CdSe/ZnSe/ZnS核壳结构量子点的壳层厚度对发光二极管性能的影响

Due to the excellent optical properties of quantum dots (QDs), QDs based light-emitting diodes (QLED) will have important application prospects in display and lighting. The efficiency of QLED is decided on the charge injection efficiency and charge balance. The energy band structure of shell material and its shell-thickness decide the height and width of energy barrier that the charges should surmount, respectively. Therefore, it is very important for QLED to choose appropriate shell material and shell-thickness of QDs. The high HOMO energy level of ZnSe could improve injection efficiency of holes, and then enhance the charge balance. ZnSe could not localize the carriers, while ZnS could localize the carriers effectively. Therefore, in this project, CdSe/ZnSe/ZnS core/shell QDs with very thin outer shell, which will be employed as the emitting layer of QLED, will effectively enhance hole injection efficiency, charge recombination efficiency and stability, and then improve the efficiency of QLED greatly.

由于荧光量子点所具有的优异的光学性能，量子点发光二极管（QLED）将在显示、照明等领域具有广阔的应用前景。QLED器件的效率决定于载流子的注入效率和注入平衡。因为量子点壳层材料的能级结构和厚度分别决定了载流子注入量子点过程中需要克服的势垒高度和宽度。因此，选用合适的壳层材料及壳层厚度对于构筑高性能的QLED器件至关重要。ZnSe具有较高的HOMO能级，能够提高QLED中的空穴注入效率和载流子的注入平衡。但是其对载流子的限域能力较差，会导致载流子的复合效率降低、器件的稳定性变差，而ZnS对载流子的限域能力较强。因此，本项目将采用CdSe/ZnSe/ZnS核壳结构量子点作为发光活性材料构筑QLED器件，以ZnSe为中间壳层，利用其较高的HOMO能级提高空穴的注入效率，以极薄的ZnS为外壳层，更有效地限域载流子，提高载流子的复合几率以及量子点和器件的稳定性，从而有效地提高QLED器件的性能。

由于量子点发光二极管（QLED）具有单色性好、稳定性佳等优点，其在显示、照明等领域将具有广阔的应用前景。QLED 器件的效率取决于载流子的注入效率和注入平衡。本质上，QLED 器件的电荷注入效率和注入平衡均与量子点外层包覆的壳层材料有关。因此，本项目采用CdSe/ZnSe/ZnS核壳结构量子点作为发光活性材料构筑QLED器件，以ZnSe为中间壳层，利用其较高的价带顶能级提高空穴的注入效率，以ZnS为外壳层，更有效地限域载流子，提高载流子的复合效率以及量子点和器件的稳定性，从而有效地提高QLED器件的性能。通过调整优化中间壳层、外壳层厚度以及界面的合金化等，构筑的基于CdSe/ZnSe/ZnSeS/ZnS量子点的器件其最高亮度及最大外量子效率分别达到550,000 cd/m2和20.06%，基于ZnCdSe/ZnSe/ZnS量子点的器件其最大外量子效率达到23%，且具有较低的效率滚降。