Broadband Perfect Absorber Based on TiN-Nanocone Metasurface

Based on an integrated array of refractory titanium nitride (TiN), a metasurface perfect absorber (MPA) in the visible-to-near infrared (NIR) band is reported. The systematic and detailed simulation study of the absorption of the MPA is performed with the finite-different time-domain (FDTD) method. Tailoring the structure, the MPA realizes as high an average as 99.6% broadband absorption, ranging from 400 nm to 1500 nm. The broadband perfect absorption can be attributed to localized surface plasmonic resonance (LSPR), excited by the continuous diameter evolution from the apex to the base of the nanocone, and the gap plasmons excited among the nanocones, as well as in the spacer layer at longer wavelengths. Particularly, the coupling of the resonances is essentially behind the broadening of the absorption spectrum. We also evaluated the electric field intensity and polarization-dependence of the nanocone MPA to offer further physical insight into light trapping capability. The MPA shows about 90% average absorption even at an oblique incidence up to 50 degrees, which improves the acceptance capability of light-harvesting system applications. This unique design with the TiN nanocone array/aluminium oxide (Al2O3)/TiN structure shows potential in imminent applications in light trapping and thermophotovoltaics.