Here, we report the progress of detector-grade metal halide perovskite and device fabrication for X-ray and gamma-ray detection. For the 3D perovskite, the all-inorganic perovskite CsPbBr₃ grown by either solution or melt method demonstrates an energy resolution of ~7% for 5.49 MeV ²⁴¹Am α particles, while exhibits a good peak discrimination for 59.5 keV ²⁴¹Am γ-rays. In terms of organic-inorganic hybrid perovskite, solution grown FAPbBr₃ resolves 59.5 keV ²⁴¹Am γ-rays with an energy resolution of 40.1% at room temperature for the first time. To further improve the perovskite stability resulted from the ion migration, dimensional reduction engineering was employed on the 3D perovskite. The 2D hybrid perovskite by incorporating large organic cations into CsPbBr₃, the resulting (BDA)CsPb₂Br₇ detector shows a capability for detecting 5.49 MeV ²⁴¹Am α-particles with an energy resolution of 37%, while possesses high X-ray sensitivity up to 725.5 μC∙Gy^-1∙cm^-2 with excellent working stability. Furthermore, we also demonstrate a potential candidate the 0-D perovskite material Cs2TeI6 grown by electrostatic assisted spray (E-spray) deposition, as a sensitive all-inorganic X-ray photoconductor for direct photon-to-current conversion X-Ray detectors. The electrospray apparatus can be readily automated and fully integrated with the existing display systems based on TFT or CMOS, which will help to implement and scale up this device for manufacturing next generation of flat panel X-ray imagers.

Metal halide perovskites have fascinated the research community over the past decade, and demonstrated unprecedented success in the field of photovoltaics, light emitting devices and photodetection. In particular, perovskites have emerged as excellent candidates to detect ionizing radiation, mainly including direct detection and indirect devices with an additional scintillation process. Compared with visible photons, ionizing radiations have higher energy and long penetration depth, and require much thicker absorbing layers, i.e. a few hundreds of micrometers. Hence, we have to fabricate thick junction devices to effectively absorb X-ray or  g-ray. On the other hand, charge transport and recombination losses are another issue for direct detection of ionizing radiations, limited by the moderate mobility-lifetime product. In this talk, I mainly introduce three strategies to prepare thick-junctions, which are based on perovskite /polymer composite films, perovksite single crystals and co-evaporated perovskite thick films. The balance between absorption and charge transport will be discussed, which is also correlated with the device performance, e.g., dark and noise current, photogeneration, response time and linear dynamic range.

Advances in medical imaging relay equally on enhancements in computing power required by the increasing demand of machine learning and further material and technology improvements which will lead to better image quality and medical outcomes. Hybrid inorganic-organic perovskite materials like methylammonium lead triiodide (MAPbI₃) promise direct conversion detectors with higher image quality, owing to their strong X-ray absorption, high electron and hole diffusion lengths with high charge carrier mobility and long carrier lifetime. However, their incorporation into pixelated sensing arrays remains challenging. Here we show a novel manufacturing process that decouples the fabrication of the several micrometre thick absorber layer and its integration onto an amorphous Silicon transistor backplane. Since no consideration of the limitations of the backplane electronics is necessary, the options for the production parameters of the wafers are not restricted. We chose a so-called mechanical soft-sintering approach for the fabrication of the 230 µm thick and freestanding MAPbI₃ wafer. A photoresist grid functions as a mechanical anchor and recrystallized MAPbI₃ acts as an adhesion promoter for the soft-sintered absorber layer. The resulting X-ray imaging detector with 508 pixels per inch combines a low detection limit of 0.22 nGy_air frame^-1, a sensitivity of 1060 µCGy_air^-1cm^-2 with a high spatial resolution of 6 line-pairs mm^-1. In conclusion, polycrystalline MAPbI₃ X-ray imaging detectors provide a very high potential to stable and excellent detection over the whole energy range of X-ray application. Our fabrication technology offers the possibility of simply scale-up to large detector areas.

Our sequential physical vapor deposited methylammonium lead tri-iodide (MAPbI3) thin films and solar cells have shown remarkable resilience (hardness) under high energy (5.5 MeV) alpha radiation beams from americium 241 (241Am). Analyses of the structural, optical, morphological, and photoelectric properties of the perovskite thin films and solar cells with and without irradiation with alpha particles (He2+) were performed. An increase in crystallinity and a decrease in compression micro-strain of tetragonal MAPbI3 with an increased flux of He2+ were observed after XRD analysis. In the UV-Vis absorption spectrum, there was little change in absorbance up to a flux of 7.36 x 1012 He2+ cm-2. The decrease in bandgap for the irradiated films paralleled the non-irradiated up to a fluence of 3.07 x 1012 He2+cm-2, after that, there was a large difference. Photographs taken with a digital camera showed visible changes on the thin irradiated films at fluence levels exceeding 3.07 x 1012 He2+ cm-2 and electron micrographs confirmed that the changes are a result of pits forming in grains. The performances of irradiated and non-irradiated hole transport layer-free solar cells were monitored for the same period. A reduction in power conversion efficiency (PCE) from 6.56% to 6.42%, which is not significant, was observed up to a radiation dose of 1.23 x 1012 He2+ cm-2, thereafter, a substantial drop from 6.42% to 4.75% as the flux increased to 7.36 x 1012 He2+ cm-2. In contrast, the non-irradiated solar cell experienced a reduction in PCE from 6.39% to 6.23% within 48 hours, and as the time interval increased to 288 hours, there was a gradual decline from 6.23% to 5.70%. Based on what we found, MAPbI3 thin films can withstand He2+doses up to 3.07 x 1012 He2+ cm-2, and MAPbI3 solar cells can withstand doses up to 1.23 x 1012 He2+ cm-2 in space and He2+ environments.

