Enhanced electrochromic properties of TiO2 nanocrystal embedded amorphous WO3 films

Abstract

We investigated the effect of nanocrystalline TiO2 doping on the electrochromic properties of tungsten trioxide (WO3) films. Here, we prepared various TiO2 nanocrystal-embedded amorphous WO3 films by a simple one-step dip-coating method. XRD data of the films show amorphous nature for both undoped and nanoparticle TiO2 doped WO3 films with anatase phase of TiO2 having (101) plane, which were further confirmed by TEM measurements. XPS of TiO2 doped WO3 film shows +6 oxidation state of W atom, implying the stoichiometric WO3 composition. The electrochromic properties of the films were investigated by in situ spectroelectrochemical methods, showing the markedly different behaviors of the films depending on the amount of nanocrystalline TiO2 doped. In particular, charge deintercalation kinetics of the films were significantly affected by the content of nanocrystalline TiO2 in amorphous WO3 matrix with 7 times faster deintercalation process by 30 wt% of TiO2 doping into WO3 at the expense of the reduced bleaching transmittance. This phenomenon may be associated with the effect of nanocrystalline TiO2 particles on blocking accessibility of Li ions to the trapping sites which has to be de-trapped if the ions are to be released.