Quadruple-layer film for daytime radiative cooling in high humidity environments

Daytime radiative cooling materials that both reflect sunlight and pump heat out of objects on Earth into cold outer space, without consuming any energy, have attracted considerable attention in recent years. The key to daytime radiative cooling is to selectively control the radiation properties in the solar and mid-infrared spectra. In addition, sky conditions can also affect the performance of radiative cooling, especially solar radiation intensity and humidity. Here, we report on the development of a daytime radiative cooler for an environment with high solar radiation and high humidity. The cooler consists of polyvinyl fluoride (PVF), fused silica, silver (Ag) and SiO2. Due to the intrinsic optical properties of the fused silica and PVF layers, the cooler possessed a low mean absorptivity (3–4%) at 0.3–2.5 μm and a high mean emissivity of over 90% at 8–13 μm. The outdoor experiments were conducted in Xiamen, Fujian Province, China, achieving a continuous reduction of 4.5 °C on a sunny summer day in the southern subtropical maritime monsoon climate of the southeastern coastal region of China. These results have the potential for significant impact on the energy consumption patterns in hot and humid regions around the world.