A method for preparing FAPbI3 perovskite thin films in air via two-step coating and its application

Abstract

The application discloses a method for preparing FAPbI3 perovskite film by two-step blade coating in air. The method uses ionic liquid methylamine formate as a solvent of lead iodide to prepare a uniform and porous lead iodide film at a proper temperature, which is beneficial to the penetration reaction of formamidinium iodide in the second step of blade coating. Meanwhile, proper pressure applied by a blade in the second step of blade coating is also helpful to the penetration and reaction of formamidinium iodide. By the method, stable alpha-phase FAPbI3 perovskite can be obtained, the whole preparation process is carried out in air and on the same equipment, and the preparation of high-quality FAPbI3 perovskite film can be simply and quickly completed. Meanwhile, the method can be used for preparing large-area perovskite film, and has high industrialization prospect. Finally, the photoelectric conversion efficiency of the prepared device can reach 22.3%, which is in a leading position in the preparation of FAPbI3 perovskite photovoltaic devices by blade coating in air.

Description

Technical Field

[0001] This invention relates to a method for preparing FAPbI3 perovskite thin films by two-step air coating and its application in improving the performance of perovskite solar cells, belonging to the field of perovskite cell technology. Background Technology

[0002] With the continuous development of society, the environmental problems caused by the large-scale use of fossil fuels have attracted increasing attention, making the development of clean energy an urgent priority. Solar energy, as an inexhaustible and clean renewable energy source, is an ideal substitute for fossil fuels. Photovoltaic technology is a technology that converts solar energy into electrical energy. For decades, photovoltaic technology has flourished, resulting in three generations of solar cells: the first generation is crystalline silicon solar cells, the second generation is thin-film solar cells, and the third generation consists of novel solar cells, including organic solar cells, dye-sensitized solar cells, and perovskite solar cells. Among these, perovskite solar cells, using perovskite materials as the light-absorbing layer, have developed very rapidly. In just ten years, their photoelectric conversion efficiency has increased from 3.9% in 2009 to 25.7%, comparable to crystalline silicon solar cells. Furthermore, perovskite solar cells are solution-processable, have simple manufacturing processes, and low production costs, making them promising for industrialization.

[0003] The crystal structure of perovskite materials is a typical ABX3 type cubic structure. A is generally an organic cation CH3NH3. + (MA + ) and NH2CH=NH2 + (FA + (or inorganic cations Cs+, B is mostly metallic Pb) 2+ Metal Sn 2+ There are also a few reports; X is Cl - ,Br - I - It can be composed of single or mixed halogen ions. As can be seen, perovskites have a wide variety of compositions, among which FAPbI3 possesses the most suitable band gap and absorption range for use as an active layer. However, the instability of its photovoltaic α phase restricts its application. Therefore, developing a method for preparing FAPbI3 perovskite thin films with a stable α phase is crucial. Summary of the Invention

[0004] The technical problem solved by this invention is to propose a method for preparing FAPbI3 perovskite thin films with a stable α phase through a simple two-step coating process, with the entire preparation process carried out in air on the same coating machine. The photoelectric conversion efficiency of the device can reach 22.3%, which is in a leading position in the coating preparation of FAPbI3 perovskite photovoltaic devices.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention includes the following steps:

[0006] Step (1): Dissolve lead iodide and formamidine in methylamine formate ionic liquid and isopropanol respectively. Heat and stir the lead iodide solution, and stir the formamidine solution at room temperature. After complete dissolution, use it as a scraping ink.

[0007] Step (2): Drop the prepared lead iodide ink onto the preheated substrate in the air, adjust the distance between the coating blade and the substrate, drag the blade from the top to the bottom of the substrate at a speed of 5 mm / s to spread the liquid, and anneal it directly on the blade coating machine at 120°C to obtain a lead iodide film.

