Abstract
Thin films of the BiSI/Bi 13 S 18 I 2 semiconductor compound were synthesized via a simple chemical bath deposition method from solution. The deposition duration significantly affects the morphology, phase composition, and crystallinity of the resulting films. Optimized deposition conditions resulted in homogeneous microstructures with preferred crystallographic orientation and stable chemical composition, as confirmed by Scanning Electron Microscopy (SEM), X‐ray diffraction, and Energy‐Dispersive X‐ray Spectroscopy (EDX) analyses. Photoelectrochemical studies demonstrated that both the composition and pH of the electrolyte markedly influence the photocurrent density, charge transfer efficiency at the semiconductor/electrolyte interface, and the incident photon‐to‐current conversion efficiency. Comparative photoelectrochemical measurements in different electrolytes containing iodide (I − ), sulfide (S 2− ), or their combination revealed the synergistic effect of redox‐active species on the interfacial charge dynamics and overall device performance. A maximum photocurrent density of 350 μA/cm 2 , a charge transfer efficiency of ≈85%, and an incident photon‐to‐current efficiency of ≈52% were achieved under monochromatic illumination ( λ = 465 nm, 10 mW/cm 2 ) in a mixed electrolyte containing 0.05 M KI and 0.05 M Na 2 S in 0.5 M Na 2 SO 4 . These results confirm the promising potential of BiSI thin films as efficient photoanode materials for use in photoelectrochemical cells, visible‐light‐driven sensors, and other optoelectronic or solar energy conversion devices.