An improved perovskite solar cell and a preparation method thereof

Abstract

The application relates to an improved perovskite solar cell, which has a passivation layer on the surface of an organic-inorganic composite perovskite thin film light absorption layer, and the passivation layer comprises a passivation agent described in the following formula I. The application applies a newly designed and synthesized organic molecule containing a plurality of halogen atoms, utilizes the space size of the halogen atoms in the organic framework, passivates uncoordinated Pb defects on the perovskite surface, and realizes the highest efficient defect passivation by adjusting the matching concentration. The perovskite thin film passivation method is simple in operation, high in operability and controllability, greatly improves the energy conversion efficiency and operation stability of the perovskite solar cell, and has great potential application value.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology and relates to an improved perovskite solar cell and its preparation method. Background Technology

[0002] Currently, environmental pollution and the increasing depletion of fossil fuels are hindering the sustainable development of human society. Solar energy, as an inexhaustible and renewable clean energy source, has received widespread attention globally and has become a crucial breakthrough for solving environmental and energy shortage problems. Solar cells based on the photovoltaic effect are the effective units for converting solar energy into electrical energy. In recent years, organic-metal halides with perovskite structures have attracted great attention in the photovoltaic industry due to their strong light absorption and carrier transport capabilities. In 2009, Miyasaka et al. used methylamine-intercalated lead halide as a light-absorbing material in dye-sensitized solar cells, achieving a photoelectric conversion efficiency of 3.8%. Over the past decade, the photoelectric conversion efficiency of organic-inorganic hybrid perovskite solar cells has increased from the initial 3.8% to 25.7%. These rapid efficiency improvements not only rely on optimized thin-film crystallization to reduce internal crystal defects but also benefit from the passivation of electronic defects on the perovskite film surface and grain boundaries to suppress non-radiative recombination. Compared to benign bulk defects in perovskites, surface defects in perovskites typically act as deep defects that dominate nonradiative charge recombination and are easily formed. Therefore, passivating surface defects in the light-absorbing layer is a crucial strategy for reducing charge recombination and improving the photoelectric conversion efficiency of perovskite solar cells. Various surface passivation agents, such as functional organic molecules, polymers, and organohalide salts, neutralize dangling bonds in the perovskite layer, particularly halide vacancies which result in a large number of uncoordinated Pb ions due to their low formation energy. Among these, halogen-containing organic salts have been widely used due to their strong Pb-X bonds, providing highly efficient passivation.

[0003] Existing technologies report on passivating agents for organic-inorganic hybrid perovskite solar cells, including functional organic molecules (Reference 1), polymers (Reference 2), and salts of organic halides (References 3 and 4). In particular, salts of organic halides, due to the low formation energy of halide vacancies, have been shown to possess excellent passivation properties. For example, choline chloride and phenyltrimethylammonium chloride have demonstrated effective passivation of perovskite surface defects. However, Cl... - Anions, compared to Br, - I - The smaller radius of the anions makes them easier to bind into the perovskite lattice, distorting the lead halide octahedron and causing some undesirable transformations in the perovskite phase structure, which may reduce the performance and long-term stability of perovskite solar cells.

[0004] Reference 1, Yang, S.; Dai, J.; Yu, Z.; Shao, Y.; Zhou, Y.; Xiao, X.; Zeng, X. C.; Huang, J. Tailoring Passivation Molecular Structures for Extremely Small Open-Circuit Voltage Loss in Perovskite Solar Cells. J. Am. Chem. Soc. 2019, 141, 5781 - 5787.

[0005] Reference 2, Bella, F.; Griffini, G.; Correa-Baena, J.-P.; Saracco, G.; Gratzel, M.; Hagfeldt, A.; Turri, S.; Gerbaldi, C. Improving Efficiency and Stability of Perovskite Solar Cells with Photocurable Fluoropolymers. Science 2016, 354, 203 - 206.

