A method for preparing perovskite thin films on a silicon substrate by air-flow assisted inkjet printing

Abstract

The present invention discloses a method for preparing a perovskite thin film on a silicon substrate by air flow-assisted inkjet printing. The method includes: preparing a perovskite precursor ink; printing the perovskite precursor ink on the silicon substrate by inkjet printing to obtain a perovskite wet film; using an air flow-assisted process to uniformly remove most of the solvents in the perovskite precursor wet film to obtain the perovskite pre-crystallized film; annealing the perovskite pre-crystallized dry film to obtain a perovskite thin film. This process uses high-precision inkjet printing on a silicon wafer to prepare a perovskite thin film, enabling the perovskite to form a dense and shrinkage-free film on the silicon substrate, forming good contact with the underlying silicon wafer. The air flow-assisted process can slowly remove the solvents of the wet film, effectively improving the coffee ring effect caused by inkjet printing.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaics, and particularly relates to a method for preparing a perovskite wet film by inkjet printing on a silicon substrate, and using a weak air flow to assist its crystallization annealing to form a dense perovskite film to improve the performance of a conventional silicon-based solar cell. Background Art

[0002] Perovskite materials can be used in series / multi-junction arrangements to improve the performance of conventional silicon-based solar cells. However, the surface of a conventional commercial crystalline silicon solar cell usually has an antireflection layer composed of pyramids with a size of 500 nm - 5 μm. Therefore, the perovskite films prepared by processes such as spin coating, slot coating, and blade coating used in laboratories cannot effectively cover the silicon substrate, resulting in many shrinkage holes and uneven textures, seriously affecting the interface between the perovskite layer and the crystalline silicon bottom cell. Inkjet printing sprays perovskite ink droplets onto the surface of the silicon substrate through the power of injectors in the form of thermal or acoustic control, with higher resolution, and can form a good coverage on the uneven silicon substrate.

[0003] The preparation process of the perovskite film usually removes organic solvents quickly through vacuum, air gun, antisolvent, etc. to form a pre-crystallized dry film, and then anneals the pre-crystallized dry film to obtain the final perovskite film. However, due to the surface tension of the perovskite ink droplets formed by inkjet printing on the silicon substrate surface, countless spherical droplets with a thick middle and thin edges will be formed. Since the surface area to volume ratio of the droplet edge is larger, the solvent evaporation rate per unit volume is faster, and the solvent molecules in the middle of the droplet will carry the solute (perovskite raw material) to the edge for replenishment. Also, due to the frictional resistance generated by the solid surface on the droplet, it prevents the solid-liquid interface from shrinking inward. In this way, the solute accumulates at the edge continuously, and the color gradually deepens, which is the coffee ring effect. This effect seriously affects the electrical properties and film density of the perovskite film. Therefore, it is necessary to develop a technology that can improve the efficient and stable preparation of high-quality perovskite films by inkjet printing on a silicon substrate. Summary of the Invention

[0004] To overcome the deficiencies of the prior art, the present invention provides a method for efficiently and stably preparing high-quality perovskite thin films on a silicon substrate. A crystallization promoter is added to the perovskite precursor ink, enabling the perovskite precursor solution to rapidly nucleate under the action of a weak air flow. The ink is used to prepare the perovskite thin film by high-precision inkjet printing. Then, through an air flow-assisted process on the surface of the wet film, the organic solvents in the wet film are uniformly removed, and a perovskite pre-crystallized dry film is rapidly and uniformly formed under the action of the crystallization promoter. The perovskite thin film is obtained by annealing the pre-crystallized dry film. This inkjet printing process improves the coverage problem of the perovskite thin film on the silicon substrate, and the air flow-assisted process effectively solves the coffee ring effect of the inkjet-printed perovskite thin film. The combination of the two realizes the rapid, uniform, and stable deposition of a large-area perovskite thin film on the silicon substrate.

[0005] The present invention provides a method for preparing a perovskite thin film on a silicon substrate by air flow-assisted inkjet printing, and the steps are as follows:

[0006] Prepare a perovskite precursor ink;

[0007] Cover the silicon substrate with the perovskite precursor ink through an inkjet printing process to obtain a perovskite wet film;

[0008] Use an air flow-assisted process to uniformly remove most of the solvents in the perovskite precursor wet film to obtain the perovskite pre-crystallized film;

[0009] Anneal the perovskite pre-crystallized dry film to obtain a perovskite thin film;

[0010] Optionally, the general formula of the perovskite in the perovskite precursor ink is ABX3, and the raw materials can be prepared from the following substances: organic ammonium halide salts, organic amidinium halide salts, Group IA metal salts, and BX2, where B is a Group IVA metal cation and X is a halogen.