[0008] Step (3): After the surface temperature of the doctor blade coating machine drops to 60-90℃, the prepared formamidine iodide ink is dropped onto the lead iodide film mentioned above. The doctor blade is dragged from the end of the substrate back to the top at a speed of 10mm / s, which drives the formamidine iodide ink to spread and causes lead iodide and formamidine iodide to react to form perovskite. The perovskite film is then placed on the doctor blade coating machine and annealed at 150℃ to obtain a formamidine lead iodide perovskite film with a stable α phase.

[0009] Preferably, in step (3): after the surface temperature of the blade coating machine drops to 70°C, the prepared formamidine ink is dropped onto the lead iodide film. The blade is dragged back from the end of the substrate to the top at a speed of 10 mm / s, which spreads the formamidine ink and causes lead iodide and formamidine to react to form perovskite. The perovskite film is then placed on the blade coating machine and annealed at 150°C to obtain a formamidine lead iodide perovskite film with a stable α phase.

[0010] Preferably, in step (1), the concentration range of lead iodide ink is 400-800 mg / mL, the concentration range of formamidinium iodide ink is 60-120 mg / mL, and the coating process is carried out in an air environment with an air humidity of 20%-80%.

[0011] Preferably, in step (2), the preheating temperature of the substrate is 80-120℃, the distance between the scraper and the substrate is 0.1-0.5mm, the scraper speed is 1-30mm / s, and the thickness of the prepared FAPbI3 perovskite film is 0.3-2μm, with an area of ​​5-100cm². 2 .

[0012] To solve the above-mentioned technical problems, another technical solution proposed by the present invention is: the prepared perovskite thin film can be used in perovskite solar cells. The perovskite solar cell includes, from bottom to top, a glass substrate (1), a bottom electrode layer (2), a bottom charge transport layer (3), a perovskite thin film layer (4), a top charge transport layer (5), and a top electrode layer (6); the bottom electrode layer (2) is placed on the upper surface of the glass substrate (1) and directly contacts the unconnected layer; the perovskite thin film layer (4) is above the bottom electrode layer (2) and connected in the middle by the bottom charge transport layer (3); the top charge transport layer (5) and the top electrode layer (6) are placed on the upper side of the perovskite thin film layer (4); at least one side of the bottom electrode layer (2) and the top electrode layer (6) is transparent.

[0013] Preferably, the bottom electrode layer (2) is an FTO transparent electrode.

[0014] Preferably, the bottom charge transport layer (3) is tin dioxide, and the specific preparation steps are as follows:

[0015] (1) Tin dioxide was spin-coated onto the cleaned FTO conductive glass surface under spin-coating conditions of 4000 rpm for 30 seconds.

[0016] (2) The spin-coated film was annealed on a hot plate at 150°C for 30 minutes to prepare a tin dioxide film.

[0017] Preferably, the top charge transport layer (5) is Spiro-OMeTAD, and the specific preparation steps are as follows:

[0018] (1) Dissolve 73.2 mg of Spiro-OMeTAD in 1 mL of chlorobenzene;

[0019] (2) Dissolve 520 mg of lithium bis(trifluoromethanesulfonate) in 1 mL of acetonitrile solution;

[0020] (3) Add 28.8 μL of TBP solution to Spiro-OMeTAD solution;

[0021] (4) Add 17.6 μL of lithium salt solution to Spiro-OMeTAD solution;

[0022] (5) Stir the mixed solution at room temperature for 2 hours;

[0023] (6) 25 μL of mixed solution was dropped onto the surface of the perovskite film, and the top charge transport layer was prepared by spin coating. The spin coating conditions were 3000 rpm for 30 s.

[0024] Preferably, the top electrode layer (6) is molybdenum oxide / silver, and the specific preparation steps are as follows:

[0025] MoO3 / Ag is deposited on the top charge transport layer, with a MoO3 thickness of 5 nm and a metal Ag electrode thickness of 100 nm.

