Transition metal nitride/oxide-based multilayer PVD coating with sol–gel derived ormosil passivation layer as an efficient solar absorber: Studies on high temperature stability and performance evaluation

Abstract

We describe a hybrid multilayer solar absorber coating consisting of physical vapor deposited (PVD) Ti interlayer, aluminum titanium nitride (AlTiN) main absorber layer, aluminum titanium oxynitride (AlTiON) semi-absorber layer, aluminum titanium oxide (AlTiO) anti-reflection layer and sol–gel deposited ormosil passivation layer. The ormosil layer, which is essentially organically modified silica, also acts like an anti-reflection coating, thus, increasing the absorptance (α) of the multilayer stack to ∼ 0.950 (c.f., α = 0.930 for the PVD coating on stainless steel substrate) along with an emittance (ε) of 0.17@82 °C. Generally, pure inorganic sol–gel coatings like silica contain defects, which allow gases and corrosive substances to penetrate the coating/substrate interface, thereby, deteriorating the performance of the coating under extreme environments. However, the presence of an organic moiety in the inorganic network results in a dense microstructure with improved mechanical flexibility and hardness. We discuss in detail the effect of ormosil layer on the performance of the PVD deposited solar absorber coating. We report that the unique and stable microstructure of the ormosil layer helps in increasing the thermal stability of the underneath PVD coated solar absorber coating, particularly suitable for applications in concentrating solar collectors useful for solar steam generation.