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 $4cm2/Vs$ 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 $2.5cm2/Vs$⁠. The moderate anisotropy favors high performance in polycrystalline thin-film transistors of the compound, where charge transport is inevitably mixed for all directions.