A Polyfluoroalkyl‐Containing Non‐fullerene Acceptor Enables Self‐Stratification in Organic Solar Cells

The elaborate control of the vertical phase distribution within an active layer is critical to ensuring the high performance of organic solar cells (OSCs), but is challenging. Herein, a self‐stratification active layer is realised by adding a novel polyfluoroalkyl‐containing non‐fullerene small‐molecule acceptor (NFSMA), EH‐C8F17, as the guest into PM6:BTP‐eC9 blend. A favourable vertical morphology was obtained with an upper acceptor‐enriched thin layer and a lower undisturbed bulk heterojunction layer. Consequently, a power conversion efficiency of 18.03 % was achieved, higher than the efficiency of 17.40 % for the device without EH‐C8F17. Additionally, benefiting from the improved charge transport and collection realised by this self‐stratification strategy, the OSC with a thickness of 350 nm had an impressive PCE of 16.89 %. The results of the study indicate that polyfluoroalkyl‐containing NFSMA‐assisted self‐stratification within the active layer is effective for realising an ideal morphology for high‐performance OSCs. A polyfluoroalkyl‐containing guest acceptor (EH‐C8F17) enables self‐stratification in the active layer of bulk‐heterojunction organic solar cells. The favorable vertical phase separation and molecular stacking increases the mobility, increases carrier lifetimes, and reduces trap‐assisted recombination, leading to significantly improved device performance.