Sputtering deposition and characterization of tandem absorbers for photo-thermal systems operating at mid temperature

In this paper the first results of a work concerned with the development of TiAlON selective solar absorbers with high solar absorptance and low thermal emittance are presented. These absorbers are thought for solar collectors application at operational temperature of about 300 °C. Solar absorber tandems, consisting of an absorbing TiAlON compound sputtered on a TiC buffer layer deposited on a metal (Cu) substrate, have been produced in two ways: by changing the nitrogen flux percentage in (Ar + N2 + O2) mixture at fixed thickness (300 nm) and by varying the absorber thickness at fixed nitrogen percentage (5%) in the sputtering gas. The optical response in the UV–IR range is discussed. The tuning of the nitrogen flux allows to change the metal elements ratio (Ti/Al) in the oxynitride layer, varying the reflectance intensity both in the IR and visible range. The thickness variation permits to shift the cut-off wavelength of the transition from short wavelength high absorptance to long wavelength low emittance. The tuning of these two parameters (nitrogen flux and absorber thickness) enables to control the optical response of the samples to make them suitable for photo-thermal device application.

► Cu/TiC/TiAlON tandem solar absorber have been sputtered and optically characterized. ► The tuning of nitrogen allows the tuning of the films optical constants. ► The tuning of the films thickness allows the shift of the cut-off wavelength.