One-Pot Synthesis of Conjugation-Extended Isomeric Dimer Acceptors for High-Performance Q‑PHJ Solar Cells

End group modification is a crucial strategy for fine-tuning non-fullerene acceptors in organic solar cells (OSCs). Extending the conjugation of end groups enhances electron delocalization, promotes tighter intermolecular stacking, and improves crystallinity and spectral absorption. In this study, a series of isomeric dimer acceptors with conjugation-extended end groups is synthesized to investigate how the position of end group extension affects the performance of dimers. Using a one-pot Still coupling method, three dimers with inner end group extensions are efficiently synthesized, significantly reducing synthesis time and cost. Among these, the device based on dBSeIC-ɛNIC exhibited a higher power conversion efficiency (PCE) compared to the dBSeIC-γIC device, which lacks conjugated extension. Building on this, the connection site of the inner end group is optimized and extended the conjugation from the outer end group. As a result, the Q-PHJ device using dBSeNIC-γIC/PBQx-H-TF achieved a maximum PCE of 17.68%, largely due to a notable increase in fill factor (FF). The study reveals the critical impact of end group conjugation extension on dimer acceptor performance and underscores the importance of selecting the optimal connection site for enhancing OSC efficiency.