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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 (VCu), various cation anti site defects (CuZn, ZnCu, ZnSn, SnZn and CuZn) as well as interstitials (Cui, Zni) in a wide range of off-stoichiometric polycrystalline powder samples synthesized by 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. Additional to the known off-stoichiometry types A to H new types (I to 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. Additional to the offstoichiometry type specific defects Cu/Zn disorder is always present in the CZTSe phase. In Cupoor/Zn-rich CZTSe, a composition considered as the one that delivers the best photovoltaic performance, mainly copper vacancies, ZnCu and ZnSn anti sites are present. Also this compositional region shows the lowest degree of Cu/Zn disorder.

An off-stoichiometric but single phase Cu1.95Zn1.1Sn0.96Se4 kesterite powder was investigated by temperature dependent transient surface photovoltage (SPV) spectroscopy. SPV signals excited at different wavelengths were transformed into SPV spectra that depended on the response time of measurement. Shallow electronic states and states with transition energies at 0.83 eV or 0.78… 0.9 eV were distinguished. The temperature dependence of the band gap of Cu1.95Zn1.1Sn0.96Se4 was obtained. Results were discussed on the basis of defects in Cu-poor and Zn-rich kesterite.