[0026] Beneficial effects:

[0027] (1) The band gap (~1.48V) of FAPbI3 perovskite is the closest to the ideal band gap (1.3V-1.4V) among known perovskite materials. However, the instability of the α phase, which exhibits photovoltaic effect, is a recognized problem in the industry. This invention prepares FAPbI3 perovskite through a two-step coating method, achieving FAPbI3 perovskite with a stable α phase. Simultaneously, in the second coating step, the formamidine iodide ink penetrates more easily into the lead iodide film under the pressure of the doctor blade, resulting in a more complete reaction and larger perovskite grains. This enables the fabrication of FAPbI3 perovskite solar cells with a photoelectric conversion efficiency of 22.3%, placing China in a leading position in the field of FAPbI3 perovskite coating preparation.

[0028] (2) Unlike the traditional two-step method which is more complicated, the two-cloth coating method only involves one piece of equipment and only requires one back-and-forth movement of the scraper to prepare FAPbI3 perovskite film. The process is extremely simple and can be used to prepare large-area films. Compared with spin coating, it has a high raw material utilization rate and has high industrialization value.

[0029] (3) In this invention, the first step of the coating annealing temperature and the second step of the coating speed are both important influencing factors. Research shows that the optimal coating speed is 120℃ for the first step and 10mm / s for the second step. The resulting perovskite film has higher quality, larger grains, less defect state density, and a photoelectric conversion efficiency of 22.3%. For example, in Example 2, the first step of the coating was carried out at 150℃, forming a FAPbI3 perovskite film with uneven grain size and a photoelectric conversion efficiency of 18.0%. In Example 3, the second step of the coating was carried out at 30mm / s, forming a FAPbI3 perovskite film with blurred boundaries and a lot of unreacted lead iodide residue on the surface, resulting in a photoelectric conversion efficiency of 19.9%. In Comparative Example 1, spin coating was used, resulting in uneven film over a large area, radial textures and obvious color differences on the film surface, and inconsistent morphology in different areas. In Comparative Example 2, the second step of the coating was carried out at 1mm / s, forming a FAPbI3 perovskite film with poor film uniformity.

[0030] (4) The entire preparation process is carried out in air. The introduction of ionic liquid solvent enhances the processing stability of the process in air. At the same time, its adjustable viscosity is more conducive to improving the repeatability of the scraping process and has a perfect match with the scraping process in air. Attached Figure Description

[0031] Figure 1Schematic diagram of two-step coating process for preparing FAPbI3 perovskite;

[0032] Figure 2 Structure diagram of a perovskite solar cell device;

[0033] Figure 3 Scanning electron microscope image of lead iodide thin film surface prepared by 120℃ blade coating;

[0034] Figure 4 XRD patterns of FAPbI3 perovskite prepared by PbI2 coating at 120℃ and FAI coating at medium speed;

[0035] Figure 5 Scanning electron microscope images of FAPbI3 perovskite thin films prepared by PbI2 coating at 120℃ and FAI coating at medium speed.

[0036] Figure 6 Current density-voltage scan curves of FAPbI3 perovskite solar cell devices prepared by PbI2 coating at 120℃ and FAI coating at medium speed.

[0037] Figure 7 Scanning electron microscope image of lead iodide thin film surface prepared by scraping at 150℃;

[0038] Figure 8 Scanning electron microscope images of FAPbI3 perovskite thin films prepared by PbI2 coating at 150℃ and FAI coating at medium speed.

[0039] Figure 9 Current density-voltage scan curves of FAPbI3 perovskite solar cell devices prepared by PbI2 coating at 150℃ and FAI coating at medium speed.

[0040] Figure 10 XRD patterns of FAPbI3 perovskites prepared by PbI2 coating at 120℃ and FAI coating at rapid temperature.

[0041] Figure 11 Scanning electron microscope images of FAPbI3 perovskite thin films prepared by PbI2 coating at 120℃ and FAI rapid coating at 120℃.

[0042] Figure 12 Current density-voltage scan curves of FAPbI3 perovskite solar cell devices prepared by PbI2 coating at 120℃ and FAI coating by rapid coating at 120℃.

