Zero-Dimensional Lead-Free FA3Bi2I9 Single Crystals for High-Performance X-ray Detection

Exploring Non-Toxic Lower Dimensional Perovskites for Next-Generation X-Ray Detectors

Owing to their extraordinary photophysical properties, organometal halide perovskites are emerging as a new material class for X-ray detection. However, the existence of toxic lead makes their commercialization questionable and should readily be replaced. Accordingly, several lead alternatives have been introduced into the framework of conventional perovskites, resulting in various new perovskite dimensionalities. Among these, Pb-free lower dimensional perovskites (LPVKs) not only show promising X-ray detecting properties due to their higher ionic migration energy, wider and tunable energy bandgap, smaller dark currents, and structural versatility but also exhibit extended environmental stability. Herein, first, the structural organization of the PVKs (including LPVKs) is summarized. In the context of X-ray detectors (XDs), the outstanding properties of the LPVKs and active layer synthesis routes are elaborated afterward. Subsequently, their applications in direct XDs are extensively discussed and the device performance, in terms of the synthesis method, device architecture, active layer size, figure of merits, and device stability are tabulated. Finally, the review is concluded with an in-depth outlook, thoroughly exploring the present challenges to LPVKs XDs, proposing innovative solutions, and future directions. This review provides valuable insights into optimizing non-toxic Pb-free perovskite XDs, paving the way for future advancements in the field.

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.

Dimensionality Engineering of Organic-Inorganic Halide Perovskites for Next-Generation X-Ray Detector

The next-generation X-ray detectors require novel semiconductors with low material/fabrication cost, excellent X-ray response characteristics, and robust operational stability. The family of organic-inorganic hybrid perovskites (OIHPs) materials comprises a range of crystal configuration (i.e., films, wafers, and single crystals) with tunable chemical composition, structures, and electronic properties, which can perfectly meet the multiple-stringent requirements of high-energy radiation detection, making them emerging as the cutting-edge candidate for next-generation X-ray detectors. From the perspective of molecular dimensionality, the physicochemical and optoelectronic characteristics of OIHPs exhibit dimensionality-dependent behavior, and thus the structural dimensionality is recognized as the key factor that determines the device performance of OIHPs-based X-ray detectors. Nevertheless, the correlation between dimensionality of OIHPs and performance of their X-ray detectors is still short of theoretical guidance, which become a bottleneck that impedes the development of efficient X-ray detectors. In the review, the advanced studies on the dimensionality engineering of OIHPs are critically assessed in X-ray detection application, discussing the current understanding on the "dimensionality-property" relationship of OIHPs and the state-of-the-art progresses on the dimensionality-engineered OIHPs-based X-ray detector, and highlight the open challenges and future outlook of this field.

High-Performance Flat-Panel Perovskite X-ray Detectors Enabled by Defect Passivation in Ruddlesden-Popper Perovskites

Halide perovskites have emerged as promising candidates in X-ray detection due to their strong X-ray absorption and excellent optoelectronic properties. The development of sensitive and stable flat-panel X-ray detectors with high resolution is crucial for practical applications. In this paper, we introduce a novel flat-panel X-ray detector that integrates quasi-two-dimensional (2D) Ruddlesden-Popper (RP) perovskite with a pixeled thin film transistor (TFT) backplane. We incorporate 2,5-dibromopyrimidine (DBPM) as an additive to passivate the Lewis acid defects in the quasi-2D RP perovskite. This modification results in suppressed ion migration, improved optoelectronic performance, and enhanced operational stability of the device. Impressively, the activation energy of the RP perovskite increases from 0.96 to 1.35 eV with the DBPM additive. As a result, X-ray detectors exhibit a high sensitivity of ∼13,600 μC Gyair-1 cm-2, a low detection limit of 6.56 nGyair s-1, and excellent operational stability. Moreover, the flat-panel detectors demonstrate a high spatial resolution of 3.7 line pairs per millimeter and excellent X-ray imaging properties under a remarkably low X-ray dose of ∼50 μGyair, which is just half of the X-ray dose typically used in commercial equipment. This study opens new avenues for the development of flat-panel perovskite X-ray detectors with significant potential for various applications.

