Effect of zirconium doping on structural, optical, and electrochemical properties of NiO thin films: Electrochromic application

Abstract

Herein, we deposited pure and Zirconium-doped nickel oxide (NiO) thin films on amorphous glass and ITO-coated glass substrates using the chemical spray pyrolysis method. Then physicochemical properties such as the crystalline structure, morphology, optical behavior, and electrochemical performance are studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV-Vis-NIR spectrophotometry, voltammetry (CV), and chronoamperometry (CA) measurements. XRD pattern shows a single polycrystalline cubic phase with a typical preferential growth along (111) plane. The purity of the crystalline phase is confirmed by Raman spectra that show only two vibration modes corresponding to NiO material. SEM images exhibit relatively smooth and homogeneous surfaces without major cracks. Optical analysis shows a relatively high transmittance for all films about 70 %-80 % in the visible and IR optical light ranges. The electrochemical investigation revealed that all the films presented a pseudo-capacitive behavior. The specific capacitance increased due to zirconium doping reaching its maximum for the NZO6 sample (75 F.g−1 at 10 mv.s−1) in comparison with the undoped one (46 F.g−1 at 10 mv.s−1). The NZO2 thin film demonstrated the shortest response times to the bleaching/coloration process (tb = 3.37 s / tc = 4.68 s), an improved optical modulation (49 %), and the highest coloring efficiency (65.52 cm2.C−1). The outcomes of this investigation propose that the fabricated Zr-doped NiO thin films are potentially useful materials for application as anodic-colored electrodes in electrochromic devices.