Distance–resilient conductivity in p-doped polythiophenes

Abstract

Scalable organic electronic devices necessitate effective charge transport over long distances. We assess here the conductivity and its distance–resilience in doped polythiophene films with alkyl and oligoether side chains. We find that the polymers with oligoether side chains retain 80–90% of the conductivity over five orders of magnitude in distance (from tens of nanometers to millimeters), when doped with 2,3,5,6-tetrafluoro-tetracyanoquinodimethane (F₄TCNQ). For P(g₄2T-T) co-processed with F₄TCNQ, this leads to an over 100 times enhanced long-range conductivity (43 S cm⁻¹) compared to doped poly(3-hexylthiophene) (P3HT, 0.2 S cm⁻¹). Optimization of the oligoether side chain length and doping protocol pushes the conductivity to 330 S cm⁻¹. Kinetic Monte Carlo simulations of nanoscale terahertz conductivity data reveal that the local mobility of the doped P(g₄2T-T):F₄TCNQ film benefits from a higher dielectric constant (reduced Coulomb binding to the ionized dopant) and from lower energetic disorder. Those benefits persist on the macroscopic scale, while spatial charge confinement and a lack of connectivity hinder the long-range transport of moderately doped P3HT:F₄TCNQ. However, strongly doping P3HT using magic blue leads to enhanced conductivity with distance-resilience >80%. The distance–resilience is generalized for different polymer:dopant systems once a highly conductive regime (>30 S cm⁻¹) is reached. This highlights an effective strategy to overcome limitations in terms of electrostatic binding and multi-scale polymer ordering, enhancing both the short-range and the long-range conductivity of doped conjugated polymers.