Preparation method of large-area perovskite microcrystalline thin film and X-ray detector

Abstract

The application relates to a preparation method of a large-area perovskite microcrystalline thin film and an X-ray detector. The method comprises the following steps: 1) firstly, a polycrystalline perovskite precursor solution is coated on a hole transport material modified conductive substrate by using a doctor blade method, and a nano-thickness large-area perovskite polycrystalline thin film is obtained through annealing treatment; 2) combining a reverse temperature crystallization method, the perovskite polycrystalline thin film obtained in the step 1) is introduced into a perovskite saturated growth solution as a growth template to induce growth of a large-area microcrystalline thin film, and the size of the polycrystalline thin film determines the size of the microcrystalline thin film; and 3) an isostatic pressing and hot pressing process is adopted to perform flattening treatment on the surface of the microcrystalline thin film. The method can overcome the problems of a traditional bulk perovskite single crystal, such as too large longitudinal thickness and limited lateral size, and the problems of a polycrystalline perovskite thin film, such as small grain size and large defect density, and the sensitivity of a device to X-ray detection is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of X-ray detection technology, specifically relating to a method for preparing large-area perovskite microcrystalline thin films and an X-ray detector. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] X-ray detectors are devices that receive X-rays and convert them into electrical signals, enabling accurate detection of the fine internal structures of samples such as biological organisms and metals. Metal halide perovskite materials have become promising materials for direct X-ray detection due to their high X-ray absorption efficiency, large carrier lifetime product, high resistivity, and good radiation damage resistance.

[0004] Currently, large-area perovskite polycrystalline thin films prepared by conventional spin-coating methods consist of numerous nanoscale grains with a maximum thickness of only a few micrometers. This thickness cannot guarantee effective attenuation of X-rays. Furthermore, the presence of numerous grain boundaries between grains increases the defect density of the film, restricting carrier transport during device operation and further reducing the sensitivity of the X-ray detector. On the other hand, single-crystal perovskites possess superior photoelectric properties compared to polycrystalline perovskites. X-ray detectors fabricated from high-quality perovskite single crystals grown from various compositions have achieved continuous breakthroughs in parameters such as sensitivity and minimum detection limit. However, growing large-volume bulk perovskite single crystals remains challenging, let alone controllably integrating them onto conductive substrates. Additionally, the thickness of bulk single crystals necessitates a relatively high bias voltage for carriers to be collected by the electrodes at both ends, which can exacerbate ion migration within the X-ray detector device. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a method for preparing a dense, flat, substrate-integrated large-area perovskite microcrystalline thin film and an X-ray detector.

[0006] To solve the above technical problems, the technical solution of the present invention is as follows:

[0007] In a first aspect, a method for preparing a large-area perovskite microcrystalline thin film is provided, the method comprising:

[0008] 1) First, the polycrystalline perovskite precursor solution was coated onto a conductive substrate modified with hole transport material using a blade coating method, and then annealed to obtain a large-area polycrystalline perovskite film with a nanometer thickness.

[0009] 2) Combining the reverse temperature crystallization method, the perovskite polycrystalline film obtained in step 1) is used as a growth template and introduced into the perovskite saturated growth solution to induce the growth of large-area microcrystalline films. The size of the polycrystalline film determines the size of the microcrystalline film.

[0010] 3) The surface of the microcrystalline film is smoothed by isostatic pressing hot pressing process.

[0011] The preparation method of the present invention can overcome the problems of excessive longitudinal thickness and limited lateral size of traditional bulk perovskite single crystals, as well as small grain size and high defect density of perovskite polycrystalline thin films.

[0012] The preparation method of this invention involves obtaining a large-area perovskite polycrystalline thin film in step 1), and then using the polycrystalline thin film as a growth template to induce the growth of a large-area microcrystalline thin film in a perovskite saturated solution. Perovskite microcrystals combine the excellent properties of bulk single crystals with the advantages of easy large-area substrate integration of polycrystalline materials, thus solving the problems of large-area integration and thickness control of bulk single crystals with substrates. Furthermore, X-ray detectors based on perovskite microcrystalline thin films have successfully achieved excellent X-ray response at 0V bias, further solving the problems of ion migration and signal drift caused by high bias voltages in perovskite-based X-ray detectors.

