Halide lead perovskites for ionizing radiation detection

Lithium Chloride-Substituted Methylammonium Lead Tribromide Perovskites for Dual γ/Neutron Sensing

Dual γ/neutron radiation sensors are a critical component of the nuclear security mission to prevent the proliferation of a special nuclear material (SNM). While high-performing semiconductors such as high purity germanium (HPGe) and CdZnTe (CZT) already exist in the nuclear security enterprise, their high cost and/or logistical burdens make widespread deployment difficult to achieve. Metal lead halide perovskites (MHPs) have attracted interest in recent years to address this challenge. In particular, methylammonium lead tribromide (CH₃NH₃PbBr₃, MAPbBr₃, or MAPB) has been widely evaluated for its radiation sensing capabilities. While previous studies have demonstrated low-energy X-ray and α particle sensing of MAPB-based detectors and several studies discuss the potential for γ ray sensing, neutron sensing of this material has been rarely explored. Here, we explore the incorporation of lithium in the form of LiCl into the MAPB structure to add thermal neutron sensitivity. Characterizations of the lithium-doped MAPB crystals demonstrate that quality growths are achievable with single crystals that exhibit high crystallinity, no phase change, and high macroscopic bulk quality. Finally, we report on the first demonstrated γ ray and thermal neutron sensing based on lithium-doped MAPB single crystals, which is a significant milestone in the development of 3D dual γ/neutron MHP sensors.

Surface-Passivated Single-Crystal Micro-Plates for Efficient Perovskite Solar Cells

Perovskite solar cells (PeSCs) prepared with single crystals (SCs) ideally exhibit higher power conversion efficiencies (PCEs) because they possess a lower density of structural imperfection and superior charge transport. However, the density of the surface defects on the SCs is still very high, thereby inevitably affecting the device performance. Herein, perovskite single-crystal micro-plates were grown on a hole-transporting material, poly[bis(4-phenyl)(2,4,6-trimethylphenyl) amine], through a space-limited inverse temperature crystallization method. The surfaces of the as-prepared SCs were passivated using trioctylphosphine oxide (TOPO) during the device fabrication to alleviate the impact of surface defects. The PCE values are averagely improved from 11.90 ± 0.30% to 14.76 ± 0.65% after the surface passivation; the champion device even exhibits a PCE of 15.65%. The results from photoluminescence and hole-only devices reveal that TOPO treatments effectively reduce the number of surface defects on the single crystals, thereby improving the photovoltaic performance. The surface passivation also inhibits the hysteresis behavior due to the lower defect density. Finally, the TOPO treatment also improves the stability of the single-crystal PeSCs, presumably due to the hydrophobic long alkyl chains. Thus, this work provides an effective approach to achieving high efficiencies of single-crystal PeSCs.

Efficient Eco-Friendly Flexible X-ray Detectors Based on Molecular Perovskite

Next-generation wearable electronics requires mechanical robustness. In addition to the previously reported eco-friendliness, low cost, and light weight of molecular perovskites, flexibility is also a desired merit for their practical use. Here we design a flexible X-ray detector based on a novel molecular perovskite, DABCO-CsBr₃ (DABCO = N-N'-diazabicyclo[2.2.2]octonium), which is the missing link between metal-free molecular perovskites A(NH₄)X₃ (A = divalent organic ammoniums) and conventional metal halide based ABX₃ (B = divalent metal cations) perovskites. DABCO-CsBr₃ inherits its band nature from A(NH₄)X₃, while it exhibits a stronger stopping power. DABCO-CsBr₃ shows potential for high-performance ionizing radiation detectors due to low dark current, low ion migration, and an efficient mobility-lifetime (μτ) product. Finally, a molecular-perovskite-based flexible X-ray detector is demonstrated on the basis of the DABCO-CsBr₃/poly(vinylidene fluoride) composite, with a sensitivity of 106.7 μC Gy_air^-1 cm^-2. This work enriches the molecular perovskite family and highlights the promise of molecular perovskites for the next-generation eco-friendly and wearable optoelectronic devices.

Wafer-Scale Photolithography-Pixeled Pb-Free Perovskite X-ray Detectors

Pb-free perovskite material is considered to be a promising material utilized in next-generation X-ray detectors due to its high X-ray absorption coefficient, decent carrier transport properties, and relatively low toxicity. However, the pixelation of the perovskite material with an industry-level photolithography processing method remains challenging due to its poor structural stability. Herein, we use Cs₂AgBiBr₆ perovskite material as the prototype and investigate its interaction with photolithographic polar solvents. Inspired by that, we propose a wafer-scale photolithography patterning method, where the pixeled perovskite array devices for X-ray detection are successfully prepared. The devices based on pixeled Pb-free perovskite material show a high detection sensitivity up to 19118 ± 763 μC Gy_air^-1 cm^-2, which is comparable to devices with Pb-based perovskite materials and superior to the detection sensitivity (∼20 μC Gy_air^-1 cm^-2) of the commercial a-Se detector. After pixelation, the devices achieve an improved spatial resolution capacity with the spatial frequency from 2.7 to 7.8 lp mm^-1 at modulation-transfer-function (MTF) = 0.2. Thus, this work may contribute to the development of high-performance array X-ray detectors based on Cs₂AgBiBr₆ perovskite material.

Improving device performance of MAPbI3photovoltaic cells by manipulating the crystal orientation of tetragonal perovskites

The properties of CH₃NH₃PbI₃(MAPbI₃) crystalline thin films and the device performance of highly efficient MAPbI₃photovoltaic cells are investigated by varying the temperature of the antisolvent from 20 °C to 50 °C during the washing enhanced nucleation (WEN) process. The surface, structural, optoelectronic and defect properties of the perovskite thin films are characterized through atomic-force microscopy, X-ray diffractometry and photoluminescence spectrometry. The experimental results show that changing the temperature of the antisolvent during the WEN process can manipulate the MAPbI₃crystalline thin films from the (110)-(002) complex phase to a (002) preferred phase. It is noted that the highest power conversion efficient of the inverted MAPbI₃photovoltaic cells is 19.30%, mainly due to the increased carrier collection efficiency and reduced carrier recombination when the temperature of the antisolvent is 30 °C.

