A New Metal-Free Molecular Perovskite-Related Single Crystal with Quantum Wire Structure for High-Performance X-Ray Detection.

The family of metal-free molecular perovskites, an emerging novel class of eco-friendly semiconductor, welcomes a new member with a unique 1D hexagonal perovskite structure. Lowering dimensionality at molecular level is a facile strategy for crystal structure conversion, optoelectronic property regulation, and device performance optimization. Herein, the study reports the design, synthesis, packing structure, and photophysical properties of the 1D metal-free molecular perovskite-related single crystal, rac-3APD-NH4I3(rac-3APD= racemic-3-Aminopiperidinium), that features a quantum wire structure formed by infinite chains of face-sharing NH4I6 octahedra, enabling strong quantum confinement with strongly self-trapped excited (STE) states to give efficient warm orange emission with a photoluminescence quantum yield (PLQY) as high as ≈41.6%. The study accordingly unveils its photoexcited carrier dynamics: rac-3APD-NH4I3 relaxes to STE state with a short lifetime of 10 ps but decays to ground state by emitting photons with a relatively longer lifetime of 560 ps. Additionally, strong quantum confinement effect is conducive to charge transport along the octahedral channels that enables the co-planar single-crystal X-ray detectors to achieve a sensitivity as high as 1556 µC Gyair -1 cm-2. This work demonstrates the first case of photoluminescence mechanism and photophysical dynamics of 1D metal-free perovskite-related semiconductor, as well as the promise for high-performance X-ray detector.

Low Dimensional, Metal-Free, Hydrazinium Halide Perovskite-Related Single Crystals and Their Use as X-Ray Detectors.

Metal-free halide perovskites (MFHaPs) have garnered significant attention in recent years due to their desirable properties, such as low toxicity, light weight, chemical versatility, and potential for optoelectronics. MFHaPs with the formula A2+ B+ X-3 (where A is a large organic divalent cation, B+ is typically NH4 + , and X is a halide) have been studied extensively, but few studies have examined alternative cations at the B position. This paper reports the synthesis of three MFHaP-related single crystals, DABCO-N2 H5 -X3 (DABCO = N-N-diazabicyclo[2.2.2]octonium, X = Br and I) and (DABCO)3 -N2 H5 (NH4 )2 Cl9 , which feature hydrazinium (N2 H5 ) at the B position. The crystals have a perovskite-like, one-dimensional, edge-connected structure and exhibit optical and band structure properties. The crystals were then tested as X-ray detectors, where they showed excellent photoresponsivity, stability, and low background noise, owing to the large semi-gap that dictates long lifetimes. The detectors exhibited sensitivity as high as 1143 ± 10 µC Gyair -1 cm-2 and a low detection limit of 2.68 µGy s-1 at 10 V. The researchers suggest that the stronger hydrogen bonding in N2 H5 + compounds compared to NH4 + MFHaPs may contribute to the detectors' enhanced stability.

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 Gyair-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.

HARNU-Net: Hierarchical Attention Residual Nested U-Net for Change Detection in Remote Sensing Images.

Change detection (CD) is a particularly important task in the field of remote sensing image processing. It is of practical importance for people when making decisions about transitional situations on the Earth's surface. The existing CD methods focus on the design of feature extraction network, ignoring the strategy fusion and attention enhancement of the extracted features, which will lead to the problems of incomplete boundary of changed area and missing detection of small targets in the final output change map. To overcome the above problems, we proposed a hierarchical attention residual nested U-Net (HARNU-Net) for remote sensing image CD. First, the backbone network is composed of a Siamese network and nested U-Net. We remold the convolution block in nested U-Net and proposed ACON-Relu residual convolution block (A-R), which reduces the missed detection rate of the backbone network in small change areas. Second, this paper proposed the adjacent feature fusion module (AFFM). Based on the adjacency fusion strategy, the module effectively integrates the details and semantic information of multi-level features, so as to realize the feature complementarity and spatial mutual enhancement between adjacent features. Finally, the hierarchical attention residual module (HARM) is proposed, which locally filters and enhances the features in a more fine-grained space to output a much better change map. Adequate experiments on three challenging benchmark public datasets, CDD, LEVIR-CD and BCDD, show that our method outperforms several other state-of-the-art methods and performs excellent in F1, IOU and visual image quality.

