Ambition for the Future of Space Components from the Viewpoint of a Researcher

in the Field of Space Solar Cells

Masafumi Yamaguchi

Toyota Technological Institute (Nagoya, Japan)

Outline

1. Introduction2. Personal R&D Profile in PV3. Experience of Space Flight Demonstration

and Space Application of Solar Cells Developed under Terrestrial (NEDO) Project

4. Future Prospects in the Field of Space Solar Cells - Seeds for Space Applications from Products Developed for Terrestrial Use -

5. Summary

1.Introduction

Invention of solar cells at the Bell Telephone Labs. (1954)

The first Si space solar cells for the Vanguard 1 (1958)

Contribution of the space solar cells to the Space Station from the Vanguard 1.

Schematic cross section of Si space solar cells developed by Sharp Co.

2. Personal R&D Profile in PV

Personal R&D Profile in PV (1)

1984: Discovery of minority-carrier injection-enhanced annealing of defects in InP

1987: Proposal of DH-structure tunnel junction for MJ solar cells

1987: 20.2% AlGaAs /GaAs 2-junction cell

1989: 20% GaAs-on-Si cells1990: Launching of MUSES-

A using InP cells

Development of space solar cells (InP, AlGaAs/GaAs 2-junction and GaAs-on-Si cells)

1982-89

Impurity effects of defect generation in Si

Radiation damage to Si devices including solar cells

1969-70ResultsR&D projectsYear

Personal R&D Profile in PV (2)

2003: 27% large-area (7,000cm2) concentrator 3-junction cell modules

2004: 39.2% InGaP/InGaAs /Ge concentrator 3-J cell

Development of super-high-efficiency concentrator MJ cellsand modules(NEDO, METI)

2001-

1996: Proposal of anomalous degradation mechanism of Si space cells

1997: Discovery of minority-carrier injection-enhanced defects annealing in InGaP

Fundamental studies of high-efficiency MJ and other solar cells, and materials(TTI)

1994-

1997:33.3% InGaP/GaAs Development of super -high-efficiency MJ solar cells (NEDO, MITI)

/InGaAs 3-junction cell1990

-2000

ResultsR&D projectsYear

Discovery of Superior radiation-resistance of InP solar cells (1984), under dark and light illumination

conditions compared to Si and GaAs cells.

DLTS analysis for minority-carrier injection phenomena of radiation-induced defects in InP materials and solar cells.

Temperature dependence of annealing rates of major radiation-induced defects in InP and GaAs under thermal and injection annealing.

Technology transfer of InP solar cell fabrication technologies from my previous NTT lab. to the Nippon Mining Corp.

First InP space solar cells (1x2cm2, 2x2cm2), made using the thermal diffusion method, by the Nippon Mining Corp. for Japanese scientific satellite “MUSES-A”.

First space flight of InP space solar cells using Lunar Mission Japanese scientific satellite “MUSES-A”(1990).

1.1eV (Si)

(a) 2-junction cell (b) 3-junction cell

Potential of high-efficiency for monolithic cascade III-V/Si multi-junction solar cells

Reduction in dislocation density (etch-pit density) in GaAs films on Si due to thermal cycle annealing (TCA).

Transmission electron microscope image of GaAs film on Si thermal cycle annealed (TCA).

Mechanisms for dislocation motion in III-V compound film on Si substrate

PropagationDeflection+Propagation

Deflectionto edge Annihilation

Hetero-epitaxial Film

Combination+Re-emission

Substrate

ＳｉS ub .

n -G aA s+

n-G aA s

p -G aA sp -A lG aA s+

A R (S i N )3 4

n -InG aA s

/n -G aA s

S L S

+

+

n -A lG aA s

/n -G aA s

S L

+

+

+

n -G aA s+

The structure and I-V curve (AM0) of a high-efficiency GaAs-on-Si solar cell.

0

2

4

6

8

10

ＡＭ０ Efficiency　（％）

Num

ber

Average ＡＭ０

Efficiency

１６．８６％

16.0 16.4 16.8 17.2 17.6

AM0 efficiency distribution of 48 2cmx2cm GaAs-on-Si solar cells with 50μm and 100μm thick cover glass.

