Closed coating system based on surface acoustic wave, chiral perovskite thin film and preparation method thereof

Abstract

The application relates to the field of microfluidic technology, in particular to a closed film coating system based on a surface acoustic wave, a chiral perovskite film and a preparation method thereof. The system comprises a piezoelectric substrate, a first interdigital transducer, a second interdigital transducer and a reaction pool arranged on the piezoelectric substrate. The first interdigital transducer and the second interdigital transducer are oppositely arranged in a staggered mode, and the reaction pool is arranged between the first interdigital transducer and the second interdigital transducer. The electrical signals on the first interdigital transducer and the second interdigital transducer oppositely arranged in a staggered mode are converted into deformation under the action of the piezoelectric substrate. The periodic deformation constitutes a surface acoustic wave and propagates along the surface of the piezoelectric substrate and acts on the precursor solution in the reaction pool, pushes the precursor solution to rotate, and completes the film coating process on the lower surface of the target substrate. The closed film coating system based on the surface acoustic wave has the advantages of simple structure, simple and convenient process in the film coating process of the target substrate, effectively reduced cost, and no need of an inert gas environment.

Description

Technical Field

[0001] This invention relates to the field of microfluidics, and in particular to a closed coating system based on surface acoustic waves, a chiral perovskite thin film, and a method for preparing the same. Background Technology

[0002] Chiral organic / inorganic hybrid perovskites (OIHPs) are optical semiconductor materials characterized by their asymmetric structure, meaning they cannot be superimposed on their mirror image. The chiral lattice structure, formed through induced growth or direct participation of organic molecules, endows chiral perovskites with unique optical properties, including circular dichroism resulting from the difference in absorption of left-handed and right-handed circularly polarized light. OIHPs combine chirality with the excellent optoelectronic properties of perovskites, thus finding wide applications in solar cells, photoelectric sensing, biosensing, and spintronics.

[0003] Currently, many techniques are available for depositing chiral OIHPs thin films. The most traditional and simplest method is spin coating, initially reported by Kojima et al. in 2009. This method requires rapid rotation of the substrate to uniformly distribute the precursor solution, remove excess solution, and promote film growth through annealing. With the development of OIHPs thin film synthesis technology, more complex techniques have emerged. For example, Kim et al. reported blade coating in 2015, which removes excess solution by adjusting the distance between the blade and the substrate. Similarly, Vak et al. proposed slit coating in the same year, which improves solution efficiency by allowing solution to flow out through a slit. Other methods, such as meniscus-assisted solution coating and inkjet coating, have also been introduced. Each of these methods has its own characteristics; however, these techniques rely on sophisticated mechanical devices or pumping systems, which significantly increases the cost of preparing OIHPs thin films.

[0004] Furthermore, most OIHP materials exhibit varying degrees of stability issues, especially when exposed to high humidity and oxygen-rich environments, which accelerates their decomposition. Therefore, the preparation of OIHP thin films requires stringent environmental conditions, further limiting their fabrication and research.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a closed coating system based on surface acoustic waves, a chiral perovskite thin film and a method for preparing the same, in order to solve the problems of complex coating processes, high costs and the need for an inert gas environment in the existing coating process.

[0007] The technical solution of the present invention is as follows:

[0008] A closed coating system based on surface acoustic waves includes a piezoelectric substrate, and a first interdigital transducer, a second interdigital transducer, and a reaction cell disposed on the piezoelectric substrate.

[0009] The first interdigital transducer and the second interdigital transducer are offset from each other and arranged opposite to each other, and the reaction cell is disposed between the first interdigital transducer and the second interdigital transducer.

[0010] In the aforementioned closed-loop coating system based on surface acoustic waves, the misalignment between the first interdigital transducer and the second interdigital transducer is 40%-60%.

[0011] In the aforementioned closed coating system based on surface acoustic waves, the wavelength of the first interdigital transducer is 200-300 micrometers; the wavelength of the second interdigital transducer is 200-300 micrometers.

[0012] The aforementioned closed coating system based on surface acoustic waves includes a transition layer between the piezoelectric substrate and the first interdigital transducer, and between the piezoelectric substrate and the second interdigital transducer; the thickness of the transition layer is 8nm-15nm.

