A method for forming a single-crystal perovskite thin film and a perovskite thin film

Abstract

The application provides a method for forming a single-crystal perovskite film and the perovskite film, and the method comprises the following steps: configuring a perovskite precursor solution by using a perovskite precursor, diethanolamine and a solvent, wherein the perovskite precursor at least comprises lead iodide; and forming a single-crystal perovskite film by using the perovskite precursor solution as raw material through a space confinement growth process. Based on the characteristics of the single-crystal growth process, diethanolamine is introduced into the perovskite precursor solution, and the coordination of diethanolamine and lead iodide and the complex of diethanolamine and lead iodide is utilized to control the particle size of the precursor particles, so that a single-crystal perovskite film with higher quality is obtained.

Description

Technical Field

[0001] This application relates to the field of perovskite solar cells, and in particular to a method for forming a single-crystal perovskite thin film and the perovskite thin film itself. Background Technology

[0002] Perovskite solar cells have become one of the most competitive candidates for next-generation photovoltaic technology due to their excellent photoelectric properties, solution processability, and potential low manufacturing cost. In existing perovskite cells, the perovskite light-absorbing layer is usually formed by slot coating or spin coating processes, and the resulting perovskite light-absorbing layer is a polycrystalline thin film. The large number of grain boundaries and surface defects in the polycrystalline structure tends to lead to high defect density, which in turn results in low photoelectric conversion efficiency of the device.

[0003] Compared to polycrystalline thin films, single-crystal perovskite thin films have been shown to possess excellent optoelectronic properties, including low defect state density, high carrier mobility, and long carrier recombination lifetime. Although some documents have proposed that single-crystal perovskite thin films can be prepared using spatial confinement processes, lattice vacancies and dislocations are still easily generated during crystallization, resulting in a photoelectric conversion efficiency of less than 20% for single-crystal thin films, and an efficiency decay rate exceeding 30% under illumination.

[0004] Therefore, it is necessary to further improve the existing single-crystal perovskite thin film formation process to solve the problem of lattice defects easily generated inside the film during growth and reduce the defect density of the film.

[0005] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0006] The purpose of this invention is to provide a method for growing single-crystal perovskite thin films to obtain higher crystal quality and higher photoelectric conversion efficiency of devices.

[0007] To address the aforementioned problems, firstly, this application provides a method for forming a single-crystal perovskite thin film, comprising the following steps:

[0008] S1. A perovskite precursor solution is prepared by using a perovskite precursor, diethanolamine and a solvent, wherein the perovskite precursor includes at least lead iodide.

[0009] S2. Using the perovskite precursor solution as raw material, a single-crystal perovskite thin film is formed through a spatial confinement growth process.

[0010] Based on the characteristics of single-crystal growth process, this application introduces diethanolamine into the perovskite precursor solution and utilizes its coordination with lead iodide and its complexes to achieve particle size control of the precursor particles, thereby obtaining higher quality single-crystal perovskite thin films.

[0011] In step S1, the perovskite precursor consists of a first precursor having an AX structure and a second precursor having a BX2 structure, wherein the second precursor includes at least lead iodide; wherein A is a monovalent cation, B is a divalent metal cation, and X is a halide anion. This scheme is highly compatible with existing processes and can be applied to most perovskite systems.

[0012] The monovalent cations include one or more of formamidinium cations, methylammonium cations, cesium ions, and rubidium ions; the divalent metal cations include one or more of lead ions and tin ions; and the halide anions include one or more of iodide ions, bromide ions, and chloride ions. This scheme is highly compatible with existing processes and is applicable to most perovskite systems.

[0013] In the perovskite precursor solution, the concentration of diethanolamine is 1-5 mol%. Within this range, high-quality crystallization can be achieved without excessive additives that could be trapped within the perovskite lattice during crystal growth, becoming new defect sources.

[0014] In step S2, the spatial confinement growth process includes: introducing the perovskite precursor solution into a two-dimensional confinement space and performing a heat preservation treatment to crystallize the perovskite precursor solution and form the single-crystal perovskite thin film.

