A polymer passivated perovskite thick film for x-ray detection and a preparation method and application thereof

Abstract

This invention discloses a polymer-passivated perovskite thick film for X-ray detection, its preparation method, and its application. The focus is on polymer passivation modification of the perovskite absorption layer in direct conversion X-ray detectors. The thick film comprises polycrystalline lead halide perovskite microcrystals and a polymer passivating agent containing ester-oxygen structural units distributed in the intergranular regions. The preparation method includes: providing lead halide perovskite microcrystal powder; mixing the microcrystal powder, the polymer passivating agent, and an organic solvent to form a coatable slurry; and obtaining a polymer-passivated lead halide perovskite thick film through film formation and drying. The addition of the polymer passivating agent can improve the density of the thick film and reduce the adverse effects of grain boundary defects on dark current, dark current drift, and low-dose response, making it suitable for direct conversion X-ray detection and flat-panel imaging absorption layers.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor radiation detection materials technology, specifically relating to a polymer passivated lead halide perovskite thick film for X-ray direct conversion detection and its preparation method, as well as the application of this thick film as a perovskite absorbing layer in a direct conversion X-ray detector. Background Technology

[0002] Direct-conversion X-ray detectors directly convert X-ray photons into electrical signals through a semiconductor absorption layer. Their basic structure and readout methods have been extensively studied and applied. For this type of detector, one of the keys determining low-dose response, dark current, and stability lies in the semiconductor absorption layer material itself, especially the internal defects, grain boundaries, and ion migration behavior of the absorption layer.

[0003] Lead halide perovskites, containing elements with high atomic numbers, possess superior X-ray attenuation capabilities and advantages in solution processing, making them important candidate materials for absorption layers in direct-conversion X-ray detection. Unlike conventional thin-film optoelectronic devices, direct-conversion X-ray detection typically requires films hundreds of micrometers thick to achieve sufficient X-ray absorption. Therefore, the polycrystalline microcrystal stacking, grain boundary contacts, and pore defects within the thick film have a more significant impact on the device's dark current and signal-to-noise ratio.

[0004] Solution-prepared polycrystalline lead halide perovskite thick films typically contain numerous grain boundaries, voids, cracks, and uncoordinated ion defects. The shell formed during solvent evaporation and internal pressure release can also induce poor intergranular contact. These defects provide pathways for leakage current, trap-assisted recombination, and ion migration, leading to increased dark current, dark current drift, and low-dose signal overwhelmance during direct conversion detection.

[0005] Existing work has proposed various perovskite material preparation and detector structure schemes, but there is still room for improvement in the polymer passivation of grain boundaries in thick-film absorption layers for X-ray direct conversion detection. If the polymer content is insufficient, the passivation sites at the grain boundaries are inadequate; if the content is too high, the insulating polymer may form a carrier transport barrier at the grain boundaries. Therefore, there is an urgent need for a polymer passivation scheme for absorption layers in direct conversion X-ray detection that can improve the compactness of thick perovskite films, grain boundary defects, and bias voltage stability without changing the basic working principle of the detector. Summary of the Invention

[0006] This invention aims to address the problems of numerous pores and defects, high grain boundary defect density, significant ion migration, and high dark current and dark current drift associated with lead halide perovskite thick films used as X-ray direct conversion detection absorption layers. Unlike protecting the existing X-ray detector structure itself, this invention focuses on providing a polymer-passivated perovskite thick film for direct conversion detection absorption layers and its preparation method.

[0007] First, this invention provides a polymer-passivated perovskite thick film for direct conversion detection absorption layers, comprising lead halide perovskite polycrystalline microcrystals and a polymer passivating agent distributed in the intergranular regions of the lead halide perovskite polycrystalline microcrystals; wherein the polymer passivating agent is a polymer containing ester-oxygen structural units. The polymer passivating agent is used to improve the compactness of the lead halide perovskite thick film and reduce the influence of grain boundary defects on the X-ray direct conversion detection electrical signal.

[0008] In one embodiment, the polymer passivating agent includes polyvinyl acetate, vinyl acetate copolymers, polymers containing vinyl acetate structural units, or combinations thereof.

