Preparation method and application of (nh4)az3 type ternary metal halide monocrystal nanosheet

Abstract

The application relates to the field of metal halide perovskite materials, in particular to a preparation method and application of (NH4)AZ3 type ternary metal halide monocrystal nanosheets. First, a layered (NH4)AZ3 type ternary halide monocrystal material is prepared by using a chemical gas phase transport method, taking metal Bi and Sb and NH4I and NH4Br as precursors, taking elemental iodine or Br as a transport agent, and controlling the reactant composition, the reaction end and growth end temperature and the temperature difference, and (NH4)AZ3 nanosheets are obtained by a mechanical stripping method or a solution intercalation stripping method. The method is simple in process, the obtained ternary halide monocrystal material does not need to introduce long-chain amine organic ligands to passivate the surface and can be stripped into monocrystal nanosheets, different layer number monocrystal nanosheets can be obtained by controlling the stripping conditions, the monocrystal nanosheets have thickness-dependent band gaps, high crystalline quality and photoelectric properties, and can be widely applied to light-emitting diodes, photoelectric detectors and other photoelectric devices.

Description

Technical Field

[0001] This invention relates to the field of metal halide perovskite materials, specifically to a method for preparing (NH4)AZ3 type ternary metal halide single-crystal nanosheets and their applications. Background Technology

[0002] Ternary metal halide perovskites, due to their high carrier mobility and high light absorption coefficient, have broad application prospects in solar cells, light-emitting diodes, and photodetectors. Compared to three-dimensional (3D) metal halide perovskites, 2D metal halide perovskite materials with quantum confinement effects exhibit greater advantages in optoelectronic devices due to their stronger stability, higher photosensitivity, and thickness-dependent band gap. However, 2D perovskite materials are typically formed by introducing long-chain amine organic ligands into the 3D perovskite structure and cutting the 3D structure along a certain direction to create a layered structure. Although the passivation effect of long-chain amine organic ligands on surface dangling bonds and defects greatly improves the stability of 2D perovskite materials, the resulting 2D perovskite materials always exhibit strong H-halogen interactions, which can easily suppress the transport properties of optoelectronic materials. Moreover, during the preparation process, the lattice mismatch between the organic amine and the perovskite can easily lead to large lattice distortions.

[0003] Layered materials are a new type of material where the layers are bonded by strong covalent or ionic bonds within each other, while the layers are stacked together by weak van der Waals forces. These materials can be easily exfoliated to obtain corresponding 2D nanosheets. Chemical vapor transport (CVT) is a method for growing high-quality single-crystal materials. It typically involves heating or other conditions to volatilize substances and induce chemical reactions, which are then transported to a lower temperature location to crystallize and grow a single crystal. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing (NH4)AZ3 type ternary metal halide single-crystal nanosheets and its application. This method is easy to control and adopts chemical vapor transport method. Different layered single crystals are obtained by controlling the composition of reactants, the temperature and temperature difference between the reaction end and the growth end, and the exfoliation conditions are controlled to obtain single-crystal nanosheets with different numbers of layers.

[0005] The technical solution of this invention is:

[0006] A method for preparing (NH4)AZ3 type ternary metal halide single-crystal nanosheets involves first using a chemical vapor transport method with metal Bi or Sb and NH4I or NH4Br as precursors and elemental iodine or bromine as transport agent to prepare layered (NH4)AZ3 ternary halide single-crystal materials. Then, single-crystal nanosheets are obtained by mechanical exfoliation or solution intercalation exfoliation. This method obtains different layered (NH4)AZ3 type ternary halide materials by controlling the type of precursor salt, the temperature and temperature difference between the reaction end and the growth end, and controls the exfoliation conditions to obtain single-crystal nanosheets with different numbers of layers.

[0007] The preparation method of the (NH4)AZ3 type ternary metal halide single crystal nanosheets, which uses the "chemical vapor transport" method to prepare layered (NH4)AZ3 type ternary halide single crystal materials, is as follows: First, the reactants, which are a mixture of metal Bi or Sb, halide salt NH4I or NH4Br, and elemental iodine or bromine, are sealed in a quartz reactor; then, the quartz reactor is placed in a tube furnace, and the temperature at both ends of the quartz reactor is controlled so that the reactants volatilize, decompose, and undergo a chemical reaction at the high-temperature reaction end, and then the layered (NH4)AZ3 type ternary halide single crystal material is deposited and grown at the low-temperature growth end; finally, the elemental iodine or bromine is removed by vacuum heating.

