Preparation And Photoelectric Properties Of Quasi-two-dimensional Organic-Inorganic Hybrid Perovskite Materials

With the continuous development of modern science and technology,photoelectric detection technology,as an effective means to study the interaction between light and matter and to transmit information,has developed into an important part of modern information science.Photodetector is the core device of photoelectric detection technology,which is widely used in optical communication,medical imaging,space remote sensing,image sensing and other fields.However,commercial Si,Ga N and other traditional photodetectors usually require a thick active layer to ensure a strong optical response,which not only increases the cost,but also limits the application of such materials in flexible,small-scale high-end sensor components.In recent years,quasi-two-dimensional organic-inorganic perovskite has attracted extensive attention in the field of optoelectronics because of its excellent characteristics such as high absorption coefficient,long carrier diffusion distance,adjustable direct band gap,simple preparation process and low cost.However,there are usually many defects in the quasi-two-dimensional organic-inorganic perovskite films,which lead to the recombination of some photogenerated carriers.Meanwhile,the quantum limiting effect and dielectric confinement effect caused by the layered structure of quasi-two-dimensional perovskite restrict the carrier transport,which greatly affects the performance of the corresponding photoelectric devices.Therefore,finding a way to reduce the defects in quasi-two-dimensional organic-inorganic perovskite films and improve the transport of photogenerated carriers has become a challenge in this field.Based on this,this paper takes BA₂FAPb₂I₇quasi-two-dimensional perovskite as the research object,through optimizing the process flow and rare earth doping auxiliary crystal growth,effectively regulates the defects in the film,and successfully produces a high-performance photodetector with high sensitivity,fast response time and strong detection ability.In addition,the BA₂FAPb₂I₇material structure is controlled by pressure to further optimize the performance of the device.The content and structure of this paper are as follows:（1）BA₂FAPb₂I₇ quasi-two-dimensional perovskite films were synthesized by one step spin coating method,and the standard structural model of BA₂FAPb₂I₇ films was obtained by first principles.It is found that the fluorescence peaks of BA₂FAPb₂I₇ films are about 577 nm,640 nm and 780 nm,respectively,where577 nm and 640 nm are from exciton emission,780 nm is from defect emission.The absorption peaks are about 570 nm and 635 nm,respectively,with a band gap of 2.12 e V.Because the original film surface morphology is very rough,we adopted an optimized preparation process（including hot casting time and temperature,precursor composition and concentration）and non-toxic lanthanide ion doping(including Ce³⁺,Sm³⁺,Ho³⁺,Er³⁺)induce the optimal crystal growth,and prepare high crystal quality and morphology controllable perovskite materials.The results show that the ideal morphology of perovskite precursor solution with a concentration of 0.6 M and DMF:DMSO=1:4 can be obtained under the conditions of preheating at200℃for 5 minutes and annealing at 150℃for 10 minutes.The optimal morphology can be obtained by doping 0.5%Ce³⁺with an average grain size of about 10μm.The surface of the film is smooth and compact,and there is almost no obvious grain boundary.This optimal morphology greatly reduces the defect density,maximizes the photoinduced carrier extraction and photocapture capability,and inhibits the photoelectron-hole recombination.（2）Based on BA₂FAPb₂I₇ quasi-two-dimensional perovskite thin films,the transverse structure of the photodetector is prepared,and the photoelectric performance is explored.It is found that process optimization and non-toxic lanthanide ion doping control method can generate more free carriers and effectively enhance the photocurrent of the device.Eventually the device has dark current as low as 5.1×10^-11 A,on/off ratio as high as 2.2×10⁵,responsiveness as high as 4.51 A/W,detection rate as high as 4.31×10¹³ Jones,and response time as fast as 37.3μs/38.7μs.Under the bias voltage of 2 V and illumination intensity of 10μW/cm²,the photocurrent of the optimized device is increased by 86.6 times,the on/off ratio is increased by 10.3 times,the responsivity is increased by about 90 times,and the detection ratio is increased by 49 times.At the same time,the performance parameters of the device have significant advantages in the quasi-two-dimensional perovskite photoconductive detectors reported so far.（3）BA₂FAPb₂I₇:Ce³⁺quasi-two-dimensional perovskite films were studied in situ by using diamond anvil device.After pressure,all fluorescence peaks of BA₂FAPb₂I₇:Ce³⁺continued to redshift until disappearing.During pressure relief,the exciton peak began to appear at 3.81 GPa and gradually increased with the decrease of pressure.At 0.82 Gpa,another new fluorescence peak appeared,and the fluorescence intensity of exciton peak decreased.After complete pressure relief,exciton peak disappeared and PL intensity of new fluorescence peak increased.Before and after pressure relief,the fluorescence peak position changes and the carrier lifetime increases significantly,which indicates that pressure regulation can optimize the properties of BA₂FAPb₂I₇:Ce³⁺material.In addition,it is found that BA₂FAPb₂I₇:Ce³⁺samples have photoelectric response under the incident light of ultraviolet（365 nm）,visible（405 nm）and near infrared（980 nm）.At 0.19 Gpa,the maximum response and detection rate are increased 1.8 and 1.3 times,1.5 and1.1 times,2.8 and 2.76 times,respectively,compared with atmospheric pressure.After pressure relief,the photoelectric response of BA₂FAPb₂I₇:Ce³⁺samples under 365 nm and 405 nm laser irradiation are also significantly improved compared with the initial state.These results indicate that the photoresponse of perovskite photodetectors can be optimized by pressure induction to further enhance the detection performance of the devices.