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R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 1
Band-Gap-Engineered Architectures for High-Efficiency Multijunction
Concentrator Solar Cells
Richard R. King, A. Boca, W. Hong, X.-Q. Liu, D. Bhusari, D. Larrabee, K. M. Edmondson, D. C. Law, C. M. Fetzer,
S. Mesropian, and N. H. Karam
Spectrolab, Inc.A Boeing Company
24th European Photovoltaic Solar Energy ConferenceSep. 21-25, 2009
Hamburg, Germany
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 2
• Carl Osterwald, Keith Emery, Larry Kazmerski, Martha Symko-Davies, Fannie Posey-Eddy, Holly Thomas, Manuel Romero, John Geisz, Sarah Kurtz – NREL
• Rosina Bierbaum – University of Michigan, Ann Arbor
• Pierre Verlinden, John Lasich – Solar Systems, Australia
• Kent Barbour, Russ Jones, Jim Ermer, Peichen Pien, Dimitri Krut, Hector Cotal, Mark Osowski, Joe Boisvert, Geoff Kinsey, Mark Takahashi, and the entire multijunction solar cell team at Spectrolab
This work was supported in part by the U.S. Dept. of Energy through the NREL High-Performance Photovoltaics (HiPerf PV) program (ZAT-4-33624-12), the DOE Technology Pathways Partnership (TPP), and by Spectrolab.
AcknowledgmentsAcknowledgments
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 3
• Solar cell theoretical efficiency limits– Opportunities to change ground rules for higher terrestrial efficiency– Cell architectures capable of >70% in theory, >50% in practice
• Metamorphic semiconductor materials– Control of band gap to tune to solar spectrum
OutlineOutline
Tunnel Juncti
on
Top Cell
Wide-Eg Tunnel
Middle Cell
p-GaInP BSF
p-GaInP base
n-GaInAs emitter
n+-Ge emitter
p-AlGaInP BSF
n-GaInP emittern-AlInP windown+-GaInAs
contact
AR
p-Ge baseand substratecontact
p-GaInAsstep-graded buffer
Bottom Cell
p++-TJn++-TJ
p-GaInAs base
nucleation
n-GaInP window
p++-TJ
n++-TJTunnel J
unction
Top Cell
Wide-Eg Tunnel
Middle Cell
p-GaInP BSF
p-GaInP base
n-GaInAs emitter
n+-Ge emitter
p-AlGaInP BSF
n-GaInP emittern-AlInP windown+-GaInAs
contact
AR
p-Ge baseand substratecontact
p-GaInAsstep-graded buffer
Bottom Cell
p++-TJn++-TJ
p-GaInAs base
nucleation
n-GaInP window
p++-TJ
n++-TJ
• High-efficiency terrestrial concentrator cells– Metamorphic (MM) and lattice-matched (LM) 3-junction
solar cells with >40% efficiency– 4-junction MM and LM concentrator cells– Inverted metamorphic structure, semiconductor bonded technology (SBT) for MJ terrestrial concentrator cells
• The solar resource and concentrator photovoltaic (CPV) system economics
0.75-eV GaInAs cell 5
1.1-eV GaInPAs cell 4
semi-conductor
bondedinterface
1.4-eV GaInAs cell 3
1.7-eV AlGaInAs cell 2
2.0-eV AlGaInP cell 1
metal gridline
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 4
High-Efficiency
Multijunction Cell
Architectures
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 5
Theoretical
95% Carnot eff. = 1 – T/Tsun T = 300 K, Tsun ≈ 5800 K93% Max. eff. of solar energy conversion
= 1 – TS/E = 1 – (4/3)T/Tsun (Henry)
72% Ideal 36-gap solar cell at 1000 suns (Henry)
56% Ideal 3-gap solar cell at 1000 suns (Henry)50% Ideal 2-gap solar cell at 1000 suns (Henry)
44% Ultimate eff. of device with cutoff Eg: (Shockley, Queisser)43% 1-gap cell at 1 sun with carrier multiplication
(>1 e-h pair per photon) (Werner, Kolodinski, Queisser)
37% Ideal 1-gap solar cell at 1000 suns (Henry)
31% Ideal 1-gap solar cell at 1 sun (Henry)30% Detailed balance limit of 1 gap solar cell at 1 sun
(Shockley, Queisser)
Measured
