Advancing Energy Efficiency in Smart Windows via Dual‐Responsive Electro‐Thermochromism

ABSTRACT Implementing dynamic smart windows is imperative toward the construction of net‐zero buildings. However, the prevailing ion (de‐)embedding‐based electrochromic (EC) or thermosensitive hydrogel‐based thermochromic (TC) windows fail to achieve large optical modulation across the solar spectrum owing to their optical absorption mechanisms. Herein, a dual‐responsive electro‐thermochromic smart window is designed and assembled by coupling an anodically coloring Prussian blue (PB) electrode with hydroxyl cellulose‐based hydrogel electrolyte (HPC). Through judicious formulation, the HPC hydrogel electrolyte affords large TC transmittance modulation ( ∆ T ∼ 83% @633 nm), mechanical stability (strain = 514%), and a high ionic conductivity (σ = 62.58 mS/cm), enabling the PB electrode with a high coloration efficiency (CE = 108.21 cm 2 C −1 ) and fast switching kinetics (t b = 5 s, t c = 6.8 s). As a result, the as‐assembled smart window features four distinct operating modes, exhibiting outstanding visible‐light T% modulation (ΔT lum = 87.3%) and superior solar modulation capability (ΔT sol = 50.5%), enabling a 35%–55% reduction in annual energy consumption in representative regions, and achieving annual energy savings up to 129 MJ m −2 . This dual‐responsive smart window is an embodiment of coupled opto‐thermal regulation strategies toward building energy modulation, inspiring future efforts in energy‐efficient optoelectronics in the era of decarbonization.