| Semiconductor light-emitting diodes（LEDs）,as a kind of photoelectric devices that directly convert electric energy into light energy,have the advantages of high electro-optical conversion efficiency,fast response speed,light weight and energy saving,and are widely used in information display and solid-state lighting.At present,light-emitting diodes based on a class of low-dimensional semiconductors,quantum dots（QDs,QLEDs）,have shown advantages such as wide color gamut,wide viewing angle and excellent color purity,and have become a hot research direction of new display technologies.However,the current research in this field encountered many problems,such as less types of quantum dot with excellent performance and complicated preparation process.It is urgent to develop new high-performance quantum dot materials and corresponding light-emitting devices with low synthesis cost.Halide perovskites,stand out from the field of solar cell research because of their excellent optoelectronic properties,which show amazing and rapid improvement of device performance,and gradually began to show great potential in the field of luminescence.Therefore,exploring the application of perovskite quantum dot materials in LEDs devices,in-depth study of the luminescence behavior of the materials and the corresponding device optimization mechanism is very important for expanding the quantum dot family members and promoting their possible commercial applications in the future.In this dissertation,a series of perovskite QLEDs devices based on high temperature thermal injection method and room temperature synthesis method are developed,and the key factors affecting the performance of the materials and corresponding light emitting devices are studied in detail.High performance QLEDs devices are realized by means of surface ligand purification,device structure optimization and surface inorganic ligand optimization.The main findings are summarized as follows:（1）Multi-color QLEDs devices with all-inorganic cesium-lead halide perovskite quantum dots.By using high temperature thermal injection synthesis technology,Cs Pb X3quantum dots with high crystallinity,single morphology and narrow size distribution were prepared,and the multi-color QLEDs devices based on such quantum dots were successfully illuminated for the first time.In the synthesis,the emission wavelength of the prepared quantum dots in the visible light range counld be easily adjusted by the size control and the component control strategy,wherein the fluorescence quantum yield of the green light is as high as 90%.Based on this,by designing appropriate functional layers of the device,electrons and holes are met at the quantum dot layer to form excitons,and then emitting by radiative recombination,and finally the blue,green and orange inorganic perovskite QLEDs devices are successfully constructed.The three QLEDs devices achieved device brightness of 742 cd/m2,946 cd/m2,and 528 cd/m2,respectively,with external quantum efficiencies of 0.07%,0.12%,and 0.09%,respectively.The three-color Cs Pb X3 QLEDs exhibit extremely narrow FWHM（FWHM<30nm）and show good prospects in future flexible HD display,lighting and optical communication applications.（2）Hybrid solvent purification method to improve the performance of inorganic perovskite QLEDs.Aiming at the problem that the ionic characteristics of CsPbBr3 quantum dots and the purification of surface ligands are difficult and the efficiency of QLEDs devices is low,a method for surface ligand purification using ethyl acetate and hexane mixed solvent is proposed to achieve high stability of quantum dot ink.Coexistence of four elements such as high uniformity of quantum dot film,high photoluminescence efficiency,and effective charge injection.Thanks to this,the CsPbBr3 QLEDs device with 6.27%external quantum efficiency（EQE）has been improved by nearly 50 times compared with the previous period,and the brightness has also increased by an order of magnitude,exceeding 15,000 cd/m2.This method solves the problem of purification of perovskite quantum dots to a certain extent,and helps to further improve the performance of perovskite quantum dot materials and devices.（3）High-performance QLEDs devices based on room temperature synthesis of CsPbBr3 quantum dots.Aiming at the ionic crystal characteristics of Cs Pb X3 material,a room temperature synthesis method was proposed to prepare high quality CsPbBr3 quantum dots（QDs）and high performance QLEDs devices were constructed by designing corresponding device structures.High-ink stability and over 90%fluorescence quantum yield（PLQY）of CsPbBr3 quantum dot were obtained by synergistic cooperation of tetraoctyl ammonium bromide,dodecyldimethylammonium bromide and octanoic acid short-chain ligand at room temperature without inert gas protection.At the same time,the short-chain ligands used in the synthesis enable the QDs luminescent layer film to have more efficient carrier transport properties.In addition,the introduction of a small amount of organic formazan as a dopant reduced the non-radiative recombination center of the QDs film,further improving the PLQY of the QDs film.Finally,the high luminescence properties and effective electrical injection and transmission characteristics of the room temperature QDs film increased the maximum EQE of the CsPbBr3 QLEDs device to 11.6%.In addition,QLEDs devices made by QDs under high-volume synthesis have successfully achieved more than 10%EQE.（4）The strategy of inorganic-organic ligand hybrid passivation optimizes the performance of CsPbBr3 QLEDs devices.A generalized strategy for organic-inorganic hybrid ligand-passivated quantum dots was proposed to improve the performance of CsPbBr3 QDs films and LEDs devices by using a class of metal bromides such as Zn Br2（Mn Br2,In Br3 or Ga Br3）.Through the basic characteristics of the quantum dots before and after the adoption of the strategy and the optical properties of the assembled films,the electrical properties were studied in depth,and it was found that the strategy can effectively reduce the surface defect sites of perovskite QDs,inhibit non-radiative recombination,and ensure efficient light emission of QDs films.In addition,the introduction of inorganic ligands could significantly improve carrier injection and transport properties,thereby improving the composite efficiency of the device.Finally,a peak EQE of up to 16.48%for CsPbBr3 QLEDs devices was achieved,which is the highest efficiency reported based on inorganic perovskite QLEDs devices reported to date.In addition,after the introduction of inorganic ligands,the lifetime of CsPbBr3 quantum dot materials and devices was improved,and the device lifetime was increased from 37 min to 136min. |
PDF Full Text Request