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Strain-Balanced Quantum Well Solar Cells From Multi-Wafer Production

Strain-Balanced Quantum Well Solar Cells From Multi-Wafer Production. Jessica Adams 33 rd IEEE Photovoltaic Specialists Conference 12 th May 2008. Can we manufacture the strain-balanced quantum well solar cell on a multi-wafer production run?. 2”. 4”. Research wafers.

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Strain-Balanced Quantum Well Solar Cells From Multi-Wafer Production

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  1. Strain-Balanced Quantum Well Solar Cells From Multi-Wafer Production Jessica Adams 33rd IEEE Photovoltaic Specialists Conference 12th May 2008

  2. Can we manufacture the strain-balanced quantum well solar cell on a multi-wafer production run? 2” 4” Research wafers Industrial wafers

  3. Overview • Introduction • Quantum well solar cell • Strain-balancing • Photon recycling • Details of devices • Experimental results • Spatial reflectivity • Quantum efficiency • Modeling results • Dark current suppression • Predicted efficiencies • Summary

  4. Eg V Ea n p i Strain-Balanced Quantum Well Solar Cell (I) • Wells inserted in i-region of p-i-n • Extends absorption energy range to below that of bulk

  5. Motivation for SB-QWSC In0.1GaAs GaAs 1000 Suns • Cells designed to work under concentrator conditions • Need smaller band-gap than GaAs to operate at efficiency peak [1] J. Ward et al., Photovoltaic Specialists Conference,1993., Conference Record of the Twenty Third IEEE, pages 650-654, 1993.

  6. Strain-Balanced Quantum Well Solar Cell (II) GaAsP (barriers) InGaAs (wells) GaAs (bulk) > 65 wells without misfit dislocations

  7. Photon Recycling Contact AR coat • Photons not absorbed on first pass reflected => increased JSC • Photons from radiative recombination loss reflected back through wells => photon recycling => increased VOC • Efficiency increased ~1 % absolute p Quantum wells i n Distributed Bragg reflector (mirror)

  8. Distributed Bragg Reflector (DBR)

  9. p,n GaAs • In0.11Ga0.89As wells • GaAs0.9P0.1 barriers p-i-n diodes Device Structures Growth: MOVPE 50 quantum wells Control + DBR substrates Run-1 Run-2 • Devices taken from 2 positions on 2 wafers • Stepped p-region emitter • Heavy window doping • Devices taken from 5 positions across 3 wafers X1 Y2A Ctrl X2 Ctrl DBR Y1 Y2B DBR DBR

  10. DBR Spatial Reflectivity Wavelength of maximum reflectivity varies from 924 nm to 904 nm

  11. X1 X1 X1 X1 Y1 Y1 Y1 Y1 Experimental QE - Run-1

  12. Y2A Y2A Y2B Y2A X2 Y2A X2 Y2B X2 X2 Experimental QE - Run-2

  13. Modeling - SOL (I) Fit QE to experimental data using parameters from literature Carrier transport Quantum well absorption Carrier distributions Shockley injection current Radiative current SRH current in terms of single non-radiative carrier lifetime 1 parameter fit to dark current! [2] J. Connolly, et al., Proc. 19th European Photovoltaic SolarEnergy Conference, Paris, 2004.

  14. Modeling - SOL (II) Run-1 X1 -edge Run-1 Y1 -edge Reduced radiative dark current in all of the DBR devices investigated Evidence of photon recycling Reduced Shockley injection current in stepped emitter devices Evidence of reduced surface recombination current

  15. Predicted Efficiencies 28.0 Run-2 Run-1 X2 27.5 X1 27.0 Efficiency (%) Y2A 26.5 26.0 Y1 Y2B 25.5 AM1.5D x500 5% shading

  16. Summary • Investigated SB-QWSCs from 2 multi-wafer production runs • Found suppressed radiative recombination in devices with DBRs • Photon recycling • Improved efficiency • Investigated impact of stepped emitter • Reduced surface recombination • Improved efficiency • Found that similar efficiencies can be produced from across the wafers • Results hold for both control and DBR substrates • Multi-wafer manufacture potentially viable

  17. Acknowledgments Keith Barnham, James Connolly and the QPV group at Imperial College London J.S. Roberts and G. Hill at the EPSRC National Centre for III-V Technologies T. Tibbits of QuantaSol Ltd. M. Geen of IQE Europe M. Pate of the Centre for Integrated Photonics http://www.sc.ic.ac.uk/~q_pv

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