Complementary hybrid electrodes for high contrast electrochromic devices with fast response

Abstract

Fast switching `transparent-to-black' electrochromic devices are currently under investigation as potential candidates in modern applications like e-papers or with additional functionality as ultracompact iris or switchable neutral filter in camera systems. However, recent electrochromic devices show either a lack of contrast or slow response times. To overcome these deficiencies we focus on a careful material composition of the colouring hybrid electrodes in our device. We have established a nanoporous Sb-doped SnO2 electrode as supporting electrode for chemisorbed electrochromic tetraphenylbenzidine molecules due to its good conductivity in the redox potential range of the molecule. This hybrid electrode was combined with a modified nanoporous TiO2/viologen electrode to realize a high performance, complementary electrochromic device. Fast switching time constants of 0.5 s and concurrently high change in optical density Delta OD = 2.04 at 605 nm confirm our successful concept. The achieved colouration efficiency of 440 cm(2) C-1 exceeds every high contrast device presented so far.