Effect of Cu/(Zn plus 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 T-s=623 K and post-deposition annealed at T-pa = 723 K for I 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-Omega-cm depending on Cu/(Zn+Sn) ratio. (C) 2009 Elsevier B.V. All rights reserved.