Preparation Of MAPbI₃-Based Single Crystals And Study On Their Photoelectric And Photostriction Properties

In the past few years,halide perovskite,as a promising light-collection material with broad application prospects,has received extensive attention and set off a revolution in the photovoltaic field.The perovskite single crystal without grain boundaries is expected to further improve the device performance due to its advantages of low trap state density,high carrier mobility and long diffusion length.In this paper,large-size and high-quality single crystals of MAPbI₃ and FA_0.7Ma_0.25C_S0.05PbI₃ perovskite were prepared by optimizing the process parameters and using an improved inversion crystallization method.The basic phase,electrical,optical and photostrictive properties of the two perovskite single crystals were systematically characterized.The research contents are as follows:（1）High-quality single crystals of MAPbI₃ and FA_0.7MA_0.25C_S0.05PbI₃ single crystals over5 mm were prepared by an improved inversion crystallization method,which has excellent semiconductor transport properties.The band gaps of MAPbI₃ and FA_0.7MA_0.25C_S0.05PbI₃ single crystals are 1.53 e V and 1.47 e V,respectively.Compared with MAPbI₃ single crystal,the fluorescence lifetime and diffusion length of FA_0.7MA_0.25C_S0.05PbI₃ single crystal have been greatly improved,while the hole and electron mobility have increased by 48%and 10%,respectively.When illuminated,the capacitance of FA_0.7MA_0.25C_S0.05PbI₃ single crystal reaches more than 2 times of that in darkness,and its capacitance and impedance decay time reaches sub-second level at the moment of darkness after illumination.（2）It is found that MAPbI₃ single crystal has a huge photostriction effect.Under the irradiation of a 532 nm laser with a light intensity of 795.5 m W/cm²,the single crystal of MAPbI₃ with thickness of 0.1-1.5 mm shows a positive strain of 0.73 to 0.24%.By changing the light intensity,the photostriction of the single crystal can be continuously changed from several hundred picometers to several microns;a high-precision light-driven actuator with adjustable optical path can be prepared by adding a mirror on the surface of the single crystal.Compared with piezoelectric actuator,this new actuator has the advantages of wireless,light weight,small size,simple structure,low cost,large strain,and linear relationship between crystal strain and laser intensity.（3）Compared with MAPbI₃ and FAPbI₃,FA_0.7MA_0.25C_S0.05PbI₃ single crystal can be stored at room temperature and air environment for a long time,and it still remains excellent semiconductor and photostrictive properties.The doping of MA⁺and Cs⁺ions can effectively reduce the lattice stress,and significantly improve the air stability and thermal stability of the single crystal;the thermal decomposition temperature of the single crystal is increased to 320℃,and its properties did not change significantly after 50 days of storage at room temperature and air environment.Due to its high stability and excellent photoelectric properties,FA_0.7MA_0.25C_S0.05PbI₃ has great application potential.