Effect of methylammonium lead tribromide perovskite based-photoconductor under gamma photons radiation

Gamma-ray dose threshold for MAPbI3 solar cells

In this work, we report on the effects observed in MAPbI3 polycrystalline films and solar cells under moderate gamma-ray doses of 3-21 kGy. We applied several instrumental techniques such as photoluminescence spectroscopy, time-resolved photoluminescence, Suns-VOC measurement, and impedance spectroscopy to characterize exposed samples. We observed a nonlinear dependency of such characteristics as PL intensity, career lifetime, ideality factor, and recombination resistance on the exposure dose. Small doses of 3-5 kGy annihilate some of the defect centers in the material, which results in improved carrier extraction and prolonged carrier lifetime, while with larger doses of 10 kGy and above, nonradiative recombination becomes predominant. In this way, we revealed a gamma-ray threshold for MAPbI3 films of around 10 kGy, above which it is not recommended to exploit this material. In space environment, yearly doses rarely exhibit 0.1 kGy (10 krad), and the MAPbI3 material has a sufficient margin of safety for space applications. Moreover, this unusual behaviour opens up the opportunity to use gamma-ray sources as an effective method to improve the quality of defective polycrystalline perovskite films before actual exploitation in an ionizing radiation-free environment.

Self-Healing Behavior of the Metal Halide Perovskites and Photovoltaics

Perovskite solar cells have achieved rapid progress in the new-generation photovoltaic field, but the commercialization lags behind owing to the device stability issue under operational conditions. Ultimately, the instability issue is attributed to the soft lattice of ionic perovskite crystal. In brief, metal halide perovskite materials are susceptible to structural instability processes, including phase segregation, component loss, lattice distortion, and fatigue failure under harsh external stimuli such as high humidity, strong irradiation, wide thermal cycles, and large stress. Developing self-healing perovskites to further improve the unsatisfactory operational stability of their photoelectric devices under harsh stimuli has become a cutting-edge hotspot in this field. This self-healing behavior needs to be studied more comprehensively. Therefore, the self-healing behavior of the metal halide perovskites and photovoltaics is classified and summarized in this review. By discussing recent advances, underlying mechanisms, strategies, and existing challenges, this review provides perspectives on self-healing of perovskite solar cells in the future.

Halide Perovskites and Their Derivatives for Efficient, High-Resolution Direct Radiation Detection: Design Strategies and Applications

The past decade has witnessed a rapid rise in the performance of optoelectronic devices based on lead-halide perovskites (LHPs). The large mobility-lifetime products and defect tolerance of these materials, essential for optoelectronics, also make them well-suited for radiation detectors, especially given the heavy elements present, which is essential for strong X-ray and γ-ray attenuation. Over the past decade, LHP thick films, wafers, and single crystals have given rise to direct radiation detectors that have outperformed incumbent technologies in terms of sensitivity (reported values up to 3.5 × 106 µC Gyair -1 cm-2 ), limit of detection (directly measured values down to 1.5 nGyair s-1 ), along with competitive energy and imaging resolution at room temperature. At the same time, lead-free perovskite-inspired materials (e.g., methylammonium bismuth iodide), which have underperformed in solar cells, have recently matched and, in some areas (e.g., in polarization stability), surpassed the performance of LHP detectors. These advances open up opportunities to achieve devices for safer medical imaging, as well as more effective non-invasive analysis for security, nuclear safety, or product inspection applications. Herein, the principles behind the rapid rises in performance of LHP and perovskite-inspired material detectors, and how their properties and performance link with critical applications in non-invasive diagnostics are discussed. The key strategies to engineer the performance of these materials, and the important challenges to overcome to commercialize these new technologies are also discussed.

