Vacuum drying system of perovskite thin film, regulation and control method and perovskite thin film

Abstract

The invention discloses a vacuum drying system of a perovskite thin film, a regulation and control method and the perovskite thin film, and belongs to the technical field of perovskite photovoltaics. According to the method, the vacuum drying process of the perovskite thin film is divided into two stages, the first stage is a primary solvent volatilization stage, and the vacuum degree of a vacuum drying cavity is reduced to a first set vacuum degree through a mechanical pump; and the second stage is a perovskite thin film crystallization stage, and the vacuum degree is reduced to a second set vacuum degree through the molecular pump. The mechanical pump and the molecular pump are introduced into the vacuum drying system at the same time for the first time, the mechanical pump and the molecular pump are emphasized to be used in different stages of perovskite film vacuum drying by combining the air exhaust performance of the two pumps, staged accurate regulation and control of the vacuum environment are achieved, and the differentiated requirements of different crystallization stages for the air exhaust rate and the vacuum degree are met. The method and the system provided by the invention can effectively control the solvent evaporation rate in different stages, optimize the crystallization environment and improve the crystallization quality, and are suitable for the preparation of high-efficiency perovskite solar cells.

Description

Technical Field

[0001] The present invention belongs to the field of perovskite photovoltaic cells, and in particular relates to a vacuum drying system and a control method for a perovskite film, and a perovskite film. Background Art

[0002] Perovskite solar cells, due to their high efficiency, low cost, and lightweight characteristics, have become a research hotspot in the field of novel photovoltaics in recent years. The crystallization quality of perovskite films is the most critical factor affecting the performance of perovskite solar cells, directly affecting the device's photoelectric conversion efficiency and long-term stability. During the preparation process, after being coated into a wet film, the perovskite film enters the vacuum drying-assisted film formation stage. This stage is the key crystallization stage for perovskite nucleation and crystal growth. Therefore, factors such as the solvent evaporation rate and the vacuum environment during the perovskite film crystallization process at this stage will have a significant impact on the grain size, film surface flatness, and defect density.

[0003] VCD (Vacuum Crystallization Drying), also known as vacuum drying equipment, is one of the core equipment for perovskite film preparation. The most commonly used vacuum drying-assisted film formation method for preparing perovskite films is to place the coated wet film into a VCD, where vacuum evaporation is performed to provide a good crystallization environment for the film. Current technology typically uses a single vacuum device (such as a mechanical pump or molecular pump) to evacuate the cavity to achieve the desired vacuum level. However, using a single pump to control vacuum often has the following disadvantages: 1. The pumping capacity of a single-pump device is limited to a specific vacuum range, making it difficult to meet the vacuum requirements of the entire process from initial solvent volatilization to crystal nucleation. A mechanical pump can only provide a relatively low vacuum degree. Using a single mechanical pump throughout the entire process will result in a large amount of residual gas under low vacuum conditions. The residual gas molecules will affect the uniform volatilization of the solvent, resulting in uneven crystallization of the film. At the same time, residual water vapor, oxygen, etc. will chemically react with the perovskite material or the incompletely volatilized solvent, affecting the crystallization quality and stability of the film. Although molecular pumps can achieve a higher vacuum degree and provide a high-cleanliness environment, they have a slow startup speed and cannot quickly handle large gas volume pumping requirements. Using only a single molecular pump will cause the initial solvent of the film to evaporate too quickly, causing instability in the crystallization process.

[0004] 2. The solvent evaporation rates required at different stages are different, and a single pump device cannot dynamically adjust the pumping rate, making it difficult to ensure crystallization uniformity and film density. Mechanical pumps are suitable for coarse pumping, and molecular pumps are suitable for fine pumping. However, the speed of solvent evaporation needs to be controlled at different stages from nucleation to grain growth of perovskite films, so the required pumping rates are different. If a single mechanical pump is used throughout the process, excessive solvent evaporation or rapid film shrinkage due to excessive pumping rates will easily form pinholes and cracks. If a single molecular pump is used throughout the process, the pumping rate will be too slow, and the solvent evaporation rate cannot be controlled in time in the early stages of film crystallization, resulting in uneven distribution of crystal nuclei. Therefore, using a single pump cannot dynamically adjust the pumping rate according to the solvent evaporation requirements at different stages of perovskite crystallization, resulting in poor crystallization quality.

[0005] 3. The single-pump vacuum drying technology has poor adaptability to material formulations and process parameters, making it difficult to be widely used in the preparation of perovskite films under different conditions, and has poor repeatability.

[0006] In summary, a single pump is currently used for vacuum drying to assist film formation in the preparation of perovskite films. However, the vacuum degree and pumping rate cannot be precisely controlled according to the requirements of different stages of perovskite crystallization, resulting in problems such as small grain size, poor film uniformity, and many defects in the perovskite film, which seriously affects the photoelectric performance and long-term stability of perovskite solar cells. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a vacuum drying system and control method for perovskite films, as well as perovskite films, so as to solve the technical problems in the prior art of using a single pump for vacuum drying to assist film formation during the preparation of perovskite films, resulting in the inability to accurately control the vacuum degree and the pumping rate according to the requirements of different stages of perovskite film crystallization, resulting in small grain size of the perovskite film, poor film uniformity, and many defects.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: A method for controlling vacuum drying of a perovskite film comprises the following steps: S1, placing the perovskite wet film in a VCD cavity, and reducing the vacuum degree of the VCD cavity to a first set vacuum degree by a mechanical pump within a first set time to remove the solvent; during the mechanical pumping process, the molecular pump rotates and stands by; S2, within the second set time, the vacuum degree of the VCD cavity is reduced from the first set vacuum degree to the second set vacuum degree by the molecular pump, and maintained for a third set time, and the perovskite wet film is crystallized; S3, inflating the VCD cavity to restore the pressure of the VCD cavity to standard atmospheric pressure, and obtaining a vacuum-dried perovskite film.

[0009] A further improvement of the present invention is: Preferably, in S1, the first set vacuum degree is 5-15 Pa, and the first set time is 15-25 s.

