Electrochemical and photoelectrochemical behaviour of polythiophenes in non-aqueous solutions - Part 2. The effect of charge trapping

The irreversibility of the doping-undoping processes and its effect on the electrochemical and photoelectrochemical behaviour of conducting polymers w as studied for a series of polythiophene derivatives: polybithiophene, poly -3-methylthiophene and poly-3-phenylthiophene. For the three polymers it wa s confirmed that both anodic and cathodic undoping processes involve a cons iderable amount of residual charge trapped in the polymer phase. The nature of charge trapping for all the polymers was related to the incompleteness of the undoping processes rather than the chemical modification of the poly mer, although the latter was also shown to occur. It was demonstrated that the trapped charge can be removed not only electrochemically (at the beginn ing of the polymer doping process of the opposite sign), as has been shown earlier, but also photoelectrochemically, by illuminating the polymer in so lution at appropriate electrode potentials where the cathodic photocurrents are observed. The latter fact suggests that the photoelectrochemical undop ing of these polymers observed by us earlier is in fact related to the phot oassisted removal of the trapped charge. (C) 2000 Elsevier Science B.V. All rights reserved.