Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films are obtained using ionic liquids as additives. Upon adding 1-ethyl-3-methylimidazolium tetracyanoborate (EMIM TCB) to the conducting polymer, the conductivity increases to 2084 S cm-1; this is attributed to the phase separation of PSS leading to a structural change in the film. A comparative study with 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIM BF4) shows that EMIM TCB gives higher conductivity and transmittance and can be regarded as one of the most promising additives for the preparation of indium tin oxide (ITO)-free organic devices using PEDOT:PSS/EMIM TCB as electrodes.