[0010] Preferably, in S2, the second set vacuum degree is 0-1 Pa, and the second set time is 5-10 s.

[0011] Preferably, in S2, the third set time is determined according to the solvent type of the perovskite wet film.

[0012] Preferably, in S2, when the solvent of the perovskite wet film is pure DMF, the third set time is 35-45 s.

[0013] Preferably, in S2, when the solvent of the perovskite wet film is a mixed solution of DMSO and DMF, or a mixed solution of DMPU and DMF, the third set time is 40-100 s.

[0014] Preferably, in S3, the pressure of the VCD cavity is restored to standard atmospheric pressure within 3-5 seconds.

[0015] A vacuum drying system for implementing any of the above-mentioned vacuum drying control methods for perovskite films comprises a VCD cavity, a mechanical pump and a molecular pump, wherein the VCD cavity is connected to both the mechanical pump and the molecular pump, and the VCD cavity is connected to an inflation device.

[0016] Preferably, the molecular pump and the VCD cavity are connected through a plurality of molecular pump exhaust pipes, the molecular pump exhaust ports at the connection points between the molecular pump exhaust pipe and the VCD cavity are arranged in an array at the bottom of the VCD cavity, and the lengths of the plurality of molecular pump exhaust pipes are equal; The inflation device is connected to the VCD cavity through a plurality of inflation ports, and the inflation ports are equally divided along the circumference of the side wall of the VCD cavity.

[0017] A perovskite film prepared by any one of the above vacuum drying control methods, wherein the perovskite film is used to prepare a perovskite solar cell.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention discloses a vacuum drying control method for perovskite thin films, which combines the performance characteristics of mechanical pumps and molecular pumps to dynamically match the vacuum environment of perovskite solvent volatilization and crystal growth processes. The method includes a first stage of preliminary solvent volatilization and a second stage of perovskite film crystallization. For the first time, the present invention realizes precise control of vacuum degree and pumping rate in the process of vacuum drying-assisted film formation by switching between mechanical pumps and molecular pumps in different time periods in the preparation of perovskite films. In the first stage of preliminary solvent volatilization, the mechanical pump has the advantage of high efficiency and rough pumping, and a large pumping rate is used for rapid initial pumping, so as to quickly reduce the air pressure in the cavity to a vacuum degree range suitable for preliminary solvent volatilization, thereby avoiding defects such as pinholes and cracks in the crystal caused by insufficient solvent volatilization in the early stage. In the crystallization stage, the molecular pump has the advantages of high vacuum degree, low pumping rate and high clean environment, and the vacuum degree is further precisely controlled within the range of a second set vacuum degree. A low pumping rate is used to achieve dynamic balance of solvent volatilization, thereby providing a stable and clean high vacuum environment for the perovskite film, reducing residual gas, significantly improving the uniformity and crystallization quality of the film, and thus improving the photoelectric performance and stability of the perovskite solar cell device. The present invention fully utilizes the advantages of mechanical pumps and molecular pumps to achieve a dynamic balance in the vacuum environment regulation required for solvent volatilization in different stages. By limiting the pumping time, the requirements of solvent volatilization and crystallization on time and pumping rate in the two stages are met, avoiding the situation where the vacuum degree and pumping rate do not meet the requirements within the set time, thereby affecting each stage. The method is highly versatile and can be applied to the preparation of various types of perovskite films.

[0019] 2. The present invention also discloses a vacuum drying system for perovskite thin films, which implements the aforementioned vacuum drying control method. This system, for the first time, incorporates both a mechanical pump and a molecular pump into a VCD system for combined use in vacuum drying of perovskite thin films. Leveraging their complementary strengths, the mechanical and molecular pumps are specifically targeted at different stages of perovskite film crystallization, meeting the vacuum level and pumping rate requirements at each stage. This allows the solvent evaporation rate from the wet perovskite film to be precisely controlled as needed, providing an optimal growth environment for perovskite film crystallization and improving perovskite film crystallization quality. Compared to single-pump vacuuming technology, the dual-pump (mechanical pump + molecular pump) vacuuming technology provides dynamic optimization conditions for perovskite film crystallization by precisely controlling the vacuum level, pumping rate, and environmental cleanliness, fundamentally improving film quality and device performance. This innovative technology has broad application prospects and is particularly suitable for the large-scale production of high-efficiency perovskite solar cells.

[0020] 3. The present invention also discloses a perovskite film prepared by the above-mentioned vacuum drying control method. The perovskite film prepared by the method of the present invention has a larger grain size and a more uniform grain size, which is beneficial to improving the carrier transmission efficiency of the battery; the surface of the film is smoother and has no obvious pinholes or cracks; when the perovskite film prepared by the method of the present invention is used to prepare a perovskite solar cell device, the photoelectric conversion efficiency of the perovskite solar cell is increased from 18.94% to 20.02%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the preparation process of the perovskite film of the present invention; Figure 2 Schematic diagram of the structure of the vacuum drying system of the present invention; Figure 3 The perovskite solar cell device structure prepared by the present invention; Figure 4 SEM surface and cross-sectional comparison of the PVK film obtained by using a dual-pump VCD vacuum drying process in Example 1 of the present invention and the PVK film obtained by using a single-pump VCD vacuum drying process in the comparative example; Figure 5 This is an XRD comparison diagram of the PVK film obtained by using a dual-pump VCD vacuum drying process in Example 1 of the present invention and the PVK film obtained by using a single-pump VCD vacuum drying process in the comparative example; Figure 6 This is a comparison chart of the efficiencies of perovskite solar cells produced by vacuum drying using dual-pump VCD in Example 1 of the present invention and single-pump VCD in the comparative example.

