Prolonged lifetime of electrochromism of amorphous WO 3 –TiO 2 thin films

The lifetime of the electrochromism of the WO 3 –TiO 2 films prepared by vacuum evaporation is found to exceed that of WO 3 films by a factor of five. X‐ray diffraction has revealed that the crystal structure of WO 3 –TiO 2 films stays amorphous, while crystalline compounds are formed in amorphous WO 3 films after colouring and bleaching. WO 3 –TiO 2 films stay amorphous after they are annealed at 400°C, although WO 3 films crystallize. SIMS and XPS analyses have revealed that half the amount of lithium injected during a colouring cycle is stored as OLi bonds in the bleached film. In WO 3 –TiO 2 films the number of bonds such as WOH and WO in which lithium ions accumulate is reduced. We conclude that the lifetime of the electrochromism is prolonged for amorphous WO 3 –TiO 2 films, because lithium does not accumulate and the WO 3 –TiO 2 films stay amorphous.