AlN–Ag based low-emission sputtered coatings for high visible transmittance window

Abstract Despite the availability of high performance glass technologies a preconceived idea that glass is the weak point in a building envelope still persists [1] . Thanks to the continuous improvement in thermal insulation performance combined with new methods of modulating solar heat and visible transmittance, glazing has strengthened its position as smart opportunity for energy savings in green buildings. In the field of smart glazing, low-emission (low-E) coatings have contributed to change glass from an energy liability to an energy asset, acting like filters to manage heat transfer, in a manner that some energy wavelengths pass through, while others are rejected. Low-E glass can retain furnace heat, when it is cold outside, or rejects excessive solar heat, when it is hot outside. In this work, by means of a semi-empirical method, low-E coatings based onto a multilayered structure have been designed, ideal for mild to hot climates. These coatings consist of thin silver layers sandwiched between two dielectric layers of aluminum nitride, obtained by sputtering deposition technique. Stacked structures with two or more dielectric/metal/dielectric sequences have been considered in order to maximize high visible transmittance and to minimize emissivity value at room temperature. Starting from optical parameters of bulk materials and by means of a simulation tool, thicknesses of the different layers and of the overall stacked structure have been determined and a highly effective low-E filter has been optimized having high visible transmittance (82%) and very low emissivity (8%).