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 larg-er dipole moments and stronger intermolecular bonding energy than their symmetric counterparts thereby mak-ing them promising candidates for high-performance polymer solar cells(PSCs).Herein,we report two efficient acceptor-donor-acceptor(A-D-A)type NFAs(M14 and M18)with asymmetric side chains that show enhanced intermolecular interactions compared with their corre-sponding counterparts(M17 and M19)based on symmet-ric side chains.Furthermore,M14 and M18 exhibit elevated lowest unoccupied molecular orbitals and smal-ler π-π stacking distances in comparison with M17 and M19,respectively.In combination with the benchmark polymer donor of PM6,the PM6:M14 blend affords super-ior 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 best-performing 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 high-performance PSCs.