Compared with the widely reported MAPbBr 3 single crystals, formamidinium-based (FA-based) hybrid perovskites FAPbBr 3 (FPB) with superior chemical and structure stability are expected to be more efficient and perform as more reliable radiation detectors at room temperature. Here, we employ an improved inverse temperature crystallization method to grow FPB bulk single crystals, where issues associated with the retrograde solubility behavior are resolved. A crystal growth phase diagram has been proposed, and accordingly, growth parameters are optimized to avoid the formation of NH 4 Pb 2 Br 5 secondary phase. The resulting FPB crystals exhibit a high resistivity of 2.8 × 10 9 Ω•cm and high electron and hole mobility−lifetime products (μτ) of 8.0 × 10 −4 and 1.1 × 10 −3 cm 2 •V −1 , respectively. Simultaneously, the electron and hole mobilities (μ) are evaluated to be 22.2 and 66.1 cm 2 •V −1 •s −1 , respectively, based on the time-of-flight technique. Furthermore, a Au/FPB SC/Au detector is constructed that demonstrates a resolvable gamma peak from 59.5 keV 241 Am γ-rays at room temperature for the first time. An energy resolution of 40.1% is obtained at 30 V by collecting the hole signals. These results demonstrate the great potential of FAPbBr 3 as a hybrid material for γ-ray spectroscopy and imaging.

Despite the high performance of lead-halide perovskite-based X-ray detectors, the toxicity and instability of lead require the development of lead-free perovskites for X-ray detection applications. Here, we demonstrate lead-free and environmentally friendly, all-inorganic millimeter-sized Cs2AgBiCl6 double perovskite single crystal (SC) for X-ray detection and imaging. The high dark resistivity (3.1 × 1010 Ω cm), high carrier mobility-lifetime product (5.36 × 10–4 cm2 V–1), and lower trap density (1.18 × 109 cm–3) in these double perovskite SCs render them a potential material for X-ray detection. The fabricated vertical structured X-ray detector exhibits a sensitivity of 325.78 μC Gy air–1 cm–2 and a limit of detection of 241 nGy s–1. Additionally, the Cs2AgBiCl6 SCs exhibit self-powered X-ray detection at zero bias with a sensitivity of 7 μC Gy air–1 cm–2. Moreover, the fabricated perovskite X-ray detector exhibits a stable and robust performance under continuous X-ray irradiation and long-term ambient storage. Further, we demonstrated the imaging capability of the Cs2AgBiCl6 X-ray detector using a metal test object and obtained a distortion-free image. Our findings demonstrate that the Cs2AgBiCl6 single crystal-based X-ray detectors have great potential as practical X-ray detectors and imaging for medical radiography.

We have investigated the performance of formamidinium lead bromide (FAPbBr3) perovskite X-ray detectors fabricated from polycrystalline material that is pressed into a pellet at high pressures. FAPbBr3 has been shown to exhibit a remarkable combination of electrical and physical properties, such that mechanically-formed polycrystalline pellets exhibit good charge transport properties suitable for use as X-ray detectors. We characterise the morphology and structure of FAPbBr3 pellets using photoluminescence (PL), electron microscopy (SEM) and X-ray diffraction (XRD), and demonstrate an improvement in the microstructure, density, and charge transport performance of the material as the pressure is increased from 12 MPa to 124 MPa. The use of annealing of the pellets after pressing also improves the stability and charge transport performance of the devices. Using a 40 kV X-ray beam, a maximum X-ray sensitivity of 169 µC Gy−1 cm−2 was measured, and the fast time response of the devices was demonstrated using a chopped X-ray beam.

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