Chiral-Achiral Cations Intercalation Induced Lead-Free Chiral-Polar Hybrid Perovskites Enable Self-Powered X-Ray and Ultraviolet-Visible-Near-Infrared Photo Detection

Lead halide hybrid perovskites have made great progress in direct X-ray detection and broadband photodetection, but the existence of toxic Pb and the demand for external operating voltage have severely limited their further applications and operational stability improvements. Therefore, exploring "green" lead-free hybrid perovskite that can both achieve X-ray detection and broadband photodetection without external voltage is of great importance, but remains severely challenging. Herein, using centrosymmetric (BZA)3BiI6 (1, BZA = benzylamine) as a template, a pair of chiral-polar lead-free perovskites, (BZA)2(R/S-PPA)BiI6 (2-R/S, R/S-PPA = (R/S)-1-Phenylpropylamine) are successfully obtained by introducing chiral aryl cations of (R/S)-1-Phenylpropylamine. Compared to 1, chiral-polar 2-R presents a significant irradiation-responsive bulk photovoltaic effect (BPVE) with an open circuit photovoltage of 0.4 V, which enables it with self-powered X-ray, UV-vis-NIR broadband photodetection. Specifically, 2-R device exhibits an ultralow detection limit of 18.5 nGy s-1 and excellent operational stability. Furthermore, 2-R as the first lead-free perovskite achieves significant broad-spectrum (377-940 nm) photodetection via light-induced pyroelectric effect. This work sheds light on the rational crystal reconstruction engineering and design of "green" hybrid perovskite toward high-demanded self-powered radiation detection and broadband photodetection.

Self-Powered Wide-Narrow Bandgap-Laminated Perovskite Photodetector with Bipolar Photoresponse for Secure Optical Communication

Perovskite photodetectors with bipolar photoresponse characteristics are expected to be applied in the field of secure optical communication (SOC). However, how to realize the perovskite photodetector with bipolar response remains challenging. Herein, by introducing bismuth iodide (BiI3 ) into Sn-Pb mixed perovskite precursor solution, 2D perovskite FA3 Bi2 I9 is spontaneously formed at the bottom to realize a wide-narrow bandgap-laminated perovskite film. Wavelength-dependent bipolar response is realized based on the absorption difference of the photoactive region with different bandgap combined with the carrier competition of the homotypic transport layer adopted in the as-fabricated photodetector. Under the visible/near-infrared (NIR) light irradiation, the bottom/top of the film generates a higher carrier concentration, where electrons are easier to be separated and transported by the SnO2 /PC61 BM to the bottom/top electrodes, respectively, resulting in a negative and positive bipolar response. Finally, based on positive NIR signal as the effective signal and negative visible signal as the interference signal, the SOC system is realized, where the positive NIR signal is well hidden by the negative visible signal. This work provides a simple and feasible strategy for fabrication of laminated perovskite films to achieve bipolar response.

Synthesis and Characterization of New Hybrid Organic-Inorganic Metal Halides [(CH3)3SO]M2I3 (M = Cu and Ag)

Recently, all-inorganic copper(I) metal halides have emerged as promising optical materials due to their high light emission efficiencies. This work details the crystal structure of the two hybrid organic-inorganic metal halides [(CH3)3SO]M2I3 (M = Cu and Ag) and their alloyed derivatives [(CH3)3SO]Cu2-xAgxI3 (x = 0.2; 1.25), which were obtained by incorporating trimethylsulfoxonium organic cation (CH3)3SO+ in place of Cs+ in the yellow-emitting all-inorganic CsCu2I3. These compounds are isostructural and centrosymmetric with the space group Pnma, featuring one-dimensional edge-sharing [M2I3]- anionic double chains separated by rows of (CH3)3SO+ cations. Based on density functional theory calculations, the highest occupied molecular orbitals (HOMOs) of [(CH3)3SO]M2I3 (M = Cu and Ag) are dominated by the Cu or Ag d and I p orbitals, while the lowest unoccupied molecular orbitals (LUMOs) are Cu or Ag s and I p orbitals. [(CH3)3SO]Cu2I3 single crystals exhibit a semiconductor resistivity of 9.94 × 109 Ω·cm. Furthermore, a prototype [(CH3)3SO]Cu2I3 single-crystal-based X-ray detector with a detection sensitivity of 200.54 uCGy-1 cm-2 (at electrical field E = 41.67 V/mm) was fabricated, indicating the potential use of [(CH3)3SO]Cu2I3 for radiation detection applications.

