Precise orientation control of a liquid crystal organic semiconductor via anisotropic surface treatment

• Published in: NPG Asia materials 2022-12, Vol.14 (1), p.28, Article 28
• Main Authors: Han, Moon Jong, Wei, Dayan, Yun, Hee Seong, Lee, Seong-hun, Ahn, Hyungju, Walba, David M., Shin, Tae Joo, Yoon, Dong Ki
• Format: Article
• Language: English
• Subjects: 639/301/923/919; 639/301/923/966; Alignment; Biomaterials; Carrier mobility; Chemistry and Materials Science; Crystal structure; Current carriers; Electronic devices; Energy Systems; Field effect transistors; Liquid crystals; Materials Science; Optical and Electronic Materials; Optical microscopy; Organic semiconductors; Orientation; Rubbing; Semiconductor devices; Structural Materials; Substrates; Surface and Interface Science; Surface treatment; Thin Films; Transistors
• ISSN: 1884-4049; 1884-4057
• DOI: 10.1038/s41427-022-00377-5

We report a three-dimensional (3D) molecular orientation control of a liquid crystal organic semiconductor (LC-OSC) based on the long-range ordering characteristic of an LC material. To this end, a synthetic LC-OSC molecule, MeOPh-BTBT-C8, with a fluidic nematic (N) phase that is essential for alignment control over a large area and a smectic E (SmE) phase showing high ordering, was prepared. A simple flipping of a sandwich cell made of the LC-OSC material between the top and bottom substrates that have uniaxial–planar degenerated alignment as well as crossed rubbing directions responds to the given surface anchoring condition and temperature gradient. Optical observation of the alignment-controlled LC-OSC was carried out by polarized optical microscopy (POM), and the corresponding charge carrier mobility was also measured by fabricating organic field-effect transistors (OFETs). Our platform offers a facile approach for multidirectional and multifunctional organic electronic devices using the stimulus–response characteristics of LC materials. It is the first work demonstrating the modulating opto-electrical signals of organic semiconductors by the liquid crystal properties. Through flipping the anisotropic surface treatment-based sandwich cells, the liquid crystal organic semiconductor responds to the given surface anchoring condition with temperature gradient, showing tunable molecular orientation with the corresponding charge carrier mobility of organic field-effect transistors.