Effect of post-sulfurization on the structural and optical properties of Cu2ZnSnS4 thin films deposited by vacuum evaporation method

The influence of post deposition annealing in sulfur atmosphere on the structural and optical properties of Cu2ZnSnS4 (CZTS) thin films was investigated. The samples were deposited by thermal evaporation under vacuum method at different glass substrate temperatures ranging from 60 °C to 210 °C. After the deposition, all CZTS thin films were annealed in a furnace in sulfur atmosphere at a temperature of 400 °C during 2 h so as to optimize the kesterite CZTS phase. Structural characterization was carried out using X-ray diffraction and Raman Scattering whereas optical characterization was performed by recording transmittance and reflectance of the samples in the spectral range of 300 nm-2400 nm. The X-ray diffraction spectra indicated that polycrystalline CZTS films were obtained after annealing and the samples exhibit (112) preferred diffraction plane. Hence, crystallinity was enhanced with substrate temperature as well as with post deposition annealing due to the diffusion of sulfur in the film during the annealing process. Optical study reveals that after annealing, the absorption coefficient is found to be higher than 105 cm− 1 whereas the direct band gap energy varies in the range of 1.4 eV-1.6 eV.