Photonic Crystal-Integrated Thermo-Responsive Smart Windows with Multicolor and Enhanced NIR Shielding

Smart windows have attracted significant attention due to their potential for energy conservation. However, their practical applications are limited by the monotonous color variation and poor near-infrared (NIR) shielding performance. In this study, a novel smart window was constructed by integrating a crack-free photonic crystal array (100 mm×100 mm) with poly(N-isopropylacrylamide) (PNIPAm), sodium carboxymethyl cellulose (CMC), and antimony tin oxide (ATO) nanoparticles. The photonic band gap of the photonic crystal array endows the smart window with unique visible light modulation properties and temperature indication functionality, enabling dynamic color variation at various surrounding temperatures. The smart window exhibits excellent solar light modulation (ΔTsol=38%) and NIR transmittance (TIR=30%), which is attributed to the synergistic effect of ATO nanoparticles and PNIPAm hydrogel. The incorporation of CMC enhances the optical modulation capability and durability of the PNIPAm hydrogel. Due to the heat-absorbing and NIR absorption properties of ATO nanoparticles and the thermochromic and heat insulation characteristics of PNIPAm hydrogel, the smart window achieves a maximum temperature difference of 7.2 °C compared with normal glass. This work provides a novel strategy for constructing smart windows based on photonic crystals, demonstrating great potential in temperature monitoring, heat insulation, and other applications.