Optimizing Cu ₂ SnS ₃ thin films through graphene interlayer integration and sulfurization temperature control

Abstract In this study, the effect of a graphene as an interlayer on the structural, optical and electrical properties of Cu ₂ SnS ₃ (CTS) absorber films was investigated. CTS thin films were deposited via spin coating onto glass substrates with and without graphene interlayer, followed by employing Rapid Thermal Processing (RTP) at 475 °C, 500 °C, and 525 °C for 300 s sulfurization process. CTS thin films composition were determined by the EDX technique and the results given all films displayed Cu-poor composition. XRD and Raman analyses revealed that films sulfurized at 475 °C were predominantly by monoclinic CTS phase with slightly suppressed secondary phases, whereas higher temperatures led to sulfur loss and CuS phase dominance, regardless of the presence of the graphene interlayer. SEM results showed that graphene-supported films exhibited smoother surfaces and more uniform grain distribution, especially at 475 °C. Optical measurements indicated that the band gap remained in the range of 0.98–1.04 eV, independent of graphene presence, aligning with reported values for monoclinic CTS phase. Hall effect measurements demonstrated p-type conductivity in all samples, with the highest carrier concentration obtained for the CTS film sulfurized at 475 °C (1.19 × 10 ¹⁹ cm ⁻³ ). These findings demonstrate that incorporating graphene and optimizing the sulfurization temperature at 475 °C significantly improves film quality, offering a potential approach for high-performance CTS-based solar cells.