title: Secondary phases and their influence on the composition of the kesterite phase in CZTS and CZTSe thin films.
abstract: Secondary phases zinc sulfide/selenide and copper sulfide in Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) thin film samples are investigated by X-ray absorption near edge structure (XANES) analysis at the chalcogen K-edges. Because of the formation of secondary phases the composition of the kesterite phase can deviate significantly from the total sample composition. For a large set of non-stoichiometric samples we find that the cation ratios of the kesterite phase never exceed Zn/Sn = 1 even for Zn-rich CZTS and CZTSe, with all excess Zn being contained in secondary phases. For CZTS the cation ratios are found to be additionally constrained by Cu/Sn ≤ 2, which means that Cu-excess always leads to the formation of CuxS secondary phases. These results give clear bounds on the Cu-rich and Zn-rich sides of the single phase region in polycrystalline CZTS/Se thin films.
authors.affiliation: Department Structure and Dynamics of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner Platz 1, 14109 Berlin, Germany. justus.just@helmholtz-berlin.de unold@helmholtz-berlin.de.
authors.forename: Justus
authors.initials: J
authors.lastname: Just
authors.forename: Carolin M
authors.initials: CM
authors.lastname: Sutter-Fella
authors.forename: Dirk
authors.initials: D
authors.lastname: Lützenkirchen-Hecht
authors.forename: Ronald
authors.initials: R
authors.lastname: Frahm
authors.forename: Susan
authors.initials: S
authors.lastname: Schorr
authors.forename: Thomas
authors.initials: T
authors.lastname: Unold