Organic phosphorescent scintillation from copolymers by X-ray irradiation

Scintillators that exhibit X-ray-excited luminescence have great potential in radiation detection, X-ray imaging, radiotherapy, and non-destructive testing. However, most reported scintillators are limited to inorganic or organic crystal materials, which have some obstacles in repeatability and processability. Here we present a facile strategy to achieve the X-ray-excited organic phosphorescent scintillation from amorphous copolymers through the copolymerization of the bromine-substituted chromophores and acrylic acid. These polymeric scintillators exhibit efficient X-ray responsibility and decent phosphorescent quantum yield up to 51.4% under ambient conditions. The universality of the design principle was further confirmed by a series of copolymers with multi-color radioluminescence ranging from green to orange-red. Moreover, we demonstrated their potential application in X-ray radiography. This finding not only outlines a feasible principle to develop X-ray responsive phosphorescent polymers, but also expands the potential applications of polymer materials with phosphorescence features.

Low-dose X-ray irradiation combined with FAK inhibitors improves the immune microenvironment and confers sensitivity to radiotherapy in pancreatic cancer

Radiation therapy offers limited clinical benefits for patients with pancreatic cancer, partly as a result of the predominantly immunosuppressive microenvironment characteristic of this specific type of cancer. A large number of abnormal blood vessels and high-density fibrous matrices in pancreatic cancer will lead to hypoxia within tumor tissue and hinder immune cell infiltration. We used low-dose X-ray irradiation, also known as low-dose radiation therapy (LDRT), to normalize the blood vessels in pancreatic cancer, while simultaneously administering an inhibitor of focal adhesion kinase (FAK) to reduce pancreatic cancer fibrosis. We found that this treatment successfully reduced pancreatic cancer hypoxia, increased immune cell infiltration, and increased sensitivity to radiation therapy for pancreatic cancer.

Centimeter-sized lead-free iodide-based hybrid double perovskite single crystals for efficient X-ray photoresponsivity

Hybrid organic-inorganic lead halide perovskites (HOIPs) possess significant photoelectric characteristics for solar energy conversion, but the presence of lead causes issues for eco-friendly applications. Halide double perovskites represent a green option for application in the optoelectronic field, especially X-ray detection systems. Despite the great efforts, the exploration of large-size lead-free iodide-based hybrid double perovskite single crystals for X-ray detection has been unsuccessful. Herein, we demonstrate that a large single crystal of the 2D (two-dimensional) semiconducting perovskite (C₆H₁₆N₂)₂CuBiI₈·0.5H₂O can serve as an X-ray detection candidate. A perovskite crystal, as large as 35 × 31 × 3 mm³, was grown using a low-cost, simple cooling solution approach. To the best of our knowledge, this is the first time a centimeter-sized 2D BiCu iodide double perovskite single crystal has been used for X-ray detection. The perovskite crystal exhibited unique properties for X-ray detection, such as a significant X-ray absorption coefficient, considerable μτ product, and low trap density. Moreover, X-ray detection with a sensitivity of 5.51 μC Gy_air^-1 cm^-2 was achieved based on a single crystal. This work opens new ways to explore specially designed organic cations for stabilizing 2D HOIPs that show great potential in optoelectronics.

Transient Suppression of Carrier Mobility Due to Hot Optical Phonons in Lead Bromide Perovskites

In lead halide perovskites, owing to the strong Fröhlich coupling, carrier dynamics that governs the optoelectronic performance is greatly affected by the lattice vibrations. In this emerging class of materials, injected hot carriers quickly relax by emitting optical phonons, and if this process is sufficiently fast, hot optical phonons can be generated, which may in turn hamper the carrier transport. However, the transient interaction between hot phonons and carriers has not yet been investigated. Herein, we identified the transient absorption feature of hot phonons in lead bromide perovskites and then extracted the hot-phonon dynamics. The hot-phonon decay mechanism was uncovered by temperature-dependent measurements. The hot-phonon decay in lead bromide perovskites was an order of magnitude faster than that in GaAs, attributed to the large anharmonicity arising from the lattice softness and structural fluctuation. The carrier mobility was also transiently suppressed by hot phonons, and the mobility recovery was accompanied by the decay of hot phonons.

Interlayer-Assisted Growth of Si-Based All-Inorganic Perovskite Films via Chemical Vapor Deposition for Sensitive and Stable X-ray Detection

All-inorganic perovskites are considered as preferred materials for next-generation X-ray detectors. However, preparing high-quality thick films by traditional solution-based methods remains challenging due to the low solubility of the precursors. In this work, chemical vapor deposition technology is employed to grow Si-based all-inorganic cesium-lead-bromide perovskite thick films. By introducing a SnO₂ nanocrystal interlayer onto the Si substrate to facilitate the heterogeneous nucleation of the perovskite, we are able to grow high-quality films with a smooth surface and compact grains at a relatively low substrate temperature of 260 °C. The resultant X-ray detectors exhibit a decent sensitivity of 2930 μC Gy_air^-1 cm^-2, a small dark current density of 1.5 nA cm^-2, and a low detection limit of 120 nGy_air s^-1. Moreover, the devices show excellent biasing stability with a record small baseline drift of 4.6 × 10^-9 nA cm^-1 s^-1 V^-1 under a large electric field of 1100 V/cm among all perovskite polycrystalline film-based detectors ever reported.

