A perovskite thin film, a perovskite solar cell based thereon, and a method for fabricating the same.

Abstract

This invention discloses a perovskite thin film and a perovskite solar cell based thereon, as well as a method for preparing the same, belonging to the field of perovskite solar cell technology. The method for preparing the perovskite thin film of this invention includes the following steps: S1: preparing a perovskite precursor solution; S2: coating the perovskite precursor solution onto a substrate to obtain a perovskite precursor thin film; S3: annealing the perovskite precursor thin film to form a perovskite thin film; wherein the perovskite in the formed perovskite thin film is ABX3 type perovskite, where the A-site contains a monovalent cation, the B-site is a divalent metal cation, and the X-site is a halide anion; the perovskite precursor solution contains an additive with the general formula C6H5-COO-R, where R is a C1-C3 alkyl group. The perovskite thin film obtained by this invention has an octahedral [PbX6] perovskite lattice. 4‑ The structure is more stable and orderly, suppressing the formation of defects at the source.

Description

Technical Field

[0001] This invention belongs to the field of perovskite solar cell technology, specifically relating to a perovskite thin film, a perovskite solar cell based thereon, and a method for preparing the same. Background Technology

[0002] Perovskite solar cells have rapidly become a research hotspot in the photovoltaic field over the past decade due to their advantages such as high photoelectric conversion efficiency, solution processability, and low cost. The performance and stability of these cells are fundamentally limited by the quality of the perovskite active layer.

[0003] During thin film formation, the rapid and uncontrolled crystallization of perovskite easily leads to small grain size, high grain boundary density, and the introduction of numerous pinholes. These microstructural defects not only become centers for nonradiative recombination of charge carriers, reducing the open-circuit voltage and fill factor of the device, but also provide channels for the penetration of moisture and oxygen and ion migration, severely affecting the long-term stability of the device. Furthermore, the abundant presence of uncoordinated lead ions (Pb) on the surface and grain boundaries of the perovskite lattice... 2+ Defect states such as halogen vacancies and halogen vacancies are key factors that induce carrier recombination and lead to performance loss. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a perovskite thin film and a perovskite solar cell based thereon, as well as a method for preparing the same, in order to solve the technical problem of how to select a structurally well-defined and readily available small organic molecule that can effectively stabilize the octahedral structure of the perovskite lattice through multiple mechanisms of action, thereby inhibiting defect formation, improving crystal quality, and ultimately enhancing the performance of the perovskite solar cell.

[0005] This invention introduces the general formula C6H5-COO-R (where R is a C1-C3 alkyl group) as a functional additive into a perovskite precursor solution, utilizing the carbonyl group to passivate poorly coordinated Pb. 2+ Meanwhile, the benzene ring provides hydrophobic and steric hindrance effects, and the interaction between the ester group and FA ions regulates crystallization, thereby improving the performance of perovskite solar cells.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing a perovskite thin film, comprising the following steps: S1: Prepare perovskite precursor solution; S2: The perovskite precursor solution is coated onto the substrate to obtain a perovskite precursor film. S3: Anneal the perovskite precursor film to form a perovskite film; The perovskite in the formed perovskite film is an ABX3 type perovskite, wherein the A-site contains a monovalent cation, the B-site contains a divalent metal cation, and the X-site contains a halide anion; the perovskite precursor solution contains an additive; the additive has the general formula C6H5-COO-R, wherein R is a C1-C3 alkyl group.

[0007] Preferably, in the perovskite precursor solution, the molar ratio of the additive to the perovskite precursor used to form the B-site divalent metal cation is 1%-10%.

[0008] Preferably, the additive includes any one of methyl benzoate, ethyl benzoate, and propyl benzoate.

[0009] Preferably, the perovskite solute in the perovskite precursor solution comprises formamidine halide (FAX), cesium halide (CsX), lead halide (PbX2), and methylamine halide (MAX), wherein the halogen in the halide comprises at least one of chlorine (Cl), bromine (Br), and iodine (I).

[0010] More preferably, the solvent of the perovskite precursor solution is N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), and the volume ratio of N,N-dimethylformamide to dimethyl sulfoxide is 4:1.

[0011] Preferably, the monovalent cation at position A includes formamidinium ion, cesium ion, and methylamine ion; the divalent metal cation at position B is lead ion; and the halide anion at position X includes at least one of chloride ion, bromide ion, and iodide ion.

[0012] Preferably, in step S3, the annealing temperature is 150°C and the time is 10 minutes.

