A method for preparing high-quality FAPbBr3 thin film in an ethyl acetate atmosphere in air

Abstract

The present application is directed to the problem that FAPbBr3 perovskite material is unstable in air and prone to phase change, and provides a method for preparing high-quality FAPbBr3 thin film in ethyl acetate atmosphere in air. The method adopts a spin coating process, and introduces ethyl acetate vapor atmosphere for treatment before annealing of the FAPbBr3 precursor wet film. Ethyl acetate effectively extracts high-boiling solvents in the precursor, while forming a hydrophobic protective atmosphere, inhibiting the erosion of moisture in the air to the thin film, and inducing the thin film to directly crystallize into a stable phase with photoactivity. The thin film prepared by the method has dense crystal grains, no pinholes and low defect state density, and the process is simple, does not require vacuum or glove box equipment, greatly reduces the preparation cost, and is conducive to large-area popularization and application.

Description

Technical Field

[0001] This invention relates to the field of electroluminescence technology, specifically to a method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air. Background Technology

[0002] Perovskite materials, as a novel semiconductor material, have shown great application potential in fields such as solar cells, light-emitting diodes (LEDs), and photodetectors. Among them, formamidine lead bromide (FAPbBr3) exhibits better thermal stability and superior photoelectric properties compared to the traditional methylamine lead bromide (MAPbBr3). However, FAPbBr3 suffers from severe phase instability. Furthermore, the preparation of perovskite thin films typically requires a glove box filled with inert gas (such as nitrogen) and strict control of water and oxygen content, which significantly increases production costs and process complexity. If FAPbBr3 is prepared in air, the moisture in the air makes it difficult to control the crystallization rate, resulting in a rough film surface, numerous pores, and high defect density, severely affecting the luminous efficiency and stability of the device. Currently, a simple and effective method for preparing high-quality FAPbBr3 thin films in high-humidity air environments is lacking. Summary of the Invention

[0003] This invention addresses the problem of how to prepare high-quality FAPbBr3 films in air by providing a method for crystallization assisted by an ethyl acetate atmosphere. This method introduces an ethyl acetate (EA) vapor atmosphere during film formation, utilizing the properties of ethyl acetate as an antisolvent and its immiscibility with water to effectively extract the precursor solvent and shield against water vapor, ultimately forming a dense and smooth FAPbBr3 film.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air, employing spin coating combined with an atmosphere-assisted annealing process; The precursor solution was prepared by dissolving FABr and PbBr2 in a DMF mixed solvent; The key step in film formation is to treat the wet film in an ethyl acetate vapor atmosphere after spin coating and before annealing.

[0005] In this invention, organic-inorganic hybrid FAPbBr3 is used as the luminescent thin film material. After spin-coating the precursor solution in air, a large amount of high-boiling-point solvent (DMF) remains in the wet film. If direct thermal annealing is performed, the solvent evaporates too quickly and is easily affected by air humidity, leading to pinholes. Placing the wet film in an ethyl acetate atmosphere allows ethyl acetate molecules to penetrate into the wet film, extracting the internal solvent, promoting a uniform increase in supersaturation, and inducing the formation of the mesophase. Simultaneously, the ethyl acetate atmosphere forms a protective layer on the film surface, preventing contact between air moisture and FAPbBr3 and inhibiting the occurrence of water-induced phase transition. After subsequent annealing, the mesophase is transformed into a high-quality pure-phase FAPbBr3 thin film with high crystallinity and uniform grain size.

[0006] Preferably, the treatment time in the ethyl acetate atmosphere needs to be strictly controlled. If the time is too short, the solvent extraction will be incomplete, and pores will easily be generated during annealing; if the time is too long, it may lead to excessive crystallization of the film or excessive solvent exchange, resulting in increased surface roughness.

[0007] The annealing temperature is set at 70°C, which is conducive to the formation of a stable phase and the removal of residual organic solvents.

