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Hot Carriers in Strain Balanced Quantum Well Solar Cells

Hot Carriers in Strain Balanced Quantum Well Solar Cells. M. F. Führer, J.P. Connolly, M. Mazzer , I. M. Ballard, D.C. Johnson, K. W. J. Barnham , A.Bessière , J. S. Roberts, R. Airey , C. Calder, G. Hill Contact: markus.fuhrer01@imperial.ac.uk. Quantum Well Solar Cells.

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Hot Carriers in Strain Balanced Quantum Well Solar Cells

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  1. Hot Carriers in Strain Balanced Quantum Well Solar Cells M. F. Führer, J.P. Connolly, M. Mazzer, I. M. Ballard, D.C. Johnson, K. W. J. Barnham, A.Bessière, J. S. Roberts, R. Airey, C. Calder, G. Hill Contact: markus.fuhrer01@imperial.ac.uk

  2. Quantum Well Solar Cells Extended Absorption Strain Balancing Increased Efficiency

  3. Our Samples various depth InGaAs Wells GaAsP Barriers Concentrator Masks: Homogeneous at high bias

  4. Electroluminescence Setup

  5. Results – Single Medium Well

  6. Results – Ten Medium Well

  7. Results – 50 Deep Wells

  8. Bias Dependence

  9. Results - Depth dependence?

  10. Interpretations • Sample Heating • Non-Equilibrium Effects (Hot Carriers) • High Exciton Density Effects

  11. Interpretations – Sample Heating • Yes, some samples are heating up… identify with: • EG • Bulk slope …and discard. • However, effect persists even in samples without changing bulk T. • Not just sample heating.

  12. Interpretations • Model for Recombination: Generalised Planck • Non-equilibrium interpretations focus on T and EF • Other interpretations focus on (E) • Measuring these quantities is difficult

  13. Interpretations – Hot Carriers

  14. Interpretations – Hot Carriers • assume constant absorption • Vary T and EF for non-equilibrium effects

  15. Interpretations – Hot Carriers • Raises possibilities of hot carrier solar cells • (which bypass Shockley-Queisser limit) • Most attractive Interpretation • Fits data reasonably well

  16. Interpretations – Exciton Effects • Most of the recombination stems from recombining excitons • Excitons are bosons only at long distance • Interactions amplified by confinement in the quantum well

  17. Interpretations – Exciton Effects

  18. Interpretations – Exciton Effects

  19. Interpretations – Exciton Effects • Kink in the ISCvs Power curve suggests decreased absorption beyond a certain optical bias • Some evidence against heating • Needs further study

  20. Conclusions • Significant evidence of a high-bias effect in GaAs based quantum well solar cells • relative reduction in peak exciton emission • Several interpretations • Hot Carriers • Exciton Interactions • More work needed.

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