High-performance X-ray Detection Research Articles

Stereo-Hindrance Engineering of A Cation toward -Oriented 2D Perovskite with Minimized Tilting and High-Performance X-Ray Detection.

2D <100>-oriented Dion-Jacobson or Ruddlesden-Popper perovskites are widely recognized as promising candidates for optoelectronic applications. However, the large interlayer spacing significantly hinders the carrier transport. <110>-oriented 2D perovskites naturally exhibit reduced interlayer spacings, but the tilting of metal halide octahedra is typically serious and leads to poor charge transport. Herein, a <110>-oriented 2D perovskite EPZPbBr4 (EPZ = 1-ethylpiperazine) with minimized tilting is designed through A-site stereo-hindrance engineering. The piperazine functional group enters the space enclosed by the three [PbBr6 ]4- octahedra, pushing Pb─Br─Pb closer to a straight line (maximum Pb─Br─Pb angle ≈180°), suppressing the tilting as well as electron-phonon coupling. Meanwhile, the ethyl group is located between layers and contributes an extremely reduced effective interlayer distance (2.22 Å), further facilitating the carrier transport. As a result, EPZPbBr4 simultaneously demonstrates high µτ product (1.8 × 10-3 cm2 V-1 ) and large resistivity (2.17 × 1010 Ω cm). The assembled X-ray detector achieves low dark current of 1.02 × 10-10 A cm-2 and high sensitivity of 1240 µC Gy-1 cm-2 under the same bias voltage. The realized specific detectivity (ratio of sensitivity to noise current density, 1.23 × 108 µC Gy-1 cm-1 A-1/2 ) is the highest among all reported perovskite X-ray detectors.

1D Pb halide perovskite-like materials for high performance X-ray detection.

The strategy of bandgap regulation is important for X-ray detection, but has not been reported for 1D Pb halide perovskite materials. In this work, three such materials, 1, 2 and 3, with a tunable bandgap, were fabricated for application in X-ray detection. 3 shows high sensitivity, far superior to commercial X-ray detectors.

Defect mitigation in lead-free Cs3Bi2I9 single crystals for high performance X-ray detection and imaging

Defect mitigation in lead-free Cs₃Bi₂I₉ single crystals for high performance X-ray detection and imaging

Exploring centimeter-sized single crystal of 2D Dion-Jacobson halide perovskite toward efficient X-ray detection

Two-dimensional (2D) Halide hybrid perovskites have become feasible semiconductors for high-performance X-ray detection due to their strong radiation-blocking ability, high volume resistivity, and large mobility-lifetime (μτ) product. However, the absence...

Water-assisted mass preparation of CsPbBr3-CsPb2Br5-CsPbIxBr3-x composite wafers for high-performance X-ray detection

Lead halide perovskite wafers with large lateral size, controllable thickness, and desirable optoelectronic characteristics are promising for X-ray detectors. Herein, CsPbBr3-CsPb2Br5-CsPbIxBr3-x composite wafers are prepared via water-assisted coprecipitation and spray coating. The preparation involved pressure-induced aggregation of the CsPbBr3-CsPb2Br5 powder produced through coprecipitation using of H2O/MeOH mixed solvent into CsPbBr3-CsPb2Br5 wafers, followed by spraying a CsI/H2O solution onto the wafer surface to transform it into a CsPbBr3-CsPb2Br5-CsPbIxBr3-x composite wafer. Multiple favorable properties, including compact surface, high crystallinity, excellent carrier transportation, large/adjustable size, low cost, and mass producibility, can be identified for the CsPbBr3-CsPb2Br5-CsPbIxBr3-x composite wafer. An X-ray detector with high performance and excellent stability is realized with this wafer. It yields high resistivity (ρ; 1.3 × 109 Ω cm−2, exceptional carrier mobility (μ)/lifetime (τ) (μτ) product (1.01 × 10−3 cm2 V−1), high sensitivity (20555.1 μC Gyair−1 cm−2), and low detection limit (127.7 nGy s−1). Hence, our research provides a reliable strategy for optimizing the structure and performance of perovskite wafer-based X-ray detectors and enabling mass preparation.

Supple Formamidinium-Based Low-Dimension Perovskite Derivative for Sensitive and Ultrastable X-ray Detection.

