Intrinsic Point Defects In Off-Stoichiometric Cu2znsnse4: A Neutron Diffraction Study

This work is an experimental study of intrinsic point defects in off-stoichiometric kesterite type CZTSe by means of neutron powder diffraction. We revealed the existence of copper vacancies (V-Cu), various cation anti site defects (Cu-Zn, Zn-Cu, Zn-Sn, Sn-Zn, and Cu-Zn), as well as interstitials (Cu-i, Zn-i) in a wide range of off-stoichiometric polycrystalline powder samples synthesized by the solid state reaction. The results show that the point defects present in off-stoichiometric CZTSe agree with the off-stoichiometry type model, assuming certain cation substitutions accounting for charge balance. In addition to the known off-stoichiometry types A-H, new types (I-L) have been introduced. For the very first time, a correlation between the chemical composition of the CZTSe kesterite type phase and the occurring intrinsic point defects is presented. In addition to the off-stoichiometry type specific defects, the Cu/Zn disorder is always present in the CZTSe phase. In Cu-poor/Zn-rich CZTSe, a composition considered as the one that delivers the best photovoltaic performance, mainly copper vacancies, Zn-Cu and Zn-Sn anti sites are present. Also, this compositional region shows the lowest degree of Cu/Zn disorder. Published by AIP Publishing.