Engineering Ambipolar Charge Transport in Stable Solution-Processed Nanofilms of Electrically Conductive Liquid-Crystalline Anthraquinones

The realization of ambipolar charge transport with long-term operational and environmental stability of the transport layer is a rarely addressed challenge in organic electronics, especially with respect to solution-processed devices. This study reports the molecular engineering of redox-active liquid-crystalline anthraquinones with triazole and cyanovinylene functional units to stabilize ordered columnar mesophases at room temperature. In addition to high thermal stability, solution-processed nanofilms of these discotic liquid crystals (DLCs) also demonstrate effective charge-extraction from injecting electrodes in diode devices, with their electrical conductivity values among the highest reported for DLC nanofilms (10–4 S/m). Alongside ultra-stable electrical performance over repeated electrical cycling, these devices exhibit long-term stability for up to two years without encapsulation under ambient storage conditions. Balanced ambipolarity is achieved via the fabrication of single-carrier devices where hole and electron mobilities both match at an order of 10–3 cm2/Vs. Being a pioneering report dedicated to detailed electrical conductivity studies and ambient stability of solution-processed ambipolar DLC films, the present work enriches the scope of practical DLC-based electronic devices from the fundamental viewpoint of molecular design.