Method for promoting vertical orientation growth of two-dimensional perovskite film by applying electric field

Abstract

The invention belongs to the technical field of perovskite solar cells, and particularly relates to a method for promoting vertical orientation growth of a two-dimensional perovskite thin film by applying an electric field, which comprises the following steps of: 1, fixing a composite substrate on a spin coating table; 2, spin-coating a precursor solution on the composite substrate, and applying an electric field in the vertical direction in the step 2; the electric field is introduced, the inorganic layer is arranged perpendicular to the composite substrate under the action of the electric field, formation of horizontal orientation is reduced, a carrier transmission path is optimized, charge transmission efficiency is improved, the method is suitable for various precursor solutions and substrate materials, the process is simple and easy to control, uniform growth of a large-area film can be achieved, and the method is suitable for large-scale production. Good industrial application prospects are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of perovskite solar cells, and in particular relates to a method for promoting the vertical orientation growth of a two-dimensional perovskite film by applying an electric field. Background Art

[0002] Perovskite solar cells have become a research hotspot in the field of solar photovoltaics in recent years due to their excellent photoelectric conversion efficiency, adjustable band gap and low-cost preparation process. Although traditional three-dimensional perovskite materials (such as CH3NH3PbI3) have shown extremely high photoelectric performance, their inherent stability issues, such as intolerance to moisture, have restricted their industrial development. Compared with three-dimensional perovskites, two-dimensional perovskite materials have a layered structure and show better environmental stability, especially in terms of moisture resistance.

[0003] Two-dimensional perovskites are usually composed of alternating long-chain organic cations and inorganic layers, in which the inorganic layer (such as PbI6 octahedron) constitutes the dominant part of light absorption and charge transport, while the organic layer acts as an insulating "barrier" layer. Such a structure enables two-dimensional perovskites to exhibit excellent moisture resistance, because the organic layer can effectively prevent moisture from penetrating into the inorganic layer, thereby extending the life of the device.

[0004] The orientations of two-dimensional perovskite films are mainly vertical orientation (Vertical Orientation) and horizontal orientation (Horizontal Orientation). Vertical orientation means that the inorganic layers are arranged in a direction perpendicular to the substrate, and the organic layers are stacked alternately in the vertical direction. Vertical orientation can provide an efficient charge transfer path, allowing carriers to pass through the inorganic layers unimpeded in the vertical direction, thereby reducing recombination losses and improving photoelectric conversion efficiency. Horizontal orientation means that the inorganic layers are arranged parallel to the substrate, and the charge transfer needs to pass through multiple organic layers, which increases the obstacles to the charge during the transfer process, resulting in an increase in the recombination rate and a reduction in the efficiency of the device. From the above analysis, it can be seen that the orientation of the two-dimensional perovskite film has an important influence on its photoelectric performance. The orientation of the film directly determines the carrier transfer efficiency, recombination rate and the final device efficiency.

[0005] In order to optimize the orientation of two-dimensional perovskite films, researchers have developed a variety of control technologies, including precursor solution control, substrate surface treatment, film formation process control, and the use of additives. Precursor solution control mainly refers to regulating the crystal growth orientation of perovskite by adjusting the ratio of organic long-chain cations to inorganic cations in the precursor solution; for example, appropriately increasing the concentration of organic cations can increase the number of stacking times of two-dimensional perovskite layers, thereby affecting the arrangement direction of the layers. Substrate surface treatment mainly refers to modifying the substrate surface, such as using surface passivation, introducing self-assembled monolayers (SAMs), etc., to control the growth direction of perovskite crystals on the substrate surface. Film formation process control mainly refers to improving the orientation of perovskite by adjusting the volatilization rate of the solution, the film formation speed, the annealing temperature, etc. during the film deposition process. The use of additives mainly refers to adding an appropriate amount of additives, such as DMSO, DMF, amine salts, small organic molecules, polymers, and inorganic materials, to the precursor solution to regulate the kinetic behavior during the crystallization process, thereby regulating the growth direction of the crystal. The above-mentioned control technology is easily limited by the precursor solution and substrate material and has poor applicability. Therefore, it is of great significance to develop a universal control technology for the orientation of two-dimensional perovskite films. Summary of the invention

