A promising conducting polymer poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) experiences significant conductivity enhancement when treated with proper ionic liquids (ILs). Based on the hard-soft-acid-base principle, we propose a combination of a hydrophilic hard cation A+ (instead of the commonly used 1-ethyl-3-methyl imidazolium, EMIM+) and a hydrophobic soft anion X– (such as tetracyanoborate, TCB–) as the best ILs for this purpose. Such ILs would decouple hydrophilic-but-insulating PSS– from conducting-but-hydrophobic PEDOT+ most efficiently by strong interactions with hydrophilic A+ and hydrophobic X–, respectively. Such a favorable ion exchange between PEDOT+:PSS– and A+:X– ILs would allow the growth of conducting PEDOT+ domains decorated by X–, not disturbed by PSS– or A+. Using density functional theory calculations and molecular dynamics simulations, we demonstrate that a protic cation- (aliphatic N-alkyl pyrrolidinium, in particular) combined with the hydrophobic anion TCB– indeed outperforms EMIM+ by promptly leaving hydrophobic TCB– and strongly binding to hydrophilic PSS–.