3-gap GaInP/GaInAs/Ge LM cell, 364 suns (Spectrolab) 41.6%3-gap GaInP/GaInAs/Ge MM cell, 240 suns (Spectrolab) 40.7%
3-gap GaInP/GaAs/GaInAs cell at 1 sun (NREL) 33.8%
1-gap solar cell (silicon, 1.12 eV) at 92 suns (Amonix) 27.6%1-gap solar cell (GaAs, 1.424 eV) at 1 sun (Kopin) 25.1%
1-gap solar cell (silicon, 1.12 eV) at 1 sun (UNSW) 24.7%
ReferencesC. H. Henry, “Limiting efficiencies of ideal single and multiple energy gap terrestrial
solar cells,” J. Appl. Phys., 51, 4494 (1980). W. Shockley and H. J. Queisser, “Detailed Balance Limit of Efficiency of p-n Junction
Solar Cells,” J. Appl. Phys., 32, 510 (1961). J. H. Werner, S. Kolodinski, and H. J. Queisser, “Novel Optimization Principles and
Efficiency Limits for Semiconductor Solar Cells,” Phys. Rev. Lett., 72, 3851 (1994).
R. R. King et al., "Band-Gap-Engineered Architectures for High-Efficiency Multijunction Concentrator Solar Cells," 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009.
R. R. King et al., "40% efficient metamorphic GaInP / GaInAs / Ge multijunction solar cells," Appl. Phys. Lett., 90, 183516 (4 May 2007).
M. Green, K. Emery, D. L. King, Y. Hishikawa, W. Warta, "Solar Cell Efficiency Tables (Version 27)", Progress in Photovoltaics, 14, 45 (2006).
A. Slade, V. Garboushian, "27.6%-Efficient Silicon Concentrator Cell for Mass Production," Proc. 15th Int'l. Photovoltaic Science and Engineering Conf., Beijing, China, Oct. 2005.
R. P. Gale et al., "High-Efficiency GaAs/CuInSe2 and AlGaAs/CuInSe2 Thin-Film Tandem Solar Cells," Proc. 21st IEEE Photovoltaic Specialists Conf., Kissimmee, Florida, May 1990.
J. Zhao, A. Wang, M. A. Green, F. Ferrazza, "Novel 19.8%-efficient 'honeycomb' textured multicrystalline and 24.4% monocrystalline silicon solar cells," Appl. Phys. Lett., 73, 1991 (1998).
Maximum Solar Cell Maximum Solar Cell EfficienciesEfficiencies
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 6
Metamorphic (MM) Metamorphic (MM) 33--Junction Solar CellJunction Solar Cell
Tunnel Ju
nction
Top Cell
Wide-Eg Tunnel
Middle Cell
p-GaInP BSF
p-GaInP base
n-GaInAs emitter
n+-Ge emitter
p-AlGaInP BSF
n-GaInP emittern-AlInP windown+-GaInAs
contact
AR
p-Ge baseand substratecontact
p-GaInAsstep-graded buffer
Bottom Cell
p++-TJn++-TJ
p-GaInAs base
nucleation
n-GaInP window
p++-TJn++-TJ
Tunnel Ju
nction
Top Cell
Wide-Eg Tunnel
Middle Cell
p-GaInP BSF
p-GaInP base
n-GaInAs emitter
n+-Ge emitter
p-AlGaInP BSF
n-GaInP emittern-AlInP windown+-GaInAs
contact
AR
p-Ge baseand substratecontact
p-GaInAsstep-graded buffer
Bottom Cell
p++-TJn++-TJ
p-GaInAs base
nucleation
n-GaInP window
p++-TJn++-TJ
Lattice-Mismatchedor Metamorphic (MM)
0
0.05
0.1
0.15
0.2
0.25
0.3
0 0.5 1 1.5 2 2.5 3 3.5Voltage (V)
Cur
rent
Den
sity
/ In
cide
nt In
tens
ity (
A/W
)
MJ cell
subcell 1
subcell 2
subcell 3
• Metamorphic growth of upper two subcells, GaInAs and GaInP
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 7
0
10
20
30
40
50
60
70
80
90
100
300 500 700 900 1100 1300 1500 1700 1900
Wavelength (nm)
Cur
rent
Den
sity
per
Uni
t W
avel
engt
h (m
A/(c
m2 μ
m))
0
10
20
30
40
50
60
70
80
90
100
Exte
rnal
Qua
ntum
Effi
cien
cy (
%)
AM1.5D, low-AODAM1.5G, ASTM G173-03
AM0, ASTM E490-00aEQE, lattice-matched
EQE, metamorphic
External QE of LM and MM External QE of LM and MM 33--Junction CellsJunction Cells
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 8
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
1.0 1.1 1.2 1.3 1.4 1.5 1.6
Eg2 = Subcell 2 Bandgap (eV)
E g1 =
Sub
cell
1 (T
op) B
andg
ap (
eV)
.