[0008] Compared with the prior art, the present invention has the following beneficial effects: (1) The method of the present invention enables FAPbBr3 thin films to be prepared in a high humidity air environment, eliminating the dependence on inert gas glove boxes and significantly reducing equipment and production costs; (2) The introduction of ethyl acetate atmosphere treatment effectively solved the problem that FAPbBr3 is prone to phase transition in air. The prepared film is a pure phase perovskite without yellow impurities. (3) The thin film prepared by this method has dense grains, high coverage, and smooth surface, and has excellent photoluminescence intensity, making it suitable for the preparation of high-performance perovskite light-emitting diodes. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of a method for preparing high-quality FAPbBr3 thin films under an ethyl acetate atmosphere. The diagram shows the ethyl acetate fumigation process, in which a FAPbBr3 precursor solution is first added dropwise, then the wet film is placed in the ethyl acetate atmosphere for fumigation, and finally placed on an annealing station for annealing.

[0010] Figure 2 This is a scanning electron microscope (SEM) image of Example 1 after fumigation in an ethyl acetate atmosphere for 2 minutes.

[0011] Figure 3 This is a scanning electron microscope (SEM) image of Example 2 after fumigation in an ethyl acetate atmosphere for 1 minute.

[0012] Figure 4This is a scanning electron microscope (SEM) image of Comparative Example 1 without ethyl acetate atmosphere treatment.

[0013] Figure 5 This is a scanning electron microscope (SEM) image of Comparative Example 2 after fumigation in a chlorobenzene atmosphere.

[0014] Figure 6 The images show the photoluminescence intensity of the examples and comparative examples. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should all be covered within the protection scope of this invention.

[0016] The present invention describes a method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air. The coating method is as follows: Figure 1 As shown: A layer of FAPbBr3 film was first prepared by spin coating in air. The prepared FAPbBr3 film was then placed in an ethyl acetate atmosphere for fumigation. After fumigation, it was placed on an annealing table for annealing to form a FAPbBr3 film with high crystallinity and uniform grain size.

[0017] Example 1 The thin film preparation method is described as follows: a glass substrate / FAPbBr3 thin film is prepared by the following steps: 1) Use D90 cleaning solution, deionized water, ethanol and isopropanol in sequence to ultrasonically clean the glass substrate for 15 minutes, blow it dry with nitrogen, and finally clean it in a plasma cleaner for 15 minutes. 2) Prepare perovskite precursor solution: Dissolve FABr and PbBr2 (molar ratio 1.1:1) in 1 mL of N,N-dimethylformamide (DMF) to achieve a total solute concentration of 1.0 M. Stir at 20-25℃ for 2-12 hours and filter for later use. 3) Transfer the substrate to an air environment with a relative humidity of 40%-50%. Drop the precursor solution onto the substrate and spin coat at 4000 rpm for 45 seconds; 4) After spin coating, immediately transfer the substrate in the wet film state into a sealed, alternating culture dish pre-filled with ethyl acetate liquid (the substrate does not contact the liquid), cover it, and fumigate with ethyl acetate vapor for 2 minutes. 5) Remove the substrate and anneal it on a hot plate at 70°C for 1 minute.

[0018] The resulting film was observed to be a uniform deep orange color, as shown in the SEM image ( Figure 2 The film appears dense and non-porous with a uniform grain size distribution. PL spectroscopy reveals an extremely strong green emission peak (around 540 nm).

[0019] Example 2 The thin film preparation method is described as follows: a glass substrate / FAPbBr3 thin film is prepared by the following steps: 1) Use D90 cleaning solution, deionized water, ethanol and isopropanol in sequence to ultrasonically clean the glass substrate for 15 minutes, blow it dry with nitrogen, and finally clean it in a plasma cleaner for 15 minutes. 2) Prepare perovskite precursor solution: Dissolve FABr and PbBr2 (molar ratio 1.1:1) in 1 mL of N,N-dimethylformamide (DMF) to achieve a total solute concentration of 1.0 M. Stir at 20-25℃ for 2-12 hours and filter for later use. 3) Transfer the substrate to an air environment with a relative humidity of 40%-50%. Drop the precursor solution onto the substrate and spin coat at 4000 rpm for 45 seconds; 4) After spin coating, immediately transfer the substrate in the wet film state into a sealed, alternating culture dish pre-filled with ethyl acetate liquid (the substrate does not contact the liquid), cover it, and fumigate with ethyl acetate vapor for 1 minute. 5) Remove the substrate and anneal it on a hot plate at 70°C for 1 minute.

