Direct X-ray Detector Based on One-Dimensional Bismuth-Based Perovskite Materials and Preparation Method

Abstract

The present invention relates to a direct X-ray detector based on a one-dimensional bismuth-based perovskite material and a preparation method thereof. The direct X-ray detector includes a one-dimensional bismuth-based perovskite material. The molecular formula of the one-dimensional bismuth-based perovskite material is (2-FBA)2BiI5, and it is a single crystal. Its inorganic chain [BiI5] 2‑ is oriented along the crystallographic c-axis. 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 ionic activation energy under X-ray irradiation, solves the technical problems of environmental pollution and serious internal ion migration of traditional three-dimensional lead-based perovskites, 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 particularly 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 penetration ability. By utilizing the differences in the X-ray absorption capabilities of the objects to be detected, the composition and internal information of the objects to be detected can be inferred, which has attracted great attention in the fields of national defense, medical diagnosis, and scientific research. However, traditional semiconductor materials for X-ray detectors face many problems. For example, the X-ray absorption coefficient of α-Se is small, and the growth conditions of CZT (cadmium zinc telluride single crystal) are extremely harsh, which severely restricts their development.

[0003] In recent years, due to excellent optoelectronic properties and strong X-ray absorption, the application of three-dimensional (3D) organic-inorganic lead halide perovskites in X-ray detectors has achieved great success. However, the lead element in the 3D lead halide perovskites poses 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 a new type of green perovskite material to achieve X-ray detection with high sensitivity, low detection limit, and high stability. Summary of the Invention

[0005] (I) Technical Problems to be Solved

[0006] In view of the problems existing in the semiconductor materials of X-ray detectors in the prior art, such as small X-ray absorption coefficient, high preparation cost, environmental unfriendliness of organic-inorganic lead halide perovskites, and insufficient stability, the present invention provides a direct X-ray detector based on a 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, enabling the X-ray detector to have advantages such as high sensitivity, low detection limit, high carrier migration lifetime product, and operating stability, and solving the technical problems of environmental pollution and serious ion migration of traditional lead-based perovskites.

[0007] (II) Technical Solutions

[0008] In the 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. The molecular formula of the one-dimensional bismuth-based perovskite material is (2-FBA)2BiI5, and it is a single crystal, and its inorganic chain [BiI5] 2- is oriented along the crystallographic c-axis.

[0009] Preferably, the X-ray detector further includes two electrodes, which are arranged at two ends of the surface of the one-dimensional bismuth-based perovskite material away from each other, and the electrodes are metal electrodes or conductive adhesives; a power supply and a galvanometer are connected between the two electrodes.

[0010] Preferably, the X-ray detector further 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; preferably, the substrate is a quartz sheet.

[0011] Preferably, the one-dimensional bismuth-based perovskite material is prepared as follows: Mix bismuth trioxide, 2-fluorobenzylamine solution, hydroiodic acid and hypophosphorous acid solution to obtain a perovskite precursor dispersion; heat and stir the precursor dispersion until it is completely dissolved to obtain a solution; seal the solution in a reaction vessel, place it in an environment of 80 °C and keep it at a constant temperature for 6-12 h, then cool the solution at a rate of 1-2 °C per day to 25 °C, then filter and collect the perovskite crystals, use an adsorbent material to absorb the residual microcrystals and solvents on the crystal surface, and perform a drying treatment to obtain the one-dimensional bismuth-based perovskite material (2-FBA)2BiI5, which is sealed and stored under vacuum.

[0012] Preferably, seal the solution in a reaction vessel, place it in an environment of 80 °C and keep it at a constant temperature for 12 h, then cool the solution at a constant rate to 55 °C in 144 h, then cool it to 30 °C at a rate of 1 °C per day, and continue to cool the solution to 25 °C in 72 h, and keep it at 25 °C for 24 h, and then filter and collect the perovskite crystals.

[0013] Among them, bismuth trioxide provides a bismuth source (Bi 3+ donor), reacts with HI to form a BiI3 precursor, 2-fluorobenzylamine abbreviated as 2-FBA provides an organic cation (C7H7FNH3 + ), coordinates with the [BiI5] 2- inorganic chain through protonation by hydrogen bonding, and hypophosphorous acid is used as a reducing agent to prevent Bi 3+ from being oxidized and provides 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 made to be 5% in excess to compensate for volatilization to ensure the integrity of the [BiI5] 2- chain.

[0014] Preferably, heat and stir the precursor dispersion at a temperature of 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 solvents in the hydroiodic acid and hypophosphorous acid solutions are both water.

[0015] Preferably, when sealing the solution in the reaction vessel, fill the reaction vessel with an N2 atmosphere for sealing, which is beneficial to reducing iodine vacancies; preferably, the reaction vessel 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 1-2 h.