[0013] In some embodiments of the present invention, the polycrystalline perovskite precursor components are MAPbI3 and FA. x MA 1-x One or more of PbI3, MAPbBr3, or FAPbBr3. Further, the solvent is DMF (N,N-dimethylformamide) or GBL (γ-butyrolactone). For example, a DMF solution of MAI / PbI2 or MABr / PbBr2 can be prepared.

[0014] In some embodiments of the present invention, the polycrystalline thin film is prepared by blade coating or spin coating. Furthermore, during blade coating, the distance between the blade and the substrate is 20-80 μm. Furthermore, the spin coating speed is 2000-4000 rpm.

[0015] This application primarily employs a two-step method to grow large-area microcrystalline thin films, with a thickness and grain size of approximately several hundred micrometers. The microcrystalline thin films prepared in this application have large grains and low defect density, and their photoelectric properties are closer to those of perovskite single crystals.

[0016] In some embodiments of the present invention, in step 1), the annealing temperature is 80-120°C and the annealing time is 10-20 min.

[0017] In some embodiments of the present invention, the growth temperature of the perovskite microcrystalline film in step 2) in the saturated solution is 60-100°C.

[0018] In some embodiments of the present invention, the growth time using the reverse temperature crystallization method (i.e., the solubility of perovskite material in a specific solvent decreases as the temperature increases, thereby precipitating crystals) is 30-120 minutes.

[0019] In some embodiments of the present invention, the surface smoothing treatment in step 3) is one or more of the following methods: mechanical hot pressing, grinding, polishing, etc. This reduces surface roughness, thereby forming a uniform, dense, and smooth large-area microcrystalline film.

[0020] Secondly, the application of the method for preparing large-area perovskite microcrystalline thin films described in the first aspect above in the field of preparing perovskite X-ray detectors.

[0021] Thirdly, an X-ray detector, wherein the absorber layer of the X-ray detector is made of the large-area perovskite microcrystalline thin film described in the first aspect above. Further, the structure of the X-ray detector comprises a cathode, an electron transport layer, a hole blocking layer, an X-ray absorber layer, a hole transport layer, and an anode, stacked sequentially.

[0022] Fourthly, the method for preparing the X-ray detector described in the third aspect above, wherein the method is as follows:

[0023] 1) A PEDOT:PSS solution was spin-coated onto conductive glass, followed by annealing, to obtain a hole transport layer;

[0024] 2) Using the hole transport layer modified ITO conductive glass obtained in step 1) as a substrate, a large area perovskite microcrystalline thin film is grown on the substrate according to the preparation method of the first aspect above.

[0025] 3) An electron transport layer and a hole blocking layer C are vapor-deposited on the surface of the large-area perovskite microcrystalline thin film obtained in step 2). 60 / BCP;

[0026] 4) Copper electrodes are vapor-deposited onto the electron transport layer obtained in step 3) to obtain a perovskite microcrystalline X-ray detector.

[0027] In some embodiments of the present invention, the annealing temperature in step 1) is 120-160°C, preferably 150°C.

[0028] In some embodiments of the present invention, the annealing time of the hole transport layer is 10-20 min, and the thickness of the electron transport layer is 10-30 nm.

[0029] One or more technical solutions of the present invention have the following beneficial effects:

[0030] (1) Large-area perovskite microcrystalline films can be rapidly synthesized using perovskite polycrystalline films as templates, solving the area limitation problem when traditional high-quality bulk single crystals are applied to the field of X-ray detection. This enables large-scale production and meets commercial needs. (2) Solution-grown microcrystalline films are low-cost and the film composition and thickness are controllable, solving the problem that traditional spin-coating methods cannot prepare thick perovskite films, further ensuring the effective attenuation of X-rays by the device. (3) The prepared microcrystalline films are composed of single crystals of hundreds of micrometers in size, with large grain size and low defect density. The films can be integrated with conductive substrates, significantly improving the sensitivity of the device to X-ray detection. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of this application. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0032] Figure 1 Photographs of large-area (a) MAPbI3 and (b) MAPbBr3 microcrystalline films induced by polycrystalline thin film growth;

[0033] Figure 2 This is a scanning electron microscope image of the MAPbBr3 microcrystalline thin film after surface planarization treatment.

