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

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 (K Omega) increase with the W:V atomic ratio in both planar films and inverse opal films series. K Omega plays a decisive role on coloration switching time, for instance, there exists a range of K Omega where switching time vastly decreases with an increase of K Omega and beyond this range, switching time is independent of K Omega and remains constant. The introduction of macroporosity, however, greatly reduces the low critic K Omega. CE is co-affected by both K Omega and Rct. K Omega and Rct collaboratively impact on EC cycling stability: K Omega plays a key role on cycling stability since the best cycling stability corresponds to highest K Omega. 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 Omega.