PROLONGED LIFETIME OF ELECTROCHROMISM OF AMORPHOUS WO3-TIO2 THIN-FILMS

The lifetime of the electrochromism of the WO3-TiO2 films prepared by vacuum evaporation is found to exceed that of WO3 films by a factor of five. X-ray diffraction has revealed that the crystal structure of WO3-TiO2 films stays amorphous, while crystalline compounds are formed in amorphous WO3 films after colouring and bleaching. WO3-TiO3 films stay amorphous after they are annealed at 400-degrees-C, although WO3 films crystallize. SIMS and XPS analyses have revealed that half the amount of lithium injected during a colouring cycle is stored as O-Li bonds in the bleached film. In WO3-TiO2 films the number of bonds such as W-OH and W-O in which lithium ions accumulate is reduced. We conclude that the lifetime of the electrochromism is prolonged for amorphous WO3-TiO2 films, because lithium does not accumulate and the WO3-TiO2 films stay amorphous.