Disordered GaInP top subcell Ordered GaInP top subcell
38%
54%
42%
46%
50%
52%
3-junction Eg1/ Eg2/ 0.67 eV cell efficiency240 suns (24.0 W/cm2), AM1.5D (ASTM G173-03), 25oCIdeal efficiency -- radiative recombination limit
40.7% 40.1%
48%
44%
40%
MMLM
Metamorphic (MM) Metamorphic (MM) 33--Junction Solar CellJunction Solar Cell
• Metamorphic GaInAs and GaInP subcells bring band gap combination closer to theoretical optimum
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 9Concentrator cell light I-V and efficiency independently verified by J. Kiehl, T. Moriarty, K. Emery – NREL
• First solar cell of any type to reach over 40% efficiency
SpectrolabMetamorphic
GaInP/ GaInAs/ Ge CellVoc = 2.911 V Jsc = 3.832 A/cm2
FF = 87.50%Vmp = 2.589 V
Efficiency = 40.7% ± 2.4% 240 suns (24.0 W/cm2) intensity0.2669 cm2 designated area25 ± 1°C, AM1.5D, low-AOD spectrum Ref.: R. R. King et al., "40% efficient
metamorphic GaInP / GaInAs / Ge multijunction solar cells," Appl. Phys. Lett., 90, 183516, 4 May 2007.
Record Record 40.7%40.7%--Efficient Efficient Concentrator Solar CellConcentrator Solar Cell
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 10
Growth on Ge or GaAs substrate, followed by substrate removal from sunward surface
GrowthDirection
cap
1.9 eV (Al)GaInP subcell 1
1.4 eV GaInAs subcell 2
graded MM buffer layers
1.0 eV GaInAs subcell 3
Ge or GaAs substrate
Ge or GaAs substrate
cap
Metamorphic (MM) 3Metamorphic (MM) 3--Junction Cells Junction Cells –––– Inverted 1.0Inverted 1.0--eV GaInAs SubcelleV GaInAs Subcell
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 11
1
1.1
1.2
1.3
1.4
1.5
1.6
0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3Eg3 = Subcell 3 Bandgap (eV)
E g2 =
Sub
cell
2 B
andg
ap (
eV)
.
48%
53%
44%
46%
50%
52%
3-junction 1.9 eV/ Eg2/ Eg3 cell efficiency500 suns (50 W/cm2), AM1.5D (ASTM G173-03), 25oCIdeal efficiency -- radiative recombination limitX
51%
Inverted Metamorphic (IMM) Inverted Metamorphic (IMM) 33--Junction CellJunction Cell
• Raising band gap of bottom cell from 0.67 for Ge to ~1.0 eV for IMM GaInAs raises theoretical 3J cell efficiency
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 12
44--Junction Upright Metamorphic Junction Upright Metamorphic (MM) Terrestrial Concentrator Cell(MM) Terrestrial Concentrator Cell
0.67-eV Ge cell 4 and substrate
transparent buffer
1.2-eV GaInAs cell 3
1.55-eV AlGaInAs cell 2
1.8-eV (Al)GaInP cell 1
metal gridline
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 13
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5Eg3 = Subcell 3 Bandgap (eV)
E g2 =
Sub
cell
2 B
andg
ap (
eV)
.
