A two-dimensional perovskite single crystal and a preparation method thereof, and an X-ray detector

Abstract

The application provides a two-dimensional perovskite single crystal and 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 a small organic molecule by using a hydrogen halide acid to obtain a modified molecule; S2, adding the modified molecule 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. The two-dimensional perovskite single crystal prepared by using the preparation method can enhance a dipole moment due to the modified organic molecule as an organic spacer cation, the enhanced dipole moment can induce a local electric field, the strong dipole of the organic spacer layer can prevent ion migration, the induced local electric field can promote carrier separation, and the working stability and electrical performance of the perovskite device are improved.

Description

Technical Field

[0001] This invention relates to a two-dimensional perovskite single crystal and its preparation method, as well as an X-ray detector comprising the two-dimensional perovskite single crystal. Background Technology

[0002] Two-dimensional hybrid perovskites with large-radius cations are considered promising candidates for optoelectronics due to their excellent photoelectric properties, low detection limits, and superior environmental stability. This is because perovskites possess layered PbX6... 2− The intrinsic quantum well structure, composed of octahedral elements and organic spacers, results in relatively poor electrical performance and severe carrier recombination. Currently, most work on improving two-dimensional hybrid perovskites focuses on quantum well engineering, such as reducing the organic layer thickness or increasing PbX6 content. 2- The thickness of octahedral networks is often increased to improve photoelectric properties. However, this approach often weakens structural stability and leads to severe ion migration, resulting in decreased device stability. Therefore, a method is needed to improve the photoelectric properties of perovskites while maintaining their stability.

[0003] On the one hand, in order to maintain structural stability, Cs needs to be added during the process of increasing the thickness of the octahedral network layer. + MA + Small molecules are used in perovskites. However, these small molecules migrate more easily within the perovskite, leading to severe ion migration; simultaneously, perovskites are prone to phase segregation, resulting in weakened chemical stability of the material. On the other hand, reducing the thickness of the organic layer also involves using smaller molecules as organic molecules, but the same problems occur, causing a decrease in perovskite stability.

[0004] In summary, no method has yet been found that can improve the photoelectric properties of two-dimensional perovskites while simultaneously preventing ion migration and enhancing the chemical stability of the materials. Summary of the Invention

[0005] This invention aims to solve the problems of deteriorating chemical stability and severe ion migration when improving photoelectric performance in two-dimensional perovskite quantum well engineering. It proposes a two-dimensional perovskite single crystal, its preparation method, 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 method comprising: S1, modifying small organic molecules with hydrogen halide 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 this single crystal as the base material to prepare a radiation detector.

[0008] Optionally, the small organic molecule includes one or more of ethylamine, methylamine, formamidinium, 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; and 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, lead halide, and precursor solvent is 1-10 g: 1-5 g: 10-20 mL.

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

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

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

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

[0015] The distance between adjacent inorganic layers in the two-dimensional perovskite single crystal is 3-6 Å. The two-dimensional perovskite single crystal has a non-zero polarization intensity, and the ion activation energy of the two-dimensional perovskite single crystal is greater than 0.7 eV in both the in-plane and out-of-plane directions.

[0016] The present invention also provides an X-ray detector comprising the above-described two-dimensional perovskite single crystal.

[0017] The beneficial effects of this invention are:

[0018] The two-dimensional perovskite single crystals prepared by the method of this invention can enhance the dipole moment by using modified organic molecules as organic spacer cations. The enhanced dipole moment can induce a local electric field. The strong dipoles of the organic spacer layer can prevent ion migration, while the induced local electric field can promote carrier separation, thereby improving the working stability and electrical performance of the perovskite device.

[0019] This invention uses a cooling crystallization method to obtain single crystals with a two-dimensional layered structure. This method is simple, efficient, and environmentally friendly, and is suitable for large-scale industrial production.

