Titanyl phthalocyanine/C60 heterojunctions: Band-edge offsets and photovoltaic device performance

Michael Brumbach, Diogenes Placencia, Neal R. Armstrong

Research output: Contribution to journalArticle

149 Scopus citations

Abstract

Planar heterojunction organic photovoltaic devices have been created using oxo-titanium phthalocyanine (TiOPc) as the donor layer and fullerene (C60) as the acceptor layer, with comparisons to devices based on copper phthalocyanine (CuPc) as the donor. TiOPc/C60 and CuPc/C60 heterojunctions were first characterized by a combination of UV-photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) to estimate the frontier orbital energy offset (EHOMOD - ELUMOA), which is related to the open-circuit photopotential (VOC). A small interface dipole effect was seen at the TiOPc/C60) interface (eD ≈ 0.02 eV), whereas a significant interface dipole was observed for the CuPc/C60 interface (eD ≈ 0.3 eV). On the basis of the work presented here and previously reported electrochemical and UPS/XPS studies, we estimate an EHOMOD - ELUMOA energy offset of ca. 1.1 eV for the TiOPc/C60 heterojunction and 0.7 eV for the CuPc/C60 heterojunction. Maximum VOC values observed at room temperature for corresponding planar heterojunction photovoltaic devices were 0.3-0.4 V lower than the energy offset potentials, even at high light intensities, where the maximum VOC, at room temperature, was achieved. TiOPc/C60 heterojunctions offer higher VOC values than CuPc/C60 heterojunctions, but with a lower intrinsic driving force for exciton dissociation (photoinduced charge transfer).

Original languageEnglish (US)
Pages (from-to)3142-3151
Number of pages10
JournalJournal of Physical Chemistry C
Volume112
Issue number8
DOIs
StatePublished - Feb 28 2008

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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