Growth Of Two-dimensional Formamidine Lead Bromide Perovskite Single-crystalline Sheets And Their Optoelectronic Properties

Recently,hybrid organic-inorganic perovskite（HOIP）CH（NH₂）₂PbX₃（X=Cl,Br,I）（FAPbX₃,FA=CH（NH₂）₂⁺）has attracted extensive attention due to its excellent photoelectric properties,such as strong light absorption,low exciton energy band and long electron-hole diffusion length.Reducing dimensionality of the hybrid perovskite crystal usually comes up with superior properties in the aspect of optics,electricity or mechanics of materials.However,to the best of our knowledge,the current researches on 2D FAPbX₃perovskites are mainly limited to nanocrystals and colloidal quantum dots,which are not suitable for constructing complex systems.In this paper,we reported the fabrication of ultrathin 2D FAPbBr₃ sheets using liquid-phase epitaxy technique and investigated their optical properties.We also studied photo-induced carrier properties via 2D FAPbBr₃based devices.The main research results as follows:（1）The 2D HOIP FAPbBr₃ single-crystalline sheets are fabricated following the liquid-phase epitaxy method,and the grown 2D FAPbBr₃crystal has a thickness under10 nm and the lateral dimension could reach to tens ofμm.（2）The 2D HOIP FAPbBr₃single-crystalline sheet was tested by grazing incident X-ray diffraction（GIXRD）,electron energy spectrum and time resolved photoluminescence spectrum（TRPL）.Through testing and analysis,it can be found that the crystalline quality is high,the elements distribution uniform,the photoluminescence（PL）performance excellent,it has a long carrier life of 17～140 ns.As the 2D FAPbBr₃single-crystalline sheet thickness decreased,its PL emissions blue shifted.Research indicated that tightening halides and shrinking[PbBr₆]octahedra caused via thickness reduction are the main reasons for the increase of crystal band gap.（3）Based on 2D HOIP FAPbBr₃single-crystalline sheet,we have fabricated the photodetector with the structure of gold electrode/Perovskite/gold electrode.Firstly,the I-V characteristic curve of device under dark field was tested.The dark current of 10^-12A,defect density of 2.58×10¹¹cm^-3,carrier mobility of 31 cm²V^-1s^-1,carrier diffusion length of 1.2μm.And then the I-V characteristic curve of the device was tested under different optical power densities.The on/off current ratio of the device can be up to 10³,and the maximum light response rate of 730 A/W under the 10 V bias and 405 nm（86n W/cm²）illumination,and finally the transient light response characteristic cure of the device was tested.The result shows the maximum transient current value of 30 n A,and the rising and falling time of the device’s light response are 162 ms and 138 ms,respectively.The photodetector based on 2D HOIP FAPbBr₃can obtain good device parameters.