A SnO2 nanoparticle electron transport layer and perovskite solar cell

Abstract

This invention relates to the field of solar cells and discloses a SnO2 nanoparticle electron transport layer and a perovskite solar cell. The method includes: adding a divalent tin source and an organic ligand to deionized water, adjusting the pH of the solution to 1.5-3.0 with a pH control agent, mixing thoroughly to obtain a precursor solution; immersing a conductive glass substrate in the precursor solution, performing in-situ deposition in a closed environment at below 100°C, and then annealing to obtain a SnO2 nanoparticle electron transport layer assembled from uniform ultra-small nanoparticles of 3-5 nm. The tin dioxide electron transport layer film prepared by this invention exhibits conformal properties and a high electron extraction rate. When applied to perovskite solar cell devices, it significantly reduces carrier recombination loss at the bottom interface, improves the open-circuit voltage and fill factor of the cell device, with an open-circuit voltage loss of less than 300 meV and a fill factor greater than 86%.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, specifically to a SnO2 nanoparticle electron transport layer and a perovskite solar cell. Background Technology

[0002] Perovskite solar cells (PSCs), as an emerging photovoltaic technology, have achieved a photoelectric conversion efficiency (PCE) exceeding 27%, making them one of the most promising photovoltaic technologies. The widespread application of textured fluorine-doped tin dioxide (FTO) substrates can reduce light loss and increase photocurrent, making them a crucial component in achieving high-efficiency PSCs. However, for such substrates, the performance of photovoltaic devices with light-harvesting advantages is limited by excessive carrier recombination at the textured bottom interface, a problem that is more severe in nip (pin-mounted) devices. Even with the best-performing SnO2 nanoparticle electron transport layer currently available, the open-circuit voltage and fill factor are far below the theoretical limits of nip photovoltaic devices and their Shockley–Queisser (SQ) model, limiting the device PCE to 26%. Therefore, in nip PSCs, a new strategy for suppressing carrier recombination at the SnO2 electron transport layer / perovskite textured bottom interface is urgently needed to minimize open-circuit voltage and fill factor losses.

[0003] Sol-gel and chemical bath deposition methods are common approaches for preparing electron transport layers of tin dioxide nanoparticles. However, how to achieve the fabrication of a dense, conformal tin dioxide electron transport layer on a textured substrate to suppress carrier accumulation at the SnO2 / perovskite interface in perovskite solar cells remains a prominent problem that urgently needs to be solved.

[0004] While commercial sol-gel methods offer relative ease of operation, they cannot achieve conformal deposition on wrinkled substrates, limiting further improvements in device performance. Currently, chemical bath deposition (CBD) offers potential for conformal deposition by depositing tin dioxide nanoparticles in situ to create tunable tin dioxide electron transport layers. However, during CBD deposition, uneven nanoparticle size distribution and uncontrolled in-situ self-assembly of nanoparticles lead to poor tin dioxide film deposition on textured, wrinkled substrates, resulting in pores and grooves that accumulate. This is a significant cause of severe nonradiative recombination of charge carriers at the interface, severely limiting device performance, particularly open-circuit voltage and fill factor.

[0005] Therefore, understanding the in-situ growth mechanism of chemical bath deposition and achieving uniform and conformal deposition of tin dioxide films on wrinkled substrates through effective nanoparticle size control strategies to suppress non-radiative recombination loss at the bottom interface are currently major challenges. Summary of the Invention

[0006] The purpose of this invention is to address the problem of excessive nonradiative recombination caused by uneven contact in the bottom interface transport layer in current technologies, by providing a tin dioxide nanoparticle electron transport layer and a perovskite solar cell using this electron transport layer. The performance improvement of this perovskite solar cell device mainly comes from the in-situ construction of a uniform, dense, and conformal tin dioxide electron transport layer. First, it is clarified that the chemical bath deposition of tin dioxide thin films is highly dependent on the properties of organic ligands. The carbon chain length and type of the ligand backbone significantly affect the conductivity of the film; the acidity constant pKa of the ligand anchoring group significantly affects the interaction with tin; and the steric hindrance of the ligand anchoring group and the ionization of the tail group affect the nanoparticle size and film uniformity. Building upon this foundation, by employing a ligand steric hindrance effect strategy in in-situ chemical bath deposition, the traditionally used small steric hindrance, single-anchored organic ligands are combined with research on the in-situ growth mechanism of chemical bath deposition. This innovatively utilizes a dual-anchored ligand with a low acidity constant pKa anchoring group and a conjugated high conductivity, large steric hindrance benzene ring framework. This achieves a uniform, ultra-small tin dioxide nanoparticle assembly of 3-5 nm electron transport layer films, avoiding the uneven deposition and aggregation phenomena caused by nanoclusters exceeding 100 nm obtained by traditional methods. This significantly reduces the surface defect state density at the bottom interface, suppresses non-radiative recombination losses at the buried interface of photovoltaic devices, and ultimately achieves a significant improvement in the open-circuit voltage and fill factor of perovskite solar cells.

