Ultrafast Hole-Transfer Dynamics in Polymer/PCBM Bulk Heterojunctions

Authors

  • Artem A. Bakulin,

    1. Zernike Institute for Advanced Materials, University of Groningen Nijenborgh 4, 9747 AG Groningen (The Netherlands)
    2. Current address: Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge, CB3 0HE (UK)
    Search for more papers by this author
  • Jan C. Hummelen,

    1. Stratingh Institute for Chemistry, University of Groningen Nijenborgh 4, 9747 AG Groningen (The Netherlands)
    Search for more papers by this author
  • Maxim S. Pshenichnikov,

    Corresponding author
    1. Zernike Institute for Advanced Materials, University of Groningen Nijenborgh 4, 9747 AG Groningen (The Netherlands)
    • Zernike Institute for Advanced Materials, University of Groningen Nijenborgh 4, 9747 AG Groningen (The Netherlands).
    Search for more papers by this author
  • Paul H. M. van Loosdrecht

    1. Zernike Institute for Advanced Materials, University of Groningen Nijenborgh 4, 9747 AG Groningen (The Netherlands)
    Search for more papers by this author

Abstract

Ultrafast dynamics of the hole-transfer process from methanofullerene to a polymer in a polymer/PCBM bulk heterojunction are directly resolved. Injection of holes into MDMO-PPV is markedly delayed with respect to [60]PCBM excitation. The fastest component of the delayed response is attributed to the PCBM–polymer hole-transfer process (30 ± 10 fs), while the slower component (∼150 fs) is provisionally assigned to energy transfer and/or relaxation inside PCBM nanoclusters. The charge generation through the hole transfer is therefore as fast and efficient as through the electron-transfer process. Exciton harvesting efficiency after PCBM excitation crucially depends on the concentration of the methanofullerene in the blend, which is related to changes in the blend morphology. Ultrafast charge generation is most efficient when the characteristic scale of phase separation in the blend does not exceed ∼20 nm. At larger-scale phase separation, the exciton harvesting dramatically declines. The obtained results on the time scales of the ultrafast charge generation after PCBM excitation and their dependence on blend composition and morphology are instrumental for the future design of fullerene-derivative-based photovoltaic devices.

Ancillary