Growth of thin rubrene single crystals from 1-propanol solvent

Rubrene (5,6,11,12-tetraphenyltetracene) single crystals were grown by using the solution-slow-cooling technique with 1-propanol (PrOH) solvent. Thin hexagonal crystals with an orthorhombic system, typically 300×200×50 μm3 in size, were obtained. The crystals had flat terraces (∼7 μm) separated by monomolecular steps. Organic field-effect transistors (OFETs) with the single crystals showed carrier mobilities as high as ∼1.6 cm2 V−1 s−1. We also obtained thin parallelogram-shaped crystals, typically 300×200×20 μm3 in size. X-ray diffraction analysis solved that the crystals belong to triclinic system. The crystals showed lower carrier mobilities of ∼0.1 cm2 V−1 s−1. This is the first report on the growth and characterization of two polymorphs of rubrene crystal.