Constructing a Semi-Coherent TiO2 Heterointerface for Rapid and Stable Dual-Band Electrochromism

Dual-band electrochromic smart windows, which enable independent regulation of visible (VIS) and near-infrared (NIR) light, offer significant potential for reducing building energy consumption and improving occupant comfort. However, their practical application is often limited by insufficient optical modulation, slow switching speeds, and poor cycling stability. In this study, we designed and fabricated a hierarchical TiO2 nanorod/nanosheet (TNR/TNS) heterostructure film through a two-step in situ-oriented growth strategy. Rutile-phase TiO2 nanorods were first hydrothermally grown on FTO substrates, leveraging high lattice compatibility to form a single-crystalline electron pathway and mechanical scaffold. Anatase-phase TiO2 nanosheets were subsequently grown epitaxially onto the nanorods, creating an interpenetrating porous structure with a semi-coherent interface (lattice mismatch ∼0.1) that facilitates efficient charge transfer and ion diffusion. The resulting TNR/TNS composite film demonstrates significant dual-band modulation capabilities, with optical modulations of 60.2% at 1300 nm ("bright-cool" state) and 65.1% at 700 nm ("privacy-insulation" state), alongside rapid switching kinetics. Moreover, it shows remarkable cycling stability, maintaining 92% of its original optical modulation after 2000 cycles due to synergistic effects of structural buffering, strong interfacial adhesion, and efficient ion/electron transport. This work provides an effective strategy based on crystal phase and interface engineering for constructing high-performance electrochromic materials, with promising applications in energy-efficient architectural windows.