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

Abstract

Giant dimeric donors possess definite chemical structures and regulatable molecular skeletons and are expected to become alternative photovoltaic materials for polymer donors 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 linker design, we synthesized three interesting giant dimeric donors with relative monomer positions ranging from parallel to staircase to perpendicular in their optimized conformation. Unusually, the hyperconjugation effect in the semi-flexible linker stabilizes the perpendicular conformation, which results in the strongest homo-molecular interactions exhibiting non-planar molecular conformation. Combining calculations and multiple morphology characterization 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 achieved a satisfactory efficiency of 15.68% with a cutting-edge short-circuit current of 27.39 mA cm⁻² and an improved photostability with a T₈₀ of 630 hours. Our results provide hyperconjugated linker design for efficient and stable OSC devices with definite structures, as well as a deep understanding of the assembly in both pure and mixed systems.