Exciton Regeneration Dynamics in Model Donor−Acceptor Polymer Heterojunctions

John Glenn S. Ramon and Eric R. Bittner*
Department of Chemistry and Center for Materials Chemistry, University of Houston, Houston, Texas 77204
J. Phys. Chem. B, 2006, 110 (42), pp 21001–21009
DOI: 10.1021/jp061751b
Publication Date (Web): September 20, 2006
Copyright © 2006 American Chemical Society
*

 Address correspondence to this author. E-mail:  bittner@uh.edu.

Abstract

We present a theoretical investigation on various semiconducting materials that exhibit photovoltaic and photoluminecent properties. Our focus is on the relaxation dynamics that occur upon photoexcitation of a couple of type II donor−acceptor heterojunction systems. In addition to the diabatic approach our two-band exciton model employs to study the phonon-assisted relaxations, we adopt the Marcus−Hush semiclassical method to incorporate lattice reorganization. This enables us to look at the state-to-state interconversions from the relaxed excited-state configurations in model polymer blends of poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) with poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine) (PFB) with F8BT. Our results stress the significance of vibrational relaxation in the state-to-state relaxation. Furthermore, while a tightly bound charge-transfer state (exciplex) remains the lowest excited state, we show that the regeneration of the optically active lowest excitonic state in TFB:F8BT is possible via the existence of a steady state.

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History

  • Published In Issue October 26, 2006
  • Received March 21, 2006
    Revised August 17, 2006

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