Interlayer-Spacing Engineering of Lead-Free Perovskite Single Crystal for High-Performance X-Ray Imaging

Anomalous Photovoltaic Effect in a Chiral Alternating-Cation Intercalation-Type Perovskite for Efficient Self-Driven X-Ray Detection

Organic-inorganic hybrid perovskites (OIHPs) exhibiting intrinsic anomalous photovoltaic (APV) effects have attracted considerable attention due to their exceptional optoelectronic and photovoltaic properties. However, the ionizing radiation-induced APV effect, a promising mechanism for self-powered X-ray detection, remains underexplored in OIHPs. Here, this study reports for the first time the radiation-induced APV in 2D OIHPs for efficient self-driven X-ray detection. Specifically, the 2D chiral alternating cation-intercalated perovskite (R)-PPA(MOPA)PbBr₄ (where PPA = 1-phenylpropylammonium and MOPA = 3-methoxypropylammonium) demonstrates an intrinsic radiation-induced APV of 4 V, which facilitates the separation and transport of X-ray-generated carriers. Remarkably, leveraging this intrinsic APV, highly efficient X-ray detection is achieved with a high sensitivity of 475 µC Gy⁻¹ cm⁻2 at zero bias, surpassing most existing self-powered X-ray detectors. These findings underscore the potential of radiation-responsive APV effects in advanced self-driven X-ray detection and pave the way for future practical applications.

Realization of Tunable X-ray Detection in 2D Chiral-Polar Hybrid Perovskites

Metal halide perovskites have emerged as outstanding X-ray detection absorption candidates, benefiting from their excellent carrier mobility, strong radiation absorption capability, and ease of preparation. However, the realization of highly anisotropic X-ray detection with a tunable performance has rarely been investigated. Two-dimensional (2D) chiral-polar hybrid perovskites with the natural multiple quantum wells (MQWs) structure and the bulk photovoltaic effect (BPVE) present a prospective solution to meet the requirement of highly anisotropic X-ray detection. The pair of 2D chiral-polar perovskites has been synthesized in this work, termed (R-β-MPA)PAPbI4 and (S-β-MPA)PAPbI4 (1R and 1S, MPA = methylphenethylamine and PA = propylamine), aiming to achieve unique anisotropic X-ray detection resulting from the coupling of the distinctive MQWs structure and the BPVE. As expected, photodetectors based on high-quality single crystals of 1R result in a high dichroism ratio (Imax/Imin ≈ 7) for self-powered polarized-light detection. Strikingly, these photodetectors achieve high anisotropic ratios, reaching up to 9 under X-ray irradiation. This work reveals a strong correlation between X-ray detection performance and the coupling of specially oriented crystals with the BPVE, opening new possibilities for the realization of tunable X-ray detection.

High-Performance X-ray Detection Made of Bismuth Perovskite Single Crystal Based on Hydrogen-Bond-Free and Interlayer-Spacing Engineering Strategies

Hybrid organic-inorganic halide perovskites (HPs) show great potential for optoelectronic applications. However, their poor stability against moisture and oxygen significantly limits their practical applications. Developing hybrid perovskites with improved stability is essential yet remains a considerable challenge. Lead-free A3Bi2I9 perovskites have become attractive semiconductor materials for next-generation X-ray sensing because of their elevated bulk resistivity, efficient X-ray absorption, and low ion migration. Nonetheless, the increased spacing between lamellae along the c-axis hinders carrier mobility in the vertical orientation, thereby presenting difficulty in enhancing the detection sensitivity of these materials. In this work, we present two practical approaches that offer innovative solutions to the aforementioned challenges. The first approach, termed the "hydrogen-bond elimination" strategy, focuses on improving the stability of low-dimensional (LD) HPs by preventing the organic components from establishing strong hydrogen bonds with external water molecules. The "interlayer-spacing engineering" approach focuses on improving carrier transport in the vertical direction. As a proof-of-concept application, a novel large sterically hindered A-site cation, phenyltrimethylammonium (C9H14N+), without hydrogen bonding, is introduced to reduce the interlayer spacing through inducing greater structural distortions. The large (C9H14N)3Bi2I9 single crystals (SCs) grown exhibit reduced interlamellar spacing, resulting in a mobility-lifetime (μτ) product of 8.53 × 10-3 cm2 V-1. This value surpasses that of the top-performing MA3Bi2I9 SC by a factor of 3, which has a μτ product of 2.87 × 10-3 cm2 V-1. As a result, X-ray detection devices using (C9H14N)3Bi2I9 SCs demonstrate a remarkable sensitivity of 1373.27 μC Gyair-1 cm-2 under a minimal field strength (5.71 V mm-1) and an exceptionally low detection limit (LoD) of 4.69 nGy s-1. These findings pave the way for creating efficient X-ray detection devices using A3Bi2I9-type perovskite or perovskite-like materials, offering an alternative that avoids the use of toxic elements.

