Two-dimensional perovskite single crystal, preparation method thereof and X-ray detector

Abstract

The invention provides a two-dimensional perovskite single crystal, a preparation method thereof and an X-ray detector. The preparation method of the two-dimensional perovskite single crystal comprises the following steps: S1, modifying small organic molecules by adopting haloid acid to obtain modified molecules; s2, adding the modified molecules and lead halide into a precursor solvent to obtain a precursor solution; and S3, crystallizing the precursor solution to obtain a two-dimensional perovskite single crystal, and preparing the X-ray detector by taking the single crystal as a base material. According to the two-dimensional perovskite single crystal obtained by the preparation method disclosed by the invention, the modified organic molecules are used as organic spacer cations, so that the dipole moment can be enhanced, and the enhanced dipole moment can induce a local electric field; the strong dipole of the organic spacing layer can prevent ion migration, and the induced local electric field can promote carrier separation, and at the same time, the working stability and the electrical performance of the perovskite device are improved.

Description

Technical Field

[0001] The invention relates to a two-dimensional perovskite single crystal and a preparation method thereof, and an X-ray detector comprising the two-dimensional perovskite single crystal. Background Art

[0002] Two-dimensional hybrid perovskites with large-radius cations are considered promising candidates for optoelectronics due to their good optoelectronic properties, low detection limits, and excellent environmental stability. 2- The intrinsic quantum well structure composed of octahedrons and organic spacers leads to relatively poor electrical properties and severe carrier recombination. Currently, most people's work on improving two-dimensional hybrid perovskites focuses on quantum well engineering, by reducing the thickness of the organic layer or increasing the PbX6 2- The photoelectric performance can be improved by increasing the layer thickness of the octahedral network. However, this approach will weaken the structural stability in most cases and lead to severe ion migration, which will lead to a decrease in device stability. Therefore, it is necessary to develop a method that can improve the photoelectric performance of perovskite while maintaining its stability.

[0003] On the one hand, by increasing the thickness of the octahedral network layer, Cs is added to maintain structural stability. + 、MA + However, the above small molecules are more likely to migrate in perovskite, resulting in severe ion migration; at the same time, perovskite is prone to phase segregation, resulting in weakened chemical stability of the material. On the other hand, in the process of reducing the thickness of the organic layer, smaller molecules are used as organic molecules, but the above problems will also occur, resulting in reduced stability of the perovskite.

[0004] In summary, there is currently no method that can prevent ion migration and improve the chemical stability of materials while improving the photoelectric performance of two-dimensional perovskites. Summary of the invention

[0005] The present invention aims to solve the problems of poor chemical stability and serious ion migration when two-dimensional perovskite quantum well engineering improves photoelectric performance, and proposes a two-dimensional perovskite single crystal and a preparation method thereof, and an X-ray detector.

[0006] The technical method of the present invention is as follows:

[0007] A method for preparing a two-dimensional perovskite single crystal, the preparation method comprising: S1, using hydrohalic acid to modify small organic molecules to obtain modified molecules; S2, adding the modified molecules and lead halide to a precursor solvent to obtain a precursor solution; S3, crystallizing the precursor solution to obtain a two-dimensional perovskite single crystal, and using the single crystal as a basic material to prepare a radiation detector.

[0008] Optionally, the small organic molecules include one or more of ethylamine, methylamine, formamidine, dimethylamine, guanidine, and propylamine.

[0009] Optionally, the hydrohalic acid in step S1 includes one or more of hydrofluoric acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid; the precursor solvent in step S2 includes one or more of hydrobromic acid, hydroiodic acid, hydrochloric acid, dimethylformamide, dimethyl sulfoxide, and γ-butyrolactone; the lead halide in step S2 includes one or more of lead chloride, lead iodide, and lead bromide.

[0010] Optionally, the molar ratio of the hydrohalic acid to the small organic molecule is 1-3:1; the ratio of the modified molecule, the lead halide, and the precursor solvent is 1-10 g: 1-5 g: 10-20 mL.

