Selective absorption of solar energy in granular metals: The role of particle shape

Abstract

Coatings for efficient photothermal conversion of solar energy should have high absorption at wavelengths λ<λc and low absorption at λ≳λc, where λc is ∼2 μm. For granular metals, we show by computation that λc depends strongly on the shape of the metal particles. Increasing eccentricity of ellipsoidal grains is seen to displace λc towards the infrared. A similar shift is found also for spherical metallic shells surrounding dielectric cores of increasing size. Some implications for practical absorber surfaces are pointed out.