The influence of charge capacity ratio on the performance of a complementary electrochromic system

One of the problems encountered with complementary, solid-state electrochromic devices is the development of discoloration as a result of storage or cycling. The cause of discoloration in the bleached state is the charge imbalance on one of the electrodes. This paper deals with balancing the electrode capacities in a complementary, solid-state electrochromic device so as to optimize its optical attenuation range. Complementary electrochromic system, comprising a tungsten oxide and Prussian blue (PB) thin film couple in combination with a proton-conducting, copolymer electrolyte, is studied. It has been shown experimentally that, for two complementary electrochromic layers each with an individual thickness, the charge capacities of the two electrochromic layers have to be matched in order to achieve the maximum optical attenuation range. The effect of cell size on the switching response of the complementary system is also studied. (C) 1999 Elsevier Science B.V. All rights reserved.