Removal of protonic doping from PEDOT:PSS by weak base for improving aluminum solid electrolytic capacitor performance

Abstract

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a promising conductive polymer material, but its acidic nature leads to device deterioration and poor long-term durability. It is usual practice to neutralise PEDOT:PSS solutions with bases, resulting in a decrease of conductivity. The causes of the decline in conductivity remain disputed and uncertain. In this study, three bases (sodium hydroxide, ammonium hydroxide, and imidazole) were employed to treat PEDOT:PSS to investigate their effects on doping level, composition, and structure. The results show that bases may dedope PEDOT:PSS by removing the proton doping from the PEDOT chain. Meanwhile, insulating PSS is removed, and the aggregated structure is optimised to ensure that conductivity is not significantly reduced. The PEDOT:PSS treated with the weak base imidazole showed the least loss of conductivity due to only a modest decrease in doping level and the greatest loss of insulating PSS. Aluminium electrolytic capacitors made using imidazole pH-adjusted solutions have a capacitance ratio of up to 98.28% and an equivalent series resistance of 26 mΩ. These findings provide a valuable reference for developing high electrical characteristics and neutral PEDOT:PSS materials.