[0009] In one embodiment, the lead halide perovskite comprises inorganic lead halide perovskite, organic-inorganic hybrid lead halide perovskite, or a combination thereof; the lead halide perovskite comprises APbX3 type lead halide perovskite, wherein A includes Cs. + , methylamine cation, formamidin cation or a combination thereof, X including Cl - ,Br - I - Or a combination thereof.

[0010] This invention also provides a method for preparing the polymer-passivated lead halide perovskite thick film. The method uses lead halide perovskite microcrystalline powder as the main component, and introduces a polymer passivating agent into an organic solvent-based slurry, allowing the passivating agent to distribute in the grain boundary regions of the polycrystalline microcrystals during film formation and drying. The polymer chains can improve the filling and connection between microcrystals, reducing porosity and grain gaps in the thick film; polymers containing ester-oxygen structural units can also reduce the impact of grain boundary defects on charge transport and dark current. Specifically, the method includes the following steps:

[0011] Obtain lead halide perovskite microcrystalline powder; mix the lead halide perovskite microcrystalline powder, polymer passivator and organic solvent to prepare a coatable slurry containing polymer passivator; form the coatable slurry on a conductive substrate or a conductive substrate with an interface control layer and dry it to obtain a lead halide perovskite polycrystalline thick film.

[0012] In one embodiment, the mass concentration of the polymer passivating agent in the coatable slurry is 0.2-10 mg / mL. -1 To achieve a balance between passivation of grain boundary defects and carrier transport.

[0013] In one embodiment, the film-forming method includes blade coating, slot coating, screen printing, spraying, or casting; the drying is performed at 50-120 °C for 0.5–12 h.

[0014] This invention also provides a perovskite absorber layer assembly for an X-ray direct conversion detector. The assembly may include a first electrode and a second electrode disposed opposite to each other, and the aforementioned polymer-passivated lead halide perovskite thick film located between the first electrode and the second electrode, wherein the polymer-passivated lead halide perovskite thick film serves as an X-ray absorption and charge generation layer. This invention does not focus on improving the basic structure of the X-ray detector, but rather on the polymer-passivated perovskite absorber layer located within that structure as its core technical feature.

[0015] The present invention also provides the application of polymer passivated perovskite thick film for X-ray detection in the preparation of direct conversion X-ray detectors, low-dose X-ray detectors or X-ray flat panel imaging devices.

[0016] The beneficial effects of this invention are as follows:

[0017] 1. This invention introduces a polymer passivating agent into the lead halide perovskite thick film absorption layer, thereby focusing the protection efforts on the modification of perovskite materials in direct conversion X-ray detectors.

[0018] 2. The polymer passivating agent in this invention can improve the microstructure of thick films, making the contact between grains closer and reducing pore defects, thereby improving the compactness of the perovskite thick film absorber layer.

[0019] 3. The present invention uses polymers containing ester-oxygen structural units to passivate grain boundary regions, which can reduce the adverse effects of grain boundary defects on leakage current, ion migration and low-dose response.

[0020] 4. The direct conversion detection component using the polymer passivated lead halide perovskite thick film of the present invention as the absorption layer has higher resistivity, lower dark current, smaller dark current drift and higher ion migration activation energy, which can improve the resolvability of low-dose X-ray signals.

[0021] 5. The thick film preparation method of the present invention is compatible with large-area film formation processes such as blade coating, slot coating, and screen printing, and can be used as a perovskite absorbing layer material for direct conversion X-ray detection and flat panel imaging. Attached Figure Description

[0022] Figure 1 This is a comparison of the microstructure of lead halide perovskite thick films before and after the addition of polyvinyl acetate (PVAc) in an embodiment of the present invention, showing the improvement in density.

[0023] Figure 2 This is a comparison of the current-voltage curves and resistivity of the control device and the PVAc passivated device in the embodiments of the present invention.

[0024] Figure 3 This is a comparison diagram of dark current drift between the control device and the PVAc passivated device in the embodiments of the present invention.