[0006] Reference 3, Xiong, Z.; Chen, X.; Zhang, B.; Odunmbaku, G. O.; Ou, Z.; Guo, B.; Yang, K.; Kan, Z.; Lu, S.; Chen, S.; et al. Simultaneous Interfacial Modification and Crystallization Control by Biguanide Hydrochloride for Stable Perovskite Solar Cells with PCE of 24.4%. Adv. Mater. 2022, 34, e2106118

[0007] Reference 4, Wang, H.; Ye, F.; Liang, J.; Liu, Y.; Hu, X.; Zhou, S.; Chen, C.; Ke, W.; Tao, C.; Fang, G. Pre-Annealing Treatment for High-Efficiency Perovskite Solar Cells via Sequential Deposition. Joule 2022, 6, 1 - 16.

[0008] Therefore, designing a highly efficient passivating agent to improve the efficiency and stability of perovskite solar cells and the future industrialization of solar cell modules is of great significance. Summary of the Invention

[0009] To address the shortcomings of existing perovskite surface deep defect passivation methods, this invention utilizes organic molecules containing multiple halogen atoms to simultaneously passivate perovskite surface defects at multiple sites to fabricate high-performance, high-stability perovskite solar cells.

[0010] The present invention achieves the above objectives through the following technical solutions:

[0011] This invention first provides an improved perovskite solar cell, which has a passivation layer on the surface of an organic-inorganic composite perovskite thin film light-absorbing layer, the passivation layer comprising a passivating agent as described in Formula I:

[0012]

[0013] Where n is an integer from 1 to 4, such as 1, 2, 3, 4; R1 is independently selected from X or X is a halogen atom, provided that there is at most one halogen atom X on a benzene ring, and at least one R1 is... * indicates a chemical bond.

[0014] Furthermore, the halogen atom is selected from at least one of F, Cl, Br, and I.

[0015] Furthermore, the passivating agent comprises at least one having one of the following structural formulas:

[0016]

[0017]

[0018] Verification has shown that the large-sized organic molecule containing halogen atom X of the present invention exhibits a smaller size than that of the Cl-containing organic molecule in the prior art. - The better passivation effect of anionic salts on the surface of perovskite films is likely due to the strong covalent bonds between halogen atoms (such as Cl) and the organic framework, which prevent halogen atoms from binding into the bulk lattice. Furthermore, organic molecules containing multiple halogen atoms form a large organic framework with low volatility and mobility, improving the long-term stability of perovskite solar cells. This invention effectively passivates surface defects in perovskite films by forming strong PB-X bonds (such as Pb-Cl) with the halogens, particularly Cl atoms, of the aforementioned passivating agents, thereby improving energy conversion efficiency. Simultaneously, it avoids the X-bonding associated with halogen-containing organic salts. -Anions enter the bulk lattice, thus ensuring the long-term operational stability of the solar cell fabricated after passivation of the perovskite thin film according to this invention. By adjusting the spatial positions of halogen atoms in the passivating agent, we found that when the distance between halogen atoms in the molecule matches the distance between halide ions in the perovskite, surface defects of the perovskite thin film can be passivated to the maximum extent. Therefore, we selected the passivating agent with the above structure, dissolved the selected organic molecules in a benign solvent, and suspended them on the surface of the perovskite thin film. The prepared substrate was placed on a hot plate and heat-treated to allow the halogen-containing organic molecules to interact with the perovskite layer, forming a modified layer interface.

[0019] Furthermore, the improved perovskite solar cell includes, from bottom to top, a conductive substrate, an electron transport layer, an organic-inorganic composite perovskite thin film light-absorbing layer, a passivation layer, a hole transport layer, and a top electrode.

[0020] The organic-inorganic composite perovskite thin film light-absorbing layer is well known in the art. In a specific embodiment of the present invention, it is an α-FAPbI3 perovskite structure, which is obtained by coating an electron transport layer with a perovskite precursor solution. The perovskite precursor solution contains solutes of 1.5-2M FAI, 1.5-2M PbI2, and 0.6-0.1M MACl, and the solvent is a mixed solvent of DMF and DMSO in a volume ratio of 3-6:1-2.

