Field dependent photoluminescence quenching and free charge generation in low-offset organic solar cells
Manasi Pranav a b, Bowen Sun b, Safa Shoaee b, Dieter Neher a
a Soft Matter Physics, Institute of Physics and Astronomy, University of Potsdam, 14476 Germany
b Optoelectronics of Disordered Semiconductors, Institute of Physics and Astronomy, University of Potsdam, 14476 Germany
nanoGe Fall Meeting
Proceedings of Materials for Sustainable Development Conference (MAT-SUS) (NFM22)
#BRIGHT - Recent Breakthroughs in Organic Photovoltaics
Barcelona, Spain, 2022 October 24th - 28th
Organizers: Thomas Anthopoulos and Safa Shoaee
Poster, Manasi Pranav, 321
Publication date: 11th July 2022

Since the breakthrough work on PM6:Y6 non-fullerene acceptor (NFA) based organic solar cells [1], low-energetic offset material systems have been the focus for numerous studies around the fundamental processes in organic photovoltaic (OPV) blends. Studies have targeted questions around the nature of charge carrier generation, recombination, transport dynamics in relation to the energy offset, among others. [2, 3] The NFA Y5 has a similar molecular structure to Y6, but exhibits a lower offset between its highest occupied molecular orbital (HOMO) and that of PM6. Here, we use different transient and steady-state techniques to study the pathway of free charge carrier generation in this blend and how it differs from the prototypical PM6:Y6 blend. Through time-delayed collection field (TDCF) experiments, we find a clear field-dependence of free charge carrier generation, unlike most previously studied NFA based OPV systems including the 1:1 PM6:Y6 blend. Surprisingly, these devices also exhibited a pronounced effect of the electric field on the steady state photoluminescence (PL). By modifying the device structure, we can extend the study to high-field limits (above 108 V/m) and truly map the effect of the effective field on charge carrier generation and PL, approaching the regime of photocurrent/charge saturation. Correlating high field TDCF, high reverse bias current-voltage and bias-dependent linear PL data shows that the field dependence of photocurrent, free charge carrier generation and PL quenching are governed by the same mechanism: likely field-induced exciton dissociation. This work-in-progress provides new data to the current discussions around OPVs, given the low-offset nature of Y5 and its similarity to Y6.

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