[0011] Optionally, the step S1 includes: replacing hydrogen in the small organic molecule with halogen.

[0012] Optionally, in the step S2, the heating temperature is 40-70°C and the insulation time is 12-24h.

[0013] Optionally, the crystallization step includes: keeping the precursor solution warm for a period of time, and then cooling it to 40°C-room temperature; wherein the keeping temperature is 35-70°C, the keeping time is 20-24h, and the cooling rate is 0.4-3°C / 24h.

[0014] The present invention also provides a two-dimensional perovskite single crystal, which is obtained by the above-mentioned method for preparing the two-dimensional perovskite single crystal.

[0015] The distance between adjacent inorganic layers in the two-dimensional perovskite single crystal is The two-dimensional perovskite single crystal has a non-zero polarization strength, and the ion activation energy of the two-dimensional perovskite single crystal is greater than 0.7 eV in the in-plane direction or the out-of-plane direction.

[0016] The present invention also provides an X-ray detector, which includes the above-mentioned two-dimensional perovskite single crystal.

[0017] The beneficial effects of the present invention are:

[0018] (1) The two-dimensional perovskite single crystal prepared by the preparation method of the present invention can enhance the dipole moment due to the modified organic molecules as organic spacer cations, and the enhanced dipole moment can induce a local electric field; the strong dipole of the organic spacer layer can prevent ion migration, and the induced local electric field can promote carrier separation, while improving the working stability and electrical performance of the perovskite device.

[0019] (2) The present invention adopts a cooling crystallization method to prepare a single crystal with a two-dimensional layered structure. The method is simple, efficient, environmentally friendly, and suitable for large-scale industrial production.

[0020] (3) When the two-dimensional perovskite single crystal provided by the present invention is used as an X-ray detector, the X-ray detection sensitivity and detection limit of the single crystal are at the leading level among two-dimensional perovskites, and the dark current drift is 3.6×10 -8 nA -1 s -1 V -1 It is the lowest value among two-dimensional RP perovskites. The response signal of the X-ray detector is stable, and the response current hardly decreases after long-term irradiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of small molecule modification in Example 1;

[0022] Figure 2 Schematic diagram of (Br-EA)2PbBr4 perovskite crystal of Example 1;

[0023] Figure 3 This is a heating stability diagram of the (Br-EA)2PbBr4 perovskite crystal of Example 1;

[0024] Figure 4 The conductivity characteristic curve of the (Br-EA)2PbBr4 perovskite crystal of Example 1;

[0025] Figure 5 This is a crystal diagram of (Br-EA)2PbBr4 perovskite in Example 1;

[0026] Figure 6 is a comparison diagram of the theoretically calculated XRD obtained in Example 2 and the XRD of Example 2;

[0027] Figure 7 This is the dark current drift test diagram of Application Example 1;

[0028] Figure 8 is the response current diagram of Application Example 2;

[0029] Fig. 9 Graphs of ferroelectric sensitivity, photosensitivity and total sensitivity for Application Example 2;

[0030] FIG10 is a diagram showing the detector sensitivity, detection limit and response stability of Application Example 2; wherein, Fig.10a This is the detector sensitivity diagram for Application Example 2. Fig.10b This is the detection limit diagram of Application Example 2. Fig.10c 10d is the in-plane directional stability diagram of application example 2, and 10d is the out-of-plane directional stability diagram of application example 2;

[0031] Fig.11 This is a comparison chart of the detection performance of the (Br-EA)2PbBr4 detector and the performance of common materials;

[0032] Fig.12 A comparison of the pentagonal capabilities of (Br-EA)2PbBr4 materials and existing two-dimensional perovskites. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention provides a method for preparing a two-dimensional perovskite single crystal, the preparation method comprising:

[0035] S1. Using hydrohalic acid to modify small organic molecules to obtain modified molecules.

