Highly Crystalline Selenium‐Substituted C‐Shaped Ortho‐Benzodipyrrole‐Based A‐D‐A‐Type Nonfullerene Acceptor Enabling Solution‐Processed Single‐Crystal‐Like Thin Films for Air‐Stable, High‐Mobility N‐Type Transistors

Abstract C‐shaped ortho‐benzodipyrrole‐based A‐D_NB_ND‐A non‐fullerene acceptors (NFAs), derived from the removal of the A′ thiadiazole moiety in Y6, emerge as a new class of structurally simplified A‐D‐A‐type NFAs. In this work, a selenium‐substitution strategy is applied to the central D_NB_ND ladder‐π‐core, yielding asymmetric CB‐Se and symmetric CB‐2Se. Asymmetric CB‐Se demonstrates a less ordered 3D trapezoid‐like packing structure, which promotes a more favorable intermixed donor‐acceptor morphology with PM6 polymer, achieving a higher power conversion efficiency (PCE) of 17.87% in organic photovoltaics (OPVs). This value represents the highest reported value among the selenium‐incorporated A‐D‐A‐type NFAs. Symmetric CB‐2Se forms a kaleidoscope‐like 3D single‐crystal structure with enhanced intermolecular interactions. This enables the development of a single‐crystal‐like solution‐processed thin film, which transitions from a kinetically trapped face‐on π–π stacking orientation to a thermodynamically stable edge‐on configuration upon thermal annealing. The CB‐2Se‐based organic field‐effect transistor (OFET) achieved a remarkable electron mobility of 1.18 cm² V⁻¹ s⁻¹ with exceptional n‐type air stability, which outperformed the corresponding A‐D_NA′_ND‐A‐type Y6‐based materials by two orders magnitudes and represents the highest reported value for solution‐processed n‐type OFETs utilizing A‐D‐A‐type small molecules.