Chemical structure of a carbon-rich layer at the wet-chemical processed Cu2ZnSn(S,Se)4/Mo interface

D. Hauschild*, S. J. Wachs, W. Kogler, L. Seitz, J. Carter, T. Schnabel, B. Krause, M. Blum, W. Yang, E. Ahlswede, C. Heske, L. Weinhardt

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


The carbon-rich layer at the back-contact interface of a solution-processed Cu2ZnSn(S,Se)4 (CZTSSe) absorber is investigated with a combination of surface-sensitive X-ray photoelectron and bulk-sensitive X-ray emission spectroscopy. For absorber deposition, an aqueous ammonium-thioglycolate (ATGL) solution was used, and the 'buried' back-contact interface was accessed by cleaving in a liquid nitrogen environment. In the pertinent literature, it is reported that such a carbon layer at the absorber/back-contact interface could have beneficial effects, e.g., to reduce series resistance or increase the short circuit current. Here, a detailed picture of the chemical structure of this carbon-rich layer at the back contact is derived, which consists of carbon (74 ± 7%), selenium (19 ± 4%), and sulfur (7 ± 3%). The selenium in this layer is found as elemental inclusions, possibly from not fully reacted selenium during the absorber production. The sulfur content in this carbon-rich layer is twice that of sulfur in the absorber. A detailed analysis of the chemical environment suggests that residuals from the aqueous ATGL solution are the origin of sulfur in this carbon-rich layer. Furthermore, underneath the carbon-rich layer, S-Mo bonds are found at the Mo back contact.

Original languageEnglish (US)
Article number9384891
Pages (from-to)658-663
Number of pages6
JournalIEEE Journal of Photovoltaics
Issue number3
StatePublished - May 2021
Externally publishedYes


  • Back contact
  • Chemical structure
  • Kesterite
  • Photoelectron spectroscopy
  • Thin-film solar cell
  • Wet-chemical processing
  • X-ray emission spectroscopy (XES)

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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