Data related to manuscript ['Bipolarons rule the short-range terahertz conductivity in electrochemically doped P3HT', Materials Horizons (2022), https://pubs.rsc.org/en/content/articlelanding/2022/mh/d1mh01343b]

Doping of organic semiconductor films enhances their conductivity for applications in organic electronics, thermoelectrics and bioe- lectronics. However, much remains to be learnt about the proper- ties of the conductive charges in order to optimize the design of the materials. Electrochemical doping is not only the fundamental mechanism in organic electrochemical transistors (OECTs), used in biomedical sensors, but it also represents an ideal playground for fundamental studies. Benefits of investigating doping mechanisms via electrochemistry include controllable doping levels, reversibility and high achievable carrier densities. We introduced here a new technique, applying in situ terahertz (THz) spectroscopy directly to an electrochemically doped polymer in combination with spectro- electrochemistry and chronoamperometry. We evaluate the intrin- sic short-range transport properties of the polymer (without the effects of long-range disorder, grain boundaries and contacts), while precisely tuning the doping level via the applied oxidation voltage. Analysis of the complex THz conductivity reveals both the mobility and density of the charges. We find that polarons and bipolarons need to co-exist in an optimal ratio to reach high THz conductivity (B300 S c