(1994)

0.4

0.5

0.6

0.7

0.8

0.9

1

Various space solar cells evaluated using ＥＴＳ－ＶＩ

Rem

ainin

g Fac

tor

of

Pm

ax

（％

）

ＧａＡｓ－ｏｎ－Ｓｉ Cell

（５０um Cover Glass）

ＧａＡｓ－ｏｎ－Ｓｉ Cell

（１００um Cover Glass）

ＧａＡｓ－ｏｎ－ＧａＡｓ Bulk Cell

（５０um Cover Glass）

５０um-thick Ｓｉ Cell

（５０um Cover Glass）

１００um-thick Ｓｉ Cell

（５０um Cover Glass）

２００um-thick Ｓｉ Cell

（５０um Cover Glass）

Remaining factor of maximum power for GaAs-on-Si cells after 94 days from launching in comparison with those for

LPE-grown GaAs-on-GaAs cells and thin Si cells.

A M 1 .5 S p e ctrum and W id e B and S p e ctral

R e sp onse b y M ulti-Junction S olar C e ll

A M 1.5 S p e ctrum

0.5 1.0 2.01.5

Spectral Irra

diance

[kW

/m2. μ

m ]

0 .5

1.0

1.5

0

W ave le ng th (μm )

InG aP

G aA s

G e

Beginning of MJ solar cell studies (1982)Proposing and starting NEDO R&D project (1990): MJProposing and modifying NEDO R&D project (2001): Conc. MJ

0.8

1.0

1.2

1.4

1.6

1.4 1.6 1.8 2.0

Bandgap E

nerg

y of Bottom C

ell (eV)

B an dg ap E ne rg y of T op C ell (eV )

34363738

GaAs

In0.5Ga0.5P

AM1.5, 1-sun, T=300K

２T erm inal

T unnel J.

B ottom C ell

T op C ell P

P

N

N

N++P++

Potential of high-efficiency 2-junction cell

VOLTAGE (V)

-0.5

0

0.5

1

1.5

2

0.0 0.1 0.2 0.3 0.4

CU

RR

ENT

DEN

SITY

(A/c

m2 )

AlInP/InGaP DH

without AlInP

-0.1

InGaP TJ

Changes in I-V curves of the InGaP tunnel diodesby introducing the DH structure.

Tunn

el p

eak

curr

ent d

ensi

ty(A

/cm

) 2

X=0 X=0.6

X=0.9

top cellPAl Ga Asx 1-X

p++GaAsn++GaAs

nAl Ga Asx 1-X

nGaAs subbottom cell

Annealing temperature dependence of tunnel peak current densities for double hetero structure tunnel diodes.

X is the Al mole fraction in AlxGa1-xAs barrier layers.

Mechanism of Impurity Diffusion in the Tunnel Junction

Voc = 2.1VIsc = 13.8 mA/cm2

FF = 0.70Eff. = 20.2%

A structure and I-V curve of a high-efficiency AlGaAs/GaAs 2-junction cell (1987)

3. Experience of Space Flight Demonstration and Space Application of Solar Cells Developed under Terrestrial (NEDO) Project

Voltage [mV]

0

10

20

30

40

50

60

70

80

0 500 1000 1500 2000 2500

Cur

rent

[mA

]

Isc: 67.4 [mA]Voc: 2451 [mV]

FF: 88.1 [%]η: 26.9 [%]

AM0, 28.1 °CCell: 2cm x 2cm

Au (Back contact)p+ GaAs : Subs.<1x1019 cm-3 : Zn

p+ GaAs : 0.3 µm.7x1018 cm-3 : Zn

p+ InGaP : 0.1 µm.2x1018 cm-3 : Zn

P GaAs : 3.0 µm.1x1017 cm-3 : Zn

n+ GaAs : 0.1 µm.2x1018 cm-3 : Si

n+ AlInP : 0.05 µm.1x1019 cm-3 : Si

n+ InGaP : 0.015 µm.1x1019 cm-3 : Si

p+ InGaP : 0.015 µm.8.0x1018 cm-3 : Zn

p+ AlInP : 0.03 µm.<5x1017 cm-3 : Zn p+ InGaP : 0.03 µm.2x1018 cm-3 : Zn

p InGaP : 0.55 µm.1.5x1017 cm-3 : Zn

n+InGaP : 0.05 µm. 2x1018 cm-3 : Si

n+ AlInP : 0.03 µm<2x1018 cm-3 : Si

n+GaAs 0.30 µm <5x1018 cm-3 : Si

AR MgF2/ZnSAu/Au-Ge/Ni/Au (Front contact)

GaA

sE

g=1.

