JPhys Energy (Jan 2023)

n-type CdTe:In for photovoltaics: in situ doping, type verification and compensation effects

  • Theodore D C Hobson,
  • Luke Thomas,
  • Laurie J Phillips,
  • Leanne A H Jones,
  • Matthew J Smiles,
  • Christopher H Don,
  • Pardeep K Thakur,
  • Huw Shiel,
  • Stephen Campbell,
  • Vincent Barrioz,
  • Vin Dhanak,
  • Tim Veal,
  • Jonathan D Major,
  • Ken Durose

DOI
https://doi.org/10.1088/2515-7655/acfbf8
Journal volume & issue
Vol. 5, no. 4
p. 045012

Abstract

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We explored the in-situ doping of cadmium telluride thin films with indium to produce n-type absorbers as an alternative to the near-universal choice of p-type for photovoltaic devices. The films were grown by close space sublimation from melt-synthesised feedstock. Transfer of the indium during film growth was limited to 0.0014%–0.014%—unless reducing conditions were used which yielded 14%–28% efficient transport. While chunks of bulk feedstock were verified as n-type by the hot probe method, carrier type of thin film material was only able to be verified by using hard x-ray photoelectron spectroscopy to determine the Fermi level position within the band gap. The assignment of n-type conductivity was consistent with the rectification behaviour of a p-InP/CdTe:In junction. However, chloride treatment had the effect of compensating n-CdTe:In to near-intrinsic levels. Without chloride, the highest dopant activation was 20% of the chemical concentration of indium, this being for a film having a carrier concentration of n = 2 × 10 ^15 cm ^−3 . However, the activation was often much lower, and compensation due to over-doping with indium and native defects (stoichiometry) are discussed. Results from preliminary bifacial devices comprising Au/P3HT/ZnTe/CdTe:In/CdS/FTO/glass are presented.

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