Novel ways to significantly enhance the conductivity of transparent PEDOT:PSS

Two novel approaches are reported to significantly enhance the conductivity of transparent PEDOT:PSS (PEDOT:PSS = poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)). The first method is to add anionic surfactants into aqueous solution of PEDOT:PSS. Conductivity enhancement by a factor of hundreds was observed, and it was strongly dependent on the chemical structure of the surfactant. Conductivity enhancement from 0.16 S cm-1 to 80 S cm-1 was observed, when anionic surfactant SDS was added. The effect of the anionic surfactants on the conductivity of PEDOT:PSS was attributed to the substitution of the PSS anions by the surfactant anions. The addition of a nonionic surfactant had moderate effect on the conductivity of PEDOT:PSS, while cationic surfactant almost did not affect the conductivity. The second method to significantly enhance the conductivity is to treat the PEDOT:PSS film with solutions of certain salts. CuCl2 or InCl3 solution could enhance the conductivity by a factor of hundreds, while the effect by NaCl is negligible. The salt effect on the conductivity of PEDOT:PSS is attributed to the loss of PSS from PEDOT:PSS and conformational change of PEDOT chains during the treatment.