Zinc doping effects on the microstructural, electrical and optical properties of nanostructured ZnxBi2-xS3 ([formula omitted]) thin films grown by ultrasonic spray pyrolysis

Abstract

Zinc-doped bismuth sulfide (Bi2-xZnxS3) nanocrystalline thin films were deposited on glass substrates by using an ultrasonic spray pyrolysis (USP) technique and their structural, morphological, electrical and optical properties experimentally addressed. X-ray diffraction (XRD) and micro-Raman spectroscopy have confirmed the generation of a single-phase polycrystalline orthorhombic material. The crystallite size and micro-deformation of the films was found to depend on the dopant concentration. The surface appears condensed and dense with a uniform spatial grain distribution, as revealed by scanning electron microscopy (SEM) images. Energy dispersive X-ray spectroscopy (EDS) studies revealed a certain Bi deficiency in both undoped and Zn-doped films. When the nominal Zn doping concentration increases from x = 0 to x = 0.09, the crystallite size decreases from 30 to 21 nm. The optical band gap of the films increased from 1.62 to 1.65 eV with Zn content increasing up to x = 0.06, then reducing to 1.58 eV for the maximum Zn content. Optical measurements showed a high absorption coefficient (α > 104 cm−1) in the visible and near-infrared ranges. The Urbach energy followed a similar behavior as a function of doping concentration. The electrical conductivity as well as the sheet carrier mobility of the Bi2-xZnxS3 films increase sharply by increasing the Zn content up to x = 0.06. For this doping concentration, mobility reaches 1.37 × 105 cm2/Vs while keeping carrier concentration above 1017 cm−3. Our experimental results provide strong evidence that Zn-doping is a suitable method to increase Bi2S3 light-harvesting efficiency in solar cell devices.