Electrochromic effect refers to the optical property of materials, which means the color of the materials carry out a stable and reversible changing phenomenon under the effect of the current or the applied electric field. WO₃ is the most typical non-organic electrochromic material, the electrochromic film which is made of it has been most studied, with the high coloration efficiency, good reversibility, short response time, long life, low cost, and other advantages, it meets the future development trend of smart materials. This film has a wide range of applications in the fields, like architectural dimming window, rearview mirror and windshields, electrochromic storage device, flat panel displays ect..

 

Fully understand the electrochromic mechanism is not only the prerequisite for preparing practical electrochromic thin films, but also the essential condition for making the electrochromic film properties for the full application. Currently, the generally accepted of interpretation model is that the ions and electrons have co-implantation on both sides of the film, thus leading to the occurrence of film electrochromic, the reaction equation is as follow:

WO₃+xM⁺+xe^- ＝M_xWO₃ (blue) [wherein the reaction promoting to the right means coloring process, push left means fading process]

M in the formula refers to H+ or Li+ ions of small radius positive;

 

Since the semiconductor property of the tungsten trioxide, when the electrons have been injected and localized on the particular W⁵⁺ ions, also they enter 5d orbit, and W⁵⁺ ions also resides within this, then its internal tends to maintain electrical neutrality, thus forming MxWO₃; and since W⁵⁺ and W⁶⁺ ions coexist with the mix prices and exist respectively on two levels, then to produce the electron energy transition and to generate the electrochromic phenomenon. The original state of WO₃ electrochromic thin film appears in a slight blue, during the energized reaction, the film gradually turns to show a deepen color, while with the continuous reaction time, the film constantly changing color from pale blue to the final dark blue; during the bleaching process, the film color is gradually changing from dark blue back to the original light blue, but a slightly deeper than the original state.