Nano-resonator based broadband metamaterial absorber with angular stability operating in visible light spectrum for solar energy harvesting applications

Solar energy harvesting has become an attractive technique for nanotechnology. The absorption of electromagnetic (EM) radiations in the visible range requires unique absorbers of particular optical characteristics. In this research paper, a novel metamaterial solar absorber (MMSA) is suggested for solar energy harvesting in the nearly-entire visible light spectrum 400 to 800 THz. The compact unit cell of the proposed absorber is formed by three thin layers Nickel (Ni)-Silicon dioxide (SiO2)-Nickel (Ni), its period P is optimized as 400 nm. The top layer on Ni is based on a novel symmetric nano-meta resonator consisting of a square-shaped outer ring coupled to the inner ring which surrounds five small circles. The total thickness of the two Ni layers and the intermediate SiO2 dielectric layer is 150 nm. The absorption qualities of the proposed structure have been analyzed by the finite element method (FEM) via the high frequency structure simulator (HFSS). The proposed MMSA shows remarkable absorption efficiency for the normal incidence of light and good impedance matching around these resonances. High absorption ability rate above 90%is obtained over a wide-band within 479.8 – 722.5 THz spectrum range with an average absorption of 95.82% over this operating band. Absorption peaks of the order of 99.86 and 99.91% are observed at the resonances of 501.6 THz and 606.6 THz, respectively. Furthermore, the simple unique shape of the unit cell with rotational symmetry makes the suggested MMSA insensitive to the polarization angle on the one hand and the angular stability at oblique incidence up to 60° for both transverse electric (TE) and transverse magnetic (TM) modes on the other hand. Based on its qualities, the proposed MMSA can be considered as a promising candidate for utilizations in several fields such as optical sensors and filters. It can be also incorporated into photovoltaic devices as a solar-energy harvester.