In this study, we investigated an absorber based on a center-aligned tandem nanopillar array for ultra-broadband solar energy harvesting theoretically. A high-efficiency, omnidirectional absorber was obtained by introducing the center-aligned tandem nanopillar array embedded in an Al₂O₃ dielectric layer. The multi-coupling modes at different wavelengths were interpreted. The strong absorption can be adjusted by changing the radii and heights of nanopillars. According to the simulation results, the average absorptance of the absorber exceeded 94% in the wavelength range from 300 nm to 2000 nm. In addition, the high-efficiency absorption was insensitive to the incident angle and polarization state. The research not only proposed an absorber which possesses a huge potential value for application areas, such as thermal photovoltaic systems, infrared detection, and isotropic absorption sensors, but also pointed out a new way to design an absorber with high efficiency in an ultrabroad wavelength range.

This paper proposes a near-perfect absorption device based on a cross-shaped titanium nanostructure and a multilayered structure. The multilayered bottom structure consists of alternately SiO₂ and Ti. The whole device is put on a TiN substrate. The coupling between cross-shaped titanium nanostructures, and that between the cross-shaped titanium nanostructure and bottom multilayer, can further enhance the absorption at some wavelength where most of the energy is reflected or passes through in the device with a single structure. According to the simulation results, the device presents a nearly perfect absorption in a wavelength range from 300 nm to 2000 nm. The average absorptance in the wavelength range from 500 nm to 1400 nm exceeds 96%. This paper also provides a new idea for realizing perfect absorption, which is extensively used in sensing, controllable thermal emission, solar energy harvesting solar thermo-photovoltaic devices, and optoelectronic metrology.