Defect Passivation And Optoelectronic Properties Of Tin-Based Chalcogenide Nanowires

As an important part of optoelectronic devices,photodetectors play an important role in video imaging,environmental monitoring,encrypted information transmission,military detection,etc.Traditional photodetectors made of semiconductor silicon materials have problems such as expensive cost,cumbersome preparation process and low device performance.Among them,CsSnI₃has become one of the popular materials for perovskite research because of its non-toxic properties.However,CsSnI₃perovskite suffers from the problems that Sn²⁺is easily oxidized to Sn⁴⁺,and is easily eroded by water and oxygen in the air and has a large number of mismatches and defects.Therefore,we used defect passivation to improve the performance and stability of perovskite CsSnI₃nanowires with respect to some problems of CsSnI₃,and prepared high-performance and highly stable all-inorganic perovskite CsSnI₃nanowire photodetectors.The main contents of this thesis are as follows.In the first part,ultra-stable high-performance CsSnI₃nanowire photodetectors were prepared by adding 1-butyl-2,3-dimethylimidazolium chloride salt（BMIMCl）ionic liquid to the CsSnI₃nanowires.The dark current of the device was significantly reduced to an ultra-low value of 2×10^-11A,and the photodetector showed high performance with a response rate of0.237 A/W,a detection rate of 1.18×10¹²Jones,and a linear dynamic range of 180 d B.In addition,our unencapsulated CsSnI₃nanowire photodetector exhibits ultra-high stability:the device performance is basically unchanged after more than 1200 seconds of prolonged light exposure;after 60 days of storage in air（25℃,50%humidity）,the device performance does not show any significant dramatic degradation,and the device performance is still maintained at more than 90%of the original performance.Theoretical calculations and a series of experimental characterizations have confirmed that the addition of BMIMCl to prepare high-performance and high-stability CsSnI₃nanowire photodetectors is due to the combination of BMIM⁺ions with Sn²⁺,which prevents Sn²⁺from being oxidized to Sn⁴⁺,effectively passivates Sn-related defects,suppresses the dark current of the device,prevents the erosion of water oxygen molecules in air,and improves the stability of the photodetector.The second part was prepared by adding oleylamine iodide into the CsSnI₃nanowires,and the CsSnI₃nanowire photodetectors were prepared with lower dark currents,lower noise and higher detectivity.The I_noiseand D^*of the device reach 2.4×10¹⁵A/Hz^1/2and 2.1×10¹²Jones,respectively.In addition,the CsSnI₃nanowire photodetector has high device stability,with no degradation in device stability after continuous irradiation at a high light intensity of4 m W/cm²for about 1400 s.The device stability at high temperature is also high.The stability of the device at high temperature is also very good,such as continuous heating at 150℃for 1h,the device performance can maintain more than 90%of the initial performance.Experimental characterization demonstrates that the enhanced performance and stability of the nanowire photodetector is due to the ability of oleylamine iodide to suppress carrier transfer between the inorganic backbones in CsSnI₃nanowires,which results in lower dark currents,lower noise,and higher detection.And the large organic spacer ions in oleylamine ions can enhance the stability of the device.