Exciton size and binding energy limitations in one-dimensional organic materials

Koerner, C.; Leo, K.; Scholz, R.; Plasser, F.

doi:10.1063/1.4938527

Title: Exciton size and binding energy limitations in one-dimensional organic materials

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Abstract

In current organic photovoltaic devices, the loss in energy caused by the charge transfer step necessary for exciton dissociation leads to a low open circuit voltage, being one of the main reasons for rather low power conversion efficiencies. A possible approach to avoid these losses is to tune the exciton binding energy to a value of the order of thermal energy, which would lead to free charges upon absorption of a photon, and therefore increase the power conversion efficiency towards the Shockley-Queisser limit. We determine the size of the excitons for different organic molecules and polymers by time dependent density functional theory calculations. For optically relevant transitions, the exciton size saturates around 0.7 nm for one-dimensional molecules with a size longer than about 4 nm. For the ladder-type polymer poly(benzimidazobenzophenanthroline), we obtain an exciton binding energy of about 0.3 eV, serving as a lower limit of the exciton binding energy for the organic materials investigated. Furthermore, we show that charge transfer transitions increase the exciton size and thus identify possible routes towards a further decrease of the exciton binding energy.

Authors:

Koerner, C.; Leo, K. ^[1]; Scholz, R. ^[1]; Plasser, F. ^[2]

Institut für Angewandte Photophysik, Technische Universität Dresden, Dresden (Germany)
Institute for Theoretical Chemistry, University of Vienna, A-1090 Vienna (Austria)

Publication Date:: Mon Dec 28 00:00:00 EST 2015

OSTI Identifier:: 22493435

Resource Type:: Journal Article

Journal Name:: Journal of Chemical Physics

Additional Journal Information:: Journal Volume: 143; Journal Issue: 24; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606

Country of Publication:: United States

Language:: English

Subject:: 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; BINDING ENERGY; CONVERSION; DENSITY FUNCTIONAL METHOD; DISSOCIATION; EFFICIENCY; ELECTRIC POTENTIAL; EV RANGE; EXCITONS; MOLECULES; ONE-DIMENSIONAL CALCULATIONS; ORGANIC MATTER; PHOTONS; PHOTOVOLTAIC EFFECT; POLYMERS; TIME DEPENDENCE

Citation Formats


                    Kraner, S., E-mail: stefan.kraner@iapp.de, Koerner, C., Leo, K., Scholz, R., Dresden Center of Computational Materials Science, Technische Universität Dresden, D-01062 Dresden, and Plasser, F. Exciton size and binding energy limitations in one-dimensional organic materials.  United States: N. p., 2015. 
        Web.  doi:10.1063/1.4938527.

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                    Kraner, S., E-mail: stefan.kraner@iapp.de, Koerner, C., Leo, K., Scholz, R., Dresden Center of Computational Materials Science, Technische Universität Dresden, D-01062 Dresden, & Plasser, F. Exciton size and binding energy limitations in one-dimensional organic materials.  United States.  https://doi.org/10.1063/1.4938527

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                    Kraner, S., E-mail: stefan.kraner@iapp.de, Koerner, C., Leo, K., Scholz, R., Dresden Center of Computational Materials Science, Technische Universität Dresden, D-01062 Dresden, and Plasser, F. 2015.  
        "Exciton size and binding energy limitations in one-dimensional organic materials".  United States.  https://doi.org/10.1063/1.4938527.

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@article{osti_22493435,

  title        = {Exciton size and binding energy limitations in one-dimensional organic materials},

  author       = {Kraner, S., E-mail: stefan.kraner@iapp.de and Koerner, C. and Leo, K. and Scholz, R. and Dresden Center of Computational Materials Science, Technische Universität Dresden, D-01062 Dresden and Plasser, F.},

  abstractNote = {In current organic photovoltaic devices, the loss in energy caused by the charge transfer step necessary for exciton dissociation leads to a low open circuit voltage, being one of the main reasons for rather low power conversion efficiencies. A possible approach to avoid these losses is to tune the exciton binding energy to a value of the order of thermal energy, which would lead to free charges upon absorption of a photon, and therefore increase the power conversion efficiency towards the Shockley-Queisser limit. We determine the size of the excitons for different organic molecules and polymers by time dependent density functional theory calculations. For optically relevant transitions, the exciton size saturates around 0.7 nm for one-dimensional molecules with a size longer than about 4 nm. For the ladder-type polymer poly(benzimidazobenzophenanthroline), we obtain an exciton binding energy of about 0.3 eV, serving as a lower limit of the exciton binding energy for the organic materials investigated. Furthermore, we show that charge transfer transitions increase the exciton size and thus identify possible routes towards a further decrease of the exciton binding energy.},

  doi          = {10.1063/1.4938527},

  url          = {https://www.osti.gov/biblio/22493435},
  journal      = {Journal of Chemical Physics},

  issn         = {0021-9606},

  number       = 24,

  volume       = 143,

  place        = {United States},

  year         = {Mon Dec 28 00:00:00 EST 2015},

  month        = {Mon Dec 28 00:00:00 EST 2015}

}

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