The Design And Application Of Photoelectric Detectors Based On Two-dimensional Halogen Perovskite

Photoelectric detectors are a kind of components,which can convert the optical signal into the analysable electrical signal,have played crucial role in environmental monitoring,industrial control,intelligent remote sensing,precision guidance,health and medical and other major fields.The core of photodetector is semiconductor material,so the development of new semiconductor materials with excellent performance is the key to promote the upgrading of photodetectors and upgrading of industry.High-efficiency solar energy conversion in photovoltaic devices,high color purity and quantum efficiency in light-emitting devices,low-cost and simple solution preparation methods have collectively made halide perovskites（HPs）rapidly grow into a star material system in recent years.HPs are highly variable and adjustable in crystal structure,therefore have rich derivative sub-systems.Among them,two-dimensional（2D）HPs stand out due to their unique advantages（including morphological anisotropy,adjustable quantum confinement effect,good stability,etc.）,and have achieved considerable progress in optoelectronic devices including solar cells,light-emitting diodes,and photodetectors.In order to promote the practical application of 2D HPs,more in-depth researches are needed on the synthesis,performance characterization and device application.This dissertation carried out related research,the main research results are as follows:（1）Flexible photodetectors based on 2D CsPbBr₃ nanoplatelets.Firstly,2D CsPbBr₃nanoplatelets are prepared by room-temperature solution method,and their phase structure,morphology and optical properties are studied.Subsequently,the 2D CsPbBr₃ nanosheets are used as the active material to construct an efficient and low-cost flexible photodetector,in which the common writing paper is used as the substrate and the electrodes are drawn by pencil.At a relatively low bias voltage（9 V）,high external quantum efficiency（EQE）and responsivity up to 485%and 2.1A W^-1 are obtained,respectively.The paper substrate,graphite electrode,and 2D CsPbBr₃ nanosheets are all mechanically flexible,allowing them to maintain functionality even when the device is bent.This work also studies the flexibility,repeatability and stability of the photodetectors.Finally,thanks to the simple and repeatable fabrication process,an integrated array of photodetectors is fabricated and based on which clear images are obtained.（2）UV detector based on 2D perovskite CsPbCl₃ nanoplatelets.Firstly,to solve the poor processability of CsPbCl₃ caused by the low solubility,an intermediate phase-assisted synthesis method is designed starting from better soluble lead chloride（Pb Cl₂）and protonated octadecylamine（OA⁺）,Ruddlesden-Popper type HP products with 2D morphology are synthesized.Subsequently,cesium acetate（Cs Ac）is introduced into the colloidal solution,and the exchange between Cs⁺and OA⁺converted the Ruddlesden-Popper imtermediate phase to CsPbCl₃ while retaining its 2D morphology,2D CsPbCl₃ nanosheets are synthesized thereby.The planar detector based on the commercial interdigital electrode shows excellent detection performance,the responsivity reaches 3.64 A W^-1（light intensity is 1μW）,LDR is up to 107 d B,the photodetector also shows excellent moisture stability and photostability.（3）Underwater photodetectors based on quasi-2D layered HPs.A 2D layered HP system with excellent water stability is proposed,and the advantages of corresponding photodetectors in full-spectrum underwater optical communication are introduced.The 2D layered HPs system has strong hydrophobicity and exhibits good photoelectric properties even when completely exposed to water.At the same time,the insulating long-chain alkyl amine greatly reduces the noise of the device,so that the photodetector has a high sensitivity to weak light.By adjusting the dimensionality,the optical response of the 2D HPs product can cover the entire transmission spectrum of water（<800 nm）,thereby realizing full-spectrum underwater optical communication.（4）Near-infrared narrow-band detector based on CsPb_0.5Sn_0.5I₃:PEA₂Pb I₄.Taking advantages of the oriented growth of 2D layered HPs,the 2D HP PEA₂Pb I₄ as an additive improves the crystallinity and coverage of the 3D HP CsPb_0.5Sn_0.5I₃ polycrystalline film,hence realizing high-performance near-infrared photodetector.Especially,the bandwidth and detection limit of the photodetector reach 543 k Hz and 0.33 n W,respectively,along with an ultralow noise current(1.65×10^-13 A Hz^-1/2)and an extremely high specific detectivity(5.4×10¹⁴ Jones).At the same time,a precise all-dielectric optical microcavity（NPB/（Li F/NPB）⁵/Li F/Li F/（NPB/Li F）⁵NPB）is designed and mounted on the above infrared photodetector,a narrow-band photoelectric response with a full-width at half maximum（FWHM）of<50 nm in the near infrared band can be achieved.Finally,the application of the photodetector in biological detection is explored.