finite element simulations of compositionally graded ingan solar cells

Finite element simulations of compositionally graded InGaN solar

cells G.F. Brown a,b,* , J.W.AgerIIIb, W.Walukiewicz b, J.Wua,b,a

Advisor: H.C. KuoReporter: H.W. Wang

Solar Energy Materials & Solar Cells 94 (2010) 478–483

a Department of Materials Science&Engineering , University of California , Berkeley,California94720,USAb Materials Sciences Division , Lawrence Berkeley National Laboratory , Berkeley,California94720,USA

1. Introduction

2. Properties of InxGa1-xN used in simulations 3. Simulation results

Outline:

4. Conclusions

Broad band InN - 0.7eV GaN - 3.42eV

Cheep fabrication process Grown on Si substrates by a low temperature

processHigh effiency

Advantage

DisadvantageIndium composition (<30%)

P-type doping

High absorption

Large lattice mismatch between InN and GaN alloysValence band discontinuity

Introduction

Properties of InxGa1-xN used in simulations

Caughey–Thomas approximation

Absorption Coefficient

APSYS simulation toolSelf-consistancePoisson equationCarrier drift diffusion equation

InGaN - wurtzite crystal structureFermi level at the InGaN/GaN - un-pinnedNo reflection and light trapping effects No surface recombination losses

Simulation results

P-GaN

In0.5Ga0.5N

100nm

1mm

AM 1.5

Optical carrier generation rate

p-GaN

n-In0.5Ga0.5N

100nm

1mm

AM 1.5

5x1018cm-3

1x1017cm-3

Band diagram

I–V curve

P-GaN

InXGa1-XN

AM 1.5

Efficiency

Fill factor and Short-circuit current V.S. Indium composition

p-GaN

n-In0.5Ga0.5N

100nm

1mm

AM 1.5

5x1018cm-3

1x1017cm-3

50nm1x1017cm-3

n-InXGa1-XN

Band diagramEfficiency

p-GaN

n-In0.5Ga0.5N

100nm

1mm

AM 1.5

5x1018cm-3

1x1017cm-3

n-InXGa1-XN

Efficiency

Band diagram

p-GaN

n-In0.5Ga0.5N

100nm

1mm

AM 1.5

5x1018cm-3

1x1017cm-3

50nm1x1017cm-3

n-InXGa1-XN

Minority hole life time in InGaN layer

p-GaN

n-In0.5Ga0.5N

100nm

1mm

AM 1.5

5x1018cm-3

1x1017cm-3

50nm1x1017cm-3

n-InXGa1-XN

p-Si

n-Si

n-Si

5x1019cm-3

1x1016cm-3

1x1019cm-3

100nm

495mm

5mm

Efficiency

Conclusions

Simulate graded p-GaN/InxGa1-xN heterojunctionGraded layer between

hetrojunctionImprove valence band discontinuity

Doping and widthLight doping & thin layer → high efficencyDouble junction – InGaN/Si28.9% → high efficiency & low cost substrate