Growth Regulation And Photoelectric Properties Of Organic Metal Halide Perovskite Single Crystals

Due to global warming and soaring fossil prices,the world is facing an urgent requirement to modify the energy structure and reduce energy consumption,so as to achieve the goal of energy conservation and emission reduction of carbon peak and carbon neutrality.Therefore,it is urgent to develop advanced semiconductor optoelectronic devices such as high-efficiency solar cells,photodetectors and light emitting diodes（LEDs）.As a new generation of semiconductor materials,organometallic halide perovskite has become a hot material for scientific research because of its excellent photoelectric properties,wide source of raw materials,and manufacture by solution method.In addition,perovskite single crystal materials have the advantages of long carrier diffusion distance,less non radiative recombination and favorable stability due to their structural characteristics such as no internal grain boundary and low defect density.Moreover,perovskite single crystal materials have the potential to improve the performance of optoelectronic devices.In recent years,optoelectronic devices based on perovskite single crystal have developed rapidly.The optical and electrical properties of three-dimensional organometallic halide perovskite single crystals are anisotropic due to the different arrangement of atoms on each crystal surface.Crystal plane orientation engineering is an important strategy to adjust the physical and chemical properties of perovskite crystals,and additive engineering is the main method to regulate crystal orientation growth.At present,there are few kinds of additives that can make perovskite crystals grow in orientation,and the application of orientation growth in single crystal solar cells also needs further research.Although the efficiency of perovskite single crystal solar cells has increased from 1.88%to 22.8%in just six years,its operational stability still needs to be improved.At the same time,the most widely used methylamine lead iodide（MAPb I₃）and formamidinium lead iodide（FAPb I₃）perovskite single crystals are difficult to obtain a stable cubic phase structure at room temperature,and the stable cubic phase is conducive to improving the photoelectric properties such as carrier transport of three-dimensional perovskite,which is of great significance for improving the performance of photoelectric devices.Compared with three-dimensional organometallic halide perovskites,which are limited by tolerance factors,resulting in low cation selectivity,two-dimensional organometallic halide perovskites have the characteristics of diversity of components and designable organic molecular structures,and have achieved rapid development in photoluminescence and other fields in recent years.In particular,white light two-dimensional perovskite materials with self-trapped exciton emission have potential applications in artificial lighting,mini LED display,optical communication and other fields.However,two-dimensional perovskite faces challenges such as low luminous efficiency,poor water and thermal stability,and fast decay of light-emitting devices.Therefore,it is of great significance to design and grow white light emitting two-dimensional perovskite single crystals with high efficiency and stability.Therefore,starting from the basic principles of crystal growth thermodynamics and dynamics,this paper regulates the growth process of three-dimensional perovskite single crystals through additive engineering,component engineering,solvent engineering and other means,and prepares perovskite single crystal solar cells with improved stability and optoelectronic devices with low defect density and high light dark current ratio;Through molecular design,solvent engineering and component engineering,white light two-dimensional perovskite single crystals were grown,and white light LED devices with high efficiency and stability were prepared.It mainly includes the following specific contents:1.Orientation engineering of three-dimensional perovskite single crystal and its application in solar cellsIn the process of growing methylamine lead iodine single crystal by inverse temperature method,a kind of additive that can make crystal orientation grow,that is,it can dissolve in univalent inorganic or organic salt containing iodine ion.Iodine ion in the salt can coordinate with lead ion to form lead iodine octahedron[Pb I₆]^2-,increase the solubility of methylamine lead iodine,and the cation can interact with[Pb I₆]² on the surface of the growing crystal,which hinders the diffusion of methylamine cation（MA⁺）into the lattice to form perovskite.According to the principle of crystal growth dynamics,with the increase of additive concentration,MA⁺is more inhibited on the（110）crystal plane rich in lead ions than on the（100）crystal plane,so the growth speed slows down and causes the crystal plane to be exposed,and the inhibition effect of phenylethylamine with greater steric hindrance is stronger.At the same time,additive engineering can reduce