[0022] Among them, 1-VCD cavity; 2-carrying platform; 3-inlet; 4-outlet; 5-inflating valve; 6-monitor; 7-gate valve; 8-flow control valve; 9-fore valve; 10-pre-pumping valve; 11-molecular pump; 12-mechanical pump. DETAILED DESCRIPTION

[0023] The present invention is described in further detail below with reference to the accompanying drawings: The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0024] A first aspect of the present invention discloses a method for controlling vacuum drying of a perovskite film, comprising the following steps: S1, placing the perovskite wet film in a VCD cavity, and reducing the vacuum degree of the VCD cavity to a first set vacuum degree by a mechanical pump within a first set time to remove the solvent; during the mechanical pumping process, the molecular pump rotates and stands by; S2, within the second set time, the vacuum degree of the VCD cavity is reduced from the first set vacuum degree to the second set vacuum degree by the molecular pump, and maintained for a third set time, and the perovskite wet film is crystallized; S3, inflating the VCD cavity to restore the pressure of the VCD cavity to standard atmospheric pressure, and obtaining a vacuum-dried perovskite film.

[0025] Vacuum drying-assisted film formation technology typically includes two key stages: the initial solvent evaporation stage and the crystallization process of the perovskite film. Each stage has different requirements for vacuum degree and pumping rate: In the first stage, the initial solvent evaporation stage, since the wet film has just been placed in the VCD chamber, most of the solvent in the wet film has not yet evaporated. To avoid the formation of non-uniform crystal nuclei, the pressure in the vacuum chamber needs to be quickly reduced from atmospheric pressure to the first set vacuum degree. The first set vacuum degree is a medium vacuum degree to promote rapid and uniform initial evaporation of the solvent. In the second stage, the perovskite film crystallization process, as the solvent concentration gradually decreases, the system enters the crystal nucleus stabilization and grain growth stage. Therefore, the vacuum needs to be further and steadily reduced to below 1Pa to provide a low-pressure, high-purity environment to suppress impurity interference and slowly remove residual solvent. At the same time, this stage requires a stable pumping process and precise vacuum control to avoid crystal stress or irregular growth caused by pressure fluctuations and ensure that the crystals can grow in an orderly manner. Based on the distinct characteristics of these two stages, the present method meticulously divides the vacuum requirements for each phase. By employing a combination of mechanical and molecular pumps, different pumps are used at different stages to quickly meet the required vacuum level within the VCD cavity, improving the overall crystallization quality. Providing the required vacuum conditions and pressure gradients at each stage regulates the solvent evaporation rate from the film surface and interior, ensuring more uniform crystal growth. The present method utilizes the high cleanliness of the molecular pump to remove residual gas molecules (such as H2O and O2) during the critical crystallization stage, preventing crystal defects caused by external impurities and improving the film's optoelectronic properties and long-term stability.

[0026] During S1, while the mechanical pump is evacuating the chamber, the molecular pump is fully loaded and ready for use. This process is the initial solvent evaporation phase: the coated perovskite film is placed into the VCD chamber, the chamber door is closed, and the molecular pump is started, bringing the molecular pump speed to full load (24,000 rpm) and maintaining this speed until ready for use. The molecular pump configuration in this step ensures rapid startup during Phase 2, meeting application requirements.

[0027] In some embodiments of the present invention, in S1, the first set vacuum level is 5-15 Pa, and the first set time is 15-25 seconds. On the one hand, this stage requires a high pumping speed, but does not require an extremely low vacuum level. A vacuum level above 15 Pa results in a high residual gas concentration, which reduces crystallization uniformity. A vacuum level below 5 Pa can lead to overly rapid crystallization, resulting in small grains and stress defects. On the other hand, since reactive molecules in the air may react with the film to form compounds, residual gas molecules can enter the film and form impurities, affecting film purity. By controlling the vacuum level and pumping time, various residual gas molecules in the chamber environment can be removed to minimize these adverse effects. More importantly, this vacuum range allows for rapid expulsion of the primary solvent (such as DMF or DMSO) from the perovskite wet film without causing excessive evaporation rates and unstable crystallization. If the pumping rate is outside this range, excessive residual solvent can result, leading to excessive solvent residue on the film surface, hindering uniform nucleation in the next stage and ultimately causing uneven crystallization and surface defects. If the pumping time is too long, a large number of grains are likely to nucleate at this stage, leaving less room for subsequent crystal growth and resulting in smaller final grain size.

[0028] As a preferred solution, the first set vacuum degree is 10 Pa and the first set time is 20 s. Setting the vacuum degree to this pressure provides sufficient time and pressure difference for the volatilization of the solvent, while also providing a higher vacuum starting point for the subsequent crystallization process.

[0029] In some embodiments of the present invention, in S2, the second set vacuum degree is 0-1Pa, and the second set time is 5-10s. This stage can provide a high-clean, low-pressure environment, inhibit the interference of residual impurities such as oxygen and water vapor on crystal growth, promote the orderly expansion of crystal nuclei and the formation of large grains, thereby improving the uniformity of the film layer and the stability of the final device. This stage can also be judged by judging whether the solvent has completely evaporated to determine whether it has ended. Whether the solvent has completely evaporated can be judged by the color change of the film layer (for example, in the DMF system, after the solvent has evaporated, the perovskite wet film layer will change from light orange to light brown), or by the pressure change in the cavity tending to be stable for preliminary judgment.

[0030] As a preferred solution, the second set vacuum degree is 0.5 Pa, and the second set time is 6 s.

[0031] In some embodiments of the present invention, in S2, the third set time is related to the solvent type of the perovskite wet film. Because different solvents have different evaporation concentrations and evaporation conditions, and some perovskite wet films use mixed solvents, different evaporation times are set for different solvent types to ensure effective solvent evaporation.

[0032] In some specific embodiments, in S2, if the solvent of the perovskite wet film is pure DMF, the third setting time is 35-45 s, preferably 40 s.

[0033] In some specific embodiments, if the solvent in the perovskite wet film is a mixed solution of DMSO and DMF, or a mixed solution of DMPU and DMF, then in S2 , the third set time is 40-100 s.

[0034] If the above process is too short, it is easy to cause solvent residue, insufficient crystal growth, small grains and defects; if the time is too long, it is easy to cause the material surface to be over-dry, reduce the uniformity of film formation and even induce cracks.

