| 题名 | 超级碳纳米点和纳米晶电荷传输层的制备及应用研究 |
| 作者 | 娄庆 |
| 学位类别 | 博士 |
| 答辩日期 | 2015-05 |
| 授予单位 | 中国科学院大学 |
| 导师 | 赵家龙,曲松楠 |
| 关键词 | 胶体量子点 纳米材料 电致发光 发光二极管 电荷传输层 |
| 其他题名 | Synthesis and Applications of Supra-(Carbon Nanodots) and Nanocrystals for Charge Transport Layers |
| 学位专业 | 凝聚态物理 |
| 中文摘要 | 胶体量子点作为半导体纳米晶体系重要成员材料，由于其具有独特的量子尺寸效应、表面效应，使其具有连续可调发光波段，窄的发射线宽，较高的发光量子效率和好的光学稳定性。其表面修饰配体后可在溶液中进行柔性处理，可采用旋涂和印刷技术制备成膜，是应用于新一代电致发光平板显示与固态照明的核心材料。经过科研人员的不懈努力，合成了各种高效发光的量子点，主要包括发光来源于激子发光的II-VI族和III-V族量子点，发光主要来源于掺杂离子及复合发光中心发光的Mn、Cu掺杂量子点，及发光来源机制存在争议的IV族Si、C量子点。随着材料和器件制备工艺不断进步，以及器件物理研究的不断深入，基于胶体量子点发射体的发光二极管器件（LED）性能（外量子效率，亮度和稳定性）得到了快速提升。目前，我国科学家利用激子发光的CdSe量子点制备了全溶液加工的发光二极管的外量子效率达20.5%，最大亮度达42000 cd m-2和寿命达100000 h。然而相对于CdSe量子点LED，具有绿色环保优势的碳纳米点LED的最大亮度仅有90 cd m-2, 其电致发光机理尚不清楚，与实际应用及商业化生产还有很长距离。因此，研究和优化无镉碳纳米点发光性质，以及选择和优化量子点LED电荷传输层，对于提升无镉量子点LED发光性能具有重要的意义。本论文从这两方面出发，取得的主要工作成果如下： 1．通过对可溶液加工氧化石墨烯进行弱化学还原处理将其应用于CdSe量子点LED的空穴注入层，并考察了不同还原程度对器件性能的影响。发现旋涂相同厚度氨水处理氧化石墨烯空穴注入层的正置CdSe量子点LED器件，氨水还原后的器件性能显著改善，其中还原时间为3小时的器件性能最优。通过紫外光电子能谱，吸收光谱和原子力显微镜扫描分析得出：氨水还原后氧化石墨烯的导电率增强，功函数提升，这两个因素一方面增强了CdSe量子点LED器件的空穴传输，另一方面抑制空穴的注入。通过对这两种因素的折中，我们得到了性能最优的CdSe量子点LED器件，即为3小时氨水还原氧化石墨烯用作空穴注入层制作的器件。 2．用低温溶液沉淀法合成的TiO2与ZnO纳米粒子用作电子传输层分别制备了倒置CdSe量子点LED，并研究了电致发光机理。发现ZnO电子传输层掺入部分CsCO3会改善电子传输层电子到量子点层的注入，提高量子点LED的亮度和效率。同时，更高的掺杂浓度会导致电子传输层具有较低的电荷迁移率和更大的表面粗糙度，进而不利于器件性能的提高。另外，通过对比量子点层到TiO2与ZnO纳米粒子电子传输层的寿命，得出利用TiO2纳米粒子用作电子传输层具有进一步提高量子点LED发光效率的潜力。 3．制备了部分十二烷基链修饰的两亲性的碳纳米点，利用其自组装性质得到了具有水致荧光增强特性的“超级碳点”。通过将“超级碳点”与纸复合得到了有水致荧光增强特性的纸复合物。通过使用该“超级碳点”纸复合物，进行喷水打印和简单指尖按压获得了高质量的荧光图像和指纹汗孔荧光图像。通过时间分辨光谱，形貌表征，共聚焦成像和核磁表征得到了该碳纳米点水致荧光增强的机理，并进一步开发了该智能荧光碳纳米材料在光信息存储，司法鉴定和医疗诊断等领域的潜在应用。进一步的，利用完全十二烷基链修饰的油性的碳纳米点作为新型环保量子点LED发光层制备了器件，发现发射波长随电压变化而改变。 |
| 英文摘要 | Colloidal quantum dots (QDs), as an important member of semiconductor nanocrystals, exhibit very unique quantum confinement and surface effects，which make them have emission-wavelength tenability in applications, narrow emission linewidth, high photoluminesece quantum yield (PL QY), and good photostability. After functionalizing with ligands, QDs have demonstrated solution-processing, good compatibility with spin-coating and ink-printing technology, which can be considered as key materials for the next generation of electroluminescent flat-panel display and solid-state lightings. After steady progresses for developing QDs, various high PL QY QDs have been synthesized by researcher, including II-VI and III-V semiconductor based QDs exhibiting excitons related emission, Mn, Cu-doped QDs orginating from doping cations or radiative recombination centers related emission, and IV semiconductor based Si, C QDs with a controversial luminescent mechanism. With the advance in materials and device architectures as well as the research of the device physics, performances of light-emitting devices (LEDs) based on colloidal QD emitters, such as external quantum efficiency (EQE), brightness, and device stability, have been pushed forward. Currently, solution-processed QD-LEDs based on CdSe QDs exhibiting exciton emission have been developed by Chinese scientists, maximum EQE of up to 20.5 percent, maximum brightness of up to 42000 cd m-2 and operational lifetime of more than 100,000 hours. However, by contrast, eco-friendly C based QD-LEDs have a low maximum brightness of up to 90 cd m-2, an intangible electroluminescent