A method for preparing a lead-free antimony bismuth double perovskite film

Abstract

This invention relates to the field of lead-free perovskite optoelectronic materials technology, and discloses a method for preparing lead-free antimony-bismuth double perovskite thin films, comprising the following steps: (1) CsBr, AgBr, and BiBr3 are mixed in stoichiometric ratio and dissolved in a mixed solvent composed of DMF and DMSO to obtain a precursor solution; (2) substrate pretreatment; (3) pulse spraying of the precursor solution using a multi-zone temperature-controlled nozzle, and film formation is achieved through gradient crystallization; (4) in-situ laser thickness measurement is performed simultaneously during the spraying process, and the film thickness is monitored in real time and controlled in a closed loop; (5) high-temperature annealing is performed after spraying to obtain a lead-free antimony-bismuth double perovskite thin film. This invention optimizes the microstructure of the thin film and improves its optoelectronic performance through a gradient crystallization control strategy. By using a multi-zone temperature-controlled nozzle and pulse spraying technology, the process stability and product uniformity are improved, and raw material waste is reduced. In-situ laser thickness measurement is used to synchronize deposition and detection, shortening the debugging cycle and improving product yield.

Description

Technical Field

[0001] This invention relates to the field of lead-free perovskite optoelectronic materials technology, specifically to a method for preparing a lead-free antimony-bismuth double perovskite thin film. Background Technology

[0002] Perovskite luminescent materials represent a promising next-generation luminescent technology for solid-state lighting, with luminous efficiency increasing from less than 5% in 2015 to over 25%. Among traditional lead-based perovskite luminescent materials, methylammonium lead bromide (MAPbBr3) has been extensively studied due to its excellent luminescent properties. However, the toxicity of lead severely restricts its large-scale industrial application, especially in fields with stringent environmental requirements such as automotive lighting. Therefore, developing lead-free perovskite alternatives has become an urgent industry need.

[0003] In lead-free perovskite systems, antimony-bismuth double perovskite (Cs₂AgBiBr₆) has attracted widespread attention due to its advantages such as good chemical stability, low toxicity, and suitable optical band gap. This material has a cubic double perovskite structure with a space group of Fm-3m, and its three-dimensional framework is constructed from alternating AgBr₆ and BiBr₆ octahedra. + It fills the interstices of octahedrons. Currently, the preparation of antimony-bismuth double perovskites is mainly done by solution methods, with mainstream processes including one-step solution spin coating, stepwise vapor deposition, and solution spraying. The one-step solution method dissolves CsBr, AgBr, and BiBr3 precursors in DMF or DMSO in stoichiometric ratios, and then spin-coates or sprays them before annealing and crystallizing at 150-300℃ to form a film. The stepwise vapor deposition method first evaporates and deposits BiBr3, and then co-evaporates CsBr and AgBr to complete the phase transformation. The solution spraying method can atomize and spray the precursors onto a heated substrate to form a film in situ, which has the advantage of large-area preparation.

[0004] One-step solution deposition suffers from significant differences in the solubility and volatilization rates of the three precursors, leading to elemental segregation during drying. CsBr tends to precipitate prematurely, while BiBr3 is easily lost through volatilization, resulting in deviations from the stoichiometric ratio. Furthermore, the narrow annealing temperature window and temperature fluctuations easily generate impurities such as Cs3Bi2Br9 and AgBr, significantly increasing non-radiative recombination losses and resulting in a marked decrease in luminous efficiency. Simultaneously, the intrinsic photoluminescence quantum yield (PLQY) of Cs2AgBiBr6 is only 10-15%, far below the 30% or higher required for commercial automotive LED chips. While existing doping or passivation strategies can increase the quantum yield to 25%, they suffer from poor doping uniformity, are prone to concentration quenching, and the dopant elements easily migrate at high temperatures, leading to luminous performance degradation and failing to meet the long-term reliability requirements of automotive lights. Stepwise vapor deposition (PVD) involves complex equipment, and stepwise deposition can easily lead to poor interfacial bonding, uneven component distribution, and low stoichiometric control accuracy, making it difficult to guarantee film density and crystal quality, thus hindering its suitability for large-scale production.

