A two-dimensional Cs2PbI2(SCN)2 perovskite solar cell based on thiocyanogen and a preparation method thereof

Abstract

This invention discloses a two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate and its preparation method, belonging to the field of solar cell technology. The perovskite solar cell consists of a sequentially arranged FTO substrate, a TiO₂ dense layer, a perovskite light-absorbing layer, a buffer layer, a hole transport layer, and a gold electrode layer. The perovskite light-absorbing layer is Cs₂PbI₂(SCN)₂ doped with formamidinium hydrochloride, and the buffer layer is a trimethylammonium bromide-based material. Chloride ions from the formamidinium hydrochloride act as a grain size regulating template within the perovskite lattice. The generation of chloride ions and their intermediate products regulates the crystallization process, fully leveraging the grain homogenization effect, effectively improving carrier transport performance, and significantly increasing carrier lifetime. Simultaneously, the use of a trimethylammonium bromide-based material as a buffer layer overcomes the defect of difficulty in uniformly depositing the hole transport layer within the perovskite transport layer, ultimately maximizing the advantages of photoelectric performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solar cells, and particularly relates to a two-dimensional Cs2PbI2(SCN)2 perovskite solar cell based on a thiocyanide group and a preparation method thereof. BACKGROUND

[0002] With the vigorous development of organic-inorganic perovskite materials, its certified efficiency has reached 25.5%. However, this three-dimensional perovskite still has some shortcomings that need to be improved, such as heat, light, humidity stability. Compared with three-dimensional perovskite materials, low-dimensional perovskite, especially two-dimensional perovskite material, has higher adjustability, excellent photophysical performance and higher stability. For a typical 2D perovskite structure (its molecular general formula is A2BX4), A is a cation, such as Cs + , MA + or FA + cation, B is a divalent metal ion, and X is a halide anion. Metal ions and halide ions are tightly connected through covalent bonds, thereby forming an inorganic layer composed of an octahedral framework. Due to its larger band gap, two-dimensional perovskite has a narrower absorption; at room temperature, it can form stable excitons, and the exciton binding energy is as high as hundreds of meV. However, so far, compared with organic-inorganic hybrid two-dimensional perovskite, all-inorganic two-dimensional perovskite has received less attention. Compared with the potential barrier formed by the organic group in the organic-inorganic hybrid two-dimensional perovskite, the dielectric constant mismatch between the inorganic potential well and the inorganic potential barrier in the all-inorganic two-dimensional perovskite is reduced, and the large-size organic group spacer layer is eliminated to improve the photoelectric performance. This all-inorganic perovskite two-dimensional perovskite material takes into account stability and good electronic structure, providing a new direction for realizing functional devices made entirely of inorganic perovskite.

[0003] So far, the method for obtaining two-dimensional perovskite in most studies is to partially or completely break the three-dimensional structure by using a large cation at the A site to form a layered two-dimensional perovskite structure. In fact, replacing halide anions with pseudo-halide anions (SCN - ) by adjusting the X site anion is also a method for obtaining two-dimensional perovskite. Due to the asymmetric electronic structure and geometry of SCN - anion, the lead halide octahedron loses part of the co-apex ability, and is thus divided into a (PbX4(SCN)2) octahedral framework, in which SCN -The anions occupy the axial atomic coordinates in the lead halide octahedron. In principle, this type of two-dimensional perovskite has much smaller lead halide octahedral interlayer spacing than two-dimensional perovskite types composed of large A-site cations, and is worthy of further study, however, up to now, there are only two published scientific papers on this thiocyanate two-dimensional Cs2PbI2(SCN)2 perovskite solar cell, namely document 【1】(J. Mater. Chem. C, 2020, 8, 4294-4302) and document 【2】(Sci. China Mater. 64, 61-72 (2021)). The thiocyanate two-dimensional Cs2PbI2(SCN)2 perovskite solar cell prepared in document 【1】 has a photoelectric conversion efficiency of 2.04%. The thiocyanate two-dimensional Cs2PbI2(SCN)2 perovskite solar cell prepared in document 【2】 has a much higher photoelectric conversion efficiency than that in document 【1】, and finally obtains a photoelectric conversion efficiency of 4.24%, a fill factor of 35%. It is worth noting that document 【2】 uses PMMA as a buffer layer between the perovskite light absorption layer and the hole transport layer, but the specific parameters of the solar cell without PMMA as a buffer layer are not listed in the document. It is speculated that the low fill factor of the cell is caused by the poor conductivity of PMMA.

[0004] In view of the above problems, on the basis of this, formamidine hydrochloride is added to the perovskite to improve the perovskite crystallization process, enhance the light absorption capacity of the perovskite thin film, and improve the short-circuit current of the battery. Further, a trimethylammonium bromide type buffer layer is deposited to block the effect of the device hole transport layer on the perovskite, thereby obtaining a high-efficiency thiocyanate two-dimensional perovskite solar cell. At the same time, this thiocyanate two-dimensional Cs2PbI2(SCN)2 perovskite solar cell presents a positive red color, and therefore has certain commercial value in the field of building integrated photovoltaics. SUMMARY

[0005] In order to solve the above problems, the application provides a thiocyanate two-dimensional Cs2PbI2(SCN)2 perovskite solar cell, which is composed of an FTO substrate, a TiO2 dense layer, a perovskite light absorption layer, a buffer layer, a hole transport layer and a gold electrode layer arranged in sequence. The material of the perovskite light absorption layer is formamidine hydrochloride doped Cs2PbI2(SCN)2, and the material of the buffer layer is a trimethylammonium bromide type substance.

