Interfacial Phenomena Determining Conductance Modulation in Electrolyte‐Gated Transistors: Roles of Alkali Ion Solvation and Ion–Fluorinated Self‐Assembled Monolayer Interactions

ABSTRACT In electrolyte‐gated transistors (EGTs), controlling ion dynamics at the electrolyte/channel interface is crucial for precise modulation of channel conductance. Accordingly, functional interlayers have been explored to modulate interfacial ion dynamics. However, previous studies have mainly focused on increasing ion–interlayer affinity, even though multiple factors, including ion solvation and ion–interlayer interactions, influence ion dynamics at the interface. Herein, we elucidate the multicomponent interfacial ion interactions that determine conductance modulation through a comparative study of three alkali ion‐based EGTs. The polyethylene oxide (PEO) electrolytes with different alkali ions (Li + , Na + , and K + ) are systematically employed to induce distinct ion solvation environments and ion interaction strengths. A fluorinated self‐assembled monolayer (FSAM) is additionally introduced on the channel layer as an ion trapping interlayer. Owing to the differences in ionic radius, the alkali ions exhibit distinct coordination with PEO and anions as well as different interactions with the FSAM, leading to ion‐dependent interfacial behaviors. Computational and chemical analyses reveal that the resulting synaptic behavior is determined by the coupled and competing effects of cation solvation and cation–FSAM interactions. This comprehensive study bridges the gap between interfacial ion interactions and electrical properties, highlighting the importance of multicomponent interactions for understanding cation behavior and the resulting synaptic properties.