Study On The Size, Morphology And Properties Of CsPbX₃ Perovskite Nanocrystals

With the rapid development of the global economy,the demand and consumption of energy are continuously increasing.Irrational development and utilization of non-renewable energy leads to resource exhaustion and environmental destruction.To solve the problem of energy and the environment,scientists have turned to renewable energy development.As a newly renewable energy,solar energy provides human beings with inexhaustible energy.The solar cell can convert solar energy into thermal or electrical energy,which is a sort of sustainable way to solve the energy crisis.Therefore,developing solar cells with prominent electricity conversion efficiency is bear the brunt of necessary tasks.In 2009,the organic-inorganic hybrid perovskite nanomaterials and Ti O₂ composite solar cells achieved a photoelectric conversion efficiency of 3.8%.With the progress of science and technology,the latest efficiency of single-junction perovskite solar cells has reached 25.2%so far and the practical application is immeasurable in the future.Compared with organic-inorganic hybrid perovskite,the all-inorganic halide perovskite CsPbX₃（X=Cl,Br,I）nanomaterials have attracted continuous attention of scientists in recent years because of their better stability and wider applicability.But in the hot injection synthesis method of the inorganic perovskite,high temperature and inert atmosphere protection are required.In addition,artificial operation and the influence of environmental factors lead to batch difference,which make the mass synthesis of perovskite nanomaterials and the industrialization difficult.Perovskite nanowires（NWs）and nanorods（NRs）are important 1D/quasi 1D semiconductor nanomaterials and have shown the great application potential in optics and optoelectronics applications because of the adaptability of flexible components,good carrier transmission performance and polarization characteristics of absorption and emission.Therefore,due to the nature of the highly dependence of the morphology,the development of synthetic method which can achieve the adjustable diameter and length of 1D/quasi 1D the perovskite is vital.However,the controllable diameter and length of CsPbX₃ NRs/NWs within the scope of the strong quantum confinement is still a huge challenge for scientists.In this paper,we conducted in-depth research on batch-controlled synthesis method of perovskite materials,controlled synthesis,and reversible conversion of 1D CsPbX₃ NRs/NWs,polarization optical properties and polarization detector.The innovation points are as follows:1)In the process of batch CsPbX₃ controllable synthesis,we prioritized microfluidic method.By means of control of a single variable method,the reaction temperature,injection rate,PTFE capillary diameter and the precursor ratio etc.have been explored respectively.After statistically analyzing the size,morphology,PL emission spectra and UV absorption spectra of the obtained CsPbBr₃ nanocrystalline under different synthesis conditions,the optimum synthesis conditions were obtained.In other words,when the reaction temperature at 280°C,the sampling rate of 0.12m L/min,PTFE pipe diameter of 0.5 mm,Pb and Cs mole ratio of 8:1,the perovskite nanocrystalline possesses uniform size,narrow half peak width and high luminous intensity.Moreover,this synthesis condition can be derived to synthesize Cs Pb Cl₃ and Cs Pb I₃.During the analysis of morphology under different conditions,we deem the combination of microfluidic reactor with artificial intelligence can greatly facilitate our screening and collection of nanocrystals.2)At room temperature,we got 2*500 nm CsPbX₃ NWs by simply aging.The method has the advantages of high yield,uniform morphology of NWs,and easy synthesis process.In relatively high concentrations（>50 mg/m L）,CsPbX₃ NWs can exist in nonpolar solvent stably.If the solution is diluted to low concentration,after a certain amount of time,the NWs are gradually to the NRs conversion.Furthermore,the length and diameter of NRs can be controllable by adjusting diluted concentration and aging time.The higher initial concentration leads to greater length diameter ratio of the NRs.Then this phenomenon is analyzed from the perspective of chemical equilibrium,as a response to chemical equilibrium,chemical reactions can be carried out by any direction,so we believe that NRs can be changed back to NWs under certain conditions.And we verified the inference by dispersing the converted NRs into original mother liquor of the NWs,as expected,the reversible conversion of the NRs to NWs realized.The concept of equilibrium control proposed in this study opens a new way for the reversible morphological transformation of perovskite nanocrystals,which is expected to be extended to other nanocrystals.3)Since the axial and radial geometrical dimensions of CsPbBr₃ NRs/NWs are different,the physical properties such as polarization fluorescence will be anisotropic and the anisotropy can be adjusted by morphology.Therefore,we tested the polarization optical properties of NRs and NWs respectively.The CsPbBr₃ NRs/NWs films were assembled on glass substrate by different methods at room temperature,and the polarization fluorescence of the films was 0.9 times higher than the nanowires dispersed in cyclohexane solution.The polarized photoelectric detector was prepared by brush coating method and obtained the photoelectric response curve under polarized light by applying linearly polarized light to it.