Block Copolymer Assembled Antireflective Coatings with Self-Cleaning Properties

Abstract

Reflection losses at optical interfaces are detrimental for many applications in optics and optoelectronics. Antireflection coatings (ARCs) are typically based on the principle that light reflected at the ARC’s interfaces interferes destructively to maximise light transmission. Advances in the fabrication of porous thin films have enabled to achieve refractive indices low enough to meet conditions for zero-reflectance off substrate materials like glass. Yet, many widespread applications require robustness and self-cleaning of ARCs, as well as low processing temperatures and compatibility with plastic substrates. In this chapter a new concept is presented which relies on the use of a high molecular weight block copolymer system with a large volume fraction of the hydrophobic block in combination with silica sol-gel chemistry. Spontaneous dense packing of colloidal micelles results in the co-assembly of the inorganic material in an inverse-opal like morphology. Subsequent removal of the polymer host leads to robust and continuous inorganic films with refractive indices as low as 1.13. The polymer-driven self-assembly route to ultralow refractive index films enables to replace up to 50 w% silica with high refractive index photocatalytic TiO2 nanocrystals, which freely disperse within the inorganic network. The resulting ARCs show good optical and self-cleaning properties and can be processed onto flexible plastic substrates.