Methylamine formamidino perovskite single crystal, preparation method thereof and X-ray detector

Abstract

The invention discloses a methylamine formamidino perovskite single crystal, a preparation method thereof and an X-ray detector, and belongs to the technical field of perovskite single crystal X-ray detectors. Methyl iodide amine, formamidino hydriodate and lead iodide are used as raw materials, anhydrous acetic acid is used as an additive, growth is carried out in a solvent through a seed crystal method, and the methylamine formamidino perovskite single crystal is obtained. Anhydrous acetic acid and formamidine generate hydrogen-bond interaction, formamidine is pulled to enter crystal lattices, so that phase separation is eliminated, acetate and Pb coordinate to delay formation of a lead-iodine framework, the speed of methylamine and formamidine entering the crystal lattices is balanced, meanwhile, the stability of a methylamine formamidine perovskite precursor solution is improved, stable growth of methylamine formamidine perovskite single crystals is achieved, and the methylamine formamidine perovskite single crystals are obtained. The single crystal has the advantages of high crystallinity, low defect density, large size and favorable X-ray response performance. The methylamine formamidine perovskite single crystal is high in controllability in the growth process, and the preparation method is high in operability, simple and easy to implement, short in preparation period, low in equipment requirement and low in cost.

Description

Technical Field

[0001] This invention relates to the field of perovskite single crystal X-ray detector technology, specifically to a methylamine formamidinium-based perovskite single crystal, its preparation method, and an X-ray detector. Background Technology

[0002] High-performance X-ray detectors play an irreplaceable role in medical imaging, security inspection, and basic scientific research. In recent years, hybrid metal halide perovskites have rapidly become strong candidates for next-generation radiation detection materials due to their high X-ray absorption coefficient, excellent carrier transport properties, and solution-processable advantages. Among them, perovskite single crystals, with their ultra-low defect density and long carrier diffusion length, exhibit performance far superior to traditional radiation detectors and have become a key platform for achieving ultra-high sensitivity and low detection limit X-ray detection.

[0003] The crystal growth of methylamine-formamidine-based perovskite single crystals is mainly carried out using the inverse-temperature crystallization method. This method not only allows for preparation at lower temperatures but also offers a competitive cost advantage. However, inverse-temperature crystallization is highly sensitive to environmental changes; temperature fluctuations, local concentration variations, supersaturation changes, and substrate stress can all significantly impact its growth. Among these, the difference in the lattice entry rates of methylamine (MA) and formamidine (FA) is a crucial factor limiting the crystal quality of methylamine-formamidine-based perovskite single crystals and the performance of their optoelectronic devices. MA ions have a small radius and low migration barrier, allowing for rapid lattice entry in the early stages of crystallization, while FA ions have a large radius, requiring higher energy and exhibiting a slower lattice entry rate. This severe mismatch in A-site cation insertion rates leads to spatial composition gradients, or phase separation, in the slowly growing single crystal. This inhomogeneity not only introduces carrier traps but also disrupts lattice periodicity, severely degrading carrier mobility and lifetime, thus fundamentally limiting further improvements in detector performance. Summary of the Invention

[0004] This invention provides a methylamine-formamidinium-based perovskite single crystal, its preparation method, and an X-ray detector. It effectively solves the technical problem of poor X-ray detector performance caused by phase separation in the prepared single crystal due to the sequential entry of methylamine and formamidinium into the crystal lattice during the inverse-temperature crystallization method. This invention uses anhydrous acetic acid as an additive to assist in the growth of mixed-cation perovskite single crystals, effectively suppressing the aging of the precursor solution and phase separation of the single crystal. This results in a high-quality, low-defect-density, large-size methylamine-based perovskite single crystal, thereby obtaining a high-sensitivity X-ray detector.

[0005] The first objective of this invention is to provide a method for preparing methylamine methylammonium perovskite single crystals, comprising the following steps: Using methylamine iodide, formamidine hydroiodide, and lead iodide as raw materials, and anhydrous acetic acid as an additive, the perovskite was grown in a solvent via a seed crystal method. Anhydrous acetic acid formed hydrogen bonds with formamidine, which increased the rate at which formamidine entered the crystal lattice and eliminated phase separation. The coordination of acetate with Pb delayed the formation of the lead-iodine framework and balanced the rate at which methylamine and formamidine entered the crystal lattice, thus obtaining methylamine-formamidine-based perovskite single crystals.

