Beneficial Effect of Post-Deposition Treatment in High-Efficiency Cu(In,Ga)Se2 Solar Cells through Reduced Potential Fluctuations: Article No. 063106

Stephen Glynn, Patricia Dippo, Dean Levi, Darius Kuciauskas, Ana Kanevce

Research output: Contribution to journalArticlepeer-review

74 Scopus Citations

Abstract

World-record power conversion efficiencies for Cu(In,Ga)Se2 (CIGS) solar cells have been achieved via a post-deposition treatment with alkaline metals, which increases the open-circuit voltage and fill factor. We explore the role of the potassium fluoride (KF) post-deposition treatment in CIGS by employing energy- and time-resolved photoluminescence spectroscopy and electrical characterization combined with numerical modeling. The bulk carrier lifetime is found to increase with post-deposition treatment from 255 ns to 388 ns, which is the longest charge carrier lifetime reported for CIGS, and within ~40% of the radiative limit. We find evidence that the post-deposition treatment causes a decrease in the electronic potential fluctuations. These potential fluctuations have previously been shown to reduce the open-circuit voltage and the device efficiency in CIGS. Additionally, numerical simulations based on the measured carrier lifetimes and mobilities show a diffusion length of ~10 um, which is ~4 times larger than the film thickness. Thus, carrier collection in the bulk is not a limiting factor for device efficiency. By considering differences in doping, bandgap, and potential fluctuations, we present a possible explanation for the voltage difference between KF-treated and untreated samples.
Original languageAmerican English
Number of pages7
JournalJournal of Applied Physics
Volume120
Issue number6
DOIs
StatePublished - 2016

NREL Publication Number

  • NREL/JA-5J00-65144

Keywords

  • CIGS
  • KF
  • PDT
  • potential fluctuations
  • TRPL

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