High‐Performance Zinc‐Anode Dual‐Band Electrochromic Devices Based on Tungsten Oxide Quantum Dots for all‐Season Building Energy Savings

Zinc‐anode electrochromic windows capable of actively controlling light and heat transfer on demand, have been emerged as an intriguing technology for indoor thermal management. However, their practical development has been hindered by slow switching speeds, limited cycling stability and unclear operating mechanisms. Herein, we present a high‐performance Zn‐anode dual‐band electrochromic device utilizing tungsten oxide quantum dot (WO 3 QD) cathode, and reveal their detailed charge transfer mechanism. This device not only can control the visible light and near‐infrared effectively and independently through bright, cool and dark modes, but also shows excellent electrochromic properties with a high optical modulation (78.8% at 633 nm), fast response and long‐term cycling stability (92.1% capacity retention after 10,000 cycles). The ultra‐small size and large hexagonal tunnel of WO 3 QDs notably enhance ion diffusion kinetics and structure stability during cycling. Furthermore, we reveal a synergistic co‐insertion mechanism of Zn 2+ and H + with a molar ratio of 2:1 in nonaqueous electrolytes. Outdoor tests and simulation results confirm the higher energy‐saving performance of our device than the commercial low‐emissivity glass in most climate zones around the world. This work paves the way toward designing high‐performance electrochromic smart windows for future zero‐carbon buildings.