Branched Oligo(ether) Side Chains: A Path to Enhanced Processability and Elevated Conductivity for Polymeric Semiconductors

Commercialization of stable conjugated polymers (CPs) with tunable electronic properties will remain a challenge without adequate solution processability due to the importance of techniques such as roll-to-roll manufacturing. Consequently, modifying CP backbones with polar side chains has recently resurged as an attractive structural design approach to improve polymer solubility and to provide CPs with the capability of transporting both electrons and ions, which is crucial for applications such as organic electrochemical transistors (OECTs). Here, a new dioxythiophene copolymer comprised of 2,​2'-bis-(3,4-ethylenedioxy)thiophene (biEDOT) and 3,4-propylenedioxythiophene (ProDOT) substituted with branched oligo(ether) side chains (PE₂-biOE2OE3) is synthesized using two direct hereto(arylation) polymerization (DHAP) techniques. The typical DHAP technique results in a lower molecular weight polymer (PE₂-biOE2OE3(L)), which is soluble in acetone and demonstrated a solid-state conductivity after oxidative doping of 55 ± 3 S cm⁻¹. Alternatively, a unique temperature ramp DHAP methodology results in a higher molecular weight polymer (PE₂-biOE2OE3(H)) with an especially high solid-state conductivity of 430 ± 60 S cm⁻¹. Notably, the first OECT fabricated from an acetone-processed polymer is reported, which is stable up to 500 cycles and can provide a pathway for future material design aimed at eliminating the use of toxic chlorinated solvents in OECT active layer processing.