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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 62: Electrical, Dielectrical and Optical Properties of Thin Films

CPP 62.3: Vortrag

Donnerstag, 4. April 2019, 18:15–18:30, H8

Exciton binding energy of organic materials: ground-state vs. excited-state charge-transfer complexes — •Andreas Opitz¹, Paul Beyer¹, Norbert Koch^1,2, and Wolfgang Brütting³ — ¹Humboldt-Universität zu Berlin — ²Helmholtz-Zentrum Berlin für Materialien und Energie GmbH — ³Universität zu Berlin Augsburg

Organic semiconductors are materials with a high exciton binding energy (EBE), which significantly affects their electronic and optical properties. The EBE is the difference between the electronic gap (obtained by direct and inverse photoelectron spectroscopy) and the lowest optical transition energy (determined from absorption spectroscopy). In this contribution, the EBE is investigated for thin films of pristine organic semiconductor as well as charge-transfer complexes.

The EBE of pristine diindenoperylene (DIP) is about 0.50 eV. DIP combined with fullerene as acceptor was studied for photovoltaic cells and the very weak absorbtion exhibits an EBE of approx. 0.07 eV. A comparably low value was determined for the weakly interacting ground-state CTC of DIP with a dicyanoperylene-bis(dicarboxyimide) derivative (PDIR-CN2). The acceptor hexafluoro-tetracyano-naphthoquinodimethane (F6TCNNQ) forms a strongly interacting ground-state CTC with DIP and reveals an EBE of 0.79 eV.

The CTCs have to be distinguished by ground-state (GS) and excited-state (ES) interaction, which we will relate to the determined EBEs. The properties of the CTC excitons range here from CT to Frenkel like and are strongly dependent on interaction scheme between donor and acceptor.