Nanoparticle-polymer hybrid dual-layer coating with broadband solar reflection for high-performance daytime passive radiative cooling

The passive cooling technology is refrigerant-free and energy-free, making it an appealing alternative to reduce the energy consumption of traditional cooling systems. Although effective in optical design, the materials involving optical structures and metal reflectors are rarely cost-effective or readily applicable. Radiative cooling materials with promising optical properties and good practical applicability remain an urgent research need. We present a simple and scalable method to fabricate a dual-layer nanoparticle-polymer hybrid coating which achieves a high diffused solar reflection of 92.2 % without using metal reflectors, and a strong mid-infrared emission of 95.3 % within the atmospheric window. The coating allows continuous sub-ambient cooling in both daytime and nighttime. Promisingly, the coating reaches about 4 °C lower temperature than ambient under intensive solar irradiation, along with a 78.9 Wm⁻² cooling power generation. Moreover, the cooling coating exhibits great reliability and cooling effect when applied as an exterior coating on model houses and the roof of a real building. Applying the proposed material as a roofing material is capable to save cooling energy across various climate zones, especially in the hot climate, which confirms the material's possibility for carbon reduction and tackling global climate change.