Isotropic charge transport in highly ordered regioregular poly(3-hexylthiophene) monolayer

Abstract

Charge transport anisotropy in π-stacked poly(3-hexylthiophene-2,5-diyl) (P3HT) monolayers was investigated. The monolayers were prepared using a Langmuir–Blodgett technique and were uniaxial but homogeneous two-dimensional sheets. Nanoscale electrical measurements were carried out using metal electrodes with a submicrometre gap between them in order to exclude breaches that occasionally occur along the chains. A remarkable degree of isotropy in both the conductivity and mobility was found. The conductivity isotropy implies that charge transport is dominated by fatal defects in polymers arising at structural and electrical discontinuities, even in the absence of large morphological defects. It was found that the mobility along the π-stacking direction can exceed that along the polymer chain in monolayers with good crystallinity. This high mobility along the π-stacking direction is thought to be an inherent charge transport characteristic that has so far been obscured in solid state conjugated polymers with complex microstructures.