The spectral properties and thermal stability of CrAlO-based solar selective absorbing nanocomposite coating

A novel four-layer structured Cr-Al-O tandem nano-multilayer composite coating has been prepared by cathodic arc ion plating for solar selective absorbing. The four-layer structured coating consists of pure chromium layer, low oxygen content Cr-Al-O layer (LOCL), middle oxygen content Cr-Al-O layer (MOCL) and high oxygen content Cr-Al-O layer (HOCL). The composition, structure, and surface morphology of the coating were characterized using SEM, EDS, XPS, TEM, and AFM. The optical performances of the coating were measured by spectrophotometer, while the thermal stability of the coating was evaluated by Raman spectroscopy. Results showed that LOCL and MOCL, in which amorphous Cr-Al-Ox nanolayers and composite Cr-Al-Ox nanolayers embedded with Cr ₂Al nanograins alternated with each other, were the main absorbers, while HOCL acted as an antireflection layer. The coating exhibited a relatively high absorptance of 0.924 and a relatively low emittance of 0.21, as well as an outstanding thermal stability with a selectivity of 0.919/0.225 even after annealing at 700 C for 2 h in air, which properties rendered the four-layer structured Cr-Al-O tandem coating a potential material for photo-thermal conversion at high temperatures.