The ratio of sulfonate to thiophene sulfur in the acid treated PEDOT:PSS decreased from 2.08:1 to 0.41:1 as the acid treatment concentration increased from 20% to 95% sulfuric acid (Figure ). This reflected a modulation of PSS content from 0.68 down to 0.29 PSS mol fraction (with respect to combined PSS and PEDOT content). Electrochemical deposited PEDOT film (soaked in 100mM RbBr solution for ion exchange) was used as a PSS-free (0.0 PSS mol fraction) standard, lacking any fixed cationic charge.