Daytime Radiative Cooling Sheet Functionalized by Al₂O₃-Assisted Organic Composite

Daytime radiative cooling presents a compelling technology, noted for its efficiency and environmental friendliness. Recent studies have focused on not only the cooling capacity but also the applicability and versatility of this technology. This study introduces a daytime radiative cooler as a sheet with exceptional cooling performance. Its matrix is composed of polymethylmethacrylate (PMMA) and thermoplastic polyurethane (TPU), which are emerging organic materials suitable for radiative cooling. Furthermore, aluminum oxide (Al₂O₃) is employed as a supporting dielectric particle to enhance cooling performance. An Al₂O₃-assisted organic composite (AOC) is created through electrospinning and hot-pressing, resulting in a bendable sheet form. The AOC sheet demonstrates a light reflectance of 97.9% across the solar spectral region (0.3-2.5 µm) and an emissivity of 95.2% within the atmospheric transparency window (ATW) of 8-13 µm. The cooling power, derived from optical properties, is calculated to be 120.1 Wm^-2. Experimental findings confirm the AOC sheet's capability to achieve 4.9 °C below ambient temperature and, when applied to a car model, to reduce the interior temperature by 12.7 °C.