[0006] The molar ratio of methyl iodide, formamidinium hydroiodate, lead iodide, and anhydrous acetic acid is 0.1~0.9:0.1~0.9:1:0.05.

[0007] In the above technical solution, using anhydrous acetic acid as an additive increases the rate at which formamidin enters the crystal lattice, thereby effectively eliminating phase separation. Regarding the amount of anhydrous acetic acid, if the amount is too small, the H₂ provided by the anhydrous acetic acid will be insufficient. + If the concentration is too low, the deprotonation of methylamine and formamidin cannot be suppressed, leading to the formation of MFA and DMFA byproducts. This, in turn, results in a decrease in the bulk resistivity of the X-ray detector, a drop in sensitivity, and an increase in the detection limit. Conversely, if the amount of anhydrous acetic acid is excessive, it will cause over-coordination of acetate and lead, thereby inhibiting crystallization, resulting in stagnant single crystal growth or tiny crystal size, poor crystallinity, and an increased full width at half maximum (FWHM), thus making it impossible to fabricate an X-ray detector with the expected performance.

[0008] In a preferred embodiment, the solvent is γ-butyrolactone.

[0009] As a preferred embodiment, the method for preparing the methylamine formamidinium-based perovskite single crystal is as follows: using methylamine iodide, formamidinium hydroiodate, and lead iodide as raw materials, and anhydrous acetic acid as an additive, the mixture is stirred in a solvent at room temperature to obtain a perovskite single crystal precursor solution, which is then grown by a seed crystal method to obtain the methylamine formamidinium-based perovskite single crystal.

[0010] In a preferred embodiment, the concentration of the perovskite single crystal precursor in the perovskite single crystal precursor solution is 1.25 mol / L.

[0011] As a preferred embodiment, the growth by seed crystal method specifically involves: dividing the perovskite single crystal precursor solution into two portions; taking the first portion of the perovskite single crystal precursor solution and gradually increasing the temperature from an initial temperature of 90°C to 100°C~120°C to obtain an initial seed crystal; adding the second portion of the perovskite single crystal precursor solution to the initial seed crystal and gradually increasing the temperature from an initial temperature of 70°C~86°C to 90°C~106°C to obtain a methylamine methylammonium perovskite single crystal.

[0012] In a preferred embodiment, the temperature rise rate of the programmed temperature rise is 5°C / h, and the temperature rise rate of the stepped temperature rise is 1°C / h.

[0013] A second objective of this invention is to provide a methylaminomamidinium-based perovskite single crystal, prepared using any of the above-described methods for preparing methylaminomamidinium-based perovskite single crystals.

[0014] A third objective of this invention is to provide an X-ray detector, wherein the X-ray detector is obtained by using the methylaminomamidinium perovskite single crystal as the photosensitive and ionization-sensitive active layer, and by fabricating electrodes on both sides of the photosensitive and ionization-sensitive active layer. The X-ray detector is composed of a gold electrode-methylaminomamidinium perovskite single crystal-indium gallium alloy or a gold electrode-methylaminomamidinium perovskite single crystal-silver electrode.

[0015] In a preferred embodiment, the electrode is made of at least one of gold, indium gallium alloy and silver.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a methylamine formamidine-based perovskite single crystal, using methylamine iodide, formamidine hydroiodate, and lead iodide as raw materials, and anhydrous acetic acid as an additive. Growth is achieved in a solvent via a seed crystal method. Anhydrous acetic acid forms hydrogen bonds with formamidine, pulling the formamidine into the crystal lattice and eliminating phase separation. Simultaneously, acetate coordination with Pb delays the formation of the lead-iodine framework, achieving a balance in the entry rates of methylamine and formamidine into the crystal lattice. This also improves the stability of the methylamine formamidine-based perovskite precursor solution, enabling stable growth of the single crystal. The growth process of the methylamine formamidine-based perovskite single crystal obtained by this invention is highly controllable, the preparation method is easy to operate, simple and convenient, has a short preparation cycle, low equipment requirements, and low cost. The final methylamine formamidine-based perovskite single crystal exhibits high crystallinity, low defect density, large size, and excellent X-ray response performance. Attached Figure Description

