High Conductivities of Disordered P3HT Films by an Electrochemical Doping Strategy

In this work, we demonstrate that high solid-state conductivities of simply spin-coated poly(3-hexylthiophene) (P3HT) films can be obtained by means of an ex situ electrochemical doping strategy using 4-line electrodes. With increasing electrochemical doping potential, we find an increase in conductivity over 6 orders of magnitude, giving a maximum conductivity up to 224 S cm–1 with maximum hole densities of 1021 holes per cm3. Most intriguingly, highly conducting states are achieved over a very broad potential range from 0.4 to 0.8 V versus Fc/Fc+ in the doped state. The experiments are complemented by UV–vis–NIR absorption and electron paramagnetic resonance spectroscopy in the solid state as well as with in situ electrochemical measurements which confirm that the electrochemically generated doped species can be successfully transferred into the solid state. Our results suggest that for reaching high conducting states, P3HT has to be present in different redox states and that the plateau conductivity region should arise from the coexistence of overlapping polaron and bipolaron states. Comparisons to films of regiorandom P3HT and pure redox polymer systems based on diphenyl-3,3′-bicarbazyl are further presented, which highlight the role of mixed valence states in conducting polymers. Last but not least, the highly conducting films are simply spin-coated and therefore rather disordered, adding new aspects to the discussion whether high crystallinity is a prerequisite for achieving high conductivities in conjugated polymers.