Method for regulating perovskite crystallization based on magnetic self-assembly monolayer buried bottom interface

Abstract

The application provides a method for buried interface regulation of perovskite crystallization based on magnetic self-assembled monolayer, and belongs to the field of photoelectric conversion materials. The method comprises the following steps: preparing a self-assembled monolayer (SAM) containing a magnetic functional group on the surface of a conductive substrate; placing the magnetic SAM modified substrate in an external magnetic field; depositing a perovskite precursor solution on the magnetic SAM layer in the presence of a magnetic field and performing annealing treatment. The magnetic SAM forms a single monolayer with magnetic responsiveness on the surface of the substrate, and under the action of an external magnetic field, a magnetic template is provided for the nucleation of perovskite, and the preferential oriented growth of perovskite crystals at the buried interface is induced. Compared with traditional bulk phase magnetic field regulation, the application precisely focuses the magnetic field on the buried interface region without changing the perovskite bulk phase composition. The method is simple to operate and has strong universality, can significantly improve the crystallization quality of perovskite thin films, and is suitable for the preparation of high-efficiency and stable perovskite solar cells.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric conversion materials and relates to a method for regulating perovskite crystallization based on a magnetic self-assembled monolayer buried interface. Background Technology

[0002] Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted widespread attention in the photovoltaic field due to their excellent photoelectric performance, low cost, and simple fabrication process. Currently, the certified photoelectric conversion efficiency of single-junction perovskite solar cells has exceeded 26%, showing great commercial potential. However, the crystal quality of perovskite films and the density of buried interface defects remain key bottlenecks restricting device performance and stability.

[0003] The crystallization process of perovskite thin films determines the crystal orientation, grain size, and defect density, which directly affect the photoelectric conversion efficiency and long-term stability of the device. The buried interface, as the interface between the perovskite layer and the charge transport layer, is not only the starting region for perovskite nucleation and crystallization but also a key channel for carrier transport. The physicochemical properties of the buried interface directly affect the growth orientation of the perovskite crystal and the interface defect density. In recent years, self-assembled monolayers (SAMs) have been widely used as hole transport layers or interface modification layers in perovskite solar cells due to their tunable work function, low interface resistance, and simple fabrication process. SAM-based PSCs have shown a power conversion efficiency of approximately 27%.

[0004] In the prior art, methods for controlling perovskite crystallization using magnetic fields have been reported. For example, Chinese patent CN107482121B discloses a method for preparing perovskite thin films based on a rotating magnetic field, which promotes perovskite crystallization by introducing a rotating magnetic field during spin coating or blade coating. However, this method applies a uniform rotating magnetic field across the entire perovskite precursor solution, controlling the entire bulk perovskite layer, and the effect of the magnetic field on the buried interface is limited. Another example is Chinese patent CN113421978B, which discloses a method for preparing magnetic perovskite thin films with a weak magnetic field, which improves film stability by doping magnetic cobalt ions into the perovskite precursor solution and applying a static magnetic field. This method introduces magnetic ions through bulk doping, changing the intrinsic composition of the perovskite layer, and the magnetic ions may introduce additional recombination centers.

[0005] Therefore, developing a new method that can precisely control the crystallization orientation of perovskite at the buried interface without changing the bulk composition of perovskite or introducing additional defect centers is of great significance for improving the efficiency and stability of perovskite solar cells. Summary of the Invention

[0006] The purpose of this invention is to provide a method for controlling perovskite crystallization based on a magnetic self-assembled monolayer buried interface, in order to solve the technical problems in the prior art where the crystallization orientation of the buried interface is difficult to control precisely and the bulk magnetic field control method has limited effect on the interface.

