2D / 3D heterojunction layer, preparation method and large-area direct perovskite wafer X-ray detector

Abstract

This invention relates to a 2D / 3D heterojunction layer, its fabrication method, and a large-area direct-type perovskite wafer X-ray detector, belonging to the field of perovskite radiation detection technology. A 2D / 3D heterojunction is constructed by combining bismuth iodide (BiI3) with perovskite. BiI3 serves as the heterolayer on the perovskite light-absorbing layer, and is then used in a large-area direct-type perovskite wafer X-ray detector. Under dynamic pressure, the two-dimensional planes of BiI3 gradually become perpendicular to the direction of the applied force, resulting in a uniform orientation, i.e., a single-crystal orientation. This leads to electrical anisotropy in the layer, providing a barrier to ion migration. Simultaneously, the formation of a heterostructure that matches energy levels facilitates charge separation and collection, thereby improving X-ray detection performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a 2D / 3D heterojunction layer, a preparation method and a large-area direct perovskite wafer X-ray detector, and belongs to the technical field of perovskite radiation detection. BACKGROUND

[0002] Perovskite wafer X-ray detectors are attracting attention as emerging X-ray detectors due to their low cost, controllable thickness, and scalable large-scale production technology. Considering the actual application scenarios, when the detector device is continuously irradiated or subjected to a high external bias during the entire operation period, the operational stability remains an important issue and becomes an important evaluation indicator for the commercialization of this new type of polycrystalline perovskite detection technology.

[0003] For improving the working stability of polycrystalline X-ray detector, the existing technical solutions are mostly committed to improving the characteristics of perovskite itself. At present, the following measures are mainly used to maintain the stability of perovskite wafer detector: (1) Optimizing crystal quality, reducing defect density. Chemical treatment of raw material powder or heat treatment of wafer can promote grain growth and form large and dense grains under pressure, thereby reducing the defect density caused by grain boundaries. Finally, the perovskite wafer is compact and compact, realizes high migration lifetime product, and enhances the working stability of the detector. (Literature: PbI2-DMSO assisted insitu growth of perovskite wafers for sensitive direct X-ray detection).(2) Using interactive fixed ions, such as enhancing the binding energy with halogenated ions or hydrogen bond strength. Introducing methyl groups into perovskite to adjust the tolerance factor and enhance hydrogen bonding, which suppresses ion migration and optimizes structural stiffness, ultimately making it exhibit significant stability in long-term temperature aging (-40~85℃) (Literature: Metal-free PAZE-NH4X3·H2O perovskite for flexible transparent X-ray detection and imaging).(3) Constructing hybrid heterostructure. Introducing passivation materials into perovskite wafers to weaken polycrystalline defects and suppress ion migration. Finally, the detector realizes small baseline drift and low noise characteristics, significantly improving the radiation stability of the device (Literature: Heteroepitaxial passivation of Cs2AgBiBr6 wafers with suppressed ionic migration for X-ray imaging).(4) Constructing layered heterostructure. In the porous polymer film, various hybrid 2D perovskite types are combined with 3D perovskite to form a stable network, establishing a layered heterojunction, achieving a complex balance between spontaneous charge separation / transport, X-ray attenuation, and mechanical durability, and finally making the thick film X-ray detector have high performance, self-driven X-ray detection and imaging capability Flexible characteristics such as (Literature: Flexible large-scale self-driven perovskite X-ray detector by precise heterogeneous integration). However, the presence of organic cations in hybrid perovskite hinders the transport of photo-generated carriers to some extent, which is not conducive to the performance of the detector.

[0004] In addition to the improvement of the crystal quality of the perovskite active layer, the ion migration problem caused by the weak ionic bond in the intrinsic halide perovskite still needs to be considered in terms of the stability of the entire polycrystalline wafer device. For perovskite detector devices that work for a long time in the outer space environment, this unstable intrinsic source will eventually cause distortion of the recorded signal, eventually leading to incorrect decision-making. Therefore, in terms of maintaining stability, it is necessary to select a stable perovskite material and adopt appropriate strategies to allow carrier (electron or hole) transport while limiting the passage of other types of ions, thereby achieving suppression of ion migration. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a 2D / 3D heterojunction layer, a preparation method and a large-area direct perovskite wafer X-ray detector.

[0006] To achieve the above-mentioned purpose, the technical solutions of the present application are as follows.

