Metal halide perovskite nanocrystalline film and preparation method and application thereof

Abstract

The invention relates to the technical field of electroluminescent materials, in particular to a metal halide perovskite nanocrystalline film and a preparation method and application thereof, and the method comprises the following steps: providing cesium bromide, lead bromide and an organic amine ligand; the preparation method comprises the following steps: dissolving cesium bromide and lead bromide in N, N-dimethylformamide to obtain a precursor solution; dissolving an organic amine ligand in the precursor solution to obtain a precursor-ligand mixed solution; and spin-coating the precursor-ligand mixed solution on a substrate, and carrying out annealing treatment to obtain the metal halide perovskite nanocrystalline film loaded on the substrate. The method can effectively inhibit the defect formation of the metal halide perovskite nanocrystalline film, and improves the photoluminescence performance of the metal halide perovskite nanocrystalline film.

Description

Technical Field

[0001] The present invention relates to the technical field of electroluminescent materials, and particularly relates to a metal halide perovskite nanocrystal thin film, a preparation method thereof, and an application thereof. Background Art

[0002] As a newly emerging electroluminescent material, metal halide perovskite has attracted wide attention worldwide due to its excellent photoluminescence quantum yield and stability. The optical and electronic properties of metal halide perovskite have a high tolerance to structural defects in the crystal, high synthesis feasibility, good optical properties, and excellent optoelectronic properties.

[0003] The main factors hindering the development and application of metal halide perovskite are the defect states inherent in the material itself. Generally speaking, the formation of defects is due to the different solubilities and ionic diversities of perovskite precursors in polar solvents (such as N,N-dimethylformamide or dimethyl sulfoxide), as well as the uncontrollable crystallization rate and crystallization process during the spin-coating process of the thin film. When preparing CsPbBr3 thin films, defects (such as pinholes, grain boundaries, and non-coordinated ions) will inevitably be introduced during the high-speed spin-coating process of film formation. Non-coordinated Pb ions are the most common ions in perovskite, and the presence of Pb ions destroys the integrity of the perovskite crystal structure. At the same time, through theoretical simulation calculations and experimental result analysis, it is shown that the incomplete perovskite octahedral structure will form defect states in the energy band, capture excitons at the same time, and reduce the exciton recombination efficiency, affecting the luminescence performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a metal halide perovskite nanocrystal thin film, a preparation method thereof, and an application thereof, which can effectively inhibit the formation of defects in the metal halide perovskite nanocrystal thin film and improve the photoluminescence performance of the metal halide perovskite nanocrystal thin film.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] In the first aspect, the present invention discloses a preparation method of a metal halide perovskite nanocrystal thin film, which includes:

[0007] Providing cesium bromide, lead bromide, and an organic amine ligand;

[0008] Dissolving cesium bromide and lead bromide in N,N-dimethylformamide to obtain a precursor solution;

[0009] Dissolving the organic amine ligand in the precursor solution to obtain a precursor ligand mixture;

[0010] Spin-coating the precursor ligand mixture on a substrate and performing annealing treatment to obtain a metal halide perovskite nanocrystal thin film supported on the substrate.

[0011] Furthermore, the concentration of the precursor in the precursor ligand mixture is 20 - 60 mM.

[0012] Furthermore, the concentration ratio of the organic amine ligand to the precursor in the precursor ligand mixture is 0.5 - 2:1.

[0013] Furthermore, the molar ratio of cesium bromide to lead bromide in the precursor solution is 1:1.

[0014] Furthermore, the organic amine ligand includes hexylamine, cyclohexylamine, octylamine, 4 - aminopiperidine or melamine.

[0015] Furthermore, the temperature of the annealing treatment is 120 - 125 °C, and the time is 20 - 30 min.

[0016] Furthermore, spin - coating the precursor ligand mixture on the substrate specifically includes: fixing the substrate on a spin coater, preheating the substrate at a preset temperature, dropping the precursor ligand mixture on the substrate, after standing for a preset time, performing spin - coating according to preset spin - coating parameters.

[0017] Furthermore, the substrate material is glass. Before spin - coating the precursor ligand mixture on the substrate, the substrate is pretreated; the pretreatment includes: placing the substrate in the prepared Piranha solution, then putting the solution with the substrate into a heating container box for heating to remove impurities on the substrate surface; then washing with ultrapure water, and after washing, storing the substrate in an anhydrous ethanol solution.

