Controllable Synthesis And Optical Properties Of CsPbBr₃ Perovskite Nanosheets

In the last few years,perovskite materials are widely concerned and have broad application prospects,with fluorescence spectra covering the whole visible region,which are the research hotspots in optoelectronics.For the completely inorganic perovskite Cs Pb X₃(X=Cl,Br,I),various methods,such as changing the reaction temperature in experiments,adjusting the ligand chain length,using different ligand mixes and introducing specific impurities,can be used to achieve the purpose of modulating the size,morphology and crystalline phase of perovskite nanocrystals,which can modulate their luminescence,photoelectric effect and carrier transport behavior to obtain the enhancement of optoelectronic properties.Therefore,all-inorganic perovskite with different morphologies have been prepared successively,such as nanowires,nanorods and nanosheets.Among them,two-dimensional perovskite nanosheets are of great interest because of their anisotropy,easy film formation,and better in-plane carrier transport channels.These two-dimensional nanomaterials offer their unique advantages besides increasing the specific surface area.Their narrow absorption edges and emission spectra and often high photoluminescence quantum yields make them good candidates for photoemission applications.In this thesis,two methods were used to synthesize two-dimensional CsPbBr₃perovskite nanosheets.One was synthesized by reducing the reaction rate during precursor injection at 180?.The obtained nanosheets were thin and irregular in morphology.The other one is by modulating the ligand by introducing the short-chain ligand octylamine octanoate,and the use of the short-chain ligand makes the synthesized nanosheets have a large lateral dimension while their vertical dimension is always in a strong quantum confinement.The countenancen and photornetrics of CsPbBr₃ nanosheets were studied by transmission electron microscope(TEM),uv-visible absorption spectrum(UV),photoluminescence spectra(PL),X-ray diffraction spectroscopy and time-resolved fluorescence lifetime.Analysis of absorption and fluorescence spectra showed that the absorption peak and emission peak were narrow,small Stokes shifts and half-height widths.Its time-resolved fluorescence lifetime is longer compared to nanocrystals,which due to the smaller band gap of larger size NSs,which partially eliminates the nonradiative paths and reduces the attenuation channels,making the fluorescence lifetime increase.It also shows that NSs have fewer surface defects.The synthesized CsPbBr₃ nanosheets were subjected to white light irradiation,and the peak positions of the emission peaks obtained remained essentially the same and were more stable under light.The variable temperature photoluminescence spectra of CsPbBr₃ perovskite nanosheets and nanocrystals were investigated by varying the temperature.The fluorescence(PL)peak positions of both CsPbBr₃ nanosheets and nanocrystals are blueshifted with increasing temperature.With the rise of temperature,the half-height width(FWHM)increases.The larger exciton binding energy of nanosheets than nanocrystals indicates that the nanosheet structure has stronger Coulomb interactions,which ensures that the nanosheets have a more stable structure.