Organic-inorganic Halide Two-dimensional Perovskite Photo Transistors Assisted By Ferroelectric Dielectrics

In recent years,organic-inorganic hybrid perovskite materials have received extensive attention due to their unique optical and electrical properties and relatively simple preparation processes.As a new type of semiconductor material,perovskite materials have achieved great success in the field of solar cells,and their photoelectric conversion efficiency has increased from 3.8%in 2009 to more than 22%now.And breakthroughs in the field of solar cells have also led to the use of this material as a new type of semiconductor in other optoelectronic devices.Because of its good light absorption coefficient,carrier mobility and simple preparation process,many researchers have tried to use organic-inorganic hybrid perovskite materials to produce high-performance,large-area optical field effect transistors.Compared with the most researched three-dimensional organic-inorganic hybrid perovskite,the two-dimensional organic-inorganic hybrid perovskite has a unique van der Waals force stacked layer structure,which makes it have relatively good lateral conductivity and stability.Only limited researches were about the photoelectric properties of the two-dimensional perovskite and the use of this material for optical field effect transistors.In this article,the optical and electrical characterization of ferroelectric thin film poly?vinylidene fluoride-trifluoroethylene??P?VDF-TrFE??and novel two-dimensional perovskite material?C₆H₅C₂H₄NH₃?₂SnI₄??PEA?₂SnI₄?were systematically carried out.Then,the ferroelectric thin film was used as the gate dielectric layer to fabricate a field effect transistor with the novel two-dimensional perovskite material as the channel.The unique optical and electrical properties of the two-dimensional perovskite field effect transistor under the effect of the ferroelectric field were studied.The main results obtained were shown as below:1.The electrical properties of the two-dimensional perovskite optical field effect transistors were enhanced:In this work,we fabricated transistors based on the two-dimensional perovskite?PEA?₂SnI₄ as channel and use P?VDF-TrFE?as the back-gate dielectrics.We also fabricated transistors using traditional SiO₂ thin film as dielectrics for comparison.Through the transfer characteristic curve and output characteristic curve of the devices,it was found that due to the defect states of the two-dimensional perovskite material itself,the transfer characteristic curve on the conventional SiO₂ had a large hysteresis,which hindered its application in the field of high-speed devices.In the ferroelectric thin film device,hysteresis was significantly reduced by the effect of the ferroelectric field,and the subthreshold swing was reduced from 6250 mV dec^-1 of SiO₂dielectric device to 440.5 mV dec^-1.The lower subthreshold swing meant that the device could have a faster switching speed and been applied in high-speed devices.In addition,under the effect of the ferroelectric field,the transfer characteristic curve of the device also shows a higher on/off switching ratio,close to 10⁵.By analyzing the transfer characteristic curve,the carrier mobility could be up to 0.04cm² V^-1 s^-1.This work has important significance as a reference for further research on the electrical transport properties of new type perovskite materials under the effect of ferroelectricity.2.Optical-electric performance enhancement of two-dimensional perovskite photodetectors:Here we systematically studied the changes in photodetection performance of two-dimensional perovskite photodetectors under different polarization states of ferroelectric dielectrics.It has been verified by the transfer characteristic curve and the output characteristic curve of the field effect transistor device that?PEA?₂SnI₄ is a P-type semiconductor.When the polarization direction of the ferroelectric thin film was downward by the gate voltage,the channel was in extraction state,and the carrier concentration was increased.The high carrier concentration compensated for the effect of defect hindrance,thereby improving the response speed of the device.The fastest speeds of the rising and falling edges of the photocurrent could reach 50 ms and 1.5 s,respectively.When the polarization direction of the ferroelectric thin film was made upward by the gate voltage,the channel was depleted,the carrier concentration was greatly reduced,and the dark current was lowered.Due to the effective suppression of dark current,the device had a higher photo switching on/off ratio in this polarization state,and the switching ratio reaches 100.At the same time,due to the reduction of dark current,the response sensitivity of the device became better.Under the illumination of 470 nm monochromatic light,the responsivity R reached14.57 A W^-1,and the detection rate D*reached 1.74 x 10¹² Jones.Device parameters are at the leading edge among similar materials.This work investigated ferroelectric effect on the performance of two-dimensional perovskite photodetectors,providing a new dimension for further improving the performance of perovskite photodetectors,except for the traditional doping or passivation method.