[0018] In a second aspect, the present invention discloses a metal halide perovskite nanocrystal thin film, which is prepared by using the above - mentioned preparation method of the metal halide perovskite nanocrystal thin film.

[0019] In a third aspect, the present invention discloses an application of the above - mentioned metal halide perovskite nanocrystal thin film in the preparation of luminescent materials.

[0020] The present invention has the following unexpected beneficial effects: The present invention uses an organic amine (hexylamine, cyclohexylamine, octylamine, 4 - aminopiperidine or melamine) as a ligand. On the one hand, the organic amine ligand enters the interior of the perovskite crystal through certain chemical actions, and the N element in the organic amine ligand interacts with Pb and Br elements, reducing the generation of non - coordinated ions and avoiding damaging the integrity of the perovskite crystal structure. On the other hand, the organic amine carbonizes and polymerizes at high temperatures, thereby forming a "protective shell" outside the crystal, playing a protective role for the perovskite, so that a higher temperature is required during pyrolysis to make the pyrolysis rate of the perovskite reach the fastest. The metal halide perovskite nanocrystal thin film prepared by the method of the present invention has good photoluminescence quantum yield, film fluorescence intensity retention rate, and good moisture and heat resistance stability. Description of the Drawings

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention.

[0022] Figure 1 Shows the ultraviolet-visible absorption spectra of metal halide perovskite nanocrystal films prepared based on different organic amine ligands in the embodiments of the present invention.

[0023] Figure 2 Shows the photoluminescence spectra of metal halide perovskite nanocrystal films prepared based on different organic amine ligands in the embodiments of the present invention.

[0024] Figure 3 Shows the SEM images and particle size distribution diagrams of metal halide perovskite nanocrystal films prepared based on different organic amine ligands in the embodiments of the present invention.

[0025] Figure 4 Shows the X-ray diffraction patterns of metal halide perovskite nanocrystal films prepared based on different organic amine ligands in the embodiments of the present invention.

[0026] Figure 5 Shows the fluorescence change curve diagrams of the water resistance stability of metal halide perovskite nanocrystal films prepared based on different organic amine ligands in the embodiments of the present invention.

[0027] Figure 6 Shows the fluorescence decay curves of metal halide perovskite nanocrystal films prepared based on different organic amine ligands in the embodiments of the present invention.

[0028] Figure 7 Shows the TGA heating curves and the corresponding first derivative curves of metal halide perovskite nanocrystal films prepared based on different organic amine ligands in the embodiments of the present invention

[0029] Figure 8 Shows one of the FT-IR spectra of metal halide perovskite nanocrystal films obtained based on different organic amine ligands in the embodiments of the present invention.

[0030] Figure 9 Shows another one of the FT-IR spectra of metal halide perovskite nanocrystal films obtained based on different organic amine ligands in the embodiments of the present invention.

[0031] Figure 10 Shows the XPS spectra of metal halide perovskite nanocrystal films prepared based on different organic amine ligands in the embodiments of the present invention. Specific Embodiments

[0032] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, rather than for limiting the protection scope of the present invention.

[0033] In one embodiment, the present invention provides a method for preparing a metal halide perovskite nanocrystal thin film, which includes:

[0034] Providing cesium bromide, lead bromide, and an organic amine ligand.

[0035] Dissolving cesium bromide and lead bromide in N,N-dimethylformamide to obtain a precursor solution.

[0036] Dissolving the organic amine ligand in the precursor solution to obtain a precursor ligand mixture.

[0037] Spin-coating the precursor ligand mixture on a substrate and performing annealing treatment to obtain a metal halide perovskite nanocrystal thin film supported on the substrate.

[0038] The present invention uses an organic amine (hexylamine, cyclohexylamine, octylamine, 4-aminopiperidine, or melamine) as a ligand, which can enter the interior of the perovskite crystal through certain chemical actions. The N element in the organic amine ligand interacts with Pb and Br elements, reducing the generation of non-coordinated ions and avoiding the destruction of the integrity of the perovskite crystal structure, which is beneficial to the formation of a stable and regular crystal structure and lays a foundation for the realization of subsequent excellent properties. A stable crystal structure is the key to ensuring the material properties and avoids the problem of performance degradation caused by crystal structure defects.

