Abstract
The absorber-reflector tandem configuration is used for the realization of a selective absorbing surface for the photothermal conversion of solar energy. The infrared reflector consists of a stainless steel substrate, covered or not with a W or Mo thick film. The visible absorbing function is realized by a thin, low cost, FeAl 2O 3 cermet film. The cermet films are prepared by rf cosputtering onto a rotating stainless steel substrate. The target consists of a circular Al 2O 3 plate covered with small discs, the concentration varying with the Fe disc number. The optical properties of the thin FeAl 2O 3 films are studied as a function of the Fe volume fraction from 0.2 to 0.9. The dielectric function is calculated from the reflectivity and transmittivity measurements in the 300–50000 nm spectral range. The films exhibiting the required selective properties (high absorptivity in the visible, high transparency in the infrared) are selected. A sandwich, composed of a thin Al 2O 3 antireflecting film, the cermet film (with adequate thickness and composition) and the reflecting substrate, exhibits a good selectivity for the photothermal conversion at low and middle temperatures ( α = 0.95; ε(300 K) = 0.06; ε(700 K) = 0.14 ).
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