Exploring the Additive Effects on Charge Generation in a PM6:Y6 Organic Solar Cells

Organic solar cells (OSCs) are promising as alternative solar energy technology, and their efficiencies are continuously increasing, currently with a record PCE~18%. The processes involved in charge generation and recombination in the active layer govern device performance. However, these processes are all entangled and hard to measure quantitatively, which limits progress in performance. We use an advanced charge extraction technique, time delay collection field, to disentangle and quantify each process occurring in a record OSC system PM6:Y6 as a function of additive, chloronapthalene, concentration. We quantify generation current and separate geminate and bimolecular recombination currents, all at operating conditions of the OSC devices. We find that geminate recombination is reduced with the additive, but generation is eventually hampered by extreme phase separation caused by the plasticizing additive. We additionally selectively excite the acceptor and donor molecules and find that Y6 generates relatively less charge than PM6, potentially due to the domain structure. Understanding these processes will help in materials design and device fabrication.