Simulations of micro-sphere/shell 2D silica photonic crystals for radiative cooling

Passive daytime radiative cooling has recently become an attractive approach to address the global energy demand associated with modern refrigeration technologies. One technique to increase the radiative cooling performance is to engineer the surface of a polar dielectric material to enhance its emittance atwavelengths in the atmospheric infrared transparency window (8-13 mu m) by outcoupling surface-phonon polaritons (SPhPs) into free-space. Here we present a theoretical investigation of new surface morphologies based upon self-assembled silica photonic crystals (PCs) using an in-house built rigorous coupled-wave analysis (RCWA) code. Simulations predict that silica micro-sphere PCs can reach up to 73 K below ambient temperature, when solar absorption and conductive/convective losses can be neglected. Micro-shell structures are studied to explore the direct outcoupling of the SPhP, resulting in near-unity emittance between 8 and 10 mu m. Additionally, the effect of material composition is explored by simulating soda-lime glass micro-shells, which, in turn, exhibit a temperature reduction of 61 K below ambient temperature. The RCWA code was compared to FTIR measurements of silica micro-spheres, self-assembled on microscope slides. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

Passive daytime radiative cooling is a promising approach for addressing global energy demand associated with refrigeration technologies, by enhancing the emittance of polar dielectric surfaces. The use of self-assembled silica photonic crystals has shown potential in achieving significantly lower temperatures through outcoupling surface-phonon polaritons (SPhPs) into free-space. Additionally, the simulation of soda-lime glass micro-shells also suggests a considerable reduction in temperature below ambient levels.