When it comes to electrochromism, you may think of hydrated tungsten trioxide film, which is important for researching. And such film may be more and more widely applied on smart windows. Therefore, people have begun to become interested in the preparation process of hydrated WO3 film.

WO3 electrochromic film is a smart material that can be applied to architectural glass to obtain the so-called smart windows for thermal insulation and energy conservation. There are many methods for preparing such WO3 electrochromic film, such as, a spray method, a hydrothermal method, and an electrodeposition method.

Nano WO3 electrochromic film can be prepared by a hydrothermal method. At present, many researchers have adopted hydrothermal method to prepare nano WO3 films. However, preparation of WO3 film by hydrothermal process is complicated with cumbersome steps. And high temperature long-term reaction is often required. Also, the seed layer coated on the surface of the conductive substrate is required to be high. In addition, the preparation conditions including high temperature and high pressure limit the choice of conductive substrates.

Smart material mentioned here refers specifically to smart glass, i.e., electrochromic glass, and tungsten trioxide can be used in this new type of smart glasses. Why can WO3 be applied in building glasses for building energy efficiency?

Mo-doping tungsten oxide film can be prepared by doping molybdenum oxide (MoO3) into a tungsten oxide film. The tungsten oxide film with different MoO3 doping ratio can be prepared by electron beam evaporation method. Among them, the doping of Mo element has a certain influence on the electrochromic properties of WO3 film.

Cycle performance of Ti-doping tungsten trioxide electrochromic film is superior to that of undoped WO3 film. This is because during the lithium ion injection process, the WO3 transforms from the monoclinic phase to the cubic phase, while the Ti-doped WO3 has no change in crystal structure before and after discoloration. And the lattice strain caused by discoloration is reduced. That is to say, the energy barrier to be overcome is reduced, the roughness variation is reduced. And thus the cycle performance of Ti-doping WO3 film is superior to that of the undoped WO3 film.

Compared with the pure WO3 film, the Ti doped tungsten oxide film has no change in the color change amplitude. While the coloring and fading response speeds are obviously increased. And the amount of charge stored in the reaction is increased. Moreover, after a plurality of cycles, the current decay becomes small, the cycle stability increases, and the film cycle life increases. In addition, WO3 is converted from a monoclinic system to a cubic system. And at the same time, Ti4+ ions suppress grain growth to make the degree of crystallization lowered.

Ti-WO3 film is more favorable for the electrochromic reaction than the undoped WO3 film. Experts said that comparing the SEM image of WO3 and Ti-doped WO3 film, as shown below, you can see:

Some experts have prepared the Ti doping tungsten oxide electrochromic film by the following methods in order to study the influence of different oxygen partial pressures on the structural properties of Ti doped WO3 thin films.

Some experts prepared Ti-doped tungsten trioxide film on FTO conductive glass substrates by pulsed DC reactive magnetron sputtering method under different oxygen tension conditions. They found that: