Our study is focused on the relationship between the structural coherence and intrinsic carrier transport in a regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) nanofiber, particularly in an isolated nanofiber, formed in various ratios of good and poor solvent mixtures. The P3HT nanofiber, which is formed in solvent mixtures, had a whisker structure with the length of several $\mu$m, the height decreased from 9 to 2 nm as estimated by scanning force microscope observation, and the structural coherent length along the longitudinal axis increased from 40 to 59 $\AA$ as determined by x-ray-diffraction measurement, with increasing ratio of the good solvent. The $I$-$V$ characteristics measured by the four-probe method showed that the activation energy of hopping conduction, which was considerably related with the structural disorder, decreased with increasing ratio of the good solvent. Moreover, the field-effect-transistor characteristics of the nanofiber showed that the carrier mobility increased with increasing ratio of the good solvent, and the nanofiber formed under the good-solvent-rich condition showed the mobility from $3.8\times {10}^{-2}$ to $5.6\times {10}^{-2}$ cm${}^2$ V${}^{-1}$ s${}^{-1}$. The tendency of the mobility to increase has been explained on the basis of the change in the structural coherent length and thermal activation energy, assuming the model that regarded the nanofiber as a one-dimensional array of electronically coherent regions and incoherent defects, and hence the relationship between the structural coherence and carrier transport has been clarified.

• Received 14 December 2010

DOI:https://doi.org/10.1103/PhysRevB.83.115314