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

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 similar to 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 cm(2)/C), compared with OP-c-WO3 film (25.1 cm(2)/C) and a-WO3 film (35.2 cm(2)/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.