Interfacial Engineering with Hydrophobic Self-Assembled Monolayers Boosting Ionic and Electronic Conduction in <i>N</i> -Type Organic Electrochemical Transistors

Interface engineering has proven to be an effective strategy for improving the performance of thin-film optoelectronic devices. However, in bioelectronic devices, especially in organic electrochemical transistors (OECTs) using mixed ionic-electronic conductors as the active layer, the influence of self-assembled monolayers (SAMs) at the substrate-semiconductor interface remains comparatively underexplored. In this study, four different silane-based hydrophobic SAMs were systematically investigated on glass substrates, offering a novel approach to enhancing the performance of n-type OECTs. It was demonstrated that these SAM-modified interfaces not only effectively promote the crystallization of conjugated Homo-gDPP polymer films but also trigger the spontaneous formation of porous microstructures, overall yielding significant improvements in n-type device characteristics. Upon the SAM's incorporation, we observed a nearly doubled mobility-volumetric capacitance (μC*) (from 49.4 to 89.7 F·cm^-1·V^-1·s^-1) and a 2.5-fold increase in normalized transconductance (<i>g</i>_m,norm). These notable enhancements can be attributed to facilitated ion penetration and improved electronic transport within the semiconducting layer, likely stemming from reduced lateral ionic impedance, interface trap density, and elevated charge conductivity. Furthermore, the hydrophobic SAM-treated OECTs exhibit greater operational stability and an accelerated temporal response, highlighting the potential of interfacial modification as a versatile and scalable approach for advancing high-performance bioelectronic devices.