Preparation And Luminescent Properties Of Cs_nPbx_n+2 All-inorganic Perovskite

Cs_nPbX_n+2 type all-inorganic lead-halide perovskite?n=1,CsPbX₃;n=4,Cs₄PbX₆;X=Cl,Br,I?has been applied to many fields due to its unique photoelectric properties,such as:solar cells,light-emitting diodes,photodetectors and lasers.At present,the maximum external quantum efficiency?EQE?of CsPbI₂Br-based LED is 20.3%,which fully shows the great application prospect of such materials in the field of optoelectronics.With the in-depth study of CsPbX₃,the related derivatives Cs₄PbBr₆ and CsPb₂Br₅ have gradually become the research objects.Currently,the main methods to prepare their nanomaterials are high temperature thermal injection method and room temperature saturation recrystallization method.Due to the harsh experimental conditions and complex process required by the thermal injection method,CsPbBr₃ quantum dots and Cs₄PbX₆/CsPbX₃ composite microcrystals were successfully prepared by room temperature saturation recrystallization method in this paper.The main research contents are as follows:1.Square CsPbBr₃ quantum dots were synthesized by saturated recrystallization at room temperature using oleic acid?OA?and oleamine?OAm?and the solubility difference of solvents before and after recrystallization.The edge length of CsPbBr₃ quantum dots was 7-11 nm.Quantum dots exhibit strong emission at 510 nm under 365 nm excitation light.By changing the reaction temperature and the amount of antisolvent,it was found that the shape of CsPbBr₃quantum dots remained unchanged and the size of quantum dots changed slightly.Due to the quantum size effect,quantum dots'absorption edge and emission wavelength will move slightly with the size.Transient fluorescence lifetime shows that its short lifetime is 10 ns,accounting for more than 80%,indicating that its main luminescence comes from bandgap direct recombination luminescence,with fewer defects.However,the stability of quantum dot solution stored at room temperature is poor.2.Cs₄PbBr₆/CsPbBr₃ composite microcrystals were prepared by saturated recrystallization.Both the XRD pattern and the TEM image indicate that the two coexist,and the TEM high resolution image further indicates that the two substances exhibit a wrapped state.The band gaps of Cs₄PbBr₆ and CsPbBr₃ calculated by UPS and absorption are 2.34 eV and 3.88 eV,respectively.The wide bandgap and 0D stable structure of Cs₄PbBr₆ not only protects the internal CsPbBr₃,but also enhances its luminescence by FERT.Comparing the different ligand usage,it was found that microcrystalline prepared with 0.50 mL of OAm and 0.25 mL of OA?relative to 5 mL DMF?has the highest luminescence intensity.Comparing different polar antisolvents,it was found that the composite microcrystals prepared by dichloromethane and DMF has the highest PL and PLQY.3.By comparing different raw material ratios?CsBr and PbBr₂?,it was found that the optimum ratio for preparing Cs₄PbBr₆/CsPbBr₃ composite microcrystals was 1:1,and excessive CsBr would remain.The effect of temperature on the morphology,structure and luminescence properties of the composite crystallites indicates that the crystallite size changes,and as the temperature increases,the size becomes larger,and the absorption and emission peaks are red-shifted.Various microcrystalline Cs₄PbX₆/CsPbX₃?X=Cl,Br,I or mixtures thereof?were prepared by varying the halogen composition of the raw material.,and the band gap varied with the halogen composition,and the emission wavelength was in the range of 414-696 nm.The half width?FWHM?is in the range of 20-35 nm.The Cs₄PbBr₆/CsPbBr₃ microcrystals were placed in 50%humidity air,which shows good stability and still has 80%of the original PL strength after 50 days.