Methylamine lead bromide single crystal, preparation method and gamma ray energy spectrum detector

Abstract

The invention discloses a methylamine lead bromide single crystal, a preparation method and a gamma ray energy spectrum detector. The preparation method mainly comprises the following steps: growing a precursor consisting of methylamine bromide, lead bromide and an additive in a molar ratio of (1-2): (0.1-1): 1; the method comprises the following steps: preparing a methylamine lead bromide single crystal raw material, adding the methylamine lead bromide single crystal raw material into a solvent, stirring at room temperature to obtain a precursor solution for growing the methylamine lead bromide single crystal, and preferably performing secondary culture growth by using the precursor solution to obtain the methylamine lead bromide single crystal. The method is high in operability and repeatability, the solution property is adjusted, the deprotonation inhibitor is introduced, deprotonation of the precursor solution is effectively inhibited, the stability of the precursor solution is effectively guaranteed, the methylamine lead bromide perovskite single crystal with high crystallinity and low defect density grows, and the methylamine lead bromide perovskite single crystal is used for preparing an energy spectrum grade gamma ray detector.

Description

Technical Field

[0001] The present invention relates to the technical field of perovskite gamma-ray detection, and more specifically, to a methylammonium lead bromide single crystal, a preparation method, and a gamma-ray energy spectrum detector. Background Art

[0002] Radiation detection is applicable to a wide range of application scenarios, such as medical imaging, nuclear energy, homeland security, industrial inspection, astronomy, and so on. According to the working principle of the device, radiation detectors can be divided into indirect radiation detectors and direct radiation detectors. Among them, the energy resolution of indirect detectors is generally low. Direct detectors utilize the photoelectric effect of semiconductors and are expected to achieve higher energy resolution. Currently, commercially available direct high-energy gamma-ray energy spectrum detectors mainly rely on Cd1-xZnxTe (CZT) single crystal detectors, which can operate at room temperature and have excellent gamma-ray attenuation ability and energy spectrum resolution. However, the material and manufacturing costs of CZT detectors are extremely high, and a working bias voltage as high as 1000V is also required. Therefore, it is necessary to develop materials for high-performance gamma-ray detectors with lower costs.

[0003] Perovskite materials at room temperature have great potential in high-energy ray detection. Most research work focuses on thin-film perovskite materials. The research on single crystal materials started relatively late. Since single crystals have better thermal stability, a wider light absorption range, higher carrier mobility, and lower defect state density, optoelectronic devices made of single crystal perovskite are theoretically expected to have better ray detection performance. Moreover, perovskite single crystals can be prepared by solution methods, further ensuring their cost advantages.

[0004] However, the application of perovskite single crystals in the field of gamma-ray energy spectrum detection is still in the early exploration stage. Achieving energy spectrum detection places higher requirements on the quality of single crystals. As the most common perovskite single crystal, methylammonium lead bromide (MAPbBr3) single crystal, if it can achieve energy spectrum detection of gamma rays, will have far-reaching significance for the field of energy spectrum detection of perovskite single crystals. However, almost no such reports have been seen at present, mainly due to the crystal quality problems of methylammonium lead bromide single crystals. The crystal growth of methylammonium lead bromide needs to use solution methods. The precursor solution of methylammonium lead bromide is mainly an organic solution of methylammonium bromide and lead bromide. The deprotonation of methylammonium cations (MA + ) in this methylammonium bromide, and the deprotonation of MA + results in volatile methylamine molecules. Coupled with the volatilization of organic solvents, the ratio and concentration of solutes will change during the crystal growth process, especially promoting the crystal growth to deviate from the steady state, thereby generating a large number of defects and causing the crystal quality to decline. Summary of the Invention

[0005] Aiming at the deprotonation of MA during the solution growth of methylammonium lead bromide single crystals+ To address the problem of crystal growth deviating from the steady state and the decline in crystal quality caused by deprotonation and solution evaporation, the present invention provides a methylammonium lead bromide single crystal, a preparation method, and a gamma-ray energy spectrum detector. By changing the precursor ratio and introducing a deprotonation inhibitor, the present invention realizes the steady-state growth of methylammonium lead bromide single crystals, with strong controllability during the growth process. The finally prepared single crystals have excellent quality and large size. Using these crystals to prepare devices enables spectral-level detection of gamma rays.

