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

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 T₈₀ lifetime extended from 415 to 983 h.