Reconfigurable perovskite X-ray detector for intelligent imaging

In-sensor multilevel image adjustment for high-clarity contour extraction using adjustable synaptic phototransistors

Robotic vision has traditionally relied on high-performance yet resource-intensive computing solutions, which necessitate high-throughput data transmission from vision sensors to remote computing servers, sacrificing energy efficiency and processing speed. A promising solution is data compaction through contour extraction, visualizing only the outlines of objects while eliminating superfluous backgrounds. Here, we introduce an in-sensor multilevel image adjustment method using adjustable synaptic phototransistors, enabling the capture of well-defined images with optimal brightness and contrast suitable for achieving high-clarity contour extraction. This is enabled by emulating dopamine-mediated neuronal excitability regulation mechanisms. Electrostatic gating effect either facilitates or inhibits time-dependent photocurrent accumulation, adjusting photo-responses to varying lighting conditions. Through excitatory and inhibitory modes, the adjustable synaptic phototransistor enhances visibility of dim and bright regions, respectively, facilitating distinct contour extraction and high-accuracy semantic segmentation. Evaluations using road images demonstrate improvement of both object detection accuracy and intersection over union, and compression of data volume.

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

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

Self-Assembled Subwavelength Nanophotonic Structures for Spatial Object Localization and Tracking

Subwavelength resonant nanostructures have facilitated strong light-matter interactions and tunable degrees of freedom of light, such as spectrum, polarization, and direction, thus boosting photonic applications toward light emission, manipulation, and detection. For photodetection, resonant nanostructures have enabled emerging technologies, such as light detection and ranging, spectrometers, and polarimeters, within an ultracompact footprint. However, resonant nanophotonics usually relies on nanofabrication technology, which suffers from the trade-offs between precision and scalability. Here, we first realize the self-assembly of subwavelength resonant nanostructures of metal-halide perovskites for spatial object localization and tracking. By steering crystallization along capillary corner bridges localized at edges, we achieve single crystallinity, subwavelength size, and resonant coupling between perovskite nanowires, thus leading to an angle-resolved photodetector with an angular resolution of 0.523°. Furthermore, we integrate multiple pairs of coupled resonant nanowires along two orthogonal orientations to form angle-resolved photodetector arrays for spatial light localization of both static and moving objects with an error of less than 0.6 cm. These findings create a platform for self-assembled resonant nanostructures, thus paving the way for multifunctional nanophotonic and optoelectronic devices.

In-Situ Growth of One-Dimensional Blocking Layer to Mitigate Deficient Surface of Single-Crystal Perovskites

Organic-inorganic halide perovskite (OIHP) single crystals are promising for optoelectronic application, but their high surface trap density and associated ion migration hinders device performance and stability. Herein, a one-dimensional (1D) perovskites are designed and proposed as blocking layer at the crystal/electrode interface to mitigate the surface issues. As a model system, the interface ion migration in Cs0.05FA0.95PbI3 (FA=formamidinium) single-crystal perovskite solar cells (PSCs) is obviously suppressed, leading to increase of T90 lifetime from 260 to 1000 hours, five times better than previously reported results. Besides, the reduction of surface iodide ion vacancies inhibits nonradiative recombination, thus increasing the efficiency from 22.1 % to 23.8 %, which is one of the highest values for single-crystal PSCs. Since the deficient crystal surface is a universal and open issue, our strategy is instructive for optimizing diverse single-crystal perovskite devices.

Large-Area Metal-Organic Framework Glasses for Efficient X-Ray Detection

Cutting-edge techniques utilizing continuous films made from pure, novel semiconductive materials offer promising pathways to achieve high performance and cost-effectiveness for X-ray detection. Semiconductive metal-organic framework (MOF) glass films are known for their remarkably smooth surface morphology, straightforward synthesis, and capability for large-area fabrication, presenting a new direction for high-performance X-ray detectors. Here, a novel material centered on MOF glasses for highly uniform glass film fabrication customized for X-ray detection is introduced. MOF glasses, composed of zinc and imidazole derivatives, enable the transition from solid to liquid at low temperatures, facilitating the straightforward preparation of large-area and continuous MOF films with high mobility for X-ray device fabrication. Remarkably, MOF glass detectors demonstrate an exceptional sensitivity of 112.8 µC Gyair -1 cm-2 and a detection limit of 0.41 µGyair s-1, making them one of the most sensitive and with the best detection limits reported to date for MOF X-ray detectors. Clear X-ray images are successfully conducted using these developed MOF glass detectors for the first time. This breakthrough in X-ray sensitivity, and detection limit along with the spatial imaging resolution establishes a new standard for developing large-area and efficient MOF-based X-ray detectors with practical applications in medical and security screening.

