A novel perovskite X-ray detector and its fabrication method

Abstract

This invention provides a novel perovskite X-ray detector, comprising, from bottom to top, a transparent conductive substrate, an electron transport layer, a bismuth-based perovskite polycrystalline thick film, a hole transport layer, and a metal electrode; wherein the bismuth-based perovskite polycrystalline thick film is an A3Bi2X9 polycrystalline thick film with a thickness of 800–1200 μm, and is prepared by a blade coating method. This invention also provides a method for fabricating the above-mentioned novel perovskite X-ray detector. The advantages of this invention are: it uses a high-performance bismuth-based perovskite polycrystalline thick film as the light-absorbing layer, enabling large-area, rapid imaging, which is superior to existing single-crystal imaging methods.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of X-ray detectors, in particular to a novel perovskite X-ray detector and a preparation method thereof. BACKGROUND

[0002] When X-rays pass through human tissues, workpieces or materials with different densities and thicknesses, the X-rays are absorbed to different extents. When X-rays irradiate a direct detection material, electron-hole pairs are generated, and these electrons and holes form an electric current under the action of an applied bias electric field. The current is then integrated on a TFT panel or other readout system to form stored charge. By reading out the amount of charge, the X-ray dose at each point can be determined. People can diagnose some diseases that are not visible to the naked eye or detect the nature, size and distribution of various macroscopic or microscopic defects in workpieces by observing the changes and distribution of X-ray intensity. Existing CdTe / CZT detectors are applied to CT imaging through splicing, but they do not have advantages in large-area and fast imaging and cannot be used for flat-panel detector imaging in digital radiography.

[0003] When perovskite materials are irradiated by X-rays, they absorb photons to generate electron-hole pairs. These perovskite materials often have a low carrier recombination probability and a high carrier mobility, and the diffusion distance and lifetime of the carriers are long, making them a promising X-ray detection material. Currently, research on perovskite X-ray detectors mainly focuses on lead-based perovskites. However, lead ions (Pb 2+ ) are a heavy metal ion with high biological toxicity, strong ecological system cycling stability and difficulty in degradation. In addition, the instability of the structure of lead-based perovskites restricts the development of lead-based perovskite X-ray detectors and will severely limit their future practical applications. Compared with lead-based perovskites, the migration inhibition of bismuth-based perovskites is the reason for the improvement of their stability.

[0004] Currently, high-performance bismuth-based perovskite X-ray detectors are mostly single-crystal materials. Although X-ray detectors based on bismuth-based perovskite single crystals have good X-ray response performance, the preparation of large single crystals and wafer processing are challenging due to the fragile nature of single crystals, and large-area fast imaging cannot be achieved. Therefore, from the perspective of practical application, the preparation of high-performance bismuth-based perovskite polycrystals (thick films) is expected to provide a key material basis for large-area fast X-ray imaging. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a novel perovskite X-ray detector and a preparation method thereof, which uses high-performance bismuth-based perovskite polycrystal thick films as the light-absorbing layer and can achieve large-area fast imaging.

[0006] The present application solves the above technical problems by adopting the following technical solutions:

[0007] A novel perovskite X-ray detector, from bottom to top, comprises a transparent conductive substrate, an electron transport layer, a bismuth-based perovskite polycrystalline thick film, a hole transport layer and a metal electrode; wherein the bismuth-based perovskite polycrystalline thick film is an A3Bi2X9 polycrystalline thick film with a thickness of 800-1200 um, and is prepared by a doctor blade method.

[0008] As one of the preferred modes of the present application, the transparent conductive substrate is transparent conductive glass on which indium tin oxide or fluorine-doped tin dioxide is deposited.

[0009] As one of the preferred modes of the present application, the electron transport layer is one of tin dioxide, titanium dioxide and fullerene derivative.

[0010] As one of the preferred modes of the present application, the hole transport layer is nickel oxide or 2,2',7,7'-tetra[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene.

[0011] As one of the preferred modes of the present application, the metal electrode is a gold electrode or a silver electrode.