Molecular Doping of Flexible Lead-Free Perovskite-Polymer Thick Membranes for High-Performance X-Ray Detection.

X-ray detectors have broad applications in medicine and industry. Although flexible lead-free perovskite films are competitive because of their lightweight and low toxicity, they are less efficient due to low charge transport. Herein, we report low-toxicity, flexible X-ray detectors based on p-type doped MA3 Bi2 I9 (MA=methylammonium) perovskite-filled membranes (PFMs). Strong coordination between dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and MA3 Bi2 I9 and the establishment of charge-transfer complex (CPX) improved the conductivity by four times. The flexible X-ray detector achieved a high sensitivity of 2065 µC Gyair -1 cm-2 and an ultra-low detection limit of 2.71 nGyair s-1 , which is among the highest values in all environmentally friendly flexible X-ray detectors. Importantly, the PFMs retained excellent charge transport under mechanical stress. All of those make flexible MA3 Bi2 I9 membranes more competitive as next-generation X-ray detection.

Distributed time-varying optimization control protocol for multi-agent systems via finite-time consensus approach.

This paper addresses a distributed time-varying optimization problem with inequality constraints based on multi-agent systems over switching communication graphs. To reduce the influence of time-varying inequality constraints, an exact penalty method and smoothing technique are employed. Then, a Hessian-based distributed control protocol is presented to seek the time-varying optimal solution of the distributed time-varying optimization problem by virtue of only local information and interaction. It is shown that all agents not only achieve finite-time consensus but also track the time-varying global optimal target eventually. Compared with the existing distributed optimization protocols, the proposed control protocol is suitable for more general distributed time-varying optimization problems and enjoys high-efficiency convergence. Finally, numerical examples and experiment on moving target tracking of Unmanned Aircraft Vehicle (UAV) are performed to illustrate the effectiveness of the proposed control protocol.

"One-Click Restart" Recycling of Metal-Free Perovskite X-Ray Detectors.

Halide perovskites have shown great potential in X-ray detection due to outstanding optoelectronic properties. However, finding a cost-effective and environmentally sustainable method for handling end-of-life devices has remained challenging. Here, a "One-Click Restart" eco-friendly recycling strategy is introduced for end-of-life perovskite X-ray detectors. This method, utilizing water, allows for the recapture and reuse of both perovskite and conductor materials. The process is straightforward and environmentally friendly, eliminating the need for further chemical treatment, purification, additional additives or catalysts, and complex equipment. A sustainable device cycle is developed by reconstructing flexible perovskite membranes for wearable electronics from recycled materials. Large-scale, flexible membranes made from metal-free perovskite DABCO-N2H5-I3 (DABCO = N-N'-diazabicyclo[2.2.2]octonium) achieve remarkably impressive average sensitivity of 6204 ± 268 µC Gyair -1 cm-2 and a low detection limit of 102.3 nGyair s-1, which makes highly effective for X-ray imaging. The sensitivity of recycled flexible devices not only matches that of single-crystal devices made with fresh materials but also ranks as the highest among all metal-free perovskite X-ray detectors. "One-Click Restart" applies to scalable flexible devices derived from aged single-crystal counterparts, offering significant cost, time, and energy savings compared to their single-crystal equivalents. Such advantages significantly boost future market competitiveness.

Biocompatible Metal-Free Perovskite Membranes for Wearable X-ray Detectors.

