Tunable wetting properties of poly(3-hexylthiophene) films with different doping levels.

This work systematically investigates the wetting properties of electrochemically doped poly(3-hexylthiophene) (P3HT) films at different oxidation states. In situ spectroelectrochemistry and ex situ opto-electronic characterization of the doped films confirm that the polaron and bipolaron states have successfully been obtained through electrochemical doping. Sessile drop and dynamic water contact angle measurements yield reproducible results that strongly depend on the applied electrochemical doping potential, with a maximum water contact angle variation of up to 43° from the neutral to the fully doped state. The evolution of wettability correlates with the doping states and is heavily influenced by morphological changes upon doping. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) reveal that wrinkle-like structures appear at high doping levels which is consistent with predominant bipolaron formation accompanied by doping-induced swelling followed by drying. Complementary grazing-incidence wide-angle X-ray scattering (GIWAXS) shows that doping to the polaronic state leads to lamellar expansion with a contraction of the π-π stacking distance within crystalline domains. Despite these lattice changes, the edge-on orientation is largely preserved, indicating that the overall crystalline texture remains stable even at the highest studied doping levels.