Optimizing thermal radiation control with ultra-broadband metamaterials for high passive radiative cooling efficiency

Managing high energy consumption and thermal energy has become crucial for ensuring a sustainable and stable environment. Recently, passive radiative cooling (PRC) has emerged as an innovative method for reducing environmental energy density without requiring external energy input. This study focused on three wavelength ranges: 2.5-5 μm, 8-13 μm, and 16-27 μm, to optimize net cooling power. We acquired the optical and electrical properties of the materials utilized in this study through density functional theory (DFT). A honeycomb structure was designed as a spectrally selective emitter by using Finite Element Method (FEM) method to enhance radiative properties. We analyzed how geometric parameters affect absorbance and emissivity performance. With the optimal geometry, we achieved a net cooling power of 150.4 W/m² under 994 W/m² of direct solar irradiation during the day. At night, in the absence of sunlight, the net cooling power increased to 198 W/m². The system reached equilibrium temperatures of 256 K during the day and 244 K at night, assuming an ambient temperature of 300 K. Even when considering parasitic convection and conduction, the cooler successfully maintained sub-ambient temperatures. Furthermore, the designed cooler exhibited polarization independence and high emissivity across a wide range of incidence angles (from 0° to 75°).