| In a simplified picture of an organic photovoltaics active layer the molecular orbital energies are used to predict photo-induced charge transfer between potential electron donors and acceptors, a crucial step in the generation of electrical power from light. Yet often systems that are projected to work by this metric, in fact, do not work; perhaps there is more to it. The work presented in this thesis adds to the understanding of how solid-state microstructure ultimately affects photoinduced charge transfer. Two distinctive small molecule electron donors are presented and determined to undergo microstructure-modulated charge transfer for different reasons. Time-resolved microwave conductivity is used to detect photogenerated charges and powder x-ray diffraction, transmission electron microscopy, and solid-state photophysics are used to elucidate the film microstructure. In the first system presented, a helical nanofilament heterojunction is shown to yield more charge transfer than a lamellar structuring of the same materials; a competing pathway for charge generation is proposed. In the second system, a series of PBTTT-inspired small molecules with varied alkoxy tail lengths demonstrates systematic differences in the microstructure, photophysics, and charge transfer driving forces and therefore yield. In both cases solid-state microstructure is conclusively has considerable effect on the photophysical properties and charge transfer in organic donor-acceptor blends. |
