fourth subcell comprising
(Si,Sn)Ge underlying the third subcell; wherein, each of the
subcells is lattice matched to each of the other subcells; the
third subcell is characterized by a bandgap from 0.83 eV to 1.22
eV; and the third subcell is characterized by an internal quantum
efficiency greater than 70% at an irradiance energy throughout the
range from 0.95 eV to 1.55 eV at a junction temperature of
25.degree. C.
[0020] According to the invention, multijunction photovoltaic cells
comprise a first subcell comprising (Al)InGaP; a second subcell
comprising (Al In)GaAs underlying the first subcell; a third
subcell comprising Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
underlying the second subcell; and a fourth subcell comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z underlying the third
subcell; wherein, each of the subcells is lattice matched to each
of the other subcells; each of the fourth subcell and the third
subcell is characterized by a bandgap with a range from 0.83 eV to
1.3 eV; and each of the fourth subcell and the third subcell is
characterized by an internal quantum efficiency greater than 70% at
an irradiance energy throughout the range from 0.95 eV to 1.55
eV.
[0021] According to the invention, multijunction photovoltaic cells
comprise a first subcell comprising (Al)InGaP; a second subcell
comprising (Al,In)GaAs underlying the first subcell; a third
subcell comprising Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
underlying the second subcell; a fourth subcell comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z underlying the third
subcell; a fifth subcell comprising (Si,Sn)Ge underling the fourth
subcell; wherein, each of the subcells is lattice matched to each
of the other subcells; each of the fourth subcell and the third
subcell is characterized by a bandgap with a range from 0.83 eV to
1.3 eV; and each of the fourth subcell and the third subcell is
characterized by an internal quantum efficiency greater than 70% at
an irradiance energy throughout the range from 0.95 eV to 1.55
eV.
[0022] According to the invention, photovoltaic modules comprise at
least one multijunction photovoltaic cell provided by the present
disclosure.
[0023] According to the invention, photovoltaic systems comprise at
least one multijunction photovoltaic cell provided by the present
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Those skilled in the art will understand that the drawings
described herein are for illustration purposes only. The drawings
are not intended to limit the scope of the present disclosure.
[0025] FIG. 1 is a schematic cross-section of a multijunction
photovoltaic cell with three subcells according to embodiments of
the present disclosure.
[0026] FIGS. 2A and 2B are schematic cross-sections of
multijunction photovoltaic cells with four subcells according to
embodiments of the present disclosure.
[0027] FIG. 2C is a schematic cross-section of a multijunction
photovoltaic cell having four subcells according to embodiments of
the present disclosure.
[0028] FIG. 3 shows the internal quantum efficiency as a function
of irradiance wavelength for GaInNAsSb subcells having different
band gaps from 0.82 eV to 1.24 eV.
[0029] FIG. 4A shows the internal quantum efficiency as a function
of irradiance energy for a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell having a band
gap of 1.113 eV, where xis 7.9, y is 1.7, and z is from 0.7 to
0.8.
[0030] FIG. 4B shows the internal quantum efficiency as a function
of irradiance energy for a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell having a band
gap of 1.115 eV, where x is 7.8, y is 1.82, and z is from 0.4 to
0.8.
[0031] FIG. 4C shows the internal quantum efficiency as a function
of irradiance energy for a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell having a band
gap of 0.907 eV, where xis from 17 to 18, y is from 4.3 to 4.8, and
z is from 1.2 to 1.6.
[0032] FIG. 5 shows the open circuit voltage Voc for GaInNAsSb
subcells having different band gaps.
[0033] FIG. 6A shows the internal quantum efficiency as a function
of irradiance wavelength for each subcell of a three junction
(Al)InGaP/(AlIn)GaAs/Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
photovoltaic cell measured using a 1 sun AM1.5D spectrum.
[0034] FIG. 6B shows the internal quantum efficiency as a function
of irradiance wavelength for each subcell of a three junction
(Al)InGaP/(AlIn)GaAs/Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
photovoltaic cell measured using a 1 sun AM0 spectrum.
[0035] FIG. 6C shows a short circuit/voltage curve for a three
junction
(Al)InGaP/(Al,In)GaAs/Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
photovoltaic cell measured using a 1 sun AM0 spectrum
[0036] FIG. 7A shows a short circuit/voltage curve for a
four-junction
(Al)InGaP/(AlIn)GaAs/Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z/Ge
photovoltaic cell.
[0037] FIG. 7B shows the internal quantum efficiency as a function
of irradiance wavelength for each subcell of the four-junction
(Al)InGaP/(Al,
In)GaAs/Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z/Ge
photovoltaic cell presented in FIG. 7A.
[0038] FIG. 8 shows examples of subcell compositions for
three-junction, four-junction, and five-junction photovoltaic
cells.
[0039] FIG. 9A shows the external quantum efficiency for each
subcell of a four junction (Al)InGaP/(Al,
In)GaAs/Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z/Ga.sub.1-xIn.sub.xN-
.sub.yAs.sub.1-y-zSb.sub.z photovoltaic cell. The short circuit
current density J.sub.SC and band gap for each of the subcells are
provided in Table 5.
[0040] FIG. 9B shows the internal quantum efficiency of each
subcell of a four-junction
(Al)InGaP/(Al,In)GaAs/Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.zGa.sub-
.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z photovoltaic cell. The
short circuit current density J.sub.SC and band gap for each of the
subcells are provided in Table 5.
[0041] FIG. 10 summarizes the composition and function of certain
layers of a four junction
(Al)InGaP/(Al,In)GaAs/Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z/Ge
multijunction photovoltaic cell.
DETAILED DESCRIPTION
[0042] GaInNAsSb semiconductor materials are advantageous as
photovoltaic cell materials because the lattice constant can be
varied to be substantially matched to a broad range of substrates
and/or subcells formed from other than GaInNAsSb materials. The
lattice constant can be controlled by the relative fractions of the
different group IIIA and group VA elements. Thus, by tailoring the
compositions (i.e., the elements and quantities) of a GaInNAsSb
material, a wide range of lattice constants and band gaps may be
obtained. Further, high quality material may be obtained by
optimizing the composition around a specific lattice constant and
band gap, while limiting the total Sb content to no more than 20
percent of the Group V lattice sites, in certain embodiments to no
more than 3 percent of the Group V lattice sites, and in certain
embodiments, to no more than 1 percent of the Group V lattice
sites. Sb is believed to act as a surfactant to promote smooth
growth morphology of the III-AsNV alloys. In addition, Sb can
facilitate uniform incorporation of nitrogen and minimize the
formation of nitrogen-related defects. The incorporation of Sb can
enhance the overall nitrogen incorporation and reduce the alloy
band gap, aiding the realization of lower band gap alloys. However,
there are additional defects created by Sb and therefore it is
desirable that the total concentration of Sb should be limited to
no more than 20 percent of the Group V lattice sites. Further, the
limit to the Sb content decreases with decreasing nitrogen content.
Alloys that include In can have even lower limits to the total
content because In can reduce the amount of Sb needed to tailor the
lattice constant. For alloys that include In, the total Sb content
may be limited to no more than 3 percent of the Group V lattice
sites, and in certain embodiments, to no more than 1 percent of the
Group V lattice sites. For example,
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z, disclosed in U.S.
Application Publication No. 2010/0319764, can produce a high
quality material when substantially lattice-matched to a GaAs or Ge
substrate in the composition range of 0.08.ltoreq.x.ltoreq.0.18,
0.025.ltoreq.y.ltoreq.0.04 and 0.001.ltoreq.z.ltoreq.0.03, with a
band gap of at least 0.9 eV.
[0043] In certain embodiments of
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z provided by the
present disclosure, the N composition is not more than 7 percent of
the Group V lattice sites. In certain embodiments the N composition
is not more than 4 percent, and in certain embodiments, not more
than 3 percent.
[0044] The present invention includes multijunction photovoltaic
cells with three or more subcells such as three-, four- and five
junction subcells incorporating at least one
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell. The band
gaps of the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z materials
can be tailored by varying the composition while controlling the
overall composition of Sb. Thus,
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell with a band
gap suitable for integrating with the other subcells may be
fabricated while maintaining substantial lattice-matching to the
other subcells. The band gaps and compositions of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells can be
tailored so that the short-circuit current produced by the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells will be the
same as or slightly greater than the short-circuit current of the
other subcells in the photovoltaic cell. Because
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-x-y-zSb.sub.z materials provide
high quality, lattice-matched and band gap tunable subcells, the
disclosed photovoltaic cells comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells can achieve
high conversion efficiencies s. The increased in efficiency is
largely due to less light energy being lost as heat, as the
additional subcells allow more of the incident photons to be
absorbed by semiconductor materials with band gaps closer to the
energy level of the incident photons. In addition, there will be
lower series resistance losses in these multijunction photovoltaic
cells compared with other photovoltaic cells due to the lower
operating currents. At higher concentrations of sunlight, the
reduced series resistance losses become more pronounced. Depending
on the band gap of the bottom subcell, the collection of a wider
range of photons in the solar spectrum may also contribute to the
increased efficiency.
[0045] Designs of multijunction photovoltaic cells with more than
three subcells in the prior art predominantly rely on metamorphic
growth structures, new materials, or dramatic improvements in the
quality of existing subcell materials in order to provide
structures that can achieve high efficiencies. Photovoltaic cells
containing metamorphic buffer layers may have reliability concerns
due to the potential for dislocations originating in the buffer
layers to propagate over time into the subcells, causing
degradation in performance. In contrast,
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z materials can be used
in photovoltaic cells with more than three subcells to attain high
efficiencies while maintaining substantial lattice-matching between
subcells, which is advantageous for reliability. For example,
reliability testing on
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells provided by
the present disclosure has shown that multijunction photovoltaic
cells comprise a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcell, such devices can survive the equivalent of 390 years of
on-sun operation at 100.degree. C. with no failures. The maximum
degradation observed in these subcells was a decrease in
open-circuit voltage of about 1.2%.
[0046] For application in space, radiation hardness, which refers
to minimal degradation in device performance when exposed to
ionizing radiation including electrons and protons, is of great
importance. Multijunction photovoltaic cells incorporating
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells provided by
the present disclosure have been subjected to proton radiation
testing to examine the effects of degradation in space
environments. Compared to Ge-based triple junction photovoltaic
cells, the results demonstrate that these
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z containing devices
have similar power degradation rates and superior voltage retention
rates. Compared to non-lattice matched (metamorphic) triple
junction photovoltaic cells, all metrics are superior for
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z containing devices.
In certain embodiments, the photovoltaic cells include (Al) InGaP
subcells to improve radiation hardness compared to (Al,In)GaAs
subcells.
[0047] Due to interactions between the different elements, as well
as factors such as the strain in the layer, the relationship
between composition and band gap for
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z is not a simple
function of composition. The composition that yields a desired band
gap with a specific lattice constant can be found by empirically
varying the composition.
[0048] The thermal dose applied to the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z material, which is
controlled by the intensity of heat applied for a given duration of
time (e.g., application of a temperature of 600.degree. C. to
900.degree. C. for a duration of between 10 seconds to 10 hours),
that a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z material
receives during growth and after growth, also affects the
relationship between band gap and composition. In general, the band
gap increases as thermal dose increases.
[0049] As development continues on
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z materials and
photovoltaic cells comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, it is
expected that material quality will continue to improve, enabling
higher efficiencies from the same or similar compositions described
in the present disclosure. It should be appreciated, however, that
because of the complex interdependence of the GaInNAsSb material
composition and the processing parameters it cannot necessarily be
determined which combination of materials and processing conditions
will produce suitable high efficiency subcells having a particular
band gap.
