Metal Halide Nanocrystals@Silica Aerogel Composite with Enhanced Dispersion Stability and Light Output for Efficient X-Ray Imaging in Harsh Environment.

Metal halide nanocrystals (MHNCs) embedded in a polymer matrix as flexible X-ray detector screens is an effective strategy with the advantages of low cost, facile preparation, and large area flexibility. However, MHNCs easily aggregate during preparation, recombination, under mechanical force, storage, or high operating temperature. Meanwhile, it shows an unmatched refractive index with polymer, resulting in low light yield. The related stability and properties of the device remain a huge unrevealed challenge. Herein, a composite screen (CZBM@AG-PS) by integrating MHNCs (Cs2ZnBr4: Mn2+ as an example) into silica aerogel (AG) and embedded in polystyrene (PS) is successfully developed. Further characterization points to the high porosity AG template that can effectively improve the dispersion of MHNCs in polymer detector screens, essentially decreasing nonradiative transition, Rayleigh scattering, and performance aging induced by aggregation in harsh environments. Furthermore, the higher light output and lower optical crosstalk are also achieved by a novel light propagation path based on the MHNCs/AG and AG/PS interfaces. Finally, the optimized CZBM@AG-PS screen shows much enhanced light yield, spatial resolution, and temperature stability. Significantly, the strategy is proven universal by the performance tests of other MHNCs embedded composite films for ultra-stable and efficient X-ray imaging.

Organic Cation Modulation in Manganese Halides to Optimize Crystallization Process and X-Ray Response Toward Large-Area Scintillator Screen.

Manganese halides are one of the most potential candidates for large-area flat-panel detection owing to their biological safety and all-solution preparation. However, reducing photon scattering and enhancing the efficient luminescence of scintillator screens remains a challenge due to their uncontrollable crystallization and serious nonradiative recombination. Herein, an organic cation modulation is reported to control the crystallization process and enhance the luminescence properties of manganese halides. Given the industrial requirements of the X-ray flat-panel detector, the large-area A2MnBr4 screen (900 cm2) with excellent uniformity is blade-coated at 60 °C. Theoretical calculations and in situ measurements reveal that organic cations with larger steric hindrance can slow down the crystallization of the screen, thus neatening the crystal arrangement and reducing the photon scattering. Moreover, larger steric hindrance can also endow the material with higher exciton binding energy, which is beneficial for restraining nonradiative recombination. Therefore, the BPP2MnBr4 (BPP = C25H22P+) screen with larger steric hindrance exhibits a superior spatial resolution (>20 lp mm-1) and ultra-low detection limit (< 250 nGyair s-1). This is the first time steric hindrance modulation is used in blade-coated scintillator screens, and it believes this study will provide some guidance for the development of high-performance manganese halide 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.

Metal-Free Perovskites for X-Ray Detection.

Metal-free perovskites are a promising class of materials for X-ray detection due to their unique structural, optical, and electrical properties. Here, we first delve into the stoichiometry and geometric argument of metal-free perovskites. Followed, the alternative A/B/X ions and hydrogen-bonding are clearly introduced to further optimize the materials' stability and properties. Finally, we provide a comprehensive overview of their potential applications for flexible X-ray images and prospects for metal-free perovskite development. In conclusion, metal-free perovskite is a promising material for X-ray detection. Its stoichiometric and geometric parameters, ion, and hydrogen bond selection, and application prospects are worthy of further study.

Graphdiyne-polymer composites for a hybrid bound-state pulsed fiber laser.

In this paper, the graphdiyne (GDY)-polymethyl methacrylate (PMMA) films are prepared by a spin-coating method. The PMMA films have the function of isolating GDY from air and protecting the GDY from mechanical damage. The nonlinear optical properties of GDY-PMMA films are probed experimentally. The nonlinear optical responses of GDY-PMMA films with a modulation depth of ∼4.94% and saturated magnetization of ∼0.3M W/c m 2 are proved. When the GDY-PMMA films are applied to an erbium-doped hybrid passively mode-locked fiber laser (saturable absorber), the bound-state solitons, which are also called soliton molecules, can be obtained. The soliton molecule has a time separation of 13.31 ps, and the spectral modulation period of 0.58 nm. Along with the pump power increase, the separation of bound-state pulses becomes larger. When the pump power is fixed, stable bound solitons can be observed without any degeneration for more than 4.5 h. It is demonstrated that GDY-PMMA films have excellent nonlinear optical performance in a near-infrared regime, which we believe can be a novel type of photonics instrument and has a number of properties that are potentially promising in the ultrafast properties of laser.