[0007] A 2D / 3D heterojunction layer, comprising a two-dimensional material and a perovskite material, the two-dimensional material being bismuth iodide (BiI3), the two-dimensional material being used as a hetero layer of a perovskite light absorption layer; the perovskite material being an A2M(I)M(III)X6 type compound, the energy band being 2-2.5 eV, M(I) being a positive monovalent metal ion, M(III) being a positive trivalent metal ion; the mass ratio of bismuth iodide (BiI3) and the perovskite material being 0.5-3:9; using Cu target Kα diffraction, the X-ray powder diffraction pattern of bismuth iodide expressed in terms of 2θ angle has strong diffraction peaks at 27.00°, 35.28° and 46.22°, and weak diffraction peaks at 12.85°, 25.81° and 39.12°.

[0008] Preferably, the thickness of the bismuth iodide (BiI3) is 80-120 μm, and the thickness of the perovskite light absorption layer is 800-1200 μm.

[0009] Preferably, the mass ratio of the bismuth iodide (BiI3) and the perovskite material is 1-2:9.

[0010] Preferably, the perovskite material is an A2M(I)M(III)X6 type compound, wherein the A site cation is one of CH3NH3 + , NH2-CH=NH2 + , Cs + , C4H9NH3 + , CH6N3 + , Rb + and K + ; M(I) is Cu + or Ag + , and M(III) is Bi.3+ or Sb 3+ X is Cl - ,Br - Or I - .

[0011] A method for preparing a 2D / 3D heterojunction layer according to the present invention includes the following steps:

[0012] According to the stoichiometric ratio, AX, M(I)X and M(III)X3 were added to hydrobromic acid (HBr), stirred, and sealed. The mixture was then heated to 90–120°C until the powder was completely dissolved. The temperature was then decreased by 10–15°C at a rate of 1–3°C / min, followed by a further decrease of 2–5°C at a rate of 0.02–0.06°C / min until nucleation occurred at the liquid surface. The mixture was kept at this temperature for 2–4 hours, and then cooled to room temperature at a rate of 0.5–1°C / min. The mixture was then filtered and washed to obtain perovskite crystals.

[0013] Perovskite crystals are ground to obtain perovskite powder, which is then placed in a mold and pressed at 10–20 MPa for 5–10 min to obtain a perovskite wafer. The mold is then opened, and fully ground bismuth iodide (BiI3) powder is spread evenly on the surface of the perovskite wafer. The wafer is then pressed at 10–20 MPa for 2–4 h. After pressing, the wafer is removed and annealed on a hot stage at 100–200 °C for 2–4 h to obtain a 2D / 3D heterojunction layer.

[0014] Preferably, the particle size of the bismuth iodide (BiI3) powder is 1-2 μm.

[0015] Preferably, the purity of the bismuth iodide (BiI3) is above 98.0%.

[0016] A large-area direct-type perovskite wafer X-ray detector includes a 2D / 3D heterojunction layer as described in this invention, with a thickness of 0.9–1.2 mm.

[0017] Preferably, the large-area direct-type perovskite wafer X-ray detector includes a metal electrode layer, a 2D / 3D heterojunction layer, and a metal electrode layer arranged sequentially from bottom to top.

[0018] Preferably, the metal electrode layer is a carbon electrode, gold, copper, silver, aluminum, chromium metal or an alloy containing the above metals, and the thickness of the electrode layer is 80-500 nm.

[0019] Beneficial effects

[0020] This invention provides an application of an inorganic two-dimensional material: bismuth iodide (BiI3) combined with perovskite to construct a 2D / 3D heterojunction. This two-dimensional material is added as a heterolayer on a perovskite light-absorbing layer and then used in a large-area direct-type perovskite wafer X-ray detector. Under dynamic pressure, the two-dimensional surface of this material gradually becomes perpendicular to the direction of the applied force, resulting in a uniform orientation, i.e., a single-crystal orientation. This leads to electrical anisotropy in the layer, providing a barrier to ion migration. After forming a heterostructure with energy level matching, it facilitates charge separation and collection, thereby improving X-ray detection performance. Furthermore, adjusting the thickness of bismuth iodide to an appropriate level can provide optimal carrier transport distance and the number of photogenerated carriers, thus achieving maximum sensitivity.

[0021] This invention provides a 2D / 3D heterojunction layer that combines high-resistivity bismuth iodide (BiI3) with high-charge-mobility perovskite material, solving the problem of ion migration in perovskite crystals and potentially addressing the poor operational stability issue in lead-free perovskite devices. Furthermore, the proposed inorganic layered 2D / 3D heterostructure may offer greater advantages in balancing sensitivity and stability.

