Coloration dynamics of tungsten oxide based all solid state electrochromic device

An electrochromic thin film of amorphous WO₃nH₂O was fabricated by spin-coating a peroxo-polytungstate solution. Coloration and bleaching kinetics of the film in contact with a solid polymer electrolyte were investigated by a chrono-amperometric method using a cell, Li/Polymer/WO₃nH₂O, ITO. The transition currents were analyzed on the basis of a newly proposed theory for the diffusion-controlled current generated by a voltage step in such a cell without a reference electrode. It was found that both kinetics were controlled by the diffusion process and the chemical diffusion coefficients of lithium were, in common, about 5 × 10^-12 cm² s^-1.