Preparation method and application of chiral perovskite / perovskite quantum dot heterojunction nonlinear optical active film

Abstract

The application belongs to the field of optoelectronic materials and nonlinear optical applications, and particularly relates to a preparation method of a chiral perovskite / perovskite quantum dot heterojunction nonlinear optical active film. The method comprises the following steps: (1) configuring a chiral perovskite precursor solution; (2) preparing a perovskite quantum dot solution; (3) purifying the perovskite quantum dots; and (4) preparing a chiral perovskite / perovskite quantum dot heterojunction double-layer film. The technical scheme combines a chiral perovskite film with a perovskite quantum dot film, and the chiral perovskite / perovskite quantum dot heterojunction double-layer film constructed has the advantages of simple and fast preparation process, and strong nonlinear optical activity. In addition, the chiral perovskite / perovskite quantum dot heterojunction double-layer film is conducive to integration into a device and helps to realize a circularly polarized light emitting and detecting dual-function device.

Description

A method for preparing and applying a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film. Technical Field

[0001] This invention relates to the fields of optoelectronic materials and nonlinear optics, specifically to a method for preparing and applying a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film. Background Technology

[0002] Perovskite is a semiconductor material with superior photophysical and photochemical properties, and it is widely used in solar cells, light-emitting diodes, memristors, photocatalysis, and other fields. The crystal structure of conventional perovskite materials can be represented in the form ABX3, where A represents an organic cation, B represents a metal cation, and X represents a halide anion. By changing different chemical components in the perovskite structure, the semiconductor physical properties of perovskite materials, such as photoelectric and magnetic properties, can be effectively controlled. Based on the unique crystal structure of perovskite materials, replacing the non-chiral organic cation at the A-site with a chiral organic cation can form a chiral organic-inorganic hybrid perovskite, hereinafter referred to as chiral perovskite. Chiral perovskite materials exhibit significant chiral optical response, i.e., natural optical activity, such as circular dichroism and circularly polarized luminescence. This makes chiral perovskite materials promising for applications in nonlinear optics fields such as circularly polarized luminescence, detection, and lasers.

[0003] Currently, chiral perovskite single crystals are ideal materials for circularly polarized light sources. However, due to the preparation methods of such single crystal materials and the inherent shortcomings of the materials themselves, the application range of chiral perovskite single crystals is greatly limited. The defects of existing preparation methods are: (1) The preparation process of chiral perovskite single crystals is cumbersome and time-consuming; (2) The yield of synthesized single crystals is low; (3) Excess solvent remains in the single crystals, resulting in low purity; (4) The single crystal morphology is mostly needle-like or powdery, which is not conducive to device integration. The defects of the materials themselves include: (1) The introduced chiral organic molecules have complex structures and large volumes, which easily cause high distortion or local stress in the chiral perovskite crystal structure, resulting in the formation of new defect states inside the crystal. These defect states often act as non-radiative recombination centers, causing excitons to dissipate energy without emitting light, significantly reducing the luminescence efficiency. (2) Strong exciton-phonon coupling effects are common in low-dimensional chiral perovskite single crystals (e.g., two-dimensional or zero-dimensional), which easily form self-trapped excitons. Self-trapped excitons are excited-state particles that are bound by local lattice distortions and are difficult to efficiently emit radiative recombination light. (3) Although chiral perovskite single crystals can produce broadband emission in some cases, their luminous efficiency is usually low and they are not suitable for high-brightness and high-efficiency electroluminescent devices. In addition, another method to obtain nonlinear optical effects is to construct a chiral-chiral perovskite-chiral perovskite core-shell structure through a self-assembly chemical method, in which the chiral perovskite is used as the shell and the three-dimensional chiral perovskite is used as the core. Although the nonlinear optical activity of this core-shell structure is indeed stronger than that of a single chiral perovskite single crystal, its preparation process is relatively complex, the experimental conditions are demanding, the core-shell structure is uncontrollable and unstable during the preparation process, the experiment takes a long time, the characterization of the core-shell structure of the sample is relatively complex, and it is not conducive to device integration, which seriously restricts the development of nonlinear optical devices. Summary of the Invention

[0004] To simplify the preparation method and experimental steps of chiral perovskite single crystals, this invention provides a method for preparing chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin films. This technical solution utilizes the miscibility of chiral bromide ligands, lead bromide, and organic polar solvents to directly prepare a chiral perovskite precursor solution, and then prepares the chiral perovskite thin film by solution spin coating. This eliminates the need to prepare chiral perovskite single crystals and chiral perovskite-chiral perovskite core-shell structures, and also eliminates the need for high-temperature heat sources and oil bath devices.