[0005] While solution spraying can achieve large-area deposition, traditional processes lack coordinated control over atomized particle size, spraying speed, and substrate temperature, resulting in poor film thickness uniformity (RSD > 15%). The spread of atomized droplets is significantly affected by ambient humidity, easily leading to pinholes and cracks, which can cause failure under the thermal cycling conditions of automotive lights. Furthermore, the lack of in-situ thickness monitoring means that deposition rates cannot be fed back in real time, resulting in long process debugging cycles and poor batch consistency, making it difficult to meet the stringent requirements of the automotive industry for yield (>95%) and reliability. In addition, traditional solution methods suffer from low precursor utilization and organic solvent pollution. Large amounts of DMF and DMSO volatilize during annealing, resulting in precursor utilization rates below 60%. High-boiling-point solvent residues can easily form defect states, reducing luminous efficiency, and solvent volatilization poses environmental and health risks, which is inconsistent with the trend of green manufacturing. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing lead-free antimony-bismuth double perovskite thin films, aiming to solve at least one problem existing in the prior art, such as poor film uniformity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a lead-free antimony-bismuth double perovskite thin film includes the following steps: (1) CsBr, AgBr and BiBr3 were mixed in stoichiometric ratio and dissolved in a mixed solvent of DMF and DMSO to obtain a precursor solution; (2) Substrate pretreatment; (3) A multi-zone temperature-controlled nozzle is used to pulse spray the precursor solution, and film formation is achieved through gradient crystallization; (4) In-situ laser thickness measurement is performed simultaneously during the spraying process to monitor and control the film thickness in real time; (5) After the coating is completed, high-temperature annealing is performed to obtain a lead-free antimony bismuth double perovskite film.

[0008] Preferably, the molar ratio of CsBr, AgBr and BiBr3 is 2:1:1; the mixed solvent is composed of DMF and DMSO in a volume ratio of (6-8):(4-2).

[0009] Preferably, the mixed solvent is composed of DMF and DMSO in a volume ratio of 7:3.

[0010] Preferably, during substrate pretreatment, the substrate is ultrasonically cleaned sequentially with detergent, deionized water, anhydrous ethanol, and isopropanol, dried with nitrogen, and then treated with ultraviolet ozone to obtain a hydrophilic substrate.

[0011] Preferably, the multi-zone temperature control nozzle includes a first heating zone, a second heating zone, and a spiral heating wire; the temperature of the first heating zone is 80-100℃, the temperature of the second heating zone is 150-180℃, and the temperature of the spiral heating wire is 200-250℃.

[0012] Preferably, during gradient crystallization, when the film grows to 0-20% of the target thickness, the substrate temperature is 200-250°C; when the film grows to 20%-100% of the target thickness, the substrate temperature is 250-280°C.

[0013] Preferably, pulse spraying is performed by alternating pulse spraying and nitrogen purging. During pulse spraying, the pulse width is 10-100 ms and the purging time is 100-500 ms. During nitrogen purging, the nitrogen flow rate is 500-1000 sccm and the purging time is 100-300 ms.

[0014] Preferably, in-situ laser thickness measurement uses a 532nm or 650nm laser, and collects thickness data at a frequency of 10-100Hz, with the beam incident perpendicularly on the thin film surface.

[0015] Preferably, during high-temperature annealing, the annealing temperature is 270-290℃ and the annealing time is 8-15 minutes.

[0016] Preferably, the precursor solution contains a MAPbI2Br dopant, and the molar ratio of CsBr, AgBr, BiBr3 and MAPbI2Br is 2:1:1:0.45.

