Fast fabrication of a WO ₃·2H ₂O thin film with improved electrochromic properties

By using electrochemical activated FTO glass as both a substrate and catalyst, we developed a facile and fast method to fabricate a WO ₃·2H ₂O thin film with a thickness of ∼100 nm. Due to the specific layered crystal structure of the dihydrated phase and the good contact with the transparent conductive oxides (TCOs) layer, the as-prepared WO ₃·2H ₂O thin film achieved a fast coloration/bleaching response speed (t _c,90% = 3.2 s, t _b,90% = 1.2 s), excellent cyclic stability, wide optical modulation range up to 53.8% and a high coloration efficiency of 107.8 cm ² C ^-1. A solid-state electrochromic device with a size of 5 cm × 5 cm was also fabricated, exhibiting high transparency contrast and good reversibility between the bleached and colored states.