Ultra-wideband solar absorber based on refractory metal titanium for high-performance photothermal conversion

In recent years, metamaterial absorbers are widely used in solar energy harvesting and utilizations. Nevertheless, it is difficult to achieve simultaneously high absorption, insensitivity with a large angle of incidence, polarization independence and, highly efficient photothermal conversion over a wide range of wavelengths for existing solar energy absorbers. Herein, an ultra-wideband and high-performance solar perfect absorber for the spectral range of 200–5000 nm has been proposed. It consists of a Ti metal substrate, a Ti-Al₂O₃ pattern layer with etched square annular air cavity, and a Si₃N₄ dielectric layer surrounding the bottom of the pattern layer. Over the spectral range spanning from 200 to 5000 nm, the average absorbance is 97.7 %, and the minimum absorbance is above 91 %. In solar energy system, its total photothermal conversion efficiency is 90.9 % at 1000 K, with as much as 96.41 % of sunlight absorbed. The interactions between surface plasmon resonance (SPR), guided mode resonance (GMR), magnetic resonance (MR), and cavity resonance (CR) are responsible for excellent performance of the ultra-broadband absorber. Additionally, the absorber is not sensitive to wide angles of incidence and is polarization independent. More interestingly, large angle incidence at TE and TM polarizations has equally excellent performance. Besides, the absorber meets a certain tolerance for geometric manufacturing errors, allowing for low-cost practical manufacturing. The designed absorber is expected to be applied to solar cells and thermo-photovoltaic devices.