Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

Asymmetric nonfullerene acceptors (NFAs) possess larger dipole moments and stronger intermolecular bonding energy than their symmetric counterparts thereby making them promising candidates for high-performance polymer solar cells (PSCs). Herein, we report twoefficient acceptor-donor-acceptor (A-D-A) type NFAs (M14 and M18) with asymmetric side chains that show enhanced intermolecular interactions compared with their corresponding counterparts (M17 and M19) based on symmetric side chains. Furthermore, M14 and M18 exhibit elevated lowest unoccupiedmolecular orbitals and smaller p-p stacking distances in comparison with M17 and M19, respectively. In combination with the benchmark polymer donor of PM6, the PM6:M14 blend affords superior charge transport properties, and more importantly, an increased power conversion efficiency (PCE) of 15.49% in comparison with the M17-based counterpart (13.01% PCE). Similarly, the asymmetric M18-based blend also shows a higher PCE of 13.00% than the M19-based blend (11.55%). Through further interface engineering, the bestperforming M14-based device delivers an enhanced PCE of 16.46%, which represents a record value among all asymmetric A-D-A type NFAs. Our results provide new insights into the design of asymmetric NFAs with enhanced intermolecular interactions for highperformance PSCs.