Efficient And Stable Lead Halide Perovskite Quantum Dots For White LEDs

In recent years,perovskite quantum dots have attracted much attention because of their excellent photoelectric properties.Compared with traditional inorganic semiconductor quantum dots,perovskite quantum dots have wider adjustable emission wavelength range,more excellent photoelectric transmission performance,simple synthesis,low cost and other advantages,thus the perovskite quantum dots have a good application prospect in photoelectric devices.However,the perovskite quantum dots greatly sufferfromtheir poor stability.Air,water and other factors can lead to the decrease of luminescence efficiency or even can complete quench the luminescence of the perovskite quantum dots.In addition,anion exchange exists in perovskites universally,which may limit its application in multi-colour display and lighting.In this paper,we start from the synthesis route of perovskite quantum dots,and we try to coat perovskite quantum dots with SiO₂ or dope other metal cation in perovskite quantum dots by changing the ligand and precursor components,so as to improve the stability of the perovskite quantum dots and maintain their high fluorescence quantum efficiency.The main work and innovation of our work are as follows:（1）SiO₂-coated perovskite quantum dots（MAPbX₃/SiO₂）were prepared in room temperature and in air using the silane ligand assisted method.The silane in the precursor is dissolved in toluene instead of DMF in traditional method and this can prevent the reaction between the silane and DMF which may lead to untimely hydrolysis of the silane.Consequently,the fluorescence quantum efficiency of the quantum dots was improved.By controlling the ratio of materials in precursor,the quantum dotshave tunable light emission from 460 nm to 662 nm,and the blue,green,and red light quantum yield were 56%,95%,70%,which is equal to highest level of the reported similar perovskite quantum dots.SiO₂ coated on the surface of the quantum dots can greatly improve the stability of the quantum dots.After 72 hours placed in the air,the fluorescence quantum yield of SiO₂ coated quantum dots decreases by 6%,while that of MAPbX₃ quantum dots decreases by 36%under the same conditions.Thermal stability study shows that after heating under 60°C for 30min,thequantum yield of SiO₂ coated quantum dots is 61%,while MAPbX₃ quantum dots are almost completely quenched after the same treatment.At the same time,the resistance to polar solvents of the SiO₂ coated quantum dots is also improved significantly.Anion exchange reaction can be prevented by coating SiO₂.Therefore,red and green quantum dots can be mixed with PS to form a film,which can be covered on the commercialGaN blue light-emitting diode to prepare a white light diode,which have CRI of 85 and color temperature of 6581 K.（2）We prepared organic-inorganic hybrid perovskite MAPbI3 quantum dots co-doped with europium and manganese by ligand-assisted reprecipitation method at room temperature in air.The perovskite quantum dots with different doping compositions and proportions can be obtained by adding MnI₂ and EuI₂ in the precursor and adjusting the proportion of each component.The fluorescence quantum yield can reach about 75%,which is equal to highest level of the reported similar perovskite quantum dots.Elemental analysis showed that a small amount of Mn²⁺and Eu²⁺were successfully doped in the quantum dots.Compared with the undoped perovskite quantum dots,the Eu²⁺and Mn²⁺co-doped quantum dots synthesized in this work have obvious stability improvement.The undoped quantum dots almost quench within 40 h when placed in air,while the Eu²⁺and Mn²⁺co-doped quantum dots still maintain 19%fluorescence quantum yield after 96 h in air.Our work provides a simple and universally applicable method for synthesizing high brightness and stable doped perovskite quantum dots.