Structure and thermal stability of spectrally selective absorber based on AlCrON coating for solar-thermal conversion applications

A novel four-layered Mo/AlCrON(HMVF)/AlCrNO(LMVF)/AlCrOx tandem coating was designed and fabricated by cathodic arc ion plating for solar-thermal conversion applications. The chemical composition, structures and thermal stability of the coating were systematically investigated by SEM, EPMA, XRD, TEM, XPS and Raman. The optical properties of the as-deposited and annealed coatings were measured by spectrophotometers. The high-temperature emittance of the coating was measured by a steady-state measurement system. Results showed that tandem coating exhibited a high solar absorptance of 0.921, and a low emittance of 0.12 at 25 °C, as well as emittance of 0.26-0.35 at temperatures range of 300−519 °C. The structure analysis showed that the nano-multilayered structured HMVF and LMVF layers, acting as the main absorber, were consisted of the Cr2Al nanograins embedding in the amorphous AlCrON phases. While the top AlCrOx layer was amorphous in nature, and could act as an antireflection layer. After heat-treatment at 600 °C in air for 7 days, only slight microstructure changes were observed from the tandem coating, and very similar solar selectivity of 0.922/0.14 to the as-deposited one was obtained, which indicated the relatively good thermal stability of the coating. These results indicated that the coating could be possibly applied to the high temperature solar-thermal conversion system.