[0016] Preferably, a nylon mesh with a filtration pore size of 500 μm is used to collect perovskite crystals and filter out microcrystals, and then filter paper is used to suck clean the residual microcrystals and solvents on the crystal surface.

[0017] In a second aspect, the present invention also provides a preparation method of a direct X-ray detector based on a one-dimensional bismuth-based perovskite material, which includes:

[0018] Fix a clean and defect-free (without residual microcrystals and solvents) (2-FBA)2BiI5 single crystal material on a quartz wafer substrate, set an electrode at each end of the surface of the (2-FBA)2BiI5 single crystal material, and connect a power supply and a galvanometer between the two electrodes to obtain an X-ray detector.

[0019] Preferably, use a conductive adhesive of silver or platinum to adhere the wires to both ends of the surface of the (2-FBA)2BiI5 single crystal material, and connect the power supply and the galvanometer through the wires; the conductive adhesives respectively form an electrode, and the wires are high-conductivity metal wires such as copper, silver, platinum or gold.

[0020] A direct X-ray detector is a detector that directly converts X-ray photon energy into an electrical signal without an intermediate conversion step, and its technical core relies on a semiconductor material with a high atomic number (Z). The working process of a direct X-ray detector: X-ray → semiconductor material → electron-hole pair → direct electrical signal.

[0021] (III) Beneficial effects:

[0022] (1) The present invention provides a one-dimensional bismuth-based perovskite material, namely a single crystal with the molecular formula (2-FBA)2BiI5. This material has the characteristics of high resistivity, low trap state density, and high carrier mobility-lifetime product (μτ product). These material properties are crucial for the performance and operation stability of X-ray detectors. High resistivity can reduce the intrinsic carrier concentration, making the dark current density of the detector extremely small when there is no irradiation, and increasing the sensitivity of the detector; low trap state density helps to extend the carrier lifetime and ensure complete charge collection; the high μτ product perovskite promotes the leapfrog development of X-ray detectors towards ultra-sensitive, low-dose, and multimodal directions through the synergistic optimization of charge transport and defect suppression.

[0023] (2) The present invention uses a slow cooling technique to prepare the perovskite material, which has low cost and is easy to operate. The one-dimensional bismuth-based perovskite material ((2-FBA)2BiI5 single crystal) uses an F-π inhibition ion migration technique. By performing H / F substitution on benzylamine and utilizing the intermolecular interaction between F and the benzene ring, the ion migration channels inside the material are inhibited, thereby enhancing the stability of the X-ray detector prepared based on this material.

[0024] (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, solving the technical problems of environmental pollution and serious internal ion migration in traditional 3D lead-based perovskites, and improving the operating stability of the X-ray detector. Description of the Drawings

[0025] Figure 1 It is a physical diagram of the (2-FBA)2BiI5 single crystal material.

[0026] Figure 2 It is an XRD diagram of the (2-FBA)2BiI5 single crystal material.

[0027] Figure 3 It is an ion activation energy diagram of the (2-FBA)2BiI5 single crystal material.

[0028] Figure 4 It is a schematic structural diagram of a direct X-ray detector based on the one-dimensional bismuth-based perovskite material of the present invention.

[0029] Figure 5 It is an I-V diagram of the direct X-ray detector under different bias voltages and different dose rates.

[0030] Figure 6 It is a scatter plot of the fitted I-V of the direct X-ray detector under a 5V bias voltage. Detailed Embodiments

[0031] In order to better explain the present invention for easy understanding, the present invention will be described in detail below in conjunction with the drawings through specific embodiments.

[0032] Example 1

[0033] Prepare the (2-FBA)2BiI5 single crystal material, including the following steps:

[0034] (1) Take a beaker, add 15 ml of hydroiodic acid (HI) and 1 ml of hypophosphorous acid (H2PO2) solution to the beaker, then weigh 0.61 g of bismuth trioxide and add it to the beaker. After stirring evenly, add 0.63 ml of 2-fluorobenzylamine solution (solvent DMF) to obtain a perovskite precursor dispersion.

[0035] (2) Transfer the precursor dispersion to a heatable glass bottle, place it on a heating table, heat and stir at 80 °C until completely dissolved. Then tightly seal the glass bottle and place it in an oven. Then set the oven parameters to keep the solution at a constant temperature of 80 °C for 12 h, then cool it at a constant rate to 55 °C over 144 h (6 days), then cool it at a rate of 1 °C per day to 30 °C, and finally cool the solution to 25 °C in 72 h. After keeping it at 25 °C for 24 h, take out the glass bottle from the oven, open the glass bottle, filter and collect the perovskite crystals, and use filter paper to adsorb the residual microcrystals and solvent on the crystal surface. Vacuum dry it at 80 °C for 2 h using an infrared drying oven to obtain a one-dimensional bismuth-based perovskite material, which is the (2-FBA)2BiI5 single crystal material, and store it in a sealed and evacuated manner. See the physical object of the material Figure 1 as shown, it is a red translucent material.

