While EG/GOPS-PEDOT:PSS is a prototypical conjugated polymer/polyelectrolyte composite OMIEC, polythiophenes with oligoethylene glycol side chains have become increasingly popular conjugated polymer electrolyte OMIECs. In particular, pg2T-TT (Figure ) has been investigated for a variety of applications. Lacking any fixed ionic charge, Donnan exclusion is not expected in pg2T-TT, and both cations and anions appeared in the XRF spectra (Figure ). The florescence spectra at 200eV below the Rb absorption edge were collected to deconvolute and Rb Kα peaks from the overlapped Br Kβ peaks (Figure ). XRF following electrolyte exposure revealed the passive uptake of both anions and cations, 0.16 Br -and 0.04 Rb + per repeat unit (Figure ). This was in agreement with previous qualitative measurements of ion uptake in contact with ionic liquid electrolytes. However, here the calibrated quantitative measure of individual ion concentrations revealed that anions and cations did not uptake in equal amount, indicating extensive passive doping of pg2T-TT. This is attributed to its relatively shallow HOMO allowing for rather efficient doping via ambient oxygen. The passive uptake of Rb + led to a cation concentration that subtly varied with doping (oxidation) state. Initial cycling between the doped state (+0.5V vs Ag/AgCl) and dedoped state (-0.2V vs Ag/AgCl) greatly modulated the Br -anion concentration, though even when a reductive electrochemical potential was applied a large excess of anions (uncompensated by cations) remained. Unlike the PEDOT:PSS cycling, it should be noted here that the reductive potentials applied were sufficient to fully dedope the polymer. These initial phenomena persisted upon multiple cycles, equilibrating to seemingly permanent presence of 0.021 charged balanced anions and cations per repeat unit, and a further uncompensated 0.29 excess anions per repeat unit (Figure and the second right column in Figure ). Due to the energetic favorability of charge neutrality, these seemingly uncompensated excess anions are presumably counterbalanced by localized positive charge on the polymer backbone (i.e. trapped electronic charge). This measured trapping level (~10 20 cm -3 ) is much higher than expected defect levels in polythiophenes (10 13 -10 19 cm -3 ). Thus it is surmised that electrochemical cycling of the films does not simply passivate existing trapped electronic charge with excess anions, but induces many additional trap sites as well.