Oxygen vacancy modulated amorphous tungsten oxide films for fast-switching and ultra-stable dual-band electrochromic energy storage smart windows

Abstract

Dual-band electrochromic energy storage (DEES) windows, which are capable of selectively controlling visible (VIS) and near-infrared (NIR) light transmittance, have attracted research attention as energy-saving devices that integrate electrochromic (EC) and energy storage functions. However, there are few EC materials with spectrally selective modulation. Herein, oxygen vacancy modulated amorphous tungsten oxide (a-WO_3−x–O_V) is firstly shown to be a potential material for DEES windows. Furthermore, experimental results and density functional theory (DFT) calculations demonstrate that an oxygen vacancy not only enables the a-WO_3−x–O_V films to modulate NIR light transmittance selectively, but also enhances ion adsorption and diffusion in the a-WO_3−x host to obtain excellent EC performance and a large energy storage capacity. Consequently, the a-WO_3−x–O_V film can selectively control VIS and NIR light transmittance with a state-of-the-art EC performance, including high optical modulation (91.8% and 80.3% at 633 and 1100 nm, respectively), an unprecedentedly fast switching speed (t_b/t_c = 4.1/5.3 s), high coloration efficiency (167.96 cm² C⁻¹), high specific capacitance (314 F g⁻¹ at 0.5 A g⁻¹), and ultra-robust cycling stability (83.3% optical modulation retention after 8000 cycles). The fast-switching and ultra-stable dual-band EC properties with efficient energy recycling are also successfully demonstrated in a DEES prototype. The results demonstrate that the a-WO_3−x–O_V films show great potential for application in high-performance DEES smart windows.