[0036] Perform purity detection on the (2-FBA)2BiI5 single crystal: Place the single crystal in a mortar and grind it into powder, place it in an oven at 60 °C and dry it for 6 h, and perform detection by powder X-ray diffraction (XRD) to obtain the X-ray powder diffraction pattern, as Figure 2 shown. From Figure 2 it can be seen that XRD confirmed their phase purity, and no phase change occurred even after being stored in air for three months. This proves that the method of the present invention can indeed prepare a pure-phase (2-FBA)2BiI5 single crystal, and the good stability of the (2-FBA)2BiI5 single crystal can be proved by comparing the changes in the XRD patterns before and after three months.

[0037] Further, perform stability detection on the (2-FBA)2BiI5 single crystal prepared in this example: Place the single crystal on a quartz sheet and fix it, use silver conductive glue to stick conductive copper wires on both sides of the crystal surface, place the obtained device on a Lincoln hot stage, heat it from 25 °C to 80 °C at an interval of 5 °C, and measure the I-V data for each temperature segment to draw an ion activation energy diagram. The experimental results are as Figure 3 shown. Calculate the ion activation energy value of the single crystal by fitting the slope of the high-temperature segment. The results show that the ion activation energy of the (2-FBA)2BiI5 single crystal is as high as 0.81 eV. Such a high ion activation energy ensures the stability of the long-term operation of the X-ray detector.

[0038] Figure 3 where the abscissa is 1,000 / T (K-1 )represents the reciprocal of temperature × 1000, ln( σT ) represents the natural logarithm of the product of the conductivity σ and the temperature T.

[0039] Example 2

[0040] In this example, the (2-FBA)2BiI5 single crystal material prepared in Example 1 was fabricated into a direct X-ray detector, and the structure of the direct X-ray detector is as Figure 4 shown. The preparation method of the direct X-ray detector is as follows: (1) Select a (2-FBA)2BiI5 single crystal material with a smooth surface and no obvious defects. The single crystal material has adsorbed the residual microcrystals and solvents on the crystal surface with filter paper and was dried in an infrared drying oven at 80 °C for 2 h to achieve the purpose of removing surface impurities.

[0041] (2) As Figure 4 shown, place the (2-FBA)2BiI5 single crystal material 1 on the quartz wafer 2 and fix it. Use silver conductive adhesive to bond the conductive copper wires on both sides of the crystal surface as the first electrode 3 and the second electrode 4 respectively, and connect the power supply and the ammeter, then a direct X-ray detector based on one-dimensional bismuth-based perovskite material of the present invention is obtained.

[0042] Place the direct X-ray detector fabricated in this example under the X-ray light source. Under the irradiation of X-rays with different dose rates, measure the I-t (current-time) graphs of the device at 5 V - 50 V respectively. By fitting the data of these I-t graphs, obtain Figure 5 . From Figure 5 it can be seen that as the bias voltage increases, the current density increases linearly, and at a bias voltage of 50 V, the X-ray detector exhibits a high sensitivity of 1482.6 μC Gy -1 cm -2 .

[0043] Figure 6 shows the detection limit of the direct X-ray detector under a 5 V bias voltage condition. The detection limit is defined as the minimum X-ray dose rate that can be reliably identified. According to the international standard, the detection limit corresponds to the response signal equivalent dose rate when the signal-to-noise ratio (SNR) reaches 3. According to Figure 6 the data shown, the detection limit of the X-ray detector is as low as 18.6 nGy / s. This means that it can work effectively at an extremely low radiation dose rate, and its detection limit is only about 1 / 300 of that of a traditional commercial α-Se semiconductor material X-ray detector, thus 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.

[0044] In summary, the present invention proposes a solution adopting the F-π ion migration inhibition technology. By replacing the ortho-hydrogen (H) of benzylamine with fluorine (F), the intermolecular interaction force between fluorine and the benzene ring is utilized to inhibit the ion migration channels inside the material. Combining this method with the slow temperature cooling technology, a one-dimensional bismuth-based perovskite (2-FBA)2BiI5 single crystal with excellent properties is successfully synthesized. The direct X-ray detector prepared based on this single crystal not only has a simple structure, is easy to manufacture and has a low cost, but also exhibits high sensitivity, low detection limit and high stability under X-ray irradiation. In particular, in Example 2, the detection limit value of this direct X-ray detector reaches approximately 1 / 300 of that of the traditional commercial α-Se semiconductor material X-ray detector, which indicates that it can achieve effective direct X-ray detection at an extremely low radiation dose rate, significantly improving the efficiency and safety of the detection system. In summary, this new type of detector provides a more optimized option for X-ray detection technology.

