skip to main content

Title: Seleno groups control the energy-level alignment between conjugated organic molecules and metals

The charge injection from metallic electrodes into hole transporting layers of organic devices often suffers from deviations from vacuum-level alignment at the interface. Even for weakly interacting cases, Pauli repulsion causes an interface dipole between the metal and conjugated organic molecules (COMs) (so called “push-back” or “cushion” effect), which leads notoriously to an increase of the hole injection barrier. On the other hand, for chalcogenol self assembled monolayers (SAMs) on metal surfaces, chemisorption via the formation of chalcogen-metal bonds is commonly observed. In these cases, the energy-level alignment is governed by chalcogen-derived interface states in the vicinity of the metal Fermi-level. In this work, we present X-ray and ultraviolet photoelectron spectroscopy data that demonstrate that the interfacial energy-level alignment mechanism found for chalcogenol SAMs also applies to seleno-functionalized COMs. This can be exploited to mitigate the push-back effect at metal contacts, notably also when COMs with low ionization energies are employed, permitting exceedingly low hole injection barriers, as shown here for the interfaces of tetraseleno-tetracene with Au(111), Ag(111), and Cu(111)
Authors:
; ; ;  [1] ;  [2] ;  [3] ; ;  [4] ;  [2] ;  [5] ;  [6] ; ;  [2] ;  [1] ;  [7]
  1. Institut für Physik, Humboldt-Universität zu Berlin, 12489 Berlin (Germany)
  2. Graduate School of Advanced Integration Science, Chiba University, Chiba 263-8522 (Japan)
  3. (FUNSOM), Soochow University, Suzhou 215123 (China)
  4. Institut für Angewandte Physik, Universität Tübingen, 72076 Tübingen (Germany)
  5. (China)
  6. Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, BESSY II, 12489 Berlin (Germany)
  7. (Germany)
Publication Date:
OSTI Identifier:
22253649
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 1; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALIGNMENT; CHALCOGENIDES; CHEMISORPTION; CONTROL; DIPOLES; FERMI LEVEL; INJECTION; INTERFACES; PHOTOELECTRON SPECTROSCOPY; SILVER 111; TETRACENE; X RADIATION