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  • 1.
    Hultell (Andersson), Magnus
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Electron-Lattice Dynamics in pi-Conjugated Systems2007Licentiate 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.

    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, p. 446-450Article 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, p. 104304-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.

    Keywords
    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
  • 2.
    Hultell (Andersson), Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Electron-lattice dynamics in π-conjugated systems2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work presented in this thesis concerns the dynamics in π-conjugated hydrocarbon systems. Due to the molecular bonding structure of these systems there exists a coupling between the electronic system and the phonons of the lattice. If this interaction, which is referred to as the electron-phonon (e-ph) coupling, is sufficiently strong it may cause externally introduced charge carriers to self-localize in a polarization cloud of lattice distortions. These quasi-particles are, if singly charged, termed polarons, the localization length of which, aside from the e-ph coupling strength, also depend upon the structural and energetic disorder of the system. In disordered systems localization is strong and transport is facilitated by nonadiabatic hopping of charge carriers from one localized state to the next, whereas in well-ordered systems, where extended states are formed, adiabatic transport models apply.Despite great academic efforts a unified model for charge transport in π-conjugated systems is still lacking and further investigations are necessary to uncover the basic physics at hand in these systems. The call for such efforts has been the main guidelines for the work presented in this thesis and are related to the topics of papers I-IV. In order to capture the coupled electron-lattice dynamics, we use a methodological approach where we obtain the time-dependence of the electronic degrees of freedom from the solutions to the time-dependent Schrödinger equation and determine the ionic motion in the evolving charge density distribution by simultaneously solving the lattice equation of motion within the potential field of the ions. The Hamiltonian used to describe the system is derived from an extension of the famous Su-Schrieffer-Heeger (SSH) model extended to three-dimensional systems.In papers I-III we explore the impact of phenylene ring torsion on delocalization and transport properties in poly(para-phenylene vinylene) (PPV). The physics that we are particularly interested in relates to the reduced electron transfer integral strength across the interconnection between the phenylene rings and the vinylene groups upon ring torsion. Keeping this in mind, we demonstrate in paper I the impact of static ring torsion on intrachain mobility and provide a detailed analysis of the influence of the potential barriers (due to consecutive ring torsion) on the nature of charge carrier propagation. In paper II we extend our initial approach to include also the dynamics of ring torsion. We show that without any externally applied electric field, this type of dynamics is the dominant property controlling intrachain propagation, but that when an external electric field is applied, charge carriers may traverse the potential barriers through a process that involves nonadiabatic effects and a temporary delocalization of the polaron state. Finally, in paper III we study the impact of the lattice dynamics on the electron localization properties in PPV and show that the phenylene ring torsion modes couples strongly to the electronic wave function which gives rise to electron localization at room temperature.In papers IV and V we focus on the dynamics of molecular crystals using a stack of pentacene molecules in the single crystal configuration as a model system, but study, in paper IV, the transport as a function of the intermolecular interaction strength, J. We observe a smooth transition from a nonadiabatic to an adiabatic polaron drift process over the regime 20<J<120 meV. For intermolecular interaction strengths above J≈120 meV the polaron is no longer stable and transport becomes band-like. In paper V, finally, we study the internal conversion processes in these systems, which is the dominant relaxation channel from higher lying states. This process involves the transfer of energy from the electronic system to the lattice. Our results show that this process is strongly nonadiabatic and that the relaxation time associated with large energy excitations is limited by transitions made between states of different bands.

    List of papers
    1. 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, p. 104304-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.

    Keywords
    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
    2. Impact of ring torsion dynamics on intrachain charge transport in conjugated polymers
    Open this publication in new window or tab >>Impact of ring torsion dynamics on intrachain charge transport in conjugated polymers
    2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 1, p. 014302-Article in journal (Refereed) Published
    Abstract [en]

    Based on an approach including both the time-dependent Schrodinger equation and an effective Newtons equation for the ionic motion, we study the impact of ring torsion dynamics on the intrachain charge transport process in conjugated polymers. As model systems we have used single chains of poly(para-phenylene-vinylene). Without any external electric field, the dynamics of the phenyl ring torsion is the dominant property controlling intrachain charge propagation. The charge is coupled to both ring torsions and bond lengths distortions, which results in a significantly more localized polaron state than in a planar chain. In the presence of an electric field, the charge can breach the barriers caused by ring torsions, a process that involves nonadiabatic effects and a temporary delocalization of the polaron state.

    Keywords
    conducting polymers, localised states, polarons, Schrodinger equation
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-16835 (URN)10.1103/PhysRevB.79.014302 (DOI)
    Note
    Original Publication: Magnus Hultell and Sven Stafström, Impact of ring torsion dynamics on intrachain charge transport in conjugated polymers, 2009, PHYSICAL REVIEW B, (79), 1, 014302. http://dx.doi.org/10.1103/PhysRevB.79.014302 Copyright: American Physical Society http://www.aps.org/ Available from: 2009-02-25 Created: 2009-02-20 Last updated: 2017-12-13Bibliographically approved
    3. The effect of lattice dynamics on electron localization in poly-(para-phenylene vinylene)
    Open this publication in new window or tab >>The effect of lattice dynamics on electron localization in poly-(para-phenylene vinylene)
    2009 (English)In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 159, no 21-22, p. 2219-2221Article in journal (Refereed) Published
    Abstract [en]

    The lattice dynamics in poly-(para-phenylenevinylene) and its effect on the electron localization properties have been investigated. The simulations were performed using a hybrid quantum mechanical/molecular dynamics approach including the Pariser–Parr–Pople Hamiltonian. It is found that the dynamic disorder that exists at room temperature induces electron localization. The most important lattice modes in the context of localization are the torsional modes of the phenylene rings, that are shown to couple strongly to the electronic system. Since these modes occur at low frequencies, they will also have a strong impact on intra-chain charge transport.

