Demonstrating the Impact of the Adsorbate Orientation on the Charge Transfer at Organic-Metal Interfaces

Thomas G. Boné, Andreas Windischbacher, Marie S. Sättele, Katharina Greulich, Larissa Egger, Thomas Jauk, Florian Lackner, Holger F. Bettinger, Heiko Peisert, Thomas Chassé, Michael G. Ramsey, Martin Sterrer, Georg Koller, Peter Puschnig*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Charge-transfer processes at molecule-metal interfaces play a key role in tuning the charge injection properties in organic-based devices and thus, ultimately, the device performance. Here, the metal's work function and the adsorbate's electron affinity are the key factors that govern the electron transfer at the organic/metal interface. In our combined experimental and theoretical work, we demonstrate that the adsorbate's orientation may also be decisive for the charge transfer. By thermal cycloreversion of diheptacene isomers, we manage to produce highly oriented monolayers of the rodlike, electron-acceptor molecule heptacene on a Cu(110) surface with molecules oriented either along or perpendicular to the close-packed metal rows. This is confirmed by scanning tunneling microscopy (STM) images as well as by angle-resolved ultraviolet photoemission spectroscopy (ARUPS). By utilizing photoemission tomography momentum maps, we show that the lowest unoccupied molecular orbital (LUMO) is fully occupied and also, the LUMO + 1 gets significantly filled when heptacene is oriented along the Cu rows. Conversely, for perpendicularly aligned heptacene, the molecular energy levels are shifted significantly toward the Fermi energy, preventing charge transfer to the LUMO + 1. These findings are fully confirmed by our density functional calculations and demonstrate the possibility to tune the charge transfer and level alignment at organic-metal interfaces through the adjustable molecular alignment.

Original languageEnglish
Pages (from-to)9129-9137
Number of pages9
JournalThe Journal of Physical Chemistry C
Volume125
Issue number17
DOIs
Publication statusPublished - 6 May 2021

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • General Energy
  • Surfaces, Coatings and Films
  • Physical and Theoretical Chemistry

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