Fabrication of electrochromic TiO2:Nb films by ultrasonic spray pyrolysis

Abstract

In this work, Nb-doped TiO2 (NTO) films were fabricated on the ITO glass substrates by ultrasonic spray pyrolysis (USP) method. The effects of deposition temperature and film thickness on the microstructure and electrochromic property of NTO film were investigated. With the increase of deposition temperature, the crystallinity of NTO films is improved and the substitution rate from Ti4+ to Nb5+ is increased, leading to an enhancement of the film electrochromic properties. Additionally, the growth direction of NTO grains strongly depends on the film thickness. With increasing the film thickness, the grain growth changes from random to (004) plane orientation. Correspondingly, the surface morphology of NTO grains also have changed from “equiaxed structure” to “sheet structure”. The NTO films composed of sheet-structured grains are porous. The porous structure is good for Li+ ions insertion/extraction. In this case, the NTO films have a higher electrochromic property. When the film thickness is 300 nm, the NTO films with sheet-structured grains have the optimal properties, which exhibit the precise independent spectral control over material transmittance in the visible (vis) and near-infrared (NIR) regimes. The optical contrast (ΔT%) is 30.73% in vis region and 39.72% in NIR region. The coloring and bleaching time are 35s and 8s, respectively. Moreover, the electrochemical property is still stable after 1000 cycles.