[0050] As the composition is varied within the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z material system, the
growth conditions need to be modified. For example, for
(Al,In)GaAs, the growth temperature will increase as the fraction
of Al increases and decrease as the fraction of In increases, in
order to maintain the same material quality. Thus, as a composition
of either the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
material or the other subcells of the multijunction photovoltaic
cell is changed, the growth temperature as well as other growth
conditions can be adjusted accordingly.
[0051] Schematic diagrams of the three junction, four junction, and
five junction photovoltaic cells are shown FIGS. 1, 2A, 2B, and 2C
to create a complete multijunction photovoltaic cell, including an
anti-reflection coating, contact layers, tunnel junction,
electrical contacts and a substrate or wafer handle. As discussed
herein, FIG. 10 shows an example structure with these additional
elements. Further, additional elements may be present in a complete
photovoltaic cell, such as buffer layers, tunnel junctions, back
surface field, window, emitter, and front surface filed layers,
[0052] FIG. 1 shows an example of a multijunction photovoltaic cell
according to the invention that has three subcells, with the bottom
subcell being a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcell. All three subcells are substantially lattice-matched to
each other and may be interconnected by tunnel junctions, which are
shown as dotted regions. The
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell at the bottom
of the stack has the lowest band gap of the three subcells and
absorbs the lowest-energy light that is converted into electricity
by the photovoltaic cell. The band gap of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z material in the
bottom subcell is between 0.7-1.1 eV. The upper subcells can
comprise (Al)InGaP or AlInGaP.
[0053] FIG. 2A shows a multijunction photovoltaic cell according to
the invention that has four subcells, with the bottom subcell being
a Ge subcell and an overlying subcell being a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell. All four
subcells are substantially lattice-matched to each other and may be
interconnected by two tunnel junctions, which are shown as dotted
regions. The band gap of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can be
between 0.7 eV and 1.1 eV. The upper subcells can comprise GaAs and
either (Al,In)GaAs and (Al)InGaP.
[0054] FIG. 2B shows a multijunction photovoltaic cell according to
the invention that has four subcells, with the bottom subcell being
a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell and an
overlying subcell being a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell. All four
subcells are substantially lattice-matched to each other and may be
interconnected by tunnel junctions, which are shown as dotted
regions. The band gap of the bottom
Ga.sub.1-xIn.sub.yAs.sub.1-y-zSb.sub.z subcell is between 0.7 eV to
1.1 eV, and the band gap of the overlying
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell is between
0.7 eV and 1.3 eV. The upper subcells can comprise (Al,In)GaAs and
(Al)InGaP.
[0055] The specific band gaps of the subcells, within the ranges
given in the preceding as well as subsequent embodiments, are
dictated, at least in part, by the band gap of the bottom subcell,
the thicknesses of the subcell layers, and the incident spectrum of
light. Although there are numerous structures in the present
disclosure that will produce efficiencies exceeding those of three
junction photovoltaic cells, it is not the case that any set of
subcell band gaps that falls within the disclosed ranges will
produce an increased photovoltaic conversion efficiency. For a
certain choice of bottom subcell band gap, or alternately the band
gap of another subcell, incident spectrum of light, subcell
materials, and subcell layer thicknesses, there is a narrower range
of band gaps for the remaining subcells that will produce
efficiencies exceeding those of other three junction photovoltaic
cells.
[0056] In each of the embodiments described herein, the tunnel
junctions are designed to have minimal light absorption. Light
absorbed by tunnel junctions is not converted into electricity by
the photovoltaic cell, and thus if the tunnel junctions absorb
significant amounts of light, it will not be possible for the
efficiencies of the multijunction photovoltaic cells to exceed
those of the best triple junction photovoltaic cells. Accordingly,
the tunnel junctions must be very thin (preferably less than 40 nm)
and/or be made of materials with band gaps equal to or greater than
the subcells immediately above the respective tunnel junction. An
example of a tunnel junction fitting these criteria is a
GaAs/AlGaAs tunnel junction, where each of the GaAs and AlGaAs
layers forming the tunnel junction has a thickness between 5 nm and
15 nm. The GaAs layer can be doped with Te, Se, S and/or Si, and
the AlGaAs layer can be doped with C.
[0057] In each of the embodiments described and illustrated herein,
additional semiconductor layers are present in order to create a
photovoltaic cell device. Specifically, cap or contact layer(s),
anti-reflection coating (ARC) layers and electrical contacts (also
denoted as the metal grid) can be formed above the top subcell, and
buffer layer(s), the substrate or handle, and bottom contacts can
be formed or be present below the bottom subcell. In certain
embodiments, the substrate may also function as the bottom subcell,
such as in a Ge subcell. Other semiconductor layers, such as
additional tunnel junctions, may also be present. Multijunction
photovoltaic cells may also be formed without one or more of the
elements listed above, as known to those skilled in the art.
[0058] In operation, a multijunction photovoltaic cell is
configured such that the subcell having the highest band gap faces
the incident photovoltaic radiation, with subcells characterized by
increasingly lower band gaps situated underlying or beneath the
uppermost subcell.
[0059] In the embodiments disclosed herein, each subcell may
comprise several layers. For example, each subcell may comprise a
window layer, an emitter, a base, and a back surface field (BSF)
layer.
[0060] In operation, the window layer is the topmost layer of a
subcell and faces the incident radiation. In certain embodiments,
the thickness of a window layer can be from about 10 nm to about
500 nm, from about 10 nm to about 300 nm, from about 10 nm to about
150 nm, and in certain embodiments, from about 10 nm to about 50
nm. In certain embodiments, the thickness of a window layer can be
from about 50 nm to about 350 nm, from about 100 nm to about 300
nm, and in certain embodiments, from about 50 nm to about 150
nm.
[0061] In certain embodiments, the thickness of an emitter layer
can be from about 10 nm to about 300 nm, from about 20 nm to about
200 nm, from about 50 nm to about 200 nm, and in certain
embodiments, from about 75 nm to about 125 nm.
[0062] In certain embodiments, the thickness of a base layer can be
from about 0.1 .mu.m to about 6 .mu.m, from about 0.1 .mu.m to
about 4 .mu.m, from about 0.1 .mu.m to about 3 .mu.m, from about
0.1 .mu.m to about 2 .mu.m, and in certain embodiments, from about
0.1 .mu.m to about 1 .mu.m. In certain embodiments, the thickness
of a base layer can be from about 0.5 .mu.m to about 5 .mu.m, from
about 1 .mu.m to about 4 .mu.m, from about 1.5 .mu.m to about 3.5
.mu.m, and in certain embodiments, from about 2 .mu.m to about 3
.mu.m.
[0063] In certain embodiments the thickness of a BSF layer can be
from about 10 nm to about 500 nm, from about 50 nm to about 300 nm,
and in certain embodiments, from about 50 nm to about 150 nm.
[0064] In certain embodiments, an (Al)InGaP subcell comprises a
window comprising AlInP, an emitter comprising (Al)InGaP, a base
comprising (Al)InGaP, and a back surface field layer comprising
AlInGaP.
[0065] In certain embodiments, an (Al)InGaP subcell comprises a
window comprising AlInP having a thickness from 10 nm to 50 nm, an
emitter comprising (Al)InGaP having a thickness from 20 nm to 200
nm, a base comprising (Al)InGaP having a thickness from 0.1 .mu.m
to 2 .mu.m, and a BSF layer comprising AlInGaP having a thickness
from 50 nm to 300 nm.
[0066] In certain of such embodiments, an (Al)InGaP subcell is
characterized by a band gap from about 1.9 eV to about 2.2 eV.
[0067] In certain embodiments, an (Al,In)GaAs subcell comprises a
window comprising (Al)In(Ga)P or (Al,In)GaAs, an emitter comprising
(Al)InGaP or (Al,In)GaAs, a base comprising (Al,In)GaAs, and a BSF
layer comprising (Al,In)GaAs or (Al)InGaP. In certain embodiments,
an (Al,In)GaAs subcell comprises a window comprising (Al)InGaP
having a thickness from 50 nm to 400 nm, an emitter comprising
(Al,In)GaAs having a thickness from 100 nm to 200 nm, a base
comprising (Al,In)GaAs having a thickness from 1 .mu.m to 4 .mu.m,
and a BSF layer comprising (Al,In)GaAs having a thickness from 100
nm to 300 nm.
[0068] In certain embodiments, an (Al,In)GaAs subcell comprises a
window comprising (Al)InGaP having a thickness from 200 nm to 300
nm, an emitter comprising (Al,In)GaAs having a thickness from 100
nm to 150 nm, a base comprising (Al,In)GaAs having a thickness from
2 .mu.m to 3.5 .mu.m, and a BSF layer comprising (Al(In)GaAs having
a thickness from 150 nm to 250 nm.
[0069] In certain of such embodiments, an (Al(In)GaAs subcell is
characterized by a band gap from about 1.4 eV to about 1.7 eV.
[0070] In certain embodiments, an (Al) InGaAsP subcell comprises a
window comprising (Al)In(Ga)P, an emitter comprising (Al) InGaP or
(Al) InGaAsP, a base comprising (Al) InGaAsP, and a BSF layer
comprising (Al(In)GaAs or (Al)InGaP. In certain embodiments, an
(Al)InGaAsP subcell comprises a window comprising (Al)In(Ga)P
having a thickness from 50 nm to 300 nm, an emitter comprising
(Al)InGaP or (Al)InGaAsP having a thickness from 100 nm to 200 nm,
a base comprising (Al)InGaAsP having a thickness from 0.5 .mu.m to
4 .mu.m, and a BSF layer comprising Al(In)GaAs or (Al)InGaP having
a thickness from 50 nm to 300 nm.
[0071] In certain of such embodiments, an (Al)InGaAsP subcell is
characterized by a band gap from about 1.4 eV to about 1.8 eV.
[0072] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell comprises a
window comprising (Al)InGaP or (Al(In)GaAs, an emitter comprising
(In)GaAs or a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z, a base
comprising a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z, and a
BSF layer comprising (In)GaAs.
[0073] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell comprises a
window comprising (Al)InGaP or (In)GaAs, having a thickness from 0
nm to 300 nm, an emitter comprising (In)GaAs or a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z alloy having a
thickness from 100 nm to 200 nm, a base comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z having a thickness
from 1 .mu.m to 4 .mu.m, and a BSF layer comprising (In)GaAs having
a thickness from 50 nm to 300 nm. In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z alloy subcell
comprises an emitter comprising InGaAs or a III-AsNV alloy having a
thickness from 100 nm to 150 nm, a base comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z alloy having a
thickness from 2 .mu.m to 3 .mu.m, and a BSF layer comprising
(In)GaAs having a thickness from 50 nm to 200 nm.
[0074] In certain of such embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell is
characterized by a band gap from about 0.7 to about 1.1 eV, or
about 0.9 eV to about 1.3 eV. In certain of such embodiments, the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell is a
GaInNAsSb subcell.
[0075] In certain of such embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell has a
compressive strain of less than 0.6%, meaning that the in-plane
lattice constant of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z material in its fully
relaxed state is between 0.0% and 0.6% greater than that of the
substrate. In certain of such embodiments, the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell contains Sb
and does not contain Bi.
[0076] In certain embodiments, a Ge subcell comprises a window
comprising (Al)InGaP or (Al,In)GaAs, having a thickness from 0 nm
to 300 nm, an emitter comprising (Al,In)GaAs, (Al,Ga)InP, or
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z, having a thickness
from 10 nm to 500 nm, and a base comprising the Ge substrate. It is
to be noted that multijunction photovoltaic cells may also be
formed on a Ge or GaAs substrate wherein the substrate is not part
of a subcell.
[0077] In certain embodiments, one or more of the subcells has an
emitter and/or a base in which there is a graded doping profile.
