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

Nanostructured surfaces are common in nature and exhibit properties such as antireflectivity (moth eyes), self-cleaning (lotus leaf)(i) iridescent colors (butterfly wing), 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 difficulty nonplanar surfaces. Here, we report a solution process based on block copolymer (BCP) self-assembly to fabricate subwavelength structures, on large areas of optical and, curved surfaces with feature sizes and spacings designed to efficiently scatter visible light. Si nanopillars (SiNPs) with diameter of similar to 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 and 900 nm. at an angle of incidence of 30 degrees. Significantly, the reflectivity remains below 1/5% up to incident angles of 75 degrees. Modeling the efficiency of-a SiNP PV suggests a 24.6% increase in efficiency, representing a 3.52% (absolute) of 16.7% (relative) increase in electrical energy-output from-the PV system Compared to AR-coatect device.