[0013] The present invention also provides a perovskite thin film prepared by the method described above.

[0014] The present invention also provides a perovskite solar cell comprising the perovskite thin film.

[0015] Preferably, it comprises, in sequence: a substrate, a bottom electrode, a first charge transport layer, the perovskite light-absorbing layer, a second charge transport layer, and a top electrode; the perovskite light-absorbing layer is the perovskite thin film.

[0016] Preferably, the first charge transport layer is a hole transport layer, and the second charge transport layer is an electron transport layer.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing perovskite thin films. An additive with the general formula C6H5-COO-R (where R is a C1-C3 alkyl group) is added to a perovskite precursor solution. The ester molecules in this additive synergistically stabilize the perovskite lattice through multiple mechanisms. From a molecular structure perspective, the ester group (-COO-) in the additive exhibits Lewis basicity and can react with uncoordinated lead ions (Pb) in the perovskite. 2+ These cations form coordination bonds to fill the coordination vacancies of lead ions. Simultaneously, their benzene ring structure and alkyl chains provide moderate steric hindrance, helping to guide the orderly arrangement of organic cations during crystallization, reducing lattice distortion, and maintaining the octahedral [PbX6] structure of the perovskite lattice. 4- The structure is more stable and orderly, suppressing the formation of defects at the source.

[0018] Furthermore, the molar ratio of additives is limited to 1% to 10%. When the concentration is too low (<1%), the interaction between the additive molecules and the precursor is limited and insufficient to regulate the octahedral [PbX6] lattice of the perovskite. 4- The structure and defect passivation effect are limited; if the concentration is too high (>10%), new impurity phases may be introduced due to molecular aggregation, or crystallization may be excessively delayed, resulting in non-uniform perovskite films. This concentration range ensures that the additive molecules can fully interact with the perovskite precursor without disrupting the homogeneity of the perovskite precursor solution and the crystallization process, thus achieving the best performance improvement effect.

[0019] Furthermore, the annealing temperature was limited to 100°C to 150°C, and the time to 5 to 20 minutes. These annealing conditions, combined with the addition of ethyl benzoate, synergistically optimized the crystallization process. The appropriate temperature (100-150°C) ensures sufficient evaporation of solvent and additive molecules while avoiding excessively high temperatures (>120°C) that could lead to a sharp increase in iodine vacancies and perovskite decomposition. The annealing time (5-20 minutes) provides sufficient growth time for the grains, allowing ethyl benzoate molecules to fully interact at grain boundaries and surfaces, resulting in a denser film with fewer defects. This condition, combined with the slow-crystallization effect of the additive, achieves a balance between high crystallinity and low defect density.

[0020] The present invention also provides a perovskite thin film prepared by the above method. Due to the use of ethyl benzoate additive and optimized process, the resulting perovskite thin film has a more stable octahedral lattice structure, fewer grain boundary defects and more uniform grain size, thereby exhibiting higher carrier mobility, longer carrier lifetime and better environmental stability.

[0021] This invention also provides a perovskite solar cell, comprising a perovskite light-absorbing layer of a perovskite thin film. A high-quality perovskite light-absorbing layer directly improves the photoelectric conversion efficiency of the perovskite solar cell: reduced defects decrease non-radiative recombination losses, increased grain size reduces grain boundary scattering, and a stable lattice suppresses performance degradation caused by ion migration. Detailed Implementation

[0022] To enable those skilled in the art to understand the features and effects of the present invention, the following descriptions and definitions are only general descriptions of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in the event of any conflict, the definitions in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0024] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0025] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0026] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0027] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0028] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0029] To obtain high-quality perovskite thin films, introducing functional additives into the perovskite precursor solution has become an important process optimization approach. Ideal additives should simultaneously achieve the following functions: 1) regulating crystallization kinetics: delaying the crystallization process, promoting the formation of large, dense grains, and reducing pinholes; 2) passivating intrinsic defects: effectively passivating uncoordinated Pb. 2+ 3) Maintain process compatibility: It has good compatibility with precursor solutions, does not affect the film formation process, and does not introduce unfavorable impurities or phase separation into the film.

[0030] Against this backdrop, the present invention introduces a class of additives with simple structure but outstanding effects—alkyl benzoates with the general formula C6H5-COO-R (where R is a C1-C3 alkyl group). These molecules can simultaneously act as crystallization regulators and defect passivators, exerting a synergistic effect in perovskite precursor solutions, significantly improving the quality of perovskite thin films and the performance of their optoelectronic devices.

