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Charge Transport Simulations for Organic Electronics: A Kinetic Monte Carlo Approach
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis we focus on the modelling and simulation of organic electronic devices, investigating their structural and electronic properties. Organic devices have attracted great interest for their innovative properties, but their functioning still represent a theoretical and technological challenge. They are composed by one or more organic materials depending on the particular application. The morphology of organic devices in the single phase or at the interface is known to strongly determine mobility and efficiency of the devices. The structural disorder is studied through molecular dynamics (MD) simulations. Marcus formula is used to calculate the hopping rate of the charge carriers and the model developed is tested by simulations in a Kinetic Monte Carlo scheme. The dependence of the transfer integrals on the relative molecular orientation is achieved through a weighted Mulliken formula or through a dimer projection approach using the semi-empirical Hartree Fock method ZINDO. Electrostatic effects, have been included through atomic charges and atomic polarizabilities, calculated at the B3LYP level of theory. The inclusion of electrostatic effects has been shown (through simulations in 4PV and C60) to be crucial to obtain a good qualitative agreement with experiments, for both mobility field and temperature dependence in the single phase. In particular the external reorganization energy, calculated through the polarization of the environment, has been shown to have a great impact on the conduction, shifting the inverse Marcus region and helping CT state separation at the interface (between C60 and anthracene).

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. , 64 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1738
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-122991DOI: 10.3384/lic.diva-122991ISBN: 978-91-7685-878-3 (print)OAI: oai:DiVA.org:liu-122991DiVA: diva2:875495
Presentation
2016-01-15, Planck, Fisikhuset, Campus Valla, Linköpings universitet, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2015-12-01 Created: 2015-12-01 Last updated: 2016-04-08Bibliographically approved
List of papers
1. Transition fields in organic materials: From percolation to inverted Marcus regime. A consistent Monte Carlo simulation in disordered PPV
Open this publication in new window or tab >>Transition fields in organic materials: From percolation to inverted Marcus regime. A consistent Monte Carlo simulation in disordered PPV
2015 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 9, 094503- p.Article in journal (Refereed) Published
Abstract [en]

In this article, we analyze the electric field dependence of the hole mobility in disordered poly (p-phenylene vinylene). The charge carrier mobility is obtained from Monte Carlo simulations. Depending on the field strength three regions can be identified: the percolation region, the correlation region, and the inverted region. Each region is characterized by a different conduction mechanism and thus a different functional dependence of the mobility on the electric field. Earlier studies have highlighted that Poole-Frenkel law, which appears in the correlation region, is based on the type of correlation caused by randomly distributed electric dipoles. This behavior is thus observed in a limited range of field strengths, and by studying a broader range of electric fields, a more fundamental understanding of the transport mechanism is obtained. We identify the electric fields determining the transitions between the different conduction mechanisms in the material and we explain their physical origin. In principle, this allows us to characterize the mobility field dependence for any organic material. Additionally, we study the charge carrier trapping mechanisms due to diagonal and off-diagonal disorder, respectively. (C) 2015 AIP Publishing LLC.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-117234 (URN)10.1063/1.4913733 (DOI)000350973900041 ()25747090 (PubMedID)
Note

Funding Agencies|Swedish Research Council (VR); MATTER Network; SERC (Swedish e-Science Research Center)

Available from: 2015-04-22 Created: 2015-04-21 Last updated: 2017-12-04
2. Effect of Polarization on the Mobility of C60: A Kinetic Monte-Carlo Study
Open this publication in new window or tab >>Effect of Polarization on the Mobility of C60: A Kinetic Monte-Carlo Study
Show others...
2016 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 12, no 2, 812-824 p.Article in journal (Refereed) Published
Abstract [en]

We present a study of mobility field and temperature dependence for C60 with Kinetic Monte-Carlo simulations. We propose a new scheme to take into account polarization effects in organic materials through atomic induced dipoles on nearby molecules. This leads to an energy correction for the single site energies and to an external reorganization happening after each hopping. The inclusion of polarization allows us to obtain a good agreement with experiments for both mobility field and temperature dependence.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-122989 (URN)10.1021/acs.jctc.5b00975 (DOI)000370112900032 ()
Note

Vid tiden för disputation förelåg publikationen endast som manuskript

Funding agencies:  SeRC (Swedish e-Science Research Center)

Available from: 2015-12-01 Created: 2015-12-01 Last updated: 2017-12-01Bibliographically approved
3. Charge-transfer state dynamics at C60-anthracene interfaces: a kinetic Monte Carlo approach
Open this publication in new window or tab >>Charge-transfer state dynamics at C60-anthracene interfaces: a kinetic Monte Carlo approach
2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The morphology of organic interfaces plays an important role in charge-transfer (CT) state splitting, and therefore has a significant impact on the efficiency of organic solar cells. In this article, we use our kinetic Monte Carlo (KMC) method on molecular dynamics-simulated anthracene-C60 interfaces to study the relation between interface morphology and CT state splitting. These KMC simulations were performed at a range of applied electric fields, and with the fields applied at a range of angles to the interface. The results show that depending on the relative orientation of the anthracene and C60 molecules, CT state splitting shows different behavior with respect to both applied field strength and applied field angle. Different orientations may be better suited for different applications. The inclusion of polarization in our model is shown to  increase CT state splitting for both orientations studied.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-122990 (URN)
Available from: 2015-12-01 Created: 2015-12-01 Last updated: 2015-12-01Bibliographically approved

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Volpi, Riccardo

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