The Research On Synthesis And Emitting Properties Of CsPbBr₃ Perovskite Nanoplatelets

The photoelectric properties of halide perovskite with high carrier mobility,high photoluminescence quantum yield（PLQY）and high defect tolerance have attracted wide attention of researchers.Two-dimensional（2D）CsPbBr₃ nanoplatelets（NPLs）not only maintain the excellent properties of halide perovskite but also have the characteristics of high exciton binding energy and tunable emission wavelength by controlling the layer numbers（n）of[Pb Br₆]^4-octahedral,which promoting the 2D material in perovskite blue-emitting research.In this thesis,the controllable synthesis of CsPbBr₃ nanosheets at room temperature was explored,and the phase structure,micro morphology,optical properties of the synthesized CsPbBr₃ NPLs were systematically analyzed.To improve the optical properties and stability of the CsPbBr₃ NPLs,the passivation strategy and surface ligand modification were employed.The main results are as follows:（1）The CsPbBr₃ NPLs with cubic phase structure was prepared by ligand-assisted reprecipitation method.After Ni-Br passivation,Pb²⁺ions were substituted by Ni²⁺ions,which resulted in the lattice shrinking and crystalline interplanar spacing reducing of the CsPbBr₃NPLs.The spectrum,phase structure,and morphology characterizations showed that the CsPbBr₃ NPLs achieved optimal performance when the reaction time was controlled at 30minutes and the Ni-Br mixed solution was introduced at 3.5μl.Compared with pristine NPLs,the emission intensity of Ni-Br passivated CsPbBr₃ NPLs was improved significantly.The emission peak was shifted from～454 nm to～464 nm,and its PLQY increased from 33.2%to78%,the full width at half maxima（FWHM）decreased from 23.4 nm to 14.1 nm,the color purity improved obviously,and the morphology was more uniform after passivation,the thickness was measured about～3 nm（n=5）.The obtained Urbach energy of CsPbBr₃ NPLs before and after passivation are 31.9 me V and 25.7 me V respectively calculated by absorption spectrum.XPS results showed the binding energy of Br 3d and Pb 4f were slightly increased after passivation,indicating that the performance improvement of CsPbBr₃ NPLs could be attributed to the reduction of surface defect density and the improvement of lattice stability.After 30 days of storage at room temperature,the emission intensity of unpassivated CsPbBr₃NPLs was only 45.8%of the initial emission intensity,while the passivated NPLs still retained86.3%of the initial emission intensity.Further,the passivated CsPbBr₃ NPLs solution was used to construct monochromatic liquid LED,the luminescence saturation did not appear as the driving current reached 190 m A,demonstrating the potential application in practical world.（2）The CsPbBr₃ NPLs was synthesized by an emulsion method at room temperature by using oleylamine and tri-n-octylphosphine as surface ligands.The synthesized CsPbBr₃ NPLs（n=5）with side thicknesses of 3 nm showed strong blue emission at～464 nm,and the PLQY reached as high as 87.1%,the Urbach energy is 20.1 me V based on the absorption spectrum.Due to the stacking between plates,obvious periodic diffraction peaks could be found in the low-angle region of XRD.In addition,the N-H and weakly P-Pb absorption peaks can also be detected based on Fourier-transform infrared spectroscopy,which confirms that the selected ligand was adsorbed on the surface of the CsPbBr₃ NPLs.After one heating-cooling cycle,the emission intensity of NPLs could still maintain～97.6%of the initial emission intensity.Moreover,the emission peak of CsPbBr₃ NPLs did not shift under continuous ultraviolet irradiation for 120 min.It is suggested that the excellent optical properties of the CsPbBr₃ NPLs may be derived from the strong binding force between surface ligands and NPLs,which inhibits the ligands desorption and surface atomic vibration,thus reducing the generation of defects.Finally,Mn²⁺was introduced into CsPbBr₃ NPLs,due to the strong energy transfer between the NPLs host and Mn²⁺,blue-to-red conversion luminescent materials were achieved.