[0006] To achieve the above object, the present invention is realized through the following technical solutions:

[0007] I. A methylammonium lead bromide single crystal:

[0008] It is mainly grown from a precursor composed of methylammonium bromide (MABr), lead bromide (PbBr2), and an additive. The molar ratio of methylammonium bromide (MABr), lead bromide (PbBr2), and the additive is 1 - 2:0.1 - 1:1, specifically a methylammonium lead bromide perovskite single crystal.

[0009] The additive is one or more of ammonium bromide, ammonium acetate, acetic acid, formic acid, methylammonium bromide, dimethylammonium bromide, trimethylammonium bromide, and methylamidinium bromide.

[0010] II. A preparation method of a methylammonium lead bromide single crystal:

[0011] Step S1: Preparation of methylammonium lead bromide single crystal raw materials: Prepare methylammonium bromide (MABr), lead bromide (PbBr2), an additive, and a solvent;

[0012] Step S2: Preparation of the precursor solution: Add the methylammonium bromide (MABr), lead bromide (PbBr2), and additive prepared in Step S1 according to the molar ratio of 1 - 2:0.1 - 1:1 to the solvent, and stir at room temperature for 24 h to obtain a precursor solution for growing methylammonium lead bromide single crystals;

[0013] Step S3: Preparation of methylammonium lead bromide single crystals:

[0014] Use the precursor solution for secondary growth to obtain methylammonium lead bromide single crystals.

[0015] In Step S1, the additive is one or more of ammonium bromide, ammonium acetate, acetic acid, formic acid, methylammonium bromide, dimethylammonium bromide, trimethylammonium bromide, and methylamidinium bromide;

[0016] The solvent is one or more of γ-butyrolactone, N,N-dimethylformamide, propylene carbonate, or dimethyl sulfoxide;

[0017] In Step S2, the concentration of lead bromide (PbBr2) in the solvent is 0.7 - 1.8 mol / L.

[0018] The purity of the methylammonium bromide is 99.8%, and the purity of the lead bromide is 98%.

[0019] The specific steps of step S3 are as follows:

[0020] S31: Take a precursor solution with a smaller volume, place it on a heating stage, and heat it at a stepwise heating rate of 4 °C per hour until seeds with a fixed size of about 1 mm appear at the bottom of the solution as the initial seeds;

[0021] S32: Place the initial seeds at the bottom of a precursor solution with a larger volume. After the seed size is stabilized, heat it at a stepwise heating rate of 1 °C per day until the crystal grows to the specified size and then stop.

[0022] Specifically, the volume of the precursor solution in S32 is larger than that of the precursor solution in S31.

[0023] In step S2, the precursor solution is prepared and stirred at room temperature for 24 h. The seed growth temperature is controlled at 60–120 °C, and then the temperature of the heating stage is controlled at 40-100 °C during the subsequent growth process;

[0024] The stepwise heating rate in step S31 is from room temperature to 60-120 °C;

[0025] The stepwise heating rate in step S32 is from room temperature to 40-100 °C.

[0026] The seed size stabilization treatment in step S32 is to continuously add measures to prevent the seeds in the precursor solution from getting smaller.

[0027] Specifically: at a certain temperature, if the seeds placed in the precursor solution gradually dissolve in the precursor solution, raise the temperature of the heating stage, place the seeds in the precursor solution again, and observe whether the seeds dissolve and disappear again. If they disappear, continue to raise the temperature of the heating stage and place another seed. Repeat the above steps continuously until the seed size does not decrease within 2 h, then it is determined that the seed size is stable.

[0028] The seeds in the above addition measures are the initial seeds.

[0029] III. A methylammonium lead bromide single crystal gamma-ray energy spectrum level detector, the X-ray detector includes the above-mentioned methylammonium lead bromide single crystal, and the methylammonium lead bromide single crystal is used to prepare the X-ray absorption layer in the gamma-ray energy spectrum level detector.

[0030] The detector is a photoconductive detector. The structure of the photoconductive detector is electrode, perovskite single crystal, electrode. The electrode material of the photoconductive detector is one or more of gold, indium gallium alloy, bismuth, and copper.

