Photoelectric Properties Of CH₃NH₃PbI₃ Crystals

Recently,organic–inorganic hybrid perovskites have been widely concerned due to their successful application in photodetectors,photovoltaic cells,light-emitting devices and photo sensor.At present,most of the research on devices made of organic-inorganic hybrid perovskite materials is based on the（100）and（112）planes,and few studies have been conducted on the relationship between crystal crystal axis and device properties.In this work,we cut the sample at different angles to the crystal axis of the CH₃NH₃PbI₃ crystal.Photodetectors and organic field effect transistors（OFETs）were fabricated from the cut samples,and the performance parameters of the devices were measured.The effect of the crystal axis of CH₃NH₃PbI₃ crystals on the photoelectric properties of the devices was investigated.In this paper,organic-inorganic hybrid perovskite CH₃NH₃PbI₃ crystals are studied.The main research contents are listed as follows:Firstly,CH₃NH₃PbI₃ single crystal was prepared by reverse temperature crystallization.The materials were characterized by X-ray powder diffractometry,scanning electron microscopy,Raman spectroscopy,photoluminescence spectroscopy and UV-Vis-NIR absorption spectroscopy.The experimental results show that the crystal surface is flat and has good uniformity and density on the microscopic level.The composition of CH₃NH₃PbI₃single crystal is pure and free of impurities.The peak position of Raman spectrum is standard and no offset,while the peak of photoluminescence spectrum is slightly blue-shifted.The absorption spectrum shows a clear absorption edge.The experimental results show that the prepared CH₃NH₃PbI₃ crystal has high quality and a low trap density.Secondly,the effect of the crystal axis of CH₃NH₃PbI₃ single crystal on the photoelectric properties of the photodetector was studied.The direction of the crystal plane was determined by X-ray single crystal diffractometer,and then the crystal was cut along the direction parallel to and perpendicular to the crystal axis.After polishing,the electrode was vapor-deposited on the corresponding crystal plane to prepare a photodetector.The photosensitive surface of the photodetector is irradiated by laser with different wavelengths and polarization directions,and the photoelectric characteristics of the device are tested.The experimental results show that when the electric field component E is parallel to the crystal axis,the photocurrent density of the photodetector is two orders of magnitude larger than the photocurrent density of the electric field component E perpendicular to the crystal axis.By calculation,the optical responsivity light-dark current ratio and external quantum efficiency values of the electric field component E of the laser is parallel to the crystal axis of photodetector are 58 times,10times and 66 times of the perpendicular condition,respectively.Additionally,the effect of the crystal axis of the CH₃NH₃PbI₃ crystal on the performance of the fabricated OFET was further investigated.The crystal was cut along the electric field component E and the crystal axis in the directions of 0°,30°,60°,90°and 180°.After polishing,using polyvinylidene fluoride（PVDF）as an insulating layer,a top gate structure OFET was prepared.Using a semiconductor characterization system to provide different source voltages and observe the I-V curve of the current as a function of the applied electric field.The experimental results show that the prepared OFET has good output characteristics.As the electric field component E changes with the crystal axis angle of the CH₃NH₃PbI₃crystal,the current I_DSS between the source and the drain also changes.The current I_DSS at 0°is larger than other angles.In addition,when the electric field component E is 0°with the crystal axis,the current I_DSS reaches a saturation value at V_DS=5 V,and there is no significant saturation at other angles.