Highly‐Efficient 2D Nonfullerene Acceptors Enabled by Subtle Molecular Tailoring Engineering

Abstract The conjugate expansion of nonfullerene acceptors is considered to be a promising approach for improving organic photovoltaic performance because of its function in tuning morphological structure and molecular stacking behavior. In this work, two nonfullerene acceptors are designed and synthesized using a 2D π‐conjugate expansion strategy, thus enabling the construction of highly‐efficient organic solar cells (OSCs). Compared with YB2B (incorporating dibromophenanthrene on the quinoxaline‐fused core), YB2T (incorporating dibromobenzodithiophene on the quinoxaline‐fused core) has red‐shifted spectral absorption and better charge transport properties. Moreover, the more orderly and tightly intermolecular stacking of YB2T provides the possibility of forming a more suitable phase separation morphology in blend films. Through characterization and analysis, the YB2T‐based blend film is found to have higher exciton dissociation efficiency and less charge recombination. Consequently, the power conversion efficiency (PCE) of 17.05% is achieved in YB2T‐based binary OSCs, while YB2B‐based devices only reached 10.94%. This study demonstrates the significance of the aromatic‐ring substitution strategy for regulating the electronic structure and aggregation behavior of 2D nonfullerene acceptors, facilitating the development of devices with superior photovoltaic performance.