Thermal absorber with epsilon-near-zero metamaterial based on 2D square spiral design

Abstract

A novel, to the best of our knowledge, design of a wavelength-selective solar thermophotovoltaic (STPV) absorber based on a 2D square spiral grating is numerically proposed and analyzed. The suggested STPV absorber is made of tungsten (W) with a spacer of aluminum-doped zinc oxide (AZO). In particular, the AZO is epsilon-near-zero material where its dielectric permittivity can be engineered over a broad wavelength range in the near-infrared. The refractory AZO-W metamaterial exhibits marked radiative optical properties, which control the thermal absorption through an engineered dielectric response function. The geometrical parameters and optical properties of the proposed design are studied using the finite difference time domain method to maximize the absorption through the studied wavelength range. The physical mechanism beyond the geometrical effects is also investigated with the inductor and capacitor model. The 2D square spiral STPV absorber achieves the photon-to-heat conversion efficiency of 75.2% at 1000 K. It is also found that the absorption of the proposed STPV absorber is insensitive to the incident angles from normal incident to 60º for transverse magnetic and transverse electric polarizations. The absorption enhancement is due to the effective coupling among the magnetic polariton, surface plasmon polariton, and intrinsic losses of the tungsten metal.