[0043] Figure 13 Scanning electron microscope image of lead iodide thin film surface prepared by spin coating;

[0044] Figure 14 Scanning electron microscope image of the surface of FAPbI3 perovskite thin film prepared by the traditional two-step spin coating method; Specific Implementation

[0045] To more clearly illustrate the present invention, specific embodiments are provided below for further explanation, but these are not intended to limit the scope of the invention.

[0046] Example 1

[0047] This embodiment provides a two-step scraping method ( Figure 1 A method for preparing FAPbI3 perovskite thin films in air and its application in solar cells. Figure 2 As shown, the structure of this battery includes: a glass substrate, a bottom electrode layer (transparent electrode ITO), a bottom charge transport layer (tin dioxide), a perovskite layer (FAPbI3), a top charge transport layer (Spiro-OMeTAD), and a top electrode layer (molybdenum oxide / silver). The specific steps are as follows:

[0048] 1. Preparation of the coating ink: Dissolve 691 mg PbI2 in 1 mL of MAfa ionic liquid solvent and heat and stir at 60°C for 12 hours for later use; dissolve 100 mg FAI and 5 mg MACl in 1 mL of isopropanol and stir at room temperature for 3 hours for later use.

[0049] 2. Preparation of Spiro-OMeTAD solution: Dissolve 73.2 mg of Spiro-OMeTAD in 1 mL of chlorobenzene, dissolve 520 mg of lithium bis(trifluoromethanesulfonate)imide in 1 mL of acetonitrile solution, add 28.8 μL of TBP solution to the Spiro-OMeTAD solution, add 17.6 μL of lithium salt solution to the Spiro-OMeTAD solution, and stir the mixture at room temperature for 2 hours before use.

[0050] 3. Preparation of tin dioxide thin film: Tin dioxide was spin-coated onto the cleaned FTO conductive glass surface under the following conditions: spin-coating at 4000 rpm for 30 seconds. The spin-coated film was then annealed on a hot stage at 150°C for 30 minutes to prepare the tin dioxide thin film.

[0051] 4. Perovskite film preparation: 25 μL of lead iodide ink was dropped onto a substrate preheated to 120℃ and spread at a blade coating speed of 5 mm / s. After coating, the sample was placed on the surface of a blade coater at 120℃ for annealing for 5 minutes to form a PbI2 film. The blade was then fixed to the end of the substrate. The surface morphology of the lead iodide film was uniform and porous. Figure 3 This facilitates the penetration of formamidine iodide; after lowering the surface temperature of the coating machine to 70℃, 15μL of formamidine iodide ink is dropped onto the lead iodide film, and the doctor blade is dragged in the opposite direction at a speed of 10mm / s. After coating, the surface temperature of the coating machine is raised to 150℃, and the resulting film is annealed for 5 minutes to form a FAPbI3 perovskite film. Figure 4 The surface morphology of perovskite thin films is as follows: Figure 5 As shown, the maximum grain size is 5 μm, and the large-area film is relatively uniform with consistent morphology. The perovskite film was prepared in air with a humidity of 60%.

[0052] 5. Preparation of Spiro-OMeTAD thin film: 25 μL of the prepared Spiro-OMeTAD mixed solution was dropped onto the surface of the perovskite thin film, and the top charge transport layer was prepared by spin coating at 3000 rpm for 30 s.

[0053] 6. Top electrode fabrication: MoO3 / Ag is deposited on the top charge transport layer by vapor deposition, with a MoO3 thickness of 5 nm and a metal Ag electrode thickness of 100 nm;

[0054] 7. Test characterization: The battery was tested at AM1.5G, 100mW / cm². 2 The current density-voltage (JV) performance curve of the battery was tested under illumination, as shown in the figure. Figure 6 As shown, the short-circuit current density of the battery is 24.5 mA / cm². 2 The open-circuit voltage is 1.12V, the fill factor is 81.4%, and the photoelectric conversion efficiency is 22.3%.

