Uniaxial Alignment of Spin Coated Polymer Films for High-Performance Field Effect Transistors

Chain alignment has been a major method for improving the performance of polymer field effect transistors (PFETs). A nanogrooved substrate is a promising media for fabricating high-performance polymer transistors due to its effectiveness. However, the application of nanogrooved substrates in polymer spin coating suffers from the liquid repelling nature of the substrate. This work demonstrates that with the help of an α-chloronaphthalene (α-CN) additive in the chloroform solution, the highly aligned poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b′]-dithiophen-2-yl)-alt-[1,2,5]thiadiazolo-[3,4-c]pyridine] (PCDTPT) polymer films can be fabricated by spin coating onto the nanogrooved substrates. The chloroform matrix ensures the uniform film formation, and the incorporation of α-CN significantly improves the polymer chain orientation. The resulting PCDTPT thin films show an absorbance dichroic ratio as high as 16, which is among the highest ones ever reported. The polymer field effect transistors based on the aligned PCDTPT films show an average mobility of 4.42 cm² V^–1 s^–1 (the highest as 5.03 cm² V^–1 s^–1), which is about 6 times that of the control devices with a mean mobility of 0.77 cm² V^–1 s^–1. Despite the simplicity of this method, the resulting devices show comparable and even better performances than the aligned polymer film-based devices reported in the literature. The uniaxially aligned spin coated polymer film provides a simple but effective approach to fabricating high-performance PFETs.