Amorphous/ordered porous crystalline stacked WO3 films fabricated by electrodeposition-assisted sol–gel and its application to electrochromic devices

Abstract

WO3 is currently the most widely used and promising electrochromic material, but the preparation of WO3 thin films with excellent optoelectronic properties is a formidable challenge. The amorphous WO3/ordered porous crystalline WO3 stacked films (a-WO3/OP-c-WO3) were prepared by electrodeposition-assisted sol–gel method with polystyrene (PS) spheres as the templates. The microstructure and properties of a-WO3/OP-c-WO3 films were significantly influenced by electrodeposition time (150 s ∼ 300 s). The optimized a-WO3/OP-c-WO3 films exhibited even better electrochromic properties (at 633 nm) with high cycling stability, superior optical modulation (53.9 %), fast response time (3.9 s/6.1 s for bleaching /coloration), and especially high coloration efficiency (51.3 cm2/C), compared with OP-c-WO3 film (25.1 cm2/C) and a-WO3 film (35.2 cm2/C), which is unique synergistic effect between the top layer of a-WO3 and the bottom layer of OP-c-WO3 film. The ordered porous structure allows the film to fully contact with the electrolyte, thereby providing a greater specific surface area and more active sites for the electrochemical reaction. The electrochromic device (EDC) prototype assembled with a-WO3/OP-c-WO3 laminated film as the electrochromic layer has better electrochromic properties.