Multiple Interactions in Polar Lead-Free Perovskites toward Highly Stable X-Ray Detection

Lead-free halide perovskites have emerged as a promising class of high-performance "green" X-ray detecting semiconductors due to their nontoxicity and strong X-ray absorption. However, ion migration caused by high operating electric field remains a bottleneck limiting the long-term stability of perovskite X-ray detectors. Herein, by introducing multiple halogen interactions in lead-free perovskites, stable X-ray detection is successfully realized. Specifically, 0D polar bismuth halide perovskites (R/S-BPEA)4Bi2I10 (1R/1S, R/S-BPEA = R/S-1-(4-bromophenyl)ethylammonium) are designed by introducing Br-substituted chiral organic cation BPEA, which exists with the molecular electrostatic forces between the Br atom and neighboring benzene ring and halogen interaction of Br···I. Notably, their introduction improves the activation energy of ion migration, which makes the dark current drift of the X-ray detector as low as 3.25 × 10-8 nA cm-1 s-1 V-1 at 2500 V cm-1. Furthermore, the excellent operational stability under prolonged X-ray irradiation and unchanged device sensitivity after 90 days of exposure to air, further demonstrates the improved stability of perovskites. Meanwhile, the chiral-polar characteristic of the 1R/1S gives them potential for self-powered detection, with a low detection limit of 183 nGy s-1 at zero bias for single-crystal devices. This study opens new avenues for the future development of "green", highly stable, self-powered radiation detectors.

Stable and Ultrasensitive X-Ray Detectors Based on Oriented Single-Crystal Perovskite Rods

Metal-halide perovskite single crystals (SCs) are promising candidates for next-generation X-ray detectors. X-ray detectors fabricated using perovskite FAPbI3 SCs exhibit high detection sensitivity. However, two pressing issues still need to be addressed for practical applications: the orientation-controlled growth and environmentally friendly acquisition of high-quality FAPbI3 SCs. In this study, large high-quality perovskite FAPbI3 SC rods (SCRs) with unique orientation are grown using a biomass-derived green solvent. Owing to the high carrier mobility and large bulk resistivity of the oriented FAPbI3 SCRs, the SC detectors realize a record high X-ray detection sensitivity (2.16 × 105 µC Gy-1 cm-2) and high sensitivity to dark current density ratio (1.93 × 109 Gy-1 s). Furthermore, the detectors exhibit both ultralow dark and X-ray current drifts, as well as a detection limit of 2 nGy s-1. These characteristics enable the detectors to achieve high-resolution X-ray imaging, even at dose rates as low as 12 nGy s-1. This study not only contributes a new technical solution for low-dose X-ray detection, but also establishes a new approach for the low-cost and environmentally friendly production of core materials for X-ray detectors.

Green Fabrication of Sulfonium-Containing Bismuth Materials for High-Sensitivity X-Ray Detection

Organic-inorganic hybrid materials based on lead and bismuth have recently been proposed as novel X- and gamma-ray detectors for medical imaging, non-destructive testing, and security, due to their high atomic numbers and facile preparation compared to traditional materials like amorphous selenium and Cd(Zn)Te. However, challenges related to device operation, excessively high dark currents, and long-term stability have delayed commercialization. Here, two novel semiconductors incorporating stable sulfonium cations are presented, [(CH3CH2)3S]6Bi8I30 and [(CH3CH2)3S]AgBiI5, synthesized via solvent-free ball milling and fabricated into dense polycrystalline pellets using cold isostatic compression, two techniques that can easily be upscaled, for X-ray detection application. The fabricated detectors exhibit exceptional sensitivities (14 100-15 190 µC Gyair -1 cm-2) and low detection limits (90 nGyair s-1 for [(CH3CH2)3S]6Bi8I30 and 78 nGyair s-1 for [(CH3CH2)3S]AgBiI5), far surpassing current commercial detectors. Notably, they maintain performance after 9 months of ambient storage. The findings highlight [(CH3CH2)3S]6Bi8I30 and [(CH3CH2)3S]AgBiI5 as scalable, cost-effective and highly stable alternatives to traditional semiconductor materials, offering great potential as X-ray detectors in medical and security applications.

Multifunctional 0D Manganese-Based Organic-Inorganic Hybrid Halide for Ultraviolets and X-Ray Detection

Multifunctional photodetectors have driven the development of traditional optical communication technologies and emerging artificial intelligence fields. While three-dimensional (3D) organic lead trihalides have recently demonstrated potential as versatile photodetectors, the device performance is constrained by ion mobility limitations. In contrast, low-dimensional metal halide perovskites (MHPVKs) exhibit enhanced intrinsic stability, suppressed ion migration, and exceptional photoelectric properties. Inspired by these advantages, a zero-dimensional (0D) manganese (Mn)-based organic-inorganic hybrid halide (MA2MnBr4) and fabricated high-quality films at room temperature via a facile melt-growth method is presented. Subsequently, Ultraviolet (UV) and X-ray detectors based on MA2MnBr4 films are fabricated, and their device performance is systematically characterized. The UV photodetector based on an MA2MnBr4 film showed a response rate of 11 mA W-1 and a detection rate of 1.4 × 1012 Jones. Meanwhile, the MA2MnBr4-based X-ray detector has a high sensitivity of 1959.9 µC Gyair -1 cm-2 and an exceptionally low detection dose rate of 73.1 nGyair s-1, both of which are required for medical diagnosis. This study not only advances the understanding of Mn-based material but also highlights their promise for high-performance UV and X-ray detection.