[0006] Adding formamidinium hydrochloride to a two-dimensional Cs₂PbI₂(SCN)₂ perovskite precursor solution and then briefly heat-treating it causes chloride ions in the formamidinium hydrochloride to enter the crystal lattice. Due to the small size of the chloride ions (smaller than iodide and thiocyanate ions), the lead halide octahedral framework collapses. As the heat treatment time increases, the small chloride ions cannot stably exist in the crystal lattice and therefore leave the lattice. The entry and exit of chloride ions modulates crystallization, and the formation of intermediate products slows down the crystallization rate, increases the grain size, and makes the grain size of the film more uniform. This effectively improves the carrier transport performance, extends the carrier lifetime, and reduces the defect concentration. At the same time, the light absorption capacity of the perovskite light absorption layer film is significantly enhanced, the space charge confinement voltage is lower, and the current density of the two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell device is significantly improved, thus effectively improving the photoelectric performance of the cell.

[0007] This invention relates to a two-dimensional Cs2PbI2(SCN)2 perovskite solar cell based on thiocyanate. Trimethylammonium bromide is used as a buffer layer to post-process the interface between the perovskite light-absorbing layer and the hole transport layer. This solves the problem of incomplete coating caused by direct coating of the hole transport layer on the perovskite surface and effectively blocks the interaction between the hole transport layer and the perovskite light-absorbing layer, reducing damage to the perovskite layer from the hole transport layer, ensuring the integrity of the light-absorbing layer, improving photoelectric performance, and making the Cs2PbI2(SCN)2 thin film more suitable for application in solar cells.

[0008] The leading group of the trimethylammonium bromide is phenyl, hexadecyl, dodecyl, or octyl; specifically, it includes phenyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, or octyltrimethylammonium bromide.

[0009] The thickness of the perovskite light-absorbing layer is not less than 100 nm, the thickness of the TiO2 dense layer is 20–30 nm, the thickness of the buffer layer is 5–10 nm, the thickness of the hole transport layer is 150–220 nm, and the thickness of the gold electrode layer is 65–75 nm.

[0010] A method for preparing a two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate includes the following steps:

[0011] 1) Using FTO conductive glass as FTO substrate, a TiO2 precursor solution was deposited on the FTO substrate by solution method, and a dense TiO2 layer was obtained by annealing.

[0012] 2) Spin-coat the perovskite precursor solution onto the TiO2 dense layer, heat at low temperature and then cool to obtain the perovskite light-absorbing layer.

[0013] 3) Spin-coat the buffer layer solution onto the perovskite light-absorbing layer to obtain the buffer layer;

[0014] 4) Spin-coat the hole transport layer solution onto the buffer layer to obtain the hole transport layer;

[0015] 5) A gold electrode layer was prepared on the surface of the hole transport layer by vacuum evaporation to obtain a two-dimensional Cs2PbI2(SCN)2 perovskite solar cell.

[0016] Before use, FTO conductive glass is cleaned and dried, and then subjected to UV surface treatment.

[0017] Titanium tetrachloride liquid was used as the TiO2 precursor solution; the TiO2 precursor solution was deposited on an FTO substrate using a solution method; the annealing temperature was 200℃ and the annealing time was 30-40 min.

[0018] Furthermore, the solution method is as follows: 4-5 mL of titanium tetrachloride solution is dropped onto an ice block made of 200-250 mL of deionized water, and the FTO substrate is immersed in the solution after the ice block melts. The substrate is treated at 70-80°C for 1 hour, then the solution is poured off, and the deposited FTO substrate is treated at 200°C for 30-40 minutes.

[0019] The perovskite precursor solution preparation process in step 2) is as follows: Formamidinium hydrochloride, cesium iodide, and lead thiocyanate are weighed, dissolved in an organic solvent, heated, stirred thoroughly, and filtered to obtain the perovskite precursor solution. The concentration of the perovskite precursor solution, calculated as lead thiocyanate, is 0.5–0.7 mol / mL, wherein the concentration ratio of cesium iodide to lead thiocyanate is 2:1, and the concentration of formamidinium hydrochloride is 0.02–0.04 mol / mL. The organic solvent is dimethyl sulfoxide, the heating temperature is 60–80℃, and the stirring time is 6–10 h.

[0020] In the preparation of the perovskite light-absorbing layer, the amount of perovskite precursor solution used is 20–25 μL / cm². 2 The spin coating speed is 2000-3000 rpm, the heating table temperature is 90-100℃, and the heating time is 3-5 min.

[0021] The buffer layer solution is prepared by dissolving trimethylammonium bromide powder in a solvent and stirring. The concentration of trimethylammonium bromide in the buffer layer solution is 1–3 mg / mL. The solvent is isopropanol.

[0022] During the preparation of the buffer layer, the volume of buffer solution used is 20–25 μL / cm³. 2 The spin coating speed is 3000-4000 rpm, the heating table temperature is 60-90℃, and the heating time is 5-10 min.

[0023] The hole transport layer solution is prepared by adding tributyl phosphate (TBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and bis(trifluoromethanesulfonyl)imide salt (FK209Co(Ⅲ)) to chlorobenzene solvent, using spiro-OMeTAD as the hole transport layer.