Retina-Inspired X-Ray Optoelectronic Synapse Using Amorphous Ga2O3 Thin Film

Machine vision techniques are widely applied for object identification in daily life and industrial production, where images are captured and processed by sensors, memories, and processing units sequentially. Neuromorphic optoelectronic synapses, as a preferable option to promote the efficiency of image recognition, are hotly pursued in non-ionizing radiation range, but rarely in ionizing radiation including X-rays. Here, the study proposes an X-ray optoelectronic synapse using amorphous Ga2O3 (a-Ga2O3) thin film. Boosted by the interfacial VO 2+ defects and its slow neutralization rate, the enhanced electron tunneling process at metal/a-Ga2O3 interface produces remarkable X-ray-induced post-synaptic current, contributing to a sensitivity of 20.5, 64.3, 164.1 µC mGy-1 cm-2 for the 1st, 5th, and 10th excitation periods, respectively. Further, a 64 × 64 imaging sensor is constructed on a commercial amorphous Si (a-Si) thin film transistor (TFT) array. The image contrast can be apparently improved under a series of X-ray pulses due to an outstanding long-term plasticity of the single pixel, which is beneficial to the subsequent image recognition and classification based on artificial neural network. The merits of large-scale production ability and good compatibility with modern microelectronic techniques belonging to amorphous oxide semiconductors may promote the development of neuro-inspired X-ray imagers and corresponding machine vision systems.

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

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

Wafer-Sized CsPbBr3/CsPbCl3 Heterojunction: Breaking the Trade-Off between Sensitivity and Dark Current for Efficient X-ray Detector

Polycrystalline lead halide perovskite finds promising use in fabricating X-ray detectors with a large lateral size, adjustable thickness, and diverse synthesis processes. However, a large dark current hinders its development for weak signal detection. Herein, we propose a multistep pressing strategy for manufacturing a CsPbBr3/CsPbCl3 heterojunction wafer for a reduced dark current X-ray detector, and the device keeps a high sensitivity value after the insertion of a barrier by heterojunction; thus, the trade-off between sensitivity and dark current can be broken. The X-ray detector with a metal-semiconductor-metal structure yields a sensitivity of 6.32 × 104 μC Gyair-1 cm-2 at a bias of 12 V, a 1/f noise of 1.02 × 10-13 A/Hz-1/2, and a detection limit of 66.58 nGy s-1. These performance parameters are considerably better than those of a similar X-ray detector based on the single-structure wafer. The improved device performance of the heterostructure X-ray detector is ascribed to the suppressed carrier recombination, enhanced carrier transportation of the heterojunction, and strong X-ray attenuation of the CsPbCl3 layer. The pixel array device is further used in imaging applications. Hence, this study provides an efficient strategy for fabricating heterostructure polycrystalline lead halide perovskite wafers for use in high-performance wafer-based X-ray detectors.

Quantitative modeling of perovskite-based direct X-ray flat panel detectors

Direct X-ray detectors based on semiconductors have drawn great attention from researchers in the pursuing of higher imaging quality. However, many previous works focused on the optimization of detection performances but seldomly watch them in an overall view and analyze how they will influence the detective quantum efficiency (DQE) value. Here, we propose a numerical model which shows the quantitative relationship between DQE and the properties of X-ray detectors and electric circuits. Our results point out that pursuing high sensitivity only is meaningless. To reduce the medical X-ray dose by 80%, the requirement for X-ray sensitivity is only at a magnitude of 103 μCGy-1⋅cm-2. To achieve the DQE = 0.7 at X-ray sensitivity air from 1248 to 8171 μCGy-1air⋅cm-2, the requirements on dark current density ranges from 10 to 100 nA⋅cm-2 and the fluctuation of current density should fall in 0.21 to 1.37 nA⋅cm-2.

