Conjugation-Broken Dimer Acceptors Enable High-Efficiency, Stable, and Flexibility-Robust Organic Solar Cells.

Dimer acceptors in organic solar cells (OSCs) offer distinct advantages, including a well-defined molecular structure and excellent batch-to-batch reproducibility. Their high glass transition temperature (T) aids in achieving an optimal kinetic morphology, thereby enhancing device stability. Currently, most of dimer acceptor materials are linked with conjugated units in order to obtain high power conversion efficiencies (PCEs). In this study, different from previous works on conjugation-linked dimer acceptors, a novel series of dimer acceptors are synthesized (named T1, T4, T6, and T12), each linked with different flexible alkyl linkers, and investigated their PCEs, device stability, and flexibility robustness. When blended with PM6, the T6-based device achieves a PCE of 17.09%, comparable to the fully conjugated T0-based device's PCE of 17.12%. The molecular dynamics simulations and density functional theory calculations suggested that flexible conjugation-broken linkers (FCBLs) promote intermolecular electronic couplings, thereby maintaining good electron mobilities of dimer acceptors. Notably, the T6-based device exhibits impressive long-term stability with a T80 lifetime of 1427 h, while in the T0-based device, T is only 350 h. The present work has thus established the relationship between the length of flexible alkyl linkers in such dimer acceptors and the performance and stability of OSCs, which is important to further designing new materials for the fabrication of efficient and stable OSCs.