High-Entropy Alloy Nitride AlMo_0.5NbTa_0.5TiZrN_x-Based High-Temperature Solar Absorber Coating: Structure, Optical Properties, and Thermal Stability

Advanced solar thermal technologies, including solar thermal collectors, solar thermophotovoltaic systems, and concentrated solar power systems, depend heavily on solar selective absorber coatings (SSACs) for photothermal conversion. Efforts for the research work of SSACs focus not only on optical properties but also on their high-temperature applications over a wide temperature range. Here, an SSAC based on an AlMo0.5NbTa0.5TiZrNx high-entropy alloy nitride ceramic is first designed and fabricated on a stainless steel (SS) substrate via the magnetron sputtering method. The multilayer AlMo0.5NbTa0.5TiZrNx-based solar absorber coatings show good optical properties with a high absorptance value of 0.932 and a low infrared emittance value of 0.063. For the thermal stability of this coating, the as-fabricated coatings are subjected to the annealing process in vacuum at different temperatures. It is interesting that the spectral selectivity deteriorates to 0.798/0.067 at 673 K for 2 h but increases to 0.855/0.08 at 973 K for 2 h. In addition, finite difference time domain (FDTD) calculations are employed to determine the evolution of the optical absorption contributing to intrinsic absorption. The obvious attenuation of the electric field was caused by the change in the optical constants of the bimetallic ceramic layer, as evidenced by systematic analysis.