Direct X-ray detector based on one-dimensional bismuth-based perovskite material and preparation method

Abstract

The invention relates to a direct X-ray detector based on a one-dimensional bismuth-based perovskite material and a preparation method of the direct X-ray detector, the direct X-ray detector comprises the one-dimensional bismuth-based perovskite material, the molecular formula of the one-dimensional bismuth-based perovskite material is (2-FBA) 2BiI5, the one-dimensional bismuth-based perovskite material is a single crystal, and the inorganic chain [BiI5] < 2-> of the one-dimensional bismuth-based perovskite material is directionally arranged along a crystallographic c axis. The X-ray detector based on the one-dimensional bismuth-based perovskite material ((2-FBA) 2BiI5 single crystal) shows high sensitivity, low detection limit and high ion activation energy under X-ray irradiation, solves the technical problems of environmental pollution and serious internal ion migration of traditional three-dimensional lead-based perovskite, and improves the operation stability of the X-ray detector.

Description

Technical Field

[0001] The present invention belongs to the technical field of X-ray detection, and in particular relates to a direct X-ray detector based on a one-dimensional bismuth-based perovskite material and a preparation method thereof. Background Art

[0002] X-rays have strong penetrating power. By using the difference in the X-ray absorption ability of the detected object, the composition and internal information of the detected object can be inferred, which has attracted great attention in the fields of national defense, medical diagnosis and scientific research. However, traditional X-ray detector semiconductor materials face many problems, such as the small X-ray absorption coefficient of α-Se and the extremely harsh growth conditions of CZT (cadmium zinc telluride single crystal), which seriously restricts its development.

[0003] In recent years, thanks to its excellent optoelectronic properties and strong X-ray absorption, the application of three-dimensional (3D) organic-inorganic lead halide perovskite in X-ray detectors has achieved great success. However, the lead element in 3D lead halide perovskite has potential hazards to environmental safety and human health. At the same time, there is serious ion migration inside the 3D lead halide perovskite single crystal, which greatly affects the service life and stability of the device.

[0004] Therefore, it is necessary to design and construct an efficient and stable X-ray detector based on new green perovskite materials to achieve X-ray detection with high sensitivity, low detection limit and high stability. Summary of the invention

[0005] 1. Technical issues to be resolved: In view of the problems of small X-ray absorption coefficient, high preparation cost, environmental unfriendliness and insufficient stability of organic-inorganic lead halide perovskite and other problems existing in the semiconductor materials of prior art X-ray detectors, the present invention provides a direct X-ray detector based on one-dimensional bismuth-based perovskite material. The one-dimensional bismuth-based perovskite material has high resistivity, low trap state density and high ion activation energy, so that the X-ray detector has the advantages of high sensitivity, low detection limit, high carrier migration lifetime product and operation stability, etc., which solves the technical problems of traditional lead-based perovskite polluting the environment and serious ion migration.

[0006] (II) Technical solution: In a first aspect, the present invention provides a direct X-ray detector based on a one-dimensional bismuth-based perovskite material, which includes a one-dimensional bismuth-based perovskite material, wherein the molecular formula of the one-dimensional bismuth-based perovskite material is (2-FBA)2BiI5, and the material is a single crystal, and the inorganic chain [BiI5] 2- Oriented along the crystallographic c-axis.

[0007] Preferably, the X-ray detector further comprises two electrodes, the two electrodes are arranged at two ends of the surface of the one-dimensional bismuth-based perovskite material far away from each other, the electrodes are metal electrodes or conductive glue; a power supply and an ammeter are connected between the two electrodes.

[0008] Preferably, the X-ray detector further comprises a substrate, which is disposed below the one-dimensional bismuth-based perovskite material and is used to support the one-dimensional bismuth-based perovskite material; preferably, the substrate is a quartz sheet.

[0009] Preferably, the one-dimensional bismuth-based perovskite material is prepared as follows: bismuth trioxide, 2-fluorobenzylamine solution, hydroiodic acid and hypophosphorous acid solution are mixed to obtain a perovskite precursor dispersion; the precursor dispersion is heated and stirred until it is completely dissolved to obtain a solution; the solution is sealed in a reaction container, placed in an environment of 80°C and maintained at a constant temperature for 6-12 hours, and then the solution is cooled to 25°C at a rate of 1-2°C per day, and then the perovskite crystals are collected by filtration, and the residual microcrystals and solvents on the surface of the crystals are cleaned with an adsorption material, and dried to obtain a one-dimensional bismuth-based perovskite material (2-FBA)2BiI5, which is sealed and vacuumed for storage.

