Electrochromic mixed WO3-TiO2 thin films produced by sputtering and the sol-gel technique: a comparison

Because of their dense structure, electrochromic sputtered tungsten oxide thin films often show low coloration efficiency, low ion mobility and the tendency to incorporate lithium ions irreversibly. An interesting possibility to modify the structure is the admixture of other non-absorbing metal oxides. Recent results from Japan indicate improved electrochromic behaviour of evaporated WO3 TiO2 mixed films. In order to verify this effect for different deposition techniques, we examined thin films of WO3-TiO2 produced by the sol-gel method and DC magnetron sputtering. Both types of films were characterized optically and electrochemically in organic LiClO4 solutions. The cycling stability as a function of titania concentration was recorded. The film structure was examined by IR polarized reflection spectroscopy. Improved electrochromic properties were found for both sputtered and sol-gel films.