Optimizing Branching Linkers in Dimerized Acceptors for Enhanced Efficiency and Stability in Organic Solar Cells.

Most high-performing dimerized acceptors are based on Y-series precursors with superior conjugated π-backbones. The utilization of branch-connected dimerized acceptors can fully leverage the four end groups to enhance molecular packing, thereby potentially improving both the stability of organic solar cells (OSCs) while maintaining high power conversion efficiency (PCE). Therefore, optimizing the linker is critical to fully realizing their potential in improving device performance. In this study, three dimerized acceptors are synthesized with conjugated and conjugation-break linkers in the branching direction to systematically investigate the effects of different linker structures on molecular properties and device performance. By introducing an appropriate flexible chain, favorable solubility, and superior morphology are achieved, which facilitates charge generation and transport while suppressing recombination. As a result, the OSC based on dYTAT-C6-F exhibits a significantly improved PCE of 18.08%, the highest among dimerized acceptors with linkers in the branching direction. Additionally, the OSC based on dYTAT-C6-F demonstrates a T80 lifetime of 1840 h. These results indicate that conjugation breakages can tune molecular solubility, aggregation, and carrier mobility and that optimizing the linker length further improves these characteristics. The findings highlight the significant potential of engineering linkers in the branching direction to achieve outstanding OSC performance.