Doping Glyocolated Polythiophenes with Lithium Salts

Polymer-based mixed ionic/electronic conductors (MIECs) are receiving increased attention, in part due to their utility across a wide-range of applications. MIECs show valuable properties, including volumetric capacitance changes, transduction of ionic and electronic signals, and biocompatibility. These properties result in a number of useful features, enabling their use in applications such as batteries and ultracapacitors, (bio)sensors, actuators, and organic electrochemical transistors (OECTs). Homopolymer MIECs originally showed limited ionic mobility due to their highly hydrophobic backbones. There has been a significant improvement in their ionic conductivity by introducing polar groups into the solubilizing side chains; the most popular chemistry for the polar side chains is oligoethylene glycol (oEG). This strategy of introducing oEG has driven significant improvements in MIEC performance in a number of conjugated polymer backbones.<br/><br/>Side chains are known to have a profound influence on the morphology, crystallinity, charge carrier concentration, charge thermal stability and ion/water uptake properties of conjugated polymers. By studying a range of polythiophenes across LiTFSI doping concentrations, we are able to elucidate how variations in the side chain architecture influence the evolution of morphology with increasing levels of LiTFSI doping, highlighting the importance of the architecture of oEG side chains in determining the blended material's morphology and resultant ionic and electronic conductivity. The presentation will focus on how small changes in the side chain structure can affect where the LiTFSI is located and thus the conductivity of the materials.