Ultra-broadband perfect absorber based on nanoarray of multilayered quadrangular frustum pyramid in the UV-NIR spectrum

A metamaterial perfect absorber working in the ultraviolet-to-near infrared region is proposed. It consists of a periodic nanoarray of quadrangular frustum pyramids with a homogeneous titanium nitride (TiN) film as the ground. Each unit cell of the nanoarray is composed of alternately stacked TiN and dielectric patches with their width tapered linearly from the bottom to the top. The absorption mechanism was qualitatively explained by analyzing the electric and magnetic field distributions at the resonance wavelengths, and the absorption performance was simulated as a function of its geometric parameters and the angle and polarization of incident beam as well. Optimal geometric parameters are presented. With the optimal parameters, the absorption efficiency at normal incidence is above 99.3% over the entire spectral region from 300 to 2500 nm, and a high average absorption of 99.9% is achieved. The ultrabroadband perfect absorption behaviors are attributed to the localized surface plasmonic resonance effect of the pyramid, the intrinsic loss of the TiN material and the coupling of resonance modes between two adjacent pyramids. In addition, the absorber also shows polarization insensitivity and good angular acceptance capability of oblique incidence up to 70°. The unique and compact structure provides a new way for achieving an ultrabroadband solar absorber, showing great application prospects in the fields of solar energy harvesting and the corresponding (thermo-)photovoltaics.