Nanostructured Quasiplanar Heterointerface for a Highly Stable and Ultrafast Switching Flexible Inorganic Electrochromic Smart Window

Electrochromic (EC) technology can adjust optical properties under electrical stimulation with broad applications in smart windows, displays, and camouflage. However, significant challenges remain in developing inorganic EC films with high durability, rapid response, and mechanical flexibility due to intrinsic brittleness and dense microstructure. Herein, a nanostructured quasiplanar heterointerface (Q-PHI) is first introduced into the electrode/EC interlayer to realize a robust, ultrafast switching tungsten trioxide (WO 3 ) EC film. The 200 nm-thick Q-PHI WO 3 film exhibits remarkable EC performance, including large optical contrast (81.8% and 83.4% at 700 and 1500 nm), ultrafast switching of 2.4 and 1.8 s, and excellent stability (10,000 cycles with 21.3% optical-contrast loss). A large-area (20 × 15 cm 2 ) flexible EC smart window is also successfully achieved. The mechanism lies in the intense built-in electric field and strong interfacial bonding induced by the Q-PHI with unique longitudinal gradient distribution, greatly enhancing the electron/ion transport kinetics, surface ion adsorption, and durability.