Hyperconjugated linker design in giant dimeric donors enabled superior short-circuit current in organic solar cells

Giant dimeric donors possess definite chemical structures and regulatable molecular skeletons, and are expected to become alternative photovoltaic materials for polymer donor with batch differences. However, the design of giant dimeric donors is still at an early stage and needs to be further explored. Here, through creative semi-flexible and flexible linkers design, we synthesized three interesting gaint dimeric donors with relative monomer positions ranging from parallel to staircase to perpendicular in their optimized conformation. Unusually, resulted from the hyperconjugation effect in the semi-flexible linker, the less planar the molecular backbone, the stronger the homo-molecular interaction. Combining calculations and multiple morphology characterizations on dynamic and thermal packing, we systematically analyze the hyperconjugation effects, flexibility, and hetero-molecular interaction on the assembly. As a result, applying Y6 as an acceptor, the giant dimeric donor of BDT-Dimer3 with a semi-flexible non-planar linker performed a satisfactory efficiency of 15.68% with cutting-edge short-circuit current of 27.39 mA cm-2 and an improved photo-stability with T80 of 630 hours. Our results provide hyperconjugated linker design for efficient and stable OSCs devices with definite structure, as well as a deep understanding of the assembly in both pure and mixed systems.