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

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-WO3-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-WO3-x-O-V films to modulate NIR light transmittance selectively, but also enhances ion adsorption and diffusion in the a-WO3-x host to obtain excellent EC performance and a large energy storage capacity. Consequently, the a-WO3-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 cm(2) 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-WO3-x-O-V films show great potential for application in high-performance DEES smart windows.

Automated summary

Through experiments and theoretical calculations, it is found that oxygen vacancy modulated amorphous tungsten oxide films have excellent electrochromic performance and energy storage capacity, making them suitable for high-performance dual-band electrochromic energy storage (DEES) smart windows.