[0005] The specific technical solution of this invention is as follows:

[0006] 1. A method for preparing a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film, comprising the following steps:

[0007] (1) Prepare a chiral perovskite precursor solution by mixing a chiral organic ligand, lead bromide solid powder and a polar solution to obtain a chiral perovskite precursor solution, wherein the chiral organic ligand is R-(+)-3-bromo-1-phenylethylamine bromide or S-(-)-3-bromo-1-phenylethylamine bromide;

[0008] (2) To prepare the perovskite quantum dot solution, firstly, lead bromide, tetra-n-octylammonium bromide and toluene were dissolved to prepare a lead bromide precursor solution; then, cesium carbonate solution and formamidine acetate solution were mixed to prepare a cesium precursor solution; dodecyl dimethylammonium bromide and 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene were mixed with toluene and completely dissolved, and labeled as passivating agent A and passivating agent B, respectively. The lead bromide precursor solution and the cesium precursor solution were mixed and stirred evenly, then passivating agent A was added and stirred evenly, then passivating agent B was added and stirred evenly. The solution was sealed and allowed to stand to obtain the CsPbBr3 perovskite quantum dot solution.

[0009] (3) Purification of perovskite quantum dots: After an orange precipitate appears in the CsPbBr3 perovskite quantum dot solution, take the supernatant and mix it with methyl acetate solution. Centrifuge the mixture to collect the precipitate. Then mix the precipitate with n-hexane and methyl acetate and centrifuge to collect the final precipitate. Disperse the precipitate in a non-polar solvent to obtain the purified perovskite quantum dot solution.

[0010] (4) Preparation of chiral perovskite / perovskite quantum dot heterojunction bilayer film: A chiral perovskite precursor solution is spin-coated or blade-coated on the substrate to obtain a chiral perovskite film. Then, a perovskite quantum dot solution is deposited on the chiral perovskite film by spin-coating or blade-coating to obtain a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active film.

[0011] The solvent used for chiral perovskites is a polar solvent, while the solvent used for perovskite quantum dots is a nonpolar solvent. This ensures that the chiral perovskite film and the perovskite quantum dot film do not dissolve in each other, thus allowing them to be well compatible and forming a chiral perovskite / perovskite quantum dot heterojunction bilayer film.

[0012] Preferably, in step (1), a chiral perovskite precursor solution is prepared by taking equal parts by mass of chiral ligand R-(+)-3-bromo-1-phenylethyl bromide and chiral ligand S-(-)-3-bromo-1-phenylethyl bromide and placing them in containers A and B respectively. Then, equal parts by mass of lead bromide solid powder are placed in containers A and B respectively. The same volume of N,N-dimethylformamide solution is added to containers A and B respectively. The solutions in containers A and B are stirred thoroughly at 50°C until clear, thus obtaining two chiral perovskite precursor solutions with R configuration and S configuration.

[0013] Preferably, the mass-to-volume ratio (mg / mg / ml) of lead bromide, tetra-n-octylammonium bromide, and toluene in step (2) is 367:1093.6:10.

[0014] Preferably, the cesium carbonate solution in step (2) is prepared by dissolving cesium carbonate and octanoic acid in a mass-to-volume ratio (mg / ml) of 32.5:1. The formamidine acetate solution is prepared by dissolving formamidine acetate and octanoic acid in a mass-to-volume ratio (mg / ml) of 20.8:1. The volume ratio of the cesium carbonate solution to the formamidine acetate solution is 0.85:0.15.