Metal-Free PAZE-NH4 X3 ⋅H2 O Perovskite for Flexible Transparent X-ray Detection and Imaging

Metal-free perovskites are of interest for their chemical diversity and eco-friendly properties, and recently have been used for X-ray detection with superior carrier behavior. However, the size and shape complexity of the organic components results in difficulties in evaluating their stability in high-energy radiation. Herein, we introduce multiple hydrogen-bond metal-free PAZE-NH₄ X₃ ⋅H₂ O perovskite, where H₂ O leads to more hydrogen bonds appearing between organic molecules and the perovskite host. As suggested by the theoretical calculations, multiple hydrogen bonds promote stiffness of the lattice, and increase the diffusion barrier to inhibit ionic migration. Then, low trap density, high μτ products and structural flexibility of PAZE-NH₄ Br₃ ⋅H₂ O give a flexible X-ray detector with the highest sensitivity of 3708 μC Gy_air ^-1  cm^-2 , ultra-low detection limit of 0.19 μGy_air ^-1  s^-1 and superior spatial resolution of 5.0 lp mm^-1 .

The Landé factors of electrons and holes in lead halide perovskites: universal dependence on the band gap

The Landé or g-factors of charge carriers are decisive for the spin-dependent phenomena in solids and provide also information about the underlying electronic band structure. We present a comprehensive set of experimental data for values and anisotropies of the electron and hole Landé factors in hybrid organic-inorganic (MAPbI₃, MAPb(Br_0.5Cl_0.5)₃, MAPb(Br_0.05Cl_0.95)₃, FAPbBr₃, FA_0.9Cs_0.1PbI_2.8Br_0.2, MA=methylammonium and FA=formamidinium) and all-inorganic (CsPbBr₃) lead halide perovskites, determined by pump-probe Kerr rotation and spin-flip Raman scattering in magnetic fields up to 10 T at cryogenic temperatures. Further, we use first-principles density functional theory (DFT) calculations in combination with tight-binding and k ⋅ p approaches to calculate microscopically the Landé factors. The results demonstrate their universal dependence on the band gap energy across the different perovskite material classes, which can be summarized in a universal semi-phenomenological expression, in good agreement with experiment.

The Landé factors govern all the spin-related basic phenomena and are the key parameters which guide spintronics applications. Here, Kirstein et al. demonstrate a universal dependence of the Landé factors on the bandgap energy of several perovskite materials.

Halide Perovskite Solar Cells for Building Integrated Photovoltaics: Transforming Building Façades into Power Generators

The rapid emergence of organic-inorganic lead halide perovskites for low-cost and high-efficiency photovoltaics promises to impact new photovoltaic concepts. Their high power conversion efficiencies, ability to coat perovskite layers on glass via various scalable deposition techniques, excellent optoelectronic properties, and synthetic versatility for modulating transparency and color allow perovskite solar cells (PSCs) to be an ideal solution for building-integrated photovoltaics (BIPVs), which transforms windows or façades into electric power generators. In this review, the unique features and properties of PSCs for BIPV application are accessed. Device engineering and optical management strategies of active layers, interlayers, and electrodes for semitransparent, bifacial, and colorful PSCs are also discussed. The performance of PSCs under conditions that are relevant for BIPV such as different operational temperature, light intensity, and light incident angle are also reviewed. Recent outdoor stability testing of PSCs in different countries and other demonstration of scalability and deployment of PSCs are also spotlighted. Finally, the current challenges and future opportunities for realizing perovskite-based BIPV are discussed.

Recent advances in the applications of thorium-based metal-organic frameworks and molecular clusters

This perspective highlights the recent advances in the structural and practical aspects of thorium-based metal-organic frameworks (Th-MOFs) and molecular clusters. Thorium, as an underexplored actinide, features surprisingly rich coordination geometries and accessibility of the 5f orbital. These features lead to a myriad of topologies and electronic structures, many of which are undocumented for other tetravalent metal-containing MOFs or clusters. Moreover, Th-MOFs inherit the modularity, structural tunability, porosity, and versatile functionality of the state-of-the-art MOFs. Recognizing the radioactive nature of these thorium-bearing materials that may limit their practical uses, Th-MOFs and Th-clusters still have great potential for various applications, including radionuclide sequestration, hydrocarbon storage/separation, radiation detection, photoswitch, CO₂ conversion, photocatalysis, and electrocatalysis. The objective of this updated perspective is to propose pathways for the renaissance of interest in thorium-based materials.

Halide perovskites and perovskite related materials for particle radiation detection

Radiation detectors are widely used in physics, materials science, chemistry, and biology. Halide perovskites are known for their superior properties including tunable bandgaps and chemical compositions, high defect tolerance, solution-processable synthesis of films and crystals, and high carrier diffusion length. Recently, halide perovskites have attracted enormous interest as particle radiation detectors for both charged (α and β) and uncharged (neutrons) particles. Solid-state detectors based on single crystal perovskites can detect α particles and thermal neutrons with energy-resolved spectra. Halide perovskite scintillators are also able to detect β particles and fast neutrons. In this review, we briefly introduce the fundamentals of radiation detection and summarize the recent progress on halide perovskite detectors for particle radiation.

Recent advances in lead-free double perovskites for x-ray and photodetection

Over the last decade, lead halide perovskites have attracted significant research attention in the field of photovoltaics, light-emitting devices, photodetection, ionizing radiation detection, etc, owing to their outstanding optoelectrical properties. However, the commercial applications of lead-based perovskite devices are restricted due to the poor ambient stability and toxicity of lead. The encapsulation of lead-based devices can reduce the possible leakage of lead. However, it is hard to ensure safety during large-scale production and long-term storage. Recently, considerable efforts have been made to design lead-free perovskites for different optoelectronic applications. Metal halide double perovskites with the general formula of A₂M^IM^IIIX₆or A₂M^IVX₆could be potentially considered as green and stable alternatives for different optoelectronic applications. In this review article, we focus on the recent progress and findings on lead-free halide double perovskites for x-ray and UV-vis photodetection applications. Lead-free halide double perovskite has recently drawn a great deal of attention for superior x-ray detection due to its high absorption coefficient, large carrier mobility-lifetime product, and large bulk resistance. In addition, these materials exhibit good performance in photodetection in the UV-vis region due to high photocarrier generation and efficient carrier separation. In this review, first, we define the characteristics of lead-free double perovskite materials. The fundamental characteristics and beneficial properties of halide perovskites for direct and indirect x-ray detection are then discussed. We comprehensively review recent developments and efforts on lead-free double perovskite for x-ray detection and UV-vis photodetection. We bring out the current challenges and opportunities in the field and finally present the future outlook for developing lead-free double perovskite-based x-ray and UV-vis photodetectors for practical applications.

