| In recent years,lead halide perovskite materials have excellent light absorption,adjustable energy band and long carrier migration distance in the visible light range,showing great application potential in the fields of photovoltaic,photoelectricity,laser and photoluminescence,and becoming one of the research hotspots in the field of new energy materials.In this paper,pure inorganic lead bromide CsPbBr3 single crystal,methylamine mixed cationic lead halide perovskite MA1-xCsxPbI3,MA1-xCsxPbBr3 single crystal as the main research object,through the anti-solvent and inversion growth method,the growth of large-size crystal,The structure and optical properties of the crystal were studied.A series of photodetectors were prepared by using the grown single crystal and photoelectric properties of CsPbBr3,MA1-xCsxPbI3 and MA1-xCsxPbBr3 single crystals were studied.The main contents are as follows:Firstly,PbBr2 and CsBr were dissolved in DMSO,and CsPbBr3 single crystal was grown by using methanol as anti-solvent:By comparing the growth rate and size of CsPbBr3 single crystal under different experimental conditions,it was found that the growth temperature was 40? and the solution concentration was 0.4mol/L,large-sized CsPbBr3 single crystal was easily obtained.XRD study found that CsPbBr3 crystal is orthorhombic(space group is Pnma),unit cell parameters a=8.24A,b=11.75A,c=8.20A.The interface structure and growth mechanism of the most exposed(101)crystal plane of CsPbBr3 single crystal were studied by optical microscopy and AFM.It was found that CsPbBr3 single crystal is a two-dimensional nucleation growth mechanism.The optical properties were studied by UV-vis,PL and fluorescence lifetime.The absorption edge is located at 560 nm,the band gap is 2.16 eV lower than that of polycrystalline film,the fluorescence peak is at 540 nm,?1=4.4 ns,?2=30 ns.Using the grown CsPbBr3 single crystal,the Au interdigitated photodetector was fabricated,and the parameters such as ?,photoresponse rate,EQE,photodetection rate,switching ratio and corresponding time were studied.The study found that the highest response rate and EQE are 0.028 A/W and 7.00%and the highest switching ratio can reach 100,and the corresponding time of rise and decay are<100 ms at a wavelength of 450 nm.Compared with the polycrystalline film,the performance of CsPbBr3 single crystal is better than that of polycrystalline film,so CsPbBr3 single crystal has great potential in the field of photodetectors.The PbBr2,CsBr and synthesized MABr were mixed and dissolved in DMF,and the MA1-xCsxPbBr3(x=0%,1%,3%)single crystal was grown by inverse temperature method.MA1-xCsxPbBr3 single crystal were classified to be cubic system(space group is Pm3 m)by XRD patterns,and the unit cell parameters are slightly smaller after doping;The existence of Cs+in the crystal was determined by XPS and EMPA.The effects of Cs+ enter into MAPbBr3 on optical properties were studied by UV-vis,PL and fluorescence lifetime.We found that Cs+does not affects the optical absorption of MAPbBr3 single crystal after entering the lattice,and the absorption edges both are located at 575 nm,the band gap was 2.13 eV.The fluorescence peak of MAPbBr3 was located at 522 nm,but the fluorescence peak of MA1-xCsxPbBr3 single crystal shifted red to 529 nm,and the fitting ?1 associated with surface defects was basically unchanged,and the fitting ?2 associated with internal defects has increased.The sandwich photodetector device and the planar photodetector device were prepared based on MA1-xCsxPbBr3 single crystal.In further,conductivity,defect density(nt),?-?,on/off ratio and the corresponding time were researched.It was found that the entry of Cs+reduced the defect density in the MAPbBr3 crystal,and increased the photocurrent and reduced the dark current,indicating that Cs+ is of great significance in improving the photoelectric performance and stability of the device.The PbI2,CsI and the synthesized MAI were mixed and dissolved in GBL,and the MA1-xCsxPbI3(x=0%,2%,5%)single crystal was grown by the inversion temperature method.MA1-xCsxPbI3 single crystal were classified to be tetragonal system(space group is I4/mcm)by XRD patterns,and the unit cell parameters are slightly smaller after doping;the true contents of Cs in MA0.98Cs0.02PbI3 and MA0.95Cs0.05PbI3 are determined to be 6%and 11%by XPS,respectively.It is obvious that the true contents of Cs are higher than the theoretical values.The effects of Cs+ enter into MAPbI3 on optical properties were studied by UV-vis,PL and fluorescence lifetime.We found that Cs+does not affects the optical absorption of MAPbI3 single crystal after entering the lattice,and the absorption edges both are located at 840 nm.But the band gap of MA0.95Cs0.05PbI3 is higher than that of MAPbI3,and the position of the fluorescence peak of MA0.95Cs0.05PbI3 has blue-shifted;the fitting ?1 associated with surface defects has increased,and the fitting ?2 associated with internal defects has decreased.These indicated that Cs+ passivates the crystal surface to improve the crystal stability and causes the increase of internal defects of the crystal.The sandwich photodetector device and the planar photodetector device were prepared based on MA1-xCsxPbI3 single crystal.In further,defect density(nt),?-?,and on/off ratio were researched.It is found that the higher the content of Cs+,the more crystal defects.MA0.98Cs0.02PbI3 has the highest photocurrent and lowest dark current,while MA0.95Cs0.05PbI3 has the highest dark current,indicating that the appropriate amount introduction of Cs+ passivates the crystal surface,and the recombination of carriers is suppressed,the photoelectric performance of the crystal is improved.But the excess Cs+ causes more defects,which promotes carrier recombination and destroys the crystal performance.When the doping proportion is 2%,the photoelectric performance of the crystal is the best.However,when the doping amount is too high,the photoelectric performance of the crystal decreases. |
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