Enhancing N-Type Organic Electrochemical Transistor Performance via Blending Alkyl and Oligoglycol Functionalized Polymers

Compared to their p-type counterparts, n-type organic mixed ionic-electronic conductors (OMIECs) generally exhibit inferior stability, slower ion injection kinetics, and reduced sensitivity when used as the active layer in organic electrochemical transistors (OECTs). Enhancing the performance of n-type OMIECs is crucial for advancing next-generation technologies that rely on mixed conduction, including bioelectronics, neuromorphic computing, and energy storage. Here, we investigate how blending two n-type conjugated polymers with oligoglycol and alkyl side chains impacts OECT performance. Specifically, we examine NDI(biOE2)-T2, which has branched oligoglycol side chains, and N2200, which has branched alkyl side chains. Blending these polymers in a 90:10 NDI(biOE2)-T2:N2200 ratio results in a twofold increase in the electronic mobility volumetric capacitance product (μC*) compared to pure NDI(biOE2)-T2. However, at higher N2200 concentrations, the μC* product declines sharply. The enhancement in μC* arises from an increase in electronic mobility (μ), likely due to reduced polymer swelling upon N2200 addition. Using nanoscale infrared imaging with photoinduced force microscopy (PiFM), we visualize the spatial distribution of the two polymers and observe that higher N2200 content leads to phase separation, contributing to the drop in μC*. Overall, our study highlights polymer blending as a promising strategy for improving the performance of n-type OMIECs.