表面配体选择对量子点电致发光器件中的电荷注入及发光效率影响研究

The carrier injection efficiency is one of the key factors of performance improvement of quantum dot light-emitting devices (QD-LEDs). Meanwhile,the injection efficiency of carriers into emissive layer is of the highest priority. For now, long-chain organic surface capping ligands, which were widely used during the synthesis of luminescent quantum dots (QDs), form major barriers for the efficient injection of carriers into the emissive layer. This study comprises researches of controllable replacement of long-chain organic surface capping ligand of core-shell structured QDs with excellent conductive new type of ligands including inorganic complexes and short-chain organic ligands. Comparison and analysis of differences in performances of luminance and efficiency of QD-LEDs using CdSe/ZnS and ZnxCd1-xSe/ZnS QDs with different type of capping ligands would be conducted extensively. Furthermore, Kelvin probe technique will be introduced to study the relationship between the performance of QD-LEDs and the variation in interface barriers aroused by the ligand exchange. Such researches can help us to get a better understanding of the effects of different kinds of surface ligands on the charge injection process and device performance and to know more clearly about the mechanism for such QD-based electroluminescence, which will offer useful theoretical and technical references for further optimization of device structures and applied researches.

电荷注入效率的提高是改善荧光量子点的薄膜电致发光器件性能的关键因素之一。而发光层的电荷注入效率无疑是影响发光效率的重中之重。目前，荧光量子点合成过程中所广泛采用的长链有机表面配体构成了发光层电荷注入的主要障碍。本研究拟采用导电性能优异的新型无机及短链有机配体对核壳结构的CdSe/ZnS及ZnxCd1-xSe/ZnS量子点开展可控的表面配体取代并进行相应的器件制备测试，在亮度及效率等关键参数上开展与使用长链有机配体的量子点发光器件的对比测试及分析；在此基础上，通过引入开尔文探针系统来进一步探究配体交换所引起的界面势垒变化及其与器件性能之间的相互关系。该课题的开展将有助于我们更好的理解不同类型表面配体对电荷注入过程及器件性能的影响，从而更加清晰地理解其内在发光机制，为下一步的器件设计及应用研究提供有益的理论和实验参考。

荧光量子点由于荧光量子产率高、单色性佳、稳定性高、荧光光谱随尺寸可调等独特的性质，使其在生物标记、光伏器件、激光、发光二极管等领域引起了广泛关注。特别是基于量子点的发光二极管出现以来，其应用前景也愈发诱人。量子点的结构、组分及表面配体的设计以及器件结构的优化，对于改善荧光量子点薄膜电致发光器件的性能非常关键。按研究计划，本项目以ZnCdSe及相关核壳结构量子点为主要材料体系；在配体的选择上，使用无机配体的初衷在于自身稳定性较好且可降低量子点之间距离，提高载流子传输效率，但无机配体的修饰存在量子点不稳定及器件漏电流大等问题。采用具有强结合力的短链巯基配体是更佳的选择。我们设计了一系列以Zn、Cd、Se、S为元素主体的多种核壳和合金结构量子点材料，如多壳层蓝绿红三色量子点；非闪烁且具有单指数荧光衰减特性的ZnCdSe/ZnS核壳结构量子点和无壳层CdSe1-xSx合金结构荧光量子点等。在表面配体的筛选和设计的研究中，采用短链的八烷基硫醇及针对QD-LEDs中荧光量子点的应用要求筛选的多齿硫醇配体，制备得到多种高效量子点及具有不同链长的三齿单链硫醇配体修饰的Zn1-xCdxSe/ZnS核壳结构绿色荧光量子点。通过元素组分调控及壳层结构设计、QD-LEDs多层结构的优化，实现非辐射跃迁的有效抑制以及适配高效电荷注入的能级梯度平滑，实现了高效率、高亮度的多色QD-LEDs发光器件的构筑。在器件结构的优化方面，尝试贵金属离子对传输层掺杂以及导电聚合物对量子点层的掺杂，以降低载流子输运壁垒及优化多层结构间的能级匹配，在QD-LEDs的应用上得到了较为理想的结果。