[0007] This invention utilizes a bifunctional group control strategy involving anchoring groups with large steric hindrance and a highly conjugated benzene ring framework during in-situ chemical bath deposition. This enables the fabrication of a uniform and ultra-small tin dioxide electron transport layer with high conductivity over a timescale. The thin film can be deposited in a conformal and dense manner on a textured substrate, significantly suppressing carrier recombination at the bottom interface. This results in a positive perovskite solar cell with high open-circuit voltage and fill factor.

[0008] To achieve the above objectives, the present invention provides a method for preparing an electron transport layer of SnO2 nanoparticles, comprising the following steps:

[0009] S1, add divalent tin source and organic ligand to deionized water, adjust the pH of the solution to 1.5-3.0, and mix well to obtain the precursor solution;

[0010] Wherein: the organic ligand is 3-sulfobenzoic acid or 4-sulfobenzoic acid;

[0011] S2 involves immersing a textured conductive glass substrate in a precursor solution, performing in-situ deposition in a sealed environment at temperatures below 100 °C, and then annealing to obtain an electron transport layer of SnO2 nanoparticles assembled from uniform ultra-small nanoparticles of 3-5 nm.

[0012] As a further preferred embodiment of the present invention, the divalent tin source is stannous chloride dihydrate.

[0013] As a further preferred technical solution of the present invention, in step S1, 0.0008-0.0020 mol of divalent tin source and 0.00025-0.00040 mol of organic ligand are added to every 100 mL of deionized water; more preferably, the divalent tin source is 0.0012 mol and the organic ligand is 0.00035 mol per 100 mL of deionized water.

[0014] As a further preferred technical solution of the present invention, in step S2, the in-situ deposition temperature is 60-95 ℃, more preferably 90 ℃; the annealing temperature is 150-180 ℃, and the time is 0.5-2 h.

[0015] As a further preferred embodiment of the present invention, the thickness of the tin dioxide electron transport layer is 10-100 nm.

[0016] As a further preferred embodiment of the present invention, the conductive glass is textured FTO glass or ITO glass.

[0017] As a further preferred technical solution of the present invention, in step S1, a pH control agent is used to adjust the pH value of the solution. The pH control agent is one or two of an acid and a base. The acid is concentrated hydrochloric acid or citric acid, and the base is urea or ammonia.

[0018] According to another aspect of the present invention, the present invention also provides a perovskite solar cell, which includes a conductive glass, an electron transport layer, a perovskite active layer, an organic ammonium salt passivation layer, a hole transport layer and a metal electrode sequentially laminated along the thickness direction, wherein the electron transport layer is prepared by the preparation method of the first aspect described above.

[0019] As a further preferred technical solution of the present invention, the conductive glass is textured FTO glass or ITO glass;

[0020] And / or, the material of the perovskite active layer is selected from FAPbI3, MA x FA 1-x PbI3, MA x Cs y FA 1-x-y PbI3, Cs x FA 1-x At least one of PbI3, wherein x and y are both less than 1;

[0021] And / or, the material of the organic ammonium salt passivation layer is selected from phenylethylamine bromide, phenylethylamine iodide, or n-octylamine bromide;

[0022] And / or, the material of the hole transport layer is selected from Spiro-OMeTAD;

[0023] And / or, the material of the metal electrode is a conductive metal or a conductive metal alloy.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) In the process of chemically depositing tin dioxide electron transport layer, the present invention introduces a bifunctional organic ligand with a conjugated benzene ring linker to ensure the high conductivity of tin dioxide as an electron transport layer. In addition, due to the rigidity and large steric hindrance effect of the short-chain benzene ring ligand, the aggregation problem of colloidal particles in the precursor is effectively suppressed, and uniform and ultra-small 3-5 nm tin dioxide nanoparticles are constructed in situ in the precursor, thus realizing a dense and shape-preserving tin dioxide electron transport layer.

