Amorphous WO3 ･H2O films were fabricated via spin-coating of a WOCl4 solution at a low temperature of 80 °C, and the influence of gas atmosphere during film formation on electrochromic (EC) performances was systematically investigated. The films prepared under an Ar atmosphere exhibited a relatively porous morphology compared to those formed under air, which showed a more uniform and compact surface structure. These morphological differences significantly affected charge transport and electrochemical behavior. In particular, the films formed under air demonstrated enhanced electrical conductivity and faster ion transport due to the formation of a uniform surface morphology, leading to superior response speed and coloration efficiency. In contrast, films formed in the Ar atmosphere suppressed partial crystallization of WO3, thereby increasing the amorphous WO3 ･H2O fraction with abundant oxygen bonding sites that act as electrochemically active sites. This characteristic enabled a wider optical modulation during coloration. These results indicate that processing gas-atmospherecontrolled amorphous WO3 ･H2O films at low-temperature is an effective strategy for improving EC performance and expanding their applicability to flexible devices and energy-efficient smart window technologies.

In the present study, vanadium oxide(V2O5) films for electrochromic(EC) application are fabricated using sol-gel spin coating method. In order to optimize the EC performance of the V2O5 films, we adjust the amounts of polyvinylpyrrolidone(PVP) added to the solution at 0, 5, 10, and 15 wt%. Due to the effect of added PVP on the V2O5 films, the obtained films show increases of film thickness and crystallinity. Compared to other samples, optimum weight percent(10 wt%) of PVP led to superior EC performance with transmittance modulation(45.43 %), responding speeds(6.0 s at colored state and 6.2 s at bleached state), and coloration efficiency(29.8 cm2/C). This performance improvement can be mainly attributed to the enhanced electrical conductivity and electrochemical activity due to the increased crystallinity and thickness of the V2O5 films. Therefore, V2O5 films fabricated with optimized amount of PVP can be a promising EC material for high-performance EC devices.