Lattice engineering for stabilized black FAPbI3 perovskite single crystals for high-resolution x-ray imaging at the lowest dose

Preliminary theoretical analyses indicate that lattice relaxation may be used to release lattice strain in the FAPbI3 perovskite to warrant both high x-ray detection performance and improved stability. Herein, we demonstrate stable black α-phase FAPbI3 single crystals (SCs) realized by lattice engineering via annealing in the ambient atmosphere. The engineered α-FAPbI3 SC detector shows almost all the best figures of merit including a high sensitivity of 4.15 × 105 μC Gyair-1 cm-2, a low detection limit of 1.1 nGyair s-1, a high resolution of 15.9 lp mm-1, and a short response time of 214 μs. We further demonstrate high-definition x-ray imaging at a dose rate below 10 nGyair s-1 on the FAPbI3 SC, indicating a minimal dose-area product of 0.048 mGyair cm2 to the patient for one-time posteroanterior chest diagnosis, which is more than 3000 times lower than the international reference level of 150 mGyair cm2. In addition, the robust long-term stability enables the FAPbI3 SC x-ray detector to work steadily for more than 40 years.

Structural Transition in (C2H5NH3)3Bi2-xSbxI9:[(Bi/Sb)2I9]3- Dimers to [(Bi/Sb)3I12]3- Trimers to (∞1)[(Bi/Sb)2I93-] 1D Infinite Chains

Antimony/bismuth-based lead-free hybrid halide defect 2D perovskites have been generating enormous research interest due to their inherent excellent optical properties. Exploration of new phases and understanding of their structural and optoelectronic properties are of paramount importance in the process of developing materials for practical solar cell applications. In this article, we have reported a structural transition from the 0D hexagonal phase containing isolated [M2I9]3- (M = Bi/Sb) units to the 1D orthorhombic phase via a new monoclinic phase with novel isolated trimeric [M3I12]3- units in (C2H5NH3)3Bi2-2xSb2xI9. The hexagonal phase is stable up to 2x = 0.6 in (C2H5NH3)3Bi2-2xSb2xI9. With gradual substitution of Sb, the cation-cation repulsion increases, which destabilizes the [M2I9]3- unit, and hence, the hexagonal phase becomes unstable. At intermediate composition, 2x = 0.8-1.6, a new monoclinic phase (S.G.: C2/m) with the composition (C2H5NH3)2Bi2-2xSb2xI8 is formed, containing isolated [M3I12]3- units. The symmetry reduction resulted in larger distortion, which relaxes the strain and stabilizes the trimeric unit in the intermediate compositions. Finally, at higher Sb compositions (2x = 1.9-2.0), the compounds crystallize in the orthorhombic 1D phase. In all three phases of (C2H5NH3)3Bi2-2xSb2xI9, the cationic ethylammonium units are completely disordered over the whole unit cell. Raman study clearly shows the phase transition in (C2H5NH3)3Bi2-2xSb2xI9 and also the structural distortion in (C2H5NH3)2Bi2-2xSb2xI8. Optical property study shows that all the compounds are of indirect band gap type. Furthermore, PL study shows better emission properties of the 1D orthorhombic Sb compounds as compared to the 0D hexagonal and monoclinic phases.

