Optical simulation and experimental optimization of Al/NbMoN/NbMoON/SiO2 solar selective absorbing coatings

Highlight
• The Al/NbMoN/NbMoON/SiO2 coating is optimized by using optical simulation.
• The optical constants are calculated with suitable dielectric function models.
• The optimized coating has high absorptance and low emittance at 80 °C.
• The coating exhibits excellent thermal stability at 400 °C in vacuum.
• It offers a good method to quickly reach the ideal spectral selectivity.

For the applications in solar thermal power, the preparation and optimization of an Al/NbMoN/NbMoON/SiO2 multilayer solar selective absorbing coating are carried out by combining experiments with optical simulation. A series of NbMoN and NbMoON single layers are deposited by magnetron reactive sputtering method with different N2/O2 gas flowing rates. And then their optical constants are obtained by fitting their reflection (R) and transmission (T) spectra in the wavelength range of 300–2500 nm using SCOUT software. These optical constants are used to design the Al/NbMoN/NbMoON/SiO2 solar selective absorbing coating so as to get the ideal spectral selectivity, i.e. high α/ε ratio. According to the optical design of the coating structure, we prepared the all-layer coating, and the thickness of each layer was optimized until the best spectral selective properties are obtained. The experimental reflectance spectrum fits very well with the simulated result. The optimized solar absorbing coating deposited on stainless steel substrate exhibited high absorptance (α=0.948) and low emittance (ε=0.050) at 80 °C. It offers a good method to quickly reach the ideal spectral selectivity through optical simulation. The thermal stability of the coating is evaluated, and it exhibits a good thermal stability in vacuum at 400 °C.