Efficient small molecular organic light emitting diode with graphene cathode covered by a Sm layer with nano-hollows and n-doped by Bphen:Cs2CO3 in the hollows
Efficient small molecular organic light emitting diode with graphene cathode covered by a Sm layer with nano-hollows and n-doped by Bphen:Cs2CO3 in the hollows
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DOI：
10.1088/1361-6528/aa55e5
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发表时间：
2017-01
期刊：
影响因子：
3.5
通讯作者：
L. Yao;Lei Li;Laixiang Qin;Yaoguang Ma;W. Wang;Hu Meng;Weifeng Jin;Yilun Wang;Wanjin Xu-
中科院分区：
文献类型：
--
作者：
L. Yao;Lei Li;Laixiang Qin;Yaoguang Ma;W. Wang;Hu Meng;Weifeng Jin;Yilun Wang;Wanjin Xu-
石墨烯是有机发光二极管（OLED）电极的理想材料。石墨烯具有非常高的功函数，约为4.5eV，并且在用作OLED的阳极时已经被广泛研究。为了使用石墨烯作为阴极，石墨烯阴极和电子传输层之间的电子注入势垒必须足够低。用4，7-二苯基-1，10-邻菲咯啉（Bphen）：Cs2 CO 3对石墨烯进行n掺杂是一种很好的方法，但Bphen：Cs2 CO 3与n掺杂石墨烯之间的电子注入势垒仍然很高，达不到1.0 eV。在这项工作中，为了进一步降低电子注入势垒，提出了一种新的方法。在石墨烯阴极上，沉积具有大量纳米中空的Sm层，随后沉积Bphen：Cs2 CO 3层。Bphen：Cs_2CO_3对石墨烯进行了n掺杂，提高了石墨烯的费米能级。纳米Sm层非常容易被氧化。吸附在石墨烯表面的氧可以与Sm反应形成O−-Sm+偶极层。在没有纳米空洞的Sm氧化物偶极子层的区域上，偶极子层可以进一步降低电子注入势垒。电子倾向于主要通过偶极层存在的较低电子势垒注入。基于这一思想，本文提出了一种有效的倒置型小分子有机电致发光器件，其结构为：石墨烯/1 nm Sm层（具有大量纳米空洞）/Bphen：Cs2 CO 3/Alq 3：C545 T/NPB/MoO 3/Al。具有1 nm Sm层的OLED的最大电流效率和最大功率效率分别是没有任何Sm层的参考OLED的最大电流效率和最大功率效率的约2倍和3倍。
Graphene is a favorable candidate for electrodes of organic light emitting diodes (OLEDs). Graphene has quite a high work function of ∼4.5 eV, and has been extensively studied when used as anodes of OLEDs. In order to use graphene as a cathode, the electron injection barrier between the graphene cathode and the electron transport layer has to be low enough. Using 4,7-diphenyl-1,10-phenanthroline (Bphen):Cs2CO3 to n-dope graphene is a very good method, but the electron injection barrier between the n-doped graphene and Bphen:Cs2CO3 is still too high to be ∼1.0 eV. In this work, in order to further reduce the electron injection barrier, a novel method is suggested. On the graphene cathode, a Sm layer with a lot of nano-hollows, and subsequently a layer of Bphen:Cs2CO3, are deposited. The Bphen:Cs2CO3 can n-dope graphene in the nano-hollows, and the Fermi level of the graphene rises. The nano Sm layer is very easily oxidized. Oxygen adsorbed on the surface of graphene may react with Sm to form an O−–Sm+ dipole layer. On the areas of the Sm oxide dipole layer without nano-hollows, the electron injection barrier can be further lowered by the dipole layer. Electrons tend to mainly inject through the lower electron barrier where the dipole layer exists. Based on this idea, an effective inverted small molecular OLED with the structure of graphene/1 nm Sm layer with a lot of nano-hollows/Bphen:Cs2CO3/Alq3:C545T/NPB/MoO3/Al is presented. The maximum current efficiency and maximum power efficiency of the OLED with a 1 nm Sm layer are about two and three times of those of the reference OLED without any Sm layer, respectively.