[0017] The present invention has the following beneficial effects: 1. This invention achieves gradient crystallization of the thin film from the surface to the interior by controlling the solvent evaporation rate and substrate temperature through a gradient crystallization strategy. The surface layer of the thin film is a rapid nucleation region, forming a dense protective layer; the interior is a slow growth region, forming large-sized grains; a continuous gradient transition structure is formed between the surface and the interior, avoiding abrupt changes in the crystallization rate. In the initial stage of spraying, when the film grows to 0-20% of the target thickness, the substrate temperature is controlled at 200-250℃. The atomized droplets evaporate rapidly, and the supersaturation of the precursor increases rapidly, forming a large number of fine crystal nuclei on the substrate surface. The grain size is about 50-100nm, and the grain boundaries are dense, which can inhibit impurity penetration and reduce surface recombination. In the middle and later stages of spraying, when the film grows to 20%-100% of the target thickness, the substrate temperature rises to 250-280℃. The solvent evaporation rate slows down, the precursor rearranges and grows fully, and the grain size increases to 300-500nm. The number of grain boundaries is significantly reduced, which is beneficial for long-range carrier transport. By segmented temperature control, a gradient transition layer with a thickness of about 200-300nm is formed. The grains continuously increase from the surface to the inside, which can release thermal stress and avoid film cracking. This strategy can significantly reduce surface roughness, increase grain size, improve carrier mobility, and reduce defect state density. 2. This invention incorporates a first heating zone, a second heating zone, and a spiral heating wire within the nozzle. Combined with a temperature sensor and a PID controller, it achieves independent and precise temperature control across multiple zones of the precursor flow channel. The first heating zone, located at the nozzle inlet, operates at 80-100°C and is used for precursor preheating, reducing solution viscosity, and improving atomization uniformity. The second heating zone, located in the middle of the nozzle, operates at 150-180°C and is used for partial vaporization of the atomized droplets, shortening spreading time and increasing film density. The spiral heating wire, arranged around the nozzle outlet, operates at 200-250°C and is used to eliminate the temperature gradient at the nozzle outlet, ensuring uniform droplet temperature. Each heating zone measures its temperature in real-time and adjusts its power in a closed-loop manner, achieving a temperature control accuracy of ±2°C. Multi-zone temperature control significantly improves nozzle temperature uniformity and film thickness uniformity, increases precursor utilization, and reduces batch-to-batch performance fluctuations. 3. This invention integrates a laser thickness sensor below the nozzle, which works synchronously with the spraying system to achieve in-situ, real-time thickness monitoring during the deposition process. It uses a 532 nm or 650 nm laser, with the beam perpendicularly incident on the film surface, to collect thickness data in real time and upload it to the control system. Based on the deviation between the measured thickness and the target thickness, the system dynamically adjusts parameters such as spraying speed and precursor flow rate to achieve closed-loop thickness control. Combined with a two-dimensional scanning platform, it can perform gridded thickness monitoring of the substrate, identify weak areas such as edges, and automatically perform compensatory spraying, significantly improving the uniformity of large-area film thickness. This technology can greatly shorten the process debugging cycle, improve thickness control accuracy, and enhance batch yield and product consistency. 