The doping profile may be linear, exponential or with other
dependence on position. In certain of such embodiments, one or more
of the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells has
an exponential or linear doping profile over part or all of the
base, with the doping levels between 1.times.10.sup.15 and
1.times.10.sup.19 cm.sup.-3, or between 1.times.10.sup.16 .sub.and
5.times.10.sup.18 cm.sup.-3. Further, the region of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z base that is closest
to the emitter may have constant or no doping, as disclosed, for
example, in U.S. Application Publication No. 2012/0103403, which is
incorporated by reference in its entirety. Examples of dopants
include, for example, Be, Mg, Zn, Te, Se, Si, C, and others known
in the art.
[0078] A tunnel junction may be disposed between each of the
subcells. Each tunnel junction comprises two or more layers that
electrically connect adjacent subcells. The tunnel junction
includes a highly doped n-type layer adjacent to a highly doped
p-type layer to form a p-n junction. Typically, the doping levels
in a tunnel junction are between 10.sup.18 cm.sup.-3 and 10.sup.21
cm.sup.-3.
[0079] In certain embodiments, a tunnel junction comprises an
n-type (Al,In)GaAs or (Al)InGaP(As) layer and a p-type (Al,In)GaAs
layer. In certain embodiments the dopant of the n-type layer
comprises Si and the dopant of the p-type layer comprises C. A
tunnel junction may have a thickness less than about 100 nm, less
than 80 nm, less than 60 nm, less than 40 nm, and in certain
embodiments, less than 20 nm. For example, in certain embodiments,
a tunnel junction between (Al)InGaP subcells, between an (Al)InGaP
subcell and an (Al,In)GaAs or (Al)InGaAsP subcell, or between
(Al,In)GaAs subcells may have a thickness less than about 30 nm,
less than about 20 nm, less than about 15 nm, and in certain
embodiments, less than about 12 nm. In certain embodiments, a
tunnel junction separating an (Al,In)GaAs and III-AsNV alloy
subcell, separating adjacent III-AsNV alloy subcells, or separating
a III-AsNV alloy and a (Si,Sn)Ge or Ge subcell may have a thickness
less than 100 nm, less than 80 nm, less than 60 nm, and in certain
embodiments, less than 40 nm.
[0080] A multijunction photovoltaic cell may be fabricated on a
substrate such as a Ge substrate. In certain embodiments, the
substrate can comprise GaAs, InP, Ge, or Si. In certain
embodiments, all of the subcells are substantially lattice-matched
to the substrate. In certain embodiments, one or more of the layers
that are included within the completed photovoltaic cell but are
not part of a subcell such as, for example, anti-reflective coating
layers, contact layers, cap layers, tunnel junction layers, and
buffer layers, are not substantially lattice-matched to the
subcells.
[0081] In certain embodiments, the multijunction photovoltaic cell
comprises an anti-reflection coating overlying the uppermost
subcell. The materials comprising the anti-reflection coating and
the thickness of the anti-reflection coating are selected to
improve the efficiency of light capture in the multijunction
photovoltaic cell. In certain embodiments, one or more contact
layers overlie the uppermost subcell in the regions underlying or
near the metal grid. In certain embodiments, the contact layers
comprise (In)GaAs and the dopant may be Si or Be.
[0082] GaInNAsSb-containing multijunction photovoltaic cells
provided by the present disclosure may be incorporated into a
photovoltaic power system. A photovoltaic power system can comprise
one or more photovoltaic cells provided by the present disclosure
such as, for example, one or more photovoltaic cells having at
least three, at least four subcells or at least five subcells,
including one or more GaInNAsSb subcells. In certain embodiments,
the one or more photovoltaic cells have a GaInNAsSb subcell as the
bottom subcell or the subcell immediately above the bottom subcell.
In certain embodiments, the photovoltaic power system may be a
concentrating photovoltaic system, wherein the system may also
comprise mirrors and/or lenses used to concentrate sunlight onto
one or more photovoltaic cells. In certain embodiments, the
photovoltaic power system comprises a single or dual axis tracker.
In certain embodiments, the photovoltaic power system is designed
for portable applications, and in other embodiments, for
grid-connected power generation. In certain embodiments, the
photovoltaic power system is designed to convert a specific
spectrum of light, such as AM1.5G, AM1.5D or AM0, into electricity.
In certain embodiments, the photovoltaic power system may be found
on satellites or other extra-terrestrial vehicles and designed for
operation in space without the influence of a planetary atmosphere
on the impinging light source. In certain embodiments, the
photovoltaic power system may be designed for operation on
astronomical bodies other than earth. In certain embodiments, the
photovoltaic power system may be designed for satellites orbiting
about astronomical bodies other than earth. In certain embodiments,
the photovoltaic power system may be designed for roving on the
surface of an astronomical body other than earth.
[0083] Photovoltaic modules are provided comprising one or more
multijunction photovoltaic cells provided by the present
disclosure. A photovoltaic module may comprise one or more
photovoltaic cells provided by the present disclosure to include an
enclosure and interconnects to be used independently or assembled
with additional modules to form a photovoltaic power system. A
module and/or power system may include power conditioners, power
converters, inverters and other electronics to convert the power
generated by the photovoltaic cells into usable electricity. A
photovoltaic module may further include optics for focusing light
onto a photovoltaic cell provided by the present disclosure such as
in a concentrated photovoltaic module. Photovoltaic power systems
can comprise one or more photovoltaic modules, such as a plurality
of photovoltaic modules.
[0084] In certain embodiments provided by the present disclosure,
the semiconductor layers composing the photovoltaic cell, excepting
the substrate, can be fabricated using molecular beam epitaxy (MBE)
and/or chemical vapor deposition (CVD). In certain embodiments,
more than one material deposition chamber is used for the
deposition of the semiconductor layers comprising the photovoltaic
cell. The materials deposition chamber is the apparatus in which
the semiconductor layers composing the photovoltaic cell are
deposited. The conditions inside the chamber may range from
10.sup.-11 Torr to 10.sup.3 Torr pressures. In certain embodiments
the alloy constituents are deposited via physical and/or chemical
processes. Each materials deposition chamber can have different
configurations which allow for the deposition of different
semiconductor layers and can be independently controlled from other
materials deposition chambers. The semiconductor layers may be
fabricated using metal organic chemical vapor deposition (MOCVD),
MBE, or by other methods, including a combination of any of the
foregoing.
[0085] The movement of the substrate and semiconductor layers from
one materials deposition chamber to another is defined as the
transfer. For example, a substrate is placed in a first materials
deposition chamber, and then the buffer layer(s) and the bottom
subcell(s) are deposited. Then the substrate and semiconductor
layers are transferred to a second materials deposition chamber
where the remaining subcells are deposited. The transfer may occur
in vacuum, at atmospheric pressure in air or another gaseous
environment, or in any environment in between. The transfer may
further be between materials deposition chambers in one location,
which may or may not be interconnected in some way, or may involve
transporting the substrate and semiconductor layers between
different locations, which is known as transport. Transport may be
done with the substrate and semiconductor layers sealed under
vacuum, surrounded by nitrogen or another gas, or surrounded by
air. Additional semiconductor, insulating or other layers may be
used as surface protection during transfer or transport, and
removed after transfer or transport before further deposition.
[0086] In certain embodiments provided by the present disclosure, a
plurality of layers is deposited on a substrate in a first
materials deposition chamber. The plurality of layers may include
etch stop layers, release layers (i.e., layers designed to release
the semiconductor layers from the substrate when a specific process
sequence, such as chemical etching, is applied), contact layers
such as lateral conduction layers, buffer layers, or other
semiconductor layers. In one specific embodiment, the sequence of
layers deposited is buffer layer(s), then release layer(s), and
then lateral conduction or contact layer(s). Next the substrate is
transferred to a second materials deposition chamber where one or
more subcells are deposited on top of the existing semiconductor
layers. The substrate may then be transferred to either the first
materials deposition chamber or to a third materials deposition
chamber for deposition of one or more subcells and then deposition
of one or more contact layers. Tunnel junctions are also formed
between the subcells.
[0087] In certain embodiments provided by the present disclosure,
the GaInNAsSb subcells are deposited in a first materials
deposition chamber, and the (Al)InGaP, (Al,In)GaAs and (Al)InGaAsP
subcells are deposited in a second materials deposition chamber,
with tunnel junctions formed between the subcells. In a related
embodiment of the invention, GaInNAsSb layers are deposited in a
first materials deposition chamber, and other semiconductor layers
that contain Al are deposited in a second materials deposition
chamber. In another embodiment of the invention, a transfer occurs
in the middle of the growth of one subcell, such that the said
subcell has one or more layers deposited in one materials
deposition chamber and one or more layers deposited in a second
materials deposition chamber.
[0088] In certain embodiments provided by the present disclosure,
some or all of the layers composing the GaInNAsSb subcells and the
tunnel junctions are deposited in one materials deposition chamber
by molecular beam epitaxy (MBE), and the remaining layers of the
photovoltaic cell are deposited by chemical vapor deposition in
another materials deposition chamber. For example, a substrate is
placed in a first materials deposition chamber and layers that may
include nucleation layers, buffer layers, emitter and window
layers, contact layers and a tunnel junction are grown on the
substrate, followed by one or more GaInNAsSb subcells. If there is
more than one GaInNAsSb subcell, then a tunnel junction is grown
between adjacent subcells. One or more tunnel junction layers may
be grown, and then the substrate is transferred to a second
materials deposition chamber where the remaining photovoltaic cell
layers are grown by chemical vapor deposition. In certain
embodiments, the chemical vapor deposition system is a MOCVD
system. In a related embodiment of the invention, a substrate is
placed in a first materials deposition chamber and layers that may
include nucleation layers, buffer layers, emitter and window
layers, contact layers and a tunnel junction are grown on the
substrate by chemical vapor deposition. Subsequently, the top
subcells, two or more, are grown on the existing semiconductor
layers, with tunnel junctions grown between the subcells. Part of
the topmost GaInNAsSb subcell, such as the window layer, may then
be grown. The substrate is then transferred to a second materials
deposition chamber where the remaining semiconductor layers of the
topmost GaInNAsSb subcell may be deposited, followed by up to three
more GaInNAsSb subcells, with tunnel junctions between them.
[0089] In certain embodiments provided by the present disclosure,
the photovoltaic cell is subjected to one or more thermal annealing
treatments after growth. For example, a thermal annealing treatment
includes the application of a temperature of 400.degree. C. to
1000.degree. C. for between 10 seconds and 10 hours. Thermal
annealing may be performed in an atmosphere that includes air,
nitrogen, arsenic, arsine, phosphorus, phosphine, hydrogen, forming
gas, oxygen, helium and any combination of the preceding materials.
In certain embodiments, a stack of subcells and associated tunnel
junctions may be annealed prior to fabrication of additional
subcells.
[0090] An example of the multiple layer structure of a four
junction photovoltaic cell is shown in FIG. 10. The four junction
photovoltaic cell shown in FIG. 10 includes active (Si,Sn)Ge,
GaInNAsSb, (Al,In)GaAs, and (Al)InGaP subcells. The four junction
photovoltaic cell shown in FIG. 10 can be fabricated using
MBE/MOCVD processing steps. A Ge substrate is provided and oxide is
removed by annealing at a temperature greater than 600.degree. C.
for at least 10 minutes. A Si-doped (Al)InGaP nucleation layer is
then deposited. A Si-doped I(Al,In)GaAs lattice matched back
surface field layer is grown over the Si-doped (Al)InGaP nucleation
layer. A tunnel junction is formed by providing epitaxial layers of
Si-doped (Al,In)GaAs and C-doped (Al,In)GaAs. A back surface field
(BSF) layer of Be-doped (Al,In)GaAs is grown over the tunnel
junction. The second subcell comprises a GaInNAsSb base layer grown
over a Ge-doped GaInNAsSb layer having a graded doping profile. A
Si-doped (Al,In)GaAs emitter layer overlies the GaInNAsSb base and
a second tunnel junction formed of a layer of Si-doped (Al,In)GaAs
and a layer of C-doped (Al,In)GaAs are grown over the emitter.
