Controllable Synthesis And Properties Of Perovskite Quantum Dots And Heterojunctions

With the rapid development of China’s economy and the acceleration of the process of industrialization and urbanization,the energy demand keeps growing,and the depletion of fossil fuels is bound to bring about the world’s energy crisis.Since the beginning of this century,solar energy and other new energy sources have become important alternative energy sources,among them,solar energy,as an emerging renewable clean energy,shows a rapid growth trend,and the research on solar cells has also received more and more attention.Application of perovskite semiconductor materials in solar cells has been developing rapidly in the past decade.Its energy conversion efficiency has increased from 3.8%in 2009 to 25.2%in 2020,and its growth rate has surpassed that of silicon-based solar cells,making it a hot star material in the field of photovoltaic.Recently,perovskite quantum-dot material has become a new member of the"quantum dots family",showing characteristics such as narrow emission wavelengths and simple preparation processes,which meets the needs of quantum-dot backlight applications.It is expected to become a new generation of display materials.It has potential application in the fields of electroluminescence,laser,and optical detection.The luminescent properties of quantum dots are closely related to factors such as their size,morphology,composition,and surface.Therefore,the regulation of luminescent properties is the basis for conducting physical property research and developing device applications.However,perovskite materials are very sensitive to polar solvents,temperature,etc.,so the research on the stability of perovskite is still a huge challenge.For the control of perovskite,its size,morphology and luminescence also directly affect the chemical and physical properties of perovskite.At the same time,it is increasingly important to study new properties of perovskite nanocomposites.The new properties brought by perovskite will have special advantages in improving device performance and developing new applications.Aiming at the above background of perovskite research,this article focused on the research of Cs Pb X₃and FAPb X₃quantum dots,with controlled shape,size and luminous range of perovskite.We synthesized nano-scale pure inorganic perovskites and their nano-heterogeneous Junction and organic-inorganic hybrid perovskite quantum dots.The morphological characteristics were observed through the corresponding test equipment,the corresponding components were determined,the energy transfer of the perovskite nano-heterojunction was studied,and its application in the fields of photovoltaics,optoelectronics,and sensing was explored.The specific synthesis method and test results are as follows:（1）The precursor was first formed into a transparent solution at high temperature,and then cubic perovskite quantum dots were synthesized by thermal injection method.In course of the reaction,the synthesis conditions of cubic structure perovskite quantum dots were explored by adjusting the change of reaction time,reaction temperature and concentration.The results showed that the optimal reaction temperature,reaction time,and Cs:Pb ratio of Cs Pb X₃quantum dots are 150℃,5 s,and 1:8,respectively.The optimal reaction temperature,reaction time,and FA:Pb ratio of FAPb X₃quantum dots are 170℃,5 s,and 4.7:1,respectively.TEM and XRD proved that Cs Pb X₃and FAPb X₃quantum dots with cubic phase were synthesized,and their sizes were uniform.（2）As a special perovskite material,chiral perovskite quantum dots have been the focus of research.We synthesized perovskite by ball milling at room temperature,and then added oleic acid ligands for further grinding to make them have good monodispersity.A bright green color can be observed under room temperature and daylight conditions.The perovskite quantum dots obtained after ball milling are proved to be cubic crystals with a size of about 60 nm by TEM.The results show that the synthesized perovskite has chiral characteristics.In addition,after the perovskite is synthesized at high temperature,the method of ligand exchange at room temperature also obtains the chiral perovskite.When chiral perovskite was reacted with different alcohols at room temperature,the appearance did not change significantly after periods of time.（3）In recent years,due to the physical and chemical properties of perovskite nano-heterojunction materials that are different from or better than that of individual heterojunction components,not only has academic research value,but also has great potential for applications in energy and information.But the controllable aspects of the structure still need to be improved.In view of the above conclusions,we have studied perovskite nano-heterojunctions.Through the previous control,we have obtained perovskite quantum dots with uniform morphology and size.Based on this,we synthesized them by adding a sulfur source at room temperature The Cs Pb X₃-Pb S quantum dot heterojunction was introduced.During the experiment,the volume of the sulfur source was continuously adjusted to finally obtain a nano-heterojunction with a uniform shape.TEM and other testing methods have proved that only a small part of the perovskite structure is destroyed,and the spectrogram shows that the photoluminescence wavelength of the synthesized heterojunction is in the visible region and the near-infrared region,which are attributed to Cs Pb X₃and Pb S quantum dots,respectively.The exciton dynamics of energy transfer was studied using transient absorption spectroscopy,and it was proved that during the reaction,energy was transferred from Cs Pb X₃to Pb S quantum dots,leading to an increase in the lifetime of Pb S quantum dots.