[0015] Preferably, the concentration of the purified perovskite quantum dot solution in step (3) is in the range of 80-100 mg / mL, and the solution is n-hexane.

[0016] Preferably, in step (4), the spin coating speed of the chiral perovskite precursor solution is 1000-2000 rpm and the spin coating time is 30 s, while the spin coating speed of the perovskite quantum dot solution is 1000-8000 rpm and the spin coating time is 10-60 s.

[0017] Preferably, after spin-coating the chiral perovskite precursor solution in step (4), it can be placed on a heating table and annealed at 100°C for 10 minutes. After spin-coating the perovskite quantum dot solution, the film is transferred into a low-pressure chamber and placed for 10-20 minutes.

[0018] Preferably, before the chiral perovskite precursor solution described in step (4) is deposited on the substrate by a scraping method, the substrate is preheated on a hot stage at 70-90°C for 20-30 minutes.

[0019] 2. The chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film prepared according to the above method.

[0020] 3. Application of a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film in a dual-function device integrating circularly polarized light emission and detection.

[0021] The beneficial effects of this invention are:

[0022] (1) The present invention utilizes the excellent optical activity of chiral perovskite and the high luminous efficiency of perovskite quantum dots to effectively combine the two and construct a chiral perovskite / perovskite quantum dot heterojunction nonlinear optical thin film. Based on the advantage of the adjustable chemical composition of chiral perovskite and perovskite quantum dots, the recombination efficiency of electron-hole carriers at the heterojunction interface is enhanced by changing the energy level structure of the two, thereby improving the nonlinear optical response of the chiral perovskite / perovskite quantum dot heterojunction.

[0023] (2) When chiral perovskites and perovskite quantum dots have the same halogen composition, chiral organic molecules can act as passivators for the perovskite quantum dot layer, reducing interface defects between the two thin films and enabling an efficient chiral transfer process. This fully utilizes the excellent luminescence properties of perovskite quantum dots to enhance the overall nonlinear optical activity of the heterojunction. Furthermore, compared to chiral perovskite single crystals and chiral-chiral perovskite core-shell structures, chiral perovskite / perovskite quantum dot heterojunction nonlinear optical films have advantages in terms of preparation methods, optical activity, and application prospects. Moreover, chiral perovskite / perovskite quantum dot heterojunction nonlinear optical films are easy to integrate into devices and can be directly applied to dual-function devices for circularly polarized emission and detection.

[0024] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0026] Figure 1 shows the absorption spectra of (R-3BrMBA)2PbBr4 monolayer, (S-3BrMBA)2PbBr4 monolayer, and perovskite quantum dot CsPbBr3 monolayer.

[0027] Figure 2 shows the X-ray diffraction patterns of (R-3BrMBA)2PbBr4 monolayer and (S-3BrMBA)2PbBr4 monolayer films;

[0028] Figure 3 shows the absorption spectra of the (R-3BrMBA)2PbBr4 / CsPbBr3 heterojunction bilayer film and the (S-3BrMBA)2PbBr4 / CsPbBr3 heterojunction bilayer film.

[0029] Figure 4 shows the circular dichroism spectrum of the (R / S-3BrMBA)2PbBr4 thin film;

[0030] Figure 5. Circular dichroism spectra of (R-3BrMBA)2PbBr4 / CsPbBr3 and (S-3BrMBA)2PbBr4 / CsPbBr3 heterojunction bilayer films;

[0031] Figure 6. Circular polarization degree of (R-3BrMBA)2PbBr4 / CsPbBr3 and (S-3BrMBA)2PbBr4 / CsPbBr3;

[0032] Figure 7. Schematic diagram of the structure of chiral perovskite (R / S-3BrMBA)2PbBr4 / CsPbBr3 that can be used in spin / circularly polarized light-emitting devices and circularly polarized light-emitting devices. Detailed Implementation

[0033] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand 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 other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0034] In this invention, all chemical reagents required for preparing chiral perovskite / perovskite quantum dot heterojunction bilayer films are of analytical grade and require no further purification. The main materials used in the experiment include:

[0035] (a) R-(+)-3-bromo-1-phenylethylammonium bromide (R-(+)-3-Bromo-1-Phenylethylammonium Bromide), abbreviated as R-3BrMBA; S-(-)-3-bromo-1-phenylethylammonium bromide (S-(-)-3-Bromo-1-Phenylethylammonium Bromide), abbreviated as S-3BrMBA. Both chiral ligands are white powders. Material purity: >98.0% (for chromatographic purposes). Brand: Xi'an Yu Riguang Energy.

