Alkali-induced grain boundary reconstruction on Cu(In,Ga)Se2 thin film solar cells using cesium fluoride post deposition treatment

Tzu Ying Lin, Ishwor Khatri, Junpei Matsuura, Kosuke Shudo, Wei Chih Huang, Mutsumi Sugiyama, Chih Huang Lai, Tokio Nakada

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4 Citations (Scopus)


Heavy alkali metal treatment is a key factor to approach high efficiency in Cu(In, Ga)Se2 (CIGS) solar cells. Here, we show that the Cs-induced surface modification on CIGS thin-film solar cells, especially on grain boundary reconstruction generated from cesium fluoride post-deposition treatment (CsF-PDT). The CsInSe2 phase can be synthesized by CsF-PDT process without extra assistant species, and specifically favors grain boundaries (GBs), which was further characterized by FE-EPMA, TEM, and SIMS analysis. The Cs-contained GBs may both create the valence-band downshift and conduction-band upward. By controlling the Cs-contained layer thickness and modifying absorber, the spike at conduction-band can be overcome by tunneling while remaining high valence-band downshift to suppress the GBs recombination. The efficiency was improved from 15.1 to 18.3% after CsF-PDT; the voltage loss of Eg/q–Voc was down below 0.4 V. Those improvements are mainly contributed from the grain boundary reconstruction at the junction area using CsF-PDT to reduce the recombination.

Original languageEnglish
Article number104299
JournalNano Energy
Publication statusPublished - Feb 2020


  • CIGS
  • CsF
  • Grain boundary
  • Heavy alkali
  • PDT
  • V loss

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