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

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 104 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 μm2) to 500×500 μm (2.5×105 μm2). 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 Rs and a film capacitance C. These two parameters together define a characteristic temporal frequency fc=1/(2πRsC). By normalizing the impedance with respect to Rs (Zn=|Z|/Rs) and the frequency with respect to fc (fn=f/fc), we found that all of the experimental Bode curves could be collapsed onto a single master plot of Zn vs. fn. 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. Film cast: Electrochemical impedance spectroscopy is used to characterize the charge‐transport properties of both spin‐cast and electrochemically deposited PEDOT films on a series of designed electrodes with systematic variations in size. The spectra are analyzed in terms of a two‐element equivalent circuit model with a solution resistance Rs and film capacitance C. By normalizing the impedance with respect to Rs (Zn=|Z|/Rs) and the frequency with respect to fc (fn=f/fc), all of the experimental Bode curves can be collapsed into a single master plot of Zn versus fn.