Effects of tunneling-based access resistance in layered single-crystalline organic transistors

7-Decyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C10) is a soluble organic semiconductor that can afford high mobility organic thin-film transistors (OTFTs). The material exhibits inherent high layered crystallinity due to the formation of bilayer-type layered-herringbone packing that involves nearly independent π-electron core layers and alkyl-chain layers within the crystals. Here, we discuss that the bottom-gate/top-contact OTFTs composed of single-crystalline Ph-BTBT-C10 channel layers exhibit noticeable effects in the device characteristics caused by the highly insulating nature of the alkyl-chain layers. Notable layer-number (n) dependence was observed in the nonlinear current–voltage characteristics and the device mobility (2–14 cm2/Vs, with TFT ideality factor 15–46%, mainly due to large threshold voltages), which can be clearly ascribed to the tunneling-based interlayer access resistance across the alkyl-chain layers. The gated-four-probe measurements of single-crystalline OTFTs also revealed quite high mobility more than 40 cm2/Vs along the channel semiconducting layer, whereas highly insulating effects due to the alkyl-chain layers were also apparent as the large hysteresis in the gate-off states of OTFTs. We discuss the whole features of the tunneling-based access resistance in the device operations of single-crystalline OTFTs, on the basis of comparison between experimental results and model simulations.