[0026] (2) The tin dioxide electron transport layer thin film prepared by the present invention has conformal properties and high electron extraction rate. When applied to perovskite solar cell devices, it significantly reduces the carrier recombination loss at the bottom interface, improves the open-circuit voltage and fill factor of the device, and has an open-circuit voltage loss of less than 300 meV and a fill factor of more than 86%. Attached Figure Description

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] Figure 1 The image shown is a scanning electron microscope (SEM) image of 4BSA-SnO2 from Example 1, showing a densely deposited thin film.

[0029] Figure 2 The image shown is a transmission electron microscope (TEM) image of 4BSA-SnO2 from Example 1, which shows 3-5 nm ultra-small nanoparticles uniformly distributed in the precursor.

[0030] Figure 3 The image shown is a scanning electron microscope (SEM) image of 3BSA-SnO2 from Example 2, showing a densely deposited thin film.

[0031] Figure 4 The image shown is a TEM image of 3BSA-SnO2 from Example 2, which shows 3-5 nm ultra-small nanoparticles uniformly distributed in the precursor.

[0032] Figure 5 The MTA-SnO2 scanning electron microscope (SEM) image of the control example 1 shows obvious particle aggregation.

[0033] Figure 6 The MTA-SnO2 transmission electron microscope (TEM) image is shown in Comparative Example 1, showing the aggregation of particles larger than 100 nanometers in the precursor.

[0034] Figure 7 The image shows a BMA-SnO2 scanning electron microscope (SEM) image of control example 2, indicating particle aggregation.

[0035] Figure 8 The image shows a BMA-SnO2 transmission electron microscope (TEM) image for Comparative Example 2, revealing an uneven distribution of nanoparticles in the precursor.

[0036] Figure 9 The images show scanning electron microscope (SEM) images of a pure FTO substrate and control example 3, BAA-SnO2. After BAA ligand modification, almost no nanoparticles were deposited on the FTO substrate to form a SnO2 film.

[0037] Figure 10 The image shown is a scanning electron microscope (SEM) image of 2BSA-SnO2 in Comparative Example 4, indicating that a small number of particles still aggregate in the film.

[0038] Figure 11 The image shown is a cross-sectional transmission electron microscope (TEM) image of BSA-SnO2 in Example 1, demonstrating a dense, shape-preserving tin dioxide electron transport layer.

[0039] Figure 12 The figures show the current-voltage curves of the tin dioxide electron transport layer in Example 1, Comparative Example 1, and Comparative Example 2.

[0040] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0041] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0042] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods. Example 1

[0043] This embodiment provides a method for preparing an electron transport layer of SnO2 nanoparticles, as detailed below:

[0044] S1, Preparation of precursor solution:

[0045] Dissolve 1.25 g of urea in 100 mL of water, add 1.25 mL of concentrated hydrochloric acid (37% by mass), 0.274 g of stannous chloride dihydrate, and 1 mL of 10 mg / mL organic ligand 4-sulfobenzoic acid, mix thoroughly to obtain a precursor solution with pH=3.

[0046] S2, Preparation of tin dioxide thin film:

[0047] Take freshly prepared precursor solution, immerse the cleaned textured FTO substrate in the precursor solution, seal the reaction vessel, and place it in a 90 ℃ oven for 2 hours. After the reaction is completed, take out the FTO substrate with deposited tin dioxide film, wash it with ultrapure water, and then anneal it at 180 ℃ for 1 hour to obtain the SnO2 nanoparticle electron transport layer, which is labeled as 4BSA-SnO2.

[0048] from Figure 1 Scanning electron microscopy (SEM) revealed that the film of Example 1 exhibited a uniform and dense particle coverage, composed of... Figure 2 Transmission electron microscopy (TEM) showed that uniform 3-5 nm nanoparticles were formed in situ in the precursor. Example 2

[0049] This embodiment provides a method for preparing an electron transport layer of SnO2 nanoparticles, as detailed below:

[0050] S1, Preparation of precursor solution:

[0051] Dissolve 1.25 g of urea in 100 mL of water, add 1.25 mL of concentrated hydrochloric acid (37% by mass), 0.274 g of stannous chloride dihydrate, and 1 mL of 10 mg / mL organic ligand 3-sulfobenzoic acid, mix thoroughly to obtain a precursor solution with pH=3.

