Ultra-black Pythagorean-tree metasurface antenna array based absorber and emitter for applications in solar thermophotovoltaics

High temperature tolerance is a crucial need for solar thermal applications. A polarization-insensitive and wide-angle, broadband metasurface absorber and narrowband emitter for solar thermal photovoltaic (STPV) system, which is highly thermally robust, is presented for energy harvesting applications. The absorber has near-unity absorption in visible and near-infrared regions with low emission at longer wavelengths. The STPV systems intend to bar the Shockley-Queisser limit of the conversion efficiency of the PV cell. The presented absorber is a subwavelength refractory plasmonic structure consisting of three layers with top and bottom layers made up of a transition metal nitride (ZrN). It is thermally and chemically stable with a melting point of 3253 K. The impedance of the simulated device matches that of the free space at resonance wavelength, and it has 93.47% average absorption in 400 – 800 nm range. The STPV absorber efficiency (η
abs
) of the design presented is 65.42% for blackbody radiation at 5778 K and 65.35% for AM 1.5 spectrum. The emitter exhibits spectral selective behavior to efficiently couple the energy to solar cell and matches the bandgaps of GaInAs, GaAs, and GaInP solar cells (BGs: 1.05 eV, 1.42 eV and 1.85 eV, respectively), with emittance values of 99.05%, 99.57% and 94.78 %, respectively, depending upon dimensions.