CIOMP OpenIR  > 中科院长春光机所知识产出
核/壳结构量子点的可控合成和发光性质及LED制备研究
徐威
学位类型博士
导师赵家龙
2014-07
学位授予单位中国科学院大学
学位专业凝聚态物理
摘要利用高温热注入法合成核/壳结构二元量子点、多元合金和掺杂量子点,不仅可以调控核的尺寸而且还可以调控壳层的厚度,使量子点的发光性质随尺寸、组分和结构可调。量子点具有发光效率高,光、热及化学稳定性好,简单的溶液加工和成膜的特点,使其在电致发光器件方面具有广泛的应用前景。目前,核/壳结构量子点作为荧光下转换材料已被用于液晶电视的背光源。含镉量子点薄膜作为发光层的量子点电致发光二极管(QD-LED)最大亮度达218800 cd m-2,最大外量子效率为18 %,寿命达10000 h。然而,QD-LED的寿命还不能满足商品应用的需求,需要选择合适的电荷传输材料,优化器件结构,实现高效率、高亮度及长寿命等方面性能平衡、稳定的量子点电致发光器件。另外,绿色环保的CuInS2-基量子点以及具有大的斯托克斯位移的Mn-掺杂量子点的电致发光性质研究尚处于起步阶段,具有广泛的研究意义和应用前景。基于以上立题思想,本论文主要取得了以下研究结果:1. 利用成核掺杂方式在MnS/ZnS(~ 2 MLs)核/壳量子点表面包覆不同厚度的CdS壳层,合成了Mn-掺杂ZnxCd1-xS核/壳量子点,通过增加CdS壳层厚度即减小Zn/Cd比例来控制ZnxCd1-xS的组分,使其吸收带边在425-475 nm范围可调;通过对Mn-掺杂ZnxCd1-xS核/壳量子点的形貌、晶体结构及选择激发发射谱和选择发光激发谱表征,证实了Mn2+离子周围的晶格环境是ZnxCd1-xS合金;结合变温光谱和时间分辨光谱对Mn-掺杂ZnxCd1-xS核/壳量子点的发光动力学进行了分析,研究表明Mn-掺杂ZnxCd1-xS核/壳量子点发光来源包括Mn2+离子的发光和缺陷态发光两部分。用ZnO电子传输层和Mn-掺杂ZnxCd1-xS(Zn/Cd=0.64)核/壳量子点制备了倒置QD-LED,器件的最大亮度为54 cd m-2,最大亮度效率为0.056 cd A-1,其电致发光光谱与光致发光光谱相比出现较大的红移和展宽,可能是由于电场离化激发机制下Mn-掺杂量子点中Mn-Mn对以及缺陷态发光显著增强。2. 利用高温热注入法合成了Cu-Zn-In-S/ZnS核/壳量子点,对其形貌、晶体结构及发光性质进行了表征,结合其合成路线、变温光谱及荧光寿命分析深入理解了其发光机理,讨论了其发光来源。用绿光和红光Cu-Zn-In-S/ZnS核/壳量子点作为荧光下转换材料制备了蓝光InGaN LED激发的白光LED,发现当工作电流在20-100 mA范围,器件的色温稳定;然而当工作电流提高到150 mA时,器件的色温明显升高;通过绿光量子点的循环变温光谱(300 K-400 K-R300 K 和300 K-480 K-R300 K)性质研究,表明热猝灭引起的发光量子效率降低将导致在高电流下器件色温升高。用黄光Cu-Zn-In-S/ZnS核/壳量子点制备了倒置QD-LED,获得了饱和色量子点电致发光光谱,器件的最大亮度为187 cd m-2,最大亮度效率为0.22 cd A-1。3. 采用TiO2、TiO2/ZnO和ZnO为电子传输层和发光峰位位于624 nm、发光线宽为24 nm的红光CdSe/CdS/ZnS核/壳量子点为发光层,制备了倒置QD-LED,获得了饱和色量子点电致发光光谱。基于TiO2、TiO2/ZnO和ZnO的器件最大亮度分别为2119、2908和3861 cd m-2,最大亮度效率分别为5.0、3.9和3.0 cd A-1。另外,基于TiO2的器件中在较高的电流密度下(20 mA cm-2)达到最大亮度效率,是由于量子点带负电导致的。研究表明ZnO纳米粒子电子传输层的表面形貌有利于旋涂连续的量子点薄膜,并制备高亮度的QD-LED;TiO2相对ZnO电子传输层具有较低的电荷迁移率能够改善器件中的电荷注入平衡,有助于获得较高效率的QD-LED;利用TiO2/ZnO复合电子传输层可以实现器件亮度与效率之间的权衡。
其他摘要Bianry, multicomponent alloy and doped quantum dots (QDs) with core/shell structures are typically synthesized with the hot-injection method, which is used to not only control the core size but also change the shell thickness. These QDs have exhibited size- and composition-tunable luminescent properties, high photoluminesece quantum yield (PL QY), good stability, solution-processing and printed films from ink, which make them promising in applications for light-emitting devices (LEDs). Currently, QDs down-converters are being used for backlighting in LCD Vision and the quantum dot light-emitting diodes (QD-LEDs) with CdSe-based QDs as emitter exhibit the maximum brightness of 218800 cd m-2, the maximum external quantum efficiency of 18 % and the lifetime recorded up to 10000 h. However, the performance of the QD-LEDs does not meet the requirement of the large-area display devices, therefore the device architectures and the charge-transporting materials used for QD-LEDs need to be optimized to achieve tradeoff between the luminance and efficiency, and a new recorded lifetime. In addition, the electroluminescent properties of cadmium-free CuInS2-based and Mn-doped QDs with large stokes shifts have been fully on the top of potential rearch, which are interesting and promissing. Based on the above ideas,the original works are given as follows:1. We have synthesized Mn-doped ZnxCd1-xS QDs by growing a thin ZnS layer on the MnS nuclei and then growing a CdS layer with different thickness to vary the composition using nucleation-doping