Study On The Synthesis Of Inorganic Halide Perovskite Nanocrystals And Modulation Of Their Luminescent Properties

Inorganic halide perovskite nanocrystals（IHP NCs）are favored by researchers because of their excellent optoelectronic properties（high absorption coefficients,high carrier mobility,tunable band gaps,high photoluminescence quantum yields,and narrow emission linewidths）,and IHP NCshave become promising semiconductor materials for use in the next generation of optoelectronic device applications.However,as a result of their inherent ionic crystal characteristics and their poor resistance to the external environment,IHP NCsshow significant structural and optical instabilities that have limited the development of practical applications using these materials.In addition,the toxicity of lead represents another bottleneck that is hindering practical application of lead halide perovskite materials.Therefore,the development of lead-free IHP materials that offer high efficiency,high stability,and environmental friendliness represents one of the most important problems to be solved in the field.In view of these factors,this paper presents an approach to improve the stability of IHP NCsand inhibit Pb toxicity by adopting an inorganic oxide coating strategy to realize effective encapsulation of IHP NCsfrom the bulk matrix to the single nanoparticle level.Optimization of the composite structure allows the stability and optical emission performance of IHP NCsto be improved significantly,and Pb leakage is suppressed to a certain extent.Furthermore,to solve the Pb toxicity problem effectively,lead-free Cs₃Cu₂X₅NCsare prepared,and their luminescence and stability mechanisms are demonstrated by theoretical calculation.The main contents of this paper are summarized as follows.（1）The CsPbBr₃@SiO₂composite matrix was prepared successfully in situ hydrolysis of an organosilicon capping agent（3-aminopropyltriethoxysilane,APTES）using the“one-pot hot injection”synthesis strategy.The composite matrix not only improves the light emission performance of the CsPb Br₃NCs（photoluminescence quantum yield（PLQY）of 83%）,but also greatly improves their stability in the external environment.In particular,under heat treatment and ultraviolet irradiation conditions,the CsPb Br₃@SiO₂composite demonstrated better heat resistance and better photo-oxidation resistance than bare CsPb Br₃NCs.Additionally,the CsPb X₃@SiO₂composite matrices with various halogen components can still maintain their original emission spectra after mixing,indicating that the anion exchange reaction was suppressed effectively.Furthermore,the CsPb Br₃@SiO₂composite matrix and K₂SiF₆:Mn⁴⁺（KSF）/CsPb Br_0.6I_2.4NCspowder were used as the green and red light-emitting layers,respectively,and combined with Ga N chips to construct light-conversion white light-emitting diodes（WLEDs）.These WLEDs displayed high-quality white light emission with high color purity（green light:97.5%;red light:96.5%）,wide color gamut（more than120%of the National Standards Television Commission’s standard range）and high luminous efficiency(40 lm W^-1).（2）To realize the monodisperse encapsulation structure for these IHP NCs,the hydrolysis rate of tetraethoxysilane（TEOS）was inhibited effectively by introducing the hydrophobic multi-branch ligand trioctylphosphine oxide（TOPO）as the surfactant for the CsPb Br₃NCs,and the monodisperse CsPb Br₃/SiO₂core-shell NCswere prepared successfully in nonpolar solvents.The structures and the optical properties of the core-shell NCswere optimized by adjusting the amount of TEOS used such that CsPb Br₃/SiO₂core-shell NCswith 87%PLQY were obtained.The exciton emission dynamics of these NCswere studied in detail.Benefiting from the protection of their TOPO and SiO₂shell,the CsPb Br₃/SiO₂core-shell NCsshowed remarkably improved stability with respect to thermal treatment,UV irradiation,and water when compared with CsPb Br₃NCs.Furthermore,the high-efficiency CsPb Br₃/SiO₂and CsPb Br_0.6I_2.4/SiO₂（PLQY:75%）core-shell NCswere combined with the Ga N chip to construct a WLED device with a full IHP NC luminescence conversion layer.This device exhibited a high color-rendering index of 90 and luminous efficiency of 65 lm W^-1.（3）With the aid of the iodide additive-assisted synthesis strategy,we successfully replaced the elemental Pb in the lead halide perovskite with elemental Cu to fabricate environmentally-friendly blue-emitting and green-emitting Cs₃Cu₂X₅（X=Cl,Br,I）lead-free IHP NCs.In particular,the Cs₃Cu₂I₃NCsexhibited high-efficiency deep blue light emission at440 nm（PLQY:96.6%）that made up for the low-efficiency emission of the lead-halide perovskites in the blue region.Specifically,optimizing the amount of In I₃to be added not only allowed the ratio of Cu⁺/I^-ions to be balanced and the iodine vacancies to be repaired,but also provided additional In³⁺ions that can inhibit overgrowth of the crystals and promote the formation of pure-phase high-fluorescence-efficiency Cs₃Cu₂I₃NCs.In addition,with the aid of first-principles calculations and transient spectra testing,we investigated the luminescence dynamics of the Cs₃Cu₂I₃NCsin detail.The results showed that the blue light emission originated from the self-trapped exciton emission in the Cs₃Cu₂I₃NCs,and that the self-trapped exciton was formed by lattice distortion of[Cu₂I₅]^3-nanoclusters in the Cs₃Cu₂I₅NCsunder light excitation.Finally,the prepared Cs₃Cu₂I₅NCsshowed good environmental stability,and explored its thermodynamic and kinetic stability mechanisms.