[0010] Preferably, the solution is sealed in a reaction container, kept at a constant temperature of 80°C for 12 hours, then cooled to 55°C at a constant rate of 144 hours, then reduced to 30°C at a rate of 1°C per day, and then cooled to 25°C in 72 hours, kept warm at 25°C for 24 hours, and the perovskite crystals were collected by filtration.

[0011] Among them, bismuth trioxide provides bismuth source (Bi 3+ donor), reacts with HI to form BiI3 precursor, and 2-fluorobenzylamine (2-FBA) provides organic cation (C7H7FNH3 + ), through protonation with [BiI5] 2- Inorganic chain hydrogen bond coordination, hypophosphorous acid as a reducing agent to prevent Bi 3+ Oxidation and provide an acidic environment together with hydroiodic acid. In the perovskite precursor dispersion, the theoretical molar ratio of Bi, I, and 2-FBA is 1:5:2, and HI is 5% excessive to compensate for volatilization, ensuring [BiI5] 2- Chain complete.

[0012] Preferably, the precursor dispersion is heated and stirred at 80-100° C. to promote the complete dissolution of bismuth trioxide; preferably, the solvent in the 2-fluorobenzylamine solution is a polar aprotic solvent such as MDF or DMSO to better control the crystallization process; the solvent in the hydroiodic acid and hypophosphorous acid solutions is water.

[0013] Preferably, when the solution is sealed in a reaction container, N2 atmosphere is filled into the reaction container for sealing, which is conducive to reducing iodine vacancies; preferably, the reaction container is a Teflon sealed reactor. Preferably, the drying treatment is vacuum drying in an infrared drying oven to avoid oxidation of the crystal surface; the drying conditions are drying at 80-100°C for 1-2h.

[0014] Preferably, a nylon mesh with a filtration aperture of 500 μm is used to collect the perovskite crystals and filter out the microcrystals, and then the microcrystals and solvent remaining on the surface of the crystals are cleaned with filter paper.

[0015] In a second aspect, the present invention further provides a method for preparing a direct X-ray detector based on a one-dimensional bismuth-based perovskite material, comprising: A (2-FBA)2BiI5 single crystal material with a clean and defect-free surface (without residual microcrystals and solvent) is fixed on a quartz substrate, an electrode is set at both ends of the surface of the (2-FBA)2BiI5 single crystal material, and a power supply and an ammeter are connected between the two electrodes to obtain an X-ray detector.

[0016] Preferably, a silver or platinum conductive glue is used to adhere the wires to both ends of the surface of the (2-FBA)2BiI5 single crystal material, and the power supply and the ammeter are connected through the wires; the conductive glue constitutes an electrode respectively, and the wires are metal wires with high conductivity such as copper, silver, platinum or gold.

[0017] Direct X-ray detectors are detectors that convert X-ray photon energy directly into electrical signals without the need for intermediate conversion steps. The core technology of direct X-ray detectors is based on high atomic number (Z) semiconductor materials. The working process of direct X-ray detectors is: X-rays → semiconductor materials → electron-hole pairs → direct electrical signals.

[0018] (III) Beneficial effects: (1) The present invention provides a one-dimensional bismuth-based perovskite material, i.e., a single crystal with a molecular formula of (2-FBA)2BiI5, which has the characteristics of high resistivity, low trap state density, and high carrier migration lifetime product (μτ product). These material properties are crucial to the performance and operational stability of X-ray detectors. High resistivity can reduce the intrinsic carrier concentration, making the dark current density of the detector extremely small when not irradiated, and increasing the sensitivity of the detector; low trap state density helps to extend the carrier lifetime and ensure full charge collection; high μτ product perovskite promotes the leapfrog development of X-ray detectors towards ultra-sensitive, low-dose, and multi-modal directions through the coordinated optimization of charge transport and defect suppression.

