Improving the Electrical Connection of n-Type Conjugated Polymers through Fluorine-Induced Robust Aggregation

Abstract

Naphthalene diimide (NDI)-based conjugated polymers with bithiophene or dithienylethene (TVT) units can form large crystal domains through NDI-driven self-assembly and are widely used in organic electronic devices as n-type materials. However, improving electron transport in these semiconducting polymers has been a significant challenge mainly due to poor electrical connections between the crystal domains. Formation of an interconnected network of small domains with short-range ordering and mixed orientations could be an effective way of increasing the electron mobility (μe) of polymeric materials. The present study demonstrates the feasibility of this approach using an NDI-based polymer composed of fluorinated TVT (FTVT) units. The FTVT unit enhances intermolecular interactions between the polymer chains, leading to robust aggregation. This aggregation was found to suppress NDI-driven self-assembly, resulting in interconnected small crystal domains with short-range ordering and good thermal stability at elevated temperatures. This microstructure provided transistor devices with improved μe by lowering energetic disorder as well as consistent electrical connectivity at different annealing temperatures.