Bioinspired Design of a Binary Synergistic Photonic Structure for Daytime Radiative Cooling

Passive daytime radiative cooling (PDRC) technology provides a promising path for combating global climate warming. Natural photonic structures with efficient radiative cooling performance exist in Saharan silver ants, enabling them to cater to extremely hot weather in the desert. However, previously reported bioinspired structured coolers are easily dampened by environmental aging and contamination, making cooling ineffective. Herein, a bioinspired binary hybrid (Bio-BH) film fabricated via drop casting and unidirectional rubbing methods is presented. The Bio-BH film possesses resonant hollow particles inside the polymer and a nano/microscale photonic structure on the surface composed of a triangular prism array and nanospheres uniformly atop the array, exhibiting high solar reflectance (0.93) and enhanced thermal emissivity (0.94). A temperature drop of ∼6.9 °C is achieved at noon under direct sunlight. Moreover, after fluoride treatment, the dual-scale rough surface endows the film with superhydrophobicity of a water contact angle (WCA) of ∼157°. Combining self-cleaning and durable capacities, this work will pave the way for long-term PDRC performance in real-world application scenarios.