Optimization of Self-Assembled Particle Deposition for Colloidal Lithography Nano/Micro-Patterning

• Autor(a) principal: Oliveira, Rui Daniel de
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/117485
• topic: Light-trapping in Photovoltaics; Photonic structuring; Colloidal lithography; Langmuir-Blodgett; Particle Self-assembly; Domínio/Área Científica::Engenharia e Tecnologia::Nanotecnologia

Colloidal lithography (CL) is nowadays considered a preferential nano/micro-patterning method for photovoltaic structuring, as it is an inexpensive and highly scalable soft-lithography technique allowing nanoscale precision over indefinitely large areas. Photonic wavelength-sized structures are on the top of the list of solutions that can boost photovoltaic performance without significantly increasing cost, as they enable pronounced broadband anti-reflection, LT effects, and even self-cleaning functionality. In particular, recent research suggested that these micro-structures can boost not only the efficiency but also the stability of the emergent perovskite solar cell technology. CL methods critically depend on the long-range ordered self-assembly that can be attained upon deposition of the particles’ array used as a mask, which is performed via the Langmuir-Blodgett method. However, it is still challenging to achieve the desired deposition quality particularly with the preferential polystyrene colloids with wavelength-scale dimensions. This thesis is focused on tackling this challenge and in the optimization of the self-assembly deposition of polystyrene nanospheres monolayers onto flexible substrates, as a part of a full CL method for photonic-enhancement purposes in thin-film solar cells. In this work, we report a breakthrough in our Langmuir-Blodgett (LB) method which prevents wavelength-sized particles from sinking into the aqueous sub-phase and spontaneously form the desired close-packed hexagonal monolayer. This was attained by using sodium dodecyl sulfate (SDS) to reduce the aqueous sub-phase surface tension and hence improve the air-water interface stability of polystyrene spheres of various diameters. The addition of SDS, with best results at 4.5 mg/l concentration, showed remarkable improvement on the self-assembly step, by avoiding the nanospheres sinking and by producing uniform high-quality monolayer films. The quality of the deposition was also improved by controlling the LB barrier closing rate and increasing the self-assembly work area, which resulted in fully patterned flexible substrates.