[0055] Example 2

[0056] This embodiment provides a two-step scraping method ( Figure 1 A method for preparing FAPbI3 perovskite thin films in air and its application in solar cells. Figure 2 As shown, the structure of this battery includes: a glass substrate, a bottom electrode layer (transparent electrode ITO), a bottom charge transport layer (tin dioxide), a perovskite layer (FAPbI3), a top charge transport layer (Spiro-OMeTAD), and a top electrode layer (molybdenum oxide / silver). The specific steps are as follows:

[0057] 1. Preparation of the coating ink: Dissolve 691 mg PbI2 in 1 mL of MAfa ionic liquid solvent and heat and stir at 60°C for 12 hours for later use; dissolve 100 mg FAI and 5 mg MACl in 1 mL of isopropanol and stir at room temperature for 3 hours for later use.

[0058] 2. Preparation of Spiro-OMeTAD solution: Dissolve 73.2 mg of Spiro-OMeTAD in 1 mL of chlorobenzene, dissolve 520 mg of lithium bis(trifluoromethanesulfonate)imide in 1 mL of acetonitrile solution, add 28.8 μL of TBP solution to the Spiro-OMeTAD solution, add 17.6 μL of lithium salt solution to the Spiro-OMeTAD solution, and stir the mixture at room temperature for 2 hours before use.

[0059] 3. Preparation of tin dioxide thin film: Tin dioxide was spin-coated onto the cleaned FTO conductive glass surface under the following conditions: spin-coating at 4000 rpm for 30 seconds. The spin-coated film was then annealed on a hot stage at 150°C for 30 minutes to prepare the tin dioxide thin film.

[0060] 4. Perovskite film preparation: 25 μL of lead iodide ink was dropped onto a substrate preheated at 150℃ and spread at a doctor blade speed of 5 mm / s. After coating, the sample was placed on the surface of a doctor blade coater at 150℃ for annealing for 5 minutes to form a PbI2 film. The doctor blade was then fixed to the end of the substrate. The surface morphology of the lead iodide film was uniform and dense. Figure 7 This process hinders the penetration of formamidine iodide. After lowering the coating machine surface temperature to 70°C, 15 μL of formamidine iodide ink is dropped onto the lead iodide film. The doctor blade is dragged in the opposite direction at a speed of 10 mm / s. After coating, the coating machine surface temperature is raised to 150°C, and the resulting film is annealed for 5 minutes to form a FAPbI3 perovskite film. The surface morphology of the perovskite film is as follows: Figure 8 As shown, the grain size is not uniform, with an average grain size of only 500 nm. This is mainly due to the excessive density of the lead iodide film, which prevents formamidinium from penetrating deeply and also reduces the growth space of the perovskite. The large-area film is relatively uniform, with a consistent morphology in all areas. The perovskite film was prepared in air with a humidity of 60%.

[0061] 5. Preparation of Spiro-OMeTAD thin film: 25 μL of the prepared Spiro-OMeTAD mixed solution was dropped onto the surface of the perovskite thin film, and the top charge transport layer was prepared by spin coating at 3000 rpm for 30 s.

[0062] 6. Top electrode fabrication: MoO3 / Ag is deposited on the top charge transport layer by vapor deposition, with a MoO3 thickness of 5 nm and a metal Ag electrode thickness of 100 nm;

[0063] 7. Test characterization: The battery was tested at AM1.5G, 100mW / cm². 2 The current density-voltage (JV) performance curve of the battery was tested under illumination, as shown in the figure. Figure 9 As shown, the short-circuit current density of the battery is 23.5 mA / cm². 2 The open-circuit voltage is 1.05V, the fill factor is 72.9%, and the photoelectric conversion efficiency is 18.0%, which is similar to the perovskite solar cell in Example 1. Figure 6 Compared to the previous method, the performance of the lead iodide was significantly reduced in all aspects. The main reason is that the lead iodide was too dense, the perovskite lacked growth space, the grain size was small, there were more defect states, and the degree of nonradiative recombination of charge carriers in the thin film was increased.

