Light reflection from surfaces is ubiquitous in nature. Diverse optoelectronic devices need durable, omnidirectional, and transparent ultra-antireflective surfaces. Here, we engineered antireflective transparent surfaces composed of silica nanocaps through a simple thermal treatment of a silica-coated monolayer colloidal crystal template. The relationship between the structure and the antireflective performance of the silica nanocaps was systematically studied both experimentally and numerically. On the basis of the understanding of the structure-antireflection relationships, ultra-antireflection coatings with a transmittance of ∼98.75 ± 0.15% in the visible wavelength range were prepared by fabricating two differently sized silica nanocaps. More importantly, the antireflection of the coatings formed by two differently sized nanocaps demonstrated poor dependence on the angle of the incident light (i.e., omnidirectionality). The reflection is <2.5% even at an incident angle of 60°. The prepared ultra-antireflective silica nanocap coatings outperform state-of-the-art transparent antireflective coatings regarding the antireflection performance, the wavelength range, and the omnidirectionality. The silica nanoshells were welded together with the underlying fused silica. Therefore, they can sustain common mechanical friction and scratching, demonstrating extraordinary mechanical durability as verified by sand abrasion tests. Further, the silanized silica nanocaps turned out to be hydrophobic with an outstanding self-cleaning performance without prominently influencing the transmittance. The durable and omnidirectional ultra-antireflective transparent silica nanocaps will have promising applications in solar energy conversion and storage, displays, optical lenses, and a wide range of optoelectronic devices.
Keywords: coating; colloidal lithography; monolayer colloidal crystal; nanocap array; omnidirectional antireflection surface.