April 14, 2017
Keio University
Researcher Masahiro Shibuta (full-time lecturer at the Keio University Graduate School of Science and Technology) of the Keio Institute of Pure and Applied Sciences and principal investigator Atsushi Nakajima (professor at the Keio University Faculty of Science and Technology) have succeeded in forming a single-crystal thin film of anthracene molecules, a component of organic thin-film devices, at room temperature, and have clarified the state of charge separation in the photoelectric conversion process.
Photoelectric conversion devices (solar cells, light-emitting devices) using functional organic molecular thin films are expected to be a fundamental technology for solving the environmental and energy problems that have become more serious in recent years. To improve photoelectric conversion efficiency, it is necessary to fabricate thin films with high crystallinity in which organic molecules are regularly arranged. However, with conventional thin-film fabrication methods, it has been difficult to ensure high crystallinity at room temperature, which has limited the photoelectric conversion efficiency. Furthermore, to clarify the mechanism of photoelectric conversion, precise observation of the ultrafast photoexcitation process in thin films with excellent crystallinity was required.
This research group has now succeeded in fabricating an ultimately thin organic single-crystal thin film with regularly arranged molecules using an extremely simple method: simply immersing a gold substrate in a solution of molecules with a chemically modified anthracene skeleton. Furthermore, upon investigating the photoexcitation process in this single-crystal thin film using femtosecond time-resolved photoelectron spectroscopy, they succeeded in observing for the first time in the world the phenomenon of energy exchange between excitons in the crystal thin film and excited electrons spread over the surface. These results are considered to be of high value as a fundamental technology for making organic photoelectric conversion devices more efficient. The results of this research were published in the online ASAP Articles section of "ACS NANO," an academic journal of the American Chemical Society, on April 11, 2017 (U.S. time).
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