Lead-Free Halide Perovskites for Direct X-Ray Detectors

Lead halide perovskites have made remarkable progress in the field of radiation detection owing to the excellent and unique optoelectronic properties. However, the instability and the toxicity of lead-based perovskites have greatly hindered its practical applications. Alternatively, lead-free perovskites with high stability and environmental friendliness thus have fascinated significant research attention for direct X-ray detection. In this review, the current research progress of X-ray detectors based on lead-free halide perovskites is focused. First, the synthesis methods of lead-free perovskites including single crystals and films are discussed. In addition, the properties of these materials and the detectors, which can provide a better understanding and designing satisfactory devices are also presented. Finally, the challenge and outlook for developing high-performance lead-free perovskite X-ray detectors are also provided.

Perovskite-Based X-ray Detectors

X-ray detection has widespread applications in medical diagnosis, non-destructive industrial radiography and safety inspection, and especially, medical diagnosis realized by medical X-ray detectors is presenting an increasing demand. Perovskite materials are excellent candidates for high-energy radiation detection based on their promising material properties such as excellent carrier transport capability and high effective atomic number. In this review paper, we introduce X-ray detectors using all kinds of halide perovskite materials along with various crystal structures and discuss their device performance in detail. Single-crystal perovskite was first fabricated as an active material for X-ray detectors, having excellent performance under X-ray illumination due to its superior photoelectric properties of X-ray attenuation with μm thickness. The X-ray detector based on inorganic perovskite shows good environmental stability and high X-ray sensitivity. Owing to anisotropic carrier transport capability, two-dimensional layered perovskites with a preferred orientation parallel to the substrate can effectively suppress the dark current of the device despite poor light response to X-rays, resulting in lower sensitivity for the device. Double perovskite applied for X-ray detectors shows better attenuation of X-rays due to the introduction of high-atomic-numbered elements. Additionally, its stable crystal structure can effectively lower the dark current of X-ray detectors. Environmentally friendly lead-free perovskite exhibits potential application in X-ray detectors by virtue of its high attenuation of X-rays. In the last section, we specifically introduce the up-scaling process technology for fabricating large-area and thick perovskite films for X-ray detectors, which is critical for the commercialization and mass production of perovskite-based X-ray detectors.

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

Lead-free A₃ Bi₂ I₉ -type perovskites are demonstrated as a class of promising semiconductors for high-performance X-ray detection due to their high bulk resistivity and strong X-ray absorption, as well as reduced ion migration. However, due to their long interlamellar distance along their c-axis, their limited carrier transport along the vertical direction is a bottleneck for their detection sensitivity. Herein, a new A-site cation of aminoguanidinium (AG) with all-NH₂ terminals is designed to shorten the interlayer spacing by forming more and stronger NH···I hydrogen bonds. The prepared large AG₃ Bi₂ I₉ single crystals (SCs) render shorter interlamellar distance for a larger mobility-lifetime product of 7.94 × 10^-3  cm²  V^-1 , which is three times higher than the value measured on the best MA₃ Bi₂ I₉ SC (2.87 × 10^-3  cm²  V^-1 ). Therefore, the X-ray detectors fabricated on the AG₃ Bi₂ I₉ SC exhibit high sensitivity of 5791 uC Gy^-1  cm^-2 , a low detection limit of 2.6 nGy s^-1, and a short response time of 690 µs, all of which are far better than those of the state-of-the-art MA₃ Bi₂ I₉ SC detectors. The combination of high sensitivity and high stability enables astonishingly high spatial resolution (8.7 lp mm^-1 ) X-ray imaging. This work will facilitate the development of low-cost and high-performance lead-free X-ray detectors.

