Formation of a K-In-Se surface species by NaF/KF postdeposition treatment of Cu(In,Ga)Se2 thin-film solar cell absorbers

Evelyn Handick, Patrick Reinhard, Regan G. Wilks, Fabian Pianezzi, Thomas Kunze, Dagmar Kreikemeyer-Lorenzo, Lothar Weinhardt, Monika Blum, Wanli Yang, Mihaela Gorgoi, Eiji Ikenaga, Dominic Gerlach, Shigenori Ueda, Yoshiyuki Yamashita, Toyohiro Chikyow, Clemens Heske, Stephan Buecheler, Ayodhya N. Tiwari, Marcus Bär

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61 Citations (Scopus)


A NaF/KF postdeposition treatment (PDT) has recently been employed to achieve new record efficiencies of Cu(In,Ga)Se2 (CIGSe) thin film solar cells. We have used a combination of depth-dependent soft and hard X-ray photoelectron spectroscopy as well as soft X-ray absorption and emission spectroscopy to gain detailed insight into the chemical structure of the CIGSe surface and how it is changed by different PDTs. Alkali-free CIGSe, NaF-PDT CIGSe, and NaF/KF-PDT CIGSe absorbers grown by low-temperature coevaporation have been interrogated. We find that the alkali-free and NaF-PDT CIGSe surfaces both display the well-known Cu-poor CIGSe chemical surface structure. The NaF/KF-PDT, however, leads to the formation of bilayer structure in which a K-In-Se species covers the CIGSe compound that in composition is identical to the chalcopyrite structure of the alkali-free and NaF-PDT absorber.

Original languageEnglish
Pages (from-to)3581-3589
Number of pages9
JournalACS Applied Materials and Interfaces
Issue number4
Publication statusPublished - 2017 Feb 1
Externally publishedYes


  • Alkali postdeposition treatment
  • Chalcopyrite thin-film solar cells
  • Chemical surface structure
  • Photoelectron spectroscopy
  • X-ray spectroscopy

ASJC Scopus subject areas

  • Materials Science(all)


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