4. This invention employs a dual-valve pulse controller and a micro-flow precision valve to change the precursor delivery mode from continuous to pulsed mode. Each pulse includes an injection phase (10-100ms) and a nitrogen purging phase (100-500ms). The film growth rate and composition are controlled by adjusting the pulse width and frequency. The system uses two independent precision valves to control the main precursor solution (a mixed solution of CsBr+AgBr+BiBr3) and the dopant precursor solution (such as MAPbI2Br solution), respectively. By adjusting the pulse timing and duty cycle, a gradient distribution of dopant elements can be achieved. For example, the doping ratio can be increased in the early stage of film growth and gradually decreased in the later stage, resulting in a highly doped surface and a low-doped interior. The system features a complex gradient structure; the micro-flow valve enables high-precision flow control, with a minimum flow resolution of 0.1 μL / min, ensuring stable stoichiometry for the thin film. This precision is crucial for controlling the stoichiometry, especially since an Ag / Bi ratio deviation exceeding 5% can trigger impurity phase formation. After the pulse ends, high-purity nitrogen is used to purge the nozzle and chamber to remove residual precursors and prevent cross-contamination. This system significantly improves the stoichiometry control accuracy and doping uniformity, reducing the stoichiometry control accuracy from ±5% to ±1%, shortening the response time (pulse switching response time from 500 ms to 50 ms), increasing film density, and reducing defects such as pinholes. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: Preparation of antimony-bismuth double perovskite thin films A method for preparing a lead-free antimony-bismuth double perovskite thin film includes the following steps: (1) Preparation of precursor solution: Weigh CsBr (0.4 mmol), AgBr (0.2 mmol) and BiBr3 (0.2 mmol) according to the stoichiometric ratio Cs:Ag:Bi=2:1:1, add 2 mL of a mixed solvent of DMF and DMSO with a volume ratio of 7:3, and stir magnetically at 60℃ for 2 hours until completely dissolved to obtain a precursor solution with a concentration of 0.4 M. Filter the solution through a 0.22 μm PTFE filter membrane to remove insoluble particles in the solution and set aside for later use. (2) Substrate pretreatment: FTO conductive glass was selected as the substrate for preparing the thin film. It was ultrasonically cleaned for 15 minutes in sequence with detergent, deionized water, anhydrous ethanol and isopropanol to remove oil, impurities and residual moisture on the substrate surface. After cleaning, it was dried with nitrogen and then placed in an ultraviolet ozone cleaner for 20 minutes to further remove residual pollutants on the surface and improve the hydrophilicity of the substrate surface to obtain a hydrophilic substrate, which is convenient for subsequent thin film deposition. (3) Spraying deposition and temperature control: The filtered precursor solution is loaded into the solution storage tank of the multi-zone temperature-controlled nozzle. The temperature of each heating zone of the nozzle is set as follows: the temperature of the first heating zone is 90℃, the temperature of the second heating zone is 160℃, and the temperature of the spiral heating wire is 220℃ to ensure that the precursor solution is preheated and partially vaporized uniformly. The gradient crystallization temperature control mode is adopted. In the stage of film growth to 0-20% of the target thickness, the temperature of the substrate heating stage is controlled at 220℃-250℃ to achieve rapid nucleation on the film surface. In the stage of film growth to 20%-100% of the target thickness, the temperature of the substrate heating stage is raised to 250℃-280℃ to achieve slow growth of grains inside the film. The pulse spraying mode is adopted, and the pulse spraying and nitrogen purging are alternated. The pulse width is set to 50ms, the pulse interval is 300ms, the nitrogen purging flow rate is 800sccm, the distance between the nozzle and the substrate is set to 30mm, the two-dimensional scanning speed is 20mm / s, and the spraying system is started to begin film deposition. (4) In-situ thickness monitoring: The laser thickness sensor is started synchronously. A 532nm laser is used. The beam is incident perpendicularly on the film surface. The film thickness is calculated by interference signal. The thickness data is collected in real time at a set frequency and transmitted to the control system. The control system dynamically adjusts the spraying parameters according to the deviation between the real-time monitored thickness and the target thickness (500nm) to ensure uniform film thickness. When the film thickness reaches the target thickness of 500nm, the system automatically stops spraying and records the thickness-time curve for subsequent process optimization. (5) Annealing and crystallization: After the coating is completed, the substrate carrying the film is placed on a hot table at 280°C for annealing for 10 minutes to promote further growth of film grains, completely evaporate residual solvent, and improve the crystallization quality of film; after annealing, the substrate is naturally cooled to room temperature to obtain Cs2AgBiBr6 lead-free antimony bismuth double perovskite film.

