High-Performance n-Type Organic Electrochemical Transistors Enabled by Aqueous Solution Processing of Amphiphilicity-Driven Polymer Assembly

Abstract

Despite the growing attention on organic electrochemical transistors (OECTs), most research has focused on the design of p-type active materials, and the number of high-performance n-type materials is limited. Herein, a series of naphthalene diimide-based polymers incorporated with asymmetrically branched oligo(ethylene glycol) (OEG) side chains are developed to enable green-solvent-processed, high-performance n-type OECTs. The branched OEG side chains afford sufficient solubility in eco-friendly ethanol/water solvent mixtures. Importantly, taking advantage of the amphiphilic nature of OEG-based polymers, ethanol/water solvents selectively solvate hydrophilic OEG side chains, while producing assembled pi-pi stacks of hydrophobic backbones. This enables highly ordered polymer packing with a preferential edge-on orientation, and thus excellent lateral charge transport. In particular, the fine-tuned OEG side chains of P(NDIMTEG-T) provide compact backbone packing, effective polaron generation, and superior electrochemical stability with optimized swelling capability. The resultant n-type OECT shows the best electrical/electrochemical performance in the family, represented by a high transconductance (g(m)) of 0.38 S cm(-1) and a large figure-of-merit (mu C*) of 0.56 F V-1 cm(-1) s(-1). This study demonstrates the use of aqueous processing in OECTs, for the first time, and suggests important guidelines for the design of n-type organic mixed ionic-electronic conductors with excellent OECT characteristics.