Honey-Comb Structured WO3/TiO2 Thin Films with Improved Electrochromic Properties

The electrochromic properties of 90:10 WO3/TiO2 thin films produced by anodizing co-sputtered W/Ti films in a fluorinated ethylene glycol solution are investigated in relation to corresponding pure WO3 films. SEM images revealed that the TiO2 content resulted in a more open honey-comb structure that increased the charge accommodation ability by 250%. The superior charge storage property of the WO3/TiO2 meant that it had a better light modulation range, with transmittance of <1% at 800 nm in the colored state. The electrochromic kinetic processes associated with coloration and bleaching are also much faster in the presence of TiO2, with data generated by electrochemical impedance spectroscopy revealing that this is due to a reduction in the resistance to the insertion of Li+ ions. Materials characterization techniques revealed that the WO3/TiO2 composite maintains the monoclinic structure of the WO3 and that the Ti atoms are substituted into the WO3 matrix, rather than forming discrete TiO2 blocks. (c) The Author(s) 2015. Published by ECS. All rights reserved.