[0020] (6) Characterization test: The performance of the prepared Cs2AgBiBr6 lead-free antimony bismuth double perovskite film was characterized. XRD test results showed that the sample was a high-purity cubic phase Cs2AgBiBr6, without impurity phase peaks such as Cs3Bi2Br9 and AgBr, and had good crystallinity. SEM observation showed that the surface of the lead-free antimony bismuth double perovskite film was dense and uniform, without obvious pinholes, cracks and other defects, and the grain size was uniform, about 400 nm. UV-Vis absorption spectroscopy test showed that the optical band gap of the film was 1.92 eV, with excellent photoelectric properties, which can meet the requirements of subsequent applications.

[0021] Example 2: Preparation of antimony-bismuth double perovskite thin films The preparation process of Example 2 is basically the same as that of Example 1, except that MAPbI2Br doping is used and gradient doping is controlled to narrow the optical band gap of the thin film.

[0022] Precursor solution preparation: 15 mol% MAPbI2Br was added to the precursor solution of Example 1, so that the molar ratio of CsBr:AgBr:BiBr3:MAPbI2Br was 2:1:1:0.45. The spraying process adopted a dual-valve pulse control system, which independently controlled the main precursor valve and the doping precursor valve. The pulse timing was set as follows: in the 0-20% stage of film growth to the target thickness, the duty cycle of the doping precursor pulse was 30%, forming a highly doped layer on the surface; in the 20%-80% stage of film growth to the target thickness, the duty cycle was reduced to 15%, forming a gradient transition layer; in the 80%-100% stage of film growth to the target thickness, the duty cycle was reduced to 5%, so that the film interior was kept low doped. This gradient doping method can narrow the band gap while reducing the total amount of lead used.

[0023] Characterization results show that the UV-Vis absorption edge of the obtained film is red-shifted, and the optical band gap is narrowed from 1.92 eV to 1.75 eV; XRD test shows that the sample is still a high-purity cubic phase structure with no phase separation; the photoelectric conversion efficiency is increased from 3.4% to 5.0%.

[0024] Example 3: Preparation of large-area thin films (100 cm²) The preparation process of Example 3 is basically the same as that of Example 1, except that the substrate size is increased to 10×10cm² to verify the feasibility of large-area preparation.

[0025] Process adjustments: The 2D scanning speed was reduced to 10mm / s to ensure consistent deposition per unit area; the laser thickness sensor was enabled with grid mapping function, dividing the substrate into 25 regions of 5×5, and the thickness of each region was monitored independently; thickness uniformity compensation: when the system detects that the thickness of the edge region is too low, it automatically performs compensation spraying, adding 1-2 scans to the edge region; after testing, the obtained film thickness uniformity RSD is 4.8%, which meets the requirements for industrialization.

[0026] Device fabrication and testing: A TiO2 electron transport layer, a Spiro-OMeTAD hole transport layer, and an Au top electrode were sequentially deposited on an FTO / Cs2AgBiBr6 thin film to fabricate a solar cell. Sixteen effective small cells (each cell area 6cm²) were obtained by cutting a 100cm² thin film. The photoelectric conversion efficiency ranged from 4.2% to 4.8%, with an average of 4.5% and a standard deviation of 0.15%, showing excellent batch consistency.

[0027] Example 4: Effect of different annealing temperatures on film properties The preparation process of Example 4 is basically the same as that of Example 1, except that annealing is carried out at 220℃, 250℃, 280℃ and 310℃ respectively to investigate the effect of annealing temperature on the crystallization quality and photoelectric properties of the film.

[0028] Annealing at 220℃: The film has low crystallinity, contains a small amount of amorphous phase, has a grain size of about 150nm, moderate density, and a photoelectric conversion efficiency of 2.8%. Annealing at 250℃ significantly improves crystallinity, with a grain size of approximately 300nm, and increases photoelectric conversion efficiency to 4.1%. Annealing at 280℃: optimal crystallinity, grain size of 400–500 nm, clear grain boundaries, and peak photoelectric conversion efficiency of 4.6%; Annealing at 310℃: XRD showed a small number of Cs2AgBiBr6 impurity phase peaks, and a second phase precipitated at the grain boundaries. The photoelectric conversion efficiency dropped to 3.9%, indicating that excessively high temperatures can easily lead to phase decomposition.

[0029] Conclusion: The optimal annealing temperature of this system is 280℃, and the suitable temperature window is approximately ±20℃. The multi-zone temperature control system of this invention can achieve precise temperature control within this range.

