Preparation And Luminescence Properties Of Lead-free Halide Perovskite Materials

Lead-free halide perovskite,as a substitute for similar products based on lead,has been widely concerned by people.It has solved a series of problems such as lead toxicity and instability of lead halide.Among them,double perovskite containing Cs₂AgInCl₆components has become one of the hot spots in the study of perovskite materials because of its excellent optical properties and its photopoluminescence can be improved by doping.In this paper,focusing on the method of solution evaporation,the Li⁺and Bi³⁺co-doped lead-free halide double perovskite Cs₂Ag_1-xLi_xInCl₆:Bi was prepared first,and the relevant structure and optical properties were tested.The results show that Li⁺and Bi³⁺co-doping can improve the photoluminescence quantum yield of the materials.Secondly,by preparing Cs₂Li_xAg_1-xBiCl₆double perovskite nanocrystals（NCs）,the relevant structure and optical properties were tested.The results show that Li⁺doping can also improve the photoluminescence quantum yield.The electronic structure of Cs₂Li_xAg_1-xBiCl₆（x=0,0.25,0.50,0.75,1）was calculated by first principles,and it was found that the band gap values varied with the different x values,indicating that doping Li⁺can realize the adjustment of the band gap of Cs₂AgBiCl₆material.In conclusion,this paper,through the experimental preparation of Cs₂AgInCl₆and Cs₂AgBiCl₆double perovskite metal ion doping materials and the analysis and summary of the experimental results,has laid a solid foundation for the follow-up research and potential commercial application of lead-free halide perovskite.1.Cs₂AgInCl₆with broadband emission characteristics is a good substitute for lead halide perovskite due to its unique properties.In order to improve the photoluminescence quantum yield（PLQY）,solution evaporation method（spray evaporation method）was used in this study to prepare lead-free double perovskite Cs₂Ag_1-xLi_xInCl₆:Bi combined with Li⁺and Bi³⁺co-doping.The experimental results showed that the PLQY of Cs₂AgInCl₆increased from 0.30%to 35.92%after Li⁺doping,and reached 76.02%after Bi³⁺doping.Among them,the optimization of Li⁺doping found that Cs₂Ag_0.7Li_0.3InCl₆:Bi has the highest PLQY,and its stability under ultraviolet irradiation is very good.In the photoelectric application,Cs₂Ag_0.7Li_0.3InCl₆:Bi material is used as a white light emitting device（WLED）made of solid phosphors.The color coordinate is（0.37,0.37）,the color rendering index is84.1,and the correlation color temperature is 4331K,indicating that the device has excellent performance.Therefore,double perovskite has potential applications in luminescence and photoelectric display.2.For Cs₂AgBiCl₆double perovskites,a series of Li⁺doped Cs₂Li_xAg_1-xBiCl₆（x=0,0.25,0.5,0.75 and 1）nanocrystals（NCs）have been prepared by thermal assisted solution evaporation method.These NCs have cubic crystal structure and wide-band emission.It is found that the optical properties of Cs₂Li_0.5Ag_0.5BiCl₆double perovskite are the best when x=0.5.By adjusting the value of x,the optical band gap can be increased from 3.39 e V（x=0）to 3.82e V（x=1）,and the photoluminescence quantum yield can be increased by nearly 30times from 2.24%to 30.59%.In addition,the electronic structure of Cs₂Li_xAg_1-xBiCl₆（x=0,0.25,0.5,0.75 and 1）twin perovskites has been calculated by density functional theory.The results of band structure and state density also confirm that the band gap increases with the increase of x value.Therefore,both experimental and theoretical results show that by controlling the doping amount of Cs₂AgBiCl₆with Li⁺,the band gap regulation of this kind of double perovskite can be realized,and the quantum yield of photoluminescence can be significantly improved.These metal-doped lead-free double perovskite nanocrystals have potential commercial value in optoelectronic device applications due to their excellent optical properties.3.In recent years,traditional silicon-based semiconductors are faced with process bottlenecks and architecture bottlenecks.In order to break these bottlenecks,it is urgent to find new materials,new devices and new architectures to realize more efficient computing.Because of its simple structure and excellent electrical performance,memristor has great potential in realizing high capacity data storage,fast transmission,fast reading and writing and low power consumption.In this paper,based on the above two studies,Cs₂Li_xAg_1-xBiCl₆is applied to the device.Raman spectroscopy is used to test its structure and measure its current-voltage characteristic curve.It is found that with the change of x value,when Ag is completely alloyed by Li,the high-low resistance state of Cs₂Li BiCl₆device can be opened to the maximum.The results show that the distinct resistance state is the most clear,and it has the relevant characteristics as the material for the preparation of resistance memory devices,which provides a new idea for the research of Cs₂Li_xAg_1-xBiCl₆as the memristor device.To sum up,the research content of this paper has made considerable contributions to the study of alkali metal ions doped lead-free halide perovskite,and provided directions and ideas for the subsequent continuous exploration of improving optical properties such as photoluminescent quantum yield or stability of lead-free halides by changing their doping elements,doping proportion,experimental methods and experimental conditions.It is helpful to promote the commercial application of these alloyed double perovskites in light-emitting and display optoelectronic devices and lay a solid foundation for their commercial development.