[0052] S2, Preparation of tin dioxide thin film:

[0053] Take freshly prepared precursor solution, immerse the cleaned textured FTO substrate in the precursor solution, seal the reaction vessel, and place it in a 90 ℃ oven for 2 hours. After the reaction is completed, take out the FTO substrate with deposited tin dioxide film, wash it with ultrapure water, and then anneal it at 180 ℃ for 1 hour to obtain the SnO2 nanoparticle electron transport layer, which is labeled as 3BSA-SnO2.

[0054] from Figure 3 Scanning electron microscopy (SEM) revealed that the film of Example 2 exhibited a uniform and dense particle coverage, composed of... Figure 4 Transmission electron microscopy (TEM) showed that uniform 3-5 nm nanoparticles were formed in situ in the precursor. Comparative Example 1

[0055] The difference from Example 1 lies in the change of the type of organic ligand; the specific preparation method of its electron transport layer is as follows:

[0056] S1, Preparation of precursor solution:

[0057] Dissolve 1.25 g of urea in 100 mL of water, add 1.25 mL of concentrated hydrochloric acid (37% by mass), 0.274 g of stannous chloride dihydrate, and 1 mL of 10 mg / mL organic ligand mercaptoacetic acid. Mix thoroughly to obtain the precursor solution.

[0058] S2, Preparation of tin dioxide thin film: Same as in Example 1. The final sample was labeled MTA-SnO2.

[0059] This comparative example benefits from the small steric hindrance of the thiol group in the anchoring group of the thioglycolic acid ligand. Figure 5 Scanning electron microscopy (SEM) can reveal the uneven distribution of nanoparticles in the thin film, and Figure 6 Transmission electron microscopy (TEM) revealed that the precursor contained aggregates of particles over 100 nanometers in size. Comparative Example 2

[0060] The difference from Example 1 lies in the change of the type of organic ligand; the specific preparation method of its electron transport layer is as follows:

[0061] S1, Preparation of precursor solution:

[0062] Dissolve 1.25 g of urea in 100 mL of water, add 1.25 mL of concentrated hydrochloric acid (37% by mass), 0.274 g of stannous chloride dihydrate, and 1 mL of 10 mg / mL 4-mercaptobenzoic acid. Mix thoroughly to obtain the precursor solution.

[0063] S2, Preparation of tin dioxide thin film: Same as in Example 1. The final sample is labeled BMA-SnO2.

[0064] Although the ligands of Comparative Example 2 have slightly greater steric hindrance compared to Comparative Example 1, from Figure 7 Scanning electron microscopy (SEM) also revealed uneven distribution of nanoparticles in the thin film, and Figure 8 Transmission electron microscopy (TEM) revealed that nano- to micron-sized particle aggregates formed in the precursor. Comparative Example 3

[0065] The difference from Example 1 lies in the change of the type of organic ligand; the specific preparation method of its electron transport layer is as follows:

[0066] S1, Preparation of precursor solution:

[0067] Dissolve 1.25 g of urea in 100 mL of water, add 1.25 mL of concentrated hydrochloric acid (37% by mass), 0.274 g of stannous chloride dihydrate, and 1 mL of 10 mg / mL 4-aminobenzoic acid. Mix thoroughly to obtain the precursor solution.

[0068] S2, Preparation of tin dioxide thin film: Same as in Example 1. The final sample is labeled BAA-SnO2.

[0069] In this comparative example, because the strong acidity constant (pKa of approximately 5) of the amino anchoring group in 4-aminobenzoic acid is greater than the pH value of the solution (approximately 3), the amino group cannot be deprotonated under strongly acidic conditions and therefore cannot interact with Sn in tin oxide. Thus, from... Figure 9 According to scanning electron microscopy (SEM), the film almost presents the morphology of a bare, wrinkled FTO substrate. Comparative Example 4

[0070] The difference from Example 1 lies in the change of the type of organic ligand; the specific preparation method of its electron transport layer is as follows:

[0071] S1, Preparation of precursor solution:

[0072] Dissolve 1.25 g of urea in 100 mL of water, add 1.25 mL of concentrated hydrochloric acid (37% by mass), 0.274 g of stannous chloride dihydrate, and 1 mL of 10 mg / mL 2-sulfobenzoic acid. Mix thoroughly to obtain the precursor solution.

[0073] S2, Preparation of tin dioxide thin film: Same as in Example 1. The final sample is labeled 2BSA-SnO2.

