Chlorine-containing organic potassium salt-modified perovskite solar cell electron transport layer, perovskite solar cell and preparation method thereof

Abstract

The present invention discloses a chlorine-containing organic potassium salt modified electron transport layer of a perovskite solar cell, a perovskite solar cell and a preparation method thereof. The modification method is: the chlorine-containing organic potassium salt is uniformly distributed on the surface of the electron transport layer; or: the chlorine-containing organic potassium salt is uniformly distributed inside the electron transport layer; or: the chlorine-containing organic potassium salt is uniformly distributed inside and on the surface of the electron transport layer. The present invention modifies the electron transport layer by using the chlorine-containing organic potassium salt. + The synergistic effect of cations and organic anions passivates interfacial defects, fills oxygen vacancies on the surface of the electron transport layer, and promotes carrier transport. By assembling the cell with hole transport materials, FTO conductive glass, and metal electrodes, the open-circuit voltage, cell efficiency, and stability of the perovskite solar cell are significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cells, and in particular relates to a chlorine-containing organic potassium salt-modified perovskite solar cell electron transport layer, a perovskite solar cell and a preparation method thereof. Background Art

[0002] As early as the last century, the excellent properties of perovskite semiconductors had been discovered, but they had not been applied in the field of solar cells. The earliest research on perovskite solar cells (PSCs) originated in 2009. The Miyasaka team at the University of Tokyo in Japan used methylamine lead halide instead of traditional organic dyes as a sensitizer for the first time, and obtained a perovskite solar cell with an efficiency of 3.8% for the first time. After decades of development, researchers around the world have done a lot of optimization research on the material composition, preparation process and stability of perovskite solar cells. In 2021, UNIST in South Korea reported the highest certified efficiency of perovskite solar cells (25.7%). Therefore, perovskite solar cells have become the most promising candidate in the photovoltaic field.

[0003] The structural formula of the perovskite material used as the light-absorbing layer in perovskite solar cells can be described as ABX3, where the X position is a halogen anion (Cl, Br, I); the A position is generally an organic cation or an alkali metal ion, such as methylamine (MA, CH3NH3 + ), formamidine (FA, CH(NH2)2 + ), cesium (Cs + ) etc.; the B position is a metal ion with a larger size, including lead (Pb 2+ ), tin (Sn 2+ ) etc. The A-site cations are usually located at the vertices of the hexahedron, while the B-site cations are coordinated with the X-site anions at the body center to form a BX6 octahedron. The ideal cubic structure of perovskite crystals is often distorted due to the different sizes of the A-site, B-site, and X-site ions, resulting in their optical, electronic, magnetic, and dielectric properties being tunable with the composition. In addition to tunable composition, perovskite materials also have many excellent properties: high absorption coefficient, low exciton binding energy, high defect tolerance (due to the antibonding nature of the valence state, most intrinsic point defects in perovskites tend to form shallow energy level defects rather than recombination centers), ultra-long carrier diffusion length and lifetime, and moderate carrier mobility. These advantages combined lead to the excellent performance of perovskite solar cells.

[0004] At present, almost all high-efficiency perovskite solar cells are prepared based on polycrystalline perovskite films, rather than single crystal films. However, the growth of perovskite films will undergo high-temperature annealing and rapid crystallization processes, so a large number of charged defects will inevitably be generated in the body, grain boundaries and interfaces of polycrystalline perovskite films. Due to the nature of the ionic compound of the perovskite material and the high ion migration speed, these film charged defects will migrate inside the device under the action of the electric field, affecting the photovoltaic performance of the perovskite device. Studies have shown that the interface of perovskite solar cells usually contains a higher concentration of defects, about 100 times that of the defects in the body of the perovskite film. The dangling bonds at the heterojunction interface can easily capture carriers, accumulate and induce carrier recombination, which has an adverse effect on the carrier transport process. These defects affect the extraction of interface carriers, resulting in an increase in the series resistance of the device and a reduction in the open circuit voltage (V OC ), short-circuit current density (J SC ) and fill factor (FF); in addition, the carrier capture and de-trapping process induced by defects inside perovskite devices is also considered to be an important cause of device instability and hysteresis effects.

