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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!