Large Block Copolymer Self-Assembly for Fabrication of Subwavelength Nanostructures for Applications in Optics

Parvaneh Mokarian-Tabari, Ramsankar Senthamaraikannan, Colm Glynn, Timothy W. Collins, Cian Cummins, David Nugent, Colm O’Dwyer, Michael A. Morris

Nanostructured surfaces are common in nature and exhibit properties such as antireflectivity (moth eyes), self-cleaning (lotus leaf), iridescent colors (butterfly wings) and water harvesting (desert beetles). We now understand such properties and can mimic some of these natural structures in the laboratory. However, these synthetic structures are limited since they are not easily mass produced over large areas due to the limited scalability of current technologies such as UV-lithography, the high cost of infrastructure and the inability to pattern non-planar surfaces. Here, we report a solution process based on block copolymer (BCP) self-assembly to fabricate sub-wavelength structures on large areas of optical and curved surfaces with feature sizes and spacings designed to efficiently scatter visible light. Si nanopillars (SiNPs) with diameters of ~115±19 nm, periodicity of 180 ± 18 nm and aspect ratio of 2-15 show a reduction in reflectivity by a factor of 100, < 0.16% between 400-900 nm at AOI 30°. Significantly, the reflectivity remains below 1.75% up to incident angles of 75°. Modelling the efficiency of a SiNP PV suggests a 24.6% increase in efficiency - representing a 3.52% (absolute) or 16.7% (relative) increase in electrical energy output from the PV system compared to the AR-coated device.