[0064] Example 3

[0065] This embodiment provides a two-step scraping method ( Figure 1 A method for preparing FAPbI3 perovskite thin films in air and its application in solar cells. Figure 2 As shown, the structure of this battery includes: a glass substrate, a bottom electrode layer (transparent electrode ITO), a bottom charge transport layer (tin dioxide), a perovskite layer (FAPbI3), a top charge transport layer (Spiro-OMeTAD), and a top electrode layer (molybdenum oxide / silver). The specific steps are as follows:

[0066] 1. Preparation of the coating ink: Dissolve 691 mg PbI2 in 1 mL of MAfa ionic liquid solvent and heat and stir at 60°C for 12 hours for later use; dissolve 100 mg FAI and 5 mg MACl in 1 mL of isopropanol and stir at room temperature for 3 hours for later use.

[0067] 2. Preparation of Spiro-OMeTAD solution: Dissolve 73.2 mg of Spiro-OMeTAD in 1 mL of chlorobenzene, dissolve 520 mg of lithium bis(trifluoromethanesulfonate)imide in 1 mL of acetonitrile solution, add 28.8 μL of TBP solution to the Spiro-OMeTAD solution, add 17.6 μL of lithium salt solution to the Spiro-OMeTAD solution, and stir the mixture at room temperature for 2 hours before use.

[0068] 3. Preparation of tin dioxide thin film: Tin dioxide was spin-coated onto the cleaned FTO conductive glass surface under the following conditions: spin-coating at 4000 rpm for 30 seconds. The spin-coated film was then annealed on a hot stage at 150°C for 30 minutes to prepare the tin dioxide thin film.

[0069] 4. Perovskite film preparation: 25 μL of lead iodide ink was dropped onto a substrate preheated to 120℃ and spread at a blade coating speed of 5 mm / s. After coating, the sample was placed on the surface of a blade coater at 120℃ for annealing for 5 minutes to form a PbI2 film. The blade was then fixed to the end of the substrate. The surface morphology of the lead iodide film was uniform and porous. Figure 3 This facilitates the penetration of formamidine iodide; after lowering the surface temperature of the coating machine to 70℃, 15μL of formamidine iodide ink is dropped onto the lead iodide film, and the doctor blade is dragged in the opposite direction at a speed of 30mm / s. After coating, the surface temperature of the coating machine is raised to 150℃, and the resulting film is annealed for 5 minutes to form a FAPbI3 perovskite film containing a large amount of PbI2. Figure 10 The surface morphology of perovskite thin films is as follows: Figure 11As shown, the maximum grain size is 3 μm, but the boundaries are relatively blurred, and there are many unreacted lead iodide residues on the surface. The large-area film is relatively uniform, and the morphology is relatively consistent in all places. The perovskite film was prepared in air with an air humidity of 60%.

[0070] 5. Preparation of Spiro-OMeTAD thin film: 25 μL of the prepared Spiro-OMeTAD mixed solution was dropped onto the surface of the perovskite thin film, and the top charge transport layer was prepared by spin coating at 3000 rpm for 30 s.

[0071] 6. Top electrode fabrication: MoO3 / Ag is deposited on the top charge transport layer by vapor deposition, with a MoO3 thickness of 5 nm and a metal Ag electrode thickness of 100 nm;

[0072] 7. Test characterization: The battery was tested at AM1.5G, 100mW / cm². 2 The current density-voltage (JV) performance curve of the battery was tested under illumination, as shown in the figure. Figure 12 As shown, the short-circuit current density of the battery is 21.9 mA / cm². 2 The open-circuit voltage is 1.16V, the fill factor is 78.4%, and the photoelectric conversion efficiency is 19.9%, which is similar to the perovskite solar cell in Example 1. Figure 6 Compared to the previous method, the short-circuit current and fill factor were significantly reduced, while the open-circuit voltage was increased to some extent. The main reason is that the second-step coating speed was too fast, which resulted in incomplete reaction between lead iodide and formamidine iodide, leaving a large amount of lead iodide residue. This reduced the light absorption intensity of the perovskite film, and some lead iodide passivated the defects at the grain boundaries.

