Tailoring the optical properties of rubrene films through epitaxy-induced amorphous-to-crystal transition

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Abstract
Crystalline rubrene (RUB) in the orthorhombic structure can be regarded as a workhorse in organic optoelectronics. So far, however, its great potential for device integration has been held back by the struggle to obtain high quality and photo-oxidation resistant RUB thin films. Here, we propose an effective strategy to obtain homogeneous, highly crystalline, and oriented RUB thin films, which relies on a spontaneous amorphous-to-crystal transition driven by organic epitaxy occurring at room temperature in vacuum: this crucial process dictates the final morphological, structural, and optoelectronic properties of the film. To probe the kinetics of the transition, we combine an ex-situ analysis via polarized optical spectroscopy and atomic force microscopy with a photoluminescence investigation carried out in-situ, based on monitoring the efficiency of the singlet fission process typical of crystalline RUB. Building on the insights gained, we tune the thin film growth and post-growth parameters, so as to obtain centimeter-scale, highly homogeneous and crystalline RUB thin films, constituted by several μm-sized and coherently oriented domains, featuring oxidation resistance.
Funding Information
  • Ministero dell'Università e della Ricerca (PRIN 2022SCWMT2)

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