Ultra-broadband metamaterial absorber for high solar thermal energy conversion efficiency

In this paper, a titanium cross-shaped based-metamaterial absorber in the visible and near-infrared regions is presented. The proposed solar thermal absorber consists of a cross-shaped titanium/SiO₂ spacer/TiN ground film structure enabling high broadband absorption and solar-thermal conversion efficiency. The broadband near-perfect absorption spectra with the proposed structure reach 97% for both TE and TM-polarization in the wavelength ranges of (from 386 to 1178 nm) and (from 300 to 1140 nm), respectively. Furthermore, the proposed structure exhibits a high solar thermal conversion efficiency of 96% under continuously variable of C from 1 to 1000, maintained over the wide operating temperature range 373–779 K. Remarkably, the performance of the structure has been promising for the enhancement of the solar thermal energy harvesting devices at middle to high temperatures.