Growth And Characterization Of Organic-inorganic Double Halogen Hybrid Perovskite Single Crystals

In recent years,perovskite single crystal materials with ABX₃ structure possesee their excellent and unique optoelectronic properties,such as small binding energy of exciton,high dielectric constant,fast charge carrier diffusion rate,long carrier lifetime,low recombination probability,wide absorption spectrum range,and high absorption coefficient.It has become a key research field in the application of optoelectronic devices,such as solar cells,X-ray detector and light-emitting diodes.Among them,organic-inorganic perovskite single crystal materials have the advantages of wider absorption spectrum range,smaller bandgap width E_g,and higher stability compared to fully inorganic perovskite single crystal materials.Thus,organic-inorganic perovskite single crystals have become the primary research target in perovskite materials.At the same time,in the perovskite with ABX₃ structure,the elements at the sites of A,B,and X can exhibit abnormal valence or mixed valence states,organic or inorganic elements,and even also be replaced by other elements with similar radius without changing its lattice structure.The flexibility of these A,B,and X elements makes the perovskite materials have some special properties.At present,the preparation methods of perovskite single crystals include traditional cooling crystallization,anti-solvent vapor-assisted crystallization,dual-source co-evaporation crystallization,and inverse temperature crystallization.Compared with other crystallization methods,the inverse temperature crystallization method has the advantages of fast crystallization speed,high crystal quality,strong crystal density and stable properties.Therefore,in this paper,the inverse temperature crystallization method is used to grow organic-inorganic double halogen hybrid perovskite single crystals.Under the condition that the A site is CH₃NH₃⁺ion and the B site is Pb²⁺ion,the chemical control method is employed to change or dope the halogen Cl,Br,I at the X position,and to investigate the optoelectronic,physical and chemical properties of the grown CH₃NH₃Pb Br_3–xCl_x and CH₃NH₃Pb I_3–yBr_y single crystalsThe specific research work of this paper is as follows:A new stoichiometric method PbX₂+[（1–z）CH₃NH₃Y+z CH₃NH₃X]was used to synthesize the growth precursors of CH₃NH₃Pb Br_3–xCl_x and CH₃NH₃Pb I_3–-yBr_y single crystals,in which X and Y represent one of the three halogens Cl,Br and I respectively,the value of z ranges from 0 to 1.By changing the value of z,the halogen content in the precursor can be changed.Then,centimeter-scaled CH₃NH₃Pb Br_3–xCl_x and CH₃NH₃Pb I_3-yBr_y single crystals were grown in different environments.Firstly,we observe the macroscopic morphology and color of multiple groups of single crystals to explore the effect of changes halogens.Then,a series of characterization tests such as Energy Dispersive X-Ray Spectroscopy,X Ray Fluorescence,X-ray Diffraction,Ultraviolet and Visible Spectrophotometry,Photoluminescence Spectroscopy,and Thermogravimetric Analysis were performed on the single crystals to analyze the influence of halogen types and contents on the optoelectronic,physical and chemical properties of the single crystals.Finally,the corresponding changes are summarized.