[0024] Further, the specific formulation is as follows: spiro-OMeTAD is 72.3 mg / mL, tributyl phosphate (TBP) is 28.8 μL, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is 17.5 μL, and bis(trifluoromethanesulfonyl)imide salt (FK209Co(Ⅲ)) is 8 μL, dissolved in 1 mL of chlorobenzene solvent;

[0025] During the preparation of the hole transport layer, the volume of the hole transport layer solution used is 15–18 μL / cm². 2 The spin coating speed is 3500-4000 rpm.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. The purpose of this invention is to provide a method for improving the performance of perovskite devices. First, after adding formamidine hydrochloride, chloride ions in formamidine hydrochloride first enter the perovskite lattice during the heat treatment process, generating intermediate products. As the heat treatment time increases, chloride ions leave the perovskite lattice due to their small size. However, the generation of intermediate products regulates the crystallization process, slows down the crystallization rate, and promotes more uniform grain size, which can effectively improve the carrier transport performance and thus improve the photoelectric performance of the battery.

[0028] 2. The light absorption capacity of the perovskite light absorption layer film after adding formamidinium hydrochloride in this invention is significantly enhanced. The film has a longer carrier lifetime, and the device composed of it has a lower space charge confinement voltage and a smaller defect concentration.

[0029] 3. The two-dimensional Cs2PbI2(SCN)2 perovskite solar cell of the present invention uses trimethylammonium bromide as a buffer layer to treat the interface between the perovskite light absorption layer and the hole transport layer. This overcomes the defect that the spiro-OMeTAD organic material in the hole transport layer is difficult to be uniformly set on the perovskite transport layer. It effectively blocks the interaction between the hole transport layer material and the light absorption layer material, which can further improve the current density, open-circuit voltage and photoelectric conversion efficiency of the two-dimensional Cs2PbI2(SCN)2 perovskite solar cell device, and helps to promote the commercial application of all-inorganic two-dimensional perovskite solar cells. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of a perovskite solar cell.

[0031] Figure 2 X-ray diffraction images of formamidin hydrochloride after different heat treatment times (left: full image, right: magnified image);

[0032] Figure 3 SEM images of the perovskite surface before (left) and after (right) doping with formamidinium hydrochloride;

[0033] Figure 4 The UV-Vis absorption spectra of the film before and after doping with formamidin hydrochloride;

[0034] Figure 5 Time-resolved photoluminescence fitting spectra and data for thin films before and after formamidin hydrochloride doping;

[0035] Figure 6 Space charge confinement current spectra and analysis of devices before and after doping with formamidin hydrochloride;

[0036] Figure 7 SEM images of the spin-coated hole transport layer with (left) and without (right) trimethylammonium bromide.

[0037] Figure 8 IV test results of perovskite solar cells before and after doping with formamidinium hydrochloride and before and after treatment with trimethylammonium bromide. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0039] A two-dimensional all-inorganic perovskite solar cell doped with formamidinium hydrochloride and passivated with trimethylammonium bromide, such as Figure 1 The perovskite solar cell shown is composed of an FTO substrate, a TiO2 dense layer, a perovskite light-absorbing layer, a buffer layer, a hole transport layer, and a gold electrode layer arranged sequentially. The material of the perovskite light-absorbing layer is Cs2PbI2(SCN)2 doped with formamidinium hydrochloride, and the material of the buffer layer is a trimethylammonium bromide, specifically including phenyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, octyltrimethylammonium bromide, etc.

[0040] I. Thin film structure of FTO / TiO2 / perovskite light-absorbing layer doped with formamidinium hydrochloride prepared by the method of the present invention

[0041] Example 1

[0042] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0043] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride liquid was slowly dripped onto an ice block made of 200 mL of deionized water. After UV treatment, the FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. Then the solution was poured off and the deposited substrate was treated at 200 °C for 30 min.

[0044] 2) Preparation of perovskite light-absorbing layer:

[0045] 2-1) Dissolve 1 mol CsI, 0.5 mol Pb(SCN)2 and 0.02 mol formamidin hydrochloride in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0046] 2-2) Take 40 μL of the above perovskite precursor solution and drop it onto an FTO substrate covered with a TiO2 dense layer preheated at 70℃. Rotate it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 1 min.

[0047] The fabricated device consists of, from bottom to top, an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), and a perovskite light absorption layer (a two-dimensional perovskite material of Cs2PbI2(SCN)2 doped with formamidinium hydrochloride).

[0048] Example 2

[0049] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0050] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride solution was slowly dripped onto an ice block made of 200 mL of deionized water. After UV treatment, the FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. Then the solution was poured off and the deposited FTO substrate was treated at 200 °C for 30 min.

[0051] 2) Preparation of perovskite light-absorbing layer:

[0052] 2-1) Dissolve 1 mol CsI, 0.5 mol Pb(SCN)2 and 0.02 mol formamidin hydrochloride in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0053] 2-2) Take 40 μL of perovskite precursor solution and drop it onto an FTO substrate covered with a TiO2 dense layer preheated at 70℃. Spin-coat it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 2 min.

[0054] The fabricated device consists of, from bottom to top, an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), and a perovskite light absorption layer (a two-dimensional perovskite material of Cs2PbI2(SCN)2 doped with formamidinium hydrochloride).

[0055] Example 3

[0056] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0057] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride solution was slowly dripped onto an ice block made of 200 mL of deionized water. After UV treatment, the FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. Then the solution was poured off and the deposited FTO substrate was treated at 200 °C for 30 min.

[0058] 2) Preparation of perovskite light-absorbing layer:

[0059] 2-1) Dissolve 1 mol CsI, 0.5 mol Pb(SCN)2 and 0.02 mol formamidin hydrochloride in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0060] 2-2) Take 40 μL of perovskite precursor solution and drop it onto an FTO substrate covered with a TiO2 dense layer preheated at 70℃. Spin-coat it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 3 min.

