Journal
PHYSICAL REVIEW B
Volume 99, Issue 20, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.99.205201
Keywords
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Funding
- Horizon-2020 EU project EXTMOS [646176]
- Horizon-2020 EU project MOSTOPHOS [646259]
- European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant agreement MolDesign [795206]
- Ministry of Science, Research and the Arts Baden-Wurttemberg
- DFG (Deutsche Forschungsgemeinschaft)
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We present an ab initio computational study of triplet exciton diffusion in four phosphorescent emitters commonly used in organic light-emitting diodes (OLEDs). By kinetic Monte Carlo simulations, triplet diffusion lengths are obtained for these emitters in neat films and as a guest in two different hosts. The triplet transfer rates governing the diffusion contain a transfer integral factor that includes both Forster and Dexter contributions and a Franck-Condon weighted density of vibrational states that includes the coupling to all intramolecular vibrations in a fully quantum mechanical way. We find that at guest concentrations around 10 mol% the Forster transfer contribution is most important. At larger concentrations of about 30-40 mol% the Dexter contribution becomes dominant. We show that obtaining the triplet transfer rates by the semiclassical Marcus theory yields diffusion lengths that are too short and that using a simple cubic lattice in combination with the often used Miller-Abrahams rates instead of using a real morphology with the ab initio rates leads to an underestimation of the diffusion lengths due to transfers down in energy that are too slow.
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