Large-area lead-free perovskite single crystal film, preparation method and application thereof

Abstract

The application discloses a large-area lead-free perovskite single crystal film, a preparation method and application thereof, relates to the technical field of photoelectric detection, and has the technical points that the preparation method of the large-area lead-free perovskite single crystal film utilizes gas-liquid surface and interface action, a large-area (C7H 16 N)2CuBr4 perovskite structure single crystal film is obtained by adjusting a solvent and growth conditions. The growth method of the perovskite single crystal film can be extended unlimitedly in theory, and the thickness of the obtained single crystal film can be adjusted to 3-560 mu m. The photoelectric response switch ratio of an X-ray detector prepared by using the single crystal film with a thickness of 560 mu m reaches 91.8, and the dark current is as low as 0.11 pA. The growth method of the single crystal film is simple, raw materials are cheap and easy to obtain, is suitable for large-area single crystal film growth, and has potential application value in X-ray detectors.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photoelectric detection, in particular to a large-area lead-free perovskite single crystal film, a preparation method and applications thereof. BACKGROUND

[0002] The rapid development of organic-inorganic hybrid perovskite promotes its application in photoelectric detection. This kind of material has the advantages of simple preparation process and low cost. Moreover, it can be applied in the fields of photoelectric detection and solar cells due to its long carrier diffusion length and strong light absorption capacity. Among them, X-ray detectors have important significance in imaging, security inspection, non-destructive testing and scientific research, and have wide application value. The semiconductor X-ray detector converts X-rays into electrical signals. This direct detection has the advantages of high detection sensitivity and simple preparation. Among them, metal halide perovskite performs well in X-ray direct detection performance, and has the characteristics of simple preparation and high sensitivity.

[0003] Among the above-mentioned compounds, lead-based halide perovskites are particularly prominent and have received great attention in the field of optoelectronics, including solar cells, light-emitting diodes, lasers, photodetectors, etc. (Materials Horizons 2015, 2, 228-231. ACS Photonics 2020, 7, 10-28.). Although halide perovskites have made significant progress in these aspects, their application is limited due to the serious environmental pollution problem of lead-containing perovskites, so it is imperative to find a non-toxic element to replace lead. Among the candidate materials to replace lead, copper is an abundant, low-cost and environmentally friendly element. In addition, compared with three-dimensional perovskites, two-dimensional perovskites have better chemical stability, optoelectronic tunability and other excellent properties. However, most of the perovskite materials reported for photodetection are polycrystalline films prepared by spin coating, drop coating, blade coating, etc. (Energy Environ. Sci. 2014, 7, 2944-2950; Advanced Science 2021, 8. 2102081; Adv. Mater. 2017, 29, 1702643.), which limits the performance and application of perovskites due to the structural defects of the randomly oriented polycrystalline films. In addition, some researchers use physical tearing or cutting methods to reduce the thickness of the perovskite layer, but this physical peeling method causes more serious structural damage in two-dimensional organic-inorganic hybrid perovskites, and due to the presence of the organic layer, the van der Waals interaction between the layers is weaker and more prone to breakage (Layers. Nat. Mater. 2016, 15, 1255-1260; Materials Today Energy 2018, 7, 149-160.). Therefore, it is necessary to develop a large-area lead-free perovskite single crystal film with small defects and good photodetection performance.

[0004] To this end, the present application aims to provide a large-area lead-free perovskite single crystal film, a preparation method and applications thereof to solve the above problems. SUMMARY

[0005] The present application aims to solve the above problems and provides a large-area lead-free perovskite single crystal film, a preparation method and applications thereof. The preparation method is to prepare a lead-free perovskite single crystal film by utilizing the interface effect of air-solvent. The method has the advantages of simple preparation, low cost and easy operation. The prepared film has the characteristics of continuity, large area and smooth surface, and can realize a thickness of 3-560 μm. The X-ray detector prepared based on the perovskite realizes ultra-low dark current and high on-off ratio.

[0006] In order to achieve the above object, the technical scheme of the present application is as follows:

[0007] A large-area lead-free perovskite single crystal film, which is a crystal material composed of a compound of the following molecular formula: (C7H 16 N)2CuBr4.