[0022] This invention provides a large-area direct perovskite wafer X-ray detector. The device, built from a 2D / 3D heterostructure, has good operational stability, opening up a new way to simultaneously improve X-ray detection performance and detector stability, and contributing to the development of low-cost and high-resolution large-area X-ray imaging equipment. Attached Figure Description

[0023] Figure 1 The XRD patterns are for Experimental Example 1 and Comparative Example 3.

[0024] Figure 2 This is a high-resolution FE-SEM image of the cross-section of Experiment Example 1.

[0025] Figure 3 The graph shows the statistical values ​​of the X-ray sensitivity of the devices fabricated in Experimental Examples 1-3 and Comparative Example 4.

[0026] Figure 4 Statistical graphs showing the X-ray sensitivity of the devices fabricated in Experimental Example 1 and Comparative Examples 1-4.

[0027] Figure 5 The detection limit diagrams are for the devices in Experimental Example 1 and Comparative Example 4.

[0028] Figure 6 The diagram shows the radiation stability of the device fabricated in Experiment Example 1. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments.

[0030] A method for fabricating a large-area direct-type perovskite wafer X-ray detector, comprising the following steps:

[0031] Step 1: Weigh the perovskite crystals and grind them thoroughly to obtain a uniform powder. Place the powder into a circular mold and apply vertical pressure to the mold using a hydraulic press, maintaining this pressure for two hours. The thickness of the wafer can be controlled by adjusting the amount of powder and the applied pressure.

[0032] Step 2: Open the upper part of the mold and spread bismuth iodide (BiI3) powder evenly on the top of the perovskite.

[0033] Step 3: After reinstalling the upper part of the mold, press it at 10MPa for two hours;

[0034] Step 4: After removing the wafer, perform annealing on a hot plate at 100°C for two hours;

[0035] Step 5: Under high vacuum conditions, an electron transport layer is deposited on the perovskite light absorption layer; under high vacuum conditions, a metal layer is deposited on the heterojunction crystal wafer to prepare a large-area direct-type perovskite wafer X-ray detector.

[0036] Experimental Example 1

[0037] Step 1: Place 0.426 g of cesium bromide (CsBr), 0.449 g of bismuth bromide (BiBr3), and 0.188 g of silver bromide (AgBr) in a glass bottle, add 12.5 ml of hydrobromic acid (HBr), and stir appropriately. Seal the glass bottle with 3M tape and heat it in an oil bath to 95°C until the powder is completely dissolved, forming a pale yellow solution. Reduce the oil bath temperature to 85°C at a rate of 3°C / h, then continue cooling to 82°C at a rate of 0.05°C / h until nucleation occurs at the liquid surface. After nucleation, maintain this temperature for three hours, then cool again to room temperature at a rate of 0.5°C / h. Finally, pour off the remaining solution and wash the crystals with ethanol and isopropanol to obtain Cs2AgBiBr6 crystals.

[0038] Step 2: Weigh 1g of Cs2AgBiBr6 crystals and grind them thoroughly to obtain uniform Cs2AgBiBr6 powder.

[0039] Step 3: Place the powder into a circular mold and apply a vertical pressure of 10 MPa to the mold using a hydraulic press (equivalent to the powder being subjected to a pressure of 187 MPa) and hold for two hours.

[0040] Step 4: Open the upper part of the mold and spread 0.2g of ground BiI3 powder evenly on top of Cs2AgBiBr6. After reinstalling the upper part of the mold, press it at 10MPa for two hours.

[0041] Step 5: After removing the heterogeneous crystal sheet, anneal it on a hot plate at 100°C for two hours.

[0042] Step 6: Transfer the sample obtained in Step 5 to a high vacuum evaporation machine and deposit 50nm Au electrodes on both sides to finally obtain a large-area wafer X-ray detector.

[0043] Experiment Example 2

[0044] The same preparation process as in Experimental Example 1 was used, except that in step 4, 0.4 g of ground BiI3 powder was added, while other conditions remained the same.

[0045] Experimental Example 3

[0046] The same preparation process as in Experimental Example 1 was used, except that in step 4, 0.6g of ground BiI3 powder was added, while other conditions remained the same.

[0047] Comparative Example 1

[0048] Step 1: Dissolve p-fluorophenylethyl ammonium iodide (F-PEAI) and BiI3 in hydroiodic acid (HI) at a molar ratio of 3:1. Then, stir at 110°C for several hours and immediately filter through a 0.45-micron PTFE filter. After cooling the solution at a rate of 2°C / h, (F-PEA)3BiI6 crystals are obtained.