[0019] (2) The present invention adopts slow cooling technology to prepare the perovskite material, which is low-cost and easy to operate. The one-dimensional bismuth-based perovskite material ((2-FBA)2BiI5 single crystal) adopts F-π inhibition ion migration technology, by replacing benzylamine with H / F, and utilizing the intermolecular interaction between F and the benzene ring to inhibit the ion migration channel inside the material, thereby enhancing the stability of the X-ray detector prepared based on the material.

[0020] (3) The X-ray detector based on the one-dimensional bismuth-based perovskite material ((2-FBA)2BiI5 single crystal) of the present invention exhibits high sensitivity, low detection limit and high ion activation energy under X-ray irradiation, which solves the technical problems of environmental pollution and serious internal ion migration of traditional 3D lead-based perovskites and improves the operating stability of the X-ray detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a physical picture of (2-FBA)2BiI5 single crystal material.

[0022] Figure 2 This is the XRD pattern of (2-FBA)2BiI5 single crystal material.

[0023] Figure 3 This is the ion activation energy diagram of (2-FBA)2BiI5 single crystal material.

[0024] Figure 4 This is a schematic structural diagram of a direct X-ray detector based on a one-dimensional bismuth-based perovskite material according to the present invention.

[0025] Figure 5 IV diagram of the direct X-ray detector at different bias voltages and different dose rates.

[0026] Figure 6 Scatter plot of fitted IV for direct X-ray detector at 5V bias. DETAILED DESCRIPTION

[0027] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0028] Example 1 Preparation of (2-FBA)2BiI5 single crystal material, comprising the following steps: (1) Take a beaker, add 15 ml of hydroiodic acid (HI) and 1 ml of hypophosphorous acid (H2PO2) solution into the beaker, then weigh 0.61 g of bismuth trioxide into the beaker, stir evenly, and then add 0.63 ml of 2-fluorobenzylamine solution (solvent DMF) to obtain a perovskite precursor dispersion.

[0029] (2) The precursor dispersion was transferred to a heatable glass bottle, placed on a heating table, heated and stirred at 80°C until completely dissolved, and then the glass bottle was completely sealed and placed in an oven. The oven parameters were set to keep the solution at a constant temperature of 80°C for 12 hours, and then cooled to 55°C at a constant rate of 144 hours (6 days), and then reduced to 30°C at a rate of 1°C per day. Finally, the solution was cooled to 25°C over 72 hours. After keeping warm at 25°C for 24 hours, the glass bottle was removed from the oven, opened, and the perovskite crystals were collected by filtration. The residual microcrystals and solvent on the surface of the crystals were adsorbed with filter paper, and vacuum dried at 80°C for 2 hours in an infrared drying oven to obtain a one-dimensional bismuth-based perovskite material, namely the (2-FBA)2BiI5 single crystal material, which was sealed and vacuum-dried for storage. For the actual material, see Figure 1 Shown is red translucent material.

[0030] The purity of (2-FBA)2BiI5 single crystal was tested: the single crystal was ground into powder in a mortar, dried in an oven at 60°C for 6 hours, and tested by powder X-ray diffraction (XRD). The obtained X-ray powder diffraction pattern was as follows: Figure 2 As shown. Figure 2 It can be seen that XRD confirms their phase purity, and no phase change occurs even after being stored in air for three months. This proves that the method of the present invention can indeed prepare pure phase (2-FBA)2BiI5 single crystals, and by comparing the changes in the XRD graphs before and after three months, it can be proved that the (2-FBA)2BiI5 single crystals have good stability.

[0031] The (2-FBA)2BiI5 single crystal prepared in this example was further tested for stability: the single crystal was placed on a quartz plate and fixed, and conductive copper wires were bonded to both sides of the crystal surface using silver conductive glue. The obtained device was placed on a Lincoln hot table and heated from 25°C to 80°C with a 5°C difference. The IV data of each temperature range was measured and an ion activation energy diagram was plotted. The experimental results are shown in Figure 2. Figure 3 As shown in the figure, the ion activation energy of the single crystal is calculated by fitting the slope of the high temperature section. The results show that the ion activation energy of the (2-FBA)2BiI5 single crystal is as high as 0.81eV. Such a high ion activation energy ensures the stability of the long-term operation of the X-ray detector.