[0013] The aforementioned closed coating system based on surface acoustic waves, wherein the reaction tank consists of a tank wall and a tank bottom attached to the side of the tank wall near the piezoelectric substrate.

[0014] The aforementioned closed coating system based on surface acoustic waves, wherein the depth of the reaction cell is 3nm-6nm and the inner diameter of the reaction cell is 8mm-14mm.

[0015] A method for preparing a chiral perovskite thin film includes the following steps:

[0016] Provides a closed-loop coating system based on surface acoustic waves;

[0017] A perovskite precursor solution is injected into the reaction cell, and a substrate is placed on the side of the reaction cell away from the piezoelectric substrate.

[0018] Rayleigh waves are emitted using the first interdigital transducer and the second interdigital transducer and applied to the perovskite precursor solution in the reaction cell to obtain a substrate coated with the perovskite precursor solution.

[0019] The substrate coated with the perovskite precursor solution was annealed to obtain a chiral perovskite film.

[0020] The method for preparing the chiral perovskite thin film, wherein the solute in the perovskite precursor solution is selected from (S / R-MBA)₂PbI₄, PbBr₂-CsBr-S- / R-NEABr, (S- / R-NEA)₂PbI₄, etc.4(1-γ) Br 4γ , (S- / R-NEA)2PbI4, (S- / R-NEA)PbI3, (S-MBA)2PbI 4(1-x) Br 4x One or more of (R- / S-MBA)2CuCl4; the solvent in the perovskite precursor solution is selected from one or more of N,N-dimethyl sulfoxide and dimethyl sulfoxide.

[0021] The method for preparing the chiral perovskite thin film, wherein the annealing temperature is 90℃-110℃ and the annealing time is 7min-10min.

[0022] A chiral perovskite thin film is prepared using a chiral perovskite thin film preparation method.

[0023] Beneficial Effects: This invention provides a closed-loop coating system based on surface acoustic waves (SAWs), a chiral perovskite thin film, and a method for preparing the same. The closed-loop coating system includes a piezoelectric substrate, and a first interdigital transducer, a second interdigital transducer, and a reaction cell disposed on the piezoelectric substrate. The first and second interdigital transducers are offset from each other, and the reaction cell is disposed between the first and second interdigital transducers. This invention utilizes the electrical signals on the offset first and second interdigital transducers, which are converted into deformations under the action of the piezoelectric substrate. The periodic deformation constitutes a SAW and propagates along the surface of the piezoelectric substrate, then acts on the precursor solution in the reaction cell, causing it to rotate and completing the coating process on the lower surface of the target substrate covering the top of the reaction cell. Furthermore, the reaction cell and the target substrate covering the top of the reaction cell form a closed environment, isolating air while constraining the precursor solution within the cell to form a vortex, thus achieving coating of the target substrate. This closed coating system based on surface acoustic waves has a simple structure, and the coating process on the target substrate is simple, fast, and effectively reduces costs, without requiring an inert gas environment. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a closed coating system based on surface acoustic waves according to the present invention;

[0025] Figure 2 This is a schematic diagram of the layout of the first interdigital transducer and the second interdigital transducer.

[0026] Figure 3 This is a graph showing the reflection coefficient of a single IDT in Example 1;

[0027] Figure 4 This is a graph showing the surface displacement test results of the IDT measured by the laser vibrometer in Example 1;

[0028] Figure 5 SEM image of the SAW film in Example 1;

[0029] Figure 6 This is an SEM image of the spin-coated film in Example 1;

[0030] Figure 7 The XRD diffraction patterns of the SAW membrane in Example 1 after 1, 3, 5, and 12 days in a laboratory environment;

[0031] Figure 8 The absorption spectra of the SAW film and spin-coated film in Example 1 are shown.

[0032] Figure 9 The direct band gap diagrams are shown for the SAW film and spin-coated film in Example 1.

[0033] Figure 10 The circular dichroism spectra of the SAW film and spin-coated film in Example 1 are shown.

