Carbazole-bridged triphenylamine-bipyridine bipolar hosts for high-efficiency low roll-off multi-color PhOLEDs |
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| Affiliation: | 1. Department of Chemistry, National Taiwan University, Taipei, 10617, Taiwan;2. Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, 202, Taiwan;3. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan;1. CNRS, Centrale Lille, ISEN, Univ. Valenciennes, UMR 8520-IEMN, Univ. Lille, 59000 Lille, France;2. University of Monastir Department of Physics, Microelectronics and Instrumentation Laboratory, Av de l''environnement, 5019 Monastir, Tunisia;1. State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Microelectronics and Solid-state Electronics, University of Electronic Science and Technology of China (UESTC), Chengdu 610054, PR China;2. School of Optoelectronic Information, University of Electronic Science and Technology of China (UESTC), Chengdu 610054, PR China;3. State Key Laboratory of Synthetic Chemistry, Institute of Molecular Functional Materials, Department of Chemistry, The University of Hong Kong, Hong Kong, PR China;1. School of Chemical & Biotechnology, SASTRA Deemed University, Thanjavur-613401 Tamil Nadu, India;2. Department of Chemistry, Kalasalingam Deemed University, Krishnan Kovil 626126, India;3. Beamline Department, Pohang Accelerator Laboratory, 80 Jigokro-127beongil, Nam-gu, Pohang, Gyeongbuk, South Korea;1. School of Optoelectronic Information, University of Electronic Science and Technology of China (UESTC), Chengdu 610054, PR China;2. Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, PR China;1. Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India;2. Departament de Química, Universitat de les Illes Balears, Crta. De Valldemossa km 7.5, 07122 Palma (Baleares), Spain |
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| Abstract: | Three new bipolar molecules composed of carbazole, triarylamine, and bipyridine were synthesized and utilized as host materials in multi-color phosphorescent OLEDs (PhOLEDs). These carbazole-based materials comprise a hole-transport triarylamine at C3 and an electron-transport 2,4′- or 4,4′-bipyridine at N9. The different bipyridine isomers and linking topology of the bipyridine with respect to carbazole N9 not only allows fine-tuning of physical properties but also imparts conformational change which subsequently affects molecular packing and carrier transport properties in the solid state. PhOLEDs were fabricated using green (ppy)2Ir(acac)], yellow (bt)2Ir(acac)], and red (mpq)2Ir(acac)] as doped emitters, which showed low driving voltage, high external quantum efficiency (EQE), and extremely low efficiency roll-off. Among these new bipolar materials, the 2Cz-44Bpy-hosted device doping with 10% (ppy)2Ir(acac) as green emitting layer showed a high EQE of 22% (79.8 cd A?1) and power efficiency (PE) of 102.5 lm W?1 at a practical brightness of 100 cd m?2. In addition, the device showed limited efficiency roll-off (21.6% EQE) and low driving voltage (2.8 V) at a practical brightness of 1000 cd m?2. |
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| Keywords: | Bipolar host Carbazole Bipyridine Electrophosphorescence |
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