Manipulating the Intermolecular Interactions through Side Chain Engineering and Unilateral π‐Bridge Strategy for Efficient Small Molecular Photovoltaic Acceptor

Thanks to the development of acceptor-donor-acceptor (A-D-A) type electron acceptors, organic solar cells (OSCs) have achieved marvelous progress in recent years. However, a systematic investigation about the structure-efficiency relationship is still highly desired to better understand the working mechanisms inside a bulk heterojunction (BHJ). In this study, new acceptors with the synergistic effect of side chain and unilateral pi-bridge strategy are designed, accounting for lower energy loss, expanded absorption, modulated intermolecular interactions and BHJ morphology. As a consequence, the resultant A-D-pi-A acceptor ID-C6Ph-ST-4F based binary solar cell receives an impressive efficiency up to 15.36%, much greater than the A-D-A analog ID-C6Ph-4F (10.75%), and ranks the best among all small molecular acceptors with symmetric or asymmetric pi-bridges. The results highlight the promising manipulation of phenylalkyl side chain and unilateral pi-bridge on intermolecular interactions among acceptor molecules and interactions between donor and acceptor (D/A) molecules. Superior interactions among acceptor molecules are an essential precondition to ensure preferable molecular assembly for charge transport, and meanwhile, moderately enhanced D/A interactions are also crucial for proper phase-separation networks with efficient exciton dissociation and charge generation.