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

One of the problems encountered with complementary, solid-state electrochro mic devices is the development of discoloration as a result of storage or c ycling. The cause of discoloration in the bleached state is the charge imba lance on one of the electrodes. This paper deals with balancing the electro de capacities in a complementary, solid-state electrochromic device so as t o optimize its optical attenuation range. Complementary electrochromic syst em, 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 l ayers each with an individual thickness, the charge capacities of the two e lectrochromic layers have to be matched in order to achieve the maximum opt ical attenuation range. The effect of cell size on the switching response o f the complementary system is also studied. (C) 1999 Elsevier Science B.V. All rights reserved.