Improving the Performance and High-Field Stability of FAPbBr3 Single Crystals in X-Ray Detection with Chenodeoxycholic Acid Additive

Organometal halide perovskite single crystals are one of the most promising radiation detection materials due to their unique advantages of high absorption coefficient, long carrier diffusion length, and low defect density. However, the severe ion migration in perovskites deteriorates the X-ray detection performance under longtime and high-field operating conditions. This work reports an effective additive of chenodeoxycholic acid (CDCA), which can suppress the ion migration and improve the performance and the operational stability of FAPbBr₃ single crystals (SCs) in X-ray detection significantl. The CDCA molecules in precursors effectively suppress the decomposition of FA ions, resulting in a better crystal orientation and stoichiometry. The trace amounts of CDCA residues in FAPbBr₃ SCs improve the thermal stability and effectively suppress the ion migration. The resulting detector shows an impressive X-ray sensitivity up to 21 386.88 µC Gy_air ^-1 cm^-2 under -500 V and a detection limit of 15.23 nGy_air s^-1 . The response current of the detector at 225 V cm^-1 field is barely changed under the 7200 s irradiation with a dose rate of 1.949 mGy_air s^-1 . This work provides insights for the additive selection and improving the operational stability of perovskite single crystals for commercial applications.

Recent Development of Halide Perovskite Materials and Devices for Ionizing Radiation Detection

Ionizing radiation such as X-rays and γ-rays has been extensively studied and used in various fields such as medical imaging, radiographic nondestructive testing, nuclear defense, homeland security, and scientific research. Therefore, the detection of such high-energy radiation with high-sensitivity and low-cost-based materials and devices is highly important and desirable. Halide perovskites have emerged as promising candidates for radiation detection due to the large light absorption coefficient, large resistivity, low leakage current, high mobility, and simplicity in synthesis and processing as compared with commercial silicon (Si) and amorphous selenium (a-Se). In this review, we provide an extensive overview of current progress in terms of materials development and corresponding device architectures for radiation detection. We discuss the properties of a plethora of reported compounds involving organic-inorganic hybrid, all-inorganic, all-organic perovskite and antiperovskite structures, as well as the continuous breakthroughs in device architectures, performance, and environmental stability. We focus on the critical advancements of the field in the past few years and we provide valuable insight for the development of next-generation materials and devices for radiation detection and imaging applications.

Perovskite Dimensional Evolution Through Cations Engineering to Tailor the Detection Limit in Hard X-ray Response

Halide perovskites with various compositions are potential candidates in low-dosage X-ray detection due to their large sensitivity and tunable optoelectronic properties. Here, cations engineering induced dimensional evolution of halide perovskites between 0D, 2D, and 3D is reported. Centimeter-sized 2D lead-free perovskite single-crystal of 4-fluorophenethylammonium antimony iodide (FPEA₃ SbI₆ ) is synthesized. In contrast to the 0D phenethylammonium antimony iodide (PEA₃ Sb₂ I₉ ), face-shared [Sb₂ I₉ ]^3- of the bi-octahedral structure of PEA₃ Sb₂ I₉ is split into corner-shared [SbI₆ ]^3- by intermolecular interactions and steric hindrance of FPEA⁺ ions in 2D FPEA₃ SbI₆ . Two Sb³⁺ ions share three octahedral [SbI₆ ]^3- , leaving one-third of Sb³⁺ vacancies in the framework of FPEA₃ SbI₆ . Furthermore, Sn²⁺ ions can be filled into the vacancies to form continuous 2D frameworks to tune the anisotropic conductivity and device sensitivity to hard X-rays. The dimensional evolution of perovskite single-crystals from 3D to 2D or 0D to 2D maximizes the signal/noise ratio to facilize the adjustability of detection limit in hard X-ray detection, which is determined by both device sensitivity and device noise current. A record low detection limit coefficient of 0.65 is achieved in the 2D FPEA₃ SbSn_0.5 I₇ single-crystal sample, which results from selective charges collection over mobile ions/noise current in the 2D perovskite structure.

