Universalityin Solvent-Dependent Conductivity ofConjugated Thiophene-Based Copolymers with Expanded Core Monomer Designs

Conjugated polymers are promising materials for organic electronic devices; however, to achieve metal-like electrical properties, these materials need to be chemically doped. In this work, a series of structurally tailored thiophene-based copolymers are studied to elucidate relationships between copolymer design, doping method, solubility, and electrical conductivity. The results show that increasing the distance between side chains along the conjugated backbone increases thin film conductivity, with conductivities surpassing that of poly­(3-hexylthiophene) (P3HT) by several orders of magnitude for solution and sequential doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). In addition, the conductivities of films subjected to sequential doping show a dependence on the polymer–solvent interaction energy, which appears universal for this series of thiophene-based copolymers, offering a potentially predictive basis for choosing an optimal solvent for doping. These studies also show that sequential doping provides higher thin film conductivity at lower concentrations of anionic F4TCNQ. This indicates that sequential doping is superior in that less dopant is necessary to achieve the same, if not greater, electrical performance for these thiophene-based copolymers. Overall, this work provides fundamental insight into how copolymer design, doping method, and strength of polymer–solvent interaction energy impact electrical performance, paving the way for printed electronics, sensors, and other applications for chemically doped conjugated polymers.