Synthesis and electrochromic behavior of lithium-doped WO3 films

The electrochromic properties of amorphous peroxotungsten films prepared via the sol–gel route were determined. By means of the addition of LiCF3SO3 to the precursor solutions, films with different electrochemical properties were obtained. The electrochromic properties of the films were investigated using in situ spectroelectrochemical method and impedance measurements in propylene carbonate (PC) with 0.1 M LiClO4 as electrolyte. During the cathodic polarization at −0.7 V, a blue color was observed with a reversible variation between 25% and 80% of the transmittance in the visible and near infrared range in the 5 mol% doped film. It reached a maximum cathodic charge density of 8 mC/cm2. The bleaching process in the lithium-doped films was complete, whereas in the films without Li+, a residual color was observed. The impedance response of the WO3 films showed the influence of the doping level on the electronic conduction and ionic transport of Li+ through the films.