Ultrasensitive and Robust 120 keV Hard X-Ray Imaging Detector based on Mixed-Halide Perovskite CsPbBr3- n In Single Crystals

The relatively low resistivity and severe ion migration in CsPbBr₃ significantly degrade the performance of X-ray detectors due to their high detection limit and current drift. The electrical properties and X-ray detection performances of CsPbBr₃ -nIn single crystals are investigated by doping the iodine atoms into the melt-grown CsPbBr₃ . The resistivity of CsPbBr₃ -nIn single crystals increases from 3.6 × 10⁹ (CsPbBr₃ ) to 2.2 × 10¹¹ (CsPbBr₂ I) Ω cm, restraining the leak current and decreasing the detection limit of the detector. Additionally, CsPbBr₃ -nIn single crystals exhibit stable dark currents, arising from their high ion migration activation energy. A record sensitivity of 6.3 × 104 µC Gy^-1 cm^-2 (CsPbBr_2.9 I_0.1 ) and a low detection limit of 54 nGy s^-1 (CsPbBr₂ I) are achieved by CsPbBr₃ -nIn single crystals for the 120 keV hard X-ray detection under a 5000 V cm^-1 electrical field. The CsPbBr_2.9 I_0.1 detector shows a stable current response with a dark current density of 0.58 µA cm^-2 for 30 days and clear imaging for 120 keV Xrays at ambient conditions. The effective iodine atom doping strategy makes the CsPbBr₃ -nIn single crystals promising for reproducible high-energy hard X-ray imaging systems.

Ultralow Detection Limit and Robust Hard X-ray Imaging Detector Based on Inch-Sized Lead-Free Perovskite Cs3Bi2Br9 Single Crystals

Halide perovskites are promising candidates for soft X-ray detection (<80 keV) owing to their high X-ray absorption coefficient, resistivity, and mobility lifetime product. However, the lack of large high-quality single crystals (SCs) renders it challenging to manufacture robust hard X-ray imaging systems (>100 keV) with a low detection limit and stable dark current. Herein, high-quality inch-size two-dimensional (2D) Cs₃Bi₂Br₉ (CBB) single crystals are grown from a melt via the Bridgman method. The crystal quality is enhanced by eliminating inclusions of CsBr-rich phases and restraining the trap-state density, leading to an enhanced resistivity of 1.41 × 10¹² Ω cm and a mobility lifetime product of 8.32 × 10^-4 cm² V^-1. The Au/CBB/Au single-crystal device exhibits a high sensitivity of 1705 μC Gy_air^-1 cm^-2 in all-inorganic bismuth-based perovskites and an ultralow detection limit of 0.58 nGy_air s^-1 in all of the bismuth-based perovskites for 120 keV hard X-ray detection. The CBB detector exhibits high work stability with an ultralow dark current drift of 2.8 × 10^-10 nA cm^-1 s^-1 V^-1 and long-term air environment reliability under a high electric field of 10 000 V cm^-1 owing to the ultrahigh ionic activation energy of the 2D structure. The proposed robust imaging system based on CBB SC is a promising tool for X-ray medical imaging and diagnostics.

Nucleation Engineering in Sprayed MA3Bi2I9 Films for Direct-Conversion X-ray Detectors

Metal halide perovskite and its derivatives show great promise in X-ray detection. However, large-scale fabrication of high-quality thick perovskite films is still full of challenges due to the complicated crystal nucleation process that always introduces lots of cracks or pinholes in the final perovskite film. Here, a MA₃Bi₂I₉ film was fabricated by the cost-effective, scalable spraying process, and MACl was used as an additive to effectively tune the crystallization process. As a result, a dense MA₃Bi₂I₉ film constituted by large grains was obtained, which has a high carrier mobility of ∼1 cm² V^-1 s^-1 and a large activation energy (E_a) for ion migration of 0.91 eV. Thanks to the outstanding optoelectronic characteristics, X-ray detectors with a configuration of ITO/MA₃Bi₂I₉/Au show a sensitivity of 35 μC Gy_air^-1 cm^-2 and a limit of detection (LoD) of 0.14 μGy_airs^-1, which is outstanding compared with commercial α-Se detectors.

Perovskite materials: from single crystals to radiation detection

Pb- and Bi-based perovskite materials have high potential for detecting ionizing radiation but an enhanced research effort is needed to achieve large-size, high-performance single crystals at a competitive cost to accelerate this development.

