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Posted: Oct 22, 2013
A simple method to fabricate self-cleaning, antireflection coatings
(Nanowerk News) Low-cost antireflection coatings (ARCs) on large optical surfaces are an ingredient-technology for high-performance solar cells. While nanoporous thin films that meet the zero-reflectance conditions on transparent substrates can be cheaply manufactured, their suitability for outdoor applications is limited by the lack of robustness and cleanability.
In a new paper in Nano Letters ("Self-Cleaning Antireflective Optical Coatings"), an international research team now reports the manufacture of a highly porous ARC with high TiO2-nanoparticle loading that combines excellent optical antireflectivity with efficient photocatalytic activity.
The fabrication strategy relies on the self-assembly of a blockcopolymer in combination with silica-based sol-gel chemistry and preformed TiO2 nanocrystals. The spontaneous dense packing of copolymer micelles followed by a condensation reaction results in an inverse opal-type silica morphology that is loaded with TiO2 photocatalytic hot-spots.
The team's fabrication strategy relies on the assembly of high molecular weight blockcopolymer micelles that assemble into a sacrificial opal-type structure. After solidification by a sol-gel condensation reaction, this gives rise to a silica network with porosities of up to 73%. This enabled the addition of high weight fractions of TiO2 nanocrystals without compromising the refractive index required for high performance ARCs.
The combined antireflective and photocatalytic properties should substantially improve the long-term optical properties of porous ARCs, or even remove applied contaminants such a fingerprints.
The low-temperature ARC processing enables the coating of flexible plastic substrates, paving the way for low-cost large area ARC manufacture.