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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. a Department of Materials Science&Engineering , University of California , Berkeley,California94720,USA

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Finite element simulations of compositionally graded InGaN solar cells

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  1. Finite element simulations of compositionally graded InGaN solar cells G.F. Brown a,b,* , J.W.AgerIIIb, W.Walukiewiczb, 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

  2. Outline: 1. Introduction 2. Properties of InxGa1-xN used in simulations 3. Simulation results 4. Conclusions

  3. Introduction 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

  4. Properties of InxGa1-xN used in simulations Caughey–Thomas approximation

  5. Absorption Coefficient

  6. APSYS simulation tool • Self-consistance • Poisson equation • Carrier drift diffusion equation • InGaN- wurtzitecrystal structure • Fermi level at the InGaN/GaN - un-pinned • No reflection and light trapping effects • No surface recombination losses

  7. Simulation results Optical carrier generation rate AM 1.5 P-GaN 100nm In0.5Ga0.5N 1mm

  8. AM 1.5 • I–V curve p-GaN 100nm 5x1018cm-3 n-In0.5Ga0.5N 1x1017cm-3 1mm Band diagram

  9. AM 1.5 P-GaN InXGa1-XN Fill factor and Short-circuit current V.S. Indium composition Efficiency

  10. AM 1.5 p-GaN 5x1018cm-3 100nm 50nm n-InXGa1-XN 1x1017cm-3 n-In0.5Ga0.5N 1x1017cm-3 1mm Efficiency Band diagram

  11. AM 1.5 p-GaN 5x1018cm-3 100nm n-InXGa1-XN Band diagram n-In0.5Ga0.5N 1x1017cm-3 1mm Efficiency

  12. AM 1.5 Minority hole life time in InGaNlayer p-GaN 5x1018cm-3 100nm 50nm n-InXGa1-XN 1x1017cm-3 n-In0.5Ga0.5N 1x1017cm-3 1mm

  13. AM 1.5 Efficiency p-GaN 5x1018cm-3 100nm 50nm n-InXGa1-XN 1x1017cm-3 n-In0.5Ga0.5N 1x1017cm-3 1mm p-Si 5x1019cm-3 100nm n-Si 1x1016cm-3 495mm n-Si 1x1019cm-3 5mm

  14. Conclusions • 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% → highefficiency & low cost substrate

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