[0017] Figure 1 The methylamine methylammonium-based perovskite single crystals (MA) prepared in Examples 1 to 9 of this invention x FA 1-x PbI3) images, where a is Example 1, b is Example 2, c is Example 3, d is Example 4, e is Example 5, f is Example 6, g is Example 7, h is Example 8, and i is Example 9. Figure 2 The 1H NMR spectra of the perovskite precursors in the control and blank groups of this invention are shown below. 1 The figure shows the H NMR spectra, where FAI is the FAI precursor of the blank group, MAI is the MAI precursor of the blank group, FAI-HAC is the FAI precursor of the control group, and MAI-HAC is the MAI precursor of the control group. Figure 3 MA prepared in Example 4 and Comparative Example 1 of this invention 0.4 FA 0.6The rocking curve of PbI3, in which the homogeneous single crystal is Example 4 and the phase-separated single crystal is Comparative Example 1. Figure 4 MA prepared in Example 4 and Comparative Example 1 of this invention 0.4 FA 0.6 Thermogravimetric analysis (TGA) images of PbI3, where the homogeneous single crystal is Example 4 and the phase-separated single crystal is Comparative Example 1.

[0018] Figure 5 MA prepared in Example 4 and Comparative Example 1 of this invention 0.4 FA 0.6 Photoluminescence (PL) spectrum of PbI3, where a is Example 4 and b is Comparative Example 1.

[0019] Figure 6 MA prepared in Example 4 of the present invention 0.4 FA 0.6 PbI3 detector sensitivity diagram under different bias voltages. Detailed Implementation

[0020] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0021] As mentioned in the background section of this invention, when preparing methylamine formamidinium-based perovskite single crystals using reverse-temperature crystallization, methylamine (MA) ions have a small radius and low migration barrier, allowing them to rapidly enter the crystal lattice in the early stages of crystallization. In contrast, formamidinium (FA) ions have a large radius, requiring higher energy and resulting in a low lattice entry rate. This severe mismatch in A-site cation insertion rates leads to spatial composition gradients, or phase separation, in the slowly growing single crystal. This inhomogeneity not only introduces carrier traps but also disrupts lattice periodicity, severely degrading carrier mobility and lifetime, thus fundamentally limiting further improvements in detector performance. To address these technical problems, this invention provides a methylamine formamidinium-based perovskite single crystal, its preparation method, and an X-ray detector.

[0022] The technical solution of the present invention will be described in detail below.

[0023] This invention provides a methylamine formamidine-based perovskite single crystal, which is grown in a solvent using methylamine iodide, formamidine hydroiodate, and lead iodide as raw materials and anhydrous acetic acid as an additive via a seed crystal method. Anhydrous acetic acid forms hydrogen bonds with formamidine, increasing the rate at which formamidine enters the crystal lattice and eliminating phase separation. Acetate groups coordinate with Pb to delay the formation of the lead-iodine framework, balancing the rates at which methylamine and formamidine enter the crystal lattice, thus obtaining the methylamine formamidine-based perovskite single crystal.

[0024] The molar ratio of methyl iodide, formamidinium hydroiodate, lead iodide, and anhydrous acetic acid is 0.1~0.9:0.1~0.9:1:0.05.

[0025] In the above technical solution, anhydrous acetic acid is used as an additive. Due to the hydrogen bonding between anhydrous acetic acid and formamidine, formamidine is pulled into the crystal lattice, eliminating the phase separation problem. At the same time, the coordination of acetate and Pb delays the formation of the lead-iodine framework, achieving a balance between the entry rates of methylamine and formamidine into the crystal lattice. This also improves the stability of the methylamine-formamidine-based perovskite precursor solution, enabling the stable growth of methylamine-formamidine-based perovskite single crystals.

[0026] The technical effects of the present invention will be described below through specific embodiments and comparative examples.

[0027] Example 1 A method for preparing methylamine methylammonium perovskite single crystals includes the following steps: S1, methylamine iodide powder (99.9% purity), formamidinium hydroiodate powder, lead iodide powder, and anhydrous acetic acid (99% purity) were mixed in γ-butyrolactone solvent at room temperature for 2 hours to obtain a methylamine formamidinium perovskite precursor solution with a concentration of 1.25 mol / L.

[0028] S2: Measure 1 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1, and heat it from an initial temperature of 90°C to 120°C at a heating rate of 5°C / h to obtain initial seed crystals. Measure 5 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1 into a bottle, place the initial seed crystal at the bottom center of the bottle, and heat it from an initial temperature of 70°C to 90°C at a heating rate of 1°C / h. After the crystal grows to a fixed size, retrieve the single crystal and place it on a heating stage. Heat the single crystal at 120°C to remove residual surface solvent, obtaining a methylaminemidine perovskite single crystal, denoted as MA. 0.1 FA 0.9 PbI3.

