Aqueous formulation of concentrated semi-conductive fluid using polyelectrolyte complexation*

A processable fluid containing extremely high concentration of conjugated polymer can be formed via the coacervation of a conjugated polyelectrolyte (CPE) with a polymeric ionic liquid (PIL). The phase diagram of the CPE-PIL mixture shows a broad region of coacervation that stretches across all polymer concentrations. The viscous coacervate contains up to 50 wt% polymer, approximately 50 times higher than concentrations commonly achieved in conventional solution processing. This coacervate was blade-coated into solid films of mm-scale thickness with improved CPE conjugation length, likely due to the reduction in backbone torsional disorders. As a result, the electronic conductivity of the complexed film upon subsequent acid doping is twice as high as that of the CPE film, despite the fact that half of the complexed film is composed of an insulator. This work shows that polyelectrolyte complexation is a promising route to the formulation of highly loaded conjugated polymer fluids for industrial-scale fabrication, with added benefits on charge transport through the improved control of the conjugated polymer conformation.