Synergistic Quaternary Polymerization Strategy for Highly Efficient and Reproducibility Polymer Solar Cells

To overcome the limitations of batch‐to‐batch variations and donor material robustness in polymer solar cells (PSCs), we designed quaternary (H1–H9), ternary (H10–H15), and binary (PM6, PBQ10, PBDS‐T) polymer donors via precise monomer ratio modulation. Due to the synergistic coordination among multiple components, the H4‐based blend film demonstrated enhanced intermolecular interactions and provides additional low‐energy‐barrier pathways for efficient charge carrier transport. After blending with L8‐BO, the H4‐based films displayed a more desirable morphology and effective charge carrier transport than the categories. As a result, the H4:L8‐BO‐based PSCs achieved impressive power conversion efficiency (PCE) of 19.66% for binary device and 20.34% for ternary device. Besides, the introduced functional groups disrupt the regularity of the matrix polymer main chain, leading to stable and robust film morphologies. Consequently, the H4:L8‐BO‐based blend film not only demonstrates improved mechanical robustness, with a crack onset strain (COS) of 17.8%, and maintains a PCE of 16.35% in flexible devices, but also exhibits excellent batch‐to‐batch stability with significant variations in molecular weight. This work presents a strategy to simultaneously enhance device performance, mechanical robustness, and reproducibility through quaternary copolymerization, enabling controlled crystallinity and additional multichannel charge transport.