Abstract
The change in electrical conductivity of poly(3,4‐ethylenedioxythiophene) (PEDOT) when going from the oxidized state to the neutral state was measured using impedance spectroscopy. The electrical conductivity is reduced by nearly three orders of magnitude upon dedoping, a value much less than usually reported for conjugated polymers. The high conductivity in the neutral state 
explains the fast switching of PEDOT even when deposited on a nonconducting substrate. The doping process is also studied using rapid in situ optical spectroscopy of solid‐state electrochemical cell having PEDOT as one electrode. The absence of a conducting current collector enables studies of the propagation of the reaction front from the electrical contact throughout the polymer film Optical and electrical measurements support earlier suggestions that the doping process consists of two proves occurring at differ potentials.