The influence of charge capacity ratio on the optical attenuation of a tungsten oxide-polyaniline electrochromic device

Hybrid inorganic/organic complementary electrochromic device (ECD), comprising a tungsten oxide (WO,) and polyaniline (PAni) thin film couple in combination with a proton-conducting polymer electrolyte, is studied. Spectroelectrochemical measurements were done to characterize both the electrochromic thin films and the devices. The safe operating voltage of the device can be determined from these data and ranging from +1.0V to -0.3V. The primary motivation of the present investigation is to examine the connection between the optical attenuation range and the charge capacity ratio of WO, relative to PAni. It was found, experimentally, that the performance of the complementary ECD is limited by the electrode with the least charge capacity. Furthermore, it has been verified 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. That is, the principle in obtaining the maximum optical attenuation in a complementary ECD is to equalize the charge capacity on both electrochromic layers.