Regensburg 2019 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: Organic Electronics and Photovoltaics I - Charge Transport and Electronic Devices

CPP 9.6: Talk

Monday, April 1, 2019, 16:45–17:00, H18

Why are charge-carrier mobilities in organic semiconductors typically low? The instructive case of quinacridone — •Christian Winkler, Florian Mayer, Oliver T. Hofmann, Gernot J. Kraberger, and Egbert Zojer — Institute of Solid State Physics, NAWI Graz, Graz University of Technology, Petersgasse 16, 8010 Graz

In this contribution, using first principles approaches, we study the interplay between transport relevant parameters, total energy, and crystal structure by using the instructive example of quinacridone. For this material, one finds three polymorphs with fundamentally different packing motifs. Additionally, based on the α-polymorph, an artificial coplanar quinacridone crystal can be constructed. The latter allows correlating electronic properties like transfer integrals t and effective masses m* with the total energy of the crystal. This yields a clear correlation between energetic minima and poor transport parameters suggesting that in π-stacked systems Pauli-exchange repulsion triggers a shift between neighboring molecules such that the inter-molecular electronic coupling is minimized. Possible strategies for overcoming this negative correlation can be derived from the properties of β- and γ-quinacridone, where larger transfer integrals result from modified van der Waals interactions and complex H-bonding networks.