Halide perovskites are emerging as promising materials for X-ray detection owing to their compatibility with flexible fabrication, cost-effective solution processing, and exceptional carrier transport behaviors. However, the challenge of removing lead from high-performing perovskites, crucial for wearable electronics, while retaining their superior performance, persists. Here, we present for the first time a highly sensitive and robust flexible X-ray detector utilizing a biocompatible, metal-free perovskite, MDABCO-NH4I3 (MDABCO = methyl-N'-diazabicyclo[2.2.2]octonium). This wearable X-ray detector, based on a MDABCO-NH4I3 thick membrane, exhibits remarkable properties including a large resistivity of 1.13 × 1011 Ω cm, a high mobility-lifetime product (µ-τ) of 1.64 × 10-4 cm2 V-1, and spin Seebeck effect coefficient of 1.9 nV K-1. We achieve a high sensitivity of 6521.6 ± 700 µC Gyair-1 cm-2 and a low detection limit of 77 nGyair s-1, ranking among the highest for biocompatible X-ray detectors. Additionally, the device exhibits effective X-ray imaging at a low dose rate of 1.87 µGyair s-1, which is approximately one-third of the dose rate used in regular medical diagnostics. Crucially, both the MDABCO-NH4I3 thick membrane and the device showcase excellent mechanical robustness. These attributes render the flexible MDABCO-NH4I3 thick membranes highly competitive for next-generation, high-performance, wearable X-ray detection applications.

One-stone-for-two-birds strategy to attain beyond 25% perovskite solar cells.

Even though the perovskite solar cell has been so popular for its skyrocketing power conversion efficiency, its further development is still roadblocked by its overall performance, in particular long-term stability, large-area fabrication and stable module efficiency. In essence, the soft component and ionic-electronic nature of metal halide perovskites usually chaperonage large number of anion vacancy defects that act as recombination centers to decrease both the photovoltaic efficiency and operational stability. Herein, we report a one-stone-for-two-birds strategy in which both anion-fixation and associated undercoordinated-Pb passivation are in situ achieved during crystallization by using a single amidino-based ligand, namely 3-amidinopyridine, for metal-halide perovskite to overcome above challenges. The resultant devices attain a power conversion efficiency as high as 25.3% (certified at 24.8%) with substantially improved stability. Moreover, the device without encapsulation retained 92% of its initial efficiency after 5000 h exposure in ambient and the device with encapsulation retained 95% of its initial efficiency after >500 h working at the maximum power point under continuous light irradiation in ambient. It is expected this one-stone-for-two-birds strategy will benefit large-area fabrication that desires for simplicity.

Stabilizing Precursor Solution and Controlling Crystallization Kinetics Simultaneously for High-Performance Perovskite Solar Cells.

The efficiency of metal halide perovskite solar cells (PSCs) has skyrocketed; however, defects created by aging precursor solutions and during crystallization pose a significant barrier to the reproducibility and efficiency of solar cells. In this work, fluoro-N,N,N″,N″-tetramethylformamidinium hexafluorophosphate (F-(CH3 )4 CN2 PF6 , abbreviated as TFFH) is introduced to stabilize precursor solution and improve crystallization dynamics simultaneously for high-performance formamidinium lead iodide (FAPbI3 )-based perovskite indoor photovoltaics. The TFFH stabilizes the precursor solution by inhibiting oxidation of I- and reducing newly generated I0 to I- , and passivates undercoordinated Pb2+ by interacting with the Pb─I framework. Time-resolved optical diagnostics show prolonged perovskite crystallization dynamics and in situ defect passivation due to the presence of strong FA+ ···TFFH···Pb─I interaction. Simultaneous regulation of precursor solution and crystallization dynamics guarantee larger perovskite grain sizes, better crystal orientation, fewer defects and more efficient charge extraction in PSCs. The optimized PSCs achieve improved reproducibility and better stability and reach an efficiency of 42.43% at illumination of 1002 lux, which is the highest efficiency among all indoor photovoltaics. It is anticipated that the concurrent stabilization of solutions and regulation of crystallization dynamics will emerge as a prevalent approach for enhancing the reproducibility and efficiency of perovskite.

In Situ Self-Elimination of Defects via Controlled Perovskite Crystallization Dynamics for High-Performance Solar Cells.