strategy. PL excitation spectra of the yellow emission (575 nm) of Mn2+ ions in Mn-doped ZnxCd1-xS QDs are tuned from 425 nm to 475 nm by growing the CdS layer. Combined morphology, crystal structure and steady-state spectroscopy of the Mn-doped ZnxCd1-xS QDs indicate that the lattice environment of the host around Mn2+ ions is ZnxCd1-xS alloy. Further, the PL of Mn-doped nanocrystals is composed of emissions of Mn2+ ions and defect states based on temperature-dependent PL spectra and PL decay kinetics. We have fabricated inverted QD-LEDs using ZnO as the electron contacts and Mn-doped ZnxCd1-xS QDs with Zn/Cd ratio of 0.64 as the emitters, which exhibits a maximum brightness of 54 cd m-2 and a maximum current efficiency of 0.056 cd m-2, the electroluminescence spectra are broader, exhibiting a large red shift relative to the PL spectra, which may orginate from Mn-Mn or defects related emission.2. We have synthesized Cu-Zn-In-S/ZnS core/shell QDs with hot-injection method and characterized their morphology, crystal structure and luminescent properties. The origin and mechanism of PL in Cu-Zn-In-S/ZnS core/shell QDs is discussed based on the routes of synthesis, temperature denpendent PL spectra and PL decay kinetics. Red and green Cu-Zn-In-S/ZnS core/shell QD down-converters are used for fabrication of white LEDs, the CCT of the device increases at high current, which is attributed to the thermal quenching of luminescence based on the recircled temperature-dependent spectra in the range of 300 K-400 K-R300 K and 300 K-480 K-R300 K. The inverted QD-LEDs with yellow QDs as emitter exhibit a maximum brightness of 187 cd m-2 and a maximum current efficiency of 0.22 cd A-1.     3. We have fabricated the inverted QD-LEDs with CdSe/CdS/ZnS core/shell QDs as the emitters with emission peak of 624 nm and full width at half maximum (FWHM) of 24 nm. The TiO2, TiO2/ZnO, and ZnO were utilized to deeply understand the underlying mechanism of efficient inverted QD-LEDs with different metal-oxide materials as the electron injection layer (EIL). The maximum luminance of the red QD-LEDs is 2119, 2908, and 3861 cd m-2 for TiO2,TiO2∕ZnO, and ZnO-based devices, respectively. The peak current efficiency of the red QD-LEDs is 5.0, 3.9, and 3.0 cd A-1 for TiO2,TiO2∕ZnO, and ZnO-based devices, respectively. In addition, the rise of current efficiency with increasing current density from 0.1 to 20 mA cm-2 was attributed to the negatively charged QDs.The introduction of the ZnO layer can lead to the formation of spin-coated uniform QD films and fabrication of high luminance QD-LED. The TiO2 layer improves the balance of charge injection due to its lower electron mobility relative to the ZnO layer. These results offer a practicable platform for the realization of a trade-off between the luminance and efficiency in the inverted QD-LED with TiO2/ZnO composites as the electron contact layer.
语种中文
文献类型学位论文
条目标识符http://ir.ciomp.ac.cn/handle/181722/41489
专题中科院长春光机所知识产出
推荐引用方式
GB/T 7714
徐威. 核/壳结构量子点的可控合成和发光性质及LED制备研究[D]. 中国科学院大学,2014.
条目包含的文件
文件名称/大小 文献类型 版本类型 开放类型 使用许可
徐威.pdf(5394KB) 开放获取CC BY-NC-SA请求全文
个性服务
推荐该条目
保存到收藏夹
查看访问统计
导出为Endnote文件
谷歌学术
谷歌学术中相似的文章
[徐威]的文章
百度学术
百度学术中相似的文章
[徐威]的文章
必应学术
必应学术中相似的文章
[徐威]的文章
相关权益政策
暂无数据
收藏/分享
所有评论 (0)
暂无评论
 

除非特别说明,本系统中所有内容都受版权保护,并保留所有权利。