mechanism, and a hopeless commercialization. Therefore, it is meaningful to improve the performances of cadmium-free C based QD-LEDs through optimizing the luminescence of C QDs as well as the charge transport layers. Based on the above considerations, the original works are listed as follows: 1. We synthesized slightly reduced graphene oxide (GO) through ammonia reduction, which was used as hole injection layers of CdSe QD-LEDs by solution-processing, and then investigated the performances of QD-LEDs through controlling the degree of reduction of GO. It was found that for the conventional CdSe QD-LEDs spin-coating with isopachous reduced GO as hole injection layers, the performances of QD-LEDs were largely improved after the ammonia reduction, and the best device was fabricated with GO by 3h ammonia reduction. Combined UV-photoelectron spectroscopy (UPS), absorption spectroscopy (Abs) and atomic force microscopy (AFM) indicated that the conductivity of GO was enhanced, and the work function of GO was elevated after the reduction, which separately enhanced hole transport and inhibited hole injection. The best device was realized through a trade-off between hole transport and hole injection in the CdSe QD-LED, which was fabricated with GO by 3 h ammonia reduction. 2. We prepared TiO2 and ZnO nano particles via low temperature solution precipitation, which were utilized as the electron transport layer (ETL) to deeply probe the electroluminescent mechanism of inverted CdSe QD-LEDs. We found that doping with CsCO3 in ZnO would enhance electron injection from ETL to QD layer, further improved the luminance and efficiency of QD-LEDs. Meanwhile, higher doping level would decrease the conductivity and increase the surface roughness of ETL, which was adverse to the properties of QD-LEDs. Moreover, TiO2, as ETL, had the potential for further improving the efficiency of QD-LEDs by comparing the lifetime between QD layer and ETLs (TiO2 and ZnO). 3. We synthesized partially alkyl-chain-functionalized amphipathic carbon dots (CD-Ps), and obtained supra-carbon-nanodots (supra-CDs) through the self-assembly of CD-Ps, whose luminescence show weak emission in toluene and decompose when meeting water, resulting in strong photoluminescence. And supra-CDs/paper composite with the same water-induced enhanced photoluminescent behavior was achieved via coating paper with supra-CDs. With the supra-CDs/paper composite, we demonstrated water-jet printing luminescence patterns and mapping human sweat pore patterns by pressing a fingertip on the composite. Time-resolved PL spectroscopy, morphology characterization, fluorescence microscopy and NMR characterization unveiled the mechanism for the water triggered luminescent enhancement, and further demonstrated practical applications in optical information storage, forensic and healthcare. In addition, we fabricated novel QD-LEDs using full alkyl-chain-functionalized CDs (CD-Fs) as emitters, whose emission wavelengths were changed with the increase of the applied voltage. |
| 公开日期 | 2015-12-24 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ciomp.ac.cn/handle/181722/48877]  |
| 专题 | 长春光学精密机械与物理研究所_中科院长春光机所知识产出 |
| 推荐引用方式 GB/T 7714 | 娄庆. 超级碳纳米点和纳米晶电荷传输层的制备及应用研究[D]. 中国科学院大学. 2015. |
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