[0030] Example 5: The preparation process of Example 5 is basically the same as that of Example 1, except that the precursor solution is prepared by DMF:DMSO volume ratio of 9:1, 7:3, 5:5 and 3:7 respectively, and the effect of solvent ratio on film morphology and photoelectric properties is investigated.

[0031] 9:1 ​​(High DMF): The solvent evaporates too quickly, resulting in pinholes and cracks on the film surface, and the photoelectric conversion efficiency is 2.5%. 7:3 (equilibrium ratio): The solvent evaporation rate is moderate, the film is dense and uniform, and the photoelectric conversion efficiency is 4.6%; 5:5 (high DMSO): The solvent evaporates slowly, and residual solvent after annealing is prone to causing defects; the photoelectric conversion efficiency is 3.8%. 3:7 (extremely high DMSO): The film was not dried sufficiently, the crystal quality was poor, and the photoelectric conversion efficiency was 2.1%.

[0032] Conclusion: The optimal solvent ratio is DMF:DMSO = 7:3 (volume ratio). The microflow control system of this patent can precisely control the solvent ratio.

[0033] The antimony-bismuth double perovskite thin film prepared using the technology of this invention exhibits the following key properties after testing: Regarding the crystal structure, XRD tests showed that the obtained sample was a high-purity cubic phase Cs2AgBiBr6 (space group Fm-3m), with characteristic diffraction peaks located at 2θ=15.2°, 21.5°, 26.8°, and 30.9°, respectively. There were no diffraction peaks for impurity phases such as Cs3Bi2Br9, AgBr, and BiBr3, and the impurity phase content was less than 2%.

[0034] Regarding the film morphology, SEM observation showed that the film was dense and uniform, with no obvious pinholes or cracks; the surface roughness RMS was 9.5 nm, which was significantly better than the 35-50 nm of the traditional process level; the average grain size was about 420 nm, with clear grain boundaries and uniform grain size distribution.

[0035] In terms of optical performance, UV-Vis absorption spectroscopy tests show that the absorption edge of the thin film is located at 645 nm, and the optical band gap is 1.92 eV. After MAPbl2Br doping, the band gap can be narrowed to 1.75 eV, and the light absorption range can be extended to 710 nm.

[0036] In terms of electrical performance, Hall effect tests showed that the thin film carrier concentration was 1.2 × 10⁻⁶. 15 cm -3 The migration rate reached 18.5 cm. 2 / V·s, significantly superior to traditional processes 5-8cm 2 / V·s; Time-resolved photoluminescence (TRPL) testing showed a carrier lifetime of 380 ns, indicating a significant reduction in internal defect recombination centers in the thin film.

[0037] In terms of device performance, the solar cell assembled using the FTO / TiO2 / Cs2AgBiBr6 / Spiro-OMeTAD / Au structure achieves a photoelectric conversion efficiency of 4.6% under AM1.5G standard illumination, corresponding to an open-circuit voltage of 0.82V, a short-circuit current density of 7.8mA / cm², and a fill factor of 72%. After doping optimization, the photoelectric conversion efficiency is improved to 5.0%, reaching a relatively high level for lead-free double perovskite devices.

[0038] In terms of large-area preparation, the film thickness uniformity RSD is 4.8% with a film area of ​​100cm². The 16-cell small battery made from this film has an average photoelectric conversion efficiency of 4.5% and a standard deviation of 0.15%, with excellent batch consistency, which can meet the requirements of industrial production.

