Small-molecule bulk heterojunctions: Distinguishing between effects of energy offsets and molecular packing on optoelectronic properties

K. Paudel, B. Johnson, A. Neunzert, M. Thieme, B. Purushothaman, M. M. Payne, J. E. Anthony, O. Ostroverkhova

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


We report on the dependence of time-resolved photoluminescence (PL) and photocurrent in small-molecule bulk heterojunctions on the donor-acceptor (D/A) LUMO offset, D/A separation, and acceptor domain structure. We chose a high-performance functionalized fluorinated anthradithiophene (ADT) derivative, ADT-TES-F, as the donor and two other fluorinated ADT derivatives, ADT-R-F (where R is a variable side group), as well as two functionalized fluorinated pentacene (Pn) derivatives, Pn-R-F8, as acceptors. The choice of ADT and Pn acceptors enabled us to separate the effects of the D/A LUMO offset, which was approximately zero in the case of ADT acceptors and ∼0.55 eV in the case of Pn acceptors, from those of molecular packing on the optoelectronic properties. The acceptor side groups R were chosen based on (i) packing motifs in the solid state and (ii) size, to achieve different D/A separations at the D/A interface. Addition of an ADT-R-F acceptor to the ADT-TES-F donor introduced disorder, which resulted in increased PL emission, depending on the acceptor's packing motif, and in reduced photocurrents. In ADT-TES-F/Pn-R-F8 films, charge transfer from ADT-TES-F to Pn-R-F8 was observed with an acceptor packing-dependent formation of an exciplex, which dissociated under applied electric field, contributing to charge carrier photogeneration. However, this contribution was not sufficient to compensate for a photocurrent reduction due to an increased disorder at Pn-R-F8 concentrations of 7 wt % and above, regardless of the acceptor's R-groups and packing motifs.

Original languageEnglish
Pages (from-to)24752-24760
Number of pages9
JournalJournal of Physical Chemistry C
Issue number47
StatePublished - Nov 27 2013

ASJC Scopus subject areas

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


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