[0005] In recent years, efforts to reduce these interface defects have focused on surface passivation, and interface engineering has been proven to be an effective method. Compared with the top surface of the perovskite film, the bottom surface has more serious semiconductor heterogeneity, which may be derived from the difference between the top and bottom surfaces caused by the crystallization process of the perovskite polycrystalline film solution growth. The electron transport layer (ETL) and the perovskite heterojunction must have good band matching and excellent conductivity to avoid excessive band offset and maintain efficient carrier extraction and transport. However, passivation and the buried interface at the interface between the electron transport layer and the perovskite layer are difficult because the surface treatment agent on the electron transport layer is likely to dissolve when covering the perovskite film, resulting in uncontrollable doping.

[0006] So far, some molecules have been developed to passivate the defects of ETL / perovskite interface, which can be roughly divided into the following categories according to the type of passivation material: ① Inorganic compounds, represented by alkali metal compounds, including KCl, KI, KOH, etc. +It has been proven to be an effective passivating agent for eliminating JV hysteresis in perovskite devices, inhibiting carrier capture by interface defects, and suppressing ion migration, and is widely used in planar formal perovskite devices. ② Organic molecules with specific functional groups, such as amines (-NH2), sulfonic acids, carboxylic acids (-COO), and halides (F, Cl…), often act as Lewis bases (or acids) and have a tendency to coordinate with undercoordinated Sn, Pb, I, etc. at the interface. This can significantly affect the surface energy level of the electron transport layer, inhibit surface trap states, and improve the efficiency and stability of perovskite devices. However, the ETL / perovskite interface may contain a large number of positively charged defects (such as oxygen vacancies and halogen vacancies) and negatively charged defects (such as cation vacancies), making it difficult to passivate these charged defects simultaneously with existing technologies. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to solve the above-mentioned deficiencies in the prior art and provide a chlorine-containing organic potassium salt modified perovskite solar cell electron transport layer, a perovskite solar cell and a preparation method thereof. + The chlorine-containing organic potassium salt molecules modify the surface of the electron transport layer, improve the efficiency and stability of the perovskite material, and assemble stable and efficient perovskite thin-film solar cells.

[0008] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0009] Provided is a perovskite solar cell electron transport layer modified with a chlorine-containing organic potassium salt, wherein the modification method is:

[0010] The chlorine-containing organic potassium salt is evenly distributed on the surface of the electron transport layer; or:

[0011] The chlorine-containing organic potassium salt is evenly distributed inside the electron transport layer; or:

[0012] The chlorine-containing organic potassium salt is evenly distributed inside and on the surface of the electron transport layer.

[0013] According to the above scheme, the chlorine-containing organic potassium salt is one of potassium 4-chlorobenzenesulfonate, potassium 3-chlorobenzenesulfonate, potassium 2,5-dichlorobenzenesulfonate, potassium 2,4,5-trichlorobenzenesulfonate, potassium 2-chlorobenzoate, potassium 4-chloro-3,5-dinitrobenzenesulfonate, potassium 4-chloro-3-nitrobenzenesulfonate, potassium 2-chloro-5-nitrobenzenesulfonate, and potassium 2-amino-3-chloro-5-methylbenzenesulfonate.

[0014] According to the above scheme, when the chlorine-containing organic potassium salt is uniformly distributed on the surface of the electron transport layer, the thickness is 1 to 10 nm; when the chlorine-containing organic potassium salt is uniformly distributed inside the electron transport layer, the doping amount is 0.05 to 1.0 mol·mL -1 .

[0015] According to the above solution, the electron transport layer is a tin oxide (SnO2) thin film with a thickness of 20 to 40 nm.

[0016] Provided is a perovskite solar cell, which comprises a base, an electron transport layer, a perovskite light absorbing layer, a hole transport layer and a top electrode in sequence; wherein the electron transport layer is the above-mentioned chlorine-containing organic potassium salt-modified perovskite solar cell electron transport layer.

[0017] According to the above scheme, the perovskite material of the perovskite light absorbing layer is ABX n The structure of the type, A position is selected from methylamine (MA), formamidine (FA), cesium (CS), potassium (K), sodium (Na), B position is selected from lead (Pb), tin (Sn 2+ ), strontium (Sr 3+ ), cadmium (Cd 2+ ), calcium (Ca 2+ ), X is selected from Cl, Br, I, and n=1, 2, 3. Preferably, the perovskite material is FA*MAPbI3, FAPbI3 or CsFAPbBr3.

