Investigation On Atomic Scale Visualization Of Fine Structure In CsPbBr₃ Quantum Dots By Transmission Electron Microscopy

Lead Halide Perovskites(LHPs)have attracted extensive attention in recent years as an important materials in the field of photoelectric detector,laser and LED devices.Due to its excellent photoelectric properties,it has gradually become a low-cost optical material solution.All inorganic lead halide perovskite quantum dots(LHPs QDs)has become a kind of photoelectric material with more extensive application prospect due to their excellent luminescence performance and quantum effect advantages,as well as their better stability compared with their organ-ic-inorganic hybrid counterpart.Semiconductor quantum dot materials are generally regarded as single crystal materials due to their extremely small size.However,as a kind of ionic crystal lead halide perovskite quantum dot inevitably has a high defect density and a large number of intrinsic defects.But at the moment due to lack of a detailed and systemetic characterization and analysis of the defects for this material,people still utilize the first principles calculation to study.Most understanding of it are based on analogy with?-?,?-?semiconductor quantum dot defect category,limited to the defects such as,interstitial atoms,hanging bond on the surface etc.However,it is very unfavorable to understand the whole material system and the optical properties and structural relations of the devices.In this paper,three intrinsic grain boundary defects in CsPbBr₃ quantum dots are systematically studied by means of spherical aberration corrected transmission electron microscopy and first principle calculations.The separation of perovskite phase from lead deficient Ruddlesden-Popper phase was found in a single quantum dot,which may be caused by insufficient local lead content during the growth process.As a common impurity and environmental pollution source in the system of lead halide perovskite,lead leakage is one of the main obstacles to the large-scale device applications,which has attracted great attention in recent years.Lead leakage will not only introduce deep energy level defects and seriously affect exciton radiation recombination,which will seriously damage the luminescence efficiency of devices,but also bring about environmental hazards such as continuous accumulation of heavy metal lead in organisms and the environment.However,the atomic structure evolution of lead halide perovskite caused by lead leakage and the accompanying changes in electronic structure as well as their effects on device performance have not been thoroughly studied.In this paper,the atomic structure changes of CsPbBr₃ quantum dots caused by lead leakage are studied by means of spherical aberration corrected transmission electron microscope.The results show that the precipitation of lead can lead to the formation of lead deficient RP phase.When RP phase and perovskite phase encounter,a grain boundary will form inside the quantum dot.Based on our previous first principles calculations,the electrons and holes would be separated at either side of the phase interface,forming a microscopic electronic structure similar to the P-N junction.The built-in electric field generated by P-N junction will affect the free carrier transportation.Therefore,in the quantum point of lead separation,not only the lead particle will act as a non-radiation compound center of exciton,which will affect the luminescence performance of the device.The phase interface caused by the change of local chemical composition due to lead separation also constitutes a barrier for carrier migration.The results of this study have special guiding significance for the understanding of interface and lead precipitation for the structure and material growth of lead halide perovskite devices.One of the bottlenecks in the widespread use of quantum dot materials is how to achieve"quantum dot connectivity".It is very difficult to realize a confined but connected quantum dots interconnection.For the traditional?-??-?semicon-ductor quantum dots,people have explored many confined but connected method.In this paper,the unique ionic crystal characteristics of CsPbBr₃ quantum dots allow us to stitch single quantum dot to form a network.By pinning the surface ligand with the electron beam,we can control the degree to which the reaction occurs.And we found that further fusion would allow quantum dots to grow into micron lines with a very large aspect ratio on the order of 100 microns.We also characterize the fusion process of quantum dots in this case by atomic resolution and find that quantum dots have a tendency of oriented attachment growth.This result has important significance for the growth of CsPbBr₃ micron line structure and even for the growth of other lead halide perovskite micron line structure,which expands the ideas for their application in laser devices.