A Photonic Smart Window for Season-Adaptive Energy Harvesting and Thermal Regulation

Season-adaptive smart windows require multifunctional photonic systems that can regulate solar transmission, thermal radiation, and energy flow according to seasonal demands. Here, we present a photonic smart window for season-adaptive energy harvesting and thermal regulation based on a vertically stacked architecture consisting of a PDMS-based luminescent solar concentrator (LSC), a thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel, and a low-emissivity insulator–metal–insulator (IMI) transparent electrode. The PDMS LSC doped with 9,10-diphenylanthracene (DPA) harvests UV light while maintaining high optical quality, showing a luminous transmittance of 68.1%. The high LWIR emissivity of the LSC further enables passive radiative cooling in summer. The PNIPAM hydrogel acts as a thermo-responsive optical modulator. At 45 °C, thermally induced scattering reduces the luminous transmittance to 17.86% and the NIR transmittance to 6.38%, thereby suppressing solar heat gain under hot conditions. This scattering-assisted photon recycling in the LSC/PNIPAM/IMI structure enhances photovoltaic performance, increasing the power conversion efficiency (PCE) from 1.76% to 4.32%. The IMI layer further serves as a NIR/LWIR reflector and transparent Joule heater, enabling passive heat retention and active heating in winter. At 3 V, the heater reaches approximately 160 °C and rapidly defrosts the PNIPAM hydrogel at −10 °C. Outdoor demonstrations confirm reduced solar-induced heating in summer and improved heat retention in winter. This work demonstrates a polymer-integrated photonic smart window capable of energy harvesting, passive radiative cooling, thermal insulation, active heating, and rapid defrosting through coordinated spectral management.