43 e

VB

otto

m C

ell

InG

aPE

g=1.

88eV

T

op c

ell

Tunnel Junction

The structure and I-V curve of a high-efficiency InGaP/GaAs 2-junction solar cell under AM0 illumination:

Previous world-record efficiency at AM0.

Recovery of radiation-induced defects in InGaP cells

Recovery of InGaPcells is due to theanneal-out of some of the radiation-induced defects during deviceoperation which has been confirmed by DLTS.

This unique property of radiation damage recovery in InGaP cells demonstrates InGaP materialsand devices have greatpotential for space applications.

The maximum power recovery of the single-junction InGaP cell due to

current injection at various temperatures.

0.75

0.8

0.85

0.9

0 5 10 15 20

Pow

er R

atio

PI/P

0

Injection Time (min)

75 °C

50 °C

25 °C

1 MeV-1016 e/cm2

Injection Current: 100mA/cm2

0.5 min

20 min

10 min

5 min

p-InGaP

200 250 300 350

emission rate=1005 s-1

0 minD

LTS

Sig

nal (

a.u.

)

Temperature (K)

Injection anneals100mA/cm2 at 25 oC

(b) Double carrier pulseVR = 3VIst pulse Amplitude = 0V2nd pulse Amplitude = -2V (80 mA cm-2)

NT (

x 1

014 c

m-3)

100 150 200 250 300 350

1

2

3

4

5

6

7

8

Period width = 20 mspulse width = 3 µ sec

H2 (0.50 eV) (a) Single carrier Pulse VR = 3V Pluse Amplitude = 0V

Temperature (K)

Minority-carrier injection enhanced annealing of major radiation-induced defect H2 in InGaP and evidence of recombination center confirmed by the DLTS method.

Space flight demonstration of InGaP/GaAs 2-junction cells by the Mission Demonstration test Satellite-1 (MDS-1, 2002)

InGaP/GaAs Tandem Cell

0.60

0.70

0.80

0.90

1.00

1 10 100 1000MET (days after launch)

Rem

aini

ng F

acto

r

Tandem-100 (Isc)Tandem-500 (Isc)Tandem-100 (Voc)Tandem-500 (Voc)

Superior radiation-tolerance of InGaP/GaAs 2-junction cells confirmed by the Mission Demonstration test Satellite-1 (MDS-1, 2002-2003)

Surface, interface recombination loss reduction

Bulk recombination loss reduction

Lattice matching

High quality ep.

Carrier confinement

Photon confinement

Current matching

Material selection

Device structure

Contact loss reduction 0ptical loss reduction

(AR)

Cell interconnection loss reduction

(Tunnel junction)

Key issues for high efficiency MJ cells

Band Diagram of DH Tunnel Junction

MiddleCell

TunnelJunction

Top Cell

Eg1

Eg2Eg1>Eg2

Tunnel Junction

InGaAs Middle Cell

AR Coating Front Contact

Back Contact

InGaP Top Cell

Buffer Layer

n+ (In)GaAsn+ AlInP [Si]n+ InGaP [Si]p InGaP [Zn]p AlInP [Zn]p++ AlGaAs [C]n++ InGaP [Si]n+ AlInP [Si]n+ (In)GaAs [Si]p (In)GaAs [Zn]p+ InGaP [Zn]

p Ge Substrate

p++ AlGaAs [C]n++ InGaP [Si]

n+ GaAs : 0.1µmn+ (In)GaAs [Si]

n

Tunnel Junction

Ge Bottom Cell

Structure of Triple-Junction (3J) Cell

Characteristics of 3J Cell (x=0.01)

0

20

40

60

80

100

Qua

ntum

Eff

icie

ncy

(%)

Wavelength (nm)

In0.49Ga0.51P

400 800 1200 1600

In Ga As

Ge

0 0.5 1 1.5 2 2.5 3Voltage (V)

