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 2h 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 300nm–2400nm. 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 105cm−1 whereas the direct band gap energy varies in the range of 1.4eV–1.6eV. •Growth of Cu2ZnSnS4 (CZTS) films on heated substrates by thermal evaporation method•Annealing of CZTS thin films in sulfur vapor under vacuum at 400°C•XRD and Raman results revealed that Kesterite CZTS is the major crystalline phase.•Post-annealed films demonstrated a high absorption coefficient (>104cm−1).•Post-annealed films showed an optical band gap between 1.46eV and 1.66eV.