Double-Sided Bonding Process Enables X-ray Flat Panel Detectors.

Metal halide perovskites have demonstrated superior sensitivity, lower detection limits, stability, and exceptional photoelectric properties in comparison to existing commercially available X-ray detector materials, showing their potential for shaping the next generation of X-ray detectors. Nevertheless, significant challenges persist in the seamless integration of these materials into pixelated array sensors for large-area X-ray direct detection imaging. In this article, we propose a strategy for fabricating large-scale array devices using a double-sided bonding process. The approach involves depositing a wet film on the surface of a thin-film transistor substrate to establish a robust bond between the substrate and δ-CsPbI3 wafer via van der Waals force, thereby facilitating area-array imaging. Additionally, the freestanding polycrystalline δ-CsPbI3 wafer demonstrated a competitive ultralow detection limit of 3.46 nGyair s-1 under 50 kVP X-ray irradiation, and the δ-CsPbI3 wafer still maintains a stable signal output (signal current drift is 3.5 × 10-5 pA cm-1 s-1 V-1) under the accumulated radiation dose of 234.9 mGyair. This strategy provides a novel perspective for the industrial production of large-area X-ray flat panel detectors utilizing perovskites and their derivatives.

High-Performance Hard X-Ray Imaging Detector Using Facet-Dependent Bismuth Vanadate.

Bismuth vanadate (BiVO4) exhibits large absorption efficiency for hard X-rays, which endows it with a robust capacity to attenuate X-ray radiation across a broad energy range. The anisotropic properties of BiVO4 allow for the manipulation of their physical and chemical characteristics through crystallographic orientation and exposed facets. In this study, the issue of heavy recombination caused by sluggish electron transport in BiVO4 is successfully addressed by enhancing the abundance of the (040) crystal face ratio using a Co2+ crystal face exposure agent. The facet-dependent modifications exhibit excellent and balanced intrinsic charge transport properties, and finely optimize both the sensitivity and detection limit of BiVO4 X-ray detectors. As a result, ultra-stable BiVO4 metal oxide X-ray detectors demonstrate a high sensitivity of 3164 µC Gyair -1 cm-2 and a low detection limit of 20.76 nGyair s-1 under 110 kVp hard X-rays, establishing a new benchmark for X-ray detectors based on polycrystalline Bi-halides and metal oxides. These findings highlight the significance of crystal orientation in optimizing materials for X-ray detection, setting a new sensitivity record for X-ray detectors based on polycrystalline Bi-halides and metal oxides, which paves the way for the development of advanced, low-dose, and highly stable imaging systems specifically for hard X-rays.

High-Performance Flat-Panel Perovskite X-ray Detectors Enabled by Defect Passivation in Ruddlesden-Popper Perovskites.

Halide perovskites have emerged as promising candidates in X-ray detection due to their strong X-ray absorption and excellent optoelectronic properties. The development of sensitive and stable flat-panel X-ray detectors with high resolution is crucial for practical applications. In this paper, we introduce a novel flat-panel X-ray detector that integrates quasi-two-dimensional (2D) Ruddlesden-Popper (RP) perovskite with a pixeled thin film transistor (TFT) backplane. We incorporate 2,5-dibromopyrimidine (DBPM) as an additive to passivate the Lewis acid defects in the quasi-2D RP perovskite. This modification results in suppressed ion migration, improved optoelectronic performance, and enhanced operational stability of the device. Impressively, the activation energy of the RP perovskite increases from 0.96 to 1.35 eV with the DBPM additive. As a result, X-ray detectors exhibit a high sensitivity of ∼13,600 µC Gyair-1 cm-2, a low detection limit of 6.56 nGyair s-1, and excellent operational stability. Moreover, the flat-panel detectors demonstrate a high spatial resolution of 3.7 line pairs per millimeter and excellent X-ray imaging properties under a remarkably low X-ray dose of ∼50 µGyair, which is just half of the X-ray dose typically used in commercial equipment. This study opens new avenues for the development of flat-panel perovskite X-ray detectors with significant potential for various applications.

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.

Halide perovskites for sensitive, stable and scalable X-ray detection and imaging.

Halide perovskites have attracted significant research interests in the X-ray detection and imaging field. Their strong X-ray attenuating ability and good carrier transportation endow them with high sensitivity, which is better than those of commercialized amorphous selenium (a-Se) and CdZnTe (CZT). However, ion migration has been identified as a critical factor that deteriorates the performance of three-dimensional (3D) lead-based halide perovskite detectors. Moreover, large dark current has hindered their application in low-dose X-ray detection. Another major challenge is to fabricate large area, high-quality thick perovskites that can be integrated with commercial electronic readout backplanes, such as thin-film transistors (TFTs) and complementary metal-oxide-semiconductor (CMOS) transistors, to produce multipixel flat-panel detectors for X-ray imaging. Bismuth-based halide perovskites have been demonstrated to be competitive candidates due to their low ionic migration and small dark current. Fabrication methods, including pressing, membrane filling, blade coating, spray coating etc., will be summarized and discussed in detail. This feature article discusses the potential and challenges in perovskite X-ray detection and imaging, providing new research directions for future development.

Additive-Induced Synergies of Ion Migration Inhibition and Defect Passivation toward Sensitive Perovskite X-ray Detectors.

