Mesoscale Morphology and Charge Transport in Colloidal Networks of Poly(3-hexylthiophene)

We identify and characterize the mesoscale morphology of poly(3-hexylthiophene) (P3HT) fibers crystallized through colloidal self-assembly in various aromatic solvents. The network structure of the P3HT is evaluated through in situ small-angle neutron scattering (SANS) and ultra small-angle neutron scattering (USANS) experiments and by electron microscopy. Through model fitting to the scattering data, we are able to determine that P3HT forms network structures in solution prior to deposition. We directly obtain structural parameters such as the fraction of P3HT in nanofiber form, the cross-sectional fiber shape, and the fractal dimension of the colloidal networks. The structural parameters are shown to be strongly dependent on the solvent choice. Ex situ microscopy experiments are also performed to provide complementary structural information such as type and frequency of fibrillar junctions and the network size. The structural parameters are also analyzed within the context of the hole mobility in organic field effect transistors (OFET).