Silicon Passivation and Photosensitisation Using Organic Monolayers and Light-Harvesting Chromophores

Wood, Ben and Danos, Lefteris and Coogan, Michael (2024) Silicon Passivation and Photosensitisation Using Organic Monolayers and Light-Harvesting Chromophores. PhD thesis, Lancaster University.

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Abstract

The work set out in this thesis looks to provide insights into the development of thin-film crystalline silicon photovoltaics by: i) passivation of silicon using organic monolayers, followed by ii) photosensitisation of passivated silicon using light- harvesting complexes. Chapter 1 introduces current trends in energy and photovoltaics, with a focus on silicon-based solar cells. This serves as the motivation for the project, as society continues to look for cheaper and more sustainable energy resources. Chapter 2 will introduce the key technical concepts explored in this thesis, including semiconductor physics, and the analytical methods used in this work. In chapter 3, silicon wafers are chemically passivated using wet-chemical methods. The chlorination-alkylation method is used to form self-assembled organic monolayers on the surface of silicon. The fabricated surfaces are analysed by X-ray photoelectron spectroscopy to prove successful bonding had been achieved. The samples are then analysed using photoluminescence techniques to measure the emission and decay spectra of the surfaces, indicating the quality of passivation. In chapter 4, energy transfer between light-harvesting complexes and silicon is explored. The aforementioned passivated surfaces are further modified through coupling reactions in order to form a covalent tether between the silicon surface and light-harvesting complexes. Energy transfer is measured via fluorescence lifetime imaging spectroscopy. In chapter 5, the Langmuir-Blodgett technique is deployed to measure the effects of distance dependent energy transfer. Distance between silicon and light-harvesting complex can be modified by introducing layers of stearic acid spacers. Multiple layers of stearic acid are built upon the silicon to control the separation distance between complex and silicon. The fluorescence lifetimes are plotted to examine the relationship between energy transfer and distance.