Hydrogen Bonds Strengthened Metal-Free Perovskite for Degradable X-ray Detector with Enhanced Stability, Flexibility and Sensitivity.

Metal-free perovskites (MFPs) with flexible and degradable properties have been adopted in flexible X-ray detection. For now, figuring out the key factors between structure and device performance are critical to guide the design of MFPs. Herein, MPAZE-NH4 I3 ⋅ H2 O was first designed and synthesized with improved structural stability and device performance. Through theoretical calculations, the introducing methyl group benefits modulating tolerance factor, increases dipole moment and strengthens hydrogen bonds. Meanwhile, H2 O increases the hydrogen bond formation sites and synergistically realizes the band nature modulation, ionic migration inhibition and structural stiffness optimization. Spectra analysis also proves that the improved electron-phonon coupling and carrier recombination lifetime contribute to enhanced performance. Finally, a flexible and degradable X-ray detector was fabricated with the highest sensitivity of 740.8 µC Gyair -1 cm-2 and low detection limit (0.14 nGyair s-1 ).

Vertically Oriented Porous PET as Template to Integrated Metal Halide for High-Performance Large-Area and Ultra-Flexible X-Ray Detector.

High-performance X-ray detectors have immense potential in medical and security inspections. However, the current X-ray detectors are limited in flexible, high-spatial-resolution large-scale detection, and integration for imaging. Here, nuclear track-etched porous polyethylene terephthalate (PET) is developed as the template for preparing uniform, large-area (≥105 cm2 ), and flexible metal halide (MH)-based X-ray detectors. Adjustable high-density vertically oriented porous PET with adjustable thickness can provide proper physical support for flexible thick absorption film, thus improving X-ray absorption ability with excellent bending stability. Moreover, vertical channels can block the ion migration, lateral charge diffusion, and water/oxygen attacks, increasing activation energy for ionic transport, charge collection rate of electrodes, and environmental stability. Hence, the related detectors eventually obtain large sensitivity (6722 µC Gyair -1 cm-2 ), low detection limit (1.87 nGyair s-1 ), and high spatial resolution (5.17 lp mm-1 ) compared to the detectors without porous PET template. Meanwhile, the device shows no degradation after storage or working under various thermal attacks. MH-filled-PET is also monolithically integrated on the bottom circuit with different MHs and it is applied to single-pixel mode and fast linear-array imaging in a broad range of X-rays photon energy (20 to 160 keV).

Ordered Element Distributed C3 N Quantum Dots Manipulated Crystallization Kinetics for 2D CsPbI3 Solar Cells with Ultra-High Performance.

Two-dimensional (2D) CsPbI3 is developed to conquer the phase-stability problem of CsPbI3 by introducing bulky organic cations to produce a steric hindrance effect. However, organic cations also inevitably increase the formation energy and difficulty in crystallization kinetics regulation. Such poor crystallization process modulation of 2D CsPbI3 leads to disordered phase-arrangement, which impedes the transport of photo-generated carriers and worsens device performance. Herein, a type of C3 N quantum dots (QDs) with ordered carbon and nitrogen atoms to manipulate the crystallization process of 2D CsPbI3 for improving the crystallization pathway, phase-arrangement and morphology, is introduced. Combination analyses of theoretical simulation, morphology regulation and femtosecond transient absorption (fs-TA) characterization, show that the C3 N QDs induce the formation of electron-rich regions to adsorb bulky organic cations and provide nucleation sites to realize a bi-directional crystallization process. Meanwhile, the quality of 2D CsPbI3 film is improved with lower trap density, higher surface potential, and compact morphology. As a result, the power conversion efficiency (PCE) of the optimized device (n = 5) boosts to an ultra-high value of 15.63% with strengthened environmental stability. Moreover, the simple C3 N QDs insertion method shows good universality to other bulky organic cations of Ruddlesden-Popper and Dion-Jacobson, providing a good modulation strategy for other optoelectronic devices.

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 Gyair -1 cm-2 , ultra-low detection limit of 0.19 µGyair -1 s-1 and superior spatial resolution of 5.0 lp mm-1 .

Origin, Influence, and Countermeasures of Defects in Perovskite Solar Cells.

