Solar selective properties of copper-aluminium composite films

613-617Composite films of copper and aluminium were deposited by reactive direct current co-sputtering of copper and aluminium. The number of copper pieces was varied during deposition which made it possible to vary the composition of the films. In order to understand the optical behaviour of the coatings, the optical constants were determined by fitting model dielectric functions to the transmittance and the near normal reflectance spectra in the wavelength range 300-2500 nm. The thicknesses of the layers obtained by modeling were confirmed by surface profilometry. The XPS studies of the samples reveal that the number of copper pieces used during co-sputtering control the formation of copper oxide. Computer simulations on layers of Cu-Al composites on metallic substrate with anti-reflection coatings were carried out to optimize solar absorptance using the optical data from the model. Solar absorptance as high as 0.91 with anti-reflectance coating was obtained from the simulation