[0035] Preferably, if the solvent of the perovskite wet film is a mixed solution of DMF and DMSO in a volume ratio of 6:1, the third set time is 60 seconds.

[0036] Preferably, if the solvent of the perovskite wet film is a mixture of DMF and DMSO in a volume ratio of 5:1, the third set time is 80 s.

[0037] Preferably, if the solvent of the perovskite wet film is a mixed solution of DMPU and DMF in a volume ratio of 6:1, the third set time is 80 seconds.

[0038] Preferably, if the solvent of the perovskite wet film is a mixed solution of DMPU and DMF in a volume ratio of 5:1, the third set time is 100 s.

[0039] In some embodiments of the present invention, in S3, the pressure of the VCD chamber is restored to standard atmospheric pressure within 3-5 seconds. Since the perovskite crystallization process is continuous, to prevent grain coarsening and growth and ensure that the grain size is the target size, the entire system must be quickly restored to standard atmospheric pressure after crystallization is completed for subsequent processing steps to ensure crystallization quality.

[0040] In some embodiments of the present invention, the monitor 6 is used to monitor the vacuum degree in the VCD cavity in real time during the entire process, and the vacuum degree is adjusted to a preset value in a timely manner according to the feedback information.

[0041] See also Figure 1 It should be noted that the method of the present invention is one of the stages in the perovskite film preparation process, and the perovskite film preparation process includes the following steps: Step 1: Preparation of perovskite wet film This stage includes the preparation and coating process of perovskite precursor solution.

[0042] The present invention has no particular limitation on the perovskite material, which can be a material or a combination thereof known to those skilled in the art, for example, a perovskite material having an ABX3 structure, wherein the perovskite ABX3 raw material is composed of a metal halide and an organic salt or an inorganic salt; the metal halide is BX2, B is a cation Pb2+ 、Sn 2+ Or Ge 2+ ; The organic salt or inorganic salt is AX, A is the methylamine cation (MA + 、CH3NH3 + ), formamidinium cation (FA + , CH(NH2) 2+ ) or cesium Cs + ; X is an anion Cl - Br - or I - The perovskite thin film material can be methylamine lead iodide (CH3NH3PbI3), formamidine lead iodide ((NH2)2CHPbI3), methylamine lead iodide / bromide (CH3NH3PbI2Br), cesium lead iodide (CsPbI3), and cesium lead iodide / bromide (CsPbI2Br).

[0043] The perovskite precursor solution is prepared by selecting metal halides and organic or inorganic salts as needed, and then dissolving them in a solvent to obtain the desired concentration. Typical solvents include pure DMF ((N,N-dimethylformamide)), pure DMSO (dimethyl sulfoxide), a mixture of DMF and DMSO, or a mixture of DMPU and DMF.

[0044] The present invention has no particular restrictions on the preparation process and thickness of the perovskite wet film. It can be a method known to those skilled in the art, as long as the purpose of the present invention can be achieved. For example, a solution spin coating method, a solution blade coating method or a slit coating method can be used to coat the perovskite precursor solution on the substrate. The coating thickness is obtained by setting the process parameters as needed to ensure that a wet film with good uniformity is obtained.

[0045] Step 2: Vacuum drying The above-mentioned S1-S3 was used for preparation.

[0046] Step 3: Annealing The vacuum-dried perovskite film is annealed to further optimize the crystallization quality of the perovskite film and complete the preparation of the perovskite film.

[0047] In a specific embodiment of the present invention, a method for controlling vacuum drying of a perovskite film is disclosed, comprising the following steps: S1. Initial solvent evaporation stage: Place the coated perovskite wet film into the VCD chamber, close the chamber door, and start the molecular pump. Bring the molecular pump speed to full load (24,000 rpm) and maintain this speed until ready for use. After the molecular pump speed reaches full load, open the pre-evacuation valve and mechanical pump. Use the mechanical pump to reduce the vacuum level in the VCD chamber from atmospheric pressure to 5-15 Pa within 15-25 seconds to initially remove the solvent.

[0048] Among them, the specific operating steps of using a mechanical pump to reduce the vacuum degree in the VCD cavity from atmospheric pressure to 5-15Pa within 15-25s are as follows: turn on the mechanical pump, set the air pressure in the VCD cavity to 5-15Pa, set the vacuuming time to 15-25s, open the pre-vacuum valve, and vacuum according to the settings. When the vacuum degree reaches 5-15Pa, close the pre-vacuum valve.

[0049] S2, crystallization stage: After the vacuum degree reaches 5-15Pa, close the pre-evacuation valve, open the front stage valve and the gate valve in sequence, and immediately use the molecular pump to reduce the vacuum degree to 0-1Pa within 5-10s; maintain the vacuum degree environment of 0-1Pa until the solvent is completely evaporated, and close the gate valve, front stage valve, molecular pump and mechanical pump in sequence.

[0050] The specific operating steps for using a molecular pump to reduce the vacuum degree to 0-1Pa within 5-10s are as follows: pre-set the air pressure in the VCD cavity to 0-1Pa, set the pumping time to 5-10s, open the front valve and the gate valve, and use the molecular pump to pump air according to the settings to reduce the vacuum degree to 0-1Pa; during the operation of the molecular pump, the mechanical pump maintains the original speed.

[0051] S3, inflation stage: After step S2, immediately open the inflation valve to let in clean dry air. The pressure in the VCD cavity is restored to the standard atmospheric pressure within 3-5 seconds. Close the inflation valve, open the chamber door, and move the perovskite film out of the VCD cavity for annealing.

[0052] See also Figure 2 The second aspect of the present invention discloses a vacuum drying system for realizing the vacuum drying control method of the above-mentioned perovskite film, comprising a VCD cavity 1, a mechanical pump 12 and a molecular pump 11, wherein the VCD cavity 1 is connected to the mechanical pump 12 and the molecular pump 11 at the same time; the VCD cavity 1 is connected to an inflation device.

[0053] A loading platform 2 for placing a film is provided in the VCD cavity 1 , a sample inlet 3 is provided on one side of the VCD side wall, and a sample outlet 4 is provided on the other side; a monitor 6 is provided inside the VCD cavity 1 .