[0020] The two-dimensional perovskite single crystal provided by this invention, when used as an X-ray detector, exhibits leading X-ray detection sensitivity and detection limit among two-dimensional perovskites, with a dark current drift of 3.6 × 10⁻⁶. -8 nA cm -1 s -1 V -1 This is the lowest value among two-dimensional RP perovskites. The X-ray detector exhibits good response signal stability, with almost no decrease in response current over long-term irradiation. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the small molecule modification in Example 1;

[0022] Figure 2 This is a schematic diagram of the (Br-EA)2PbBr4 perovskite crystal from Example 1;

[0023] Figure 3 The diagram shows the heating stability of the (Br-EA)2PbBr4 perovskite crystal in Example 1.

[0024] Figure 4 The electrical conductivity characteristic curve of the (Br-EA)2PbBr4 perovskite crystal in Example 1 is shown.

[0025] Figure 5 The image shows a perovskite crystal of Example 1 (Br-EA)2PbBr4.

[0026] Figure 6 This is a comparison chart of the theoretically calculated XRD obtained in Example 2 and the XRD of Example 2.

[0027] Figure 7 The dark current drift test diagram is shown in Example 1.

[0028] Figure 8 The response current diagram for Application Example 2;

[0029] Figure 9 The graphs for ferroelectric sensitivity, optical sensitivity, and total sensitivity are shown in Example 2.

[0030] Figure 10a The detector sensitivity diagram is shown in Example 2. Figure 10b To apply the detection lower limit chart of Example 2, Figure 10c The in-plane stability diagram is shown for Application Example 2, and 10d is shown for the out-of-plane stability diagram of Application Example 2.

[0031] Figure 11A comparison chart of the detection performance of (Br-EA)2PbBr4 detector with the properties of common materials;

[0032] Figure 12 A comparison of the pentagonal capabilities of (Br-EA)2PbBr4 material with existing two-dimensional perovskites. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention provides a method for preparing two-dimensional perovskite single crystals, the method comprising:

[0035] S1. Small organic molecules are modified using hydrohalic acid to obtain modified molecules.

[0036] Specifically, the modification steps include: mixing small organic molecules with a hydrohalic acid solution, heating and stirring, followed by evaporation and concentration. The modification in this invention is achieved by halogenating and substituting organic molecules. For example, ethyl bromide molecules are obtained by mixing ethylamine and hydrobromic acid, heating to 135-145 °C for 12 hours, then cooling and evaporating to 75 °C, followed by rapid 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, formamidinium, dimethylamine, guanidine, and propylamine.

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

[0040] In one embodiment, step S1 includes replacing hydrogen in the small organic molecule with a halogen. Here, the substituted hydrogen can be located at any position within the small organic molecule. Preferably, the substituted hydrogen can be located at the end of the small organic molecule chain. Specifically, the small organic molecule of the present invention is modified to have a halogen molecule at the end of the molecular chain, resulting in an asymmetrical molecular charge distribution and thus generating an enhanced molecular dipole moment. This enhanced dipole moment generates a local electric field, strengthens the interionic forces, makes ion movement more difficult, and makes the material more difficult to decompose, thereby improving chemical stability.

[0041] S2. Add the modified molecule and lead halide to the precursor solvent, heat to 40-70℃, and keep it at this temperature for 12-24 h to obtain the precursor solution.

[0042] In one embodiment, the ratio of the modified molecule, lead halide, and precursor solvent is 1-10 g: 1-5 g: 10-20 mL. For example, the ratio can be 2 g: 1 g: 12 mL, 5 g: 1 g: 15 mL, or 7 g: 1 g: 18 mL. Here, the concentration of the precursor solution ranges from 0.5 to 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, lead halides include 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 the following methods: cooling crystallization, reverse temperature crystallization, evaporation crystallization, melt crystallization, and antisolvent crystallization.

