Degradation mechanisms in electrochromic devices based on sol-gel deposited thin films

Laminated electrochromic devices have been constructed using sol-gel deposited tungsten oxide as the electrochromic layer, sol-gel deposited titanium dioxide as the counter-electrode, and a polymer electrolyte based on lithium-doped 3PEG5000. These devices have been constructed using two different techniques to allow the dismantling and reconstruction of the devices after the device has been tested. This allows degradation in different components of the devices to be studied in a quantitative fashion. In this paper we describe the device fabrication techniques, and some initial results on the degradation of devices based on sol-gel deposited electrodes. The results show that while the tungsten oxide electrodes can be cycled many hundreds of times in liquid electrolytes, degradation appears in the TiO₂ electrode. The results also allow investigation of the effect of polymer conductivity on the device performance by adjustment of the electrode spacing.