Development of highly conductive nanodomains in poly(3-hexylthiophene) films studied by conductive atomic force microscopy

The growth of highly conductive nanodomains in regioregular poly(3-hexylthiophene) (P3HT) thin films was visualized with a resolution of 20 nm by conductive atomic force microscopy (C-AFM). The current distribution images by C-AFM indicated that P3HT nanocrystallites with sizes smaller than 20 nm were dispersed in a matrix of disordered phase in the film spin-cast from chloroform; with thermal annealing, highly conductive spots appeared in the image. In contrast, the film spin-cast from o-dichlorobenzene showed a large number of conductive domains with dimensions from 20 to 200 nm. The conductive domains occupied 52% of the entire surface, and the current carried through the domains accounted for 66% of the total current, demonstrating that these conductive networks are essential for obtaining a sufficient macroscopic conductivity. The increase in macroscopic conductivity of the P3HT films was well explained from the viewpoint of nanoscale charge transport through the development of the conductive nanodomains.