[0034] Figure 11 The asymmetry factor g of the SAW film in Example 1 CD Data chart;

[0035] Figure 12 This is a graph showing the relationship between the absorbance and wavelength of the SAW film in Example 1. Detailed Implementation

[0036] This invention provides a closed-loop coating system based on surface acoustic waves, a chiral perovskite thin film, and a method for preparing the same. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0037] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0038] like Figure 1 and Figure 2 As shown, the present invention provides a closed coating system based on surface acoustic waves, including a piezoelectric substrate 10, and a first interdigital transducer 20, a second interdigital transducer 30 and a reaction cell 40 disposed on the piezoelectric substrate 10.

[0039] The first interdigital transducer 20 and the second interdigital transducer 30 are offset from each other and arranged opposite to each other, and the reaction tank 40 is disposed between the first interdigital transducer 20 and the second interdigital transducer 30.

[0040] In this embodiment, the electrical signals on the first and second interdigital transducers, which are staggered and oppositely positioned, are converted into deformations under the action of a piezoelectric substrate. The periodic deformations constitute surface acoustic waves (SAWs) that propagate along the surface of the piezoelectric substrate and then act on the precursor solution in the reaction tank, causing it to rotate and completing the coating process on the lower surface of the target substrate covering the top of the reaction tank. Furthermore, the reaction tank and the target substrate covering the top of the reaction tank can form a closed environment, isolating air while constraining the precursor solution within the tank to form a vortex, thus achieving coating of the target substrate. This surface acoustic wave-based closed coating system (SAWM) has a simple structure, is convenient and fast in coating the target substrate, effectively reduces costs, and does not require an inert gas environment.

[0041] Specifically, the electrical signals on the first and second interdigital transducers, which are positioned at different relative positions, are converted into deformations under the action of the piezoelectric substrate. The periodic deformations constitute surface acoustic waves and propagate along the surface of the piezoelectric substrate, generating shear force on the precursor solution in the reaction cell. The precursor solution forms a vortex under the constraint of the reaction cell. The precursor solution rotates and is coated on the lower surface of the target substrate covering the top of the reaction cell. Since the target substrate covers the top of the reaction cell and forms a closed space with the reaction cell, it can isolate the air while constraining the precursor solution in the cell to form a vortex, thus completing the coating. Furthermore, due to the characteristics of surface acoustic waves (SAWs), after the two wave beams generated by the first and second interdigital transducers come into contact with the precursor solution in the reaction tank, their energy is rapidly coupled to the precursor solution, propelling it into motion. The misalignment between the first and second interdigital transducers causes the two wave trains to generate shear forces and produce vortices. The precursor solution begins to rotate and maintains contact with the lower surface of the target substrate, simultaneously initiating adsorption and nucleation, thus completing the coating of the target substrate. Finally, annealing promotes crystal growth, allowing the crystals to gradually cover the target substrate and form a perovskite thin film. In addition, the aforementioned closed-loop coating system based on SAWs can be used for chiral perovskite coatings under conventional environments. Furthermore, tests have shown that films prepared using the SAW system exhibit higher crystallinity and narrower band gaps compared to traditional spin-coated films.

[0042] In some implementations, such as Figure 2As shown, the misalignment (denoted by α) between the first interdigital transducer and the second interdigital transducer is 40%-60%. When the electrical signals on the first interdigital transducer and the second interdigital transducer are converted into deformation under the action of the piezoelectric substrate, and the periodic deformation constitutes a surface acoustic wave that propagates along the surface of the piezoelectric substrate, the first interdigital transducer and the second interdigital transducer, with the misalignment controlled between 40%-60%, can exert a pushing effect on the precursor solution in the reaction cell, causing the precursor solution to rotate and form a vortex, and complete the coating on the lower surface of the target substrate at the top of the reaction cell.

[0043] In a preferred embodiment, the misalignment between the first interdigital transducer and the second interdigital transducer is 50%, that is, the relative width of the interdigital fingers of the first interdigital transducer and the second interdigital transducer in the working interval is half of the total width, so that the two columns of surface acoustic waves generated by the first interdigital transducer and the second interdigital transducer shear the precursor solution in the reaction cell and form vortices to complete the coating of the target substrate.

