Post-annealing-induced enhancement of structural, optical and electrical properties in copper tin sulphide (CTS) thin films

Abstract This study investigates the impact of post-annealing on the enhancement of structural, optical and electrical properties of Copper Tin Sulfide (CTS) thin films. The CTS thin films were synthesized using the Successive Ionic Layer Adsorption and Reaction (SILAR) method, then annealed at temperatures of 100 °C, 200 °C, and 300 °C and characterized using XRD, SEM, FTIR, UV–vis-NIR, and EDAX. The results show improved crystallinity, optical transmittance and electrical conductivity with increasing annealing temperature. The films show high bandgap energies (3.68–3.90 eV) and strong UV absorption. The transmittance curves reveal low transmittance in the UV region and high transmittance in the visible region. Post-annealing resulted in a decrease in film thickness, suggesting improved uniformity and density. An inverse relationship between crystallite size and bandgap energy was observed. These findings introduce a new paradigm for tailoring the bandgap energy and optical transmittance of CTS thin films through controlled post-annealing, enabling their application in high-performance optoelectronic devices.