The crystal structure of kesterite type compounds: A neutron and X-ray diffraction study

Abstract

The atomic structure of the potential photovoltaic materials Cu 2ZnSnS 4 (CZTS) and Cu 2ZnSnSe 4 (CZTSe) is discussed on the basis of a structural analysis of neutron powder diffraction data refined by the Rietveld analysis. Both compounds were found to crystallize in the kesterite type structure, but with a disorder within the Cu–Zn layers at z=1/4 and 3/4. The latter causes Cu Zn and Zn Cu anti-site defects, whose concentration depends on the sample growth conditions. The temperature dependent structural phase transition in CZTS was studied by in-situ high temperature diffraction experiments using high energy synchrotron X-rays. The transition from the tetragonal kesterite to the cubic sphalerite type structure is discussed by means of the interplay of increasing and decreasing cation–anion–cation bond angles in the coordination tetrahedra, reflected by the shift of the anion atomic coordinates to more ideal ( x and y) or non-ideal ( z) values. This striking behavior may be connected with frustrations that occur due to the triangular geometry of the coordination tetrahedra.