基于能量传递原理构建胶体半导体量子点薄膜及其LED的发光性质研究

Understanding the control of energy transfer and charge separation processes in the highly efficient luminescent colloidal semiconductor quantum dot (QD) based thin films used as emissive layers and optimizing the structures of the QDs and their light-emitting diodes (LEDs) is the key scientific question for obtaining highly efficient QD-LEDs. In this work several kinds of core/shell QDs with the surface modification of semiconductor shells with different thicknesses and organic functional molecules and their high performance films with controlled thicknesses are used to control the electronic coupling between QDs for achieving highly efficient QD-LEDs, realizing the control of charge/energy transfer from organic/inorganic charge transport materials to the QD films and charge transport/energy transfer between QDs for enhancing the quantum efficiencies of exciton emissions in the films. The research project includes the following works: 1)the preparation of highly efficient photoluminescent core/shell QDs and their high performance solid films on organic/inorganic charge transport layers as well as the measurement of the photo/thermal stability; 2) the study of energy/charge transfer in QD thin films for understanding the effect of the QD structures on the luminescent, electrical and structural properties of the QD films; 3) the study on the improvement of the energy transfer and charge injection processes between the QD layers and charge transport materials for exploring the relation between the properties of the QD films and the performacence of QD-LEDs. These make us better understand the control of the charge transfer, carrier transport and exciton energy transfer for designing and preparing the optimal core/shell QDs and their thin films. Therefore, the study on these questions above is very important for us to further optimize thes structures of luminescent QDs and their devices for significantly improving the performance of the present LEDs as the next generation solid state lighting and display.

利用能量传递和电荷分离原理，优化量子点结构和构建高性能的胶体半导体量子点薄膜发光层是获得高效率量子点发光二极管(LED)的关键科学问题。本项目将利用各种半导体壳层和有机功能分子，调控量子点之间的电子耦合，制备高性能量子点薄膜发光层，实现对从有机/无机电荷传输材料到发光层的电荷注入/能量传递、量子点层中载流子传输/激子能量传递和激子复合发光过程的调控以获得高效量子点LED。合成各种高效发光的核壳量子点和在有机/无机电荷传输层上制备量子点固体以及测定它们的光/热稳定性；研究量子点薄膜中的能量传递和电荷分离等过程，分析量子点的壳层结构和表面功能分子对薄膜的发光效率和结构的影响；研究有机/无机电荷传输材料到量子点发光层的能量传递和电荷注入效率改善机制，理解量子点薄膜性质与多层结构量子点LED的性能关系。上述关键科学问题的研究对量子点及其器件结构优化和性能改进及量子点LED的商品化提供物理基础。

量子点发光二极管（LED）具有尺寸和组分调谐的发光，因此有望应用于新一代照明光源和显示。利用能量传递和电荷转移原理，优化量子点结构，构建高性能量子点薄膜发光层是获得高效率量子点LED的关键科学问题。在本项工作中，我们制备了红绿蓝和白光量子点及LED，研究了其量子点薄膜中的能量传递和电荷转移过程。详细内容如下：.1）制备了CdSe/CdZnS/ZnS和ZnSe/ZnS等量子点LED，研究了量子点薄膜及其与有机电荷传输材料之间的能量传递和电荷转移，调控量子点及其LED结构以提高LED的性能。发现：利用厚壳层包覆的量子点发光层的量子点LED具有更好的电致发光效率；使用双层空穴传输层CBP和mCP，可减小电荷注入势垒和提高注入效率；在CdSe量子点层与有机空穴传输层CBP之间引入薄的电子传输层TPBi，可提高其性能指标如电流和功率效率30%；获得红光CdSe量子点LED的电流效率超过16 cd/A, 最大亮度接近40000 cd/m2。获得倒置结构的蓝光ZnSe/ZnS量子点LED的电流效率和最大亮度分别是0.51 cd/A和1170 cd/m2。.2）利用蓝光 GaN芯片与量子点结合，制备了基于CuMn双掺杂和Cu掺杂的ZnInS量子点的白光LED，其流明效率为73 lm/W，色温为5090 K，显色指数高达95。另一方面，研究了Mn掺杂的ZnS、ZnSe和ZnSSe量子点薄膜的变温发光光谱，发现在500 K温度下Mn:ZnS的发光几乎没有被热猝灭。此外，研究了Cu掺杂的ZnInS量子点薄膜的发光热稳定性。这些结果表明，基质的能级结构和壳层厚度影响了离子发光的热稳定性，包覆厚壳层可有效地提高掺杂量子点的发光热稳定性。.3）研究了CdSe、CuInS2和掺杂ZnInS量子点或薄膜与TiO2、石墨烯和有机功能分子之间的壳层结构依赖的能量传递和电荷转移过程。尤其发现由于大的Stokes效应，Cu或Mn掺杂ZnInS量子点薄膜中的能量传递过程可以忽略不计。而本征半导体CdSe/ZnS量子点中的能量传递效率很高，导致其薄膜的荧光效率明显下降。这些实验结果表明，通过增加壳层的厚度，可有效地提高量子点成膜时的发光效率。. 上述的研究结果对量子点LED在照明和显示的实际应用提供了物理基础和制备技术。