Fabrication and characterization of biomimetic antireflective surfaces with reduced glare

Abstract

Providing antireflection in the visible spectrum is useful for a number of applications. Solar cells, LCD screens, optical lenses and stealth surfaces are a few examples of applications that can benefit from antireflection. In this work, maximizing the performance of a biomimetic motheye metamaterial antireflection layer via optimization of its design parameters was investigated. Additionally, case studies of designing optimized antireflection solutions were carried out for some of the most demanding applications such in solar cells and stealth coatings. More specifically, simulations of the moth-eye design parameters for feature period, height, density factor, shape and topology were carried out. For feature height, it was found that for a height larger than 400nm, the gains in providing antireflection for the visible spectrum are low, so it is not necessary to create features taller than this to achieve a good antireflection performance. For feature density factor an almost linear monotonic relationship was observed, so for this design parameter, maximization is necessary. For the feature period parameter, it was found that a simple rule could not be extracted and thus to optimize performance, a tailoring of the period for each application has to be done whilst taking into account the incident spectrum. An optimization of the feature period was carried out for monocrystalline silicon solar cells and the AM 1.5 solar spectrum and it was found that for this spectrum, the optimum period is 397nm. Feature topology was not found to provide a significant advantage to the antireflection behaviour of the metamaterial layer in terms of power, however it does provide a more diffuse scattering of the backscattering diffraction order which emanates from the structure at high angles of incidence, an attribute which is very useful for stealth applications. To verify simulation results, fabrication of moth-eye antireflection structures were carried out via nano-imprint, electron-beam and nanosphere lithography. The nanosphere lithography technique presented was optimized specifically for the samples required in this thesis. Complete monolayer coverage of large areas (2x2cm2) was accomplished and thus complex biomimetic feature topologies could be readily investigated. Optical experiments measuring specular reflectance and the backscattered diffraction orders were carried out both with readily available and custom built optical setups. The simulation trends were all verified successfully and a summary of suggested design parameters for a range of different applications has been suggested.

More information

Identifiers

Catalogue record

Export record