11:30 AM - 11:45 AM
[15a-A41-10] Crystallization of Organic Semiconductor Films Induced by Surface Monolayer
Keywords:Organic semiconductor, Crystallization, Fullerene derivatives
Crystal structures of organic semiconductor thin films are important for enhancing the performances of organic electronics devices such as organic light emitting diodes, organic field effect transistors and organic solar cells. Molecular template (or epitaxial) growth from substrates is widely studied for controlling crystal structures including orientation, morphology and so on. However, there are many challenges for the application of the method in the devices because a choice of substrates is limited and they mostly relies on a vacuum deposition.
In this work, we discovered a new phenomenon that a surface segregated monolayer induced a change of a crystal structure of organic semiconductor thin films. We synthesized a new surface modifier of a fullerene derivative with an oligosiloxane as a side chain. It formed a monolayer at the surface on the PCBM film after spincoating from a mixed solvent of PCBM and the surface modifier due to a low surface energy of the oligosiloxane. Two-dimensional grazing incidence X-ray diffraction revealed that the crystal structure of the surface modified film was uniaxially orientated perpendicular to the substrate, and was completely different from that of a normal PCBM film. We concluded the surface monolayer acted as a template layer for the crystal growth because the phenomenon was dominated by a concentration of the surface modifier and not limited by a choice of substrates. In addition, conductive AFM measurement showed that an electron mobility increased by the change of the crystal structure. Our results demonstrated a potential of the use of the surface monolayer for controlling crystal structures of organic semiconductor thin films.
In this work, we discovered a new phenomenon that a surface segregated monolayer induced a change of a crystal structure of organic semiconductor thin films. We synthesized a new surface modifier of a fullerene derivative with an oligosiloxane as a side chain. It formed a monolayer at the surface on the PCBM film after spincoating from a mixed solvent of PCBM and the surface modifier due to a low surface energy of the oligosiloxane. Two-dimensional grazing incidence X-ray diffraction revealed that the crystal structure of the surface modified film was uniaxially orientated perpendicular to the substrate, and was completely different from that of a normal PCBM film. We concluded the surface monolayer acted as a template layer for the crystal growth because the phenomenon was dominated by a concentration of the surface modifier and not limited by a choice of substrates. In addition, conductive AFM measurement showed that an electron mobility increased by the change of the crystal structure. Our results demonstrated a potential of the use of the surface monolayer for controlling crystal structures of organic semiconductor thin films.