Growth And Photoelectric Properties Of Halide Perovskite MAPbBr₃ Crystal

The halide perovskite MAPbBr₃?MA=CH₃NH₃?crystal has attracted widespread attention in the field of optoelectronic devices due to its excellent optoelectronic properties.Compared with polycrystalline films,single crystal is considered to be an ideal optoelectronic material,with lower defect density,longer carrier diffusion length,and higher mobility.In recent years,many solution methods have been used to grow MAPbBr₃ single crystals.However,their surface structures are different under various growth conditions.So it is particularly important to reveal the relationship of the crystal surface structure and its growth mechanism.Furthermore,the application of MAPbBr₃crystal in radiation detection is still in the exploratory stage.In this paper,the growth mechanism of MAPbBr₃ crystal by anti-solvent vapor-assisted crystallization?Anti-solvent vapor-assisted crystallization,AVC?method was deeply investigated,and high-quality MAPbBr₃ single crystal was prepared with process optimization.The phase structure,photoelectric properties and basic performance of plane detector are investigated.MAPbBr₃single crystals were grown by AVC method.Its growth process was successfully explored by adjusting the molar ratio of Pb Br₂ and MABr,the concentration of solution,the type of anti-solvent,the concentration of anti-solvent,the time of volatilization and the temperature.The AVC process was optimized by diluting the anti-solvent,and the crystal dimension increased from 5×5×1.5 mm³ to 9×9×3 mm³.Under anti-solvent dilution conditions,the cubic-shaped MAPbBr₃ crystal was fabricated with the molar ratio of 1:1 at the aboved two solutes,while triangular-prism-shaped MAPbBr₃ crystals were obtained when the molar ratio was 0.8:1.XRD results show that the cubic-shaped and triangular-prism-shaped MAPbBr₃crystals had the same phase structure,but their natural exposed surfaces were different owing to the different growth kinetics.The crystal quality was improved obviously after diluting with anti-solvent.The?100?surface of MAPbBr₃ single crystal was observed with the help of optical microscope,scanning electron microscope and atomic force microscope.It can be seen that the growth process of MAPbBr₃ crystal followed the step growth mechanism of screw dislocation.A spiral step was formed around the central screw dislocation,and the step expanded outward in a direction normal to the edge,resulting in the continuous growth of MAPbBr₃crystal.In addition,there are many pits with different depths on the crystal surface,the number and depth of the pits gradually increase with solution concentration,mainly related to the excessive and uneven growth rate.The pits hinder the step slipping and affect the ideal lattice arrangement around it,leading to the structure mismatch to introduce more defects.The surface defect density of the crystal was reduced and the corresponding optical transmittance was increased after polishing.The UV-Vis-NIR spectroscopy results show that MAPbBr₃-2 crystal with diluting anti-solvent had the higher optical transmittance in the wavelength range of 500-800 nm than MAPbBr₃-1 without diluting anti-solvent.The PL spectrum analysis shows that the emission peak of MAPbBr₃ crystal of 540-550 nm belongs to the exciton peak near the band edge,while the emission peaks of 600-700 nm belong to composite peaks related to defects.Especially,MAPbBr₃-2 crystal had the sharper exciton peak and weaker defect composite luminescence peaks,suggesting a higher crystal quality.I-V results show that the resistivity of the crystal was improved about one order of magnitude after diluting the anti-solvent,reaching the order of 10⁸?×cm.The results of photoresponse show that MAPbBr₃-2 crystal had faster photoresponse speed and more stable photocurrent platform.The laser-induced photocurrent spectrum shows that the mobility of holes with MAPbBr₃crystal was up to 185 cm² V^-1s^-1.Based on the above properties of MAPbBr₃ crystal,we have developed high resistance MAPbBr₃ simple planar detector with different electrode structures,including Au/MAPbBr₃/Au,Au/MAPbBr₃/Al,Au/MAPbBr₃/Ag,Au/MAPbBr₃/In and Au/MAPbBr₃/Cu.It can be seen that their I-V curves tend to be linear.Among them,I-V curve of Au/MAPbBr₃/Au detector had the best linear relationship,and its symmetry was better,deduced that Au was the best material to form typical ohmic contact with MAPbBr₃ crystal.Furthermore,it was found by I-t measurement that Au/MAPbBr₃/Au device had the largest switch ratio and better photocurrent stability,while other anode devices had smaller switch ratio.It can be explained that the large contact barrier between metal electrodes?Al,In,Ag,Cu?and MAPbBr₃ crystal,hinders the transmission of some photo-generated carriers and weakens the photocurrent and dark current in varying degrees.