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X-ray detectors are broadly utilized in medical imaging and product inspection. Halide perovskites recently demonstrate excellent performance for direct X-ray detection. However, ionic migration causes large noise and baseline drift, limiting the detection and imaging performance. Here we largely eliminate the ionic migration in cesium silver bismuth bromide (Cs 2 AgBiBr 6 ) polycrystalline wafers by introducing bismuth oxybromide (BiOBr) as heteroepitaxial passivation layers. Good lattice match between BiOBr and Cs 2 AgBiBr 6 enables complete defect passivation and suppressed ionic migration. The detector hence achieves outstanding balanced performance with a signal drifting one order of magnitude lower than all previous studies, low noise (1/ f noise free), a high sensitivity of 250 µC Gy air −1 cm –2 , and a spatial resolution of 4.9 lp mm −1 . The wafer area could be easily scaled up by the isostatic-pressing method, together with the heteroepitaxial passivation, strengthens the competitiveness of Cs 2 AgBiBr 6 -based X-ray detectors as next-generation X-ray imaging flat panels.

Double perovskite Cs 2 AgInCl 6 is newly reported as a stable and environmentally friendly alternative to lead halide perovskites. However, the fundamental properties of this material remain unexplored. Here, we first produced high-quality Cs 2 AgInCl 6 single crystals (SCs) with a low trap density of 8.6 × 10 8 cm −3 , even lower than the value reported in the best lead halide perovskite SCs. Through systematical optical and electronic characterization, we experimentally verified the existence of the proposed parity-forbidden transition in Cs 2 AgInCl 6 and identified the role of oxygen in controlling its optical properties. Furthermore, sensitive (dectivity of ∼10 12 Jones), fast (3 dB bandwidth of 1035 Hz), and stable UV photodetectors were fabricated based on our Cs 2 AgInCl 6 SCs, showcasing their advantages for optoelectronic applications.

Se; [8] Park and co-workers reported sensitivities of CH 3 NH 3 PbI 3 X-ray detectors as high as 11 000 µC Gy air −1 cm −2 . [9] On the other hand, inorganic lead halide perovskites have demonstrated high carrier mobilities, good stability, and low ionic migrations compared to organic-inorganic hybrid perovskite [11] and, therefore, provide higher detection sensitivity toward X-rays; however, they have rarely been studied as X-ray detectors.Another challenge is the fabrication of a thick perovskite film with controlled orientations. A thickness of hundreds of micrometers to millimeters is the prerequisite for complete X-ray attenuation. The uniform orientation of perovskite films is beneficial for charge transport and collection along the electric field direction, thereby requiring a quasi-monocrystalline film. Here, we define a quasi-monocrystalline as the crystal with the same orientation and without grain boundaries along the vertical direction. Current perovskite film-based X-ray detectors face the issue of random orientation and, thus, inefficient charge collection. [9] A new method to fabricate thick quasimonocrystalline perovskite films for X-ray detection is urgently needed.For the first time, here, we employ a hot-pressing method to fabricate thick quasi-monocrystalline inorganic perovskite CsPbBr 3 films. The thickness of the film reaches hundreds of micrometers, which guarantees complete X-ray attenuation. The good orientation of the films is tuned to promote carrier transport close to that of the single-crystal samples. Most importantly, as-fabricated CsPbBr 3 X-ray detectors demonstrate a high sensitivity of 55 684 µC Gy air −1 cm −2 as a result of high carrier mobility, large µτ product, and photoconductive gain effect. Additionally, CsPbBr 3 detectors also exhibit relatively fast response speed, negligible baseline drift, and good stability, which together make the CsPbBr 3 X-ray detector extremely competitive in high-contrast X-ray detection and imaging applications.Currently, the synthesis of high-quality millimeter-thick perovskite films is still a great challenge, because the typical solution-based process often results in many pinholes when the solvent is evaporated out of the film. [9] Here, we propose and demonstrate a hot-pressing method to obtain thick perovskite films. The hot-pressing method avoids the use of any solvent, An X-ray detector with high sensitivity would be able to increase the generated signal and reduce the dose rate; thus, this type of detector is beneficial for applications such as medical imaging and product inspection. The inorganic lead halide perovskite CsPbBr 3 possesses relatively larger density and a higher atomic number in contrast to its hybrid counterpart. Therefore, it is expected to provide high detection sensitivity for X-rays; however, it has rarely been studied as a direct X-ray detector. Here, a hot-pressing method is employed to fabricate thick quasi-monocrystalline CsPbBr 3 films, and a record sensitivity of 55 684 µC Gy air −1 cm −2 is achieved, surpas...