[0048] For example, the cooling crystallization step includes: holding the precursor solution at a certain temperature for a period of time, and then cooling it to 40℃-room temperature. The holding temperature can be 35-70℃, the holding time can be 20-24 h, and the cooling rate can be 0.4-3℃ / 24 h. During the cooling process, the oven atmosphere should be kept sealed and completely protected from light. For example, the holding temperatures can be 40℃, 45℃, 50℃, 55℃, 60℃, and 65℃. The holding times can be 21 h, 22 h, and 23 h. The cooling rates can be 0.7℃ / 24 h, 1℃ / 24 h, 1.5℃ / 24 h, 2℃ / 24 h, 2.5℃ / 24 h, and 2.7℃ / 24 h. Taking hydrobromic acid as an example, the holding temperature determines the stability of the hydrobromic acid solvent and the solubility of the crystallizing solute. Too high a temperature easily decomposes the hydrobromic acid, while too low a temperature results in insufficient solubility of the solute, leading to a lower yield. This holding temperature maintains the stability of the precursor solvent and ensures the crystal yield. The cooling rate can control the crystal nucleation rate and growth rate; a lower rate ensures the quality of crystal growth, therefore, 0.4-3℃ / 24 h is optimal.

[0049] The modified organic molecules of the present invention serve as organic spacer cations (e.g., Br-EA).+ The strong dipoles of the organic spacer layer can enhance the dipole moment, which in turn can induce a local electric field. The strong dipoles of the organic spacer layer can prevent ion migration, while the induced local electric field can promote carrier separation, thereby improving the operating stability and electrical performance of the perovskite device.

[0050] This invention also provides a two-dimensional perovskite single crystal, which is obtained by the above-described method for preparing two-dimensional perovskite single crystals. The distance between adjacent inorganic layers in the two-dimensional perovskite single crystal is 3-6 Å, the two-dimensional perovskite single crystal has non-zero polarization, and the ion activation energy of the two-dimensional perovskite single crystal is greater than 0.7 eV in both the in-plane and out-of-plane directions.

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

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

[0053] Here, the prepared X-ray detector is subjected to X-ray detection, and detection performance data including sensitivity, detection limit, dark current drift, and operational stability are collected and analyzed. The single crystal has high X-ray detection sensitivity, good response signal stability, and the response current hardly changes after long-term irradiation.

[0054] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below. Example 1

[0055] This embodiment provides a method for preparing two-dimensional perovskite single crystals, such as... Figure 1 As shown, it includes the following steps:

[0056] Step S1: Mix HBr and ethylamine (EA) and heat to 135-145 °C for 12 h, then cool and evaporate to concentrate to 75 °C, and then rapidly cool to 5 °C to precipitate crystals to obtain bromoethylamine (Br-EA); wherein the molar ratio of HBr to EA is 1-3:1;

[0057] Step S2: Add Br-EA and PbBr2 to 10 mL HBr in a molar ratio of 2:1, heat to 40-70℃, and keep warm for 12-24 h to obtain a 0.5 mol / L precursor solution (the concentration of the precursor solution is the same as the concentration of the product BrEA2PbBr4).

[0058] Step S3: Place the precursor solution in an oven at an initial temperature of 40°C and keep it at that temperature for 24 hours. Then, start to slowly cool it down at a rate of 0.5°C / 24 hours. During the cooling process, keep the oven sealed and completely dark, allowing the temperature to slowly decrease to room temperature to obtain (Br-EA)2PbBr4.

[0059] Among them, (Br-EA)2PbBr4 consists of alternating Br-EA cation organic layers and PbBr6 with common angles. 4- It consists of inorganic layers, with a minimum distance of 5.76 Å between the inorganic layers.

