Developed by Dalian Institute of Chemical Technology and other applications for X-ray imaging of zero-dimensional non-lead perovskite single crystal

[ Instrument R&D of Instrumentation Network ] Recently, the team of Liu Shengzhong, a researcher of the thin film silicon solar cell research group of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, cooperated with doctors Liu Yucheng, Xu Zhuo, and Yang Zhou of Shaanxi Normal University. The technology accumulation of single crystal growth and a complete scientific research platform have successfully designed and integrated large-scale zero-microstructure non-lead (type) perovskite single crystal high-performance X-ray imaging devices.

Perovskite refers to a class of ceramic oxides whose molecular formula is ABO3; such oxides were first discovered as calcium titanate (CaTiO3) compounds present in perovskites, hence the name. Because of the many structural characteristics of such compounds, they are widely used and studied in condensed matter physics, so physicists and chemists often refer to them as the ratio of each compound in the molecular formula (1:1:3), so The name "113 Structure". Cube-shaped crystal form. Cubic crystals often have stripes with parallel prisms, which is the result of producing polycrystalline twin crystals when the high-temperature variant is transformed into a low-temperature variant.

Perovskite is named after the Russian geology Preosvik, and its structure usually has a simple perovskite structure, a double perovskite structure and a layered perovskite structure. The chemical formula of a simple perovskite compound is, where X is usually a small radius or, the double-perovskite structure (Double-Perovskite) has a composition formula, the layered perovskite structure composition is more complicated, and more researched Is a general formula and has superconducting properties and three-layered layered perovskite. The most studied are compounds of perovskite structure type.

Perovskite materials are one of the most popular semiconductor materials in recent years. Compared with the perovskite microcrystalline thin film, the low defect state, high mobility and more stable large-size perovskite single crystal are more suitable for X-ray and other high-energy radiation detection. At present, there have been several three-dimensional/two-dimensional (3D/2D) perovskite single crystal materials used in X-ray detectors, but there are still many deficiencies. On the one hand, the three-dimensional perovskite single crystal has a high mobility and a large carrier diffusion length, but due to the higher carrier concentration, the photovoltaic device exhibits a high dark current. In addition, the internal ions of the three-dimensional perovskite are easy to migrate, especially in the high electric field, the ion migration is abnormally obvious, resulting in the detector is not stable under working conditions, the device has low signal-to-noise ratio, severe baseline drift, unstable response, even the device itself easily damaged.

Previous studies have shown that low ion migration and high bulk resistivity are necessary conditions to ensure stable output of high-energy ray detectors under high electric fields, and are therefore a great challenge to achieve high-performance X-ray imaging. In addition, how to obtain high-quality, large-size perovskite single crystals, and to replace highly toxic lead elements without sacrificing photoelectric performance, is a major problem in this field.

An x-ray detector is a device that converts X-ray energy into an electrical signal that can be recorded. It receives radiation and then generates an electrical signal proportional to the intensity of the radiation. Usually the strength of the radiation signal received by the detector depends on the density of the tissue in the cross-section of the human body at that location. Tissues with high density, such as bones, absorb more x-rays, and the signal received by the detector is weak; tissues with lower density, such as fat, absorb less x-rays, and the signal obtained by the detector is stronger. The different x-ray absorption values ​​of different tissues can be expressed by the tissue absorption coefficient m, so the signal strength received by the detector reflects the different m values ​​of human tissues, so as to make judgments on the nature of the tissues.

Using low-temperature solution growth strategy, the team successfully prepared large-size zero-dimensional structure bismuth-based perovskite (CH3NH3) 3Bi2I9 (MA3Bi2I9) single crystal. Tests have proved that the single crystal has a high X-ray absorption rate, a very low density of defect states, a low ion mobility, a high volume resistivity, and good environmental stability. The integrated X-ray detector designed and prepared on the MA3Bi2I9 single crystal shows excellent performance. Under the electric field of 60 Vmm-1, the sensitivity of the detector reaches 1947.3 μCGyair-1cm-2, and the detection limit is lower than 83 nGyairs-1, which is far lower than the conventional medical diagnostic dose standard (5.5 μGyairs-1). In addition, the baseline drift rate of the MA3Bi2I9 single crystal X-ray detector is 5.0×10-10 nAcm-1s-1V-1, which is 7 orders of magnitude lower than the three-dimensional structure of the MAPbI3 perovskite single crystal (2.0×10-3 nAcm-1s -1V-1), to ensure the device's good working stability and high signal-to-noise ratio, thereby achieving highly sensitive and stable X-ray imaging.

Source: Dalian Institute of Chemical Physics, Encyclopedia