[0029] Example 2 A method for preparing methylamine methylammonium perovskite single crystals includes the following steps: S1, methylamine iodide powder (99.9% purity), formamidinium hydroiodate powder, lead iodide powder, and anhydrous acetic acid (99% purity) were mixed in γ-butyrolactone solvent at room temperature for 2 hours to obtain a methylamine formamidinium perovskite precursor solution with a concentration of 1.25 mol / L.

[0030] S2: Measure 1 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1, and heat it from an initial temperature of 90°C to 120°C at a heating rate of 5°C / h to obtain initial seed crystals. Measure 5 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1 into a bottle, place the initial seed crystal at the bottom center of the bottle, and heat it from an initial temperature of 72°C to 92°C at a heating rate of 1°C / h. After the crystal grows to a fixed size, retrieve the single crystal and place it on a heating stage. Heat the single crystal at 120°C to remove residual surface solvent, obtaining a methylaminemidine perovskite single crystal, denoted as MA. 0.2 FA 0.8 PbI3.

[0031] Example 3 A method for preparing methylamine methylammonium perovskite single crystals includes the following steps: S1, methylamine iodide powder (99.9% purity), formamidinium hydroiodate powder, lead iodide powder, and anhydrous acetic acid (99% purity) were mixed in γ-butyrolactone solvent at room temperature for 2 hours to obtain a methylamine formamidinium perovskite precursor solution with a concentration of 1.25 mol / L.

[0032] S2: Measure 1 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1, and heat it from an initial temperature of 90°C to 120°C at a heating rate of 5°C / h to obtain initial seed crystals. Measure 5 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1 into a bottle, place the initial seed crystal at the bottom center of the bottle, and heat it from an initial temperature of 74°C to 94°C at a heating rate of 1°C / h. After the crystal grows to a fixed size, retrieve the single crystal and place it on a heating stage. Heat the single crystal at 120°C to remove residual surface solvent, obtaining a methylaminemidine perovskite single crystal, denoted as MA. 0.3 FA 0.7 PbI3.

[0033] Example 4 A method for preparing methylamine methylammonium perovskite single crystals includes the following steps: S1, methylamine iodide powder (99.9% purity), formamidinium hydroiodate powder, lead iodide powder, and anhydrous acetic acid (99% purity) were mixed in γ-butyrolactone solvent at room temperature for 2 hours to obtain a methylamine formamidinium perovskite precursor solution with a concentration of 1.25 mol / L.

[0034] S2: Measure 1 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1, and heat it from an initial temperature of 90°C to 120°C at a heating rate of 5°C / h to obtain initial seed crystals. Measure 5 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1 into a bottle, place the initial seed crystal at the bottom center of the bottle, and heat it from an initial temperature of 76°C to 96°C at a heating rate of 1°C / h. After the crystal grows to a fixed size, retrieve the single crystal and place it on a heating stage. Heat the single crystal at 120°C to remove residual surface solvent, obtaining a methylaminemidine perovskite single crystal, denoted as MA. 0.4 FA 0.6 PbI3.

[0035] Example 5 A method for preparing methylamine methylammonium perovskite single crystals includes the following steps: S1, methylamine iodide powder (99.9% purity), formamidinium hydroiodate powder, lead iodide powder, and anhydrous acetic acid (99% purity) were mixed in γ-butyrolactone solvent at room temperature for 2 hours to obtain a methylamine formamidinium perovskite precursor solution with a concentration of 1.25 mol / L.

[0036] S2: Measure 1 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1, and heat it from an initial temperature of 90°C to 120°C at a heating rate of 5°C / h to obtain initial seed crystals. Measure 5 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1 into a bottle, place the initial seed crystal at the bottom center of the bottle, and heat it from an initial temperature of 78°C to 98°C at a heating rate of 1°C / h. After the crystal grows to a fixed size, retrieve the single crystal and place it on a heating stage. Heat the single crystal at 120°C to remove residual surface solvent, obtaining a methylaminemidine perovskite single crystal, denoted as MA. 0.5 FA 0.5 PbI3.

