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 Conference Sep. 21-25, 2009 Hamburg, Germany R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

1

Acknowledgments • 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.

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

2

Outline contact AR

• Solar cell theoretical efficiency limits – Opportunities to change ground rules for higher terrestrial efficiency – Cell architectures capable of >70% in theory, >50% in practice

n+-GaInAs n-AlInP window n-GaInP emitter

Ce

p To

p-GaInP base

p-AlGaInP BSF p++-TJ n++-TJ

W

id

n-GaInP window n-GaInAs emitter p-GaInAs base

M

E e-

g

Tu

e dl id

ll

el nn

Ce

ll

p-GaInP BSF p-GaInAs step-graded buffer

• Metamorphic semiconductor materials – Control of band gap to tune to solar spectrum • 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

p++-TJ n++-TJ

Tu

el nn

nucleation

n+-Ge emitter p-Ge base and substrate

t Bo

Ju

m to

nc

t io

Ce

n

ll

contact

metal gridline

semiconductor bonded interface

2.0-eV AlGaInP cell 1 1.7-eV AlGaInAs cell 2 1.4-eV GaInAs cell 3 1.1-eV GaInPAs cell 4 0.75-eV GaInAs cell 5

• The solar resource and concentrator photovoltaic (CPV) system economics

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

3

High-Efficiency Multijunction Cell Architectures

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

4

Maximum Solar Cell Efficiencies Measured Theoretical References C. 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).

95% 93%

Carnot eff. = 1 – T/Tsun T = 300 K, Tsun ≈ 5800 K 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% 50%

Ideal 3-gap solar cell at 1000 suns Ideal 2-gap solar cell at 1000 suns

(Henry) (Henry)

44% 43%

Ultimate eff. of device with cutoff Eg: (Shockley, Queisser) 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

31% 30%

Ideal 1-gap solar cell at 1 sun (Henry) Detailed balance limit of 1 gap solar cell at 1 sun (Shockley, Queisser)

3-gap GaInP/GaInAs/Ge LM cell, 364 suns (Spectrolab) 41.6% 3-gap GaInP/GaInAs/Ge MM cell, 240 suns (Spectrolab) 40.7%

(Henry)

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%

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

5

Metamorphic (MM) 3-Junction Solar Cell

contact n+-GaInAs n-AlInP window n-GaInP emitter

Ce

p To

p-GaInP base

p-AlGaInP BSF p++-TJ n++-TJ

W

i

-E de

n-GaInP window n-GaInAs emitter p-GaInAs base

M

g

Tu

e dl id

ll

el nn

Ce

ll

p-GaInP BSF p-GaInAs step-graded buffer p++-TJ n++-TJ

n Tu

ne

nucleation

n+-Ge emitter p-Ge base and substrate

t Bo

l

n t io nc u J

m to

l Ce

l

contact

Lattice-Mismatched or Metamorphic (MM)

C urrent D ensity / Incident Intensity (A /W )

0.3

AR

MJ cell 0.25

subcell 1 subcell 2

0.2

subcell 3

0.15

0.1

0.05

0 0

0.5

1

1.5

2

2.5

3

3.5

Voltage (V)

• 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

6

External QE of LM and MM 3-Junction Cells 100

100 AM1.5D, low-AOD AM1.5G, ASTM G173-03 AM0, ASTM E490-00a

90

Current Density per Unit Wavelength (mA/(cm 2μm))

EQE, lattice-matched

80

EQE, metamorphic

80

70

70

60

60

50

50

40

40

30

30

20

20

10

10

0 300

500

700

900

1100

1300

1500

1700

External Quantum Efficiency (%)

90

0 1900

Wavelength (nm) R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

7

Metamorphic (MM) 3-Junction Solar Cell Eg1 = Subcell 1 (Top) Bandgap (eV) .

2.1 3-junction Eg1/ Eg2/ 0.67 eV cell efficiency 240 suns (24.0 W/cm2), AM1.5D (ASTM G173-03), 25oC 2 Ideal efficiency -- radiative recombination limit

MM 40.7%

1.9

LM 40.1%

1.8 54%

1.7 52%

1.6

50% 48%

1.5

46% 44%

1.4

42%

40%

1.3 1.0

1.1

1.2

1.3

1.4

38%

1.5

1.6

Eg2 = Subcell 2 Bandgap (eV) Disordered GaInP top subcell

Ordered GaInP top subcell

• 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

8

Record 40.7%-Efficient Concentrator Solar Cell

Spectrolab Metamorphic GaInP/ GaInAs/ Ge Cell Voc Jsc FF Vmp

= = = =

2.911 V 3.832 A/cm2 87.50% 2.589 V

• First solar cell of any type to reach over 40% efficiency

Efficiency = 40.7% ± 2.4% 240 suns (24.0 W/cm2) intensity 0.2669 cm2 designated area 25 ± 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.