[0031] In one embodiment, a Keithley 2400 source meter is used to test the dark current of the radiation detector in a dark environment. Meanwhile, a Keithley 2400 source meter is used to apply a bias voltage to the device, and an AMETEK 527A shaping amplifier and an EASY-MCA8k multi-channel analyzer are used for signal processing and gamma-ray spectrum generation. The operating bias voltage of the radiation detector is 40 - 100 V, the dark current is less than 20 nA, and the radiation source is one of Am, Co, and Cs.

[0032] In specific implementation, a UV-3600i is used to test the ultraviolet-visible absorption spectrum of the precursor solution, and the Pb-Br coordination situation can be obtained. A high Pb-Br coordination number is beneficial to crystal growth.

[0033] In addition, XED is used to characterize the single crystal structure of MABX3 perovskite to obtain an X-ray diffraction (XRD) pattern, and the full width at half maximum of the rocking curve of the single crystal is tested to characterize the crystallinity of the crystal. The instrument used is an X’PERRT 3MRD, with Cu K α radiation 40 KV, 30 mA is used to characterize the rocking curve, and a full width at half maximum lower than 0.05° can be regarded as having a relatively high crystallinity.

[0034] The present invention develops a preparation method of methylammonium lead bromide single crystal. By changing the ratio of solutes in the precursor solution and introducing a deprotonation inhibitor as an additive, the crystal growth kinetics is regulated to achieve steady-state growth. Using this preparation method, high-quality methylammonium lead bromide single crystals can be obtained, and devices can be prepared using such single crystals to achieve energy spectrum-level detection of gamma rays.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] The present invention has strong operability and repeatability. By changing the ratio of the precursor, the properties of the solution are adjusted, and a deprotonation inhibitor is introduced to effectively inhibit the deprotonation of the precursor solution, effectively ensuring the stability of the precursor solution. Methylammonium lead bromide perovskite single crystals with high crystallinity and low defect density can be grown, which can be used to prepare energy spectrum-level gamma-ray detectors. Description of the Drawings

[0037] Figure 1 It is the solubility temperature curves of methylammonium lead bromide in different precursor solutions in Example 1, Example 2, and Comparative Example 1.

[0038] Figure 2 It is the ultraviolet-visible absorption spectra of different precursor solutions in Example 1, Example 2, and Comparative Example 1.

[0039] Figure 3The single crystal pictures and XRD rocking curve spectra of methylammonium lead bromide obtained in Example 1, Example 2 and Comparative Example 1.

[0040] Figure 4 Schematic diagram of the device structure of the methylammonium lead bromide single crystal gamma-ray spectroscopy detector obtained in Example 1, Example 2 and Comparative Example 1.

[0041] Figure 5 Dark current spectrum of the methylammonium lead bromide single crystal gamma-ray spectroscopy detector obtained in Example 1, Example 2 and Comparative Example 1.

[0042] Figure 6 Gamma-ray energy spectrum of the methylammonium lead bromide single crystal gamma-ray spectroscopy detector obtained in Example 1, Example 2 and Comparative Example 1, where Fig. (a) represents the gamma-ray energy spectrum of the methylammonium lead bromide single crystal gamma-ray spectroscopy detector obtained in Comparative Example 1, Fig. (b) represents the gamma-ray energy spectrum of the methylammonium lead bromide single crystal gamma-ray spectroscopy detector obtained in Example 1, and Fig. (c) represents the gamma-ray energy spectrum of the methylammonium lead bromide single crystal gamma-ray spectroscopy detector obtained in Example 2. Detailed implementation mode

[0043] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further details the present invention in combination with embodiments.

[0044] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent replacements on the basis of understanding the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0045] The embodiments of the present invention are as follows:

[0046] Example 1

[0047] This example provides a method for stably growing methylammonium lead bromide perovskite single crystals, including the following steps:

[0048] Step S1, preparation of perovskite single crystal raw materials: Prepare MABr and PbBr2, and the solvent is DMF.

[0049] Step S2, preparation of precursor solution: The ratio of MABr to PbBr2 is 2:1, the concentration of the precursor solution is 1.2 mol / L, and the precursor solution is prepared at room temperature.

