Synthesis And Modification Of Cesium Lead Halide Perovskite Quantum Dots And Their Application In Optoelectronic Devices

In the past decade,metal halide perovskites have great development of application in the field of optoelectronics.Metal halide perovskites have been aroused much attention due to their many unique advantages,such as solution processability,high photoluminescence(PL)quantum yield(PLQY),narrow emission half-maximum width(FMWH as low as 15 nm)and almost fullvisible spectrum from approximate 380 nm to 750 nm.These excellent properties have aroused people's research interest.In addition,low cost of raw materials can reduce the cost of the synthesis process,facilitating the commercial application of large-scale manufacturing.The organic-inorganic hybrid perovskite quantum dots(MA/FAPb X₃ Pe QDs)are poor thermal stability and easily phase decompositon due to the A-site organic cations,which greatly restricts the development of annealing technology and furtherly limits the commercial application.Compared with MA/FAPb X₃ Pe QDs,all-inorganic cesium lead halide perovskite quantum dots(Cs Pb X₃Pe QDs),which Cs⁺ion is A-site ion,making Cs Pb X₃Pe QDs to possess the higher thermal stability and lower moisture sensitivity.Combination of the cost of raw materials with simply synthesies method indicates that Cs Pb X₃ Pe QDs have a promising pespects of commercial application.Among Cs Pb X₃ Pe QDs system,cubic phase Cs Pb I₃Pe QDs have gained much attention due to their suitable band gap of 1.8 e V,providing a poential application in photovoltaic and display devices.However,Cs Pb I₃ Pe QDs are more prone to rotation and tilt due to their longer bond length of Pb-I in[Pb I₆]^4-octahedron(relative to[Pb Br₆]^4-),reducing the optical properties,stability and EL intensity,and further limiting their practical applications.Therefore,this paper mainly studied Cs Pb I₃ Pe QDs,modified Cs Pb I₃ Pe QDs by double-ion synergy and ligand passivation strategies respectively,and applied the modified high-quality Pe QDs to perovskite quantum dot LED(Pe LED).The specific research contents are as follows:(1)The synergistic Cs Pb I₃ Pe QDs with In Cl₃ double ions was synthesized by thermal injection.Phase analysis of the samples showed that all the samples were cubic crystal structure of?-Cs Pb I₃.The phase analysis showed that all In Cl₃-Cs Pb I₃ Pe QDs were the cubic crystal structure of?-Cs Pb I₃.According to the optical test and analysis,Cs Pb I₃-1.0%exhibits the most excellent luminescence performance,such as the increased PLQY of 82.4%from52.59%and the enhanced average lifetime of 12 ns from 70.8 ns,which indicates that Cs Pb I₃-1.0%has the least surface defects.Compared to the stability of original Cs Pb I₃ Pe QDs,Cs Pb I₃-1.0%Pe QDs can maintain stable for 24 days in the atmosphere(25±5?temperature and 80±20%humidity),while the original Cs Pb I₃ Pe QDs were losen the luminous properties due to the decomposition after 3 days.It is conclusion that Cs Pb I₃-1.0%showed excellent luminescence properties and much higher stability relative to the origional Cs Pb I₃.These excellent properties of In Cl₃-Cs Pb I₃ Pe QDs are mainly attributed to the In³⁺ions doped into the crystal lattice and the passivation surface defects by Cl^-ion,in which In³⁺ions partially replace the Pb²⁺and the excess Cl^-fills the I^-ion vacancies on the surface,reducing the surface defects of Pe QDs.(2)DHA-Cs Pb I₃ and DPA-Cs Pb I₃were prepared by thermal injection method.Firstly,the excellent optical performance of Cs Pb I₃ Pe QDs were obtained by optimal content of DHA and DPA.Secondly,in combination of phase of optical properies analysis,DPA and DHA not only can play a key role in the passivation effect on Cs Pb I₃ Pe QDs but also can remove the excess ligands on the surface.DHA has two benzene rings and a large electron cloud density,which can strongly connect with the carboxyl group of oleic acid through stong binding face of N-H bond rather than the acid-base reaction.DHA-40 and DPA-40 have better optical properties,and DPA-40 has the advantage of low ligand density.Compared with the morphology under transmission electron microscope,DHA-40 has better stability than DPA-40 and Cs Pb I₃Pe QDs.(3)The Cs Pb I₃-1.0%,DPA-40,DHA-40 and basic Cs Pb I₃ used as luminesce layers,the different Cs Pb I₃Pe LEDs were obtained.The experimental results showed that Cs Pb I₃-1.0%Pe LED displayed the increased maximum EQE of 8.3%from 1%,and an enhanced maximum brightness of 411 cd/m~2 from 124 cd/m~2.The DPA-40 Pe LEDs and DHA-40 Pe LEDs showed the increased maximum EQE of 7.8%and 7.4%from 0.98%,and the improved maximum brightness of 374 cd/m~2 and 311 cd/m~2 from 121 cd/m~2,respectively.