[0039] The organic amine will carbonize and polymerize at high temperatures to form a "protective shell" outside the crystal. This "protective shell" plays a protective role for the perovskite, making the perovskite require a higher temperature to reach the fastest pyrolysis rate during pyrolysis, enhancing the thermal stability of the perovskite. This is of great significance in practical applications. For example, in some environments that need to withstand higher temperatures, it can effectively prevent the perovskite material from failing due to pyrolysis and extend its service life and working stability.

[0040] The metal halide perovskite nanocrystal thin film prepared by this method has a good photoluminescence quantum yield. The improvement of the photoluminescence quantum yield means that more light energy is effectively utilized and converted into light emission, making the thin film have better application potential in the field of light emission (such as light-emitting diodes, fluorescence sensors, etc.) and capable of providing a brighter and more efficient light emission effect.

[0041] The metal halide perovskite nanocrystal thin film prepared by this method also has a good fluorescence intensity retention rate of the thin film, indicating that during use, the fluorescence performance of the thin film is not easily attenuated and can maintain a stable emission intensity for a long time. This is crucial for application scenarios that require long-term stable luminescence (such as display technology, bioimaging, etc.), improving the reliability and practicality of the material.

[0042] The metal halide perovskite nanocrystal thin film prepared by this method also has good damp heat stability, meaning that in a humid and high-temperature environment, the thin film can still maintain its performance and is not easily affected by moisture and heat to deteriorate. This broadens the application scope of the thin film, enabling it to be used under more complex environmental conditions, such as outdoor display devices, sensors in humid environments, etc.

[0043] The preparation method described in the present invention only requires one-step spin coating and annealing, without complex post-treatment (such as ion exchange, surface modification), and is suitable for large-scale preparation.

[0044] As a preferred embodiment of the present invention, the concentration of the precursor in the precursor ligand mixture is 20 - 60 mM.

[0045] At this concentration (20 - 60 mM), the precursor can provide more reaction sites, promote the rapid nucleation of nanocrystals, inhibit the excessive growth of crystals, and form nanocrystals with uniform size. And the ion diffusion rate in the solvent matches the crystallization rate, avoiding aggregation or defects caused by too high supersaturation. Moreover, if the concentration of the precursor is too high, it may lead to a high solution viscosity, making it difficult to spread during spin coating and forming an uneven thin film; if the concentration of the precursor is too low, uneven precipitation of nanocrystals may occur due to too fast solvent evaporation, resulting in pinholes or cracks. An appropriate precursor concentration can promote the lateral growth of nanocrystals and form a continuous thin film; too high a concentration may lead to vertical growth and form a porous structure, affecting the electrical properties.

[0046] As a preferred embodiment of the present invention, the concentration ratio of the organic amine ligand to the precursor in the precursor ligand mixture is 0.5 - 2:1.

[0047] If the concentration of the organic amine ligand is too low (lower than 0.5:1), it may not be able to completely cover the surface of the perovskite crystal and cannot effectively reduce the generation of non-coordinated ions, thus making it difficult to avoid the damage to the integrity of the perovskite crystal structure.

[0048] If the concentration of the organic amine ligand is too high (higher than 2:1), too many ligands may interfere with the normal growth of the perovskite crystal, resulting in distortion of the crystal structure, which is also not conducive to the integrity of the crystal structure.

[0049] A suitable concentration ratio helps the better carbonization and polymerization of organic amines at high temperatures to form a "protective shell". When the concentration ratio is 0.5 - 2:1, the amount of the organic amine ligand can not only ensure that there is enough amount on the crystal surface for carbonization and polymerization, but also will not be excessive to cause the carbonization and polymerization process to be too complex, affecting the quality of the "protective shell". When the concentration ratio is within this range, the thickness and compactness of the formed "protective shell" are more appropriate, which can effectively protect the perovskite and improve its thermal stability.

[0050] As a preferred embodiment of the present invention, the molar ratio of cesium bromide to lead bromide in the precursor solution is 1:1.

[0051] The general formula of metal halide perovskite is ABX3, where:

[0052] A site: Cs + (provided by CsBr);

[0053] B site: Pb 2+ (provided by PbBr2);

[0054] X site: Br - (provided jointly by CsBr and PbBr2).

[0055] When the molar ratio of CsBr to PbBr2 is 1:1, the total number of moles of Br - is 1×1 (CsBr) + 1×2 (PbBr2) = 3, meeting the stoichiometric requirement of A:B:X = 1:1:3 in the ABX3 structure.

