Electrochromic enhancement of WO3-TiO2 composite films produced by electrochemical anodization

Abstract

An enhancement of the electrochromic properties of WO3 thin films by the incorporation of TiO2 is presented. The composite films are obtained by anodizing co-sputtered tungsten / titanium on conductive glass substrates in 1 M H2SO4 solution containing 0.3 wt% NaF. As the titanium content is increased from 0 to 15 at.% a morphology evolution occurs, from nano-porous to nano-flakes and finally to nano-blocks interweaved with nano-pores. The nano-flakes, obtained at 10 at% Ti, proved to be the most conducive structure for the insertion and removal of Li+ ions such that this composition exhibits transmittance regulation abilities of 58.5%, 72% and 77.7% at 550 nm, 632.8 nm and 800 nm respectively, which are more than a 25% improvement at all wavelengths over a pure WO3 film formed in the same way. The WO3/TiO2 film with addition of 10 at.% Ti also has faster coloration/bleaching times, especially in the critical near infrared region with values of 10 s / 64 s at 800 nm compared with 32 s / 90 s of a pure WO3 thin film, as well as improved stability losing less than 5% of its capacity after 1000 switching cycles. © The Author(s) 2014.