Concentrator cell light I-V and efficiency independently verified by J. Kiehl, T. Moriarty, K. Emery – NREL R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

9

Metamorphic (MM) 3-Junction Cells –– Inverted 1.0-eV GaInAs Subcell

Ge or GaAs substrate

Ge or GaAs substrate

Growth Direction

cap

1.9 eV (Al)GaInP subcell 1 1.4 eV GaInAs subcell 2 graded MM buffer layers

1.0 eV GaInAs subcell 3

Growth on Ge or GaAs substrate, followed by substrate removal from sunward surface R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

10

Inverted Metamorphic (IMM) 3-Junction Cell 1.6

3-junction 1.9 eV/ Eg2/ Eg3 cell efficiency 2

o

Eg2 = Subcell 2 Bandgap (eV) .

500 suns (50 W/cm ), AM1.5D (ASTM G173-03), 25 C X

Ideal efficiency -- radiative recombination limit

1.5

1.4

53% 52% 51%

1.3

50% 48%

1.2 46%

1.1 44%

1 0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

Eg3 = Subcell 3 Bandgap (eV)

• 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

11

4-Junction Upright Metamorphic (MM) Terrestrial Concentrator Cell

metal gridline

1.8-eV (Al)GaInP cell 1 1.55-eV AlGaInAs cell 2 1.2-eV GaInAs cell 3 transparent buffer

0.67-eV Ge cell 4 and substrate

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

12

4-Junction Cell Optimum Band Gap Combinations 1.7

4-junction 1.9 eV/ Eg2/ Eg3/ 0.67 eV cell efficiency

Eg2 = Subcell 2 Bandgap (eV) .

2

1.6

o

500 suns (50 W/cm ), AM1.5D (ASTM G173-03), 25 C X Ideal efficiency -- radiative recombination limit

1.5 58%

1.4 56%

1.3 54%

1.2

50% 38%

46%

1.1 34%

42%

1 0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

Eg3 = Subcell 3 Bandgap (eV)

• 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

13

5-Junction Inverted Metamorphic (IMM) Cells

gro Ge o wt r G h s aA ub s str ate metal gridline

2.0-eV AlGaInP cell 1 1.7-eV AlGaInAs cell 2 1.4-eV GaInAs cell 3 transparent buffer

1.1-eV GaInAs cell 4 transparent buffer

0.75-eV GaInAs cell 5 R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

14

Semiconductor-Bonded Technology (SBT) Terrestrial Concentrator Cell • Wafer bonding for multijunction solar cells – Low band gap cells for MJ cells using high-quality, lattice-matched materials – Epitaxial exfoliation and substrate removal – Formation of latticeengineered substrate for later MJ cell growth – Bonding of high-band-gap and low-band-gap cells after 1.4-eV GaInAs cell 3 growth 1.7-eV conductance AlGaInAs cellof 2 – Electrical semiconductor-bonded 2.0-eV AlGaInP cell 1 interface – Surface effects forGe GaAs or semiconductor-togrowth substrate semiconductor bonding

semiconductor bonded interface

GaAs or Ge metal gridline growth substrate GaAs or Ge growth substrate 2.0-eV AlGaInP cell 1 2.0-eV AlGaInP cell 1 1.7-eV AlGaInAs cell 2 1.7-eV AlGaInAs cell 2 1.4-eV GaInAs cell 3 1.4-eV GaInAs cell 3 1.1-eV GaInPAs cell 4 0.75-eV GaInAs cell 5