[0056] The 1:1 ratio ensures that Cs + and Pb 2+ combine strictly according to the stoichiometric ratio, reducing the formation of A-site vacancies (V_Cs - ) and B-site vacancies (V_Pb 4- ). Vacancy defects are the main source of non-radiative recombination in perovskite materials, and the accuracy of the stoichiometric ratio directly affects the luminescence quantum yield.

[0057] When the ratio of Cs + to Pb 2+ is 1:1, the N atom in the organic amine ligand (such as hexylamine) is more likely to form a stable coordination with Pb 2+ , reducing the existence of non-coordinated Br - . If the ratio deviates, excessive Cs + or Pb 2+ will interfere with the coordination of the organic amine ligand with the target metal ion, reducing the defect passivation efficiency.

[0058] As a preferred embodiment of the present invention, the organic amine ligand includes hexylamine, cyclohexylamine, octylamine, 4-aminopiperidine or melamine.

[0059] As a preferred embodiment of the present invention, the temperature of the annealing treatment is 120-125°C, and the time is 20-30 min.

[0060] A suitable annealing temperature can effectively volatilize N,N-dimethylformamide (DMF) within a reasonable time, avoiding the adverse effects of solvent residues on the film properties. Residual solvents may cause holes or defects inside the film, affecting its uniformity and stability. Setting the annealing temperature at 120-125°C can volatilize most of the DMF, leaving a relatively dense perovskite nanocrystal structure.

[0061] Moreover, at this annealing temperature, organic amine ligands (such as hexylamine, cyclohexylamine, etc.) can undergo carbonization and polymerization reactions to form a "protective shell". The organic amine ligands start to undergo chemical changes at a temperature of 120-125°C, gradually carbonizing and polymerizing together to form a protective structure on the surface of the perovskite nanocrystals, enhancing the thermal stability and moisture and heat resistance stability of the film. If the temperature is too low, the ligands may not be fully carbonized and polymerized, and the quality and integrity of the "protective shell" will be affected; while too high a temperature may lead to excessive carbonization of the ligands, damaging the crystal structure of the perovskite.

[0062] Meanwhile, by reasonably defining the annealing process parameters, the atoms in the nanocrystals have sufficient energy to migrate and rearrange to fill the defects (such as vacancies, dislocations, etc.) in the crystal, improving the crystallinity of the crystal. Higher crystallinity is beneficial to enhancing the photoluminescence performance and electrical properties of the film and reducing non-radiative recombination centers.

[0063] As a preferred embodiment of the present invention, spin-coating the precursor ligand mixture on the substrate specifically includes the following steps:

[0064] Fix the substrate on the spin coater: Ensure that the substrate remains stable during spin coating, avoiding uneven distribution of the precursor ligand mixture due to shaking or displacement, thereby affecting the uniformity and quality of the film. Stable substrate fixation is the basis for the subsequent spin coating operation to proceed smoothly.

[0065] The substrate is preheated at a preset temperature: on the one hand, it can improve wettability. Preheating can change the physical properties of the substrate surface, enhance the wettability of the precursor ligand mixture on the substrate surface, and enable the mixture to spread more evenly on the substrate. For example, some substrates have a low surface energy at room temperature, making it difficult for the mixture to be evenly distributed. After preheating, the surface energy increases, which helps the mixture to spread. On the other hand, it can promote solvent evaporation. An appropriate preheating temperature can cause some solvents in the mixture (such as N,N-dimethylformamide) to evaporate in advance, making it easier to form a uniform thin film structure during spin coating. At the same time, it can also reduce the impact of solvent evaporation on the thin film structure during the subsequent annealing process and lower the possibility of holes or defects caused by rapid solvent evaporation.

[0066] Drop the precursor ligand mixture on the substrate: accurately dropping an appropriate amount of the mixture on the substrate is one of the key steps in forming a uniform thin film. The dropping position and amount will affect the initial distribution of the mixture on the substrate, and thus affect the thickness and uniformity of the final thin film.

[0067] Let it stand for a preset time: After dropping the mixture, let it stand for a period of time to allow the mixture to naturally diffuse and be evenly distributed on the substrate surface, reducing local non-uniformity caused by the dropping operation. This helps to form a relatively uniform liquid layer before spin coating and creates good conditions for the subsequent spin coating operation. Through the coordinated cooperation of substrate preheating and standing, it helps the precursor to form a more ordered initial arrangement on the substrate surface, providing a good foundation for the crystallization of perovskite nanocrystals during the subsequent annealing process.

