Yellow tungsten oxide is an electrochromic material, with high coloration efficiency, good reversibility, short response time, long service life and low cost. It has a very broad application in the rearview mirror and the windshield, flat panel display, electronic storage devices, electrochromic window etc. The electrochromic mechanism is related to different valence of tungsten ions and different chemical environment of oxygen ions. XPS can characterize tungsten ions valence to study the mechanism of color change. In colored state in the film, W6+ and W5+ are existed, while in bleached state, there is only W6+.
XPS is a technology using information of photoelectron intensity and electrons angular distribution to study the electronic structure of atomic, molecular and condensed phase, especially solid surface.