[0049] Step 2: Grind (F-PEA)3BiI6 crystal and Cs2AgBiBr6 crystal into powder respectively.

[0050] Step 3: After pressing 1g of Cs2AgBiBr6 powder into the mold, open the upper part of the mold and spread 0.2g of (F-PEA)3BiI6 powder evenly on top of the Cs2AgBiBr6. After reinstalling the upper part of the mold, press it at 10MPa for two hours.

[0051] Step 4: After removing the wafer, perform annealing on a hot plate at 100°C for two hours.

[0052] Step 5: Transfer the sample obtained in Step 4 to a high vacuum evaporation machine and deposit 50nm Au electrodes on both sides to finally obtain a large-area wafer X-ray detector.

[0053] Comparative Example 2

[0054] The same preparation process as in Experimental Example 1 was used, except that in steps 3 and 4, the Cs2AgBiBr6 and BiI3 powders were uniformly mixed at a mass ratio of 9:1 and then pressed. All other conditions remained the same.

[0055] Comparative Example 3

[0056] The same preparation process as in Experimental Example 1 was used, except that in steps 3 and 4, only BiI3 powder was used for pressing. All other conditions remained the same.

[0057] Comparative Example 4

[0058] The same preparation process as in Experimental Example 1 was used, except that BiI3 powder was not added in step 4, while other conditions remained the same.

[0059] Performance testing:

[0060] (1) X-ray diffraction (XRD): Test equipment: Bruker D8-DISCOVER X-ray diffractometer; Test conditions: room temperature, wafer sample.

[0061] Test results: Figure 1 The XRD characterization results of BiI3 in the perovskite wafers of Experimental Example 1 and Comparative Example 3 are shown. Compared with BiI3 powder, the XRD pattern of the BiI3 side of the heterostructure wafer showed a large change in the relative intensity of the diffraction peaks, similar to that of the pure BiI3 wafer. This indicates that when BiI3 powder is subjected to vertical orientation pressure in a limited space, its crystal orientation tends to be consistent with that of BiI3 single crystal.

[0062] (2) Field emission scanning electron microscope (FE-SEM): Test equipment: Gemini 300; Test conditions: room temperature, wafer sample.

[0063] Test results: Figure 2 The image shows a high-resolution FE-SEM image of the cross-section of the heterocrystalline sheet in Experimental Example 1. The BiI3 layer is 103.9 μm thick, and the BiI3 powder is in contact with the Cs2AgBiBr6 grains in a flat arrangement. The clear and flat interface between the two-dimensional layer and the three-dimensional substrate indicates the formation of a unidirectional 2D / 3D heterocrystalline sheet, i.e., a bilayer structure, which is conducive to the formation of an internal electric field to separate electrons and holes.

[0064] (3) X-ray detector sensitivity: Test equipment: X-ray tube (Mini-X2) and Keithley 2636B source meter. Test conditions: room temperature, wafer X-ray detector.

[0065] Test results: Figure 3The results show the statistical results of the X-ray sensitivity of the samples prepared in Examples 1-3 and Comparative Example 4 using an X-ray testing system. In Example 1, adding 10% BiI3 by total mass resulted in the heterojunction wafer exhibiting optimal sensitivity. In Examples 2 and 3, adding more BiI3 to the heterojunction wafer, i.e., a thicker BiI3 layer, showed a decrease in sensitivity. The device prepared in Comparative Example 4 struggled to achieve high sensitivity under a large electric field. Figure 4 The results show the statistical results of the X-ray sensitivity of the samples prepared in Experimental Example 1 and Comparative Examples 1-4 using an X-ray testing system. Compared with the devices in the comparative examples, the Cs2AgBiBr6 / BiI3 heterojunction wafer detector prepared in Experimental Example 1 exhibited the highest sensitivity. The addition of BiI3 provided its own X-ray response and the formation of an internal electric field, further enhancing the sensitivity of the wafer detector device.

[0066] (4) X-ray detector detection limit: Test equipment: X-ray tube (Mini-X2) and Keithley 2636B source meter. Test conditions: wafer X-ray detector at room temperature.

[0067] Test results: Figure 5 The current density is the dose rate-dependent current density in the devices of Experimental Example 1 and Comparative Example 4. The detection limit of the heterostructure wafer device in Experimental Example 1 is an order of magnitude lower than that of the device in Comparative Example 4. BiI3, as a heterolayer, provides a barrier to suppress noise and ion migration in the electric field direction, further improving the detection limit of the wafer detector device.

