Structure, optical simulation and thermal stability of the HfB₂-based high-temperature solar selective absorbing...

Transition metal borides are a kind of potential materials for high-temperature solar thermal applications. In this work, a novel SS/HfB₂/Al₂O₃ tandem absorber was prepared, which exhibited high solar spectrum selectivity (α/ε) of 0.920/0.109. The optical constants of the coating were obtained using spectroscopic ellipsometry, and the dispersion model of the HfB₂ layer was modeled with the Tauc-Lorentz dispersion formula. In addition, the reflectance spectrum simulated by the CODE software corroborated well with the experimental results. The thermal stability test indicated that the HfB₂/Al₂O₃ solar absorber coating was thermally stable in vacuum at 600 °C for 2 h. When extending the annealing time to 100 h, the coating could maintain high spectral selectivity after aging at 500 °C irrespective of whether in air or vacuum. All these results indicate that the coating has good solar selectivity and is a promising candidate for high-temperature solar thermal applications.