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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 36: Organic Electronics and Photovoltaics III

CPP 36.9: Talk

Thursday, March 21, 2024, 12:00–12:15, H 0110

The Photocurrent in Organic Solar Cells does not Vanish at Open-Circuit — •Clemens Göhler, Mónica Dyreby, Alexander Flamm, and Martijn Kemerink — Institute for Molecular Systems Engineering and Advanced Materials, Universität Heidelberg, Im Neunheimer Feld 225, 69120 Heidelberg

Organic solar cells (OSCs) have reached close to 20% of power conversion efficiency and 100% conversion yield between incident photons to extracted charge carriers, but still suffer from unexpected losses to the open-circuit voltage and fill factor. Non-thermalized charge carrier distributions---due to incomplete relaxation in a disordered density of states---can explain their current-voltage-characteristics, yet with at times uncommon ramifications: here, we will show that a non-negligible photogenerated current under open-circuit conditions is a general feature of OSCs. In more detail, we have investigated the internal quantum efficiency in non-fullerene acceptor OSCs in the steady state. Utilizing a small signal light source, modulated at low frequencies, and varying the working conditions from reverse (collection) to forward (injection regime) fields, we are able to determine the extraction efficiency of photogenerated charges at any point on the current-voltage-curve. We find that while the yield decreases towards open-circuit, it does not vanish completely; therefore, the resulting photocurrent has to be compensated by charge injection in order to reach zero net current. We were further able to reproduce these experimental findings with kinetic Monte-Carlo device simulations involving non-equilibrium dynamics.

Keywords: Organic Solar Cells; Internal Quantum Efficiency