band-gap-engineered architectures for high-efficiency multijunction concentrator solar cells

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


• 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


• 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


contact

AR



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


1.7-eV AlGaInAs cell 2

2.0-eV AlGaInP cell 1

metal gridline


High-Efficiency

Multijunction Cell

Architectures


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


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


contact

AR



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


contact

AR



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


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


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


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


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


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



1.8-eV (Al)GaInP cell 1

metal gridline


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


55--Junction Inverted Metamorphic Junction Inverted Metamorphic (IMM) Cells(IMM) Cells

transparent buffer


1.1-eV GaInAs cell 4transparent buffer




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



2.0-eV AlGaInP cell 10.75-eV GaInAs cell 5


GaAs or Ge growth substrate












semi-conductor

bondedinterface

metal gridline






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


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


GaInNAs Cell 50.98 eV

cap

contactAR


GaInP Cell 2 (low Eg)1.78 eV



tunnel junction


tunnel junction

AR

Ga(In)As buffer


0.67 eV

nucleationnucleation

back contact


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


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


High-Efficiency

Multijunction Cell

Results


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


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


contact

AR



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


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


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%


• 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%


Chart courtesy of Larry Kazmerski, NREL

Best Research Cell Best Research Cell EfficienciesEfficiencies


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


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%


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


cap

contactAR




tunnel junction

AR

Ga(In)As buffer


0.67 eV

nucleation

back contact


cap

contactAR




tunnel junction

AR

Ga(In)As buffer


0.67 eV

nucleationnucleation

back contact


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


0

10

20

30

40

50

60

70

80

90

100

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


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


The Solar Resource and CPV Economics


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


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

CPV cost superiority40% cell efficiency


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



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.


• 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

band-gap-engineered architectures for high-efficiency multijunction concentrator solar cells

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