Reactive magnetron sputter-deposited TiNxOy multilayered solar selective coatings

In this work, we have investigated multilayer structures in which TiNx as an IR reflector on the substrate due to its high infrared reflectivity, TiNxOy coatings serve as the solar absorbers, and a bi-layer N-doped TiO2/SiO2 or HfO2 layer for surface anti-reflection. Both the TiNx and TiNxOy layers were first optimized. Selected TiNx and TiNxOy layers were then used to fabricate the multilayered structures. Optical properties were assessed at room temperature and high temperatures up to 800 degrees C. While the multilayered structures having bi-layer N-doped TiO2/SiO2 as the anti-reflection layer show excellent absorption and emission up to 600 degrees C, much reduced absorption where obtained at 800 degrees C. The use of HfO2 layer to replace SiO2 improves the absorption at 800 degrees C. The relationship between material characteristics and optical performance, which has not been understood, is addressed in this study. Excellent high temperature selectivity is demonstrated.