Electron affinities of organic materials used for organic light-emitting diodes: A low-energy inverse photoemission study |
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| Affiliation: | 1. Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan;2. Idemitsu Kosan Co. Ltd., 1280 Kami-izumi, Sodegaura, Chiba 299-0293, Japan;1. Plastic Electronics and Energy Laboratory (PEEL), Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India;2. Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 305701, Republic of Korea;3. Organic and Hybrid Solar Cells Group, Physics of Energy Harvesting Division CSIR-National Physical Laboratory, New Delhi, 110012, India;4. Ultrafast Optoelectronics and Terahertz Photonics Group, Physics of Energy Harvesting Division CSIR-National Physical Laboratory, New Delhi, 110012, India;1. Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, 5268 Renmin Street, Changchun 130024, Jilin, PR China;2. School of Chemistry and Environmental Engineering, Changchun University of Science and Technology, 7989 Weixing Road, Changchun 130028, Jilin, PR China |
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| Abstract: | The electron affinity (EA) of an organic semiconductor is a measure of the electron transport level. Although reliable values of the EA are required for designing the device architecture of organic light-emitting diodes (OLED), there were no appropriate methods. Recently we have developed low-energy inverse photoemission spectroscopy which enables us to determine the EA of organic materials in solid with the precision required for research of OLED. Using this new technique, we precisely determined EA of typical OLED materials, TCTA, CBP, Ir(ppy)3, BCP, Alq3 and Liq as well as a newly developed dopant 4CzIPN. The obtained electron affinities are generally smaller by about 1 eV than the commonly believed values urging the reconsideration of the electron injection/transport mechanisms in OLED. We also compare EAs determined by various experimental and calculation methods for 29 materials. The results show that the reduction potential gives a reasonable estimate rather than the optical gap and ionization energy. |
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| Keywords: | Low-energy inverse photoemission spectroscopy Electron affinity LUMO level Organic light-emitting diode |
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