[0054] Through the above-mentioned device, the mechanical pump 12 and the molecular pump 11 can play a role in different stages of the crystallization of the perovskite thin film. The molecular pump 11 of the present invention is connected to the VCD cavity 1 through the molecular pump inflation pipe, and can quickly reduce the vacuum degree inside the VCD cavity 1 to the target vacuum degree; through the setting of the external inflation device, clean dry air can be filled into the vacuum chamber in subsequent steps.

[0055] In some embodiments of the present invention, the VCD cavity 1 is provided with a mechanical pump exhaust port correspondingly connected to the mechanical pump 12 , at least one inflation port, and several molecular pump exhaust ports correspondingly connected to the molecular pump 11 .

[0056] In some embodiments of the present invention, the vacuum drying system further includes a valve unit, which includes a backing valve 9, a pre-pumping valve 10, gate valves 7 having the same number of pumping ports as the molecular pump, flow control valves 8 having the same number of gate valves 7, and inflation valves 5 having the same number of inflation ports, and a valve controller. The valve controller is used to control the regulation of the backing valve 9, the pre-pumping valve 10, the gate valve 7, the flow control valve 8, and the inflation valve 5.

[0057] In some specific embodiments, the mechanical pump 12 is connected to the corresponding mechanical pump exhaust port through a mechanical pump exhaust pipe, and the pre-exhaust valve 10 is arranged between the mechanical pump 12 and the mechanical pump exhaust port; the pre-exhaust valve 10 is used to control the on-off of the mechanical pump exhaust pipe, thereby adjusting the initial exhaust to adjust the vacuum degree in the VCD cavity 1.

[0058] In some specific embodiments, a branch is provided on the mechanical pump exhaust pipe, which is connected to one end of the molecular pump 11. A fore-stage valve 9 is provided on the branch, and the connection between the branch and the mechanical pump exhaust pipe is located between the pre-extraction valve 10 and the mechanical pump 12; the fore-stage valve 9 is used to maintain an appropriate vacuum degree in the VCD cavity 1 before the molecular pump 11 is exhausted, to avoid overload startup of the molecular pump 11, and to ensure that the molecular pump 11 can operate stably in stage two.

[0059] In some specific embodiments, one end of the molecular pump 11 is pumped through at least one molecular pump exhaust pipe, which is connected to a corresponding molecular pump exhaust port. A gate valve 7 is provided on the molecular pump exhaust pipe, and a flow control valve 8 is provided on the molecular pump exhaust pipe between the gate valve 7 and the molecular pump exhaust port. The gate valve 7 is used to control the connection and disconnection between the molecular pump 11 and the VCD cavity, and the flow control valve 8 is used to control the amount of exhaust flow on the molecular pump exhaust pipe.

[0060] Preferably, the molecular pump exhaust ports are evenly arranged at the bottom of the VCD cavity 1, and the lengths of the molecular pump exhaust pipes between the molecular pump 11 and the VCD cavity 1 are equal. By setting the lengths of all the exhaust pipes to be the same, the exhaust distance is made consistent. Combined with the even arrangement of the molecular pump exhaust ports at the bottom of the VCD, the airflow is uniform and stable, and the airflow is balanced across the film.

[0061] In a more preferred embodiment, the molecular pump gas extraction ports are at the bottom of the VCD and can be arranged in a rectangular array or in a line array.

[0062] As a preferred solution, the molecular pump 11 is divided into four pipelines for pumping, and the four molecular pump pumping ports are arranged side by side and equidistantly along the transverse central axis of the loading platform 2 in the VCD cavity 1 at the bottom of the VCD cavity 1. A symmetrical pumping area can be formed below the large loading platform 2, which is conducive to forming a stable and uniform vacuum field in the center and edge areas. When pumping, the air flow at each base point on the surface and inside of the perovskite film is more balanced, and the crystal growth is more uniform. At the same time, the setting of this number of molecular pump pumping ports can avoid the leakage problem caused by too many molecular pump pumping ports while ensuring the pumping effect.

[0063] In some embodiments of the present invention, the inflation device is connected to the VCD cavity 1 through multiple inflation ports, and the inflation ports are equally divided circumferentially on the side wall of the VCD cavity 1; an inflation valve 5 is correspondingly provided at each inflation port for charging clean dry air (CDA) into the VCD cavity.

[0064] It should be understood that the above-mentioned circumferentially equally divided setting means that a plurality of inflation ports can be set on each side wall of the VCD cavity 1, and the inflation ports are equally divided around the circumference of the VCD cavity 1. For example, there are two inflation ports on each side wall, and each two inflation ports are equally divided horizontally on the side wall where they are located; if there is one inflation port on a side wall, each inflation port is set at the center position of the side wall.

[0065] As a preferred solution, each sidewall is provided with an inflatable port. Inflation is achieved through four inflatable ports evenly distributed around the circumference, enabling a more balanced and stable return of the airflow around the perovskite film to standard atmospheric pressure. This makes the airflow more uniform, reduces the impact of uneven airflow that can affect film quality, and allows the film to return to standard atmospheric pressure in a shorter time. Furthermore, a smaller number of inflatable ports reduces the risk of leakage.

[0066] In some embodiments of the present invention, a monitor 6 is provided in the VCD cavity 1. The monitor 6 is provided on the cavity wall of the VCD cavity 1 and is used to monitor the vacuum degree in the VCD cavity in real time and transmit it to an external display device.

[0067] In some embodiments of the present invention, the mechanical pump 12 is a rotary vane vacuum pump. Rotary vane vacuum pumps have a high pumping rate, enabling a vacuum environment to be achieved quickly, enabling the target vacuum level to be reached quickly in stage 1. Compared to other molecular pumps 11, rotary vane vacuum pumps consume less energy, which helps reduce production costs. Furthermore, rotary vane vacuum pumps are compact, occupy a small footprint, and are easy to install and maintain.