Halide perovskite materials possess excellent optoelectronic properties and have shown great potential for direct X-ray detection. Perovskite wafers are particularly attractive among various detection structures due to their scalability and ease of preparation, making them the most promising candidates for X-ray detection and array imaging applications. However, device instability and current drift caused by ionic migration are persistent challenges for perovskite detectors, especially in polycrystalline wafers with numerous grain boundaries. In this study, we examined the potential of one-dimensional (1D) δ-phase (yellow phase) formamidinium lead iodide (δ-FAPbI3) as an X-ray detection material. This material possesses a suitable band gap of 2.43 eV, which makes it highly promising for X-ray detection and imaging using compact wafers. Moreover, we found that δ-FAPbI3 has low ionic migration, low Young's modulus, and excellent long-term stability, making it an ideal candidate for high-performance X-ray detection. Notably, the yellow phase perovskite derivative exhibits exceptional long-term atmospheric stability (RH of ≈70 ± 5%) over six months, as well as an extremely low dark current drift (3.43 × 10-4 pA cm-1 s-1 V-1), which is comparable to that of single-crystal devices. An X-ray imager with a large-size δ-FAPbI3 wafer integrated on a thin film transistor (TFT) backplane was further fabricated. Direct 2D multipixel radiographic imaging was successfully performed, demonstrating the feasibility of δ-FAPbI3 wafer detectors for sensitive and ultrastable imaging applications.

Exploring centimeter-sized crystals of bismuth-iodide perovskite toward highly sensitive X-ray detection

Lead-halide perovskites exhibit outstanding performance in X-ray detection due to their intrinsic features such as high charge carrier mobility, large atomic number, and long carrier lifetime, but the toxicity of lead is regarded as the major factor hindering their development. Here, we introduce organic molecule (R)-(-)-2-methylpiperazine (R-MPz) into the bismuth-based structure to synthesize lead-free (R)-(H2MPz)BiI5 (R-MBI). The high-quality centimeter-sized single crystals have been obtained, which show a low dark current and superior environmental stability. Particularly, the single-crystal device of R-MBI exhibits a high μτ product up to 1.88 × 10−4 cm2/V and a low trap density of 1.21 × 1010 cm−3. Further, the detector displays excellent detection sensitivity of 263.58 µC Gyair−1 cm−2 and a favorable low detection limit of 4.35 µGyair/s, both of which meet the requirement for medical diagnostics. These findings shed light on the exploration of innovative bismuth-based hybrid perovskites for high-performance X-ray detection.

High temperature and water stable CaF2:Eu2+ glass ceramic for high resolution X-ray detection

The rising requirement for radiation detection materials for practical applications has inspired to burgeoning investigation of scintillator materials. High performance X-ray detection require high spatial resolution and long-term stability, particularly for targeted objects at extreme conditions. Here, the CaF2:Eu2+ glass ceramic (GC), in which the CaF2:Eu2+ nanoparticles are wrapped by the glassy matrix, is successfully obtained the melting method. The as-obtained CaF2:Eu2+ GC manifests bright blue radioluminescence (RL) emission peaked at 470 nm thanks to the effective 5d-4f transition of Eu2+ ions. In addition, the as-obtained CaF2:Eu2+ GC presents high transmittance of 84.2% and visible light, contributing an excellent spatial resolution of 15 lp/mm at room temperature. Importantly, the as-obtained CaF2:Eu2+ GC exhibits high robustness at water conditions and high thermal stability with X-ray resolution of 12.1 lp/mm at 473 K. Our work demonstrates that CaF2:Eu2+ GC scintillators provide an excellent visualization tool for high-resolution scintillators X-ray images in harsh conditions.

Perovskite band engineering for high-performance X-ray detection

Perovskite-based X-ray detector, which is widely applied in fields of scientific research and medical diagnosis, has drawn much attention for its superior optoelectrical properties. To improve the detection performance, band engineering is becoming the hot topic for perovskite properties modulation. In this article, we review the recent progress of perovskite-based X-ray detectors with band engineering process from three aspects, which are background introduction, band theory of heterojunction devices, and optimized electrode contact devices. Lastly, research status and strategies are summarized and perspectives of future progress are analyzed. We hope this review can provide constructive instructions and suggestions for future development of band engineering for perovskite-based high-performance X-ray detector.

