II-VI族半导体量子点表面缺陷特征、运移规律和抑制策略

II-VI semiconductor quantum dots are typical quasi-zero-dimensional defective systems whose key physiochemical properties are closely dependent on the classification, origin and activity of the defect states. Moreover, defect-induced fluorescence blinking hampers the application of single quantum dots. Focusing on ME (M = Zn and Cd, E = S, Se and Te) semiconductor quantum dots and using first-principles calculations, this project studies : (1) the characteristics and formation mechanism of defect states of the quantum dots, as well as the equlibrium between vacancies, charges and defects, and analyzes their thermodynamic states and intrinsic features ; (2) the interaction between defects and their migration patterns, explores the variations in intrinsic defects after changing their thermodynamic states and forming new complexes by adding ligands, and anlyzes the combination mechanism for two defects ; (3) the fluoresence quenching resulted from the defects in quantum dots and its compression strategies, analyzes the key the structural and electronic factors that have influences on the fluoresence quatum yield, reveals the physical mechanism of defect-induced fluoresence quenching, and explores the stategies for compressing fluoresence quenching by adding ligands or shells to the cores. Our findings will provide theoretical evidences for the design and preparation of quantum dots devices with high fluoresence quantum yields.

II-VI族半导体量子点是典型的准零维缺陷体系，其关键物理化学性质与缺陷态的类型、成因、活性等密切相关，由缺陷导致的荧光闪烁现象限制了单量子点的应用。本申请项目聚焦ME（M = Zn 和 Cd； E = S、Se 和 Te）量子点，利用第一性原理计算研究：（1）量子点缺陷态的特征及形成机制，缺陷形成过程的空位平衡、电荷平衡和缺陷平衡，分析缺陷的热力学状态及本征特征；（2）量子点缺陷间作用及缺陷运移规律，探索在温度等热力学状态发生改变及与配体形成新的复合物后缺陷本征特征的演化规律，分析缺陷两两作用的复合机制；（3）量子点中缺陷导致的荧光猝灭及抑制策略，分析影响量子点荧光量子产率的关键结构因素和电子因素，阐明由缺陷导致的荧光猝灭现象的物理机制，探索通过添加配体和进行核壳设计抑制荧光猝灭的策略。项目研究成果将为设计和制备高荧光量子产率量子点器件提供理论依据。

量子点因其独特的量子限域效应，随着尺寸、组分的变化表现出不同于块体材料的物理化学性质，被认为是发光器件、太阳能电池等应用的理想材料。采用基于密度泛函理论的第一性原理计算方法和团簇模型，并结合粒子群晶体结构优化算法，本项目搜索并预测了多种小尺寸量子点的几何构型，从原子层次、电子结构层面研究了不同量子点的电子迁移行为、光学性质和热力学性质。结果表明，在量子点中掺杂Mn离子可以有效增强量子点敏化太阳能电池的光电性能。在超快激光脉冲的作用下量子点具有较强的光吸收，并在较大范围波长的激光下都能够发生绝缘体-金属跃迁，此外调整量子点的尺寸能够进一步提高其光吸收性能。研究了碳量子点层内和层间极化率，发现可以通过调节电场强度、扭转角和量子点尺寸进行带隙调控。此外，还研究了静水压力下CdSe体材料和钙钛矿材料的相结构变化、电子结构和极化性质。本研究为提高量子点发光效率提供了理论指导，有助于发现具有高荧光效率的新型功能材料。