Cost-effective and durable AlN/Al/AlN multilayer coatings for energy-efficient window applications

Energy-efficient glazing technologies are critical in reducing heat gain in buildings and vehicles while maintaining visible light transmittance. Low-emissivity (Low-E) coating are widely used for this purpose, typically consisting of silver (Ag) as an infrared-reflective layer encapsulated between multiple dielectric layers, usually oxides, to protect the metal from environmental degradation. However, Ag-based coating suffers from high material cost and long-term degradation due to environmental exposure. In this work, a novel costeffective multilayer configuration consisting of aluminium nitride/aluminium /aluminium nitride (AlN/Al/AlN) is designed on the glass substrate using RF magnetron sputtering. Al is selected for its low cost, neutral appearance and self-passivating alumina layer, while AlN serves as an antireflective coating as well as protective layer for Al against environment degradation. Experimental results demonstrate an AlN/Al/AlN stack with 12nm Al realizing Tvis, infrared transmittance (TIR) and infrared reflectance (RIR) of 23.66%, 16.81% and 60%, respectively. Increasing the Al layer thickness to 16 nm resulted in an enhancement of RIR of 90% but reduces the visible and IR transmittance of 16.58% and 9.68%, respectively. Furthermore, varying AlN thickness is found to shift the position of the visible transmittance maxima due to the interference effects, governed by the constructive and destructive interference of the electromagnetic radiation. These results show tunability in the optical performance through thickness control and demonstrate the potential of Al as a cost-effective, durable alternative to conventional Ag-based low-E coating for energysaving window applications