[0008] The preparation method of the (NH4)AZ3 type ternary metal halide single crystal nanosheets, in the process of preparing layered (NH4)AZ3 type ternary halide single crystal materials by chemical vapor transport method, the content of metal Bi or Sb in the reactants is 20wt% to 38.6wt%, the content of NH4I and NH4Br in the reactants is 40wt% to 51.2wt%, and the content of transport agent elemental iodine or bromine in the reactants is 10.2wt% to 40wt%.

[0009] The preparation method of the (NH4)AZ3 type ternary metal halide single crystal nanosheets, in the process of preparing layered (NH4)AZ3 type ternary halide single crystal materials by chemical vapor transport method, controls the temperature of the high-temperature reaction end of the quartz reactor to be 450℃~750℃, the temperature of the low-temperature growth end to be 200℃~450℃, the temperature gradient between the high-temperature reaction end and the low-temperature growth end to be 25~30℃ / cm, and the reaction time to be 72h~168h.

[0010] The method for preparing (NH4)AZ3 type ternary metal halide single-crystal nanosheets involves removing the transport agent elemental iodine or bromine by vacuum annealing at a temperature of 60℃~90℃ for 12h~24h.

[0011] The method for preparing (NH4)AZ3 type ternary metal halide single-crystal nanosheets involves obtaining (NH4)AZ3 type ternary metal halide single-crystal nanosheets with different numbers of layers using mechanical exfoliation or solution intercalation exfoliation. The mechanical exfoliation method involves repeatedly thinning the ternary halide single-crystal material using Scotch tape or blue film tape. The solution intercalation exfoliation method involves placing the prepared layered (NH4)AZ3 type ternary halide single-crystal material in an N-methylpyrrolidone solution for ultrasonic exfoliation; or intercalating the single-crystal material in a reaction vessel containing a 0.5 mmol / L to 2 mmol / L n-butyllithium hexane solution, followed by ultrasonic exfoliation in solvents such as ethanol, isopropanol, or formamide.

[0012] The method for preparing (NH4)AZ3 type ternary metal halide single crystal nanosheets yields (NH4)AZ3 type ternary metal halide single crystal nanosheets with 1 to 100 layers, a thickness of 0.75 nm to 75 nm, and a band gap of 3.5 eV to 1.4 eV.

[0013] The application of the (NH4)AZ3 type ternary metal halide single-crystal nanosheets obtained by this method is that the (NH4)AZ3 type ternary metal halide single-crystal nanosheets have thickness-dependent band gaps, high crystal quality and excellent photoelectric properties, and are widely used in optoelectronic devices such as light-emitting diodes or photodetectors.

[0014] The design concept of this invention is:

[0015] This invention employs a chemical vapor transport-exfoliation method to prepare a novel (NH4)AZ3 type ternary metal halide single-crystal nanosheet. First, a layered (NH4)AZ3 type ternary metal halide single-crystal material is prepared using Bi, Sb, NH4I, and NH4Br as precursors and elemental iodine or Br as transport agents via chemical vapor transport. Elemental iodine or Br sublimates upon heating at the high-temperature reaction end, acting as a transport agent, and reacts directly with Bi or Sb to generate the corresponding trihalides BiI3, SbI3, BiBr3, and SbBr3. These metal halides, as core reactants, can further react with volatilized NH4I, NH4Br, or their decomposition products, and finally, are transported to the low-temperature growth end to crystallize and grow layered (NH4)AZ3 type ternary halide single crystals. In the (NH4)AZ3 type ternary metal halide, A represents Bi or Sb, and Z represents I or Br. This method is easily controlled; different layered (NH4)AZ3-type ternary metal halide single-crystal materials can be prepared by adjusting the reactant composition and controlling the reaction temperature and temperature difference. Since the resulting ternary halide material layers lack surface dangling bonds and are connected by weak van der Waals forces, the corresponding 2D single-crystal nanosheets can be easily obtained through exfoliation, eliminating the need for surface passivation with long-chain amine organic ligands. Furthermore, the chemical vapor transport method produces high-quality single-crystal materials with few defects, reducing the scattering of charge carriers by defects and significantly minimizing non-radiative recombination losses. In addition, the quantum confinement effect gives the band gap and photoelectric properties of the single-crystal nanosheets a layer-number dependence. Therefore, the resulting 2D single-crystal nanosheets exhibit excellent photoelectric properties and are expected to find wide applications in optoelectronic devices.