[0036] (b) Lead bromide (PbBr2): This material is a white powder. Purity: >99.999%. Metallic base, orthorhombic crystal system.

[0037] Brand: Aladdin;

[0038] (c) 1 mL N,N-Dimethylformamide (DMF): Colorless, transparent liquid. Purity: >99.9%, Brand: Aladdin;

[0039] (d) 10 mL toluene solution (C6H5CH3): This material is a colorless and transparent solution. Purity: >99.5% (analytical grade).

[0040] Brand: Chongqing Chuandong Chemical Co., Ltd.

[0041] (e) 2 mL methyl acetate (MeOAc): This material is a colorless and transparent solution. Purity: >99% (analytical grade).

[0042] Brand: Macklin;

[0043] (f) 1093.6 mg Tetra-n-octylammonium bromide (TOAB): White crystalline powder. Purity: >98%. Brand: Sigma-Aldrich;

[0044] (g) 32.5mg Cesium carbonate (CsCO3): White solid. Purity: >99.9%. Brand: Taitongyuan (Jiangsu) Science and Technology Development Co., Ltd.

[0045] (h) 20.8 mg formamidine acetate (FA): White solid. Purity: >99%. Brand: Leyan;

[0046] (i) 1 mL of octanoic acid (OATC): Clear liquid. Purity: >99%. Brand: Maclean's;

[0047] (j) 30mg dodecyl dimethyl ammonium bromide (DDAB): Crystalline powder. Purity: >97%. Brand: Maclean;

[0048] (k) 20mg 1,3,5-Tris(bromomethyl)-2,4,6-triethylbenzene (TBTB): Crystalline powder. Purity: >95%. Brand: Leyan.

[0049] Example

[0050] A method for preparing a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film includes the following steps:

[0051] Step (1): Prepare the chiral perovskite precursor solution. Prepare two SA-10 magnetic stir bar and two clean 5mL glass bottles, and place a magnetic stir bar in each glass bottle. Weigh two 73.4mg portions of lead bromide (PbBr2) solid powder at room temperature and add them to the two glass bottles respectively. Weigh 112.4mg of the halide chiral ligand R-(+)-3-bromo-1-phenylethylammonium bromide, pour it into one glass bottle and label it; similarly, weigh 112.4mg of the halide chiral ligand S-(-)-3-bromo-1-phenylethylammonium bromide, pour it into the other glass bottle and label it. Then, 1 mL of N,N-dimethylformamide (DMF) solution was added to each of the two glass bottles. The two glass bottles were then transferred into a glove box system and placed on a preheated stirring table set to 50°C. The mixture was stirred for 12 hours until the solid was completely dissolved, resulting in a clear chiral perovskite precursor solution.

