A Blending Approach for Dual Surface and Bulk Functionality in Organic Transistors

Abstract Organic transistors are versatile electronic devices that offer diverse functionalities based on device structure and operation conditions. When utilizing an electrolyte, the transistor can operate either as an Electrolyte‐Gated Organic Field‐Effect Transistor (EGOFET), where charges accumulate at the semiconductor/electrolyte interface, offering fast response times but relatively low amplification, or as an Organic Electrochemical Transistor (OECT), where ions infiltrate the channel, offering high amplification but slower response times. In this study, we report combined characteristics of OECTs and EGOFETs, in a single device depending on operation conditions. The bifunctionality is achieved by blending an organic semiconducting p‐type polymer with an Organic Mixed Ionic Electronic Conductor (OMIEC), a n‐type fullerene derivative. The microstructure controlled through the composition and thermal treatments, directs the surface and volumetric processes in the corresponding transistor device. Polymer‐rich domains at the surface facilitate surface charge accumulation and effective p‐type EGOFET operation, while bulk fullerene‐rich domains enhance ionic transport for n‐type OECT behavior. Time response measurements reveal rapid surface charging in an EGOFET‐dominated regime and slower volumetric doping in an OECT‐dominated regime, highlighting the dual transport mechanisms. This research establishes guiding principles for tuning blend composition and microstructure for high‐performance, multifunctional transistors in sensing and bioelectronics.