Scalable and Flexible Electrospun Film for Daytime Subambient Radiative Cooling

Daytime radiative cooling materials reflect solar light and dissipate heat directly to outer space without any energy consumption, and thus, have attracted much attention due to the potential applications in many fields. Recently, elaborately designed photonic crystal and metamaterials have been reported for daytime subambient radiative cooling. However, such materials and structures have the drawbacks of complex shapes, inflexibility, high cost, and limitation in scaling up. It is also extremely difficult to apply such materials to buildings, vehicles, and other objects having complex surfaces. Here, a scalable and flexible hybrid film for daytime subambient radiative cooling was fabricated by a facile electrospinning method. The hybrid film consists of poly(vinylidene fluoride)/alumina (PVDF/Al₂O₃) fibers with diameters of 0.5-2.5 μm. Owing to the efficient scattering by fibers and Al₂O₃ nanoparticles, the hybrid film exhibits an extremely high average solar reflectance of 0.97. A high average atmospheric window emittance of 0.95 is simultaneously achieved due to the molecular vibrations of PVDF and the phonon polariton resonance of Al₂O₃ nanoparticles. The composite film delivers an average net radiative cooling power of 82.7 W/m², and a temperature drop of up to 4.0 °C under direct sunlight. The hybrid film exhibits remarkable radiative cooling performance under different weather conditions including sunny, cloudy, overcast, and rainy. It can be used not only for cooling buildings and vehicles but also for delaying the melting of glaciers. This work demonstrates a promising method for scale-up production of the radiative cooling film with high performance.