High Performance OTFTs Fabricated Using a Calamitic Liquid Crystalline Material of 2-(4-Dodecyl phenyl)[1]benzothieno[3,2-b][1]benzothiophene

An air-stable calamitic liquid crystalline material, 2-(4-dodecyl phenyl)[1]benzothieno[3,2-b]benzothiophene (C12-Ph-BTBT), is designed with a highly ordered smectic X (SmX) (X = K or H) phase demonstrating high charge-carrier mobility and thermal stability in thin-film transistors. Organic thin-film transistors show mobilities as high as 8.7 cm² V⁻¹ s⁻¹ when the C12-Ph-BTBT thin film is annealed at its SmX phase before the electrode deposition. Structural characterization reveals that the as-deposited C12-Ph-BTBT thin films adopt a unilamellar structure. On the other hand, after polycrystalline thin films of C12-Ph-BTBT exhibit bilayer structure after annealing at the temperature of the SmX and the smectic E phases. The highest charge-carrier mobility is observed when the C12-Ph-BTBT thin films are annealed at the SmX phase before the electrode deposition. The results give insight into the understanding of the nature of the mesophase behavior of liquid-crystalline semiconductors and can aid the rational design of self-organizing molecular semiconductors.