Electrolysis in Electrochromic Devices Consisting of WO3 and MgF2 Thin Films

Abstract

The role of moisture in the ambient atmosphere on the operation of all-solid-state electrochromic devices has been investigated, and electrolysis of the water in electrochromic devices studied. Because of the dependence of the current passing through MgF₂ film on the polarity of the applied voltage, it is suggested that during operation of the devices, water should be supplied only near the surface of the MgF₂ film. IMA measurement and direct observation of gas discharge revealed that the water near the surface of the device is mainly dissociated, and that protons flow into the WO₃ film through the MgF₂ film, resulting in colouration. The colouration behaviour of devices with two different structures leads us to believe that moisture in the atmosphere contributes to more than half the optical density of the device. We also found that bleaching is not always accompanied by dissociation of the water.