Separated Ionic‐Electronic Conduction in Hydrophobic Conjugated Polymer/Hydrophilic Photocrosslinker Blends for Organic Electrochemical Transistors

ABSTRACT Ionic‐electronic coupling serves as the core process enabling the operation of organic mixed ionic‐electronic (semi)conductors (OMIECs) based devices, for instance, organic electrochemical transistors (OECTs). Replacing hydrophobic side chains of conjugated polymers with hydrophilic ethylene glycol/ionic ones is a well‐developed approach to enable transistor channels with coupled ionic and electronic transport. Here, in contrast, we introduce a hydrophilic glycol chain‐modified photocrosslinker (DtFGDA) for the direct photolithography process and blend it with various representative hydrophobic conjugated polymers. The precise patterning of blended films by direct photolithography is achieved while tremendous enhancements of OECTs performance are attained, with maximum six orders of magnitude higher transconductance, significantly decreased hysteresis, and lower threshold voltage. Through spectroelectrochemical characterization, surprisingly, no obvious variations in polaron absorption peaks are observed in all conjugated polymer/crosslinker blends. An ionic‐electronic separated conduction mechanism, which is never reported in OECTs before, is further proposed based on the characterization of the transmission electron microscope, wherein ions primarily migrate within the crosslinker while holes transport within the semiconducting polymer. This work proposes an efficient strategy, which involves incorporating hydrophilic chains into the photocrosslinker necessary for direct photolithography and blending it with hydrophobic semiconducting polymers, achieving synergistic ionic‐electronic transport in the blended film.