[0068] Spin coat according to the preset spin coating parameters: Spin coating parameters (such as rotation speed, acceleration time, spin coating time, etc.) play a decisive role in the thickness, uniformity, and quality of the thin film. An appropriate rotation speed can cause the mixture to spread evenly on the substrate surface under the action of centrifugal force to form a thin film with the required thickness; the acceleration time and spin coating time affect the distribution of the mixture and the solvent evaporation process. By adjusting parameters such as rotation speed and spin coating time, the thickness of the thin film can be precisely controlled to meet the requirements of different application scenarios.

[0069] By reasonably performing the spin coating operation, it helps to improve the uniformity of the thin film. A uniform thin film distribution is also conducive to forming a more regular crystal structure, improving the crystallinity of the thin film, and thus enhancing the photoluminescence performance and stability of the thin film.

[0070] Stable substrate fixation, good wettability, uniform initial distribution, and appropriate spin coating parameters can enable the precursor ligand mixture to form a thin film with uniform thickness and consistent composition on the substrate, avoiding problems such as local over-thickness or under-thickness and non-uniform composition, thus ensuring the consistency of thin film performance.

[0071] As a preferred embodiment of the present invention, the substrate material is glass, and the substrate is pretreated before spin-coating the precursor ligand mixture.

[0072] The pretreatment includes: placing the substrate in a prepared Piranha solution, which is usually composed of concentrated sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) mixed in a certain proportion and has strong oxidizing properties. It can effectively remove organic pollutants, metal impurities, and other adsorbed substances on the glass substrate surface. The strong acidity of concentrated sulfuric acid and the strong oxidizing property of hydrogen peroxide act synergistically to oxidize and decompose these impurities, causing them to detach from the substrate surface.

[0073] Then, the solution with the substrate is placed in a heating container box for heating to remove impurities on the substrate surface. Heating helps to accelerate the chemical reaction between the Piranha solution and the impurities on the substrate surface, improving the cleaning effect. At an appropriate temperature, the activity of the Piranha solution is enhanced, enabling it to remove impurities more quickly and thoroughly.

[0074] Then, ultra-pure water is used for cleaning. Ultra-pure water has extremely low impurity content and can effectively rinse off the Piranha solution remaining on the substrate surface and the oxidized and decomposed impurities. Multiple cleanings can ensure that the substrate surface is clean and residue-free, providing a clean surface for the subsequent spin-coating operation.

[0075] After cleaning, the substrate is stored in an anhydrous ethanol solution. Anhydrous ethanol has good volatility and wettability. Storing the cleaned substrate in anhydrous ethanol can, on the one hand, further remove the moisture that may remain on the substrate surface and prevent the influence of moisture on the subsequent precursor ligand mixture; on the other hand, when the substrate is taken out for spin-coating, the volatilization of ethanol can keep the substrate surface clean and active to a certain extent, which is beneficial to the uniform spreading and adhesion of the mixture on the substrate.

[0076] The clean substrate surface after pretreatment enables the precursor ligand mixture to be more evenly distributed on the substrate, reducing the uneven distribution or agglomeration of the mixture caused by surface impurities, thereby improving the uniformity and quality of the spin-coated film. The clean substrate surface improves the interaction with the precursor ligand mixture and enhances the adhesion between the film and the substrate. This makes the film less likely to fall off during subsequent annealing treatment and use, improving the stability and reliability of the film. Moreover, the removal of impurities reduces the negative impact on the performance of the perovskite nanocrystal film. For example, metal impurities may act as non-radiative recombination centers, reducing the photoluminescence quantum yield of the film; organic pollutants may affect the crystal growth and structural integrity of perovskite. Therefore, the pretreated substrate helps to prepare a film with better performance, such as higher luminescence efficiency and better stability.

[0077] In another embodiment, the present invention discloses a metal halide perovskite nanocrystal thin film, which is prepared by using the preparation method of the metal halide perovskite nanocrystal thin film described in any of the above embodiments.

[0078] In another embodiment, the present invention discloses an application of the above-mentioned metal halide perovskite nanocrystal thin film in the preparation of luminescent materials.

[0079] The following is an analysis and description in combination with specific examples.

