电荷生成层中引入超薄金属Ag层对串联有机发光二极管性能的提升

Enhancement of tandem organic light-emitting diode performance by inserting an ultra-thin Ag layer in charge generation layer

为了获得高效、长寿命的白光有机发光二极管(white organic light-emitting diode,WOLED),一种方法是将不同颜色的发光单元通过电荷生成层(charge generation layer,CGL)串联起来获得白光,即串联WOLED.其中,CGL的选择与设计是高性能串联白光器件的关键.本文首先从绿光OLED着手,通过在CGL层中引入超薄的Ag金属层,获得了高效、长寿命的串联器件.引入超薄Ag金属层的绿光串联OLED的最大亮度达到了290000 cd/m^2,分别是单层器件和无超薄Ag金属层器件的2.9倍与2.4倍;在1000 cd/m^2下,引入超薄Ag金属层的器件电流效率达到了59.5 cd/A,相比于无超薄金属层的串联器件的58.7 cd/A,以及非串联的单层器件的17.1 cd/A,分别增加了1.4%与248%;同时,与无超薄层的串联器件相比,引入超薄Ag金属层的器件工作电压从8.6 V降为7.2 V;功率效率从21.5 lm/W上升为26 lm/W.特别地,在初始测试亮度为10000 cd/m^2的条件下,包含超薄Ag金属层的串联器件的工作寿命T80超过了250 h,与无超薄层串联器件仅2.7 h寿命相比,提高近100倍.最后,我们使用优化后的CGL制备出高性能串联WOLED,在1000 cd/m^2下,电流效率达到了75.9 cd/A,功率效率达到了36.1 lm/W,且10000 cd/m^2的初始亮度下T80有77 h.这些优异的器件性能归结于超薄金属层的引入,抑制了Bphen:Cs CO_3与HAT-CN在界面处的相互扩散,同时也促进了载流子的生成与传输.这一结果为设计高效且稳定的WOLED提供了有效的思路.

White organic light-emitting diodes（WOLEDs） have attracted both scientific and industrial interest in the solidstate lighting and display applications due to their exceptional merits, such as high luminances, low power consumptions,high efficiencies, fast response times, wide-viewing angles, flexibilities and simple fabrications. The power efficiency of WOLED has been step-by-step improved in the last 20 years, however, the lifetime of WOLED is still unsatisfactory,which greatly restricts the further development of WOLED. In general, the tandem structure can be used to obtain high-efficiency and long-lifetime WOLED. One of the most important features of this kind of structure is that the different-colors emitting units can be connected by the charge generation layer. Therefore, the key to achieving a highperformance tandem device is how to design the charge generation layer. In this paper, we first develop a tandem green OLED by using an effective charge generation layer with an ultra-thin Ag layer between 4, 7-diphenyl-1, 10-phenanthroline：Cs CO_3 and hexaazatriphenylenehexacabonitrile, achieving high luminance, low voltage, high efficiency and long lifetime. The green tandem device with ultra-thin Ag layer（device C） obtains a highest luminance of 290000cd/m2, which is 1.4 and 1.9 times higher than those of the tandem devices without ultra-thin Ag（device B） and singleunit device（device A）, respectively. The driving voltage of device C is 7.2 V at 1000 cd/m2, 1.4 V lower than that of device B. Besides, the maximum current efficiency of device C is 60.4 cd/A, which is 2.4% and 220% higher than those of device B（59 cd/A） and device A（18.7 cd/A）, respectively. The power efficiency of device C is 26 lm/W, which is 21%higher than that of device B（21.5 lm/W）. Moreover, the lifetime（T80） of device C reaches 250 h at an initial luminance of 10000 cd/m2, which is nearly 100 times higher than that of device B（2.7 h）. Finally, we fabricate a white tandem device with the optimized charge generation layer, achieving a current efficiency and power efficiency of 75.9 cd/A and36.1 lm/W at 1000 cd/m2, respectively. In addition, the lifetime（T80） is 77 h at an initial luminance of 10000 cd/m2. All the excellent performances are ascribed to the introduction of the ultra-thin Ag layer into the charge generation layer,which can effectively block the charge generation layer from diffusing. This exciting discovery can provide an effective way to design efficient and stable WOLED, which is beneficial to the solid-state lighting and display markets.