[0021] The conductive substrate, electron transport layer, organic-inorganic composite perovskite thin film light-absorbing layer, hole transport layer, and top electrode are well known in the art. For example, in one specific embodiment of the present invention, the conductive substrate is selected from fluorine tin oxide (FTO) or indium tin oxide (ITO); the electron transport layer is an electron transport material thin film prepared from at least one of TiO2, SnO2, ZnO, ZnS, and Nb2O5; the hole transport layer is a p-type inorganic semiconductor layer or a p-type organic semiconductor layer, and the hole transport layer material is at least one of PTAA, P3HT, Spiro-OMeTAD, CuI, and CuSCN; the top electrode includes, but is not limited to, any one of gold, silver, gold-silver alloy, gold-copper alloy, silver-copper alloy, gold-silver-copper alloy, and carbon conductive carbon material.

[0022] The present invention also provides a method for preparing the perovskite solar cell, comprising the following steps:

[0023] (S1) The electron transport layer solution is uniformly coated on the conductive substrate and annealed to obtain the electron transport layer.

[0024] (S2) The perovskite precursor solution is uniformly coated on the electron transport layer and annealed to form an organic-inorganic composite perovskite thin film light-absorbing layer.

[0025] (S3) The passivating agent solution is uniformly coated on the surface of the light-absorbing layer of the organic-inorganic composite perovskite film, and then annealed to obtain the passivation layer.

[0026] (S4) Hole transport layer solution is uniformly coated on passivation layer to obtain hole transport layer;

[0027] (S5) Evaporate the top electrode to obtain a perovskite solar cell.

[0028] The coating method includes spin coating and blade coating. Spin coating is preferred, specifically spin coating at a speed of 2000-5000 rpm for 10-30 seconds.

[0029] Further, in step (S1), the conductive substrate is cleaned before use by ultrasonic cleaning with at least one of detergent, deionized water, acetone, ethanol, and isopropanol, followed by drying and UV-ozone treatment for 10-30 minutes; the electron transport layer solution is a deionized water dispersion of electron transport material with a concentration of 3-5 wt%; the annealing is performed at 150-180°C for 10-30 minutes. Preferably, after annealing, UV-ozone cleaning is performed for 10-30 minutes to improve surface wettability.

[0030] Further, in step (S2), the perovskite precursor includes solutes FAI, MPbI2, and MACl, and the solvent is at least one of MDF and DMSO. The annealing is performed at 130-150°C for 30-60 minutes under 15-25% humidity conditions.

[0031] Further, in step (S3), the solvent of the passivating agent solution is at least one selected from chlorobenzene, dichloromethane, trichloromethane, and 1,2-dichloroethane. The concentration of the passivating agent solution is 0.1-2 mg / mL, preferably 0.5-1 mg / mL. If the concentration is too low, the maximum passivation effect cannot be achieved; if the concentration is too high, it will accumulate in the perovskite layer, affecting surface uniformity and hindering hole migration. The above solvents are chosen because of the high volatility of these small-molecule chlorinated solvents, which will not remain on the surface of the perovskite film during device fabrication.

[0032] Further, in step (S4), the hole transport layer solution is a 5-10% solution of the hole transport material. It is generally obtained by diluting commercial colloidal or nanoparticles with deionized or ultrapure water, uniformly dispersing them, and filtering them through a 0.2-0.4 μm filter.

[0033] Further, in step (S4), a top electrode is deposited on the surface of the hole transport layer using a vacuum deposition method.

[0034] The perovskite thin-film solar cells prepared by this invention are planar or mesoporous perovskite thin-film solar cells.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] (1) This invention uses organic molecules containing multiple halogen atoms, and utilizes the appropriate spatial size of halogen atoms in the organic framework to passivate uncoordinated Pb defects on the perovskite surface. The most efficient defect passivation is achieved by adjusting the concentration ratio.

[0037] (2) The present invention uses organic molecules containing multiple halogen atoms to coat the surface of perovskite thin films, which isolates water vapor and greatly reduces device failure caused by humidity during device operation, thus improving stability.

