Designing Mesoporous Photonic Structures for High-Performance\nPassive Daytime Radiative Cooling

Abstract

Passive daytime radiative\ncooling (PDRC) has drawn significant\nattention recently for electricity-free cooling. Porous polymers are\nattractive for PDRC since they have excellent performance and scalability.\nA fundamental question remaining is how PDRC performance depends on\npore properties (e.g., radius, porosity), which is critical to guiding\nfuture structure designs. In this work, optical simulations are carried\nout to answer this question, and effects of pore size, porosity, and\nthickness are studied. We find that mixed nanopores (e.g., radii of\n100 and 200 nm) have a much higher solar reflectance <i>R̅</i>_solar (0.951) than the single-sized pores (0.811) at a\nthickness of 300 μm. With an Al substrate underneath, <i>R̅</i>_solar, thermal emittance ε̅_LWIR, and net cooling power <i>P</i>_cool reach 0.980, 0.984, and 72 W/m², respectively, under\na semihumid atmospheric condition. These simulation results provide\na guide for designing high-performance porous coating for PDRC applications.