Polarization-sensitive 2D Perovskite Narrowband Photodetectors Based On （C₄H₉NH₃）₂PbI₄

Photodetectors can sense optical signal and convert it to electrical signal;therefore,they are widely used in a range of fields such as optical communications,biological imaging,and machine vision.Among them,narrowband photodetectors can realize the selectivity of light wavelength（frequency）,and thus can be used in image recognition,biomarking and other applications.Polarization-sensitive photodetectors can discriminate the polarization state（vibration direction）of light,which are used in remote sensing and optical radar.Polarization-sensitive narrowband photodetectors can simultaneously detect the polarization states and wavelength information,and thus would find promising applications in spectral polarization imaging,polarization measurement and so on.Currently,narrowband photodetectors and polarization-sensitive photodetectors are realized by means of light dispersive elements and polarization devices respectively,which exhibit disadvantages of complex structure,bulky,difficult manufacturing process and high cost.In addition,when narrowband and polarization detection are required simultaneously,the coupling of the two systems is often needed,which makes the whole system even more complex and bulky.The polarization-sensitive narrowband photodetector with simple structure,small size and low cost can integrate the functions of wavelength discrimination and polarization sensing together.However,filterless polarization-sensitive narrowband photodetectors with simple structure and low cost have not been successfully demonstrated due to lack of suitable materials.The anisotropic conductivity of the two-dimensional perovskite and the self-trapped excitons within its band gap are conducive to high-performance narrowband photoresponse and the existence of large optical anisotropy in the in-plane and out-of-plane directions of the crystal enables it to produce a polarization-dependent photoresponse.Based on this,we use two-dimensional perovskite material（C₄H₉NH₃）₂PbI₄ to successfully demonstrate a high-performance polarization-sensitive narrowband photodetector,which integrates narrowband and polarization detection functions together,and makes the detector smaller and lighter.The research content includes the following parts:（1）Preparation and basic characterizations of two-dimensional perovskite material（C₄H₉NH₃）₂PbI₄.First,we successfully synthesized two-dimensional perovskite（BA）₂PbI₄ and（iso-BA）₂PbI₄ crystals by the solution method,which are isomers of each other and have the same molecular formula as（C₄H₉NH₃）₂PbI₄.Optical microscope,scanning electron microscope,atomic force microscopy,X-ray diffraction spectrum,reflectance spectrum and photoluminescence spectrum are acquired to ensure that pure phase crystals are obtained with high crystalline quality,suitable size,good stability.（2）The narrowband photodetector based on two-dimensional perovskite（C₄H₉NH₃）₂PbI₄.First,taking the advantage of self-trapped excitons assisted absorption in the（iso-BA）₂PbI₄ crystal and the anisotropic conductivity to promote narrowband charge collection,a narrowband photodetector with excellent performance has been demonstrated with the ability of wavelength selection.The spectral response peak of the photodetector is 552 nm,the peak response full width at half maximum（FWHM）is only 22 nm,the peak responsivity reaches 0.55 A/W,the peak external quantum efficiency（EQE）is 124%,and the specific detectivity（D*）is as high as3.5×10¹¹ Jones.In addition,in order to realize the integration of narrowband detection,we further used the（BA）₂PbI₄ crystal to fabricate a high-performance narrowband photodetector array,which has a peak response wavelength of 546 nm,the response FWHM of 24 nm,the responsivity of 1.56 A/W,the EQE of 350%,and D*of 10¹¹ Jones.In addition to narrowband detection,the detector array can also have imaging functions,which can couple wavelength selection and imaging functions together.（3）The polarization-sensitive narrowband photodetector based on two-dimensional perovskite material（iso-BA）₂PbI₄.Benefiting from the inherent orthorhombic crystal structure of（iso-BA）₂PbI₄ which leads to the large optical anisotropy between in and out of the crystal plane,we achieved a polarization-sensitive narrowband photodetector,which can not only realize wavelength discrimination but also sense the polarization of the light.When irradiated by a 552 nm light under an oblique incidence of 45°,the detector exhibited the linear dichroism of 1.56,the response FWHM of only 20 nm,the peak EQE of 114%and D*of 4.7×10¹⁰ Jones.