The metal halide perovskite solar cell has been progressively attaining the appreciable value of efficiency but it is not environment friendly due to the toxic nature of Pb. Similarly, Si solar cell has high production cost so alternative cheap, environment-friendly, and earth-abundant material is needed to mitigate the energy crisis for human civilization. The bismuth sulfide-based material could be the alternative solution to fulfill today’s energy demand because of its wide range of features in optoelectronics and photovoltaics. Among them, Bi-S-O compounds are recently studied in very few numbers in electrocatalytic, humidity sensing [1,2]. In our work, for the first time, we have studied the photovoltaic properties of the new bismuth oxysulfate compound by simple spin coating deposition method and compared it with those of Bi₂S₃ material. There are numerous factors to enhance the performance of the solar cell, annealing temperature is one of the important factors to change the morphology, optical, electrical, and structure of the thin film material.

Bismuth nitrate and thiourea were dissolved in 2-methoxyethanol and the thin films were synthesized via the spin coating method with changing annealing temperature. The annealing temperature changes the Bi₂S₃ thin film of low band gap to the bismuth oxysulfate material of high band gap along with the advancement of both open voltage and current. The structure change was confirmed by the XRD and UV-vis spectrometer. A similar kind of topological change from Bi₂S₃ precursor to bismuth oxysulfate is reported by Runze Ye et al. [1]. The thin film of Bi₂S₃ material is formed up to 360⁰C annealing temperature and above this temperature material is changed into the new family of bismuth oxysulfate material. The morphology and structure are also changed such as at low annealing temperature nanowires of Bi₂S₃ are found but at 360⁰C and higher temperature slightly thinner nanowires of bismuth oxysulfate are observed which are shown in Fig. 1. The structure of the solar cell is shown in Fig. 3. At 420⁰C annealing temperature, the open voltage is appreciably increased to as high as 0.75 V [Fig. 2] however PCE is low due to the high band gap and some other defects. Many electrical and optical properties of this family of new compound bismuth oxysulfate are still under deep observation and calculation. SEM image and EDS analysis confirmed the formation of the derivative of bismuth sulfide material at the higher annealing temperature. Hence, bismuth sulfide-based material could be an important promising material optoelectronic technology in the future era.