[0034] Figure 3 This is a cross-sectional scanning electron microscope image of a MAPbBr3 microcrystalline thin film.

[0035] Figure 4 The image shows the XRD pattern of the MAPbBr3 microcrystalline thin film.

[0036] Figure 5 This is a structural diagram of an X-ray detector based on microcrystalline thin films;

[0037] The ITO glass is the positive electrode, PEDOT:PSS is the hole transport layer, the perovskite microcrystalline film is the X-ray absorption layer, C60 / BCP is the electron transport layer, and the copper electrode is the negative electrode.

[0038] Figure 6 The IV curve of the microcrystalline thin-film X-ray detector under visible light;

[0039] Figure 7 Calculation of the variable dose IT curve and sensitivity of the X-ray detector under 0V bias voltage; Detailed Implementation

[0040] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0041] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. The invention is further described below with reference to embodiments:

[0042] Example 1

[0043] First, a 1M MAPbI3 / DMF polycrystalline thin film precursor solution was prepared. Then, the precursor solution was coated onto a 10×10cm ITO conductive substrate and annealed at 100℃ for 10 min to form a MAPbI3 polycrystalline perovskite thin film. Subsequently, the obtained polycrystalline thin film was immersed in a 1.5M MAPbI3 / GBL solution heated at 90℃ and grown using the reverse temperature crystallization method for 120 min to obtain a large-area MAPbI3 microcrystalline thin film with a thickness of about 200μm. The surface of the obtained perovskite microcrystalline thin film was planarized by isostatic hot pressing.

[0044] Example 2

[0045] First, a 1M MAPbBr3 / DMF polycrystalline thin film precursor solution was prepared. Then, the precursor solution was coated onto a 4×4cm ITO conductive substrate and annealed at 100℃ for 10 min to form a MAPbBr3 polycrystalline perovskite thin film. Subsequently, the obtained polycrystalline thin film was immersed in a 1.5M MAPbBr3 / DMF solution heated at 60℃ and grown using the reverse temperature crystallization method for 60 min to obtain a large-area MAPbBr3 microcrystalline thin film with a thickness of about 200μm. The surface of the obtained perovskite microcrystalline thin film was planarized by isostatic hot pressing.

[0046] like Figure 1 The images shown are optical photographs of large-area perovskite microcrystalline thin films MAPbI3 and MAPbBr3 obtained in Examples 1 and 2, respectively. Due to the different perovskite compositions, the two microcrystalline thin films have different morphological characteristics and photoelectric properties.

[0047] Figure 2 The image shows the MAPbBr3 perovskite microcrystalline film obtained in Example 2 after surface planarization, which shows that the surface is dense and flat.

[0048] Figure 3 The image shows a cross-sectional scanning electron microscope image of the MAPbBr3 microcrystalline thin film obtained in Example 2, which shows that its thickness is approximately 200 μm.

[0049] Figure 4 The image shows the XRD pattern of the MAPbBr3 microcrystalline film obtained in Example 2. It can be seen that the perovskite microcrystalline film has good crystallinity and orientation.

[0050] Example 3

[0051] (1) First, ultrasonically clean the ITO conductive glass in deionized water, acetone and ethanol respectively and set it aside for use.

[0052] (2) Clean the ITO substrate cleaned in step (1) with a plasma cleaner for 10-15 minutes, then spin coat it with PEDOT:PSS solution on a spin coater and anneal it to obtain a hole transport layer.

[0053] (3) Preparation of microcrystalline thin film: according to the method of Example 2.

