High-Efficiency Plasmonic Metamaterial Selective Emitter Based on an Optimized Spherical Core-Shell Nanostructure for Planar Solar Thermophotovoltaics

We propose a high-efficiency plasmonic metamaterial selective emitter based on a tungsten (W) spherical core-shell nanostructure for potential applications in planar solar thermophotovoltaics. This structure consists of silicon dioxide (SiO2)-coated W nanospheres periodically distributed on a W substrate and a thin W layer deposited on top. Using a new definition of spectral efficiency, numerical optimization is performed and its optical behaviors are systematically investigated. The numerical results show that our selective emitter has a high emissivity in the short wavelength range below the wavelength corresponding to the bandgap of the back photovoltaic cell and a low emissivity in the long wavelength range beyond it. Its spectral efficiency of 0.39 is much higher than those of other cases without the top W cover layer or the W nanospheres. Such excellent emission selectivity is attributed to the strong photonic interaction within the gaps between the adjacent core-shell nanospheres, the tightly confined optical fields in both the Omega-shaped W-SiO2-W nanocavities, and the bottom nanocavities formed by the W nanospheres and the W substrate. It is also very tolerant toward the thicknesses of the SiO2 layer and the top W cover layer.