Air stable n-channel organic semiconductors for thin film transistors based on fluorinated derivatives of perylene diimides

A series of n-type organic semiconductors based on perylene diimides were synthesized. These materials were fully characterized by FTIR and UV-vis spectra as well as elemental analysis. Thin film transistors (TFTs) using a top-contact geometry were fabricated by vapor deposition of these perylene diimide derivatives as the semiconductive channel on surface treated SiO2/Si substrates at various substrate temperatures. The measured TFT performance depended heavily on the type and the number of substituents. We found higher field-effect mobilities for compounds with stronger electron-withdrawing substituents. TFTs with fluorinated perylene diimides showed much better performance in air than a chlorinated derivative. The highest mobility, ca. 0.068 cm(2)/V s, was measured for the compound with the most fluorine substituents (i.e., N,N'-diperfluorophenyl-3,4,9,10-perylenetetracarboxylic diimide (8)). The effect of molecular structure on film morphology was observed using an atomic force microscope (AFM). The correlation between the number of fluorine substitutions and the TFT air stability was studied. Our results showed better device air stability for compounds with more fluorine substituents, due to their lower LUMO energy levels. Other factors affecting TFT performance, such as substrate temperature and SiO2 dielectric surface treatment, were also investigated.