[0091] The third subcell is then grown over the second GaInNAsSb
subcell. A Be-doped (Al,In)GaAs BSF layer is grown over the second
tunnel junction followed by a Be-doped (Al,In)GaAs base layer and a
Si-doped (Al,In)GaAs emitter layer. A Si-doped (Al)GaInP front
surface filed (FSF) layer is grown over the Si-doped (Al,In)GaAs
emitter. Both the (Al,In)GaAs base layer and the FSF layer are
characterized by graded doping profiles. A tunnel junction
comprising a Si-doped (Al,In)GaAs layer and a carbon-doped
(Al,In)GaAs layer overly the FSF layer.
[0092] The fourth subcell is formed by depositing a Be-doped
(Al)GaInP BSF layer over the (Al,In)GaAs/(Al,In)GaAs tunnel
junction. A Be-doped (Al)GaInP base layer is grown over the BSF
layer, followed by a Si-doped (Al)GaInP emitter layer characterized
by a graded doping profile. A Si-doped InAlP FSF layer is grown
over the (Al)GaInP layer.
[0093] A Si-doped (Al,In)GaAs contact layer is grown over the
topmost InAlP FSF layer.
[0094] The layers are grown by MBE or MOCVD methods known to those
skilled in the art using suitable conditions such, for example,
pressure, concentration, temperature, and time to provide high
quality multijunction photovoltaic cells. Each of the base layers
is lattice matched to each of the other base layers and to the Ge
substrate.
[0095] Various values for band gaps, short circuit current density
Jsc and open circuit voltage Voc have been recited in the
description and in the claims. It should be understood that these
values are not exact. However, the values for band gaps can be
approximated to one significant figure to the right of the decimal
point, except where otherwise indicated. Thus, the value 0.9 covers
the range 0.850 to 0.949. Also various numerical ranges have been
recited in the description and in the claims. It should be
understood that the numerical ranges are intended to include all
sub-ranges encompassed by the range. For example, a range of "from
1 to 10" is intended to include all sub-ranges between and
including the recited minimum value of 1 and the recited maximum
value of 10, such as having a minimum value equal to or greater
than 1 and a maximum value equal to or less than 10.
[0096] Three-, four-, and five junction photovoltaic cells
comprising at least one
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell have been
fabricated. The ability to provide high efficiency
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z-based photovoltaic
cells is predicated on the ability to provide a high quality
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell that can be
lattice matched to a variety of semiconductor materials including
Ge and GaAs and that can be tailored to have a band gap within the
range of 0.8 eV to 1.3 eV.
[0097] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
provided by the present disclosure are fabricated to provide a high
internal quantum efficiency. Factors that contribute to providing a
high internal quantum efficiency
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells include, for
example, the band gaps of the individual subcells, which in turn
depends on the semiconductor composition of the subcells, doping
levels and doping profiles, thicknesses of the subcells, quality of
lattice matching, defect densities, growth conditions, annealing
temperatures and profiles, and impurity levels.
[0098] Various metrics can be used to characterize the quality of a
GaInNAsSb subcell including, for example, the Eg/q-Voc, the
internal quantum efficiency over a range of irradiance energies,
the open circuit voltage Voc and the short circuit current density
Jsc. The open circuit voltage Voc and short circuit current Jsc can
be measured on subcells having a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z base layer that is 2
.mu.m thick or other thickness such as, for example, a thickness
from 1 .mu.m to 4 .mu.m. Those skilled in the art would understand
how to extrapolate the open circuit voltage Voc and short circuit
current Jsc measured for a subcell having a particular
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z base thickness to
other thicknesses.
[0099] The quality of a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can be
reflected by a curve of the internal quantum efficiency as a
function of irradiance wavelength or irradiance energy. In general,
a high quality Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcell exhibits an internal quantum efficiency (IQE) of at least
60%, at least 70% or at least 80% over a wide range of irradiance
wavelengths. FIG. 3 shows the dependence of the internal quantum
efficiency as a function of irradiance wavelength/energy for
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells having band
gaps from about 0.82 eV to about 1.24 eV.
[0100] The irradiance wavelengths for which the internal quantum
efficiencies of the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcell referred to in FIG. 3 is greater than 70% and greater than
80% is summarized in Table 1.
TABLE-US-00001 TABLE 1 Dependence of internal quantum efficiency of
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells. GaInNAsSb
Band Gap Wave- length Energy Internal Quantum Efficiency (nm/eV)
(nm) (eV) >70% >80% 1000 1.24 <900/<1.38 970/1.27
<900/<1.38 930/1.33 1088 1.14 <900/<1.38 1000/1.24
<900/<1.38 950/1.30 1127 1.10 <900/<1.38 1050/1.18
<900/<1.38 950/1.30 1181 1.05 <900/<1.38 1100/1.13
<900/<1.38 1050/1.18 1240 1.00 <900/<1.38 1150/1.08
<900/<1.38 1100/1.13 1291 0.96 <900/<1.38 1200/1.03
<900/<1.38 1100/1.13 1512 0.82 <900/<1.38 1250/0.99
<900/<1.38 1100/1.13
[0101] The Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
measured in FIG. 3 exhibit high internal quantum efficiencies
greater than 60%, greater than 70%, or greater than 80% over a
broad irradiance wavelength range. The high internal quantum
efficiency of these Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcells over a broad range of irradiance wavelengths/energies is
indicative of the high quality of the semiconductor material
forming the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcell.
[0102] As shown in FIG. 3, the range of irradiance wavelengths over
which a particular Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcell exhibits a high internal quantum efficiency is bounded by
the band gap of a particular
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell. Measurements
are not extended to wavelengths below 900 nm because in a practical
photovoltaic cell, a Ge subcell can be used to capture and convert
radiation at the shorter wavelengths. The internal quantum
efficiencies in FIG. 3 were measured at an irradiance of 1 sun
(1,000 W/m.sup.2) with the AM1.5D spectrum at a junction
temperature of 25.degree. C., for a GaInNAsSb subcell thickness of
2 .mu.m. One skilled in the art will understand how to extrapolate
the measured internal quantum efficiencies to other irradiance
wavelengths/energies, subcell thicknesses, and temperatures. The
internal quantum efficiency was measured by scanning the spectrum
of a calibrated source and measuring the current generated by the
photovoltaic cell. A GaInNAsSb subcell can include a GaInNAsSb
subcell base , an emitter, a back surface field and a front surface
field.
[0103] The Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
exhibited an internal quantum efficiency as follows:
[0104] an internal quantum efficiency of at least 70% at an
irradiance energy from 1.38 eV to 1.30 eV, and an internal quantum
efficiency of at least 80% at an irradiance energy from 1.38 eV to
1.30 eV; 1.18-1.24
[0105] an internal quantum efficiency of at least 70% at an
irradiance energy from 1.38 eV to 1.18 eV, and an internal quantum
efficiency of at least 80% at an irradiance energy from 1.38 eV to
1.30 eV; 1.10-1.14
[0106] an internal quantum efficiency of at least 70% at an
irradiance energy from 1.38 eV to 1.10 eV, and an internal quantum
efficiency of at least 80% at an irradiance energy from 1.38 eV to
1.18 eV; 1.04-1.06
[0107] an internal quantum efficiency of at least 70% at an
irradiance energy from 1.38 eV to 1.03 eV, and an internal quantum
efficiency of at least 80% at an irradiance energy from 1.38 eV to
1.15 eV; 0.99-1.01
[0108] an internal quantum efficiency of at least 70% at an
irradiance energy from 1.38 eV to 0.99 eV, and an internal quantum
efficiency of at least 80% at an irradiance energy from 1.38 eV to
1.15 eV; or 0.90-0.98
[0109] an internal quantum efficiency of at least 60% at an
irradiance energy from 1.38 eV to 0.92 eV, an internal quantum
efficiency of at least 70% at an irradiance energy from 1.38 eV to
1.03 eV, and an internal quantum efficiency of at least 80% at an
irradiance energy from 1.38 eV to 1.15 eV; 0.82
[0110] wherein the internal quantum efficiency was measured at a
junction temperature of 25.degree. C.
[0111] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 1.18 eV and 1.24 eV, exhibited an
internal quantum efficiency an internal quantum efficiency of at
least 70% at an irradiance energy from 1.38 eV to 1.30 eV, and an
internal quantum efficiency of at least 80% at an irradiance energy
from 1.38 eV to 1.30 eV, measured at a junction temperature of
25.degree. C.
[0112] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 1.10 eV and 1.14 eV, exhibited an
internal quantum efficiency of at least 70% at an irradiance energy
from 1.38 eV to 1.18 eV, and an internal quantum efficiency of at
least 80% at an irradiance energy from 1.38 eV to 1.30 eV, measured
at a junction temperature of 25.degree. C.
[0113] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 1.04 eV and 1.06 eV, exhibited an
internal quantum efficiency of at least 70% at an irradiance energy
from 1.38 eV to 1.10 eV, and an internal quantum efficiency of at
least 80% at an irradiance energy from 1.38 eV to 1.18 eV, measured
at a junction temperature of 25.degree. C.
[0114] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 0.99 eV and 1.01 eV, exhibited an
internal quantum efficiency of at least 70% at an irradiance energy
from 1.38 eV to 1.03 eV, and an internal quantum efficiency of at
least 80% at an irradiance energy from 1.38 eV to 1.15 eV, measured
at a junction temperature of 25.degree. C.
[0115] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 0.90 eV and 0.98 eV, exhibited an
internal quantum efficiency of at least 70% at an irradiance energy
from 1.38 eV to 0.99 eV, and an internal quantum efficiency of at
least 80% at an irradiance energy from 1.38 eV to 1.15 eV, measured
at a junction temperature of 25.degree. C.
[0116] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 0.80 eV and 0.86 eV, exhibited an
internal quantum efficiency of at least 60% at an irradiance energy
from 1.38 eV to 0.92 eV, an internal quantum efficiency of at least
70% at an irradiance energy from 1.38 eV to 1.03 eV, and an
internal quantum efficiency of at least 80% at an irradiance energy
from 1.38 eV to 1.15 eV, measured at a junction temperature of
25.degree. C.
[0117] The Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
also exhibited an internal quantum efficiency as follows:
[0118] an internal quantum efficiency of at least 70% at an
irradiance energy from 1.38 eV to 1.27 eV, and an internal quantum
efficiency of at least 80% at an irradiance energy from 1.38 eV to
1.30 eV;
[0119] an internal quantum efficiency of at least 70% at an
irradiance energy from 1.38 eV to 1.18 eV, and an internal quantum
efficiency of at least 80% at an irradiance energy from 1.38 eV to
1.30 eV;
[0120] an internal quantum efficiency of at least 70% at an
irradiance energy from 1.38 eV to 1.10 eV, and an internal quantum
efficiency of at least 80% at an irradiance energy from 1.38 eV to
1.18 eV;
[0121] an internal quantum efficiency of at least 70% at an
irradiance energy from 1.38 eV to 1.03 eV, and an internal quantum
efficiency of at least 80% at an irradiance energy from 1.38 eV to
1.13 eV; or
[0122] an internal quantum efficiency of at least 60% at an
irradiance energy from 1.38 eV to 0.92 eV, an internal quantum
efficiency of at least 70% at an irradiance energy from 1.38 eV to
1.03 eV, and an internal quantum efficiency of at least 80% at an
irradiance energy from 1.38 eV to 1.08 eV; wherein the internal
quantum efficiency is measured at a junction temperature of
25.degree. C.