[0007] The mechanism upon which this invention is based is as follows: Magnetic functional groups (such as ferrocene groups or organic ligands containing paramagnetic metal ions) in a magnetic self-assembled monolayer (SAM) undergo localized magnetic moment alignment under the influence of an external static magnetic field, forming a magnetic dipole array oriented along the magnetic field direction. This oriented magnetic SAM layer constructs an interface template with anisotropic magnetic moment orientation on the substrate surface. When a perovskite precursor solution is deposited on it, under the synergistic effect of the magnetic SAM interface template and the external static magnetic field, polar organic cations in the precursor (such as FA...)... + MA + The ordered orientation of the lead-iodine coordination polyhedra and the magnetic SAM layer promotes preferential nucleation and growth of the crystal along specific crystal orientations, thereby achieving crystal orientation control in the early stages of nucleation. Simultaneously, anchoring groups (such as phosphate and carboxyl groups) in the magnetic SAM layer chemically bond with the hydroxyl groups on the substrate surface, forming stable interfacial connections; their terminal functional groups further interact with uncoordinated Pb in the perovskite. 2+ It forms a coordination effect, effectively passivates defects at the buried interface, and reduces non-radiative recombination centers.

[0008] Furthermore, by continuously applying a static magnetic field during the annealing and crystallization process, the directional alignment of magnetic moments in the magnetic SAM layer can be maintained, providing stable interface orientation constraints for the crystal nuclei, reducing the probability of random nucleation and disordered growth, and promoting continuous grain growth along a consistent crystal orientation. This ultimately yields a high-quality perovskite film with highly preferred orientation, large grain size, and low density of buried interface defects. To achieve the above objectives, the present invention provides the following technical solution: A method for regulating perovskite crystallization based on a magnetically self-assembled monolayer buried interface includes the following steps: (1) Substrate pretreatment: The conductive substrate was ultrasonically cleaned with detergent, deionized water, acetone and isopropanol in sequence, then dried in an oven at 60°C for three hours and treated with ultraviolet ozone. After that, SnO2 aqueous solution was spin-coated onto the conductive substrate. (2) Preparation of magnetic SAM solution: Dissolve the self-assembled monolayer material with magnetic functional groups in an organic solvent to prepare a magnetic SAM solution with a concentration of 0.1-1.0 mg / mL; the magnetic functional groups are selected from ferrocene groups, organic ligands containing paramagnetic metal ions, or combinations thereof. (3) Preparation of magnetic SAM buried interface layer: The magnetic SAM solution prepared in step (2) is spin-coated onto the surface of the conductive substrate treated in step (1), and left to stand for 10 seconds to allow SAM molecules to self-assemble into a monolayer on the substrate surface. The substrate is then annealed at 100°C for 10 minutes to obtain a magnetic SAM modified conductive substrate. (4) Preparation of perovskite precursor solution: lead iodide (PbI2), methylamine iodide (FAI), formamidinium iodide (MAI) and cesium iodide (CsI) are dissolved in a mixed solvent in stoichiometric ratio to prepare a perovskite precursor solution. The mixed solvent is a mixture of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) in a ratio of 4:1. (5) External magnetic field assisted crystallization: The magnetic SAM modified substrate prepared in step (3) is placed in a magnetic field generating device, and a static magnetic field with a direction perpendicular to the plane of the substrate is applied. The magnetic field strength is 0.1~1.0T. Then, the perovskite precursor liquid prepared in step (4) is deposited on the magnetic SAM layer by spin coating under the magnetic field environment, and annealed at 100°C for 30 minutes to crystallize the perovskite into a film.

[0009] Further, the self-assembled monolayer material described in step (2) has the following general formula: ABC, where A is an anchoring group selected from phosphate group (-PO3H2), carboxyl group (-COOH), silyl group (-Si(OR)3), or thiol group (-SH); B is a linking chain selected from alkyl chain, aromatic chain, or a combination thereof; and C is a magnetic functional group selected from ferrocene (Fc), Co-containing... 2+ Fe 3+ Ni 2+ Gd 3+ or Mn 2+ Organometallic complexes.

[0010] Furthermore, the magnetic SAM material mentioned in step (2) is specifically selected from ferrocenylphosphonic acid (Fc-PA).

[0011] Furthermore, the magnetic field generating device mentioned in step (5) is a permanent magnet or an electromagnet, the direction of the magnetic field is adjustable, and the magnetic field strength is preferably 0.1 to 1.0 T.

[0012] Furthermore, the annealing process described in step (5) is carried out under the continuous presence of a magnetic field, the annealing temperature is preferably 100-120°C, and the annealing time is preferably 15-30 minutes.