Unprecedented Ultraviolet Circularly Polarized Light-Dependent Anomalous Photovoltaics in Chiral Hybrid Perovskites

Circularly Polarized Light (CPL)-dependent anomalous photovoltaic effect (APVE), characterized by light helicity-manipulated steady photocurrent and above-bandgap photovoltage, has demonstrated significant potential in the fields of photoelectronic and photovoltaics. However, exploiting CPL-dependent APVE in chiral hybrid perovskites, a promising family with intrinsic chiroptical activity and non-centrosymmetric structure, remains challenging. Here, leveraging the flexible structural design of chiral alternating cations intercalation-type perovskites, CPL-dependent APV, for the first time, is achieved in chiral perovskites. Specifically, by introducing lone pair electrons into the organic layers to greatly amplify the polarization, [(R)-PPA](MOPA)PbBr4 (2-R) (PPA = 1-phenylpropylammonium, MOPA = 3-methoxypropylammonium) exhibit intrinsic APVE with an above-bandgap photovoltage of 6.50 V (Eg = 3.01 eV) under ultraviolet (UV) light illumination. Strikingly, profiting from the natural chiral optical activity of chiral perovskites, unprecedented UV CPL-dependent APV is realized in 2-R, driving the high distinguishability between right-hand and left-hand CPLs with a large anisotropy factor (gIph) of 0.33. This study pioneers the realization of CPL-dependent APV within chiral perovskite, promising significant advancements in optoelectronic device technologies.

Novel Self-Powered Sensitive X-Ray Detection Crystal Bi2Mo0.36W1.64O9 with Effective Functional Motif Coupling in a Quasi-2D Perovskite Structure

The demand for medical imaging with reduced patient dosage and higher resolution is growing, driving the need for advanced X-ray detection technologies. This paper proposes a design paradigm for X-ray detection semiconductors by coupling constituent motifs through crystal structure engineering. The study introduces a strongly anisotropic Aurivillius-type quasi-2D perovskite structure, combining [Bi2O2]2+ groups with stereochemically active lone pair electrons (SCALPEs) and [W/Mo2O7]2- anionic groups, enabling enhanced X-ray Compton scattering and self-powered capabilities through local electric field ordering. This results in the first self-powered Bi-based tungstate Bi2Mo0.36W1.64O9 (BMWO) X-ray detector, achieving a record self-powered sensitivity of 381 µC Gy-1 cm-2. Additionally, the study demonstrates the imaging capability of a Bi-based perovskite X-ray detector operating in self-driven mode. The work highlights BMWO as a promising candidate for stable direct detection imaging and validates the material design strategy that leverages the large anisotropy of quasi-2D structures for sensitive and self-powered detection.

Large Scale Lead-Free Perovskite Polycrystalline Wafer Achieved by Hot-Pressed Strategy for High-Performance X-Ray Detection

Halide perovskites (HPs) have demonstrated excellent direct X-ray detection performance. Lead-free perovskite polycrystalline wafers have outstanding advantages in large-area X-ray imaging applications due to their area-scalability, thickness-controllability, large bulk resistivity, and ease of integration with large-area thin film transistor arrays. However, currently lead-free perovskite polycrystalline wafers possess low sensitivity, typically less than 1000 µC Gy-1 cm-2, which severely limits their X-ray detection applications. Here, high-quality and large scale polycrystalline wafers of AG3Bi2I9 (AG: aminoguanidinium) with short intercluster distances are successfully prepared using a hot-pressing method. The wafers possess high mobility-lifetime product of 5.66 × 10-3 cm2 V-1 and therefore achieve high X-ray sensitivity of 2675 µC Gy-1 cm-2, which can be comparable to those of the high-quality single crystal counterpart reported by the previous research (7.94 × 10-3 cm2 V-1 and 5791 µC Gy-1 cm-2), and represent the best results of the currently lead-free HP polycrystalline wafers. Besides, the wafers exhibit the X-ray detection limit as low as 11.8 nGy s-1, excellent long-term working stability, and high spatial resolution of 5.9 lp mm-1 in imaging. The findings demonstrate that AG3Bi2I9 polycrystalline wafers are feasible for high-performance X-ray detection and imaging system.

Wide-Bandgap Lead Halide Perovskites for Next-Generation Optoelectronics: Current Status and Future Prospects

Over the past decade, lead halide perovskites (LHPs), an emerging class of organic-inorganic ionic-type semiconductors, have drawn worldwide attention, which injects vitality into next-generation optoelectronics. Facilely tunable bandgap is one of the fascinating features of LHPs, enabling them to be widely used in various nano/microscale applications. Notably, wide-bandgap (WBG) LHPs have been considered as promising alternatives to traditional WBG semiconductors owing to the merits of low-cost, solution processability, superior optoelectronic characteristics, and flexibility, which could improve the cost-effectiveness and expand the application scenarios of traditional WBG devices. Herein, we provide a comprehensive review on the up-to-date research progress of WBG LHPs and their optoelectronics in terms of material fundamentals, optoelectronic devices, and their practical applications. First, the features and shortcomings of WBG LHPs are introduced to objectively display their natural features. Then we separately depict three typical optoelectronic devices based on WBG LHPs, including solar cells, light emitting diodes, and photodetectors. Sequentially, the inspiring applications of these optoelectronic devices in integrated functional systems are elaborately demonstrated. At last, the remaining challenges and future promise of WBG LHPs in optoelectronic applications are discussed. This review highlights the significance of WGB LHPs for promoting the development of the next-generation optoelectronics industry.