[0006] To solve the above problems, the present invention provides a method for promoting the vertically oriented growth of a two-dimensional perovskite film by applying an electric field, comprising: step 1, fixing a composite substrate on a spin coating table; step 2, spin coating a precursor solution on the composite substrate, and in step 2, applying an electric field in the vertical direction.

[0007] The present invention effectively solves the growth orientation problem of the two-dimensional perovskite film by applying a vertical electric field during the growth process, and has the advantages of wide application range and precise control. Traditional methods have limitations in orientation regulation and are easily affected by precursor composition, substrate treatment, etc., making it difficult to achieve stable vertical orientation. The present invention, by applying an external electric field, guides the inorganic layer of the perovskite crystal to align along the electric field direction (perpendicular to the substrate) during the film formation process, forming an excellent vertical orientation structure.

[0008] Specifically, under the action of the electric field, the organic cations and inorganic anions in the precursor solution migrate in a directional manner, causing the inorganic layers to be arranged vertically and the organic layers to be stacked alternately, thereby accelerating the vertical orientation growth of the film. When applied, the carriers are transported vertically along the inorganic layers, reducing the recombination loss and improving the charge transfer efficiency.

[0009] Furthermore, in step 1, the composite substrate includes a transparent conductive layer and a hole transport layer, the hole transport layer is disposed on the transparent conductive layer, and the precursor solution is disposed on the hole transport layer. The applied electric field uniformly covers the hole transport layer and the precursor region, avoiding local electric field unevenness.

[0010] Furthermore, in step 1, the composite substrate is preheated. Heating the composite substrate can reduce the surface tension of the precursor solution, allowing the precursor to spread evenly on the substrate, thereby forming a uniform film, thereby improving the density and uniformity of the film and reducing defects. In addition, heating the composite substrate can also accelerate the nucleation and growth process of the perovskite crystals, help form higher quality crystals, reduce disordered orientation, and enhance the photoelectric properties of the film. In addition, preheating the composite substrate can also improve the interface bonding between the layers, especially the adhesion between the hole transport layer and the precursor solution, thereby improving the stability and durability of the device.

[0011] Furthermore, the precursor solution includes an organic cation precursor, an inorganic cation precursor, a halide precursor and a solvent.

[0012] Furthermore, the organic cationic precursor includes BAI (butylammonium iodide), PEAI (phenylethylammonium iodide), HAI (hexylammonium iodide) or EDA (ethylenediamine).

[0013] Furthermore, the inorganic cation precursor includes lead iodide, tin iodide or germanium iodide.

[0014] Furthermore, the halide precursor includes MAI (methylammonium iodide), FAI (formamidiniumiodide) or MABr (methylammonium bromide).

[0015] Furthermore, the solvent includes DMF (dimethylformamide) or DMSO (dimethyl sulfoxide).

[0016] Furthermore, the electric field is a direct current electric field. The direct current electric field provides a stable and constant electric field direction, which can continuously guide the ions (such as Pb 2+ ,I - ) migrate in an orderly manner along the direction of the electric field, thereby promoting the vertical orientation growth of the perovskite film, which helps to form a high-quality vertical arrangement structure of the inorganic layer and optimize the charge transfer path. In this process, since the DC electric field is continuous and the electric field remains consistent throughout the deposition process, it is not easy to cause electric field fluctuations, avoiding orientation failure or random orientation formation during crystal growth, thereby reducing structural defects in the film.

