Oxygen-deficient tungsten oxide nanoflowers for dynamically tunable near-infrared light transmittance of smart windows

Electrochromic smart windows have attracted much attention in energy-saving buildings because of their ability to selectively modulate visible (VIS) and near-infrared (NIR) light transmittance. As is known, the NIR region accounts for about 50% of the total solar radiation. Therefore, reducing the NIR transmittance of windows will play a crucial role in reducing the energy consumption of buildings. However, for most of the reported electrochromic materials (ECMs)-based windows, it remains a long-lasting challenge about how to achieve a low NIR transmittance during the past decades. In this work, we synthesize oxygen-deficient tungsten oxide (WO_3−x) nanoflowers (NFs) by a simple and efficient method that is facile for their mass production. The WO_3−x NFs exhibit low NIR transmittance of only 4.11%, 0.60%, and 0.19% at 1200, 1600, and 1800 nm, respectively, due to the localized surface plasmon resonance (LSPR) effect. Besides, the WO_3−x NFs exhibit an excellent dual-band modulating ability for both VIS and NIR light. They are able to operate in three distinct modes, including a bright mode, a cool mode, and a dark mode. Moreover, the WO_3−x NFs exhibit a fast bleaching/coloring time (1.54/6.67 s), and excellent cycling stability (97.75% of capacity retention after 4000 s).