Structural Reconfiguration via Alternating Cation Intercalation of Chiral Hybrid Perovskites for Efficient Self-Driven X-ray Detection

2D hybrid perovskites (HPs) have great potential for high-performance X-ray detection due to their strong radiation absorption and flexible structure. However, there remains a need to explore avenues for enhancing their detection capabilities. Optimizing the detection performance through modification of their structural properties presents a promising strategy. Herein, we explore the impact of modifying the organic spacer layer in two distinct 2D layered HPs, namely, Ruddlesden-Popper (R-MPA)2PbBr4 (R-1, R-MPA = methylphenethylammonium) and (R-MPA)EAPbBr4 (EA = ethylammonium) (R-2) with alternating cation intercalation (ACI), on their X-ray detection performance. The insertion of EA into R-2 results in a flatter inorganic skeleton, narrower spacing, and higher density compared to R-1. This structural modification effectively optimizes carrier transport and X-ray absorption in R-2, enhancing the X-ray detection performance. Notably, R-2 exhibits a polar structure with intrinsic spontaneous polarization, contributing to a bulk photovoltaic of 0.4 V. This feature enables R-2 single-crystal detectors to achieve self-driven X-ray detection with a low detection limit of 82.5 nGy s-1 under a 0 V bias. This work highlights the efficacy of the ACI strategy in structural modification and its significant effect on X-ray detection properties, providing insights for the design and optimization of new materials.

Interface Engineering of Substrate-Integrated Single-Crystal Perovskite Wafers for Sensitive X-Ray Detection

Metal halide perovskite single crystals are emerging candidates for X-ray detection, however, it is challenging for growth of thickness-controlled single-crystal wafer on commercial backplanes, limiting their practical imaging application. Herein, integration of micrometer-thick methylammonium lead triiodide (MAPbI3) single-crystal wafer on indium tin oxide (ITO) substrates by methylamine (MA)-induced interface recrystallization is reported. Through selection of hole transport material with rich functional group, intimate interface contact with low trap density can be achieved, leading to superior carrier transport properties and homogeneous photoresponse. The as-fabricated X-ray detectors exhibit high sensitivity of 1.4 × 104 µC Gyair -1 cm-2 and low detection limit of 177 nGyair s-1, which are comparable to previous reports based on free-standing MAPbI3 bulk crystals. This work provides a feasible strategy for constructing substrate-integrated single-crystal perovskite wafers with controlled thickness, which may promote practical imaging application of perovskite X-ray detectors.

Pyro-phototronic Effect Enhanced Self-Powered Photoresponse in Lead-Free Hybrid Perovskite

Pyro-phototronic effect (PPE) can significantly boost the performance of hybrid perovskite (HPs) photodetectors due to the effective modulation of photogenerated charge carrier separations, transportation, and extraction. However, there are few reports on the application of PPE in lead-free HPs. Herein, a polar lead-free HP (1,3-BMACH)BiBr5 [1,3-BMACH = 1,3-bis(aminomethyl)cyclohexane] is synthesized and realized broadband self-powered photoresponse from X-rays to near-infrared (NIR) through the PPE. Particularly, this light-induced PPE in lead-free HPs breaks the limitation of the optical band gap, making them suitable for broadband self-powered photodetection. Under 405 nm illumination, compared with a purely photovoltaic system, Iphoto+pyro is boosted by 3100%, and R and D* are both enhanced by 260% after coupled PPE. It is particularly interesting that an obvious X-ray-induced PPE phenomenon is also observed, which endows (1,3-BMACH)BiBr5 with a high sensitivity of 154 μC Gy-1 cm-2 and a low detection limit of 307 nGy s-1 under the self-powered mode. The implementation of light-induced PPE from X-rays to NIR in lead-free HPs provides a new approach for constructing environmentally friendly, broadband, and self-powered optoelectronic devices in the future.

Rational Design of A-Site Cation for High Performance Lead-Free Perovskite X-Ray Detectors

Design of hypotoxic lead-free perovskites, e.g. Bismuth(Bi)-based perovskites, is much beneficial for commercialization of perovskite X-ray detectors due to their strong radiation absorption. Nevertheless, the design principles governing the selection of A-site cations for achieving high-performance X-ray detectors remain elusive. Here, seven molecules (methylamine MA, amine NH3, dimethylbiguanide DGA, phenylethylamine PEA, 4-fluorophenethylamine p-FPEA, 1,3-propanediamine PDA, and 1,4-butanediamine BDA) and calculated their dipole moments and interaction strength with metal halide (BiI3) are selected. The first-principles calculations and related spectroscopy measurements confirm that organic molecules (DGA) with large dipole moments can have strong interactions with perovskite octahedron and improve the carrier transport between the organic and inorganic clusters. Consequently, zero-dimensional single crystal (SC) (DGA)BiI5∙H2O is synthesized. The (DGA)BiI5∙H2O SCs demonstrate an exceptional carrier mobility-lifetime product of 6.55 × 10-3 cm2 V-1, resulting in the high sensitivity of 5879.4 µCGyair -1cm-2, featuring a low detection limit (4.7 nGyair s-1) and remarkable X-ray irradiation stability even after 100 days of aging at a high electric field (100 V mm-1). Furthermore, the (DGA)BiI5∙H2O SCs for imaging, achieving a notable spatial resolution of 5.5 lp mm-1 are applied. This investigation establishes a pathway for systematically screening A-site cations to design low-dimensional SCs for high-performance X-ray detection.

