高效蓝色梯度合金量子点发光二极管的制备与电致发光机理研究

Quantum dot light-emitting diodes (QDLEDs) have already showed wide market prospect in recent years. Among the red, green and blue QDLEDs used for the full-color display, fabricating high efficiency blue QDLEDs is one of the most challenging projects due to low emission efficiency and poor thermal stability of the QDs. Compared with commonly used core-shell QDs at present, gradient alloyed QDs exhibit low defect density inside the dots, high emission efficiency and good luminescence stability, therefore they will become a promising candidate for fabricating high efficiency QDLEDs. In this project, controlling the defect density and suppressing Auger recombination rate for improving quantum yields of QDs we will synthesize high efficiency blue emission CdZnS(Se) and CdZnSSe ternary and quaternary core-shell QDs through use of composition gradient alloyed structures. On the other hand, enhancing charge injection and tailoring carrier balance from charge transport layers we will fabricate high efficiency blue emission QDLEDs using the doping of metal ions to change the energy level structure of ZnO nanocrystal electron transport layers. The effects of element compositions, structure and thickness of gradient alloyed shell, QD size and other factors on the luminescent properties of blue QDs and their QDLEDs are systematically studied. Using steady-state and transient optical spectroscopy, the dynamics of exciton luminescence, energy transfer and Auger recombination processes in the QDs and QDLEDs are studied for better understanding the physical mechanisms about the enhancement, quenching and degradation of luminescence and improving their photoluminescence and electroluminescence stability. The in-depth study of these physical questions above will provide a good understanding about fabrication of blue QDLEDs with high efficiency and high stability.

量子点发光二极管（QDLED）具有广阔的市场前景。在全色彩显示所需的红绿蓝三基色中由于蓝光量子点的发光效率低和稳定性差等原因，因此高效蓝色QDLED制备成为一项具有挑战性的课题。同通常核壳量子点相比，梯度合金核壳量子点具有内部缺陷低、发光效率高等优点，是制备高效QDLED的理想材料。本项目拟合成蓝光CdZnS(Se)和CdZnSSe组分梯度合金核壳量子点，减少量子点的缺陷密度和抑制其俄歇复合率，提高激子发光效率，并利用金属离子掺杂改变ZnO纳米晶电荷传输层的能级结构，增强电荷注入和调控载流子平衡，构建高效蓝色QDLED；研究组分、梯度合金结构、尺寸等因素对蓝光量子点的电子结构及其LED发光性能的影响；利用稳态和瞬态光谱，研究量子点及LED的激子发光动力学，揭示发光增强、猝灭和退化的物理机制，改善发光稳定性。上述关键问题研究将为制备高效蓝色QDLED提供物理基础。

量子点发光二极管（QLED）具有广阔的市场前景。在全色彩显示所需的红绿蓝三基色中由于蓝光量子点的发光效率低和稳定性差等原因，因此高效蓝色QLED制备成为一项具有挑战性的课题。在本项目中我们制备了蓝绿红光CdSe基和InP基核壳量子点及其QLED，研究了这些量子点和QLED的发光性质及退化机理。此外，研究了CsPbX3钙钛矿量子点和QLED的发光性质。获得如下的代表性实验结果：.(a) 蓝绿红QLED的制备和性能提升：.制备了蓝绿红光QLED，研究了电致发光机理。蓝光微腔器件的最大外量子效率（EQE）达到11.2%，电流效率为2.92cd/A，亮度接近4630cd/m2。制备了蓝绿红三叠层结构QLED，其蓝绿红色的最大EQE分别为2.28，8.07和8.22%。制备了蓝绿红光InP基量子点，发光效率为46-97%，其QLED器件的最大EQE分别为1.4，6.88和13.6%。这些结果表明梯度合金壳层和器件结构提升了蓝绿红光QLED的光学性能。.(b) QLED的稳定性和退化机理：.研究了CdSe基QLED的退化机理，观察到恒流驱动器件的稳态光致发光光谱强度明显下降，建议注入电荷导致了量子点发光猝灭。采用锂和镁的共掺杂以及氧化镁壳包覆的氧化锌纳米颗粒层作为电子传输层，获得了高效、稳定的红色QLED，最大EQE为20.6%。在大电流下具有低的效率衰减，并且在1000cd/m2下具有超过11000h的超长T95寿命。结果表明优化壳层和器件结构有效地增加QLED的寿命。.(c) 钙钛矿纳米晶的发光机理和热稳定性:.合成了高效发光的Mn:CsPbX3纳米晶，研究了激子到Mn离子的能量传递效率的增强机制。利用CdCl2后处理使Mn:CsPbCl3钙钛矿纳米晶中红光Mn离子发光效率接近100%，揭示了高于高温下这些掺杂量子点的退化过程，并制备了高性能暖色白光Mn掺杂CsPbCl1.5Br1.5纳米晶LED。结果表明通过金属离子掺杂和壳层的使用可有效地提高钙钛矿量子点的发光效率。.上面的研究结果研究对于QLED在固态照明和发光显示方面的实际应用具有非常重要的科学意义。