Selective Defects Passivation of
GaInNAs Solar Cells by Hydrogenation
Miwa Fukuda1, Vincent R. Whiteside1, Ian R. Sellers1, Mohamed Al
Khalfioui2, Mathieu Leroux2, Lucas Phinney3, Khalid Hossain3
1. University of Oklahoma
2. CRHEA-CNRS
3. Amethyst Research Inc.
OUTLINE:
•  Introduction: Single vs. Multi-junction Solar Cells
•  Extra Junction – Dilute Nitride Material
•  How to improve the material quality
•  Dilute Nitride Solar Cells Experiments Results
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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Introduction: Single vs. Multi-junction
Single:
•  Can absorb partial of
Solar Spectra
Multi-junction:
•  Each layer absorb
different Solar spectrum
•  Need to be
-  Lattice Matched
-  Current Matched
J.F. Geisz and D.J.Freidman, Semiconductor Science and Technology 17, 769 (2002)
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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Extra Junction:
Dilute Nitride Material as 4th Layer
J.F. Geisz and D.J.Freidman, Semiconductor Science and Technology 17, 769 (2002)
Design by Kurtz: GaInNAs lattice matched to GaAs/Ge
=> potential for > 42 % efficiency SC
Problems:
•  Low Nitrogen Solubility
•  Phase Segregation
=>Short Diffusion Length
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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How to solve
the quality problems?
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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1. Rapid Thermal Anneling
•  Post-growth RTA helps improving the
material quality.
55
50
45
35
P L 30
25
E Q E (% )
40
20
R T A 9 1 0 C
R T A 8 2 5 C
15
10
5
0
500
600
700
800
900
1000 1100 1200 1300
W a velen g th (n m )
Sellers et al. Appl. Phys. Lett. 99, 151111 (2011)
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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GaInNAs in Solar Cells
•  Solar Junction achieved 43.5%
Efficient CPV using Dilute Nitride
J
Proceedings of SPIE, 8108, 810804 (2011)
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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What else
to improve the quality?
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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2. Hydrogenation
Hydrogenation has been studied
extensively in the dilute nitrides
Bissiri et al. Phys. Rev. B. 65, 235210 (2002)
“Physics and Applications of Dilute Nitrides,” Vol 21, Chapter 6, “Role of
Hydrogen in Dilute Nitrides,” Polimeni & Capizzi, published by Taylor &
Francis Group
• Passivation of Defects by Hydrogenation
• N-H bond removes effect of nitrogen in
alloy
• The Hydrogenation effect is reversible:
RTA break the bond
• Disassociation temperature different for
various centers
A. Polimeni and M. Capizzi. “Role of
Hydrogenation in Dilute Nitrides”. Physics and
Application of Dilute Nitrides 169, (2004)
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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Selective Defects Passivation
in Solar Cell Materials
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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Selective Passivation
Bulk Reference Temp.Dep.
bandgap
1.16
Energy (eV)
localized centers
1.14
1.13
1.12
1.11
localized centers
clusters/defect
4.2K
20K
40K
60K
80K
100K
120K
140K
160K
180K
200K
220K
240K
260K
280K
1060 1080 1100 1120 1140
Wavelength (nm)
Peak Energy (eV)
Bulk Hydrogenation Temp. Dep.
bandgap
Bulk Reference
1.15
1.10
0
1060 1080 1100 1120 1140
Wavelength (nm)
Intensity (arb. u.)
Intensity (arb. u)
clusters/defect
4.2K
10K
15K
20K
25K
30K
35K
40K
45K
50K
60K
70K
80K
90K
100K
110K
120K
1.16
1.15
1.14
1.13
1.12
1.11
1.10
0
Un-hydrogenated
(Top)
Hydrogenated
(Bottom)
50 100 150 200 250 300
Temperature (K)
Hydrogenation
by Amethyst
Bulk Hydrogenation
Research Inc.
Penetration
depth
approximately
2µm
Hydrogen
concentration:
50 100 150 200 250 300
1.1 x 1015cm-2
Temperature (K)
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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Structure of the Solar Cells
P+ : GaAs 5x1018 cm-3
250nm
P : Al0.7Ga0.3As 2x1018 cm-3
30nm
P : GaAs 1x1018 cm-3 250nm
I – GaInNAs
I = 500nm
•  pin
•  GaInNAs Solar Cell
I=500nm
N : GaAs 1x1018 cm-3 350nm
N+ : GaAs 6x1018 cm-3
200nm
GaAs Substrate : Si
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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I = 500nm GaInNAs Solar Cell
Temperature Dependence
Lowest Hydrogenation
290K
1050 1075 1100 1125
1040 1060 1080 1100 1120
Wavelength (nm)
170K -->
1050 1075 1100 1125
1040 1060 1080 1100 1120
Wavelength (nm)
1.14
1.12
0
60 120 180 240 300
Temperature (K)
1.18
1.16
1.14
1.12
0
60 120 180 240 300
Temperature (K)
290K
1040 1060 1080 1100 1120
Wavelength (nm)
Highest Hydrogenation
Peak Energy (eV)
1.16
170K -->
1050 1075 1100 1125
Lowest Hydrogenation
Peak Energy (eV)
Peak Energy (eV)
Reference
1.18
290K
Highest Hydrogenation
Intensity (arb.u.)
170K -->
Intensity (arb.u.)
Intensity (arb.u.)
Reference
1.18
1.16
1.14
1.12
0
60 120 180 240 300
Temperature (K)
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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I = 500nm GaInNAs Solar Cell
JV and EQE
2 J
1 JJ
J
0 JJ
-1 JJ
J
-2
-3
-4
-5
-0.2
Highest Hydrogenation 1.0mm
Highest Hydrogenation 2.5mm
sc
Highest Hydrogenation 5.0mm
sc
Lowest Hydrogenation 1.0mm
sc
Lowest Hydrogenation 2.5mm
sc
Lowest Hydrogenation 5.0mm
sc
Reference 1.0mm
sc
Reference 2.5mm
sc
Reference 5.0mm
sc
1.2
Lower Hydrogenated
1.0
EQE (%)
2
J (mA/cm )
sc
0.8
0.6
0.4
2.5mm
5.0mm
0.2
0.0
0.2
Voltage (V)
0.4
0.0
900
975 1050 1125 1200
Wavelength (nm)
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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Summary
•  Removal/reduction of defects in GaInNAs observed in both
bulk materials and non-optimized solar cells.
•  The passivation process shows the removal of low-energy
defects and impurities can be achieved without removing
substitutional nitrogen: depends on hydrogen/defect
contraction ratio
•  Selective passivation has potential to improve the
efficiency of GaInNAs based solar cells be selectively
passivating deleterious non-radiative centers, including
nitrogen clusters and unwanted impurity states improving
carrier collection
Acknowledgments
Research supported by Amethyst Research Inc. through
the state of Oklahoma, OARS 12.2-040 program
Photovoltaics Materials & Device Group, University of Oklahoma: http://www.nhn.ou.edu/~sellers/group/index.html
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