Optical and structural properties of TaC thin films: Towards design of an efficient high temperature solar absorber coating

Tantalum and Tantalum Carbide (TaC) thin films are fabricated using pulsed DC magnetron sputtering from a Ta target in an argon-acetylene (C2H2) environment at room temperature. Precise control of the TaCx film composition was achieved, with minimal impact on the films’ structure, morphology, and optical properties observed when varying C2H2 gas concentrations, ensuring high reproducibility rate. Ellipsometry analysis determined the complex refractive index of the TaCx films, enabling accurate reproduction of reflectivity spectra in both visible and infrared regions. As the knowledge of the refractive index is crucial for simulating optical structures, an optimised selective solar absorber (SSA) for use in concentrating solar-thermal power (CSP) systems was designed. It comprises TaC and SiN layers on a tungsten substrate; hence, it is capable of withstanding high temperatures. It has a solar absorptance of 0.96 and a thermal efficiency higher than 0.9 at 900 °C and 0.85 at 1100 °C for incident angles up to 50 °C for a concentration factor of 1000. Its large acceptance angle offers significant potential for energy production through heliostats where the incident angle may vary.