Structures and electrochromic properties of Ta0.3W0.7Ox thin films deposited by pulsed laser ablation

Electrochromic materials based on mixed metal oxides are of growing importance since improved durability, coloration efficiency and chemical stability, as well as a desirable neutral color could be accomplished in those multicomponent films. In this work, we have used the pulsed laser deposition technique to deposit thin films of Ta0.3W0.7Ox on ITO-coated glass substrates in reactive O2 gas environment at a substrate temperature range of 200 to 700 °C. X-ray diffraction results showed that Ta0.3W0.7Ox films begin to crystallize to a cubic phase at substrate temperatures near 700 °C, while films with amorphous structure were obtained at lower substrate temperatures. The lattice constants of the polycrystalline films are similar to those of stoichiometric Ta0.3W0.7O2.85 bulk materials. Optical transmittance of Ta0.3W0.7Ox films decreases as the O2 pressures during deposition decreasing from 5.32 Pa to 0.13 Pa. Electrochromic properties of the Ta0.3W0.7Ox films were evaluated in 0.1 M H3PO4 electrolyte and the results were compared to those of WO3 and Ta0.1W0.9Ox films deposited also by pulsed laser ablation. The results have demonstrated that the addition of one metal oxide (e.g., Ta2O5) into another (e.g., WO3) is an effective way to alter the electrochromic properties of the individual constituents.