[0012] As one of the preferred modes of the present application, the specific preparation method of the A3Bi2X9 polycrystalline thick film is as follows:

[0013] (1) The raw materials AX and BiX3 are weighed according to a molar ratio of 3:2, and 5% additives are added; the above materials are dissolved in an organic solvent to obtain a mixed precursor solution stock solution;

[0014] (2) The stock solution is stirred at a temperature of 40-60℃ for 2-6h until fully dissolved, and then the stock solution is filtered to obtain a clear and transparent 0.6-1.2M mixed precursor solution;

[0015] (3) The mixed precursor solution is coated on the electron transport layer using a doctor blade instrument to obtain a bismuth-based perovskite wet film with a corresponding thickness;

[0016] (4) The bismuth-based perovskite wet film is transferred to a vacuum oven for vacuumization, the solvent is removed, and then annealing is performed at a temperature of 100-120℃, thereby obtaining the target required A3Bi2X9 polycrystalline thick film.

[0017] As one of the preferred modes of the present application, in the A3Bi2X9 polycrystalline thick film material, A = NH4 + , PEA + ; X = I - , Br - , Cl - , SCN - .

[0018] As one of the preferred modes of the present application, the additive is one of thiourea, 2,5-dithiobiuret, benzylthiourea, 4-pyridylthiourea, thiosemicarbazide, amidinothiourea, 2-thiouracil, N-(2,5-dibromophenyl)benzothioamide, and benzenesulfonamide.

[0019] As one of the preferred modes of the present application, the organic solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, gamma-butyrolactone, 2-methoxyethanol, polyethylene glycol, and N-methyl-2-pyrrolidone.

[0020] A preparation method of a novel perovskite X-ray detector, characterized in that it comprises the following steps:

[0021] S1, preparing an electron transport layer on a transparent conductive substrate by spin coating or spraying;

[0022] S2, scraping a bismuth-based perovskite wet film with a certain thickness on the electron transport layer; transferring the wet film to a vacuum oven to be vacuumized, so that the solvent is removed, and then annealing at a temperature of 100-120 DEG C, so as to prepare a A3Bi2X9 polycrystalline thick film;

[0023] S3, preparing a hole transport layer on the perovskite polycrystalline thick film by spin coating or spraying;

[0024] S4, preparing a metal electrode on the hole transport layer by evaporation.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] (1) The present application adopts a high-performance bismuth-based perovskite polycrystalline thick film as a light-absorbing layer, which can realize large-area rapid imaging and is superior to the existing single-crystal imaging;

[0027] (2) The A3Bi2X9 perovskite material provided by the present application has a high atomic number, which is beneficial to a large X-ray absorption cross section; the defect tolerance characteristics ensure a low defect concentration, and the product of carrier lifetime and mobility is high, which is beneficial to improving the charge collection efficiency; at the same time, the characteristics of ionic compounds are beneficial to the preparation of devices at low temperature and in a large area, and the irradiation stability is excellent; the raw materials are cheap, and the polycrystalline thick film can be prepared by a solution method and the like, which can be directly integrated with a readout circuit;

[0028] (3) In the A3Bi2X9 perovskite structure, the perovskite material synthesized by A and X has better crystallinity and X-ray response performance than the same type of structure crystal mentioned in other documents;

[0029] (4) The X-ray detector provided by the application has simple preparation method and environment-friendly raw materials; meanwhile, the additive is added in the preparation of the A3Bi2X9 polycrystalline thick film, which can improve the crystallization performance of the material and decompose into corresponding cations and anions in the annealing process, so as to inhibit the formation of halogen vacancies in the polycrystalline thick film and reduce the grain boundary defects. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a schematic diagram of the overall structure of the new perovskite X-ray detector in the embodiment of the application;

[0031] Figure 2 It is a schematic diagram of the doctor blade coating for preparing the perovskite polycrystalline thick film in the embodiment of the application (in the figure, a is an appearance diagram of the large-area (6.5*6.5cm) perovskite polycrystalline thick film obtained by doctor blade coating, and b is a schematic diagram of the doctor blade coating operation);