InP growth substrate

15

6-Junction Solar Cells

cap

(Al)GaInP Cell 1

2.0 eV

wide-Eg tunnel junction

GaInP Cell 2 (low Eg) 1.78 eV wide-Eg tunnel junction

AlGa(In)As Cell 3 1.50 eV

0.1

0.08 MJ cell 0.06

subcell 1 subcell 2 subcell 3

0.04

subcell 4 subcell 5

0.02

subcell 6 0 0

1

2

tunnel junction

GaInNAs Cell 5 0.98 eV tunnel junction

Ga(In)As buffer nucleation

Ge Cell 6 and substrate 0.67 eV back contact

4

5

6

7

AM1.5D, ASTM G173-03, 1000 W/m2 1.4 Utilization efficiency of photon energy 1-junction cell 3-junction cell 1.2 6-junction cell

700 Intensity per Unit Photon Energy (W/m 2 . eV)

Ga(In)As Cell 4 1.22 eV

3

Voltage (V)

wide-Eg tunnel junction

600 500

1

400

0.8

300

0.6

200

0.4

100

0.2

0

.

AR

AR

0.12

Photon utilization efficiency

contact

Current Density / Incident Intensity (A/W )

0.14

0 0

0.5

1

1.5 2 2.5 Photon Energy (eV)

3

3.5

4

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

16

Modeled Terrestrial Concentrator Cell Efficiency Detailed balance limit efficiency Radiative recombination only Series res. and shadowing, optimized grid spacing Normalized to experimental efficiency

60%

3J 4J

Efficiency (%)

55%

50%

4J 3J

45%

4J

40%

3J

3J & 4J MM solar cells 35% 1

500

10 100 1000 10000 Incident Intensity (suns) (1 sun = 0.100 W/cm2)

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

17

High-Efficiency Multijunction Cell Results

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

18

LM and MM 3-Junction Cell Cross-Section contact

contact

AR

AR n+-Ga(In)As n-AlInP window n-GaInP emitter T

GaInP top cell

p-GaInP base

p-AlGaInP BSF

Wide-bandgap tunnel junction

p++-TJ n++-TJ

W

E eid

n-GaInP window n-Ga(In)As emitter

Ga(In)As middle cell

p-Ga(In)As base

p-GaInP BSF

Tunnel junction Buffer region

p++-TJ

M

id

g

e C

T el nn u T

e dl

e nn Tu

el C

p++-TJ n++-TJ

l

p-Ge base and substrate

M

id

d

el nn u T

g

le

el C

l

p-GaInP BSF p-GaInAs step-graded buffer

m tto o B

l

n tio nc

n-Ga(In)As buffer

n+-Ge emitter

W

E eid

n-GaInP window n-GaInAs emitter p-GaInAs base

u lJ

el C

op

p-GaInP base

p-AlGaInP BSF

n++-TJ

nucleation

Ge bottom cell

op

n+-GaInAs n-AlInP window n-GaInP emitter

ll

l Ce

l

contact

Lattice-Matched (LM)

p++-TJ n++-TJ

nucleation

n+-Ge emitter p-Ge base and substrate

e nn Tu

lJ

n io ct n u

m tto o B

Ce

ll

contact

Lattice-Mismatched or Metamorphic (MM)

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

19

New World Record 41.6% 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

Ref.: R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009.

• Incorporating high-efficiency 3J metamorphic cell structure + further improvements in grid design → strong potential to reach 42-43% champion cell efficiency

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

20

41.6% Solar Cell Eff., Voc vs. Concentration 44

Efficiency

42

0.96

Voc fit, 100 to 1000 suns 40

0.94

FF

38

0.92

36

0.90

34

0.88

32

0.86

30

0.84

28

0.82

26

0.80

24

0.78 1000.0

0.1

1.0

10.0

100.0

Fill Factor (unitless)

Efficiency (%) and Voc x 10 (V)

41.6%

Voc x 10

0.98

Incident Intensity (suns) (1 sun = 0.100 W/cm2)

• 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 R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

21

41.6% Solar Cell LIV Curves vs. Concentration Current Density / Incident Intensity (A/W)

0.16

41.6%

0.14 Inc. Intensity (suns) 2 1 sun = 0.100 W/cm

0.12

2.6

0.1

6.6

0.08

17.6 59.8

0.06 127.3 364.2

0.04

604.8

0.02

940.9

0 0

0.5

1

1.5

2

2.5

3

3.5

Voltage (V)

• 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% R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

22

Best Research Cell Efficiencies

Chart courtesy of Larry Kazmerski, NREL R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

23

Spectrolab Cell Generations in DOE TPP Program 43% C4MJ

Production Cell Efficiency (%)

43

• Terrestrial concentrator cell efficiency

42

40%

41

• Goals in Technology Pathways Partnership (TPP)

