【作者】 吴华；

【导师】 于伟泳；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2019， 博士

【摘要】 钙钛矿量子点作为一种新型量子点材料,其发光波长在可见光波段可调、荧光光谱线宽窄,并且荧光量子效率高达90%,这些优异的发光特性使钙钛矿量子点成为在显示和照明领域最有应用前景的材料之一。我们合成了一系列不同带隙的全无机钙钛矿量子点（CsPbX₃,X=Cl,Br,I）,并对其在电致发光二极管（light emitting devices,LED）中的应用展开了研究。在本论文的研究初期,钙钛矿量子点LED的报道非常少,电致发光的亮度和效率很低。除此之外,相对于传统量子点,钙钛矿量子点稳定性较差。基于上述问题,本研究以提升CsPbX₃量子点材料稳定性及其发光二极管工作性能为目标,从材料合成和器件结构两个方面提出解决方案,设计实验,并取得较理想的成果。以下是对研究内容的具体介绍。（1）量子点的表面配体组分和密度对其光电性质至关重要。在合成CsPbBr₃量子点的过程中,引入新的配体结构,进而实现对量子点表面配体组分和配体密度的调控。经过表面配体调控的CsPbBr₃量子点,其光电性质获得了明显改善,主要表现为:由于表面配体与量子点表面原子结合更加紧密,表面缺陷态也得到有效钝化,量子点溶液的放置稳定性得到改善,同时溶液的荧光量子效率由70%提升到96%;另外,表面有机长链配体密度的降低,也使得量子点薄膜具有更好的导电性。将经过表面调控的CsPbBr₃量子点应用于电致发光二极管器件,相比于未经表面调控的器件,发光性能得到明显增强,外量子效率提高了将近4倍。（2）在电子传输层ZnO纳米晶薄膜和发光层CsPbBr₃量子点之间引入Mg掺杂的ZnO（MZO）薄膜,优化了界面稳定性。通过研究不同浓度Mg掺杂ZnO薄膜的性质,我们发现Mg掺杂减少了ZnO纳米晶表面氧空位的密度,避免了ZnO表面吸附大量水氧分子导致对钙钛矿量子点的破坏,增强了薄膜的空气稳定性。同时,Mg掺杂使ZnO薄膜的禁带宽度得到展宽,导带能级上移,界面势垒降低,有效促进电子注入到发光层,从而提升了LED器件的电致发光亮度和效率。（3）我们利用聚乙烯亚胺（PEI）对CsPb（Br/I）₃量子点薄膜进行后处理。通过对后处理的薄膜进行一系列表征分析,我们发现钙钛矿量子点的绝对荧光量子效率以及荧光辐射寿命都得到了显著提高,证明PEI对量子点薄膜表面缺陷有钝化作用,减少了电子在传输过程中的损失。另外,PEI界面层对CsPb（Br/I）₃量子点的充电现象有一定的抑制作用,而且PEI界面可以提高ZnO的功函数,降低电子注入势垒。通过对PEI层和量子点的厚度进行优化,最终制备的LED器件的外量子效率达到6.3%。另外,基于这样的器件结构,通过改变发光层中钙钛矿量子点的卤素组分,我们制备了红绿蓝三颜色的电致LED器件。（4）我们将叠层透明电极MoO₃/Au/MoO₃应用于钙钛矿量子点LED器件结构,制备了双面发光的电致LED器件。经过对叠层结构中各层厚度的连续微调,LED的空穴注入过程得到增强,并在不牺牲LED电致发光的前提下将透明度最大化,最终,整个透明LED器件在可见范围最高透过率为58%,而且双面发光的光谱几乎完全一致,证明了该材料在透明发光器件领域应用的潜力。总之,我们从材料和电致发光器件结构两个角度出发,改善了钙钛矿量子点材料及其LED器件的性能,并拓展了器件的应用范围。更多还原

【Abstract】 Solution-processed perovskite quantum dots（QDs）feature excellent emission properties,including tunable emission,narrow emission line-width and high emission quantum yield up to 90%.These compelling properties make perovskite QDs as one of the most promising materials for lighting and display applications.We synthesized a series of all-inorganic perovskite QDs（CsPbX₃,X=Cl,Br,I）with tunable bandgaps by adjusting their composition of halides and studied their light emitting diode（LED）applications.At the beginning of the research of this thesis,there were very few publications about perovskite QDs and LED applications,and the electroluminescence performances were poor.In addition,compared to traditional cadmium chalcogenide QD materials,perovskite QDs suffer poor solution stability during purification and storage.This thesis focuses on exploring the surface chemistry of CsPbX₃ QDs as well as the development of highly efficient LED devices.We modified the surface properties of QDs and engineered the LED device structure to get improved material properties and LED applications.First,since the compositions and density of surface ligands for QDs greatly affect the optoelectronic properties,we synthesized CsPbBr₃ QDs with controllable surface modifications.It is demonstrated that by adding didodecyl demethyl ammonium bromide（DDAB）,the surface ligand composition and density can be changed,and eventually leads to an improvement of the material quality.On the one hand,CsPbBr₃ QDs possess higher emission quantum yield（from 70%to 96%）and better storage stability（the solution kept clear after one month in air）,which is because the new ligand bonded to the surface atoms more strongly and the surface vacancies were effectively passivated.On the other hand,the QD films featured better carrier transport ability due to the decrease of surface long-chain ligand density.Emloying the modified QDs into designed LED,we obtained a 4-time enhancement in external quantum efficiency.Secondly,by inserting an interfacial layer of Mg-doped ZnO nanocrystal between electron transport layer and emission layer,a more stable interface was obtained.The incorporation of Mg decreases the oxygen vacancy sites on ZnO nanocrystal surface,which prevents the damage of the absorbed water on ZnO surface to perovskite upper layer.As a result,the CsPbBr₃ QD layer obtained a higher stability when depositing on Mg-doped ZnO layer.Besides,Mg-doped ZnO film features a wider bandgap,and the conduction band level shifts upside,leading to a decreased electron injection barrier and more efficient LED application.Thirdly,through a post treatment to CsPb（Br/I）₃ QDs using polyethyleneimine（PEI）,the surface defects of the perovskite QDs were effectively passivated,leading to an obvious increase on film emission quantum yield and radiative lifetime.Besides,the PEI layer suppresses QD charging effect.By employing the well-passivated perovskite QD into an inverted structure and optimizing the layer thickness for charge balance,we achieved electroluminescent LEDs with 6.3%of external quantum efficiency,which was one of the highest values at that time.Also,based on the best condition,we made LED devices emitting red,green and blue light by changing the halide composition of the emission perovskite layer.Finally,transparent LEDs with double-side emission were fabricated by employing a transparent multilayered anode MoO₃/Au/MoO₃.By fine tuning the thickness of each layer,the hole injection was enhanced,and the transparency of the whole device can be maximized while maintaining the electroluminescence performance.The transparent device exhibits a highest transmittance of 58%,and shows similar electroluminescence spectra from both sides,which demonstrates the potential of perovskite QDs on transparent display application.From the point view of material science and device engineering,we have improved the perovskite QD material properties and LED applications.This study may provide a reference for future work of perovskite optoelectronic applications.更多还原