Role of LiF in polymer light-emitting diodes with LiF-modified cathodes |
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| Affiliation: | 1. Interuniversity Micro-Electronics Center (IMEC), Kapeldreef 75, Leuven B 3001, Belgium;2. Department of Chemistry, Laboratory for Molecular Dynamics and Spectroscopy, Katholieke Universiteit Leuven (K.U. Leuven), Celestijnenlaan 200 F, Leuven B 3001, Belgium;1. Faculty of Chemistry, University of Wroc?aw, F. Joliot-Curie 14, 50-383 Wroc?aw, Poland;2. Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine, Kiev 03028, Ukraine;3. Materials & Physics Research Centre, University of Salford, Salford M5 4WT, UK;1. Key Laboratory of Colloid and Interface Chemistry, Shandong University, Jinan 250100, PR China;2. Physikalisches Institut, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, Münster 48149, Germany;1. School of Physics and Materials Science, Radiation Detection Materials & Devices Lab, Anhui University, Hefei, 230601, China;2. Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and, Nanostructure, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, 230031, China;1. Natural Science Centre for Basic Research and Development, Hiroshima University, 739-8530, Japan;2. Materials Processing and Corrosion Engineering Division, BARC, Mumbai, 400085, India;3. Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima, 739-8530, Japan;4. Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashihiroshima, 739-8530, Japan;1. Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China;2. New Vision Opto-Electronic Technology Co., Ltd, Guangzhou 510530, China |
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| Abstract: | We report on high-efficiency polymer light-emitting diodes (PLEDs) based on poly 2-methoxy-5-(3′,7′-dimethyloctyloxyl)]-1,4-phenylene vinylene (OC1C10) with LiF-modified cathodes. Devices with different cathodes are made and characterized by the electroabsorption technique to measure their built-in voltage. Devices with a LiF/Al bilayer cathode or a LiF:Al composite cathode, all show significantly improved performance as compared to those with bare Al cathodes. The improvement is correlated with enhanced electron injection due to a decrease of the electron injection barrier, which is also indicated by the electroabsorption measurements. The same effect is also observed with LiF(0.6 nm)/Mg cathodes. However, inserting the same LiF thin film between Ag and OC1C10 does not improve the device performance. Cathodes composed of ultra-thin films of LiF(0.6 nm)/Al(1 nm) or LiF:Al(2 nm) covered by Ag (100 nm) show the same performance as LiF(0.6 nm)/Al bilayer cathode or a LiF:Al composite cathode, indicating that the enhancement is specific to LiF and Al. Our experiments can be explained by assuming that Li-ions can dissociate from LiF and diffuse into the OC1C10 layer, leading to an n-type zone close to the polymer/cathode interface. This n-doped layer at the interface facilitates electron injection at the cathode/polymer interface and eventually leads to the formation of an Ohmic contact. |
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