Berlin 2014 – wissenschaftliches Programm

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SYET: Symposium Exciton transfer in ordered atomic and molecular structures

SYET 1: Symposium on Exciton Transfer in Ordered Atomic and Molecular Structures

SYET 1.1: Hauptvortrag

Donnerstag, 20. März 2014, 10:30–11:00, SPA Kapelle

On the role of charge transfer excitations in mediating triplet diffusion, singlet fission and dissociation in organics — •David Beljonne — Chimie des Matériaux Nouveaux & Centre d'Innovation et de Recherche en Matériaux Polymères, Université de Mons, Belgium

Primary photoexcitations in organic materials are strongly bound singlet Frenkel-like excitons coupled to a local lattice reorganization (polaronic excitons). In some molecular crystals such as oligoacenes, singlet excitons undergo an efficient spin-conserving fission process yielding two triplet excitons. Besides being of interest from a fundamental point of view, this process opens new opportunities to break the Schockley-Queisser limit in single junction organic solar cells. Singlet fission has thus retained lots of attention recently. We will review some recent works done in our lab and elsewhere on the fundamentals of singlet fission and point in particular to the importance of charge-transfer excitations in mediating the process, through either admixture of charge-transfer character into the lowest exciton states or via a super-exchange mechanism. The same effects also affect the rates and diffusion coefficients of the resulting triplets. We will present a first-principle study of triplet transport in an organic crystal taking into account such effects in addition to thermally activated crystal phonons and molecular vibrations. Finally, if time permits, a brief discussion of the mechanisms by which bound polaron pairs can escape from their Coulomb attractive well will be presented and analyzed in the light of recent experimental results.