[0017] Furthermore, the direction of the electric field points to the spin coating station. That is, it points from the precursor solution to the spin coating station. Under this electric field direction, the ions in the precursor solution are arranged in an orderly manner in the vertical direction, thereby promoting the vertical arrangement of the inorganic layer of the perovskite along the direction of the electric field. In addition, the vertical electric field can help electrons and holes to be transmitted in the inorganic layer in the vertical direction, reduce the resistance of carriers when passing through the organic layer, avoid the transmission barrier caused by horizontal orientation, and thus improve the photoelectric performance of the solar cell.

[0018] Beneficial effects of the present invention: (1) The present invention introduces an electric field, which causes the inorganic layer to be arranged perpendicular to the composite substrate, thereby reducing the formation of horizontal orientation, optimizing the carrier transmission path, and improving the charge transmission efficiency.

[0019] (2) The present invention introduces an electric field, which guides the orderly migration of ions, reduces orientation failure and crystal defects, makes the film denser and more uniform, and improves the photoelectric conversion efficiency and stability.

[0020] (3) The present invention introduces an electric field to promote the vertically oriented growth of two-dimensional perovskite films. It is applicable to a variety of precursor solutions and substrate materials. The process is simple and easy to control. It can achieve uniform growth of large-area films and has good industrial application prospects.

[0021] Based on the above beneficial effects, the present invention has good application prospects in the field of perovskite solar cell technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a method for applying an electric field to promote the vertically oriented growth of two-dimensional perovskite films. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples.

[0024] Example 1 The present invention provides a method for promoting the vertical orientation growth of a two-dimensional perovskite film by applying an electric field, such as Figure 1 As shown, the method of the present invention mainly includes two steps. In order to clearly illustrate the present invention, this example is based on (BA)2(MA) n Pb n I 3n+1 Taking 2018 as an example, the two main steps are described as follows: The materials used in this embodiment include BAI (for introducing organic cations), MAI (for introducing organic cations methylamine cations), and PbI2 (for providing the lead ions required in the inorganic layer). The solvent is DMSO, which is used to dissolve the precursor. The substrate is ITO conductive glass, which serves as a transparent conductive layer. The hole transport layer is PEDOT:PSS. The equipment used includes a spin coating device, a hot plate, a DC power supply, and an electrode system.

[0025] Step 1: Fix the composite substrate on a spin coating table.

[0026] The composite substrate comprises a transparent conductive layer and a hole transport layer, the hole transport layer is disposed on the transparent conductive layer, and the precursor solution is disposed on the hole transport layer. In this step, the composite substrate is preheated.

[0027] Before preparing the two-dimensional perovskite film, the transparent conductive layer (ITO) is treated to ensure that the surface is clean and conducive to the attachment and growth of the film. This includes ultrasonic cleaning with deionized water, acetone, isopropyl alcohol, ethanol, etc. in sequence, and also includes the use of oxygen plasma treatment or ultraviolet ozone treatment to further clean the surface of the transparent conductive layer, so that the surface energy of the transparent conductive layer is high, which is conducive to the uniform film formation of the subsequent film.

[0028] After cleaning the transparent conductive layer, a hole transport layer was prepared on the transparent conductive layer. PEDOT:PSS was dissolved in a solvent to prepare a solution; the hole transport layer solution was coated on the ITO by spin coating, with the parameters of 2000 rpm for 30 seconds to form a uniform film; then the spin-coated transparent conductive layer was placed on a hot plate, heated to 120 °C, and baked for 10 minutes to solidify the hole transport layer.

[0029] Finally, the formed composite substrate is fixed on a spin coating stage.

[0030] Step 2: spin-coat the precursor solution on the composite substrate.

[0031] First, a precursor solution is prepared. The ratio of BAI, MAI, and PbI2 depends on the number of layers n. Taking n = 3 as an example, the molar ratio of BAI:MAI:PbI2 is 2:3:3. These solid precursors are dissolved in DMSO solvent to form a precursor solution with a concentration of 0.5 M to 1.5 M. During this time, the solution is stirred to completely dissolve and evenly mix. Then, the precursor solution is filtered using a 0.22 micron filter membrane to remove undissolved impurities and particles.