[0015] The heat preservation process temperature is 110 ℃ to 130 ℃, and the crystallization time is 10-15 hours.

[0016] In step S2, the spatial confinement growth process includes: combining two substrates to form the two-dimensional confinement space; injecting the perovskite precursor solution into the two-dimensional confinement space and filling the two-dimensional confinement space through capillary action; and performing a heat preservation treatment on the substrate to crystallize the perovskite precursor solution and form the single-crystal perovskite thin film.

[0017] In step S1, the solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, and N-methylpyrrolidone.

[0018] In step S1, by adding the diethanolamine, the particle size in the perovskite precursor solution is made to be between 1 nm and 10 nm. Reducing the size of the precursor particles to 1-10 nm allows the particles to be precisely embedded in the crystal lattice, achieving perfect lattice coordination, eliminating lattice mismatch, dislocations, and grain boundaries, and realizing an atomically perfect single-crystal structure.

[0019] Secondly, this application also provides a single-crystal perovskite thin film, which is prepared by the single-crystal perovskite thin film formation method described in any one of the first aspects.

[0020] Compared with the prior art, the beneficial effects of the present invention mainly include the following: Based on the slow nucleation growth characteristics of the single crystal growth process, this application introduces diethanolamine into the perovskite precursor solution, utilizes the coordination effect of diethanolamine and lead iodide and / or lead iodide complexes, and reduces the particle size of the precursor particles pre-assembled by precursor atoms and molecular clusters in the solution system through this coordination effect, thereby achieving particle size control of the precursor particles; by controlling the particle size of the precursor particles within a suitable range, the crystal growth rate can be reasonably controlled, and the probability of perfect matching direction between the crystal and the attached particles during crystallization can be effectively improved, which helps to obtain a single crystal thin film with a more perfect crystal structure, thereby reducing the defect state density of the device and improving the photoelectric conversion efficiency of the device. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The above are the SEM results of the single-crystal perovskite thin films of Comparative Example 1 and Example 2 in this application.

[0023] Figure 2 The SCLC results are for the perovskite solar cells of Example 2 and Comparative Example 1 in this application.

[0024] Figure 3 The results show the photoelectric conversion efficiency of the perovskite solar cells in Examples 1 to 3 and Comparative Example 1 of this application.

[0025] Figure 4 The results show the particle size statistics of the perovskite precursor solutions in Examples 1 to 3 and Comparative Example 1 of this application.

[0026] Figure 5 The results show the open-circuit voltage and photoelectric conversion efficiency of the perovskite solar cells in Example 2, Comparative Example 2, and Comparative Example 3. Detailed Implementation

[0027] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front, or back, are merely for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the present invention.

[0028] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0029] The steps in the following embodiments do not correspond one-to-one with the contents of the invention.

[0030] Example 1

[0031] The spatial confinement growth method is an existing process for forming single-crystal perovskite thin films. Its core idea is as follows: a narrow space with a very small vertical spacing is constructed using two parallel substrates (usually glass substrates or ITO conductive glass substrates). The spacing can reach the micrometer or nanometer level, and it can also be called a two-dimensional confinement space. Then, a perovskite precursor solution is injected into it, and perovskite crystals are induced to slowly nucleate and grow in the confinement space through specific processes (such as slow heating, isothermal treatment or other methods), and finally a large-area single-crystal perovskite thin film is formed in the confinement space.

[0032] However, in existing spatial confinement growth processes, some crystal defects such as lattice vacancies and dislocations are still easily generated during the crystallization of perovskites. In order to improve the defects in single crystal growth, this application proposes to introduce specific additives (i.e., diethanolamine, DEA) into the existing perovskite precursor solution to achieve fine control of the single crystal growth process.

