Self-Assembled Superlattices And Optoelectronic Properties Of Halide Perovskite Nanocrystals And Analogues

Self-assembly of colloidal nanocrystals makes it possible to bridge the nanostructrues and macro world,as well as manufacture more complicated nano-sized structures.Among various nanomaterials systems,halide perovskite nanocrystals（HPNCs）are attracting more and more attention owing to their superior optoelectronic properties.Self-assembly of HPNCs has also achieved rapid progress in recent years.However,most researches only focus on the self-assembly of CsPbBr₃ nanocubes.The as-fabricated superlattices can only assemble into cubic superlattices,which limits the understanding of physical meanings.Developing building blocks with diverse morphologies will endow more possibilities of packing architectonics,which will be benefical for investigating the electronic coupling between adjacent nanocrystals and further guarantee the promising applications of assembled superlattices.Meanwhile,the introduction of organic ligands decreases the electronic dimension and assembles into organic-inorganic hybrid nanoclusters althernatively.The hybrid nanoclusters possess orthogonal optoelectronic properties compared with HPNCs,which will promote more extended applications.This thesis mainly focuses on two primitives,i.e.,anisotropic HPNCs and organic-inorganic hybrid antimony halide nanoclusters,trying to explain the structure activity relationship between perovskite primitives,superlattices and their optoelectronic properties.The main findings are summarized as follows:1)One-dimensional assembly and pure-blue electroluminescence of quantum-confined CsPbBr₃ nanoplatelets（NPLs）Quasi-two dimensional nanoplatelets（NPLs）were synthesized via a so-called‘in situ passivation’strategy.In this synthesis condition,uniform blue-emitting NPLs were achieved via introducing inorganic hydrobromic acid as extra halide precursor to establish a halide-rich environment.The as-prepared NPLs had near-unity photoluminescence yield,narrow linewidth（12 nm）and negligible damage to eyes.In solution,NPLs could assemble into one-dimensional superlattices with longitudinal length over 100μm.The superlattices showed pronounced concentration-dependent aggregation induced luminescence properties.Based on multiple time-resolved spectroscopic characteristics,the exciton dynamics of NPLs after excitation were illustrated.Finally,pure blue light-emitting diodes（LEDs）with a maximum luminance of 62 cd/m²,a champion external quantum efficiency（EQE）of 0.124%and CIE color coordinate of（0.157,0.045）were obtained.This work would open a new door for fabricating high-quality and highly stable blue LEDs using HPNCs as active layers.2)Synthesis and surface science of truncated polyhedral CsPbBr₃ HPNCsColloidal-stable and uniform polyhedral CsPbBr₃ NCs were modulated by synergetic effect of foreign cations and tertiary amine ligands.We confirmed the corners of CsPbBr₃ NCs could be etched by foreign cations and high-index facets were then exposed.We also confirmed the tertiary amine ligands could stabilize the newly exposed facets after ligand exchange.It is revealed that the only very limited amount of foreign cations could be absorbed on the surface of polyhedral CsPbBr₃ NCs while instead,it was solely covered by protonated tertiary amine.This work directly proved tertiary amine was the key factor to stabilize unusual facets,which was responsible for the truncated polyhedral shape.It would be beneficial for further understanding the nucleation and growth of HPNCs.3)Self-assembly of polyhedral CsPbBr₃HPNCs into honeycomb superlatticesPolyhedral CsPbBr₃HPNCs could be used as building blocks for self-assembly via slowly evaporating nonpolar solvents.Unlike nanocubes,the Polyhedral CsPbBr₃HPNCs tended to have ordered hexagonal stacking and form honeycomb superlattices with lateral size over several micrometers.After assembly,（100）facets of polyhedral CsPbBr₃HPNCs were exposed and parallel to the substrate,which was also confirmed by XRD patterns.The monolayered superlattice would then stack along the out-of-plane direction via layer-by-layer deposition.More interestingly,it was found that there was a 30°tilting angle between adjacent superlattices layers,forming an ABC-ABC type high-ordered periodicity.This kind of ordered periodicity was first discovered in self-assembly of colloidal NCs.Based on spatially resolved and time resolved spectroscopy technologies,we found the hexganoal superlattices contained structural heterogeneity across the plane,where the edges of superlattices possessed redshifted PL peaks and shorter PL lifetime that should be resulted from the structural heterogeneity.4)Bulk crystals assembled from organic-inorganic hybrid antimony halide nanoclusters for X-ray scintillationAn organic-inorganic hybrid metal halide nanoclusters（Gua₃Sb Cl₆）was synthesized for the first time.Bulk single crystals could be self-assembled via anti-solvent diffusion although the primitive of Gua₃Sb Cl₆was less than 1 nm.We concluded the emission from self-trapped excitons was inherently originated from two triplet states of Sb³⁺（from ³P₁to ¹S₀ and from ³P₀ to ¹S₀）.The energy difference between the two triplet states was as narrow as about 5 me V.Further,we found Gua₃Sb Cl₆showed almost no light yield degradation upon continuous X-ray irradiation for over one hour.More importantly,Gua₃Sb Cl₆ showed temperature-dependent X-ray-activated persistent emission.At room temperature,the persistent emission could last for over 3000 s,which was comparable with the most efficient organic scintillators.A new radioluminescence at high energy region occurred when cooled down to 20 K.The afterglow intensity of this new emission strongly depended on environment temperature,indicating it was related to thermally activated delayed recombination.This work would be meaningful for materials design of scintillators and persistent afterglow under irradiation.