dpg2011 ake11.3dreyer triplejunction-waferbonding
TRANSCRIPT
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GaInP/GaAs/Si Triple-Junction Solar CellFormed by Wafer Bonding
Karen Dreyer, Elvira Fehrenbacher, Eduard Oliva, Stephanie Essig,Vera Klinger, Tobias Roesener, Antonio Leimenstoll, Felix Schätzle, Martin Hermle, Andreas Bett,Frank Dimroth
Fraunhofer-Institut fürSolare Energiesysteme ISE
DPG-Frühjahrstagung 201103/16/2011
© Fraunhofer ISE2
Outline
Triple-junction solar cells
The GaInP/GaAs/Si solar cell
Why these semiconductors?
Challenge of the fabrication process
Wafer bonding process
Results of the GaInP/GaAs/Si solar cell characterisation
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Triple-Junction Solar CellsConcentrator Technology
Single-junction Si solar cell:
η = 25.5 % Spectrum: AM 1.5g [1]
GaInP/GaInAs/Ge triple-junction solar cell:
η = 41.6 % at 364 sunsSpectrum: AM 1.5d [1]
Advantages of concentrator cells:
Efficiency enhancement underconcentrated light
Cost reduction by decreasingsolar cell size to a few mm²
Bottom cellMiddle cell
Top cell
Single-junction cell
[1] Green et al., Progress in Photovoltaics: Research and Applications 18 (5), 2010
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Triple-Junction Solar CellsIII-V Semiconductors
Wide range of possiblebandgap energies
Epitaxy: high crystal qualityfor lattice matchedsemiconductors
5,4 5,5 5,6 5,7 5,8 5,9 6,0 6,10,0
0,5
1,0
1,5
2,0
2,5
AlAs
InP
InAs
GaAs
Ga0,5
In0,5
P
Ga0,99
In0,01
As
GeIn
x Ga1-x As
Alx In
1-x As
Lattice Matched Triple Junction
Band
gap
Ener
gy [e
V]
Lattice Constant [Å]
InPx As
1-x
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Triple-Junction Solar CellsSolar Cell Designs
III-V on SiliconConventional lattice
matched triple-junction solar cell
Ge 0.66 eVGaInAs 1.4 eVGaInP 1.9 eV
Si 1.12 eVGaAs 1.42 eVGaInP 1.9 eV
Ge bottom cell produceshigh excess current
Cannot be used dueto serial connection
Higher bandgap
Higher voltage
Cheaper substratematerial
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Triple-Junction Solar CellsIII-V on Silicon
4% lattice mismatchbetween III-V dual-junction and siliconsolar cell
5,4 5,5 5,6 5,7 5,8 5,9 6,0 6,10,0
0,5
1,0
1,5
2,0
2,5
AlAs
InP
InAs
GaAs
Ga0,51
In0,49
P
GaAs
Si
Ga0,5
In0,5
P
Ga0,99
In0,01
As
Ge4% lattice mismatch
Alx In
1-x As
InPx As
1-xInx Ga
1-x As
Lattice Matched Triple Junction Triple Junction, III-V on Si
Band
gap
Ener
gy [e
V]
Lattice Constant [Å]
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III-V on SiliconProcess of Fabrication
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III-V on SiliconDirect Wafer Bonding: Surface Cleaning and Activation
Demands on bond interface:
High electrical conductivity
Transparency
Surface cleaning and activation by Ar-beam
Bonding in vacuum chamber at room temperature
Si cell
electrostatic chuck
Argon gun
Argon gun
III-V solar celltemporary stabilisation
bonding layer
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GaInP/GaAs/Si Solar CellIV-Characteristic
Remarkable cellefficiency for the firstGaInP/GaAs/Si solar cell fabricated bywafer bonding:
20.5 % under AM 1.5d spectrum
0,0 0,5 1,0 1,5 2,0 2,5 3,00
2
4
6
8
10
Cell ID: FE112x7y2
A = 0,0547 cm2
VOC
= 2,778 V
JSC
= 8,56 mA cm-2
FF = 86.3 %η = 20.5 %
Cur
rent
Den
sity
[mA
/cm
2 ]
Voltage [V]
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GaInP/GaAs/Si Solar CellExternal Quantum Efficiency
Si subcell has lowestcurrent density
limits the total current density
Energy conversion in Si has to be increased
Thickness of uppersubcells should bereduced
300 400 500 600 700 800 900 1000 1100 12000
20
40
60
80
100
Si J SC =
9,5
6 m
A c
m-2
GaA
s
J SC =
14,
3 m
A c
m-2
GaI
nP
J SC =
11,
6 m
A c
m-2
Cell ID: FE112EQE Spectrum: AM 1.5d
EQE
[%]
Wavelength [nm]
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GaInP/GaAs/Si Solar CellEfficiency under Concentrated Illumination
Efficiency starts decreasingat 24 suns
Series resistancein cell structure
1 10 10020
21
22
23
24
Maximum: 23,3 % @ 24 suns
Effic
ienc
y [%
]
Concentration [X]
Cell ID: FE112x7y2
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GaInP/GaAs/Si Solar CellTEM Analysis of Bond Interface
TEM: amorphous layerbetween GaAs and Si of 3-4 nm thickness
Reason for seriesresistance?
High Resolution TEM Image,
Bright Field, Zone Axis Si
Universität Kiel, Institut für Materialwissenschaft, Gruppe Prof. Dr. Jäger, 2010
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Summary
Successful fabrication of first GaInP/GaAs/Si by wafer bonding
Remarkable cell efficiency of 23.3 % at 24 suns
Si subcell limits the current density
Efficiency decreases strongly under high concentration
Amorphous layer at the bond interface probably reduces currentdensity under high concentration
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AcknowledgementsI thank…
…the Bundesministerium für Bildung und Forschung (BMBF) for financial support(Förderkennzeichen 03SF0329A, „III-V-Si“)
…all co-workers from the groupIII-V – Epitaxy and Solar Cells
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Thank You Very Much for Your Attention!
Karen Dreyer
www.ise.fraunhofer.de
Fraunhofer Institute for Solar Energy Systems ISE“III-V – Epitaxy and Solar Cells”
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III-V on SiProcess of Production: Lift-Off
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Triple-Junction Solar CellsTheoretical Conversion Efficiency
500 1000 1500 2000 25000
200
400
600
800
1000
1200
1400
1600
energy that can be used by a Silicon solar cell
transmission losses
thermalization losses
Spe
ctra
l Irr
adia
nce
[W/ m
2 µm]
Wavelength [nm]
AM1.5g spectrum Si (1.12 eV)
500 1000 1500 2000 25000
200
400
600
800
1000
1200
1400
1600
transmission losses
thermalization losses
Spec
tral I
rradi
atio
n [W
/m2 µm
]
AM 1.5g spectrum GaInP (1,88 eV) GaInAs (1,44 eV) Ge (0,66 eV)
Wavelength [nm]
ηtheoretical, AM 1.5g = 33,3 % ηtheoretical, AM 1.5g = 50 %