[0033] Embodiment 1 of the present invention provides a method for forming a single-crystal perovskite thin film and a perovskite thin film thereof. First, a method for forming a single-crystal perovskite thin film is provided, comprising the following steps:

[0034] Step 1: Prepare the perovskite precursor solution;

[0035] This application proposes a novel perovskite precursor solution formulation, which is mainly obtained by adding an appropriate amount of diethanolamine (DEA) to certain existing perovskite systems. Specifically, the perovskite precursor solution prepared in this application mainly comprises: a perovskite precursor, diethanolamine, and a solvent; wherein the perovskite precursor must contain at least lead iodide.

[0036] It is understandable that perovskite precursor materials refer to the precursor salts required for the crystallization of perovskite materials (ABX3 structure). In existing perovskite solar cells, the crystal structure of the perovskite light-absorbing layer is an ABX3 structure; where the A-site cation is a monovalent cation, typically including organic cations such as formamidinium cation (FA). + CH(NH2)2 + ), Methylammonium cation (MA) + CH3NH3 + ), and inorganic cations: such as cesium ions (Cs ions). + ), rubidium ions (Rb + ), etc.; the B-site cation is a divalent metal cation, such as lead ion (Pb). 2+ ), tin ions (Sn) 2+ ) etc.; the X position is a halide anion, commonly an iodide ion (I). - ), bromide ions (Br) - ) and chloride ions (Cl - Therefore, perovskite precursors can be divided into two categories: first precursors with an AX structure and second precursors with a BX2 structure.

[0037] Specifically, in this first embodiment, the perovskite precursor materials used are methylammonium iodide (MAI) and lead iodide (PbI2), and the solvent is N,N-dimethylformamide (DMF). In this first embodiment, the desired perovskite precursor solution was prepared by dissolving MAI and PbI2 in DMF solvent at a molar ratio of 1:1, and then adding 1 mol% diethanolamine.

[0038] The solutions provided in this application are not applicable to all perovskite materials. However, provided that certain criteria are met (i.e., the perovskite precursor includes at least lead iodide), the perovskite precursor material in this application can be selected with reference to existing technologies. In other embodiments, the first and second precursors can be selected using other combinations, but it must be ensured that the selected second precursor material includes at least lead iodide. In other embodiments, the solvent used to prepare the perovskite precursor solution can also be selected with reference to existing technologies, such as N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), γ-butyrolactone (GBL), and N-methylpyrrolidone.

[0039] Step 2: Form a single-crystal perovskite thin film using a spatial confinement growth process;

[0040] Using the perovskite precursor solution prepared in step 1 as raw material, a single-crystal perovskite thin film is formed through a spatial confinement growth process. As mentioned above, the spatial confinement growth process is a prior art, and its specific technical details will not be elaborated in this application. The following is only an illustration of one feasible example.

[0041] In this embodiment, the confined growth process includes introducing a perovskite precursor solution into a two-dimensional confined space and performing a heat treatment to allow the perovskite precursor solution to crystallize and form a single-crystal perovskite film. Specifically, two substrates can be combined to form a two-dimensional confined space; then, the perovskite precursor solution can be injected into the two-dimensional confined space, filling the space through capillary action; finally, the substrate can be heat-treated to allow the perovskite precursor solution to slowly crystallize and form a single-crystal perovskite film.

[0042] In this embodiment, the heat treatment process temperature is 120 °C, and the crystallization time is 12 hours. In other embodiments, the heat treatment process temperature is 110 °C to 130 °C, and the crystallization time is 10-15 hours.

[0043] In this first embodiment, a single-crystal perovskite thin film is also provided, which is prepared by the above-described method for forming a single-crystal perovskite thin film.

[0044] In this first embodiment, a single-crystal perovskite solar cell is also provided. The perovskite light-absorbing layer in the perovskite solar cell is prepared by the above-described method for forming a single-crystal perovskite thin film.

