Electrochromic films and devices have broad application prospects in smart energy-saving windows. We developed a facile and general room-temperature photochemical deposition method for fabricating a series of electrochromic and ion-storage oxide films including WO₃, V₂O₅ and NiO_x [1–7]. This method features mild reaction conditions, simple equipment, large-area coating capability, and enables precise modulation of film composition, thickness, crystallinity and porous structure [1–7]. By investigating the correlations among film composition, microstructure and performance, it is found that amorphous films exhibit superior electrochromic properties compared with crystalline counterparts. For instance, amorphous V₂O₅ films deliver richer color variations, wider optical modulation range and faster response speed [2,7]. Incorporation of structural water into WO₃ films induces pseudocapacitive behavior dominated by surface redox reactions, which drastically improves the near-infrared response speed and cycling stability of the films [4,6], as well as enhances their electrochromic energy-storage performance [5]. Tuning the V/W ratio in amorphous binary vanadium-tungsten mixed metal oxide films optimizes their ion storage performance while maintaining optical inertness [3]. Based on electrochromic and ion-storage films prepared via the photochemical method, electrochromic devices with large photothermal modulation amplitude, rapid response and high cycling stability were successfully constructed by regulating the charge balance between the two types of films [1–7]. Our work lays a solid foundation for advancing the application of electrochromic technology in smart energy-saving windows.

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