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Title: Fermi level pinning induced electrostatic fields and band bending at organic heterojunctions

The energy level alignment at interfaces between organic semiconductors is of direct relevance to understand charge carrier generation and recombination in organic electronic devices. Commonly, work function changes observed upon interface formation are interpreted as interface dipoles. In this study, using ultraviolet and X-ray photoelectron spectroscopy, complemented by electrostatic calculations, we find a huge work function decrease of up to 1.4 eV at the C{sub 60} (bottom layer)/zinc phthalocyanine (ZnPc, top layer) interface prepared on a molybdenum trioxide (MoO{sub 3}) substrate. However, detailed measurements of the energy level shifts and electrostatic calculations reveal that no interface dipole occurs. Instead, upon ZnPc deposition, a linear electrostatic potential gradient is generated across the C{sub 60} layer due to Fermi level pinning of ZnPc on the high work function C{sub 60}/MoO{sub 3} substrate, and associated band-bending within the ZnPc layer. This finding is generally of importance for understanding organic heterojunctions when Fermi level pinning is involved, as induced electrostatic fields alter the energy level alignment significantly.
Authors:
 [1] ; ;  [1] ;  [2]
  1. Institut für Physik and IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 6, 12489 Berlin (Germany)
  2. (Germany)
Publication Date:
OSTI Identifier:
22402430
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 105; Journal Issue: 22; 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; CHARGE CARRIERS; DEPOSITION; FERMI LEVEL; FULLERENES; HETEROJUNCTIONS; INTERFACES; LAYERS; MOLYBDENUM OXIDES; ORGANIC SEMICONDUCTORS; PHTHALOCYANINES; RECOMBINATION; SUBSTRATES; ULTRAVIOLET RADIATION; WORK FUNCTIONS; X-RAY PHOTOELECTRON SPECTROSCOPY; ZINC