Overcoming Microstructural Defects at the Buried Interface of Formamidinium-Based Perovskite Solar Cells

Since the advent of formamidinium (FA)-based perovskite photovoltaics (PVs), significant performance enhancements have been achieved. However, a critical challenge persists: the propensity for void formation in the perovskite film at the buried perovskite-interlayer interface has a deleterious effect on device performance. With most emerging perovskite PVs adopting the p-i-n architecture, the specific challenge lies at the perovskite-hole transport layer (HTL) interface, with previous strategies to overcome this limitation being limited to specific perovskite-HTL combinations; thus, the lack of universal approaches represents a bottleneck. Here, we present a novel strategy that overcomes the formation of such voids (microstructural defects) through a film treatment with methylammonium chloride (MACl). Specifically, our work introduces MACl via a sequential deposition method, having a profound impact on the microstructural defect density at the critical buried interface. Our technique is independent of both the HTL and the perovskite film thickness, highlighting the universal nature of this approach. By employing device photoluminescence measurements and conductive atomic force microscopy, we reveal that when present, such voids impede charge extraction, thereby diminishing device short-circuit current. Through comprehensive steady-state and transient photoluminescence spectroscopy analysis, we demonstrate that by implementing our MACl treatment to remedy these voids, devices with reduced defect states, suppressed nonradiative recombination, and extended carrier lifetimes of up to 2.3 μs can be prepared. Furthermore, our novel treatment reduces the stringent constraints around antisolvent choice and dripping time, significantly extending the processing window for the perovskite absorber layer and offering significantly greater flexibility for device fabrication.

High-Throughput Growth of Armored Perovskite Single Crystal Fibers for Pixelated Arrays

The poor machinability of halide perovskite crystals severely hampered their practical applications. Here a high-throughput growth method is reported for armored perovskite single-crystal fibers (SCFs). The mold-embedded melt growth (MEG) method provides each SCF with a capillary quartz shell, thus guaranteeing their integrality when cutting and polishing. Hundreds of perovskite SCFs, exemplified by CsPbBr3, CsPbCl3, and CsPbBr2.5I0.5, with customized dimensions (inner diameters of 150-1000 µm and length of several centimeters), are grown in one batch, with all the SCFs bearing homogeneity in shape, orientation, and optical/electronic properties. Versatile assembly protocols are proposed to directly integrate the SCFs into arrays. The assembled array detectors demonstrated low-level dark currents (< 1 nA) with negligible drift, low detection limit (< 44.84 nGy s-1), and high sensitivity (61147 µC Gy-1 cm-2). Moreover, the SCFs as isolated pixels are free of signal crosstalk while showing uniform X-ray photocurrents, which is in favor of high spatial resolution X-ray imaging. As both MEG and the assembly of SCFs involve none sophisticated processes limiting the scalable fabrication, the strategy is considered to meet the preconditions of high-throughput productions.

Lead-rivet strategy of growing perovskite nanocrystals for excellent toxicity inhibition and spinning application

Lead halide perovskite has demonstrated remarkable potential in the wearable field due to its exceptional photoelectric conversion capability. However, its lead toxicity issue has consistently been subject to criticism, significantly impeding its practical application. To address this challenge, an innovative approach called lead-rivet was proposed for the in-situ growth of perovskite crystalline structures. Through the formation of S-Pb bonds, each Pb2+ ion was firmly immobilized on the surface of the silica matrix, enabling in situ growth of perovskite nanocrystals via ion coordination between Cs+ and halide species. The robust S-Pb bonding effectively restricted the mobility of lead ions and stabilized the perovskite structure without relying on surface ligands, thereby not only preventing toxicity leakage but also providing a favorable interface for depositing protective shells. The obtained perovskites exhibit intense and narrow-band fluorescence with full-width at half-maximum less than 23 nm and show excellent stability to high temperature (above 202 °C) and high humidity (water immersion over 27 days), thus making it possible to be used in varies textile technologies including melt spinning and wet spinning. The lead leakage rate of particles is only 4.15 % demonstrating excellent toxicity inhibition performance. The prepared fibers maintained good extensibility and flexibility which could be used for 3D-printing and textiles weaving. Most importantly, the detected Pb2+ leaching was negligible as low as to 0.732 ppb which meet the standard of World Health Organization (WHO) for drinking water (<10 ppb), and the cell survival rate remained 99.196 % for PLA fluorescent filament after 24 h cultivation which showing excellent safety to human body and environment. This study establishes a controllable and highly adaptable synthesis method, thereby providing a promising avenue for the safe utilization of perovskite materials.

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

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

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

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