Near-Perfect Selective Photonic Crystal Emitter with Nanoscale Layers for Daytime Radiative Cooling

Radiative cooling, as a passive way to dissipate heat into outer space without any extra energy, has attracted considerable attention recently. However, the metal reflector of the conventional cooling radiators fails to work in the ultraviolet due to the giant absorption of the metal itself in such a waveband; meanwhile, the selective thermal emission within the atmospheric window still has much room for improvement. In this work, we propose a dual-band selective emitter design with multi-nanolayers, which not only makes up for the deficiency of metal reflectors by utilizing the bandgap of photonic crystals but also enables a broadband emissivity peak in the atmospheric window thanks to the suitable material selection. By engineering simultaneously the forbidden band and thermal emission of photonic crystals, both a near-perfect solar reflection and a considerably high thermal emission are achieved at selective wavelength ranges. The investigation suggests an alternative candidate for the radiative coolers, as well as providing a rational nanoscale design approach for similar photothermal devices.