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

Dimensional Regulation in Metal-Free Perovskites by Compositional Engineering to Achieve Record Low X-Ray Detection Limits

Utilizing the manipulation of perovskite dimensions has been proven as an effective approach in regulating perovskite properties. Nevertheless, achieving precise control over the dimensions of perovskites within the same system poses a significant challenge. In this study, we introduce a sophisticated method to attain precise dimensional control in metal-free perovskites (MFPs), specifically through the process of octahedron tailoring by compositional engineering. Accordingly, we successfully instigated a transition from HPIP-NH4I3 ⋅ H2O (3D), HPIP2-NH4I5 (2D) and HPIP3-NH4I7 (1D) structures. Notably, HPIP2-NH4I5 is the first 2D MFP. As anticipated, these perovskites exhibited completely distinct fluorescence and X-ray detection capabilities due to their differing dimensions. Remarkably, the 2D HPIP2-NH4I5 device effectively hindered ion migration perpendicular to the 2D layers, achieving the lowest detection limit of 12.2 nGyair s-1 among metal-free single crystals-based detectors. This study expands the dimensionality control strategies for MFPs and introduces, for the first time, the potential of 2D MFPs as high-performance X-ray detectors, thereby enriching the diversity of the MFPs family.

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.

Homogeneous Bridging Induces Compact and Scalable Perovskite Thick Films for X-Ray Flat-Panel Detectors

Solution-processed organic-inorganic hybrid perovskite polycrystalline thick films have shown great potential in X-ray detection. However, the preparation of compact perovskite thick films with large area is still challenging due to the limitation of feasible ink formulation and pinholes caused by solvent volatilization. Post-treatment and hot-pressing are usually involved to improve the film quality, which is however unsuitable for subsequent integration. In this work, a homogeneous bridging strategy is developed to prepare compact perovskite films directly. A stable perovskite slurry with suitable viscosity consisting of undissolved grains and supersaturated solution is formed by adding a weak coordination solvent to the pre-synthesized microcrystalline powders. Small perovskite grains in situ grow from the saturated solution during the annealing, filling the pinholes and connecting the surrounding original grains. As a result, large-area perovskite thick film with tight grain arrangement and ultralow current drift is blade-coated to achieve X-ray imaging. The optimal device displays an impressive mobility-lifetime product of 2.2 × 10-3  cm2  V-1 and a champion ratio of sensitivity to the dark current density of 2.23 × 1011  µC Gyair -1  A-1 . This work provides a simple and effective route to prepare high-quality perovskite thick films, which is instructive for the development of perovskite-based X-ray flat-panel detectors.

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.

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·Gy_air^-1 cm^-2 and a detection limit of 112.85 nGy_air 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.

Improving the Performance and High-Field Stability of FAPbBr3 Single Crystals in X-Ray Detection with Chenodeoxycholic Acid Additive

Organometal halide perovskite single crystals are one of the most promising radiation detection materials due to their unique advantages of high absorption coefficient, long carrier diffusion length, and low defect density. However, the severe ion migration in perovskites deteriorates the X-ray detection performance under longtime and high-field operating conditions. This work reports an effective additive of chenodeoxycholic acid (CDCA), which can suppress the ion migration and improve the performance and the operational stability of FAPbBr₃ single crystals (SCs) in X-ray detection significantl. The CDCA molecules in precursors effectively suppress the decomposition of FA ions, resulting in a better crystal orientation and stoichiometry. The trace amounts of CDCA residues in FAPbBr₃ SCs improve the thermal stability and effectively suppress the ion migration. The resulting detector shows an impressive X-ray sensitivity up to 21 386.88 µC Gy_air ^-1 cm^-2 under -500 V and a detection limit of 15.23 nGy_air s^-1 . The response current of the detector at 225 V cm^-1 field is barely changed under the 7200 s irradiation with a dose rate of 1.949 mGy_air s^-1 . This work provides insights for the additive selection and improving the operational stability of perovskite single crystals for commercial applications.