Study On Controlled Synthesis Of Lead Halide Perovskites At The Nanoscale And Their Growth Mechanisms

Due to the size–tunable bandgap energies and large exciton binding energy,lead halide perovskites at the nanoscale have been widely used to new-style optoelectronic devices.Many facile and scalable synthetic strategies of the nanomaterials have been developed and material dimensions could be controlled precisely.However,these synthetic routes are very unique in their own right,and they all have advantages and disadvantages.So,it is necessary to systematically generalize and summarize the reactions.In addition,it is worth exploring the nucleation and growth mechanisms of the nanomaterials in order to guide experiments and seek better synthesis routes.Moreover,they display unique optical and electrical properties of which inner mechanism need be investigated.Aiming at these problems,controlled synthesis of lead halide periveskites?CH₃NH₃PbBr₃ and CsPbBr₃?at the nanoscale is realized and the synthetic scheme and growth mechanisms are discussed in this paper.The characteristic research is done to perfect the theory construction,and a new crystal texture is found.Relevant contents are as follows:Pure nanoparticles morphology of CH₃NH₃PbBr₃ could be realized by employing lead oleate(Pb(C₁₇H₃₃COO)₂)as the sole lead source and controlled using short-and long-chain mixed alkyl ammonium.These nanoparticles were monodispersed?2.2±0.4 nm in diameter?,highly fluorescent?with a quantum yield approaching 85%?,and highly stable in the solution?for more than 30 days?.Comparative studies revealed that the shape of CH₃NH₃PbBr₃ nanomaterials was strongly dependent on the lead sources,PbBr₂ and Pb(C₁₇H₃₃COO)₂,and evolves as a function of the ratio of short-and long-chain alkyl ammoniums in the precursors.A facile and rapid synthetic approach was employed to synthesize blue luminescent CsPbBr₃ nanomaterials,which did not employ DMF at ambient temperature in air.It was found that amine protonation was the key to the formation of blue luminescent CsPbBr₃nanoplatelets by adding HBr,while fatty acid-capped green luminescent CsPbBr₃nanocubes were obtained if only oleic acid was used as ligands.The characrteristics of lead halide perovskite nanomaterials were intensively researched because of unique properties,such as large exciton binding energy,defect tolerance and spontaneous anion-exchange.The strength of the exciton features at room temperature arose because of quantum and dielectric confinement effects.No additional surface passivation was necessary to achieve a high photoluminescence quantum yield?PLQY?,and dangling bonds?from surface ligands?did not play a role in the Photoluminescence?PL?emission.The efficient exchangeable nature of the halides in this system derived from their high ion mobility and rapid diffusion in solution.The band-gap tuning could result from compositional modifications and the PL emission of the nanomaterials could be tuned across the whole visible spectrum.The mole ratios of long-and short-chain alkyl ammonium halides in the precursors can significantly affect the crystalline structures of these nanomaterials toward nanoparticles and nanoplatelets with different layers via the quantum confinement effect.Photoactivation phenomenon was also observed in CsPbBr₃ nanomaterials,which is believed as the result of light-induced structural reorganization.The photoinduced anion exchange reaction was realized by the photosensitive action upon exposure to room right or laser illumination.Blue luminescent CsPbBr₃ nanomaterials by adding HBr were proved to be mesocrystals,which consists of individual nanoparticle building units with a defined long-range order on the atomic scale.Results indicate that ligands have great influences on the growth kinetics and morphologies of CsPbBr₃ mesocrystals with standard cubic structure and high luminescent.The destabilization of ligand matrix was responsible for the self-assembly of mesocrystals through oriented attachment into larger monocrystals because of mutual crystallographic orientations of individual building blocks with a defined long-range order on the atomic scale.The work contributes to controlled synthesis of multifunctional materials with unique structure and provides new ideas for the research of other metal-halide perovskites crystals.