[0123] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 1.18 eV and 1.24 eV, exhibited an
internal quantum efficiency of at least 70% at an irradiance energy
from 1.38 eV to 1.27 eV, and an internal quantum efficiency of at
least 80% at an irradiance energy from 1.38 eV to 1.30 eV, measured
at a junction temperature of 25.degree. C.
[0124] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 1.10 eV and 1.14 eV, exhibited an
internal quantum efficiency of at least 70% at an irradiance energy
from 1.38 eV to 1.18 eV, and an internal quantum efficiency of at
least 80% at an irradiance energy from 1.38 eV to 1.30 eV, measured
at a junction temperature of 25.degree. C.
[0125] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 1.04 eV and 1.06 eV, exhibited an
internal quantum efficiency of at least 70% at an irradiance energy
from 1.38 eV to 1.10 eV, and an internal quantum efficiency of at
least 80% at an irradiance energy from 1.38 eV to 1.18 eV, measured
at a junction temperature of 25.degree. C.
[0126] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 0.94 eV and 0.98 eV, exhibited an
internal quantum efficiency of at least 70% at an irradiance energy
from 1.38 eV to 1.03 eV, and an internal quantum efficiency of at
least 80% at an irradiance energy from 1.38 eV to 1.13 eV, measured
at a junction temperature of 25.degree. C.
[0127] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
having a band gap between 0.80 eV and 0.90 eV, exhibited an
internal quantum efficiency of at least 60% at an irradiance energy
from 1.38 eV to 0.92 eV, an internal quantum efficiency of at least
70% at an irradiance energy from 1.38 eV to 1.03 eV, and an
internal quantum efficiency of at least 80% at an irradiance energy
from 1.38 eV to 1.08 eV, measured at a junction temperature of
25.degree. C.
[0128] The Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
exhibited an Eg/q-Voc of at least 0.55 V, at least 0.60 V, or at
least 0.65 V over each respective range of irradiance energies
listed in the preceding paragraph. The
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells exhibited an
Eg/q-Voc within the range of 0.55 V to 0.70 V over each respective
range of irradiance energies listed in the preceding
paragraphs.
[0129] A Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can
be characterized by a band gap of about 1.24 eV, an internal
quantum efficiency greater than 70% at irradiance energies from
about 1.27 eV to about 1.38 eV and an internal quantum efficiency
greater than 80% at irradiance energies from about 1.33 eV to about
1.38 eV.
[0130] A Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can
be characterized by a band gap of about 1.14 eV, an internal
quantum efficiency greater than 70% at irradiance energies from
about 1.24 eV to about 1.38 eV and an internal quantum efficiency
greater than 80% at irradiance energies from about 1.30 eV to about
1.38 eV.
[0131] A Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can
be characterized by a band gap of about 1.10 eV, an internal
quantum efficiency greater than 70% at irradiance energies from
about 1.18 eV to about 1.38 eV and an internal quantum efficiency
greater than 80% at irradiance energies from about 1.30 eV to about
1.38 eV.
[0132] A Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can
be characterized by a band gap of about 1.05 eV, an internal
quantum efficiency greater than 70% at irradiance energies from
about 1.13 eV to about 1.38 eV and an internal quantum efficiency
greater than 80% at irradiance energies from about 1.18 eV to about
1.38 eV.
[0133] A Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can
be characterized by a band gap of about 1.00 eV, an internal
quantum efficiency greater than 70% at irradiance energies from
about 1.08 eV to about 1.38 eV and an internal quantum efficiency
greater than 80% at irradiance energies from about 1.13 eV to about
1.38 eV.
[0134] A Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can
be characterized by a band gap of about 0.96 eV, an internal
quantum efficiency greater than 70% at irradiance energies from
about 1.03 eV to about 1.38 eV and an internal quantum efficiency
greater than 80% at irradiance energies from about 1.13 eV to about
1.38 eV.
[0135] A Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can
be characterized by a band gap of about 0.82 eV, an internal
quantum efficiency greater than 70% at irradiance energies from
about 0.99 eV to about 1.38 eV and an internal quantum efficiency
greater than 80% at irradiance energies from about 1.13 eV to about
1.38 eV.
[0136] The quality of a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell is reflected
in a high short circuit current density Jsc, a low open circuit
voltage Voc, a high fill factor, and a high internal quantum
efficiency over a broad range of irradiance
wavelengths/energies.
[0137] These parameters are provided for certain
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells having a
band gap from 0.907 eV to 1.153 eV in Table 2.
TABLE-US-00002 TABLE 2 Properties of certain
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells.
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z Eg/q- Base Mole
Fraction Jsc Voc Voc FF PL BG thickness Subcell In(x) N(y) Sb(z)
(mA cm.sup.2) (V) (V) (%) (eV) (.mu.m) A 6.8-7.8 1.0-1.7 0.4-0.8
9.72 0.53 0.623 0.75 1.153 2 B 7.9 1.7 0.7-0.8 9.6 0.48 0.633 0.74
1.113 2 C 7.8 1.82 0.4-0.8 9.8 0.46 0.655 0.73 1.115 2 D 17-18
4.3-4.8 1.2-1.6 15.2 0.315 0.592 0.62 0.907 2
[0138] In Table 2, FF refers to the fill factor and PL BG refers to
the band gap as measured using photoluminescence.
[0139] For each of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells presented in
Table 2, the external quantum efficiency (EQE) was about 87% and
the internal quantum efficiency (IQE) was about 89% at a junction
temperature of 25.degree. C. The dependence of the internal quantum
efficiencies as a function of irradiance energy for subcells B, C,
and D. Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells are
shown in FIGS. 4A, 4B, and 4C, respectively. The internal quantum
efficiencies are greater than about 70% at irradiance energies from
about 1.15 eV to about 1.55 eV (1078 nm to 800 nm).
[0140] The internal quantum efficiencies for
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells B, C, and D
are presented in graphical form in FIGS. 4A, 4B, and 4C and are
summarized in Table 3.
TABLE-US-00003 TABLE 3 Composition and internal quantum
efficiencies of Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcells as a function of irradiance energy. Internal Quantum
Efficiency (%) Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z Band
at Irradiance Energy (eV) Mole Fraction Gap 0.95 1.05 1.15 1.25
1.35 1.45 1.55 Subcell In(x) N(y) Sb(z) (eV) eV eV eV eV eV eV eV B
7.9 1.7 0.7-0.8 1.113 -- -- 70 80 85 85 77 C 7.8 1.82 0.4-0.8 1.115
-- -- 72 82 87 86 77 D 17-18 4.3-4.8 1.2-1.6 0.907 57 73 81 87 92
92 --
[0141] As shown in FIGS. 4A, 4B, and 4C, and in Table 3,
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells having a
band gap of about 1.11 eV exhibit an IQE greater than 70% over a
range of irradiance energies from about 1.15 eV to at least 1.55
eV, and an IQE greater than 80% over a range of irradiance energies
from about 1.25 eV to about 1.45 eV.
[0142] Also, as shown in FIGS. 4A, 4B, and 4C, and in Table 3,
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells having a
band gap of about 0.91 eV exhibit an IQE greater than 70% over a
range of irradiance energies from about 1.05 eV to at least 1.45
eV, and an IQE greater than 80% over a range of irradiance energies
from about 1.15 eV to at least 1.45 eV.
[0143] The quality of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z compositions provided
by the present disclosure is also reflected in the low open circuit
voltage Voc, which depends in part on the band gap of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z composition. The
dependence of the open circuit voltage Voc with the band gap of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z composition is shown
in FIG. 5. As shown in FIG. 5, the open circuit voltage Voc changes
from about 0.2 V for a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z composition with a
band gap of about 0.85 eV, to an open circuit voltage Voc of about
0.5 V for a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
composition with a band gap of about 1.2 eV.
[0144] Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells
exhibiting a band gap from 0.90 eV to 1.2 eV can have values for x,
y, and z of 0.010.ltoreq.x.ltoreq.0.18,
0.015.ltoreq.y.ltoreq.0.083, 0.004.ltoreq.z.ltoreq.0.018. A summary
of the element content, band gap, short circuit current density Jsc
and open circuit voltage Voc for certain
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells is presented
in Table 4.
TABLE-US-00004 TABLE 4 Composition and properties of
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells. Band Gap
Jsc In (x) N (y) Sb (z) (eV) (mA/cm.sup.2) Voc (V) D 0.17-0.18
0.043-0.048 0.012-0.016 0.907 15.2 0.315 E 0.12-0.14 0.030-0.035
0.007-0.014 0.96-0.97 -- -- F 0.13 0.032 0.007-0.014 0.973 -- -- B
0.079 0.017 0.007-0.008 1.113 9.6 0.48 C 0.078 0.0182 0.004-0.008
1.115 9.8 0.46 G 0.083 0.018 0.013 1.12 9.7 0.49 H 0.079 0.022
0.013 1.12 13.12 0.63 A 0.068-0.078 0.010-0.017 0.004-0.008
1.153-1.157 9.72 0.53 I 0.05 0.013 0.018 1.16 6.57 0.54 J 0.035
0.014 0.018 1.2 6.32 0.55 K 0.028 0.016 0.007 1.2 -- --
[0145] In Table 3, the short circuit current density Jsc and open
circuit voltage Voc were measured using a 1 sun AM1.5D spectrum at
a junction temperature of 25.degree. C. The
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells were 2 .mu.m
thick.
[0146] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can be
characterized by a Eg/q-Voc equal to or greater than 0.55 V
measured using a 1 sun AM1.5D spectrum at a junction temperature of
25.degree. C.
[0147] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can be
characterized by a Eg/q-Voc from 0.4 V to 0.7 V measured using a 1
sun AM1.5D spectrum at a junction temperature of 25.degree. C.
[0148] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0149] values for x, y, and z of 0.016.ltoreq.x.ltoreq.0.19,
0.040.ltoreq.y.ltoreq.0.051, and 0.010.ltoreq.z.ltoreq.0.018;
[0150] a band gap from 0.89 eV to 0.92 eV;
[0151] a short circuit current density Jsc greater than 15
mA/cm.sup.2; and
[0152] an open circuit voltage Voc greater than 0.3 V.
[0153] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0154] values for x, y, and z of 0.010.ltoreq.x.ltoreq.0.16,
0.028.ltoreq.y.ltoreq.0.037, and 0.005.ltoreq.z.ltoreq.0.016;
and
[0155] a band gap from 0.95 eV to 0.98 eV.
[0156] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0157] values for x, y, and z of 0.075.ltoreq.x.ltoreq.0.081,
0.040.ltoreq.y.ltoreq.0.051, and 0.010.ltoreq.z.ltoreq.0.018;
[0158] a band gap from 1.111 eV to 1.117 eV;
[0159] a short circuit current density Jsc greater than 9
mA/cm.sup.2; and
[0160] an open circuit voltage Voc greater than 0.4 V.
[0161] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0162] values for x, y, and z of 0.016.ltoreq.x.ltoreq.0.024,
0.077.ltoreq.y.ltoreq.0.085, and 0.011.ltoreq.z.ltoreq.0.015;
[0163] a band gap from 1.10 eV to 1.14 eV;
[0164] a short circuit current density Jsc greater than 9
mA/cm.sup.2; and
[0165] an open circuit voltage Voc greater than 0.4 V.
[0166] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0167] values for x, y, and z of 0.068.ltoreq.x.ltoreq.0.078,
0.010.ltoreq.y.ltoreq.0.017, and 0.011.ltoreq.z.ltoreq.0.004
x.ltoreq.0.008;
[0168] a band gap from 1.15 eV to 1.16 eV;
[0169] a short circuit current density Jsc greater than 9
mA/cm.sup.2; and
[0170] an open circuit voltage Voc greater than 0.5 V.