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

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

Spray-coating of AgI incorporated metal halide perovskites for high-performance X-ray detection

Metal halide perovskites have emerged as a promising candidate for ionizing radiation detection, thanks to the facile fabrication, excellent optoelectronic properties and high attenuation coefficient. In order to fully absorb the incident X-ray photons, X-ray detectors require relatively thick active layers. However, it is challenging to obtain thick perovskite films based on conventional solution-based techniques, due to the limited solubility and viscosity of the perovskite precursors. In this work, we introduced spray-coating to deposit perovskite films on various substrates, and achieved tunable and thick films. On the other hand, the charge transport is another issue limiting the device performance of perovskite X-ray detectors. Compared with conventional inorganic semiconductors, hybrid perovskites possess relatively poor charge carrier mobility and lifetime. To address this issue, we incorporate AgI within the perovskite precursor, and systematically investigated their optoelectronic properties. It was found that the optimized AgI incorporated perovskite films exhibited the highest mobility-lifetime product, resulted X-ray sensitivity up to 3433 μGyair−1 cm−2 and ultra-low detection limit of 3.5 nGyair s−1, suggesting great potential for X-ray detection.

Fine-control-valve of halide perovskite single crystal quality for high performance X-ray detection

Halide perovskite single crystals (HPSCs) provide a unique platform to study the optoelectronic properties of such emerging semiconductor materials, while the temperature induced crystal growth method often has an increased solute integration speed and/or unavoidable solute consumption, resulting in a soaring or slumping crystal growth rate of HPSCs. Here, we developed a universal and facile solvent-volatilization-limited-growth (SVG) strategy to finely control the crystal growth rate by the fine-control-valve for high quality crystal grown through solution processes. The grown HPSCs by SVG method exhibited a record low trap density of 2.8 × 108 cm−3 and a high charge carrier mobility-lifetime product (μτ product) of 0.021 cm2/V, indicating the excellent crystal quality. The crystal surface defects were further passivated by oxygen suppliers as Lewis base, which led to a reduction of surface leakage current by two times when using for low dose rate X-ray detection. Such HPSC X-ray detector displayed a high sensitivity of 1274 µC/(Gyair cm2) with a lowest detectable dose rate of 0.56 μGyair/s under 120 keV hard X-ray. Further applications including alloy composition analysis and metal flaw detection by HPSC detectors were also demonstrated, which not only shows the bright future for product quality inspection and non-destructive materials analysis, but also paves the way for growing high quality single crystals and fabricating polycrystalline films.

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

Direct X-ray detectors based on metal halide perovskites and their derivatives exhibit high sensitivity and low limit of detection (LoD). Compared with three-dimensional (3D) hybrid lead halide perovskites, low-dimensional A3Bi2I9 perovskite derivatives (A = Cs, Rb, NH4, CH3NH3(MA)) present better stability, greater environmental friendliness, and comparable X-ray detection performance. Here, we report FA3Bi2I9 (FA= CH(NH2)2) single crystals (SCs) as a new member of the A3Bi2I9 series for X-ray detection, which were prepared by the nucleation-controlled secondary solution constant temperature evaporation (SSCE) method. Centimeter-sized FA3Bi2I9 SCs show a full width at half-maximum (fwhm) of 0.0096°, which is superior to that of recently reported Cs3Bi2I9 (0.058°) and MA3Bi2I9 SCs (0.024°) obtained by inverse temperature crystallization (ITC). The as-grown FA3Bi2I9 SC shows a large resistivity of 7.8 × 1010 Ω cm and a high ion migration activation energy (Ea) of 0.56 eV, which can guarantee a low noise level and good operational stability under a large external bias. The FA3Bi2I9 SC detector exhibits a LoD of 0.2 μGyair s-1, a sensitivity of 598.1 μC Gyair -1 cm -2, and an X-ray detection efficiency of 33.5%, which are much better than those of the commercialized amorphous selenium detector. Results presented here will provide a new lead-free perovskite-type material to achieve green, sensitive, and stable X-ray detectors.

