Effect of Cu/(Zn+Sn) ratio on the properties of co-evaporated Cu2ZnSnSe4 thin films

The effect of Cu/(Zn+Sn) ratio on the properties of Cu2ZnSnSe4 (CZTSe) thin films is investigated. CZTSe thin films with Cu/(Zn+Sn) ratio in the range 0.85–1.15 are deposited using 4-source co-evaporation technique onto glass substrates held at a substrate temperature Ts=623 K and post-deposition annealed at Tpa=723 K for 1 h in the selenium atmosphere. Powder X-ray diffraction (XRD) patterns reveal that CZTSe films deposited with Cu/(Zn+Sn) ratio in the range 0.90–1.10 are single phase and polycrystalline. CZTSe films, deposited with Cu/(Zn+Sn) ratio of 0.85 contain ZnSe as secondary phase and films with ratio of 1.15 contain Cu2−XSe as the secondary phase. The films are found to exhibit kesterite structure. Band gap of the films is found to increase with decrease in Cu/(Zn+Sn) ratio. Electrical resistivity of the films is found to lie in the range 0.02–23-Ω-cm depending on Cu/(Zn+Sn) ratio.