Electrochromic Behavior Of WO₃ Thin Films Prepared By RF Magnetron Sputtering

As one of the most attractive and widely studied inorganic electrochromic materials WO3 has high coloration efficiency, good optical modulation properties and memory effects under open circuit conditions. In this study, we deposited WO3 films with good electrochromic performance by radio frequency magnetron sputtering at room temperature. Relationship between microstructure and electrochromic properties of WO3 films under different process parameters was qualitatively analyzed. Then we explored the cycle stability and solid electrochromic devices based on WO3 films. The main contents of the research are as follows:(1) The microstructure, morphology and reflectance index of the WO3 films under different preparing conditions (working pressure and oxygen partial pressure)have been analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and spectroscopic ellipsometer respectively. The results shows that with the increasement of working pressure, the crystalline phase changes to amorphous phase gradually and the film surface becomes more rough. And also the film density decrease could be found from an attenuation of reflectance index owing to the increasing working pressure..(2) The cyclic voltammetry properties, time response characteristics and optical modulation properties of as-prepared WO3 films in an acid electrolyte have been analyzed at an electrochemical workstation with a UV-visible spectrophotometer. The results shows that increasing the working pressure improves the cyclic voltammetry and optical modulation properties and speeds up the coloring and discoloring process of WO3 films.(3) A very thin SiO2 film is deposited on the WO3 film by RF magnetron sputtering. The cyclic voltammetry curve and optical transmittance spectrum of the WO3 film with or without SiO2 after many cycles have been tested either. The results tend to be clear that a thin SiO2 film protective layer on the WO3 film is very effective to improve the cycle stability both in acid electrolyte and organic lithium electrolyte, thus is a promising approach for practical application.(4) The Glass/ITO/WO3/PMMA+LiClO4+PMMA/ITO/Glass solid electrochromic device had been assembled, which can basically show good electrochromic behavior. But to achieve the same optical modulation range the solid device needs higher operating voltage compared with WO3 film in liquid electrolyte, because of the low Li+ conductivity of gel electrolyte. And the solution to this problem needs to be further explored.