Interpreting the Hall effect of highly doped conducting polymers

Accurate determination of charge carrier density and mobility is fundamental to understanding the transport physics of conducting polymers and optimizing their performance for applications. However, Hall effect measurements, which have been powerful tools for determining carrier concentrations and mobilities in other classes of metals and semiconductors, have been of limited use for conducting polymers. Estimating carrier densities directly from the conventional expression for the Hall coefficient (RH = [𝑛𝐻q]−1) consistently yields unphysically high carrier densities in heavily doped polymers. In this study, we resolve this problem by implementing a quasi-one-dimensional (Q1D) tight-binding model of the band structure of uniaxially aligned polymer films to analyze the p-type to n-type transition in both the Hall and Seebeck effects observed upon increased doping in organic electrochemical transistors. Our Q1D framework achieves excellent agreement of carrier densities extracted from Hall measurements with those extracted by other, independent methods over a wide range of doping levels. Our findings provide evidence that the transport physics of aligned polymers is governed by the topology of a single Q1D band within a simple band-filling framework and establish Hall measurements as a powerful tool for studying their charge transport physics.