[0011] Optionally, the molar ratio of the ligand in the perovskite precursor ink to the Pb2+ ions in the perovskite raw materials ranges from 3:1 to 0.5:1. The ligand includes at least one of diphenyl sulfoxide, dimethyl sulfone, and N-methylpyrrolidone. The carrier solvent generally includes one or more of ethylene glycol monomethyl ether, N,N-dimethylformamide, γ-butyrolactone, ethanol, and isopropanol. The suitable concentration range of the perovskite precursor ink is 0.2 mmol / mL to 3 mmol / mL.

[0012] Optionally, the perovskite precursor ink includes a crystallization promoter, including but not limited to hydrochloride (Cl-), bromate (Br-), and thiocyanate (SCN-). The molar ratio range of the total amount of additives to the Group IVA metal cations in the perovskite powder is 0.5:100 to 15:100.

[0013] Optionally, the silicon substrate can be a finished or semi-finished product of a heterojunction solar cell or a homojunction solar cell. The surface topography of the silicon substrate can be a polished surface or a textured surface. The polished surface can adopt one of acid polishing method, alkali polishing method or mechanical polishing method. The textured surface adopts alkali texturing method, and the undulation range of the textured surface should be within 200nm - 2um.

[0014] Optionally, when printing the perovskite precursor ink, it is necessary to ensure that the silicon wafer is cooled to room temperature. The printing resolution range of the perovskite ink is 100×100dpi - 2400dpi×2400dpi, the droplet volume range of the printing nozzle is 1 - 75pl, and the ejection frequency is 200 - 100000Hz;

[0015] Optionally, to improve the coffee ring effect of inkjet printing, the gas flow assisted blowing process must be carried out within 2 - 60s after the perovskite wet film printing is completed;

[0016] Optionally, the gas source of the gas flow assisted process can be dry air with humidity ≤ 40%, inert gases such as nitrogen, etc.;

[0017] Optionally, to ensure that the solvent in the perovskite wet film can be uniformly volatilized and carried away at a sufficient rate to form a pre-crystallized dry film, the wind speed provided by the gas flow assisted process needs to be within 0.5 - 20m / s. The uniformity P of the gas blowing outlet speed ≤ 5%, where P = (Vmin / max - Var) / Var×100% (Vmin / max: the maximum or minimum wind speed in the gas blowing process, Var: the average wind speed);

[0018] Optionally, when the perovskite pre-crystallized dry film is annealed, the annealing temperature is 70 - 280°C, and the annealing time is 2 - 80 minutes.

[0019] The perovskite thin film prepared by inkjet printing on the silicon substrate according to the present invention has good coverage on the silicon substrate. The perovskite thin film by using the gas flow assisted process has no coffee ring effect, and the preparation time is greatly shortened compared with other film forming methods. The contact between the perovskite thin film and the adjacent crystalline silicon bottom cell is good, greatly increasing the photoelectric conversion efficiency and stability of the device. It has great potential value in the industrial application of perovskite solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1Schematic diagram of the process for preparing perovskite thin films by inkjet printing in the present invention;

[0022] Figure 2 Schematic diagram of inkjet printing a perovskite wet film on a semi-finished heterojunction silicon solar cell in Example 1 of the present invention;

[0023] Figure 3 Schematic diagram of the gas flow assisted process for the perovskite wet film on a semi-finished heterojunction silicon solar cell in Example 1 of the present invention. Detailed implementation manners

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0025] Next, the technical solutions in the embodiments of the present invention patent will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention patent. Obviously, the described embodiments are only a part of the embodiments of the present invention patent, rather than all the embodiments. Based on the embodiments of the present invention patent, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention patent.

[0026] The following will detail the specific implementation of the present invention.

[0027] Figure 1 Schematic diagram of the process for preparing perovskite thin films by inkjet printing in the present invention, the steps are as follows:

[0028] S11. Prepare a perovskite precursor ink;

[0029] S13. Cover the silicon substrate with the perovskite precursor ink through an inkjet printing process to obtain a perovskite wet film;

[0030] S14. Use a gas flow assisted process to uniformly remove most of the solvents in the perovskite precursor wet film to obtain the perovskite pre-crystallized film;

[0031] S15. Anneal the perovskite pre-crystallized dry film to obtain a perovskite thin film;

[0032] Optionally, the general formula of the perovskite in the perovskite precursor ink is ABX3, and the raw materials can be prepared from the following substances: organic ammonium halide salts, organic guanidinium halide salts, Group IA metal salts, and BX2, where B is a Group IVA metal cation and X is a halogen.

