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O: Fachverband Oberflächenphysik

O 6: Organic Molecules on Inorganic Substrates I: Electronic, Optical and other Properties

O 6.5: Vortrag

Montag, 16. März 2020, 11:45–12:00, REC C 213

Exciton Fission, Fusion, Annihilation and Quantum Beating in Deposited Tetracene Films — Kevin Oldenburg, •Ingo Barke, Chris Rehhagen, Stefan Lochbrunner, and Sylvia Speller — Institute of Physics, University of Rostock

One technique to overcome the Shockley-Queisser limit in dye-sensitized solar cells is to exploit singlet fission processes, effectively doubling the number of charge carriers per photon. Here we present photoemission electron microscopy (PEEM) data of the excited state dynamics and spatial distribution of tetracene thin films. In order to locally enhance the excitation density, plasmon excitations in mass-selected silver nanoparticles (diameter ≈ 10 nm) are used [1]. Signatures of a singlet fission process are visible leading to an efficient population of a triplet state with annihilation governed decay dynamics on the order of ns to µs, while we observe an intrinsic lifetime exceeding 10 µs. Complementary fluorescence lifetime microscopy (FLIM) reveals quantum beats in the signal of delayed fluorescence on the time scale of several ns which are attributed to a coherent excitation of a triplet manifold [2]. The coherence time appears to be dependent on the exciton density which is analyzed by changing the excitation power. The characteristic lifetimes obtained by PEEM are consistent with fluorescence data (see also [3]).
[1]K. Oldenburg et al., J. Phys. Chem. C 123, 1379 (2019).
[2] J. Burdett, C.J. Bardeen, JACS 134, 8597 (2012).
[3] G.M. Akselrod et al., Nat. Commun. 5, 3646 (2014).