[0016] The advantages and beneficial effects of this invention are:

[0017] 1. This invention proposes to use trihalides with layered structures, such as BiI3, SbI3, BiBr3, and SbBr3, as core reactants to develop a chemical vapor phase transport method for preparing layered (NH4)AZ3 type ternary halide single crystal materials. Single crystal nanosheets can be obtained through simple exfoliation without surface passivation, solving the problem that the introduction of long-chain organic ligands will inhibit the transport performance of 2D ternary metal halide materials and cause lattice distortion.

[0018] 2. The (NH4)AZ3 type ternary metal halide single-crystal nanosheets obtained by this invention have thickness-dependent band gaps, high crystal quality and excellent photoelectric properties, and can be widely used in optoelectronic devices such as light-emitting diodes and photodetectors. Attached Figure Description

[0019] Figure 1 This is a flowchart of the "chemical vapor transport-exfoliation" method for preparing layered (NH4)AZ3 type ternary metal halide single crystal materials according to the present invention.

[0020] Figure 2 Macroscopic photograph (left) and microscopic transmission electron microscope photograph (right) of (NH4)BiI3 single crystal prepared by the "chemical vapor transport method" in Example 1.

[0021] Figure 3 The image shows a scanned image of a 10-15 layer (NH4)BiI3 single-crystal nanosheet obtained by mechanical peeling with Scotch tape in Example 1. Detailed Implementation

[0022] In the specific implementation process, the present invention utilizes the "chemical vapor transport" method, using metals Bi, Sb and NH4I, NH4Br as precursors, and elemental iodine or Br as transport agent. By controlling the composition of reactants, the temperature and temperature difference between the reaction end and the growth end, a ternary metal halide single crystal material with a layered structure (NH4)AZ3 is prepared. 2D single crystal (NH4)AZ3 single crystal nanosheets are obtained by mechanical exfoliation or solution intercalation exfoliation.

[0023] like Figure 1As shown, this invention first prepares layered (NH4)AZ3 type ternary metal halide single crystal materials via a "chemical vapor transport" method. The reactants, metallic Bi or Sb, halide salts NH4I or NH4Br, and transport agents, elemental iodine or bromine, are mixed and sealed in a quartz reactor. The content of metallic Bi or Sb is 20wt%–38.6wt%, the content of halide salts NH4I or NH4Br is 40wt%–51.2wt%, and the content of transport agents elemental iodine or bromine is 10.2wt%–40wt%. Then, the quartz reactor is placed in a tube furnace, allowing the reactants to volatilize, decompose, and undergo chemical reactions at the high-temperature reaction end. The reaction proceeds, thereby depositing and growing layered (NH4)AZ3 type ternary metal halide single crystal materials at the low-temperature growth end. The temperature at the high-temperature reaction end of the quartz reactor is 450℃~750℃, and the temperature at the low-temperature growth end is 200℃~450℃. The temperature gradient between the high-temperature reaction end and the low-temperature growth end is 25~30℃ / cm, and the reaction time is 72h~168h. After cooling to room temperature, the sample is taken out and the elemental iodine or bromine is removed by vacuum annealing at a temperature of 60℃~90℃ for 12h~24h. Finally, the obtained layered (NH4)AZ3 type ternary metal halide single crystal material was mechanically exfoliated using Scotch tape (manufactured by 3M Corporation, USA) or blue film tape; or ultrasonically exfoliated in N-methylpyrrolidone (NMP) solution; or intercalated in a reaction vessel with a solution of 0.5 mmol / L to 2 mmol / L n-butyllithium hexane, and ultrasonically exfoliated in solvents such as ethanol, isopropanol or formamide to obtain 1 to 100 layers of (NH4)AZ3 type ternary metal halide single crystal nanosheets with a thickness of 0.75 nm to 75 nm and a band gap of 3.5 eV to 1.4 eV.

