Photothermal conversion of solar energy by gold cermet coatings: applicability of the Bruggeman effective medium theory

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Abstract
Efficient photothermal conversion of solar energy requires high absorption at wavelengths λ≲2 μm and low absorption at λ≳2 μm. This absorptance profile can be achieved by coatings consisting of ultrafine metal particles in an insulating matrix. I compare available optical data for concentrated gold cermet films with calculations based on the non‐self‐consistent Maxwell Garnett theory and on the self‐consistent Bruggeman theory. The latter is found to be superior for MgO+25 vol% Au and for Al2O3+18 vol% Au, whereas no firm conclusions can be drawn for MgF2+Au.