[0020] The only difference from Example 1 is that the fumigation time in the ethyl acetate atmosphere was adjusted to 1 minute. SEM image ( Figure 3 The results showed that the film quality was good, the surface smoothness was slightly better than that of Example 1, but the grain size was slightly smaller, and the photoluminescence intensity was comparable to that of Example 1. Both were high-quality FAPbBr3 films.

[0021] Comparative Example 1 The thin film preparation method is described as follows: a glass substrate / FAPbBr3 thin film is prepared by the following steps: 1) Use D90 cleaning solution, deionized water, ethanol and isopropanol in sequence to ultrasonically clean the glass substrate for 15 minutes, blow it dry with nitrogen, and finally clean it in a plasma cleaner for 15 minutes. 2) Prepare perovskite precursor solution: Dissolve FABr and PbBr2 (molar ratio 1.1:1) in 1 mL of N,N-dimethylformamide (DMF) to achieve a total solute concentration of 1.0 M. Stir at 20-25℃ for 2-12 hours and filter for later use. 3) Transfer the substrate to an air environment with a relative humidity of 40%-50%. Drop the precursor solution onto the substrate and spin coat at 4000 rpm for 45 seconds; 4) After spin coating is completed, remove the substrate and anneal it on a hot plate at 70°C for 1 minute.

[0022] The difference from Example 1 is that no ethyl acetate atmosphere treatment was performed. Preparation process: After spin-coating in air, the film was directly annealed on a 70°C hot plate. Result: The film was yellowish-white after annealing, and the surface roughness was visible to the naked eye. SEM image ( Figure 4 The results showed that the film contained numerous pores and cracks, and the grain morphology was disordered. The extremely low PL spectral intensity indicated that moisture in the air severely disrupted the crystallization process, preventing the formation of an effective FAPbBr3 perovskite phase.

[0023] Comparative Example 2 The thin film preparation method is described as follows: a glass substrate / FAPbBr3 thin film is prepared by the following steps: 1) Use D90 cleaning solution, deionized water, ethanol and isopropanol in sequence to ultrasonically clean the glass substrate for 15 minutes, blow it dry with nitrogen, and finally clean it in a plasma cleaner for 15 minutes. 2) Prepare perovskite precursor solution: Dissolve FABr and PbBr2 (molar ratio 1.1:1) in 1 mL of N,N-dimethylformamide (DMF) to achieve a total solute concentration of 1.0 M. Stir at 20-25℃ for 2-12 hours and filter for later use. 3) Transfer the substrate to an air environment with a relative humidity of 40%-50%. Drop the precursor solution onto the substrate and spin coat at 4000 rpm for 45 seconds; 4) After spin coating, immediately transfer the substrate in the wet film state into a sealed Petri dish containing chlorobenzene liquid (the substrate does not contact the liquid), cover it, and fumigate with chlorobenzene vapor for 2 minutes. 5) Remove the substrate and anneal it on a hot plate at 70°C for 1 minute.

[0024] The difference from Example 1 is the use of chlorobenzene vapor instead of ethyl acetate vapor. Preparation process: Fumigation was performed using chlorobenzene as the antisolvent atmosphere. Results: Although chlorobenzene is also a commonly used antisolvent, its vapor treatment effect under an air atmosphere is not as good as that of ethyl acetate. The obtained SEM images ( Figure 5 The results showed that there were still some pinholes on the surface of the film, and the photoluminescence intensity was about 60% of that in Example 1, indicating that the dual role of ethyl acetate in moisture protection and solvent extraction is more suitable for the preparation of FAPbBr3 in an air environment.

