Charge Movement through Electrochromic Thin-Film Tungsten Trioxide

A detailed survey is given of the models devised to describe the kinetics of charge movement, both electronic and ionic, through thin-film tungsten trioxide WO3 during either reduction or oxidation. The principal models are those of Faughnan and Crandall, Green, Ingram Duffy and Monk, and of Bohnke. Adjuncts and adaptations of these models are discussed also. The inherent assumptions and kinetic details of each model are outlined, and comparisons made both between each model, and with additional data from the extensive literature on WO3 and other solid electrochromes. Because thin-film WO3 is electrochromic, much additional information can be gleaned from optical data regarding the electro-coloration and electro-bleaching reactions, as optical effects allow an additional ‘probe’ of the physicochemical processes occurring within the solid-state WO3 during electrochemical change. Many of the implications of this work may also be applied to charge transport through films of other transition-metal oxides—electrochromic or otherwise—so many other electrochromic metal oxides are also mentioned and discussed.