Patterning Smectic Liquid Crystals for OFETs at Low Temperature

The preparation of regular microstructures with liquid crystalline materials for organic field effect transistors (OFETs) is an attractive but challenging issue. However, it is usually limited by the difficulty of forming large-area single crystals aligned in a desirable direction. Herein, several terthiophene (TTP) smectic liquid crystals such as 8-TTP-8 and 12-TTP-11OH are patterned into highly crystalline microstripes by a sandwich system through a dewetting method. Morphology and orientation of the microstripes strongly depend on preparation temperature. Microstripes prepared below crystalline temperature are uniform, well-ordered, and show high field effect transistor (FET) mobility. Meanwhile, pi-pi stacking direction of the TTP backbone is perpendicular to the microstripe and the molecules stack in layer structure, standing up on the SiO2/Si substrate, which would provide an effective pathway for p-type charge transport. However, higher preparation temperatures at liquid crystalline or isotropic liquid range induce many defects in the crystal formation process and cause incline of the unit cell, thus leading to a sharp decrease in FET mobility. A possible mechanism of molecular stacking at different temperature range is proposed. This strategy promised to provide a new opportunity for the high cost-efficiency fabrication of OFETs.