Sol–gel thin film of CeO₂–SiO₂ as ion storage layer for electrochromic devices

Optical and electrochemical properties of the CeO₂–SiO₂ with 35 mol% of SiO₂ thin films deposited by sol–gel dip-coating process have been investigated. The films were deposited by dip-coating technique at a rate of 10 cm min⁻¹ and then heat treated between 300 and 400 °C during 30 min. The influence of heat treatment on electrochemical properties was investigated. Images from a scanning electron microscope (SEM) demonstrated the films’ homogeneity, and energy-dispersive spectroscopy (EDS) confirmed their elemental distributions. Optical measurements were used to evaluate optical characteristics, including transmittance and indirect bandgaps. As the film temperature increased, the indirect optical bandgap of the CeO₂–SiO₂ film was found to drop from 3.31 to 3.22 eV. The diffusion of lithium into the film was studied by electrochemical impedance spectroscopy, and the existence of SiO₂ and Ce valence state change was observed by XPS measurements. CeO₂–SiO₂ thin films are transparent in either the reduced or oxidized states. The feasibility for using these electrodes as ion storage for electrochromic devices was investigated.