Regulating Crystallization Behavior via Non‐Fused‐Ring Polymer Acceptor for High Performance Ternary Organic Solar Cells

ABSTRACT Regulating the crystallization behavior of the active layer is a key strategy for enhancing the power conversion efficiency (PCE) and stability of organic solar cells. Reports on non‐fused‐ring polymer acceptors as the third component to regulate active layer crystallinity are scarce. In this work, we report a simple benzene‐based non‐fused‐ring polymer acceptor (PW1) and introduce it into the PM6:BTP‐eC9 system. PW1 exhibits good thermal stability ( T _d = 343°C), excellent miscibility with the host binary blend, cascaded energy level alignment, and complementary absorption. Electrostatic potential (ESP) calculations indicate that PW1 has a smaller ESP value than BTP‐eC9, acts as a compatibility modifier in the PM6:BTP‐eC9 system. In situ UV–vis absorption results demonstrate that PW1 suppresses BTP‐eC9 aggregation, retards its precipitation and crystallization during film formation, and forms an appropriate phase separation size. The ternary device with 3 wt.% PW1 achieves a high PCE of 19.50% (higher than the 18.61% of the binary device), along with a high fill factor (FF) of 80.45%. The ternary system shows faster charge extraction, longer carrier lifetimes, higher and more balanced carrier mobilities, and less charge recombination. Additionally, it displays better storage stability with the T ₈₀ lifetime extended from 415 to 983 h.