[0044] In some implementations, such as Figure 2 As shown, the wavelength (denoted by λ) of the first interdigital transducer is 200-300 micrometers; the wavelength (denoted by λ) of the second interdigital transducer is 200-300 micrometers. By adjusting the wavelengths of the first and second interdigital transducers, the output wave mode and energy (Rayleigh wave) can be changed, thereby adjusting the morphology and quality of the film.

[0045] In a preferred embodiment, the wavelengths of both the first interdigital transducer and the second interdigital transducer are 200 micrometers, and the SAW wavelengths they generate are similar to those of the first interdigital transducer and the second interdigital transducer.

[0046] In some embodiments, the interdigital width (denoted by β) of the first interdigital transducer and the second interdigital transducer is 50 μm.

[0047] In some embodiments, a transition layer is further provided between the piezoelectric substrate and the first interdigital transducer, and between the piezoelectric substrate and the second interdigital transducer; the thickness of the transition layer is 8nm-15nm. By providing a transition layer between the piezoelectric substrate and the first interdigital transducer, and between the piezoelectric substrate and the second interdigital transducer, the adhesion of the first and second interdigital transducers to the piezoelectric substrate can be increased.

[0048] In a preferred embodiment, the transition layer is a chromium layer with a thickness of 10 nm.

[0049] In some embodiments, the first interdigital transducer and the second interdigital transducer are made of gold or aluminum.

[0050] In some embodiments, the piezoelectric substrate is one of lithium niobate, lithium tantalate, zinc oxide, and aluminum nitride piezoelectric substrates.

[0051] In some embodiments, the angle between the lithium niobate wafer in the lithium niobate piezoelectric substrate and the Y-axis of the lithium niobate crystal coordinate system is 128° (Y-128°), and the thickness of the lithium niobate piezoelectric substrate is 500±10μm. This is to ensure that the output wave of the designed closed coating system is a Rayleigh wave, and that the Rayleigh wave penetrates the thickness of the lithium niobate piezoelectric substrate by 1.8-2.0 times the wavelength. Excessive thickness of the piezoelectric substrate will also affect the wave mode.

[0052] In a preferred embodiment, the thickness of the lithium niobate piezoelectric substrate is 0.5 mm, and the Rayleigh wave penetrates the thickness of the lithium niobate piezoelectric substrate by 1.9 times the wavelength.

[0053] In some embodiments, the reaction cell consists of a cell wall and a cell bottom attached to the cell wall near the piezoelectric substrate. By using the cell wall and cell bottom to form the reaction cell, a target substrate is placed on top of the reaction cell during coating, creating a closed environment that isolates air. The staggered arrangement of the first and second interdigital transducers generates shear force on the precursor solution, causing the precursor solution to form a vortex under the constraint of the reaction cell. The precursor solution rotates and coats the lower surface of the target substrate above.

[0054] In some embodiments, the depth of the reaction cell is 3nm-6nm, and the inner diameter of the reaction cell is 8mm-14mm.

[0055] Specifically, the reaction cell is formed by bonding acrylic walls to a glass sheet using PDMS, with a depth of 3 nm and an inner diameter of 10 mm. This allows the precursor solution that generates vortices to more easily adsorb and nucleate on the lower surface of the target substrate covering the top of the reaction cell.

[0056] In some embodiments, the reaction tank is cylindrical.

[0057] In some embodiments, the first interdigital transducer and the second interdigital transducer are driven by an RF signal; that is, an RF signal is generated by an RF signal generator and a power amplifier to drive the first interdigital transducer and the second interdigital transducer at a resonant frequency.

