Dresden 2020 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 44: Focus: Exploitation of Anisotropy in Organic Semiconductors II (joint session CPP/HL)
HL 44.6: Talk
Wednesday, March 18, 2020, 11:00–11:15, ZEU 222
On the Origin of Electronic Gap States in Molecular Semiconductor Thin Films — •Alexander Hinderhofer1, Jan Hagenlocher1, Satoshi Kera2, and Frank Schreiber1 — 1Universität Tübingen, Institut für Angewandte Physik, 72076 Tübingen, Germany — 2Institute for Molecular Science, Myodaiji, 444-8585, Japan
Electronic gap states within the HOMO-LUMO gap of molecular semiconductors play a key role in the energy level alignment of organic-organic and organic-inorganic interfaces and therefore are a defining parameter for device functionality and efficiency. The density of gap states originates from structural defects acting as dopants and it can be varied by different film preparation methods, e.g. by temperature variation during film deposition.
We present a systematic study of anisotropic structural parameters in thin films, including grain size, strain, dislocation density, mosaicity and coherently ordered domain size (in-plane and out-of-plane) studied by X-ray scattering and atomic force microscopy. The structural properties of several molecular semiconductors (Pentacene (PEN), Perfluoropentacene (PFP), 6-Phenacene (6Phen), etc.) are correlated with their electronic gap state density studied by ultra-low background ultraviolet photoelectron spectroscopy (UPS). We discuss which types of structural parameters have the strongest impact on the gap state density. Finally, we present examples of the energy level alignment in organic-organic heterojunctions controlled by their gap state density.