[0024] To make the technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0025] Example 1:

[0026] In this embodiment, metallic Bi, the halide salt precursor NH4I, and the transport agent elemental iodine were first mixed and sealed in a quartz reactor; wherein the content of metallic Bi was 35.5 wt%, the content of NH4I was 40 wt%, and the content of elemental iodine was 24.5 wt%. Then, the quartz reactor was placed in a tube furnace, and the temperature of the high-temperature reaction end of the quartz reactor was controlled at 500°C, the temperature of the low-temperature growth end was controlled at 300°C, and the temperature gradient between the high-temperature reaction end and the low-temperature growth end was 25°C / cm. This allowed metallic Bi and I2 to sublimate and react at the high-temperature reaction end to form BiI3, which further reacted with NH4I or its decomposition products and grew into (NH4)BiI3 at the low-temperature growth end. After reacting for 100 h, the sample was cooled to room temperature and removed. After vacuum annealing at 60°C for 12 h, layered (NH4)BiI3 single crystal material was obtained. Figure 2 Finally, 10–15 layers of (NH4)BiI3 single-crystal nanosheets were obtained by mechanical exfoliation with Scotch tape. Figure 3 Its thickness is 7.5–11.25 nm and its band gap is ~2.0 eV.

[0027] The obtained (NH4)BiI3 single-crystal nanosheets were transferred onto a SiO2 / Si substrate with electrodes to fabricate a transistor-type photodetector with a detectivity of 10. 4 A / W.

[0028] Example 2:

[0029] The difference from Example 1 is that the temperature of the high-temperature reaction end of the quartz reactor was controlled at 450°C, the temperature of the low-temperature growth end was controlled at 300°C, the temperature gradient between the high-temperature reaction end and the low-temperature growth end was 28°C / cm, and the reaction time was 72h. Finally, intercalation was carried out in a reactor with a 2mmol / L n-butyllithium hexane solution, followed by ultrasonic exfoliation in isopropanol solution to obtain a dispersion of 5-10 layers of single-crystal nanosheets with a thickness of 3.75nm-8.25nm and a band gap of ~3.0eV.

[0030] The obtained (NH4)BiI3 single-crystal nanosheet dispersion was spin-coated to form a film as the light-emitting layer, and a blue light-emitting diode with the structure ITO / PEDOT:PSS / PVK / (NH4)BiI3 / TPBi / LiF / Al was prepared with an external quantum efficiency of 1.25%.

[0031] Example 3:

[0032] The difference from Example 1 is that the metal used is Sb. The mixture of Sb, NH4I, and elemental iodine contains: 32 wt% Sb, 45 wt% NH4I, and 23 wt% iodine transport agent. The temperature of the high-temperature reaction end of the quartz reactor is controlled at 600°C, and the temperature of the low-temperature growth end is controlled at 300°C, with a temperature gradient of 26°C / cm between the high-temperature reaction end and the low-temperature growth end. The reaction time is 150 h, and finally, large single crystals are obtained by vacuum annealing at 60°C for 12 h. Finally, 10–15 layers of (NH4)SbI3 single-crystal nanosheets with a thickness of 7.5–11.25 nm and a band gap of 3.1 eV are obtained by mechanically peeling with blue film tape.

[0033] The obtained (NH4)SbI3 single-crystal nanosheets were transferred onto a SiO2 / Si substrate with electrodes to fabricate a transistor-type photodetector with a detectivity of 10. 3 A / W.

[0034] Example 4:

[0035] The difference from Example 3 is that the temperature of the high-temperature reaction end of the quartz reactor was controlled at 450°C, the temperature of the low-temperature growth end was controlled at 250°C, the temperature gradient between the high-temperature reaction end and the low-temperature growth end was 25°C / cm, and the reaction time was 72h. Finally, after intercalation with 2mmol / L n-butyllithium solution, a dispersion of 5-10 layers of (NH4)SbI3 single-crystal nanosheets was obtained by exfoliation in formamide solution, with a thickness of 3.75-8.25nm and a band gap of 3.65eV.

