Broadband Enhancement of Anti-reflectivity for a High Angle of Incidence Using Nanocone Geometry

Abstract

The broadband antireflective (AR) effect for wide incident angles has a significant effect on the photoconversion efficiency of photovoltaics and visibility of large-format display panels. The fabrication of surface nanostructures has continued to attract research interest as an effective way to provide such optical performance. However, the effects of different nanostructure geometries are not fully understood, especially for wide-angle AR effects. In this work, we conduct a systematic analysis of the effect of periodic nanostructures such as nanocones (NCs) and inverted nanocones (INCs) on anti-reflectivity at high angles of incidence (AOIs) in terms of light scattering, guided-mode resonance (GMR), and internal reflections. NCs provide good coupling of light scattering and GMR because of their protruding geometry; hence, reduced reflectance can be obtained in the short wavelength region. Further, NCs exhibit relatively weaker GMR intensities and internal reflections, resulting in low reflectance in the long wavelength region. Therefore, NCs offer a superior broadband AR effect for high AOIs compared with INCs. Based on this analysis, we demonstrate an extremely low average reflectance (5.4%) compared to that of the bare substrate (34.7%) for the entire visible range at an AOI of 75° by fabricating NCs on both sides of the substrate.

Mechanically-Durable Antireflective Subwavelength Nanoholes on Glass Surfaces Using Lithography-Free Fabrication

“…Inspired by the periodic hexagonal nanosized corneal nipple arrays in the compound eyes of moths, , the wings of butterflies, , or cicadas, , biomimetic subwavelength structures with outstanding spectral and angular antireflective properties have been fabricated. During the past decade, tremendous research efforts have been dedicated to both design and fabrication of AR nanostructured surfaces with various geometrical shapes and arrangements such as nanopillars, − nanocones, − nanoholes (NHs), − and hybrid designs combining nanostructures on top of multilayer thin film stacks. − In addition to the improved optical properties, nanostructured surfaces can change the wetting of the surfaces, ,,,,,,, therefore providing self-cleaning and antifogging effects valuable in touchscreen displays, automotive windows, outdoor solar panels, to name a few. Monolithic substrates (subtractive as opposed to additive process) can also be advantageous in high-power laser applications by raising the laser-induced damage threshold values to these of the bulk material. , …”