[0013] The present invention also provides a perovskite solar cell, which comprises, from bottom to top, a conductive substrate, an electron transport layer, a magnetic SAM buried interface layer prepared by the above method, a perovskite light-absorbing layer, a hole transport layer and an electrode layer.

[0014] The present invention also provides a method for preparing a perovskite solar cell, including the above-mentioned method for controlling perovskite crystallization based on the buried interface of a magnetic self-assembled monolayer.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) Precise control of crystallization at the buried interface: Unlike traditional bulk magnetic field control methods, this invention precisely focuses the magnetic field on the buried interface region; the magnetic SAM layer forms a magnetically responsive monolayer on the substrate surface. Under the action of an external magnetic field, the magnetic moments of the magnetic SAM molecules are oriented and aligned, providing a magnetic template for perovskite nucleation and inducing the preferential orientation growth of perovskite crystals at the buried interface. (2) Does not change the phase composition of the perovskite: Existing magnetic ion doping methods (such as CN113421978B) require the magnetic ions (such as Co) to be removed. 2+ Incorporating magnetic ions into the perovskite lattice may alter the intrinsic photoelectric properties of the perovskite or introduce additional defects; the magnetic SAM of this invention exists only at the buried interface, and the perovskite bulk phase retains its intrinsic composition, thus avoiding the potential negative impact of magnetic ions on the photoelectric properties of the bulk phase. (3) Synergistic effect of interface defect passivation and crystallization regulation: The anchoring groups in magnetic SAM can interact with uncoordinated Pb in perovskite. 2+ Coordination bonds are formed, effectively passivating the defect state density at the buried interface; at the same time, the ordered arrangement of the SAM layer improves the wettability of the perovskite precursor solution and reduces pinhole defects at the interface; magnetic field-assisted crystallization and SAM chemical passivation work synergistically to achieve simultaneous optimization of crystallization quality and interface electrical properties. (4) Strong universality, applicable to a variety of perovskite systems: The magnetic SAM strategy of the present invention does not depend on specific perovskite composition and can be applied to a variety of perovskite systems such as FA-based, MA-based, and Cs-based, and has good universality. Attached Figure Description

[0016] Figure 1 A comparison of the X-ray diffraction (XRD) patterns of perovskite thin films prepared in the embodiments of the present invention and in the comparative examples; Figure 2 This is a comparison of the scanning electron microscope (SEM) morphology of the perovskite thin films prepared in the embodiments of the present invention and the comparative examples; Figure 3 This is a comparison of the current density-voltage (JV) of perovskite solar cells prepared in the embodiments of the present invention and in comparative examples; Figure 4 This is a comparison of the photoluminescence (PL) intensity at the buried interface of the devices prepared in the embodiments of the present invention and the comparative examples; Figure 5This is a comparison of the stability tests of the devices prepared in the embodiments of the present invention and those prepared in the comparative examples; Figure 6 This is a diagram illustrating the mechanism of action of the present invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0018] Example: (1) Substrate pretreatment: ITO conductive glass was ultrasonically cleaned for 15 minutes each with detergent, deionized water, acetone and isopropanol, then dried in an oven for three hours and treated with ultraviolet ozone for 15 minutes. After that, SnO2 aqueous solution was spin-coated onto the conductive substrate. (2) Preparation of magnetic SAM solution: Dissolve ferrocene phosphonic acid (Fc-PA) in anhydrous ethanol to prepare a magnetic SAM solution with a concentration of 1 mg / mL. Stir at room temperature for 30 minutes to completely dissolve the SAM solution. (3) Preparation of magnetic SAM buried interface layer: The Fc-PA solution prepared in step (2) was spin-coated onto the ITO substrate treated in step (1) at a speed of 3000 rpm for 30 seconds. After standing for 10 seconds, the SAM molecules were allowed to fully self-assemble. The substrate was then annealed at 100℃ for 10 minutes to obtain the Fc-PA modified ITO substrate. (4) Preparation of perovskite precursor solution: PbI2 (613 mg), FAI (216 mg), MAI (19 mg) and CsI (36 mg) were dissolved in a mixed solvent (DMF:DMSO=4:1, v / v, 1000 μL) and stirred at room temperature for 4 hours to obtain a 1.3 M precursor solution; (5) External magnetic field assisted crystallization: The Fc-PA modified ITO substrate prepared in step (3) is placed above the NdFeB permanent magnet, the magnetic field direction is perpendicular to the substrate plane, and the magnetic field strength is about 0.5T; under the magnetic field environment, the precursor liquid prepared in step (4) is spin-coated at 1000 rpm for 10 seconds, and then spin-coated at 3000 rpm for 30 seconds. 15 seconds before the end of spin-coating, 120 μL of CB is uniformly poured onto the perovskite layer, and then annealed at 100℃ for 30 minutes. The magnetic field continues to exist during the annealing process to obtain the perovskite film.

