Controllable Preparation Of Perovskite Nanocrystals And Their Applications In Light-emitting Diodes

Lead halide perovskite nanocrystals have attracted widespread attention due to their excellent optoelectronic properties such as wide absorption spectrum,adjustable spectral band gap,high carrier mobility,low defect density and high color purity.It is widely used in optoelectronic devices such as light-emitting diodes（LED）,solar cells,photodetectors and lasers.At present,the preparation methods of perovskite nanocrystals mainly include heat injection method,recrystallization method,ultrasonic method and solvothermal method.However,the above methods show the following disadvantages:（1）high temperature and inert atmosphere are required during the reaction process,and the material cost is relatively high;（2）a large amount of organic solvents are required,which easily pollutes the environment;（3）It is difficult to control the morphology and structure,limiting its application;（4）Lead halide perovskite has the property of ionic structure,which is very sensitive to external factors such as water,oxygen,high temperature,and light radiation.Therefore,the development of simple and efficient preparation methods to achieve effective control of the size,morphology,and structure of lead halide perovskite nanocrystals has important research significance.In view of the difficulties in the preparation and structural control of perovskite nanocrystals,we have carried out the research around surface ligand engineering.The low-temperature aqueous phase method was used to prepare perovskite nanocrystals and phosphors and the influence of different surface ligands in perovskite nanocrystals were studied.Furthermore,perovskite nanocrystals have been successfully applied to LED,and their basic properties have been studied.It mainly includes the following aspects:（1）The perovskite nanocrystals and phosphors were prepared through low-temperature method using cheap and available laundry detergents as surface ligands.The key role of the active ingredients in the laundry detergent for the preparation of perovskite nanocrystals was studied,and the growth mechanism was discussed.The controllable preparation of perovskite nanocrystals was achieved through the adjustment of the components.At the same time,the universality of the method was also proved.The method is simple and efficient,and the prepared perovskite phosphors can reach the gram level.（2）The perovskite-based composites were prepared by using carbon quantum dots（CQDs）and nitrogen-doped carbon quantum dots（N-CQDs）with good conductivity,hydrophilicity,low toxicity.By analyzing the microstructure of CQDs and N-CQDs and the effect of surface functional groups on Cs Pb Br₃ nanocrystals,it was found that CQDs are rich in carboxyl groups,which can enhance the stability of nanocrystals.N-CQDs are rich in amino groups on the surface,which can control the surface morphology of nanocrystals.The addition of N-CQDs can not only affect the basic structure and optical properties of Cs Pb Br₃nanocrystals,but also significantly enhance the optical absorption of Cs Pb Br₃ nanocrystals.The results indicate that CQDs with excellent photoelectric properties can be used as surface ligands for the preparation of perovskite nanocrystals.（3）Through the adjustment of the surface ligand concentration,the aspect ratio of Cs Pb Br₃ nanorods was adjusted at low temperature.The phosphors were encapsulated in PMMA to isolate water vapor and oxygen.Cs Pb Br₃ nanorods were successfully applied to light emission diodes,while the driving voltage is 3.6 V,and the brightness reaches 32930 cd m^-2.The corresponding fluorescence spectrum emission peak is stable at 520 nm from intrinsic green emission,and the color coordinate is stable at（0.12,0.68）.In addition,the Cs Pb Br₃ phosphors can be stable for more than half a month in the air,indicating that the phosphors were expected to be industrialized.