Doped organic semiconductors are critical to emerging device applications, including thermoelectrics, bioelectronics, and neuromorphic computing devices. It is commonly assumed that low conductivities in these materials result primarily from charge trapping by the Coulomb potentials of the dopant counterions. Here, we present a combined experimental and theoretical study rebutting this belief. Using a newly developed doping technique based on ion exchange, we prepare highly doped films with several counterions of varying size and shape and characterize their carrier density, electrical conductivity, and paracrystalline disorder. In this uniquely large data set composed of several classes of high-mobility conjugated polymers, each doped with at least five different ions, we find electrical conductivity to be strongly correlated with paracrystalline disorder but poorly correlated with ionic size, suggesting that Coulomb traps do not limit transport. A general model for interacting electrons in highly doped polymers is proposed and carefully parametrized against atomistic calculations, enabling the calculation of electrical conductivity within the framework of transient localization theory. Theoretical calculations are in excellent agreement with experimental data, providing insights into the disorder-limited nature of charge transport and suggesting new strategies to further improve conductivities.

Expression of energy filtering to boost thermoelectric performance through grain boundary engineering utilising graphene.

Grain boundaries critically limit the electronic performance of oxide perovskites. These interfaces lower the carrier mobilities of polycrystalline materials by several orders of magnitude compared to single crystals. Despite extensive effort, improving the mobility of polycrystalline materials (to meet the performance of single crystals) is still a severe challenge. In this work, the grain boundary effect is eliminated in perovskite strontium titanate (STO) by incorporating graphene into the polycrystalline microstructure. An effective mass model provides strong evidence that polycrystalline graphene/strontium titanate (G/STO) nanocomposites approach single crystal‐like charge transport. This phenomenological model reduces the complexity of analyzing charge transport properties so that a quantitative comparison can be made between the nanocomposites and STO single crystals. In other related works, graphene composites also optimize the thermal transport properties of thermoelectric materials. Therefore, decorating grain boundaries with graphene appears to be a robust strategy to achieve “phonon glass–electron crystal” behavior in oxide perovskites.