[0068] In some embodiments of the present invention, the molecular pump 11 is a compound vacuum molecular pump. The compound vacuum molecular pump has a higher pumping speed than a barrel molecular pump, a shorter braking distance, and a lower dust accumulation rate. Since the compound vacuum molecular pump operates at a high temperature, it can achieve a high vacuum degree. In addition, the compound vacuum molecular pump has good stability and can always maintain a stable vacuum degree during the crystallization process.

[0069] Preferably, the specific models of the mechanical pump 12 and the molecular pump 11 are: the mechanical pump 12 is Pfeiffer Vacuum A4 25; the molecular pump 11 is Pfeiffer TMH 071.

[0070] A third aspect of the present invention discloses a perovskite film produced by the aforementioned vacuum drying control method; the perovskite film is used to prepare a perovskite solar cell. The perovskite film has uniform grain size, good film uniformity, and low defect state density.

[0071] In some embodiments of the present invention, the prepared perovskite solar cell can be either a rigid perovskite solar cell or a flexible perovskite solar cell, or a stacked solar cell. The method of the present invention provides a more flexible, precise, and stable means of controlling the solvent evaporation rate, thereby providing a suitable growth environment for each stage of perovskite crystallization. It is widely applicable to the vacuum drying-assisted film formation stage of perovskite films with different solvent systems, different perovskite compositions, and different substrate types. The perovskite solar cell prepared using the perovskite film prepared by the present invention can effectively improve the photoelectric performance and long-term stability of the cell. The process is stable and suitable for laboratory research and large-scale industrial production.

[0072] In some specific embodiments of the present invention, the perovskite solar cell structure is as follows: comprising a transparent conductive substrate, a first functional layer, a perovskite thin film, a second functional layer, and a metal electrode stacked in sequence; the first functional layer is a hole transport layer or an electron transport layer, and the second functional layer is an electron transport layer or a hole transport layer, and the first and second functional layers are different. The perovskite thin film is prepared by coating a perovskite precursor solution onto the first functional layer to form a wet film, vacuum drying the film using the method of the present invention, and then annealing. The perovskite solar cell can have a positive or inverted structure. When the first functional layer is an electron transport layer and the second functional layer is a hole transport layer, the solar cell has a positive structure (nip); when the first functional layer is a hole transport layer and the second functional layer is an electron transport layer, the solar cell has an inverted structure (pin).

[0073] The present invention has no particular restrictions on the transparent conductive substrate of the perovskite solar cell, and any conductive substrate known in the art can be used, as long as the purpose of the present invention can be achieved. For example, the transparent conductive substrate may include a flexible conductive substrate or a rigid conductive substrate; wherein the flexible conductive substrate may be a fluorine-doped tin oxide (FTO) flexible conductive substrate or an indium-doped tin oxide (ITO) flexible conductive substrate, and the flexible conductive substrate may be at least one of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), transparent polyimide (CPI), polydimethylsiloxane (PDMS), and polyurethane (PU); the rigid conductive substrate may be an FTO conductive glass substrate or an ITO conductive glass substrate.

[0074] The present invention does not particularly limit the material of the electron transport layer of the perovskite solar cell. It can be a material or a combination thereof known to those skilled in the art, such as a titanium dioxide (TiO2) electron transport layer, a tin dioxide (SnO2) electron transport layer, a fullerene (C60) electron transport layer, or a zinc oxide (ZnO) electron transport layer. Furthermore, the present invention does not particularly limit the thickness of the electron transport layer, as long as it can achieve the purpose of the present invention. For example, the thickness of the electron transport layer can be 20 to 100 nm. The present application does not particularly limit the preparation process of the electron transport layer. For example, solution spin coating, solution blade coating, solution spraying, slit coating, hydrothermal growth, evaporation, sputtering, etc. can be used.

[0075] The present invention has no particular restrictions on the hole transport layer of the perovskite solar cell, which can be a material or a combination thereof known to those skilled in the art, for example, it can be any one of the layered structures prepared by nickel oxide, doped nickel oxide, cuprous iodide, cuprous thiocyanate, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), PEDOT: PSS or Spiro-OMeTAD; and the present invention has no particular restrictions on the thickness of the hole transport layer, as long as the purpose of the present invention can be achieved, for example, it can be 10nm~100nm; and the present invention has no particular restrictions on the preparation process of the hole transport layer, for example, solution spin coating, solution blade coating, slit coating or vapor phase method can be used.

[0076] The present invention has no particular restrictions on the material of the metal electrode of the perovskite solar cell. It can be a material or a combination thereof known to those skilled in the art, for example, it can be any one of a gold (Au) electrode, a silver (Ag) electrode, an aluminum (Al) electrode, or a copper (Cu) electrode. In addition, the present invention has no particular restrictions on the thickness of the metal electrode, as long as it can achieve the purpose of the present invention. For example, it can be 50 to 100 nm. The electrode thickness within this range can achieve better results. Of course, those skilled in the art can select a suitable electrode thickness as needed. The present invention has no particular restrictions on the preparation process of the metal electrode. For example, thermal evaporation, vapor deposition, sputtering, etc. can be used.

[0077] In addition, it should be noted that, as needed, the perovskite solar cell provided by the present invention can also include other layers, such as in order to reduce the electron state density, a passivation layer can be set between the perovskite film and the hole transport layer, for example, the material of the passivation layer can be phenylpropylammonium iodide (PPAI); a hole blocking layer can also be set between the perovskite film and the electron transport layer as needed, hole blocking materials such as o-phenanthroline, o-phenanthroline compounds, preferably 2,9-dimethyl-4,7-biphenyl-1,10-o-phenanthroline (BCP for short). The perovskite film prepared using the inventive method is of excellent quality and has strong versatility, and can be widely used in the preparation of almost all perovskite solar cells.

[0078] The following is further described with reference to specific embodiments.

