Root-Cause Analyses for 3D Intermolecular Packing Network Formation in Central Unit Extended Small Molecular Acceptors

The enhanced three-dimensional (3D) intermolecular packing network in central unit extended small molecular acceptors (SMAs) has boosted the performance of organic solar cells (OSCs) significantly by improving the inner exciton/charge photodynamic. However, the structural profiles that determine the formation of efficient 3D packing network are still shrouded in mystery. Herein, a series of SMAs (CH1, CH2, CH3, CH20 and CH8F) with/without central conjugation extension and substitutions are systematically investigated at both single-molecule and aggregate levels. Notably, by examining the evolution of packing networks and modes from CH1 to CH8F, the determining role of central unit extension and halogenation in constructing an enhanced 3D intermolecular packing network is revealed for the first time. Additionally, binary OSCs of CH8F, which combine central extension with fluorination achieve a first-class power conversion efficiency (PCE) of 19.02%, markedly outperforming its counterparts. These root-cause analyses unveil the essential structural elements for forming superior 3D packing networks and will further boost rational design of SMAs.