[0038] (3) The perovskite thin film passivation method of the present invention is simple to operate, highly operable and controllable, and greatly improves the energy conversion efficiency and operational stability of perovskite solar cells. It has great potential application value in the field of solar cells or other scientific fields. Attached Figure Description

[0039] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0040] Figure 1 Defect state density diagram of perovskite thin films;

[0041] Figure 2 Water contact angle test for perovskite thin films;

[0042] Figure 3 This is a theoretical model diagram of perovskite after passivation with passivating agents 124-TCBP and 135-TCBP;

[0043] Figure 4 The current-voltage (JV) characteristic test curve of the planar heterojunction perovskite solar cell prepared in this invention;

[0044] Figure 5 This is a graph showing the photoelectric conversion efficiency of perovskite solar cells after long-term storage.

[0045] Figure 6 This is a stability graph of a perovskite solar cell after 500 hours of continuous illumination. Detailed Implementation

[0046] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0047] The compounds of Formula I of the present invention have a wealth of synthetic strategies in the prior art. For example, for the compound of Formula I-1, wherein X is Cl, 1,3,5-tris(4-chlorophenyl)benzene (abbreviated as 135-TCBP); and the compound of Formula I-2, wherein X is Cl, 1,2,4-tris(4-chlorophenyl)benzene (abbreviated as 124-TCBP), they can be prepared by the cyclotrimerization reaction of p-chlorophenylacetylene as described in the literature (Reference 5).

[0048] Document 5: Fan, J.-T.; Fan, X.-H.; Gao, C.-Y.; Wei, J.; Yang, L.-M. additive.Org.Chem.Front.2022,9,2357-2367.

[0049] Example 1:

[0050] A perovskite solar cell using an organic molecule with multiple halogen atoms as a passivating agent is obtained by the following method:

[0051] (1) Femtosecond laser etching of transparent conductive substrate FTO glass with sheet resistance of 15Ω / was performed. The substrate was then ultrasonically cleaned for 15 minutes each with detergent, deionized water, acetone, ethanol, and isopropanol, and finally stored in isopropanol solution. Before use, the substrate was dried with a dry nitrogen gun and then treated with ultraviolet-ozone for 10 minutes to remove residual organic matter from the surface.

[0052] (2) A SnO2 nanoparticle dispersion (commercially available 15% SnO2 nanoparticles diluted with deionized water at a volume ratio of 1:2) was spin-coated onto an FTO substrate at 4000 rpm for 30 s. The substrate was then annealed in ambient air at 180°C for 30 min. After the operation, the SnO2 substrate was cleaned with UV-ozone for 10 min.

[0053] (3) The perovskite light-absorbing layer was prepared using a one-step method. The perovskite precursor solution contained 1.8M FAI (formamidinium iodide), 1.8M PbI2 (lead iodide), and 0.63M MACl (methylamine chloride) dissolved in a DMF / DMSO (857 μL / 143 μL) mixed solvent. The perovskite precursor solution was spin-coated onto a UV-ozone-treated SnO2 layer at 5000 rpm for 30 s in a nitrogen glove box to prepare the perovskite layer. Ten seconds after spin-coating, 750 μL of diethyl ether was rapidly dropped onto the substrate as an antisolvent. The perovskite precursor film was then removed from the nitrogen glove box and placed in ambient air. It was annealed at 130°C for 40 min at a humidity of 15–25% to form a perovskite thin film.

[0054] (4) 135-TCBP was dissolved in chloroform solution to prepare a 0.5 mg / mL solution. The solution was spin-coated onto the surface of the perovskite film at a speed of 5000 rpm for 30 s to complete the uniform coating process. The obtained film was annealed at 100℃ for 5 minutes to obtain the passivated perovskite film.

[0055] (5) Prepare a hole transport layer solution containing 90 mg Spiro-OMeTAD, 23 μl Li-TFSI (520 mg / mL Li-TFSI dissolved in acetonitrile), 37 μl 4-tert-butylpyridine and 15 μl FK209 Co(III)TFSI salt (300 mg / mL Co(III)TFSI dissolved in acetonitrile). All of the above materials are dissolved in 1 mL of chlorobenzene and spin-coated onto the perovskite surface at 3000 rpm for 30 s.

[0056] (6) A metal electrode with a thickness of 80 nm was deposited on the surface of Spiro-OMeTAD by vacuum deposition.