[0039] The present invention has the following beneficial effects: 1. The gradient crystallization control strategy achieves synergistic optimization of thin film surface densification and internal large grains, reducing surface roughness by 75%, increasing grain size by 2-3 times, improving carrier mobility by more than 2 times, and reducing defect state density by two orders of magnitude. 2. By using multi-zone temperature-controlled nozzles, the nozzle temperature uniformity is improved from ±15℃ to ±2℃, the film thickness uniformity is improved from RSD15% to within RSD5%, and the precursor utilization rate is improved from 60% to over 85%, significantly reducing raw material costs. 3. In-situ laser thickness measurement and monitoring technology has achieved the integration of deposition and measurement, shortening the process debugging cycle from 2-3 weeks to 3-5 days, improving the film thickness control accuracy from ±50nm to ±10nm, and increasing the batch yield from 80% to over 95%; 4. By using pulse spraying technology, nano-level spraying volume control is achieved, improving the control accuracy of thin film stoichiometry from ±5% to ±1%, and reducing the pulse switching response time from 500ms to 50ms, providing a technical basis for gradient doping and multilayer structure fabrication; 5. The overall process is green and environmentally friendly, reducing the amount of organic solvents by 40% and increasing the utilization rate of precursors by 25%, which meets the requirements of green manufacturing and sustainable development and has good prospects for industrial application.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a lead-free antimony-bismuth double perovskite thin film, characterized in that, Includes the following steps: (1) CsBr, AgBr and BiBr3 were mixed in stoichiometric ratio and dissolved in a mixed solvent of DMF and DMSO to obtain a precursor solution; (2) Substrate pretreatment; (3) A multi-zone temperature-controlled nozzle is used to pulse spray the precursor solution, and film formation is achieved through gradient crystallization; (4) In-situ laser thickness measurement is performed simultaneously during the spraying process to monitor and control the film thickness in real time; (5) After the coating is completed, high-temperature annealing is performed to obtain a lead-free antimony bismuth double perovskite film.

2. The method for preparing lead-free antimony-bismuth double perovskite thin films according to claim 1, characterized in that, The molar ratio of CsBr, AgBr and BiBr3 is 2:1:1; the mixed solvent is composed of DMF and DMSO in a volume ratio of (6-8):(4-2).

3. The method for preparing lead-free antimony-bismuth double perovskite thin films according to claim 2, characterized in that, The mixed solvent consists of DMF and DMSO in a volume ratio of 7:

3.

4. The method for preparing lead-free antimony-bismuth double perovskite thin films according to claim 1, 2, or 3, characterized in that, During substrate pretreatment, the substrate is ultrasonically cleaned sequentially with detergent, deionized water, anhydrous ethanol, and isopropanol. After being dried with nitrogen, it is treated with ultraviolet ozone to obtain a hydrophilic substrate.

5. The method for preparing lead-free antimony-bismuth double perovskite thin films according to claim 1, 2, or 3, characterized in that, The multi-zone temperature-controlled nozzle includes a first heating zone, a second heating zone, and a spiral heating wire; the temperature of the first heating zone is 80-100℃, the temperature of the second heating zone is 150-180℃, and the temperature of the spiral heating wire is 200-250℃.

6. The method for preparing lead-free antimony-bismuth double perovskite thin films according to claim 1, 2, or 3, characterized in that, During gradient crystallization, the substrate temperature is 200-250℃ when the film grows to 0-20% of the target thickness; and 250-280℃ when the film grows to 20%-100% of the target thickness.

7. The method for preparing lead-free antimony-bismuth double perovskite thin films according to claim 1, 2, or 3, characterized in that, Pulse spraying is performed by alternating between pulse spraying and nitrogen purging. During pulse spraying, the pulse width is 10-100 ms and the purging time is 100-500 ms. During nitrogen purging, the nitrogen flow rate is 500-1000 sccm and the purging time is 100-300 ms.

8. The method for preparing lead-free antimony-bismuth double perovskite thin films according to claim 1, 2, or 3, characterized in that, In-situ laser thickness measurement uses a 532nm or 650nm laser to collect thickness data at a frequency of 10-100Hz, with the beam incident perpendicularly on the thin film surface.

9. The method for preparing lead-free antimony-bismuth double perovskite thin films according to claim 1, 2, or 3, characterized in that, During high-temperature annealing, the annealing temperature is 270-290℃ and the annealing time is 8-15 minutes.

10. The method for preparing a lead-free antimony-bismuth double perovskite thin film according to claim 1, 2 or 3, characterized in that, The precursor solution contains MAPbI2Br dopant, and the molar ratio of CsBr, AgBr, BiBr3 and MAPbI2Br is 2:1:1:0.45.