Optical and Photocatalytic Properties of CuxS/ZnO Composite Thin Films Deposited by Robotic Spray Pyrolysis Deposition

Abstract

This article reports on VIS-active composite thin films based on zinc oxide (ZnO) and copper sulfide (CuxS) deposited using robotic spray pyrolysis deposition (SPD) for the study of the optical and photocatalytic properties. The first step involves the SPD deposition of a CuxS layer onto the glass substrate at 300°C. The second step consists of the deposition of a ZnO layer onto the CuxS layer to form glass/CuxS-ZnO composites that were further annealed at 400°C. The development of the composite thin films was confirmed by XRD and EDX analyses. The band gap energy ( $E_{\text{g}}$ ) of the bare ZnO thin films decreased from 3.15 eV to an activation energy value of 2.8 eV after the deposition of the ZnO thin layer onto the CuxS layer and from 2.8 to 2.08 eV after annealing the CuxS-ZnO composite at 400°C. The UV-VIS irradiation (5.5% of UV, $G=55\text{W}/{\text{m}}^2$ ) of a 10 ppm methylene blue solution was used to investigate the photocatalytic properties of the CuxS-ZnO composites. The annealed CuxS-ZnO thin films at 400°C demonstrates better photocatalytic activity compared to CuxS-ZnO composites deposited at 300°C. The enhanced photocatalytic efficiency of the annealed CuxS-ZnO thin films may be the result of the diode structure and the increased crystallinity that prevent the electron-hole recombination.