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M. Blatnik, P. Jacobson, M. Schmid, J. Cechal, U. Diebold, M. Wagner:
"Structural Details of a Prototypical Organic-Inorganic Interface: CuPc on In₂O₃(111)";
Poster: DPG-Frühjahrstagung (DPG Spring Meeting) of the Surface Science Division, SurfaceScience21, virtual; 01.03.2021.

Indium oxide (In2O3) is a ubiquitous material in OLEDs and photovoltaics due to an ideally matched optical transmission window and metal-like conductivity at room temperature when doped with Sn (as ITO). When In2O3 is paired with organic materials, a nearly universal fabrication step is the introduction of a thin organic buffer layer to improve the charge injection efficiency from In2O3 to the organic active layers. Using a combination of STM, nc-AFM and local spectroscopy (STS), we probe the adsorption structure and density of states (DOS) at the prototypical copper phthalocyanine (CuPc)-In2O3 interface. We focus on the stoichiometric (111) surface but also investigate the effects of dissociated water coadsorbed in UHV. STM/AFM imaging reveals single CuPc molecules adsorb in a flat, slightly tilted geometry in three symmetry-equivalent orientations. Increasing the coverage leads to (densely packed) 1D chains oriented along the <110> directions. With increasing coverage up to 1 ML, first a (2×2) and then a (1×1) superstructure is found. Finally, differential conductance (dI/dV) measurements reveal the energetic positions of the HOMO and LUMO states which are critical for improving charge injection.