Improvement of Electrochromic Performance by Embedding ITO Nanocrystals in Amorphous WO3 Film

The electrochromic films featuring the well dispersed ITO nanocrystal (about 10 nm) in amorphous WO3 (ITO@WO3) have been successfully fabricated with a solution process. The structure and electrochromic properties of the as-prepared films were studied by high resolution transmission electron microscope, scanning electron microscope, X-ray photoelectron spectroscopy, X-ray diffraction, and electrochemical methods. The measured coloration/bleach time decreases from 10.5/27.8 s to 5.7/0.9 s with the increasing of ITO/AMT ratio indicating that embedded ITO nanocrystals induce the nanocrystal/glassy interface effect remarkably improving the ion diffusion coefficient and electrochemical activity. The optimal Delta T at 633 nm of 0.1 ITO@WO3 films is about 53.80% much higher than that of pure WO3 (about 42.09%). But in near-infrared (NIR) range the pure WO3 films show the best transmittance modulation rather than the composite films. The above stated results are indicative that the interface effects of embedded ITO nanocrystals play the key role while its plasmon-induced electrochromic effects are limited because of not only excellent NIR modulation capability of amorphous WO3 itself but also the relative large size of ITO nanocrystals used, demonstrating that smaller nanocrystal size (similar to 5 nm) are required for better electrochromic performance of the composite films. (C) 2019 The Electrochemical Society.