38%46%
54%
56%
50%
42%
4-junction 1.9 eV/ Eg2/ Eg3/ 0.67 eV cell efficiency500 suns (50 W/cm2), AM1.5D (ASTM G173-03), 25oCIdeal efficiency -- radiative recombination limitX
58%
34%
44--Junction Cell Junction Cell Optimum Band Gap CombinationsOptimum Band Gap Combinations
• Lowering band gap of subcells 2 and 3, e.g., with MM materials, gives higher theoretical 4J cell efficiency
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 14
55--Junction Inverted Metamorphic Junction Inverted Metamorphic (IMM) Cells(IMM) Cells
transparent buffer
0.75-eV GaInAs cell 5
1.1-eV GaInAs cell 4transparent buffer
1.4-eV GaInAs cell 3
1.7-eV AlGaInAs cell 2
2.0-eV AlGaInP cell 1
metal gridline
Ge or GaAs
growth substrate
SemiconductorSemiconductor--Bonded Technology Bonded Technology (SBT) Terrestrial Concentrator Cell(SBT) Terrestrial Concentrator Cell
InP growth substrateGaAs or Ge growth substrate
1.4-eV GaInAs cell 3
1.7-eV AlGaInAs cell 2
2.0-eV AlGaInP cell 10.75-eV GaInAs cell 5
1.1-eV GaInPAs cell 4
GaAs or Ge growth substrate
1.4-eV GaInAs cell 3
1.7-eV AlGaInAs cell 2
2.0-eV AlGaInP cell 1
1.4-eV GaInAs cell 3
1.7-eV AlGaInAs cell 2
2.0-eV AlGaInP cell 1
GaAs or Ge growth substrate
1.4-eV GaInAs cell 3
1.7-eV AlGaInAs cell 2
2.0-eV AlGaInP cell 1
GaAs or Ge growth substrate
semi-conductor
bondedinterface
metal gridline
0.75-eV GaInAs cell 5
1.1-eV GaInPAs cell 4
1.4-eV GaInAs cell 3
1.7-eV AlGaInAs cell 2
2.0-eV AlGaInP cell 1
semi-conductor
bondedinterface
metal gridline
– Low band gap cells for MJ cells using high-quality, lattice-matched materials– Epitaxial exfoliation and substrate removal– Formation of lattice-engineered substrate for later MJ cell growth– Bonding of high-band-gap and low-band-gap cells after growth– Electrical conductance of semiconductor-bonded interface– Surface effects for semiconductor-to-semiconductor bonding
• Wafer bonding for multijunction solar cells
15
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 16
cap
contactAR
(Al)GaInP Cell 1 2.0 eVwide-Eg tunnel junction
GaInP Cell 2 (low Eg)1.78 eV
wide-Eg tunnel junction
AlGa(In)As Cell 31.50 eV
tunnel junction
Ga(In)As Cell 41.22 eV
tunnel junction
AR
Ga(In)As buffer
Ge Cell 6and substrate
0.67 eV
nucleation
back contact
wide-Eg tunnel junction
GaInNAs Cell 50.98 eV
cap
contactAR
(Al)GaInP Cell 1 2.0 eVwide-Eg tunnel junction
GaInP Cell 2 (low Eg)1.78 eV
wide-Eg tunnel junction
AlGa(In)As Cell 31.50 eV
tunnel junction
Ga(In)As Cell 41.22 eV
tunnel junction
AR
Ga(In)As buffer
Ge Cell 6and substrate
0.67 eV
nucleationnucleation
back contact
wide-Eg tunnel junction
GaInNAs Cell 50.98 eV
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0 1 2 3 4 5 6 7Voltage (V)
Cur
rent
Den
sity
/ In
cide
nt In
tens
ity (
A/W
)
MJ cellsubcell 1subcell 2subcell 3subcell 4subcell 5subcell 6
66--Junction Solar CellsJunction Solar Cells
0
100
200
300
400
500
600
700
0 0.5 1 1.5 2 2.5 3 3.5 4Photon Energy (eV)
Inte
nsity
per
Uni
t Pho
ton
Ener
gy(W
/m 2
. eV
)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Phot
on u
tiliz
atio
n ef
ficie
ncy
.
