The present invention relates to a process for producing a liquid composition comprising a functionalized π-conjugated polythiophenes, comprising the process steps of i) providing a liquid phase comprising a) thiophene monomers of the general formula (I) wherein X,Y are identical or different and are O, S, or NR1, wherein R1 is hydrogen or an aliphatic or aromatic residue having 1 to 18 carbon atoms; A is organic residue carrying an anionic functional group; b) an oxidizing agent; and c) a solvent; ii) oxidatively polymerizing the thiophene monomers of the general formula (I) to obtain a liquid composition comprising functionalized π-conjugated polythiophenes; wherein (α1) the pH of the liquid phase provided in process step i) is adjusted to a value below 7.0, wherein the pH is determined at a temperature of 20° C.; and (α2) the chloride content of the liquid phase provided in process step i) is less than 10000 ppm, based on the total weight of the liquid phase. The present invention also relates to the liquid composition obtainable by this process, to a liquid composition comprising a functionalized π-conjugated polythiophene, wherein the com-position is characterized by a certain ratio of mass average molecular weight Mw and the molar average molecular weight Mn of the functionalized π-conjugated polythiophene, to a liquid composition comprising a functionalized π-conjugated polythiophene, wherein the functionalized π-conjugated polythiophene comprises different repeating units in a defined amount, to a process for the preparation of such a liquid composition, to a process for the preparation of a capacitor in which these liquid compositions are used for the formation of the solid electrolyte, to a capacitor obtainable by this process and to the use of the liquid compositions for the preparation of a conductive layer.