[0033] Optionally, the molar ratio of the ligand in the perovskite precursor ink to the Pb2+ ions in the perovskite raw material ranges from 3:1 to 0.5:1, and the ligand includes at least one of diphenyl sulfoxide, dimethyl sulfoxide, and N-methylpyrrolidone. The carrier solvent generally contains one or more of ethylene glycol monomethyl ether, N,N-dimethylformamide, γ-butyrolactone, ethanol, and isopropanol. The suitable concentration range of the perovskite precursor ink is 0.2 mmol / mL to 3 mmol / mL.

[0034] Optionally, the perovskite precursor ink includes a crystallization promoter, including but not limited to hydrochloride (Cl-), bromate (Br-), and thiocyanate (SCN-). The molar ratio of the total amount of the additive to the Group IVA metal cations in the perovskite powder ranges from 0.5:100 to 15:100.

[0035] Optionally, the silicon substrate can be a finished or semi-finished product of a heterojunction solar cell or a homojunction solar cell. The surface topography of the silicon substrate can be a polished surface or a textured surface. The polished surface can adopt one of acid polishing, alkali polishing, or mechanical polishing methods. The textured surface adopts an alkali texturing method, and the range of the surface roughness of the textured surface should be 200nm - 2μm.

[0036] Optionally, when printing the perovskite precursor ink, it is necessary to ensure that the silicon wafer is cooled to room temperature. The printing resolution range of the perovskite ink is 100×100 dpi - 2400 dpi×2400 dpi, the droplet volume range of the printing nozzle is 1 - 75 pl, and the ejection frequency is 200 - 100000 Hz;

[0037] Optionally, to improve the coffee ring effect of inkjet printing, the air flow-assisted blowing process must be carried out within 2 - 60 s after the perovskite wet film printing is completed;

[0038] Optionally, the gas source of the air flow-assisted process can be dry air with a humidity ≤ 40%, inert gases such as nitrogen, etc.;

[0039] Optionally, to ensure that the solvent in the perovskite wet film can be uniformly volatilized and carried away at a sufficient rate to form a pre-crystallized dry film, the wind speed provided by the air flow-assisted process needs to be 0.5 - 20 m / s. The uniformity P of the air blowing outlet speed ≤ 5%, where P = (Vmin / max - Var) / Var×100% (Vmin / max: the maximum or minimum wind speed in the air blowing process, Var: the average wind speed);

[0040] Optionally, when the perovskite pre-crystallized dry film is annealed, the annealing temperature is 70 - 280 °C, and the annealing time is 2 - 80 minutes.

[0041] Example 1: Use the process of the present invention to prepare the perovskite precursor ink for air flow-assisted inkjet printing.

[0042] 1. Weighing of perovskite powder:

[0043] Weigh 13.93 g of formamidinium iodide (FAI), 1.55 g of cesium iodide (CsI), 25.01 g of lead iodide (PbI2), and 5.78 g of lead bromide (PbBr2) respectively to obtain perovskite powder with the general formula FA 0.8 MA 0.2 Pb(I 0.8 Br 0.2 )3.

[0044] 2. Preparation of perovskite solution:

[0045] Add N-methylpyrrolidone (NMP) with the same amount of substance as Pb 2+ in the powder as the ligand solvent. In this example, the amount of substance of Pb 2+ in the powder is 70 mol, so add 5.23 ml of N-methylpyrrolidone. Finally, add (50 - V NMP ) ml of dmf and mix and stir for 2 h to obtain 50 ml of perovskite solution with a concentration of 1.4 mmol / mL

[0046] 3. Preparation of perovskite precursor ink:

[0047] Weigh 5% of lead chloride (PbCl2) and 2% of lead thiocyanate (Pb(SCN)2) powder based on the amount of perovskite substance. Add the crystallization-promoting powder to the perovskite solution and mix and stir for 20 min to obtain perovskite precursor ink.

[0048] Figure 2 This is a schematic diagram of inkjet printing a perovskite wet film on a semi-finished heterojunction silicon solar cell in Example 1 of the present invention; Figure 3 This is a schematic diagram of the gas flow-assisted process for the perovskite wet film on a semi-finished heterojunction silicon solar cell in Example 1 of the present invention.