[0018] According to the above solution, the thickness of the perovskite light-absorbing layer is 600-800 nm.

[0019] According to the above scheme, the substrate is FTO glass with a thickness of 300-500nm; the hole transport layer is Spiro-OMeTAD with a thickness of 200-300nm; and the top electrode is gold (Au) with a thickness of 70-100nm.

[0020] A method for preparing the above-mentioned perovskite solar cell is provided, comprising the following steps:

[0021] 1) Preparing an electron transport layer modified with a chlorine-containing organic potassium salt on the surface of a substrate: first preparing an electron transport layer on the surface of the substrate, and then preparing a chlorine-containing organic potassium salt modification layer on the surface of the electron transport layer; or mixing an electron transport material precursor with a chlorine-containing organic potassium salt solution to form a composite electron transport layer on the surface of the substrate; or first mixing an electron transport material precursor with a chlorine-containing organic potassium salt solution to form a composite electron transport layer in which the electron transport material and the chlorine-containing organic potassium salt are mixed on the surface of the substrate, and then preparing a chlorine-containing organic potassium salt modification layer on the surface of the composite electron transport layer;

[0022] 2) preparing a perovskite light absorbing layer on the surface of the electron transport layer modified with the chlorine-containing organic potassium salt obtained in step 1);

[0023] 3) preparing a hole transport layer and a top electrode on the surface of the perovskite absorption layer obtained in step 2) to obtain a perovskite solar cell.

[0024] According to the above scheme, in step 1), an electron transport layer is prepared on the surface of the substrate, and the specific methods are: blade coating, spin coating, spray coating, chemical bath deposition, and atomic force deposition.

[0025] According to the above scheme, in step 1), a chlorine-containing organic potassium salt modification layer is prepared on the surface of the electron transport layer or the composite electron transport layer by spin coating. First, a chlorine-containing organic potassium salt solution is prepared, and then prepared according to the following parameters: a rotation speed of 2000-4000 r / s, an acceleration of 2000-4000 r / s, a spin coating time of 25-40s, and after spin coating, heating at 100-120°C for 10-20min to obtain a chlorine-containing organic potassium salt modification layer; the composite electron transport layer is prepared by mixing the chlorine-containing organic potassium salt solution with the electron transport material precursor solution, and then depositing it on the substrate surface by blade coating, spin coating, chemical bath deposition or spraying. Preferably, the concentration of the chlorine-containing organic potassium salt solution is 0.05-5.0 mg mL -1 .

[0026] According to the above scheme, in step 2), a perovskite light-absorbing layer is prepared on the surface of the modified layer by a spin coating method. The specific steps are: spin coating the perovskite precursor solution onto the electron transport layer modified with a chlorine-containing organic potassium salt, with a rotation speed of 3000-7000 r / s, an acceleration of 1000-6000 r / s, and a spin coating time of 25-40s. After spin coating, the perovskite light-absorbing layer is heated at 100-150°C for 40-100 minutes to obtain the perovskite light-absorbing layer.

[0027] According to the above scheme, the solvent of the chlorine-containing organic potassium salt solution is one or a mixture of two or more of pure water (H2O), methanol (MT), and isopropyl alcohol (IPA).

[0028] According to the above scheme, the solvent of the perovskite precursor solution is one or a mixture of two or more of isopropyl alcohol (IPA), chlorobenzene, toluene, ethyl acetate (EA), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and diethyl ether.

[0029] The present invention contains K + The surface of the electron transport layer is modified by a chlorine-containing organic potassium salt material composed of an organic anion with a multifunctional organic functional group, and the positively charged defects (Sn 4+ , Pb 2+) and negatively charged defects (O vacancies). Passivation with chlorine-containing organic potassium salts significantly reduces the number of trap states on the surface of the electron transport layer, effectively filling oxygen vacancies. The electron defect density of the perovskite film is significantly reduced. The surface energy level of the electron transport layer shifts upward, better matching the energy level of the perovskite light-absorbing layer. This lowers the potential barrier during carrier transport, helps reduce the probability of carrier recombination, and thus improves the carrier extraction capacity of the functional layer. Compared to standard perovskite solar cells, passivation with chlorine-containing organic potassium salts significantly improves the performance of perovskite solar cells.

