Dithienonaphthobisthiadiazole Fused‐Core Acceptor for Optical and Morphology‐Optimized High‐Performance Ternary Solar Cells

ABSTRACT Ternary organic solar cells (OSCs) offer a promising route to surpass the performance limits of binary systems, yet their success relies critically on identifying the third components that complement optical absorption while preserving or enhancing solid‐state order. Here, we report NT‐T20, a newly designed fused‐core non‐fullerene acceptor based on a π‐extended dithienonaphthobisthiadiazole (NTz) framework featuring a planar, centro‐symmetric A–D–DAD–D–A architecture. NT‐T20 exhibits a well‐positioned absorption band that precisely fills the spectral gap between D18 and L8‐BO, along with a suitable energy level alignment that facilitates exciton dissociation and charge transport. Results reveal that NT‐T20 likely prefers to be distributed along the D18:L8‐BO interfaces, which refines the film‐forming kinetics and optimizes photon utilization by dual mechanisms of charge transfer and energy transfer. These synergistic effects yield improved charge extraction, suppressed charge recombination, and more balanced carrier mobilities. As a result, the ternary OSC achieves a power conversion efficiency of 19.42%, outperforming the 18.54% binary reference. This work demonstrates the potential of planar NTz‐based fused‐core acceptors as effective third components and highlights a molecular design strategy for advancing next‐generation high‐performance ternary OSCs.