Keywords: Methylammonium lead tri-iodide perovskite, sequential physical vapor deposition, He2+irradiation, perovskite solar cells, remarkable resilience, space environment, and He2+ environments.

Metal halide perovskite materials are being explored as functional materials for a variety of optoelectronic applications but a general uncertainty exists about the relevant mechanisms governing the electronic operation. The presence of mobile ions and how these species alter the internal electrical field and interact with the contact materials or modulate electronic properties is still a challenging subject. In order to understand their working mechanisms, here, ionic current and electronic impedance in two different perovskite-based devices were independently monitored, showing self-consistent patterns. Firstly, analyzing the bias and time dependence of bulk resistance informs about the accumulation and relaxation dynamics of the moving ionic species in high-quality thick MAPbBr₃ single crystals. Secondly, the change of the electronic doping profile within the bulk, determined by the ion inner distribution, induced a time dependence in the electronic conductivity and reproduces time patterns of the type ∝ t^1/2, a clear fingerprint of diffusive transport in MAPI microcrystalline-pellets. Our findings point to a coupling of ionic and electronic properties as a dynamic doping effect caused by moving ions that act as mobile dopants. In conclusion, this research provides a connection between ionic and electronic properties that allow us progressing into the halide perovskite device physics and operating modes.

Ionizing radiation, wherever present, e.g., in medicine, nuclear environment, or homeland security, due to its strong impact on biological matter, should be closely monitored. Availability of semiconductor materials with distinctive characteristics required for an efficient high-energy photon detection, especially with high atomic numbers (high Z), in sufficiently large, single-crystalline forms, which would also be both chemically and mechanically robust, is still very limited.

Metal halide perovskite were indeed found to meet all aforementioned key requirements, at an extremely low cost. In this work γ-ray detectors based on crystals of methylammonium lead tribromide (MAPbBr₃) equipped with carbon electrodes were fabricated, allowing radiation detection by photocurrent measurements at room temperatures with record sensitivities (333.8 μC Gy^-1 cm^-2 ). Importantly, the devices operated at low bias voltages (<1.0 V), which may enable future low-power operation in energy-sparse environments, including space. The detector prototypes were exposed to radiation from a ⁶⁰Co source at dose rates up to 2.3 Gy h^-1 under ambient and operational conditions for over 100 h, without any sign of degradation. We postulate that the excellent radiation tolerance stems from the intrinsic structural plasticity of the organic-inorganic halide perovskites, which can be attributed to a defect-healing process by fast ion migration at the nanoscale level.

Furthermore, since the sensitivity of the γ-ray detectors is proportional to the volume of the employed MAPbBr₃ crystals, a unique crystal growth technique is introduced, baptized as the “oriented crystal-crystal intergrowth” or OC2G method, yielding crystal specimens with volume and mass of over 1000 cm3 and 3.8 kg, respectively. Large-volume specimens have a clear advantage for radiation detection; however, the demonstrated kilogram-scale crystallogenesis coupled with future cutting and slicing technologies may have additional benefits, for instance, enable the development for the first time of crystalline perovskite wafers, which may challenge the status quo of present and future performance limitations in all optoelectronic applications.

Here I will give insight into the uniqueness and challenges of charge transport in halide perovskites. Despite the tremendous efforts in the study of their electric properties, the free carriers - defects interactions and some critical defect properties are still unclear in methylammonium lead halide perovskites (MHPs). Here we use a multi-method approach to quantify and characterize defects in single crystal MAPbI3 giving a cross-checked overview of their properties. Time of Flight current waveform spectroscopy (ToF CWF) reveals the interaction of carriers with five shallow and deep defects. Photo Hall (PHES) and Thermoelectric effect spectroscopy (TEES) assess the defect density, cross-section, and relative (to the valence band) energy. The detailed reconstruction of free carrier relaxation through Monte Carlo (MC) simulation allow quantifying the lifetime, mobility, and diffusion length of hole and electron separately. We demonstrate that the dominant part of defects releases free carriers after trapping; this happens without non-radiative recombination with consequent positive effects on the photoconversion and charge transport properties. On the other hand, shallow traps decrease the drift mobility sensibly. Our results provide a trustworthy picture for future consideration on the defect properties in MAPbI3 thanks to the verification of our statements with multiple methods. Our results will be key for the optimization of the charge transport properties and defects in MHP and will contribute to the research aiming to improve their stability[1].

Sensitive detection of X-rays, gamma rays, and energetic particles plays a key role in medical imaging, nonproliferation, homeland security, environmental monitoring, and fundamental scientific research. In this presentation, we will summarize the latest progress in the development of perovskite single crystal detectors and report our efforts in developing double perovskites for improved radiation detection. Detailed material characterization and detector tests will be presented and discussed. Examples include Cs₂AgBiBr₆ single crystals with different stoichiometry. These crystals have some desired characteristics, such as suitable bandgap energy, low density of trap states, low dark carrier concentration, and high mu-tau (μ-τ) product, for ionizing radiation detection applications. The measurement results show that perovskite crystals could serve as an emerging class of radiation detector materials for ionizing radiation detection.