Imaging of morphological changes and phase segregation in doped polymeric semiconductors

The electrical conductivity and morphological characteristics of two conjugated polymers, P3HT and PCPDTBT, p-doped with the strong electron acceptor tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) are studied as a function of dopant concentration. By combining scanning and transmission electron microscopy, SEM and TEM, with electrical characterization, we observe a correlation between the saturation in electrical conductivity and the formation of dopant rich clusters. We demonstrate that SEM is a useful technique to observe imaging contrast for locating doped regions in thin polymer films, while in parallel monitoring the surface morphology. The results are relevant for the understanding of structure property relationships in doped conjugated polymers.