[0019] Comparative Example: The difference from the Example is that the Comparative Example does not have a SAM layer preparation process, and no magnetic field is applied in step (5); the remaining steps are the same as those in the Example.

[0020] Performance characterization: The perovskite films prepared in the examples and the comparative examples were subjected to X-ray diffraction (XRD) tests. The results showed that the diffraction peak intensity ratio of the film in the example on the (110) crystal plane was significantly higher than that of the comparative example, indicating that magnetic SAM induced the preferential orientation growth of the perovskite crystal under the assistance of a magnetic field. Scanning electron microscopy (SEM) grain morphology shows that the perovskite film in the embodiment has larger grain size and more dense arrangement, and there are no obvious voids or pinhole defects at the buried interface. Photoluminescence (PL) testing showed that the PL intensity of the example was significantly higher than that of the comparative example, indicating that the density of defects at the buried interface was effectively reduced. Device performance tests show that the photoelectric conversion efficiency of the perovskite solar cells prepared in the examples is 15-25% higher than that of the comparative examples, and still maintains more than 85% of the initial efficiency after 500 hours of maximum power point tracking.

Claims

1. A method for controlling perovskite crystallization based on a magnetically self-assembled monolayer buried interface, characterized in that, Includes the following steps: (a) A magnetic self-assembled monolayer (SAM) is prepared on the surface of a conductive substrate, wherein the magnetic SAM contains magnetic functional groups; (b) The magnetic SAM-modified substrate prepared in step (a) is placed in an external magnetic field; (c) Under the presence of a magnetic field, a perovskite precursor liquid is deposited on the magnetic SAM layer and annealed to obtain a perovskite film.

2. The method according to claim 1, characterized in that, The magnetic SAM described in step (a) is formed from a self-assembled monolayer material having the general formula ABC, wherein A is an anchoring group selected from phosphate (-PO3H2), carboxyl (-COOH), silyl (-Si(OR)3), or thiol (-SH); B is a linking chain selected from alkyl chains, aromatic chains, or combinations thereof; and C is a magnetic functional group selected from ferrocene (Fc), organometallic complexes containing Fe³⁺, Ni²⁺, Gd³⁺, or Mn²⁺.

3. The method according to claim 1, characterized in that, The magnetic SAM material mentioned in step (a) is selected from ferrocene-based phosphonic acid (Fc-PA).

4. The method according to claim 1, characterized in that, The concentration of the magnetic SAM solution in step (a) is 0.1–5.0 mg / mL, and the deposition method is spin coating, immersion or spray coating.

5. The method according to claim 1, characterized in that, The external magnetic field mentioned in step (b) is a static magnetic field with a magnetic field strength of 0.05 to 2.0 T, preferably 0.1 to 1.0 T.

6. The method according to claim 1, characterized in that, The direction of the external magnetic field in step (b) is perpendicular or parallel to the base plane.

7. The method according to claim 1, characterized in that, The annealing process in step (c) is carried out at a temperature of 80–150°C for 10–60 minutes, and the magnetic field is present continuously during the annealing process.

8. A perovskite solar cell, characterized in that, From bottom to top, it includes a conductive substrate, an electron transport layer, a magnetic self-assembled monolayer buried interface layer prepared by any one of claims 1-7, a perovskite light-absorbing layer, a hole transport layer, and an electrode layer.

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