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Generally, the differences in crystal polymorph exhibit different narrow band structures, electron-phonon coupling, optoelectronic characteristics and charge transport properties, thus leading to different device performances of organic semiconductors for application in organic field-effect transistors (OFETs). Nowadays it still remains a big challenge to control organic crystal polymorph because the slight non-directional intermolecular interactions lead to the very small differences instructure and energy of cystal phases with several alternative packing arrangements. Therefore, the control of the crystal polymorphism towards high device performance has become a crucial issue in the field of organic semiconductors.
Thienoacenes have been intensively investigated as very promising organic semiconductors with high stability and superior mobility for OFETs in the last decade. However, scare studies focused on the crystal polymorph of thienoacenes. Herein, we report the controllable growth of different crystal phases of dihexyl-substituted dibenzo[d,d′]thieno[3,2-b;4,5-b′]dithiophene (C6-DBTDT), which was synthesized in a new, facile and efficient method. Furthermore, OFETs based on microribbon-shaped β phase crystals showed the hole mobility up to 18.9 cm2 V-1 s-1, which is one of the highest value for p-type organic semiconductors measured under ambient conditions, while platelet-shaped α phase crystals displayed the lower hole mobility of 8.5 cm2 V-1 s-1. We clearly demonstrated that the selective growth of different crystal polymorph for C6-DBTDT can be achieved by using different substrate and solvents. The simple drop-cast fabrication with controllable crystal phase and air operation stability would open the possibility of thienoacene derivatives in the construction of micro- and nanoelectronics.
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