Impact of CdTe surface composition on doping and device performance in close Space sublimation deposited CdTe solar cells

Authors

  • J. D. Major,

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    • Department of Physics, University of Durham, Durham, UK
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    • Now at: Stephenson Institute for Renewable Energy, School of Physical Sciences, Chadwick Building, University of Liverpool, L69 7ZF, UK
  • Y. Y. Proskuryakov,

    1. Department of Physics, University of Durham, Durham, UK
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    • Now at: Stephenson Institute for Renewable Energy, School of Physical Sciences, Chadwick Building, University of Liverpool, L69 7ZF, UK
  • K. Durose

    1. Department of Physics, University of Durham, Durham, UK
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    • Now at: Stephenson Institute for Renewable Energy, School of Physical Sciences, Chadwick Building, University of Liverpool, L69 7ZF, UK

Correspondence: J. D. Major, Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK.

E-mail: Jon.Major@liverpool.ac.uk

ABSTRACT

Cool-down after close-space sublimation growth of cadmium telluride films has been shown to lead to the formation of a Cd-rich surface that can block the subsequent in-diffusion of cadmium chloride that is used in post-growth doping of solar cell devices. Pre-etching of the as-grown surfaces using a nitric–phosphoric acid etch prior to doping leads to increase in chlorine and oxygen in-diffusion, and an associated improvement in device efficiency from <3% to 12% in controlled trials. Capacitance-voltage analysis of such devices revealed an increase in the acceptor concentration from 3.76 × 1013 cm−3 to 5.6 × 1014 cm−3, whereas thermal admittance spectroscopy revealed fewer deep states at energies >0.4 eV for etched devices. Impedance analysis showed the improved cadmium chloride treatment—resulting from the additional etching step—removed the grain boundary component from the equivalent circuit, indicating a grain boundary passivation effect. Copyright © 2011 John Wiley & Sons, Ltd.

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