    Keywords
    Electron localization; Molecular dynamics; Torsional modes
    National Category
    Other Physics Topics
    Identifiers
    urn:nbn:se:liu:diva-12589 (URN)10.1016/j.synthmet.2009.08.035 (DOI)
    Available from: 2008-09-16 Created: 2008-09-16 Last updated: 2017-12-13
    4. 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, p. 446-450Article 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
    5. Nonradiative relaxation processes in molecular crystals
    Open this publication in new window or tab >>Nonradiative relaxation processes in molecular crystals
    2008 (English)In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 128, no 12, p. 2019-2026Article in journal (Refereed) Published
    Abstract [en]

    Internal conversion is the dominant relaxation channel from higher lying excited states in molecular crystals and involves the transfer of energy from the electronic system to the lattice. In this work, we present results from simulations of the nonradiative relaxation process with an emphasis on both intra- and interband transitions. We find the internal conversion process to be strongly nonadiabatic and the associated relaxation time in the case of large energy excitations to be limited by the transitions made between states of different bands.

    Keywords
    Internal conversion, Frenkel excitons, Interstate transitions, Pentacene single crystal
    National Category
    Other Physics Topics
    Identifiers
    urn:nbn:se:liu:diva-12587 (URN)10.1016/j.jlumin.2008.07.001 (DOI)
    Projects
    Center of Organic Electronics
    Available from: 2008-09-16 Created: 2008-09-16 Last updated: 2017-12-13
  • 3.
    Hultell (Andersson), Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström , Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Impact of ring torsion dynamics on intrachain charge transport in conjugated polymers2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 1, p. 014302-Article in journal (Refereed)
    Abstract [en]

    Based on an approach including both the time-dependent Schrodinger equation and an effective Newtons equation for the ionic motion, we study the impact of ring torsion dynamics on the intrachain charge transport process in conjugated polymers. As model systems we have used single chains of poly(para-phenylene-vinylene). Without any external electric field, the dynamics of the phenyl ring torsion is the dominant property controlling intrachain charge propagation. The charge is coupled to both ring torsions and bond lengths distortions, which results in a significantly more localized polaron state than in a planar chain. In the presence of an electric field, the charge can breach the barriers caused by ring torsions, a process that involves nonadiabatic effects and a temporary delocalization of the polaron state.

  • 4.
    Hultell (Andersson), Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Impact of ring torsion on the intrachain mobility in conjugated polymers2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 10, p. 104304-Article in journal (Refereed)
    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.

  • 5.
    Hultell (Andersson), Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Nonradiative relaxation processes in molecular crystals2008In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 128, no 12, p. 2019-2026Article in journal (Refereed)
    Abstract [en]

    Internal conversion is the dominant relaxation channel from higher lying excited states in molecular crystals and involves the transfer of energy from the electronic system to the lattice. In this work, we present results from simulations of the nonradiative relaxation process with an emphasis on both intra- and interband transitions. We find the internal conversion process to be strongly nonadiabatic and the associated relaxation time in the case of large energy excitations to be limited by the transitions made between states of different bands.

  • 6.
    Hultell (Andersson), Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Polaron dynamics in highly ordered molecular crystals2006In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 428, no 4-6, p. 446-450Article in journal (Refereed)
    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.

  • 7.
    Linares, Mathieu
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Hultell (Andersson), Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    The effect of lattice dynamics on electron localization in poly-(para-phenylene vinylene)2009In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 159, no 21-22, p. 2219-2221Article in journal (Refereed)
    Abstract [en]

    The lattice dynamics in poly-(para-phenylenevinylene) and its effect on the electron localization properties have been investigated. The simulations were performed using a hybrid quantum mechanical/molecular dynamics approach including the Pariser–Parr–Pople Hamiltonian. It is found that the dynamic disorder that exists at room temperature induces electron localization. The most important lattice modes in the context of localization are the torsional modes of the phenylene rings, that are shown to couple strongly to the electronic system. Since these modes occur at low frequencies, they will also have a strong impact on intra-chain charge transport.

  • 8.
    Stafström, Sven
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Hultell, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Electron Lattice Dynamics as a Method to Study Charge Transport in Conjugated2011In: Charge and Exciton transport through molecular wires / [ed] L. Siebbeles and F. Grozema, Wiley-VCH Verlagsgesellschaft, 2011Chapter in book (Refereed)
    Abstract [en]

    As functional elements in opto-electronic devices approach the singlemolecule limit, conducting organic molecular wires are the appropriateinterconnects that enable transport of charges and charge-like particles such as excitons within the device. Reproducible syntheses and athorough understanding of the underlying principles are therefore indispensable for applications like even smaller transistors, molecularmachines and light-harvesting materials. Bringing together experiment and theory to enable applications in real-life devices, this handbookand ready reference provides essential information on how to control and direct charge transport. Readers can therefore obtain a balancedview of charge and exciton transport, covering characterization techniques such as spectroscopy and current measurements together with quantitative models. Researchers are thus able to improve the performance of newly developed devices, while an additional overview of synthesis methods highlights ways of producing different organic wires. Written with the following market in mind: chemists, molecularphysicists, materials scientists and electrical engineers

1 - 8 of 8
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