[0058] In some embodiments, the surface acoustic wave-based closed coating system is manufactured using a two-stage process of photolithography and vapor deposition. First, photolithography is performed using a UV exposure lithography system (Medas-MDA400M, South Korea), where a homogenizer is used to uniformly coat a lithium niobate substrate with photoresist (SUN-lift 1303, Xingtai Technology, China). The lithium niobate substrate is then heated at 65-70°C for 30-40 seconds, followed by further heating at 90-100°C for 80-90 seconds, and then exposed to UV light for approximately 2 seconds. This process heats and dries the spin-coated photoresist, simultaneously mitigating internal stress caused by spin coating and improving adhesion. Subsequently, the UV-exposed lithium niobate substrate is sequentially heated at 65-70°C for 20-30 seconds, at 95-100°C for 20-30 seconds, and at 100-105°C... The process involves heating for 100-110 seconds to achieve a stable exposure reaction, and segmentation helps prevent photoresist cracking. After heating, the substrate is allowed to cool to room temperature, then developed in a developer solution (SUN-238D, Xingtai Technology, China) for 15 seconds, followed by rinsing with deionized water to remove any residual developer. A high-vacuum evaporation machine (Pengcheng-PCZF500, China) is then used for evaporation to fabricate the first and second interdigital transducers. Finally, the coated lithium niobate wafer is immersed in acetone for stripping, completing the fabrication of the surface acoustic wave (SAW) closed-loop coating system. In this process, development removes the photoresist partially covered by the mask, leaving the uncovered portion as the device pattern. Metal is directly deposited onto the uncovered portion to form the device. The portion covered by photoresist is stripped by immersion in acetone, causing the photoresist to detach along with the coating, leaving only the portion directly deposited on the substrate to form the device.

[0059] In addition, the present invention also provides a method for preparing a chiral perovskite thin film, comprising the following steps:

[0060] Step S10: Provide a closed coating system based on surface acoustic waves;

[0061] Step S20: Inject a perovskite precursor solution into the reaction cell and cover the side of the reaction cell away from the piezoelectric substrate with a substrate;

[0062] Step S30: Rayleigh waves are emitted using the first interdigital transducer and the second interdigital transducer and acted on the perovskite precursor solution in the reaction cell to obtain a substrate coated with the perovskite precursor solution.

[0063] Step S40: Anneal the substrate coated with the perovskite precursor solution to obtain a chiral perovskite film.

[0064] In this embodiment, utilizing the closed coating system based on surface acoustic waves, the electrical signals on the first and second interdigital transducers, positioned at offset relative positions, are converted into deformations under the action of the piezoelectric substrate. These periodic deformations constitute surface acoustic waves that propagate along the surface of the piezoelectric substrate, generating shear force on the perovskite precursor solution within the reaction tank. The perovskite precursor solution forms vortices under the constraint of the reaction tank, rotating and maintaining contact with the lower surface of the substrate. Simultaneously, adsorption and nucleation begin, completing the coating on the substrate. Finally, annealing promotes crystal growth, and the crystals gradually cover the substrate to form a chiral perovskite thin film. This method for preparing chiral perovskite thin films allows for coating in a laboratory environment and can produce films with higher crystallinity and narrower band gaps. Furthermore, the system allows for film control and is scalable.

[0065] In some embodiments, the solute in the perovskite precursor solution is selected from organic / inorganic hybrid perovskites (S / R-MBA)₂PbI₄, PbBr₂-CsBr-S- / R-NEABr, (S- / R-NEA)₂PbI₄. 4(1-γ) Br 4γ , (S- / R-NEA)2PbI4, (S- / R-NEA)PbI3, (S-MBA)2PbI 4(1-x) Br 4x The perovskite precursor solution contains one or more of (R- / S-MBA)₂CuCl₄; the solvent in the perovskite precursor solution is an organic solvent, including one or more of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Preferably, the solute in the perovskite precursor solution is (S / R-MBA)₂PbI₄, and the organic solvent is N,N-dimethylformamide. Chiral perovskite films can be prepared using the above perovskite precursor solution. Here, MBA is methylbenzylamine, NEA is ethylamine, and the preceding S and R refer to the S-chirality and R-chirality of these two organic compounds, respectively.

[0066] In some embodiments, in step S20, the substrate is cleaned and activated before coating; this includes the steps of ultrasonically cleaning the substrate with alcohol and water for 10 minutes each, followed by PLASMA treatment for one minute to activate its surface. Activation treatment enhances its hydrophilicity and promotes the adsorption and nucleation process of the perovskite precursor solution.

[0067] In some embodiments, the substrate includes, but is not limited to, a glass sheet.

