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Pentacene Excitons in Strong Electric Fields.

Klaus Kuhnke1, Volodymyr Turkowski2, Alexander Kabakchiev1

  • 1Max-Planck Institut für Festkörperforschung, Heisenbergstr. 1, 70569, Stuttgart, Germany.

Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry
|December 15, 2017
PubMed
Summary
This summary is machine-generated.

Scanning tunneling microscope electroluminescence reveals insights into organic semiconductor excited states. Researchers identified a charge-transfer exciton in pentacene, crucial for understanding photovoltaic applications.

Keywords:
density functional calculationselectroluminescenceexcitonspentacenescanning probe microscopy

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Area of Science:

  • Physical Chemistry
  • Materials Science
  • Organic Electronics

Background:

  • Electroluminescence spectroscopy in scanning tunneling microscopes (STM) offers unique insights into organic semiconductor excited states.
  • Understanding exciton polarizability is key to optimizing organic electronic devices.

Purpose of the Study:

  • To investigate the polarizability of neutral excited states in organic semiconductors using STM-induced electroluminescence.
  • To assign the observed Stark shift to a specific exciton type in pentacene nanocrystals.

Main Methods:

  • Utilizing electroluminescence spectroscopy within a scanning tunneling microscope (STM) junction.
  • Combining experimental data with density functional theory (DFT) and time-dependent DFT (TDDFT) calculations.

Main Results:

  • The lowest singlet exciton at 1.6 eV in pentacene was identified as a charge-transfer (CT) exciton.
  • The exciton's charge separation was found to be perpendicular to the applied electric field.
  • Moderate polarizability and strong STM electric fields prevent dissociation of parallel-polarized CT excitons.

Conclusions:

  • The study provides a detailed characterization of a CT exciton in pentacene.
  • The findings are relevant for understanding and designing materials for photovoltaic applications.
  • Electric-field-induced anisotropy of exciton potential energy surfaces is important for device performance.