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Electron-Lattice Dynamics in pi-Conjugated Systems
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis we explore in particular the dynamics of a special type of quasi-particle in pi-conjugated materials termed polaron, the origin of which is intimately related to the strong interactions between the electronic and the vibrational degrees of freedom within these systems. In order to conduct such studies with the particular focus of each appended paper, we simultaneously solve the time-dependent Schrödinger equation and the lattice equation of motion with a three-dimensional extension of the famous Su-Schrieffer-Heeger (SSH) model Hamiltonian. In particular, we demonstrate in Paper I the applicability of the method to model transport dynamics in molecular crystals in a region were neither band theory nor perturbative treatments such as the Holstein model and extended Marcus theory apply. In Paper II we expand the model Hamiltonian to treat the revolution of phenylene rings around the sigma-bonds and demonstrate the great impact of stochastic ring torsion on the intra-chain mobility in conjugated polymers using poly[phenylene vinylene] (PPV) as a model system. Finally, in Paper III we go beyond the original purpose of the methodology and utilize its great flexibility to study radiationless relaxations of hot excitons.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2007. , 15 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1295
Keyword [en]
Polaron dynamics, Exciton dynamics, pi-conjugated systems, Su-Schrieffer-Heeger (SSH) model, Adiabaticity, Charge carrier transport, Organic electronics.
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:liu:diva-7996Local ID: LiU-TEK-LIC-2007:4ISBN: 978-91-85715-90-9 (print)OAI: oai:DiVA.org:liu-7996DiVA: diva2:22901
Presentation
2007-02-09, Planck, Fysikhuset, 13:15 (English)
Opponent
Supervisors
Note
Report code: LiU-TEK-LIC-2007:4.Available from: 2007-03-06 Created: 2007-03-06 Last updated: 2009-04-30Bibliographically approved
List of papers
1. Polaron dynamics in highly ordered molecular crystals
Open this publication in new window or tab >>Polaron dynamics in highly ordered molecular crystals
2006 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 428, no 4-6, 446-450 p.Article in journal (Refereed) Published
Abstract [en]

From a numerical solution of the time-dependent Schrödinger equation and the lattice equation of motion we obtain a microscopic picture of polaron transport in highly ordered molecular crystals in the presence of an external electric field. We have chosen the pentacene single crystal as a model system, but study the transport as a function of the intermolecular interaction strength, J. We observe a smooth transition from a nonadiabatic to an adiabatic polaronic drift process over the regime 20 < J < 120 meV. For intermolecular interaction strengths above 120 meV the polaron is no longer stable and the transport becomes band like.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-14208 (URN)10.1016/j.cplett.2006.07.042 (DOI)
Available from: 2007-03-06 Created: 2007-03-06 Last updated: 2017-12-13
2. Impact of ring torsion on the intrachain mobility in conjugated polymers
Open this publication in new window or tab >>Impact of ring torsion on the intrachain mobility in conjugated polymers
2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 10, 104304- p.Article in journal (Refereed) Published
Abstract [en]

Wehave developed a fully three-dimensional model based on the solutionof the time-dependent Schrödinger equation for studies of polaron mobilityin twisted polymer chains. Variations in ring torsion angles alonga conjugated polymer chain are shown to have a strongeffect on the intrachain charge carrier mobility. An increase inring torsion between two neighboring monomers can cause electron localizationand then result in a transition of the type oftransport from adiabatic polaron drift to nonadiabatic polaron hopping. Inparticular, we show the sensitivity for such a transition inthe case of random variations in the ring torsion anglesalong a poly(phenylene vinylene) chain. The effective energy barrier associatedwith the change in torsion angle also depends on theapplied electric-field strength, and by increasing the field strength atransition back to adiabatic transport can be obtained.

Keyword
electron-lattice dynamics, carrier mobility, localised states, polarons, hopping conduction
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16943 (URN)10.1103/PhysRevB.75.104304 (DOI)
Projects
Center of Organic Electronics (COE)
Note

Original Publication: Magnus Hultell and Sven Stafström, Impact of ring torsion on the intrachain mobility in conjugated polymers, 2008, Physical Review B. Condensed Matter and Materials Physics, (75), 10, 104304. http://dx.doi.org/10.1103/PhysRevB.75.104304 Copyright: American Physical Society http://www.aps.org/

Available from: 2009-02-25 Created: 2009-02-25 Last updated: 2017-12-13Bibliographically approved
3. Radiationless relaxation of hot excitons in molecular crystals
Open this publication in new window or tab >>Radiationless relaxation of hot excitons in molecular crystals
(English)Manuscript (Other (popular science, discussion, etc.))
Identifiers
urn:nbn:se:liu:diva-14210 (URN)
Available from: 2007-03-06 Created: 2007-03-06 Last updated: 2010-01-14

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Hultell (Andersson), Magnus

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