[0025] Figure 4 This is a comparison diagram of the ion migration activation energies of the control device and the PVAc passivated device in the embodiments of the present invention.

[0026] Figure 5 This is a comparison diagram of the X-ray sensitivity of the control device and the PVAc passivated device in the embodiments of the present invention.

[0027] Figure 6 This is a comparison chart of the low-dose signal-to-noise ratio and detection limit of the control device and the PVAc passivated device in the embodiments of the present invention.

[0028] Figure 7 This is a test diagram of the long-term working stability of the PVAc passivated device in an embodiment of the present invention.

[0029] Figure 8 This is an image showing the imaging effect obtained by the X-ray flat panel imaging device in an embodiment of the present invention. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments. It should be understood that the embodiments are only used to illustrate the polymer passivation perovskite absorber layer scheme of the present invention and are not intended to limit the scope of protection of the present invention. Without departing from the concept of the present invention, equivalent substitutions or conventional adjustments made by those skilled in the art to the lead halide perovskite composition, polymer passivating agent type, solvent type, film formation parameters, electrode material and readout backplane form should all fall within the scope of protection of the present invention.

[0031] Example 1: Preparation process of polymer passivation perovskite thick film for X-ray detection of APbX3 type lead halide perovskite.

[0032] Step 1: Dissolve the APbX3 type lead halide perovskite raw material in a precursor solvent according to the stoichiometric ratio of A, Pb, and X. The precursor solvent is a polar organic solvent capable of dissolving the A-site cation source, lead source, and halogen source to form a lead halide perovskite precursor solution, preferably dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone, or a mixture thereof. Prepare a solution of 0.1–2.0 mol / L. -1 Lead halide perovskite precursor solution.

[0033] Step 2: Add the lead halide perovskite precursor solution to the antisolvent to precipitate lead halide perovskite microcrystals; wherein the volume ratio of the antisolvent to the precursor solution is 1:1–10:1.

[0034] Step 3: After separating and washing the precipitate, dry it at 20–80 °C for 12–96 h, preferably at 35–60 °C for 24–72 h, to obtain lead halide perovskite microcrystalline powder.

[0035] Step 4: Mix the lead halide perovskite microcrystalline powder, polymer passivator and organic solvent to prepare a coatable slurry containing polymer passivator.

[0036] Step 5: After thoroughly grinding or stirring the coatable slurry, apply it to a conductive substrate or a conductive substrate with an interface control layer using an adjustable scraper to form a wet film.

[0037] Step 6: Dry the wet film at 50–120 °C for 0.5–12 h, preferably under vacuum at 60–90 °C for 2–6 h, to obtain a lead halide perovskite polycrystalline thick film.

[0038] Example 2: Based on Example 1, the preparation process of a polyvinyl acetate (PVAc) passivated perovskite absorber layer using CsPbI2Br as an example:

[0039] Step 1: Dissolve CsI, PbBr2, and PbI2 in dimethyl sulfoxide in a ratio that satisfies the stoichiometric relationship between Cs and PbI2Br to prepare a solution of 0.85 mol / L. -1 CsPbI2Br precursor solution.

[0040] Step 2: Take 18 mL of the CsPbI2Br precursor solution and add it to 44 mL of anhydrous ethanol to precipitate CsPbI2Br microcrystals.

[0041] Step 3: The precipitate was centrifuged and washed with anhydrous ethanol, and then dried at 45 °C for 60 h to obtain CsPbI2Br microcrystalline powder.

[0042] Step 4: Mix the CsPbI2Br microcrystalline powder, polyvinyl acetate, and N-methylpyrrolidone to prepare a coatable slurry containing polyvinyl acetate. For comparison, a control slurry without added polyvinyl acetate and several slurries with different polyvinyl acetate contents were prepared, wherein the mass concentration of polyvinyl acetate in the slurries with added polyvinyl acetate was between 0.8 and 6.5 mg / mL. -1 Within the range.

[0043] Step 5: After thoroughly grinding or stirring the coatable slurry, apply it to a conductive substrate or a conductive substrate with an interface control layer using an adjustable scraper to form a wet film.