A lead-free halide hybrid perovskite (TMHD)BiCl5 for ultraviolet photodetection

Lead halide hybrid perovskites with a wide bandgap (e.g., CH3NH3PbCl3) have gained tremendous attention in the field of ultraviolet (UV) photodetection due to their brilliant optoelectronic activity.

Durable Flexible Polymer-Encapsulated Cs4PbI6 Thin Film for High Sensitivity X-ray Detection

Because of the extraordinary properties including high atomic numbers and large μτ products, metal halide perovskites have been widely employed and used for radiation detecting. Cs₄PbI₆ material has a high X-ray attenuation coefficient and excellent electrical properties that have a good potential in X-ray detection applications. Here, we have designed a flexible polymer-encapsulated Au/Cs₄PbI₆/Au X-ray detector with outstanding sensitivity of 256.20 μC Gy^-1 cm^-2 irradiated by 30 keV X-ray at 10 V bias, long-time stability, and durable flexibility without obvious degradation after bending for 600 cycles. These features demonstrate that this polymer-encapsulated durable flexible and sensitive X-ray detector could open a new possibility for next-generation radiation applications in dosimeter, imaging technologies.

PbI2-TiO2 Bulk Heterojunctions with Long-Range Ordering for X-ray Detectors

High-performance X-ray detectors are usually based on single crystals, due to the long-range ordering and hence outstanding electronic properties. On the other hand, bulk heterojunctions (BHJs) that can effectively enhance photogenerated exciton dissociation are widely used for photodetectors. The benefits of both spur investigation into how to combine these two strategies to enhance X-ray detection. Here, TiO₂ networks are incorporated into PbI₂ crystals to form interpenetrating type II heterojunctions, namely BHJs. These BHJs exhibit long-range ordering in molecular packing similar to that of single crystals. Compared with single crystals, the long-range ordered BHJs facilitate the separation of photogenerated electrons and holes to inhibit recombination, extend the mobility lifetime product by 6.4 times, and consequently improve X-ray sensitivity by 5.8 times. Hence, this work provides a new strategy using gel-grown crystals to fabricate high-performance X-ray detectors as well as a new platform for studying the behavior of X-ray-generated carriers in BHJs with long-range ordering.

Solvent Free Laminated Fabrication of Lead Halide Perovskites for Sensitive and Stable X-ray Detection

The halide perovskite X-ray detector can meet the urgent needs of low-dose medical imaging by X-rays. However, there is still a pressing challenge in lacking robust methods for large-scale fabrication of high-quality perovskite films with tunable thickness. Here we report a laminated fabrication of polycrystalline MAPbI₃ by using solvent-free liquid perovskite molten-salt (PMS), that offers reduced toxic issue, scalable fabrication, and highly tunability in film thickness. Nylon membrane was chosen as a scaffold for the infiltration of PMS, which simultaneously acts as a physical barrier to suppress the ionic migration in the MAPbI₃-nylon composite (denoted as MAPbI₃-LLP). The enhanced material properties result in good stability and high performance of X-ray detectors that show low detection limit and high sensitivity. Additionally, single gamma-ray photon detection was realized by MAPbI₃-LLP detectors. The promising performance characteristics of such polycrystalline detectors can accelerate the adoption of polycrystalline perovskites in X-ray imaging and gamma-ray detection.

Scalable Production of Ambient Stable Hybrid Bismuth-Based Materials: AACVD of Phenethylammonium Bismuth Iodide Films*

Large homogeneous and adherent coatings of phenethylammonium bismuth iodide were produced using the cost-effective and scalable aerosol-assisted chemical vapor deposition (AACVD) methodology. The film morphology was found to depend on the deposition conditions and substrates, resulting in different optical properties to those reported from their spin-coated counterparts. Optoelectronic characterization revealed band bending effects occurring between the hybrid material and semiconducting substrates (TiO2 and FTO) due to heterojunction formation, and the optical bandgap of the hybrid material was calculated from UV-visible and PL spectrometry to be 2.05 eV. Maximum values for hydrophobicity and crystallographic preferential orientation were observed for films deposited on FTO/glass substrates, closely followed by values from films deposited on TiO2 /glass substrates.