[0074] In this comparative example, although the sulfonyl group with large steric hindrance in 2-sulfobenzoic acid is anchored on the nanoparticle surface, and the adjacent tail group can also undergo deprotonation and electrostatic adsorption on FTO, the electrostatic repulsion between the tail groups of the anchoring group sulfonyl and the tail-modifying group carboxyl is significantly reduced because they are adjacent to each other. Therefore, the aggregation of nanoparticles is not well suppressed. Thus, from... Figure 10 Scanning electron microscopy (SEM) revealed that the film still exhibited an uneven distribution of aggregated particles.

[0075] In the comparative experiments above, Comparative Example 1 used the commonly used organic ligand mercaptoacetic acid, which lacked a benzene ring. The linear ligand resulted in low conductivity of the final film, and the steric hindrance was not significant, leading to large and non-uniform nanoparticle sizes. Comparative Example 2 introduced a benzene ring into the ligand, but the steric hindrance of the mercapto group of the ligand anchoring group was not as large as that of the sulfonate group in Example 1, resulting in non-uniform nanoparticle sizes. Comparative Example 3 introduced a benzene ring, but the acidity constant of the anchoring group was higher than the pH value of the precursor solution, making it impossible to react with tin dioxide to form a film. Comparative Example 4 introduced a benzene ring and an organic ligand with a low acidity constant, but the anchoring group and the tail group were in the ortho position, significantly weakening the electrostatic repulsion between nanoparticles and resulting in insignificant suppression of aggregation.

[0076] Figure 11 Cross-sectional TEM images show that the tin dioxide film prepared in Example 1 is uniformly and conformally coated on the textured (wrinkled) FTO substrate. Since the application of a textured FTO substrate can increase the photocurrent of the device, depositing a conformal tin dioxide transport layer on the textured substrate is the best way to obtain the maximum photocurrent gain and reduce the series resistance of electron extraction, thereby increasing the device fill factor. Furthermore, since the tin dioxide electron transport layer needs to be very thin, only tens of nanometers, to ensure low series resistance, it requires the stacking of small and uniform 3-5 nm nanoparticles into a uniform film. Example 1 meets this requirement, while the nanoparticles formed in Comparative Examples 1 and 2 are non-uniform, even exceeding hundreds of nanometers. This results in a non-dense film with pores, significantly increasing parallel resistance and leakage current, leading to a degraded device performance.

[0077] Figure 12 The IV curves show that the conductivity is highest in Example 1, at 7.17 × 10⁻⁶. -3 mS cm -1 The relatively poor results for Comparative Examples 1 and 2 were 6.41 × 10⁻⁶. -3 mS cm -1 and 6.82 × 10 -3 mS cm -1 The obtained conductivity data indicate that the benzene ring conjugated structure is more conducive to realizing a high-conductivity tin dioxide electron transport layer.

[0078] Based on the tin dioxide electron transport layer (with a textured FTO substrate) prepared in Example 1, Comparative Example 1, and Comparative Example 2, perovskite solar cell devices were further fabricated according to the following methods:

[0079] 1. Preparation of perovskite active layer:

[0080] In a solvent system of N,N-dimethylformamide (DMF):dimethyl sulfoxide (DMSO) at a ratio of 4:1, 1.4 mol / L formamidinium iodide (FAI), 1.6 mol / L lead iodide (PbI2), 0.084 mol / L cesium iodide (CsI), and 0.14 mol / L chloromethylamine (MACl) were added and mixed and shaken for no more than 5 hours until completely dissolved. 20 μL of the resulting perovskite precursor solution was dropped onto the substrate with the prepared tin dioxide electron transport layer, and then spin-coated for 35 seconds at an acceleration of 1000 rpm / s to 4000 rpm. During the last 8 seconds of the spin-coating process, 150 μL of ethyl acetate was added as an antisolvent. After spin-coating, the formed wet film was annealed on a hot plate at 130 °C for 60 minutes to form a perovskite active layer film with a thickness of 900 nm.

[0081] 2. Deposition of the upper interface passivation layer:

[0082] After the substrate has cooled to room temperature, a layer of large cationic organic amine salt interface passivating agent is coated on its surface. The specific procedure is as follows: a 4 mg / mL solution of n-octylamine bromide isopropanol (100 μL) is uniformly dropped onto the substrate with the perovskite active layer, and then spin-coated at an acceleration of 4000 rpm / s to 4000 rpm for 30 seconds to complete the interface modification treatment.

