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Nano Research

Article Title

Ultrathin planar broadband absorber through effective medium design

Keywords

ultrathin planar film, broadband absorber, effective medium design, solar energy

Abstract

Ultrathin planar absorbers hold promise in solar energy systems because theycan reduce the material, fabrication, and system cost. Here, we present a generalstrategy of effective medium design to realize ultrathin planar broadbandabsorbers. The absorber consists of two ultrathin absorbing dielectrics to designan effective absorbing medium, a transparent layer, and metallic substrate.Compared with previous studies, this strategy provides another dimension offreedom to enhance optical absorption; therefore, destructive interference canbe realized over a broad spectrum. To demonstrate the power and simplicity of thisstrategy, we both experimentally and theoretically characterized an absorber with5-nm-thick Ge, 10-nm-thick Ti, and 50-nm-thick SiO2 films coated on an Agsubstrate fabricated using simple deposition methods. Absorptivity higher than80% was achieved in 15-nm-thick (1/50 of the center wavelength) Ge and Tifilms from 400 nm to near 1 μm. As an application example, we experimentallydemonstrated that the absorber exhibited a normal solar absorptivity of 0.8 witha normal emittance of 0.1 at 500 °C, thus demonstrating its potential in solar thermalsystems. The effective medium design strategy is general and allows materialversatility, suggesting possible applications in real-time optical manipulation usingdynamic materials.

Graphical Abstract

Publisher

Tsinghua University Press

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