Research On Room-Temperature Synthesis Of Inorganic Perovskite Nanocrystals And Its Application In Light-Emitting Diodes

In recently years,halide perovskite materials have shown wide application prospects in the fields of third-generation thin-film solar cells,lighting and display,and information technology.Especially in the area of lighting and display,halide perovskite materials are expected to become the leader of the new generation of light-emitting and display technology due to their high fluorescence quantum yield,wide color gamut,continuously tunable emission wavelength and solution processability.Currently,the external quantum efficiency（EQE）of red and green light-emitting diodes（LEDs）has exceeded 20%,and the EQE of pure blue LEDs has exceeded 10%.Among the reported high-efficiency LED devices,nanocrystal-based systems demonstrate good device stability and high color purity,with obvious technical advantages.The synthesis of conventional nanocrystals is based on the hot injection method,but its harsh synthesis conditions limit its potential for large-scale production and commercial application,while the low-temperature synthesis of high-efficiency nanocrystals is still challenging.In this dissertation,inorganic cesium-lead-bromine（Cs Pb Br₃）and cesium-lead-iodine（Cs Pb I₃）nanocrystals were synthesized by room-temperature method,and green and red LEDs were prepared.The photoelectric properties and stability of Cs Pb Br₃ nanocrystal films and corresponding LED devices were improved by forming high-entropy alloys through A-site and B-site ion doping.The main studies are as follows:1)Perovskite NCs materials generally use organic amine ligands to maintain the dispersion of NCs,and the choice of amine ligands can greatly affect the stability and optoelectronic properties of NCs.In this work,the Cs Pb Br₃ nanocrystalline material is doped with rubidium ions（Rb⁺）at the A-site and silver ions（Ag⁺）at the B-site to form a high-entropy alloy while maintaining good dispersion,thus improving the stability of the nanocrystalline material.Transmission electron microscopy and X-ray diffraction photoelectron spectroscopy showed that the size of the NCs tended to decrease significantly after doping,and the X-ray photoelectron spectroscopy detected distinctive peaks of Rb⁺and Ag⁺,which indicated that Rb⁺and Ag⁺were successfully doped into the NCs.The energy dispersive spectroscopy elemental analysis can calculate that（Rb+Cs）:（Ag+Pb）:Br≈1:1:3 in the Rb⁺/Ag⁺co-doped NCs,which indicates that Rb⁺and Cs⁺jointly occupy the A-site structure of perovskite and Ag⁺and Pb²⁺jointly occupy the B-site structure of perovskite.The substitution ratio of Ag⁺for Pb²⁺reached 16.94%,which greatly reduced the toxicity of lead.Both in air and under UV light irradiation,the nanocrystalline films after doping have higher stability than undoped nanocrystalline films.In addition,the stability of LED devices made of doped NCs has also been greatly improved.2)In lighting and display,color is mainly synthesized through the red,green and blue primary colors,so the synthesis of blue and red materials also has equal importance.Blue devices generally require the participation of chloride ions（Cl^-）,and the high mobility of Cl^-makes blue devices extremely unstable.While red light devices generally have the participation of iodide ions（I^-）,stable Cs Pb I₃ nanocrystal generally require high-temperature hot injection method to prepare,and Cs Pb I₃nanocrystals synthesized by room-temperature method will quickly change to non-luminous yellow phase under atmospheric conditions.In this work,it was found that Cs Pb I₃ nanocrystals with red luminescence could be synthesized at room-temperature using dodecylamine iodide as a ligand,and finally red LED devices were fabricated.At room-temperature,the solution without the addition of cesium source first becomes a quasi-two-dimensional green light-emitting material.After the addition of cesium source,the solution changed from green-emitting quasi-two-dimensional structure to red NCs structure,and this finding opened up a new research idea for the preparation and study of red nanocrystal LEDs.