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Theoretical Study of the Charge-Transfer State Separation within Marcus Theory: The C-60-Anthracene Case Study
Linköping University, Department of Physics, Chemistry and Biology, Bioinformatics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. University of Southern Denmark, Denmark.
Linköping University, Department of Physics, Chemistry and Biology, Bioinformatics. Linköping University, Faculty of Science & Engineering.
2016 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 37, 24722-24736 p.Article in journal (Refereed) Published
Abstract [en]

We study, within Marcus theory, the possibility of the charge-transfer (CT) state splitting at organic interfaces and a subsequent transport of the free charge carriers to the electrodes. As a case study we analyze model anthracene-C-60 interfaces. Kinetic Monte Carlo (KMC) simulations on the cold CT state were performed at a range of applied electric fields, and with the fields applied at a range of angles to the interface to simulate the action of the electric field in a bulk heterojunction (BHJ) interface. The results show that the inclusion of polarization in our model increases CT state dissociation and charge collection. The effect of the electric field on CT state splitting and free charge carrier conduction is analyzed in detail with and without polarization. Also, depending on the relative orientation of the anthracene and C-60 molecules at the interface, CT state splitting shows different behavior with respect to both applied field strength and applied field angle. The importance of the hot CT in helping the charge carrier dissociation is also analyzed in our scheme.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC , 2016. Vol. 8, no 37, 24722-24736 p.
Keyword [en]
organic solar cell; charge transfer state; splitting separation; interface; Marcus theory; kinetic Monte Carlo
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-132221DOI: 10.1021/acsami.6b06645ISI: 000384033600054PubMedID: 27561228OAI: oai:DiVA.org:liu-132221DiVA: diva2:1039798
Note

Funding Agencies|SERC (Swedish e-Science Research Center)

Available from: 2016-10-25 Created: 2016-10-21 Last updated: 2016-12-20
In thesis
1. 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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