Halogen Bonding as a Tool to Control Morphology and Charge Transport in Organic Semiconductors

The solid-state structure and morphology of organic semiconductors (OSCs) are critical in determining the performance of organic electronic devices, as they directly influence charge carrier mobility. Improved molecular packing and ordering are key to achieving better device performance. While halogen bonding (XB) has been extensively used in supramolecular crystal engineering, its potential for organic electronics remains largely untapped. Here, we show that strong and directional XB can significantly enhance the morphology and optoelectronic properties of a pyridine-substituted naphthalene diimide (NDI) derivative. By employing various XB donors with differing interaction strengths and comparing them to a nonbonding reference compound, we achieve a two-orders-of-magnitude improvement in field-effect mobility and I_ON-I_OFF ratio. Furthermore, the geometric substitution pattern of the XB donors is found to strongly influence molecular packing, crystalline domain formation, and, ultimately, device performance.