Multi-layer nanoring array-based ultra-wideband solar absorber for photothermal conversion

In this work, based on the finite difference time domain method, we propose and investigate an efficient nanoscale solar absorber based on multilayer nanorings. The absorber is made up of a 4-layer TiO₂-TiN nanoring array, a TiO₂ insulating layer and a Ti substrate, all of which are high-melting materials. The absorber exhibits an absorption efficiency surpassing 95 % across a wavelength span of 280–4000 nm, thereby attaining a bandwidth of 3720 nm. Additionally, it maintains an average absorption efficiency of 98.8 % throughout the entire wavelength spectrum. Furthermore, calculations reveal that the absorber possesses a solar spectrum-weighted absorption of up to 99 %. The analysis of the electric field distribution indicates that the observed intense absorption is attributed to the plasmonic resonance phenomenon, along with the near-field coupling effects exhibited by the multi-turn nanorings. In addition, our calculations revealed a remarkably high thermal radiation efficiency for this absorber, specifically 99.2 % at 2000 K and 98.9 % at 1500 K, respectively. Therefore, we then calculated the photothermal conversion efficiency of the absorber. At the solar concentration factor C = 1000, the photothermal conversion efficiency surpasses 90 % across the entire temperature range. At C = 100, it is still greater than 80 % at 1000 K. At C = 10, it is still greater than 80 % at 700 K. And at C = 1, it is still greater than 80 % at 500 K. These results indicate that absorbers can be used in a variety of environments. Furthermore, the absorber sustains its superior absorption capabilities at wider solar radiation angles, demonstrating insensitive properties to polarization variations and robust tolerance to manufacturing inaccuracies. These exceptional attributes render it highly suited for diverse applications in solar energy harvesting and photothermal transformation.