image: Fig. 1. Design of the M-PCM radiative cooling ultrathin film. (a) The proposed M-PCM film consisting of the PDMS elastomer embedded with a monolayer of SiO2 microsphere array on the top and an Ag back reflector. (b) Refractive index and extinction coefficients of PDMS and SiO2. (c) The normalized scattering cross-section of a single 10 µm-diameter SiO2 microsphere on the top of the PDMS with various embedding depths (inset: the schematic diagram of its corresponding structure). (d) The simulated solar reflectivity and infrared emissivity of the PDMS/Ag, SiO2/PDMS/Ag and M-PCM film structures in the normalized Air Mass Global (AM 1.5G) solar spectrum and the longwave infrared atmospheric transparency window. (e-g) The schematic diagrams of the PDMS/Ag structure, the SiO2/PDMS/Ag structure, and the M-PCM film structure with 3/4 SiO2 microspheres embedded, along with the corresponding electric field intensity profiles of the central cross-sectional (x, z)-plane at the peak wavelengths. The represented wavelengths for each structure are noted above the electric field intensity profiles.
Credit: PhotoniX
In the face of intensifying climate change and rising global temperatures, conventional cooling systems, including air conditioners, have contributed nearly one billion metric tons of greenhouse gas emissions in the last three decades — a pressing factor accelerating the climate crisis. Now, scientists have unveiled an innovative solution: a scalable, ultra-thin and high-performance selective passive radiative cooling film based on a novel microsphere-polymer coupled metasurface (M-PCM) design. This breakthrough hinges on a powerful optical coupling effect between dielectric microspheres and polymer layers, enabling strong and spectrally selective infrared emission while maintaining high solar reflectivity. The resulting structure is remarkably thin — only ~10.5 μm, far thinner than conventional polymer radiative cooling films, which typically exceed 50 μm, representing a major advance in material efficiency and integration potential.
The M-PCM film consists of a monolayer of hexagonally close-packed silica (SiO2) microspheres partially embedded in a polydimethylsiloxane (PDMS) elastomer layer atop a reflective substrate. This arrangement induces multiple Mie resonances selectively within the atmospheric transparency window (8-13 μm) while suppressing emission outside this range (Fig. 1). The synergy between microspheres and polymer not only maximizes infrared emissivity (~0.96) and spectral selectivity (~1.50), but also achieves exceptional solar reflectivity (~0.96), offering a daytime sub-ambient cooling of up to 7.1°C under realistic rooftop testing (Fig. 2). Beyond laboratory performance, the M-PCM film demonstrates scalable manufacturing capability using an automatic roll-to-roll process, making it suitable for large-area applications such as building exteriors, automobile surfaces, and energy-efficient coatings for containers and infrastructure (Fig. 3). Modeling predicts that adopting this film in urban buildings could reduce cooling energy use by up to nearly 40% and cut CO₂ emissions by several tons per building each year— a significant stride toward carbon neutrality.
This scalable and ultra-thin selective radiative cooling film marks a transformative leap in radiative cooling technology. By harnessing the optical coupling between microspheres and polymer layers, it achieves unprecedented performance, scalability, and material efficiency, paving the way for sustainable cooling solutions with far-reaching environmental benefits.
Journal
PhotoniX
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Scalable, ultrathin, highly selective and emissive films by microsphere-polymer coupled metasurfaces for passive radiative cooling
Article Publication Date
12-Sep-2025
COI Statement
The authors declare no conflict of interest.