[0054] (4) An electron transport layer C with a thickness of 10-30 nm is deposited on the surface of the microcrystalline thin film after the planarization treatment in step (3). 60 / BCP;

[0055] (5) Copper electrodes are deposited on the electron transport layer to obtain a microcrystalline thin film X-ray detector.

[0056] The structure of the obtained X-ray detector is as follows Figure 5 As shown in the diagram. ITO glass is the positive electrode, PEDOT:PSS is the hole transport layer, perovskite microcrystalline film is the X-ray absorption layer, C60 / BCP is the electron transport layer, and copper electrode is the negative electrode.

[0057] Experimental Example 1

[0058] The X-ray detector obtained in Example 3 was used to perform photo-dark current tests under visible light, and the results are as follows: Figure 6 As shown, from Figure 6 As can be seen, this device exhibits a significant on / off ratio under an applied bias voltage, and also displays photovoltaic characteristics under illumination, with an open-circuit voltage of 608mV, indicating that the detector is operating in photodiode mode.

[0059] Experiment Example 2

[0060] The X-ray detector obtained in Example 3 was tested for X-ray response by changing the X-ray dose under a 0V bias voltage. As shown in Figure 7(a), the photocurrent of the detector increases significantly with the increase of X-ray dose, demonstrating excellent X-ray response.

[0061] Experimental Example 3

[0062] The X-ray detector obtained in Example 3 was used for sensitivity testing. Linear fitting was performed on the device photocurrent at different doses, as shown in Figure 7(b). The resulting sensitivity of the X-ray detector was 1460.8 μC Gy. air -1 cm -2 .

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An X-ray detector, characterized in that: The structure of an X-ray detector consists of a cathode, an electron transport layer, a hole blocking layer, an X-ray absorption layer, a hole transport layer, and an anode, which are stacked in sequence. The absorber layer material of the X-ray detector is a large-area perovskite microcrystalline thin film. The X-ray detector achieves excellent X-ray response at a bias voltage of 0 V; The method for preparing the large-area perovskite microcrystalline thin film is as follows: 1) First, a polycrystalline perovskite precursor solution is coated onto a conductive substrate modified with hole transport material using a blade coating method, followed by annealing to obtain a large-area polycrystalline perovskite film with a nanometer thickness. 2) Combining the reverse temperature crystallization method, the perovskite polycrystalline film obtained in step 1) is used as a growth template and introduced into the perovskite saturated growth solution to induce the growth of large-area microcrystalline films. The size of the polycrystalline film determines the size of the microcrystalline film. 3) The surface of the microcrystalline thin film is smoothed using an isostatic hot pressing process; In step 1), the annealing temperature is 80-120℃ and the annealing time is 10-20 minutes. In step 2), the growth temperature of the perovskite microcrystalline film in the saturated solution is 60-90℃; The growth time for reverse temperature crystallization is 30-120 min; The polycrystalline perovskite precursor consists of MAPbI3 and FA. x MA 1-x One or more of MAPbBr3 or FAPbBr3; The large-area perovskite microcrystalline film has a thickness and grain size of several hundred micrometers. The solvent is N,N-dimethylformamide or γ-butyrolactone.

2. The X-ray detector as described in claim 1, characterized in that: Polycrystalline thin films are prepared by blade coating or spin coating.

3. The X-ray detector as described in claim 2, characterized in that: During the coating process, the distance between the doctor blade and the substrate is 20-80μm.

4. The X-ray detector as described in claim 2, characterized in that: Spin coating speed 2000-4000 rpm.

5. The method for preparing the X-ray detector according to claim 1, characterized in that: The method is as follows: 1) A PEDOT:PSS solution is spin-coated onto conductive glass and then annealed to obtain a hole transport layer; 2) Using the conductive glass obtained in step 1) as a substrate, a large-area perovskite microcrystalline thin film is grown on the substrate according to any one of claims 1-4 for the X-ray detector. 3) An electron transport layer C is deposited on the surface of the large-area perovskite microcrystalline thin film obtained in step 2). 60 / BCP; 4) Copper electrodes are deposited on the electron transport layer obtained in step 3) to obtain an X-ray detector.

Images