Environmentally Durable Au-Based Low-e Coatings

Low-emissivity (low-e) coatings are used in architectural and automotive glazing for energy-saving applications. These are used to minimise heat transmission through the windows by reflection. Low-e coatings are semi-transparent coatings that typically comprise a metallic layer that reflects infrared light, sandwiched between two dielectric layers that protect the metal and enhance its visible transmittance. Ag is usually used as the metallic layer because of its colour neutrality and low optical absorption in the visible range. However, Ag-based low-e coatings easily degrade upon atmosphere exposure; therefore, they need to be placed inside the cavities of multiple-pane windows. In this paper, Au was used as an alternative to Ag and was sandwiched between WO3, SnO2 and Nb2O5 dielectric layers. The thickness of each layer was optimised to achieve the highest visible transmittance and infrared reflectance. The durability of the coatings was assessed by means of corrosion and abrasion resistance tests. We demonstrate that the Nb2O5/Au/Nb2O5 coating system provides a visible light transmittance of 56%, an emissivity as low as 0.04 and outstanding corrosion resistance (1000 h of salt spray testing), indicating its excellent potential to be used as first surface low-e coating.