Vacancy Engineering in Tungsten Oxide for Enhanced Temperature-Modulated Electrochromic Smart Windows

High-temperature control depends on the modulation of visible (VIS) and near-infrared (NIR) radiation for a pleasant living environment. However, achieving a strong absorption of NIR light is still a challenge for electrochromic materials. In this work, a high NIR absorbance is achieved by Ag-doped tungsten oxide (Ag@WO_<i>x</i>) through enhanced local surface plasmon resonance. The assembled electrochromic smart window shows a temperature difference of 6.3 °C compared with nontreated tungsten oxide (WO_<i>x</i>). The low transmittance of 2.64% at 1800 nm in the dark mode ensures excellent temperature modulation in hot weather. The high optical modulation of 91% ensured visible light transmission. The crystal structure modification is theoretically confirmed by DFT calculations to shorten the coloration time (9.9 s) and bleaching time (7.4 s). The high cycling stability shows a small decay after 20,000 cycles, making it an ideal candidate for high-performance electrochromic energy-saving smart windows.