| As a new type of optoelectronic materials,semiconductor nanocrystals with excellent optical,electrical,thermal and magnetic properties have drawn extensive attention of researchers due to their unique surface effect,quantum confinement effect and quantum tunneling effect.In contrast with traditional binary semiconductor nanocrystals(CdS,CdSe,InP,etc.),all-inorganic cesium lead halide CsPbX3(X=Cl,Br,I)perovskite nanocrystals exhibit excellent optoelectronic properties such as tunable emission wavelength,high photoluminescence quantum yield(PLQY),narrow spectral line width,wide color gamut,and large light absorption cross-section,which show a prospect application in light emitting diodes(LED),photodetectors,lasers and solar cells.However,there are great challenges for controllable and large-scale synthesis of CsPbX3 perovskite nanocrystals because of their unclear growth dynamics and morphology transformation mechanism.In addition,the emissive efficiency and stability of blue/cyan-emitting CsPbX3 perovskite nanocrystals lag far behind other color-emissive perovskites,which seriously hinder their practical application in the photoelectric devices.Hence,it is greatly significant to solve the above problems for promoting the development and commercial application of all-inorganic CsPbX3 perovskite nanocrystals.Herein,the dissertation of this paper is intended to regulate the growth kinetics of all-inorganic cesium lead halide CsPbX3 perovskite nanocrystals by the ligand engineering strategy.The effects of surface ligands on the composition,structure,morphology and optical properties of CsPbBr3 perovskite nanocrystals were systematically studied,and the morphology transformation mechanisms of perovskite nanocrystals were revealed.Besides,the intrinsic relationships between the microstructures and surface characteristics of CsPbX3 perovskite nanocrystals and their optical properties were clarified,and the feasibility of controllable and large-scale preparation of all-inorganic perovskite nanocrystals was investigated.Furthermore,a series of CsPbX3 perovskite composite materials with excellent fluorescence performance and high stability were fabricated by using the organic polymers and inorganic oxides as matrices,and their applications potential in the fields of solid-state luminescence,fluorescence detection and temperature sensing were evaluated.The specific research contents and main results are as follows:(1)A room temperature supersaturation recrystallization strategy was proposed to prepared the all-inorganic CsPbBr3 perovskite nanocrystals by the with utilizing oleic acid(OA),n-octylamine(OTAm)and octanethiol(OT)as surface ligands,and the effects of Cs/Pb ratio,perovskite precursors concentration,ligands concentration and ratio on the composition,structure,morphology and optical properties of perovskite nanocrystals were systematically investigated.The results showed that the monodisperse and orthorhombic CsPbBr3 perovskite nanocrystals with excellent uniformity can be obtained by optimizing the Cs/Pb ratio,perovskite precursors concentration and ligands concentration,respectively.Based on a facile anion exchange reaction,the obtained CsPbX3 perovskite nanocrystals with different halogen composition exhibit tunable emission of 443.3～649.1 nm.In addition,profiting by the synergistic mediation of triple ligands on the growth kinetics,the controllable and large-scale preparation of CsPbBr3 perovskite nanocrystals was successfully realized.By adjusting the ligands ratio of OTAm/OT,the all-inorganic CsPbBr3 perovskite nanocubes and nanorods could be obtained respectively.It was revealed that the morphology transformation mechanism of CsPbBr3 perovskite nanocrystals induced by the OTAm ligands based on a variety of characterization methods and density functional theory(DFT)calculations.Meantime,the universality of alkyl amine ligands for mediating the shape and optical properties of CsPbBr3 perovskite nanocrystals was also demonstrated.Notably,the CsPbBr3 perovskite nanorods prepared at the OTAm/OT ratio of 1:1 exhibited relatively high PLQY(91.2%)and stability due to the outstanding passivation and protection effect of surface ligands.A white light emitting diode(WLED)is fabricated by using the CsPbBr3 perovskite nanorods as the green-emitting layers,which showed a bright white light and wide color range(121.2%of National Television System Committee(NTSC)standard),indicating their great application potential in the indoor lighting and display field.