PEDOT:PSS, a conjugated polymer, has demonstrated great potential in emerging applications due to its variable conductivity and spectral attenuation. However, it is necessary to understand the relationship between these properties and the doping state of PEDOT:PSS. This work uses an in situ spectroelectrochemical experiment to measure conductance and spectral attenuation of PEDOT:PSS while being dedoped quasi-statically with lithium ions. Results show a reversible decrease in conductivity during dedoping with a maximum on/off ratio of 2500. The relationship between conductivity and doping
state displays a sigmoidal shape with minimum conductivity at ~1.2mC of intercalated charge. Migration speed of lithium through PEDOT:PSS was found to have a power-law speed-time relationship, where the exponent was on average 0.715 for applied voltages of 2V-5V. This work provides important parameters to facilitate simulation of complex PEDOT:PSS polymer-electrolyte devices.