[0032] Figure 3 In the middle, the horizontal axis is 1,000 / T (K -1 ) represents the inverse of temperature × 1000, ln( σT ) represents the natural logarithm of the product of conductivity σ and temperature T.

[0033] Example 2 In this embodiment, the (2-FBA)2BiI5 single crystal material prepared in Example 1 is prepared into a direct X-ray detector. The structure of the direct X-ray detector is as follows: Figure 4 The preparation method of the direct X-ray detector is as follows: (1) A piece of (2-FBA)2BiI5 single crystal material with a smooth surface and no obvious defects is selected. The single crystal material has been adsorbed with filter paper to remove the residual microcrystals and solvent on the surface of the crystal, and then dried in an infrared drying oven at 80°C for 2 hours to remove surface impurities.

[0034] (2) If Figure 4 As shown, the (2-FBA)2BiI5 single crystal material 1 is placed on a quartz plate 2 and fixed, and conductive copper wires are adhered to both sides of the crystal surface using silver conductive glue as the first electrode 3 and the second electrode 4 respectively, and a power supply and an ammeter are connected to obtain a direct X-ray detector based on a one-dimensional bismuth-based perovskite material of the present invention.

[0035] The direct X-ray detector manufactured in this embodiment is placed under an X-ray light source, and the It (current-time) graphs of the device at 5V-50V are measured under X-ray irradiation at different dose rates. By fitting the data of these It graphs, we can obtain Figure 5 .from Figure 5 It can be seen that with the increase of bias voltage, the current density increases linearly, and under 50V bias voltage, the X-ray detector exhibits 1482.6μC Gy -1 cm -2 High sensitivity.

[0036] Figure 6 The detection limit of the direct X-ray detector under 5V bias condition is shown. The detection limit is defined as the minimum X-ray dose rate that can be reliably identified. According to international standards, the detection limit corresponds to the response signal equivalent dose rate when the signal-to-noise ratio (SNR) reaches 3. Figure 6 The data shown in Figure 2 show that the detection limit of the X-ray detector is as low as 18.6nGy / s. This means that it can work effectively at extremely low radiation dose rates, and its detection limit is only about 1 / 300 of that of traditional commercial α-Se semiconductor material X-ray detectors, thereby significantly reducing the radiation dose rate required for X-ray detection, which is of great significance to the safety and efficiency of the entire detection system.

[0037] In summary, the present invention proposes a scheme using F-π to inhibit ion migration technology, by replacing the ortho hydrogen (H) of benzylamine with fluorine (F), and using the intermolecular interaction between fluorine and the benzene ring to inhibit the ion migration channel inside the material. This method, combined with slow temperature cooling technology, successfully synthesized a one-dimensional bismuth-based perovskite (2-FBA)2BiI5 single crystal with excellent performance. The direct X-ray detector prepared based on this single crystal is not only simple in structure, easy to manufacture and low in cost, but also exhibits the characteristics of high sensitivity, low detection limit and high stability under X-ray irradiation. In particular, in Example 2, the detection limit value of the direct X-ray detector reached about 1 / 300 of that of the traditional commercial α-Se semiconductor material X-ray detector, which shows that it can achieve effective direct X-ray detection at extremely low radiation dose rates, significantly improving the efficiency and safety of the detection system. In summary, this new detector provides a more optimized choice for X-ray detection technology.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. These modifications or replacements, or the technical features in the above embodiments may be combined in the manner described in the embodiments if they do not conflict with each other, and these modifications, replacements or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A direct X-ray detector based on one-dimensional bismuth-based perovskite material, characterized in that: The one-dimensional bismuth-based perovskite material comprises a molecular formula of (2-FBA)2BiI5 and is a single crystal, and its inorganic chain [BiI5] 2- Oriented along the crystallographic c-axis.

2. The direct X-ray detector based on one-dimensional bismuth-based perovskite material according to claim 1, characterized in that: The X-ray detector also includes two electrodes, which are arranged at two ends of the surface of the one-dimensional bismuth-based perovskite material that are far away from each other, and the electrodes are metal electrodes or conductive glue; a power supply and an ammeter are connected between the two electrodes.