(2)To further improve the stability of all-inorganic perovskite nanocrystals,one-step electrospinning strategy was developed for the in-situ preparation of CsPbBr3@PVDF-HFP/PS perovskite composite nanofibers by using polystyrene(PS)and poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP)as organic polymeric matrices,and the influences of polymer mass fraction,spinning parameters,perovskite precursors concentration and ligands concentration on the morphology and optical properties of perovskite composite nanofibers were systematically investigated.The results showed that the minimum average diameter and maximum PLQY of CsPbBr3@PVDF-HVP/PS perovskite composite nanofibers could reach to 49.9±2.2 nm and 90%.In addition,the superhydrophobic performance of CsPbBr3@PVDF-HVP/PS perovskite composite nanofibers were obtained via combining the perfluorodecyltrimethoxysilane(PFDTMS)assisted electrospinning technology and the post-treatment process,which presented excellent long-term water stability.Notably,the universality of perfluorosilane(PFs)to improve the hydrophobicity of perovskite@polymer composite fibers was demonstrated.By adjusting the halogen composition of perovskite precursors,the as-prepared CsPbX3@PVDF-HVP/PS perovskite composite nanofibers showed tunable emission wavelength covering the whole visible range of 451.5～650.8 nm.Based on their ultrafine diameter,excellent luminescent and hydrophobic properties,the perovskite composite nanofiber membranes were successfully applied to the accurate detection of organic fluorescent dyes Rhodamine 6G(R6G)and Rhodamine B(RhB)aqueous solution,and the corresponding fluorescence resonance energy transfer(FRET)efficiency could reach up to 80.9%and 69.7%,respectively,as well as the detection limit could be as low as 0.001 ppm.Futhermore,an efficient WLED device with wide color gamut covering the 117%NTSC standard is fabricated based on the composite nanofiber membranes,suggesting their promising prospect for fluorescence detection and solid-state lighting.(3)To improve the emissive efficiency of all-inorganic cyan/blue-emitting perovskite nanocrystals,a feasible strategy was proposed for synthesizing the high-quality cyan/blue-emitting CsPbClxBr3-x perovskite nanocrystals by exploiting the room temperature supersaturated recrystallization method and the DDAB ligand-assisted post-treatment process,and the effects of addition amounts of DDAB ligands on the composition,structure,morphology and fluorescence properties of perovskite nanocrystals were systematically investigated.The results indicated that the prepared cyan-emitting DDAB-CsPbCl0.8Br2.2 and blue-emitting DDAB-CsPbCl2.oBr1.0 perovskite nanocrystals exhibited significantly enhanced PLQY of 83.1%and 75.3%,which are due to the effective elimination of surface defects by the ligand-exchange reaction and halogen-compensation mechanisms during the DDAB ligands-assisted post-treatment process.The universality of alkyl brominated quaternary ammonium salts to improve the optical properties of CsPbClxBr3-x perovskite nanocrystals was demonstrated.In addition,the cyan-emissive SiO2@DDAB-CsPbCl0.8Br2.2/SIS and blue-emissive SiO2@DDAB-CsPbCl2.0Br1.0/SIS perovskite composite materials were obtained by grafting the perovskite nanocrystals onto the silica(SiO2)nanospheres and then encapsulating into polystyrene-polyisoprene-polystyrene(SIS)films.Notably,the as-prepared cyan and blue perovskite composite films showed excellent storage,light and water stability resulted from the triple efficient protection of DDAB ligands,SiO2 nanospheres and SIS films.Most importantly,the cyan-emitting SiO2@DDAB-CsPbCl0.8Br2.2/SIS and blue-emitting SiO2@DDAB-CsPbCl2.0Br1.0/SIS perovskite composite films displayed superb temperature-sensitivity(30～160℃)performance and heating-cooling cycle stability.Furthermore,the fabricated SiO2@DDAB-CsPbCl2.0Br1.0/SIS films were successfully assembled into a bright WLED device with Commission Internationale de l’Eclairage(CIE)coordinates of(0.30,0.32)and high color rendering index(CRI)of 83.4,indicating their promising application prospect in multifunctional flexible photoelectric devices. |
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