[0032] Figure 3 It is a schematic diagram of the circuit of the new perovskite X-ray detector in the embodiment of the application;

[0033] Figure 4 It is an X-ray response performance diagram of the new perovskite X-ray detector in the embodiment of the application;

[0034] Figure 5 It is an XRD crystallinity characterization comparison of the (NH4)3Bi2I9 polycrystalline thick film with and without additive in the embodiment of the application. DETAILED DESCRIPTION

[0035] The embodiment of the application will be described in detail below, which is implemented on the premise of the technical scheme of the application, and detailed implementation mode and specific operation process are given, but the protection scope of the application is not limited to the following embodiment.

[0036] Embodiment 1

[0037] The new perovskite X-ray detector in the embodiment is shown in the figure, which includes, from bottom to top, a transparent conductive substrate, an electron transport layer, a bismuth-based perovskite polycrystalline thick film, a hole transport layer and a metal electrode. Figure 1 The transparent conductive substrate adopts transparent conductive glass with deposited indium tin oxide; the electron transport layer adopts tin dioxide; the hole transport layer adopts 2,2',7,7'-tetra[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene; the metal electrode adopts a gold electrode; and the bismuth-based perovskite polycrystalline thick film adopts A3Bi2X9 polycrystalline thick film (A=NH4 + ; X=I - ), with a thickness of 800um and prepared by the doctor blade coating method.

[0038] The preparation method of the X-ray detector above:

[0039] S1, spin-coat tin dioxide on a transparent conductive substrate at a rotation speed of 4800 rpm for 50 s (20 uL / cm -2 ), and anneal in air at an annealing temperature of 80℃ for 60 minutes to prepare an electron transport layer;

[0040] S2, weigh raw materials NH4I and BiI3 in a molar ratio of 3:2, 5% 2, 5-dithiodiurea, dissolve in a mixed solvent of N, N-dimethylformamide, dimethyl sulfoxide and polyethylene glycol (volume ratio of 4:1:1) to obtain a mixed precursor solution stock solution; stir the stock solution at a temperature of 40℃ for 6h until fully dissolved, then filter the stock solution to obtain a clear transparent mixed precursor solution (concentration of 1.2mol / L);

[0041] S3, refer to Figure 2 , use a doctor blade to coat the mixed precursor solution of S2 on the electron transport layer of S1 to obtain a bismuth-based perovskite wet film with a thickness of 800um; transfer the wet film to a vacuum oven and instantaneously vacuumize to instantaneously remove the solvent, then anneal at a temperature of 100℃ to prepare a (NH4)3Bi2I9 polycrystalline thick film;

[0042] S4, prepare a hole transport layer on the perovskite polycrystalline thick film by spin-coating 2, 2', 7, 7'-tetra[N, N-bis(4-methoxyphenyl)amino]-9, 9'-spirobifluorene;

[0043] S5, prepare a metal electrode on the hole transport layer by evaporation.

[0044] Example 2

[0045] A new type of perovskite X-ray detector of the present embodiment, as shown in Figure 1 , includes a transparent conductive substrate, an electron transport layer, a bismuth-based perovskite polycrystalline thick film, a hole transport layer and a metal electrode from bottom to top. The transparent conductive substrate is a fluorine-doped tin dioxide transparent conductive glass; the electron transport layer is tin dioxide; the hole transport layer is 2, 2', 7, 7'-tetra[N, N-bis(4-methoxyphenyl)amino]-9, 9'-spirobifluorene; the metal electrode is a gold electrode; the bismuth-based perovskite polycrystalline thick film is a A3Bi2X9 polycrystalline thick film (A=NH4 + ; X=Br - ), with a thickness of 900um and prepared by a doctor blade method.