0

2

4

68

10

12

14

16

AM1.5G, 1cm2 Jsc: 14.46 mA/cm2 Voc: 2.552 V FF: 85.8 % Eff.: 31.7 %C

urre

nt D

ensi

ty (A

/cm

0.01 0.992 )

A structure of a high efficiency InGaP/GaAs/Ge 3-junction cell fabricated on a Ge substrate.

p-GaAs

n-GaAs

n-Ge

p-Ge Substrate

n+-GaAs

n-InGaP

p-InGaP

n-GaAs

GaAs Cap Layer ARC

N Contact

P Contact

ＩｎGaP Top Cell

GaAs Middle Cell

Ge Bottom Cell

Buffer Layer

Tunnel Junction

Tunnel Junction

InGaP/GaAs/Ge 3-junction space solar cell made by Sharp Co.(Technology transfer from terrestrial use to space use)

0

20

40

60

80

0 500 1000 1500 2000 2500 3000

VOLTAGE (mV)

CU

RR

EN

T (

mA

)

Size : 2x2 cm2

Voc: 2567 mV

Jsc: 17.9 mA/cm2

FF: 0 .858Eff : 29 .2 %

AM0, 135.5mW/cm2, 28℃

Current-voltage of InGaP/GaAs/Ge 3-junction space solar cell made by Sharp Co.

4. Future Prospects in the Field of Space Solar Cells

- Seeds for Space Applications from Products Developed for Terrestrial Use -

0

10

20

30

40

50

0 10 20 30 40 50 60

AM1.5 Efficiency (%)

AM

0 Ef

ficie

ncy

(%)

3-J

2-J Conc.2-JGaAsInP Conc.

SiInPGaAs-on-Si

CIGSa-Si

Correlation between AM0 and AM1.5 Efficiencies for Various Solar Cells

Terrestrial use Space use

Prim

ary

Ener

gy S

uppl

y [E

J/Y]

1,600

1,400

1,200

1,000

800

600

400

200

0

WBGU: German Advisory Council on Global Change

WBGU’s World Energy Vision 2100

YEAR2000 2060 2070 20820502010 2020 2030 2040 2100

GeothermalOther REsSolar heat

Solar electricity

Wind

Biomass adv

Nuclear PWGasCoalOil

Biomass tradHydro-PW

Prim

ary

Ener

gy S

uppl

y [E

J/Y]

1,600

1,400

1,200

1,000

800

600

400

200

02000 2010 2020 2030 2040 2050

YEAR

WBGU: German Advisory Council on Global Changehttp://www.wbgu.de/

0.01

0.1

1

10

100

1000

1995 2000 2005 2010 2015 2020 2025 2030

Year

Cum

ulat

ive

Insta

lled

Capa

city

(GW

)

Cumulated Cumulated（20％Growth）Cumulated（30％Growth） NSS MilestoneScenario 1 Scenario 2

Cumulated installed capacity of PV systems in Japan by year.

Module (Cell) efficiency target (%) in Japanese PV2030 road map.

15 (18)10 (15)6 (10)Dye-sensitized

40 (50)35 (45)28 (40)Super-High η

22 (25)18 (25)13 (19)CIS

18 (20)14 (18)12 (15)Thin-Film Si

22 (25)19 (25)16 (20)Thin-BulkMulti-c-Si

203020202010CELL TYPE

0

10

20

30

40

50

1970 1980 1990 2000 2010 2020

Year

Prod

uctio

n-le

vel A

M0

Effic

ienc

y (%

)

Si cells GaAs cells MJ cells Future cells

Toward 50% Efficiency for Future Space Solar Cells

High Efficiency InGaP/InGaAs/Ge 3-Junction Solar Cell and Its Concentrator Application

Concentration Ratio Dependence of High Efficiency InGaP/InGaAs/Ge 3-Junction Solar Cells

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3 3.5

VOLTAGE ('V)

CU

RR

EN

T (

A)

498sun Voc: 3.12 V Isc: 3.46 A FF: 0.88 Eff: 38.9%

38.9% at 498-suns AM1.5(39.2% at 200-suns AM1.5)

Most Recent Results: I-V Curve of a High Efficiency InGaP/InGaAs/Ge 3-Junction Solar Cell under 498-suns AM1.5

Future Predictions of Solar Cell Efficiencies(Original idea by Prof. A. Goetzberger.

