High efficient ultra-broadband nanoscale solar energy absorber based on stacked bilayer nano-arrays structure

Solar energy harvesting is widely used in heating and cooling system desalination of sea water, PV and solar-thermal power generation, in which high efficient broadband solar energy absorber is a key technology and challenge. In this paper, an excellent nanoscale solar energy absorber based on stacked bilayer nano-arrays (SBNA) structure is proposed and investigated. By introducing 1D Ti grating in the first layer nano-array, the absorptivity in the long-wavelength range is enhanced and the absorption band is much broadened. Besides, combined the circular and elliptical nano-disks stacked with Ti - Al2O3 – Ti - Al2O3 in the second layer nano-array, the average absorptivity in the whole work band can be improved, especially in short-wavelength range that dominates most solar energy. The result shows that the average absorptivity is up to 97.71% in the solar energy concentration range from 300 nm to 2500 nm. In the whole work band from 300 nm to 4000 nm, the average absorptivity is 94.10% and the absorption bandwidth (A > 90%) reaches 3080 nm. It's calculated that the solar spectral weighted absorption efficiency reaches to 98.35% in 300 nm–4000 nm, which is a rather high efficiency among the similar structure. Moreover, the solar energy absorber is polarization independent and is insensitive to large-angle incidence in 300 nm–2500 nm. The results provide a theoretical basis to design the absorption metamaterials in solar energy harvesting element.