Highly efficient green, blue, and white phosphorescent inverted organic light-emitting diodes by improving charge injection and balance,Journal of Materials Chemistry C

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Highly efficient green, blue, and white phosphorescent inverted organic light-emitting diodes by improving charge injection and balance
Journal of Materials Chemistry C ( IF 5.7 ) Pub Date : 2017-09-06 00:00:00 , DOI: 10.1039/c7tc02795h
Hyunkoo Lee _{1,

2,

3,

4} , Min-Jae Maeng _{4,

5,

6,

7} , Jong-Am Hong _{4,

5,

6,

7} , Rokeya Najnin _{4,

5,

6,

7} , Jaehyun Moon _{1,

2,

3,

4} , Hyunsu Cho _{1,

2,

3,

4} , Jonghee Lee _{1,

2,

3,

4} , Byoung-Gon Yu _{1,

2,

3,

4} , Yongsup Park _{4,

5,

6,

7} , Nam Sung Cho _{1,

2,

3,

4}

Affiliation

To improve the performance of inverted organic light-emitting diodes (OLEDs), we investigated the electrical, optical, and interfacial properties of three different lithium (Li)-doped electron transport materials (ETMs): tris(3-(3pyridyl)mesityl)borane (3TPYMB), 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB), and 1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPB). The electron injection barriers (EIBs) between indium-tin-oxide and the ETMs were deduced for both pristine and Li-doped cases from ultraviolet photoelectron spectroscopy measurements and optical band gap values. The Li-doped ETMs showed EIB values of approximately 0.03 eV, 0.77 eV, and 0.81 eV for 3TPYMB, TmPyPB, and BmPyPB, respectively, which are much lower than those of their pristine counterparts of 0.94 eV, 1.14 eV, and 1.48 eV, respectively. The Li-doped ETMs were employed as electron injection layers (EILs) of inverted bottom-emission OLEDs (IBE-OLEDs) with green phosphorescence. IBE-OLEDs with 3TPYMB, TmPyPB, and BmPyPB EILs exhibited driving voltages of 3.6 V, 4.0 V, and 4.5 V at 1000 cd m⁻² and maximum external quantum efficiencies (EQEs) of 20.3%, 19.7%, and 16.5%, respectively. From the low EIB of Li-doped 3TPYMB, we also demonstrated highly efficient blue and white phosphorescent IBE-OLEDs. We optimized the device structure to improve the charge balance and out-coupling efficiency by changing the hole injection layer and the thickness of the hole and electron transport layers with optical simulation. The blue device showed a maximum EQE and luminous current efficiency of 22.9% and 43.1 cd A⁻¹, respectively. In addition, the white device exhibited a high EQE and luminous efficacy of 19.3% and 37.8 lm W⁻¹ at 3 mA cm⁻² (∼1000 cd m⁻²), respectively. To the best of our knowledge, the efficiencies of these green, blue, and white devices are the highest values obtained to date with a low driving voltage for IBE-OLEDs without any additional light-extraction structure. Since the Li-doped 3TPYMB has an extremely low EIB and shows good device performance, it can be utilized as an effective EIL in inverted-structure devices.

中文翻译：

通过改善电荷注入和平衡，实现高效的绿色，蓝色和白色磷光反向有机发光二极管

为了提高反向有机发光二极管（OLED）的性能，我们研究了三种不同的掺杂锂（Li）的电子传输材料（ETM）的电学，光学和界面特性：tris（3-（3pyridyl）mesityl）硼烷（3TPYMB），1,3,5-三（间吡啶-3-基-苯基）苯（TmPyPB）和1,3-双（3,5-二吡啶-3-基-苯基）苯（BmPyPB ）。通过紫外光电子能谱测量和光学带隙值，推导出了氧化铟锡和ETM之间的电子注入势垒（EIB），用于原始和掺杂Li的情况。掺锂的ETM对3TPYMB，TmPyPB和BmPyPB的EIB值分别约为0.03 eV，0.77 eV和0.81 eV，远低于其原始的0.94 eV，1.14 eV和1.48 eV的EIB值，分别。掺锂的ETM被用作具有绿色磷光的倒底发射OLED（IBE-OLED）的电子注入层（EIL）。具有3TPYMB，TmPyPB和BmPyPB EIL的IBE-OLED在1000 cd m时表现出3.6 V，4.0 V和4.5 V的驱动电压^-2和最大外部量子效率（EQE）分别为20.3％，19.7％和16.5％。从掺锂3TPYMB的低EIB，我们还展示了高效的蓝色和白色磷光IBE-OLED。我们通过光学仿真更改了空穴注入层以及空穴和电子传输层的厚度，从而优化了器件结构，以改善电荷平衡和输出耦合效率。蓝色器件显示的最大EQE和发光电流效率分别为22.9％和43.1 cd A^-1。此外，白色器件在3 mA cm^-2（〜1000 cd m^-2）下具有很高的EQE和19.3％的发光效率和37.8 lm W^-1的发光效率。），分别。据我们所知，这些绿色，蓝色和白色器件的效率是迄今为止获得的最高值，而对于IBE-OLED而言，其驱动电压很低，而没有任何其他的光提取结构。由于掺锂的3TPYMB具有极低的EIB并显示出良好的器件性能，因此可以将其用作倒装结构器件中的有效EIL。

更新日期：2017-09-18

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