Energy Transfer Assisted Fast X-ray Detection in Direct/Indirect Hybrid Perovskite Wafer

Metal halide perovskite scintillators encounter unprecedented opportunities in indirect ionizing radiation detection due to their high quantum yields. However, the long scintillation lifetime of microseconds upon irradiation, known as the afterglow phenomenon, obviously limits their fast development. Here, a new type of hybrid X-ray detector wafer combining direct methylamine lead iodide (MAPbI3 ) semiconductor and indirect zero-dimensional cesium copper iodide (Cs3 Cu2 I5 ) scintillator through low-cost fast tableting processes is reported. Due to the fast energy transfer from Cs3 Cu2 I5 to MAPbI3 , the device response time to X-rays is dramatically reduced by nearly 30 times to 36.6 ns, which enables fast X-ray detection capability by a large area detector arrays within 1 s. Moreover, Cs3 Cu2 I5 exists at the grain boundaries of MAPbI3 crystals, and blocks the paths of mobile ions of perovskite, leading to the lowest detectable dose rate of hybrid X-ray detector is thus reduced by 1.5 times compared with control MAPbI3 direct-type semiconductor, and 10 times compared with the Cs3 Cu2 I5 indirect-type scintillator. The direct/indirect hybrid wafer also exhibits improved operation stability at ambient conditions without any encapsulation. This new kind of hybrid X-ray detectors provides strong competitiveness by combining the advantages of both direct perovskite semiconductors and indirect perovskite scintillators for next-generation products.

Vertical matrix perovskite X-ray detector for effective multi-energy discrimination

Multi-energy X-ray detection is sought after for a wide range of applications including medical imaging, security checking and industrial flaw inspection. Perovskite X-ray detectors are superior in terms of high sensitivity and low detection limit, which lays a foundation for multi-energy discrimination. However, the extended capability of the perovskite detector for multi-energy X-ray detection is challenging and has never been reported. Herein we report the design of vertical matrix perovskite X-ray detectors for multi-energy detection, based on the attenuation behavior of X-ray within the detector and machine learning algorithm. This platform is independent of the complex X-ray source components that constrain the energy discrimination capability. We show that the incident X-ray spectra could be accurately reconstructed from the conversion matrix and measured photocurrent response. Moreover, the detector could produce a set of images containing the density-graded information under single exposure, and locate the concealed position for all low-, medium- and high-density substances. Our findings suggest a new generation of X-ray detectors with features of multi-energy discrimination, density differentiation, and contrast-enhanced imaging.

Doping MAPbBr3 hybrid perovskites with CdSe/CdZnS quantum dots: from emissive thin films to hybrid single-photon sources

We report the first doping of crystalline methyl-ammonium lead bromide perovskite (MAPbBr₃) films with CdSe/CdZnS core/shell quantum dots (QDs), using a soft-chemistry approach that preserves their high quantum yield and other remarkable luminescence properties. Our approach produces MAPbBr₃ films of around 100 nm thickness, doped at volume ratios between 0.01 and 1% with colloidal CdSe/CdZnS QDs whose organic ligands were exchanged with halide ions to allow for close contact between the QDs and the perovskite matrix. Ensemble photoluminescence (PL) measurements demonstrate the retained emission of the QDs after incorporation into the MAPbBr₃ matrix. Photoluminescence excitation (PLE) spectra exhibit signatures of wavelength-dependent coupling between the CdSe/CdZnS QDs and the MAPbBr₃ matrix, i.e., a transfer of charges from matrix to QD, which increases the QD luminescence by up to 150%, or from QD to matrix. Spatially-resolved PL experiments reveal a strong correlation between the positions of QDs and an enhancement of the PL signal of the matrix. Lifetime imaging of the doped films furthermore shows that the emission lifetime of MAPbBr₃ is slower in the vicinity of QDs, which, in combination with the increased PL signal of the matrix, suggests that QDs can act as local nucleation seeds that improve the crystallinity of MAPbBr₃, thus boosting its emission quantum yield. Luminescence antibunching measurements provide clear evidence of single-photon emission from individual QDs in perovskite. Finally, the analysis of blinking statistics indicates an improvement of the photostability of individual QDs in perovskite as compared to bare CdSe/CdZnS QDs. At high CdSe/CdZnS QD doping levels, this work thus opens a route to hybrid solar concentrators for visible-light harvesting and hybrid-based LEDs, while a low degree of doping could yield hybrid single-photon sources than can be embedded in field-effect devices for single-charge control, which would allow the construction of nanophotonic devices via low-cost solution-processing techniques as an alternative to solid-state quantum dots.

Photoinduced Transformation of Cs2Au2Br6 into CsPbBr3 Nanocrystals

Lead-free halide double perovskites offer an environmentally friendly alternative to lead halide perovskites for designing optoelectronic solar cell devices. One simple approach to synthesize such double halide perovskites is through metal ion exchange. CsPbBr₃ nanocrystals undergo exchange of Pb²⁺ with Au(I)/Au(III) to form double perovskite Cs₂Au₂Br₆. When excited, a majority of the charge carriers undergo quick recombination in contrast to long-lived charge carries of excited CsPbBr₃ nanocrystals. This metal ion exchange process is reversible as one can regenerate CsPbBr₃ by adding excess PbBr₂ to the suspension. Interestingly, when subjected to visible light irradiation, Cs₂Au₂Br₆ nanocrystals eject reduced Au from the lattice as evidenced from the formation of larger gold nanoparticles. The presence of residual Pb²⁺ ions in the suspension restores the original CsPbBr₃ composition. The results presented here provide insight into the dynamic nature of Au within the perovskite lattice under both chemical and light stimuli.

