Electrochromic (EC) smart windows regulate light transmittance and reduce building energy consumption, supporting the goals of carbon peak and carbon neutrality. Amorphous tungsten oxide (WO₃) films are attractive EC materials owing to their abundant ion channels and fast switching response (Fig. 1), but their optical modulation and long-term stability need improvement. Here, amorphous WO₃-based films, including Bi-doped WO₃ (Bi-WO₃), graphene-oxide/Bi-WO₃ (GO/Bi-WO₃), crystalline/amorphous composite Bi-WO₃ and WO₃-nanowire/Bi-WO₃ films, were prepared by a sol-gel spin-coating route, and the Bi/W molar ratio, calcination temperature and precursor concentration were systematically optimized. Bi³⁺ doping and the amorphous structure markedly enhance the EC performance. The optimized amorphous Bi-WO₃ film exhibits an optical modulation of ΔT = 70% at 630 nm with coloring/bleaching times of 3 s/0.9 s. GO incorporation improves film adhesion and structural stability, retaining 86.4% of the initial performance after 10,200 cycles. The crystalline/amorphous composite film overcomes the local detachment suffered by amorphous films and achieves ΔT = 82.7%, a coloration efficiency of 102.2 cm² C^-1 and 84.5% retention after 10,200 cycles. Combined with a WO₃ nanowire underlayer in a mixed-ion electrolyte, over 24,000 cycles are achieved. These strategies offer a facile route to high-performance, long-lived amorphous WO₃-based electrochromic films for smart windows.
 

Tungsten oxide,Electrochromic films