Investigation on intermediate band formation and photoresponsivity enhancement of spray deposited Sn doped CuGaS2 (CuGa1-xSnxS2) thin films

•Partial substitution of Ga by Sn in CuGaS2 thin films is achieved via a facile spray route.•Optical studies confirm the Sn-induced intermediate bands in CuGaS2.•Additional humps in PL spectra confirm intermediate band transitions.•Photoresponsivity of 0.173 A/W is observed for 0.02 at.% Sn-doped CuGaS2. The intermediate band in CuGa1-XSnXS2 chalcopyrite has been explored through both theoretical and experimental approaches. Structural and electronic properties of pristine and Sn-doped CuGaS2 were analyzed using density functional theory (DFT) and various characterization techniques, including PXRD, SEM with EDS, XPS, UV–Vis-NIR spectroscopy, and Hall measurements. The films exhibited a polycrystalline tetragonal structure with sprouts and tiny rod-like particles on the surface, as observed from the SEM analysis. EDS results confirmed the uniform distribution of elements in the films, matching the intended doping composition. XPS analysis confirmed the valence state of Sn, indicating Sn4+ as the dominant oxidation state in the doped films. Sn doping reduced the optical bandgap from 2.53 eV to 2.50 eV, and an intermediate band was observed between 1.04 eV and 0.87 eV. The 0.02 at.% Sn-doped CGS films demonstrated the lowest resistivity (2.23 × 10−3 Ω·cm) and highest carrier concentration (9.13 × 1021 cm−3), showing enhanced photoresponsivity (0.173 AW−1 compared to 0.08 AW−1 for pristine CGS). The results indicate that Sn-doping successfully introduces an intermediate band without significantly altering the crystal structure or material integrity. The 0.02 at.% Sn-doped CGS (CuGa0.98Sn0.02S2) material emerges as a promising candidate for intermediate band solar cells, offering improved electrical and optical properties.