Construction Of Coating Strategy Of Perovskite Nanocrystalline SiO₂ And Study On Interface Modification Of SiO₂ Layer

Metal halide perovskites APbX₃（A=CH₃NH₃⁺,CH（NH₂）₂⁺,Cs⁺;X=Cl^-,Br^-,I^-）nanocrystals（PNCs）have attracted intensive interest in recent years,due to their excellent photoelectric properties,such as wide spectral absorption,direct and precisely tunable band gap,high defect tolerance,high photoluminescence quantum yields（PLQYs）,narrow full width at half-maximum（FWHM）,and high carrier mobility.Up to date,they have been widely researched and applied to fabricate high-performance optoelectronic devices in the fields of photovoltaic,such as light-emitting diodes（LED）,lasers,solar cells and photodetectors.Nevertheless,the lability of PNCs upon the external disturbance,e.g.,humidity,thermal treatment,light illumination,appears to be the bottleneck that impedes their practical applications tremendously.Therefore,how to improve PNCs’stability becomes an important prerequisite for their further development.Among many coating methods,silica is an ideal packaging agent for optical materials because of its friendly environment,stable properties,and transparent material.Herein,we reported some SiO₂ coating strategies to synthesize stable CsPbBr₃@SiO₂ NPs.The studies mainly include:（1）In-situ crystallization of perovskite in hollow SiO₂ templates is an effective means to obtain SiO₂ coated PNCs（CsPbBr₃@SiO₂ NPs）.Nevertheless,the high surface energy of the obtained CsPbBr₃@SiO₂ NPs lead CsPbBr₃@SiO₂ NPs easily to aggregate,hindering their real applications.In this chapter,the hollow mesoporous silica templates（HSNSs）were synthesized and then were modified with long chain ligands（oleic acid chloride,OACl）and short chain ligands（trimethylbromosilane,TMBS）through nucleophilic substitution reaction,which leads to the formation of HSNSs-ML（mixed ligand,ML）.Finally,the CsPbBr₃@HSNSs-ML NPs are obtained by the evaporation-induced crystallization of 0.1 M CsPbBr₃precursors within HSNSs-ML.The mixed organic chains can endow the outer surface of the template with high entropy characteristics and show good solution processing ability in non-polar solvents.（2）In this chapter,a simple one-step method for the synthesis for SiO₂-coated CsPbBr₃ NPs at room temperature.First,all precursors are mixed homogeneously.Subsequently,the water was added and thenthe nucleophilic substitution reaction with TMBS was triggered to release HBr,which would react with cesium and lead based salts to form Cs Br and Pb Br₂ respectively,Then,CsPbBr₃ NCs was formed rapidly due to the small binding energy of perovskite crystals.Meanwhile,the APTES coordinated on perovskite surface hydrolyzed to form SiO₂ under HBr catalysis to realize the synchronous encapsulation of CsPbBr₃@SiO₂ NPs.The absolute PL quantum yields（PLQYs）of 78%are obtained for the liquid-state CsPbBr₃@SiO₂NPs due to the protection of redundant HBr.