Steady state minority carrier lifetime and defect level occupation in thin film CdTe solar cells

Zimeng Cheng, Alan E. Delahoy, Zhaoqian Su, Ken K. Chin

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

A model consisting of Shockley Read Hall (SRH) recombination under steady state conditions of constant photon injection is proposed in this work to study the steady state minority carrier lifetime in CdS/CdTe thin film solar cells. The SRH recombination rate versus optical injection level is analytically approximated in the junction and neutral regions. In the neutral region, it is found that the recombination rate through certain defect levels has one constant value under lower optical injection conditions and another constant value under higher optical injection conditions with the transition occurring at a critical optical injection level. By simultaneously solving the equations of charge neutrality, charge conservation and SRH recombination in the neutral region, it is found that the compensation of doping and the reduction of minority carrier lifetime by donors in the p-type semiconductor can each be remedied by optical injection. It is also demonstrated that this optical-dependent SRH recombination is significant in large bandgap thin films. The measured minority carrier diffusion length in a CdS/CdTe solar cells, as determined from the steady-state photo-generated carrier collection efficiency, shows the predicted transition of minority carrier lifetime versus optical injection level. A numerical fitting of the indirectly-measured minority carrier lifetime by assuming the minority carrier mobility gives a non-intuitive picture of the p-n junction with a low free hole concentration but a narrow depletion region width.

Original languageEnglish (US)
Pages (from-to)391-399
Number of pages9
JournalThin Solid Films
Volume558
DOIs
StatePublished - May 2 2014

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Materials Chemistry

Keywords

  • Cadmium Telluride
  • Minority carrier diffusion length
  • Minority carrier lifetime
  • Recombination
  • Solar cells

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