[0052] Step (2): Synthesis of perovskite CsPbBr3 quantum dots. Prepare a magnetic stir bar (model HL2050) and a 50 mL beaker. Weigh 367 mg of lead bromide (PbBr2) and 1093.6 mg of tetraoctylammonium bromide (TOAB) at room temperature and add them to the beaker. Then add 10 mL of toluene and stir on a stirring table until the solid powders are completely dissolved to prepare the lead bromide precursor solution. Prepare two 10 mL centrifuge tubes, labeled centrifuge tube 1 and tube 2. Weigh 32.5 mg of cesium carbonate (CsCO3) at room temperature and add it to centrifuge tube 1. Weigh 20.8 mg of formamidine acetate (FA) and add it to centrifuge tube 2. Add 1 mL of octanoic acid (OATC) to each centrifuge tube. After the solution is completely dissolved in an ultrasonic cleaner for 15 minutes, mix 0.85 mL of the cesium carbonate solution and 0.15 mL of the formamidine acetate solution to obtain the cesium precursor solution. Prepare two more 10mL centrifuge tubes, labeled tube 3 and tube 4. Weigh 30mg of dodecyl dimethyl ammonium bromide (DDAB) and add it to tube 3 under outdoor conditions. Then weigh 20mg of 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene (TBTB) and add it to tube 4. Add 3mL of toluene to each of tubes 3 and 4. Place the centrifuge tubes in an ultrasonic cleaner for 15 minutes until the solids are completely dissolved, completing the passivation agent preparation. Take 9mL of lead bromide precursor solution and add 1mL of cesium precursor solution. Stir on a stirring table for 2 minutes. Then add 3mL of DDAB solution (centrifuge tube 3) and stir for another 3 minutes. Then add 3mL of TBTB solution (centrifuge tube 4) and stir for 5 minutes. Remove the beaker from the stirring table, wrap it in aluminum foil, and let it stand for 2 hours.

[0053] Step (3): Purification of perovskite quantum dots. After waiting for 2 hours, an orange precipitate appeared in the beaker. Take 1 mL of the light green supernatant and add it to a 10 mL volumetric centrifuge tube. Then add 2 mL of methyl acetate solution to the centrifuge tube. Repeat 6 times to obtain a total of 6 centrifuge tube solutions. Centrifuge at 7000 rpm for 5 minutes in a high-speed centrifuge. Discard the supernatant and collect the precipitate. Add 1 mL of n-hexane and 2 mL of methyl acetate. Centrifuge again at 7000 rpm for 5 minutes. Collect the final precipitate. Disperse the precipitate in 1 mL of n-hexane to obtain the purified perovskite quantum dot solution.

[0054] Step (4): Preparation of chiral perovskite / perovskite quantum dot heterojunction bilayer film. A 1.6cm*1.6cm glass substrate was cleaned of surface dust using a high-purity nitrogen gun, then ultrasonically cleaned in deionized water, acetone, and anhydrous ethanol, followed by baking in an 80℃ oven for 30 minutes, and finally hydrophilic treatment in a plasma cleaner. After transferring the glass substrate into a nitrogen-environment glove box, chiral perovskite films were prepared using a solution spin-coating method. 60µL of chiral perovskite precursor solution was dropped onto a clean glass substrate and spin-coated at 2000rpm for 30s. The substrate was then transferred to a heating stage and annealed at 100℃ for 10 minutes to evaporate the solvent and rapidly crystallize to form chiral perovskite films (R-3BrMBA)2PbBr4 and (S-3BrMBA)2PbBr4. The chiral perovskite film was transferred into a low-pressure chamber and placed for 10 minutes. Then it was placed on a spin coater. 70 μL of perovskite quantum dot solution CsPbBr3 was taken and spin-coated at 2000 rpm for 30 seconds. After that, the film was transferred into a low-pressure chamber and placed for 10 minutes to obtain a chiral perovskite / perovskite quantum dot heterojunction film.

[0055] Figure 1 shows the visible light absorption characteristics of monolayer chiral perovskite (R-3BrMBA)₂PbBr₄ and (S-3BrMBA)₂PbBr₄ films, as well as monolayer perovskite quantum dot CsPbBr₃ films. As can be seen from the figure, the absorption curves of chiral perovskite (R-3BrMBA)₂PbBr₄ and (S-3BrMBA)₂PbBr₄ are almost identical, with only one distinct absorption peak at approximately 380 nm. This indicates that the (R-3BrMBA)₂PbBr₄ and (S-3BrMBA)₂PbBr₄ films possess a low-dimensional structure (n=1). Furthermore, the absorption characteristics of the monolayer perovskite quantum dot CsPbBr₃ film were also tested, and the experimental results show that the CsPbBr₃ film also has only one absorption peak at approximately 500 nm. By comparing the light absorption characteristics of (R-3BrMBA)2PbBr4, (S-3BrMBA)2PbBr4, and CsPbBr3 films, it can be seen that the absorption peaks of (R-3BrMBA)2PbBr4 and (S-3BrMBA)2PbBr4 originate from the low-dimensional crystalline phase, while the absorption peak of CsPbBr3 film originates from the three-dimensional crystalline phase.