AM1.5D, ASTM G173-03, 1000 W/m2Utilization efficiency of photon energy 1-junction cell 3-junction cell 6-junction cell
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 17
35%
40%
45%
50%
55%
60%
1 10 100 1000 10000Incident Intensity (suns) (1 sun = 0.100 W/cm2)
Effic
ienc
y (%
)Detailed balance limit efficiencyRadiative recombination onlySeries res. and shadowing, optimized grid spacingNormalized to experimental efficiency
5003J & 4J MM solar cells
3J
3J
3J
4J
4J
4J
Modeled Terrestrial Modeled Terrestrial Concentrator Cell EfficiencyConcentrator Cell Efficiency
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 18
High-Efficiency
Multijunction Cell
Results
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 19
Tunnel Ju
nction
Top Cell
Wide-Eg Tunnel
Middle Cell
p-GaInP BSF
p-GaInP base
n-Ga(In)As emitter
n+-Ge emitter
p-AlGaInP BSF
n-GaInP emittern-AlInP windown+-Ga(In)As
contact
AR
p-Ge baseand substratecontact
n-Ga(In)As buffer
Bottom Cell
p++-TJn++-TJ
p-Ga(In)As base
nucleation
Wide-bandgap tunnel junction
GaInP top cell
Ge bottom cell
n-GaInP window
p++-TJn++-TJ
Ga(In)As middle cell
Tunnel junction
Buffer regionTunnel
Juncti
on
Top Cell
Wide-Eg Tunnel
Middle Cell
p-GaInP BSF
p-GaInP base
n-GaInAs emitter
n+-Ge emitter
p-AlGaInP BSF
n-GaInP emittern-AlInP windown+-GaInAs
contact
AR
p-Ge baseand substratecontact
p-GaInAsstep-graded buffer
Bottom Cell
p++-TJn++-TJ
p-GaInAs base
nucleation
n-GaInP window
p++-TJn++-TJ
Lattice-Matched (LM) Lattice-Mismatchedor Metamorphic (MM)
LM and MM 3LM and MM 3--Junction Junction Cell CrossCell Cross--SectionSection
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 20
New World RecordNew World Record41.6% Multijunction Solar Cell41.6% Multijunction Solar Cell
• 41.6% efficiency demonstrated for 3J lattice-matched Spectrolab cell, a new world record• Highest efficiency for any type of solar cell measured to date• Independently verified by National Renewable Energy Laboratory (NREL)• Standard measurement conditions (25°C, AM1.5D, ASTM G173 spectrum) at 364 suns (36.4 W/cm2)• Lattice-matched cell structure similar to C3MJ cell, with reduced grid shadowing as planned for C4MJ cell• Incorporating high-efficiency 3J metamorphic cell structure + further improvements in grid design → strong potential to reach 42-43%champion cell efficiency
Ref.: R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009.
