Energy level offset at organic semiconductor heterojunctions

A. Rajagopal, C. I. Wu, Antoine Kahn

Research output: Contribution to journalArticle

186 Scopus citations

Abstract

We present an investigation via ultraviolet photoemission spectroscopy of the electronic structure of three organic-organic heterojunctions formed between the standard electron-transport emissive material tris(8-hydroxy-quinoline) aluminum (Alq3) and two hole-transport materials, i.e., 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA), and N,N′-diphenyl-N,N′- bis(l-naphthyl)-1-1′biphenyl-4,4″diamine (α-NPD). We measure directly the energy offsets between highest occupied molecular orbitals during the formation of the interfaces. We show that the relative positions of the highest occupied and lowest unoccupied molecular orbitals across the Alq3/PTCDA and Alq3/α-NPD interfaces are qualitatively different and explain, in part, the difference in the performance of electroluminescent devices based on these heterojunctions. We demonstrate the existence of charge transfer-induced dipoles which shift the molecular levels of one organic with respect to the other and invalidate the usual assumption of vacuum level alignment across organic heterojunctions. Finally, we show that the molecular level alignment is independent of the deposition sequence of the organic films and that transitivity applies to these organic "band offsets."

Original languageEnglish (US)
Pages (from-to)2649-2655
Number of pages7
JournalJournal of Applied Physics
Volume83
Issue number5
DOIs
StatePublished - Jan 1 1998

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

Fingerprint Dive into the research topics of 'Energy level offset at organic semiconductor heterojunctions'. Together they form a unique fingerprint.

  • Cite this