[0080] Example 1, a preparation method of a metal halide perovskite nanocrystal thin film, which includes the following steps:

[0081] Step 1, treatment of the glass substrate: Cut a brand-new unused glass sheet into a glass slide of 1 cm × 5 cm with a scribing instrument, then place the cut glass slide in a newly prepared Piranha solution, and then put the solution into an oven at 60 °C and heat for 1 h to fully remove organic and inorganic impurities on its surface. After treatment, wash the cut glass slide 3 times with ultrapure water, and then store it in an anhydrous ethanol solution. When in use, take out the glass slide and dry it, and then it can be used.

[0082] Step 2, provide 0.1 mmol of cesium bromide, 0.1 mmol of lead bromide and 0.2 mmol of octylamine (OA). First, dissolve 0.1 mmol of cesium bromide and 0.1 mmol of lead bromide in 2 mL of N,N-dimethylformamide (DMF). After the cesium bromide and lead bromide are completely dissolved, a precursor solution is obtained. Then add 0.2 mmol of octylamine to the precursor solution, dissolve it by ultrasonic treatment, and let it stand at room temperature for later use to obtain a precursor ligand mixture.

[0083] Step 3, dry the glass substrate reserved in anhydrous ethanol after the treatment in Step 1, fix it on a spin coater, turn on the spin coater, and set the rotation speed of the spin coating parameters to 1000 rpm and the time to 60 s.

[0084] Preheat the glass substrate to 50 °C, take 200 μL of the precursor ligand mixture prepared in Step 2 and drop it on the glass substrate, let it stand for 2 min, and then click the start button to perform spin coating.

[0085] After the spin coating is completed, raise the temperature to 125 °C and perform annealing treatment for 20 min. After the annealing is completed, wait for the temperature to gradually drop to room temperature, take out the successfully prepared thin film, and the obtained metal halide perovskite nanocrystal thin film is denoted as OA-CsPbBr3.

[0086] Example 2, different from Example 1, the provided organic amine ligand is 0.2 mmol of hexylamine (HA), and the remaining steps are the same as those in Example 1. The prepared metal halide perovskite nanocrystal film is denoted as HA-CsPbBr3.

[0087] Example 3, different from Example 1, the provided organic amine ligand is 0.2 mmol of cyclohexylamine (cHA), and the remaining steps are the same as those in Example 1. The prepared metal halide perovskite nanocrystal film is denoted as cHA-CsPbBr3.

[0088] Example 4, different from Example 1, the provided organic amine ligand is 0.1 mmol of 4-aminopiperidine (AP), and the remaining steps are the same as those in Example 1. The prepared metal halide perovskite nanocrystal film is denoted as AP-CsPbBr3.

[0089] Example 5, different from Example 1, the provided organic amine ligand is 0.05 mmol of melamine (MA), and the remaining steps are the same as those in Example 1. The prepared metal halide perovskite nanocrystal film is denoted as MA-CsPbBr3.

[0090] The metal halide perovskite nanocrystal films prepared in Examples 1 to 5 were characterized and analyzed.

[0091] 1) The metal halide perovskite nanocrystal films prepared in Examples 1 to 5 were respectively subjected to ultraviolet-visible absorption spectroscopy (UV-vis) analysis, and the results are shown in Figure 1 . It can be seen from Figure 1 that except for the metal halide perovskite nanocrystal film prepared based on 4-aminopiperidine in Example 4 with a maximum absorption wavelength at 510 nm, the maximum absorption wavelengths of the metal halide perovskite nanocrystal films prepared with other organic amine ligands are all around 515 nm, indicating that the film prepared with 4-aminopiperidine as the organic amine ligand has a relatively small size.

[0092] 2) The metal halide perovskite nanocrystal films prepared in Examples 1 to 5 were respectively subjected to photoluminescence spectroscopy analysis, and the results are shown in Figure 2 . It can be seen from Figure 2 the photoluminescence spectrum that the full width at half maximum of the emission peaks of the films prepared based on different organic amine ligands is about 11 nm, indicating that the prepared films have relatively good purity. At the same time, it can be seen from Figure 2 that the metal halide perovskite nanocrystal film prepared based on 4-aminopiperidine in Example 4 has the strongest fluorescence intensity.

[0093] 3) The metal halide perovskite nanocrystal films prepared in Examples 1 to 5 were respectively subjected to SEM analysis, and the results are shown in Figure 3 . It can be seen from Figure 3It can be seen that the sizes of the metal halide perovskite nanocrystal thin films prepared based on different organic amine ligands are relatively uniform. Moreover, the metal halide perovskite nanocrystal thin film prepared in Example 4 based on 4-aminopiperidine is different from other thin films. It is rod-shaped, relatively closely distributed, with a crystal size range of 16-26 nm and an average particle size of 18 nm.

