Asymmetric Non-Fullerene Acceptors with Branched Alkyl-Chains for Efficient Organic Solar Cells with High Open-Circuit Voltage

The emergence of Y-series non-fullerene acceptors (NFAs) has inspired the development of various materials for high-performance organic solar cells (OSCs). In this work, a novel asymmetric NFA named Y6-1OBO bearing branched alkyl and alkoxy side chains was designed and synthesized. When diiodomethane was selected as the solvent additive, the Y6-1OBO-based devices achieved an efficiency of 18.02% with an open-circuit voltage of 0.93 V and a fill factor of 77.1%, which is much higher than that of Y6-1O-based devices (16.81%). The effects of solvent additives were also systematically investigated, and the results demonstrate that the selective solubility to NFA of different additives can significantly affect the film morphology. This work not only provides a new Y-series NFA but also highlights the choice of solvent additives according to the properties of materials in the active layer for the future optimization of OSCs.