Theoretical studies of the structure-property relationships of hole- and electron-transport materials for organic photovoltaic applications
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Donor-acceptor and thiophene based π-conjugated molecules and polymers, along with fullerene derivatives, are extensively used active components in the photoactive layer of organic photovoltaic devices. In this dissertation, we make use of several computational methodologies to investigate structure-property relationships of these organic systems in their molecular forms. We begin with an overview of the field of organic photovoltaics and some of the important problems in organic solar cells that are currently being investigated. This is then followed by a brief review of the electronic-structure methods (e.g. Hartree-Fock theory, Density Functional Theory, and Time-dependent Density Functional Theory) that are employed. We then present the main results of the dissertation. Chapter 3 provides a broad overview on how changes to the donor-acceptor copolymer chemical structure impacts its intrinsic geometric, electronic, and optical properties. Chapter 4 focuses on the characterization of the lowest excited-states and optical absorption spectra in donor-acceptor copolymers. In Chapter 5, we investigate the effects of alkyl side-chain placements in the π-conjugated backbone of oligothiophenes and how that impacts their intramolecular properties as well as the oligomer:fullerene interfacial interactions. Chapter 6 presents our investigation on the role of oligomer:fullerene configuration and reorganization energy on exciton-dissociation and charge-recombination processes. Finally, a synopsis of the work and further considerations are presented in Chapter 7.