Bittner, Eric R.2017-06-232017-06-23December 22016-12December 2Portions of this document appear in: Eric R. Bittner and Allen Kelley, "The role of structural fluctuations and environmental noise in the electron/hole separation kinetics at organic polymer bulk-heterojunction interfaces," Physical Chemistry Chemical Physics 17 (2015): 28853-28859. doi:10.1039/C5CP05037Ehttp://hdl.handle.net/10657/1830We investigate the electronic dynamics of model organic photovoltaic (OPV) system consisting of polyphenylene vinylene (PPV) oligomers and [6,6]-phenyl C61-butyric acid methylester (PCBM) blend using a mixed molecular mechanics/quantum mechanics (MM/QM) approach. The π-MDX code is introduced and a methodology that allows the quantum treatment of the π systems of large clusters of molecules near the interface is developed. Using a heuristic model that connects energy gap fluctuations to the average electronic couplings and decoherence times, we provide an estimate of the state-to-state internal conversion rates within the manifold of the lowest few electronic excitations. We find that the lowest few excited states of a model interface are rapidly mixed by C=C bond fluctuations and low frequency torsional modes such that the system can sample both intermolecular charge-transfer and charge-separated electronic configurations on a time scale of 20fs. We show that the electronic dynamics of the OPV are dramatically altered by varying the positions of the molecules simulated at the interface. Our simulations support an emerging picture of carrier generation in OPV systems in which interfacial electronic states can rapidly decay into charge-separated and current producing states via coupling to vibronic degrees of freedom.application/pdfengThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).Electron/Hole separation MM/QM2017-06-23Thesisborn digital