Heterojunction Photodetectors Based On Organic-Inorganic Hybrid Perovskite Single Crystals

Organic-inorganic hybrid perovskite materials have attracted intensive attention in the research and application of optoelectronic devices due to their excellent optoelectronic properties.Particularly,perovskite single crystals have emerged as a hot candidate in the fields of high-efficiency solar cells,board optical range photodetectors and high-energy ray detectors due to its advantages of no grain boundary,low defect density,high light absorption coefficient and long carrier diffusion distance.In this work,perovskite single crystal heterojunctions were successfully fabricated by liquid phase epitaxy and space limited methods based on the modified inverse temperature crystallization method.The construction of heterojunction promotes the separation of photogenerated carriers,enhances the carrier extraction in single crystal devices,inhibits the dark current,and then significantly improves the responsivity and detectivity of the heterojunction photodetectors.Meanwhile,due to the self-filtering property,the perovskite single crystal heterojunction photodetectors exhibit narrowband effect in a wide range of visible light region.The main research contents of this paper are as follows.Firstly,MAPbBr₃ single crystal layer was grown on the MAPbCl₃ single crystal by liquid phase epitaxy method.A series of characterization such as X-ray diffraction,photoluminescence and scanning electron microscopy have verified that the MAPbBr₃/MAPbCl₃ heterojunction has excellent crystal quality and smooth surface morphology.The results of the current-voltage（I-V）characteristic measurement and current-time（I-t）response photocurrent curves show that the heterojunction exhibits unidirectional conductivity,the responsivity of the photoelectric device reaches as high as 93.2 m A/W,and the detectivity reaches up to 7×10¹¹ Jones.In addition,the heterojunction shows excellent long-term stability with only 4%drop in current after 45days in ambient condition.Secondly,MAPbBr₃/Si single crystal heterojunction was prepared on the Si substrate by the space limited method.The barrier of band structure limits a super low the dark current of only a few nanoamps in the heterojunction device at 10 V bias,which enables a high detectivity of 6×10¹² Jones under 1.5μW/cm² light illumination,far superior to the detectivity of intrinsic perovskite single crystal devices.Meanwhile,the self-filtering property of perovskite single crystals realizes the green light narrowband detectivity in the heterojunction device.Furthermore,the photocurrent loss is only 10.25%after 60 days in the air environment,which ensures the long-term application of the device.Finally,based on MAPbBr₃/Si heterojunction,MAPbBr_3-XCl _X/Si single crystal heterojunctions with different wavelength light absorbing layers were prepared by adjusting the ratio of halogen elements.MAPbBr_3-XCl _X/Si single crystal heterojunction device successfully realizes the adjustable narrowband light detection with only a 20 nm full width at half maximum（FWHM）in the visible light range of 440 nm to 520 nm.The maximum responsivity reaches 0.4 A/W,and the light-to-dark ratio is up to 50,effectively realizing the weak light detection.In this thesis,the liquid phase epitaxy method and space limited growth strategies of perovskite single crystals provide new insights for the construction of perovskite heterojunctions.The variable wavelength narrowband detection in the visible light range further broadens the application of perovskite single crystals,and enriches the possibility of narrowband photodetectors.