[0046] The preparation method of the X-ray detector above:

[0047] S1, spin-coat tin dioxide on a transparent conductive substrate at a rotation speed of 4800 rpm for 50 s (20 uL / cm -2 ), and anneal in air at an annealing temperature of 80℃ for 60 minutes to prepare an electron transport layer;

[0048] S2, weigh raw materials NH4Br and BiBr3 in a molar ratio of 3:2, 5% thiourea, dissolve in a mixed solvent of N, N-dimethylformamide, dimethyl sulfoxide and polyethylene glycol (volume ratio of 4:1:1) to obtain a mixed precursor solution stock solution; stir the stock solution at a temperature of 50℃ for 4h until it is fully dissolved, then filter the stock solution to obtain a clear transparent mixed precursor solution (concentration of 0.8mol / L);

[0049] S3, refer to Figure 2 , use a doctor blade to coat the mixed precursor solution of S2 on the electron transport layer of S1 to obtain a bismuth-based perovskite wet film with a thickness of 900um; transfer the wet film to a vacuum oven and instantaneously evacuate, so that the solvent is instantaneously removed, and then anneal at a temperature of 110℃ to prepare a (NH4)3Bi2Br9 polycrystalline thick film;

[0050] S4, prepare a hole transport layer on the perovskite polycrystalline thick film by spin-coating 2, 2', 7, 7'-tetra[N, N-bis(4-methoxyphenyl)amino]-9, 9'-spirobifluorene;

[0051] S5, prepare a metal electrode on the hole transport layer by evaporation.

[0052] Example 3

[0053] A new type of perovskite X-ray detector of this embodiment, as shown in Figure 1 , includes a transparent conductive substrate, an electron transport layer, a bismuth-based perovskite polycrystalline thick film, a hole transport layer and a metal electrode from bottom to top. The transparent conductive substrate is a fluorine-doped tin dioxide transparent conductive glass; the electron transport layer is titanium dioxide; the hole transport layer is nickel oxide; the metal electrode is a silver electrode; the bismuth-based perovskite polycrystalline thick film is an A3Bi2X9 polycrystalline thick film (A = PEA + ; X = Cl - ), with a thickness of 1000um and prepared by a doctor blade method.

[0054] The preparation method of the above X-ray detector:

[0055] S1, spray titanium dioxide on a transparent conductive substrate to prepare an electron transport layer;

[0056] S2, raw materials PEA Cl and BiCl3 were weighed according to a molar ratio of 3:2, 5% additive benzyl thiourea was added, and the mixture was dissolved in a mixed solvent of N, N-dimethylformamide, dimethyl sulfoxide, and 2-methoxyethanol (volume ratio of 4:1:1) to obtain a mixed precursor solution stock solution; the stock solution was stirred at 50°C for 4h until it was fully dissolved, and then the stock solution was filtered to obtain a clear and transparent mixed precursor solution (concentration of 1.0 mol / L);

[0057] S3, referring to Figure 2 , a mixed precursor solution of S2 was coated on the electron transport layer of S1 using a doctor blade to obtain a bismuth-based perovskite wet film with a thickness of 1000um; the wet film was transferred to a vacuum oven for instant vacuumization, and the solvent was instantaneously removed, and then annealed at a temperature of 110°C to obtain a PEA3Bi2Cl9 polycrystalline thick film;

[0058] S4, a hole transport layer was prepared on the perovskite polycrystalline thick film by spraying nickel oxide;

[0059] S5, a metal electrode was prepared on the hole transport layer by evaporation.

[0060] Example 4

[0061] A new type of perovskite X-ray detector according to the present embodiment, as shown in Figure 1 , includes, from bottom to top, a transparent conductive substrate, an electron transport layer, a bismuth-based perovskite polycrystalline thick film, a hole transport layer, and a metal electrode. The transparent conductive substrate is transparent conductive glass with deposited indium tin oxide; the electron transport layer is a fullerene derivative; the hole transport layer is 2, 2', 7, 7'-tetra[N, N-bis(4-methoxyphenyl)amino]-9, 9'-spirobifluorene; the metal electrode is a silver electrode; and the bismuth-based perovskite polycrystalline thick film is a A3Bi2X9 polycrystalline thick film (A = PEA + ; X = I - ), with a thickness of 1200um and prepared by a doctor blade method.