[0171] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0172] values for x, y, and z of 0.011.ltoreq.x.ltoreq.0.015,
0.04.ltoreq.y.ltoreq.0.06, and 0.016.ltoreq.z.ltoreq.0.020;
[0173] a band gap from 1.14 eV to 1.18 eV;
[0174] a short circuit current density Jsc greater than 6
mA/cm.sup.2; and
[0175] an open circuit voltage Voc greater than 0.5 V.
[0176] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0177] values for x, y, and z of 0.012.ltoreq.x.ltoreq.0.016,
0.033.ltoreq.y.ltoreq.0.037, and 0.016.ltoreq.z.ltoreq.0.020;
[0178] a band gap from 1.18 eV to 1.22 eV;
[0179] a short circuit current density Jsc greater than 6
mA/cm.sup.2; and an open circuit voltage Voc greater than 0.5
V.
[0180] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0181] values for x, y, and z of 0.026.ltoreq.x.ltoreq.0.030,
0.024.ltoreq.y.ltoreq.0.018, and 0.005.ltoreq.z.ltoreq.0.009;
[0182] a band gap from 1.18 eV to 1.22 eV.
[0183] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0184] values for x, y, and z wherein 0.075.ltoreq.x.ltoreq.0.082,
0.016.ltoreq.y.ltoreq.0.019, and 0.004.ltoreq.z.ltoreq.0.010, and
the subcell can be characterized by,
[0185] a band gap from 1.12 eV to 1.16 eV;
[0186] a short circuit current density Jsc of at least 9.5
mA/cm.sup.2; and
[0187] an open circuit voltage Voc of at least 0.40 V,
[0188] wherein the Jsc and the Voc are measured using a 1 sun
AM1.5D spectrum at a junction temperature of 25.degree. C.
[0189] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0190] values for x, y, and z wherein 0.011.ltoreq.x.ltoreq.0.016,
0.02.ltoreq.y.ltoreq.0.065, and 0.016.ltoreq.z.ltoreq.0.020, and
the subcell can be characterized by,
[0191] a band gap from 1.14 eV to 1.22 eV;
[0192] a short circuit current density Jsc of at least 6
mA/cm.sup.2; and
[0193] an open circuit voltage Voc of at least 0.50 V,
[0194] wherein the Jsc and the Voc are measured using a 1 sun
AM1.5D spectrum at a junction temperature of 25.degree. C.
[0195] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
[0196] values for x, y, and z wherein
0.016.ltoreq.x.ltoreq.0.0.024, 0.077.ltoreq.y.ltoreq.0.085, and
0.010.ltoreq.z.ltoreq.0.016, and
[0197] the subcell can be characterized by,
[0198] a band gap from 1.118 eV to 1.122 eV;
[0199] a short circuit current density Jsc of at least 9
mA/cm.sup.2; and
[0200] an open circuit voltage Voc of at least 0.40 V,
[0201] wherein the Jsc and the Voc are measured using a 1 sun
AM1.5D spectrum at a junction temperature of 25.degree. C.
[0202] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can be
characterized by a bandgap from 0.8 eV to 1.3 eV; and values for x,
y, and z of 0.03.ltoreq.x.ltoreq.0.19, 0.008.ltoreq.y.ltoreq.0.055,
and 0.001.ltoreq.z.ltoreq.0.05.
[0203] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
0.06.ltoreq.x.ltoreq.0.09, 0.01.ltoreq.y.ltoreq.0.025, and
0.004.ltoreq.z.ltoreq.0.014, and the subcell can be characterized
by,
[0204] a bandgap from 1.12 eV to 1.16 eV;
[0205] a short circuit current density Jsc equal to or greater than
9.5 mA/cm.sup.2; and
[0206] an open circuit voltage Voc equal to or greater than 0.40
V,
[0207] wherein the Jsc and the Voc are measured using a 1 sun
AM1.5D spectrum at a junction temperature of 25.degree. C.
[0208] In certain embodiments, a
Ga.sub.1-xIn.sub.xl\l.sub.yAs.sub.1-y-zSb.sub.z subcell can have
values of 0.004.ltoreq.x.ltoreq.0.08, 0.008.ltoreq.y.ltoreq.0.02,
and 0.004.ltoreq.z.ltoreq.0.014, and the subcell can be
characterized by,
[0209] a bandgap from 1.14 eV to 1.22 eV;
[0210] a short circuit current density Jsc equal to or greater than
6 mA/cm.sup.2; and
[0211] an open circuit voltage Voc equal to or greater than 0.50
V,
[0212] wherein the Jsc and the Voc are measured using a 1 sun
AM1.5D spectrum at a junction temperature of 25.degree. C.
[0213] In certain embodiments, a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can have
values of 0.06.ltoreq.x.ltoreq.0.09, 0.01.ltoreq.y.ltoreq.0.03, and
0.004.ltoreq.z.ltoreq.0.014, and the subcell can be characterized
by,
[0214] a bandgap from 1.118 eV to 1.122 eV;
[0215] a short circuit current density Jsc equal to or greater than
9 mA/cm.sup.2; and
[0216] an open circuit voltage Voc equal to or greater than 0.40
V,
[0217] p wherein the Jsc and the Voc are measured using a 1 sun
AM1.5D spectrum at a junction temperature of 25.degree. C.
[0218] Multijunction photovoltaic cells provided by the present
disclosure can comprise at least one subcell comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z semiconductor
material or subcell provided by the present disclosure, and wherein
each of the subcells is lattice matched to each of the other
subcells. Such multijunction photovoltaic cells can comprise three
junctions, four junctions, five junctions, or six junctions, in
which at least one of the junctions or subcells comprises a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z semiconductor
material provided by the present disclosure. In certain
embodiments, a multijunction photovoltaic cell comprises one
subcell comprising a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
semiconductor material provided by the present disclosure, and in
certain embodiments, two subcells comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z semiconductor
material provided by the present disclosure. The
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z semiconductor
material can be selected to have a suitable bandgap depending at
least in part on the structure of the multijunction photovoltaic
cell. The band gap of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z semiconductor
material can be, for example, from about 0.80 eV to about 0.14
eV.
[0219] Three junction photovoltaic cells having a bottom
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell (J3), a
second (Al,In)GaAs subcell (J2), and a top InGaP or AlInGaP subcell
(J1) were fabricated. Each of the subcells is lattice matched to
(Al,In)GaAs. Therefore, each of the subcells is lattice matched to
each of the other subcells The parameters for the three junction
photovoltaic cells measured using a 1 sun (1366 W/m.sup.2) AM0
spectrum at 25.degree. C. are provided in Table 5. The internal
quantum efficiencies for each of the subcells is shown in FIG.
6A.
TABLE-US-00005 TABLE 5 Properties of three-junction
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z- containing
photovoltaic cells. (Al)InGaP/(Al,In)GaAs/GaInNAsSb Voc (V) 2.87
Jsc (mA/cm.sup.2) 17.6 FF (%) 86.7 Efficiency (%) 32 J1 band gap
(eV); (Al)InGaP 1.9 J2 band gap (eV); (Al,In)GaAs 1.42 J3 band gap
(eV); GaInNAsSb 0.96
[0220] The three junction photovoltaic cells using a bottom
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell (J3) exhibit
a high Voc of about 2.9 V, a high Jsc of about 16 mA/cm.sup.2, a
high fill factor of about 85%, and a high efficiency of around 30%,
illuminated with an AM0 spectrum. (Al)InGaP/(Al,In)GaAs/GaInNAsSb
photovoltaic cells are characterized by an open circuit voltage Voc
of at least 2.8 V, a short circuit current density of at least 17
mA, a fill factor of at least 80%, and an efficiency of at least
28%, measured using a 1 sun AM0 spectrum at a junction temperature
of 25.degree..
[0221] (Al)InGaP/(Al,In)GaAs/GaInNAsSb photovoltaic cells are
characterized by an open circuit voltage Voc from 2.8 V to 2.9 V, a
short circuit current density from 16 mA/cm.sup.2 to 18
mA/cm.sup.2, a fill factor from 80% to 90% and an efficiency from
28% to 34%, illuminated with an AM0 spectrum.
[0222] (Al)InGaP/(Al,In)GaAs/GaInNAsSb photovoltaic cells are
characterized by an open circuit voltage Voc from 2.85 V to 2.95 V,
a short circuit current density from 15 mA/cm.sup.2 to 17
mA/cm.sup.2, a fill factor from 80% to 89% and an efficiency from
25% to 35%, measured using a 1 sun AM0 spectrum at a junction
temperature of 25.degree. C.
[0223] In certain embodiments, a three junction multijunction
photovoltaic cell can comprise:
[0224] a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell
characterized by a bandgap from 0.9 eV to 1.1 eV;
[0225] an (Al,In)GaAs subcell overlying the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell, wherein the
(Al,In)GaAs subcell is characterized by a bandgap from 1.3 eV to
1.5 eV; and
[0226] an (Al)InGaP subcell overlying the (Al,In)GaAs subcell,
wherein the (Al)InGaP subcell is characterized by a bandgap from
1.8 eV to 2.10 eV; wherein,
[0227] each of the subcells is lattice matched to each of the other
subcells; and
[0228] the multijunction photovoltaic cell can be characterized by,
[0229] an open circuit voltage Voc equal to or greater than 2.5 V;
[0230] a short circuit current density Jsc equal to or greater than
12 mA/cm.sup.2; [0231] a fill factor equal to or greater than 75%;
and [0232] an efficiency of at least 28%, [0233] measured using a 1
sun AM1.5D or AM0 spectrum at a junction temperature of 25.degree.
C.
[0234] In certain embodiments, a three junction multijunction
photovoltaic cell can be characterized by,
[0235] an open circuit voltage Voc from 2.5 V to 3.2 V;
[0236] a short circuit current density Jsc from 15 mA/cm.sup.2 to
17.9 mA/cm.sup.2;
[0237] a fill factor from 80% to 90%; and
[0238] an efficiency from 28% to 33%,
[0239] measured using a 1 sun AM0 spectrum at a junction
temperature of 25.degree. C.
[0240] In certain embodiments, a three junction multijunction
photovoltaic cell can be characterized by,
[0241] an open circuit voltage Voc from 2.55 V to 2.85 V;
[0242] a short circuit current density Jsc from 13.0 mA/cm.sup.2 to
15 mA/cm.sup.2;
[0243] a fill factor from 75% to 87%; and
[0244] an efficiency from 28% to 35%,
[0245] measured using a 1 sun AM1.5 D spectrum at a junction
temperature of 25.degree. C.
[0246] In certain embodiments, a multijunction photovoltaic cell
can comprise:
[0247] a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell
characterized by a bandgap from 0.9 eV to 1.05 eV;
[0248] a (Al,In)GaAs subcell overlying the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell, wherein the
(Al,In)GaAs subcell is characterized by a bandgap from 1.3 eV to
1.5 eV; and
[0249] an (Al)InGaP subcell overlying the (Al,In)GaAs subcell,
wherein the (Al)InGaP subcell is characterized by a bandgap from
1.85 eV to 2.05 eV; wherein, [0250] each of the subcells is lattice
matched to each of the other subcells; and [0251] the multijunction
photovoltaic cell can be characterized by, [0252] an open circuit
voltage Voc equal to or greater than 2.5 V; [0253] a short circuit
current density Jsc equal to or greater than 15 mA/cm.sup.2; [0254]
a fill factor equal to or greater than 80%; and [0255] an
efficiency equal to or greater than 28%, [0256] measured using a 1
sun AM1.5D spectrum at a junction temperature of 25.degree. C.