Triple-Cation and Mixed-Halide Perovskite Single Crystal for High-Performance X-ray Imaging.

Low ionic migration is required for a semiconductor material to realize stable high-performance X-ray detection. In this work, successful controlled incorporation of not only methylammonium (MA+ ) and cesium (Cs+ ) cations, but also bromine (Br- ) anions into the FAPbI3 lattice to grow inch-sized stable perovskite single crystal (FAMACs SC) is reported. The smaller cations and anions, comparing to the original FA+ and I- help release lattice stress so that the FAMACs SC shows lower ion migration, enhanced hardness, lower trap density, longer carrier lifetime and diffusion length, higher charge mobility and thermal stability, and better uniformity. Therefore, X-ray detectors made of the superior FAMACs SCs show the highest sensitivity of (3.5 ± 0.2) × 106 μC Gyair -1 cm-2 , about 29 times higher than the latest record of 1.22 × 105 μC Gyair -1 cm-2 for polycrystalline MAPbI3 wafer under the same 40 keV X-ray radiation. Furthermore, the FAMACs SC X-ray detector shows a low detection limit of 42 nGy s-1 , stable dark current, and photocurrent response. Finally, it is demonstrated that high contrast X-ray imaging is realized using the FAMACs SC detector. The effective triple-cation mixed halide strategy and the high crystalline quality make the present FAMACs SCs promising for next-generation X-ray imaging systems.

Lead-free halide perovskite Cs3Bi2Br9 single crystals for high-performance X-ray detection

All-inorganic lead-free halide perovskites have attracted interest owing to their high ambient and thermal stabilities, excellent optoelectronic properties, and environmental friendliness. Herein, the bismuth-based halide perovskite Cs3Bi2Br9 single crystals were successfully grown to a diameter of 12 mm and length of 40 mm using a modified Bridgman method for the first time. The resistivity and transmittance of transparent and crack-free Cs3Bi2Br9 single crystal are ~6.8×1011 Ω cm and ~80%, respectively. The carrier mobility of the (−120) plane is 0.17 cm2 V−1 s−1 along the [010] orientation (b axis), and the trap density is 9.7×1010 cm−3. Moreover, Cs3Bi2Br9 single crystals exhibit excellent potential for X-ray detection, including a high absorption coefficient, a superior X-ray sensitivity of ~230.4 µC Gyair−1 cm−2, and an ultra-low and no-drift dark current density of ~17.8 pA mm−2, which enables lower noise and is also beneficial to the ultra-low detection limit for X-ray detectors. Our study shows that Cs3Bi2Br9 is a promising candidate for X-ray detection applications.

Highly efficient copper halide scintillators for high-performance and dynamic X-ray imaging.

Progress towards high performance X-ray detection and dynamic imaging applications, including nondestructive inspection, homeland security, and medical diagnostics, requires scintillators with a high light yield, a reasonable decay time, low cost, and eco-friendliness. Recently, copper halide scintillators have drawn tremendous attention due to their outstanding radioluminescence performance. Here, we first employed β-Cs3Cu2Cl5 as a high-performance scintillator, with a photoluminescence quantum yield (PLQY) of 94.6%, a radioluminescence light yield of 34 000 ± 4000 photons per MeV, a low detection limit of 81.7 nGyair s-1, and good operational stability under a total X-ray dose of 174.6 Gyair in air. In addition, this scintillator presents a high spatial resolution of 9.6 lp mm-1 at the modulation transfer function of 0.2 and a superb performance at 60 frames per second in our X-ray imaging system. Overall, this highly efficient scintillator demonstrates outstanding comprehensive performance and shows great potential for broad applications in X-ray detection and dynamic imaging.

A Photoconductive X-ray Detector with a High Figure of Merit Based on an Open-Framework Chalcogenide Semiconductor.

