Dimerization-Induced Orientation Control in Ambipolar M-Series Acceptors Enables Efficient and Stable Organic Solar Cells

• • Dimerization of MC16 into DMC16 induces a face-on orientation, reversing charge-transport anisotropy from lateral to vertical, which is critical for efficient vertical charge extraction in OSCs. • • DMC16-based OSCs achieve a PCE of 19.04% in ternary blends with PM6:M36, ranking among the highest for ADA-type small-molecule acceptors, and retain 94% of initial efficiency after 1800 h at 85 °C and 74% after an additional 1000 h at 120 °C, demonstrating exceptional thermal stability. • • The dimerization strategy suppresses over-aggregation and molecular diffusion, addressing morphological stability issues that typically plague small-molecule acceptors, thereby enhancing long-term operational stability. • • Scalability is demonstrated with a minimodule efficiency exceeding 15% over an active area of 10.15 cm2, indicating commercial viability for large-area organic photovoltaics.