Impact of impedance on electrochromic properties of W-doped V2O5 films

Abstract

Two series of W-doped V2O5 films, planar films, and inverse opal films, were synthesized. The evolution of their electrochromic properties, including switching time, cycling stability, and color efficiency (CE), were systematically investigated as a function of electrochemical impedance. Both charge transfer resistance (Rct) and ion diffusion ability (KΩ) increase with the W:V atomic ratio in both planar films and inverse opal films series. KΩ plays a decisive role on coloration switching time, for instance, there exists a range of KΩ where switching time vastly decreases with an increase of KΩ and beyond this range, switching time is independent of KΩ and remains constant. The introduction of macroporosity, however, greatly reduces the low critic KΩ. CE is co-affected by both KΩ and Rct. KΩ and Rct collaboratively impact on EC cycling stability: KΩ plays a key role on cycling stability since the best cycling stability corresponds to highest KΩ. Rct plays its role only when it is low enough to reduce the possibility of chemical dissolution of the intermediate product of vanadium-containing ions: the present critical value could be around 76 Ω.