[0045] It should be understood that in the existing perovskite solar cell field, diethanolamine is commonly used in the fabrication process of polycrystalline perovskite thin films, primarily as a passivation and self-assembly material, and sometimes as a stabilizer for specific crystal phases. However, the applicant's research has revealed that in perovskite precursor solution systems containing lead iodide, diethanolamine can coordinate with lead iodide and / or its complexes (coordination products of lead iodide and solvent), thereby reducing the size of particles composed of precursor atoms and molecular clusters in the solution system. This has led to the realization of its potential for specific applications in single-crystal thin film growth. The technical solution of this application primarily utilizes the coordination of diethanolamine with lead iodide and its complexes to control the particle size of precursor particles, thereby achieving the formation of high-quality single-crystal thin films.

[0046] As is well known, the growth conditions required for single-crystal perovskites differ significantly from those for polycrystalline perovskites. In the growth of single-crystal perovskites, particles composed of precursor atoms and molecular clusters remain stable in solution during crystallization. However, during crystal growth, because the particles are pre-assembled, the particle-attached growth mode often leads to difficulties in forming high-quality single-crystal films. On one hand, the energy barrier of each atom or molecule in the pre-assembled particles is low, which can lead to excessively high crystal growth rates during attachment growth; furthermore, the random Brownian motion and irregular shape of the particles also result in a low probability of perfect alignment between the crystal and the attached particles. Ultimately, this leads to the widespread presence of defects such as dislocations, grain boundaries, and twins in materials grown by particle attachment. Recognizing this, and combining the applicant's discovery of the particle size control effect of diethanolamine molecules on precursor particles, this application proposes adding diethanolamine molecules to the precursor solution to coordinate with and decompose the particles in the solution, thereby reducing the particle size. After controlling the particle size in the perovskite precursor solution within a suitable range (preferably between 1 nm and 10 nm), the corresponding single crystal growth process can be combined to reasonably control the crystal growth rate and increase the probability of perfect matching direction between the crystal and the attached particles during crystallization, ultimately successfully growing a high-quality single-crystal perovskite film.

[0047] The growth conditions for polycrystalline perovskite differ from those for single-crystalline perovskite. Polycrystalline perovskite typically requires pre-assembled particles with larger sizes. In polycrystalline processes, due to the rapid nucleation growth, decomposing the particles in the precursor solution reduces particle size, leading to smaller nuclei, smaller grains, and consequently, an increase in grain boundaries, ultimately decreasing the quality of the resulting perovskite film. In contrast, single-crystalline growth, a slower nucleation process, allows particles to adhere to the surface of a small number of nuclei in the initial stage, enabling them to grow. Therefore, smaller particle sizes contribute to a more perfect crystal structure.

[0048] Example 2

[0049] In this second embodiment, a method for forming a single-crystal perovskite thin film and the perovskite thin film are provided. The method and the perovskite thin film in this second embodiment are basically the same as those in the first embodiment, the main difference being that the amount of diethanolamine added to the prepared perovskite precursor solution is 3 mol%.

[0050] In this second embodiment, a single-crystal perovskite solar cell is also provided. The perovskite light-absorbing layer in the perovskite solar cell is prepared by a single-crystal perovskite thin film formation method of this second embodiment.

[0051] Example 3

[0052] In this third embodiment, a method for forming a single-crystal perovskite thin film and the perovskite thin film are provided. The method and the perovskite thin film in this third embodiment are basically the same as those in the first embodiment, the main difference being that the amount of diethanolamine added to the prepared perovskite precursor solution is 5 mol%.

[0053] In this third embodiment, a single-crystal perovskite solar cell is also provided. The perovskite light-absorbing layer in the perovskite solar cell is prepared by a single-crystal perovskite thin film formation method of this third embodiment.

[0054] Comparative Example 1

[0055] In this Comparative Example 1, a method for forming a single-crystal perovskite thin film and the perovskite thin film are provided. The method and perovskite thin film in this Comparative Example 1 are basically the same as those in Example 1, the main difference being that diethanolamine is not added to the prepared perovskite precursor solution.

[0056] In this Comparative Example 1, a single-crystal perovskite solar cell is also provided. The perovskite light-absorbing layer in the perovskite solar cell is prepared by a single-crystal perovskite thin film formation method described in this Comparative Example 1.

