Tin oxide electron transport layer and application thereof in perovskite solar cell

Abstract

This invention discloses a tin oxide electron transport layer and its application in perovskite solar cells. The tin oxide electron transport layer is a Cr₂O₃ / SnO₂ nanoheterojunction formed by chromium trioxide distributed on the surface of tin oxide nanoparticles. Its preparation method includes the following steps: adding ammonium chromate to a tin oxide nanoparticle precursor solution, processing a tin oxide precursor film on a substrate, and annealing to obtain the final product. In this invention, ammonium chromate can effectively improve the agglomeration of tin oxide, thereby obtaining a flat, high-quality tin oxide electron transport layer. The Cr₂O₃ / SnO₂ transport layer induces the formation of a regular, low-residual-stress perovskite film during the epitaxial growth of perovskite, resulting in larger grain sizes and fewer pinholes and grain boundaries, reducing bulk phase recombination, and effectively improving the efficiency and long-term stability of the solar cell. The energy conversion efficiency of a perovskite solar cell with tin oxide nanoparticles as the electron transport layer, treated using the method of this invention, can reach 25.3%.

Description

Technical Field

[0001] This invention relates to a tin oxide electron transport layer and its application in perovskite solar cells, belonging to the field of optoelectronic functional materials and devices technology. Background Technology

[0002] Solar cells are devices that convert sunlight into electrical energy, offering advantages such as being pollution-free, renewable, and distributed. However, currently widely used silicon solar cells suffer from drawbacks such as high energy consumption during fabrication and complex manufacturing processes, and cannot meet the demands for thin, flexible photovoltaic cells in applications such as building-integrated photovoltaics, portable energy, and wearable energy. Perovskite photovoltaics, as an emerging photovoltaic technology, not only rivals the efficiency of crystalline silicon photovoltaics in laboratory settings but also boasts significant advantages in cost and manufacturing processes (J. Park, J. Kim, HSYun, MJ Paik, E. Noh, HJ Mun, MG Kim, TJShin, SISeok, Nature 2023, 616, 724-730.), while also possessing advantages such as thinness and flexibility, making it a potential complementary technology to crystalline silicon solar cells in the future. Since its initial development in 2012, the power conversion efficiency (PCE) of perovskite solar cells has increased at an astonishing rate (Q. Tan, Z. Li, G. Luo, X. Zhang, B. Che, G. Chen, H. Gao, D. He, G. Ma, J. Wang, J. Xiu, H. Yi, T. Chen, Z. He, Nature 2023. DOI:10.1038 / s41586-41023-06207-41580.), currently reaching a record efficiency of 26.0%. Furthermore, perovskite photovoltaics exhibit excellent photoelectric properties, characterized by high absorption coefficients, tunable photoelectric characteristics, and excellent bipolar delivery capabilities. At the same time, it has the advantages of low material consumption, low component price, and low investment cost, which makes perovskite photovoltaics more promising in terms of application scenarios. In the future, it is expected to bring photovoltaic applications into thousands of households and provide energy for household appliances (B.Parida, A.Singh, A.K.Kalathil Soopy, S.Sangaraju, M.Sundaray, S.Mishra, S.F.Liu, A.Najar, Adv Sci 2022, 9, e2200308.).

