Studying interlayer molecular diffusion in donor-acceptor systems

Denys Priadko^a, Christina Saller^b, Frank-Julian Kahle^a, Thomas Müller^a, Tobias Hahn^a, Steffen Tscheuschner^a, Peter Strohriegl^b^,^c^,^d, Heinz Bässler^c, Anna Köhler^a^,^c

^aSoft Matter Optoelectronics, University of Bayreuth, Germany, Bayreuth, Germany

^bMacromolecular Chemistry I, Department of Chemistry, University of Bayreuth, 95447 Bayreuth, Germany

^cBayreuth Institute of Macromolecular Science, University of Bayreuth, 95440, Bayreuth, Germany

^dBavarian Polymer Institute (BPI), University of Bayreuth, Germany, Bayreuth, Germany

Proceedings of Interfaces in Organic and Hybrid Thin-Film Optoelectronics (INFORM)

València, Spain, 2019 March 5th - 7th

Organizers: Natalie Stingelin, Hendrik Bolink and Michele Sessolo

Poster, Denys Priadko, 009
Publication date: 8th January 2019

We report a novel all-optical method for monitoring the diffusion of a small quencher molecule through a polymer layer in a bilayer architecture.[1,2] Experimentally, we injected C60 molecules from a C60 layer into the adjacent donor layer by stepwise heating, and we measured how the photoluminescence (PL) of the donor layer becomes gradually quenched by the incoming C60 molecules. By analyzing the temporal evolution of the PL, the diffusion coefficient of C60 can be extracted, as well as its activation energy and an approximate concentration profile in the film. We applied this technique to three carbazole-based low-bandgap polymers with different glass temperatures with a view to study the impact of structural changes of the polymer matrix on the diffusion process. We find that C60 diffusion is thermally activated and not driven by WFL-type collective motion above Tg but rather by local motions mediated by the sidechains. The results are useful as guidance for material design and device engineering, and the approach can be adapted to a wide range of donor and acceptor materials.

References:

[1] Fischer, F., Hahn, T., Bässler, H., Bauer, I., Strohriegl, P. and Köhler, A., 2014. Measuring reduced C60 diffusion in crosslinked polymer films by optical spectroscopy. Adv. Funct. Mater. 39 (2014) 6172-6177

[2] Saller, C., Kahle, F.J., Mueller, T., Hahn, T., Tscheuschner, S., Priadko, D., Strohriegl, P., Bässler, H. and Köhler, A.,2018. A Facile Method for the Investigation of Temperature-Dependant C60 Diffusion in Conjugated Polymers. ACS Appl. Mater. Interfaces 10 (2018) 21499−21509

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