Fabrication of Cu-rich CZTS thin films by two-stage process: Effect of gas flow-rate in sulfurization process

Abstract

In this study, CZTS thin films were prepared using a two-stage process consisting of sputter deposition of Cu, Sn and ZnS layers on the glass substrates to form CuSn/ZnS/Cu stacked precursor films followed by sulfurization process under various flow-rate (0, 20, 40, 60, 80, 100 sccm) of Ar+H2 mix gas in a tubular furnace. The EDX measurements of the precursor and reacted films are Cu-rich and Zn-rich composition. However, Zn and Sn loss was observed for samples annealed under the flow-rate of gas above the 60 sccm. The XRD pattern of the samples showed diffraction peaks of pure kesterite CZTS structure and the FWHM values extracted from their XRD patterns and W-H plot calculations demonstrated that CZTS-40 thin film had a more desired crystallite size. The Raman spectra of the samples confirmed the formation of CZTS phase for all samples and indicated the formation of some secondary phases such as Cu2SnS3, SnS2, Sn2S3 except for CZTS-40 thin film. All the samples displayed dense and polycrystalline microstructure according to their SEM images. The optical band gap values of CZTS samples showed variation between 1.40 and 1.48 eV. The room-temperature PL spectra of the samples revealed a broad band that had a peak value at around 1.36–1.40 eV that are close to the optical band gap values for prepared CZTS samples.