The effect of annealing time on the structural and optical properties of Cu3SnS4 hin films grown by spin coating method

In this study, Cu3SnS4 thin films were fabricated on limestone glass substrates using the spin coating technique under different annealing conditions. The films were prepared at 550 °C in a quartz furnace under nitrogen gas flow, using H2S:Ar (1:9) sulfur flow rates of 30 and 40 sccm for durations of 15 and 30 minutes. The morphological, optical, and crystalline properties of the samples were analyzed using various measurement systems, including AFM, UV-Vis, photoluminescence (PL), XRD, and Raman spectroscopy. X-ray diffraction (XRD) patterns revealed that all the Cu3SnS4 thin films had a polycrystalline structure. The crystallite size, dislocation density, microstrain, and crystallite number of the Cu3SnS4 thin films were calculated from the XRD spectra. Among the samples, the CTS-1 thin film, annealed for 15 minutes under a 30 sccm sulfur flow, exhibited the best crystalline structure. The surface morphology of the thin films showed spherical microcrystal formations. Analysis of the Cu3SnS4 thin films indicated that the surfaces were composed of valleys and peaks. The valley regions appeared relatively smooth, while the peak regions displayed a crystal structure with specific orientations. Ultraviolet-visible spectrophotometry (UV-Vis) measurements demonstrated that the absorption in the visible light range varied with sulfur flow rate and annealing time. The energy band gap ranged between 1.36 eV and 1.96 eV. The refractive index and high-frequency dielectric constant of the CTS samples were calculated using Herve and Vandamme, Moss, and Ravindra models, and the results were found to be consistent with each other. The PL spectrum revealed peaks at approximately 1.41 eV and 1.80 eV. A broad emission band was observed at wavelengths of 549 nm and 567 nm, as well as at 689.42 nm and 882.6 nm.