Cation concentration was positively correlated with pH, rising from 0.008 (0.008) Rb + per repeat unit in acidic conditions to 0.072 (0.056) Rb + per repeat unit in basic conditions in the doped (dedoped) state (Figure ). This reflects the competition in acidic solution between the Rb + and proton counterbalancing the halide anion, and in the case of basic solutions, counterbalancing the hydroxide anion. The trapped anion concentration shows an opposite trend with pH, falling from 0.31 trapped excess Br -per repeat unit in acidic conditions to 0.16 trapped excess Br -per repeat unit in basic conditions (Figure ). This likely reflects the effect of protonation of the polymer on both free carrier and defect/trap density. The modulated Br -concentration (difference between doped and dedoped state) was nominally identical in neutral and basic conditions (0.53 and 0.54 Br -dopants per repeat unit, respectively, see Figure ). This indicated that basic pH seemed not to effect the doping/dedoping process. However, the acid condition displayed a diminished degree of Br -dopant modulation of only 0.31 Br -dopants per repeat unit, indicating the protonation of thiophene rings may disrupt the doping/dedoping process. Summarizing the contrast between EG/GOPS-PEDOT:PSS and pg2T-TT, EG/GOPS-PEDOT:PSS undergoes an initial exchange of protons in the film with metal cations from the electrolyte. The excess polyelectrolyte in EG/GOPS-PEDOT:PSS simplifies the composition situation by Donnan excluding uptake of mobile anions and buffering the film against pH and electrolyte concentration, such that doping/dedoping involves a fairly consistent modulation of >0.2 cations per EDOT repeat unit. However, this cation modulation brings with it a large flux of water molecules in/out of the film. Conversely, pg2T-TT undergoes passive electrolyte uptake (water and anion-cation pairs) and passive doping. Electrochemical cycling accumulates a remarkably high concentration of excess anions that apparently balance/trap electronic charge in the polymer. Lacking fixed charge, pg2T-TT is unbuffered, and the resulting film composition is highly sensitive to electrolyte concentration and pH.