Nanostructures for Efficient Hole Transport in Poly(3-hexylthiophene) Film: A Study by Conductive Atomic Force Microscopy

The growth of hole-transporting nanostructures of regioregular poly­(3-hexylthiophene) (P3HT) films with thermal annealing were examined by conductive atomic force microscopy (C-AFM). The C-AFM current images visualized spatially inhomogeneous hole transport in the film on a nanometer scale, with relatively low conductive regions and high conductive domains. The high conductive domains were attributed to the relatively high density regions of P3HT nanocrystallites in the film, which were determined during spin-coating. The current images obtained from the same area of the P3HT film showed that thermal annealing improved the hole-transporting property of the film on average, but both the size and spatial distributions of the relatively high conductive domains in the as-spun film remained almost the same even after annealing. Furthermore, we found that the increase in current flow proceeded mostly in the relatively high conductive domains. In these domains, the electrical connectivity among the crystalline phases was effectively improved by the growth of individual nanocrystallites, leading to the formation of preferred hole-transporting pathways in the direction of film thickness.