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Effect of Polarization on the Mobility of C60: A Kinetic Monte-Carlo Study
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Denmark.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
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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. Vol. 12, no 2, 812-824 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-122989DOI: 10.1021/acs.jctc.5b00975ISI: 000370112900032OAI: oai:DiVA.org:liu-122989DiVA: diva2:875485
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: 2016-12-20Bibliographically approved
In thesis
1. Charge Transport Simulations for Organic Electronics: A Kinetic Monte Carlo Approach
Open this publication in new window or tab >>Charge Transport Simulations for Organic Electronics: A Kinetic Monte Carlo Approach
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:nbn:se:liu:diva-122991 (URN)10.3384/lic.diva-122991 (DOI)978-91-7685-878-3 (ISBN)
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
2. Modelling Charge Transport for Organic Solar Cells within Marcus Theory
Open this publication in new window or tab >>Modelling Charge Transport for Organic Solar Cells within Marcus Theory
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With the technological advancement of modern society, electronic devices are getting progressively more integrated in our everyday lives. Their continuouslygrowing presence is generating numerous concerns about costs, efficiency and the environmental impact of the electronic waste. In this context, organic electronics is finding its way through the market, allowing for potentially low-cost, light, flexible, transparent and environmentally friendly electronics. Despite the numerous successes of organic electronics, the functioning of several categories of organic devices still represents a technological challenge, due to problems like low efficiencies and stabilities (degradation over time).

Organic devices are composed by one or more organic materials depending on the particular application. The conformation and electronic structure of the organic molecules as well as their supramolecular arrangement in the single phase or at the interface are known to strongly a affect the mobility and/or the efficiency of the device. While there is consensus on the fundamental physics of organic devices, we still lack a detailed comprehensive theory able to fully explain experimental data. In this thesis we focus on trying to expand our knowledge of charge transport in organic materials through theoretical modelling and simulation of organic electronic devices. While the methodology developed is generally valid for any organic device, we will particularly focus on the case represented by organic photovoltaics.

The morphology of the system is obtained by molecular dynamics simulations. Marcus theory is used to calculate the hopping rate of the charge carriers and subsequently study the possibility of free charge carriers production in an organic solar cell. The theory is then compared both with Kinetic Monte Carlo simulations and with experiments to identify the main pitfalls of the actual theory and ways to improve it. The Marcus rate between two molecules depends on the molecular orbital energies, the transfer integral between the two molecules and the reorganization energy. The orbital energies and the transfer integrals between two neighbouring molecules are obtained through quantum mechanical calculations in vacuum. Electrostatic effects of the environment are included through atomic charges and atomic polarizabilities, producing a correction both to the orbital energy and to the reorganization energy. We have studied several systems in the single phase (polyphenylene vinylene, C60, PC61BM) and at the interface between two organic materials (anthracene/C60, TQ1/PC71BM).

We show how a combination of different methodologies can be used to obtain a realistic ab-initio model of organic devices taking into account environmental effects. This allows us to obtain qualitative agreement with experimental data of mobility in the single phase and to determine whether or not two materials are suitable to be used together in an organic solar cell.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. 54 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1815
National Category
Theoretical Chemistry Condensed Matter Physics Physical Chemistry
Identifiers
urn:nbn:se:liu:diva-133329 (URN)10.3384/diss.diva-133329 (DOI)9789176856192 (ISBN)
Public defence
2017-02-10, Planck (J206), Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2016-12-20 Created: 2016-12-20 Last updated: 2017-01-17Bibliographically approved

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