Tailoring radiative properties of a complex trapezoidal grating solar absorber by coupling between SPP and multi-order MP for solar energy harvesting

Abstract

The coupling resonance effect between surface plasmon polariton (SPP) and multi-mode magnetic polariton (MP) is very complicated. In this study, we propose a complex trapezoidal grating solar absorber (CTGSA) with nanoscale structure, which is made of two tungsten trapezoids and a silicon dioxide spacer lying on the tungsten substrate, to study the coupling resonance between SPP and multi-mode MP in detail, not just the fundamental mode. The finite-difference time-domain method is employed to calculate spectral absorptivity and electromagnetic distribution. The coupling between SPP and MP of different modes can be clearly shown through the electromagnetic field, which is conducive to the investigation of the physical mechanisms of the four close-to-unity peaks in the absorptivity curve. The effects of geometric parameters on the resonance conditions are also explored. The coupling between SPP and MP renders the manual control of the absorptance of the structure possible. Calculations of directional absorptance at peak wavelengths for solar radiative intensity show that the absorptance of the proposed CTGSA is stable for a wide range of incident angles. Abnormal behaviors of directional absorptance are observed due to Wood’s anomaly. Besides, for steam generation application, the solar-thermal conversion efficiency is up to 74%, which has a practical significance. By providing a detailed analysis of the coupling of SPP and multi-order MP based on electromagnetic distribution, this paper will fill the gap in the field of MP resonance generated in the space between trapezoidal ridges and present a nanoscale structure with remarkable properties for harvesting broadband solar energy, which can provide a useful reference for optimizing design of solar absorbers.