Over 18% Efficiency of All‐Polymer Solar Cells with Long‐Term Stability Enabled by Y6 as a Solid Additive

Morphology control greatly influences the power conversion efficiency (PCE) and long-term stability of all-polymer solar cells (all-PSCs); however, it remains challenging owing to their complex crystallization behavior. Herein, a small amount of Y6 (2 wt%) is introduced as a solid additive into a PM6:PY-DT blend. Y6 remained inside the active layer and interacted with PY-DT to form a well-mixed phase. Increased molecular packing, enlarged phase separation size, and decreased trap density are observed for the Y6-processed PM6:PY-DT blend. The corresponding devices showed simultaneously improved short-circuit current and fill factor, achieving a high PCE of over 18% and excellent long-term stability, with a T₈₀ lifetime of 1180 h and an extrapolated T₇₀ lifetime of 9185 h at maximum power point tracking (MPP) conditions under continuous one-sun illumination. This Y6-assisted strategy is successfully applied to other all-polymer blends, demonstrating its universality for all-PSCs. This work paves a new way for the fabrication of all-PSCs with high efficiency and superior long-term stability.