[0061] The fabricated device consists of, from bottom to top, an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), and a perovskite light absorption layer (a two-dimensional perovskite material of Cs2PbI2(SCN)2 doped with formamidinium hydrochloride).

[0062] Example 4

[0063] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0064] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride solution was slowly dripped onto an ice block made of 200 mL of deionized water. After UV treatment, the FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. Then the solution was poured off and the deposited FTO substrate was treated at 200 °C for 30 min.

[0065] 2) Preparation of perovskite light-absorbing layer:

[0066] 2-1) Dissolve 1 mol CsI, 0.5 mol Pb(SCN)2 and 0.02 mol formamidin hydrochloride in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0067] 2-2) Take 40 μL of perovskite precursor solution and drop it onto an FTO substrate covered with a dense TiO2 layer preheated at 70℃. Spin-coat it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 4 min.

[0068] The fabricated device consists of, from bottom to top, an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), and a perovskite light absorption layer (a two-dimensional perovskite material of Cs2PbI2(SCN)2 doped with formamidinium hydrochloride).

[0069] Example 5

[0070] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0071] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride solution was slowly dripped onto an ice block made of 200 mL of deionized water. After UV treatment, the FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. Then the solution was poured off and the deposited FTO substrate was treated at 200 °C for 30 min.

[0072] 2) Preparation of perovskite light-absorbing layer:

[0073] 2-1) Dissolve 1 mol CsI, 0.5 mol Pb(SCN)2 and 0.02 mol formamidin hydrochloride in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0074] 2-2) Take 40 μL of perovskite precursor solution and drop it onto an FTO substrate covered with a TiO2 dense layer preheated at 70℃. Spin-coat it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 5 min.

[0075] The fabricated device consists of, from bottom to top, an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), and a perovskite light absorption layer (a two-dimensional perovskite material of Cs2PbI2(SCN)2 doped with formamidinium hydrochloride).

[0076] II. Thin Film Structure of Undoped Formamidin Hydrochloride-based FTO / TiO2 / Perovskite Optical Absorbing Layer

[0077] Comparative Example 1

[0078] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0079] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride liquid was slowly dripped onto an ice block made of 200 mL of deionized water. The UV-treated FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. After that, the solution was poured off and the FTO substrate with the TiO2 precursor solution deposited was treated at 200 °C for 30 min.

[0080] 2) Preparation of perovskite light-absorbing layer:

[0081] 2-1) Dissolve 1 mol CsI and 0.5 mol Pb(SCN)2 in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0082] 2-2) Take 40 μL of the above perovskite precursor solution and drop it onto an FTO substrate covered with a TiO2 dense layer preheated at 70℃. Rotate it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 5 min.

[0083] The fabricated device consists of, from bottom to top, an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), and a perovskite light absorption layer (a two-dimensional perovskite material of Cs2PbI2(SCN)2 without formamidinium hydrochloride).

[0084] III. Preparation of FTO / TiO2 / perovskite light-absorbing layer / buffer layer structure doped with formamidinium hydrochloride using the method of the present invention.

[0085] Example 6

[0086] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0087] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride solution was slowly dripped onto an ice block made of 200 mL of deionized water. After UV treatment, the FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. Then the solution was poured off and the deposited FTO substrate was treated at 200 °C for 30 min.

[0088] 2) Preparation of perovskite light-absorbing layer:

[0089] 2-1) Dissolve 1 mol CsI, 0.5 mol Pb(SCN)2 and 0.02 mol formamidin hydrochloride in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0090] 2-2) Take 40 μL of perovskite precursor solution and drop it onto an FTO substrate covered with a TiO2 dense layer preheated at 70℃. Spin-coat it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 5 min.

[0091] 3) Buffer layer preparation

[0092] 3-1) Dissolve 1 mg of phenyltrimethyltrimethylammonium bromide in 1 mL of IPA to obtain a solution with a concentration of 1 mg / mL. Stir the solution on a stirring table at room temperature for 2 hours until fully dissolved, and then filter the solution through a 45 μm filter head.

[0093] 3-2) Take 40 μL of perovskite solution and drop it onto the cooled perovskite light absorption layer obtained in step 2). Spin-coat it at 4000 rpm for 30 seconds and then heat it on a 70℃ heating stage for 10 minutes.

[0094] The fabricated device, from bottom to top, consists of an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), a perovskite light absorption layer (a two-dimensional perovskite material of Cs2PbI2(SCN)2 doped with formamidinium hydrochloride), and a buffer layer (a trimethylammonium bromide-like substance with a phenyl front end group).

[0095] IV. Fabrication of a solar cell structure without formamidin hydrochloride doping and without a buffer layer: FTO / TiO2 / perovskite light absorption layer / hole transport layer / gold electrode layer

[0096] Comparative Example 2

[0097] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0098] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride solution was slowly dripped onto an ice block made of 200 mL of deionized water. After UV treatment, the FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. Then the solution was poured off and the deposited FTO substrate was treated at 200 °C for 30 min.

[0099] 2) Preparation of perovskite light-absorbing layer:

[0100] 2-1) Dissolve 1 mol CsI and 0.5 mol Pb(SCN)2 in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0101] 2-2) Take 40 μL of perovskite precursor solution and drop it onto an FTO substrate covered with a TiO2 dense layer preheated at 70℃. Spin-coat it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 5 min.

