(562a) Invited: Effective Radiative Cooling By Paint-Format Microsphere-Based Photonic Random Media

Study of radiative daytime cooling by sophisticated nanostructures has gained significant interest in recent years. These structures typically include precious metals, such as silver, to achieve high solar reflectance, while it is desired to eliminate such expensive materials and deposition processes for practical purposes. In this talk, I will demonstrate that photonic media, when properly randomized to minimize the photon transport mean free path, can be used to coat a black substrate and reduce its temperature by radiative cooling. Even under strong solar radiation, the substrate temperature could reach substantially below that of the ambient air. Our random media that consist of silica microspheres considerably outperform commercially available solar-reflective white paint for daytime cooling. We have achieved the outstanding cooling performance through a systematic study on light scattering, which reveals that the structural parameters of the random media for maximum scattering are significantly different from those of the commercial paint. We have created the random media to maximize optical scattering in the solar spectrum and to enhance thermal emission in the atmospheric transparency window. In contrast to previous studies, our random media do not require expensive processing steps or materials (e.g. silver), and can be applied to almost any surface in a paint format. The facile and scalable processing steps for our random media point to a possibility that low-cost coatings can be used for efficient radiative cooling.