Rare Earth Complex as Electron Trapper and Energy Transfer Ladder for Efficient Red Iridium Complex Based Electroluminescent Devices

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• 作者：Liang Zhou ; Leijiao Li ; Yunlong Jiang ; Rongzhen Cui ; Yanan Li ; Xuesen Zhao ; Hongjie Zhang
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：July 29, 2015
• 年：2015
• 卷：7
• 期：29
• 页码：16046-16053
• 全文大小：518K
• ISSN：1944-8252

文摘

In this work, we experimentally demonstrated the new functions of trivalent rare earth complex in improving the electroluminescent (EL) performances of iridium complex by codoping trace Eu(TTA)₃phen (TTA = thenoyltrifluoroacetone, phen = 1,10-phenanthroline) into a light-emitting layer based on PQ₂Ir(dpm) (iridium(III)bis(2-phenylquinoly-N,C^{2鈥?/sup>)dipivaloylmethane). Compared with a reference device, the codoped devices displayed higher efficiencies, slower efficiency roll-off, higher brightness, and even better color purity. Experimental results demonstrated that Eu(TTA)₃phen molecules function as electron trappers due to its low-lying energy levels, which are helpful in balancing holes and electrons and in broadening recombination zone. In addition, the matched triplet energy of Eu(TTA)₃phen is instrumental in facilitating energy transfer from host to emitter. Finally, highly efficient red EL devices with the highest current efficiency, power efficiency and brightness up to 58.98 cd A鈥? (external quantum efficiency (EQE) of 21%), 61.73 lm W鈥? and 100870 cd m鈥?, respectively, were obtained by appropriately decreasing the doping concentration of iridium complex. At certain brightness of 1000 cd m鈥?, EL current efficiency up to 51.94 cd A鈥? (EQE = 18.5%) was retained. Our investigation extends the application of rare earth complexes in EL devices and provides a chance to improve the device performances.}