Effect of coating temperature on the physical properties of Bi₂S₃ thin films for photodetector applications

In this study, nebulizer spray pyrolysis was used to develop Bi₂S₃ thin films at various coating temperatures (250 to 375 °C) for photodetector application. Studies on the Bi₂S₃ thin film’s structural, morphological, and optical effects upon coating temperature were conducted. The Bi₂S₃ thin films feature an orthorhombic structure, with the increase in crystallite size as the coating temperature increases at 350 °C. Using FESEM measurement, the morphology of the thin film surface has uneven grain shape and size distribution which improves upon high coating temperature. The increment in optical absorbance and decrement in bandgap was observed with the increase in coating temperature through UV–Vis. spectroscopy. According to photoluminescence spectroscopy, the excitonic recombination and existence of defects related to Bi and S ions in the host material caused the origin of luminescence peaks. Finally, the calculated optical sensing metrics, including responsivity (R), detectivity (D*), external quantum efficiency (EQE), and response/ decay times were found to be 1.58 × 10⁻¹A/W, 9.75 × 10⁹Jones, 50.8%, and 0.3/0.4 s, respectively for the Bi₂S₃ film coated at 350^◦C based photodetector. The results of this study suggest that the bismuth sulfide thin film photodetector coated at 350 °C could be optimal for use in commercial optoelectronic applications.