[0037] Example 6 A method for preparing methylamine methylammonium perovskite single crystals includes the following steps: S1, methylamine iodide powder (99.9% purity), formamidinium hydroiodate powder, lead iodide powder, and anhydrous acetic acid (99% purity) were mixed in γ-butyrolactone solvent at room temperature for 2 hours to obtain a methylamine formamidinium perovskite precursor solution with a concentration of 1.25 mol / L.

[0038] S2: Measure 1 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1, and heat it from an initial temperature of 90°C to 120°C at a heating rate of 5°C / h to obtain initial seed crystals. Measure 5 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1 into a bottle, place the initial seed crystal at the bottom center of the bottle, and heat it from an initial temperature of 80°C to 100°C at a heating rate of 1°C / h. After the crystal grows to a fixed size, retrieve the single crystal and place it on a heating stage. Heat the single crystal at 120°C to remove residual surface solvent, obtaining a methylaminemidine perovskite single crystal, denoted as MA. 0.6 FA 0.4 PbI3.

[0039] Example 7 A method for preparing methylamine methylammonium perovskite single crystals includes the following steps: S1, methylamine iodide powder (99.9% purity), formamidinium hydroiodate powder, lead iodide powder, and anhydrous acetic acid (99% purity) were mixed in γ-butyrolactone solvent at room temperature for 2 hours to obtain a methylamine formamidinium perovskite precursor solution with a concentration of 1.25 mol / L.

[0040] S2: Measure 1 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1, and heat it from an initial temperature of 90°C to 120°C at a heating rate of 5°C / h to obtain initial seed crystals. Measure 5 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1 into a bottle, place the initial seed crystal at the bottom center of the bottle, and heat it from an initial temperature of 82°C to 102°C at a heating rate of 1°C / h. After the crystal grows to a fixed size, retrieve the single crystal and place it on a heating stage. Heat the single crystal at 120°C to remove residual surface solvent, obtaining a methylaminemidine perovskite single crystal, denoted as MA. 0.7 FA 0.3 PbI3.

[0041] Example 8 A method for preparing methylamine methylammonium perovskite single crystals includes the following steps: S1, methylamine iodide powder (99.9% purity), formamidinium hydroiodate powder, lead iodide powder, and anhydrous acetic acid (99% purity) were mixed in γ-butyrolactone solvent at room temperature for 2 hours to obtain a methylamine formamidinium perovskite precursor solution with a concentration of 1.25 mol / L.

[0042] S2: Measure 1 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1, and heat it from an initial temperature of 90°C to 120°C at a heating rate of 5°C / h to obtain initial seed crystals. Measure 5 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1 into a bottle, place the initial seed crystal at the bottom center of the bottle, and heat it from an initial temperature of 84°C to 104°C at a heating rate of 1°C / h. After the crystal grows to a fixed size, retrieve the single crystal and place it on a heating stage. Heat the single crystal at 120°C to remove residual surface solvent, obtaining a methylaminemidine perovskite single crystal, denoted as MA. 0.8 FA 0.2 PbI3.

[0043] Example 9 A method for preparing methylamine methylammonium perovskite single crystals includes the following steps: S1, methylamine iodide powder (99.9% purity), formamidinium hydroiodate powder, lead iodide powder, and anhydrous acetic acid (99% purity) were mixed in γ-butyrolactone solvent at room temperature for 2 hours to obtain a methylamine formamidinium perovskite precursor solution with a concentration of 1.25 mol / L.

[0044] S2: Measure 1 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1, and heat it from an initial temperature of 90°C to 120°C at a heating rate of 5°C / h to obtain initial seed crystals. Measure 5 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1 into a bottle, place the initial seed crystal at the bottom center of the bottle, and heat it from an initial temperature of 86°C to 106°C at a heating rate of 1°C / h. After the crystal grows to a fixed size, retrieve the single crystal and place it on a heating stage. Heat the single crystal at 120°C to remove residual surface solvent, obtaining a methylaminemidine perovskite single crystal, denoted as MA. 0.9 FA 0.1 PbI3.

[0045] To further illustrate the technical effects of the present invention, a comparative example is provided, as follows.

[0046] Comparative Example 1 The difference compared to Example 4 is that anhydrous acetic acid is not introduced as an additive.

[0047] A method for preparing methylamine methylammonium perovskite single crystals includes the following steps: S1, methylamine iodide powder, formamidinium hydroiodate powder and lead iodide powder with a purity of 99.9% were mixed in γ-butyrolactone solvent at room temperature for 2 hours to obtain a methylamine formamidinium perovskite precursor solution with a concentration of 1.25 mol / L.