[0068] In some embodiments, the annealing temperature is 90°C-110°C, and the annealing time is 7 min-10 min. Annealing promotes crystal growth, and the crystal gradually covers the substrate to form a chiral perovskite thin film.

[0069] In a preferred embodiment, the annealing temperature is 100°C and the annealing time is 8 minutes.

[0070] In some embodiments, in step S20, before injecting the perovskite precursor solution into the reaction cell, 2 microliters of coupling liquid (composed of equal mass of glycerol and water) are dropped at the bottom of the reaction cell to ensure that the reaction cell is fully in contact with the piezoelectric substrate to promote the propagation of surface acoustic waves.

[0071] Specifically, steps S20 and S30 include: mixing the prepared (S / R-MBA)2PbI4 powder with the solvent DMF according to the mass ratio, and shaking until completely dissolved to obtain a perovskite precursor solution with a mass fraction of 30 wt%; filling the reaction cell with the perovskite precursor solution, covering it with a treated substrate glass plate, connecting it with an RF signal of the corresponding frequency, amplifying the RF signal with a power amplifier, and then splitting it equally between two interdigital transducers through a power equalizer, and converting it into Rayleigh waves that propagate along the piezoelectric substrate and act on the perovskite precursor solution in the reaction cell.

[0072] In this embodiment, to avoid damage to the device due to excessive power, a coating is applied using an input power of 4W (2W for a single interdigital transducer) for 10 minutes.

[0073] In addition, the present invention also provides a chiral perovskite thin film, which is prepared using the method for preparing the chiral perovskite thin film.

[0074] In this embodiment, the chiral perovskite thin film prepared by the method described above has higher crystallinity and narrower band gap. This method can improve the crystallinity of the film and reduce the band gap, while also allowing for parameter adjustment to control the film, thus exhibiting a certain degree of scalability.

[0075] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0076] Example 1

[0077] This embodiment provides a closed coating system based on surface acoustic waves, and uses this system to prepare chiral perovskite thin films, as detailed below:

[0078] The surface acoustic wave-based closed coating system (SAWM) provided in this embodiment mainly consists of a lithium niobate piezoelectric substrate, interdigital transducers (IDTs), and a reaction cell. A 10nm thick chromium layer is first deposited on the lithium niobate piezoelectric substrate as a transition layer, followed by a 100nm thick gold layer as the electrode of the IDT. A 0.5 misalignment is introduced between the two interdigital transducers, meaning the relative width of the interdigital fingers of the two opposing transducers in the working area is half the total length. The reaction cell is formed by bonding acrylic walls to a glass sheet using PDMS, with a depth of 3mm and an inner diameter of 10mm.

[0079] The closed-loop coating system based on surface acoustic waves in this embodiment is characterized as follows:

[0080] Reflection coefficient curves during testing using a network vector analyzer. Figure 3 This is a reflection coefficient curve of a single IDT, reflecting that the IDT's operating frequency is around 18.2 MHz, and its curve shape conforms to the Rayleigh wave mode; specifically, its excitation resonant frequency is 18.181 MHz. The surface displacement of the IDT was measured using a laser vibrometer, and the test results are as follows... Figure 4 As shown, with an input power of 4W (2W for a single IDT), the vibration amplitude of the IDT is 628nm, and the amplitude increases with increasing power, indicating that the power and the amplitude of the IDT are directly related.

[0081] The following describes the preparation of chiral perovskite thin films using this system, specifically including:

[0082] Before coating, the substrate glass slide was ultrasonically cleaned with alcohol and water for 10 minutes each, followed by PLASMA treatment for one minute to activate its surface. The prepared (S / R-MBA)₂PbI₄ powder was mixed with DMF solvent according to the mass ratio and shaken until completely dissolved to obtain a 30 wt% perovskite precursor solution. Two microliters of coupling liquid (a mixture of glycerol and water by mass) were first dropped into the bottom of the reaction cell. Then, the perovskite precursor solution was filled into the reaction cell, and the treated substrate glass slide was placed on top. An RF signal of the corresponding frequency was connected. After amplification by a power amplifier, the RF signal was split equally between two interdigital transducers by a power equalizer, converting it into Rayleigh waves that propagate along the piezoelectric substrate and act on the perovskite precursor solution in the reaction cell. The coating was performed using a 4W input power (2W per IDT) for 10 minutes. After coating, the film was annealed at 100°C for 8 minutes to evaporate the solvent and promote film growth, resulting in a chiral perovskite film (hereinafter referred to as a SAW film).

