Thermo‐Responsive Smart Window Coupled with Heat Storage Effect

Thermo-responsive smart windows, despite their ability to dynamically modulate solar transmittance, inevitably reject and waste a significant portion of solar energy, which limits their application potential in carbon-neutral buildings. Here, a dual-layer thermo-responsive smart window (DLTS) is reported that integrates optical regulation with solar heat storage, transforming smart windows from passive light modulators into active energy management systems. DLTS comprises a thermochromic poly(N-isopropyl acrylamide) (PNIPAM) layer and a controllable supercooled calcium chloride hexahydrate (CCH) phase-change layer. By use of dimethylacetamide (DMA) and tartaric acid (TA), the thermo-responsive temperature (T_r) of PNIPAM can be adjusted up or down successively from 7 to 70 °C, which is the broadest range reported. Simultaneously, depending on ethanol and urea, the T_r of CCH can be tuned facilely from 9 to 31 °C, first-time covering the seasonal temperature change. More importantly, the supercooling degree of 50 °C allows the smart windows to remain transparent across the wide ambient temperature variation, while their stored high latent heat of 199 J g^-1 can be released upon triggering to provide indoor heating. The correlated dual-layer with well-matched T_r points endows the DLTS with a remarkable solar modulation (ΔT_sol = 70.1%). Compared to normal glass, DLTS can achieve more than 20% annual energy savings in heating, ventilation, and air conditioning (HVAC) systems in typical worldwide cities.