[0257] In certain embodiments, a three junction multijunction
photovoltaic cell can be characterized by,
[0258] an open circuit voltage Voc from 2.6 V to 3.2 V;
[0259] a short circuit current density Jsc from 15.5 mA/cm.sup.2 to
16.9 mA/cm.sup.2;
[0260] a fill factor from 81% to 91%; and
[0261] an efficiency from 28% to 32%,
[0262] measured using a 1 sun AM0 spectrum at a junction
temperature of 25.degree. C.
[0263] In certain embodiments a four junction photovoltaic cell can
have the general structure as shown in FIG. 2A, having a bottom Ge
subcell (J4), an overlying GaInNAsSb subcell (J3), an overlying
(Al,In)GaAs subcell (J2), and a top (Al)InGaP subcell (J1). Each of
the subcells is substantially lattice matched to each of the other
subcells and to the Ge subcell. The multijunction photovoltaic
cells do not comprise a metamorphic buffer layer between adjacent
subcells. The composition of each of the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell, the
(Al,In)GaAs subcell and the (Al)InGaP subcell is selected to
provide lattice matching to the (Si,Sn)Ge subcell and to provide an
appropriate band gap.
[0264] In certain four junction photovoltaic cells, the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell (J3) can have
a band gap from 0.98 eV to 1.22 eV, from 0.98 eV to 1.20 eV, from
0.98 eV, to 0.18 eV, from).98 eV to 0.16 eV, from 0.98 eV to 0.14
eV, from 0.98 eV to 1.12 eV, from 0.99 eV to 1.11 eV, or from 01.00
eV to 1.10 eV. The Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
can be selected to substantially match the lattice constant of the
(Si,Sn)Ge subcell and to provide a suitable band gap within a
range, for example, from 0.98 eV to 1.12 eV.
[0265] In certain embodiments of a four junction photovoltaic cell,
the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell (J3) can
have values for x, y, and z in which 0.075.ltoreq.x.ltoreq.0.083,
0.015.ltoreq.y.ltoreq.0.020, and 0.003.ltoreq.z.ltoreq.0.009.
[0266] In certain embodiments of a four junction photovoltaic cell,
the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell (J3) can
have values for x, y, and z in which 0.077.ltoreq.x.ltoreq.0.081,
0.0165.ltoreq.y.ltoreq.0.0185, and 0.004.ltoreq.z.ltoreq.0.009.
[0267] In certain embodiments of a four junction photovoltaic cell,
the Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell (J3) can
have values for x, y, and z in which 0.078.ltoreq.x.ltoreq.0.080,
0.017.ltoreq.y.ltoreq.0.018, and 0.004.ltoreq.x.ltoreq.0.008.
[0268] In certain four junction photovoltaic cells the (Al,In)GaAs
subcell (J2) can have a band gap from 1.4 eV to 1.53 eV, from 1.42
eV to 1.51 eV, from 1.44 eV to 1.49 eV, or from 1.46 eV to 1.48
eV.
[0269] The (Al,In)GaAs composition can be selected to match the
lattice constant of the (Si,Sn)Ge subcell and to provide a suitable
band gap with a range, for example, from 1.4 eV to 1.53 eV.
[0270] In certain four junction photovoltaic cells the (Al)InGaP
subcell (J1) can have a band gap from 1.96 eV to 2.04 eV, from 1.97
eV to 2.03 eV, from 1.98 eV to 2.02 eV, or from 1.99 eV to 2.01 eV.
The (Al)InGaP composition is selected to match the lattice constant
of the Ge subcell and to provide a suitable band gap within the
range, for example, from 1.96 eV to 2.04 eV.
[0271] The composition of each of the subcells is selected to have
an internal quantum efficiency of at least 70% or at least 80% over
a certain range of irradiance wavelengths or energies.
[0272] For example, a Ge subcell can exhibit an internal quantum
efficiency greater than 85% at irradiance energies from about 0.77
eV to about 1.03 eV (about 1600 nm to 1200 nm), a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can exhibit
an internal quantum efficiency greater than 85% at irradiance
energies from 1.13 eV to 1.38 eV (1100 nm to 900 nm), a (Al,In)GaAs
subcell can exhibit an internal quantum efficiency greater than 90%
at irradiance energies from 1.51 eV to 2.00 eV (820 nm to 620 nm),
and a (Al)InGaP subcell can exhibit an internal quantum efficiency
greater than 90% at irradiance energies from 2.07 eV to 3.10 (600
nm to 400 nm).
[0273] Certain properties of four junction
(Si,Sn)Ge/GaInNAsSb/(Al,In)GaAs/(Al)InGaP photovoltaic cells are
shown in FIG. 7A and FIG. 7B. FIG. 7A shows a JN curve for a four
junction (Si,Sn)Ge/GaInNAsSb/(Al,In)GaAs/(Al)InGaP photovoltaic
cell characterized by a short circuit current density Jsc of 15.4
mA/cm.sup.2, an open circuit voltage Voc of 3.13 V, a fill factor
of 84.4%, and an efficiency of 29.8%. The measurements were made
using a 1 sun AM0 spectrum at a junction temperature of 25.degree.
C. FIG. 7B shows the internal quantum efficiency for each of the
four subcells as a function of irradiance wavelength. efficiency is
greater than about 90% over most of the irradiance wavelength range
from about 400 nm to about 1600 nm.
[0274] Various properties of the four junction
(Si,Sn)Ge/GaInNAsSb/(Al,In)GaAs/(Al)InGaP photovoltaic cells shown
in FIG. 7A and FIG. 7B are provided in Table 6.
TABLE-US-00006 TABLE 6 Properties of four junction GaINAsSb-
containing photovoltaic cells.
(Al)InGaP/(Al,In)GaAs/GaInNAsSb/(Si,Sn)Ge Four Junction Cell (1)
Four Junction Cell (2) Voc (V) 3.13 3.15 Jsc (mA/cm.sup.2) 15.4
15.2 FF (%) 84 85.5 EQE (%) 29.8 29.9 J1 - (Al)InGaP -- 15.15/1.97
Jsc (mA/cm.sup.2)/Eg (eV) J2- (Al,In)GaAs -- 15.67/1.47 Jsc
(mA/cm.sup.2)/Eg (eV) J3 - GaInNAsSb -- 16/1.06 Jsc
(mA/cm.sup.2)/Eg (eV) J4 - (Si,Sn)Ge -- 15.8/0.67 Jsc
(mA/cm.sup.2)/Eg (eV)
[0275] In certain embodiments, a multijunction photovoltaic cell
can comprise:
[0276] a first subcell comprising (Al)InGaP;
[0277] a second subcell comprising (Al,In)GaAs underlying the first
subcell;
[0278] a third subcell comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z underlying the second
subcell; and
[0279] a fourth subcell comprising (Si,Sn)Ge underlying the third
subcell; wherein, [0280] each of the subcells is lattice matched to
each of the other subcells; [0281] the third subcell is
characterized by a bandgap from 0.83 eV to 1.22 eV; and [0282] the
third subcell is characterized by an internal quantum efficiency
greater than 70% at an irradiance energy throughout the range from
0.95 eV to 1.55 eV at a junction temperature of 25.degree. C.
[0283] In certain embodiments, a multijunction photovoltaic cell
can comprise Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell
characterized by an internal quantum efficiency greater than 80% at
an irradiance energy throughout the range from 1.1 eV to 1.5
eV.
[0284] In certain embodiments, a four-junction multijunction
photovoltaic cell comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can be
characterized by,
[0285] an open circuit voltage Voc equal to or greater than 2.5
V;
[0286] a short circuit current density Jsc equal to or greater than
8 mA/cm.sup.2;
[0287] a fill factor equal to or greater than 75%; and
[0288] an efficiency greater than 25%,
[0289] measured using a 1 sun AM1.5D or AM0 spectrum at a junction
temperature of 25.degree. C.
[0290] In certain embodiments, a four-junction multijunction
photovoltaic cell comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can be
characterized by,
[0291] an open circuit voltage Voc equal to or greater than 3.0
V;
[0292] a short circuit current density Jsc equal to or greater than
15 mA/cm.sup.2;
[0293] a fill factor equal to or greater than 80%; and
[0294] an efficiency greater than 25%,
[0295] measured using a 1 sun AM1.5D or AM0 spectrum at a junction
temperature of 25.degree. C.
[0296] In certain embodiments, a four-junction multijunction
photovoltaic cell comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can be
characterized by,
[0297] an open circuit voltage Voc from 2.5 V to 3.5 V;
[0298] a short circuit current density Jsc from 13 mA/cm.sup.2 to
17 mA/cm.sup.2;
[0299] a fill factor from 80% to 90%; and
[0300] an efficiency from 28% to 36%,
[0301] measured using a 1 sun AM0 spectrum at a junction
temperature of 25.degree. C.
[0302] In certain embodiments, a four-junction multijunction
photovoltaic cell comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can be
characterized by,
[0303] an open circuit voltage Voc from 3.0 V to 3.5 V;
[0304] a short circuit current density Jsc from 8 mA/cm.sup.2 to 14
mA/cm.sup.2;
[0305] a fill factor from 80% to 90%; and
[0306] an efficiency from 28% to 36%,
[0307] measured using a 1 sun AM1.5D spectrum at a junction
temperature of 25.degree. C.
[0308] In certain embodiments, a four-junction multijunction
photovoltaic cell comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can
comprise:
[0309] a first subcell having a bandgap from 1.9 eV to 2.2 eV;
[0310] a second subcell having a bandgap from 1.40 eV to 1.57
eV;
[0311] a third subcell having a bandgap from 0.98 eV to 1.2 eV;
and
[0312] a fourth subcell having a bandgap from 0.67 eV.
[0313] In certain embodiments of a four-junction multijunction
photovoltaic cell comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell values for x,
y, and z are 0.075.ltoreq.x.ltoreq.0.083,
0.015.ltoreq.y.ltoreq.0.020, and 0.003.ltoreq.z.ltoreq.0.09.
[0314] In certain embodiments of a four-junction multijunction
photovoltaic cell comprising a
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell, the
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell can be
characterized by,
[0315] an open circuit voltage Voc from 0.42 V to 0.57 V;
[0316] a short circuit current density Jsc from 10 mA/cm.sup.2 to
13 mA/cm.sup.2; and
[0317] a bandgap from 1.0 eV to 1.17 eV,
[0318] measured using a 1 sun AM1.5D spectrum at a junction
temperature of 25.degree. C.
[0319] To increase the photovoltaic cell efficiency, five junction
photovoltaic cells can be fabricated. Examples of the composition
of photovoltaic cell stacks for three junction, four junction, and
five junction photovoltaic cells are shown in FIG. 8. As shown in
FIG. 8, for five junction and six junction cells, two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells may be
used.
[0320] To demonstrate the feasibility of using adjacent
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, four
junction photovoltaic cells having a bottom
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell and an
overlying Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell
were fabricated and evaluated. The four junction photovoltaic cells
were fabricated on a GaAs substrate. Each of the subcells is
substantially lattice matched to each of the other subcells and to
the GaAs substrate. The multijunction photovoltaic cells do not
comprise a metamorphic buffer layer between adjacent subcells. The
composition of each of the two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, the
(Al,In)GaAs subcell, and the (Al)InGaP subcell is selected to
lattice match to the GaAs substrate and to provide an appropriate
band gap.
[0321] The four junction photovoltaic cells had a bottom
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell (J4), an
overlying Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell
(J3), an overlying (Al,In)GaAs subcell (J2), and a top (Al)InGaP
subcell (J1). The band gaps and Jsc under a 1 sun AM1.5D or AM0
spectrum are shown in Table 7.
