Impedance Spectroscopy of Spin‐Cast and Electrochemically Deposited PEDOT:PSS Films on Microfabricated Electrodes with Various Areas

Abstract We have examined the electrochemical impedance spectroscopy (EIS) of PEDOT:PSS‐coated gold electrodes in various electrolytes as a function of temporal frequency (from 0.1 to 10 4 Hz) by using a custom‐designed microfabricated substrate. The electrode areas were systematically varied over a broad range in nominal size from 10×10 μm (100 μm 2 ) to 500×500 μm (2.5×10 5 μm 2 ). Comparisons were made between spin‐cast PEDOT:PSS crosslinked with GOPS and electrochemically deposited PEDOT:PSS films with similar thicknesses. The impedance spectra of the PEDOT:PSS‐coated electrodes with various sizes could all be reasonably well described by a two‐element equivalent circuit model with a solution resistance R s and a film capacitance C . These two parameters together define a characteristic temporal frequency f c =1/(2π R s C ). By normalizing the impedance with respect to R s ( Z n =| Z |/ R s ) and the frequency with respect to f c ( f n = f / f c ), we found that all of the experimental Bode curves could be collapsed onto a single master plot of Z n vs. f n . In addition, analytical formulas that allow the estimation of the film impedance magnitude | Z | and phase ϕ were derived and experimentally validated. These results are of fundamental interest and are also anticipated to be important for the design, characterization, and optimization of conjugated polymer films for interfacing biomedical devices with living tissue.