[0102] 3) Preparation of the hole transport layer:

[0103] Preparation of the spiro-OMeTAD hole transport layer: Two hours before use, prepare the hole transport layer solution; the solvent consists of 1 mL chlorobenzene, 72.3 mg spiro-OMeTAD powder, 28.8 μL TBP, 17.5 μL LiTFSI, and 8 μL Co(III)TFSI. After the sample has cooled to room temperature, drop 30 μL of the hole transport layer solution onto the sample and spin-coate (3500 rpm, 20 s).

[0104] 4) Evaporation of gold electrode layer: using a vacuum deposition machine at a depth of 1×10 -5 A 65nm thick gold film was deposited under Pa as an electrode.

[0105] The fabricated device, from bottom to top, consists of an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), a perovskite light-absorbing layer (Cs2PbI2(SCN)2 two-dimensional perovskite material without formamidinium hydrochloride doping), a hole transport layer (spiro-OMeTAD), and a gold electrode layer. V. Fabrication of a solar cell structure with an FTO / TiO2 / perovskite light-absorbing layer / hole transport layer / gold electrode layer without a buffer layer.

[0106] Comparative Example 3

[0107] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0108] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride solution was slowly dripped onto an ice block made of 200 mL of deionized water. After UV treatment, the FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. Then the solution was poured off and the deposited FTO substrate was treated at 200 °C for 30 min.

[0109] 2) Preparation of perovskite light-absorbing layer:

[0110] 2-1) Dissolve 1 mol CsI, 0.5 mol Pb(SCN)2 and 0.02 mol formamidin hydrochloride in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0111] 2-2) Take 40 μL of perovskite precursor solution and drop it onto an FTO substrate covered with a TiO2 dense layer preheated at 70℃. Spin-coat it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 5 min.

[0112] 3) Preparation of the hole transport layer:

[0113] Preparation of the spiro-OMeTAD hole transport layer: Two hours before use, prepare the hole transport layer solution; the solvent consists of 1 mL chlorobenzene, 72.3 mg spiro-OMeTAD powder, 28.8 μL TBP, 17.5 μL LiTFSI, and 8 μL Co(Ⅲ)TFSI. After the sample has cooled to room temperature, drop 30 μL of the hole transport layer solution onto the sample and spin-coate (3500 rpm, 20 s).

[0114] 4) Evaporation of gold electrode layer: using a vacuum deposition machine at a depth of 1×10 -5A 65nm thick gold film was deposited under Pa as an electrode.

[0115] The fabricated device structure, from bottom to top, consists of an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), a perovskite light absorption layer (a two-dimensional perovskite material of Cs2PbI2(SCN)2 doped with formamidinium hydrochloride), a hole transport layer (spiro-OMeTAD), and a gold electrode layer.

[0116] VI. Fabrication of a solar cell structure with undoped formamidinium hydrochloride: FTO / TiO2 / perovskite light absorption layer / buffer layer / hole transport layer / gold electrode layer

[0117] Comparative Example 4

[0118] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0119] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride solution was slowly dripped onto an ice block made of 200 mL of deionized water. After UV treatment, the FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. Then the solution was poured off and the deposited FTO substrate was treated at 200 °C for 30 min.

[0120] 2) Preparation of perovskite light-absorbing layer:

[0121] 2-1) Dissolve 1 mol CsI and 0.5 mol Pb(SCN)2 in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0122] 2-2) Take 40 μL of perovskite precursor solution and drop it onto an FTO substrate covered with a TiO2 dense layer preheated at 70℃. Spin-coat it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 5 min.

[0123] 3) Buffer layer preparation

[0124] 3-1) Dissolve 1 mg of phenyltrimethyltrimethylammonium bromide in 1 mL of IPA to obtain a solution with a concentration of 1 mg / mL. Stir the solution on a stirring table at room temperature for 2 hours until fully dissolved, and then filter the solution through a 45 μm filter head.

[0125] 3-2) Take 40 μL of perovskite solution and drop it onto the cooled perovskite light absorption layer obtained in step 2). Spin-coat it at 4000 rpm for 30 seconds and then heat it on a 70℃ heating stage for 10 minutes.

[0126] 4) Hole transport layer fabrication:

[0127] Preparation of the spiro-OMeTAD hole transport layer: Two hours before use, prepare the hole transport layer solution, which consists of 1 mL chlorobenzene, 72.3 mg spiro-OMeTAD powder, 28.8 μL TBP, 17.5 μL LiTFSI, and 8 μL Co(III)TFSI. After the sample has cooled to room temperature, take 30 μL of the hole transport layer solution and drop it onto the sample for spin coating (3500 rpm, 20 s).

[0128] 5) Evaporation of gold electrode layer: using a vacuum deposition machine at 1×10 -5 A 65nm thick gold film was deposited under Pa as an electrode.

[0129] The fabricated device structure is shown in the attached figure. Figure 1 As shown, the device, from bottom to top, consists of an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), a perovskite light absorption layer (a two-dimensional perovskite material of Cs2PbI2(SCN)2 without formamidinium hydrochloride), a buffer layer (a trimethylammonium bromide-like substance with a phenyl front end group), a hole transport layer (spiro-OMeTAD), and a gold electrode layer.

[0130] VII. A solar cell structure prepared using the method of this invention, comprising a formamidinium hydrochloride-doped FTO / TiO2 / perovskite light absorption layer / buffer layer / hole transport layer / gold electrode layer.