Two-dimensional (2D) Ruddlesden-Popper (RP) metal halide perovskites have emerged as a promising material for X-ray detection. However, defects and ion migration generated nonradiative recombination and high dark current could cause severe performance degradation, which hinders their application. Herein, rubrene was added to the precursor solution of BA2MA3Pb4I13 to modulate the performance of the 2D RP perovskite X-ray detectors. The cation-π interaction between rubrene and perovskite could passivate the defects and inhibit the ion migration, resulting in improved performance and stability. The detectors made with rubrene exhibited a sensitivity of 354.30 µC·Gyair-1 cm-2 and a detection limit of 112.85 nGyair s-1. This work highlights the synergistic effect of rubrene in defect passivation and ion migration inhibition, providing a facile approach toward sensitive perovskite X-ray detectors.

Nucleation Engineering in Sprayed MA3Bi2I9 Films for Direct-Conversion X-ray Detectors.

Metal halide perovskite and its derivatives show great promise in X-ray detection. However, large-scale fabrication of high-quality thick perovskite films is still full of challenges due to the complicated crystal nucleation process that always introduces lots of cracks or pinholes in the final perovskite film. Here, a MA3Bi2I9 film was fabricated by the cost-effective, scalable spraying process, and MACl was used as an additive to effectively tune the crystallization process. As a result, a dense MA3Bi2I9 film constituted by large grains was obtained, which has a high carrier mobility of ∼1 cm2 V-1 s-1 and a large activation energy (Ea) for ion migration of 0.91 eV. Thanks to the outstanding optoelectronic characteristics, X-ray detectors with a configuration of ITO/MA3Bi2I9/Au show a sensitivity of 35 µC Gyair-1 cm-2 and a limit of detection (LoD) of 0.14 µGyairs-1, which is outstanding compared with commercial α-Se detectors.

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.

Efficient X-ray Attenuation Lead-Free AgBi2I7 Halide Rudorffite Alternative for Sensitive and Stable X-ray Detection.

The poor attenuation capability of high-energy X-ray photons hinders the application of X-ray detectors in medical and astrophysical areas. Halide-based perovskites are promising candidates for X-ray detection because of their improved sensitivity. However, their inferior attenuation coefficient is still unsatisfactory for broadband X-ray detection. Here, a new kind of X-ray detection material, AgBi2I7 rudorffite single crystal (SC), is prepared and applied in X-ray detection for the first time, and it shows a higher attenuation coefficient than halide-based perovskites, commercialized a-Se, and the currently outstanding Cd0.9Zn0.1Te (CZT). The AgBi2I7 rudorffite SCs possess outstanding electric properties and excellent stability. AgBi2I7-SC detectors demonstrate a limit of detection (LoD) of 72 nGyair s-1 and a sensitivity of 282.5 µC Gyair-1cm-2 to X-rays and show only a slight performance degradation after ontinuous X-ray irradiation with a total dose of 58 Gyair. This work opens up a new perspective and broad opportunities for halide rudorffite in X-ray detection.

Robust Fabrication of Hybrid Lead-Free Perovskite Pellets for Stable X-ray Detectors with Low Detection Limit.

X-ray detectors are widely utilized in medical diagnostics and nondestructive product inspection. Halide perovskites are recently demonstrated as excellent candidates for direct X-ray detection. However, it is still challenging to obtain high quality perovskites with millimeter-thick over a large area for high performance, stable X-ray detectors. Here, methylammonium bismuth iodide (MA3 Bi2 I9 ) polycrystalline pellets (PPs) are developed by a robust, cost effective, and scalable cold isostatic-pressing for fabricating X-ray detectors with low limit of detection (LoD) and superior operational stability. The MA3 Bi2 I9 -PPs possess a high resistivity of 2.28 × 1011 Ω cm and low dark carrier concentration of ≈107 cm-3 , and balanced mobility of ≈2 cm2 V-1 s-1 for electrons and holes. These merits enable a sensitivity of 563 µC Gyair -1 cm-2 , a detection efficiency of 28.8%, and an LoD of 9.3 nGyair s-1 for MA3 Bi2 I9 -PPs detectors, and the LoD is much lower than the dose rate required for X-ray diagnostics used currently (5.5 µGyair s-1 ). In addition, the MA3 Bi2 I9 -PPs detectors work stably under high working bias field up to 2000 V cm-1 after sensing an integrated dose >320 Gyair with continuous X-ray radiation, demonstrating its competitive advantage in practical application. These findings provide an approach to explore a new generation of low LoD, stable and green X-ray detectors based on MA3 Bi2 I9 -PPs.

Defect Passivation in Hybrid Perovskite Solar Cells by Tailoring the Electron Density Distribution in Passivation Molecules.

Commercialization of perovskite solar cells (PSCs) requires developing high-efficiency devices with good stability. Ionic defects existing in the perovskite layer can serve as nonradiative recombination centers to deteriorate the performance of PSCs and can introduce chemical degradation of the perovskite material introducing instability issues. Here, passivation molecules with various electron density distributions (EDD) are employed as an ideal model to reveal the role of EDD on defect passivation in perovskite thin films. Power conversion efficiency (PCE) exceeding 21% with good stability in humid air was obtained for planar PSCs with the 4-aminobenzonitrile (ABN) additive, higher than the reference PSCs with a PCE of 20.22%. The improved stability and performance features are attributed to the efficient passivation for charged defects in perovskites by adding ABN, which guarantees a smaller Urbach energy, longer carrier lifetime, and less traps in the perovskite films.