Chemical Potential Diagram Guided Rational Tuning of Electrical Properties: A Case Study of CsPbBr3 for X-ray Detection

Controlling the carrier polarity and concentration underlies most electronic and optoelectronic devices. However, for the intensively studied lead halide perovskites, the doping tunability is inefficient. In this work, taking CsPbBr₃ as an example, it is revealed that the coexistence of metallic Pb or CsBr₃ /Br₂ , rather than the precursor ratio, can provide Pb-rich/Br-poor or Br-rich/Pb-poor chemical conditions, enabling the tunability of electrical properties from weak n-type, intrinsic, to moderate p-type. Experimentally, under Br₂ -exposure treatment, a shift of the Fermi level as large as 1.00 eV is achieved, which is one of the highest value among all kinds of doping methods. The X-ray detector based on the intrinsic CsPbBr₃ exhibits excellent performance, with a negligible dark-current drift of 7.1 × 10^-4 nA cm^-1 s^-1 V^-1 , a low detection limit of 103.6 nGy_air s^-1 , and a high sensitivity of 9085 μC Gy_air ^-1 cm^-2 . This work provides a critical understanding and guidance for tuning the electrical properties of lead halide perovskites, which establishes good foundations for achieving intrinsic perovskite semiconductors and also constructing potential homojunction devices.

Formamidinium Perovskitizers and Aromatic Spacers Synergistically Building Bilayer Dion-Jacobson Perovskite Photoelectric Bulk Crystals

Two-dimensional (2D) multilayer Dion-Jacobson (DJ) phase organic inorganic hybrid perovskites (OIHPs) have attracted extensive research attention due to the high stability and excellent charge-transport properties in the optoelectronic field. However, the synthesis of 2D multilayer DJ OIHPs is still very challenging. Until now, only few multilayer DJ perovskites have been reported and most of them are based on volatile methylamine (MA) cations. Compared with MA-based OIHPs, the OIHPs constructed with formamidinium (FA) as perovskitizers not only improve the stability but also extend the light absorption range. Meanwhile, the introducing aromatic diamines as spacers could promote the electron-hole separation in such DJ hybrids. However, the DJ OIHP bulk single crystal constructed by using the advantages of FA as perovskitizers and aromatic diamines as spacers is still blank. Herein, we integrate the properties of organic cations and inorganic skeletons at a molecular-scale to construct a broadband-responsive 2D bilayer DJ perovskite (3AMPY)(FA)Pb₂I₇ [3AMPY = 3-(aminomethyl)pyridinium], which shows a fascinating detectivity from X-ray (5.23 × 10⁴ μC Gy_air^-1 cm^-2 at 200 V bias) and visible light (6 × 10¹² jones at 637 nm) to the near-infrared region (2.6 × 10⁹ jones at 780 nm). After an in-depth analysis of structure and optical properties, we found that the distortion degree of Pb-I-Pb bond angles between adjacent PbI₆ octahedra plays a crucial role on optical properties; on the other hand, the interlayer spacer cations (3AMPY) and intralayer perovskitizers (FA) mutual participate in the contribution of the conduction band, making (3AMPY)(FA)Pb₂I₇ have a narrow optical band gap of 1.54 eV. Such a 2D perovskite material with a wide spectra response will be the preferred choice for photodetection under complex conditions.

A Universal Cosolvent Evaporation Strategy Enables Direct Printing of Perovskite Single Crystals for Optoelectronic Device Applications

Solution-processed metal halide perovskite (MHP) single crystals (SCs) are in high demand for a growing number of printed electronic applications due to their superior optoelectronic properties compared to polycrystalline thin films. There is an urgent need to make SC fabrication facile, scalable, and compatible with the printed electronic manufacturing infrastructure. Here, a universal cosolvent evaporation (CSE) strategy is presented by which perovskite SCs and arrays are produced directly on substrates via printing and coating methods within minutes at room temperature from drying droplets. The CSE strategy successfully guides the supersaturation via controlled drying of droplets to suppress all crystallization pathways but one, and is shown to produce SCs of a wide variety of 3D, 2D, and mixed-cation/halide perovskites with consistency. This approach works with commonly used precursors and solvents, making it universal. Importantly, the SC consumes the precursor in the droplet, which enables the large-scale fabrication of SC arrays with minimal residue. Direct on-chip fabrication of 3D and 2D perovskite photodetector devices with outstanding performance is demonstrated. The approach shows that any MHP SC can now be manufactured on substrates using precision printing and scalable, high-throughput coating methods.

Metal Halide Perovskites Demonstrate Radiation Hardness and Defect Healing in Vacuum

Herein, we subject formamidinium lead iodide films to oxygen-containing gases (flowing O₂ or free diffusion of lab atmosphere), inert gases (flowing He, Ar, or N₂), and vacuum. Our films are irradiated by Cu Kα X-rays and held at 75 °C while X-ray diffraction is recorded. Under all gas conditions, we observe a reproducible 1.1 ± 0.5 ų perovskite lattice contraction from an initial unit cell volume of 256.5 ± 0.8 ų concurrent with continuous perovskite loss and lead iodide growth. Oxygen-containing gases increase the reaction rates without materially altering perovskite structural changes. Under the same temperature and irradiation conditions in vacuo, a self-healing reaction is observed, exhibited by a reproducible (0.9 ± 0.3 ų) lattice expansion and stabilization of the perovskite. Interactions between the perovskite, defects, and minority phases are simulated by generalized gradient approximation Perdew-Burke-Ernzerhof (GGA-PBE) density functional theory. Lattice contraction indicates an increase in the concentration of Schottky defects─pairs of formamidinium and iodine vacancies. Under irradiation in every atmospheric condition, a solid solution of Schottky defects with a concentration of several percent diffuses and precipitates forming lead iodide and consuming the defects. In the presence of ionized gases, this framework is modified to include the continual loss of formamidinium and iodine ions from the perovskite forming Schottky defects.