[0036] The obtained (NH4)SbI3 single-crystal nanosheet dispersion was used to prepare a light-emitting layer by spin coating, and a blue light-emitting diode with the structure ITO / PEDOT:PSS / PVK / (NH4)SbI3 / TPBi / LiF / Al was prepared with an external quantum efficiency of 0.3%.

[0037] Example 5:

[0038] The difference from Example 4 is that, after intercalation with a 0.5 mmol / L n-butyllithium hexane solution, a dispersion of 50-60 single-crystal nanosheets with a thickness of ~37.5 nm and a band gap of ~2.5 eV was obtained by ultrasonic exfoliation in ethanol.

[0039] The obtained (NH4)SbI3 single-crystal nanosheet dispersion was used to prepare a light-emitting layer by spin coating, and a green light-emitting diode with the structure ITO / PEDOT:PSS / PVK / (NH4)SbI3 / TPBi / LiF / Al was prepared with an external quantum efficiency of 1.5%.

[0040] Example 6:

[0041] The difference from Example 1 is that the driving salt used was NH4Br, with an NH4Br content of 40 wt%, and the transport agent was bromine, with a content of 24.5%, the remainder being metallic Bi. The temperature of the high-temperature reaction end of the quartz reactor was controlled at 650°C, and the temperature of the low-temperature growth end was controlled at 200°C, with a temperature gradient of 30°C / cm between the high-temperature reaction end and the low-temperature growth end. Metallic Bi and Br2 were sublimated and reacted at the high-temperature reaction end to form BiBr3, which further reacted with NH4Br to form layered (NH4)BiBr3. The reaction time was 160 h, and then the sample was cooled to room temperature and removed. After vacuum annealing at 80°C for 18 h, layered (NH4)BiBr3 single crystal material was obtained. Finally, ultrasonic exfoliation in NMP solution was performed to obtain 5-10 layers of single-crystal nanosheets with a thickness of 3.75 nm to 8.25 nm and a band gap of ~3.25 eV.

[0042] A transistor-type photodetector with a detectivity of 10⁻⁶ was fabricated by transferring the obtained (NH₄)BiBr₃ single-crystal nanosheets onto a SiO₂ / Si substrate with electrodes. 4 A / W.

[0043] Example 7:

[0044] The difference from Example 1 is that the driving salt used is NH4Br, with an NH4Br content of 45 wt%, and the transport agent is bromine, with a content of 34.5 wt%, with the remainder being metallic Sb. The temperature of the high-temperature reaction end of the quartz reactor is controlled at 750°C, and the temperature of the low-temperature growth end is controlled at 300°C, with a temperature gradient of 30°C / cm between the high-temperature reaction end and the low-temperature growth end. Metallic Sb and Br2 are sublimated and react to form SbBr3 at the high-temperature reaction end, which further reacts with NH4Br to form layered (NH4)SbBr3. The reaction time is 160 h, and then the sample is cooled to room temperature and taken out. After vacuum annealing at 80°C for 20 h, layered (NH4)SbBr3 single crystal material is obtained. Finally, ultrasonic exfoliation is performed in isopropanol solution to obtain 1 to 5 layers of single crystal nanosheets with a thickness of 1.25 nm to 6.05 nm and a band gap of ~3.5 eV.

[0045] The obtained (NH4)SbBr3 single-crystal nanosheets were transferred onto a SiO2 / Si substrate with electrodes to fabricate a transistor-type ultraviolet photodetector with a detectivity of 10. 4 A / W.

[0046] The results of the embodiments show that the present invention first grows a layered structure of a (NH4)AZ3 type ternary halide single crystal material using a chemical vapor transport method. Then, (NH4)AZ3 type ternary metal halide single crystal nanosheets are obtained using mechanical exfoliation or solution intercalation exfoliation. This method is simple, and by controlling the type of precursor salt, the temperature at the reaction end and the temperature difference between the growth end, different layered (NH4)AZ3 type ternary metal halide single crystals can be obtained, and single crystal nanosheets with different numbers of layers can be obtained by controlling the exfoliation conditions. The thickness and band gap of the obtained (NH4)AZ3 type ternary metal single crystal nanosheets are tunable, showing broad application potential in optoelectronic devices such as light-emitting diodes and photodetectors.