[0056] To verify the good crystallinity of the prepared chiral perovskite monolayers (R-3BrMBA)₂PbBr₄ and (S-3BrMBA)₂PbBr₄ films, X-ray diffraction patterns of these two films were further measured. As shown in Figure 2, the (R-3BrMBA)₂PbBr₄ and (S-3BrMBA)₂PbBr₄ films exhibit obvious crystallization diffraction peaks in the diffraction angle range of 0-40°, and their crystallization peak positions are the same. This indicates that the two-dimensional chiral perovskite prepared by solution spin coating has good film formation and crystallization characteristics, which lays a good foundation for preparing (R / S-3BrMBA)₂PbBr₄ / CsPbBr₃ heterojunction bilayer films with two-dimensional / three-dimensional structures.

[0057] Heterojunction bilayer films of (R-3BrMBA)2PbBr4 / CsPbBr3 and (S-3BrMBA)2PbBr4 / CsPbBr3 were prepared by solution spin-coating. As shown in Figure 3, the absorption spectra of these two heterojunction bilayer films were measured. The experimental results show that both the (R-3BrMBA)2PbBr4 / CsPbBr3 and (S-3BrMBA)2PbBr4 / CsPbBr3 heterojunction bilayer films have two distinct absorption peaks, located at 380 nm and 500 nm, respectively. Comparison with the test results in Figure 1 reveals that these two absorption peaks actually originate from the absorption peaks of the chiral perovskite (R / S-3BrMBA)2PbBr4 and the perovskite quantum dot CsPbBr3, respectively. This indicates that a chiral perovskite / perovskite quantum dot heterojunction bilayer film was successfully prepared. Moreover, this heterojunction bilayer film combines the optical properties of two-dimensional chiral perovskite (R / S-3BrMBA)2PbBr4 and three-dimensional perovskite quantum dot CsPbBr3, and its structure belongs to a two-dimensional / three-dimensional heterojunction structure.

[0058] To characterize the chiral properties of the prepared chiral perovskite films, the circular dichroism (CDI) spectra of (R-3BrMBA)₂PbBr₄ and (S-3BrMBA)₂PbBr₄ films were further tested, as shown in Figure 4. The figure shows that the CDI signals of both (R-3BrMBA)₂PbBr₄ and (S-3BrMBA)₂PbBr₄ films exhibit significant symmetry, and both show three relatively strong CDI signals located at 330 nm, 375 nm, and 394 nm, respectively. The CDI signal at 394 nm is the strongest, with the (R-3BrMBA)₂PbBr₄ film reaching a CDI signal as high as 12 mdeg, which is stronger than that of conventional chiral perovskite single crystals. This indicates that the chiral perovskite films (R-3BrMBA)2PbBr4 and (S-3BrMBA)2PbBr4 prepared by solution spin coating not only have strong chiral characteristics, but this experimental technique also verifies that halide chiral ligands can efficiently transfer their chirality to the inorganic perovskite structure. Through the electronic orbital hybridization and interaction between the chiral and inorganic components, the overall chiral perovskite film exhibits nonlinear optical activity.