[0032] Then, the precursor solution was dropped onto the surface of the hole transport layer using a pipette, and a film was formed by spin coating. The spin coating parameters were first set to 1000 rpm for 10 seconds, and then increased to 4000 rpm for 30 seconds to form a uniform and smooth film.

[0033] The electrode system is installed, the lower electrode is connected to the transparent conductive layer, the upper electrode is a flexible conductive film or a mesh electrode, suspended above the precursor solution, not in direct contact with the solution, and the direction of the electric field points to the spin coating station. The electric field is applied by a DC voltage, the direction of the electric field is perpendicular to the transparent conductive layer, the voltage is several volts to tens of volts, and the ions in the precursor solution migrate in an orderly manner in the vertical direction under the action of the electric field. During the spin coating process, the electric field is continuously applied to ensure that the film can be arranged vertically along the direction of the electric field. The time for continuously applying the electric field is consistent with the spin coating time or the time for applying the electric field exceeds the spin coating time. The flexible conductive film used in the upper electrode has a large area relative to the precursor solution, and the electric field can be applied uniformly to ensure that the overall force on the film surface is consistent, and promote the vertical orientation growth of the perovskite film; the flexible conductive film is soft and easy to match with the substrate, reducing the mechanical interference to the spin coating process, and maintaining the flatness and uniformity of the film. More preferably, the upper electrode uses a mesh electrode. The mesh electrode has good air permeability and open structure, avoiding physical interference with the precursor solution, while ensuring the effective application of the electric field. The open design of the mesh electrode reduces the influence of the electrode on solution flow and solvent volatilization, which is beneficial to the uniform film formation and solvent release during annealing.

[0034] After the spin coating is completed and the electric field is applied, the film is annealed to promote its oriented growth. The annealing temperature is 100°C to 120°C and the annealing time is 10 minutes to 30 minutes.

[0035] Example 2 Based on Example 1, the two-dimensional perovskite film is (PEA)2(MA) n Pb n I 3n+1 . The materials used include PEAI (as a source of organic long-chain cations), MAI (used to provide short-chain organic cations), and PbI2 (providing lead ions required for the inorganic layer). The solvent is DMSO or DMF. The transparent conductive layer is FTO or ITO conductive glass. When preparing the precursor solution, the molar ratio of PEAI, MAI and PbI2 is 2:3:3.

[0036] Example 3 Based on Example 1, the two-dimensional perovskite film is (PEA)2(FA) n Pb n I 3n+1 . The materials used include PEAI (as a source of organic long-chain cations), FAI (used to provide short-chain organic cations), and PbI2 (providing lead ions required for the inorganic layer). The solvent is DMSO or DMF. The transparent conductive layer is FTO or ITO conductive glass. When preparing the precursor solution, the molar ratio of PEAI, FAI and PbI2 is 2:3:3.

[0037] Example 4 Based on Example 1, the two-dimensional perovskite film is (BA)2(Sn) n I 3n+1 The materials used include BAI (as a source of organic long-chain cations), SnI2 (providing Sn in the inorganic layer), 2+ As the main metal ion. The solvent is DMSO or DMF. The transparent conductive layer is FTO or ITO conductive glass. When preparing the precursor solution, the molar ratio of BAI and PbI2 is 2:1.

[0038] Typically, the spin coating process results in different thicknesses of the solution at the center and the edge. Due to the centrifugal force, the solution moves more easily to the edge of the composite substrate, making the thickness of the edge area greater than that of the center. The electric field strength in the central area is set to be larger and the electric field strength in the edge area is set to be smaller to compensate for the difference in solution thickness, which can promote the uniform growth of crystals. Specifically, by arranging multiple independent electrodes in the center and edge areas of the composite substrate, the electric field strength in each area can be more accurately controlled. For example, a slightly stronger electric field is applied in the central area, while a moderate electric field strength is maintained in the edge area, so that the crystals grow uniformly.

