Compared with tungsten trioxide film, the coloring efficiency of Ta doped WO3 film is improved. In other words, the electrochromic property of the film is improved, wherein the threshold value of the Ta doping amount is 15%, and excessive doping is not favorable for the film to show high electrochromic efficiency.
Coloring efficiency is a parameter that is important for characterizing electrochromic properties. Coloring efficiency refers to the change in optical density caused by the injection of unit charge per unit area of electrochromic material at a certain wavelength, which is calculated asη=ΔVOD/Q=log(Tb/TC)/Q.
Where Q is the charge density injected, and Tb and TC are the transmittances of the color faded and colored films, respectively. The coloring efficiency η of the Ta doping WO3 film sample in the visible light range was calculated by the above formula as shown in the following figure.
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It can be seen from the above figure that when the Ta doping amount is 5% and 10%, the coloring efficiency of Ta-doped tungsten trioxide film is greatly improved compared with the WO3 film. When the Ta doping amount is 15%, the coloring efficiency of the film is comparable to that of the undoped WO3 film. However, when the doping amount is continuously increased, the coloring efficiency of Ta-doped WO3 film is significantly reduced, as shown in the sample E (WO3 film doped with 25% Ta) and the sample F (WO3 film doped with 35% Ta), the coloring efficiency is only about 10cm2/C and about 5cm2/C, respectively. It can be seen that an appropriate amount of Ta doping is beneficial to improve the coloring efficiency of WO3 film, and the threshold value of doping amount is 15%.