Claims

1. A method for preparing (NH4)AZ3 type ternary metal halide single-crystal nanosheets, characterized in that, First, using the "chemical vapor transport" method, layered (NH4)AZ3 ternary halide single-crystal materials are prepared with metallic Bi or Sb and NH4I or NH4Br as precursors and elemental iodine or bromine as transport agents. Then, single-crystal nanosheets are obtained by mechanical exfoliation or solution intercalation exfoliation. This method obtains different layered (NH4)AZ3 ternary halide materials by controlling the type of precursor salt, the temperature and temperature difference between the reaction end and the growth end, and controls the exfoliation conditions to obtain single-crystal nanosheets with different numbers of layers. The specific process for preparing layered (NH4)AZ3 type ternary halide single crystal materials using the "chemical vapor transport" method is as follows: First, the reactants, consisting of a mixture of metallic Bi or Sb, halide salts NH4I or NH4Br, and elemental iodine or bromine, are sealed in a quartz reactor. Then, the quartz reactor is placed in a tube furnace, and the temperatures at both ends of the reactor are controlled to allow the reactants to volatilize, decompose, and undergo a chemical reaction at the high-temperature reaction end, thereby depositing and growing layered (NH4)AZ3 type ternary halide single crystal materials at the low-temperature growth end. Finally, elemental iodine or bromine is removed by vacuum heating. In the preparation of layered (NH4)AZ3 type ternary halide single crystal materials by chemical vapor transport method, the content of metallic Bi or Sb in the reactants is 20 wt% ~ 38.6 wt%, the content of NH4I and NH4Br in the reactants is 40 wt% ~ 51.2 wt%, and the content of the transport agent elemental iodine or bromine in the reactants is 10.2 wt% ~ 40 wt%. In the process of preparing layered (NH4)AZ3 type ternary halide single crystal materials by chemical vapor transport method, the temperature of the high-temperature reaction end of the quartz reactor is controlled at 450 ℃ ~ 750 ℃, the temperature of the low-temperature growth end is controlled at 200 ℃ ~ 450 ℃, the temperature gradient between the high-temperature reaction end and the low-temperature growth end is 25 ~ 30 ℃ / cm, and the reaction time is 72 h ~ 168 h.

2. The method for preparing (NH4)AZ3 type ternary metal halide single-crystal nanosheets according to claim 1, characterized in that, The transport agent elemental iodine or bromine is removed by vacuum annealing at a temperature of 60℃~90℃ for 12 h~24 h.

3. The method for preparing (NH4)AZ3 type ternary metal halide single-crystal nanosheets according to claim 1, characterized in that, Ternary metal halide single-crystal nanosheets with different numbers of layers (NH4)AZ3 were obtained by mechanical exfoliation or solution intercalation exfoliation. Mechanical exfoliation involves repeatedly thinning the ternary halide single-crystal material using Scotch tape or blue film tape. The solution intercalation exfoliation method involves placing the prepared layered (NH4)AZ3 ternary halide single-crystal material in an N-methylpyrrolidone solution for ultrasonic exfoliation; or intercalating the single-crystal material in a reaction vessel containing a 0.5 mmol / L ~ 2 mmol / L n-butyllithium hexane solution, followed by ultrasonic exfoliation in solvents such as ethanol, isopropanol, or formamide.

4. The method for preparing (NH4)AZ3 type ternary metal halide single-crystal nanosheets according to claim 1, characterized in that, The obtained (NH4)AZ3 type ternary metal halide single-crystal nanosheets have 1 to 100 layers, a thickness of 0.75 nm to 75 nm, and a band gap of 3.5 eV to 1.4 eV.

5. An application of (NH4)AZ3 type ternary metal halide single-crystal nanosheets prepared using the method described in any one of claims 1 to 4, characterized in that, This method yields (NH4)AZ3 type ternary metal halide single-crystal nanosheets with thickness-dependent band gaps, high crystallinity, and excellent photoelectric properties, which can be widely used in the fields of light-emitting diodes or photodetectors.

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