New indolo[3,2-b]carbazole derivatives for field-effect transistor applications

Abstract

The synthesis, characterization, and field-effect transistor (FET) properties of new indolo[3,2-b]carbazole (IC) based materials are reported. Instead of adding the long alkyl chains on the nitrogen atoms of the IC backbone like many other IC-based molecules, they were added at both ends of the molecule (octylthiophene, p-octylbenzene). Also, the amine groups on the IC backbone were either free or protected by methyl groups. The impact on the organization and thin-film morphology showed that the molecules stand perpendicular to the surface as demonstrated by XRD and AFM. The highest hole mobility obtained by these new p-type organic semiconductors was 0.22 cm²V⁻¹ s⁻¹ with an on/off ratio of about 10⁵. The best performance was obtained with 3,9-di(p-octylbenzene)-5,11-dihydroxyindolo[3,2-b]carbazole. This performance is one of the best obtained by both IC derivatives and materials containing a secondary amine on the backbone.