The effect of incorporation of dimethyl sulfoxide (DMSO) into poly(3,4-ethylenedioxythiophene):poly(s tyrenesulfonate) (PEDOT:PSS) on the electrical conductivity is investigated. It is shown that the values of the carrier mobility and the carrier density increase significantly for PEDOT:PSS films with DMSO addition. The high carrier mobility of PEDOT:PSS samples with the addition of DMSO is attributed to a combined effect of the modification of the electron-phonon coupling and a change in the value of the PSS-to-PEDOT ratio. The high carrier density of PEDOT:PSS samples with DMSO addition is attributed to a high affinity of DMSO for water. (C) 2016 Elsevier B.V. All rights reserved.