All‐Solid‐State Transparent Variable Infrared Emissivity Devices for Multi‐Mode Smart Windows

Abstract Smart windows that incorporate photothermal modulators (PMs) can independently regulate solar transmittance and infrared (IR) emissivity to improve building comfort and reduce energy consumption. Herein, a novel all‐solid‐state variable IR emissivity device (VED) is first designed and fabricated with a high visible irradiation transmittance (T′_vis = 0.79) and solar irradiation transmittance (T′_sol = 0.75) using an ITO/SiO₂/ITO Fabry–Perot cavity structure. The VED exhibits different IR emissivity (ɛ) values at positive (ɛ_P = 0.80) and negative (ɛ_N = 0.38) bias, allowing for dynamic regulation of radiation by controlling the electrical conductivity of the indium tin oxide (ITO) layer. Furthermore, an all‐solid‐state PM with a structure of ITO/SiO₂/ITO/Glass/ITO/NiO/ZrO₂/Li/WO₃/ITO, which is capable of independently regulating solar transmittance (ΔT'_sol = 0.31) and IR emissivity (Δɛ_{2.5–25 µm} = 0.42), is fabricated. The multi‐mode smart window incorporating PMs can achieve “bright,” “dark,” “warm,” and “cool” modes, making them suitable for deployment in diverse climate zones. The innovative smart window holds a massive potential for use in reducing building energy consumption.