Electronic structure of molybdenum-oxide films and associated charge injection mechanisms in organic devices

Jens Meyer, Antoine Kahn

Research output: Contribution to journalArticle

32 Scopus citations

Abstract

We report on the electronic structure of freshly evaporated and air-exposed Molybdenum tri-oxide (MoO3) and the energy-level alignment between this compound and a holetransport material [e.g., N,N'-diphenyl-N,N'-bis (1-naphthyl)-1,1'-biphenyl-4,4'-diamine (a-NPD)]. Ultraviolet and inverse photoelectron spectroscopy show that freshly evaporated MoO3 exhibits deep-lying electronic states with an electron affinity (EA) of 6.7 eV and ionization energy (IE) of 9.7 eV. Air exposure reduces EA and IE by ∼1 eV, to 5.5 and 8.6 eV, respectively, but does not affect the hole-injection efficiency, which is confirmed by device studies. Thus, MoO3 can be applied in low-vacuum environment, which is particularly important for low-cost manufacturing processes. Our findings of the energy-level alignment between MoO3 and α-NPD also leads to a revised interpretation of the charge-injectionmechanism, whereby the hole-injection corresponds to an electron extraction from the organic highest-occupied molecular orbital (HOMO) level via the MoO3 conduction band.

Original languageEnglish (US)
Article number11109
JournalJournal of Photonics for Energy
Volume1
Issue number1
DOIs
StatePublished - Dec 1 2011

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics
  • Renewable Energy, Sustainability and the Environment

Keywords

  • Energy levels
  • Inverse photoelectron spectroscopy
  • MoO
  • Molybdenum oxide
  • Organic electronics
  • Ultraviolet photoelectron spectroscopy

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