Exploring the Limits: Degradation Behavior of Lead Halide Perovskite Films under Exposure to Ultrahigh Doses of γ Rays of Up to 10 MGy

Herein, we show that thin films of MAPbI₃, FAPbI₃, (CsMA)PbI₃, and (CsMAFA)PbI₃, where MA and FA are methylammonium and formamidinium cations, respectively, tolerate ultrahigh doses of γ rays approaching 10 MGy without significant changes in their absorption spectra. However, among the studied materials, FAPbI₃ was the only one that did not form metallic lead due to its extreme radiation hardness. Infrared near-field optical microscopy revealed the radiation-induced depletion of organic cations from the grains of MAPbI₃ and their accumulation at the grain boundaries, whereas FAPbI₃ on the contrary lost FA cations from the grain boundaries. The multication (CsMAFA)PbI₃ perovskite underwent a facile phase segregation to domains enriched with MA and FA cations, which is a principally new radiation-induced degradation pathway. Our findings suggest that the radiation hardness of the rationally designed perovskite semiconductors could go far beyond the impressive threshold of 10 MGy we set herein for FAPbI₃ films, which opens many exciting opportunities for practical implementation of these materials.

Optimized photoelectric characteristics of MAPbCl3and MAPbBr3composite perovskite single crystal heterojunction photodetector

MAPbBr₃single crystal (SC) thin layer was successfully grown on MAPbCl₃SC substrate to form perovskite SC heterojunction. Planar structure electrodes are deposited by thermal evaporation on the surfaces of MAPbCl₃, MAPbBr₃, and SCs heterojunction, respectively to evaluate their photoelectric performance. The SC heterojunction device exhibits excellent unidirectional conductivity in the voltage-current curves. Meanwhile, the current-time curves prove that SC heterojunction devices can effectively utilize the advantages of MAPbCl₃and MAPbBr₃, possessing relatively low dark current (∼300 nA), which is comparable to the dark current of MAPbCl₃, but very high photocurrent (∼3500 nA), which is equivalent to the photocurrent of MAPbBr₃. Rather than the photocurrent overshot and decay occurring at the exposure of light illumination in the MAPbBr₃device, the photocurrent is extremely stable without overshot and decay in the SC heterojunction device. The light-to-dark ratio of the SC heterojunction device is twice that of MAPbCl₃device and three times that of MAPbBr₃device. Furthermore, the detectivity of the heterojunction device reaches as high as∼7×1011 Jones, an order of magnitude higher than MAPbCl₃and MAPbBr₃. The excellent characteristics of SC heterojunction further expand the practical application prospect of perovskite materials.

X-Ray-Induced Modification of the Photophysical Properties of MAPbBr3 Single Crystals

Methylammonium lead tribromide (MAPbBr₃) perovskite single crystals demonstrate to be excellent direct X-ray and gamma-ray detectors with outstanding sensitivity and low limit of detection. Despite this, thorough studies on the photophysical effects of exposure to high doses of ionizing radiation on this material are still lacking. In this work, we present our findings regarding the effects of controlled X-ray irradiation on the optoelectronic properties of MAPbBr₃ single crystals. Irradiation is carried out in air with an imaging X-ray tube, simulating real-life application in a medical facility. By means of surface photovoltage spectroscopy, we find that X-ray exposure quenches free excitons in the material and introduces new bound excitonic species. Despite this drastic effect, the crystals recover after 1 week of storage in dark and low humidity conditions. By means of X-ray photoelectron spectroscopy, we find that the origin of the new bound excitonic species is the formation of bromine vacancies, leading to local changes in the dielectric response of the material. The recovery effect is attributed to vacancy filling by atmospheric oxygen and water.

Environment-Induced Reversible Modulation of Optical and Electronic Properties of Lead Halide Perovskites and Possible Applications to Sensor Development: A Review

Lead halide perovskites are currently widely investigated as active materials in photonic and optoelectronic devices. While the lack of long term stability actually limits their application to commercial devices, several experiments demonstrated that beyond the irreversible variation of the material properties due to degradation, several possibilities exist to reversibly modulate the perovskite characteristics by acting on the environmental conditions. These results clear the way to possible applications of lead halide perovskites to resistive and optical sensors. In this review we will describe the current state of the art of the comprehension of the environmental effects on the optical and electronic properties of lead halide perovskites, and of the exploitation of these results for the development of perovskite-based sensors.