Investigation of electrochromic properties of tungsten oxide (WO3) thin films

In this study, Al:WO3 arrays were grown on ITO glass substrate by three electrode electrodeposition method. After production, Al:WO3 films were left to annealing in an argon atmosphere at 450 oC for 2h. Electrochromic properties of the films were investigated in a the 1 M LiClO4 (propylene carbonate) electrolyte. Under the potential bias of ± 1,0 V, the color transformation from transparent to blue was appearently seen. According to XRD analysis results, the films have a good crystalline structure. The EDS analysis show that the incertion of Al element into the lattice of WO3. Direct band gap energies are 3,62 and 3,34 eV for the WO3 and the Al:WO3, respectively, according to the optical absorbtion analysis. From the comparision of as-prepared WO3 and Al:WO3 films, Al:WO3 film shows an excellent electrochromic properties. The optical modulation of Al:WO3 film is 55,9%, the coloration efficiency 148,1 cm2C-1, response times are 1,23 s for coloring and 1,01 s for bleaching. Al:WO3 film has a cycle stability at the wavelength of 632,8 nm. The charge transfer resistance based EIS analysis shows that the Al:WO3 film has an increased electrochemical active surface. Comperable results of WO3 and the Al:WO3's enerygy levels can be seen. The Mott-Schottky results gives us the Al:WO3 film's donor concentration is in the order of 1020 cm-3. When all these results are estimated together, Al:WO3 film is a towardly electrode for smart window and display technology, but also suggests a reachable, cheaper and effective way for production of doped metal oxide film researches.