Nanostructured bismuth sulphoselenide (Bi₂(S_1−xSe_x)₃) thin films have been synthesized using a simple, cost-effective chemical bath deposition (CBD) method at room temperature (300 K). Structural, compositional, morphological and optical characterization and photoelectrochemical performance testing of these Bi₂(S_1−xSe_x)₃ thin films has been carried out. The X-ray diffraction (XRD) study demonstrates that these thin films are nanocrystalline in nature with pure orthorhombic crystal structures. X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS) show that the deposited thin films are nearly stoichiometric in nature. Field emission scanning electron microscopy (FESEM) reveals different morphologies for the Bi₂(S_1−xSe_x)₃ thin films. The linear nature of the plots seen in the UV-Vis-NIR absorption study confirms the direct allowed type of transition. J–V measurements with a solar simulator were carried out for all samples and the highest photoconversion efficiency, 0.3845%, has been recorded for the Bi₂Se₃ thin film. The significant boost in photoelectrochemical (PEC) performance might be due to the larger surface area with lower dislocation density and microstrain with a lower level of grain boundary resistance of Bi₂Se₃ thin films.