[0050] Step S3. Preparation of MAPbBr3 single crystal: Take 2 ml of the precursor solution in step S2 into a bottle, heat it to 85°C at a heating rate of 4°C per hour, then keep heating on a heating stage at 85°C to obtain a seed crystal with a size of 1 mm. Place the 1-mm-sized seed crystal into a bottle containing 10 ml of the precursor solution, cover the bottle mouth with a glass slide. After the seed crystal size is stable, start growing on a heating stage at 75°C with a heating rate of 1°C / 24 h until the crystal length and width are close to 10 mm.

[0051] Step S4. Evaporate 100 nm of Au and 100 nm of Bi on both sides of the single crystal in a vacuum thermal evaporation device to obtain a radiation detector, and perform gamma-ray energy spectrum detection.

[0052] Example 2

[0053] This example provides a method for stabilizing methylammonium lead bromide perovskite single crystals for live pigs, including the following steps:

[0054] Step S1. Preparation of perovskite single crystal raw materials: Prepare MABr, PbBr2, and an additive. The additive is formamidinium bromide (FABr), and the solvent is DMF.

[0055] Step S2. Preparation of the precursor solution: The ratio of MABr, FABr, and PbBr2 is 2:0.1:1, the concentration of the precursor solution is 1.2 mol / L, and the precursor solution is prepared at room temperature.

[0056] Step S3. Preparation of MAPbBr3 single crystal: Take 2 ml of the precursor solution in step S2 into a bottle, heat it to 95°C at a heating rate of 4°C per hour, then keep heating on a heating stage at 95°C to obtain a seed crystal with a size of 1 mm. Place the 1-mm-sized seed crystal into a bottle containing 10 ml of the precursor solution, cover the bottle mouth with a glass slide. After the seed crystal size is stable, start growing on a heating stage at 80°C with a heating rate of 1°C / 24 h until the crystal length and width are close to 10 mm.

[0057] Step S4. Evaporate 100 nm of Au and 100 nm of Bi on both sides of the single crystal in a vacuum thermal evaporation device to obtain a radiation detector, and perform gamma-ray energy spectrum detection.

[0058] Comparative Example 1

[0059] This comparative example provides a method for growing methylammonium lead bromide perovskite single crystals without adding an additive, and using the perovskite single crystal to prepare a gamma-ray detector, including the following steps:

[0060] Step S1. Preparation of methylammonium lead bromide single crystal raw materials: Prepare methylammonium bromide (MABr) and lead bromide (PbBr2), and the solvent is DMF.

[0061] Step S2, Preparation of the precursor solution: Add MABr and PbBr2 prepared in Step S1 into DMF according to the ratio of 1:1, with a concentration of 1.2 mol / L, and stir at room temperature for 24 h to obtain a precursor solution that can be used for growing methylammonium lead bromide single crystals.

[0062] Step S3, Preparation of MAPbBr3 single crystals: Take 2 ml of the precursor solution in Step S2 in a bottle, heat it to 70 °C at a heating rate of 4 °C per hour, and then keep heating on a 70 °C heating stage to obtain a seed crystal with a size of 1 mm. Place the 1 mm-sized seed crystal in a bottle containing 10 ml of the precursor solution. After the seed crystal size is stable, start growing on a 50 °C heating stage at a heating rate of 1 °C / 24 h until the crystal length and width are close to 10 mm.

[0063] Step S4, Evaporate 100 nm of Au and 100 nm of Bi on both sides of the single crystal in a vacuum thermal evaporation device to obtain a radiation detector and perform gamma-ray energy spectrum detection.

[0064] I. Solubility temperature curve analysis

[0065] According to the precursor ratios in Examples 1 and 2 and Comparative Example 1, prepare precursor solutions with different concentrations in the range of 0.7 mol / L to 1.8 mol / L. Taking Comparative Example 1 as an example, place the seed crystal in the solution at different temperatures and find that at 50 °C, the seed crystal remains unchanged and is not dissolved, so this temperature is regarded as the saturation point of MAPbBr3 in this solution. By changing the solution and temperature, a solubility temperature curve as shown in Figure 1 can be plotted. It can be seen that at the same concentration, such as 1.2 mol / L, the saturation temperatures in Examples 1 and 2 are higher than those in Comparative Example 1. The evaporation of the solvent will be more intense at high temperatures. Therefore, in the methods of Examples 1 and 2, a glass slide is used to cover the bottle mouth to inhibit the evaporation of the solution and ensure the stability of the solution.