[0073] Comparative Example 1:

[0074] This comparative example provides a method for preparing FAPbI3 perovskite thin films in air based on a traditional two-step spin coating method. The specific steps are as follows:

[0075] 1. Preparation of spin-coating solution: Dissolve 691 mg PbI2 in 1 mL of MAfa ionic liquid solvent and heat and stir at 60 °C for 12 hours for later use; dissolve 100 mg FAI and 5 mg MACl in 1 mL of isopropanol and stir at room temperature for 3 hours for later use.

[0076] 2. Perovskite film preparation: 35 μL of lead iodide solution was dropped onto a substrate preheated to 80℃, and spin-coated at 4000 rpm for 30 s. After coating, the sample was transferred to a hot plate at 120℃ and annealed for 5 minutes to form a PbI2 film. The lead iodide film had a uniform and porous surface morphology. Figure 13This facilitates the penetration of formamidine iodide; 30 μL of formamidine iodide oil solution is added to a lead iodide film preheated to 80℃, and spin-coated at 2000 rpm for 30 s. After coating, the sample is transferred to a hot plate at 150℃ and annealed for 5 minutes to form a FAPbI3 perovskite film. The surface morphology of the perovskite film is as follows. Figure 14 As shown, the film is dense and uniform, with a maximum grain size of 2 μm. However, the film is not uniform over a large area, with radial textures and obvious color differences on the surface, and the morphology is inconsistent in different areas. It can be seen that spin coating cannot be applied to the preparation of large-area films. The perovskite film was prepared in air with a humidity of 60%.

[0077] Comparative Example 2:

[0078] This comparative example provides a two-step coating method ( Figure 1 The specific steps for preparing FAPbI3 perovskite thin films in air are as follows:

[0079] 1. Preparation of the coating ink: Dissolve 691 mg PbI2 in 1 mL of MAfa ionic liquid solvent and heat and stir at 60°C for 12 hours for later use; dissolve 100 mg FAI and 5 mg MACl in 1 mL of isopropanol and stir at room temperature for 3 hours for later use.

[0080] 2. Perovskite film preparation: 25 μL of lead iodide ink was dropped onto a substrate preheated to 120℃ and spread at a blade coating speed of 5 mm / s. After coating, the sample was placed on the surface of a blade coater at 120℃ for annealing for 5 minutes to form a PbI2 film. The blade was then fixed to the end of the substrate. The surface morphology of the lead iodide film was uniform and porous. Figure 3 This facilitates the penetration of formamidine iodide. After lowering the surface temperature of the coating machine to 70°C, 15 μL of formamidine iodide ink is dropped onto the lead iodide film. The doctor blade is dragged in the opposite direction at a speed of 1 mm / s. After coating, the surface temperature of the coating machine is raised to 150°C, and the resulting film is annealed for 5 minutes to form a FAPbI3 perovskite film. The surface uniformity of the film is poor, and a "coffee ring" phenomenon is also present. This is because the formamidine iodide ink has strong fluidity. When the doctor blade speed is too slow, the formamidine iodide ink will spread prematurely due to its own fluidity, resulting in poor film uniformity. The perovskite film is prepared in air with an air humidity of 60%.

Claims

1. A method for preparing FAPbI3 perovskite thin films by two-step air coating, characterized in that: Includes the following steps: Step (1): Dissolve lead iodide in methylamine formate ionic liquid, dissolve formamidine and methylamine chloride (MACl) in isopropanol, heat and stir the lead iodide solution, stir the formamidine solution at room temperature, and use it as a scraping ink after it is completely dissolved. Step (2): Drop the prepared lead iodide ink onto the preheated substrate in the air, adjust the distance between the coating blade and the substrate, drag the blade from the top to the bottom of the substrate at a speed of 1-30 mm / s to spread the liquid, and anneal it directly on the doctor blade coating machine at 120°C to obtain a lead iodide film. Step (3): After the surface temperature of the doctor blade coating machine drops to 60-90℃, the prepared formamidine ink is dropped onto the lead iodide film. The doctor blade is dragged from the end of the substrate back to the top at a speed of 10mm / s, which drives the formamidine ink to spread and causes lead iodide and formamidine to react to form perovskite. The perovskite film is then placed on the doctor blade coating machine and annealed at 150℃ to obtain a formamidine lead iodide perovskite film with a stable α phase.

