The Green Preparation Of Perovskite Nanocrystals And Their Application In The Light-emitting Diodes

Lead halide perovskite nanocrystals have aroused tremendous research attention due to their excellent photophysical properties,such as high photoluminescence quantum yield,narrow emission spectrum and tunable spectral range.In recent years,perovskite nanocrystals have been widely utilized in various optoelectronic devices,such as solar cells,light-emitting diodes（LED）,lasers and photodetectors.At present,the preparation methods of perovskite nanocrystals are hot-injection method,recrystallization method,ultrasonication method,microwave-assisted method,solvothermal method and grinding method.However,perovskite is easy to be hydrolyzed because they are ionic compound.Currently,most of the liquid-phase synthesis methods have to be carried out in organic solvent.Therefore,it is of great significance to prepare perovskite nanocrystals by using environmentally friendly water as solvent.In order to solve this problem,a new low-temperature aqueous synthesis method was developed to prepare a series of perovskite nanocrystals with different components and morphologies,and the prepared perovskite nanocrystals were applied to electroluminescence（EL）based LED and photoluminescence（PL）based LED.This paper not only provides a new environment-friendly method for the preparation of perovskite nanocrystals,but also proves the potential of the materials in practical application.The main work is as follows:（1）The low-temperature aqueous synthesis method was developed.In this method,water was directly used as the reaction solvent,and perovskite nanocrystals were prepared in water by low-temperature freezing method.The effect of freezing rate on the synthesis of perovskite nanocrystals was investigated by changing the freezing method for control experiment.The results showed that the faster the freezing rate,the higher the yield of nanocrystals.（2）The influence of surfactants on perovskite nanocrystals was studied.It was found that surfactants are indispensable in the preparation strategy,and different surfactants can lead to the change of product morphology.（3）The universality of this method was discussed.CsPbX₃（X is Cl^-,Br^-,I^-）nanocrystals,organic-inorganic hybrid perovskite CH₃NH₃Pb Br₃ nanocrystals and CsPbBr₃ nanocrystals with different surfactants were prepared by low-temperature aqueous synthesis method.The results show that the solubility of precursor plays an important role in the reaction process,and by changing the solubility of precursor Pb I₂,Cs Pb I₃ nanocrystals were successfully prepared.（4）CsPbBr₃ nanocrystals were used in the PL based LED.When the voltage is 3.7 V,the brightness can reach 36490 cd m^-2.It shows the excellent optical properties of CsPbBr₃ nanocrystals.The green light with high color purity can also be produced by integrating it into EL based LED.However,due to the relatively low brightness,current efficiency and external quantum efficiency of the device,it needs to be improved.