Charge Carrier Mobility of 1,6-Dibromopyrene Single Crystal Grown by Solution Method on Substrate

Large elongated single crystals (2.91 mm × 97 μm) of 1,6-dibromopyrene were successfully obtained from solution using the slow evaporation method. Their carrier mobility was obtained via current–voltage characteristics of bottom-gate bottom-contact-type field-effect transistors. In these devices, the longitudinal direction of each crystal was parallel or perpendicular to the conductive channel. The highest mobility was 6.0 × 10−4 cm2 V−1 s−1 and 2.2 × 10−3 cm2 V−1 s−1 in the linear and saturation region, respectively, when the electric current flowed across the crystal’s longitudinal direction. The emission strength ratio and mobility ratio between the two longitudinal directions (parallel and perpendicular to the conductive channel, respectively) were 3.1 and 2.2. X-ray diffraction measurements suggested that both the emission strength and mobility are larger in the transverse intermolecular contact direction than in the stacking direction. The mobilities in the linear region were tentatively corrected by subtracting the contributions of charge injection barriers and were estimated to be 2.1–2.9 times larger than the uncorrected ones. The results of this study suggest that bromine substitution is one of the effective methods to modify the optical properties and improve the solution processability of organic semiconductor materials while maintaining the carrier mobility.