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Molecular exciton-polaritons exhibit long-range, ultrafast propagation, yet recent experiments have reported far slower propagation than expected. In this work, we implement a nonperturbative approach to quantify how static energetic disorder renormalizes polariton group velocity in strongly coupled microcavities. The method requires no exact diagonalization or master equation propagation and depends only on measurable parameters: the mean exciton energy and its probability distribution, the microcavity dispersion, and the Rabi splitting. Using parameters corresponding to recently probed organic microcavities, we show that exciton inhomogeneous broadening slows both lower and upper polaritons, particularly when the mean exciton energy fluctuation approaches the collective light–matter coupling strength. A detailed discussion and interpretation of these results is provided using perturbation theory in the limit of weak resonance scattering. The magnitude of the effects examined in this work supports the conclusion that most of the reported polaritonic slowdown arises from dynamical (phonon-assisted) disorder, with static energetic disorder contributing only secondarily.
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Charge separation boosts exciton diffusion in fused ring electron acceptors
Non-fullerene acceptors (NFAs) are highly promising materials for organic photovoltaics (OPVs). Exciton diffusion in NFAs is crucial to their photovoltaic performance, but is not yet well understood. Here we systematically examine exciton diffusion in a fused-ring electron acceptor (IDIC) based on a first-principles framework. We discover that low-energy excitons in disordered IDIC are charge-separated with electrons and holes residing on neighboring molecules, yielding long exciton lifetimes. With low energetic disorder, high exciton density of states (DOS) and long lifetimes, the disordered IDIC is predicted to exhibit large exciton diffusion lengths and high quantum efficiency. The temperature and energy dependences of exciton diffusion are explored and the manner in which various materials properties (exciton energy, DOS, energetic disorder, and phonon frequency) conspire to influence exciton diffusion is elucidated. Finally, we show that dilation could be an effective strategy to increase the exciton diffusion length in IDIC.
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- Award ID(s):
- 1828019
- PAR ID:
- 10226271
- Date Published:
- Journal Name:
- Journal of Materials Chemistry A
- Volume:
- 8
- Issue:
- 44
- ISSN:
- 2050-7488
- Page Range / eLocation ID:
- 23304 to 23312
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0ta08666e
