Study On The Ionic Liquid Assisted Preparation And Photoluminescence Properties Of Cu-In-Zn-S And CsPbX₃ Nanocrystals

Semiconductor nanocrystals(NCs)have drawn extensive attention in the fields of light-emitting diodes(LEDs),solar cells,photoelectric detection,and bioimaging owing to their unqie photoelectric properties.At present,Cd-based NCs have been successful adapted for commercial use.However,the problems of tedious preparation process and high preparation cost become the stumbling blocks on the road of large-scale applications.Therefore,it is of great significance to develop new type NCs and the corresponding preparation technology.This dissertation is intended to prepare NCs with the assistance of ionic liquids(ILs)based on their special physical and chemical properties.The interaction mechanisms of ILs on the preparation of multiple and provskite NCs are explored by using different types of ILs.Moreover,the growth and photoluminescence kinetics of NCs can be effective modulated by making full use of the synergistic effect of ILs and ligands.The research work is carried out from the following four aspects:(1)In view of the problems of long reaction time and low photoluminescence quantum yields(PLQYs)for multiple Cu-In-Zn-S(CIZS)NCs prepared in aqueous solution,we developed a novel IL assisted hydrothermal approach to prepare water-soluble CIZS NCs.The dangling bonds on the NC surface could be effective eliminated by the corrosion of F^- deriving from the decomposition of fluorine-containing IL1-methylimidazolium tetrafluoroborate([Mim]BF₄)during the reaction process.Meanwhile,a wide bandgap semiconductor ZnS was employed to coat on the NC surface,which could well passivate the surface defects of NCs,resulting in the enhancement of PLQY from 6.2%to 31.2%.Moreov er,the instantaneous nucleation rate of NCs was improved due to the lower surface tension of IL,leading to the shortening of reaction time from 5 to 1 h.A composite was further obtained by embedding CIZS/ZnS NCs into polyvinylpyrrolidone(PVP)matrix.Consequently,a WLED achieved the luminous efficacy(LE)of 90.11 lm/W,color rending index(CRI)of 87.2,and correlated color temperature(CCT)of 4977 K by using CIZS/ZnS/PVP composites and Lu₃Al₅O₁₂:Ce³⁺phosphors combining with a blue LED chip,suggesting the great potential for solid state lighting application.(2)In order to obtain NCs with low preparation cost and excellent emission performance,a facile supersaturated recrystallization approach was employed to synthesize CsPbBr₃ NCs with the assistance of IL.The surface property of NCs could be regulated by introducing bromine-containing IL1-butyl-3-methylimidazolium bromide([Bmim]Br),which could improve the content of bromine element on the NC surface and trigger ed the transformation from Br-poor surface to Br-rich surface,resulting in the increase of PLQY from 78.73%to 91.04%.Furthermore,the morphology and grain size of CsPbBr₃ NCs could be adjusted by adding[Bmim]Br,and the NCs with homogeneous size distribution could also be achieved.More importantly,the photo-and storage-stability of NCs were remarkable enhanced.The prepared CsPbBr₃ NCs still maintained over 80%of the initial emission intensity after storage for 91 days or continuous irradiation under UV light for 24 h.Finally,a series of CsPbX₃ NCs with different compositions were prepared via anion exchange,which exhibited tunable emission in the range of 462?665 nm and a wide color gamut of 129.65%of the National Television Standards Committee(NTSC)standard.These findings provide a reference for the preparation of high-quality perovskite NCs and their application in photoelectric field.(3)In response to problems of low emission property and poor stability of perovskite NCs caused by the surface Pb defect.A facile and efficient in-situ passivation strategy for surface defect was proposed by introducing fluoride acid-containing IL 1-butyl-3-methylimidazolium tetrafluoroborate([Bmim]BF₄)during the synthesis of NCs.The undesired surface uncoordinated Pb atoms and surface dangling bonds were effectively eliminated by the synergistic effect of both cation and anion in IL,which could sufficient passivate the surface defect of NCs,resulting in the increase of PLQY from 63.82% to 94.63%.Furthermore,together with the successf ul preparation of CsPbBr₃ NCs with improved emission property by introducing different fluoride acid radical ILs,we demonstrated that fluoride containing ILs were universal additives for the perovskite community.Thanks to the existence of[Bmim]⁺on NC surface,a hydrophobicity and protective barrier could be formed,resulting in the significant enhancement of storage-,photo-,water resistance,and thermal stability.Finally,a white LED was fabricated b y using the modified CsPbBr₃ NCs and KSF:Mn⁴⁺phosphors,which exhibited high LE(100.07 lm/W)and wide color gamut(140.64%of NTSC),demonstrating its great application potential in backlight display field.(4)To further improve the stability of CsPbBr₃ NCs,we developed a simple and fast route to prepare CsPbBr₃@SiO₂ NCs by taking full use of the greater polarity and hygroscopicity of IL[Bmim]BF₄,which was beneficial to capture the moisture in air,resulting in the rapid hydrolysis of APTES and formation of SiO₂ shell on the NC surface.The optimal growth time for SiO₂shell could be reduced from 10 min to 20 s.Furthermore,the hydrophobic organic cation could effective avoid the attenuation of emission property of NCs caused by the erosion of water or alcohol during the hydrolysis process of APTES.Therefore,the stabilit y of CsPbBr₃@SiO₂ NCs exhibited remarkable enhancement compared with the naked NCs,and the coated NCs could maintain 96.12%of initial emission intensity after storing for 120 days.Subsequently,CsPbX₃@SiO₂ NCs with different compos itions were prepared,showing a broad wavelength tunable range(421.2?651.6 nm)and a wide color gamut(143.57%of NTSC).Moreover,the electrons and holes could be confined into the CsPbX₃cores due to the higher conduction band minimum and lower valence band maximum of SiO₂ compared with CsPbX₃ NCs,resulting in the well passivation of surface defects and improvement of emission performance.A white LED device with excellent photoelectric performance was fabricated on the basis of the prep ared CsPbBr₃@SiO₂ NCs and CIZS/ZnS/PVP composites,which showed a high CRI of 90.5,CCT of4715 K,and LE of 41.57 lm/W.This route lays a solid foundation for the rapid controllable preparation and photoelectric applications of CsPbX₃@SiO₂ NCs.