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A Study of the Physics of Organic Electronic Materials and Devices

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A flexible OLED device


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Mechanism of an OLED device


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Fluorescence and Phosphorescence
of an OLED device


Research into organic optoelectronic devices is currently attracting great interest, spurred on by the realization of organic electroluminescence displays. For the development of a new generation of organic optoelectronic devices, we are conducting intensive research focusing on: 1) new designs and syntheses of functional organic materials with outstanding properties, 2) fabrication and evaluation of organic devices, and 3) the elucidation of basic physics governing the processes of organic devices. On the basis of the technologies used in organic light-emitting diodes (OLEDs), we are trying to develop high-performance organic transistors, organic solar cells, and organic laser diodes. Our research interests also include the fabrication of well-organized supramolecular nanostructures and the control of molecular orientation toward high-performance organic devices, as well as the creation of novel bio-photonic devices that combine biological molecules with the technology of the organic devices.

Organic Light-Emitting Diode (OLED)

Organic light emitting diodes (OLEDs) based on multi-layer OLED structures were first developed in the 1980s. Organic materials and devices are a prime focus of OLED research. Successful OLED technology has already been put to practical use in car monitors, mobile phone displays and organic televisions. OLED developments aimed at high efficiency and long product lifetimes have now been extensively studied both in academia and industry worldwide. OLEDs have been a huge success in the display market, since they have a rapid response of under a microsecond, and offer full color and high contrast ratios. Further, major efforts have been made to increase their emission efficiency and to improve their stability. OLEDs have a simplified device structure, and ultra thin films of organic material (typically 100nm) can be deposited on transparent electrode (ITO) substrates by using various techniques.

For organic semiconductors, we combine electron and hole transport layers with an emitter layer to enhance EL efficiency, and we select highly efficient emitter materials to be used as emitters. We can also realize an exceptionally low driving-voltage for OLEDs by making proper choices in the selection of organic materials and in device configuration. The key technology for OLEDs is the usage of organic phosphorescence molecules. Although OLEDs using fluorescence materials have grown to have significant reliability, EL efficiency remains low because of the limitations of singlet exciton production efficiency (~25 %) achieved by electrical excitation. Since the exciton production ratio under electrical pumping is 1:3 for a singlet-to-triplet exciton, phosphorescence materials are crucial to achieving high EL efficiency. Recently OLEDs using phosphorescence materials achieved exciton production efficiency of ~100 %, resulting in 20% external EL efficiency.

Department of Applied Chemistry
Professor Chihaya Adachi
Associate Professor Hajime Nakanotani
Assistant Professor Kenichi Goushi
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