Positive Effects of a Perovskite Film on the Radioluminescence Properties of a ZnO:Ga Crystal Scintillator

To improve the radioluminescence (RL) performance of ZnO:Ga (GZO) crystal scintillators and overcome the challenge of their self-absorption, we proposed a two-layer composite scintillator consisting of a GZO wafer and a 70 nm lead halide perovskite film(CsPbBr₃, CH₃NH₃PbBr₃). The effects of the perovskite film on the RL properties were studied. The results showed that the perovskite quantum dot film substantially changed the RL spectrum of GZO and prevented self-absorption. The RL of the samples were enhanced by 66% to 151% through the photoluminescence (PL) of the perovskite film, while the energy-resolving power and spatial-resolving power were maintained at the same level as that of GZO image converters. The present experiments and discussions confirmed that the perovskite film improved the RL, and this study suggests a new wavelength regulation method among scintillators, converters, and back-end optical devices. The applications of perovskites in the field of radiation detection and imaging have been extended.

Unveiling the new function of uranyl molecular clusters as fluorometric sensors for UV and X-ray dosimetry

Simple synthetic modulation based on uranyl acetate and phenanthroline has resulted in two uranyl clusters (1 and 2) with different topologies and nuclearities. Notably, the dimeric complex exhibits distinct luminescence quenching upon UV and X-ray irradiation with detection limits of 4.30 × 10^-6 J and 0.32 Gy, respectively. To advance the practical application, 1 was further fabricated with polyvinylidene fluoride into a flexible strip as a UV and X-ray indicator.

All-inorganic perovskite nanocrystals: next-generation scintillation materials for high-resolution X-ray imaging

With super strong penetrability, high-energy X-rays can be applied to probe the inner structure of target objects under nondestructive situations. Scintillation materials can down-convert X-rays into visible light, enabling the reception of photon signals and photoelectric conversion by common sensing arrays such as photomultiplier tubes and amorphous-Si photodiode matrixes. All-inorganic perovskite nanocrystals are emerging photovoltaic and scintillation materials, with tremendous light-conversion efficiency and tunable luminous properties, exhibiting great potential for high-quality X-ray imaging. Recent advancements in nanotechnology further accelerate the performance improvement of scintillation materials. In this review, we will provide a comprehensive overview of novel all-inorganic perovskite nano-scintillators in terms of potential applications in low-dose X-ray medical radiography. Compared with conventional scintillators, the merits/drawbacks, challenges, and scintillation performance control will be the focus of this article.

Thermally activated delayed fluorescence (TADF) organic molecules for efficient X-ray scintillation and imaging

X-ray detection, which plays an important role in medical and industrial fields, usually relies on inorganic scintillators to convert X-rays to visible photons; although several high-quantum-yield fluorescent molecules have been tested as scintillators, they are generally less efficient. High-energy radiation can ionize molecules and create secondary electrons and ions. As a result, a high fraction of triplet states is generated, which act as scintillation loss channels. Here we found that X-ray-induced triplet excitons can be exploited for emission through very rapid, thermally activated up-conversion. We report scintillators based on three thermally activated delayed fluorescence molecules with different emission bands, which showed significantly higher efficiency than conventional anthracene-based scintillators. X-ray imaging with 16.6 line pairs mm^-1 resolution was also demonstrated. These results highlight the importance of efficient and prompt harvesting of triplet excitons for efficient X-ray scintillation and radiation detection.

Further Advancement of Perovskite Single Crystals

Halide perovskite (HP) single crystals (SCs) are garnering extensive attention as active materials to substitute polycrystalline counterparts in solar cells, photodiodes, and photodetectors, etc. Nevertheless, the large thickness and defect-rich surface results in severe carrier recombination and becomes the major bottleneck for augmented performance. In this perspective, we are looking forward to explaining in detail why the SCs hardly unleash their engrossing potential and introduce two parallel paths for further advancement. First is the modification of thick SCs by reducing the prepared thickness or surface passivation. Second is the large thickness that is conducive to the sufficient absorption of high-energy rays with strong penetrating ability and is beneficial to the thermoelectric effect due to the ultralow thermal conductivity of HPs. These applications provide a roundabout strategy to exploit freestanding SCs with a large thickness. Herein, direct modification and application of thick SCs are systematically introduced, expecting to give rise to the prosperity of HP SCs.

Counterdiffusion-in-gel growth of high optical and crystal quality MAPbX3 (MA = CH3NH3+, X = I−, Br−) lead-halide perovskite single crystals

Halide perovskites are promising semiconductor materials for optoelectronics.

Luminometric dosimetry of X-ray radiation by a zwitterionic uranium coordination polymer

A novel X-ray dosimeter based on a uranium coordination polymer has been developed by the judicious synergy between the luminescent uranyl centres and zwitterionic tritopic ligands.

Reveal the Humidity Effect on the Phase Pure CsPbBr3 Single Crystals Formation at Room Temperature and Its Application for Ultrahigh Sensitive X-Ray Detector

Generally, growing phase pure CsPbBr₃ single crystals is challenging, and CsPb₂ Br₅ or Cs₄ PbBr₆ by-products are usually formed due to the different solubilities of CsBr and PbBr₂ in the single solvent. Herein, the growth of high-quality phase pure CsPbBr₃ perovskite single crystals at room temperature by a humidity controlled solvent evaporation method is reported first. Meanwhile, the room temperature phase transition process from three dimensional (3D) cubic CsPbBr₃ to two dimensional (2D) layered tetragonal CsPb₂ Br₅ and the detailed mechanism induced by humidity are revealed. Moreover, compared with the organic-inorganic perovskite, the prepared CsPbBr₃ single crystals are much more stable under high humidity, which satisfies the long-term working conditions of X-ray detectors. The X-ray detectors based on CsPbBr₃ single crystals show a high sensitivity and a low detection limit of 1.89 μGy_air s^-1 , all of which meet the needs of medical diagnosis.

