Electrochromic characteristics of a complementary tungsten trioxide/Prussian blue cell

Optically switchable electrochromic materials are of importance in the automobile industry for the control of solar heat load, glare reduction, and privacy applications. A complementary electrochromic cell consisting of a cathodically colouring tungsten trioxide (WO₃) film, an anodically colouring Prussian blue (PB) film, and a Li⁺ conducting polymer electrolyte was made. Cycling characteristics and colouration efficiency of the cell at various stages of cycling were evaluated. It was shown that the complementary cell requires less energy for operation compared to cells with a single film. The WO₃/PB was cycled up to 1300 times. A gradual decrease in the contrast between the coloured and the bleached states upon cycling was observed during the first 400 cycles. The colouration efficiency of 102 cm²C^-1 at the first cycle decreased to 67 cm²C^-1 after 387 cycles. The cause of degradation is attributed to the lack of K⁺ ions available to PB film.