LAUSR

Abstract The quaternary compound semiconductor Cu2ZnSn(S1-xSex)4 (CZTSSe) which crystallizes in the kesterite-type structure, is a promising material to be used as p-type absorber layer in thin film solar cell applications based on earth abundant elements. The absorber band tailing caused by an exceptionally high Cu/Zn disorder is believed to be one of the reasons for the limited open-circuit voltage in CZTSSe-based photovoltaic devices. This work is an experimental study of the Cu/Zn disorder in a unique set of single phase, stoichiometric CZTSSe mixed crystals, synthesized by solid state reaction, by means of neutron powder diffraction and anomalous X-ray powder diffraction. The existence of Cu/Zn disorder was revealed as the only intrinsic point defect in these mixed crystals within the detection limits of our measurements. The order parameter Q was calculated on the basis of the occurring CuZn and ZnCu anti site defects causing the Cu/Zn disorder. Variations of the order parameter with anion composition and the effect on the optoelectronic properties of the partial substitution of Se with S in Cu2ZnSn(S1-xSex)4 was elaborated.