[0044] Step 6: The wet film is dried in a vacuum oven at 76 °C for 4.2 h to obtain a CsPbI2Br polycrystalline thick film; Figure 1 As shown, the addition of polyvinyl acetate (PVAc) significantly improves the film density of lead halide perovskite thick films.

[0045] Example 3: Performance changes of PVAc passivated perovskite absorber layer when used for direct conversion detection.

[0046] To evaluate the effectiveness of the polyvinyl acetate passivated CsPbI2Br thick film prepared in Example 2 as a direct conversion detector absorption layer, a silver top electrode was formed on the surface of the obtained thick film by screen printing. The effective area defined by the mask was 0.01 cm². 2 After printing the silver paste, it is dried under vacuum at 50 °C for 2 h to obtain a vertical detection component containing a PVAc passivated perovskite absorption layer. Depending on the requirements, the silver top electrode can be replaced with other conductive electrodes, and the bottom conductive substrate can be replaced with an ITO electrode, a thin-film transistor pixel electrode, or other conductive readout substrate.

[0047] In dark-state IV testing, the relevant current-voltage curves and resistivity comparisons are as follows: Figure 2 As shown, the resistivity of the control device without polyvinyl acetate is 5.43 × 10⁻⁶. 10 The resistivity of polyvinyl acetate passivated devices increased to 5.23 × 10⁻⁶ Ω cm. 11 Ω cm.

[0048] Dark current drift tests were conducted at a bias voltage of 135 V mm⁻¹. The relevant results are as follows: Figure 3 As shown, the dark current drift rate of the control device is 0.298 pA cm⁻¹. -1 s -1 V -1 The passivation effect of polyvinyl acetate on the device was reduced to 0.0722 pA cm⁻¹. -1 s -1 V -1 ,

[0049] like Figure 4 As shown, by fitting the temperature-dependent conductivity using Arrhenius, the ion migration activation energy of the control device is 593 meV, while that of the polyvinyl acetate passivated device is increased to 696 meV, indicating that polyvinyl acetate passivation can improve the ion migration energy barrier and alleviate field-driven ion migration.

[0050] Sensitivity comparison Figure 5 As shown, the low-dose signal-to-noise ratio and detection limit results are as follows: Figure 6 As shown. At 27 V mm -1 Under the electric field, the dark current density of the control device is 4.57 nA cm⁻¹. -2 The dark current density of polyvinyl acetate passivated devices decreased to 0.41 nA cm⁻¹. -2 Under the same electric field (27V mm) -1 Sensitivity increased from 112.13 μC Gy air-1 cm⁻² increased to 127.83 μCGy air -1 cm -2 At low doses, 53 nGy air s -1 The time signal-to-noise ratio was improved from 5.23 to 14.13, and the detection limit was increased from 38.3 nGy. air s-1 decreased to 14.5 nGy air s -1 .

[0051] like Figure 7 As shown, at 27 V mm -1 13.3 μGy air s -1 Under the specified conditions, the polyvinyl acetate passivated device did not show significant photocurrent attenuation after being placed in air for 15 days, indicating that the thick film structure has a certain degree of operational stability.

[0052] Example 4: Array imaging application of PVAc passivated perovskite absorption layer.

[0053] By integrating the polyvinyl acetate passivated CsPbI2Br thick film obtained in Example 2 as a perovskite absorption layer onto an a-Si thin-film transistor readout backplane, a direct conversion X-ray flat panel imaging sample can be obtained. The thin-film transistor backplane includes multiple pixel units arranged in an array, with the thick film covering at least a portion of the pixel units; in one specific sample, the backplane dimensions are 44.64 × 46.64 mm. 2 The active region area is 32×32 mm. 2 The pixel array is 64×64, and the pixel size is 500×500 μm.

[0054] Under X-ray irradiation, flat-panel imaging samples containing a PVAc passivated perovskite absorbing layer can output 8-bit grayscale images. Dark-field images are used to evaluate dark current baseline, flat-field images are used to evaluate pixel response uniformity, and object transmission images are used to evaluate spatial imaging capabilities.

