Regensburg 2019 – scientific programme
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DS: Fachverband Dünne Schichten
DS 16: Organic Thin Films, Organic-Inorganic Interfaces
DS 16.11: Talk
Wednesday, April 3, 2019, 12:15–12:30, H39
Switching the surface electronic properties of polar ZnO crystals with photochromic pyridyl-dihydropyrene molecular layers — •Qiankun Wang1, Giovanni Ligorio1, Raphael Schlesinger1, Valentin Diez-Cabanes2, David Cornil2, Yves Garmshausen1, Stefan Hecht1, Jérôme Cornil2, Emil J. W. List-Kratochvil1, and Norbert Koch1 — 1Humboldt-Universität zu Berlin — 2University of Mons
Remote control of the electronic energy levels by external stimuli such as light will enable optoelectronic devices with improved or additional functionalities. Here, we demonstrate that the electronic properties of ZnO interfaced with molecular negative T-type photoswitches, i.e., pyridyl-dihydropyrene (Py-DHP), can indeed be photomodulated. Using photoemission spectroscopy and density functional theory (DFT) modelling, we show that the photochromic ring closure/opening process results in reversible shift of the frontier occupied molecular level by 0.7 eV with respect to the Fermi level. Notably, in both molecular configurations, the energy level alignment at the ZnO/Py-DHP interface is governed by a Fermi level pinning of the lowest unoccupied molecular level. Moreover, upon switching, we observe an increase in the ionization energy for Py-DHP multilayers compared to that of a monolayer. We attribute this to a different preferred molecular orientation in monolayer versus multilayer films. Our results show that dynamic tuning of the interface energy level alignment at inorganic/organic junctions by external stimuli is indeed possible and will aid the development of photoprogrammable opto-electronic devices.