[0036] Specifically, the modification step includes: mixing a small organic molecule with a hydrohalic acid solution, heating and stirring, and then evaporating and concentrating. The modification of the present invention is obtained by halogenating and replacing the organic molecule. For example, the bromoethylamine molecule is obtained by mixing ethylamine and hydrobromic acid and heating to 135-145°C for 12 hours, then cooling and evaporating and concentrating to 75°C, and then rapidly cooling to 5°C to precipitate crystals.

[0037] In one embodiment, the hydrohalic acid includes one or more of hydrofluoric acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid.

[0038] In one embodiment, the small organic molecule includes one or more of ethylamine (EA), methylamine, formamidine, dimethylamine, guanidine, and propylamine.

[0039] In one embodiment, the molar ratio of the hydrohalic acid to the small organic molecule is 1-3: 1. For example, the ratio may be 1: 1, 2: 1, or 3: 1.

[0040] In one embodiment, step S1 includes: hydrogen in the small organic molecule is replaced by a halogen. Here, the replaced hydrogen may be located at any position of the small organic molecule. Preferably, the replaced hydrogen may be located at the end of the small organic molecule chain. Specifically, the small organic molecule of the present invention is modified, and there is a halogen molecule at the end of the molecular chain, so that the molecular charge distribution is asymmetric, thereby generating an enhanced molecular dipole moment. The enhanced dipole moment generates a local electric field, which enhances the interaction between ions, making it difficult for ions to move and the material more difficult to decompose, thereby improving chemical stability.

[0041] S2. Add the modified molecules and lead halide to the precursor solvent, raise the temperature to 40-70° C., and keep it at this temperature for 12-24 hours to obtain a precursor solution.

[0042] In one embodiment, the ratio of the modified molecule, the lead halide, and the precursor solvent is 1-10 g: 1-5 g: 10-20 mL. For example, the ratio may be 2 g: 1 g: 12 mL, 5 g: 1 g: 15 mL, 7 g: 1 g: 18 mL. Here, the concentration range of the precursor solution is 0.5-1.5 mol / L.

[0043] Optionally, the precursor solvent includes one or more of hydrobromic acid, hydroiodic acid, hydrochloric acid, dimethylformamide, dimethyl sulfoxide, and γ-butyrolactone.

[0044] In one embodiment, the lead halide includes one or more of lead fluoride, lead chloride, lead iodide, and lead bromide.

[0045] In one embodiment, the precursor solvent includes one or more of hydrobromic acid, hydroiodic acid, hydrochloric acid, dimethylformamide, dimethyl sulfoxide, and γ-butyrolactone.

[0046] S3. Crystallize the precursor solution to obtain a two-dimensional perovskite single crystal.

[0047] In one embodiment, the crystallization is one of cooling crystallization, inversion crystallization, evaporation crystallization, melt crystallization, and anti-solvent crystallization.

[0048] For example, the step of cooling crystallization includes: keeping the precursor solution warm for a period of time, and then cooling it to 40°C-room temperature. Among them, the temperature of the insulation can be 35-70°C, the time of the insulation can be 20-24h, and the rate of cooling can be 0.4-3°C / 24h. Here, the oven atmosphere is kept closed during the cooling period, and the whole is protected from light. For example, the temperature of the insulation can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C. The time of insulation can be 21h, 22h, 23h. The rate of cooling can be 0.7°C / 24h, 1°C / 24h, 1.5°C / 24h, 2°C / 24h, 2.5°C / 24h, 2.7°C / 24h. Here, taking hydrobromic acid as an example, the temperature of the insulation determines the stability of the hydrobromic acid solvent and the solubility of the crystallization solute. If the temperature is too high, hydrobromic acid is easy to decompose, and if the temperature is too low, the solubility of the solute is insufficient, resulting in a low yield. This holding temperature maintains the stability of the precursor solvent and ensures the yield of the crystal. The cooling rate can control the crystal nucleation rate and growth rate. A lower rate can ensure the growth quality of the crystal, so 0.4-3℃ / 24h is the best.