Hollow MoS2-supported MAPbI3 composites for effective photocatalytic hydrogen evolution

A facile and effective electrostatic adsorption method was developed to fabricate H-MoS2/MAPbI3 composites, which improved hydrogen evolution activity and stability.

Template directed perovskite X-ray detectors towards low ionic migration and low interpixel cross talking

The metal halide perovskites exhibit excellent performance as the direct X-ray detectors owing to their strong absorption capability, long carrier lifetime and diffusion length, radiation ruggedness, etc. For imaging applications, the ionic migration of perovskites and charge sharing effect between the adjacent pixels have a significantly negative impact on the spatial resolution. Herein, for the first time, the porous anodic aluminum oxides (AAO) have been used as a template to grow the CsPbBr2I thick film for the direct X-ray detection. Benefiting from the oxygen passivation effect, the activation energy for ionic migration has been observed to increase to 0.701 eV, whereas the dark current drift (1.01 × 10-5 nA cm-1s-1V-1) is one to two orders of magnitude lower than the other lead halide perovskite single crystals and films. Moreover, the AAO insulating wall effectively blocks the charge diffusion effect across a pixel pitch of 10 μm. Overall, the findings reported in this study open a new route for reducing the ionic migration and pixel crosstalk, thus, bringing the perovskite X-ray detectors close to the practical applications.

Lead-Dominated Hyperfine Interaction Impacting the Carrier Spin Dynamics in Halide Perovskites

The outstanding optical quality of lead halide perovskites inspires studies of their potential for the optical control of carrier spins as pursued in other materials. Entering largely uncharted territory, time-resolved pump-probe Kerr rotation is used to explore the coherent spin dynamics of electrons and holes in bulk formamidinium caesium lead iodine bromide (FA_0.9 Cs_0.1 PbI_2.8 Br_0.2 ) and to determine key parameters characterizing interactions of their spins, such as the g-factors and relaxation times. The demonstrated long spin dynamics and narrow g-factor distribution prove the perovskites as promising competitors for conventional semiconductors in spintronics. The dynamic nuclear polarization via spin-oriented holes is realized and the identification of the lead (²⁰⁷ Pb) isotope in optically detected nuclear magnetic resonance proves that the hole-nuclei interaction is dominated by the lead ions. A detailed theoretical analysis accounting for the specifics of the lead halide perovskite materials allows the evaluation of the underlying hyperfine interaction constants, both for electrons and holes. Recombination and spin dynamics evidence that at low temperatures, photogenerated electrons and holes are localized at different regions of the perovskite crystal, resulting in their long lifetimes up to 44 μs. The findings form the base for the tailored development of spin-optoelectronic applications for the large family of lead halide perovskites and their nanostructures.

Applications of Halide Perovskites in X-ray Detection and Imaging

X-ray detection plays an extremely significant function in medical diagnosis, nondestructive testing, safety testing, scientific research, environmental monitoring and other practical applications. However, conventional inorganic semiconductors such as amorphous selenium,...

Decreasing Structural Dimensionality of Double Perovskites for Phase Stabilization toward Efficient X-ray Detection

Halide double perovskites have attracted substantial attention for optoelectronic applications owing to their low toxicity and high stability. However, double perovskites have strict requirements in terms of the halide type, thus rendering many of their properties unchangeable, including the band gap, atomic number, and carrier transport. By introducing long-chain organic amines, the chloride site of double perovskites can be completely replaced by bromide. Using this strategy, two dimensions silver-indium-bromide double perovskites (PEA)₄AgInBr₈ and (i-BA)₄AgInBr₈ were successfully synthesized [(PEA)⁺ = C₆H₅(CH₂)₂NH₃⁺, (i-BA)⁺ = CH(CH₃)₂CH₂NH₃⁺]. Density functional theory calculations and spectroscopy characterizations were performed to unveil the semiconducting behaviors and photoluminescence properties of the title compounds. Electrical characterization confirms their good carrier-transport property (μτ product: 2.0 × 10^-3 cm² V^-1) and low dark current. Moreover, the presence of heavy atoms, together with the ultrastable baseline contributes to a high X-ray detection sensitivity (185 μC Gy_air^-1 cm^-2), greater than that of most previous double-perovskite detectors. Our work lays the foundation for broadening the family of potential double perovskites, creating a new path for the realization of long-sought perovskites with low toxicity and high stability that retain good optoelectronic performance.

In Situ Epitaxial Growth of Centimeter-Sized Lead-Free (BA)2CsAgBiBr7/Cs2AgBiBr6 Heterocrystals for Self-Driven X-ray Detection

Halide perovskite heterocrystals, composed of distinct perovskite single crystals, have generated great interest for both fundamental research and applied device designs. One of the key advantages of using such a heterocrystal is its built-in electric potential, which enhances charge transport and suppresses the noise in the solid-state devices. On the basis of this strategy, high-performance optoelectronic devices (e.g., X-ray detectors) have been successfully demonstrated. However, the toxicity of metal cations (Pb) in those reported heterocrystals hinders their wider applications. Thus, developing lead-free halide perovskite heterocrystals is significant but remains highly challenging. Here, we report a solution-processed in situ heteroepitaxial approach that enables us to create the first lead-free halide perovskite heterocrystal, (BA)₂CsAgBiBr₇/Cs₂AgBiBr₆(BA = n-butylammonium), with dimensions of up to 10 × 7 × 6 mm³. The as-grown heterocrystals have high crystalline quality and present near atomically sharp interfaces. More excitingly, the (BA)₂CsAgBiBr₇/Cs₂AgBiBr₆ heterogeneous integration allows the formation of a built-in electric potential in the junction, which triggers spontaneous charge separation/transport. Consequently, X-ray detectors using the heterocrystals can operate in a self-driven mode and exhibit an impressive sensitivity (206 μC Gy^-1 cm^-2) superior to that of the pristine Cs₂AgBiBr₆ crystal detectors, an ultralow dark current, and operational stability. Our findings provide the first demonstration of lead-free halide perovskite heterocrystals and may open up opportunities for a host of sustainable and miniaturized perovskite optoelectronic devices.

