Molecular Orientation Control of Liquid Crystal Organic Semiconductor for High-Performance Organic Field-Effect Transistors
Moon Jong Han, Don‐Wook Lee, Eun Kyung Lee, Jooyoung Kim, Ji Young Jung, Hyunbum Kang, Hyungju Ahn, Tae Joo Shin, Dong Ki Yoon, Jeong‐Il Park
Abstract
The control of molecular orientation and ordering of liquid crystal (LC) organic semiconductor (OSC) for high-performance and thermally stable organic thin-film transistors is investigated. A liquid crystalline molecule, 2-(4-dodecyl thiophenyl)[1]dibenzothiopheno[6,5-b:6′,5′-f]-thieno[3,2-b]thiophene (C12-Th-DBTTT) is synthesized, showing the highly ordered smectic X (SmX) phase, demonstrating molecular reorganization via thermal annealing. The resulting thermally evaporated polycrystalline film and solution-sheared thin film show high charge carrier mobilities of 9.08 and 27.34 cm2 V–1 s–1, respectively. Atomic force microscopy and grazing-incidence X-ray diffraction analyses prove that the random SmA1-like structure (smectic monolayer) is reorganized to the highly ordered SmA2-like structure (smectic bilayer) of C12-Ph-DBTTT at the crystal-SmX transition temperature region. Because of the strong intermolecular interactions between rigid DBTTT cores, the thin film devices of C12-Th-DBTTT show excellent thermal stability up to 300 °C, indicating that LC characterization of conventional OSC materials can obtain high electrical performance as well as superior thermal durability.