[0066] II. Analysis of the coordination situation of the precursor solution

[0067] In methylammonium lead bromide perovskite single crystals, Pb and Br are coordinated in the form of Pb-Br octahedrons, and then form a framework by sharing Br atoms. MA + is located in the interstitial space of the octahedron. The Pb atoms and Br atoms in the solution form colloidal particles through coordination, and the coordination situation therein is more complex, and the coordination of Pb-Br is dispersed proportionally between 2 and 6. Changing the ratio of MABr to PbBr2 can effectively regulate the ratio of Br-Pb in the precursor solution, and then change the coordination situation of Pb-Br in the solution. As shown in Figure 2The UV-visible absorption spectra of the solutions in Examples 1, 2 and Comparative Example 1 are shown. It can be seen that the proportion of [[PbBr4]] coordinated in Examples 1 and 2 is higher than that in Comparative Example 1. -2 The coordination ratio is higher than that in Comparative Example 1.

[0068] Crystal growth can be kinetically divided into surface reaction steps and diffusion steps. When the surface reaction is slower than diffusion, more groups accumulate at the interface between the crystal and the solution, which will cause a decrease in crystal quality. A higher proportion of Pb-Br ligands is closer to the structure of perovskite single crystals and is more likely to enter the lattice of perovskite single crystals at the interface between the perovskite single crystal and the solution. In Examples 1 and 2 of the present invention, the presence of a higher proportion of high-coordination ligands helps to increase the surface reaction rate during crystal growth, achieve better kinetic crystal growth, and is conducive to obtaining higher-quality methylammonium lead bromide single crystals.

[0069] III. Crystal Quality

[0070] As Figure 3 shown, the pictures of methylammonium lead bromide single crystals and XRD rocking curve spectra obtained in Examples 1, 2 and Comparative Example 1 are shown. The crystals obtained by the three methods have little difference in appearance, but the rocking curve results of the three show that the full width at half maximum of Examples 1 and 2 is smaller than that of Comparative Example 1, indicating that their crystal crystallinity is high and the defect density is low.

[0071] Combined with the Pb-Br coordination situation, it is further explained that the increase in the number of Br atoms increases the proportion of Pb-Br high-coordination ligands, which is beneficial to the improvement of crystal quality.

[0072] In addition, in Example 1, the ratio of MABr to PbBr2 is 2:1. The presence of additional MA + organic cations has an inhibitory effect on the deprotonation of MA + . At the same time, the excess MA + compensates for the component loss caused by the deprotonation of MA + . This makes the precursor solution in Example 1 more stable than that in Comparative Example 1 during crystal growth, which is conducive to the improvement of crystal quality.

[0073] In Example 2, on the basis of the ratio of MABr to PbBr2 being 2:1, the organic cation FA + is further introduced. In the hot precursor solution, FA + is more likely to undergo a protonation reaction, which further inhibits the deprotonation reaction of MA + . Therefore, the crystal quality in Example 2 is the highest.

[0074] IV. Device Performance

[0075] As Figure 4As shown, it is a schematic diagram of a methylammonium lead bromide calcium titanate single crystal gamma-ray energy spectrum detector, and the device structure is 100nm Au / MAPbBr3 / 100nm Bi.

[0076] The test results of the dark current of the device are as Figure 5 shown. The device operates under reverse bias. Among them, the dark current in Example 2 is the lowest, followed by Example 1, and the dark current in Comparative Example 1 is the largest. This shows that the resistivity of the crystals obtained in Examples 1 and 2 is high and the crystal quality is good.

[0077] Gamma-ray energy spectrum tests were carried out under a Co-122KeV ray source, and the obtained gamma-ray energy spectrum data are as Figure 6 shown. Among them, there is almost no energy spectrum resolution in Comparative Example 1. After fitting, the energy spectrum resolution of the device in Example 1 is 31.8%, and the energy spectrum resolution of the device in Example 2 is 8.9%. It can be seen that the methylammonium lead bromide calcium titanate single crystal obtained in the present invention can be used to prepare a gamma-ray energy spectrum detector and achieve high-resolution gamma-ray energy spectrum detection.

