Influence of the IR-mirror layer composition in the mechanical properties of solar selective coatings made from Mo:Si3N4 cermet

Solar selective coating multilayers deposited by magnetron sputtering and containing Mo:Si3N4 cermet as the absorber layer and Ag as infrared reflector (IR-mirror) have shown excellent optical characteristics for concentrated solar power applications at high temperatures. However, mechanical reliability of such optical coatings is a concern due to the large thermal mismatch between the Mo:Si3N4 cermet and the Ag IR-mirror layer. The substitution of the Ag IR-mirror layer by a Ti/Ag bilayer can improve mechanical reliability at the operating conditions, but at the expense of deteriorating the optical properties of the solar selective coating. In this work, we study the evolution of the mechanical and optical properties of Mo:Si3N4/Ti/Ag solar selective coatings, as a function of the Ti/Ag ratio, with the objective of finding a compromise between the optical and mechanical properties. The substitution of Ag by Ti improves the multilayers scratch resistance without deteriorating the optical properties. As a result, we suggest an optimal composition of the Ti/Ag IR-mirror bilayer.