[0030] The beneficial effects of the present invention are:

[0031] 1. The present invention provides a chlorine-containing organic potassium salt-modified electron transport layer for a perovskite solar cell. By modifying the electron transport layer with a chlorine-containing organic potassium salt, oxygen vacancies are effectively filled, which is more closely matched with the energy level of the perovskite layer, significantly reducing the energy level barrier during carrier transport. At the same time, the smaller wettability of the electron transport layer surface is more conducive to the growth of the perovskite film, thereby improving the film quality and reducing the trap density inside the film, thereby further improving the performance of the device. When applied to a perovskite solar cell, the effect and open-circuit voltage are high, and the stability is excellent. The efficiency is as high as 24.27%, which is much higher than that of a standard perovskite solar cell (22.72%). The device has a maximum open-circuit voltage of 1.191 V. The unpackaged device retains nearly 80% of its initial efficiency after aging for 1000 hours at 80°C, while the efficiency of the standard perovskite device decreases by nearly 50%.

[0032] 2. This application provides a perovskite solar cell and its preparation method, which realizes the surface modification and doping of the electron transport layer by chlorine-containing organic potassium salt by a simple method, and utilizes K + The synergistic effect of cations and organic anions passivates interfacial defects, fills oxygen vacancies on the surface of the electron transport layer, and promotes carrier transport. By assembling the cell with hole transport materials, FTO conductive glass, and metal electrodes, the open-circuit voltage, cell efficiency, and stability of the perovskite solar cell are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Parameter comparison diagram of perovskite solar cells surface-modified with chlorine-containing organic potassium salt solutions of different concentrations in Example 1 of the present invention; (a) JV curve; (b) PCE distribution diagram; (c) FF distribution diagram; (d) V OC Distribution map and (e)J SC Distribution map.

[0034] Figure 2These are thermal stability diagrams of the electron transport layer modified with a chlorine-containing organic potassium salt and the unmodified electron transport layer in Example 1, including (a) thermal stability; and (b) SEM images of the device cross section before aging and after aging at 80°C for 500h.

[0035] Figure 3 XPS analysis of the electron transport layer modified with a chlorine-containing organic potassium salt and the unmodified electron transport layer in Example 1; (a) full XPS spectrum; (b) high-resolution spectra of S 2p, (c) K 2p, (d) Sn 3d, (e) Cl 2p, and (f) O 1s. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings.

[0037] All operations in the embodiments of the present invention were performed under nitrogen or argon protection.

[0038] Example 1

[0039] Preparation of a perovskite solar cell with a buried interface modified with a chlorine-containing organic potassium salt specifically comprises the following steps:

[0040] (1) Substrate pretreatment: The FTO conductive glass was cut into 10 cm × 10 cm pieces, and then patterned with a femtosecond laser to etch the FTO conductive glass in an area of ​​1.5 cm × 2 cm. The surface of the FTO glass was first wiped with detergent, and then placed in a dedicated cleaning container. Ultrasonic cleaning was performed for 20 minutes using a sufficient amount of pure water, deionized water, and anhydrous ethanol solution containing detergent. After ultrasonic cleaning, the FTO glass was removed, dried with compressed air, and stored in a dry container for later use.

[0041] (2) Preparation of electron transport layer: CBD SnO2 thin film with a thickness of about 30nm was prepared by chemical bath deposition.

[0042] The preparation process is as follows:

[0043] Preparation of SnCl2 mother solution:

[0044] Add 400 mL of pure water to a clean Shu Niu bottle and refrigerate until ready to use. Slowly add 5 mL of concentrated HCl to the prepared pure water, then add 5 g of urea and stir to dissolve. Dissolve 1.096 g of SnCl2·2H2O in the solution. Finally, add 100 μL of thioglycolic acid, shake thoroughly, and refrigerate until ready to use.

