Growth of Cu2ZnSnS4 thin films by co-evaporation-annealing route: effect of annealing temperature and duration

Cu-2 ZnSnS4 (CZTS) thin films were prepared by co-evaporation of Cu, ZnS, Sn and S and subsequent annealing. The effect of annealing temperature and duration on the growth of CZTS films were investigated. Thickness of these films was similar to 1.0 mu m. X-ray diffraction (XRD) and Raman spectra analyses were used for phase identification. XRD analysis indicated the presence of minor CuS, Cu-1.9375 S, SnS phases in case of as-deposited films, emergence of strong CZTS phase with minor SnS2 phase in films annealed at 550 degrees C for 10 min, and only formation of kesterite CZTS phase with (112) preferred orientation in films annealed at 550 degrees C for 30 min and 60 min as well as in films annealed at 580 degrees C for all durations. Energy dispersive spectroscopic analysis revealed that the films are Cu-poor CZTS in all these cases. Raman spectroscopy analysis, used to identify structurally coherent phases, Cu-2 SnS3 and ZnS, confirmed the absence of Cu-2 SnS3 phase in films annealed at 550. degrees C for 30, 60 min and in films annealed at 580 degrees C for all durations. Scanning electron microscopic studies showed improvement in particulate size from similar to 100-400 to 200-800 nm with increase in annealing duration at 550 degrees C, while such an improvement in particulate size is only observed up to 30 min at 580 degrees C. The direct band gap of CZTS films, determined from optical absorption studies, varied from 1.40 to 1.48 eV, based on annealing conditions. The electrical conductivity of these films was found to vary from 0.05 to 0.2 Omega(-1) cm(-1)