MoO3 as p-type dopant for Alq3-based p–i–n homojunction organic light-emitting diodes |
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| Affiliation: | 1. Department of Physics and State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871, People’s Republic of China;2. Haixi Collaborative Innovation Center for New Display Devices and Systems Integration, Fuzhou University, Fuzhou 350002, People’s Republic of China;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;1. Department of Physics, School of Science, East China University of Science & Technology, Shanghai 200237, China;2. Physics and Electronic Engineering College, Taishan University, Shandong Province 271021, China;3. Kunshan Hisense Electronics, Co. Ltd., Kunshan, Jiangsu 215300, China;1. Department of Electronics and Computer Engineering, Hanyang University, Seoul, 04763, South Korea;2. Division of Materials Science and Engineering, Hanyang University, Seoul, 04763, South Korea;1. Applied Chemistry Department, School of Material Science & Engineering, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, PR China;2. Institute of Advanced Materials (IAM), Nanjing Technology University, Nanjing 211800, PR China |
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| Abstract: | Using high-work-function material MoO3 as a p-type dopant, efficient single-layer hybrid organic light-emitting diodes (OLEDs) with the p–i–n homojunction structure are investigated. When MoO3 and Cs2CO3 are doped into the conventional emitting/electron-transport material tris-(8-hydroxyquinoline) aluminum (Alq3), respectively, a significant increase in p- and n-type conductivities is observed compared to that of intrinsic Alq3 thin films. With optimal doping, the hole and electron mobilities in Alq3:MoO3 and Alq3:Cs2CO3 films was estimated to be 9.76 × 10?6 and 1.26 × 10?4 cm2/V s, respectively, which is about one order of magnitude higher than that of the undoped device. The p–i–n OLEDs outperform undoped (i–i–i) and single-dopant (p–i–i and i–i–n) OLEDs; they have the lowest turn-on voltage (4.3 V at 1 cd/m2), highest maximum luminance (5860 cd/m2 at 11.4 V), and highest luminous efficiency (2.53 cd/A at 100 mA/cm2). These values are better than those for bilayer heterojunction OLEDs using the same emitting layer. The increase in conductivity can be attributed to the charge transfer process between the Alq3 host and the dopant. Due to the change of carrier concentration in the Alq3 films, the Fermi level of Alq3 is close to the highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO) energy levels upon p- and n-type doping, respectively, and the carrier injection efficiency can thus be enhanced because of the lower carrier injection barrier. The carriers move closer to the center energy levels of the HOMO or LUMO distributions, which increases the hopping rate for charge transport and results in an increase of charge carrier mobility. The electrons are the majority charge carriers, and both the holes and electrons can be dramatically injected in high numbers and then efficiently recombined in the p–i–n OLEDs. As a result, the improved conductivity characteristics as well as the appropriate energy levels of the doped layers result in improved electroluminescent performance of the p–i–n homojunction OLEDs. |
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| Keywords: | Organic light-emitting diode Single-layer Homojunction Doping |
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