Butterfly wing-inspired microstructured film with high reflectivity for efficient passive radiative cooling

Radiative cooling is a passive cooling technology that radiates heat to outer space without any energy input thus such technology is of great significance for alleviating environmental pollution and consumption of energy. However, achieving cooling during the daytime normally requires a series of complex structural designs that are economically inefficient and unscalable fabrication process. In this work, inspired by the nanostructure of Pieris rapae butterfly wings, we fabricate a double-layered polymeric film with a bead-like structure which can scatters incident light intensely for passive radiative cooling. Through optical characterization, it was demonstrated that the film can provide a high solar reflectivity of ∼92.4% and a high atmospheric window emissivity of ∼93.2%. In field tests, the film can achieve a maximum temperature drop of 6.5 °C and an average temperature drop of 3.8 °C under direct sunlight, and theoretically producing an effective cooling power of 123.8 W m-2. The as-prepared film could be fabricated through a low-cost template process, and our work presents a new approach to the application of radiative cooling technology in the field of building cooling.