[0008] The (C7H 16 N) in the molecular formula of the compound is a protonated cyclohexylmethylamine cation. +

[0009] The crystal material belongs to the orthorhombic system, crystallizes in space group Pbca, and the unit cell parameters are: a (Å) = 8.20~8.25; b (Å) = 7.75~7.80; c (Å) = 33.15~33.20; α (°) = β (°) = γ (°) = 90; V (Å 3 ) = 2106.68~2136.42.

[0010] The large-area lead-free perovskite single crystal film is composed of cyclohexylmethylamine cations and [CuBr4] 2- anions, and (C7H 16 N)2CuBr4 is a [CuBr6] 4- octahedron that is connected at the common vertex and is separated by the protonated cyclohexylmethylamine cation along the a-axis direction to form a two-dimensional perovskite layer.

[0011] The present application also provides a preparation method of a large-area lead-free perovskite single crystal film, which is prepared by a solvent evaporation method. A copper source, a bromine source, cyclohexylmethylamine, and a solvent are mixed at room temperature, and then the solvent is volatilized at 25~70°C to grow a single crystal film, thereby obtaining a large-area lead-free perovskite single crystal film. The mixed molar ratio of the copper source, the cyclohexylmethylamine, and the bromine source is about 1:2:2. The amount of substance of the copper source is calculated based on the amount of substance of copper contained therein, and the amount of substance of the bromine source is calculated based on the amount of substance of bromine contained therein.

[0012] The copper source is selected from one or more of copper bromide, copper sulfate, and copper nitrate.

[0013] The bromine source is selected from bromic acid.

[0014] Further, the method specifically comprises the following steps:

[0015] S1, preparing a precursor solution of a lead-free two-dimensional perovskite material, and processing a container to be used for single crystal growth.

[0016] ​S2, the prepared precursor solution is filtered by a corresponding filter and then added into the treated container; the filter is one of an organic filter and a water-based filter;

[0017] S3, the precursor solution is grown in situ into a single crystal under certain conditions, to obtain the lead-free two-dimensional perovskite material; the temperature for the in-situ growth of the precursor solution is 25-70 DEG C, and the film forming time is not less than 1 hour.

[0018] Further, the preparation of the precursor solution in S1 is specifically as follows: cyclohexylmethylamine is used as an organic amine cation, CuBr2 is used as a raw material, CuBr2 is fully stirred in a solvent until dissolved, then the protonated cyclohexylmethylamine is added, and the reaction is carried out at room temperature, and the solvent is volatilized and crystallized at 25-70 DEG C.

[0019] The container for single crystal growth in S1 is specifically selected from one of a 25 mL beaker, a 50 mL beaker, a 35 mm culture dish, a 60 mm culture dish or a 75 mm culture dish; the container is sequentially ultrasonically cleaned in deionized water and anhydrous ethanol for 15 min, dried by nitrogen blowing, and cleaned by an ion cleaning machine.

[0020] Further, the solvent used for the preparation of the precursor solution is one or more of deionized water, anhydrous ethanol, acetonitrile, methanol, isopropanol, dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF).

[0021] Further, the solvent used for the preparation of the precursor solution is one or a mixture of two of anhydrous ethanol and deionized water.

[0022] Further, the solvent used for the preparation of the precursor solution is anhydrous ethanol and deionized water, and the ratio of anhydrous ethanol to deionized water is 0-3:1.

[0023] The application also provides an application of the single crystal film prepared by the method for preparing a large-area lead-free perovskite single crystal film in preparing an X-ray detector.

[0024] In the application, the application provides a large-area lead-free perovskite single crystal film with adjustable thickness, which can adapt to a certain range of photovoltaic device preparation conditions. The thickness of the perovskite single crystal film prepared by the above method is adjustable in the range of 3-560 μm, and the film thickness is uniform.

[0025] The large-area lead-free perovskite single crystal film prepared by the method has high quality, the film area can be theoretically infinitely extended, and the thickness can be controlled within a certain range.

