Inorganic Multilayer Emitter for Passive Daytime Radiative Cooling

Passive radiative cooling has been actively researched to compromise problems of active cooling. Passive radiative cooling refers to the cooling of a surface using optical properties without the supply of electricity from the external. In this study, Ag/Al₂O₃/Si₃N₄/SiO₂ multilayer structure was suggested and optimized by Particle Swarm Optimization (PSO). The multilayer was fabricated by E-beam evaporation and PECVD. Fabricated multilayer also has excellent radative cooling properties with just three IR emissive layers of Al₂O₃, Si₃N₄, and SiO₂. In addition, since Al₂O₃, Si₃N₄, and SiO₂ is generally used as passivation layer, it has higher durability compared to polymer-based radiative cooler. The cooling temperature of the multilayer was measured using self-customized external cooling temperature measurement system. The cooling performance was calculated based on the optical properties of the multilayer using self-developed MATLAB tool. In Seoul which is mid-latitude and have relatively humid climate, the multilayer had cooling temperature of around 8^oC during the daytime. And the calculated net cooling power and cooling temperature of the multilayer resonator was 66.0W/m² and 7.64^oC respectively at T = 300K