[0031] Example 1 This embodiment provides a method for preparing perovskite thin films, including the following steps: Step S1: Prepare perovskite precursor solution Prepare FA solution with a concentration of 1.5 mol / L according to stoichiometric ratio. 0.95 Cs 0.05 PbI3 perovskite precursor solution. Specifically, 243.7 mg FAI (formamidine iodide), 19.49 mg CsI (cesium iodide), 961.5 mg PbI2 (lead iodide), and 20.3 mg MACl (methylamine chloride) were weighed and placed in a mixing container. 1 mL of a mixed solvent of DMF and DMSO (DMF to DMSO volume ratio of 4:1) was added to the mixing container to obtain the perovskite precursor solution. 2 μL of ethyl benzoate was added to the above perovskite precursor solution, with the molar ratio of ethyl benzoate to lead ions in the perovskite precursor being 1%. Step S2: Coating the perovskite precursor film Take 100 μL of the above perovskite precursor solution and coat it onto the substrate. First, spin coat it at 2000 rpm for 10 s, and then spin coat it at 5000 rpm for 40 s to form a liquid film. Take 200 μL of chlorobenzene as an antisolvent and spin coat it onto the liquid film for 15 s to obtain a perovskite precursor film. Step S3: Annealing to form a perovskite thin film The perovskite precursor film was annealed on a hot stage at 150°C for 10 minutes to form a perovskite film with a thickness of 400 nm.

[0032] This embodiment also provides a method for fabricating a perovskite solar cell, including the following steps: Step 1: Substrate cleaning and treatment The FTO substrate was sequentially cleaned with acetone, isopropanol, and deionized water, and then dried for later use. The FTO substrate includes a substrate and a bottom electrode. The substrate is made of glass, and the bottom electrode is made of FTO.

[0033] Step 2: Fabrication of the first charge transport layer (hole transport layer) A nickel oxide hole transport layer with a thickness of 30 nm was prepared on an FTO substrate by magnetron sputtering and then annealed at a temperature of 300 °C for 30 min. Step 3: Prepare the perovskite light-absorbing layer Using the methods in steps S1 to S3 of the above-mentioned perovskite thin film preparation method, the perovskite precursor solution is coated onto the nickel oxide hole transport layer, and after annealing, a perovskite light-absorbing layer (i.e., perovskite thin film) is formed with a thickness of 400 nm. Step 4: Fabrication of the second charge transport layer (electron transport layer) C is prepared on a perovskite light-absorbing layer by vacuum evaporation. 60 An electron transport layer with a thickness of 40 nm; Step 5: Prepare the buffer layer Using vacuum evaporation in C 60 A BCP buffer layer with a thickness of 5 nm was fabricated on the electron transport layer; Step 6: Fabrication of the top electrode Metal electrodes with a thickness of 100 nm were fabricated on a BCP buffer layer using vacuum evaporation to obtain perovskite solar cells.

[0034] Example 2 The only difference between this embodiment and Example 1 is that the amount of ethyl benzoate added in step three is 21.5 μL, and the molar ratio of ethyl benzoate to lead ions in the perovskite precursor is 10%.

[0035] Example 3 The only difference between this embodiment and Example 1 is that in step three, ethyl benzoate is replaced with methyl benzoate, and the amount added is 1.87 μL.

[0036] Example 4 The only difference between this embodiment and Example 1 is that in step three, ethyl benzoate is replaced with propyl benzoate, and the amount added is 2.41 μL.

[0037] Comparative Example 1 The difference between this comparative example and Example 1 is that no additives are added to the perovskite precursor.

[0038] I. Preparation of Perovskite Thin Films Step S1: Prepare perovskite precursor solution Prepare FA solution with a concentration of 1.5 mol / L according to stoichiometric ratio. 0.95 Cs 0.05 PbI3 perovskite precursor solution. Specifically, 243.7 mg FAI (formamidine iodide), 19.49 mg CsI (cesium iodide), 961.5 mg PbI2 (lead iodide) and 20.3 mg MACl (methylamine chloride) were weighed and placed in a mixing container. 1 mL of a mixed solvent of DMF and DMSO (DMF to DMSO volume ratio of 4:1) was added to the mixing container to obtain the perovskite precursor solution.

[0039] Step S2: Coating the perovskite precursor film Same as Example 1.

