Hybrid thermochromic microgels based on UCNPs/PNIPAm hydrogel for smart window with enhanced solar modulation

Energy-efficient smart windows can control solar energy transmission, which is one of the most promising ways to reduce building energy consumption. However, the current thermochromic smart windows based on Poly(N-isopropylacrylamide) (PNIPAm) are still far from satisfactory in regulating the infrared region of sunlight. To expand the modulation ability of infrared region, an inorganic nanoparticle filled hybrid hydrogel that blocks out most part of sunlight as the temperature rises has been developed by up-conversion nanoparticles dispersed in hydrogel matrix effectively converts infrared light into visible light, thus greatly enhancing the infrared transmittance modulation (ΔTIR) and the solar modulating ability (ΔTsol) of the hydrogel. The 4% (wt.) UCNPs@SiO2–NH2 nanoparticles doped in PNIPAm exhibits the best solar modulation ability (ΔTIR = 78.3%, ΔTsol = 79.76% and Tlum, 20°C = 82.79%). In addition, this thermochromic hybrid material, which integrates inorganic components with organic components, is also durable and reversible. By sealing the hydrogel with glasses in a sandwich structure, a smart window that can regulates broadband solar light is obtained.