LIFETIME OF ELECTROCHROMISM OF AMORPHOUS WO3-TIO2 THIN-FILMS

The degradation of the electrochromism of amorphous WO3 and WO3-TiO2 films prepared by electron-beam deposition have been studied. The lifetime of the WO3-TiO2 films is five times longer than that of the WO3 films. SIMS and XPS analyses have revealed that lithium accumulates as OLi in the WO3 films, but that it cannot accumulate in the WO3-TiO2 film. O1s electron energy loss spectroscopy (EELS) spectra have indicated that the change of the electronic structure for the WO3-TiO2 film by coloration is smaller than that for the WO3 film. The increase of plasmon energy has been obtained in low loss EELS spectrum and the increase of the bond length in the WO3-TiO2 film has been measured by Raman spectrum. From these results, the number of the defect bonds as a trapping site of lithium is reduced and the bond length of W-O decreases in the WO3-TiO2 films. We conclude that lithium cannot accumulate in the structure of the WO3-TiO2 film and that the structure gives a prolonged lifetime to the electrochromism.