[0057] Comparative Example 2

[0058] In Comparative Example 2, a method for forming a single-crystal perovskite thin film and the perovskite thin film are provided. The method and perovskite thin film in Comparative Example 2 are basically the same as those in Example 2, the main difference being that diethanolamine is not added to the prepared perovskite precursor solution, but benzoic acid is added, and the amount added is also 3 mol%.

[0059] In Comparative Example 2, a single-crystal perovskite solar cell is also provided. The perovskite light-absorbing layer in the perovskite solar cell is prepared by a single-crystal perovskite thin film formation method described in Comparative Example 2.

[0060] Comparative Example 3

[0061] In Comparative Example 3, a method for forming a single-crystal perovskite thin film and the perovskite thin film are provided. The method and perovskite thin film in Comparative Example 3 are basically the same as those in Example 2, the main difference being that diethanolamine is not added to the prepared perovskite precursor solution, but 4-fluorophenylborone is added, and the amount added is also 3 mol%.

[0062] In Comparative Example 3, a single-crystal perovskite solar cell is also provided. The perovskite light-absorbing layer in the perovskite solar cell is prepared by a single-crystal perovskite thin film formation method described in Comparative Example 3.

[0063] To illustrate the effects of this application, please refer to the following references. Figures 1 to 5As shown, the particle size of the perovskite thin film / perovskite battery obtained in Examples 1 to 3, the perovskite thin film / perovskite battery in Comparative Examples 1 to 3, and the perovskite precursor solution in Examples 1 to 3 and Comparative Example 1 were comprehensively detected and tested, and the results are as follows;

[0064] Figure 1 The SEM results of the single-crystal perovskite thin film of Embodiment 2 and Comparative Example 1 of this application are shown. Figure 1 In the figure, 'a' represents a cross-sectional SEM image of the perovskite film in Comparative Example 1. Figure 1 b in Figure 1 The enlarged view of the area highlighted in red in section 'a'; Figure 1 In this text, 'c' represents a cross-sectional SEM image of the perovskite film in Example 2. Figure 1 d in Figure 1 The enlarged view of the area highlighted in red in section c is shown. It can be observed that the film without diethanolamine (i.e., Comparative Example 1) contains pores, while the film with added diethanolamine is dense and free of obvious defects; this indicates that the addition of diethanolamine can effectively improve the crystallinity of perovskite single-crystal films.

[0065] Figure 2 The SCLC results of the perovskite solar cells of Example 2 and Comparative Example 1 in this application are shown. SCLC testing, or space charge confined current testing, is a standard electrical characterization method in perovskite solar cell device research. It mainly quantitatively assesses the defect state density of perovskite materials by analyzing the current-voltage curves in the dark state. Figure 2 As shown, in the perovskite solar cell of Example 2, the defect density is 3.82 × 10⁻⁶. 13 cm -3 The defect density of the perovskite solar cell in Comparative Example 1 is 6.28 × 10⁻⁶. 13 cm -3 The defect state density of the device was reduced by 40%.

[0066] Figure 3 The photoelectric conversion efficiency results of Embodiments 1 to 3 of this application, as well as the perovskite solar cell in Comparative Example 1, are shown. Figure 3 In this context, 'a' corresponds to the perovskite solar cell in Example 1. Figure 3 In this context, 'b' corresponds to the perovskite solar cell in Example 2. Figure 3 The 'c' in the text corresponds to the perovskite solar cell in Example 3. Figure 3In the figure, 'd' corresponds to the perovskite solar cell in Comparative Example 1. In Comparative Example 1, the photoelectric conversion efficiency of its perovskite solar cell is only about 11%; however, after adding diethanolamine, the photoelectric conversion efficiencies of the perovskite solar cells in Examples 1 to 3 are 15.02%, 20.38%, and 18.33%, respectively. The photoelectric conversion efficiency of the perovskite solar cells in the three examples is significantly improved, indicating that diethanolamine can effectively improve the perovskite crystallization process.

