Bright electroluminescent devices with tunable spectra obtained by strictly controlling the doping concentration of electron injection sensitizer |
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Authors: | Liang Zhou Jinkui Tang Zhiyong Guo Jing Feng Xiaona Li Xiyan Li Ruiping Deng Hongjie Zhang |
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Institution: | a State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China b Graduate School of the Chinese Academy of Sciences, Beijing 100049, People’s Republic of China |
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Abstract: | In this paper, we report an efficient strategy to design bright blue and blue-green electroluminescent (EL) devices by slightly doping tris(8-hydroxyquinoline) aluminum (Alq3) into N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-diphenyl-4,4′-diamine (NPB) as the light-emitting layer (EML). Bright EL devices with tunable spectra were obtained by strictly controlling the doping concentration of Alq3. With increasing current density, EL efficiencies of these devices increase first and then decrease gradually after reaching the maximum. Analyzing the current density-voltage (J−V) characteristics of hole-only and electron-only devices, we found the presence of Alq3 molecules in EML not only facilitates the injection of electrons from hole block layer (HBL) into EML but also stays the transport of holes in EML, thus causing significant enhancement of EL efficiency and brightness due to improved carriers balance and broadening of recombination zone. More interestingly, the doping concentration of Alq3 strongly influences the injection and transport processes of electrons, thus determining the distribution of holes and electrons on NPB and Alq3 molecules. |
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Keywords: | Electroluminescence Doping concentration Electron injection Band bending |
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