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

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 π−π 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 (gm) of 0.38 S cm−1 and a large figure‐of‐merit (µC*) 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. High‐performance n‐type organic electrochemical transistors (figure‐of‐merit (µC*) = 0.56 F V−1 cm−1 s−1) are achieved by using eco‐friendly ethanol/water solution processing of branched oligo(ethylene glycol) (OEG) side chain‐incorporated polymers. The ethanol/water solvent selectively solvates hydrophilic OEG side chains, resulting in highly ordered edge‐on oriented polymer crystallites, superior electron mobility, and µC*.