K Improves Cu(In,Ga)Se2 Surface Band Alignment through Reconstruction

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K, Rb, and Cs improve Cu(In,Ga)Se2(CIGS) solar cell performance, but the mechanism remains unclear. Here we use air-free transfer of multiple samples to study KF post-deposition treatments (PDTs) by X-ray photoelectron spectroscopy. The KF PDTs do not change the majority carrier concentration or Cd in-diffusion, but they boost efficiency by 6.1% absolute, improve minority carrier lifetime, and shift the surface valence band further from the Fermi energy. Unlike former reports, the valence-band shift is not a result of lower Cu/(Ga+In) or higher K/(K+Cu) composition ratios. We propose that instead, KF PDTs alter the surface valence-band alignment through a reconstructive phase transformation from chalcopyrite CIGS to K2CuIn3Se6or KInSe2, which have layered structures.

Original languageAmerican English
Pages (from-to)11328-11338
Number of pages11
JournalACS Applied Energy Materials
Issue number9
StatePublished - 26 Sep 2022

Bibliographical note

Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.

NREL Publication Number

  • NREL/JA-5K00-83188


  • chalcopyrite
  • CIGS
  • photovoltaics
  • potassium
  • reconstruction


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