[0049] The modified organic molecules of the present invention are used as organic spacer cations (e.g., Br-EA +), which can enhance the dipole moment, and the enhanced dipole moment can induce a local electric field; the strong dipole of the organic spacer layer can prevent ion migration, while the induced local electric field can promote carrier separation, while improving the working stability and electrical properties of the perovskite device.

[0050] The present invention also provides a two-dimensional perovskite single crystal, wherein the two-dimensional perovskite single crystal is obtained by the above-mentioned method for preparing the two-dimensional perovskite single crystal. The two-dimensional perovskite single crystal has a non-zero polarization strength, and the ion activation energy of the two-dimensional perovskite single crystal is greater than 0.7 eV in the in-plane direction or the out-of-plane direction.

[0051] The present invention also provides an X-ray detector, which includes the above-mentioned two-dimensional perovskite single crystal. Here, the ray source used by the detector for ray detection is an X-ray tube, and optionally, the tube voltage is 0-100 kV, and the maximum dose of the detected X-ray irradiation is 20000 μGy air s -1 .

[0052] In one embodiment, the method for preparing an X-ray detector includes: using a two-dimensional perovskite single crystal as a base material, evaporating metal electrodes on the upper and lower surfaces of the crystal to prepare an X-ray detector. The metal electrode can be one of gold, silver, copper, gallium or chromium.

[0053] Here, X-ray detection is carried out on the prepared X-ray detector, and detection performance data including sensitivity, detection lower limit, dark current drift, and working stability are collected for analysis. The single crystal has high X-ray detection sensitivity, good response signal stability of the X-ray detector, and almost no change in the response current under long-term irradiation.

[0054] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0055] Example 1

[0056] This embodiment provides a method for preparing a two-dimensional perovskite single crystal, such as Figure 1 As shown, the following steps are included:

[0057] Step S1, heating a mixture of HBr and ethylamine (EA) to 135-145° C. for 12 hours, cooling and evaporating to 75° C., and then rapidly cooling to 5° C. to precipitate crystals, to obtain bromoethylamine (Br-EA); wherein the molar ratio of HBr to EA is 1-3:1;

[0058] Step S2, adding Br-EA and PbBr2 to 10 mL HBr at a molar ratio of 2:1, heating to 40-70°C, and keeping warm for 12-24 hours to obtain a 0.5 mol / L precursor solution (the concentration of the precursor solution is the concentration of the product BrEA2PbBr4);

[0059] Step S3, placing the precursor solution in an oven with an initial temperature of 40°C, keeping it warm in the oven for 24 hours, and then slowly cooling it at a rate of 0.5°C / 24 hours. During the cooling period, the oven atmosphere is kept closed and protected from light, and the temperature is slowly reduced to room temperature to obtain (Br-EA)2PbBr4.

[0060] Among them, (Br-EA)2PbBr4 consists of alternating Br-EA cation organic layers and corner-sharing PbBr6 4- Inorganic layers, where the minimum distance between inorganic layers is

[0061] like Figure 2 As shown, the obtained single crystal was characterized by XRD, and the data in the figure showed that this was a single crystal with complete and stable structure. Figure 3 The heating stability data of the single crystal is given in the figure. The single crystal does not begin to decompose until 210°C, which proves the stability of its structure. Figure 4 The temperature-dependent conductivity characteristic curves in the single crystal are estimated to have an ion activation energy of 0.93 eV in the in-plane direction and 1.01 eV in the out-of-plane direction. These ion activation energy values ​​are much higher than those of typical two-dimensional perovskites (0.7-0.9 eV) (for example, typical two-dimensional perovskites can be butylamine lead iodine, phenylethylamine lead iodine, butylamine lead bromide, phenylethylamine lead bromide), because the strong electronegativity of Br-EA enhances the interaction between ions, making ion movement more difficult. At the same time, the smaller distance between adjacent inorganic layers in (Br-EA)2PbBr4 This will lead to stronger interlayer interactions, resulting in better stability than other two-dimensional Ruddlesden-Popper (RP) perovskites. This means that ion migration in the material is significantly suppressed and the electrical stability is greatly improved.

