The Electrochromic Behavior of Indium Tin Oxide in Propylene Carbonate Solutions

We report on a study of transparent conducting tin‐doped indium oxide (ITO) electrodes in propylene carbonate solutions containing lithium ions. The system was studied using electrochemical methods in combination with in situ techniques: ultraviolet‐visible spectroscopy, X‐ray diffraction, and quartz crystal microbalance. The results show that the cathodic process at E ≳ 1.0 V vs. mainly involves the reduction of the electrolyte solution, leading to the formation of a thin, lithium‐rich surface film. At potentials ≲ 1.0 V vs. , degradation of ITO and the formation of metallic indium take place. No evidence was obtained that lithium‐ion intercalation into ITO, which has been suggested by several workers, occurs to a significant extent. We conclude that ITO probably cannot be used as a combined ion‐storage layer and transparent conductor for all‐solid‐state and laminated electrochromic switching devices in view of long‐term stability.