Connection‐Site‐Determined Electronic and Photovoltaic Properties in Dimeric and Trimeric Oligomeric Acceptors

ABSTRACT The oligomeric acceptor is an intrinsically stable and efficient organic photovoltaic material because it combines the advantages of monomeric and polymeric acceptors. The connection site significantly influences the oligomeric acceptor properties; however, the design principles are still unclear. Herein, center‐linked (C‐Dimer and C‐Trimer) and end‐linked (E‐Dimer and E‐Trimer) oligomeric acceptors are designed and synthesized based on high‐performance quinoxaline‐based acceptors. We systematically investigated their differences in electronic structural properties, film‐formation dynamics, and morphology through calculation, in situ UV–vis and dynamic light scattering, and morphology characterizations. It is found that end‐linked acceptors have the following advantages: 1) superior electronic properties: higher super‐exchange coupling and smaller reorganization energy facilitate intra‐molecular charge transport; 2) stronger molecular interactions: pre‐aggregation in dilute or concentrated solution and stronger miscibility enable slow assembly into dense fibrous morphology, achieving concurrent efficient exciton dissociation and charge transport. Hence, the PM6: E‐Dimer‐based device achieves the optimal efficiency of 18.02% with a t 80 of 4096 hours. E‐Dimer also acts as an effective third in the classical D18: L8‐BO system to improve efficiency from 18.77% to 19.73%. Our results demonstrate the enormous potential of E‐oligomers in engineering high‐performance OSCs and provide guidance for further design of highly efficient oligomeric acceptors.