[0062] A preparation method of the X-ray detector:

[0063] S1, a fullerene derivative was spin-coated on a transparent conductive substrate at a rotation speed of 4800rpm for 50s (20uL / cm -2 ), and annealed in air at an annealing temperature of 80°C for an annealing time of 60 minutes to prepare an electron transport layer;

[0064] S2, the raw material PEAI and BiI3, 5% 4-pyridyl thiourea were weighed according to the molar ratio of 3:2, dissolved in the mixed solvent of γ-butyrolactone and polyethylene glycol (volume ratio of 4:1) to obtain a mixed precursor solution stock solution; the stock solution was stirred at 60°C for 2h until it was fully dissolved, then the stock solution was filtered to obtain a clear and transparent mixed precursor solution (concentration of 0.6mol / L);

[0065] S3, referring to Figure 2 , the mixed precursor solution of S2 was coated on the electron transport layer of S1 using a doctor blade, to obtain a bismuth-based perovskite wet film with a thickness of 1200um; the wet film was transferred to a vacuum oven for instant vacuumization, and the solvent was instantaneously removed, then annealed at a temperature of 120°C, thereby preparing a PEA3Bi2I9 polycrystalline thick film;

[0066] S4, 2,2',7,7'-tetra[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene was spin-coated on the perovskite polycrystalline thick film to prepare a hole transport layer;

[0067] S5, a metal electrode was prepared on the hole transport layer by evaporation.

[0068] Example 5

[0069] A new type of perovskite X-ray detector of the present embodiment, as shown in Figure 1 , includes, from bottom to top, a transparent conductive substrate, an electron transport layer, a bismuth-based perovskite polycrystalline thick film, a hole transport layer and a metal electrode. The transparent conductive substrate is a transparent conductive glass with deposited indium tin oxide; the electron transport layer is tin dioxide; the hole transport layer is 2,2',7,7'-tetra[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene; the metal electrode is a gold electrode; and the bismuth-based perovskite polycrystalline thick film is a A3Bi2X9 polycrystalline thick film (A = NH4 + ; X = SCN - ), with a thickness of 1200um and prepared by a doctor blade method.

[0070] The preparation method of the above X-ray detector:

[0071] S1, tin dioxide was spin-coated on a transparent conductive substrate at a rotation speed of 4800rpm for 50s (20uL / cm -2 ), and annealed in air at an annealing temperature of 80°C for 60 minutes to prepare an electron transport layer;

[0072] S2. Weigh out raw materials NH4SCN and BiSCN3 at a molar ratio of 3:2, and dissolve 5% 4-pyridylthiourea in a mixed solvent of γ-butyrolactone and polyethylene glycol (volume ratio of 4:1) to obtain a mixed precursor solution stock solution; stir the stock solution at 60℃ for 2 hours until fully dissolved, and then filter the stock solution to obtain a clear and transparent mixed precursor solution (concentration of 0.6mol / L);

[0073] S3, Reference Figure 2 A mixed precursor solution of S2 was coated onto the electron transport layer of S1 using a blade coater to obtain a bismuth-based perovskite wet film with a thickness of 1200 μm. The wet film was then transferred to a vacuum oven and evacuated instantly to remove the solvent. The film was then annealed at 120 °C to obtain a (NH4)3Bi2SCN9 polycrystalline thick film.

[0074] S4. Spin-coat 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene onto the perovskite polycrystalline thick film to prepare a hole transport layer;

[0075] S5. A metal electrode is prepared on the hole transport layer by vapor deposition.

[0076] Furthermore, it should be noted that the X-ray detector circuit provided by this invention includes: an etched transparent conductive substrate, an electrical signal readout electrode, a metal electrode, an electrical signal readout electrode, and an electrical signal storage capacitor. The circuit principle is as follows: Figure 3 As shown, the present invention realizes signal detection and reading accordingly.

