Combined redox and plasmonic electrochromic effects in WO 3 /ITO double-layer films

In this paper, a double-layer coating with both redox and plasmonic electrochromic properties has been designed and deposited on fluorine doped tin oxide (FTO) substrates by sol-gel method. This coating consists of an amorphous WO 3 film and a nanocrystalline indium tin oxide (ITO) film. Both the valence of W atoms in WO 3 and the localized surface plasmon resonance (LSPR) frequency of ITO nanocrystals can be tuned reversibly and persistently by electrochemical process. Due to the LSPR electrochromism, the double-layer films can block near-infrared (NIR) and visible (Vis) light selectively and independently by applying different voltages, which is better and more functional than the traditional electrochromic films. High transmittance of WO 3 /ITO films is obtained both in Vis and NIR for positive applied voltages. When a weakly negative voltage is applied, the transmittance of WO 3 /ITO films in visible region is still high, while the transmittance in NIR decreases. The transmittance of the double-layer films in both Vis and NIR further decreases for increasingly more negative voltages.