Synergistic multi-resonance mode design for highly efficient broadband solar absorption and photothermal conversion using a cross-ring metamaterial array

Abstract

Solar energy, the most abundant renewable resource on Earth, offers a clean and sustainable solution to meet the rising global energy demand. However, existing metamaterial-based solar absorbers often suffer from limited broadband absorption, polarization sensitivity, and narrow angular response, which restrict their practical applicability. To overcome these challenges, we propose a novel Ti/SiO₂/Ti cross-ring metasurface absorber that synergistically exploits localized surface plasmon resonance, Fabry-Pérot cavity resonance, and magnetic resonance within a single subwavelength unit cell. This multi-resonant coupling enables broadband, polarization-insensitive, and wide-angle absorption performance. Using Lumerical FDTD simulations, the proposed absorber achieves an average absorption of 94.2 % across a wide spectral range of 280–5000 nm, with maximum average absorptions of 96.0 % and 95.8 % for transverse electric and transverse magnetic polarizations, respectively. Near-perfect absorption peaks of 99.9 % are observed at resonance wavelengths of 334 nm and 658 nm. Moreover, the absorption closely matches the AM1.5 solar spectrum, resulting in an excellent solar absorption efficiency of 97 % in the 280–5000 nm range. The structure retains high absorption from normal incidence up to 60° and exhibits a thermal emission efficiency of 96.96 % at 2000 K, along with a photothermal conversion efficiency exceeding 91.5 % over the temperature range of 300–1000 K at a solar concentration factor of 1000. These enhancements demonstrate that the proposed metastructure is a highly promising candidate for advanced solar-thermal applications, including solar water heating, photothermal therapy, and concentrated solar power systems.