[0045] Preparation of CBD SnO2 thin film:

[0046] Transfer 20 mL of the mother liquor to a clean glass container and add 100 mL of pure water, shaking and diluting. Remove the cleaned FTO glass and pre-treat it with UVO for 15 minutes with the front side facing up. Then, blow it clean with dry compressed air. Place the FTO glass, backside up, in a container containing the diluent. Seal the container with PE film and heat it in a 90°C oven for 180 minutes.

[0047] After heating is complete, remove the glass container and rinse the glass 3-5 times with deionized water. Then, add an appropriate amount of water and ultrasonically clean it for 4 minutes. After the ultrasonic cleaning is complete, rinse it again with deionized water 3-5 times. Finally, add an appropriate amount of IPA mixed with water and ultrasonically clean it for 4 minutes. Finally, remove the FTO glass, blow dry it with dry compressed air, and finally anneal it at 170°C for 60 minutes. After cooling to room temperature, place it in a clean container and store it until ready for use.

[0048] (3) Preparation of chlorine-containing organic potassium salt solution: Under an inert atmosphere, take 2,4,5-trichlorobenzenesulfonic acid potassium (3Cl-BSAK) solid powder in a container, add deionized water, seal the container and shake until dissolved. The prepared concentrations are 0.05 mg mL -1 , 0.1mg mL -1 , 0.5mg mL -1 , 1.0mg mL -1 , 2.0mg mL -1 Prepare a 3Cl-BSAK solution and shake it to dissolve completely. Filter and store for later use.

[0049] (4) 3Cl-BSAK modification of SnO2 film: UV-treat the FTO / SnO2 substrate with the front side facing up for 15 minutes. After removal, blow the surface clean with clean compressed air. Use a pipette to draw an appropriate amount of organic potassium salt solution and evenly apply it to the FTO / SnO2 surface. Set the spin coating parameters as follows: 3000 rpm, acceleration 3000 rpm / s, 30 seconds. After the spin coating is completed, remove the substrate and place it on a hot plate at 100°C for 15 minutes to remove surface moisture. Finally, quickly transfer the substrate to a nitrogen glove box and set aside.

[0050] (5) Preparation of perovskite light-absorbing layer: Transfer of SnO2 substrate modified with 3Cl-BSAK and perovskite precursor (FAPbI3) 0.95 (MAPbBr3) 0.05) solution into a nitrogen glove box (the glove box temperature is not higher than 25°C), filter the perovskite precursor solution and set aside. Use a pipette to take an appropriate amount of perovskite solution and evenly apply it to the SnO2 substrate modified with 3Cl-BSAK, and set the coater program to Step 1: 1000rpm, acceleration 2000rpm / s, rotation 10s; Step 2: 5000rpm, acceleration 2000rpm / s, rotation 30s. At the 15th second before Step 2, quickly drop 120μL of EA, and a transparent wet film will be obtained after the coater rotation ends. Transfer the wet film to a 100°C hot plate for annealing for 60 minutes, then remove it, cool it, and store it in a clean container for later use. The thickness of the perovskite film is about 700nm.

[0051] (6) Preparation of hole transport layer:

[0052] Prepare Spiro-OMeTAD solution: Weigh 520 mg of Li-TFSI powder on a balance and dissolve it in 1 mL of ACN solvent, then shake it evenly, filter it and make a Li salt solution for later use. Weigh 300 mg of Co-TFSI on a balance and dissolve it in 1 mL of ACN solvent, then shake it evenly, filter it and make a Co salt solution for later use. Weigh 73 mg of Spiro-OMeTAD powder on a balance, add 1 mL of CBZ, 18 μL of Li salt solution, 29 μL of Co salt solution and 30 μL of tBP respectively, seal it and place it in an oscillator and shake until completely dissolved for later use.

[0053] Transfer the prepared Spiro-OMeTAD solution to a nitrogen glove box. Use a pipette to spin-coat an appropriate amount of the Spiro-OMeTAD solution onto the annealed perovskite film. The spin-coating parameters are: 3000 rpm, 3000 rpm / s, and 30 seconds. After the hole transport layer is prepared, transfer the semi-device to a desiccating cabinet. The hole transport layer thickness is approximately 200 nm.

