Abstract
<title>Abstract</title> <p>Nanosphere-structured n-CuIn(S,Se)₂ thin-film photoanodes were successfully deposited on fluorine-doped tin oxide (FTO) substrates using a low-temperature chemical bath deposition (CBD) technique at 60°C. The effect of Cu/In compositional variation (1.35–4.21) on the structural, morphological, optical, electrical, and photoelectrochemical (PEC) properties of the films was systematically investigated. X-ray diffraction (XRD) analysis confirmed the formation of a dominant chalcopyrite CuIn(S,Se)₂ phase with a strong (112) preferential orientation and an average crystallite size of approximately 19 nm, indicating nanocrystalline growth. Energy-dispersive X-ray analysis (EDAX) revealed non-stoichiometric compositions with controlled Cu/In ratios. FESEM and AFM studies demonstrated the formation of uniform, crack-free nanosphere morphologies, with grain sizes decreasing from 43 to 23 nm as the Cu/In ratio decreased. TEM, HRTEM, and SAED analyses further verified the spherical nanostructure, high crystallinity, and polycrystalline nature of the films, with an interplanar spacing of 0.158 nm corresponding to the (112) plane. Optical measurements showed strong absorption in the visible region and a tunable direct band gap ranging from 1.54 to 2.24 eV, attributed to quantum confinement effects. Electrical conductivity increased with temperature, confirming semiconducting behavior, while the activation energy decreased with increasing Cu/In ratio. PEC studies revealed that films with lower Cu/In ratios exhibited enhanced photoelectrochemical performance. The optimized photoanode (G6) delivered the highest short-circuit current density of 60 mA cm⁻² and maximum power output. These findings demonstrate that compositional engineering of nanosphere CuIn(S,Se)₂ thin films is an effective strategy for improving PEC performance, highlighting their potential for high-efficiency solar energy conversion applications.</p>