Dresden 2020 – scientific programme
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O: Fachverband Oberflächenphysik
O 44: Ultrafast Electron Dynamics II (joint session O/MA)
O 44.7: Invited Talk
Tuesday, March 17, 2020, 12:15–12:45, WIL B321
Ultrafast dynamics of charge transfer and Frenkel excitons in molecular thin films — •Benjamin Stadtmüller — University of Kaiserslautern and Research Center OPTIMAS, Erwin-Schroedinger-Str. 46, 67663 Kaiserslautern, Germany
Molecular complexes are highly flexible materials with intriguing opportunities for future photovoltaic and spintronic applications. The crucial device-relevant processes in molecular materials are the excited state dynamics and the carrier transport. Despite their common origin - the molecular band structure - their interplay is far from being understood. In this work, we focus on the link between the excited state dynamics of excitons in fullerene thin films and the resulting ensemble dynamics of the transport states of the entire film using time- and momentum resolved photoemission with fs-XUV radiation. Upon the optical excitation of excitons in C60 films, we reveal a transient modification of the energy level alignment of the molecular valence states, which can be identified as the signature of charge transfer (CT) excitons in molecular materials [1]. Taking advantage of this observation, we are able to disentangle the dynamics of CT and Frenkel excitons in (endohedral) fullerene films. We find different decay dynamics depending on the sample temperature or the charge doping concentration of the molecular film. Finally, we will provide a first view onto the momentum-space signature of CT and Frenkel excitons as a first step towards imaging the orbital character of both types of excitons in molecular films. [1] Nat. Commun. 10, 1470 (2019)