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Title: Exciton dynamics in disordered conjugated polymers
Author: Tozer, Oliver
ISNI:       0000 0004 6496 5477
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2016
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Conjugated polymers have been the subject of many experimental and theoretical studies in recent years, with the interesting behaviour of their low-energy excited states depending on both electron-electron and electron-nuclear interactions, as well as the disorder which is almost universally present in these materials. Their potential use in optoelectronic devices, such as LEDs and photovoltaic cells, adds to this interest, with the behaviour of the low energy excited states being primarily dictated by the p-conjugation. In this thesis we model the transport of energy in phenylene-based conjugated polymers, where the primary low energy excited states are Frenkel excitons that can be described by the disordered Frenkel-Holstein Hamiltonian. Initially, the eigenstates of this Hamiltonian are investigated using the density matrix renormalization group method. The results of this investigation show that the vibrational phonons of the polymer cause only a small change in the exciton wavefunction, while the relevant torsional normal modes are low enough in frequency that they can be treated classically. This allows the exciton states in the dynamics simulations to be calculated using the more numerically tractable Frenkel Hamiltonian with the coupling of the exciton to the vibrational modes being treated by the inclusion of appropriate polaron binding energies in the energy of the state and of Franck-Condon factors in the transition rates. The first dynamics simulations are an investigation into the intramolecular motion of excitons on polymer chains in solution, where it is the torsional motion of the polymer chain, modelled by a Langevin dynamics algorithm, that is the main driving force behind the exciton transport. The exciton motion in the solid state, where the exciton motion results mainly from intermolecular Förster resonant exciton transfer, is then investigated, with a Monte Carlo algorithm being employed to determine the exciton diffusion length for various polymer morphologies.
Supervisor: Barford, William Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available