[0062] like Figure 5 Shown is a diagram of a (Br-EA)2PbBr4 perovskite crystal.

[0063] Example 2

[0064] This embodiment provides a two-dimensional perovskite single crystal comprising the following steps:

[0065] Step S1, heating a mixture of HBr and ethylamine (EA) to 135-145° C. for 12 hours, cooling and evaporating to 75° C., and then rapidly cooling to 5° C. to precipitate crystals, to obtain bromoethylamine (Br-EA); wherein the molar ratio of HBr to EA is 1-3:1;

[0066] Step S2, adding Br-EA and PbBr2 to 10 mL HBr at a molar ratio of 2:1, heating to 40-70°C, and keeping warm for 12-24 hours to obtain a 0.7 mol / L precursor solution (the concentration of the precursor solution is the concentration of the product BrEA2PbBr4);

[0067] Step S3, placing the precursor solution in an oven with an initial temperature of 70°C, keeping it warm in the oven for 24 hours, and then slowly cooling it at a rate of 2°C / 24 hours. During the cooling period, the oven atmosphere is kept closed and protected from light, and the temperature is slowly reduced to 40°C to obtain (Br-EA)2PbBr4.

[0068] The (Br-EA)2PbBr4 perovskite single crystal was ground into powder by Figure 6 Comparison of the powder XRD pattern shown with the XRD pattern obtained by theoretical calculation of the crystal structure obtained in Example 1 shows that the same crystal was successfully prepared.

[0069] Application Example 1

[0070] This application example provides a method for preparing an X-ray detector, including: using the two-dimensional perovskite single crystal of Example 2 as a basic material, evaporating 80nm of Au electrodes on the upper and lower surfaces of the crystal to prepare an X-ray detector.

[0071] Among them, Figure 7 As shown in the figure, in a dark environment, a dark current drift test is performed under a bias voltage of 100 V. The 3.6×10 - 8 nA -1 s -1 V -1 It is the lowest value among two-dimensional RP perovskites, proving that ion migration is significantly suppressed and current stability is greatly improved.

[0072] Application Example 2

[0073] This application example provides a method for preparing an X-ray detector, including: using the two-dimensional perovskite single crystal of Example 1 as a basic material, evaporating 80nm of Au electrodes on the upper and lower surfaces of the crystal to prepare an X-ray detector.

[0074] Here, (Br-EA)2PbBr4 perovskite single crystals were assembled into a detector with the structure of Au / (Br-EA)2PbBr4 / Au, and the horizontal device (in-plane device) and the vertical device (out-of-plane device) were used as two specific examples to demonstrate the radiation detection performance. Figure 8 As shown, the response current under X-ray irradiation can be observed, which is characterized by a slow decay from the initial maximum value to a stable value. The response current can be decomposed into a decaying signal J1 and a stable signal J2, corresponding to the iron signal and the light signal, respectively. The current J1 originates from the release of accumulated charges on the crystal surface, which are caused by the dipoles in ((Br-EA)2PbBr4 to maintain electrical neutrality. The charge accumulation and release process can be regarded as a dynamic capacitor, which depends on the carrier concentration generated by the X-rays and the polarization strength of the material. At the same time, the ferroelectric signal is also linearly related to the dose rate, which means that the ferroelectric signal can be regarded as an effective component of the detection sensitivity. Fig. 9 The ferroelectric sensitivity, photosensitivity and total sensitivity diagrams under different electric fields are given, and it can be seen that the ferroelectric signal contributes the most to the total sensitivity, which is 38.1%. Due to the saturation of ferroelectric polarization, the contribution of the ferroelectric signal decreases with the increase of the electric field. At the same time, the ferroelectric contribution is greater in the out-of-plane device, thus reducing the sensitivity difference between the out-of-plane and in-plane detectors.