[0048] S2: Measure 1 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1, and heat it from an initial temperature of 90°C to 120°C at a heating rate of 5°C / h to obtain initial seed crystals. Measure 5 mL of the 1.25 mol / L methylaminemidine perovskite precursor solution prepared in S1 into a bottle, place the initial seed crystal at the bottom center of the bottle, and heat it from an initial temperature of 76°C to 90°C at a heating rate of 1°C / h. After the crystal grows to a fixed size, retrieve the single crystal and place it on a heating stage. Heat the single crystal at 120°C to remove residual surface solvent, obtaining a methylaminemidine perovskite single crystal, denoted as MA. 0.4 FA 0.6 PbI3.

[0049] The properties of the methylamine formamidinium-based perovskite single crystals prepared in the embodiments and comparative examples of the present invention were characterized, and the results are as follows.

[0050] To verify the hydrogen bonding effect between anhydrous acetic acid as an additive and formamidin, the present invention also conducted the following experiments and 1H NMR spectroscopy tests, as detailed below.

[0051] 1. Preparation of formamidinium hydroiodide (FAI) solution and methylamine iodide (MAI)DE.

[0052] Blank group: FAI solution with a concentration of 1.25 mol / L and MAI were dissolved in 0.5 mL of deuterated dimethyl sulfoxide.

[0053] Control group: 1.25 mol / L FAI solution and 1.25 mol / L MAI solution were dissolved in 0.5 mL of deuterated dimethyl sulfoxide, and 20 μL of anhydrous acetic acid was added to each solution.

[0054] 2. Sample preparation: Place the blank group and control group into NMR tubes and seal the caps.

[0055] 3. Test Results: By Figure 2 It can be seen that the FAI nitrogen-hydrogen peak in the blank group is a single peak, the MAI nitrogen-hydrogen peak in the blank group is a single peak, the FAI nitrogen-hydrogen peak in the control group is a double peak, and the MAI nitrogen-hydrogen peak in the control group is a single peak. This indicates that anhydrous acetic acid has hydrogen bonding with formamidin and no obvious interaction with methylamine.

[0056] Figure 1Photographs of the methylammonium formamidinium lead triiodide (MA x FA 1-x PbI3) single crystals prepared in Examples 1 to 9 of the present invention. Among them, a (X = 0.1) is Example 1, b (X = 0.2) is Example 2, c (X = 0.3) is Example 3, d (X = 0.4) is Example 4, e (X = 0.5) is Example 5, f (X = 0.6) is Example 6, g (X = 0.7) is Example 7, h (X = 0.8) is Example 8, and i (X = 0.9) is Example 9. As can be Figure 1 seen, the crystal surfaces of the methylammonium formamidinium lead triiodide single crystals prepared in Examples 1 to 9 of the present invention are smooth, without obvious pores, and have distinct edges and corners, indicating excellent crystal crystallization quality. Figure 3 Rocking curve diagrams of MA 0.4 FA 0.6 PbI3 prepared in Example 4 and Comparative Example 1 of the present invention. As can be Figure 3 seen, the MA 0.4 FA 0.6 PbI3 in Example 4 of the present invention has a narrower full width at half maximum (FWHM) of 0.021°, while the FWHM of MA 0.4 FA 0.6 PbI3 in Comparative Example 1 is 0.047°. The smaller full width at half maximum of Example 4 indicates that the crystallization quality of the perovskite single crystal obtained by adding acetic anhydride as an additive in Example 4 is better. Figure 4 Thermogravimetric analyzer diagrams of MA 0.4 FA 0.6 PbI3 prepared in Example 4 and Comparative Example 1 of the present invention. As can be Figure 4 seen, the thermogravimetric analysis curve decreases more slowly in the high-temperature region. The initial temperature of significant weight loss of MA 0.4 FA 0.6 PbI3 in Example 4 is approximately 361°C, while the initial temperature of weight loss of MA 0.4 FA 0.6 PbI3 in Comparative Example 1 is approximately 337°C, indicating that the MA 0.4 FA 0.6 PbI3 prepared by introducing acetic anhydride as an additive in the present invention has higher thermal stability and decomposition temperature.