X-Ray-Induced Modification of the Photophysical Properties of MAPbBr3 Single Crystals

Methylammonium lead tribromide (MAPbBr₃) perovskite single crystals demonstrate to be excellent direct X-ray and gamma-ray detectors with outstanding sensitivity and low limit of detection. Despite this, thorough studies on the photophysical effects of exposure to high doses of ionizing radiation on this material are still lacking. In this work, we present our findings regarding the effects of controlled X-ray irradiation on the optoelectronic properties of MAPbBr₃ single crystals. Irradiation is carried out in air with an imaging X-ray tube, simulating real-life application in a medical facility. By means of surface photovoltage spectroscopy, we find that X-ray exposure quenches free excitons in the material and introduces new bound excitonic species. Despite this drastic effect, the crystals recover after 1 week of storage in dark and low humidity conditions. By means of X-ray photoelectron spectroscopy, we find that the origin of the new bound excitonic species is the formation of bromine vacancies, leading to local changes in the dielectric response of the material. The recovery effect is attributed to vacancy filling by atmospheric oxygen and water.

Amorphous NiCoB-coupled MAPbI3 for efficient photocatalytic hydrogen evolution

It was thought that the organic-inorganic hybrid perovskite MAPbI₃ could be used to collect visible light for the photocatalytic hydrogen evolution reaction (HER). However, its ability to generate H₂ is limited. Herein, we synthesized amorphous NiCoB through a redox method and coupled it with MAPbI₃ to form the NiCoB/MAPbI₃ composite photocatalyst by electrostatic self-assembly. 30% NiCoB/MAPbI₃ exhibited the maximum H₂ generation yield of 2625.57 μmol g^-1 h^-1, which was approximately 114 fold that of pristine MAPbI₃ and much better than that of Pt/MAPbI₃. In addition to the excellent photocatalytic HER capability, NiCoB/MAPbI₃ maintained good stability in the 24 h cycling hydrogen evolution experiment. The photoelectric analysis showed that NiCoB as a cocatalyst could realize rapid charge separation. This work can offer a reference for the construction of efficient photocatalysts based on lead halide perovskites.

Polymerized Hybrid Perovskites with Enhanced Stability, Flexibility, and Lattice Rigidity

The intrinsic soft lattice nature of organometal halide perovskites (OHPs) makes them very tolerant to defects and ideal candidates for solution-processed optoelectronic devices. However, the soft lattice results in low stability towards external stresses such as heating and humidity, high density of phonons and strong electron-phonon coupling (EPC). Here, it is demonstrated that the OHPs with unsaturated 4-vinylbenzylammonium (VBA) as organoammonium cations can be polymerized without damaging the perovskite structure and its tolerance to defects. The polymerized perovskites show enhanced stability and flexibility compared to regular three-dimensional and two-dimensional (2D) perovskites. Furthermore, the polymerized 4-vinylbenzylammonium group improves perovskite lattice rigidity substantially, resulting in a reduced non-radiative recombination rate because of suppressed electron-phonon coupling, and enhanced carrier mobility because of suppressed phonon scattering. 2D polymerized perovskite light-emitting diodes (PeLEDs) with strong electroluminescence at room temperature, and quasi-2D PeLEDs with an external quantum efficiency (EQE) of 23.2% and enhanced operation stability are demonstrated. The work has opened a new way of enhancing the intrinsic stability and optoelectronic properties of OHPs.

Elimination of Interfacial-Electrochemical-Reaction-Induced Polarization in Perovskite Single Crystals for Ultrasensitive and Stable X-Ray Detector Arrays

Organic-inorganic halide perovskites have exhibited bright prospects in high-sensitivity X-ray detection. However, they generally suffer from the severe field-driven polarization issue that remarkably deteriorates the detection performance. Here, it is demonstrated that the interfacial electrochemical reaction between Au electrodes and halogen in MAPbI₃ single crystals (SCs) is the major source of the dark current polarization in the metal-semiconductor-metal (MSM)-structured perovskite X-ray detectors at the initial stage of biasing. By introducing the p- and n-type charge transport layers to isolate the electrodes from contacting the SC surface, the polarization is fully eliminated under a large electric field up to 1000 V cm^-1 . Moreover, the resultant lateral p-i-n heterojunction suppresses the dark current of the devices by nearly 3 orders of magnitude as compared to the MSM counterparts and therefore enables a high sensitivity of 5.2 × 10⁶  µC Gy^-1 _air cm^-2 and a record low X-ray detection limit down to 0.1 nGy_air s^-1 . The excellent biasing stability and sensitivity of the devices allow to prepare the linear detector arrays for X-ray imaging applications.

0D Perovskites: Unique Properties, Synthesis, and Their Applications

0D perovskites have gained much attention in recent years due to their fascinating properties derived from their peculiar structure with isolated metal halide octahedra or metal halide clusters. However, the systematic discussion on the crystal and electronic structure of 0D perovskites to further understand their photophysical characteristics and the comprehensive overview of 0D perovskites for their further applications are still lacking. In this review, the unique crystal and electronic structure of 0D perovskites and their diverse properties are comprehensively analyzed, including large bandgaps, high exciton binding energy, and largely Stokes-shifted broadband emissions from self-trapped excitons. Furthermore, the photoluminescence regulation are discussed. Then, the various synthetic methods for 0D perovskite single crystals, nanocrystals, and thin films are comprehensively summarized. Finally, the emerging applications of 0D perovskites to light-emitting diodes, solar cells, detectors, and some others are illustrated, and the outlook on future research in the field is also provided.