[0057] (7) The IV curve was measured using a Newport 450W Model 91150 instrument. During the test, a stainless steel black metal sheet was used to control the incident light area to be 0.08955 cm². 2 The irradiation conditions are standard solar irradiance conditions (100 mW / cm²). 2 The perovskite solar cell prepared in Example 1 has a photoelectric conversion efficiency of 25.30%, a corresponding open-circuit voltage of 1165 mV, and a short-circuit current of 26.08 mA·cm⁻¹. -2 The fill factor is 83.25%.

[0058] Example 2

[0059] The other conditions and operations are the same as in Example 1, except that in step (4), the passivating agent is replaced by 124-TCBP instead of 135-TCBP.

[0060] After testing, the perovskite solar cell obtained in Example 2 showed a photoelectric conversion efficiency of 24.52%, a corresponding open-circuit voltage of 1.158 mV, and a short-circuit current of 25.84 mA·cm⁻¹. -2 The fill factor is 81.94%.

[0061] Figure 1 (a), (b), and (c) are the defect state density diagrams of perovskite without passivation agent, passivated with 135-TCBP, and passivated with 124-TCBP, respectively. It can be seen that after modification with organic molecules containing chlorine atoms, the defect state density of the perovskite layer is significantly reduced. 124-TCBP has a more efficient passivation effect due to its suitable spatial size, resulting in an even lower defect state density. Figure 2 (a), (b), and (c) show the water contact angles of perovskites before passivation, after passivation with 135-TCBP, and after passivation with 124-TCBP, respectively. It can be seen that the water contact angle of the perovskite surface is significantly increased after passivation, indicating that the perovskite film, after being coated with hydrophobic molecules, can effectively block the erosion of water vapor.

[0062] Comparing Example 1 and Example 2, 124-TCBP exhibits a better passivation effect than 135-TCBP. This may be because a 124-TCBP molecule can occupy three vacancies, providing a strong bond with the undercoordinated Pb, while a 135-TCBP molecule only provides two Cl atoms that interact with Pb. Figure 3 This is a theoretical model diagram of perovskite with surface passivation of 124-TCBP and 135-TCBP. The calculated binding energy of 124-TCBP to perovskite is -2.11 eV, which is stronger than the binding energy of 135-TCBP to perovskite of -1.57 eV.

[0063] We also calculated the trap density (N) according to the formula. t ):

[0064]

[0065] Where ε₀ is the vacuum permittivity, ε r It is the relative permittivity, V TFL Here, is the limiting voltage for traps, e is the electron charge, and L is the film thickness. The calculated trap densities for the pristine perovskite film, the perovskite film passivated with 135-TCBP, and the perovskite film passivated with 124-TCBP are 7.66 × 10⁻⁶. 15 6.46×10 15 5.54×10 15As expected, both 135-TCBP and 124-TCBP passivated perovskite films exhibited lower trap densities compared to the original perovskite films. The 124-TCBP passivated perovskite film showed the lowest trap density, indicating that 124-TCBP provided more passivation sites than 135-TCBP.

[0066] Figure 4 The JV diagrams are of the control device (unmodified perovskite solar cell) and the devices modified with 135-TCBP and 124-TCBP.

[0067] Example 3

[0068] We also tested the long-term stability of the perovskite solar cells of Examples 1 and 2, such as... Figure 5 As shown, the perovskite solar cells obtained in Examples 1 and 2 were placed in an environment with 25% humidity. After 1680 hours, they maintained 95.5% (135-TCBP) and 97.6% (124-TCBP) of their initial photoelectric conversion efficiency, respectively. However, the original perovskite solar cell without passivation had its photoelectric conversion efficiency drop to 87.8% of its initial value after 1680 hours of long-term placement.

[0069] The stability of the original perovskite solar cells, specifically those from Examples 1 and 2, under continuous illumination for 500 hours was further tested, and the results are as follows: Figure 6 As shown, the unpassivated perovskite solar cell exhibits a rapid decline in photoelectric conversion efficiency (PCE) within 400 hours. Example 1 (passivator 135-TCBP) retained 58% of its initial PCE after 500 hours, while Example 21 (passivator 124-TCBP) retained 90% of its initial PCE. This indicates that passivation significantly improves the stability of perovskite solar cells, with 124-TCBP, as the passivator, providing the most significant improvement.

