Room Temperature Synthesis And Application Of Perovskite Nanocrystals With Controlled Morphology And Optical Stability

Lead halide perovskite nanocrystals have attracted great attention in the fields of light-emitting diodes,solar cells,and photodetectors due to their advantages of high photoluminescence quantum yield,large carrier mobility,efficient photoelectric conversion efficiency,narrow half-peak width and high light absorption coefficient.However,perovskite nanocrystals are instable,toxic and difficult for large-scale synthesis,which limits their large-scale commercial application.To solve these problems,this study synthesised CsPbBr₃ and Mn²⁺-doped Cs Pb Cl₃ nanocrystals(Mn²⁺:Cs Pb Cl₃)at room temperature by introducing the surface ligand hexamyldisilane(HMDS),which not only controlled the crystal structure,morphology and optical properties of the product,but also improved its stability and achieved mass preparation.The detailed contents and conclusions are as follows:1)CsPbBr₃ nanocrystals with adjustable structure,morphology,optical properties and stability were obtained by HMDS assisted room temperature synthesis.The introduction of HMDS triggers the nucleation and formation of CsPbBr₃ nanocrystals.The crystal structure,morphology,size and optical properties can be tuned by changing the HMDS amounts,With the increasing HMDS,The morphologies of the products changed from nanospheres to nanocubes.It is worth mentioning that HMDS is introduced as a low surface energy organic ligand to modify the surface of CsPbBr₃nanocrystals,making the CsPbBr₃ nanocrystals film hydrophobic(the contact angle with water is 110^o),which can prevent nanocrystals to a certain extent contact reaction with water molecules,thereby improving the stability of the product in the air environment.Fourier transform infrared spectroscopy(FTIR)results showed that the surface of CsPbBr₃ nanocrystal was successfully modified by-CH₃ group due to the introduction of HMDS.The results of comparative studies show that the stability of CsPbBr₃ nanocrystals prepared by HMDS modification reaction is far superior to that of CsPbBr₃ nanocrystals prepared without HMDS,not only does the photoluminescence(PL)intensity not significantly decrease after 30 days of storage in the air environment,and the shape has no obvious change in appearance and phase structure.Using the obtained CsPbBr₃ nanocrystals in white LED,the highest color rendering index(CRI)of the device can reach 90.6.2)In the presence of HMDS,Mn²⁺precursor was introduced,and Mn²⁺-doped Cs Pb Cl₃ nanocrystals(Mn²⁺:Cs Pb Cl₃)was prepared at room temperature.When we change the feed ratio of Mn Cl₂(Mn Cl₂/Pb Cl₂),the doping concentration(Mn/(Mn+Pb))of Mn²⁺ions in the product increases with the increase of feed ratio,up to 53%.The PL spectra of doped perovskite nanocrystals have two fluorescence peaks at 400 nm and 600 nm,respectively,and with the increase of Mn²⁺ion doping concentration,the intrinsic photoluminescence peak(peak1)at 400 nm does not move significantly,while the photoluminescence peak(peak2)caused by Mn²⁺doping at 600 nm is red-shifted,and the intensity ratio of the two peaks(peak2/peak1)is also increasing.The photoluminescence quantum yield of the doped product is up to 29.8%,which is 14times higher than that of undoped Cs Pb Cl₃ nanocrystals.According to TEM and XRD test results,when the doping concentration of Mn²⁺ions is less than 50%,the average particle size of Mn²⁺:Cs Pb Cl₃ nanocrystals is 6.5±0.93 nm,and the product is tetragonal Cs Pb Cl₃.When the doping concentration of Mn²⁺ions is greater than 50%,the average particle size of Mn²⁺:Cs Pb Cl₃ nanocrystals is 6.0±0.4 nm,and the diffraction peak of the product matches that of Cs Mn Cl₃.Fourier transform infrared spectroscopy(FTIR)results show that the surface of Mn²⁺:Cs Pb Cl₃ nanocrystals contains functional groups of oleylamine,oleic acid and HMDS,indicating that these three ligands have a modification effect on the surface of nanocrystals.In addition,the optical properties of Mn²⁺:Cs Pb Cl₃ nanocrystals can be adjusted by ion exchange.It is worth mentioning that the obtained Mn²⁺:Cs Pb Cl₃ nanocrystals can not only exchange ions with Br^-,but also realize ion exchange with I^-.