Vertical tunneling transport and nonlinear access resistance in layered single-crystal organic transistors

Organic semiconductors (OSCs) are the key materials for flexible printed electronics with the suitability for solution processes under ambient conditions. Recent studies revealed that high layered crystallinity of OSCs is quite essential for providing highly uniform crystalline films and high performance organic thin-film transistors (TFTs) [1]. In the materials, substitutions with normal alkyl chains is used to improve both solvent solubility and layered crystallinity. However, these alkyl chains should exhibit insulating nature due to the lack of pi electrons, which may affect the transport properties.
Here, we report that vertical transport across the alkyl-chain layers causes tunneling-based nonlinear access resistance in single-crystalline TFTs of Ph-BTBT-C₁₀ [2]. The effect of access resistance appeared in layer-number (n)-dependent device mobility (2-20 cm²/Vs) and nonlinear I_d-V_d characteristics (1 ≤ n ≤ 15). These characteristics were reproduced by numerical simulation with assuming the tunneling-based access resistance. Based on the results of low-temperature transport measurements, we discuss the vertical transport mechanism in the layered OSC crystals.
[1] S. Inoue, et al., Chem. Mater., 27, 3809 (2015). [2] T. Hamai et al., Phys. Rev. Appl., to be published.