High Sensitivity X-Ray Detectors with Low Degradation Based on Deuterated Halide Perovskite Single Crystals

Methylammonium lead single crystal (MAPbI3 SC) possesses superior optoelectronic properties and low manufacturing cost, making it an ideal candidate for X-ray detection. However, the ionic migration of the perovskites usually leads to instability, dark current drift, and hysteresis of the detector, limiting their applications in well-established technologies. Here, a series of X-ray detectors of MAPbI3 SCs are reported with different degrees of deuteration (DxMAPbI3, x = 0, 0.15, 0.75, 0.99). By controlling the content of deuterium (D) in organic cations, the sensitivity, detection limits, ion migration, and resistivity of the detector can be controlled, thereby improving its performance. Due to stronger hydrogen bonds (N─D···I), the ion activation energy significantly increases to 886 meV. Consequently, the D0.99MAPbI3 SC detector shows more than five-fold enhancement, achieving a record-high mobility-lifetime (µτ) product of 5.39 × 10-2 cm2 V-1, with an ultrahigh sensitivity of 2.18 × 106 µC Gy-1 cm-2 under 120 keV hard X-ray and a low detection limit of 4.8 nGyair s-1, as well as long-term stability. The study provides a straightforward strategy for constructing ultrasensitive X-ray detection and imaging systems based on perovskite SCs.

Oriented Alignment of CsPbBr3 Single-Crystal Arrays for Flexible X-ray Imaging

The utilization of perovskite materials in flexible optoelectronics is experiencing distinct diversification including X-ray detection applications. Here, we report the oriented alignment of cesium lead bromide (CsPbBr3) single-crystal arrays on flexible polydimethylsiloxane (PDMS) substrates. By precisely confining the crystallization process within spatially delimited precursor droplets, we achieve a well-oriented crystal alignment through the spontaneous rotation of the CsPbBr3 microcuboids. This approach allows for precise control over the microcuboid morphologies by varying the growth temperature. We design flexible X-ray detector arrays by seamlessly integrating CsPbBr3 microcuboids with electrode arrays. The flexible X-ray detector can output a high sensitivity of 1.97 × 105 μC·Gyair-1·cm-2 and a low detection limit of 89 nGyair·s-1 after the surface passivation process. The excellent mechanical properties, outstanding X-ray detection capabilities, and high pixel uniformity are also demonstrated in conformal X-ray imaging of curved surfaces.

Pyro-Phototronic Effect Induced Circularly Polarized Light Detection with a Broadband Response

Photopyroelectric-based circularly polarized light (CPL) detection, coupling the pyro-phototronic effect and chiroptical phenomena, has provided a promising platform for high-performance CPL detectors. However, as a novel detection strategy, photopyroelectric-based CPL detection is currently restricted by the short-wave optical response, underscoring the urgent need to extend its response range. Herein, visible-to-near-infrared CPL detection induced by the pyro-phototronic effect is first realized in chiral-polar perovskites. Specifically, chiral-polar multilayered perovskites (S-BPEA)2FAPb2I7 (1-S, S-BPEA = (S)-1-4-Bromophenylethylammonium, FA = formamidinium) with spontaneous polarization shows intrinsic pyroelectric and photopyroelectric performance. Strikingly, combining its merits of the pyro-phototronic effect and intrinsic wide-spectrum spin-selective effect, chiral multilayered 1-S presents efficient photopyroelectric-based broadband CPL detection performance spanning 405-785 nm. This research first realizes photopyroelectric-based infrared CPL detection and also sheds light on developing high-performance broadband CPL detectors based on the pyro-phototronic effect in the fields of optics, optoelectronics, and spintronics.

Tailoring Multi-Phenyl Ring Cation for Stable Scalable Hybrid Bismuth Iodide Amorphous Film: Enabling Record Sensitivity and High-Performance X-Ray Array Imaging

The 329-type bismuth (Bi)-based metal halide (MH) polycrystalline films have potential to be applied in the new generation of X-ray imaging technology owing to high X-ray absorption coefficients and excellent detection properties. However, the mutually independent [Bi2X9]3- units and numerous grain boundaries in the material lead to low carrier transport and collection capabilities, severe ion migration, large dark currents, and poor response uniformity. Here, a new multi-phenyl ring methyltriphenylphosphonium (MTP) is designed to optimize the energy band structure. For the first time, the coupling between the A-site cation and [Bi2X9]3- is realized, making it the main contributor to the conduction band minimum (CBM), getting rid of dilemma that carrier transport is confined to [Bi2X9]3-. Further, the preparation of MTP3Bi2I9 amorphous large-area wafer is achieved by melt-quenching; the steric hindrance effect improves stability, increases ion migration energy, and promotes response uniformity (14%). Moreover, the amorphous structure takes advantage of A-site cation participation in the conductivity, achieving a record sensitivity (7601 µC Gy-1 cm-2) and low dark current (≈0.11 nA) in the field of amorphous X-ray detection, and features low-temperature large-area preparation. Ultimately, designing amorphous array imaging devices that exhibit excellent response uniformity and potential imaging capabilities is succeeded here.

