Single Crystal Formamidinium Lead Iodide Perovskite Preparation,Characterization And Phase Evolution

Organic and inorganic hybrid perovskite materials are widely used in solar cells with the organic and inorganic compounds characteristic that are low price,good hole and electron transport ability,wide absorption range,and narrow band gap.However,due to the short research time,there are still many problems to be solved,especially this organic and inorganic hybrid materials are very sensitive to air,light,heat,humidity and other environmental factors,which greatly reducing the stability and practical application of this perovskite material.In this paper,the formamidine lead idodide??-FAPbI₃?single crystal was prepared with solution crystallization.Compared with the literature,this way do not need lead iodide,we use lead acetate as the raw materials for preparation of single crystal,which reduce the cost of preparation of single crystal.The??-FAPbI₃?single crystal was prepared by two steps.First,the?-FAPbI₃ powder was prepared.In the HI aqueous solution,Pb?CH₃COO?₂ and formamidine acetate?NH=CHNH₂·CH₃COOH?were used as raw materials.The black?-FAPbI₃ single crystal of 3mm in size can be obtained in the?-butyrolactone?GBL?solution.This method has the advantages of short preparation time,high quantity of products and strong controllability,and suitable for preparing single crystal samples for research and application.For single crystal we research for its physical and chemical properties,including optical properties,mechanical properties and electrical properties.Mainly include:using ultraviolet visible near infrared absorption spectroscopy testing its absorption spectrum range and band gap,cathode fluorescence spectrum test the luminescence performance,the electrical conductivity of dark current voltage curve to get materials defect destiny.The investigations had shown that black formamidine lead iodide??-FAPbI₃?single crystal will transform to the yellow formamidiane lead iodide??-FAPbI₃?easily in the air.We treat the material in different conditions and found that the main factors affecting the phase transition of the material is the temperature and humidity.For further researches about temperature and humidity,it was found that the rate of transformation was the fastest at 50°C and 90%humidity.When the temperature exceeded 50°C,the phase did not change even at high humidity.Although the?-FAPbI₃ was easily changed at room temperature,it became stable after high temperature treatment.The composition,phase and microstructure of the obtained materials were characterized by high resolution Scanning Electron Microscopy,X-ray diffraction?XRD?and Transmission Electron Microscopy?TEM?.The formamidine lead iodide single crystal internal defects reduced significantly through high temperature treatment,which improve the stability of phase change without affecting the single crystal structure.It has an important role for the stability of the available formamidine lead iodide perovskite single crystal.In conclusion,we obtained the?-FAPbI₃ single crystal and studied the physical and chemical properties such as its phase stability,and the results can be used as the basis for its preparation and application.