[0003] However, during the fabrication of perovskite solar cells, the mobility of the carrier transport layer (including the electron transport layer and the hole transport layer) and the energy level matching between the carrier transport layer and the perovskite layer can affect carrier transport and easily lead to various crystal defects (J.Liu,S.Li,S.Liu,Y.Chu,T.Ye,C.Qiu,Z.Qiu,X.Wang,Y.Wang,Y.Su,Y.Hu,Y.Rong,A.Mei,H.Han,Angew.Chem.,Int.Ed.2022,61,e202202012.). These defects at the transport layer interfaces become nonradiative recombination centers for charge carriers, affecting the carrier transport process and causing mismatched energy level structures between functional layers, thus hindering the performance and stability of perovskite solar cells (JHLee, S. Lee, T. Kim, H. Ahn, GYJang, KHKim, YJCho, K. Zhang, J.-S. Park, JHPark, Joule 2023, 7, 380-397.). Lower defect density can effectively reduce nonradiative recombination of charge carriers (J. Song, H. Liu, W. Pu, Y. Lu, Z. Si, Z. Zhang, Y. Ge, N. Li, H. Zhou, W. Xiao, L. Wang, M. Sui, Energy & Environmental Science 2022, 15, 4836-4849.). Meanwhile, the morphology of the carrier transport layer affects the morphology of the perovskite photoactive material epitaxially grown on it. A rough morphology of the carrier transport layer will lead to pinholes, cracks, and large tensile stresses, thereby reducing the film quality (C.Wu, W.Fang, Q.Cheng, J.Wan, R.Wen, Y.Wang, Y.Song, M.Li, Angew.Chem.,Int.Ed.2022,61,e202210970.). Therefore, modification and alteration of the carrier transport layer is an indispensable method to improve the efficiency and stability of perovskite solar cells, and also an effective strategy to reduce grain boundary and interlayer surface defects (D.Luo, X.Li, A.Dumont, H.Yu, ZHLu,Adv.Mater.2021,33,e2006004.). Summary of the Invention

[0004] The purpose of this invention is to provide a tin oxide electron transport layer to solve the problems of rough morphology, energy level mismatch, and low electron mobility in the prior art.

[0005] The tin oxide electron transport layer provided by the present invention is a Cr2O3 / SnO2 nanoheterojunction formed by chromium trioxide distributed on the surface of tin oxide nanoparticles.

[0006] This invention also provides a method for preparing a tin oxide electron transport layer, comprising the following steps:

[0007] Ammonium chromate was added to a tin oxide nanoparticle precursor solution to form a tin oxide precursor film on a substrate; the film was then annealed to obtain the precursor.

[0008] In the above preparation method, the tin oxide nanoparticle precursor solution is obtained by dispersing tin oxide nanoparticles in a solvent;

[0009] The solvent may be one or more of water, alcohols, esters, ethers, nitriles, alkanes, chlorinated hydrocarbons, aromatic hydrocarbons, and halogenated aromatic hydrocarbons;

[0010] The alcohols include, but are not limited to, one or more of ethanol, isopropanol, n-butanol, isobutanol, isoamyl alcohol, and ethylene glycol;

[0011] The esters include, but are not limited to, one or more of ethyl acetate, methyl acetate, and butyl acetate;

[0012] The ethers include, but are not limited to, one or more of diethyl ether, methyl ethyl ether, n-propyl ether, n-butyl ether, isopropyl ether, anisole, and tetrahydrofuran;

[0013] The nitrile compounds include, but are not limited to, acetonitrile and / or benzonitrile;

[0014] The alkanes include, but are not limited to, cyclohexane and / or n-hexane;

[0015] The chlorinated hydrocarbons include, but are not limited to, chloroform;

[0016] The aromatic hydrocarbons include, but are not limited to, one or more of toluene, o-xylene, and m-xylene;

[0017] The halogenated aromatic hydrocarbons include, but are not limited to, one or more of chlorobenzene, o-dichlorobenzene, mesitylene, and trifluoromethylbenzene.

[0018] In the above preparation method, the mass concentration of tin oxide nanoparticles in the tin oxide nanoparticle precursor solution is 1% to 15%, preferably any value or any range of 1%, 5% and 15%.

[0019] In the above preparation method, the amount of ammonium chromate added is 0.1% to 5% of the molar amount of tin oxide nanoparticles, preferably any value or any range of 0.1%, 1%, 4% and 5%.

[0020] In the above preparation method, the processing methods include spin coating, blade coating, slot coating, inkjet printing, and chemical bath growth.

[0021] In the above preparation method, the annealing temperature is 100-300℃ and the time is 5-90 minutes, so as to remove the solvent in the tin oxide precursor solution and to deposit tin oxide into a smooth and dense film.

[0022] During the annealing process, due to the oxidizing properties of ammonium chromate, the ammonium chromate adsorbed on the surface of nanoparticles can undergo redox reactions with oxygen vacancies and hydroxyl groups on the surface of tin oxide.

