Ultralow Index SiO<sub>2</sub> Antireflection Coatings Produced via Magnetron Sputtering
Christian J. Ruud, Angela Cleri, Jon‐Paul Maria, Noel C. Giebink
Abstract
Antireflection (AR) coatings with graded refractive index profiles approaching air offer unparalleled AR performance but lack a scalable fabrication process that would enable them to be used more widely in applications such as architecture and solar energy conversion. This work introduces a sputtering-based sacrificial porogen process to fabricate multilayer nanoporous SiO2 coatings with tunable refractive index down to neff = 1.11. Using this approach, we demonstrate a step-graded bilayer AR coating with outstanding wide-angle AR performance (single side average reflectivity in the visible spectrum ranges from 0.2% at normal incidence to 0.7% at 40°), good adhesion, and promising environmental durability. These results open up a path to produce ultrahigh performance AR coatings over large area by using industrial-scale magnetron sputtering systems.