Moderately anisotropic field-effect mobility in dinaphtho[2,3-b:2('),3(')-f]thiopheno[3,2-b]thiophenes single-crystal transistors

Anisotropy of carrier mobility is measured for dinaphtho[2,3-b:2('),3(')-f]thiopheno[3,2-b]thiophenes single-crystal transistors. We have developed a method of local gating to restrict carrier-accumulated channels elongated radially within the herringbone planes of submillimeter crystals so that mixture of conductivity off the intended directions is minimized in the measurement. The highest mobility 4 cm(2)/V s is achieved for the a-axis direction due to the highest orbital overlaps, while the lowest mobility measured in the perpendicular direction is still as high as 2.5 cm(2)/V s. The moderate anisotropy favors high performance in polycrystalline thin-film transistors of the compound, where charge transport is inevitably mixed for all directions.