[0131] Example 7

[0132] 1) Cut the FTO conductive glass into 15mm×13mm pieces, immerse them in potassium dichromate cleaning solution for 20 minutes, remove and rinse with clean water. Then rinse with clean water, deionized water and ethanol respectively, place in an oven to dry, and perform UV surface treatment to obtain the FTO substrate.

[0133] Preparation of TiO2 dense layer: 4.5 mL of titanium tetrachloride solution was slowly dropped onto an ice block made of 200 mL of deionized water. After UV treatment, the FTO substrate was immersed in the solution after the ice block melted and treated at 70 °C for 1 h. Then the solution was poured off and the deposited FTO substrate was treated at 200 °C for 30 min to obtain a TiO2 dense layer with a thickness of 20 nm.

[0134] 2) Preparation of perovskite light-absorbing layer:

[0135] 2-1) Dissolve 1 mol CsI, 0.5 mol Pb(SCN)2 and 0.02 mol formamidin hydrochloride in 1 mL DMSO to obtain a solution with a concentration of 0.5 mol / mL. Place the solution on a 70℃ heating and stirring table and stir for 10 h until fully dissolved. Then filter the solution through a 45 μm filter head to obtain a perovskite precursor solution.

[0136] 2-2) Take 40 μL of perovskite precursor solution and drop it onto an FTO substrate covered with a TiO2 dense layer preheated at 70℃. Rotate it at 3000 rpm for 30 s. After spin coating, place it in a vacuum drying oven at 90℃ and heat it under vacuum for 5 min to obtain a perovskite light absorption layer with a thickness of 220 nm.

[0137] 3) Buffer layer preparation

[0138] 3-1) Dissolve 1 mg of phenyltrimethyltrimethylammonium bromide in 1 mL of IPA to obtain a solution with a concentration of 1 mg / mL. Stir the solution on a stirring table at room temperature for 2 hours until fully dissolved, and then filter the solution through a 45 μm filter head.

[0139] 3-2) Take 40 μL of perovskite solution and drop it onto the cooled FTO / TiO2 / perovskite light absorption layer substrate obtained in step 2). Spin-coat it at 4000 rpm for 30 s. After spin coating, place it on a 70℃ heating stage and heat for 10 min to obtain a buffer layer with a thickness of 5 nm.

[0140] 4) Hole transport layer fabrication:

[0141] Preparation of the spiro-OMeTAD hole transport layer: Two hours before use, a hole transport layer solution was prepared, comprising 1 mL chlorobenzene, 72.3 mg spiro-OMeTAD powder, 28.8 μL TBP, 17.5 μL LiTFSI, and 8 μL Co(III)TFSI. After the sample cooled to room temperature, 30 μL of the hole transport layer solution was dropped onto the sample and spin-coated (3500 rpm, 20 s) to obtain a hole transport layer with a thickness of 200 nm.

[0142] 5) Evaporation of gold electrode layer: using a vacuum deposition machine at 1×10 -5 A 65nm thick gold film was deposited under Pa as an electrode.

[0143] The fabricated device structure is shown in the attached figure. Figure 1 As shown, the device, from bottom to top, consists of an FTO substrate, a TiO2 dense layer (i.e., an electron transport layer), a perovskite light absorption layer (a two-dimensional perovskite material of Cs2PbI2(SCN)2 doped with formamidinium hydrochloride), a buffer layer (a trimethylammonium bromide-like substance with a phenyl front end group), a hole transport layer (spiro-OMeTAD), and a gold electrode layer.

[0144] VIII. Performance Testing

[0145] 1. Compare the products obtained in Examples 1-5 with those obtained in Comparative Example 1.

[0146] X-ray diffraction tests were performed on the two-dimensional perovskite films prepared in Examples 1-5 with formamidine hydrochloride added after spin-coating and heat-treated for 1-5 min, and on the blank two-dimensional perovskite film prepared in Comparative Example 1 without formamidine hydrochloride added after spin-coating and heat-treated for 5 min. The results are shown in the appendix. Figure 2 The X-ray diffraction pattern on the left shows obvious crystallization peaks of two-dimensional perovskite. According to the principle of three strong peaks, the characteristic peaks of the crystallization peaks of undoped formamidinium hydrochloride two-dimensional perovskite are marked at 9.82° (200), 19.78° (400), and 29.78° (600), which are consistent with the characteristics of the layered structure of two-dimensional perovskite.

[0147] according to Figure 2 The right-hand figure more clearly shows that the formamidinium hydrochloride-doped sample prepared by the method of this invention reaches a stable state after 5 minutes of heat treatment. Its crystallization peak is located at the same position as the crystallization peak of the undoped formamidinium hydrochloride sample. The crystallization peak of the sample heat-treated for 1–5 minutes initially shifts to a larger angle with increasing treatment time, then shifts back to its original position with a smaller angle. Since chloride ions are smaller than iodide and thiocyanate ions, the shift of the crystallization peak to a larger angle during 1–3 minutes of heat treatment is due to lattice collapse caused by the incorporation of some chloride ions. However, as the heat treatment time increases, the small chloride ions cannot stably exist in the lattice, and their extraction causes the crystallization peak to shift back to its original position with a smaller angle. This indicates that during heat treatment, chloride ions from formamidinium hydrochloride first enter the perovskite lattice, generating intermediate products. With increasing heat treatment time, the chloride ions, due to their small size, leave the perovskite lattice. However, the formation of intermediate products regulates the crystallization process and slows down the crystallization rate.

[0148] 2. The effects of formamidin hydrochloride were investigated by comparing the products obtained in Example 5 and Comparative Example 1.

