Ultra-broadband metamaterial absorber for capturing solar energy from visible to near infrared

In this paper, a metamaterial absorber for broad-spectrum absorption under solar radiation is proposed, which consists of periodic square arrays on a-Si spacer layer and Ti substrate. With the coupling of multiple resonances, the average absorption of the absorber is more than 95% within the studied spectrum (300-2000 nm) and the bandwidth of absorption over 90% is 1576 nm (from 329 nm to 1905 nm). Since the Ti material in the absorber is a refractory metal with low cost and stable mechanical properties, the absorber can operate in high temperature environment. Especially, the study results show that the absorber has a general applicability to other refractory metals. Also, the absorber is insensitive to polarization and incident angles, which is very attractive in practical manufacture and use due to a high absorption performance within a large fabrication tolerance. In addition, the absorption spectrum of the absorber is highly consistent with the solar spectrum and can maintain a high in-tegrated absorption at large incident angle. These findings show that the absorber has potential applications in many areas such as solar cells, solar energy harvesting, thermal emitters and photothermal conversion.