Preparation and electrochromic properties of NiO and ZnO-doped NiO thin films

Great optical contrast, high coloration efficiency, short response time, and good cycling stability have become the key to achieving large-scale application of electrochromic materials. In this paper, NiO thin films and ZnO-doped NiO thin films were prepared using magnetron sputtering technology. The microstructure and electrochromic properties of thin films were studied using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), electrochemical workstation and UV spectrophotometer, and the optimal preparation parameters of NiO thin films were found. The results show that NiO thin films with sputtering power of 150 W, Ar:O2 of 50:6, working pressure of 2.0 Pa and sputtering time of 20 min displayed the best electrochromic properties. In the electrolyte of 1 mol/L KOH, the optical contrast was 74.04% (@550 nm), the coloration efficiency was 8.73 cm2/C, the coloration time was 1.67 s, and the bleaching time was 1.26 s. ZnO-doped NiO thin films were prepared with the optimal parameters of NiO thin films. The results show that the ZnO-doped can improve the bleached state transmittance of the thin films. Moreover, the optical contrast reached 78.20% (@550 nm), the coloration efficiency was 11.20 cm2/C, and the cycling stability of the thin films was greatly improved. The results of electrochemical impedance measurement show that ZnO-doped in NiO thin films can reduce the charge transfer impedance and ion diffusion impedance, which is conducive to electrochromic reactions.