Preparation And Properties Of Organic Metal Halide Perovskite Nanomaterials

The organometallic halogen perovskite（OMHP）materials which is an organic-inorganic hybrid compound formed by self-assembly of organic molecules and inorganic molecules,have attracted widespread attention due to their excellent photoelectric conversion properties.There are many advantages such as high carrier mobility,long life,long diffusion length,strong light absorption,high photoelectric conversion efficiency,simple preparation,and low process cost that it can be applied to solar cel s,LEDs,lasers,FETs and photodetectors.Because of their instability at high temperatures,the method of synthesizing inorganic perovskite nanocrystals based on ionic metathesis reaction is not suitable for the preparation of OMHP nanocrystals.How to control and adjust their morphology and PL emission spectra by changing the ligand and halogen ele ments has also been studied and reported.However,little attention has been paid to the solvent effect on the formation of OMHP NCs.We investigated the solvent effect on the formation of MAPbBr₃ NCs by using Pb Br₂,MeNH₂,octylamine and HBr as precursors.It is proved that the morphology and fluorescence emission wavelength of MAPbBr₃ nanocrystals are closely related to the polarity of the solvent by characterized of the morphology,structure and optical properties of OMHP NCs obtained at different poor solvents.The nanoplatenets with blue emission were produced for the low polar solvents,such as toluene,PhC l and EtOAc.The increase in polarity of poor solvents results in the red shift of emission of obtained NCs.The much more polar solvents like acetone and CH₃CN lead to formation of MaPbBr₃NCs with cubic phase.Furthermore,the stability of MAPb Br₃ NCs dispersed in various solvents is studied.We found that MAPbBr₃ NCs are stable when dispersed in unpolar solvent.When dispersed in polar solvent,the stability is depend ing on the concentration:the higher the concentration,the more stable.Furthermore,we explored mechanism deeply.For instability of MAPb Br₃ nanocrystals under humid air,ultraviolet or high temperature conditions,we present a facile and low cost approach for the preparation of perovskite-based composite films via blending CH₃NH₃PbBr₃ nanocrystals（MAPb Br₃ NCs）with two kinds of commercially available silicone resins.The highest photoluminescence quantum yield of the prepared composite films is up to62%,which greatly improved the stability of nanocrystals.No observable PL degradation occurred for the MaPbBr₃/SSDC film upon exposure to ambient air for at least two months.After immersed in water for 36 hours,the emission of the film decays to 77%of the initial value.Compared with MaPbBr₃/SSDC composites,MAPbBr₃/PMSR composites further improve the stability of nanocrystals,which can be used for the preparation of warm white LEDs.This is because the structure of PMSR contains phenyl rings which results in the much lower water per-meability and enhanced stability against heat and UV irradiation.The two-dimensional（2D）layered crystals of(C₆H₁₃NH₃)₂PbBr₄ were synthesized on Si/SiO₂ wafers by using hexylamine as an organic ligand and volatilizing the solvent.The effects of experimental conditions such as temperature on the morphology and size of two-dimensional crystals were studied.