[0057] Figure 5 Photoluminescence spectroscopy (PL) diagrams of MA 0.4 FA 0.6 PbI3 prepared in Example 4 and Comparative Example 1 of the present invention. Among them, Diagram a is Example 4 and Diagram b is Comparative Example 1. As can be Figure 5It can be seen that the methylamine-formamidinium-based perovskite single crystal prepared in Example 4 exhibits good photostress stability; after 20 hours of laser irradiation, neither the photoluminescence intensity (PL) nor the linewidth changed significantly. In contrast, the PL of the methylamine-formamidinium-based perovskite single crystal in Comparative Example 1 decreased to 53% of its initial intensity after 20 hours of irradiation and showed a continuing downward trend. This indicates that the introduction of anhydrous acetic acid as an additive in the preparation of the methylamine-formamidinium-based perovskite single crystal in this invention results in better photostress stability of the single crystal.

[0058] Figure 6 MA prepared in Example 4 of the present invention 0.4 FA 0.6 PbI3 detector sensitivity plots under different bias voltages. Figure 6 It can be seen that the MA prepared in Example 4 of this invention 0.4 FA 0.6 The PbI3 single crystal can operate stably and maintain a linear response under a high bias voltage of 60 V / mm, indicating that the methylamine formamidinium-based perovskite single crystal prepared in this invention has very high quality, low defect density, and can withstand strong electric fields without being broken down or generating large noise.

[0059] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing methylaminomamidinium-based perovskite single crystals, characterized in that, Includes the following steps: Using methylamine iodide, formamidine hydroiodide, and lead iodide as raw materials, and anhydrous acetic acid as an additive, the perovskite was grown in a solvent by a seed crystal method. Anhydrous acetic acid formed hydrogen bonds with formamidine, which increased the rate at which formamidine entered the crystal lattice and eliminated phase separation. The coordination of acetate with Pb delayed the formation of the lead-iodine framework and balanced the rate at which methylamine and formamidine entered the crystal lattice, thus obtaining methylamine-formamidine-based perovskite single crystals. The molar ratio of methyl iodide, formamidinium hydroiodate, lead iodide, and anhydrous acetic acid is 0.1~0.9:0.1~0.9:1:0.

05.

2. The method for preparing methylamine methylammonium perovskite single crystals according to claim 1, characterized in that, The solvent is γ-butyrolactone.

3. The method for preparing methylamine methylammonium perovskite single crystals according to claim 1, characterized in that, The method for preparing the methylamine formamidinium-based perovskite single crystal is as follows: using methylamine iodide, formamidinium hydroiodate and lead iodide as raw materials, and anhydrous acetic acid as an additive, they are mixed in a solvent at room temperature to obtain a perovskite single crystal precursor solution, which is then grown by the seed crystal method to obtain the methylamine formamidinium-based perovskite single crystal.

4. The method for preparing methylamine methylammonium perovskite single crystals according to claim 3, characterized in that, The concentration of the perovskite single crystal precursor in the perovskite single crystal precursor solution is 1.25 mol / L.

5. The method for preparing methylamine methylammonium perovskite single crystals according to claim 3, characterized in that, The growth by seed method is specifically as follows: the perovskite single crystal precursor solution is divided into two parts, the first part of the perovskite single crystal precursor solution is taken, and the temperature is programmed to rise from an initial temperature of 90°C to 100°C~120°C to obtain the initial seed crystal. A second part of perovskite single crystal precursor solution was added to the initial seed crystal, and the temperature was gradually increased from an initial temperature of 70℃~86℃ to 90℃~106℃ to obtain methylamine methylammonium perovskite single crystal.

6. The method for preparing methylamine methylammonium perovskite single crystals according to claim 5, characterized in that, The temperature rise rate of the programmed temperature rise is 5℃ / h, and the temperature rise rate of the stepped temperature rise is 1℃ / h.

7. A methylaminomamidinium-based perovskite single crystal, characterized in that, It was prepared using the method for preparing methylamine methylammonium perovskite single crystals according to any one of claims 1 to 6.

8. An X-ray detector, characterized in that, The X-ray detector is obtained by using the methylamine methyl perovskite single crystal of claim 7 as the photosensitive and ionization-sensitive active layer, and by preparing electrodes on both sides of the photosensitive and ionization-sensitive active layer.

9. The X-ray detector according to claim 8, characterized in that, The electrode is made of at least one of gold, indium gallium alloy and silver.

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