Fast electrochromic effect obtained from solid-state inorganic thin-film configuration with a carrier accumulation structure

To improve the dynamic response of a solid-state electrochromic (EC) device, a new concept has been introduced into the EC operation. The device is composed of an indium tin oxide-coated glass substrate, a thin amorphous WO3 film, a thin SiO2 film, a thin amorphous Ta2O5 film, and a semitransparent top contact. The EC coloration and bleaching are measured by transient evolution in the optical transmittance under a positive or negative bias voltage V-b. The experimental results show that the response time at which the transmittance becomes 70% of the initial value reaches 100 ms at V-b=3 V. From voltammometric analyses, it is suggested that the inserted thin SiO2 film acts as a barrier for holes and electrons against diffusion or leakage, and that both the production rate of protons at the SiO2/Ta2O5 interface and their subsequent intercalation into the WO3 film are significantly accelerated. This approach is promising for the development of practical solid-state inorganic thin-film EC devices, such as a smart window and paperlike passive display.