[0077] Example 6

[0078] Performance study of the perovskite X-ray detector of this invention:

[0079] I. Taking Example 1 as an example, the X-ray response performance of the detector of the present invention is studied.

[0080] The results are as follows Figure 4 As shown, by Figure 4 It can be seen that the present invention can not only achieve large-area rapid imaging, but also has good X-ray response performance.

[0081] II. Taking Example 1 as an example, the crystallinity of the polycrystalline thick film in the detector of the present invention was studied (using (NH4)3Bi2I9 without the addition of 2,5-dithiourea additive as a control).

[0082] The results are as follows Figure 5 As shown, by Figure 5 It can be seen that, compared with the polycrystalline thick film without additives, the crystallinity of the polycrystalline thick film of the present invention is significantly improved.

[0083] The above merely describes preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A novel perovskite X-ray detector, characterized by, From bottom to top, it comprises a transparent conductive substrate, an electron transport layer, a bismuth-based perovskite polycrystalline thick film, a hole transport layer and a metal electrode; wherein the bismuth-based perovskite polycrystalline thick film adopts A3Bi2X9 polycrystalline thick film, the thickness is 800~1200 um, and is prepared by a doctor blade method, and the preparation method is: (1) raw materials AX and BiX3 are weighed according to a molar ratio of 3:2, and 5% additives are added; the above raw materials are dissolved in an organic solvent to obtain a mixed precursor solution stock solution; (2) the stock solution is stirred at a temperature of 40~60℃ for 2~6h until fully dissolved, and then the stock solution is filtered to obtain a clear and transparent 0.6~1.2M mixed precursor solution; (3) a doctor blade instrument is used to doctor blade the mixed precursor solution on the electron transport layer to obtain a bismuth-based perovskite wet film with a corresponding thickness; (4) the bismuth-based perovskite wet film is transferred to a vacuum oven for vacuumizing, the solvent is removed, and then annealing is performed at a temperature of 100~120℃, so that the A3Bi2X9 polycrystalline thick film required by the target is prepared; A3Bi2X9 polycrystalline thick film material, wherein A = NH4 + , PEA + ; X = I - , Br - , Cl - , SCN - ; and the additive is one of thiourea, 2,5-dithiobiuret, benzylthiourea, 4-pyridylthiourea, thiosemicarbazide, amidinothiourea, 2-thiouracil, N-(2,5-dibromophenyl)benzothioamide, benzenesulfonamide.

2. The novel perovskite X-ray detector according to claim 1, characterized in that, The transparent conductive substrate adopts transparent conductive glass on which indium tin oxide or fluorine-doped tin dioxide is deposited.

3. The novel perovskite X-ray detector according to claim 1, characterized in that, The electron transport layer adopts one of tin dioxide, titanium dioxide and fullerene derivative.

4. The novel perovskite X-ray detector according to claim 1, characterized in that, The hole transport layer adopts nickel oxide or 2,2',7,7'-tetrakis[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene.

5. The novel perovskite X-ray detector according to claim 1, characterized in that, The metal electrode adopts a gold electrode or a silver electrode.

6. The novel perovskite X-ray detector according to claim 1, characterized in that, The organic solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, 2-methoxyethanol, polyethylene glycol and N-methyl-2-pyrrolidone.

7. A method of manufacturing a novel perovskite X-ray detector as claimed in any one of claims 1 to 6, characterized in that, The method comprises the following steps: S1, preparing an electron transport layer on a transparent conductive substrate by spin coating or spraying; S2, doctor blading a bismuth-based perovskite wet film with a certain thickness on the electron transport layer; transferring the wet film to a vacuum oven for vacuumizing, removing the solvent, and then annealing at a temperature of 100~120℃, so that an A3Bi2X9 polycrystalline thick film is prepared; S3, preparing a hole transport layer on the perovskite polycrystalline thick film by spin coating or spraying; S4, preparing a metal electrode on the hole transport layer by evaporation.

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