Hybrid organic-inorganic light-emitting diodes based on a polythylenimine interlayer

被引：0
|
作者：
Lei Y. [1 ]
Wang R. [1 ]
Fan C. [1 ]
Yang X. [1 ]
机构：
[1] School of Physical Science and Technology, Southwest University, Chongqing
来源：
Yang, Xiaohui (xhyang@swu.edu.cn) | 1600年 / Chinese Academy of Sciences卷 / 61期
关键词：
Electron injection interlayer; Hybrid organic-inorganic light emitting devices; Light emitting polymers; Solution- processed small molecule emissive layer;
D O I：
10.1360/N972015-00065
中图分类号：
学科分类号：
摘要：
Implementation of a polyethylenimine ethoxylated (PEIE) interlayer significantly enhances electron injection efficiency from ZnO into light emitting polymers including a blue light emitting polymer with relatively low electron affinity, verified by comparison of current density-voltage characteristics of the electron-only devices with or without a PEIE interlayer. Ultraviolet photoelectron spectroscopy measurements reveal that PEIE forms interfacial dipoles and reduces the work function of ZnO by ca. 1.2 eV, thus facilitating electron injection into light emitting polymers. Neutralized amines rather than protonated amines are responsible for the formation of interfacial dipoles as manifested by N1s core level spectra of the ZnO/PEIE sample. Luminance efficiency of hybrid organic-inorganic light emitting devices employing PEIE interlayer is similar to that of the analogous conventional devices with low work-function metal cathode due to electron injection promoting and hole/exciton-blocking properties of PEIE. Compared to Cs2CO3, PEIE, which possesses similar surface energy to the organic materials and can form homogeneous film, is expected to collaborate with the adjoining organic layers, without significantly interrupting their morphology, especially for those containing low molecular weight components such as phosphorescent emitters. We envisage that this valuable tribute enables the use of small molecule light emitting materials for device fabrication and is particularly beneficial for the effective introduction of phosphorescent emitters into the emission layer of organic-inorganic light emitting devices. Phosphorescent hybrid organic-inorganic light emitting devices with solution-processed 4,4',4''-tris(carbazol-9-yl)triphenyl-amine (TCTA): 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7): Ir-complex emission layer show the maximum luminance efficiency of 64 cd/A and external quantum efficiency of 19.1%, which represent the best efficiency for organic-inorganic light emitting devices reported so far and are approximately 4 times higher than those of the analoguous devices using Cs2CO3 electron injection layer. The luminance efficiency of the devices is rather independent of Ir-complex concentration, indicating balanced hole and electron transport in the emission layer and broad emission zone due to the use of hole-transporting TCTA and electron-transporting OXD-7 as the co-hosts, together with the confinement of the emission zone inside the emission layer and homogeneous dispersion of Ir-compex into the TCTA: OXD-7 host. Furthermore, the efficiency roll-off at high luminance is rather small, for example, the luminance efficiency at 10000 cd/m2 is 62 cd/A, maintaining 97% of the maximum luminance efficiency. Our findings enrich the organic materials for the preparation of organic-inorganic light emitting devices and pave the way for the future improvement of device efficiency and stability. © 2016, Science Press. All right reserved.
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页码：740 / 747
页数：7
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