CsPbBr₃@CsPbBr_3-xCl_x Perovskite Core-shell Heterojunction Nanowires Via Post-synthetic Method With HCl Gas And Their Characteristics

Inorganic lead-halogen perovskite CsPbX₃?X=Cl,Br,I?have attracted more attentions due to their advantages of large absorption cross-section,effective and tunable photoluminescence,long electron-hole diffusion length and low trap state density.As excellent photonic and photoelectric materials,they have broad application prospects in many photoelectric devices such as light-emitting diodes,solar cells,lasers,and photodetectors.However,the current research on perovskite materials is mostly limited to monochromatic luminescence materials due to the unstable anion of CsPbX₃.It is difficult to synthesize stale core-shell CsPbX₃ to realize multicolor luminescence in a single perovskite nanostructure.In this thesis,by controlling the reaction conditions,CsPbBr₃ nanowires were synthesized,and HC1 gas was introduced as the Cl^- source to exchange with Br^- ions of CsPbBr₃ nanowires to form core-shell structure heterojunction nanowires,which achieved bicolor luminescence and studied anions switching mechanism.Main works as follows:?1?First,high-quality and well-dispersed CsPbBr₃ nanowires are synthesized by the high-temperature injection method,and their crystal form,morphology and fluorescence spectrum?PL?are analyzed.Results have shown that different reaction conditions and different ligand concentrations directly affect the morphology and fluorescence intensity of nanowires.?2?In order to obtain two-color nanowires,we first introduce anions directly into the solution through the PbCl₂ and PbI₂ solutions to exchange anions with the CsPbBr₃nanowires.The results show that the finally obtained nanowires after anion exchanged with PbCl₂ and PbI₂ solutions are more likely CsPb?BrCl?₃ or CsPb?BrI?₃ uniform alloy nanowires by fluorescence spectroscopy and nanowire crystal form analysis.These nanowires have only one independent luminescence peak under the excitation of 365nm ultraviolet light.?3?In order to facilitate to control the degree of anion exchange between Cl^-ions and Br^-ions,the introduction of Cl^-by HC1 gas is firstly proposed to anion exchange.By this method,we successfully synthesize a nanowire core-shell heterojunction with bicolor luminescence peaks.The effect of different reaction time and reaction temperature on the formation of heterojunction is studied,and the reaction mechanism is analyzed.The results show that after anion exchanged,the nanowires still maintain a good lattice structure,and their fluorescence spectrum under the excitation of 365nm ultraviolet light changes from a single independent luminescence peak to a double luminescence peaks.When the anion exchange reaction is carried out at different temperatures,the luminescence peaks of the obtained nanowires are different.Only when the anion exchange reaction is performed at a temperature of 30?,the core-shell structure nanowire heterojunction can be obtained.At the same time,anion exchange is carried out at different reaction times,and different samples are obtained.When the reaction time is short,it is difficult for Cl^-ions to enter the nanowires,of which the fluorescence spectrum shows single peak.When the reaction time is 1 minute more,the fluorescence spectrum changes from a single emission peak to a double emission peak and the blue emission peak gradually increases.But finally the emission changes to a single emission peak again along with the increasing reaction time,which uniform alloy nanowires are formed.And the lifetime of the exciton luminescence peak shows a tendency to decrease gradually with the increase of reaction time.Finally,the mechanism of anion exchange is analyzed.