Resistance to Overdoping Allows Over 2000 S cm^-1 Conductivity in P(g₃BTTT) With Anion-Exchange Doping

Chemical doping of conjugated polymers significantly enhances their conductivity, making them attractive for a large range of applications. Recently, anion-exchange doping, where the dopant counterion is replaced by inorganic anions by exposure of a p-doped film to an electrolyte, has been demonstrated as an effective way to overcome the limitations of molecular dopants in terms of bulkiness, stability and energetics. Here, we demonstrate anion-exchange doping for polymers bearing oligoether side chains and report over 2000 S cm^-1 electrical conductivity for the P(g₃BTTT) polymer. We investigate several thiophene and thienothiophene-based polymers in the high-doping regime to understand this high conductivity. We show that transport involves delocalized charges, that all generated charges participate to the transport, and that the mobility is resilient over nanometer to micrometer length scales. However, the high-doping regime also shows a trade-off between high charge density and high mobility, limiting the conductivity at excess concentrations of doubly charged species. Surprisingly, P(g₃BTTT) is resistant to this 'overdoping' effect and sustains particularly high levels of doubly charged species without drop in mobility. The exceptional conductivity of doped P(g₃BTTT) can thus be related to the high doping level that is achieved thanks to the oligoether side chains, without significant trade-off on the concomitantly high mobility.