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

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 cm² 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.