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

Abstract 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.