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Description
In organic photovoltaics, donor - acceptor bulk heterojunctions are often used as active materials due to their superior performance compared to e.g. planar layered devices. In this optically active polymer layer, a photon is absorbed and an exciton created. After diffusion to a donor-acceptor interface, the exciton is dissipated and charge carriers can be extracted at the electrodes [1].
A frequently applied and well-studied system is the combination of P3HT ( (C10H14S)n ) as electron donor and PCBM (C72H14O2) as electron acceptor. Previous studies have shown, that internal dynamics and structural layout of the active layer influence its electronic properties and thus its performance in a device [2], [3]. A novel, very promising electron donor material is PTB7 ((C41H53FO4S4)n). We produced films of PTB7, PCBM and a mixture of these two from a chlorobenzene solution and performed first quasielastic neutron scattering (QENS) experiments on this system in order to evaluate the dynamics of pure compounds as well as blend films on a pico- to nanosecond timescale and potential influences of manufacturing parameters (e.g. mixing ratio, solvent choice, annealing time/temperature). QENS experiments were performed at the MLZ - instrument TOFTOF in a temperature range between 150 K and 400 K.
[1] H. Wang et al. (2014), Materials, 7, 2411–2439
[2] A. Guilbert et al. (2016), The Journal of Physical Chemistry Letters, 7, 2252–2257
[3] T. Etampawala et al. (2015), Polymer, 61, 155–162
