Transcript 投影片 1 - National Chiao Tung University

Finite element simulations of
compositionally graded InGaN solar cells
G.F. Brown a,b,* , J.W.AgerIIIb, W.Walukiewicz b, J.Wua,b,a
a Department of Materials Science&Engineering , University of California ,
Berkeley,California94720,USA
b Materials Sciences Division , Lawrence Berkeley National Laboratory ,
Berkeley,California94720,USA
Solar Energy Materials & Solar Cells 94 (2010) 478–483
Advisor: H.C. Kuo
Reporter: H.W. Wang
1. Introduction
2. Properties of InxGa1-xN used in simulations
3. Simulation results
4. Conclusions
Advantage
 Broad band
 InN - 0.7eV
 GaN - 3.42eV
Cheep fabrication process
 Grown on Si substrates by a low temperature process
High effiency
High absorption
Disadvantage
Indium composition (<30%)
P-type doping
Large lattice mismatch between InN and GaN alloys
Valence band discontinuity
Caughey–Thomas approximation
Absorption Coefficient
APSYS simulation tool
Self-consistance
Poisson equation
Carrier drift diffusion equation
InGaN - wurtzite crystal structure
Fermi level at the InGaN/GaN - un-pinned
No reflection and light trapping effects
No surface recombination losses
Optical carrier generation rate
AM 1.5
P-GaN
100nm
In0.5Ga0.5N
1mm
AM 1.5
p-GaN
5x1018cm-3
n-In0.5Ga0.5N 1x1017cm-3
Band diagram
I–V curve
100nm
1mm
AM 1.5
P-GaN
InXGa1-XN
Fill factor and Short-circuit current
V.S. Indium composition
Efficiency
AM 1.5
p-GaN
5x1018cm-3
n-InXGa1-XN 1x1017cm-3
n-In0.5Ga0.5N 1x1017cm-3
100nm
50nm
1mm
Efficiency
Band diagram
AM 1.5
p-GaN
5x1018cm-3
100nm
n-InXGa1-XN
n-In0.5Ga0.5N 1x1017cm-3
Efficiency
1mm
Band diagram
Minority hole life time
in InGaN layer
AM 1.5
p-GaN
5x1018cm-3
n-InXGa1-XN 1x1017cm-3
n-In0.5Ga0.5N 1x1017cm-3
100nm
50nm
1mm
AM 1.5
Efficiency
p-GaN
5x1018cm-3
n-InXGa1-XN 1x1017cm-3
n-In0.5Ga0.5N 1x1017cm-3
p-Si
n-Si
5x1019cm-3
100nm
50nm
1mm
100nm
1x1016cm-3
495mm
n-Si
1x1019cm-3
5mm
Simulate graded p-GaN/InxGa1-xN heterojunction
Graded layer between hetrojunction
Improve valence band discontinuity
Doping and width
Light doping & thin layer → high efficency
Double junction – InGaN/Si
28.9% → high efficiency & low cost substrate