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.

Keywords

extended electron-deficient central block / organic solar cells / small molecule acceptor

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