[0054] (7) Preparation of gold electrode: The semi-device was transferred to the evaporation apparatus substrate, and Au with a thickness of about 80 nm was evaporated in a vacuum evaporator to obtain a complete perovskite device.

[0055] like Figure 1 The JV curves and photoelectric conversion efficiency (PCE) distributions of perovskite devices passivated with different concentrations of 3Cl-BSAK are shown, and unmodified perovskite solar cells are used for comparison. Compared with unmodified devices, devices passivated with 3Cl-BSAK show outstanding photoelectric performance. -1 Increase to 1.0 mg mL -1 When the device's V OC 、J SCand FF increased slightly, and the device efficiency increased from 22.46% to 24.10%. -1 The highest efficiency of 24.27% was obtained when V OC is 1.163V, J SC 24.71 mA cm -2 , FF was 0.844); at a modified concentration of 1.0 mg mL -1 The highest open circuit voltage (1.191 V) and efficiency of 24.10% were obtained.

[0056] Figure 2 (a) Thermal stability test of standard and 3Cl-BSAK-modified perovskite solar cells in an unencapsulated environment at 80°C and 20±5% relative humidity. The 3Cl-BSAK-passivated device retained 80% of its initial efficiency after 800 hours of stabilization in the heating environment, and 78% after 1000 hours. In stark contrast, the untreated device had already lost 50% of its initial efficiency after 1000 hours of stabilization in the heating environment. Figure 2 (b) SEM cross-sectional images of devices treated with and without 3Cl-BSAK passivation before and after 500 hours of thermal aging. Compared to the 3Cl-BSAK passivation device, the untreated perovskite device exhibits significant decomposition at the grain boundaries. In humid environments, grain boundaries with high defect densities play a key role in initiating film degradation. In such environments, water penetrates or reacts at the grain boundaries faster than at the top surface of the grains. We infer that this is because the unpassivated device has more defects at the interfaces and grain boundaries. Under the influence of temperature, the device decomposes and undergoes ion migration, further leading to a loss of device performance.

[0057] Figure 3 The XPS full spectrum of SnO2 and SnO2 / 3Cl-BSAK and the high-resolution spectrum of each element are shown below. Compared with the full spectrum of SnO2, SnO2 / 3Cl-BSAK has more peaks of K 2p, S 2p and Cl 2p. 3 / 2 and Sn3d 5 / 2 The peak position of the SnO2 is shifted by about 0.2eV toward the high binding energy direction relative to the untreated SnO2, indicating that there are additional electrons around the Sn atoms. According to the literature, this may be attributed to the high electronegativity of Cl. The additional negative charge around the under-coordinated Sn atoms caused by oxygen vacancies may be the result of electrostatic coupling between the highly electronegative Cl and Sn. In addition, we observed a small peak of Cl at 197.85eV. After reviewing the literature, we learned that this is the binding peak of Sn-Cl, which further confirms that when 3Cl-BSAK acts on the surface of the SnO2 film, the -Cl with high electron cloud density will react with Sn.4+ In addition, the characteristic peaks at 530.53eV and 531.25eV in the photoelectron spectrum of the O element of the untreated SnO2 are the Sn-O bonds and O vacancies (O V )(or adsorbed hydroxyl oxygen (O OH ); after 3Cl-BSAK modification, the peak positions shifted to 531.08 eV and 532.48 eV, respectively. Furthermore, oxygen vacancies on the SnO2 surface were significantly reduced to 32.78% after passivation, indicating effective filling of O vacancies on the SnO2 film surface and a reduction in Sn dangling bonds. We believe that on the SnO2 ETL surface, electron-rich C-Cl provides additional negative charge to partially fill O vacancies caused by Sn coordination defects. This reduction in surface defects reduces the probability of electron capture by dangling bonds, inhibiting electron accumulation and recombination on the surface of the electron transport layer, thereby promoting carrier transport.

