Preparation And Application Of Double Perovskite Cs₂Ag_xNa_1-xInCl₆:Bi Quantum Dots

Lead-free double perovskite quantum dots continue to draw increasing attention because of its non-toxic and good stability in halogen,Double perovskite are divided into two types of semiconductor,the first is indirect band gap material,like Cs2AgBiBr6 and Cs2AgBiCl6,involves not only photons but also phonons are involved in absorption and restructuring,leading a low PLQY.In contrast,double perovskites with direct band gaps exhibit high absorption coefficients,high PLQY,and fast carrier recombination rates,mainly because the absorption and recombination processes only involve photons.In recent years,Cs2AgInCl6 crystal as one of the double perovskites with direct band gap has attracted wide attention.Influenced by Luo's research group,we fabricated Cs2AgInCl6 crystal into quantum dots to promote its application in optoelectronic devices.Therefore,Cs2AgInCl6 quantum dots with quantum yields of 57.3%and 63.4%were prepared by thermal injection method and non-thermal injection method by doping Na ions and Bi ions in this paper.We constructed Cs2AgxNa1-xInCl6:Bi-SiO2 thin films based on heat injection method;The white LED of Cs2AgxNa1-xIncl6:Bi-SiO2 was synthesized by non-thermal injection method.Specific research contents are as follows:In the first chapter,we introduced the definition of quantum dots at first,then introduced the structure properties of quantum dots and the luminous mechanism,summarizes the general situation of the development of quantum dots and the development potential of the largest perovskite quantum dots,halogen lead-based perovskite pointed out the shortcoming of quantum dots and the necessity of developing lead-free perovskite quantum dots,puts forward the significance and the main research content of this thesis topic.In the second chapter,we adopted heat injection method,the ODE as solvent,OA and OLA are cosolvent and surface ligands,respectively.Cs-Oleate,Na-Oleate and In(ac)3,Agac as raw material,through the thermal injecting Cl ions to preparated Cs2AgxNa1-xInCl6:Bi quantum dots,the proportion of different Ag and Na on the influence of the luminous intensity,and observed under the different temperature response time of structure morphology of quantum dots.We also tested the stability of QDs dispersed in cyclohexane,and found that the emission intensity of QDs decreased very lightly.We also used the method of non-thermal injection to prepared CS2AgxNa1-xInCl6:Bi quantum dots,using DPE as solvent,OA and OLA as co-solvent and surface ligand,Cs-Oleate,Na-Oleate and In(ac)3,Agac as raw materials.The growth kinetics of Cs2AgxNa1-xInCl6:Bi quantum dots was studied by UV absorption and PL spectra.The results show that the Cl source and reaction time are the key factors affecting the nucleation rate of nanocrystals.Through the difference of synthesis time and synthesis temperature,we further discussed the optimized design and optical properties of the prepared QDs,aiming to obtain QDs with high crystallinity and excellent optical properties.White luminescence with a wide emission spectrum of 500 nm-800 nm was obtained by the two methods.In Chapter 3,we prepared PHPS-based Cs2AgxNa1-xInCl6:Bi-SiO2 quantum dots thin films by thermal injection synthesis,which were naturally cured at 80?,then further aged in an oven and sintered at 200? and 248?,respectively.The test results show that the waterproof performance of the thin film samples have been greatly improved,indicating that SiO2 plays a role in passivating the surface of the quantum dots,and the protective layer formed can prevent the erosion of the quantum dots by water and oxygen.The formation of-Si-O-bond can be observed obviously in the infrared test,indicating that the-Si-N-bond breaks and generates SiO2 in the heating process.At the same time,the luminescence intensity and quantum yield of the thin films decrease lightly.In the fourth chapter,Cs2AgxNa1-xInCl6:Bi-SiO2 white LED was prepared by non-thermal injection method,which changed the preparation method of white light emission by different combinations and achieved a technical breakthrough.The stability of the Cs2AgxNa1-xInCl6:Bi-SiO2 quantum dot is greatly improved.This study provides a valuable strategy for the implementation of warm white light devices.In the fifth chapter,we summarized the work of this paper,and the existing problems and prospects for the future work are analyzed.