[0060] like Figure 2 As shown, the obtained single crystal was characterized by XRD, and the data in the figure indicate that it is a structurally complete and stable single crystal. Figure 3 The paper presents the heating stability data of the single crystal, which only began to decompose at 210℃, demonstrating the stability of its structure. (Fitting data is then used to demonstrate this stability.) Figure 4 The temperature-dependent conductivity curves in the model suggest that the ion activation energy of the single crystal is 0.93 eV in the in-plane direction and 1.01 eV out-of-plane. These ion activation energies are significantly higher than those of typical two-dimensional perovskites (0.7-0.9 eV) (e.g., butylamine lead iodide, phenylethylamine lead iodide, butylamine lead bromide, phenylethylamine lead bromide). This is because the strong electronegativity of Br-EA enhances interionic interactions, making ion migration more difficult. Simultaneously, the smaller distance (5.76 Å) between adjacent inorganic layers in (Br-EA)₂PbBr₄ leads to stronger interlayer interactions, resulting in better stability than other two-dimensional Ruddlesden-Popper (RP) perovskites. This implies that ion migration in the material is significantly suppressed, leading to a substantial improvement in electrical stability.

[0061] like Figure 5 The image shown is a crystal diagram of (Br-EA)2PbBr4 perovskite. Example 2

[0062] This embodiment provides a two-dimensional perovskite single crystal, comprising the following steps:

[0063] Step S1: Mix HBr and ethylamine (EA) and heat to 135-145 °C for 12 h, then cool and evaporate to concentrate to 75 °C, and then rapidly cool to 5 °C to precipitate crystals to obtain bromoethylamine (Br-EA); wherein the molar ratio of HBr to EA is 1-3:1;

[0064] Step S2: Add Br-EA and PbBr2 to 10 mL HBr in a molar ratio of 2:1, heat to 40-70℃, and keep warm for 12-24 h to obtain a 0.7 mol / L precursor solution (the concentration of the precursor solution is the same as the concentration of the product BrEA2PbBr4).

[0065] Step S3: Place the precursor solution in an oven at an initial temperature of 70°C and keep it at that temperature for 24 hours. Then, start to slowly cool it down at a rate of 2°C / 24 hours. During the cooling process, keep the oven sealed and completely dark, and allow the temperature to slowly decrease to 40°C to obtain (Br-EA)2PbBr4.

[0066] The (Br-EA)₂PbBr₄ perovskite single crystal was ground into powder, and then processed using... Figure 6 The powder XRD pattern shown is compared with the XRD pattern obtained from the theoretical calculation of the crystal structure in Example 1, showing that the same crystal was successfully prepared.

[0067] Application Example 1

[0068] This application example provides a method for fabricating an X-ray detector, which includes: using the two-dimensional perovskite single crystal of Example 2 as the base material, depositing Au electrodes of 80 nm on both the upper and lower surfaces of the crystal to fabricate an X-ray detector.

[0069] Among them, such as Figure 7 As shown, dark current drift was tested under a 100 V bias voltage in a dark environment, and its value was 3.6 × 10⁻⁶. -8 nA cm -1 s -1 V -1 This is the lowest value in two-dimensional RP perovskites, demonstrating that ion migration is significantly suppressed and current stability is greatly improved.

[0070] Application Example 2

[0071] This application example provides a method for fabricating an X-ray detector, which includes: using the two-dimensional perovskite single crystal of Example 1 as the base material, depositing Au electrodes of 80 nm on both the upper and lower surfaces of the crystal to fabricate an X-ray detector.

[0072] Here, a detector with the structure Au / (Br-EA)2PbBr4 / Au was assembled from a (Br-EA)2PbBr4 perovskite single crystal, and the X-ray detection performance was demonstrated using two specific examples: a horizontally oriented device (in-plane device) and a vertically oriented device (out-of-plane device). Figure 8 As shown, the response current under X-ray irradiation can be observed, characterized by a slow decay from an 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 ferroelectric signal and the optical signal, respectively. Current J1 originates from the release of accumulated charge on the crystal surface, which is caused by dipoles in ((Br-EA)2PbBr4 to maintain electroneutrality. The charge accumulation and release process can be considered as a dynamic capacitor, depending on the carrier concentration generated by the X-rays and the polarization intensity of the material. Simultaneously, the ferroelectric signal is also linearly related to the dose rate, meaning that the ferroelectric signal can be considered an effective component for detection sensitivity. Figure 9 The ferroelectric sensitivity, optical sensitivity, and total sensitivity diagrams under different electric fields are presented. It can be seen that the ferroelectric signal contributes the largest percentage (38.1%) to the total sensitivity. Due to ferroelectric polarization saturation, the contribution of the ferroelectric signal decreases with increasing electric field. Furthermore, the ferroelectric contribution is greater in out-of-plane devices, thus reducing the sensitivity difference between out-of-plane and in-plane detectors.