Lead-Free Bismuth-Based Perovskite X-ray Detector with High Sensitivity and Low Detection Limit

Bismuth-based halide perovskites have shown great potential for direct X-ray detection, attributable to their nontoxicity and advantages in detection sensitivity and spatial resolution. However, the practical application of such materials still faces the critical challenge of combining both high sensitivity and low detection limits. Here, we report a new type of zero-dimensional (0D) perovskite (HIS)BiI5 (1, where HIS2+ = histamine) with high sensitivity and a low detection limit. Structurally, the strong N-H···I hydrogen bonds between HIS2+ cations and inorganic frameworks enhance the rigidity of the structure and diminish the intermolecular distance between adjacent inorganic [Bi2I10]4- dimers. By virtue of such structural merits, single crystal 1 exhibits excellent physical properties perpendicular to both the (001) and (010) faces. Perpendicular to the (010) face, 1 exhibited a high electrical resistivity (2.31 × 1011 Ω cm) and a large carrier mobility-lifetime product (μτ) (2.81 × 10-4 cm2 V-1) under X-ray illumination. Benefiting from these superior physical properties, it demonstrates an excellent X-ray detection capability with a sensitivity of approximately 103 μC Gyair-1 cm-2 and a detection limit of 36 nGyair s-1 in both directions perpendicular to the (001) and (010) crystal faces. These results provide a promising candidate material for the development of new, lead-free, high-performance X-ray detectors.

Interlamellar-Spacing Engineering of Stable and Toxicity-Reduced 2D Perovskite Single Crystal for High-Resolution X-ray Imaging

Two-dimensional (2D) lead halide perovskites are excellent candidates for X-ray detection due to their high resistivity, high ion migration barrier, and large X-ray absorption coefficients. However, the high toxicity and long interlamellar distance of the 2D perovskites limit their wide application in high sensitivity X-ray detection. Herein, we demonstrate stable and toxicity-reduced 2D perovskite single crystals (SCs) realized by interlamellar-spacing engineering via a distortion self-balancing strategy. The engineered low-toxicity 2D SC detectors achieve high stability, large mobility-lifetime product, and therefore high-performance X-ray detection. Specifically, the detectors exhibit a record high sensitivity of 13488 μC Gy1- cm-2, a low detection limit of 8.23 nGy s-1, as well as a high spatial resolution of 8.56 lp mm-1 in X-ray imaging, all of which are far better than those of the high-toxicity 2D lead-based perovskite detectors. These advances provide a new technical solution for the low-cost fabrication of low-toxicity, scalable X-ray detectors.

Enhancement of Photodetector Characteristics by Zn-Porphyrin-Passivated MAPbBr3 Single Crystals

Perovskite single crystals have garnered significant interest in photodetector applications due to their exceptional optoelectronic properties. The outstanding crystalline quality of these materials further enhances their potential for efficient charge transport, making them promising candidates for next-generation photodetector devices. This article reports the synthesis of methyl ammonium lead bromide (MAPbBr3) perovskite single crystal (SC) via the inverse-temperature crystallization method. To further improve the performance of the photodetector, Zn-porphyrin (Zn-PP) was used as a passivating agent during the growth of SC. The optical characterization confirmed the enhancement of optical properties with Zn-PP passivation. On single-crystal surfaces, integrated photodetectors are fabricated, and their photodetection performances are evaluated. The results show that the single-crystalline photodetector passivated with 0.05% Zn-PP enhanced photodetection properties and rapid response speed. The photoelectric performance of the device, including its responsivity (R), external quantum efficiency (EQE), detective nature (D), and noise-equivalent power (NEP), showed an enhancement of the un-passivated devices. This development introduces a new potential to employ high-quality perovskite single-crystal-based devices for more advanced optoelectronics.

Lead-Free Perovskite Single Crystal Linear Array Detector for High-Resolution X-Ray Imaging

0D Bi-based 329-type halide perovskite is demonstrated as a promising semiconductor for X-ray detection due to its strong X-ray absorption, superior stability, availability of large single crystals (SCs) and solution processibility at low temperature. However, its low mobility-lifetime product (µτ) limits its further improvement in detection sensitivity. Based on the first-principles calculations, this work designs a new 2D Bi-based 329-type halide perovskite using a mixed-halide-induced structural dimension regulation strategy. By using a continuous supply of a precursor solution, this work successfully grows inch-sized high-quality SCs. These SCs exhibit large µτ product, high resistivity, and low ion migration. The detectors fabricated using the SCs show X-ray detection sensitivity as high as 24,509 µC Gyair -1 cm-2, short response time of 315 µs, low detection limit of 4.3 nGy s-1, and superior stability. These properties are the best among all lead-free perovskite detectors and are comparable to those of the best lead-based perovskite detectors. The linear array detector assembled on the SCs for the first time also shows a high spatial resolution of 10.6 lp mm-1 during X-ray imaging. The high performance combined with superior stability of these new 329-type lead-free halide perovskite SCs is expected to promote a new generation of X-ray detection technologies.

Aminoazanium of A-site Cations in Metal-Free Halide Perovskite Single Crystals to Reduce Thermal Expansion for Efficient X-ray Detection

Metal-free perovskites (MFPs) have recently become a newcomer in X-ray detection due to their flexibility and low toxicity characteristics. However, their photoelectronic properties and stability should be further improved mainly through materials design. Here, the aminoazanium of DABCO2+ was developed for the preparation of NDABCO-NH4Br3 (NDABCO = N-amino-N'-diazabicyclo[2.2.2]octonium) single crystals (SCs), and its physical properties, intermolecular interactions, and device performance were systematically explored. Notably, NDABCO-NH4Br3 can achieve improved stability by enlarging defect formation energy and inducing abundant intermolecular forces. Moreover, the slight lattice distortion could ensure the weakening electron-phonon coupling for improving carrier transport. In particular, the slight lattice distortion after the long-chain NDABCO2+ introduction could retard thermal expansion for the preparation of high-quality crystals. Finally, the corresponding X-ray detector delivered a moderate sensitivity of 623.3 μC Gyair-1 cm-2. This work provides a novel strategy through rationally designed organic cations to balance the material stability and device performance.