40

38.5%

39

37%

38

37.5%

37 36 2007

2008

2009

2010

2015

Year R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

24

Spectrolab C1MJ, C2MJ, and C3MJ Cell Products ηAVG = 38.2%

C1MJ

35%

C2MJ

30%

C3MJ

ηAVG = 37.5%

25%

ηAVG = 36.9%

20% 15% 10% 5%

39.5%

39.0%

38.5%

38.0%

37.5%

37.0%

36.5%

36.0%

35.5%

35.0%

34.5%

0% 34.0%

% of Population

40%

Efficiency η at Max. Power R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

25

Prototype 3J Metamorphic Cell Builds Corrected LIV Data for Prototype 3J Metamorphic (MM) 5%-In Cells 10 runs, 22 wafers, 205 cells

40.8%

40.5%

40.2%

39.9%

39.6%

39.3%

39.0%

38.7%

38.4%

38.1%

37.8%

37.5%

37.2%

36.9%

36.6%

36.3%

36.0%

35.7%

5% 3J-MM

3J MM Cell Efficiency Bin Average Std. dev.

Isc (A) 7.601 0.135

Voc (V) 3.090 0.022

FF 0.845 0.009

Eff 39.6% 0.8%

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

26

4-Junction Lattice-Matched Cell AR

AR cap

(Al)GaInP Cell 1

1.9 eV

wide-Eg tunnel junction

AlGa(In)As Cell 2 1.6 eV wide-Eg tunnel junction

Ga(In)As Cell 3 1.4 eV tunnel junction

Ga(In)As buffer nucleation

Ge Cell 4 and substrate 0.67 eV

Current Density / Incident Intensity (A/W )

0.25

contact

MJ cell subcell 1

0.2

subcell 2 subcell 3 0.15

subcell 4

0.1

0.05

0 0

1

back contact

2

3

4

5

Voltage (V)

• 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

27

100

1600

90

1400

80 1200

70

AlGaInP subcell 1 1.95 eV GaInAs subcell 3 1.39 eV All subcells

60 50

AlGaInAs subcell 2 1.66 eV Ge subcell 4 0.72 eV AM1.5D ASTM G173-03

40

1000 800 600

30 400

20 200

10 0 300

Intensity Per Unit Wavelength (W/(m2μ m))

External Quantum Efficiency (%)

Measured 4-Junction Cell Quantum Efficiency

0

500

700

900 1100 1300 Wavelength (nm)

1500

1700

1900

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

28

Light I-V Curves Record Efficiency Cells Current Density / Inc. Intensity (A/W) .

0.16 0.14 0.12 0.10 3J Conc. Cell

0.08

3J Conc. Cell

Metamorphic V oc Jsc /inten. V mp FF conc. area

0.06 0.04

Lattice-matched

2.911 0.1596 2.589 0.875 240 0.267

LM, 822 suns

3.192 V 0.1467 A/W 2.851 V 0.887 364 suns 0.317 cm2

Eff. 40.7%

41.6%

AM1.5D, low -AOD spectrum

0.02

3J Conc. Cell

3.251 0.1467 2.781 0.841 822 0.317

4J Cell 4.398 V 0.0980 A/W 3.950 V 0.856 500 suns 0.208 cm2

40.1%

AM1.5D, ASTM G173-03

4J Conc. Cell

36.9%

AM1.5D, ASTM G173-03

Independently confirmed meas. 25°C

AM1.5D, ASTM G173-03 Prelim. meas. 25°C

0.00 0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Voltage (V)

• 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%) R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

29

The Solar Resource and CPV Economics

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

30

The Solar Resource

5 6

Ref.: http://rredc.nrel.gov/solar/old_data/ nsrdb/redbook/atlas/

• Entire US electricity demand can be provided by concentrator PV arrays using 37%-efficient cells on: 150 km x 150 km area of land

or or

ten 50 km x 50 km areas similar division across US

R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

31

Concentrator Photovoltaic (CPV) Electricity Generation

CPV cost superiority 40% cell efficiency

CPV cost superiority 50% cell efficiency

Map source: http://www.nrel.gov/gis/images/map_csp_us_annual_may2004.jpg

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

32

Summary • 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 R. R. King et al., 24th European Photovoltaic Solar Energy Conf., Hamburg, Germany, Sep. 21-25, 2009

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