The Synthesis,Photoluminescence Properties And Stability Of All Inorganic Perovskite Nanocrystals

Inorganic perovskite nanocrystals(NCs)posse the excellent optical performance,such as high photoluminescence quantum yields(PLQYs),tunable photoluminescence in the full visible spectral range and high absorption coefficient.Their advantages make them suitable for various applications,including illumination,display,solar cells,and photodetectors.However,the shortcomings of perovskite NCs in terms of toxicity,stability,simple batch preparation,etc.seriously hampered the practical application of the material.Therefore,the synthesis of perovskite NCs with stable,high efficiency and tunable photoluminescence by room temperature(RT)method has important research significance.Compared with the hot-injection reaction method,the RT synthetic method enabling to facilely produce perovskite NCs in a high yield without heating and stringent conditions.However,the poor stability and low PLQY of the NCs synthesized by RT method still need to be solved.The RT strategy is severely limited by using polar reagents(such as dimethyl sulfoxide,DMSO or N,N-dimethylformamide,DMF).These polar reagents,such as DMF,can destroy or even dissolve perovskite NCs due to the perovskite NCs are sensitive to polar reagents.Typically,CsPbI3 NCs synthesized at room temperature are easily degraded within a few days,making the room temperature method not suitable for CsPbI3 NCs.Our work is based on the synthesis method of perovskite NCs and the factors affecting their optical properties.The highly stable and bright CsPbX3(X=I,Br,Cl)NCs can be obtained by constructing a water-oil interface.Simultaneously,the application of CsPb2Br5 NCs have been broadened.In our work,the bright blue-emitting CsPb2Br5 NCs with almost 100%PLQY have been obtained by shape-controlled synthesis.The main experimental result are as follows:(1)In the RT synthetic method,we construct the water-oil interface to reduce the content of polar reagents in the NCs solution effectively by introducing aqueous solution of HX(X=Cl,Br,I)and obtained the highly stable and bright CsPbX3(X=Cl,Br,I)NCs.The HX aqueous solution will be insoluble with the CsPbBr3 NCs stock solution to form a water-oil interface because the NCs are dissolved in organic reagents.The polar reagents(i.e.,DMF,DMSO)in NCs solutions tend to dissolve in the HX aqueous solution because their polarities are similar.Therefore,it is expected that the aqueous solution of HX can be used to remove the polar regents at the water-oil surface.By controlling the reaction time,the polar reagent can be removed efficiently.(2)Using different aqueous solution of HX(HBr,HCl)to treat the pristine CsPbBr3 NCs solution can not only remove polar reagents,but also obtain high-performance CsPbClxBr3-x and CsPbBrxI3-x NCs by ion exchange reactions.Traditional ion exchange has several disadvantages:(a)the toxic benzoyl halides are often used to promote the substitution of the halide component in CsPbX3 NCs;(b)some regents of the halide source,such as alkylammonium halides,cannot be completely ionized.Therefor the amount of halide source reagent cannot be precisely controlled.Excessive alkylamine halide will lead to the conversion of CsPbBr3 NCs into Cs4PbBr6 and CsPb2Br5 NCs;(c)the degradation of NCs sometimes occurs due to ultrasonic treatments and microwave irradiations that promote the complete exchange.(d)the post-synthesis processing,such as purification to remove excess reagents and by-products,can also decrease PLQYs.In this work,these symptoms are solved.The aqueous solution of HX is employed as the halide source to demonstrate successive and accurate adjustments of the PL emission maximum of CsPbX3 NCs in the full visible spectral range(410-695 nm)by the water-oil interface.(3)The bright blue-emitting CsPb2Br5 NCs with a almost 100%PLQY have been obtained by shape-controlled synthesis.The controlled morphology of the CsPb2Br5 NCs with nanoplates,nanocubes,and flat-lying nanoplates was successfully prepared.The obtained CsPb2Br5 NCs present bright blue emission at 465 nm and a near 100%PLQY.Simultaneously,characterization methods were designed to explore the factors affecting the morphology and optical properties of CsPb2Brs NCs.This provides a theoretical basis for the study of the morphology and optical properties of perovskite NCs.Our work not only proposes the methods for synthesizing high-performance all-inorganic perovskite NCs,but also expects that the methods can be extended to other systems.