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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 36: Organic Electronics and Photovoltaics III
CPP 36.11: Talk
Thursday, March 21, 2024, 12:30–12:45, H 0110
On the competition between exciton emission and free charge generation in organic solar cells with low energetic offsets — •Manasi Pranav1, Atul Shukla1, Bowen Sun1, Rong Wang2, David Moser3, Julia Rumeney3, Sander Smeets4, Wouter Maes4, Sabine Ludwigs3, Larry Lüer2, Christoph Brabec2, Safa Shoaee1, and Dieter Neher1 — 1University of Potsdam, Germany — 2Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany — 3University of Stuttgart, Germany — 4Hasselt University, Belgium
Organic blends with low energy-offset are the fruit-flies of today's organic photovoltaics research. Low photocurrent efficiencies for low offset blends draw attention to the link between energetic offset and free charge generation. Here, we take a quantitative, methodical approach to probing the origin of field-dependent free charge generation. Blending Y6 and Y5 with different molecular weights of the PM6, we progressively tune the photovoltaic parameters from a very efficient to inefficient device with severe field dependence of generation. We find the same pronounced field-dependence in transient absorption spectroscopy, and steady state and transient photoluminescence (PL) for inefficient low offset blends. The free charge generation and PL show a strict anticorrelation as a function of bias across all model systems. Thereby, we theoretically evaluate the quantum yields of PL to demonstrate inefficient charge transfer state formation from the local exciton, without any indication of hybridization, and that the decay of the singlet exciton is the only competing process to free charge generation.
Keywords: free charge generation; exciton emission; low offset blends; organic photovoltaics; field dependence