Understanding and controlling crystallization is crucial for high-quality perovskite films and efficient solar cells. Herein, the issue of defects in formamidinium lead iodide (FAPbI3 ) formation is addressed, focusing on the role of intermediates. A comprehensive picture of structural and carrier evolution during crystallization is demonstrated using in situ grazing-incidence wide-angle X-ray scattering, ultraviolet-visible spectroscopy and photoluminescence spectroscopy. Three crystallization stages are identified: precursors to the δ-FAPbI3 intermediate, then to α-FAPbI3 , where defects spontaneously emerge. A hydrogen-sulfate-based ionic liquid additive is found to enable the phase-conversion pathway of precursors → solvated intermediates → α-FAPbI3 , during which the spontaneous generation of δ-FAPbI3 can be effectively circumvented. This additive extends the initial growth kinetics and facilitates solvent-FA+ ion exchange, which results in the self-elimination of defects during crystallization. Therefore, the improved crystallization dynamics lead to larger grain sizes and fewer defects within thin films. Ultimately, the improved perovskite crystallization dynamics enable high-performance solar cells, achieving impressive efficiencies of 25.14% at 300 K and 26.12% at 240 K. This breakthrough might open up a new era of application for the emerging perovskite photovoltaic technology to low-temperature environments such as near-space and polar regions.

Deep learning based ultrasonic visualization of distal humeral cartilage for image-guided therapy: a pilot validation study.

Background: Ultrasound is widely used for image-guided therapy (IGT) in many surgical fields, thanks to its various advantages, such as portability, lack of radiation and real-time imaging. This article presents the first attempt to utilize multiple deep learning algorithms in distal humeral cartilage segmentation for dynamic, volumetric ultrasound images employed in minimally invasive surgery. Methods: The dataset, consisting 5,321 ultrasound images were collected from 12 healthy volunteers. These images were randomly split into training and validation sets in an 8:2 ratio. Based on deep learning algorithms, 9 semantic segmentation networks were developed and trained using our dataset at Southern University of Science and Technology Hospital in September 2022. The performance of the networks was evaluated based on their segmenting accuracy and processing efficiency. Furthermore, these networks were implemented in an IGT system to assess their feasibility in 3-dimentional imaging precision. Results: In 2D segmentation, Medical Transformer (MedT) showed the highest accuracy result with a Dice score of 89.4%, however, the efficiency in processing images was relatively lower at 2.6 frames per second (FPS). In 3D imaging, the average root mean square (RMS) between ultrasound (US)-generated models based on the networks and magnetic resonance imaging (MRI)-generated models was no more than 1.12 mm. Conclusions: The findings of this study indicate the technological feasibility of a novel method for real-time visualization of distal humeral cartilage. The increased precision of ultrasound calibration and segmentation are both important approaches to improve the accuracy of 3D imaging.

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 µGyair s-1 , all of which meet the needs of medical diagnosis.

Understanding How Fundus Image Quality Degradation Affects CNN-based Diagnosis.

Quality degradation (QD) is common in the fundus images collected from the clinical environment. Although diagnosis models based on convolutional neural networks (CNN) have been extensively used to interpret retinal fundus images, their performances under QD have not been assessed. To understand the effects of QD on the performance of CNN-based diagnosis model, a systematical study is proposed in this paper. In our study, the QD of fundus images is controlled by independently or simultaneously importing quantified interferences (e.g., image blurring, retinal artifacts, and light transmission disturbance). And the effects of diabetic retinopathy (DR) grading systems are thus analyzed according to the diagnosis performances on the degraded images. With images degraded by quantified interferences, several CNN-based DR grading models (e.g., AlexNet, SqueezeNet, VGG, DenseNet, and ResNet) are evaluated. The experiments demonstrate that image blurring causes a significant decrease in performance, while the impacts from light transmission disturbance and retinal artifacts are relatively slight. Superior performances are achieved by VGG, DenseNet, and ResNet in the absence of image degradation, and their robustness is presented under the controlled degradation.

