Incorporation of an Extended Electron‐Deficient Central Block Into Small‐Molecule Acceptors Toward Enhanced‐Performance Organic Solar Cells

ABSTRACT Almost all high‐performance acceptors currently rely on a single electron‐withdrawing core or a core modified with electron‐withdrawing groups, which significantly limits structural innovation. In this study, we introduced two novel extended electron‐deficient units, [1, 2, 5]thiadiazolo[3,4‐b]pyrazine (Tz‐Qx) and [1, 2, 5]oxadiazolo[3,4‐b]pyrazine (Dz‐Qx), into the acceptor central cores. Coupled with fluorine and chlorine‐substituted terminal groups, the performance of the acceptors can be synergistically optimized. A systematic investigation elucidates the impact of the central core and terminal groups on the intrinsic photoelectronic properties of the acceptors. Among the four acceptors—Tz‐Qx‐4F, Tz‐Qx‐4Cl, Dz‐Qx‐4F, and Dz‐Qx‐4Cl—Tz‐Qx‐4F demonstrated significant near‐infrared absorption, excellent crystallinity, and enhanced aggregation capabilities. When blended with the polymer donor D18, the binary device achieved a remarkable power conversion efficiency (PCE) of 19.50%, accompanied by a record short‐circuit current density ( J SC ) of 29.3 mA cm − 2 . This performance is attributed to the balanced charge transport properties and reduced non‐radiative energy losses in the blend films. In stark contrast, Dz‐Qx‐based counterparts yielded substantially lower PCEs (∼9%), underscoring the profound influence of core heteroatom identity. This work highlights the critical influence of extended electron‐deficient units and terminal groups on the molecular photovoltaic properties, providing valuable insights for the design of enhanced‐performance organic solar cell acceptors.