[0079] Preparation of perovskite solar cells: Take MAPbI3 perovskite as an example. The structure of the solar cell is as follows: Figure 3 Shown: glass substrate / ITO / nickel oxide hole transport layer / MAPbI3 perovskite film / C60 electron transport layer / BCP hole blocking layer / metal electrode (ITO / Cu / ITO) Example 1 Step 1, ITO substrate preparation First, prepare an ITO (indium tin oxide) glass substrate. Use an ultrasonic cleaner to clean the ITO glass substrate in deionized water for approximately 15 minutes, then rinse in ethanol and acetone for 10 minutes each. Finally, rinse with deionized water and dry under a stream of nitrogen. After cleaning, place the ITO glass substrate in an oven at 120°C for 20 minutes. Allow the substrate to cool before use.

[0080] Step 2: Preparation of hole transport layer Nickel chloride (NiCl2) was dissolved in isopropyl alcohol to prepare a 0.5 M nickel oxide precursor solution. This nickel oxide precursor solution was evenly coated onto an ITO glass substrate using spin coating at 2000 rpm for 15 seconds. After coating, the substrate was placed on a hot plate and annealed at 300°C for 1 hour, resulting in a uniform 20 nm thick nickel oxide (NiO) film on the ITO glass substrate.

[0081] Step 3, Preparation of perovskite film (MAPbI3) Step 3.1, Preparation of perovskite wet film This step involves the preparation and coating of a perovskite precursor solution. Preparation of the perovskite precursor solution: Methylammonium iodide (MAI) and lead iodide (PbI2) are mixed in a 1:1 molar ratio and dissolved in a solvent (N,N-dimethylformamide, DMF) to produce a 1.2 M perovskite precursor solution. Coating to form a perovskite wet film: The perovskite precursor solution is evenly applied to the nickel oxide hole transport layer. A wet film is applied using a doctor blade coating method with a coating speed of 3 mm / s, a droplet volume of 50 ml, and a coating time of 20 seconds. During the coating process, the solution droplet volume and coating speed are appropriately adjusted to ensure the uniformity and thickness of the perovskite film.

[0082] Step 3.2 Vacuum drying S1. Place the coated perovskite film into the VCD chamber, close the chamber door, and start the molecular pump until it reaches full speed (24,000 rpm). Maintain this speed until ready for use. After the molecular pump reaches full speed, open the pre-evacuation valve and mechanical pump. Use the mechanical pump to reduce the vacuum level in the VCD chamber from atmospheric pressure to 10 Pa within 20 seconds to initially remove the solvent. S2. Use the molecular pump to reduce the pressure from 10 Pa to 0.5 Pa within 6 seconds and maintain this pressure for 40 seconds to further remove the solvent and promote crystallization of the perovskite film. S3. Fill the VCD chamber with dry, clean air. Return the pressure to standard atmospheric pressure within 3-5 seconds to obtain the vacuum-dried perovskite film. This dual-pump vacuuming ensures high-quality crystallization of the perovskite film.

[0083] Step 3.3, Annealing After the double-pump pumping was completed, the perovskite film substrate was further annealed in a temperature-controlled furnace at 100°C for 30 minutes to further optimize the crystallization quality of the perovskite film, and finally a high-quality MAPbI3 perovskite film was obtained with a thickness of about 550nm.

[0084] Step 4: Preparation of electron transport layer and hole blocking layer The electron transport layer (ETL) and hole blocking layer (HBL) were prepared sequentially on the perovskite active layer using C60 and BCP, respectively, using a spin-coating process. The spin-coating process for C60 or BCP was as follows: a spin speed of 4000 rpm, a spin-coating time of 30 seconds, and a thickness of 20 nm for C60 and 6 nm for BCP, respectively. Alternatively, vapor deposition was used for other preparations. The deposition conditions were: a C60 deposition thickness of 20 nm at a deposition rate of 0.1–0.3 A / s; a BCP deposition thickness of 6 nm at a deposition rate of 0.1 A / s.

[0085] Step 5, Preparation of Metal Electrodes (ITO / Cu / ITO) An ITO / Cu / ITO back electrode was sputtered on the BCP hole blocking layer. The vapor deposition thickness of the first layer of ITO was 30 nm, and the sputtering rate was 0.3 A / s; the vapor deposition thickness of Cu was 30 nm, and the sputtering rate was 0.6 A / s; the sputtering thickness of the second layer of ITO was 20 nm, and the sputtering rate was 0.3 A / s, thereby obtaining a perovskite solar cell.

[0086] Example 2 The difference from Example 1 is that: In step 2, a nickel oxide solution with a concentration of 0.6 M is prepared; In step 3.1, the MAPbI3 precursor solution was prepared to a concentration of 1.0 M using a 6:1 mixed solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO); In step 3.2, after the vacuum degree dropped to 10 Pa, a molecular pump was used to evacuate the air to 0.1 Pa within 10 s and maintained for 60 s to further remove the solvent and promote the crystallization of the perovskite film.

[0087] The thickness of the obtained perovskite film is about 545nm.

[0088] Example 3 The difference from Example 1 is that in step 3.2, a mechanical pump is used to reduce the vacuum level in the VCD chamber from atmospheric pressure to 5 Pa within 25 seconds to initially remove the solvent. A molecular pump is used to reduce the pressure from 5 Pa to 0 Pa within 10 seconds and maintain this pressure for 35 seconds to further remove the solvent and promote crystallization of the perovskite film. This dual-pump vacuum ensures high-quality crystallization of the perovskite film.

[0089] Example 4 The difference from Example 1 is that in step 3.2, a mechanical pump is used to reduce the vacuum level in the VCD chamber from atmospheric pressure to 15 Pa within 15 seconds to initially remove the solvent. A molecular pump is used to reduce the pressure from 15 Pa to 1 Pa within 5 seconds and maintain this pressure for 38 seconds to further remove the solvent and promote crystallization of the perovskite film. This dual-pump vacuuming ensures high-quality crystallization of the perovskite film.

[0090] Example 5 The difference from Example 1 is that in step 3.2, a mechanical pump is used to reduce the vacuum level in the VCD chamber from atmospheric pressure to 12 Pa within 18 seconds to initially remove the solvent. A molecular pump is used to reduce the pressure from 12 Pa to 0.8 Pa within 7 seconds and maintain this pressure for 45 seconds to further remove the solvent and promote crystallization of the perovskite film. This dual-pump vacuum ensures high-quality crystallization of the perovskite film.

