Molecular phase engineering of organic semiconductors based on a [1]benzothieno[3,2-b][1]benzothiophene core

Abstract

Two environmentally and thermally stable [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives, 2-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT) and 2-(4-hexylphenyl)[1]benzothieno[3,2-b][1]benzothiophene (C6-Ph-BTBT), are prepared by Suzuki coupling. Organic thin-film transistors with a top-contact and bottom-gate based on BTBT, Ph-BTBT and C6-Ph-BTBT are fabricated by vacuum-deposition on octyltrichlorosilane treated Si/SiO₂ substrates. Experimental results show that the thin-film based on BTBT sublimes instantly after the deposition of electrodes, and no semiconductor signal is detected. Ph-BTBT shows a mobility of 0.034 cm² V⁻¹ s⁻¹. Furthermore, C6-Ph-BTBT exhibits three liquid crystal phases (Sm A, Sm E and Sm K or H) and achieves the highest hole mobility of 4.6 cm² V⁻¹ s⁻¹ with an on/off ratio of 2.2 × 10⁷ for polycrystalline organic thin-film transistors in ambient air. The present study exemplifies that the introduction of mesoscopic order in molecular design provides a general approach for the high electronic performance of organic semiconductors.