Broadband solar energy harvesting and near-perfect thermal emission on a unified stepped-high concentric dual-ring metamaterial

The development of advanced solar energy harvesting systems requires metamaterial absorbers that overcome the limitations of conventional noble-metal designs, particularly their insufficient thermal stability and significant optical losses. This study introduces a stepped-height concentric dual-ring metamaterial absorber (SHCDR-MA) based on titanium nitride (TiN), which achieves an average absorptivity of 99.27% across an ultra-broadband spectrum from 150 to 3000 nm. The structure employs a vertically graded dual-ring configuration, atop a silicon dioxide (SiO2) dielectric spacer and a TiN substrate, enabling multi-resonance coupling and impedance matching. Absorption originates from the synergistic interplay of several mechanisms: a vertical impedance gradient created by the concentric ring height difference, coherent transition from TiN interband transitions and localized surface plasmon resonances at shorter wavelengths to propagating surface plasmon resonances and dielectric-guided modes at longer wavelengths, and efficient energy dissipation through magnetic hotspots and Poynting vector convergence. The absorber exhibits excellent angular independence (up to 60°) and maintains near-ideal, temperature-invariant blackbody-like emission across a wide temperature range (373–1500 K). By leveraging the refractory properties of TiN, this design provides a feasible strategy for advanced applications in solar energy harvesting and high-temperature solar thermophotovoltaics.