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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 96: Organic Electronics and Photovoltaics IV

CPP 96.3: Vortrag

Donnerstag, 19. März 2020, 15:30–15:45, ZEU 260

Why is electronic transport in conjugated organic materials rather inefficient? From organic semiconductors to covalent organic frameworks. — •Christian Winkler, Oliver T. Hofmann, and Egbert Zojer — Institute of Solid State Physics, NAWI Graz, Graz University of Technology, Petersgasse 16, 8010 Graz

In a recent work [1] we demonstrated for organic semiconductors using dispersion-corrected density-functional theory that molecular arrangements with high inter-molecular electronic couplings are typically energetically unfavorable, which can be traced back to Pauli exchange repulsion of neighboring π-systems. This correlation is not only of importance for charge transport in organic semiconductors but also plays a crucial role in electrically conductive covalent organic frameworks (COFs). COFs are crystalline structures, where the molecular building blocks are covalently bonded within a 2D plane and these planes are then π-stacked. We will show that also in these systems, Pauli exchange repulsion prevents a perfectly coplanar stacking of consecutive layers. Instead, one has to expect small shifts between consecutive layers, where these shifts have only a very minor impact on the powder x-ray diffractograms of the studied COFs. In spite of this small impact on structural parameters, the slip can change the electronic coupling between consecutive COF sheets by orders of magnitude. This suggests that for optimizing charge transport in organic materials, one cannot rely on the (self) assembly of the π-systems but needs to include additional chemical functionalities that modify the packing motif. [1] C. Winkler et al., Chem. Mater. 2019, 31, 17, 7054-7069