[0059] Figure 5 shows the circular dichroism (CDI) signals of the (R-3BrMBA)2PbBr4 / CsPbBr3 and (S-3BrMBA)2PbBr4 / CsPbBr3 heterojunction bilayer films. As shown in the figure, the (R-3BrMBA)2PbBr4 / CsPbBr3 and (S-3BrMBA)2PbBr4 / CsPbBr3 heterojunction bilayer films also exhibit a clearly symmetrical CDI signal, with a total of 5 CDI signal peaks in the 300-600 nm range, located at 340 nm, 375 nm, 425 nm, 475 nm, and 500 nm, respectively. The CDI signal at 500 nm is the strongest, greater than 45 mdeg. The experimental results show that the (R-3BrMBA)2PbBr4 / CsPbBr3 and (S-3BrMBA)2PbBr4 heterojunction bilayer films formed by combining chiral perovskite monolayer (R-3BrMBA)2PbBr4 and (S-3BrMBA)2PbBr4 films with perovskite quantum dot monolayer CsPbBr3 films exhibit nonlinear optical effects. A comparison of the circular dichroism (CDI) signals of the chiral perovskite monolayer film and the chiral perovskite / perovskite quantum dot heterojunction bilayer film reveals that the nonlinear optical activity of the heterojunction bilayer film is significantly stronger than that of the chiral perovskite monolayer film, with its CDI signal being approximately four times higher. The experimental results show that the constructed chiral perovskite / perovskite quantum dot heterojunction bilayer film can indeed significantly improve nonlinear optical activity. This also indicates that the chiral perovskite single crystal can efficiently transfer its chirality to the perovskite quantum dot layer, enabling the perovskite quantum dot layer to exhibit excellent nonlinear optical activity.

[0060] Figure 6 shows the circular polarization of the (R-3BrMBA)2PbBr4 / CsPbBr3 and (S-3BrMBA)2PbBr4 / CsPbBr3 heterojunction bilayer films. Based on the test results, the circular polarization of the (R-3BrMBA)2PbBr4 / CsPbBr3 heterojunction bilayer film is as high as 10%, and that of the (S-3BrMBA)2PbBr4 / CsPbBr3 heterojunction bilayer film is as high as 15%. These two heterojunction bilayer films have the highest circular polarization to date, indicating that the chiral perovskite / perovskite quantum dot heterojunction bilayer films constructed using the solution spin-coating method are indeed advantageous and exhibit strong nonlinear optical activity.

[0061] As shown in Figure 7, the prepared chiral perovskite / perovskite quantum dot heterojunction bilayer film can be conveniently used to integrate circularly polarized light-emitting diodes (LEDs) and circularly polarized light-detecting devices, enabling the device to simultaneously possess the dual functions of circularly polarized light emission and detection. The structure of this dual-function electronic device is: conductive glass substrate / hole injection layer / hole transport layer / chiral perovskite / perovskite quantum dot / electron transport layer / aluminum electrode. The principle of the circularly polarized light-emitting device is as follows: holes and electrons are injected from the conductive substrate and the aluminum electrode respectively. The holes then pass through the hole injection layer and the hole transport layer sequentially, and then enter the chiral perovskite. At this point, the holes are spin-polarized, giving them either spin-up or spin-down characteristics, and then they are transported to the perovskite quantum dot layer. Electrons entering from the aluminum electrode pass through the electron transport layer and then enter the perovskite quantum dot layer. Therefore, electrons and spin-polarized holes recombine in the perovskite quantum dot layer, emitting left-handed or right-handed circularly polarized light.

[0062] The working principle of circularly polarized detectors is exactly the opposite of that of circularly polarized light emitters. When left-handed or right-handed circularly polarized light is irradiated by the device, the perovskite quantum dot layer generates photogenerated electrons and hole carriers. These holes then pass through the chiral perovskite layer and the hole transport layer to reach the glass conductive substrate, while the electrons pass through the electron transport layer to reach the aluminum electrode. Finally, the electrons and spin-polarized hole carriers are detected by the source surface, thus enabling the detection of left-handed or right-handed circularly polarized light.