[0023] The specific reaction formulas for ammonium chromate and the oxygen vacancies and OH dangling bonds on the surface of tin oxide nanoparticles are as follows:

[0024]

[0025]

[0026] Therefore, ammonium chromate can effectively passivate the defect states on the surface of tin oxide nanoparticles, optimize carrier transport characteristics, reduce non-radiative recombination energy loss, and effectively enhance its ability as a carrier transport layer, thereby improving the efficiency of perovskite solar cells.

[0027] The tin oxide electron transport layer provided by this invention can be used as an electron transport layer in perovskite solar cells, and its thickness is typically 10–30 nm.

[0028] Preferably, the structure of the solar cell, from bottom to top, includes a first electrode, a first transport layer, a perovskite thin film, a second transport layer, and a second electrode.

[0029] Specifically, the solar cell adopts a forward structure, with the first transport layer being a tin oxide electron transport layer; the second transport layer is a hole transport layer, including but not limited to Spiro-OMeTAD, PEDOT-PSS, PTAA, P3HT, and nickel oxide (NiO). x Any one of them.

[0030] Compared with the prior art, the present invention has the following beneficial technical effects:

[0031] (1) The ammonium chromate added in this invention reacts with the redox reaction on the surface of tin oxide nanoparticles during the annealing process, passivating the oxygen vacancy defects and surface hydroxyl groups on the surface of tin oxide nanoparticles, reducing the defect state concentration on the surface of tin oxide, and the generated chromium trioxide is distributed on the surface of tin oxide nanoparticles to form a nano heterojunction Cr2O3 / SnO2, which reduces the recombination at the interface of adjacent nanoparticles, effectively improves the electron mobility of the electron transport layer, and optimizes the energy level arrangement between the perovskite photoactive layer.

[0032] (2) In this invention, the electron transport layer of the Cr2O3 / SnO2 heterojunction modified product and the perovskite photoactive layer form an optimized energy level arrangement: the conduction band top of the Cr2O3 / SnO2 electron transport layer moves upward, reducing the voltage loss at the interface between the perovskite photoactive layer and the electron transport layer. At the same time, the built-in electric field in the heterojunction hinders the unfavorable transport of electrons from tin oxide nanoparticles to the lower interface of the perovskite, realizing the spatial separation of electron and hole transport, thereby forming an optimized energy level arrangement.

[0033] (3) In this invention, ammonium chromate can effectively improve the agglomeration of tin oxide, thereby obtaining a flat and high-quality tin oxide electron transport layer. Through the Cr2O3 / SnO2 transport layer, a regular perovskite film with low residual stress is induced to form during the epitaxial growth of perovskite, resulting in larger grain size and fewer pinholes and grain boundaries, reducing bulk phase recombination, and effectively improving the efficiency and long-term stability of solar cells.

[0034] (4) The energy conversion efficiency of perovskite solar cells with tin oxide nanoparticles as electron transport layers treated by the method of the present invention can reach 25.3%. Attached Figure Description

[0035] Figure 1 The image shows the AFM pattern of the electron transport layer prepared by the method in Example 1 of this invention.

[0036] Figure 2 The image shows the AFM diagram of the electron transport layer prepared by the method in Comparative Example 1 of this invention.

[0037] Figure 3 These are resistance test images of the electron transport layers prepared in Example 1 and Comparative Example 1 of the present invention;

[0038] Figure 4 The images show the Raman spectra of the tin oxide electron transport layers obtained in Example 1 and Comparative Example 1 of this invention.

[0039] Figure 5 The X-ray photoelectron spectra of the tin oxide electron transport layers obtained in Example 1 and Comparative Example 1 of this invention are shown below.

[0040] Figure 6 This is an HRTEM image of ammonium chromate reacting with the surface of tin oxide nanoparticles in Example 1 of the present invention. Detailed Implementation

[0041] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0042] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0043] Example 1: Preparation of Tin Oxide Electron Transport Layer Thin Film

[0044] (1) Dilute 300 μL of tin oxide nanoparticle aqueous dispersion (15 wt%) with deionized water and stir to mix evenly. The volume ratio of tin oxide nanoparticle aqueous dispersion to deionized water is 1:2. Add 1.8 mg of ammonium chromate, which accounts for 4% of the molar fraction of tin oxide nanoparticles. Stir to dissolve evenly to obtain a mixed solution. The mass fraction of tin oxide nanoparticles in the tin oxide nanoparticle precursor solution is 5%.

