Improved electron injection in organic LED with lithium quinolate/aluminium cathode |
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| Affiliation: | 1. Department of Materials, University of Oxford, Oxford OX1 3PF, UK;2. Opsys Ltd., Unit 8, Begbroke Business and Science Park, Sandy Lane, Yarnton, Oxford OX5 1PF, UK;1. Department of Urology, University of North Carolina, Chapel Hill, North Carolina;2. Department of Urology, David Geffen School of Medicine at UCLA, Los Angeles, California;3. Department of Health Policy and Management, UCLA Fielding School of Public Health and UCLA School of Nursing, Los Angeles, California;4. Department of Urology, Weill Cornell School of Medicine, New York, New York;1. Department of Physics, Dalian Maritime University, Dalian 116023, China;2. State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, China;3. Lab for Advanced Materials, Department of Chemistry, East China University of Science and Technology, Shanghai 200237, China;1. College of Physics and Electronic Engineering, Taishan University, Tai’an, Shandong 271021, PR China;2. Department of Physics, School of Science, East China University of Science & Technology, Shanghai 200237, PR China;3. Nano-Organic Photoelectronic Laboratory and Key Laboratory of Photochemical Conversion & Optoelectronic Materials, Technical Institute of Physics & Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China;4. Department of Chemistry and Chemical Engineering, Taishan University, Tai’an, Shandong 271021, PR China;1. Department of Physics and Material Sciences Center, Philipps-Universität, D-35032 Marburg, Germany;2. Light Technology Institute (LTI), Karlsruhe Institute of Technology, D-76131 Karlsruhe, Germany;3. Ioffe Physical-Technical Institute, Russian Academy of Science, St. Petersburg 194021, Russia;1. Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei, 10607, Taiwan;2. Department of Electronic Engineering, Ming Chi University of Technology, New Taipei City, 24301, Taiwan |
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| Abstract: | Lithium quinolate (Liq), covered with aluminium, was used as an electron injection layer in a double layer organic light emitting diode consisting of NPD as the hole transport layer and Alq as the emitting layer resulting in lower turn on voltage and increased power efficiency. The driving voltage required to achieve a luminance of 100 cd/m2 decreased from 5.8 V for the Ca/Al to 4.2 V when Liq/Al was used, improving device power efficiency from 2.3 to 4.1 lm/W. The performance tolerance to layer thickness of Liq devices is also better than that of the devices with lithium fluoride (LiF). Due to the highly insulating nature of LiF, it can only be used when deposited as an ultra-thin layer, while the Liq can be deposited into layers as thick as 5 nm without significantly affecting the EL properties. An Liq electron injecting layer has also been tried in combination with Ca, Mg and Ag cathodes. Our experiments support the assumption that free lithium is released from lithium quinolate, as in the case of lithium fluoride, when Liq is over coated with active metals such as Al. |
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