Defects are considered to be one of the most significant factors that compromise the power conversion efficiencies and long-term stability of perovskite solar cells. Therefore, it is urgent to have a profound understanding of their formation and influence mechanism, so as to take corresponding measures to suppress or even completely eliminate their adverse effects on device performance. Herein, the possible origins of the defects in metal halide perovskite films and their impacts on the device performance are analyzed, and then various methods to reduce defect density are introduced in detail. Starting from the internal and interfacial aspects of the metal halide perovskite films, several ways to improve device performance and long-term stability including additive engineering, surface passivation, and other physical treatments (annealing engineering), etc., are further elaborated. Finally, the further understanding of defects and the development trend of passivation strategies are prospected.

Optical Management with Nanoparticles for a Light Conversion Efficiency Enhancement in Inorganic γ-CsPbI3 Solar Cells.

Recently, γ-CsPbI3 perovskite solar cells (PSCs) have shown potential applications in optoelectronic devices, due to their high thermal stability. However, the incomplete utilization of the solar spectra especially in the near-infrared (ca. 46%) range significantly limits the power conversion efficiency (PCE). Herein, core-shell-structured NaLuF4:Yb,Er@NaLuF4 upconversion nanoparticles (UCNPs) have been successfully synthesized and integrated into the hole transport layer for improving PCE in γ-CsPbI3 PSCs. Compared with the reference one, the short-circuit current density ( JSC) and PCE of the optimized device reached up to 19.17 mA/cm2 (18.81 mA/cm2) and 15.86% (15.51%), respectively. Actually, due to the ultralow photoluminescence quantum yield (PLQY, < 1%) obtained in UCNPs now, we proved the generally recognized upconversion effect of UCNPs in solar cells (adjusting the light absorption edge from the visible toward NIR range for extending the spectral absorption) was negligible. A further study found the UCNPs in the PSCs primarily served as scattering centers, which is beneficial to extend the sunlight optical path by combining with scattering and reflecting sunlight, leading to producing more photoelectric current. This study suggests a new insight into understanding the underlying mechanism of UCNPs in the PSCs and provides a promising strategy via light scattering effect to enhance the device performance.

All-Inorganic CsPbX3 Perovskite Solar Cells: Progress and Prospects.

Recently, lead halide-based perovskites have become one of the hottest topics in photovoltaic research because of their excellent optoelectronic properties. Among them, organic-inorganic hybrid perovskite solar cells (PSCs) have made very rapid progress with their power conversion efficiency (PCE) now at 23.7 %. However, the intrinsically unstable nature of these materials, particularly to moisture and heat, may be a problem for their long-term stability. Replacing the fragile organic group with more robust inorganic Cs+ cations forms the cesium lead halide system (CsPbX3 , X is halide) as all-inorganic perovskites which are much more thermally stable and often more stable to other factors. From the first report in 2015 to now, the PCE of CsPbX3 -based PSCs has abruptly increased from 2.9 % to 17.1 % with much enhanced stability. In this Review, we summarize the field up to now, propose solutions in terms of development bottlenecks, and attempt to boost further research in CsPbX3 PSCs.

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.

Surface Reconstruction for Efficient NiOx-Based Inverted Perovskite Solar Cells.

Functional agents are verified to efficiently enhance device performance of perovskite solar cells (PSCs) through surface engineering. However, the influence of intrinsic characteristics of molecules on final device performance is overlooked. Here, a surface reconstruction strategy is developed to enhance the efficiency of inverted PSCs by mitigating the adverse effects of lead chelation (LC) molecules. Bathocuproine (BCP) is chosen as the representative of LC molecules for its easy accessibility and outstanding optoelectronic properties. During this strategy, BCP molecules on perovskite surface are first dissolved in solvents and then captured specially by undercoordinated Pb2+ ions, preventing adverse n-type doping by the molecules themselves. In this case, the BCP molecule exhibits outstanding passivation effect on perovskite surface, which leads to an obviously increased open-circuit voltage (VOC). Therefore, a record power conversion efficiency of 25.64% for NiOx-based inverted PSCs is achieved, maintaining over 80% of initial efficiency after exposure to ambient condition for ≈1500 h.

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.

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.

Two-Dimensional Metal Halides for X-Ray Detection Applications.