[0039] In addition, in the early stage of spin coating, the precursor solution has not yet completely formed a thin film, and a strong electric field is applied to effectively guide the directional arrangement of the inorganic layer, especially to form a preliminary crystal framework in the vertical direction, laying the foundation for the orderly growth of the subsequent thin film. After the film is gradually formed, an excessively strong electric field will lead to excessively fast crystal growth and increase the probability of crystal defects. Therefore, the electric field strength is gradually reduced to slow down the crystallization rate and improve the crystallization quality and uniformity of the film. In addition, a weaker electric field can also help reduce grain boundary defects caused by excessive crystallization, allowing grains to grow for a longer time, forming a larger crystal size, and improving the electrical and optical properties of the film.

[0040] In addition to optimizing the electric field distribution and intensity, the orderly growth of crystals can also be controlled by combining substrate temperature regulation: a stronger electric field is applied in the low-temperature stage, and the electric field is weakened in the high-temperature stage to promote the orderly growth of crystals.

[0041] In summary, the present invention provides a method for promoting the vertical orientation growth of a two-dimensional perovskite film by applying an electric field, comprising: step 1, fixing a composite substrate on a spin coating table; step 2, spin coating a precursor solution on the composite substrate, and in step 2, applying an electric field in a vertical direction. The present invention introduces an electric field, and the electric field causes the inorganic layer to be arranged vertically to the composite substrate, reduces the formation of horizontal orientation, optimizes the carrier transmission path, and improves the charge transmission efficiency. The present invention is applicable to a variety of precursor solutions and substrate materials, has a simple and easy-to-control process, can achieve uniform growth of large-area films, and has good industrial application prospects.

[0042] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for promoting vertically oriented growth of a two-dimensional perovskite film by applying an electric field, comprising the following steps: Step 1, fixing the composite substrate on a spin coating table; Step 2, spin coating the precursor solution on the composite substrate; Features: In step 2, an electric field is applied in the vertical direction.

2. The method for promoting vertically oriented growth of a two-dimensional perovskite film by applying an electric field as claimed in claim 1, characterized in that: In step 1, the composite substrate comprises a transparent conductive layer and a hole transport layer, the hole transport layer is disposed on the transparent conductive layer, and the precursor solution is disposed on the hole transport layer.

3. The method for promoting vertically oriented growth of a two-dimensional perovskite film by applying an electric field as claimed in claim 1, characterized in that: In step 1, the composite substrate is preheated.

4. The method for promoting vertically oriented growth of a two-dimensional perovskite film by applying an electric field as claimed in claim 1, characterized in that: The precursor solution includes an organic cation precursor, an inorganic cation precursor, a halide precursor and a solvent.

5. The method for promoting vertically oriented growth of a two-dimensional perovskite film by applying an electric field as claimed in claim 4, characterized in that: The organic cationic precursor includes BAI, PEAI, HAI or EDA.

6. The method for promoting vertically oriented growth of a two-dimensional perovskite film by applying an electric field as claimed in claim 5, characterized in that: The inorganic cation precursor includes lead iodide, tin iodide or germanium iodide.

7. The method for promoting vertically oriented growth of a two-dimensional perovskite film by applying an electric field as claimed in claim 6, characterized in that: The halide precursor includes MAI, FAI or MABr.

8. The method for promoting vertically oriented growth of a two-dimensional perovskite film by applying an electric field as claimed in claim 7, characterized in that: The solvent includes DMF or DMSO.

9. The method for promoting vertically oriented growth of a two-dimensional perovskite film by applying an electric field according to any one of claims 1 to 8, characterized in that: The electric field is a direct current electric field.

10. The method for promoting vertically oriented growth of a two-dimensional perovskite film by applying an electric field as claimed in claim 9, characterized in that: The direction of the electric field is toward the spin coating station.

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