Fabrication And Performance Of Lead-free Double Perovskite Thin Film Photodetectors

Lead-based halide materials（APb X₃）have unique advantages such as adjustable band gap,high carrier mobility and low defects,and are widely used in photoelectric detectors,solar cells and light-emitting diodes.However,lead-based materials are unstable and toxic,which affects their large-scale application.Therefore,looking for lead-free perovskite replacement materials with high performance and stability has become the future development trend.A new type of double perovskite material(A₂m⁺M³⁺X₆)which uses univalent cation and trivalent cation to substitute B site synchronously has become an important new semiconductor photoelectric material because of its environmental friendliness,high stability and easy doping.Based on this,this paper chooses Cs₂Ag Bi Br₆ as the research object,and prepares photoconductive photodetectors,and studies its influence on the photoelectric properties of photoconductive devices by doping rare earth ions and adding Zn O electron transport layer.The specific research contents are as follows:（1）lead-free double perovskite Cs₂Ag Bi Br₆ crystal with good crystallinity was successfully synthesized by hydrothermal method.Cs₂Ag Bi Br₆ thin films were grown on silicon dioxide/silicon wafer by vacuum evaporation method,and the effect of annealing temperature on the microstructure of the thin films was systematically studied.The optimum annealing conditions were determined,and dense perovskite Cs₂Ag Bi Br₆ thin films with low defect density were obtained.（2）A photoconductive photodetector with Au/Er_x:Cs₂Ag Bi Br₆/Au planar structure was fabricated.The responsivity,detection rate and response speed of Er³⁺doped Cs₂Ag Bi Br₆ samples are obviously improved compared with the undoped samples.When the atomic ratio of Er addition is 0.25,the film performance is the best.Under the irradiation of ultraviolet light（365 nm）with an optical power density of46.51μW/cm²,the photoresponse is 1.26×10^-3 A/W and the detection rate is 7.93×10⁹ Jones,which is 3.6 times higher than that of the undoped sample.（3）A compact zinc oxide electron transport layer is added on the surface of silicon dioxide to prepare a photoconductive photodetector with a planar structure of Au/Zn O/Er_x:Cs₂Ag Bi Br₆/Au.The introduction of Zn O electron transport layer further effectively improves the photoelectric detection performance of the film.When the Er doping dose is 0.25,under the irradiation of ultraviolet light（365 nm）with an optical power density of 46.51μW/cm²,the photoresponse is 4.75×10^-3 A/W,and the specific detection rate is 3.47×10¹⁰ Jones,which is 4.4 times higher than that of the sample without Zn O.The response and recovery speed are accelerated,and the response and recovery time are 0.406 s and 0.414 s respectively.