无镉低毒性半导体量子点材料及LED器件

Quantum-dot light-emitting diodes (LEDs) possess high electroluminescence efficiencies, color-purity and other advantages, which have become an up-rising star as a powerful supplementary to OLEDs in the next-generation display and solid-state lighting technologies. However, the current quantum-dot LEDs are mainly based on quantum-dots containing heavy-metal elements (such as CdSe, etc), which goes against the large-scale production and commercial applications. Therefore, it is necessary to develop cadmium-free low-toxic quantum-dot-based materials and LEDs. The research objects of the proposal include different types of low-toxic quantum-dot-based materials and LEDs, such as I-III-VI-based and InP-based quantum dots and so on. The research content of this proposal is carried out aiming to some scientific problems in the synthesis of low-toxic quantum dots and fabrication of quantum-dot LEDs. The main research contents of the proposal can be summarized as follows: controlled-synthesis and surface modification of low-toxic quantum dots, the relationship between the nanostructures of the quantum dots and their optical properties, the influence rules of the process optimization including device structures and interfacial control on the optoelectronic parameters of the quantum-dot LEDs and the device physics problems, such as the carriers injection, transportation and recombination in the devices. The optoelectronic performance of the quantum-dot LEDs will be improved comprehensively by developing new technologies and methods in the materials synthesis and device processing, which can offer theoretical and technological support for the shift of the fundamental research to industrialization of the low-toxic quantum-dot LEDs.

量子点LED由于其发光效率高、色纯度好等优势有望作为有机电致发光二极管（OLED）的有力补充力量成为下一代照明和显示领域的后起之秀。然而，目前量子点LED主要使用含有镉元素等重金属元素的量子点，不利于大规模推广和应用。因此，发展无镉低毒性量子点材料及LED器件是非常必要的。本项目以不同类型的无镉低毒性量子点（主要包括I-III-VI族为基础的量子点和InP为代表的III-V族量子点）作为主要研究对象，针对目前无镉量子点合成及LED器件中存在的一些科学问题展开，主要研究无镉量子点材料的可控生长与表面改性，材料的不同纳米结构与光学性能的关系，量子点LED的工艺优化如器件结构与界面调控等对器件光电性能指标的影响规律以及器件中载流子注入、输运和复合等器件物理问题。从材料合成与器件工艺两方面发展新技术、新方法来全面提高无镉低毒性量子点LED的光电性能，为其从基础研究向产业化转变提供理论与技术支持。

无镉量子点具有高发光效率、高色纯度、绿色环保的潜力，有望作为下一代照明和显示材料，但低毒性无镉量子点的发光性能与镉系量子点相比还有较大差距。本项目以无镉量子点材料复杂结构的控制制备及发光性能、表面改性以及器件工艺优化作为主要研究内容，由北京交通大学，上海大学和北京理工大学共同完成。取得的主要成果包括：1)揭示了以Cu-In-Zn-S为代表的I-III-VI族量子点、以InP为代表的III-V族量子点的合成过程中形成缺陷态的根本原因，并通过多次离子注入和壳层包覆提升了材料的发光性能，其光致发光量子产率可达90%；2)从形核与生长同时出发，提出了一种反应活性控制的外延生长策略，制备出发光波长超过460 nm的大尺寸ZnSe量子点，进一步制备出高荧光效率的大尺寸ZnSe/ZnS核壳纳米晶，其光致发光量子产率为60%；3)采用不同离子掺杂和钝化策略，解决了ZnO纳米颗粒表面大量缺陷态和载流子输入不平衡的问题，并采用双空穴传输层构筑了阶梯型空穴注入势垒，使Cu-In-Zn-S基量子点LED的电流效率达到了13.1 cd/A；4)通过在InP表面上引入一层准ZnSe壳层降低了其表面缺陷态，在此基础之上构筑的红光和绿光InP基量子点LED的最大电流效率分别为16.9和41.1 cd/A；5)对钙钛矿量子点表面配体进行交换，有效改善了LED器件中载流子注入和输运的问题，开发了量子点的无烯烃溶剂、双配体、溴化配体制备工艺，制备出高色纯度且高效率的钙钛矿LED；提出了一种小分子界面修饰策略，有效消除了钙钛矿层中的空隙，得到大面积绿光钙钛矿LED，峰值外量子效率超过16%。