Passivation of Organic-Inorganic Hybrid Perovskite with Poly(lactic Acid) to Achieve Stable Red-Light Flexible Films

Low-dimensional organic-inorganic hybrid perovskites (OIHPs) have shown significant potential in the optoelectronic field due to their adjustable structure and properties. However, the poor air stability and flexibility of the OIHP crystals limit their further development. Herein, three OIHP crystals have been synthesized using cadmium chloride and the isomer of phenylenediamine as raw materials. Mn2+ doping turns on the red-light emission of Cd-based OIHPs at around 625 nm. Interestingly, the organic ligands with different steric hindrance can induce a transition of the OIHP structure from two dimensions (2D) to one dimension (1D), thereby regulating the quantum yield of red luminescence in the range of 38.4% to nearly 100%. It is found that the surface-exposed amino groups are easy to oxidize, resulting in the instability of these OIHP crystals. Therefore, poly(lactic acid) (PLA) is selected to passivate OIHPs through hydrogen bonding between C═O of PLA and -NH2 on the surface of OIHPs. As a result, the production of OIHP-based flexible films with highly efficient and stable red emission can be obtained after being encapsulated by PLA. They demonstrate enormous application potential in flexible X-ray imaging. This study not only realizes stable perovskite films but also provides an effective design idea for red flexible scintillators.

Three-Dimensional Polar Perovskites for Highly Sensitive Self-Driven X-Ray Detection

Three-dimensional (3D) organic-inorganic hybrid perovskites (OIHPs) have achieved tremendous success in direct X-ray detection due to their high absorption coefficient and excellent carrier transport. However, owing to the centrosymmetry of classic 3D structures, these reported X-ray detectors mostly require external electrical fields to run, resulting in bulky overall circuitry, high energy consumption, and operational instability. Herein, we first report the unprecedented radiation photovoltage in 3D OIHP for efficient self-driven X-ray detection. Specifically, the 3D polar OIHP MhyPbBr3 (1, Mhy=methylhydrazine) shows an intrinsic radiation photovoltage (0.47 V) and large mobility-lifetime product (1.1×10-3  cm2  V-1 ) under X-ray irradiation. Strikingly, these excellent physical characteristics endow 1 with sensitive self-driven X-ray detection performance, showing a considerable sensitivity of 220 μC Gy-1  cm-2 , which surpasses those of most self-driven X-ray detectors. This work first explores highly sensitive self-driven X-ray detection in 3D polar OIHPs, shedding light on future practical applications.

Stereo-Hindrance Engineering of A Cation toward <110>-Oriented 2D Perovskite with Minimized Tilting and High-Performance X-Ray Detection

2D <100>-oriented Dion-Jacobson or Ruddlesden-Popper perovskites are widely recognized as promising candidates for optoelectronic applications. However, the large interlayer spacing significantly hinders the carrier transport. <110>-oriented 2D perovskites naturally exhibit reduced interlayer spacings, but the tilting of metal halide octahedra is typically serious and leads to poor charge transport. Herein, a <110>-oriented 2D perovskite EPZPbBr4 (EPZ = 1-ethylpiperazine) with minimized tilting is designed through A-site stereo-hindrance engineering. The piperazine functional group enters the space enclosed by the three [PbBr6 ]4- octahedra, pushing Pb─Br─Pb closer to a straight line (maximum Pb─Br─Pb angle ≈180°), suppressing the tilting as well as electron-phonon coupling. Meanwhile, the ethyl group is located between layers and contributes an extremely reduced effective interlayer distance (2.22 Å), further facilitating the carrier transport. As a result, EPZPbBr4 simultaneously demonstrates high µτ product (1.8 × 10-3 cm2 V-1 ) and large resistivity (2.17 × 1010 Ω cm). The assembled X-ray detector achieves low dark current of 1.02 × 10-10 A cm-2 and high sensitivity of 1240 µC Gy-1 cm-2 under the same bias voltage. The realized specific detectivity (ratio of sensitivity to noise current density, 1.23 × 108 µC Gy-1 cm-1 A-1/2 ) is the highest among all reported perovskite X-ray detectors.

Perovskite materials in X-ray detection and imaging: recent progress, challenges, and future prospects

Perovskite materials have attracted significant attention as innovative and efficient X-ray detectors owing to their unique properties compared to traditional X-ray detectors. Herein, chronologically, we present an in-depth analysis of X-ray detection technologies employing organic-inorganic hybrids (OIHs), all-inorganic and lead-free perovskite material-based single crystals (SCs), thin/thick films and wafers. Particularly, this review systematically scrutinizes the advancement of the diverse synthesis methods, structural modifications, and device architectures exploited to enhance the radiation sensing performance. In addition, a critical analysis of the crucial factors affecting the performance of the devices is also provided. Our findings revealed that the improvement from single crystallization techniques dominated the film and wafer growth techniques. The probable reason for this is that SC-based devices display a lower trap density, higher resistivity, large carrier mobility and lifetime compared to film- and wafer-based devices. Ultimately, devices with SCs showed outstanding sensitivity and the lowest detectable dose rate (LDDR). These results are superior to some traditional X-ray detectors such as amorphous selenium and CZT. In addition, the limited performance of film-based devices is attributed to the defect formation in the bulk film, surfaces, and grain boundaries. However, wafer-based devices showed the worst performance because of the formation of voids, which impede the movement of charge carriers. We also observed that by performing structural modification, various research groups achieved high-performance devices together with stability. Finally, by fusing the findings from diverse research works, we provide a valuable resource for researchers in the field of X-ray detection, imaging and materials science. Ultimately, this review will serve as a roadmap for directing the difficulties associated with perovskite materials in X-ray detection and imaging, proposing insights into the recent status, challenges, and promising directions for future research.

