Optical properties and surface composition of oxidized copper for solar absorbers

Selectively absorbing surfaces of chemically oxidized copper have been studied with respect to optical properties and chemical composition. Different copper qualities, preparation parameters and post-treatments have been investigated in order to optimize the optical performance and the long-term durability. Optical and Auger analysis have been performed to characterize the oxidized copper surfaces, which have been exposed to accelerated and natural ageing. The analyses have shown that the absorption can be increased if the copper surface is mechanically brushed prior to oxidation and that a post-treatment which gives a protective layer on top of the copper oxide is essential for the durability. Among the accelerated ageing tests heat treatment was found most relevant.