Schorr, S.: The crystal structure of kesterite type compounds: A neutron and X-ray diffraction study. Solar Energy Materials and Solar Cells 95 (2011), p. 1482-1488
The atomic structure of the potential photovoltaic materials Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) is discussed on the basis of a structural analysis of neutron powder diffraction data refined by Rietveld analysis. Both compounds were found to crystallize in the kesterite type structure, but with a disorder within the Cu-Zn layers at z=¼ and ¾. The latter causes CuZn and ZnCu anti-site defects, whose concentration depends on the sample growth conditions. The temperature dependent structural phase transition in CZTS were 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 behaviour may be connected with frustrations, which occur due to the triangular geometry of the coordination tetrahedra.