Thermoelectric (TE) properties of free-standing poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT:PSS) films treated with camphorsulfonic acid (CSA) and left hand camphorsulfonic acid (L-CSA) have been systematically investigated utilizing two different methods: addition of CSA/L-CSA into the PEDOT:PSS solution; or post treatment of free-standing PEDOT:PSS films with different concentration of CSA/L-CSA solution. It is verified that the post-treatment method is much more effective than the direct addition of CSA/L-CSA into the PEDOT:PSS solution. Using post-treatment method, the highest electrical conductivity can increase up to 644.7 S/cm, which is much higher than that of the direct addition method, ~206.2 S/cm at room temperature. In both cases, there is trivial change in the Seebeck coefficient. The maximum value of ZT is 0.017 at room temperature for the PEDOT:PSS film post-treated by 0.08 M CSA solution. These results demonstrate that post treatment is a promising approach to enhance the TE properties of PEDOT:PSS thin films. The difference in optical activity between CSA and L-CSA also has an effect on the electrical conductivity of PEDOT:PSS.