[0078] The above specific embodiments are used to explain and illustrate the present invention, rather than limiting the present invention. Any modifications and changes made within the spirit and scope of the claims of the present invention fall within the protection scope of the present invention. The above is only a preferred embodiment of the present invention. Therefore, any equivalent changes or modifications made according to the structure, features and principles described in the scope of the present invention patent application are included in the scope of the present invention patent application.

Claims

1. A methylamine lead bromine single crystal, characterized in that: It is mainly grown from a precursor consisting of methylammonium bromide MABr, lead bromide PbBr2 and additives, and the molar ratio of methylammonium bromide MABr, lead bromide PbBr2 and additives is 1-2:0.1-1:

1.

2. A methylamine lead bromide single crystal according to claim 1, characterized in that: The additive is one or more of ammonium bromide, ammonium acetate, acetic acid, formic acid, methylamine bromide, dimethylamine bromide, trimethylamine bromide, and methylamine bromide.

3. A method for preparing methylamine lead bromine single crystal, characterized in that: The method comprises the following steps: Step S1, preparation of methylamine lead bromine single crystal raw materials: preparing methylamine bromide MABr, lead bromide PbBr2, additives and solvents; Step S2, preparation of a precursor solution: adding the methylamine bromide MABr, lead bromide PbBr2, and additives prepared in step S1 to a solvent in a molar ratio of 1-2:0.1-1:1, and stirring at room temperature to obtain a precursor solution that can be used to grow methylamine lead bromide single crystals; Step S3, preparation of methylamine lead bromide single crystal: The precursor solution is used for secondary culture growth to obtain methylamine lead bromide single crystal.

4. The method for preparing a methylamine lead bromine single crystal according to claim 3, characterized in that: In step S1, the additive is one or more of ammonium bromide, ammonium acetate, acetic acid, formic acid, methylamine bromide, dimethylamine bromide, trimethylamine bromide, and methylamine bromide; The solvent is one or more of γ-butyrolactone, N,N-dimethylformamide, propylene carbonate or dimethyl sulfoxide; In the step S2, the concentration of lead bromide PbBr2 in the solvent is 0.7-1.8 mol / L.

5. The method for preparing a methylamine lead bromine single crystal according to claim 3, characterized in that: The step S3 is specifically as follows: S31, taking a smaller volume of precursor solution, heating it at a step heating rate of 4° C. per hour until a seed crystal of a fixed size appears at the bottom of the solution as an initial seed crystal; S32. Take the initial seed crystal and place it at the bottom of a larger volume of precursor solution. After the seed crystal size stabilizes, increase the temperature at a step rate of 1°C per day until the crystal grows to a specified size.

6. The method for preparing a methylamine lead bromine single crystal according to claim 3, characterized in that: In the step S2, a precursor solution is prepared at room temperature and stirred for 24 hours, the temperature is controlled at 60-120°C, and the temperature of the heating stage is controlled at 40-100°C during the subsequent growth process; The step heating rate in step S31 is from room temperature to 60-120°C; The step heating rate in step S32 is from room temperature to 40-100°C.

7. The method for preparing methylamine lead bromine single crystal according to claim 5, characterized in that: The size of the seed crystals in step S32 is stabilized by continuously adding measures so that the seed crystals in the precursor solution no longer become smaller.

8. A methylamine lead bromide single crystal, characterized in that: The product is prepared by the preparation method described in any one of claims 3 to 7.

9. A methylamine lead bromine single crystal gamma ray energy spectrum detector, characterized in that: The X-ray detector comprises the methylamine lead bromine single crystal as described in any one of claims 1-2 or the methylamine lead bromine single crystal prepared using the methylamine lead bromine single crystal as described in any one of claims 3-7.

10. The methylamine lead bromine single crystal gamma ray energy spectrum detector according to claim 9, characterized in that: The detector is a photoconductive detector, and the structure of the photoconductive detector is an electrode, a perovskite single crystal, and an electrode. The electrode material of the photoconductive detector is one or more of gold, indium gallium alloy, bismuth, and copper.

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