[0083] As a comparative example, a spin coating method was used to coat the film. First, the film was spin coated at 2000 rpm for 18 seconds, and then at 4000 rpm for 30 seconds. After the coating was completed, the film was annealed at 100°C for 8 minutes to evaporate the solvent and promote film growth, thus obtaining a perovskite film (hereinafter referred to as spin-coated film).

[0084] The thin film was characterized using high-resolution X-ray diffraction (XRD) (X'pertpro, Netherlands) and a Cu-Kα radiation source (λ = 0.15406 nm), and the diffraction patterns of OIHPs were obtained. The microstructure of the chiral perovskite thin film was observed using a field emission scanning electron microscope (SEM) system (ZEISS-GeminiSEM 560, Germany). Circular dichroism data of scattering transmittance were acquired using a circular dichroism spectrometer (JASCO-J1500, Japan). Absorption spectra were obtained using a UV-Vis spectrophotometer equipped with an integrating sphere (Shimadzuu-UV 3600Plus, Japan).

[0085] The morphology of the film prepared by the SAWM system from 30 wt% (S / R-MBA)₂PbI₄ solution was characterized by SEM and TEM. Figure 5 SEM images of the SAW film are shown; the film is composed of stacked needle-like crystals. A spin-coated film prepared from a solution of the same concentration is shown... Figure 6 As shown, the film exhibits a dispersed, flocculent arrangement, and it can be observed that the film prepared using the SAWM system has larger crystals.

[0086] Comparing the XRD diffraction patterns of the two films, it can be found that the positions of the diffraction peaks are consistent, but the XRD diffraction peaks of the SAW film have higher intensity, which further verifies the high crystallinity of the SAW film.

[0087] The film thickness was measured using a profilometer. A line was drawn on the film with tweezers as a control. The average thickness of the film obtained by driving the film with a 30wt% precursor solution at 4W input for 10 minutes was approximately 1.5 μm, which is 2 to 3 times that of the spin-coated film. Furthermore, the stability of the SAW film was tested using XRD diffraction. The film was placed in a laboratory environment (25℃, 40% relative humidity) for 1, 3, 5, and 12 days. Figure 7 As shown, the intensity and position of its XRD diffraction peaks did not change significantly, indicating that the SAW film has a certain degree of chemical stability.

[0088] UV absorption measurements were performed on both the SAW film and the spin-coated film, and their band gaps were calculated to investigate the effect of the SAW method on the optical properties of the thin film. The absorption spectra are shown below. Figure 8As shown, the absorption peaks of both the SAW film and the spin-coated film are located at 486 nm. However, the absorption intensity of the SAW film is greater than that of the spin-coated film, partly due to the difference in thickness between the two films. Furthermore, the cutoff points of the absorption curves of the two films differ significantly. Their direct band gaps were calculated using Tauc plots, as shown below. Figure 9 As shown, the results indicate that the band gap of the SAW film is slightly lower than that of the spin-coated film, which implies an increase in the conductivity of the SAW film. Additionally, the circular dichroism spectrum is shown below. Figure 10 As shown, the SAW film exhibits a significant CD signal; as Figure 11 As shown, the asymmetry factor g of the SAW membrane was calculated using circular dichroism spectroscopy and absorption spectroscopy. CD Approximately 10 -3 Order of magnitude. In addition, this embodiment modified the system parameters to prepare the thin film and found that the input power had a modulation effect on the thin film absorption, such as... Figure 12 As shown, the absorption of the thin film decreases as the power increases.

[0089] In experiments, the CD size of chiral materials can be determined by the absorption asymmetry factor (g). CD ) to quantify:

[0090]

[0091] In the formula, ΔA is the absorption difference between left-handed and right-handed circularly polarized light by the chiral sample, A is the total absorption of unpolarized light, and θ is the ellipticity; for the first perovskite, its g CD The range is generally in the range of 10 -3 -10 -4 Magnitude.

