Anion effect on salt-induced conductivity enhancement of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) films

The conductivity of conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films could be significantly enhanced through a treatment with aqueous solution of a certain salt, such as CuCl2 or InCl3. The anions of the salts had pronounced effect on the conductivity enhancement. Conductivity enhancement by a factor of more than 1000 was observed when CuBr2 or InI3 aqueous solution was used, while it became less significant and negligible when CuSO4 and Cu(CH3COO)2 aqueous solutions were used, respectively. The anion effect on the conductivity enhancement is consistent with the acid dissociation constants of the anions, which suggests that the conductivity enhancement is related to the dissociation of the salts and the association of the anions with PEDOT+. A salt with higher dissociation can benefit the association of the anions with PEDOT+, which leads to the loss of more PSS chains from the PEDOT:PSS film and more significant conductivity enhancement by the salt treatment.