| Radiation detectors are widely applied in medical imaging,industrial nondestructive testing,nuclear energy industry and homeland security.Detecting ionizing radiation at room temperature still faces obstacles,which demands a balance between device performance and manufacturing costs.For instance,the sensitivity of amorphous selenium thin film detectors rapidly decreases in the high-energy region,high-purity germanium detectors requires a operate condition under liquid nitrogen cooling due to their small bandgap(0.72 eV),and CZT crystals are difficult to grow rapidly and in large sizes.In recent years,metal halide perovskites have garnered widespread attention due to their superior properties such as high absorption coefficient,large carrier mobility and lifetime product,tunable bandgap,and low-cost.Over the past few years,various semiconductor radiation detectors based on perovskite have been developed,including X-ray image sensors,y-ray energy spectrometers,thermal neutron and α-particle detectors,etc.These devices have witnessed an incredible evolution on sensitivity,energy resolution,and detection efficiency.In terms of advances in X-ray imaging,many efforts have been devoted in improving the crystalline quality of materials to enhance carrier transport efficiency,which is beneficial for fabricating X-ray detectors with high sensitivity and low detectable limit.Clinical radiological imaging demands that detectors can output high resolution images of the lesion site under a low dose irradiation,which requires detectors that can maintain high sensitivity at low dose rates.The detectable limit of X-ray detectors is related to sensitivity and dark current.However,the limited resistivity of 3D perovskites usually struggles to achieve high sensitivity at a low dark current.Moreover,the poor stability of perovskite is one of the main challenges that limit their practical applications.The irreversible decomposition process of perovskites limits the fidelity of device performance when exposed to high humidity,high temperature,strong light,and rich oxygen.Dimensional engineering is usually used to adjust resistivity and improve device stability.Herein,we exhibit a pseudohalide perovskite Cs2Pb(SCN)2X2(X=Br-,I-)X-ray detector.The original threedimensional octahedral[PbX6]4-skeleton is separated after occupying the axial atoms of the lead halide octahedron with the pseudo-halide SCN-,forming a twodimensional layered[PbX4(SCN)2]4-(X=Br-,I-)structure due to the asymmetry of the electronic structure and geometry of the SCN-.The dark current of the prepared device was suppressed due to the stronger layer structure quantum and dielectric constraint effects.Furthermore,the signal-to-noise ratio and detectable limit of the device can be optimized during the evolution of perovskites from 3D to 2D,highlighting the key role of sensitivity and noise current of devices. |