[0149] Appendix Figure 3 The images show surface scanning electron microscope (SEM) images of two-dimensional Cs₂PbI₂(SCN)₂ perovskite films with and without formamidinium hydrochloride (right image, left image). The images clearly show that although the film coverage does not change significantly, the grain size of the two-dimensional Cs₂PbI₂(SCN)₂ perovskite film with formamidinium hydrochloride is more uniform. This grain homogenization effectively improves carrier transport performance, thereby enhancing the photoelectric performance of the battery.

[0150] Appendix Figure 4The UV-Vis absorption spectra of two-dimensional Cs2PbI2(SCN)2 perovskite films with and without formamidinium hydrochloride are shown. The light absorption capability of the film is significantly enhanced after the addition of formamidinium hydrochloride, which is related to the increase in short-circuit current density of the two-dimensional Cs2PbI2(SCN)2 perovskite devices with and without formamidinium hydrochloride in Table 1 (from 7.42 mA to 8.47 mA).

[0151] Appendix Figure 5 Time-resolved photoluminescence spectra and double exponential function fitting curves of two-dimensional Cs2PbI2(SCN)2 perovskite films doped and undoped with formamidinium hydrochloride were used to study the effect of adding formamidinium hydrochloride on the carrier lifetime of the perovskite layer. Compared with the original film that completely decayed within 150 ns, the addition of formamidinium hydrochloride also played a role in grain homogenization. Therefore, the film with added formamidinium hydrochloride has a higher carrier lifetime, which is beneficial for its application in perovskite solar cells.

[0152] Appendix Figure 6 The IV curves are obtained from space charge confinement current (SCLC) analysis of a purely electronic device with an FTO / TiO2 / Cs2PbI2(SCN)2 / PCBM / Au structure. The trap fill limit voltage (V) is extracted from the intersection of the tangents of the fitted curves. TFL The V of the device based on the original Cs2PbI2(SCN)2 thin film. TFL The voltage dropped from 0.401V to 0.251V in the Cs₂PbI₂(SCN)₂ device prepared with formamidinium hydrochloride. Therefore, the trap state density in the perovskite layer is considered to decrease when formamidinium hydrochloride is added to prepare the perovskite layer; this trap state density is related to V... TFL The values ​​show a linear relationship (formula) ).

[0153] 3. Compare the products obtained in Example 5 and Example 6 to investigate the role of the buffer layer.

[0154] Because the hole transport layer uses spiro-OMeTAD, which is an organic material, it cannot be well imaged under a scanning electron microscope. Figure 7 This demonstrates scanning electron microscope images showing whether the hole transport layer was treated with a buffer layer before spin-coating. Figure 7 The middle left image shows that after the solar cell uses trimethylammonium bromide-based materials to treat the interface between the perovskite light-absorbing layer and the hole transport layer, there is no interaction between the hole transport layer and the perovskite material. Therefore, what is seen under the electron microscope is the poorly imaged hole transport layer material. Figure 7In the right image, the film untreated with trimethylammonium bromide is clearly imaged, and traces of surface interactions are visible. These conclusions demonstrate that the buffer layer effectively blocks the interaction between the hole transport layer material and the light absorption layer material.

[0155] The data in Table 1 also shows that the buffer layer prevents the interaction between the hole transport layer and the perovskite layer, which greatly helps to improve device efficiency. Device IV test data (Table 1, ...) Figure 7 The results show that after adding the buffer layer, the current density of the device increased from 8.26 mA to 8.47 mA, the open-circuit voltage increased from 0.86 V to 0.91 V, and the efficiency increased from 3.87% to 4.70%. This also confirms that the buffer layer can further improve the current density, open-circuit voltage, and photoelectric conversion efficiency of two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell devices, ultimately leveraging their photoelectric performance advantages and helping to promote the commercial application of all-inorganic two-dimensional perovskite solar cells.

[0156] 4. Compare the products obtained in Comparative Examples 3 and 4 with those obtained in Example 7.

[0157] Appendix Figure 8 Table 1 shows the Cs₂PbI₂(SCN)₂ thin films prepared with formamidinium hydrochloride in Comparative Example 3, the Cs₂PbI₂(SCN)₂ layers without formamidinium hydrochloride in Comparative Example 4 after buffer layer treatment, and the Cs₂PbI₂(SCN)₂ thin films prepared with formamidinium hydrochloride in Example 7 after buffer layer treatment, at standard AM 1.5G (100mW·cm⁻¹). -2 Under illumination, the JV curves and corresponding photovoltaic parameters of the perovskite solar cells were recorded. Enhanced photoelectric conversion efficiency can be obtained by optimizing the concentrations of formamidinium hydrochloride and the buffer layer used in the perovskite film preparation process.

[0158] The current density (J / L) of a perovskite solar cell prepared with a Cs2PbI2(SCN)2 thin film after the addition of formamidinium hydrochloride and treated with a buffer layer is shown in the figure. sc From the original 7.42 mA·cm -2 Increased to 8.47 mA·cm -2 Open circuit voltage (V) oc The voltage was increased from 0.86V to 0.91V, the photoelectric conversion efficiency increased from 3.87% to 4.70%, and the fill factor (FF) increased to 61.37%, resulting in a significant improvement in photoelectric performance. This is the highest efficiency value to date for perovskite solar cells using all-inorganic two-dimensional Cs2PbI2(SCN)2 perovskite as the absorber layer. In summary, this buffer layer treatment has greatly enhanced the matching and efficiency of Cs2PbI2(SCN)2 thin films in the field of solar cells.

