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Identifier 000419204
Title Moth-eye structures for light trapping in thin organic solar cells
Alternative Title Δομές "moth-eye" για συλλογή φωτός σε λεπτά οργανικά φωτοβολταϊκά
Author Καραβανάκης, Οδυσσέας
Thesis advisor Παπάζογλου, Δημήτρης
Reviewer Στρατάκης, Εμμανουήλ
Καφεσάκη, Μαρία
Abstract In nature, optical structures in the subwavelength range have been evolved over time and serve several purposes. For example, in the form of ‘moth-eye’ structures they show strong antireflective properties on the compound eyes or wings of various species of insects. The bioinspired antireflective structures offer broadband antireflective capabilities to both wavelength and angle because the gradient in the effective refractive index minimizes reflection through index-matching between air and the substrate. So providing antireflection, mostly, in the visible spectrum, is useful for a number of applications. Solar cells, LCD screens and optical lenses are a few examples of applications that can benefit from antireflection. A major issue in organic solar cells is the poor mobility and recombination of the photogenerated charge carriers. The active layer has to be kept thin to facilitate charge transport and minimize recombination losses. However, optical losses due to inefficient light absorption in the thin active layers can be considerable in organic solar cells. Therefore, there is a need for better light trapping in organic solar cells. In this work, case studies of designing optimized antireflection solutions were carried out. Conventional single layer thin anti-reflective coatings (ARCs) are a simple and low cost solution but only suitable for narrowband applications. A multilayer film stack is often employed for broadband applications. Analytical approaches such as transfer matrix method (TMM) are appropriate for simulation and design of these structures. More specifically, simulations of the moth-eye design parameters for feature period, height, density factor and shape 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 fill (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.
Language English
Subject Biomimetic
Cicada Wing
Issue date 2018-11-23
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Materials Science and Technology--Post-graduate theses
  Type of Work--Post-graduate theses
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