Ultra-broadband and wide-angle solar absorber based on Ti/Al2O3 cross-gap staircase structure

Abstract

High-efficiency solar energy harvesting under high-temperature conditions demands absorbers with ultra-broadband spectral response and exceptional thermal stability. In this paper, we propose a refractory metamaterial solar absorber utilizing a Ti/Al2O3 cross-gap staircase structure. The device achieves an average absorption efficiency of 98.14% across a wide wavelength range of 280-3000 nm, with a bandwidth of 2705 nm exceeding 90% efficiency. Under the AM1.5 solar spectrum, the weighted average absorption reaches 96.82%. Electromagnetic field analysis reveals that this superior broadband performance arises from the synergistic coupling of multiple resonance modes, including gap resonance, localized and propagating surface plasmon resonances (LSPR/PSPR), magnetic resonance (MR), and Fabry-Pérot (F-P) cavity resonance. Beyond solar absorption, the structure functions as a near-perfect thermal emitter, achieving radiation efficiencies of 98.83% and 99.06% at 1000 K and 2000 K, respectively, approaching the ideal blackbody. Furthermore, the absorber demonstrates excellent polarization independence and wide-angle absorption characteristics, with the average absorption efficiency remaining above 90% even at a 60° incident angle. Based on the above features, this design holds significant potential for high-efficiency solar energy harvesting and thermal radiation applications.