3. The direct X-ray detector based on one-dimensional bismuth-based perovskite material according to claim 1, characterized in that: The X-ray detector also includes a substrate, which is arranged below the one-dimensional bismuth-based perovskite material and is used to support the one-dimensional bismuth-based perovskite material.

4. The direct X-ray detector based on one-dimensional bismuth-based perovskite material according to any one of claims 1 to 3, characterized in that: The one-dimensional bismuth-based perovskite material is prepared as follows: bismuth trioxide, 2-fluorobenzylamine solution, hydroiodic acid and hypophosphorous acid solution are mixed to obtain a perovskite precursor dispersion; the precursor dispersion is heated and stirred until it is completely dissolved to obtain a solution; the solution is sealed in a reaction container, placed in an environment of 80° C. and kept at a constant temperature for 6-12 hours, and then the solution is cooled to 25° C. at a rate of 1-2° C. per day, and then the perovskite crystals are collected by filtration, and the microcrystals and solvents remaining on the surface of the crystals are cleaned by an adsorption material, and dried to obtain a one-dimensional bismuth-based perovskite material (2-FBA)2BiI5, which is sealed and vacuumed for storage.

5. The direct X-ray detector based on one-dimensional bismuth-based perovskite material according to claim 4, characterized in that: The solution was sealed in a reaction container and kept at a constant temperature of 80°C for 12 hours. The solution was then cooled to 55°C at a constant rate of 144 hours, and then reduced to 30°C at a rate of 1°C per day. The solution was further cooled to 25°C over 72 hours. The solution was kept warm at 25°C for 24 hours and the perovskite crystals were collected by filtration.

6. The direct X-ray detector based on one-dimensional bismuth-based perovskite material according to claim 4, characterized in that: The precursor dispersion is heated and stirred at 80-100° C. to promote complete dissolution of bismuth trioxide; the solvent in the 2-fluorobenzylamine solution is MDF or DMSO.

7. The direct X-ray detector based on one-dimensional bismuth-based perovskite material according to claim 4, characterized in that: When the solution is sealed in the reaction container, N2 atmosphere is filled into the reaction container to seal it; the drying treatment is vacuum drying in an infrared drying oven, and the drying conditions are drying at 80-100°C for 1-2h.

8. The direct X-ray detector based on one-dimensional bismuth-based perovskite material according to claim 4, characterized in that: A nylon mesh with a pore size of 500 μm was used to collect the perovskite crystals and filter out the microcrystals, and then the microcrystals and solvent remaining on the surface of the crystals were cleaned with filter paper.

9. A method for preparing a direct X-ray detector based on a one-dimensional bismuth-based perovskite material, characterized in that: include: A (2-FBA)2BiI5 single crystal material with a clean surface is fixed on a quartz substrate, wherein the single crystal material is a one-dimensional bismuth-based perovskite material, and its molecular formula is (2-FBA)2BiI5, an electrode is respectively arranged at both ends of the surface of the single crystal material, and a power supply and an ammeter are connected between the two electrodes to obtain an X-ray detector; The one-dimensional bismuth-based perovskite material is prepared as follows: bismuth trioxide, 2-fluorobenzylamine solution, hydroiodic acid and hypophosphorous acid solution are mixed to obtain a perovskite precursor dispersion; the precursor dispersion is heated and stirred until it is completely dissolved to obtain a solution; the solution is sealed in a reaction container, placed in an 80°C environment and maintained at a constant temperature for 6-12 hours, and then the solution is cooled to 25°C at a rate of 1-2°C per day, and then the perovskite crystals are collected by filtration, and the residual microcrystals and solvents on the surface of the crystals are cleaned by an adsorption material, and dried to obtain a one-dimensional bismuth-based perovskite material (2-FBA)2BiI5.

10. The method for preparing a direct X-ray detector based on a one-dimensional bismuth-based perovskite material according to claim 9, characterized in that: Conductive wires are bonded to the two ends of the surface of the (2-FBA)2BiI5 single crystal material using a conductive glue of silver or platinum, and a power source and an ammeter are connected through the conductive wires; the conductive glues each constitute an electrode, and the conductive wires are metal wires of copper, silver, platinum or gold.

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