A case study of comparing two dimerized acceptor molecules built by different branch-connected and terminal-connected approaches

Dimerized small-molecule acceptors (SMAs) built by the conventional connection of terminal groups of monomers have contributed to exciting long-term stabilities of organic solar cells (OSCs). However, device efficiencies, especially fill factors (FFs), still need to be improved. This probably originates from unsymmetrical molecular structure/conformation-determined less compact/ordered molecular stackings, such as ineffective stackings of constraint terminals. Herein, an exotic dimerized SMA of BC-Th is established by bridging the branched groups (BC-type, branch coupling) of two monomers rather than conventional terminal units (TC-type, terminal coupling). Benefiting from the three-dimensional conformation and more uncurbed terminals, BC-Th exhibits multiple molecular orientations along with a larger dielectric constant and electron mobility compared with TC-Th. Finally, an efficiency of 17.43