[0026] The copper-based perovskite material prepared by the method is applied in the photoelectric field, a novel X-ray detector is prepared based on the perovskite single crystal film prepared by the method, and the X-ray detector has good photoelectric response characteristics. -1 When a bias voltage of -1V is applied, an ultra-low dark current of 0.11 pA is achieved, a photocurrent of 10.1 pA is achieved, and a switching ratio of 91.8 is achieved.

[0027] Compared with the prior art, the method has the following beneficial effects:

[0028] (1) The method for preparing the large-area lead-free perovskite single crystal film has the advantages that the method for preparing the lead-free perovskite single crystal film in situ by using the surface and interface interaction of a solution and air is low in cost, simple in operation, mild in preparation condition, and green and environment-friendly, and the method solves the problems of high equipment cost and harsh preparation condition of the chemical vapor deposition method.

[0029] (2) The large-area lead-free perovskite single crystal film prepared by the method has the advantages that the thickness of the single crystal film can be controlled within a certain range, the area of the single crystal film is not obviously limited in theory, and the area of the single crystal film is infinitely increased with the increase of geometric space, and the prepared single crystal film has no obvious crystal boundary and defect and is high in quality.

[0030] (3) The large-area lead-free perovskite single crystal film has certain application prospect in the field of X-ray detection, the measured dark current is 0.11 pA, and the switching ratio is 91.8, and the application of the organic-inorganic hybrid copper-based perovskite material in the field of X-ray detection is broken through. DETAILED DESCRIPTION

[0031] Figure 1 is a schematic diagram of an X-ray detector prepared based on a (C7H 16 N)2CuBr4 single crystal;

[0032] Figure 2 is a comparison diagram for controlling the contact area of a solution surface and air in an embodiment (2#B2) of the application;

[0033] Figure 3 is a growth process of a (C7H 16 N)2CuBr4 single crystal film in an embodiment of the application;

[0034] Figure 4of (C7H 16 N)2CuBr4;

[0035] Figure 5 A single crystal structure diagram of a lead-free perovskite prepared in an embodiment of the present application;

[0036] Figure 6 X-ray response data of an X-ray detection device prepared based on a (C7H 16 N)2CuBr4 single crystal;

[0037] Figure 7 Morphology diagrams obtained by atomic force microscope observation of (C7H 16 N)2CuBr4 prepared in an embodiment of the present application, wherein (a) is 50 μm × 50 μm, and (b) is 20 μm × 20 μm;

[0038] Figure 8 Photos under a polarizing microscope of (C7H 16 N)2CuBr4 prepared in an embodiment of the present application, wherein (a) is a 3#C2 experimental group, and (b) is a 3#B2 experimental group. DETAILED DESCRIPTION

[0039] In order to make the person skilled in the art better understand the present application, the following will be further described in combination with the drawings on the specific embodiments of a (C7H 16 N)2CuBr4 perovskite single crystal film and an X-ray detector according to the present application, and the technical solutions of the present application will be further described in detail. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present application.

[0040] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail in combination with the embodiments.

[0041] Embodiment 1:

[0042] The present application provides a preparation method of a perovskite single crystal thick film (C7H 16 N)2CuBr4, specifically:

[0043] (1) 0.446 g of CuBr2 is weighed and added into appropriate amount of water, and stirred and dissolved.

[0044] (2) 0.452 g of cyclohexylmethylamine is weighed and added into appropriate amount of anhydrous ethanol, and hydrobromic acid is added according to a ratio of hydrobromic acid: cyclohexylmethylamine = 1:1 to protonate it.

[0045] (3) Mix the step (1) and (2) evenly, adjust the ratio of water and anhydrous ethanol (preferably 1:3), filter with an organic filter, transfer to a clean container (preferably a 25 mL beaker), and slowly evaporate at a constant temperature of 25 ℃, 40 ℃, 70 ℃ (preferably 25 ℃, 40 ℃), and a small hole is evenly sealed with plastic wrap, to obtain the two-dimensional perovskite single crystal film. By adjusting the solvent, growth temperature and the contact area of the solution surface with air to control the interface interaction and crystal growth time, the size of the crystal growth is controlled.

[0046] (4) The prepared single crystal film is further transferred from the solution.

