Study on the thermal stability of Al/NbTiSiN/NbTiSiON/SiO₂ solar selective absorbing coating

In this work, the NbTiSiN and NbTiSiON layers are used instead of NbTiN and NbTiON layers to further improve the thermal stability of Al/NbTiN/NbTiON/SiO₂ multilayer solar selective absorbing coating. The thermal stability of Si-doped individual layers and multilayer coatings are investigated. The X-ray diffraction (XRD) results show that Si incorporation into NbTiN (NbTiSiN) layer does not change its preferred orientation, and the Si-doped NbTiON (NbTiSiON) layer remains in amorphous phase. On the other hand, by introducing Si into NbTiN and NbTiON layers induce significant improvement of the oxidation resistance at 500°C in air. After ageing in air at 500°C for 2h, the absorptance and emittance (at 400°C) of Al/NbTiN/NbTiON/SiO₂ and Al/NbTiSiN/NbTiSiON/SiO₂ multilayer coatings change from 0.934/0.13 and 0.931/0.12 to 0.538/0.14 and 0.922/0.13, respectively. Meanwhile the surface roughness increases from 18.3 and 7.9 to 41.5 and 14.7 respectively, as atomic force microscopy (AFM) shows. The Al/NbTiSiN/NbTiSiON/SiO₂ coating still has a high absorptance (0.910) and low emittance (0.13, at 400°C) after ageing at 550°C in vacuum for 100h. It displays that Si-doping play an important role in the improvement of the thermal stability.