Control of polymorphism in solution-processed organic thin film transistors by self-assembled monolayers

Polymorphism of organic semiconductor films is of key importance for the performance of organic thin film transistors (OTFTs). Herein, we demonstrate that the polymorphism of solution-processed organic semiconductors in thin film transistors can be controlled by finely tuning the surface nanostructures of substrates with self-assembled monolayers (SAMs). It is found that the SAMs of 12-cyclohexyldodecylphosphonic acid (CDPA) and 12-phenyldodecylphosphonic acid (PhDPA) induce different polymorphs in the dip-coated films of 2-dodecyl[1]benzothieno[3,2-b][1]benzothiophene (BTBT-C12). The film of BTBT-C12 on CDPA exhibits field effect mobility as high as 28.1 cm2 V−1 s−1 for holes, which is higher than that of BTBT-C12 on PhDPA by three times. The high mobility of BTBT C12 on CDPA is attributable to the highly oriented films of BTBT C12 with a reduced in-plane lattice and high molecular alignment.