Molecular Simulations of the Bulk-Heterojunction Morphology in Organic Solar Cells
Do, Khanh Ngoc
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In this Thesis, we aim to elucidate clear connections between the chemical functionality and molecular morphologies of a number of high-performing or benchmark π-conjugated materials used in OSCs. We proceed to link these structural features to electronic properties that are important to solar cell performance. This Thesis is organized into three themes, in each of which we investigate a particular component of the chemical functionality of a specific π-conjugated material and its effects on thin-film molecular packing: (i) Fluorine substitution in a polymer donor (Chapter 3) and hole-transport molecular crystal (Chapter 6); (ii) Electron-withdrawing group and alkyl group substitution in a nonfullerene acceptor (Chapter 4); (iii) Modification of the core π-conjugated motif in a nonfullerene acceptor (Chapter 5). The results from studying these specific systems showcase the utility of computer simulations, which when used in tandem with experiment can build a molecular understanding of the BHJ morphology for OSC applications. While the parameter space of the materials studied in this Thesis remains limited, it does provide a rigorous starting point to developing a more comprehensive understanding of the structure-morphology-performance relationships in π-conjugated systems, which are necessary to systematically improve performance.