Rubrene Thin Films with Viably Enhanced Charge Transport Fabricated by Cryo-Matrix-Assisted Laser Evaporation

Abstract

Among organic semiconductors, rubrene (RB; C42H28) is of rapidly growing interest for the development of organic and hybrid electronics due to exceptionally long spin diffusion length and carrier mobility up to 20 cm2V−1s−1 in single crystals. However, the fabrication of RB thin films resembling properties of the bulk remains challenging, mainly because of the RB molecule’s twisted conformation. This hinders the formation of orthorhombic crystals with strong π–π interactions that support the band transport. In this work, RB films with a high crystalline content were fabricated by matrix-assisted laser evaporation and the associated structure, composition, and transport properties are investigated. Enhanced charge transport is ascribed to the crystalline content of the film. Spherulitic structures are observed on top of an amorphous RB layer formed in the initial deposition stage. In spherulites, orthorhombic crystals dominate, as confirmed by X-ray diffraction and the absorption and Raman spectra. Surprisingly, nanowires several microns in length are also detected. The desorption/ionization mass and X-ray photoelectron spectra consistently show minimal material decomposition and absence of RB peroxides. The observed carrier mobility up to 0.13 cm2V−1s−1, is close to the technologically accepted level, making these rubrene films attractive for spintronic and optoelectronic applications.