Scalable, ultrathin, highly selective and emissive films by microsphere-polymer coupled metasurfaces for passive radiative cooling

Abstract Passive daytime radiative cooling (PDRC) is a recently developed zero-carbon cooling technology that harnesses the coldness of the universe as an inexhaustible and environmentally sustainable energy source, holding immense promise for revolutionizing the global energy landscape. Photonic structures with tailored optical responses across solar and thermal wavelengths play pivotal roles in daytime radiative cooling. However, the design of spectrally selective structures with simultaneously high performance, scalable manufacturability and reduced material usage toward real-world deployment remains a significant challenge. Here we report scalable, ultrathin and high-performance selective radiative cooling photonic films by microsphere-polymer coupled metasurface (M-PCM), which consists of subwavelength-thick (~ 8 µm) polymeric elastomer embedded with a monolayer hexagonally close-packed microsphere array on the top and an optically thick reflector underneath via an inexpensive and scalable-manufactured strategy. By controlling the light coupling between the glass sphere and polymers, Mie resonances are spectrally selective excited or suppressed leading to a strong infrared emissivity of 0.96 within 8–13 µm and a large spectral selectivity of 1.50, with simultaneously a high solar reflectance of 0.96, surpassing the state-of-the-art selective PDRC designs. More critically, the M-PCM film yields a maximum temperature drop of 7.1 °C in a represented rooftop test. Promisingly, the mass-produced yet economically viable ultrathin flexible M-PCM films are portable to be integrated into diverse realistic scenarios, such as building exteriors, automobile bodies and water tanks, which could potentially contribute to the global energy conservation and carbon emission reduction.