[0049] Example 2: Preparation of a perovskite thin film on an M6-sized semi-finished heterojunction silicon solar cell using the process of the present invention

[0050] 1. Inject the perovskite precursor ink into the inkjet printer cartridge. Set the printing resolution to 300×900 dpi, the droplet volume of the printing nozzle to 50 pl, and the ejection frequency to 12000 Hz to complete the printing of the perovskite wet film.

[0051] 2. Perform gas flow-assisted treatment on the obtained perovskite pre-crystallized dry film. The wind speed provided by the air blowing box is 0.3 m / s, the blowing time is 10 s, and the blowing angle is perpendicular to the substrate.

[0052] 3. After the gas blowing is completed, anneal the substrate at an annealing temperature of 110 °C for 18 minutes to obtain a perovskite film.

[0053] The above has introduced the embodiments of the present invention in detail. Specific examples are used in this article to expound the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for preparing a perovskite thin film on a silicon substrate by air-assisted inkjet printing, characterized in that, The following steps are involved: a. Fully mixing the perovskite raw material, carrier solvent, additive and ligand to obtain a perovskite precursor ink; b. Covering the perovskite precursor ink on the silicon substrate through an inkjet printing process to obtain a perovskite wet film; c. Using an airflow-assisted process to evenly remove most of the solvent in the perovskite wet film to obtain a perovskite pre-crystallized dry film; d. annealing the perovskite pre-crystallized dry film to obtain a perovskite film; Wherein in step a, the additive in the perovskite precursor ink includes at least one of hydrochloride, bromate, and thiocyanate, and the molar ratio of the total amount of the additive to the halogen anion in the perovskite raw material is in the range of 0.2:100 to 10:100; In step b, the perovskite precursor ink printing resolution ranges from 100×100 dpi to 3000×3000 dpi, the printing nozzle droplet volume ranges from 1 to 30 pl, and the jetting frequency is from 10 to 100000 Hz; In step c, the wind speed provided by the airflow-assisted process needs to be 0.2~20m / s, and the uniformity of the air outlet velocity of the air blowing is P≤5%, where P=(Vmin / max-Var) / Var×100%, Vmin / max: maximum or minimum wind speed in the air blowing process, Var: average wind speed.

2. The method according to claim 1, characterized in that, In step a, the general formula of perovskite in the perovskite precursor ink is ABX3, and the perovskite raw material is prepared from the following substances: organic halogenated amine salt, organic halogenated amidine salt and Group IA metal salt and BX2, wherein B is a Group IVA metal cation and X is a halogen.

3. The method according to claim 1, wherein In step a, the molar ratio of the ligand in the perovskite precursor ink to Pb ions in the perovskite raw material ranges from 3:1 to 0.5:

1. The ligand includes at least one of diphenyl sulfoxide, dimethyl sulfoxide, and N-methylpyrrolidone. The carrier solvent is one or more of ethylene glycol monomethyl ether, N,N-dimethylformamide, γ-butyrolactone, ethanol, and isopropanol. The concentration range of the perovskite precursor ink is 0.2 mmol / mL to 3 mmol / mL. 2+ In step a, the molar ratio of the ligand in the perovskite precursor ink to Pb ions in the perovskite raw material ranges from 3:1 to 0.5:

1. The ligand includes at least one of diphenyl sulfoxide, dimethyl sulfoxide, and N-methylpyrrolidone. The carrier solvent is one or more of ethylene glycol monomethyl ether, N,N-dimethylformamide, γ-butyrolactone, ethanol, and isopropanol. The concentration range of the perovskite precursor ink is 0.2 mmol / mL to 3 mmol / mL.

4. The method according to claim 1, characterized in that In step b, the silicon substrate is a finished product or semi-finished product of a heterojunction solar cell or a homojunction solar cell, and the surface morphology of the silicon substrate is a polished surface or a velvet surface. The polished surface is polished by acid polishing, alkali polishing or mechanical polishing, and the velvet surface is polished by alkali velveting, and the velvet surface fluctuation range is 200nm-2um.

5. The method according to claim 1, wherein In step c, the gas source of the gas flow-assisted process is air or nitrogen inert gas with a humidity of ≤50%.

6. The method according to claim 1, wherein In step d, when the perovskite pre-crystallized dry film is annealed, the annealing temperature is 70-280° C. and the annealing time is 2-80 minutes.

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