[0159] Table 1. Effects of formamidin hydrochloride and buffer layer on solar cell performance

[0160]

Claims

1. A two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate, characterized in that, The perovskite solar cell is composed of an FTO substrate, a TiO2 dense layer, a perovskite light-absorbing layer, a buffer layer, a hole transport layer, and a gold electrode layer arranged sequentially. The material of the perovskite light-absorbing layer is Cs2PbI2(SCN)2 doped with formamidinium hydrochloride, the material of the buffer layer is trimethylammonium bromide, and the hole transport layer is spiro-OMeTAD. The leading group of the trimethylammonium bromide is phenyl, hexadecyl, dodecyl, or octyl; specifically, it includes phenyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, or octyltrimethylammonium bromide. The perovskite light-absorbing layer is prepared by weighing formamidine hydrochloride, cesium iodide, and lead thiocyanate, dissolving them in an organic solvent, heating and stirring thoroughly, and filtering to obtain a perovskite precursor solution. The concentration of the perovskite precursor solution is 0.5–0.7 mol / mL, wherein the concentration ratio of cesium iodide to lead thiocyanate is 2:1, and the concentration of formamidine hydrochloride is 0.02–0.04 mol / mL. The organic solvent is dimethyl sulfoxide, the heating temperature is 60–80℃, and the stirring time is 6–10 h. The perovskite precursor solution is spin-coated onto a dense TiO2 layer, heated at low temperature, and then cooled to obtain the perovskite light-absorbing layer.

2. The two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate according to claim 1, characterized in that, The thickness of the perovskite light-absorbing layer is not less than 100 nm, the thickness of the TiO2 dense layer is 20–30 nm, the thickness of the buffer layer is 5–10 nm, the thickness of the hole transport layer is 150–220 nm, and the thickness of the gold electrode layer is 65–75 nm.

3. A method for preparing a two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate as described in claim 1 or 2, characterized in that, Includes the following steps: 1) Using FTO conductive glass as FTO substrate, a TiO2 precursor solution was deposited on the FTO substrate by solution method, and a dense TiO2 layer was obtained by annealing. 2) Spin-coat the perovskite precursor solution onto the TiO2 dense layer, heat at low temperature and then cool to obtain the perovskite light-absorbing layer. 3) Spin-coat the buffer layer solution onto the perovskite light-absorbing layer to obtain the buffer layer; 4) Spin-coat a hole transport layer solution onto the buffer layer to obtain a hole transport layer, wherein the hole transport layer is spiro-OMeTAD; 5) A gold electrode layer was prepared on the surface of the hole transport layer by vacuum evaporation to obtain a two-dimensional Cs2PbI2(SCN)2 perovskite solar cell.

4. The method for preparing a two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate according to claim 3, characterized in that, TiO2 precursor solution was deposited on FTO substrate using a solution method; the annealing temperature was 200℃ and the annealing time was 30-40 min.

5. The method for preparing a two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate according to claim 4, characterized in that, The solution method is as follows: 4-5 mL of titanium tetrachloride solution is dropped onto an ice block made of 200-250 mL of deionized water. The FTO substrate is then immersed in the solution after the ice has melted. The substrate is treated at 70-80°C for 1 hour. After that, the solution is discarded, and the deposited FTO substrate is treated at 200°C for 30-40 minutes.

6. The method for preparing a two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate according to claim 3, characterized in that, Before depositing the perovskite light-absorbing layer precursor solution, the FTO substrate with the deposited TiO2 dense layer needs to be preheated at a temperature of 60–70°C.

7. The method for preparing a two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate according to claim 3, characterized in that, Step 2) Preparation of the perovskite precursor solution: Weigh formamidinium hydrochloride, cesium iodide, and lead thiocyanate, dissolve them in an organic solvent, heat and stir thoroughly, then filter to obtain the perovskite precursor solution; the concentration of the perovskite precursor solution is 0.5–0.7 mol / mL, wherein the concentration ratio of cesium iodide to lead thiocyanate is 2:1, and the concentration of formamidinium hydrochloride is 0.02–0.04 mol / mL; the organic solvent is dimethyl sulfoxide, the heating temperature is 60–80℃, and the stirring time is 6–10 h; In the preparation of the perovskite light-absorbing layer, the amount of perovskite precursor solution used is 20–22 μL / cm². 2 The spin coating speed is 2000-3000 rpm, the heating table temperature is 90-100℃, and the heating time is 3-5 min.

8. The method for preparing a two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate according to claim 3, characterized in that, The buffer layer solution is prepared by dissolving trimethylammonium bromide powder in a solvent and stirring. The concentration of trimethylammonium bromide in the buffer layer solution is 1–3 mg / mL. The solvent is isopropanol. During the preparation of the buffer layer, the volume of buffer solution used is 20–25 μL / cm³. 2 The spin coating speed is 3000-4000 rpm, the heating table temperature is 60-90℃, and the heating time is 5-10 min.

9. The method for preparing a two-dimensional Cs₂PbI₂(SCN)₂ perovskite solar cell based on thiocyanate according to claim 3, characterized in that, The hole transport layer solution is prepared by using spiro-OMeTAD as the hole transport layer, adding tributyl phosphate, lithium bis(trifluoromethanesulfonylimide) and bis(trifluoromethanesulfonylimide) salt, and dissolving them in chlorobenzene solvent. During the preparation of the hole transport layer, the volume of the hole transport layer solution used is 15–18 μL / cm². 2 The spin coating speed is 3500-4000 rpm.

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