结构优化对量子点发光二极管性能的影响研究

发布时间：2018-02-28 11:47

本文关键词： 配体交换量子点发光二极管氧化钼　出处：《河南大学》2015年硕士论文　论文类型：学位论文

【摘要】：胶体量子点(colloidal quantum dots,简称CQDs)相对于有机发光染料和无机荧光粉具有显著优势,如其本身具有的较宽的吸收范围、高的荧光量子效率、优异的光学和化学稳定性、窄的发射带宽、发射波长简单可调等出色光学特性,使得其在光电、光伏和生物标记等领域具有广泛的应用空间,尤其是在发光二极管方面的应用,量子点发光二极管将会引领显示屏和固态照明行业新一代产品的开发。现有量子点基的发光二极管(QLEDs)多采用溶液中直接合成出来的包覆长链有机配体的量子点作为发光层,遗憾的是这些长链配体一方面形成有机绝缘层降低导电能力、增大电荷注入势垒,另一方面还会增大量子点与电荷传输材料间距,降低激子能量转移的效率,以上两个方面均不利于QLEDs性能的提高。此外,QLEDs一般采用有机半导体材料PEDOT:PSS作为空穴注入层,这种材料虽然导电能力很好但易吸湿氧化、稳定性差且可以腐蚀ITO电极,极大地影响了器件的寿命。本论文则针对以上所述的两方面问题开展了研究。针对量子点表面包覆长链配体对QLEDs性能的影响问题,我们选取高荧光量子产率(QY)的蓝色Zn Cd Se/Zn Se/Zn Se S/Zn S核壳量子点,使用短链的正辛硫醇(OT)配体通过配体交换替换掉量子点表面原有的长链油酸(OA)配体,利用傅里叶红外光谱仪、透射电镜(TEM)和动态光散射仪(DLS)验证配体交换结果。然后把交换成功后的量子点作为发光层构建了QLEDs并进行了测试。器件表现出了较佳的性能,最大亮度为11600 cd/m2、峰值电流效率为2.38 cd/A、最高外量子效率(external quantum efficiency,EQE)为4.6%,并且电致光谱(EL)随着电压的升高并没有出现红移和半峰宽(FWHM)变宽的现象,EL与荧光光谱(PL)也具有较好的匹配性。针对有机半导体材料PEDOT:PSS作为空穴注入材料存在的问题,我们引入了导电性好、性质较为稳定的氧化钼(Mo O3)作为空穴注入层。我们通过溶液法合成出来了尺寸分布较窄、分散性较好的Mo O3纳米颗粒,使用了X射线粉末衍射仪(XRD)、X射线光电子能谱仪(XPS)和TEM对Mo O3样品进行了表征。接下来我们使用Mo O3作为空穴注入层构建了QLED。通过测试发现,相对于传统单纯使用PEDOT:PSS作为空穴注入层的对比器件,以Mo O3作为空穴注入层的QLED的亮度、效率等均有一定程度的改善,最大亮度达到21160 cd/m2、电流效率为2.45 cd/A、开启电压为2.2 V。此外,器件在连续通电测试下具有较好的稳定性且相对对比器件寿命提高了四倍以上。
[Abstract]:Colloidal quantum Dots (CQDs) have significant advantages over organic luminescent dyes and inorganic phosphors, such as their wide absorption range, high fluorescence quantum efficiency, excellent optical and chemical stability, narrow emission bandwidth. The excellent optical properties, such as simple and adjustable emission wavelength, make it have a wide range of applications in the fields of photoelectricity, photovoltaic and biomarker, especially in the field of light-emitting diodes. Quantum dot light emitting diodes (QDDs) will lead the development of a new generation of products in the field of display screen and solid-state lighting. The existing QD-based LEDs often use quantum dots coated with long chain organic ligands directly in solution as the luminescent layer. Unfortunately, on the one hand, these long-chain ligands form an organic insulating layer to reduce the conductivity and increase the charge injection barrier, on the other hand, they also increase the distance between the quantum dots and the charge transport materials, and reduce the efficiency of exciton energy transfer. The above two aspects are not conducive to the improvement of QLEDs performance. In addition, the organic semiconductor material PEDOT:PSS is generally used as the hole implantation layer. Although the material has good conductivity, it is easy to absorb moisture and oxidize, and its stability is poor and can corrode the ITO electrode. The lifetime of the device is greatly affected. In this paper, two problems mentioned above are studied. The effect of long chain ligand coated on the surface of quantum dots on the performance of QLEDs is discussed. The blue Zn CD Se/Zn Se/Zn se / Zn S core-shell quantum dots with high fluorescence quantum yield (QYY) were selected. The short chain n-octylmercaptan (OTO) ligand was used to replace the original long chain oleic acid (OAC) ligand on the surface of quantum dots by ligand exchange, and Fourier transform infrared spectroscopy (FTIR) was used. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to verify the ligand exchange results. Then QLEDs was constructed and tested by using the successfully exchanged quantum dots as the luminescent layer. The maximum luminance is 11600 CD / m ~ 2, the peak current efficiency is 2.38 CD / A, the external quantum efficiency EQE is 4.6, and the electroluminescence spectrum (ELL) is not red shift and half peak width FWHM broadening with the increase of voltage. Good matching. In view of the problem of the organic semiconductor material PEDOT:PSS as the hole injection material, Moo _ 3 nanoparticles with narrow size distribution and good dispersion were synthesized by solution method. The samples of MoO3 were characterized by X-ray powder diffractometer (XRDX) and TEM. Then we used MoO3 as a hole injection layer to construct QLED. Compared with the conventional contrast devices using PEDOT:PSS as the hole injection layer, the brightness and efficiency of the QLED implanted with MoO3 as the hole implantation layer have been improved to some extent. The maximum brightness is 21160 cd/ m2, the current efficiency is 2.45 cd/ / A, the opening voltage is 2.2V. The device has good stability under continuous electrification test and the relative lifetime of the device is increased by more than four times.
【学位授予单位】：河南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN312.8;O471.1

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