Investigation of organic dyes for dye-sensitized and organic solar cell applications.
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Smith, Andrew Gregory, 1991-
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Theoretical chemistry can be a driving force for experimentalists. Using computer software, molecules can be easily changed and studied, which can save experimentalists on laboratory costs and time. This work focuses on the organic dyes in dye-sensitized and organic solar cells. More specifically, the changes in fundamental properties such as molecular orbital energies, absorption spectra, and electronic coupling are studied upon heteroatom substitution using density functional theory. In Chapter Three, the changes in the properties of the D5 organic dye were studied upon heteroatom substitution for sulfur in the thiophene π-bridge. Sulfur was substituted for pnictogens, chalcogens, and various other elements in the second row of the periodic table. Dyes were adsorbed to (TiO2)16 and all substitutions besides boron had favorable electron injections. It was found that the larger elements reduce the HOMO-LUMO gap, red shift the absorption spectrum, increase the dipole moment and are energetically favorable for electron injection. In Chapter Four, the impact the π-bridge had on the photovoltaic and charge transfer parameters of an organic photovoltaic was studied. Calculations were performed on a variety of heteroatom substituted bridge units in both fused and unfused perylene diimide (PDI) dimers to directly compare with the previously studied thiophene bridge unit. Fused systems exhibit an improved charge transfer ratio compared to unfused systems, decreased reorganization energy, and had more favorable Gibbs free energies. The results of Chapter Three and Chapter Four led to asking how multiple heteroatom substitutions would affect the dye molecules. Chapter Five investigates the effects of substituting two heteroatoms, one chalcogen and one pnictogen, into the PDI bay-region by the creation of a five-membered ring. A handful of the combinations were nonplanar, which shows promise for organic solar cell (OSC) applications. All combinations using oxygen for the silicon-bridged system had absorption spectra almost covering the entire visible light region. For the charge transfer properties, the main trend observed was the charge transfer ratio, which increased by a minimum of about 104 s-1 when moving along the period of the periodic table.