Organic/organic' heterojunctions: Organic light emitting diodes and organic photovoltaic devices

Neal R. Armstrong, Weining Wang, Dana M. Alloway, Diogenes Placencia, Erin Ratcliff, Michael Brumbach

Research output: Contribution to journalReview article

175 Scopus citations

Abstract

Heterojunctions created from thin films of two dissimilar organic semiconductor materials [organic/organic' (O/O') heterojunctions] are an essential component of organic light emitting diode displays and lighting systems (OLEDs, PLEDs) and small molecule or polymer-based organic photovoltaic (solar cell) technologies (OPVs). O/O' heterojunctions are the site for exciton formation in OLEDs, and the site for exciton dissociation and photocurrent production in OPVs. Frontier orbital energy offsets in O/O' heterojunctions establish the excess free energy controlling rates of charge recombination and formation of emissive states in OLEDs and PLEDs. These energy offsets also establish the excess free energy which controls charge separation and the shortcircuit photocurrent (JSc) in OPVs, and set the upper limit for the open-circuit photopotential (Vbc). We review here how these frontier orbital energy offsets are determined using photoemission spectroscopies, how these energies change as a function of molecular environment, and the influence of interface dipoles on these frontier orbital energies. Recent examples of hetero-junctions based on small molecule materials are shown, emphasizing those heterojunctions which are of interest for photovoltaic applications. These include heterojunctions of perylenebisimide dyes with trivalent metal phthalocyanines, and heterojunctions of titanyl phthalocyanine with C 6o, and with pentacene. Organic solar cells comprised of donor/ ¡ acceptor pairs of each of these last three materials confirm that the Vbc scales with the energy offsets between the HOMO of the donor and LUMO of the acceptor (EUOMOD - ELVMQA).

Original languageEnglish (US)
Pages (from-to)717-731
Number of pages15
JournalMacromolecular Rapid Communications
Volume30
Issue number9-10
DOIs
StatePublished - May 19 2009

Keywords

  • Diodes
  • Films
  • Frontier orbitais
  • Interface dipoles
  • Organic heterojunctions
  • Organic light emitting diodes
  • Organic photovoltaics
  • Uv-photoelectron spectroscopy

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Materials Chemistry

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