Preparation Of Cs₃Sb₂Br₉ Nanoflakes And Photoelectrical Study Of Its Hybrid Devices

Lead halide perovskite（APb X₃,where A=MA,FA,Cs,X=Cl,Br,I）has drawn intense attention due to its vital role in the field of photoelectric detection.However,lead ion toxicity and inferior environmental stability of organic groups vastly hamper its practical application.Hence,the environmentally friendly and lead-free inorganic perovskite Cs₃Sb₂Br₉has aroused great interest in recent years.Cs₃Sb₂Br₉nanoflake has a band gap of 2.58 e V,and owns the characteristics of high absorption coefficient,small effective mass,direct band gap,simple preparation process and low cost.Therefore it is suitable for the practical application of optoelectronic devices.Nevertheless,it still has some shortcomings such as narrow spectral response range and low sensitivity.Both Cd Se and Cd S are direct bandgap semiconductors,and their band gaps are 1.7 and 2.4 e V,respectively.Both of them have high carrier transport capacity and excellent photoelectric properties.As a result,the combination of Cs₃Sb₂Br₉with them can effectively improve the photoelectric performance of the single Cs₃Sb₂Br₉.Based on the above-mentioned,in this thesis,Cs₃Sb₂Br₉nanoflake（NF）,Cd Se and Cd S nanobelt（NB）were prepared by inverse temperature crystallization method（ITC）and thermal evaporation method（CVD）,respectively.The hybrid Cs₃Sb₂Br₉NF/Cd Se NB and Cd S NB/Cs₃Sb₂Br₉NF photodetectors were constructed by droplet method and dry transfer method,and the photoelectric characteristics of the two hybrid devices were measured and analyzed,and the working mechanism was explored.The primary research findings of this thesis are as follows:（1）Cs₃Sb₂Br₉NF was prepared by ITC method.The samples werecharacterized by optical microscopy（OM）,scanning electron microscopy（SEM）,atomic force microscopy（AFM）,energy dispersive spectroscopy（EDS）,X-ray podwer diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,photoluminescence（PL）,UV-visible（UV-vis）and ultraviolet photoelectron spectroscopy（UPS）.Then,Ti/Au electrodes were deposited by electron beam（EBM）to prepare Cs₃Sb₂Br₉NF photodetector,and their photoelectric properties were tested.The results depict that the spectral response of Cs₃Sb₂Br₉NF photodetector reaches the maximum value at448 nm.Under these conditions,the light/dark current ratio is 2.85×10²,the responsivity is 2.6 A/W,and the external quantum efficiency is 7.3×10²%.The detectivity of 1.7×10¹²Jones is remarkable,with a rise and fall time of 10.8 ms and10.6 ms.（2）Cd Se and Cd S NB were synthesized by CVD method.It is observed that the prepared Cd Se and Cd S NB were not only thicker than 50 nm,but also smooth and flat with symmetrical width by SEM.In addition,XRD,EDS and XPS were applied to characterize the structure and chemical constituent of materials,which showed that Cd Se and Cd S NB had well crystallization and no other impurities were detected.Finally,we use PL and Raman to explore the optical properties of Cd Se and Cd S NB.（3）The hybrid Cs₃Sb₂Br₉NF/Cd Se NB photodetector were fabricated by dispersing Cd Se NB on Cs₃Sb₂Br₉NF via one-step droplet way,and the optoelectric property of the hybrid photodetector was measured.The test outcomes display that the hybrid photodetector has a wider spectral response range（300-780 nm）than the single Cs₃Sb₂Br₉NF photodetector.The light/dark current ratio of the hybrid Cs₃Sb₂Br₉NF/Cd Se NB device is up to 4.79×10³under 448 nm monochromatic light irradiation,which is 16.8 times of that of single Cs₃Sb₂Br₉NF photodetector.The external quantum efficiency and detectivity are 4.8×10⁴%and 1.1×10¹⁴Jones,respectively,which are 65.8 and 64.7 times that of single Cs₃Sb₂Br₉NF photodetector.The ascending/descending time of the hybrid is 16.5/15.7 ms.The hybrid photodetector widens the spectral response to the whole range of visible light,and elevates the effective segregation velocity of electron hole pairs,which markedbly promotes the optoelectric properties of the hybrid photodetector.（4）The hybrid polyrhizal Cd S NBs/Cs₃Sb₂Br₉NF photoelectric devices were prepared by transferring four Cd S NB to Cs₃Sb₂Br₉NF in sequence by the dry transfer strategy,and the optoelectric properties of the hybrid photodetector was measured.The consequences display that the hybrid area ratio of polyrhizal Cd S NBs/Cs₃Sb₂Br₉NF hybrid devices in the channel is up to 86%,and the spectral response range is extended to the green band（400-520 nm）.The light/dark current ratio of this device is as high as 1.54×10⁵under 448 nm monochromatic light irradiation,which is 540 times of that of a single Cs₃Sb₂Br₉NF device.The maximum response rate,external quantum efficiency and detection rate are 4.13×10³A/W,1.14×10⁶%and 1.47×10¹⁵Jones,respectively,which are 1588.5,1561.6 and864.7 times of the single Cs₃Sb₂Br₉NF device.This hybrid photoelectric device shows excellent photoelectric performance.The reason is that Cs₃Sb₂Br₉,as a high light absorption layer,forms Type-Ⅱband heterostructure with Cd S hybrid construction with high carrier transport ability.This heterojunction effectively speeds up the carrier separation speed.Four parallel Cd S NBs in the channel almost completely cover Cs₃Sb₂Br₉NF,which maximizes the photoelectric performance of the hybrid device.The work provides an effective direction for the construction of high performance Cs₃Sb₂Br₉composite photodetector and its practical application.