Design and characterization of solar absorbing multilayer stack based on Al/ Cr-N-O / SiO2 layers

Design, preparation and characterization of a solar selective absorbing coating based on chromium oxynitride are reported in this contribution. All the layers were deposited by reactive magnetron sputtering in a horizontal in-line sputtering system. The optical constants of individual layers were obtained by spectroscopic ellipsometry measurement and fitting. The absorbing multilayer stack including, from substrate to air interface, Al infrared reflective layer/ (Cr/CrNx//CrNxOy) composite absorbing layer/ SiO2 antireflective layer were then designed and fabricated based on their optical properties and thickness optimization. This absorbing coating is characterized by the simple and stable reactive magnetron sputter coating process with no need for precise control of single layer thickness and reactive gas partial pressure. A solar absorptance more than 95% and thermal emissivity less than 4% for operation temperature of 100 °C were obtained by analyzing the measured spectra data. After aging test in air at 250 °C for 200 h, the performance criterion (PC) was below 1%, and the deterioration mechanism was further analyzed combined with XPS depth profile.