Electrochromic Properties Of Amorphous WO₃ Films Prepared By Magnetron Sputtering

WO₃ is probably the most promising one of various electrochromic materials due to its excellent electrochromic properties, especially the amorphous tungsten oxide films. Because WO₃ film possesses many perfect performances, it can be applied in many fields such as display devices, smart windows, and antiglare rear-view mirror, etc.In this paper, the history, the variety and the theoretical models about the electrochromism based on different electronic structures of eletrochromic materials were introduced, and also the preparation and applications about the eletrochromic films. The rationale, development and applications about magnetron sputtering technique, and the study on the WO₃ films were summarized simply.Amorphous WO₃ films and Ti-doped WO₃ films were prepared by mid-frequency dual-target magnetron sputtering using pure tungsten and pure titanium targets.X-ray diffraction, scanning electron microscopy, X-Ray photoelectron spectroscopy (XPS) and spectrophotometer were used to characterize the structure, morphology composition and transmittance properties of the films, respectively. The effects of oxygen flow and heat treatment temperature on the films were studied. The spectral transmittance of the films treated at different temperature between colored and un-colored state and the volt-ampere Characteristics and the responding speed were tested to find out the best parameters to deposited films. Also the effect of heat treatment, oxygen content and doped on the microstructure of the films was studied.The results show it is available to deposit WO₃ electrochromic films. The as-deposited films prepared at room temperature are amorphous and deposited at higher oxygen content, annealing at proper temperature and Ti-doped show a good electrochromic property. In this paper, the films deposited at almost pure oxygen content show good electrochromism after annealing at 200 ℃, the variation of average transmittance difference between the bleached and colored state can reach up to 50% in the wavelength range between 380nm and 780nm. Ti-doped can enhance the response speed and service life, because of that the Ti atoms make the structure aberrant, which is more convenient for Li⁺ ions to inject into films corresponding to the doped films than un-doped ones. At the same time, the congener atoms congregated make the useful octahedral WO₃ decreased, so the electrochromism decline.