CYCLING STABILITY OF AN ELECTROCHROMIC SYSTEM AT ROOM-TEMPERATURE

A solid-state electrochromic transparency, of electrically conductive glass/WO3-y.mH2O/solid polymer electrolyte/Cu grid/clear glass, has been shown elsewhere to carry current efficiently over a large area. It provides electrochromic reactions without significant optical transparency loss for more than 10,000 repeated cycles at room temperature. An equivalent-circuit analysis has been applied to this electrochromic system to gain insight into the physical nature of electrochromic switching. Darkening and bleaching are treated separately due to the unsymmetrical nature of the processes. The present analysis reveals that the significant drop in the mass-transfer resistance for proton transport within the electrochromic tungsten oxide thin film, as a result of the first 200 switchings, is responsible for the observed enhancement of the bleaching speed. The result supports data reported in the literature which show that tungsten oxide films possess higher proton conductivity after darkening/bleaching cycles.