A wide range of tunability in the physical parameters of a semiconductor used for X-ray detection is desirable to achieve targeted performance optimization. However, in a dense-phase semiconductor, fine-tuning one parameter often leads to unwanted changes in other parameters. Herein, the intrinsic openness in an open-framework semiconductor has been confirmed, for the first time, to be a key structural factor that weakens the mutual exclusivity of the adjustable physical parameters owing to a non-linear control mechanism. The controllable doping of S in a zeolitic In-Se host results in an optimal balance between resistivity, band gap, and carrier mobility, which finally results in an excellent X-ray detector with a high figure of merit for the mobility-lifetime product (7.12×10-4 cm2 V-1 ); this value is superior to that of a commercial α-Se detector. The current strategy of choosing open-framework semiconductor materials opens a new window for targeting high-performance X-ray detection.

Co-axial silicon/perovskite heterojunction arrays for high-performance direct-conversion pixelated X-ray detectors

Creating monolithic silicon/perovskite structures is a promising approach to engage emerging perovskite materials with silicon circuitry, which is essential to achieve industry-scale applications such as high performance X-ray detection. In particular, to achieve pixelated perovskite is a key step to address the issue of electrical crosstalk and low spatial resolution in imaging caused by inefficient migration and collection of carriers in the direction of signal collection. However, with the existing top-down methods, the thickness of patterned perovskite is limited to be in submicron level, which is far from highly efficient absorption of X-ray energy, further compromising the detection sensitivity. Here, we successfully demonstrate 3D hybrid perovskite crystal arrays with the thickness of ~300 μm on pixelated silicon substrate (forming co-axial silicon/perovskite heterojunction arrays) by melting PbBr2 and in situ chemical vapor conversion. Both morphological and optical properties of the resulting heterojunction arrays are systematically investigated. Furthermore, we demonstrate a high performance direct-conversion flat panel X-ray detector which exhibits high sensitivity of 242 μC Gyair−1 cm−2 that is much higher than the commercially available α-Se, and fast response speed (rising and falling time are 0.5 ms and 1.3 ms, respectively). The proposed strategy addresses the trade-off problem between the high sensitivity (requiring ~ mm-thickness perovskite crystal) and high spatial resolution (patterning of perovskite crystal) to achieve high-performance X-ray detection. This work not only offers a new pathway to fabricate pixelated μm-thick perovskite-based X-ray detectors, but also impacts on the application and functionalization of perovskite materials in silicon circuitry.

Nucleation-controlled growth of superior lead-free perovskite Cs3Bi2I9 single-crystals for high-performance X-ray detection

The organic-inorganic hybrid lead halide perovskites have emerged as a series of star materials for solar cells, lasers and detectors. However, the issues raised by the toxic lead element and marginal stability due to the volatile organic components have severely limited their potential applications. In this work, we develop a nucleation-controlled solution method to grow large size high-quality Cs3Bi2I9 perovskite single crystals (PSCs). Using the technique, we harvest some centimeter-sized single crystals and achieved high device performance. We find that X-ray detectors based on PSCs exhibit high sensitivity of 1652.3 μC Gyair−1 cm−2 and very low detectable dose rate of 130 nGyair s−1, both desired in medical diagnostics. In addition, its outstanding thermal stability inspires us to develop a high temperature X-ray detector with stable response at up to 100 °C. Furthermore, PSCs exhibit high X-ray imaging capability thanks to its negligible signal drifting and extremely high stability.

Balance lead in solution-processed CH3NH3PbBrxCl(3−x) single crystals for high performance X-ray detection

Organometallic perovskites MAPbX3 (MA = CH3NH3 and X = I, Br or Cl) are considered as potential materials for X-ray and gamma ray detection due to its high Z atom, large mobility-lifetime product and growth from solution. However, perovskites with one kind halide own numbers of free charges and yielded unbearable noise current. In this work, we grow perovskite single crystals (PSC) with different halide ratio and find the MAPbBr2.5Cl0.5 PSC shows outstanding performance in electric properties. Through energy dispersive X-ray spectrum, vacancy and excess of Pb is thought as the main cause of free charges. The atomic ratio between halide and Pb as 3 in MAPbBr2.5Cl0.5 PSC and its large resistivity 5.6 × 108 Ω cm and 160 cm2 V−1 s−1 high mobility are measured. Thanks to the smaller noise current, higher electric field could be established for higher charges collect efficiency. As a result, compared with pristine perovskite single crystals, improved X-ray detection performance is demonstrated. This work provides useful information to achieve high performance X-ray detectors based on organometallic perovskites.