Controllable crystallization engineering on amorphous tungsten oxide nanoparticles for highly efficient photochromic response

Photochromic materials are promising for application in the smart window, but typical WO3 chromogenic ceramics suffer from slow color-switching speed and limited color saturation. Rational construction of amorphous–crystalline (a–c) heterostructure offers infinite expectations for developing WO3-based composites with a highly efficient photochromic response. Here, the controllable modulation of the WO3 crystallization for synthesizing a-WO3/c-WO3 hetero-nanoparticles is reported by modulating the ratio of acetic acid/sodium tungstate precursors via the synchronous dual-phase synthetic strategy. Owing to the hierarchical structure of crystalline WO3 self-embedded amorphous WO3, the ultraviolet sensitivity, color difference, and light comprehensive reflectance of the hetero-nanoparticles are enhanced by 4.25, 1.87, and 1.52 times, respectively, compared with pure amorphous WO3. Spectroscopic and photoelectrochemical results reveal that hetero-nanoparticles switched from yellow WO3 to the blue HxWO3 accompanied by an increased free carrier density, positively shifted energy levels, and narrower bandgap. For the improved photochromic response, it is ascribed to the concerted advantages of each component and the resultant strong a–c interface interaction, promoting water decomposition in the protons supply, charge transfer in the surface hydration layer, and proton intercalation in the ion-to-electron transducer layer. This work enriches the preparation avenue and mechanism interpretation for WO3-based photochromic nanocomposites that exhibit NIR shielding properties.