TABLE-US-00007 TABLE 7 Band gap and Jsc for four junction
photovoltaic cells having two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells. Subcell
Composition Band Gap (eV) Jsc (mA/cm.sup.2) J1 (Al)InGaP 2.05-2.08
12.7-13.2 J2 (Al,In)GaAs 1.60-1.64 11.8-14.2 J3
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z 1.20-1.21 15.2-16.8
J4 Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z 0.88-0.89
12.9-13.2
[0322] The internal and external quantum efficiencies for each of
the subcells of the photovoltaic cell presented in Table 6 is shown
in FIGS. 9A and 9B.
[0323] The four junction photovoltaic cells having two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells exhibit
internal and external quantum efficiencies over 70% throughout an
irradiance wavelength range from about 400 nm (3.1 eV) to about
1300 nm (0.95 eV), and over 80% throughout an irradiance wavelength
range from about 450 nm (2.75 eV) to about 1200 nm (1.03 eV).
[0324] Other four junction photovoltaic cells having two
Ga.sub.1,In.sub.xN.sub.yAs.sub.1-y-zSb.sub.z similar to those
presented in Table 7 exhibit an open circuit voltage from about
3.67 eV to about 3.69 eV, a short circuit current density from
about 9.70 mA/cm.sup.2 to about 9.95 mA/cm.sup.2, a fill factor
from about 80% to about 85% and an external quantum efficiency from
about 29.0% to about 31% measured using a 1 sun AM) or AM1.5D
spectrum at a junction temperature of 25.degree. C.
[0325] In these photovoltaic cells, the bottom
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell (J4) has a
band gap from 0.95 eV to about 0.99 eV such as from 0.96 eV to 0.97
eV, and values for x, y, and z of 0.11.ltoreq.x.ltoreq.0.15,
0.030.ltoreq.y.ltoreq.0.034 and 0.007.ltoreq.z.ltoreq.0.14, and in
certain embodiments, values for x, y, and z of
0.12.ltoreq.x.ltoreq.0.14, 0.031.ltoreq.y.ltoreq.0.033 and
0.007.ltoreq.z.ltoreq.0.14 .
[0326] In these photovoltaic cells, the second
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcell (J3) has a
band gap from 1.1 eV to about 1.3 eV, and values for x, y, and z of
0.026.ltoreq.x.ltoreq.0.030, 0.014.ltoreq.y.ltoreq.0.018 and
0.005.ltoreq.z.ltoreq.0.009, and in certain embodiments, values for
x, y, and z of 0.027.ltoreq.x.ltoreq.0.029,
0.015.ltoreq.y.ltoreq.0.017 and 0.006.ltoreq.z.ltoreq.0.008.
[0327] These results demonstrate the feasibility of incorporating
two Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells into a
photovoltaic cell to improve multijunction photovoltaic cell
performance. As shown in FIG. 8, to improve the collection
efficiency at lower wavelengths, five junction and six junction
photovoltaic cells having two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells can also
include a bottom active Ge subcell. Lattice matched five junction
photovoltaic cells as shown in FIG. 8 are expected to exhibit
external quantum efficiencies over 34% and over 36%, respectively,
under 1 sun AM0 illumination at a junction temperature of
25.degree. C.
[0328] A four-junction photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells can be
adapted for use in five junction multijunction photovoltaic cells.
The stack of
(Al)InGaP/(Al,In)GaAs/GaAs/Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
layers can overly a Ge layer that can function as the fifth
subcell. In photovoltaic cells having a Ge subcell, each of the
base layers can be lattice matched to the Ge subcell.
[0329] In certain embodiments, a four- and five junction
multijunction photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells can
comprise:
[0330] a first subcell comprising (Al)InGaP;
[0331] a second subcell comprising (Al,In)GaAs underlying the first
subcell;
[0332] a third subcell comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z underlying the second
subcell; and
[0333] a fourth subcell comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z underlying the third
subcell; wherein, [0334] each of the subcells is lattice matched to
each of the other subcells; [0335] each of the fourth subcell and
the third subcell is characterized by a bandgap with a range from
0.83 eV to 1.3 eV; and [0336] each of the fourth subcell and the
third subcell is characterized by an internal quantum efficiency
greater than 70% at an irradiance energy throughout the range from
0.95 eV to 1.55 eV.
[0337] In certain embodiments, a four- and five junction
multijunction photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, each of the
two Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells can be
characterized by an internal quantum efficiency greater than 80% at
an illumination energy throughout the range from 1.1 eV to 1.5
eV.
[0338] In certain embodiments, a four- and five junction
multijunction photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, the
multijunction photovoltaic cell can be characterized by,
[0339] an open circuit voltage Voc equal to or greater than 2.8
V;
[0340] a short circuit current density Jsc equal to or greater than
18 mA/cm.sup.2;
[0341] a fill factor equal to or greater than 80%; and
[0342] an efficiency equal to or greater than 29%,
[0343] measured using a 1 sun 1.5 AM0 spectrum at a junction
temperature of 25.degree. C.
[0344] In certain embodiments, a four- and five junction
multijunction photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, the
multijunction photovoltaic cell can comprise:
[0345] a first subcell characterized by a bandgap from 1.90 eV to
2.20 eV;
[0346] a second subcell characterized by a bandgap from 1.4 eV to
1.7 eV;
[0347] a third subcell characterized by a bandgap from 0.97 eV to
1.3 eV; and
[0348] a fourth subcell characterized by a bandgap from 0.8 eV to 1
eV.
[0349] In certain embodiments, a four- and five junction
multijunction photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, the
multijunction photovoltaic cell can comprise:
[0350] a fourth subcell comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z is characterized by a
bandgap from 0.9 eV to 1 eV;
[0351] a third subcell comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z is characterized by a
bandgap from 1.1 eV to 1.3 eV;
[0352] a second subcell comprising (Al,In)GaAs is characterized by
a bandgap from 1.5 eV to 1.7 eV; and
[0353] a first subcell comprising (Al)InGaP is characterized by a
bandgap from 1.9 eV to 2.1 eV;
[0354] wherein the multijunction photovoltaic cell can be
characterized by, [0355] an open circuit voltage Voc equal to or
greater than 3.5 V; [0356] a short circuit current density Jsc
equal to or greater than 8 mA/cm.sup.2; [0357] a fill factor equal
to or greater than 75%; and [0358] an efficiency equal to or
greater than 27%, [0359] measured using a 1 sun AM1.5D spectrum at
a junction temperature of 25.degree. C.
[0360] In certain embodiments, a four- and five junction
multijunction photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, the
multijunction photovoltaic cell can be characterized by,
[0361] an open circuit voltage Voc from 3.65 V to 3.71 V;
[0362] a short circuit current density Jsc from 9.7 mA/cm.sup.2 to
10.0 mA/cm.sup.2;
[0363] a fill factor from 80% to 85%; and
[0364] an efficiency from 29% to 31%,
[0365] measured using a 1 sun AM1.5D spectrum at a junction
temperature of 25.degree. C.
[0366] In certain embodiments, a four- and five junction
multijunction photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, the
multijunction photovoltaic cell can be characterized by,
[0367] an open circuit voltage Voc equal to or greater than 2.5
V;
[0368] a short circuit current density Jsc equal to or greater than
8 mA/cm.sup.2;
[0369] a fill factor equal to or greater than 75%; and
[0370] an efficiency equal to or greater than 25%,
[0371] measured using a 1 sun AM1.5D or AM0 spectrum at a junction
temperature of 25.degree. C.
[0372] In certain embodiments, a four- and five junction
multijunction photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, the
multijunction photovoltaic cell can be characterized by,
[0373] an open circuit voltage Voc from 2.5 V to 3.5 V;
[0374] a short circuit current density Jsc from 13 mA/cm.sup.2 to
17 mA/cm.sup.2; and
[0375] a fill factor from 80% to 90%; and
[0376] an efficiency from 28% to 36%,
[0377] measured using a 1 sun AM0 spectrum at a junction
temperature of 25.degree. C.
[0378] In certain embodiments, a four- and five junction
multijunction photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells, the
multijunction photovoltaic cell can be characterized by, an open
circuit voltage Voc from 3 V to 3.5 V;
[0379] a short circuit current density Jsc from 8 mA/cm.sup.2 to 14
mA/cm.sup.2;
[0380] a fill factor from 80% to 90%; and
[0381] an efficiency from 28% to 36%,
[0382] measured using a 1 sun AM1.5D spectrum at a junction
temperature of 25.degree. C.
[0383] Five junction multijunction photovoltaic cells are also
provided. A five junction multijunction photovoltaic cell an
comprise two Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcells. The two Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcells can overly a (Si,Sn)Ge subcell and can be lattice matched
to the (Si,Sn)Ge subcell. Each of the subcells can be lattice
matched to each of the other subcells and can be lattice matched to
the (Si,Sn)Ge subcell. A (Si,Sn)Ge subcell can have a band gap from
0.67 eV to 1.0 eV.
[0384] In certain embodiments, a five junction multijunction
photovoltaic cell comprising two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells can
comprise:
[0385] a first subcell comprising (Al)InGaP;
[0386] a second subcell comprising (Al,In)GaAs underlying the first
subcell;
[0387] a third subcell comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z underlying the second
subcell;
[0388] a fourth subcell comprising
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z underlying the third
subcell;
[0389] a fifth subcell comprising (Si,Sn)Ge underling the fourth
subcell; wherein, [0390] each of the subcells is lattice matched to
each of the other subcells; [0391] each of the fourth subcell and
the third subcell is characterized by a bandgap with a range from
0.83 eV to 1.3 eV; and [0392] each of the fourth subcell and the
third subcell is characterized by an internal quantum efficiency
greater than 70% at an irradiance energy throughout the range from
0.95 eV to 1.55 eV.
[0393] In certain embodiments of a five junction multijunction
photovoltaic cell each of the two
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z subcells can be
characterized by an internal quantum efficiency greater than 80% at
an illumination energy throughout the range from 1.1 eV to 1.5
eV.
[0394] In multijunction photovoltaic cells provided by the present
disclosure, one or more subcells can comprise AlInGaAsP where the
content each Group III and each Group V element can range from 0 to
1, and the AlInGaAsP base can be lattice matched to a substrate and
to each of the other subcells in the multijunction photovoltaic
cell. The band gap of a AlInGaAsP subcell can be from 1.8 eV to 2.3
eV. An AlInGaAsP subcell can comprise an (Al)InGaP subcell or an
(Al,In)GaAs subcell. Multijunction photovoltaic cells provided by
the present disclosure can comprise at least one
Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z and one or more of
the other subcells can comprise a AlInGaAsP subcell.
[0395] In certain embodiments of multijunction photovoltaic cells,
a subcell such as a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
and/or a AlInGaAsP subcell can be a homojunction in which the
emitter and the base of a subcell comprise the same material
composition and have the same bandgap.
[0396] In certain embodiments of multijunction photovoltaic cells,
a subcell such as a Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
and/or a AlInGaAsP subcell can be a heterojunction in which the
emitter and the base of a subcell comprise the same material but
have a different composition such that the band gap of the emitter
and the band gap of the base of a subcell are different. In certain
embodiments, the band gap of the emitter is higher than the band
gap of the base, and in certain embodiments, the band gap of the
emitter is lower than the band gap of the base. Reverse
heterojunction Ga.sub.1-xIn.sub.xN.sub.yAs.sub.1-y-zSb.sub.z
subcells are disclosed in U.S. Pat. No. 9,153,724, which is
incorporated by reference in its entirety.
[0397] It should be noted that there are alternative ways of
implementing the embodiments disclosed herein. Accordingly, the
present embodiments are to be considered as illustrative and no
restrictive. Furthermore, the claims are not to be limited to the
details given herein, and are entitled their full scope and
equivalents thereof.
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