[0091] Example 6 The difference from Example 1 is that in step 3.1, the perovskite precursor solution is prepared using a mixture of DMPU (1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone) and DMF in a volume ratio of 5:1. In step 3.2, a mechanical pump is used to reduce the vacuum level within the VCD chamber from atmospheric pressure to 8 Pa over 22 seconds to initially remove the solvent. A molecular pump is then used to reduce the pressure from 8 Pa to 0.6 Pa over 8 seconds and maintain this pressure for 100 seconds to further remove the solvent and promote crystallization of the perovskite film. This dual-pump vacuum ensures high-quality crystallization of the perovskite film.

[0092] Example 7 The difference from Example 1 is that in step 3.1, the solvent of the perovskite precursor solution is a mixed solution of DMSO and DMF with a volume ratio of 1:10; in step 3.2, the vacuum degree is reduced to 0.5 Pa using a molecular pump and maintained for 40 seconds to further remove the solvent and promote the crystallization of the perovskite film.

[0093] Comparative Example: The other steps were the same as those in Example 1, except that a single pump was used to evacuate the VCD in the vacuum drying step, and a mechanical pump was used to pump the air for 10 seconds to 10 Pa to remove residual solvent. The pressure was maintained at 10 Pa by the mechanical pump for 40 seconds.

[0094] Performance testing: Figure 4 The following are SEM surface and cross-sectional comparisons of the PVK film prepared using dual-pump VCD treatment in Example 1 of the present invention and the PVK film prepared using single-pump VCD treatment in the comparative example. Comparison of the two surface images above shows that the grain size of the perovskite after dual-pump VCD treatment is significantly larger and more uniform than that after conventional single-pump VCD treatment. Comparison of the two cross-sectional images below shows that the perovskite film prepared using the dual-pump vacuum method and system of the present invention in the lower right figure is smoother and has no obvious holes or cracks, compared to the perovskite film dried using a single-pump vacuum method in the lower left figure using conventional methods. The flatness of the conventional method is poor, and obvious holes appear. This is because the use of dual-pump VCD can ensure the rapid and sufficient removal of solution residues in the perovskite, ensuring a better environment for grain growth.

[0095] Figure 5 This is an XRD comparison chart of the PVK film treated with dual-pump VCD in Example 1 of the present invention and with single-pump VCD in the comparative example. The XRD peak intensity of the film is significantly improved after the dual-pump VCD treatment of the present invention, proving that the quality of the perovskite film is significantly improved after the dual-pump VCD co-extraction treatment.

[0096] Figure 6 This is a comparison of the efficiency of the perovskite solar cell obtained using dual-pump VCD in Example 1 of the present invention and using single-pump VCD in the comparative example. As can be seen from the figure, all parameters of the perovskite solar cell device obtained by the present invention are improved, among which the opening voltage Voc increases from 1.015 to 1.047V, and the current Jsc increases from 23.99 to 24.47mA / cm 2 , the filling factor FF increased from 77.79 to 78.14, and the final efficiency increased from 18.94% to 20.02%.

[0097] The performance test results of other embodiments of the present invention are similar to those of Example 1 and are not described in detail here. The test results of Example 1 can be used as a reference.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for controlling vacuum drying of a perovskite film, characterized in that: The following steps are involved: S1, placing the perovskite wet film in a VCD cavity, and reducing the vacuum degree of the VCD cavity to a first set vacuum degree by a mechanical pump within a first set time to remove the solvent; during the mechanical pumping process, the molecular pump rotates and stands by; S2, within the second set time, the vacuum degree of the VCD cavity is reduced from the first set vacuum degree to the second set vacuum degree by the molecular pump, and maintained for a third set time, and the perovskite wet film is crystallized; S3, inflating the VCD cavity to restore the pressure of the VCD cavity to standard atmospheric pressure, and obtaining a vacuum-dried perovskite film.

2. The vacuum drying control method for a perovskite thin film according to claim 1, characterized in that: In S1, the first set vacuum degree is 5-15 Pa, and the first set time is 15-25 s.

3. The method for controlling vacuum drying of a perovskite film according to claim 1 or 2, wherein: In S2, the second set vacuum degree is 0-1 Pa, and the second set time is 5-10 s.

4. The method for controlling vacuum drying of a perovskite film according to claim 3, wherein: In S2, the third set time is determined according to the solvent type of the perovskite wet film.

5. The method for controlling vacuum drying of a perovskite film according to claim 4, wherein: In S2, when the solvent of the perovskite wet film is pure DMF, the third setting time is 35-45 s.

6. The method for controlling vacuum drying of a perovskite film according to claim 4, wherein: In S2, when the solvent of the perovskite wet film is a mixed solution of DMSO and DMF, or a mixed solution of DMPU and DMF, the third set time is 40-100 s.

7. The method for controlling vacuum drying of a perovskite film according to claim 4, wherein: In S3, the pressure of the VCD cavity is restored to standard atmospheric pressure within 3-5 seconds.

8. A vacuum drying system for implementing the vacuum drying control method for a perovskite thin film according to any one of claims 1 to 7, characterized in that: The invention comprises a VCD cavity, a mechanical pump and a molecular pump. The VCD cavity is connected with the mechanical pump and the molecular pump at the same time, and the VCD cavity is connected with an inflation device.

9. The vacuum drying system according to claim 8, characterized in that: The molecular pump and the VCD cavity are connected through a plurality of molecular pump exhaust pipes. The molecular pump exhaust ports at the connection points between the molecular pump exhaust pipe and the VCD cavity are arranged in an array at the bottom of the VCD cavity. The lengths of the plurality of molecular pump exhaust pipes are equal. The inflation device is connected to the VCD cavity through a plurality of inflation ports, and the inflation ports are equally divided along the circumference of the side wall of the VCD cavity.

10. A perovskite film produced by the vacuum drying control method according to any one of claims 1 to 7, characterized in that: The perovskite film is used to prepare a perovskite solar cell.

Images