Design of an ultra-wideband solar absorber based on tungsten

A solar absorber based on tungsten with an ultra-wide wavelength band is investigated numerically using the finite-difference time–domain method. The designed structure consists of a cross-shaped resonator on top of the absorber and a metal thin film on the bottom that are separated by an intermediate dielectric layer. The absorber demonstrates continuous high absorptivity (>90%) over the 514–1945 nm wavelength range, and the average absorptivity ranges up to 92.36% within the 200–2000 nm range. The excitation of propagating surface plasmon resonance (SPR) and localized SPR in combination with Fabry–Pérot resonance leads to the observed wideband absorption. We also demonstrate that the proposed absorber is insensitive to both transverse electric and transverse magnetic polarizations and study its absorptive performance at larger angles of incidence. The effects of the structural parameters and of different dielectric layer materials on the absorption performance have also been investigated. Furthermore, we explain the absorption mechanism using a power flow plot and impedance matching. The proposed absorber has promising prospects for applications, including solar cells, solar energy harvesting, and thermal emitters.