光谱学与光谱分析, 2020, 40 (4): 1028, 网络出版: 2020-12-10  

基于混合空穴注入层的湿法制备高效蓝光热激活延迟有机发光二极管

Highly Efficient Solution Processed Blue Thermally Activated Delayed Fluorescent Organic Light-Emitting Devices with a Mixed Hole Injection Layer
杨剑 1,2赵谡玲 1,2,*宋丹丹 1,2徐征 1,2乔泊 1,2王鹏 1,2魏鹏 1,2
作者单位
1 北京交通大学发光与光信息技术教育部重点实验室, 北京 100044
2 北京交通大学光电子技术研究所, 北京 100044
摘要
在溶液法制备有机电致发光器件(OLEDs)的研究中, PEDOT∶PSS由于具有较好的成膜性与高透光性而常被用作器件的空穴注入层。 但相关研究表明, PEDOT∶PSS本身稳定性较差以及功函数较低, 这使得溶液法制备OLEDs的性能差且不稳定。 蓝色作为全彩色的三基色之一, 制备高效的蓝光器件对于实现高质量显示器件和固态照明装置必不可少。 而目前溶液法制备蓝光OLEDs的器件效率普遍较差, 针对此问题, 本文利用传统的蓝光热激活延迟荧光发光(TADF)材料DMAC-DPS作为发光层, 用溶液法制备了蓝光TADF OLEDs, 通过在PEDOT∶PSS中掺杂PSS-Na制备混合空穴注入层(mix-HIL)来提高空穴注入层的功函数, 研究其对于蓝光TADF OLEDs器件性能的影响。 首先在PEDOT∶PSS水溶液中掺入不同体积的PSS-Na溶液, 在相同条件下旋涂制膜, 进行器件制备。 通过观测各个实验组器件的电致发光(EL)光谱, 发现掺入PSS-Na后器件EL谱存在光谱蓝移的现象, 这是由于掺入PSS-Na水溶液后, mix-HIL层的厚度有所降低, 使得在微腔效应作用下, EL光谱发生蓝移。 通过对比各组器件的电流密度-电压-亮度(J-V-L)曲线及其计算所得器件的电流效率, 结果显示随着PSS-Na的掺入, 器件的亮度和电流都有所增大, 器件的电流效率也得到了提升, 当掺杂比例为0.5∶0.5(PEDOT∶PSS/PSS-Na)时提升幅度最大(亮度提升86.7%, 电流效率提升34.3%)。 通过在瞬态电致发光测试过程中施加或撤去驱动电压观测了器件EL强度的变化, 分析了在混合空穴注入层/发光层(mix-HIL/EML)界面处的电荷积累情况。 实验证明, 通过在PEDOT∶PSS中掺杂PSS-Na制备mix-HIL获得了蓝光TADF OLEDs器件性能的提升, 这是一个获得高效率溶液法制备OLEDs的可行方法。
Abstract
In the study of the solution-processed organic light-emitting devices (OLEDs), PEDOT∶PSS is often used as a hole injection layer (HIL) in OLEDs due to its good film-forming property and high light transmittance. However, related studies have shown that PEDOT∶PSS itself has defects, such as poor stability and low work function, which may result in poor and unstable device performance. At the same time, blue light is one of the three primary colors of the display, and the preparation of high efficient blue light OLEDs is indispensable for realizing high-quality white light and solid-state lighting devices. At present, most solution-processed blue OLEDs suffer from poor device performance, hence the research on the highly efficient solution-processedblue OLEDs will be of great significance. In this paper, we applied an efficient blue thermally activated delayed fluorescent (TADF) emitter DMAC-DPS to fabricate solution-processed blue TADF OLEDs, and the mixed hole injection layers (mix-HILs) were prepared by doping PEDOT∶PSS with PSS-Naand its effect on device performance of blue-light TADF OLEDs was investigated. First, we mixed different volumes of PSS-Na solution in PEDOT∶PSS aqueous solution and the mix-HILs were spin-casted under the same conditions to fabricate blue OLEDs. The electroluminescence (EL) spectrum is blue-shifted after the incorporation of PSS-Na, which can be attributed to the decrease in the thickness of the mix-HIL layer. The reduction in the thickness of the mix-HIL layer results in a blue shift in the EL spectrum under the effect of the microcavity. By comparing the current density-voltage-luminance (J-V-L) curves and its calculated current efficiency of each device, the results show that with the incorporation of PSS-Na, the brightness and current of the device increase, and the current efficiency of the device is also improved. The increase is the highest when the doping ratio is 0.5∶0.5 (PEDOT∶PSS/PSS-Na) of which the device brightness is increased by 86.7% and the current efficiency is increased by 34.3%. Finally, the behavior of internal carriers of blue OLEDs based on mix HILs with different doping ratios was observed by means of transient electroluminescence (EL) test system. Forward bias of 10 V was applied to the blue OLEDs. When the electroluminescence of the device reached a steady-state, the bias was removed, and the intensity of the delayed EL peak was observed. After a time delay of 50 μs, a reverse bias of 7 V was applied to observe the intensity of transient EL peak. It shows that after the removal of the forward bias, the EL spike of the device decreases as the PSS-Na incorporation ratio increases, indicating that the accumulated charge at the internal interface of the device is reduced. And the increase in the EL spike of the device after application of the reverse bias indicates that the injection of holes is more efficient after the incorporation of PSS-Na, and the injection barrier at the mix-HIL/EML interface is decreased. With the help of transient EL test system, the change of EL intensity of the device was observed by applying or removing the driving voltage, and the charge accumulation at the mix-HIL/light-emitting layer (mix-HIL/EML) interface was analyzed. The incorporation of PSS-Na increases the work function of the hole injection layer, and the accumulation of charge at the interface is reduced. By preparing the mix-HIL with doping PSS-Na into PEOT∶PSS, the device performance of blue TADF OLEDs is improved, which is a feasible method for obtaining high efficient solution-processed OLEDs.

杨剑, 赵谡玲, 宋丹丹, 徐征, 乔泊, 王鹏, 魏鹏. 基于混合空穴注入层的湿法制备高效蓝光热激活延迟有机发光二极管[J]. 光谱学与光谱分析, 2020, 40(4): 1028. YANG Jian, ZHAO Su-ling, SONG Dan-dan, XU Zheng, QIAO Bo, WANG Peng, WEI Peng. Highly Efficient Solution Processed Blue Thermally Activated Delayed Fluorescent Organic Light-Emitting Devices with a Mixed Hole Injection Layer[J]. Spectroscopy and Spectral Analysis, 2020, 40(4): 1028.

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