[0045] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements, or in the case where the technical features in the above embodiments do not conflict with each other, can be combined in the manner recorded in the embodiments, and these modifications, replacements or combinations do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A direct X-ray detector based on a one-dimensional bismuth-based perovskite material, characterized in that: It includes a one-dimensional bismuth-based perovskite material, the molecular formula of the one-dimensional bismuth-based perovskite material is (2-FBA)2BiI5, and it is a single crystal, and its inorganic chain [BiI5] 2- is oriented along the crystallographic c-axis; The one-dimensional bismuth-based perovskite material is prepared as follows: Mix bismuth trioxide, 2-fluorobenzylamine solution, hydroiodic acid, and hypophosphorous acid solution to obtain a perovskite precursor dispersion; heat and stir the precursor dispersion until completely dissolved to obtain a solution; seal the solution in a reaction vessel, place it in an environment at 80 °C and keep it at a constant temperature for 6-12 h, then cool the solution to 25 °C at a rate of 1-2 °C per day, then filter and collect the perovskite crystals, use an adsorbent material to absorb the residual microcrystals and solvent on the crystal surface completely, and perform a drying treatment to obtain the one-dimensional bismuth-based perovskite material (2-FBA)2BiI5, and seal and vacuum-preserve it.

2. The direct X-ray detector based on one-dimensional bismuth-based perovskite material according to claim 1, wherein: The X-ray detector further includes two electrodes, the two electrodes are arranged at two ends of the one-dimensional bismuth-based perovskite material that are far away from each other, and the electrodes are metal electrodes or conductive adhesives; a power supply and a galvanometer are connected between the two electrodes.

3. The direct X-ray detector based on one-dimensional bismuth-based perovskite materials according to claim 1, wherein: The X-ray detector further includes a substrate, and the substrate is arranged below the one-dimensional bismuth-based perovskite material 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 claim 1, characterized in that: Seal the solution in a reaction vessel, place it in an environment at 80 °C and keep it at a constant temperature for 12 h, then cool the solution to 55 °C at a constant rate in 144 h, then cool it to 30 °C at a rate of 1 °C per day, and continue to cool the solution to 25 °C in 72 h, and keep it at 25 °C for 24 h, and filter and collect the perovskite crystals.

5. The direct X-ray detector based on a one-dimensional bismuth-based perovskite material according to claim 1, wherein: Heat and stir the precursor dispersion at a temperature of 80-100 °C to promote the complete dissolution of bismuth trioxide; the solvent in the 2-fluorobenzylamine solution is DMF or DMSO.

6. The direct X-ray detector based on a one-dimensional bismuth-based perovskite material according to claim 1, characterized in that: When sealing the solution in the reaction vessel, fill the reaction vessel with an N2 atmosphere for sealing; the drying treatment is vacuum drying in an infrared drying oven, and the drying conditions are drying at 80-100 °C for 1-2 h.

7. The direct X-ray detector based on a one-dimensional bismuth-based perovskite material according to claim 1, characterized in that: Use a nylon mesh with a filtration pore size of 500 μm to collect the perovskite crystals and filter out the microcrystals, and then use filter paper to absorb the residual microcrystals and solvent on the crystal surface completely.

8. A preparation method of a direct X-ray detector based on a one-dimensional bismuth-based perovskite material, characterized in that, Including: Fix the clean (2-FBA)2BiI5 single crystal material on a quartz wafer substrate. The single crystal material is a one-dimensional bismuth-based perovskite material with a molecular formula of (2-FBA)2BiI5. Set an electrode at each end of the surface of the single crystal material, and connect a power supply and a galvanometer between the two electrodes to obtain an X-ray detector. The one-dimensional bismuth-based perovskite material is prepared as follows: Mix bismuth trioxide, 2-fluorobenzylamine solution, hydroiodic acid, and hypophosphorous acid solution to obtain a perovskite precursor dispersion; heat and stir the precursor dispersion until completely dissolved to obtain a solution; seal the solution in a reaction vessel, place it in an environment at 80 °C and keep it at a constant temperature for 6-12 h, then cool the solution to 25 °C at a rate of 1-2 °C per day, then filter and collect the perovskite crystals, use an adsorbent material to absorb the residual microcrystals and solvent on the crystal surface completely, and perform a drying treatment to obtain the one-dimensional bismuth-based perovskite material (2-FBA)2BiI5.

9. The preparation method of the direct X-ray detector based on the one-dimensional bismuth-based perovskite material according to claim 8, characterized in that: Use a conductive adhesive of silver or platinum to bond the wires to both ends of the surface of the (2-FBA)2BiI5 single crystal material, and connect the power supply and ammeter through the wires; the conductive adhesives respectively form an electrode, and the wires are metal wires of copper, silver, platinum or gold.

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