[0047] (5) The transferred single crystal film is dried to obtain a single crystal film with a size of 10 mm * 6.8 mm and a thickness of 0.56 mm, as shown in b of Figure 1 .

[0048] Example 2

[0049] The application provides a preparation method of a perovskite single crystal thin film (C7H 16 N)2CuBr4. Specifically,

[0050] (1) First, weigh 2.680 g of copper bromide and dissolve it in about 60 mL of solvent (anhydrous ethanol, n-propanol, isopropanol, water, mixed solvent of anhydrous ethanol and water in a corresponding ratio, preferably anhydrous ethanol, water, anhydrous ethanol and water = 1:1).

[0051] (2) Weigh 2.767 g of cyclohexylmethylamine, dilute it with a corresponding solvent, and then add hydrobromic acid to protonate it according to the ratio of hydrobromic acid to cyclohexylmethylamine = 1:1.

[0052] (3) Mix (1) and (2), then filter with a corresponding filter, and then divide it into 9 equal parts and place it in a 60 mm clean culture dish.

[0053] (4) Divide the above 9 equal parts into 3 groups and grow at a constant temperature of 25 ℃, 40 ℃, and 70 ℃, respectively.

[0054] (5) Set the three groups in step (4) as A, B, and C, and control the contact area of the solution surface with air, specifically, A is completely covered with a glass slide, B is covered with a glass slide leaving a gap of about 1 cm in the middle, and C is covered with a single glass slide, as shown in Figure 2 .

[0055] (6) Observe the growth of the control groups in step (5) and record them.

[0056] More specifically, the solvent (absolute ethanol) of Example 2 and the growth temperature, sample number and growth time, film growth condition are shown in Table 1 (here, the growth time and film growth condition only represent the time of growing the thin film into a whole thin film (60 mm 2 ), if the growth is continued, the thickness of the thin film will be increased accordingly).

[0057] Table 1: The solvent (absolute ethanol) of Example 2 and the growth temperature, sample number and growth time, film growth condition

[0058]

[0059] From the experimental results of Step (6), it can be concluded that adjusting the growth temperature and controlling the contact area between the solution surface and air can control the thickness of the thin film within a certain range, but the evaporation speed of absolute ethanol as the solvent is relatively fast, and a thin film with micron-level thickness is not obtained.

[0060] Control Group 1

[0061] According to the similar experimental steps of Example 2, absolute ethanol is replaced by pure water, and the solvent (pure water) of Control Group 1 and the growth temperature, sample number and growth time, film growth condition are recorded as shown in Table 2 (here, the growth time and film growth condition only represent the time of growing the thin film into a whole thin film (60 mm 2 ), if the growth is continued, the thickness of the thin film will be increased accordingly). Taking the 2#B2 experiment of Control Group 1 as an example, the growth process of the single crystal thin film is shown in Figure 4 .

[0062] Table 2: The solvent (pure water) of Control Group 1 and the growth temperature, sample number and growth time, film growth condition

[0063]

[0064] From the experimental results of Control Group 1, it can be concluded that using pure water as the solvent can further control the thickness of the thin film, and can make it reach micron-level thickness, even 3 microns. Here, only one example is taken as an example, the morphology of the film obtained by 2#B1 is characterized by atomic force microscope, as shown in Figure 7 , where (a) is 50 μm×50μm, (b) is 20 μm×20 μm, from the figure, it can be seen that the formed (C7H 16 N)2CuBr4 is a dense single crystal thin film, and the layered structure can also be clearly seen from the microstructure, but the disadvantage is that the growth time of Control Group 1 is longer, which needs to be further optimized.