[0094] 4) The metal halide perovskite nanocrystal thin films prepared in Examples 1 to 5 were respectively subjected to XRD analysis, and the results are shown in Figure 4 . The crystal forms of the thin films prepared based on different organic amine ligands are consistent with the XRD pattern of the orthorhombic phase CsPbBr3 standard card. It can be found in the figure that the diffraction peaks are relatively sharp and there are no obvious impurity peaks, indicating that the prepared CsPbBr3 thin film has a high purity.

[0095] 5) In order to explore the stability of the CsPbBr3 thin film prepared by the present invention, the metal halide perovskite nanocrystal thin films prepared in Examples 1 to 5 were placed in a damp heat environment with a humidity (RH) of 85% and a temperature (T) of 85 °C, and then the fluorescence spectra at different times were tested. The results are as Figure 5 shown. In the damp heat environment with a humidity (RH) of 85% and a temperature (T) of 85 °C, within 4 h, the fluorescence intensity retention rate of the thin film prepared in Example 4 based on 4-aminopiperidine is the best, which is 86.0% of the original, indicating that the prepared CsPbBr3 thin film as a whole has good damp heat stability.

[0096] 6) In order to explore the optical properties of the CsPbBr3 thin film, the photoluminescence quantum yields (PLQY) and decay lifetimes of the metal halide perovskite nanocrystal thin films prepared in Examples 3 to 5 were respectively tested. The results are as Figure 6 shown. The average lifetime (τ avr ) of the metal halide perovskite nanocrystal thin film prepared in Example 4 based on 4-aminopiperidine is 11.22 ns, and it exhibits a good photoluminescence quantum yield, with a PLQY reaching 55.7%.

[0097] 7) In order to explore the role of different organic amine ligands in the CsPbBr3 perovskite nanocrystal thin film, thermogravimetric analysis (TGA) was carried out on the metal halide perovskite nanocrystal thin films prepared in Examples 1 to 5. The results are as Figure 7 shown. Among them, the weight loss of the CsPbBr3 thin film prepared in Example 4 based on 4-aminopiperidine is only about 5.2% between 30 and 500 °C, which is due to the removal of the surface organic ligands. Then, due to the decomposition of the sample, the weight loss is very fast when the temperature is above 600 °C. The temperature at which the weight loss is the fastest is 658 °C, and the weight loss is 38.7%.

[0098] The temperature at which the weight loss of conventional ligand-free perovskite is the fastest is 585 °C, see Figure 7 As shown, for the perovskite with organic amine as the ligand, the temperature at which the weight loss is the fastest becomes about 650 °C. This may be because the perovskite crystal contains organic amine molecules, that is, the organic amine enters the interior of the perovskite crystal through a certain chemical action, and the organic amine is easily carbonized and polymerized at high temperature, thus playing a protective role for the perovskite outside the crystal, making it necessary to reach a higher temperature during pyrolysis to make the pyrolysis rate of the perovskite reach the fastest.

[0099] 8) Further understand the chemical interaction between the organic amine ligand and CsPbBr3 through Fourier transform infrared spectroscopy (FT-IR). The results are as Figure 8 and Figure 9 shown. The FT-IR spectra of CsPbBr3 thin films prepared based on different organic amine ligands all contain the stretching vibration of N-H at about 3500 cm -1 and the bending vibration of N-H at 1600 cm -1 . Pure amine has two sharp and narrow strong peaks at 3500 cm -1 and 3400 cm -1 , corresponding to the stretching vibration of N-H in the lattice. The bending vibration of N-H at 1600 cm -1 shows a sharp peak, and the overall peak intensity is relatively weaker than that of the pure amine, indicating the interaction between the organic amine ligand and CsPbBr3, and more ligands bind to the perovskite lattice. These peaks all indicate the presence of amine substances, and can also indicate good crystallinity in the lattice, no residual amine ligands, and relatively strong chemical interaction forces between the ligand and CsPbBr3.