[0083] 3. Preparation of the hole transport layer:

[0084] 72.3 mg of 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene (Spiro-OMeTAD) was weighed and added to 36 μL of a 260 mg / mL lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) acetonitrile solution and 30 μL of benzoyl butyl peroxide (t-BP) solution. These solutions were then dissolved together in 1 mL of chlorobenzene to prepare a hole transport material solution. Subsequently, this solution was dropwise added to the surface of a substrate that had undergone interface passivation treatment, and spin-coated at 4000 rpm for 30 seconds to prepare a hole transport layer with a thickness of 50 nm.

[0085] 4. Metal electrode deposition:

[0086] The battery device was fabricated by depositing an 80 nm gold electrode using vacuum evaporation.

[0087] The performance and stability of the perovskite solar cell devices prepared above were tested:

[0088] A thin metal sheet with a thickness of 0.1 mm and an opening area of ​​0.08 cm² was used as a light-shielding template. Under standard AM 1.5G illumination conditions provided by a 3A-level solar simulator, the device underwent current-voltage (current-voltage) analysis. J – V Characteristic testing. The final device performance is shown in Table 1. The comparison shows that the device fabricated based on the tin dioxide electron transport layer of Example 1 achieves an efficiency improvement of over 2%, with the open-circuit voltage... V oc and fill factor FF Significant improvements were achieved under this ligand screening strategy; the tin dioxide electron transport layer in Example 1 has the best electron extraction capability and suitable band position, which significantly reduces the nonradiative recombination loss of the device, the open-circuit voltage loss of the device is less than 300 meV, and the fill factor exceeds 86%.

[0089] The photoelectric conversion efficiency data of the perovskite photovoltaic devices further prepared based on the electron transport layers of Examples 1 and 2 and Comparative Examples 1 to 4 are summarized in Table 1.

[0090] Table 1

[0091]

[0092] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for preparing an electron transport layer of SnO2 nanoparticles, characterized in that, Includes the following steps: S1, add divalent tin source and organic ligand to deionized water, adjust the pH of the solution to 1.5-3.0, and mix evenly to obtain the precursor solution; Wherein: the organic ligand is 3-sulfobenzoic acid or 4-sulfobenzoic acid; S2 involves immersing a textured conductive glass substrate in a precursor solution, performing in-situ deposition in a sealed environment at temperatures below 100 °C, and then annealing to obtain an electron transport layer of SnO2 nanoparticles assembled from uniform ultra-small nanoparticles of 3-5 nm.

2. The method for preparing the SnO2 nanoparticle electron transport layer according to claim 1, characterized in that, The divalent tin source is stannous chloride dihydrate.

3. The method for preparing the SnO2 nanoparticle electron transport layer according to claim 1, characterized in that, Add 0.0008-0.0020 mol of divalent tin source and 0.00025-0.00040 mol of organic ligand to every 100 mL of deionized water.

4. The method for preparing the SnO2 nanoparticle electron transport layer according to claim 1, characterized in that, The temperature range for the in-situ deposition is 60-95 ℃.

5. The method for preparing the SnO2 nanoparticle electron transport layer according to claim 1, characterized in that, The conductive glass is textured FTO glass or ITO glass.

6. The method for preparing the SnO2 nanoparticle electron transport layer according to claim 1, characterized in that, In step S1, a pH control agent is used to adjust the pH value of the solution. The pH control agent is one or two of an acid and a base. The acid is concentrated hydrochloric acid or citric acid, and the base is urea or ammonia.

7. A perovskite solar cell, characterized in that, Its electron transport layer is prepared by the method described in any one of claims 1-6, which is a SnO2 nanoparticle electron transport layer.

8. The perovskite solar cell according to claim 7, characterized in that, It comprises conductive glass, an electron transport layer, a perovskite active layer, an organic ammonium salt passivation layer, a hole transport layer, and a metal electrode, which are sequentially laminated along the thickness direction.

9. The perovskite solar cell according to claim 8, characterized in that, The conductive glass is textured FTO glass or ITO glass. And / or, the material of the perovskite active layer is selected from FAPbI3, MA x FA 1-x PbI3, MA x Cs y FA 1-x-y PbI3, Cs x FA 1- x At least one of PbI3, wherein x and y are both less than 1; And / or, the material of the organic ammonium salt passivation layer is selected from phenylethylamine bromide, phenylethylamine iodide, or n-octylamine bromide; And / or, the material of the hole transport layer is selected from Spiro-OMeTAD; And / or, the material of the metal electrode is a conductive metal or a conductive metal alloy.

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