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IRTG / Soft Matter Science
Freiburger Materialforschungszentrum
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You are here: Home Events Dr. Till Biskup "Electronic Structure of Organic Semiconductors: Detailed Insights From Time-Resolved EPR Spectroscopy"

Dr. Till Biskup "Electronic Structure of Organic Semiconductors: Detailed Insights From Time-Resolved EPR Spectroscopy"

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Magnetic Resonance Laboratory, Institute of Physical Chemistry, University of Freiburg

  • Seminar
When Jan 31, 2018
from 02:15 PM to 03:00 PM
Where Seminarraum A, FMF, Stefan-Meier-Str. 21, Freiburg
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Illuminating conjugated polymers used as organic semiconductors not only leads to excited states, but sheds light on some of the most important aspects of device efficiency in organic electronics as well. The interplay between electronic structure, morphology, flexibility, and local ordering, while at the heart of structure-function relationship of organic electronic materials, is still barely understood. Time-resolved EPR (TREPR) spectroscopy has proven valuable to gain further insight.

Investigating the polymer PCDTBT, we established TREPR for probing both the orientation and degree of ordering of polymers [1], nicely complementing other methods for structure determination. In particular, TREPR allows to probe orientation and ordering in otherwise amorphous polymers. In another study using the building block Cbz-TBT, we revealed the origin of triplet states, bringing a seemingly forgotten route back into focus: spin-forbidden direct S0→T excitation, with potential high impact for device efficiency [2].

To gain insight into determining factors for exciton delocalisation, TREPR combined with DFT calculations allows to discriminate between electronic structure and planarity. Systematically studying a series of building blocks of PNDIT2 and the polymer itself lead to surprising results: The triplet exciton on PNDIT2 is highly localised, spanning no more than two repeat units, rendering the building block NDIT2-NDI a perfect model for the polymer [3].

Last but not least, we show the intrinsically high sensitivity of TREPR to the local environment of the exciton to make it an excellent tool for investigating polymer morphology. PNDIT2 shows striking differences in different solvents that can be attributed to the formation of locally highly ordered domains. Additionally, different modes of exciton delocalisation, namely intra- and interchain, dominate depending on the solvent, the latter resembling the situation in thin film [4].

[1] Till Biskup, Michael Sommer, Stephan Rein, Deborah L. Meyer, Markus Kohlstädt, Uli Würfel, and Stefan Weber. Angew. Chem. Int. Ed. 54:7707–7710, 2015.
[2] Deborah L. Meyer, Florian Lombeck, Sven Huettner, Michael Sommer, and Till Biskup J. Phys. Chem. Lett. 8:1677–1682, 2017.
[3] Deborah L. Meyer, Rukiya Matsidik, Michael Sommer, and Till Biskup Adv. Electron. Mater. 4:1700385, 2018.
[4] Deborah L. Meyer, Rukiya Matsidik, Sven Huettner, Michael Sommer, and Till Biskup Phys. Chem. Chem. Phys. 20:2716–2723, 2018.


invited by Prof. Günter Reiter

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