Preparation of Nb-doped TiO2 films by sol-gel method and their dual-band electrochromic properties

Abstract In this paper, Nb-doped TiO2 films were fabricated on ITO glass substrates by dip coating using tetrabutyl titanate as the starting material, niobium chloride as the dopant, acetylacetone as the chelating agent and methanol as the solvent. The effects of Nb doping on the microstructure and electrochromic properties have been studied. The results reveal that a simultaneous regulation of near-infrared (NIR) and visible light in pure TiO2 films can be achieved by applying the electrochemical voltage, while Nb-doped TiO2 films demonstrate the ability of selective and independent optical transmittance modulation in both regions. Varying the applied electrochemical voltage over a range of 3.5 V makes these Nb-doped TiO2 films undergo two electrochromic processes. One is local surface plasma resonant (LSPR) electrochromic process, and the other is redox electrochromism. These two electrochromic effects result in a unique optical switching behavior that is the reversible switching of “bright and warm” - “bright and cool” - “dark and cool” modes. Therefore, this kind of materials enables the dynamic control of solar radiation transmittance through windows. Furthermore, the higher the amount of Nb dopant is, the stronger the LSPR electrochromism is. Finally, the enhanced LSPR improves the redox electrochromism of Nb-doped TiO2 films, resulting in a higher dual-band electrochromic performance in NIR and visible regions.