Study On Self-assembly And Optical Properties Of Perovskite Nanocrystals

Self-assembly is ubiquitous in nature.Controllable ordered self-assembly has become a key way to improve the performance of nanomaterials.Perovskite nanocrystals possess excellent photoelectric properties,and self-assembly makes it possible to prepare hierarchical and individual macroscopic perovskite structures from composition-predetermined and nano-scale ordered nanostructures,leading to further expansion of application ranges of perovskite nanocrystals.In the field of perovskite nanocrystals,there still lacks systematic research on related self-assembly mechanisms and processes.In this thesis,controllable self-assembly methods,morphology and stability regulations and optical properties of self-assembled nanocrystals are mainly investigated.The main research contents are divided into the following two aspects:1.Appropriate methods to assemble CsPbBr₃ nanocrystals.The optical properties and stability of self-assembled nanocrystals are further explored,and the mechanism of special optical properties of self-assembled nanocrystals are investigated.It was found that the vacuum drying method is suitable for the self-assembly of perovskite nanocrystals in comparison to the solution method.The scale and size of the superlattices of self-assembled nanocrystals can be controlled by adjusting the self-assembly duration and the concentration of the reaction solution.The assembled superlattice structure shows red-shift effect of photoluminescence spectra and a decrease in photoluminescence lifetime.These phenomena are mainly resulted from the micro-band structure of superlattice,which comes along with the increased coupling strength between nanocrystals in compact configuration of assembled nanocrystals.2.Optimization of the self-assembled nanocrystals by ligand regulation.Firstly,3-aminopropyltriethoxysilane and didodecylamine are selected as the ligand molecules to regulate the stability of nanocrystals after self-assembly,respectively.The hydrolysis cross-linking of 3-aminopropyltriethoxysilane ligand provides the stability of perovskite nanocrystals after assembly,but it causes strong cross-linkages among with each nanocrystal leading to formation of assembled sphere-like morphology.In contrast,the dense steric hindrance of didodecylamine ligands realizes the high quality assembly of perovskite nanocrystals into superlattice and thus ensures the stability of self-assembled nanocrystals.The morphology of self-assembly of nanocrystals is further regulated by using different ligands.Short-carbon-chain ligands are used to partly replace the oleic acid in preparation of perovskite nanocrystals.The self-assembly growth of nanocrystals into nanorods is realized by regulating the binding energy of organic ligands with different crystal phase interfaces.By means of TEM and first-principle calculations,the mechanisms for different morphologies of assembled nanocrystals is explored.The optical properties of the self-assembled nanorods are also investigated.The nanorods show excellent emission anisotropy of up to 0.37.