Molecular Design of Layered Hybrid Silver Bismuth Bromine Single Crystal for Ultra-Stable X-Ray Detection With Record Sensitivity

Nowadays, weak interlayer coupling and unclear mechanism in layered hybrid silver bismuth bromine (LH-AgBiBr) are the main reasons for limiting its further enhanced X-ray detection sensitivity and stability. Herein, the design rules for LH-AgBiBr and its influence on X-ray detection performance are reported for the first time. Although shortening amine size can enhance interlayer coupling, its detection performance is severely hampered by its easier defect formation caused by enlarged micro strain. In contrast, an appropriate divalent amine design endows the material with improved interlayer coupling and released micro strain, which benefits crystal stability and mechanical hardness. Another contribution is to increase material density and dielectric constant; thus, enhancing X-ray absorption and carrier transport. Consequently, the optimized parallel device based on BDA2 AgBiBr8 achieves a record sensitivity of 2638 µC Gyair -1 cm-2 and an ultra-low detection limit of 7.4 nGyair s-1 , outperforming other reported LH-AgBiBr X-ray detectors. Moreover, the unencapsulated device displays remarkable anti-moisture, anti-thermal (>150 °C), and anti-radiation (>1000 Gyair ) endurance. Eventually, high-resolution hard X-ray imaging is demonstrated by linear detector arrays under a benign dose rate (1.63 µGyair s-1 ) and low external bias (5 V). Hence, these findings provide guidelines for future materials design and device optimization.

Heterointerface Design of Perovskite Single Crystals for High-Performance X-Ray Imaging

Metal halide perovskite single crystals (MHP-SCs) are known for their facile fabrication into large sizes using inexpensive solution methods. Owing to their combination of large mobility-lifetime products and strong X-ray absorption, they are considered promising materials for efficient X-ray detection. However, they suffer from large dark currents and severe ion migration, which limit their sensitivity and stability in critical X-ray detection applications. Herein, a heterointerface design is proposed to reduce both the dark current and ion migration by forming a heterojunction. In addition, the carrier transport performance is significantly improved using heterointerface engineering by designing a gradient band structure in the SCs. The SC heterojunction detectors exhibit a high sensitivity of 3.98 × 105 µC Gyair -1 cm-2 with a low detection limit of 12.2 nGyair s-1 and a high spatial resolution of 10.2 lp mm-1 during imaging. These values are among the highest reported for state-of-the-art MHP X-ray detectors. Moreover, the detectors show excellent stability under continuous X-ray irradiation and maintainclear X-ray imaging after 240 d. This study provides novel insights into the design and fabrication of X-ray detectors with high detection efficiency and stability, which are beneficial for developing inexpensive, high-resolution X-ray imaging equipment.

Tellurium-Doped 0D Organic-Inorganic Hybrid Lead-Free Perovskite for X-ray Imaging

The application of X-ray imaging in military, industrial flaw detection, and medical examination is inseparable from the wide application of scintillator materials. In order to substitute for lead, lower costs, and reduce self-absorption, organic-inorganic hybrid lead-free perovskite scintillators are emerging as a new option. In this work, novel (TEA)2Zr1-xTexCl6 perovskite microcrystals (MCs) were successfully synthesized by a hydrothermal method, with Te4+ doping, which leads to yellow triplet-state self-trapped excitons emission. The emission peak of (TEA)2Zr1-xTexCl6 located at 605 nm under X-ray excitation, which was applied to X-ray imaging, shows a clear wiring structure inside the USB connector. The detection limit (DL) of 820 nGyair/s for (TEA)2Zr0.9Te0.1Cl6 is well below the dose rate corresponding to a standard medical X-ray diagnosis is 5.5 μGyair/s. This work opens up a new path for organic-inorganic hybrid lead-free scintillators.

Metal-Free Hydrazinium Halide Perovskitoid Single Crystals for X-ray Detection

Metal-free perovskitoids (MFPs) with N2H5+ as B-site component possess higher crystal density and hydrogen bonding networks and have been recently expanded into X-ray detection. However, research on this material is in its infancy and lacks an understanding of the function of halide components on physical properties and device performance. Here, N2H5-based MFP single crystals (SCs) with different halides are fabricated, and the influence of halides on the crystal structure, band nature, charge transport characteristics, and final device performance is actively explored. Based on theory and experiments, the tolerance factor and octahedral factor jointly determine the octahedral composition. Further, halides with different electronegativities and ionic radii also affect octahedral distortion and energy band bending, further influencing carrier transport and device performance. Finally, a sensitivity of 1284 μC Gyair-1 cm-2 and low detection limits (LoD) of 5.62 μGyair s-1 were obtained by the Br-based device due to its superior physical properties.

Enhanced radioluminescence of NaLuF4:Eu3+ nanoscintillators by terbium sensitization for X-ray imaging

NaLuF4:Eu3+ nanoscintillator with enhanced radioluminescence was boosted by the sensitization effect of Tb3+ on Eu3+ with an excellent X-ray scintillation performance, and further applied in X-ray imaging with high contrast for different samples.