High temperature dependent absorber-emitter pair nanostructure metamaterial matched with low band-gap PV cell for solar thermo photovoltaic application

One of the metamaterial concepts is the integration of selective broad-band thermal emitters with broad-band solar absorption, which is the foundation of technology that is effectively coupled to a photovoltaic cell for power generation. In this study, we investigated a solar thermo photovoltaic system with a selective absorber and emitter pair that achieves high absorptance of solar radiation in the visible and near-infrared regions (0.3–2.4 μm) that targets an InGaAsSb PV cell with a band gap energy of 0.52 eV. For this work, we designed a selective solar absorber nanostructured grating composed of a tungsten ground film and a hafnium dioxide spacer. Since the absorber melting point is high, it exhibits good thermal stability and extremely high intensity, with a weighted average solar absorption efficiency of 99% at AM1.5. At normal incidence, the optimized metamaterial absorber/emitter has a potential average thermal emitter of more than 94% in the cutoff wavelength range (0.3–2.4 μm) and a total thermal emittance of less than 2% in the mid-infrared range (> 2.4 μm) at a temperature of 100 °C (373 K). According to the simulation results, the estimated total solar-to-heat conversion efficiency is 95% at 373 K without an optical concentration. On the other hand, the total solar-to-heat conversion efficiency is 92 and 62% at 973 K with an optical concentration of 100 suns and 10 suns, respectively. Furthermore, the designed absorber/emitter has thermal stability, polarization independent and exhibits good emissivity over a wide range of incidence angles from 0° to 75°. Finally, to analyze the impact of geometric parameters on the performance of solar absorptivity and thermal emissivity, metamaterial structures with different sizes, shapes and thicknesses were optimized.