[0075] Figure 10 shows the sensitivity, detection limit, and response stability of the (Br-EA)2PbBr4 single crystal detector. Figure 10(a) shows that the X-ray detection sensitivity of the single crystal is 540μC Gy air -1 cm -2 And its sensitivity gradually increases and saturates with the increase of voltage. Figure 10(b) shows the detection limit of the device, and its minimum value is 9.8nGy air s -1 , it can be seen that these two detection performance indicators are at the leading level in two-dimensional perovskites, which confirms the effectiveness of this method. Figures 10(c) and (d) show the changes in the working current of the two devices under long-term irradiation. It can be seen that the response signal stability of the device is excellent, and the long-term irradiation response current remains unchanged. Therefore, through this method, we can prepare a high-performance ray detector with significantly improved ray detection performance and device stability maintained at a very stable level.

[0076] Fig.11 The detection performance of (Br-EA)2PbBr4 detector is compared with that of common materials. The dark current drift of the single crystal and detector prepared by this method is 3.6×10 -8 nA -1 s -1 V-1 It is the lowest value among two-dimensional RP perovskites, and the ratio of sensitivity to dark current is at the leading level. It can be seen that by enhancing the dipole moment, the ion migration in the perovskite can be significantly suppressed while improving its photoelectric response, maintaining or even improving its stability. Fig.12 A pentagonal capacity diagram comparison of (Br-EA)2PbBr4 material and common two-dimensional perovskite is given. It can be seen that the material prepared by this method has balanced performance, including sensitivity, dark current drift, detection lower limit, carrier lifetime, mobility lifetime product, all of which are at an advanced level. This once again proves the effectiveness of this method and that the performance of the (Br-EA)2PbBr4 single crystal material prepared by this method is balanced and superior to that of general two-dimensional perovskite materials, which has a strong boosting effect on the practical application of perovskite in the field of radiation detection.

[0077] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a two-dimensional perovskite single crystal, characterized in that: The preparation method comprises: S1. Modifying small organic molecules using hydrohalic acid to obtain modified molecules; S2, adding the modified molecules and lead halide to the precursor solvent, heating and keeping the temperature for a period of time to obtain a precursor solution; S3. Crystallize the precursor solution to obtain a two-dimensional perovskite single crystal, and use the single crystal as the basic material to prepare a radiation detector.

2. The preparation method according to claim 1, characterized in that: The small organic molecules include one or more of ethylamine, methylamine, formamidine, dimethylamine, guanidine, and propylamine.

3. The preparation method according to claim 1, characterized in that: The hydrohalogen acid in step S1 includes one or more of hydrofluoric acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid; The precursor solvent in step S2 includes one or more of hydrobromic acid, hydroiodic acid, hydrochloric acid, dimethylformamide, dimethyl sulfoxide, and γ-butyrolactone; The lead halide in step S2 includes one or more of lead chloride, lead iodide and lead bromide.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the hydrohalic acid to the small organic molecule is 1-3:1; The ratio of the modified molecule, lead halide and precursor solvent is 1-10g: 1-5g: 10-20mL.

5. The preparation method according to claim 1, characterized in that: The step S1 comprises: hydrogen in the small organic molecule is replaced by halogen.

6. The preparation method according to claim 1, characterized in that: In the step S2, the heating temperature is 40-70°C and the insulation time is 12-24h.

7. The preparation method according to claim 1, characterized in that: The crystallization step comprises: The precursor solution is kept warm for a period of time, and then cooled to 40°C-room temperature; wherein the keeping temperature is 35-70°C, the keeping time is 20-24h, and the cooling rate is 0.4-3°C / 24h.

8. A two-dimensional perovskite single crystal, characterized in that: The two-dimensional perovskite single crystal is obtained by the preparation method of the two-dimensional perovskite single crystal according to any one of claims 1 to 7.

9. The two-dimensional perovskite single crystal according to claim 8, characterized in that: The distance between adjacent inorganic layers in the two-dimensional perovskite single crystal is The ion activation energy of two-dimensional perovskite single crystals is greater than 0.7 eV in both the in-plane and out-of-plane directions.

10. An X-ray detector, characterized in that: The X-ray detector comprises the two-dimensional perovskite single crystal according to claim 8 or 9.

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