[0058] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalences, replacements and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A chlorine-containing organic potassium salt modified perovskite solar cell electron transport layer, characterized in that: The modification method is: The chlorine-containing organic potassium salt is evenly distributed on the surface of the electron transport layer; or: The chlorine-containing organic potassium salt is evenly distributed inside the electron transport layer; or: The chlorine-containing organic potassium salt is evenly distributed inside and on the surface of the electron transport layer; wherein: The chlorine-containing organic potassium salt is one of potassium 4-chlorobenzenesulfonate, potassium 3-chlorobenzenesulfonate, potassium 2,5-dichlorobenzenesulfonate, potassium 2,4,5-trichlorobenzenesulfonate, potassium 2-chlorobenzoate, potassium 4-chloro-3,5-dinitrobenzenesulfonate, potassium 4-chloro-3-nitrobenzenesulfonate, potassium 2-chloro-5-nitrobenzenesulfonate, and potassium 2-amino-3-chloro-5-methylbenzenesulfonate; The electron transport layer is a tin oxide thin film.

2. The electron transport layer according to claim 1, characterized in that When the chlorine-containing organic potassium salt is uniformly distributed on the surface of the electron transport layer, the thickness is 1-10 nm; when the chlorine-containing organic potassium salt is uniformly distributed inside the electron transport layer, the doping amount is 0.05-1.0 mol·mL -1 .

3. The electron transport layer according to claim 1, characterized in that The thickness of the electron transport layer is 20-40 nm.

4. A perovskite solar cell comprising, in sequence, a substrate, an electron transport layer, a perovskite light absorbing layer, a hole transport layer, and a top electrode; characterized in that: The electron transport layer is the electron transport layer of a perovskite solar cell modified with a chlorine-containing organic potassium salt according to any one of claims 1 to 3.

5. The perovskite solar cell according to claim 4, characterized in that The perovskite light-absorbing layer has a thickness of 600-800 nm; the substrate is FTO glass with a thickness of 300-500 nm; the hole transport layer is Spiro-OMeTAD with a thickness of 200-300 nm; and the top electrode is gold with a thickness of 70-100 nm.

6. A method for preparing a perovskite solar cell according to claim 4, characterized in that: The following steps are involved: 1) Preparing an electron transport layer modified with a chlorinated organic potassium salt on the surface of a substrate: first preparing an electron transport layer on the surface of the substrate, and then preparing a chlorinated organic potassium salt modification layer on the surface of the electron transport layer; or mixing an electron transport material precursor with a chlorinated organic potassium salt solution to form a composite electron transport layer on the surface of the substrate; or first mixing an electron transport material precursor with a chlorinated organic potassium salt solution to form a composite electron transport layer comprising an electron transport material and a chlorinated organic potassium salt on the surface of the substrate, and then preparing a chlorinated organic potassium salt modification layer on the surface of the composite electron transport layer; 2) preparing a perovskite light absorbing layer on the surface of the electron transport layer modified with the chlorine-containing organic potassium salt obtained in step 1); 3) preparing a hole transport layer and a top electrode on the surface of the perovskite absorption layer obtained in step 2) to obtain a perovskite solar cell.

7. The preparation method according to claim 6, characterized in that In the step 1), a chlorine-containing organic potassium salt modification layer is prepared on the surface of the electron transport layer or the composite electron transport layer by spin coating. First, a chlorine-containing organic potassium salt solution is prepared, and then prepared according to the following parameters: a rotation speed of 2000-4000 r / s, an acceleration of 2000-4000 r / s, a spin coating time of 25-40s, and after spin coating, heating at 100-120°C for 10-20 minutes to obtain a chlorine-containing organic potassium salt modification layer; the composite electron transport layer is prepared by mixing the chlorine-containing organic potassium salt solution with an electron transport material precursor solution, and then depositing the mixture on the substrate surface by blade coating, spin coating, chemical bath deposition, or spray coating.

8. The preparation method according to claim 7, characterized in that The concentration of the chlorine-containing organic potassium salt solution is 0.05~5.0 mg mL -1 .

9. The preparation method according to claim 6, characterized in that In step 2), a perovskite light-absorbing layer is prepared on the surface of the modified layer by a spin coating method. The specific steps are: spin coating the perovskite precursor solution onto the electron transport layer modified with a chlorine-containing organic potassium salt at a rotation speed of 3000-7000 r / s, an acceleration of 1000-6000 r / s, and a spin coating time of 25-40 seconds. After spin coating, the perovskite light-absorbing layer is heated at 100-150° C. for 40-100 minutes to obtain the perovskite light-absorbing layer.

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