An energy-free daytime radiative cooler based on silica-coated porous anodic aluminum oxide is proposed, optimized, and experimentally realized. It is shown that a simple thin silica layer coating on porous anodic aluminum oxide can produce the spectral emissivity in the atmospheric window (8-$13\mathrm{\mu }\mathrm{m}$) required for sub-ambient cooling effect under direct sunlight. The final design, optimized using effective medium theory, exhibits high reflectance of 0.86 in the solar spectral region, and a substantial average emissivity of 0.96 in the atmospheric window. The fabricated centimeter-scale radiative cooler demonstrates a maximum cooling of 6.1 °C below ambient during the daytime. We believe that the proposed approach is a promising way to produce inexpensive and efficient radiative coolers.

提出，优化和实验实现了一种基于二氧化硅涂层的多孔阳极氧化铝的无能源日间辐射冷却器。结果表明，在多孔阳极氧化铝上简单的二氧化硅薄涂层可以在大气窗口中产生光谱发射率（8-$13\mathrm{\mu }\mathrm{米}$），以在阳光直射下达到低于室温的冷却效果。使用有效介质理论进行了优化的最终设计在太阳光谱区域显示出0.86的高反射率，在大气窗口中显示出0.96的实质平均发射率。装配好的厘米级辐射冷却器在白天的最大冷却性能为比环境温度低6.1°C。我们认为，所提出的方法是生产廉价，高效的辐射冷却器的一种有前途的方法。