Substrate temperature effects on the structural, morphological and optical properties of Bi2S3 thin films deposited by spray pyrolysis: An experimental and first-principles study

Bismuth sulfide (Bi2S3) nanostructured films were deposited on glass substrates using a spray pyrolysis method. Herein, we present a study of the effect of substrate temperature (TS) on the structural, morphological, and optical properties of the prepared nanocrystalline thin films. X-ray diffraction (XRD) and Raman spectroscopy analyses revealed the formation of polycrystalline orthorhombic Bi2S3 films. The crystallite size and micro-strain of the films changed as the substrate temperatures was varied. Scanning electron microscopy (SEM) images show a compact and dense surface, with a uniform spatial distribution of nearly spherical grains. Energy-dispersive X-ray spectroscopy (EDS) studies confirm the prevalence of Bi and S elements in the films, being films deposited at a temperature of 400 °C sulfur deficient. The crystallite size increases from 18 to 22 nm when Ts varies from 400 °C to 300 °C. The optical band gap of the films was found to vary between 1.44 and 1.58eV, while a high absorption coefficient (>104 cm−1) was measured in the visible and near-infrared spectral ranges. These experimental results were compared with ab initio calculations performed in the framework of the density functional theory (DFT). The band structure and density of states (DOS) of the Bi2S3 compound reveal an n-type semiconductor with a direct gap of about 1.52 eV. Both experimental and theoretical results provide strong evidence that our bismuth sulfide thin films can be suitable materials for light-harvesting in solar cell devices.