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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 53: Hybrid, Organic and Perovskite Optoelectronics and Photovoltaics VII

CPP 53.1: Invited Talk

Friday, March 13, 2026, 09:30–10:00, ZEU/LICH

Limits and Prospects of Organic Solar Cells — •Dieter Neher — Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str 24-25, 14476 Potsdam

Since the advent of low bandgap non-fullerene acceptors (NFAs), the performance of organic solar cells (OSCs) has improved significantly, with record efficiencies that now safely exceed 20 %. A critical parameter is the offset between the relevant frontier orbitals at the DA heterojunction, which in most NFA-based blends is the difference in HOMO energies. Here we combine a wide range of methods, from femtosecond transient absorption to steady state photoluminescence and electroluminescence, spectroscopy to study the mechanisms and efficiency of free charge generation and recombination. For a wide series of NFA-based OSCs, we find that the singlet exciton decay is the main competing pathway for free charge generation while reformation of singlet excitons from reformed CT states dominates the radiative recombination in EL. To explain our data as function of the HOMO offset, we set up a 5-state model which includes singlet and triplet excitons. Our results show that state-of-the-art OSCs already exhibit an optimum HOMO-HOMO-offset. Future work should, therefore, focus on optimizing photon harvesting and reducing bimolecular recombination in order to push the device efficiency well beyond 20 %.

Keywords: organic solar cells; non-fullerene acceptors; charge generation and recombination