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The research of the “Soft Matter Physics and Optoelectronics” group is concerned with physical processes in soft matter semiconducting layers. Our systems of interest comprise traditional soft matter materials such as organic semiconductors, but also organo-metallic perovskite semiconductors and, most recently hybrid systems based on 2D TMDcs. Our particular focus is the understanding and advancement of these systems for specific optoelectronic applications, such as photovoltaic devices and photodetectors.
At the heard of our studies is the nature and dynamics of excitations and charges in these systems. The group has therefore installed a variety of transient techniques, designed to follow the fate of these excitations in functional devices on all relevant time scales, from sub-picoseconds through steady state. The group is particularly known for our time-delayed collection field setup, which is unique with regard to temporal resolution and sensitivity, but we also make use of various all-optical techniques including steady state and time resolved fluorescence spectroscopy and femtosecond transient absorption. The results of these measurements serve as inputs for extensive drift-diffusion simulations, but also for the development of analytical models to describe the function of entire devices.
With this knowledge at hand, materials and device structures are further optimized, with the prospect to push the optoelectronic performance parameters beyond current limits.
Congratulations to Manasi for winning the best poster price at the MAT-SUS conference in Barcelona (24.Oct.2022). The title of her poster was "Field dependent photoluminescence quenching and free charge generation in low-offset organic solar cells" where they discussed different transient and steady-state techniques to study the pathway of free charge carrier generation in NFA:Y5 blend and how it differs from the prototypical PM6:Y6 blend.
Thanks to all the participants at the "Tag der Offenen Tür". Our PhD students explained various physical phenomena about light, optics, photonics, solar energy and more!
We were very happy with the result and can't wait for next year!
Congratulations to our coauthors and collaborators for this new publication.
In organic solar cells, the resulting device efficiency depends strongly on the local morphology and intermolecular interactions of the blend film. Optical spectroscopy was used to identify the spectral signatures of interacting chromophores in blend films of the donor polymer PM6 with two state-of-the-art nonfullerene acceptors, Y6 and N4, which differ merely in the branching point of the side chain. From temperature-dependent absorption and luminescence spectroscopy in solution, it is inferred that both acceptor materials form two types of aggregates that differ in their interaction energy. Y6 forms an aggregate with a predominant J-type character in solution, while for N4 molecules the interaction is predominantly in a H-like manner in solution and freshly spin-cast film, yet the molecules reorient with respect to each other with time or thermal annealing to adopt a more J-type interaction. The different aggregation behavior of the acceptor materials is also reflected in the blend films and accounts for the different solar cell efficiencies reported with the two blends.