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Nat Chem. 2014 Jun;6(6):492-7. doi: 10.1038/nchem.1945. Epub 2014 May 4.

A transferable model for singlet-fission kinetics.

Author information

  • 11] Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachussetts 02139, USA [2].
  • 21] Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachussetts 02139, USA [2].
  • 3Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachussetts 02139, USA.
  • 4Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachussetts 02139, USA.
  • 5Cavendish laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
  • 6Center for Functional Nanomaterials, Brookhaven National Laboratory, Building 735, Upton, New York 11973, USA.

Abstract

Exciton fission is a process that occurs in certain organic materials whereby one singlet exciton splits into two independent triplets. In photovoltaic devices these two triplet excitons can each generate an electron, producing quantum yields per photon of >100% and potentially enabling single-junction power efficiencies above 40%. Here, we measure fission dynamics using ultrafast photoinduced absorption and present a first-principles expression that successfully reproduces the fission rate in materials with vastly different structures. Fission is non-adiabatic and Marcus-like in weakly interacting systems, becoming adiabatic and coupling-independent at larger interaction strengths. In neat films, we demonstrate fission yields near unity even when monomers are separated by >5 Å. For efficient solar cells, however, we show that fission must outcompete charge generation from the singlet exciton. This work lays the foundation for tailoring molecular properties like solubility and energy level alignment while maintaining the high fission yield required for photovoltaic applications.

PMID:
24848234
[PubMed - indexed for MEDLINE]
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