Described is an electrolytic capacitor that includes: (a) a layer of an oxidizable metal; (b) a layer of an oxide of the oxidixable metal; (c) a solid electrolyte; and (d) a plurality of contacts. The solid electrolyte includes a polythiophene having recurring units represented by the following formulas (I-a) and/or (I-b), ##STR00001## Also described are processes for producing electrolytic capacitors, and conductive layers that include such polythiophenes.