Selectively VO ₂ /Ge-based thermochromic photonic meta-surface on infrared emission for radiative cooling regulation

Radiative cooling for buildings, which leverages long-wave infrared (LWIR) toward the sky, offers innovative solutions for passive thermal regulation. However, traditional passive radiative cooling systems, characterized by static thermal emissivity ([Formula: see text], fail to automatically regulate LWIR thermal radiation across varying hot/cold seasons, exacerbating extra cooling/heating costs. In this study, we developed a photonic structure incorporating thermochromic vanadium dioxide and germanium. This structure can intelligently regulate [Formula: see text] based on ambient temperature, turning “on” and “off” radiative cooling in the atmospheric transparency window due to the metal-insulator transition of VO 2 . We crafted a meta-surface consisting of an alternating three-layered dielectric/metal of VO 2 /Ge composition using the principles of slow-light waveguide and Fabry–Perot resonators. This design achieves near-unity absorption of unpolarized light, offering a more efficient cooling effect with a simplified structure. The [Formula: see text] is adjusted at the critical phase transition temperature within the 8–13[Formula: see text][Formula: see text]m wavelength range. Notably, [Formula: see text] can reach up to 0.998 above the critical phase transition temperature and drop to as low as 0.1 below it. Besides, the net cooling power of a metallic VO 2 -based structure can attain 127.52[Formula: see text]W/m 2 , which is 3–4 times greater than that of an insulating VO 2 -based system. This work provides a promising prospect for temperature-adaptive radiative cooling via regulating [Formula: see text] with a photonic structure for all-season applications.