[0040] Step S3: Annealing to form a perovskite thin film Same as in Example 1 (annealing at 150°C for 10 minutes).

[0041] II. Fabrication of Perovskite Solar Cells Except for step 3, in which the perovskite light-absorbing layer is the perovskite thin film prepared in the first part of this comparative example, the other steps are exactly the same as in the second part of Example 1.

[0042] Test method: All perovskite solar cell devices were tested for JV characteristics using a solar simulator and a Keithley 2400 source meter under standard test conditions (AM1.5G spectrum, 1000 W / m² irradiance, 25°C).

[0043] The test results are shown in Table 1 below: Table 1

[0044] As shown in Table 1 above, Comparative Example 1, without the addition of benzoic acid ester additives, had a photoelectric conversion efficiency of only 25.14%; while Examples 1-4, with the addition of additives of the general formula C6H5-COO-R, where R is a C1-C3 alkyl group, all achieved photoelectric conversion efficiencies of over 26%, and both open-circuit voltage and fill factor were improved. This comparison directly demonstrates that adding additives of the general formula C6H5-COO-R, where R is a C1-C3 alkyl group, to the perovskite precursor can significantly improve the overall photoelectric performance of perovskite solar cells.

[0045] The perovskite solar cells prepared with ethyl benzoate in Examples 1 and 2 exhibit photoelectric conversion efficiencies of 26.38% and 26.76%, respectively, significantly higher than those prepared with methyl benzoate in Example 3 (26.09%) and propyl benzoate in Example 4 (26.16%). This demonstrates that ethyl benzoate, among the additives of this invention, has a superior effect on optimizing the photoelectric conversion efficiency of the cells.

[0046] Effect of molar ratio: When the molar ratio of ethyl benzoate was increased from 1% (Example 1) to 10% (Example 2), the photoelectric conversion efficiency increased from 26.38% to 26.76% (the highest among all examples), and the fill factor also increased from 83.75% to 86.10% (the highest among the examples). Combined with the current density (26.32 mA·cm⁻¹), -2 The changes in open-circuit voltage (1.181 V, only slightly decreased) indicate that within the 1%-10% molar ratio range, ethyl benzoate can achieve synergistic optimization of carrier collection capacity and energy loss through more efficient crystallization control and defect passivation, ultimately improving the overall battery performance. The above content is merely illustrative of the technical concept of this invention and should not be construed as limiting the scope of protection of this invention. Any modifications made to the technical solution based on the technical concept proposed in this invention fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a perovskite thin film, characterized in that, Includes the following steps: S1: Prepare perovskite precursor solution; S2: Coat the perovskite precursor solution onto the substrate to obtain a perovskite precursor film; S3: Anneal the perovskite precursor film to form a perovskite film; The perovskite in the formed perovskite film is an ABX3 type perovskite, wherein the A site contains a monovalent cation, the B site contains a divalent metal cation, and the X site contains a halide anion; the perovskite precursor solution contains an additive with the general formula C6H5-COO-R, wherein R is a C1-C3 alkyl group.

2. The method for preparing the perovskite thin film according to claim 1, characterized in that, The additive includes any one of methyl benzoate, ethyl benzoate, and propyl benzoate.

3. The method for preparing perovskite thin films according to claim 1, characterized in that, The monovalent cation at position A includes formamidinium ion, cesium ion, and methylamine ion; the divalent metal cation at position B is lead ion; and the halide anion at position X includes at least one of chloride ion, bromide ion, and iodide ion.

4. The method for preparing perovskite thin films according to claim 3, characterized in that, In the perovskite precursor solution, the molar ratio of the additive to the perovskite precursor used to form the B-site divalent metal cation is 1%-10%.

5. The method for preparing perovskite thin films according to claim 1, characterized in that, In step S3, the annealing process is carried out at a temperature of 150°C for 10 minutes.

6. A perovskite thin film prepared by the method according to any one of claims 1 to 5.

7. A perovskite solar cell comprising the perovskite thin film of claim 6.

8. The perovskite solar cell according to claim 7, characterized in that, In order, they include: The perovskite light-absorbing layer comprises a substrate, a bottom electrode, a first charge transport layer, the perovskite light-absorbing layer, a second charge transport layer, and a top electrode; the perovskite light-absorbing layer is the perovskite thin film.

9. The perovskite solar cell according to claim 8, characterized in that, The first charge transport layer is a hole transport layer, and the second charge transport layer is an electron transport layer.

Images