[0065] Control Group 2

[0066] According to the experimental results of Example 2 and Control Group 1, the similar experimental procedures of Example 2 were followed, and anhydrous ethanol was replaced by anhydrous ethanol: water = 1 : 1, and the solvent (anhydrous ethanol: water = 1 : 1) of Control Group 2, growth temperature, sample number and growth time, film growth conditions were recorded as shown in Table 3 (here, the growth time and film growth conditions represent the time when the thin film is grown as a whole film (60 mm x 60 mm), and if it is allowed to continue to grow, the thickness of the thin film will be increased accordingly). 2

[0067] Table 3: Solvent (anhydrous ethanol: water = 1 : 1) of Control Group 2, growth temperature, sample number and growth time, film growth conditions

[0068]

[0069] The experimental results obtained from Control Group 2 show that using anhydrous ethanol: water = 1 : 1 as the solvent not only allows the thickness of the thin film to be controlled to reach the micron level, but also optimizes the growth time, which can be controlled within 62 hours. Here, only 3#B2 and 3#C2 are taken as examples, and the films obtained from 3#B2 and 3#C2 are observed by polarizing microscope, as shown in Figure 8 , where (a) is 3#C2 and (b) is 3#B2. As can be seen from the figure, 3#C2 has obvious grain boundaries and more defects, and 3#B2 has no obvious grain boundaries and defects.

[0070] Example 3

[0071] The sample obtained in Example 1 was characterized by X-ray single crystal diffractometer, and the crystal structure was analyzed by Olex2. The molecular formula is (C7H 16 N)2CuBr4. The results are shown in Figure 5 . The crystal material crystallizes in the Pbca space group, and Cu 2+ is coordinated with six Br - to form an octahedral structure, and [CuBr6] 4- octahedra are connected in an angular sharing manner and separated by protonated cyclohexylmethylamine cations along the a-axis direction to form a two-dimensional perovskite layer.

[0072] The powder XRD diffraction pattern of (C7H 16 N)2CuBr4 is shown in Figure 4 . The experimentally measured powder XRD diffraction pattern is basically consistent with the pattern obtained by simulating single crystal data, indicating that the sample prepared is a pure phase.

[0073] Example 4

[0074] ​This embodiment compares the (C7H) prepared in the preferred embodiment of embodiment 1, step (5). 16 A N)2CuBr4 perovskite single crystal film was further used to fabricate an X-ray detector. A schematic diagram of the fabricated detector is shown below. Figure 1 As shown.

[0075] The specific steps are as follows: Prepare (C7H) 16 The N)2CuBr4 perovskite single crystal film, with a thickness of approximately 0.56 mm, was dried in a vacuum drying oven, then subjected to surface treatment in a plasma cleaning machine, and finally deposited with a gold electrode with a thickness of approximately 120 nm.

[0076] The prepared (C7H) 16 The X-ray responsiveness of N)₂CuBr₄ was tested using an X-ray detector at an X-ray dose rate of 12.23 μGyair·s⁻¹. -1 The applied bias voltage is -1V. The test results are as follows: Figure 6 As shown, the detector has a dark current of 0.11 pA, a photocurrent of 10.1 pA, and an on / off ratio of 91.8.

[0077] As shown above, we have successfully prepared a novel two-dimensional copper bromide-based perovskite material. By adjusting the interfacial interaction between the solvent surface and air, we can achieve the adjustment of the (C7H) range within a certain range (3-560 μm in this example), such as (C7H). 16 The thickness of perovskite single crystal films such as N)2CuBr4 was increased to enable the application of copper bromine-based perovskites in the field of X-ray detection.

[0078] The test conditions involved in this invention are as follows:

[0079] X-ray single-crystal diffraction was performed on a Rigaku XtaLAB Synergy R, HyPix single-crystal diffractometer with a Mo target and a Kα radiation source (λ = 0.71073 nm) at a test temperature of 298 K. Crystal structure determination was performed using Olex 2 (1.5-alpha) software, with initial solution obtained using the ShelXT program and refinement completed using the shelXL program.

[0080] X-ray powder diffraction phase analysis was performed on a Rigaku Dmax X-ray diffractometer.

[0081] Photocurrent testing and analysis were performed on a Keithley 4200A-SCS parameter analyzer.

[0082] The polarizing microscope used was a Nikon Eclipse E600 POL model, and the reflected light mode was used during the test.

[0083] The atomic force microscope used was an Asylum Research atomic force microscope, model MFP-3D, with a Pt / Ir-coated silicon cantilever probe.

