Dresden 2020 – scientific programme

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O: Fachverband Oberflächenphysik

O 8: Ultrafast Electron Dynamics I: Surfaces and Interfaces (joint session O/MA)

O 8.11: Talk

Monday, March 16, 2020, 13:00–13:15, TRE Phy

Dynamics of interfacial electron-hole separation in an organic heterojunction monitored by femtosecond time-resolved X-ray photoelectron spectroscopy — •Friedrich Roth¹, Mario Borgwardt², Lukas Wenthaus³, Johannes Mahl², Steffen Palutke⁴, Günter Brenner⁴, Serguei Molodtsov^1,5, Wilfried Wurth^3,4,6, Oliver Gessner², and Wolfgang Eberhardt³ — ¹Institute of Experimental Physics, TU Bergakademie Freiberg, Leipziger Straße 23, D-09599 Freiberg, Germany — ²Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA — ³Center for Free-Electron Laser Science / DESY, D-22607 Hamburg, Germany — ⁴Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22603 Hamburg, Germany — ⁵European XFEL GmbH, Holzkoppel 4, 22869, Schenefeld, Germany — ⁶Universität Hamburg, Luruper Chaussee 149, 22761, Hamburg, German

The dynamics of ultrafast photon-to-charge conversion in a copper-phthalocyanine (CuPc)-C₆₀ heterojunction is studied by femtosecond time-resolved X-ray photoemission spectroscopy (tr-XPS) at the free-electron laser FLASH. The technique provides site-specific access to electron dynamics and monitors the generation and decay of interfacial charge-transfer (ICT) states after excitation with 775 nm photons. A previously unobserved channel for ICT separation into mobile charge carriers with an efficiency of 22 ± 7 % is identified, providing a direct measure of the internal quantum efficiency of the heterojunction for this channel.