[0070] Finally, we also tested the thermal stability of the devices. After heating at 85°C for 300 hours, the PCE of Examples 1 and 2 remained at 96.4% and 93.1% of the initial value, respectively, while the PCE of the unmodified perovskite solar cell decreased to 78.9% of the initial value. This demonstrates that the passivation strategy of the present invention comprehensively improves the stability of perovskite solar cells.

Claims

1. An improved perovskite solar cell, characterized in that a passivation layer is present on the surface of an organic-inorganic composite perovskite thin film light-absorbing layer, wherein... The passivation layer comprises the passivating agent according to Formula I: (I) Where n is an integer from 2 to 4; R1 is independently selected from X or X is a halogen atom, provided that there is at most one halogen atom X on a benzene ring, and at least one R1 is... .

2. The perovskite solar cell according to claim 1, characterized in that, The halogen atom is selected from at least one of F, Cl, Br, and I.

3. The perovskite solar cell according to claim 1, characterized in that, The passivating agent includes at least one having the following structural formula: ； X is at least one of F, Cl, Br, and I.

4. The perovskite solar cell according to claim 1, characterized in that, It includes, from bottom to top, a conductive substrate, an electron transport layer, an organic-inorganic composite perovskite thin film light-absorbing layer, a passivation layer, a hole transport layer, and a top electrode.

5. The perovskite solar cell according to claim 4, characterized in that, The conductive substrate is selected from fluorine tin oxide (FTO) or indium tin oxide (ITO); the electron transport layer is an electron transport material thin film prepared from at least one of TiO2, SnO2, ZnO, ZnS, and Nb2O5; the hole transport layer is a p-type inorganic semiconductor layer or a p-type organic semiconductor layer, and the hole transport layer material is at least one of PTAA, P3HT, Spiro-OMeTAD, CuI, and CuSCN; the top electrode includes, but is not limited to, any one of gold, silver, gold-silver alloy, gold-copper alloy, silver-copper alloy, gold-silver-copper alloy, and carbon conductive carbon material.

6. A method for preparing a perovskite solar cell according to any one of claims 1-5, characterized in that, Includes the following steps: (S1) The electron transport layer solution is uniformly coated on the conductive substrate and annealed to obtain the electron transport layer. (S2) The perovskite precursor solution is uniformly coated on the electron transport layer and annealed to form an organic-inorganic composite perovskite thin film light-absorbing layer. (S3) The passivating agent solution is uniformly coated on the surface of the light-absorbing layer of the organic-inorganic composite perovskite film, and then annealed to obtain the passivation layer. (S4) Hole transport layer solution is uniformly coated on passivation layer to obtain hole transport layer; (S5) Evaporate the top electrode to obtain a perovskite solar cell.

7. The preparation method according to claim 6, characterized in that, The coating is applied by scraping or spin coating.

8. The preparation method according to claim 7, characterized in that, Spin coating involves spin coating at a speed of 2000-5000 rpm for 10-30 seconds.

9. The preparation method according to claim 6, characterized in that, In step (S1), the conductive substrate is cleaned before use by ultrasonic cleaning with at least one of detergent, deionized water, acetone, ethanol, and isopropanol, followed by drying and UV-ozone treatment for 10-30 minutes; the electron transport layer solution is a deionized water dispersion of electron transport material with a concentration of 3-5 wt%; the annealing is performed at 150-180℃ for 10-30 minutes.

10. The preparation method according to claim 9, characterized in that, After annealing, perform UV-ozone cleaning for 10-30 minutes.

11. The preparation method according to claim 6, characterized in that, In step (S3), the solvent of the passivating agent solution is at least one of chlorobenzene, dichloromethane, trichloromethane, and 1,2-dichloroethane, and the concentration of the passivating agent solution is 0.1-2 mg / mL.

12. The preparation method according to claim 6, characterized in that, In step (S4), the hole transport layer solution is a 5-10% solution of the hole transport material.

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