Using discotic liquid crystals to prepare biaxially textured organic semiconductors

Crystal texture plays a central role in determining the performance of organic electronic devices such as organic field effect transistors (OFETs). Current methods of controlling thin film crystal texture through solution processing are limited by stochastic nucleation. We report here a facile new method to create biaxially textured crystals of organic semiconductors by directing the self-assembly of the precursor discotic liquid crystalline phase. The columnar hexagonal (Col_H) phase of HAT6 (2,3,6,7,10,11-Hexakis(hexyloxy)triphenylene) is biaxially aligned in lithographically fabricated microchannels consisting of cross-linked polystyrene (XPS) walls on silicon. Synchrotron grazing incidence wide angle X-ray scattering (GIWAXS) measurements reveal the direction of π stacking is perpendicular to the XPS walls. The biaxial alignment and the directionality of π stacking in the liquid crystalline phase is transferred to the crystalline phase by rapid quenching. As a significant fraction of organic semiconductors exhibit a liquid crystalline phase, we expect our method of creating textured crystals to be broadly applicable.