Effect of aggregation on the optical and charge transport properties of an anionic conjugated polyelectrolyte

The steady-state optical and charge transport properties of the anionic polythiophene, poly[3-(potassium-4-butanoate)thiophene-2,5-diyl], are reported. The degree of interchain aggregation in solution and in the film state can be controlled by solution processing conditions and the introduction of bulky organic counterions. Disruption of interchain contacts leads to significant changes in the absorption and emission properties. Scanning probe microscopy reveals various surface morphologies, depending on the solution history. Attempts to determine electronic charge carrier mobilities by using steady-state current-voltage (I-V) measurements using hole-only diodes gives rise to light-emitting electrochemical cell behavior, indicating ion motion and/or redistribution within the films. The use of a pulsed I-V method operating at frequencies higher than the ion response times allows measurements of electronic carrier mobilities in hole-only diodes. Hole mobilities in films with different degrees of chain aggregation reveal an order of magnitude difference (similar to 10(-8) to 10(-9) cm(2)/Vs).