Optoelectronic properties of In-doped SnS thin films

Abstract

Nanostructured un- and In-doped SnS thin films were deposited on fluorine-doped tin oxide (FTO) substrates via an electrochemical deposition technique. The deposited thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), photoluminescence (PL) spectroscopy and UV–visible spectroscopy. The XRD patterns demonstrated that all deposited thin films are made of polycrystalline SnS particles. The AFM images illustrated a distinct change in the surface topography of the SnS thin films due to In-doping. The PL spectra showed two blue emission peaks and a green emission peak for all samples. Also, they highlighted a PL peak for the In-doped thin films. The incorporation of In-dopant leads to enhance in the optical absorption of SnS lattice. The optical energy band gap (Eg) of the deposited thin films was estimated using UV–vis spectroscopy, which indicated that In-doping decreases the Eg value of SnS thin films by creating defect levels. The photocurrent results demonstrated a higher photocurrent response and photocurrent amplitude for the In-doped SnS samples relative to the un-doped SnS thin film. The Mott–Schottky analysis revealed p-type conductivity for all samples. In addition, the carrier concentration of SnS was increased after In doping. The EIS spectra declared that In-doping improves the rate of charge transfer for SnS thin films. The charge transfer resistance of In-doped SnS decreased compared to the undoped SnS thin film. Finally, according to the J-V characteristics, the conversion efficiency of the In-doped SnS thin films was higher than that of the un-doped SnS sample. Therefore, the optical and electrical performance of SnS thin films were improved due to In-doping.