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The double perovskite Cs 2 AgBiBr 6 single crystal holds great potential for detecting applications because of its low minimum detectable dose rate and toxic-free merit. Nevertheless, the disordered arrangement of Ag + /Bi 3+ usually gives rise to unexpected structural distortion and thereafter heavily influences the photoelectric properties of the Cs 2 AgBiBr 6 single crystal. Herein, phenylethylamine bromide is demonstrated to be capable of in situ regulation of the order-disorder phase transition in the Cs 2 AgBiBr 6 single crystal. The improved ordering extent of alternatively arranged [AgX 6 ] 5− and [BiX 6 ] 3− octahedra is theoretically and experimentally proven to decrease the defect density and suppress self-trapped exciton formation, and thereby tune the band gap and enhance the carrier mobility, which consequently promotes its application in an X-ray detector. The performance of a corresponding detector based on PEA-Cs 2 AgBiBr 6 single crystal displays superior performances, e.g., longer carrier drift distance, higher photoconductive gain, and faster current response (13 vs 3190 µs). Prominently, the as-fabricated PEA-Cs 2 AgBiBr 6 single-crystal X-ray detector has an extremely high sensitivity with a value of 288.8 µC Gy air −1 cm −2 under a bias of 50 V (22.7 V mm −1 ), which largely outperforms those of their counterparts with lower ordering structure.

For practical applications, the crystal quality of perovskites should be controlled in high reproducibility. However, current reports of solution-processed perovskite single crystals always meet with large fluctuations. For example, the resistivity of Pb-based perovskite SCs exhibits a wide fluctuation range from 10 7 to 10 9 Ω cm. [16][17][18] Moreover, the crystal surface is often troubled with terraces, which bring many undesired grain boundaries in the surface and negatively influence the properties. [1] These fluctuations all render the synthesis process inefficient, wasting a lot of time and raw materials.Above issues have also been observed in our recent work of Cs 2 AgBiBr 6 SC-based X-ray detectors. Due to the high average atomic number, high µτ product, and high resistivity, Cs 2 AgBiBr 6 is a potential material for direct X-ray conversion. Nevertheless, in a normal synthesis, Cs 2 AgBiBr 6 SCs are confronted with a wide resistivity range from 10 9 to 10 11 Ω cm [9] and hexagonal terraces are often seen on the surface. The wide resistivity range of Cs 2 AgBiBr 6 makes the dark current of the device with a high fluctuation range. We thus focus on the reproducible synthesis of stacking-free, high-quality Cs 2 AgBiBr 6 SCs for X-ray detectors.For solution synthesis of single crystals, there are successful theories to direct the growth process, which have been studied a lot in other materials like KH 2 PO 4 . [19,20] Principally, LaMer's [21] theories describe the crystal growth process as that the solution enters the nucleation stage upon the concentration of the precursor reaches the critical level for nucleation, and then the gradual consumption of the solute decreases the concentration into growth region where crystal nuclei could keep growing while no new nucleus could form. Further decreasing the concentration may lead to the dissolution of the products. Thereby, the nucleation and growth concentration are two key factors toward precise control over reproducibility and crystal quality. For perovskite crystal growth, such information is rarely reported, except some studies disclosed the value of solubility, [22][23][24][25] which is not enough for guiding the whole nucleation and crystal growth process.Herein, we measured the solubility and supersolubility curve to direct the growth process of Cs 2 AgBiBr 6 SCs. The supersolubility is defined as the solute concentration when nucleation starts in precursor solution, and the solubility is the Cs 2 AgBiBr 6 double perovskite recently emerges as a promising semiconductor for ionization detections because of the low detection limit and nontoxic composition. However, it suffers from unsatisfactory reproducibility and wide fluctuation of electrical properties, as also in other halide perovskite systems. Here, solubility and supersolubility are employed as quantitative indicators to direct the growth of Cs 2 AgBiBr 6 single crystals. The optimized Cs 2 AgBiBr 6 crystals exhibit smooth surface as well as high resistivity with narrow distribution from 6.10 × 10 ...