[0025] A comparison of Examples 1 and 2 with Comparative Examples 1 and 2 demonstrates that the ethyl acetate atmosphere-assisted method proposed in this invention is crucial for the stable preparation of FAPbBr3 in air. Examples 1 and 2 show that stable FAPbBr3 films can be prepared in air by controlling the treatment time of ethyl acetate vapor. Testing revealed that the film prepared in Example 1 using ethyl acetate vapor fumigation for 2 minutes exhibited the densest grain arrangement, optimal film morphology, and highest photoluminescence intensity. The photoluminescence brightness and surface morphology of the optoelectronic devices prepared in Examples 1-2 and Comparative Examples 1-2 were tested. Compared to Comparative Example 1, Example 1 introduced ethyl acetate atmosphere-assisted crystallization, effectively shielding the film from moisture and extracting the solvent, resulting in extremely high photoluminescence brightness. Furthermore, dense, non-porous perovskite grains were formed under the same scanning electron microscope, making the film grain size more regular. Compared to Comparative Example 2, Example 1 used ethyl acetate as the atmosphere solvent, resulting in a film with higher photoluminescence brightness, fuller grains, better film surface morphology, and no obvious pinholes, unlike the film formed in Comparative Example 2 using chlorobenzene vapor. Comparative Examples 1 and 2 represent either no atmosphere treatment or other less effective antisolvent atmospheres, respectively. The FAPbBr3 films prepared in these examples showed significantly worse morphological density and luminescence performance compared to the ethyl acetate atmosphere-treated group. Specifically, we can see this from... Figure 6 The photoluminescence diagrams of the embodiments and comparative examples show that...

Claims

1. A method for preparing high-quality FAPbBr3 thin films under an ethyl acetate atmosphere in air, characterized in that, include: Perovskite precursor solutions containing PbBr2 and FABr were prepared separately. A perovskite wet film was prepared on a glass substrate by spin coating; the wet film was placed in a closed atmosphere filled with ethyl acetate vapor for solvent-induced treatment, followed by annealing to obtain a FAPbBr3 perovskite thin film.

2. The method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air according to claim 1, characterized in that, The preparation of the perovskite precursor solution includes: mixing FABr and PbBr2 in a molar ratio of 1:1 to 1.2:1, adding a solvent to dissolve them, and stirring at 20-25°C for a certain period of time; the solvent of the precursor solution is N,N-dimethylformamide (DMF).

3. The method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air according to claim 2, characterized in that, The specified stirring temperature is 20-25℃, and the specified time is 2 hours to 12 hours.

4. The method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air according to claim 1, characterized in that, The process of treating the ethyl acetate atmosphere includes: placing an appropriate amount of liquid ethyl acetate at the bottom of a sealed container and allowing it to evaporate and fill the container space; placing the spin-coated wet film substrate horizontally on a rack inside the container, without directly contacting the liquid, and fumigating it with ethyl acetate vapor for a certain period of time.

5. The method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air according to any one of claims 1-4, characterized in that, The process includes the following steps: Step 1, cleaning and plasma treatment of the glass substrate; Step 2, spin-coating a FAPbBr3 precursor solution of a certain concentration onto the glass substrate, and immediately transferring it into an ethyl acetate atmosphere before or after spin-coating to induce the formation of an intermediate phase and solvent extraction; Step 3, annealing the treated film on a heating stage to transform FAPbBr3 from the intermediate phase to the pure perovskite phase.

6. The method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air according to claim 4, characterized in that, The fumigation time for the ethyl acetate vapor is 1-2 minutes.

7. The method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air according to claim 1, characterized in that, The concentration of the precursor solution is 0.5-1.5 mol / L.

8. The method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air according to claim 5, characterized in that, The annealing temperature is 70°C, and the annealing time is 1 minute.

9. The method for preparing high-quality FAPbBr3 thin films in an ethyl acetate atmosphere in air according to claim 1, characterized in that, The ethyl acetate atmosphere can effectively extract high-boiling-point solvents from the wet film and inhibit the intrusion of moisture from the air, promoting the stable formation of the pure phase of FAPbBr3.

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