Preparation And Warm White Light-Emitting Diode Applications Of Organic-Inorganic Hybrid Cuprous-Based Metal Halide Materials

Single-component fluorescent materials with stable and bright warm white light emission are highly desirable for fabrication of efficient warm white light-emitting diodes（warm-WLEDs）,however,materials with such luminescence properties are extremely rare.Although some low-dimensional lead（Pb）halide perovskites can achieve warm white photoluminescence（PL）,yet they suffer from low photoluminescence quantum yield（PLQY）,and the inherent toxicity of lead does not meet the requirements of green development.Some Pb-free perovskites,such as Cs₂AgInCl₆,can emit warm white light,but sophisticated doping strategies and the use of rare and precious metals are usually required to increase their PL intensity,which is not conducive to large-scale applications.Under such background conditions,this dissertation proposes two novel warm white light-emitting materials,both of which can be prepared by simple solution method,and meet the requirements of nontoxicity,high PLQY and dopant-free.Finally,based on the developed warm white light-emitting materials,warm-WLEDs are prepared,and the high efficiency electroluminescence application of cuprous（Cu⁺）-based metal halides is realized for the first time.In recent years,Cu⁺-based metal halides have attracted extensive attention due to their earth-abundant,green and nontoxic properties.However,most Cu⁺-based metal halides do not have the ability of warm white light emission and stable crystal components are generally limited to iodide.Based on this,a novel organic-inorganic hybrid Cu⁺-based metal halide--MA₂CuCl₃（MA⁺=CH₃NH₃⁺）is proposed in the first part of this dissertation.The results show that MA₂CuCl₃ single crystal with centimeter-scale length can be prepared by low-cost solution cooling method,and exhibits wide band warm white light emission characteristics.The synthesized single crystal is a direct bandgap semiconductor with nearly 100%PLQY and a fluorescence lifetime of up to 50 μs,Then a method of producing uniform and dense films based on methanol solution is proposed,which provides a new idea for low-cost LED film making technology.Finally,electroluminescence devices and down-conversion LEDs are fabricated with the prepared MA₂CuCl₃ thin films and single crystals,respectively,which show decent white light-emitting efficiency.This is the first successful application of organic-inorganic hybrid Cu⁺-based metal halides in white light-emitting diodes,with great potential for the single-component indoor lighting and display applications.Like most reported Cu⁺-based metal halides,MA₂CuCl₃ has a zero-dimensional（0D）crystal structure,so its electron motion will be limited to 0D.This 0D feature helps to improve PLQY,but it is not conducive to the transfer of electrons and energy within the device,thus hindering the improvement of LED performance.Therefore,in the second part of this dissertation,we report another novel Cu⁺-based metal halide--（DFPD）CuX₂（DFPD⁺=4,4-difluoropiperidinium cation;X-=Cl-,Br-）,which exhibits double two-dimensional（2D）properties in both structural and electronic dimensions.Theoretical calculations confirm that the single crystal is an indirect bandgap semiconductor with superior lateral charge transfer ability,enabling more efficient electron transfer.In addition,the prepared single crystals show excellent ambient stability,photothermal stability and efficient warm white light emission,which is a potential ideal material for the preparation of single-component warm-WLED.Through the development of two new materials,this dissertation confirms the feasibility of controlling the perovskite crystal structure and electronic structure through the A-site organic cation engineering,and provides a reference for the preparation of other metal halide materials and their dimensional control.