Preparation of visible-light-active Ag and In-doped ZnS thin film photoelectrodes by reactive magnetron co-sputtering

Ag and In-doped ZnS thin films were prepared by direct current and radio frequency reactive co-sputtering of a zinc target and an indium target covered by Ag wires in gas mixtures of argon and hydrogen sulfide. The influences of the various deposition parameters on the structural, optical and electrical performances of thin films as visible-light-active photoelectrodes have been investigated. The X-ray diffraction data revealed that the polycrystalline (Ag, In, Zn)S thin films contain mixed structures of AgIn₅S₈ and ZnS. The images from an atomic force microscopy showed that the surface roughness was significantly increased with incremental increases of plasma power, resulting in increases of the refractive index and the reduction in photocurrent. The film deposited in the optimal deposition parameters, DC and RF powers at 50 W using a hydrogen sulfide ratio of 0.40 with a substrate temperature of 300 °C, exhibits the smallest refractive index, highest donor density, and the highest photocurrent density under illumination with a solar simulator (AM 1.5) at + 1.00 V vs. Ag/AgCl. The band-gap energies of as-prepared films are found to be in the range of 2.28 to 2.39 eV and flat-band potentials determined by application of the Mott-Schottky equation vary from - 0.55 to - 0.68 V versus normal hydrogen electrode.