pH-Tunable High-Performance PEDOT:PSS Aluminum Solid Electrolytic Capacitors

The pH effect of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) water dispersion on colloidal particle size (D50), zeta potential (ζ), and electrical conductivity was investigated. An increase in the pH of the PEDOT:PSS water dispersion from 2 to 11 increased the D50 from 10 to 100 nm owing to the aggregation of the colloidal particles and decreased the electrical conductivity from 750 to 62 S cm–1 by dedoping, respectively, while the ζ remained almost constant at ca. – 50 mV. Furthermore, aluminum solid electrolytic capacitors were fabricated using PEDOT:PSS as a cathode material. It was found that the electrical characteristics of the PEDOT:PSS aluminum solid electrolytic capacitors were optimized at pH 3, where D50 and electrical conductivity played an important role for low equivalent series resistance (ESR) and high capacitance (Cap). Furthermore, the ESR decreased and Cap increased by repeating the fabrication process, where the Cap usable rate reached as high as 92% because of the increase in the surface coverage of the etched aluminum foil with the PEDOT:PSS.