Preparation and photoelectric properties of holmium-doped bismuth sulfide film

Ho-doped Bi2S3 film (Ho/Bi2S3) was prepared on the FTO substrate by successive ionic layer adsorption reaction (SILAR) and hydrothermal method. The as-prepared films were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), UV–Vis diffuse reflection spectroscopy (DRS), and X-ray Photoelectron Spectroscopy (XPS). EDS and XPS have confirmed the existence of Ho. The Ho3+ ions enter the crystal lattice of Bi2S3 and occupy the Bi3+ sites making some crystals vertical flake-like. The photovoltage of Ho/Bi2S3 increases from 0.203 V to 0.265 V by 30% and the photocurrent density increases from 0.366 mA/cm−2 to 1.09 mA/cm−2 by 1.97 times when the Ho-doping concentration is 0.5 mmol L−1. Moreover, the impurity level introduced by Ho-doping reduces the energy of the electronic transition making Ho/Bi2S3 generate more photo-generated carriers to improve the photoelectric performance.