An experimental study of a nearly perfect absorber made from a natural hyperbolic material for harvesting solar energy

• Published in: Journal of applied physics 2020-06, Vol.127 (23)
• Main Authors: Wang, Zhaolong, Yang, Peiyan, Qi, Genggeng, Zhang, Zhuomin M., Cheng, Ping
• Format: Article
• Language: English
• Subjects: Absorbers; Absorptance; Absorption; Absorptivity; Applied physics; Bismuth tellurides; Broadband; Energy harvesting; Finite difference time domain method; Incident light; Mathematical analysis; Metal surfaces; Morphology; Nanostructure; Optical properties; Roughness; Solar energy; Time domain analysis
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/5.0005700

In this paper, the absorptance of a broadband nearly perfect absorber, consisting of a metal surface covered by a rough Bi2Te3 layer, was measured and the optical properties of such a sample are calculated by using the finite-difference time-domain (FDTD) method. The results show that the measured absorptance of a designed sample with a roughness of 794 nm is larger than 0.94 in the wavelength range of 380–1800 nm, which can also be validated and explained by the calculated results. However, the absorptance of the absorber is affected by the morphology of the Bi2Te3 layer, including the roughness and the bottom width of the Bi2Te3 nanostructures. It is shown that the calculated absorptance of the absorber increases with the increasing roughness of the Bi2Te3 layer made of sharp nanostructures (with increasing cross section in the direction of incident light) if the bottom width of the Bi2Te3 nanostructures is fixed. However, the absorptance of the absorber decreases with the increase of the bottom width of Bi2Te3 nanostructures for absorbers with the same roughness. The underlying mechanisms for perfect absorbers are owing to the slow-light effect and gradient index effect, which require tall nanostructures with suitable bottom width for the total absorption of electromagnetic (EM) waves in the solar wavelength range. Furthermore, different samples were fabricated by using an electrochemical reaction method, and the measured absorption properties of these samples are shown in good agreement with calculated results.