New OLED Technology Changes Emission Color Using Same Organic Material

A Japanese research group developed an OLED technology that enables to emit red, green and blue (RGB) lights by using the same organic material without using three kinds of organic molecules emitting RGB lights respectively.

The technology was developed by a group led by Hajime Nakanotani and Chihaya Adachi, associate professor and director, respectively, of the Center for Organic Photonics and Electronics Research (OPERA), Kyushu University.

To emit RGB lights with existing OLED elements, an organic molecule is required for each of the three colors. In the case of OLED, the energy emitted by OLED molecules’ excitors shifting to a ground state is extracted as light emission. The energy of the excitor is as high as about 0.5eV, making it very difficult to freely control the exciton energy of the same molecule. Therefore, it is usually necessary to use organic molecules that emit red, green and blue lights, respectively.

This time, the research group developed an organic thin film consisting of three layers that are based on the same molecular system. And it found that it is possible to control the exciton energy (and the life-span of excitor) by changing the thickness of the middle layer.

The three layers are the (1) “donor layer” organic thin film consisting of electron-donating (donor) molecules, (2) “acceptor layer” organic thin film consisting of electron-accepting (acceptor) molecules and (3) “spacer layer” organic thin film consisting of modules whose excitation energy is higher than those of the donor and acceptor molecules. The spacer layer is sandwiched between the other two layers.

The research results proved for the first time that the excitation state of organic semiconductor molecule can be freely controlled not only by internal factors based on molecular framework but also by external factors (control of intermolecular distance). When the excitation state can be freely controlled by external factors, it is possible to create a new academic field that goes beyond the conventional concept of OLED device such as a switching device using excitors instead of electric charge, the group said.

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