Kinetically Driven Near-unity Charge Generation Yield in Organic Solar Cells

Recent advances in organic solar cell material development based around non-fullerene electron acceptors in bulk heterojunctions have propelled power conversion efficiencies to >18%, with 20% on the horizon and 25% predicted. These efficiencies are close to traditional inorganic semiconductor photovoltaics and thus focus is now turning to manufacturability and creating a viable solar cell technology. In this presentation we report the highest efficiency to date (16% with a Fill Factor >70%) in a thick junction binary organic solar cell based upon PM6:BTP-eC9. Using a very accurate approach based upon temperature dependent ultra-sensitive EQE measurements we find that this system (and a similar one based upon PM6:Y6) have near unity charge generation yields (CGY > 99%). In this regime, we observe that a small increase in CGY of only 0.5% leads to a 2.5 times more reduction in bimolecular recombination relative to the Langevin limit enabling high efficiency thick junction solar cells.