Modified by M. Yamaguchi)

0

10

20

30

40

50

1940 1960 1980 2000 2020 2040 2060

Year

Eff

icie

ncy

(%) New Mater.

Cryst. Si

CIS

Thin-FilmSi

Organica-Si

Dye-Sensitized

Multi-Junction

0.0 0.5 1.0 1.5 2.0 2.5 3.0Voltage (V)

0.0

0.5

1.0

1.5

Cur

rent

(A) Irradiance (DNI): 751 W/m2

Ambient Temperature: 35.0 CWind Velocity: 0.5 m/sArea: 196 cm2Isc: 1.533 AVoc: 2.955 VFF: 0.877η: 27.0 %

Outdoor evaluation of I-V of large-area (7,000cm2) concentrator InGaP/InGaAs/Ge 3-junction cell module

(Including loss in concentrator optics and temperature rise)

Summary of estimated cost for the concentrator PV systems vs.

concentration ratio.

Scenario of electricity cost reduction by developing concentrator solar cells.

Scenario of electricity cost reduction by developing concentrator solar cells.

1

10

100

1995 2000 2005 2010 2015 2020 2025 2030

Year

Ele

ctri

city

Cos

t　(Y

en/k

Wh)

1:Si crystal2:thin-film3:concentrator

1

2

3

1

10

100

1000

1950 1960 1970 1980 1990 2000 2010 2020 2030

Year

Spec

ifuc

Pow

er (W

/kg)

Past Future

Specific power of space solar cell arraysToward light weight (1kW/kg)

0200400600800

100012001400

0 10 20 30 40 50 60

AM0 Efficiency (%)

Spec

ific

Pow

er (W

/kg)

MJ/Ge(5.5mil)/rigid Thin/rigidMJ/Ge(5.5mil)/light MJ/Ge(2mil)/lightMJ/Si(2mil)/light Thin-Film/SS(1mil)/lightThin-Film/Poly(1.5mil)/light

Toward Developing Light Weight Space Solar Cells

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

2 2.5 3 3.51000/T (K-1)

Ann

ealin

g ra

te (s

-1)

Minority-carrier injection annealing of radiation damage to CuInGaSe2 cells

Large CIS Cell

0.60

0.70

0.80

0.90

1.00

1 10 100 1000MET (days after launch)

Rem

aini

ng F

acto

r

LA CIS-100 (Isc)LA CIS-500 (Isc)LA CIS-100 (Voc)LA CIS-500 (Voc)

Superior radiation-tolerance of CuInGaSe2 solar cells confirmed by the Mission Demonstration test Satellite-1 (MDS-1, 2002-2003)

5. SUMMARY(1)Luckily, I have discovered superior radiation-

resistance of InP and solar cells. We have developed high-efficiency InP and GaAs-on-Si solar cells and performed a space flight demonstration.

(2)We have also developed a break-through technology (DH-structure tunnel junction) for multi-junction solar cells.

(3) Based on our research results, the NEDO R&D project for high-efficiency multi-junction solar cells for terrestrial application has been started in Japan.

5. SUMMARY-Continued(4) In that project, high-efficiency InGaP/GaAs 2-

junction and InGaP/InGaAs/Ge 3-junction cells with AM0 efficiencies of 26.9% and 29.2%, respectively, have been developed and their technologies have been transferred for space use.

(5) We have sown seeds for high-efficiency and low-cost multi-junction concentrator solar cells and modules, flexible and high-efficiency thin multi-junction cells, and radiation-resistant thin-film CuInGaSe cells for space applications.

(6) However, I really expect that results from R&D on materials, devices, components and systems for space use will be transferred to terrestrial use in the similar way with the Apollo Project in USA.

0

10

20

30

40

50

0 10 20 30 40 50 60

AM1.5 Efficiency (%)

AM

0 Ef

ficie

ncy

(%)

3-J

2-J Conc.2-JGaAsInP Conc.

SiInPGaAs-on-Si

CIGSa-Si

Correlation between AM0 and AM1.5 Efficiencies for Various Solar Cells

Terrestrial use Space use !

Be Ambitious!

Let new ideas bring your wishes and dreams to humanity.

Thank you very much!