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Photocapacitance measurements on GaP alloys for high efficiency solar cells

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Photocapacitance measurements on GaP alloys for high efficiency solar cells

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  1. Photocapacitance measurements on GaP alloys forhigh efficiency solar cells Dan Hampton and Tim Gfroerer , Davidson College, Davidson, NC Mark Wanlass, National Renewable Energy Lab, Golden, CO Acknowledgements Davidson Research Initiative American Chemical Society Petroleum Research Fund Jeff Carapella for growing and processing test structures

  2. Solar Cell Operation

  3. Conduction Band Conduction Band E=hc/λ Energy + Valence Band Valence Band Valence Band Valence Band

  4. Conduction Band E=hc/λ Energy + Valence Band Valence Band

  5. Conduction Band Conduction Band Conduction Band Conduction Band Energy Electron-Hole Pair + + Valence Band Valence Band

  6. Conduction Band Conduction Band Conduction Band Conduction Band Band Edge Energy + + Valence Band Valence Band

  7. Heat Conduction Band Conduction Band Conduction Band Conduction Band Band Edge Energy Ephoton – Band Gap Energy = Energy Lost + + Valence Band Valence Band

  8. Defects

  9. Conduction Band Conduction Band Defect Levels Increasing Energy Trap Depth + + + + + + Valence Band Valence Band Valence Band Valence Band Hole

  10. Conduction Band Conduction Band + Defect Levels Defect Levels Defect Levels + Increasing Energy Capture Trap Depth + + + + + Valence Band Valence Band Valence Band Hole

  11. Conduction Band Conduction Band Defect Levels Defect Levels Defect Levels + Increasing Energy Escape Trap Depth + + + + + + Valence Band Valence Band Valence Band Hole

  12. Picture of Device 1 mm

  13. - - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - + + + + + + + + + + Photocapacitance N+ P Depletion with bias

  14. - - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - + + + + + + + + + + Photocapacitance N+ P Depletion without bias

  15. - - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - + + + + + + + + + + Depletion Layer N+ P Depletion without bias

  16. - - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - + + + + + + + + + + Depletion Layer T = 77 K N+ P Depletion without bias

  17. - - - - - - - - - - - - - - - - - - - - - - - + - - - - - - - + + + + - + + + + + + Depletion Layer T = 77 K N+ P Depletion without bias

  18. Conclusions • Optical threshold escape energies are higher than thermal threshold energies → Configuration Dependent Traps • GaAsP has a very large trap density, comparable to the density of dopants. This suggests zinc is contributing to the formation of the traps.