The nanostructure of inorganic Bi2S3 semiconductor materials has been studied in recent years due to the wide range of features in optoelectronics and nanotechnology. The fundamental properties like low band gap (1.3–1.7 eV), high absorption coefficient, and nontoxic nature have captivated the attention of researchers in the solar cell sector. There are numerous factors to enhance the performance of the solar cell, likewise, annealing temperature is one of the important factors in thin film fabrication to change the morphology, optical, electrical, and structure of the material. In this work, the effects of annealing temperature on Bi2S3 thin films were studied and coincidently it was transformed into the new bismuth oxysulfate material of high band gap and transparent nature in high annealing temperatures. Both open circuit voltage (Voc = 0.75 V) and short circuit current (Isc = 0.06 mA/cm2) have been improved in bismuth oxysulfate thin film than the Bi2S3 phase. We have studied the photovoltaic properties of bismuth sulfide and bismuth oxysulfate materials along with their structure, optical, and surface morphology by using spin coating. The thin films of Bi2S3 material were formed up to 300 °C and above this temperature material was changed to bismuth oxysulfate material supported by XRD, band gap, and EDS results. The band gap of Bi2S3 thin film slightly increases from 1.6 eV to 1.8 eV and is almost constant at 3.7 eV in bismuth oxysulfate structure in increasing the annealing temperature. The nanowire structure of Bi2S3 was changed to the nanowire of bismuth oxysulfate at 420 °C and above this temperature, nanowires changed to spherical nanoparticles at 450 °C.