[0067] Figure 4 Statistical results of the particle size of the perovskite precursor solution in Examples 1 to 3 of this application and Comparative Example 1 are presented. It can be observed that as the amount of diethanolamine added increases (0-5 mol%), the particle size of the perovskite precursor solution continuously decreases. Smaller particle sizes are beneficial for further improving the crystal quality of the single-crystal thin film, thereby enhancing device performance. However, according to the applicant's research, although smaller particle sizes result in higher film quality, excessive additives can easily be trapped within the crystal lattice during crystal growth, becoming new defect sources and even deteriorating carrier transport performance. Therefore, from the perspective of final device performance (see...),... Figure 3 As shown in the figure, the preferred amount of diethanolamine added is 3 mol.

[0068] In addition, the applicant has tried some other additives in an attempt to improve the crystal quality of single-crystal thin films and enhance the performance of devices. Figure 5 The effects of benzoic acid, 4-fluorophenylboron, and diethanolamine on the open-circuit voltage and photoelectric conversion efficiency of the device are shown. Figure 5 In this context, 'a' corresponds to the open-circuit voltage result. Figure 5 In the figure, 'b' corresponds to the photoelectric conversion efficiency result. It can be seen that, compared to other additives, diethanolamine can significantly improve the open-circuit voltage and photoelectric conversion efficiency of the device. This indicates that it coordinates with lead iodide and / or lead iodide complexes in the precursor particles, thereby reducing the particle size, improving crystal quality, and enhancing device performance.

[0069] The common English terms or letters used in this invention for clarity of description are for illustrative purposes only and are not limiting interpretations or specific uses. They should not be used to limit the scope of protection of this invention based on their possible Chinese translations or specific letters.

[0070] It should also be noted that in this article, relational terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

Claims

1. A method of forming a single-crystalline perovskite thin film, comprising: Includes the following steps: S1. A perovskite precursor solution is prepared by mixing a perovskite precursor, diethanolamine, and a solvent. The perovskite precursor includes at least lead iodide. The perovskite precursor is composed of a first precursor having an AX structure and a second precursor having a BX2 structure, wherein the second precursor includes at least lead iodide. Wherein, A is a monovalent cation, B is a divalent metal cation, and X is a halide anion. In the perovskite precursor solution, the concentration of diethanolamine is 1-5 mol%; by adding the diethanolamine, the particle size in the perovskite precursor solution is between 1 nm and 10 nm. S2. Using the perovskite precursor solution as raw material, a single-crystal perovskite thin film is formed through a spatial confinement growth process.

2. The method of claim 1, wherein the single-crystalline perovskite thin film is formed by a process comprising: The monovalent cation includes one or more of formamidinium cation, methylammonium cation, cesium ion and rubidium ion; The divalent metal cations include one or more of lead ions and tin ions; The halide anions include one or more of iodide ions, bromide ions, and chloride ions.

3. The method for forming a single-crystal perovskite thin film according to claim 1, characterized in that, In step S2, the spatial confinement growth process includes: introducing the perovskite precursor solution into a two-dimensional confinement space and performing a heat preservation treatment to crystallize the perovskite precursor solution and form the single-crystal perovskite thin film.

4. The method of claim 3, wherein the single-crystalline perovskite thin film is formed by a process comprising: The heat preservation process temperature is 110 ℃ to 130 ℃, and the crystallization time is 10-15 hours.

5. The method for forming a single-crystal perovskite thin film according to claim 3, characterized in that, In step S2, the spatially confined growth process includes: The two substrates are combined to form the two-dimensional confined space; The perovskite precursor solution is injected into the two-dimensional confined space, and the two-dimensional confined space is filled by capillary action. The substrate is subjected to a heat preservation treatment to allow the perovskite precursor solution to crystallize, forming the single-crystal perovskite thin film.

6. The method for forming a single-crystal perovskite thin film according to claim 1, characterized in that, In step S1, the solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, and N-methylpyrrolidone.

7. A single-crystal perovskite thin film, characterized in that, The single-crystal perovskite thin film was prepared by any one of the methods described in claims 1-6.

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