Metal halide perovskites have recently emerged as promising candidates for the next generation of X-ray detectors due to their excellent optoelectronic properties. Especially, two-dimensional (2D) perovskites afford many distinct properties, including remarkable structural diversity, high generation energy, and balanced large exciton binding energy. With the advantages of 2D materials and perovskites, it successfully reduces the decomposition and phase transition of perovskite and effectively suppresses ion migration. Meanwhile, the existence of a high hydrophobic spacer can block water molecules, thus making 2D perovskite obtain excellent stability. All of these advantages have attracted much attention in the field of X-ray detection. This review introduces the classification of 2D halide perovskites, summarizes the synthesis technology and performance characteristics of 2D perovskite X-ray direct detector, and briefly discusses the application of 2D perovskite in scintillators. Finally, this review also emphasizes the key challenges faced by 2D perovskite X-ray detectors in practical application and presents our views on its future development.

PF6 - Pseudohalides Anion Based Metal-Free Perovskite Single Crystal for Stable X-Ray Detector to Attain Record Sensitivity.

Metal-free perovskites (MFPs) possess excellent photophysical properties of perovskites while avoiding the introduction of toxic metal ions and organic solvents, and have been expanded to X-ray detection. However, iodine-based high-performance MFPs are tended to oxidation, corrosion, and uncontrolled ion migration, resulting in poor material stability and device performance. Herein, the strongly electronegative PF6 - pseudohalide is used to fabricate the large-size MDABCO-NH4 (PF6 )3 (MDBACO = methyl-N'-diazabicyclo[2.2.2]octonium) single crystals (SCs) for solving the problems of iodine ions. After the introduction of PF6 - pseudohalides, the Coulomb interaction and hydrogen bonding strength are enhanced to alleviate the ion-migration and stability problems. Moreover, combined with theoretical calculations, PF6 - pseudohalides increase the ion-migration barrier, and affect the contribution of its components to the energy band for a broadening bandgap. Meanwhile, the improved physical properties, such as large activation energy of ionic migration, high resistivity, and low current drift, further expand its application in low-dose and sensitive X-ray detection. Finally, the X-ray detector based on MDABCO-NH4 (PF6 )3 SCs achieves a sensitivity of 2078 µC Gyair -1 cm-2 (highest among metal-free SCs-based detectors) and the lowest detectable dose rate (16.3 nGyair s-1 ). This work has expanded the selection of MFPs for X-ray detectors and somewhat advanced the development of high-performance devices.

Enhancement of Light and X-ray Charging in Persistent Luminescence Nanoparticle Scintillators Zn2SiO4:Mn2+, Yb3+, Li.

Persistent luminescence nanoparticle scintillators (PLNS) have been attempted for X-ray-induced photodynamic therapy (X-PDT) because persistent luminescence after ceasing radiation can make PLNS use less cumulative irradiation time and dose to generate the same amount of reactive oxygen species (ROS) compared with conventional scintillators to combat cancer cells. However, excessive surface defects in PLNS reduce the luminescence efficiency and quench the persistent luminescence, which is fatal to the efficacy of X-PDT. Herein, the PLNS of SiO2@Zn2SiO4:Mn2+, Yb3+, Li+ was designed by the energy trap engineering and synthesized by a simple template method, which has excellent X-ray and UV-excited persistent luminescence and continuously tunable emission spectra from 520 to 550 nm. Its luminescence intensity and afterglow time are more than 7 times that of the reported Zn2SiO4:Mn2+ used for X-PDT. By loading a Rose Bengal (RB) photosensitizer, an effective persistent energy transfer from the PLNS to photosensitizer is observed even after the removal of X-ray irradiation. The X-ray dose of nanoplatform SiO2@Zn2SiO4:Mn2+, Yb3+, Li+@RB in X-PDT of HeLa cancer cells was reduced to 0.18 Gy compared to the X-ray dose of 1.0 Gy for Zn2SiO4:Mn for X-PDT. This indicates that the Zn2SiO4:Mn2+, Yb3+, Li+ PLNS have great potential for X-PDT applications.

Copper-based metal halides for X-ray and photodetection.

Copper-based metal halides have become important materials in the field of X-ray and photodetection due to their excellent optical properties, good environmental stability and low toxicity. This review presents the progress of research on crystal structure/morphology, photophysics/optical properties and applications of copper-based metal halides. We also discuss the challenges of copper-based metal halides with a perspective of their future research directions.