[0055] In one embodiment, the obtained X-ray transmission image can present the overall outline of the object under test and the grayscale contrast formed by local thickness differences, demonstrating the application capability of the thick film in array imaging, and the imaging effect is as follows: Figure 8 As shown.

[0056] This invention employs processes such as anti-solvent precipitation, slurry preparation, coating film formation, and low-temperature drying, resulting in a simple preparation route suitable for integration with large-area conductive substrates or thin-film transistor readout backplanes. The resulting polymer-passivated lead halide perovskite thick film can serve as a perovskite absorption layer in direct-conversion X-ray detectors, reducing dark current, minimizing dark current drift, and improving low-dose response. It can be applied in fields such as medical imaging, industrial non-destructive testing, security inspection, and scientific radiation detection.

[0057] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A polymer passivated perovskite thick film for X-ray detection, characterized in that, The mixture comprises lead halide perovskite polycrystalline microcrystals and a polymer passivating agent distributed in the intergranular region of the lead halide perovskite polycrystalline microcrystals, wherein the polymer passivating agent is a polymer containing ester oxygen structural units.

2. The polymer passivated perovskite thick film for X-ray detection according to claim 1, characterized in that, The polymer passivating agent includes polyvinyl acetate, vinyl acetate copolymers, polymers containing vinyl acetate structural units, or combinations thereof.

3. The polymer passivated perovskite thick film for X-ray detection according to claim 1, characterized in that, The lead halide perovskite includes inorganic lead halide perovskite, organic-inorganic hybrid lead halide perovskite, or a combination thereof; the lead halide perovskite includes APbX3 type lead halide perovskite, wherein A includes Cs. + , methylamine cation, formamidin cation or a combination thereof, X including Cl - ,Br - I - Or a combination thereof.

4. The polymer passivated perovskite thick film for X-ray detection according to claim 1, characterized in that, The polymer passivating agent is used to improve the compactness of the lead halide perovskite thick film and reduce the influence of grain boundary defects on the X-ray direct conversion detection electrical signal.

5. A method for preparing a polymer passivated perovskite thick film for X-ray detection as described in any one of claims 1-4, characterized in that, Includes the following steps: Obtain lead halide perovskite microcrystalline powder; The lead halide perovskite microcrystalline powder, polymer passivator, and organic solvent are mixed to prepare a coatable slurry containing polymer passivator; The coatingable slurry is deposited on a conductive substrate or a conductive substrate with an interface control layer and dried to obtain a lead halide perovskite polycrystalline thick film.

6. The method for preparing a polymer passivated perovskite thick film for X-ray detection according to claim 5, characterized in that, The mass concentration of the polymer passivating agent in the coatable slurry is 0.2-10 mg / mL. -1 .

7. The method for preparing a polymer passivated perovskite thick film for X-ray detection according to claim 6, characterized in that, The film-forming method includes blade coating, slot coating, screen printing, spraying, or casting; the drying is carried out at 50-120 °C for 0.5–12 h.

8. The method for preparing a polymer passivated perovskite thick film for X-ray detection according to claim 7, characterized in that, The lead halide perovskite microcrystalline powder is prepared by the following steps: Step 1: Dissolve the lead halide perovskite raw material, including the A-site cation source, lead source and halogen source, in the precursor solvent to prepare the lead halide perovskite precursor solution; Step 2: Add the lead halide perovskite precursor solution to the antisolvent to precipitate lead halide perovskite microcrystals; Step 3: After separating and washing the lead halide perovskite microcrystal precipitate, dry it at 20–80 ℃ for 12–96 h to obtain lead halide perovskite microcrystal powder.

9. A perovskite absorber layer assembly for an X-ray direct conversion detector, characterized in that, The invention comprises a first electrode, a second electrode, and a polymer passivated perovskite thick film for X-ray detection as described in any one of claims 1-4, wherein the polymer passivated lead halide perovskite thick film serves as an X-ray absorption and charge generation layer.

10. The use of the polymer passivated perovskite thick film for X-ray detection according to any one of claims 1-4 in the preparation of direct conversion X-ray detectors, low-dose X-ray detectors or X-ray flat panel imaging devices.

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