Atomic‐Level Regiospecific Engineering of Asymmetric Acceptors for Efficient Organic Solar Cells With Reduced Energetic Disorder

ABSTRACT To address the intrinsic trade‐off between open‐circuit voltage and charge transport in symmetric non‐fullerene acceptors, we report an asymmetric molecular engineering strategy based on regiospecific monochloro‐isomeric substitution. While the α‐ and β‐isomers differ only in chlorine positioning, they exhibit distinct electronic and morphological fingerprints. Systematic investigations reveal that the β‐chlorinated isomer, BTP‐2Cl‐βCl, orchestrates a synergistic elevation of the LUMO level and a refined electrostatic surface potential, enabling a champion efficiency of 20.32% with an exceptional fill factor of 80.93% in binary devices, surpassing both its symmetric parent and α‐isomer. By incorporating a dimer third component, the ternary devices achieve a superior PCE of 20.51%. Regiospecific β‐substitution steers the blend toward an idealized film‐formation kinetic regime and ensures superior energy‐level homogeneity. This precise control reconciles nucleation dynamics with crystal growth, fostering a high‐purity, bi‐continuous interpenetrating network that substantially suppresses non‐radiative recombination losses and minimizes energetic disorder. Our work demonstrates that subtle regiospecific modifications in asymmetric designs can serve as a decisive lever to break intrinsic performance barriers, providing a transformative paradigm for next‐generation organic photovoltaics through atomic‐level structural precision.