Investigation On Growth And Photoelectronic Properties Of Two-dimensional Hybrid Perovskite CH₃NH₃PbX₃

Recently,organic-inorganic hybrid perovskite CH₃NH₃PbX₃（X=Cl,Br,I）（MAPbX₃,MA=CH₃NH₃⁺）due to its adjustable structure,high carrier mobility,low defect density and direct bandgap It has attracted wide attention due to its excellent photoelectric properties.When the thickness of the hybrid perovskite crystal is reduced to the atomic scale,the electrons confined inside the two-dimensional material will be strongly affected by quantum confinement,showing unique optical,electrical,and mechanical properties.In addition,two-dimensional hybrid perovskite is one of the ideal materials for developing new photovoltaic devices,which fills the gap of low photoelectric efficiency of traditional two-dimensional materials.However,due to the intrinsic non-layer structure of the hybrid perovskite,it is a challenge to synthesize two-dimensional hybrid perovskite MAPbX₃ films with a large size and atomic thickness.In this paper,we have developed a low-cost and efficient method to obtain large-size,ultra-thin two-dimensional hybrid perovskites,and have studied deeply its growth habits and optoelectronic properties.The main research results are as follows:to fabricate the two-dimensional hybrid perovskite crystal,we have developed a space-confined two-dimensional hybrid perovskite liquid epitaxial growth method,which is prepared by combining physical and chemical methods.The thickness of the grown two-dimensional hybrid perovskite MAPbX₃ is less than 10nm,and the lateral dimension is hundreds of square micrometers.（1）To solve problems in the two-dimensional hybrid perovskite crystal structure and preparation,we have developed a space-confinedtwo-dimensional hybrid perovskite liquid epitaxial growth method,which is prepared by combining physical and chemical methods.The thickness of the grown two-dimensional hybrid perovskite MAPbX₃ is less than 10nm,and the lateral dimension is hundreds of square micrometers.（2）The growth driving force of two-dimensional hybrid perovskite MAPbX₃was explored.We excluded the van der Waals force as the growth driving force for two-dimensional perovskite MAPbX₃,by comparative experiments;Using density functional theory（DFT）calculation and X-ray photoelectron Energy spectroscopy（XPS）tests,wefound that the strong interaction between potassium（K）on mica and the halogen bromide（Br）around the interface may be the driving force for the growth of the two-dimensional hybrid perovskite.（3）Two-dimensional hybrid perovskite MAPbX₃ characterization revealed that the crystal quality was good,the surface had atomic flatness,the photoluminescence performance was good,and the emission intensity was uniform.The fast and low parts of fluorescence decay t was 6and 50 ns,respectively.Compared with the bulk hybrid perovskite,the photoluminescence wavelength and optical absorption edge are blue shifted.We proposed that the increase of the band gap,caused by the reduced thickness and the state of potassium atom traps at the interface,are the main reasons for the blue shift of the emission wavelength.（4）A two-dimensional hybrid perovskite MAPbX₃ photodetector was fabricated and packaged to test the photoelectronic performance.The results show that the two-dimensional hybrid perovskite photovoltaic device has a dark current of～10^-12A,a light response of 126A/W,and a carrier mobility of 36.5cm²V^-1S^-1.The on/off current ratio of the device can be Up to 10⁴,the rise time and decay time of the time-resolved response are 5 and 4.1μs,respectively,and the maximum-3d B bandwidth of the detector can reach 80 k Hz.Its excellent performance has the potential to produce practical optoelectronic devices.