High-performance two-dimensional chiral perovskite X-ray detectors based on chirality-induced spin selectivity
Organic-inorganic hybrid metal halide perovskite materials have shown enormous application values in the field of optoelectronics,such as light emitting,solar photovoltaic,laser,quantum communication,and 3D display.This is mainly owing to their unique crystal structures and excellent optoelectronic properties.Based on their tunable chemical composition and crystal structures,the two-dimensional chiral metal halide perovskite with a layered structure can be obtained by introducing chiral organic cations into the achiral inorganic frameworks,leading to the significant optical activities and spin properties of two-dimensional chiral metal halide perovskite in the absence of magnetic,optical,electrical fields,such as circular dichroism(CD),chirality-induced spin selectivity(CISS),etc.Thus,this kind of material is usually used in circularly polarized luminescence and detection,nonlinear optics,as well as spintronics,but its application research in high-energy X-ray detection remains unknown.In this work,we introduce chiral organic molecules(R/S-NEA=(R/S-C12H13N))and achiral organic molecules(rac-NEA)into the achiral inorganic octahedral frameworks(PbI6)to synthesize a two-dimensional chiral perovskite((R/S-NEA)2PbBr4)and an achiral two-dimensional chiral perovskite((rac-NEA)2PbBr4)single crystals,respectively.These crystals possess remarkable white flake-like shapes.Meanwhile,this single crystal can be used to fabricate a structurally simple direct X-ray detector(C/(R/S/rac-NEA)2PbBr4/C).We find that the sensitivity of X-ray detectors based on(S-NEA)2PbBr4 crystal is as high as 2.87 ×104 μC Gyair-1 cm-2,which is much higher than that of two-dimensional achiral metal halide perovskite polycrystalline X-ray detectors.Moreover,both the dark current and dark current drift values of the devices are only 0.15 nA and 7.6 x 10-8 nA cm-1 s-1 V-1,respectively.The product of carrier mobility and lifetime(μτ)can reach 5.85 × 10-4 cm2 V-1.The activation energy for ion migration is 219 meV.In addition,the(R/S-NEA)2PbBr4 X-ray detector exhibits excellent stability under prolonged X-ray irradiation.However,the sensitivity of X-ray detectors based on(rac-NEA)2PbBr4 crystal is merely 7.41 ×103 µC Gyair-1 cm-2,which is distinctly much lower than that of(S-NEA)2PbBr4 crystal X-ray detectors.These experimental results indicate that two-dimensional chiral perovskites crystals(R/S-NEA)2PbBr4 have outstanding electrical transport properties,which makes them have the potential to be applied in the field of high-energy X-ray detection.According to the analysis of optical activity and spintronics properties of two-dimensional chiral perovskites(R/S-NEA)2PbBr4,we conclude that the excited state can be easily polarized in the(R/S-NEA)2PbBr4 crystals through CISS interaction.The spin-polarized excitons in the(R/S-NEA)2PbBr4 X-ray detector are rapidly dissociated into a large number of spin-dependent photo-generated charge carriers under X-ray irradiation,resulting in a reduced recombination probability between spin anti-parallel electrons and holes charge carriers.The spin parallel electrons and holes charge carriers can be effectively extracted by top and bottom electrodes of detector to greatly generate photocurrent,which further improve the performance of(R/S-NEA)2PbBr4 X-ray detector.Oppositely,the achiral(rac-NEA)2PbBr4 X-ray detector without CISS property exhibits lower sensitivity.This deeply demonstrates that the CISS indeed has a significantly enhanced impaction on improvement of X-ray detector's performance.This study provides theoretical guidance and experimental supports for the development of low-cost and high-performance direct perovskite X-ray detectors.
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