Hybrid gMLP model for interaction prediction of MHC-peptide and TCR.

Understanding the interaction of T-cell receptor (TCR) with major histocompatibility-peptide (MHC-peptide) complex is extremely important in human immunotherapy and vaccine development. However, due to the limited available data, the performance of existing models for predicting the interaction of T-cell receptors (TCR) with major histocompatibility-peptide complexes is still unsatisfactory. Deep learning models have been applied to prediction tasks in various fields and have achieved better results compared with other traditional models. In this study, we leverage the gMLP model combined with attention mechanism to predict the interaction of MHC-peptide and TCR. Experiments show that our model can predict TCR-peptide interactions accurately and can handle the problems caused by different TCR lengths. Moreover, we demonstrate that the models trained with paired CDR3ß-chain and CDR3α-chain data are better than those trained with only CDR3ß-chain or with CDR3α-chain data. We also demonstrate that the hybrid model has greater potential than the traditional convolutional neural network.

Low Trap Density Para-F Substituted 2D PEA2PbX4 (X = Cl, Br, I) Single Crystals with Tunable Optoelectrical Properties and High Sensitive X-Ray Detector Performance.

Exploring halogen engineering is of great significance for reducing the density of defect states in crystals of organic-inorganic hybrid perovskites and hence improving the crystal quality. Herein, high-quality single crystals of PEA2PbX4 (X = Cl, Br, I) and their para-F (p-F) substitution analogs are prepared using the facile solution method to study the effects of both p-F substitution and halogen anion engineering. After p-F substitution, the triclinic PEA2PbX4 (X = Cl, Br) and cubic PEA2PbX4 (X = I) crystals unifies to monoclinic crystal structure for p-F-PEA2PbX4 (X = Cl, Br, I) crystals. The p-F substitution and halogen engineering, together with crystal structure variation, enable the tunability of optoelectrical properties. Experimentally, after the p-F substitution, the energy levels are lowered with increased Fermi levels, and the bandgaps of p-F-PEA2PbX4 (X = Cl, Br, I) are slightly reduced. Benefitting from the enhancement of the charge transfer and the reduced trap density by p-F substitution and halogen anion engineering, the average carrier lifetime of the p-F-PEA2PbX4 is obviously reduced. Compared with PEA2PbI4, the X-ray detector based on p-F-PEA2PbI4 perovskite single-crystal has a higher sensitivity of 119.79 µC Gyair -1·cm-2. Moreover, the X-ray detector based on p-F-PEA2PbI4 single crystals exhibits higher radiation stability under high-dose X-ray irradiation, implying long-term operando stability.

Highly Luminescent Metal-Free Perovskite Single Crystal for Biocompatible X-Ray Detector to Attain Highest Sensitivity.

Solution-processed metal-based halide perovskites have taken a dominant position for perovskite optoelectronics including light emission and X-ray detection; however, the toxicity of the included heavy metals severely restricts their applications for wearable, lightweight, and transient optoelectronic devices. Here, the authors describe investigations of large (4 × 6 × 2 mm3 ) 3D metal-free perovskite MDABCO-NH4 I3 (MDBACO = methyl-N'-diazabicyclo[2.2.2]octonium) single crystal and its charge recombination and extraction behavior for light emission and X-ray detection. Unlike conventional 3D metal-based perovskites, this lightweight and biocompatible perovskite large crystal is processed from aqueous solution at room temperature, and can achieve both an extremely long carrier lifetime up to ≈1.03 µs and the formation of self-trapped excited states for luminescence. These features contribute to a photoluminescence quantum yield (PLQY) as high as ≈53% at room temperature and an X-ray sensitivity up to 1997 ± 80 µC Gy cm-2 at 50 V bias (highest among all metal-free detectors). The ability to tune the perovskite band gap by modulating the structure under high pressure is also demonstrated, which opens up applications for the crystal as colored emitters. These attributes make it a molecular alternative to metal-based perovskites for biocompatible and transient optoelectronics.