[0084] The above detailed description of the specific embodiments of the present application is only as an example, and the present application is not limited to the above described specific embodiments. Any equivalent modifications and substitutions made by those skilled in the art to the present application are also within the scope of the present application. Therefore, equivalent transformations and modifications made without departing from the spirit and scope of the present application should be encompassed within the scope of the present application.

Claims

1. A large area lead-free perovskite single crystal film, characterized by: The large-area lead-free perovskite single-crystal film is a crystal material composed of a compound of the following molecular formula: (C7H 16 N)2CuBr4. (C7H 16 N) + is a protonated cyclohexylmethylamine cation; The crystal material belongs to an orthorhombic system, crystallizes in space group Pbca, and has cell parameters of: a (A) = 8.20~8.25; b (A) = 7.75~7.80; c (A) = 33.15~33.20; alpha (°) = beta (°) = gamma (°) = 90; V (A 3 ) =2106.68~2136.42; The large-area lead-free perovskite single-crystal film is composed of cyclohexylmethylamine cations and [CuBr4] 2- anions, and (C7H 16 N)2CuBr4 is composed of [CuBr6] 4- octahedra are connected at the same vertex, and the two-dimensional perovskite layer is separated by cyclohexylmethylamine cations protonated along the a-axis direction.

2. A method for preparing a large-area lead-free perovskite single-crystal film, characterized in that: The single crystal film is prepared by solvent evaporation method, and the copper source, bromine source, cyclohexylmethylamine and solvent are mixed at room temperature, and then the solvent is evaporated at 25-70 DEG C to grow single crystal film, so that the large-area lead-free perovskite single crystal film is prepared; the mixing molar ratio of the copper source, cyclohexylmethylamine and bromine source is 1:2:2; wherein the amount of substance of the copper source is calculated based on the amount of substance of copper element contained therein, and the amount of substance of the bromine source is calculated based on the amount of substance of bromine element contained therein. The copper source is selected from one or more of copper bromide, copper sulfate and copper nitrate. The bromine source is selected from bromic acid.

3. The method of claim 2, wherein the method further comprises: Specifically comprising the following steps: S1, preparing a precursor solution of lead-free two-dimensional perovskite material, and treating a container to be used for single crystal growth; S2, filtering the prepared precursor solution with a corresponding filter, and then adding the filtered solution into the treated container; the filter is one of an organic filter and an aqueous filter; S3, growing the precursor solution into a single crystal under certain conditions to obtain the lead-free two-dimensional perovskite material; the temperature for growing the precursor solution into a single crystal is 25-70 DEG C, and the film forming time is not less than 1 hour.

4. The method of claim 3, wherein the method further comprises: In S1, the precursor solution is prepared by using cyclohexylmethylamine as an organic amine cation and CuBr2 as a raw material, stirring CuBr2 in a solvent until it is dissolved, then adding protonated cyclohexylmethylamine, and reacting at room temperature, and then crystallizing by evaporating the solvent at 25-70 DEG C; In S1, the container to be used for single crystal growth is treated by sequentially ultrasonicating the container in deionized water and anhydrous ethanol for 15 minutes, drying the container with nitrogen, and cleaning the container with an ion cleaning machine.

5. The method of claim 4, wherein the method further comprises: The solvent used for preparing the precursor solution is one or more of deionized water, anhydrous ethanol, acetonitrile, methanol, isopropanol, dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF).

6. The method of claim 4, wherein the method further comprises: The solvent used for preparing the precursor solution is one or a mixture of two of anhydrous ethanol and deionized water.

7. The method of claim 4, wherein the method further comprises: The solvent used for preparing the precursor solution is anhydrous ethanol and deionized water, and the ratio of anhydrous ethanol to deionized water is 0-3:

1.

8. The use of the large-area lead-free perovskite single crystal film according to claim 1 in the preparation of an X-ray detector, wherein the preparation of the X-ray detector comprises the following steps: drying the prepared perovskite single crystal film with a thickness of 0.56 mm in a vacuum drying oven, treating the surface of the film in an ion cleaning machine, and then evaporating a gold electrode with a thickness of 120 nm on the surface of the film to obtain an X-ray detector based on the perovskite single crystal.

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