the growth temperature of methylamine lead iodine crystal from120℃to below 70℃,so we apply it to the preparation of single crystal solar cells to reduce the thermal stress caused by the difference in expansion coefficient between crystal and ITO substrate.The obtained（110）orientation solar cell has higher open circuit voltage and short circuit current than the（100）orientation solar cell,which proves that its carrier transport capacity is stronger,and the time required for the photoelectric conversion efficiency to decay to 85%is greatly increased compared with the（100）solar cell under a continuous illumination of a standard sunlight intensity,which proves its better stability.In addition,we also extended the additive engineering oriented growth method to the ethylene glycol methyl ether solvent system and the growth of methylamine lead bromide and formamidine lead iodide perovskite single crystals.2.Low defect and high stability three-dimensional cubic perovskite single crystal grown by A-site component engineering and its photoelectric propertiesIn order to obtain cubic perovskite single crystal with highly symmetrical lattice and further improve its photoelectric performance and air stability,we successfully prepared massive perovskite single crystal MA_0.9DMA_0.1Pb I₃ with（110）crystal plane orientation by introducing dimethylamine cation（DMA⁺）through A-site component engineering.High quality single crystal is an important prerequisite for preparing high-performance optoelectronic devices.We detected the internal bulk defects of MA_0.9DMA_0.1Pb I₃ by infrared imaging,and the results obtained are consistent with other characterization methods.The high-quality single crystal obtained by the space charge limiting current（SCLC）method has a thickness of 5.68×108 cm^-3 defect density and 612.7 cm² V^-1 S^-1hole mobility.Moreover,the dark current of the longitudinal device prepared by this method is significantly lower than that of the crystal with bulk defects,and the dark current stability of continuous output is higher under a bias voltage of 100 V mm^-1.In addition,FA_0.55MA_0.45Pb I₃ and FA_0.88MA_0.095DMA_0.025Pb I₃ perovskite single crystals were also grown.They have a broad optical absorption spectrum,with absorption band edges reaching 862 nm and872 nm respectively,and a stable cubic crystal structure.After being stored in the air for more than one year,no phase change occurs.3.Molecular design,solvent engineering growth and photoluminescence properties of two-dimensional perovskite single crystalsTwo dimensional perovskite single crystal trifluoromethylphenylethylamine lead bromide was designed and prepared by introducing trifluoromethyl with strong hydrophobicity and electron absorption.When trifluoromethyl is in the ortho and meta position of the amine group on phenylethylamine,the obtained two-dimensional perovskite has a wide emission spectrum of cold white light excited by self-trapped state.The mechanism of luminescence was described by analyzing the single crystal structure,simulating the charge distribution and characterizing the molecular vibration by infrared spectroscopy.The water,heat and air stability were further proved by experiments.More importantly,we also studied the difference between using organic solvent evaporation method,acid cooling method and cosolvent room temperature evaporation method to grow single crystals.By means of solvent engineering,we not only avoided the generation of non-luminescent mesophase,but also improved the quality of single crystals and regulated the crystal shape and growth rate.The applicability of the cosolvent room temperature evaporation method was proved by its application to the growth of trifluoromethylphenylethylamine lead iodine single crystal.4.Preparation and application of two-dimensional perovskite single crystals with high efficiency and stability by B-site regulationBy introducing Mn²⁺doping,the luminous efficiency of trifluoromethylphenylethylamine（CF₃-PEA）lead bromide single crystals was greatly improved（from 18.11%to 87.93%）,and the correlated color temperature was adjusted from cold white light to warm white light（from 10270 K to 2406 K）,and the maximum color rendering index reached 94.Further,the photoluminescent LED device assembled using white light materials has a stable emission spectrum.After continuous operation at 50 m A current for 2 months,the CIE color coordinate remains basically unchanged（0.33,032）,and the emission intensity decreases by only 10%.The research in this paper not only enriches the oriented growth theory of three-dimensional organometallic halide perovskite single crystals,verifies the influence of different additives and solvent systems on the growth of single crystals,and helps to deeply understand the relationship between perovskite single crystal structure,bulk defects and optoelectronic properties and stability of devices,but also expands the two-dimensional organometallic halide perovskite luminescent material system to provide new ideas in white LED materials with high efficiency and high stability.