Electric Double Layer Dynamics in Poly(ethylene oxide) LiClO₄ on Graphene Transistors

Formation of an electric double layer (EDL) is a powerful approach for exploring the electronic properties of two-dimensional (2D) materials because of the ultrahigh capacitance and induced charge in the 2D materials. In this work, epitaxial graphene Hall bar devices are gated with an EDL using a 1 μm thick solid polymer electrolyte, poly(ethylene oxide) and LiClO₄. In addition to carrier density and mobility, ion dynamics associated with the formation and dissipation of the EDL are measured as a function of temperature over a gate bias range of ±2 V. The room temperature EDL formation time (∼1-100 s) is longer than the dissipation time (∼10 ms). The EDL dissipation is modeled by a stretched exponential decay, and the temperature-dependent dissipation times are described by the Vogel-Fulcher-Tammann equation, reflecting the coupling between polymer and ion mobility. At low temperatures, approaching the glass transition temperature of the electrolyte, the dissipation times of both cations and anions exceed several hours, and both p- and n-type EDLs can persist in the absence of a gate bias. The measured temperature-dependent relaxation times qualitatively agree with COMSOL multiphysics simulations of time-dependent ion transport in the presence of an applied field.