[0092] In summary, this invention provides a closed-loop coating system based on surface acoustic waves (SAWs), a chiral perovskite thin film, and a method for preparing the same. The closed-loop coating system includes a piezoelectric substrate, and a first interdigital transducer, a second interdigital transducer, and a reaction cell disposed on the piezoelectric substrate. The first and second interdigital transducers are offset from each other, and the reaction cell is disposed between the first and second interdigital transducers. This invention utilizes the electrical signals on the offset first and second interdigital transducers, which are converted into deformations under the action of the piezoelectric substrate. The periodic deformation constitutes a SAW and propagates along the surface of the piezoelectric substrate, then acts on the precursor solution in the reaction cell, causing the precursor solution to rotate and completing the coating process on the lower surface of the target substrate covered on top of the reaction cell. Furthermore, the reaction cell and the target substrate covered on top of the reaction cell can form a closed environment, isolating air while constraining the precursor solution in the cell to form a vortex, thereby achieving coating of the target substrate. This closed coating system based on surface acoustic waves has a simple structure, and the coating process on the target substrate is simple, fast, and effectively reduces costs, without requiring an inert gas environment.

[0093] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a chiral perovskite thin film, characterized in that, Including the following steps: Provides a closed-loop coating system based on surface acoustic waves; A perovskite precursor solution is injected into the reaction cell, and a substrate is placed on the side of the reaction cell away from the piezoelectric substrate. Rayleigh waves were emitted by the first and second interdigital transducers, both with an input power of 2W, and applied to the perovskite precursor solution in the reaction cell for 10 minutes to obtain a substrate coated with the perovskite precursor solution. The substrate coated with the perovskite precursor solution was annealed to obtain a chiral perovskite film. The surface acoustic wave-based closed-loop coating system includes a lithium niobate piezoelectric substrate, and a first interdigital transducer, a second interdigital transducer, and a reaction cell disposed on the lithium niobate piezoelectric substrate; the first interdigital transducer and the second interdigital transducer are offset relative to each other, and the reaction cell is disposed between the first interdigital transducer and the second interdigital transducer; the offset between the first interdigital transducer and the second interdigital transducer is 50%; The wavelength of the first interdigital transducer is 200 micrometers; the wavelength of the second interdigital transducer is 200 micrometers; the interdigital width of the first and second interdigital transducers is 50 μm; A transition layer is provided between the lithium niobate piezoelectric substrate and the first interdigital transducer, and between the lithium niobate piezoelectric substrate and the second interdigital transducer; the transition layer is a chromium layer; the thickness of the transition layer is 10 nm; the angle between the lithium niobate wafer in the lithium niobate piezoelectric substrate and the Y-axis of the lithium niobate crystal coordinate system is 128°; the thickness of the lithium niobate piezoelectric substrate is 0.5 mm; the Rayleigh wave penetration thickness into the lithium niobate piezoelectric substrate is 1.9 times the wavelength; the reaction cell is formed by bonding acrylic material walls and glass sheets with PDMS; the depth of the reaction cell is 3 nm-6 nm; the inner diameter of the reaction cell is 8 mm-14 mm; the reaction cell is cylindrical; the first interdigital transducer and the second interdigital transducer are driven by RF signals; The solute in the perovskite precursor solution is selected from (S / R-MBA)₂PbI₄, PbBr₂-CsBr-S- / R-NEABr, and (S- / R-NEA)₂PbI₄. 4(1-γ) Br 4γ , (S- / R-NEA)2PbI4, (S- / R-NEA)PbI3, (S-MBA)2PbI 4(1-x) Br 4x One or more of (R- / S-MBA)2CuCl4; the solvent in the perovskite precursor solution is selected from one or more of N,N-dimethylformamide and dimethyl sulfoxide; the substrate is a glass sheet; The annealing temperature is 100°C and the annealing time is 8 minutes.

2. A chiral perovskite thin film, characterized in that, The chiral perovskite thin film was prepared using the method described in claim 1.

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