Concentrator cell light I-V and efficiency independently verified by C. Osterwald, K. Emery – NREL
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 21
24
26
28
30
32
34
36
38
40
42
44
0.1 1.0 10.0 100.0 1000.0
Incident Intensity (suns) (1 sun = 0.100 W/cm2)
Effic
ienc
y (%
) and
Voc
x 1
0 (V
)
0.78
0.80
0.82
0.84
0.86
0.88
0.90
0.92
0.94
0.96
0.98
Fill
Fact
or (
unitl
ess)
Efficiency
Voc x 10
Voc fit, 100 to 1000 suns
FF
• At peak 41.6% efficiency → 364 suns, Voc = 3.192 V, FF = 0.887• Efficiency still >40% at 820 suns, at 940 suns efficiency is 39.8%• Diode ideality factor of 1.0 for all 3 junctions fits Voc well from 100 to 1000 suns
41.6% Solar Cell41.6% Solar CellEff., Voc vs. ConcentrationEff., Voc vs. Concentration
41.6%
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 22
• At peak 41.6% efficiency → 364 suns, Voc = 3.192 V, FF = 0.887• Series resistance causes drop in Vmp above 400 suns, Voc continues to increase• Efficiency still >40% at 820 suns, at 940 suns efficiency is 39.8%
41.6% Solar Cell41.6% Solar CellLIV Curves vs. ConcentrationLIV Curves vs. Concentration
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0 0.5 1 1.5 2 2.5 3 3.5Voltage (V)
Cur
rent
Den
sity
/ In
cide
nt In
tens
ity (
A/W
)
2.6
6.6
17.6
59.8
127.3
364.2
604.8
940.9
Inc. Intensity (suns)1 sun = 0.100 W/cm2
41.6%
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 23
Chart courtesy of Larry Kazmerski, NREL
Best Research Cell Best Research Cell EfficienciesEfficiencies
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 24
37%37.5%
38.5%
40%
43%
36
37
38
39
40
41
42
43
Prod
uctio
n C
ell E
ffici
ency
(%)
2007 2008 2009 2010 2015
Year
• Terrestrial concentrator cell efficiency
• Goals in Technology Pathways Partnership (TPP)
Spectrolab Cell Generations Spectrolab Cell Generations in DOE TPP Programin DOE TPP Program
C4MJ
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 25
Spectrolab C1MJ, C2MJ, and Spectrolab C1MJ, C2MJ, and C3MJ Cell ProductsC3MJ Cell Products
0%
5%
10%
15%
20%
25%
30%
35%
40%
34.0
%
34.5
%
35.0
%
35.5
%
36.0
%
36.5
%
37.0
%
37.5
%
38.0
%
38.5
%
39.0
%
39.5
%
Efficiency η at Max. Power
% o
f Pop
ulat
ion
C1MJ
C2MJ
C3MJ
ηAVG = 36.9%
ηAVG = 37.5%
ηAVG = 38.2%
0%
5%
10%
15%
20%
25%
30%
35%
40%
34.0
%
34.5
%
35.0
%
35.5
%
36.0
%
36.5
%
37.0
%
37.5
%
38.0
%
38.5
%
39.0
%
39.5
%
Efficiency η at Max. Power
% o
f Pop
ulat
ion
C1MJ
C2MJ
C3MJ
ηAVG = 36.9%
ηAVG = 37.5%
ηAVG = 38.2%
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 26
Isc (A) Voc (V) FF EffAverage 7.601 3.090 0.845 39.6%Std. dev. 0.135 0.022 0.009 0.8%
35.7
%
36.0
%
36.3
%
36.6
%
36.9
%
37.2
%
37.5
%
37.8
%
38.1
%
38.4
%
38.7
%
39.0
%
39.3
%
39.6
%
39.9
%
40.2
%
40.5
%
40.8
%
5% 3J-MM
Corrected LIV Data forPrototype 3J Metamorphic (MM) 5%-In Cells
10 runs, 22 wafers, 205 cells
Prototype 3J Metamorphic Prototype 3J Metamorphic Cell BuildsCell Builds
3J MM Cell Efficiency Bin
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 27
cap
contactAR
(Al)GaInP Cell 1 1.9 eVwide-Eg tunnel junction
AlGa(In)As Cell 21.6 eV
Ga(In)As Cell 31.4 eV
tunnel junction
AR
Ga(In)As buffer
Ge Cell 4and substrate
0.67 eV
nucleation
back contact
wide-Eg tunnel junction
cap
contactAR
(Al)GaInP Cell 1 1.9 eVwide-Eg tunnel junction
AlGa(In)As Cell 21.6 eV
Ga(In)As Cell 31.4 eV
tunnel junction
AR
Ga(In)As buffer
Ge Cell 4and substrate
0.67 eV
nucleationnucleation
back contact
wide-Eg tunnel junction
0
0.05
0.1
0.15
0.2
0.25
0 1 2 3 4 5Voltage (V)
Cur
rent
Den
sity
/ In
cide
nt In
tens
ity (
A/W
)
MJ cell
subcell 1
subcell 2
subcell 3
subcell 4
44--Junction Junction LatticeLattice--Matched CellMatched Cell
• Current density in spectrum above Ge cell 4 is divided 3 ways among GaInAs, AlGa(In)As, GaInP cells