[0100] 8) To explore the role of organic amine in CsPbBr3 perovskite nanocrystal thin films, X-ray photoelectron spectroscopy (XPS) tests were carried out on the metal halide perovskite nanocrystal thin films prepared in Examples 3 to 5. According to the original data obtained from the XPS test and formula calculation, the element ratio Cs:Pb:Br≈1:1:3 in the prepared CsPbBr3 was obtained. The binding energies of the split peaks of the Br element in the CsPbBr3 thin film prepared based on 4-aminopiperidine in Example 4 are Br3d3 / 2 69 eV and Br3d5 / 2 68.2 eV respectively, which are 0.3 eV and 0.3 eV lower than those of the pure CsPbBr3 thin film. The binding energies of the split peaks of the Pb element are Pb4f5 / 2 143.1 eV and Pb4f7 / 2 138.2 eV respectively, which are 0.2 eV and 0.2 eV lower than those of the pure CsPbBr3 thin film. The binding energy of the N element 1s is 399.5 eV, which is 1.1 eV higher than the binding energy of the N element 1s in pure -NH2;

[0101] It can be seen from Figure 10 that in the metal halide perovskite nanocrystal film prepared with 4-aminopiperidine as the organic amine ligand, the binding energies of Pb, Br, and N elements have changed, indicating that there are chemical interactions and metal ion coordination among them. The lone pair electrons on N can be biased towards the empty orbitals of the metal to produce a coordination effect. Such electron transfer results in a decrease in the electron cloud density of N and an increase in the electron cloud density of metal ions. At the same time, there is also an interaction between Br and N elements, leading to a decrease in the electron binding energy of Br and the production of a coordination effect. From the perspective of N, the decrease in the electron cloud density is comprehensively manifested as the strengthening of the nuclear positive charge effect, thus increasing the binding energy of N element; on the other hand, the increase in the electron cloud density of metal ions increases the shielding effect, resulting in 2+ a decrease in the electron binding energy of Pb and a shift of the XPS performance towards lower energy.

Claims

1. A method for preparing a metal halide perovskite nanocrystalline film, characterized in that: include: Provide cesium bromide, lead bromide and organic amine ligands; dissolving cesium bromide and lead bromide in N,N-dimethylformamide to obtain a precursor solution; dissolving an organic amine ligand in a precursor solution to obtain a precursor-ligand mixed solution; The precursor ligand mixed solution is spin-coated on the substrate and annealed to obtain a metal halide perovskite nanocrystalline film loaded on the substrate.

2. The method for preparing a metal halide perovskite nanocrystalline thin film according to claim 1, characterized in that: The concentration of the precursor in the precursor-ligand mixed solution is 20-60 mM.

3. The method for preparing a metal halide perovskite nanocrystalline thin film according to claim 2, characterized in that: The concentration ratio of the organic amine ligand to the precursor in the precursor-ligand mixed solution is 0.5-2:

1.

4. The method for preparing a metal halide perovskite nanocrystalline thin film according to claim 1, characterized in that: The molar ratio of cesium bromide to lead bromide in the precursor solution is 1:

1.

5. The method for preparing a metal halide perovskite nanocrystalline thin film according to claim 1, characterized in that: The organic amine ligand includes hexylamine, cyclohexylamine, octylamine, 4-aminopiperidine or melamine.

6. The method for preparing a metal halide perovskite nanocrystalline thin film according to claim 1, characterized in that: The annealing treatment is performed at a temperature of 120-125° C. and for a time of 20-30 minutes.

7. The method for preparing a metal halide perovskite nanocrystalline thin film according to claim 1, characterized in that: Spin coating the precursor-ligand mixed liquid on the substrate specifically includes: fixing the substrate on a spin coater, preheating the substrate at a preset temperature, dropping the precursor-ligand mixed liquid on the substrate, letting it stand for a preset time, and then spin coating according to preset spin coating parameters.

8. The method for preparing a metal halide perovskite nanocrystalline thin film according to claim 1, characterized in that: The substrate is made of glass, and the substrate is pretreated before the precursor-ligand mixed solution is spin-coated on the substrate; The pretreatment comprises: placing the substrate in a prepared Piranha solution, and then placing the solution with the substrate in a heating container box for heating to remove impurities on the surface of the substrate; The substrate is then washed with ultrapure water, and after washing, the substrate is stored in an anhydrous ethanol solution.

9. A metal halide perovskite nanocrystalline film, characterized in that: The film is prepared by the method for preparing the metal halide perovskite nanocrystalline film as described in any one of claims 1 to 8.

10. Use of the metal halide perovskite nanocrystalline film as claimed in claim 9 in preparing a light-emitting material.

Images