[0063] In summary, this technical solution proposes combining chiral perovskite thin films with perovskite quantum dot thin films. The resulting chiral perovskite / perovskite quantum dot heterojunction bilayer film is not only simple and rapid to fabricate, but also exhibits strong nonlinear optical activity. Furthermore, the chiral perovskite / perovskite quantum dot heterojunction bilayer film is also advantageous for integration into devices, potentially enabling dual-function devices for circularly polarized emission and detection.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film, characterized in that, The steps include: (1) preparing a chiral perovskite precursor solution by mixing a chiral organic ligand, lead bromide solid powder, and N,N-dimethylformamide to obtain a chiral perovskite precursor solution, wherein the chiral organic ligand is R-(+)-3-bromo-1-phenylethylammonium bromide or S-(-)-3-bromo-1-phenylethylammonium bromide; (2) preparing a perovskite quantum dot solution by first dissolving lead bromide, tetra-n-octylammonium bromide, and toluene to prepare a lead bromide precursor solution; then mixing cesium carbonate solution and formamidine acetate solution to prepare a cesium precursor solution; mixing dodecyl dimethylammonium bromide and 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene with toluene and dissolving them completely, and labeling them as passivating agent A and passivating agent B respectively; mixing the lead bromide precursor solution and the cesium precursor solution evenly, and then adding passivating agent A. Stir evenly again, add passivating agent B and stir evenly, seal the solution and let it stand to obtain CsPbBr3 perovskite quantum dot solution; (3) Purify perovskite quantum dots: After the orange precipitate appears in the CsPbBr3 perovskite quantum dot solution, take the supernatant and mix it with methyl acetate solution, centrifuge the mixture to collect the precipitate, then mix the precipitate with n-hexane and methyl acetate and centrifuge to collect the final precipitate, disperse the precipitate in a nonpolar solvent to obtain the purified CsPbBr3 perovskite quantum dot solution; (4) Prepare chiral perovskite / perovskite quantum dot heterojunction bilayer film: spin-coat or scrape the chiral perovskite precursor solution on the substrate to obtain a chiral perovskite film, then deposit the perovskite quantum dot solution on the chiral perovskite film by spin-coating or scraping to obtain a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active film.

2. The method for preparing a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film according to claim 1, characterized in that, Step (1) Prepare a chiral perovskite precursor solution. Take equal parts by mass of chiral ligand R-(+)-3-bromo-1-phenylethyl bromide and chiral ligand S-(-)-3-bromo-1-phenylethyl bromide and place them in containers A and B respectively. Then take equal parts by mass of lead bromide solid powder and place them in containers A and B respectively. Add equal volumes of N,N-dimethylformamide solution to containers A and B respectively. Stir the solutions in containers A and B thoroughly at 50°C until they become clear to obtain two chiral perovskite precursor solutions with R and S configurations.

3. The method for preparing a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film according to claim 1, characterized in that, The mass-to-volume ratio (mg / mg / ml) of lead bromide, tetra-n-octylammonium bromide, and toluene in step (2) is 367:1093.6:

10.

4. The method for preparing a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film according to claim 1, characterized in that, The method for preparing the cesium carbonate solution in step (2) is as follows: cesium carbonate and octanoic acid are dissolved in a solution at a mass-to-volume ratio (mg / ml) of 32.5:

1. The method for preparing the formamidine acetate solution is as follows: formamidine acetate and octanoic acid are dissolved in a solution at a mass-to-volume ratio (mg / ml) of 20.8:

1. The volume ratio of the cesium carbonate solution to the formamidine acetate solution is 0.85:0.

15.

5. The method for preparing a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film according to claim 1, characterized in that, The concentration range of the purified perovskite quantum dot solution in step (3) is 80-100 mg / mL, and the non-polar solvent is n-hexane.

6. The method for preparing a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film according to claim 1, characterized in that, In step (4), the chiral perovskite precursor solution is spin-coated at a speed of 1000-2000 rpm for 30 s, and the perovskite quantum dot solution is spin-coated at a speed of 1000-8000 rpm for 10-60 s.

7. The method for preparing a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film according to claim 6, characterized in that, After spin-coating the chiral perovskite precursor solution in step (4), the film is placed on a heating stage and annealed at 100 °C for 10 min. After spin-coating the perovskite quantum dot solution, the film is transferred into a low-pressure chamber and placed for 10-20 minutes.

8. The method for preparing a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film according to claim 1, characterized in that, Before the chiral perovskite precursor solution described in step (4) is deposited on the substrate by a scraping method, the substrate is preheated on a hot stage at 70-90°C for 20-30 minutes.

9. The chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film prepared by any one of the methods of claims 1-8.

10. Application of a chiral perovskite / perovskite quantum dot heterojunction nonlinear optically active thin film in a dual-function device integrating circularly polarized light emission and detection.

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