Synthesis And Stability Of Luminescent Halide Perovskite Materials

Halide perovskites are a family of semiconductor with excellent optoelectronic properties such as high absorption coefficiency,tunable direct bandgap,high carrier transporting mobility,high defects tolerance,and solution processable in a simple way,are widely explored in modern optoelectronic areas.Since the first report of the synthesis of MAPb X₃ nanocrystals by Perez-Prieto'group,a variety of methods have been proposed for the preparation of halide perovskite nanocrystals,such as hot injection and ligand assisted reprecipitation.These solution-based methods usually require toxic organic solvent to dissolve the precursor compounds,or high temperature to ensure the formation of highly crystalline products.In addition,the previously reported halide perovskite materials are mostly lead halide perovskite,which are toxic and can cause environmental pollution.In addition,lead halide perovskites are sensitive to light,oxygen,heat and moisture.These disadvantages restrict the practical applications.Therefore,the development of simple preparation method without the use of organic solvent and the design of new non-toxic/low-toxic perovskite luminescent materials have become the research spot.Based on the above discussion,this thesis presents our research work as follows.1.In organic-inorganic hybrid halogen perovskites,the photoelectric performance are determined mainly by the inorganic semiconductor and can be adjusted by the organic component.We use trimethyl bromide methyl ammonium bromide(TMBM-Br),and lead bromide as starting materials,the luminescent perovskite(TMBM)Pb Br₃was prepared by simply grinding without adding any capping ligand under ambient conditions.Its emission peak is located at 498 nm.Compared to MAPb Br₃,the emission shows a blue-shift,indicating that the organic part causes the blue-shift of the emission light.By adding a certain amount of water and methanol,the photoluminescence intensity can be adjusted.When 40?L of water and 100?L of methanol was added in0.1 mmol precursor compounds,the photoluminescence intensity is the highest,and the quantum yields reach 7.6%and 4.7%,respectively,which are 2 to 3 times that of that without the additive.It is supposed that a small amount of water and methanol can passivate the surface defects,resulted in the enhancement of photoluminescence efficiency.In addition,the emission wavelength of(TMBM)Pb Br₃ nanocrystals can be adjusted by doping with chloride ion.2.Lead-free halide double perovskite Rb₂Ag In Cl₆ nanocrystals were prepared by hot injection method.After optimizing the concentration of the capping ligand octylamine in the precursor solution,the quantum yield of Rb₂Ag In Cl₆ nanocrystals reached 58%.Due to self-assembly effect,the photoluminescence quantum yield increased to 99%after 24 hour's storage.Rb₂Ag In Cl₆ nanocrystals possess good stability and after storage at ambient conditions for 15 days,the photoluminescence quantum yield was 84%.We supposed that water induces the formation of In OCl protective layer and improves the luminescence stability of the Rb₂Ag In Cl₆nanocrystals.In addition,we also explored the optical properties of Rb₂Ag In Cl₆nanocrystals prepared with aliphatic amine with different chain length.It was found that these nanocrystals display similar optical properties and superior stability.3.?-cyclodextrin encapsulated MAPb Br₃ nanocrystals MAPb Br₃/?-cyclodextrin were prepared through the ligand assisted reprecipitation method.Due to the encapsulation effect of cyclodextrin,MAPb Br₃/?-cyclodextrin nanocrystals have good thermal and light stability.In addition,the application of MAPb Br3 quantum dots in the biological field is limited by the toxicity of Pb.?-cyclodextrin has good biocompatibility,encapsulation structure can improve the stability of MAPb Br₃nanocrystals and extend its applications in the field of biomedicine.