We designed a self-adaptive film with a sandwich structure based on a thermochromic poly( N -isopropylacrylamide) hydrogel and polyvinylidene fluoride film, realizing highly efficient sub-ambient radiative cooling and above-ambient solar heating.

As a cutting-edge and environmentally friendly approach, thermochromic hydrogel smart windows show great potential in combating climate change and achieving carbon neutrality. However, the substantial absorption of near-infrared (NIR) energy by H₂O poses an enormous challenge in enhancing the spectral responsiveness. Herein, we propose an ingenious concept of isotope-driven D₂O-hydrogel smart windows, which can effectively resolve the inherent issue of NIR energy absorption associated with H₂O, without compromising versatility. It facilitates near-optimal transmittance modulation across the entire solar spectrum (ΔΓ_Sol = 91.97%), demonstrating a marked enhancement in NIR modulation of transmittance (ΔΓ_NIR) and reflectance (ΔR_NIR) by ~16% and ~31%, respectively, in comparison to conventional H₂O-hydrogel. Moreover, the integration of Ag-nanowires into D₂O-hydrogel further substantially augments the regulation of longwave infrared emissivity ( Δ ε L W I R = 31.89%) while preserving a comprehensive modulation ratio (ΔΓ_Sol = 66.02%, ΔR_Sol = 48.41%) that is not achieved by the existing thermochromic devices. This isotope-driven D₂O-hydrogel smart window provides another design strategy for future energy-efficient windows.

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.