In Situ Conjugated Polyelectrolyte Formation

The synthesis and characterization of a conjugated polymer with a thienothiophene-bithiophene-backbone and its corresponding polyelectrolyte structure is described. The conjugated polyelectrolyte is obtained by common nucleophilic substitution in solution, as well as by exposure of films of the neutral precursor to trimethylamine gas. X-ray photoelectron spectroscopy (XPS) analysis is used to determine the extent of conversion, at least within the top 10 nm of the film. Attempts to determine hole mobilities by using steady-state current−voltage (I−V) measurements using hole-only diodes containing the conjugated polyelectrolyte films give rise to light-emitting electrochemical 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 hole mobilities and suppresses ion motion. The reported mobilities are about 3 orders of magnitude higher than those reported for other thiophene-based polyelectrolytes. Overall, these results provide a new method for incorporating conjugated polyelectrolytes into device structures under circumstances where the material is not sufficiently soluble for deposition with standard techniques such as spin-coating.