Effective Negative Diffusion of Singlet Excitons in Organic Semiconductors.

Using diffraction-limited ultrafast imaging techniques, we investigate the propagation of singlet and triplet excitons in single-crystal tetracene. Instead of an expected broadening, the distribution of singlet excitons narrows on a nanosecond time scale after photoexcitation. This narrowing results in an effective negative diffusion in which singlet excitons migrate toward the high-density region, eventually leading to a singlet exciton distribution that is smaller than the laser excitation spot. Modeling the excited-state dynamics demonstrates that the origin of the anomalous diffusion is rooted in nonlinear triplet-triplet annihilation (TTA). We anticipate that this is a general phenomenon that can be used to study exciton diffusion and nonlinear TTA rates in semiconductors relevant for organic optoelectronics.

Citation

Anton Matthijs Berghuis, T V Raziman, Alexei Halpin, Shaojun Wang, Alberto G Curto, Jaime Gómez Rivas. Effective Negative Diffusion of Singlet Excitons in Organic Semiconductors. The journal of physical chemistry letters. 2021 Feb 04;12(4):1360-1366

PMID: 33507078

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