•Lower current and I2R resistive power loss
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 28
0
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40
50
60
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300 500 700 900 1100 1300 1500 1700 1900Wavelength (nm)
Exte
rnal
Qua
ntum
Eff
icie
ncy
(%)
0
200
400
600
800
1000
1200
1400
1600
Inte
nsity
Per
Uni
t Wav
elen
gth
(W
/(m2 μ
m))
AlGaInP subcell 1 1.95 eV
AlGaInAs subcell 2 1.66 eV
GaInAs subcell 3 1.39 eV
Ge subcell 4 0.72 eV
All subcells AM1.5DASTM G173-03
Measured 4Measured 4--Junction Cell Junction Cell Quantum EfficiencyQuantum Efficiency
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 29
Light ILight I--V CurvesV CurvesRecord Efficiency CellsRecord Efficiency Cells
• Light I-V curves for 3-junction upright MM (40.7%), 3J lattice-matched (41.6%), 3J lattice-matched at 822 suns (39.1%), and 4J lattice-matched cell (36.9%)
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5Voltage (V)
Cur
rent
Den
sity
/ In
c. In
tens
ity (
A/W
) .
Metamorphic Lattice-matched LM, 822 suns 4J Cell
3J Conc. 3J Conc. 3J Conc. 4J Conc. Cell Cell Cell Cell
Voc 2.911 3.192 V 3.251 4.398 V Jsc/inten. 0.1596 0.1467 A/W 0.1467 0.0980 A/W Vmp 2.589 2.851 V 2.781 3.950 V FF 0.875 0.887 0.841 0.856 conc. 240 364 suns 822 500 suns area 0.267 0.317 cm2 0.317 0.208 cm2
Eff. 40.7% 41.6% 40.1% 36.9%
AM1.5D, AM1.5D, AM1.5D, AM1.5D, low -AOD spectrum ASTM G173-03 ASTM G173-03 ASTM G173-03 Prelim. meas. Independently confirmed meas. 25°C 25°C
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 30
The Solar Resource and CPV Economics
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 31
5
6
5
6
• Entire US electricity demand can be provided by concentrator PV arrays using 37%-efficient cells on:
or ten 50 km x 50 km areasor similar division across US
Ref.: http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/
150 km x 150 km area of land
The Solar ResourceThe Solar Resource
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 32
Map source: http://www.nrel.gov/gis/images/map_csp_us_annual_may2004.jpg
CPV cost superiority40% cell efficiency
CPV cost superiority50% cell efficiency
Map source: http://www.nrel.gov/gis/images/map_csp_us_annual_may2004.jpg
CPV cost superiority40% cell efficiency
CPV cost superiority50% cell efficiency
Concentrator Photovoltaic Concentrator Photovoltaic (CPV) Electricity Generation(CPV) Electricity Generation
Higher multijunction cell efficiency has a huge impact on the economics of CPV, and on the way we will generate electricity.
R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009 33
• Urgent global need to address carbon emission, climate change, and energy security concerns → renewable electric power can help• Theoretical solar conversion efficiency
– Examining built-in assumptions points out opportunities for higher PV efficiency– Multijunction architectures, up/down conversion, quantum structures, intermediate bands, hot-carrier effects, solar concentration → higher η– Theo. solar cell η > 70%, practical η > 50% achievable
• Metamorphic multijunction cells have begun to realize their promise– Metamorphic semiconductors offer vastly expanded of band gaps– 40.7% metamorphic GaInP/ GaInAs/ Ge 3J cells demonstrated– First solar cells of any type to reach over 40% efficiency
• New world record efficiency of 41.6% demonstrated– Highest efficiency yet measured for any type of solar cell– 41.6% efficiency independently verified at NREL (364 suns, 25°C, AM1.5D)
• Solar cells with efficiencies in this range can transform the way we generate most of our electricity, and make the PV market explode
SummarySummary