[0073] Figure 10a The X-ray detection sensitivity of this single crystal is given as 540 μC Gy. air -1 cm -2 Furthermore, its sensitivity gradually increases with increasing voltage and then saturates. Figure 10b The detection limit of this device is given, with a minimum value of 9.8 nGy. air s -1 It can be seen that the two detection performance indicators are at the leading level in two-dimensional perovskites, which confirms the effectiveness of the method. Figure 10c and Figure 10d The changes in operating current of the two devices under long-term irradiation are presented. It can be seen that the response signal stability of the devices is extremely good, and the response current remains unchanged even after long-term irradiation. Therefore, using this method, we can fabricate a high-performance X-ray detector with significantly improved X-ray detection performance and very stable device stability.

[0074] Figure 11 The detection performance of the (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 × 10⁻⁶. -8 nA cm -1 s -1 V-1 This is the lowest value among two-dimensional RP perovskites, while the ratio of sensitivity to dark current is among the highest. It can be seen that enhancing the dipole moment can significantly suppress ion migration in the perovskite while improving its photoelectric response, maintaining or even enhancing its stability. Figure 12 A comparison of the pentagonal capability plots of (Br-EA)₂PbBr₄ material with those of common two-dimensional perovskites is presented. It can be seen that the material prepared by this method has balanced performance, and its performance in various aspects, including sensitivity, dark current drift, detection limit, carrier lifetime, and mobility-lifetime product, is at an advanced level. This further proves the effectiveness of this method and that the (Br-EA)₂PbBr₄ single crystal material prepared by this method has balanced performance and is superior to general two-dimensional perovskite materials. This has a strong boosting effect on the practical application of perovskites in the field of X-ray detection.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which 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 includes: S1. Small organic molecules are modified using hydrohalic acid to obtain modified molecules; S2. Add the modified molecule and lead halide to the precursor solvent, heat and keep warm for a period of time to obtain the precursor solution. S3. Crystallize the precursor solution to obtain a two-dimensional perovskite single crystal, and use this single crystal as the base material to prepare a radiation detector. The small organic molecules include one or more of ethylamine, methylamine, formamidinium, dimethylamine, guanidine, and propylamine; the precursor solvent in step S2 includes one or more of hydrobromic acid, hydroiodic acid, hydrochloric acid, dimethylformamide, dimethyl sulfoxide, and γ-butyrolactone. The S1 step includes: hydrogen in small organic molecules being replaced by halogens; In step S2, the heating temperature is 40-70℃, and the holding time is 12-24 h; The crystallization step includes: The precursor solution is kept at a certain temperature for a period of time, and then cooled to 40℃-room temperature. The temperature during which the solution is kept at a certain temperature is 35-70℃, the holding time is 20-24 h, and the cooling rate is 0.4-3℃ / 24 h.

2. The preparation method according to claim 1, characterized in that, The hydrohalic acid in step S1 includes one or more of hydrofluoric acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid. The lead halides in step S2 include one or more of lead chloride, lead iodide, and lead bromide.

3. 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 1-10 g: 1-5 g: 10-20 mL.

4. 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 1-3.

5. The two-dimensional perovskite single crystal according to claim 4, characterized in that, The distance between adjacent inorganic layers in the two-dimensional perovskite single crystal is 3-6 Å, and the ion activation energy of the two-dimensional perovskite single crystal is greater than 0.7 eV in both the in-plane and out-of-plane directions.

6. An X-ray detector, characterized in that, The X-ray detector comprises a two-dimensional perovskite single crystal as described in claim 4 or 5.

Images