Heidelberg 2015 – scientific programme

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MO: Fachverband Molekülphysik

MO 16: Posters 3: Novelties in Molecular Physics

MO 16.9: Poster

Wednesday, March 25, 2015, 17:00–19:00, C/Foyer

Ultrafast Exciton Dynamics at a P3HT-Gold Interface Investigated by Femtosecond Time-resolved Pump-Probe Scanning Near-Field Microscopy — •Tahir Zeb Khan, Patrice Donfack, Mehdi Mohammad Kazemi, Sidhant Bom, Veit Wagner, and Arnulf Materny — Jacobs University, Campus Ring 1, 28759 Bremen, Germany

We demonstrate that femtosecond transient absorption spectroscopy in combination with scanning near-field optical microscopy (SNOM) is a powerful technique for obtaining a realistic picture of local exciton dynamical processes in organic semiconductor devices. Here, we present the study of exciton dynamics at the interface between a regioregular P3HT layer and a gold contact. Early exciton dynamics are determined by the available ultrafast decay pathways of hot excitons, which can form e.g. interfacial charge transfer excitons. This affects the overall exciton relaxation locally. Highly localized details are however not accessible via diffraction-limited spectroscopic techniques. We show that only when high spatial resolution is achieved, the local ultrafast exciton dynamics in P3HT ( 1-2 ps) is experimentally observed and proven to be significantly faster at the Au-P3HT interface as compared to neat P3HT. Moreover, we have observed that within 15 ps the overall relaxation from the probed excited state is at least 17 % less at the interface, which clearly indicates the formation of additional long-lived trapped states. The present results provide the first experimental observation and evidence that the fate of hot excitons significantly determines the photophysics at the Au-P3HT interface.