Optical properties and electrochromic characterization of sol–gel deposited ceria films

Ceria (CeO2) films were deposited by the sol–gel spin coating process and optical and electrochromic properties have been investigated. Ceria coating solutions were prepared using cerium amonium nitrate and ethanol. The films were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-visible (UV–Vis) spectroscopy and cyclic voltammetry. XRD analysis of the films showed that they had a cerianite structure for heat treatment temperatures at or above 450°C. XPS examinations show that the film stoichiometry was CeO2. The SEM examinations showed that the surface texture was very uniform and homogeneous. Optical constants of the films were calculated from transmitance (T) spectra using optical spectrometer in the wavelength range of 300–900 nm. The refractive index (n), and extinction coefficient (k) values were n=1.82±0.01 and k=0.02±0.002 at 550 nm, respectively. The optical bandgap (Eg) of crystalline cerium oxide film was 3.1±0.003 eV. The electrochemical behavior investigated in 0.5 M LiClO4 propylene carbonate (PC) electrolyte. Cyclic voltommetry showed a reversible electrochemical insertion or extraction of the Li+ ions maintaining a high optical transmissivity. Spectroelectrochemistry showed that these films could be used as optically passive counter-electrode in transmissive electrochromic devices.