[0068] (5) Stability test: Test equipment: X-ray tube (Mini-X2) and Keithley 2636B source meter. Test conditions: room temperature, wafer X-ray detector.

[0069] Test results: Figure 6 The photocurrent of the heterocrystalline wafer device fabricated in Example 1 under continuous radiation. The heterocrystalline wafer X-ray detector operates at a cumulative dose as high as 4.015 Gy. air After X-ray irradiation, the response current decreased by only 2.6%. The addition of BiI3 improved radiation stability. In summary, BiI3 is an excellent inorganic 2D layered material that can be used to improve the sensitivity and stability of perovskite X-ray detectors, and its application in other heterojunction systems can be extended to achieve the expected results.

[0070] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A 2D / 3D heterojunction layer, characterized in that: This includes two-dimensional materials and perovskite materials. The two-dimensional material is BiI3, which is used as a heterolayer in the perovskite light-absorbing layer. The perovskite material is an A2M(I)M(III)X6 type compound, with CH3NH3 as the A-site cation. + NH2 CH=NH2 + Cs + C4H9NH3 + CH6N3 + 、Rb + and K + One of them; M(I) is Cu + or Ag + , M(III) is Bi 3+ or Sb 3+ X is Cl or Br The mass ratio of BiI3 to perovskite material is 0.5~3:9; a Cu target K is used. Diffraction, with 2 The X-ray powder diffraction pattern of BiI3, as indicated by the angle, shows strong diffraction peaks at 27.00°, 35.28°, and 46.22°, and weak diffraction peaks at 12.85°, 25.81°, and 39.12°. The fully ground BiI3 powder was spread evenly on the surface of the perovskite wafer and then pressed at 10~20 MPa for 2~4 hours. After pressing, the wafer was removed and annealed on a hot stage at 100~200℃ for 2~4 hours to obtain a 2D / 3D heterojunction layer. The 2D / 3D heterojunction layer is used for large-area direct-type perovskite wafer X-ray detectors.

2. The 2D / 3D heterojunction layer according to claim 1, characterized in that: The thickness of the BiI3 is 80~120μm, and the thickness of the perovskite light-absorbing layer is 800~1200μm.

3. The 2D / 3D heterojunction layer according to claim 1, characterized in that: The mass ratio of BiI3 to perovskite material is 1~2:

9.

4. A method for preparing a 2D / 3D heterojunction layer according to any one of claims 1 to 3, characterized in that: The method steps include: According to the stoichiometric ratio, AX, M(I)X and M(III)X3 were added to hydrobromic acid, stirred and sealed, and then heated to 90~120℃ until the powder was completely dissolved. The temperature was then reduced by 10~15℃ at a rate of 1~3℃ / min, and then further reduced by 2~5℃ at a rate of 0.02~0.06℃ / min until nucleation occurred on the liquid surface. The temperature was maintained for 2~4h, and then cooled to room temperature at a rate of 0.5~1℃ / min. The mixture was then filtered and washed to obtain perovskite crystals. Perovskite crystals are ground, and the resulting perovskite powder is placed in a mold and pressed at 10-20 MPa for 5-10 minutes to obtain a perovskite wafer. The mold is then opened, and fully ground BiI3 powder is spread evenly on the surface of the perovskite wafer. The wafer is then pressed at 10-20 MPa for 2-4 hours. After pressing, the wafer is removed and annealed on a hot stage at 100-200℃ for 2-4 hours to obtain a 2D / 3D heterojunction layer.

5. The method for preparing a 2D / 3D heterojunction layer according to claim 4, characterized in that: The BiI3 powder has a particle size of 1~2μm.

6. The method for preparing a 2D / 3D heterojunction layer according to claim 4, characterized in that: The purity of the BiI3 is above 98.0%.

7. A large-area direct-type perovskite wafer X-ray detector, characterized in that: It includes a 2D / 3D heterojunction layer as described in any one of claims 1 to 3, with a thickness of 0.9 to 1.2 mm.

8. A large-area direct-type perovskite wafer X-ray detector according to claim 7, characterized in that: The large-area direct-type perovskite wafer X-ray detector includes a metal electrode layer, a 2D / 3D heterojunction layer, and a metal electrode layer arranged sequentially from bottom to top.

9. A large-area direct-type perovskite wafer X-ray detector according to claim 8, characterized in that: The metal electrode layer is gold, copper, silver, aluminum, chromium, or an alloy containing the above metals, and the thickness of the electrode layer is 80~500nm.

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