Mixed Phases as a Route to Self-Passivation: Effect of π-Stacking Backbone on the Physical and Electrical Properties of Naphthalenediimide Derivatives

Solution processable p- and n-type organic semiconductors are candidates for low-cost, large-area, and roll-to-roll printing of inexpensive mass-production electronics. In these organic semiconductors, it is the π-conjugated backbone that plays the major role in charge-carrier transport across the channel. In order to achieve better device performance, it is required to have better packing/crystallinity to minimize defects and avoid deep traps, so that effective transfer of charge carriers can take place in the solid state. Excellent results have been reported by blending crystal-forming organic semiconductors with amorphous polymers that serve as binders or passivating agents. We show that, for some molecular structures and processing conditions, mixtures of stereoisomers can separate and self-arrange into a thin amorphous layer covered by a polycrystalline layer. In this work, we focus on two families of constitutional isomers that differ only in the position of the pyridine groups on the π-skeleton and study the effect of the structure on the physical and electrical properties using absorption spectroscopy, AFM, X-ray, and organic field-effect transistor current-voltage response.