2. The method for preparing FAPbI3 perovskite thin films by two-step air coating according to claim 1, characterized in that: Step (3): After the surface temperature of the doctor blade coating machine drops to 70°C, the prepared formamidine iodide ink is dropped onto the lead iodide film. The doctor blade is dragged from the end of the substrate back to the top at a speed of 10 mm / s, which drives the formamidine iodide ink to spread and causes lead iodide and formamidine iodide to react to form perovskite. The perovskite film is then placed on the doctor blade coating machine and annealed at 150°C to obtain a formamidine lead iodide perovskite film with a stable α phase.

3. The method for preparing FAPbI3 perovskite thin films by two-step air coating according to claim 1, characterized in that: In step (1), the concentration range of lead iodide ink is 400-800 mg / mL, and the concentration range of formamidinium iodide ink is 60-120 mg / mL. The coating process is carried out in an air environment with an air humidity of 20%-80%.

4. The method for preparing FAPbI3 perovskite thin films by two-step coating according to claim 1, characterized in that: In step (2), the preheating temperature of the substrate is 80-120℃, the distance between the scraper and the substrate is 0.1-0.5mm, the scraper speed is 5mm / s, and the thickness of the prepared FAPbI3 perovskite film is 0.3-2μm, with an area of ​​5-100cm². 2 .

5. A perovskite solar cell comprising a perovskite thin film prepared by any one of claims 1-4, characterized in that: The perovskite solar cell comprises, from bottom to top, a glass substrate (1), a bottom electrode layer (2), a bottom charge transport layer (3), a perovskite thin film layer (4), a top charge transport layer (5), and a top electrode layer (6); the bottom electrode layer (2) is placed on the upper surface of the glass substrate (1) and directly contacts the unconnected layer; the perovskite thin film layer (4) is above the bottom electrode layer (2) and connected in the middle by the bottom charge transport layer (3); the top charge transport layer (5) and the top electrode layer (6) are placed on the upper side of the perovskite thin film layer (4); at least one side of the bottom electrode layer (2) and the top electrode layer (6) is transparent.

6. The perovskite solar cell according to claim 5, characterized in that: The bottom electrode layer (2) is an FTO transparent electrode.

7. The perovskite solar cell according to claim 5, characterized in that: The bottom charge transport layer (3) is tin dioxide, and the specific preparation steps are as follows: (1) Tin dioxide was spin-coated onto the cleaned FTO conductive glass surface under spin-coating conditions of 4000 rpm for 30 seconds; (2) The spin-coated film was annealed on a hot plate at 150°C for 30 minutes to prepare a tin dioxide film.

8. The perovskite solar cell according to claim 5, characterized in that: The top charge transport layer (5) is Spiro-OMeTAD, and the specific preparation steps are as follows: (1) Dissolve 73.2 mg of Spiro-OMeTAD in 1 mL of chlorobenzene; (2) Dissolve 520 mg of lithium bis(trifluoromethanesulfonate)imide in 1 mL of acetonitrile solution; (3) Add 28.8 μL of TBP solution to Spiro-OMeTAD solution; (4) Add 17.6 μL of lithium salt solution to Spiro-OMeTAD solution; (5) Stir the mixed solution at room temperature for 2 hours; (6) 25 μL of mixed solution was dropped onto the surface of the perovskite film, and the top charge transport layer was prepared by spin coating. The spin coating conditions were 3000 rpm for 30 s.

9. The perovskite solar cell according to claim 5, characterized in that: The top electrode layer (6) is molybdenum oxide / silver, and the specific preparation steps are as follows: MoO3 / Ag was deposited on the top charge transport layer, with a MoO3 thickness of 5 nm and a metal Ag electrode thickness of 100 nm.

Images