[0045] (2) The mixed solution was dropped onto the FTO substrate and spin-coated at 3000 rpm for 30 seconds with an acceleration of 2000 rpm to form a tin oxide precursor film. The tin oxide precursor film was transferred to a hot stage and annealed at 180°C for 20 minutes to remove excess solvent and promote the reaction between ammonium chromate and the surface of tin oxide nanoparticles to obtain a tin oxide electron transport layer film.

[0046] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this embodiment (according to Application Example 1) has an open-circuit voltage of 1.172V and a short-circuit current of 25.54mA / cm. 2 The fill factor is 84.5%, and the battery conversion efficiency is 25.29%.

[0047] Example 2

[0048] The tin oxide modification method in this embodiment is the same as that in Example 1, except that the molar ratio of tin oxide nanoparticles to ammonium chromate in step (1) is 1000:1.

[0049] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this embodiment (according to Application Example 1) has an open-circuit voltage of 1.141V and a short-circuit current of 25.24mA / cm. 2 The fill factor is 82.5%, and the battery conversion efficiency is 23.76%.

[0050] Example 3

[0051] The tin oxide modification method in this embodiment is the same as that in Example 1, except that the molar ratio of tin oxide nanoparticles to ammonium chromate in step (1) is 100:1.

[0052] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this embodiment (according to Application Example 1) has an open-circuit voltage of 1.149V and a short-circuit current of 25.42mA / cm. 2 The fill factor is 82.9%, and the battery conversion efficiency is 24.21%.

[0053] Example 4

[0054] The tin oxide modification method in this embodiment is the same as that in Example 1, except that the molar ratio of tin oxide nanoparticles to ammonium chromate in step (1) is 20:1.

[0055] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this embodiment (according to Application Example 1) has an open-circuit voltage of 1.152V and a short-circuit current of 25.45mA / cm. 2 The fill factor is 83.4%, and the battery conversion efficiency is 24.45%.

[0056] Example 5

[0057] The tin oxide modification method in this embodiment is the same as that in Example 1, except that the mass fraction of tin oxide nanoparticles in the tin oxide nanoparticle precursor solution in step (1) is 15%.

[0058] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this embodiment (according to Application Example 1) has an open-circuit voltage of 1.150V and a short-circuit current of 25.05mA / cm. 2 The fill factor is 82.4%, and the battery conversion efficiency is 23.74%.

[0059] Example 6

[0060] The tin oxide modification method in this embodiment is the same as that in Example 1, except that the mass fraction of tin oxide nanoparticles in the tin oxide nanoparticle precursor solution in step (1) is 1%.

[0061] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this embodiment (according to Application Example 1) has an open-circuit voltage of 1.132V and a short-circuit current of 25.15mA / cm. 2 The fill factor is 81.1%, and the battery conversion efficiency is 23.09%.

[0062] Example 7

[0063] The tin oxide modification method in this embodiment is the same as that in Example 1, except that the annealing temperature in step (2) is 150°C and the annealing time is 30 minutes.

[0064] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this embodiment (according to Application Example 1) has an open-circuit voltage of 1.168V and a short-circuit current of 25.42mA / cm. 2 The fill factor is 84.2%, and the battery conversion efficiency is 25.00%.

[0065] Example 8

[0066] The tin oxide modification method in this embodiment is the same as that in Example 1, except that the annealing temperature in step (2) is 200°C and the annealing time is 15 minutes.

[0067] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this embodiment (according to Application Example 1) has an open-circuit voltage of 1.165V and a short-circuit current of 25.46mA / cm. 2 The fill factor is 83.1%, and the battery conversion efficiency is 24.65%.

[0068] Comparative Example 1

[0069] The preparation method of the metal oxide electron transport layer in this comparative example is the same as that in Example 1, except that ammonium chromate is not added in step (1).

[0070] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this comparative example (according to Application Example 2) has an open-circuit voltage of 1.136V and a short-circuit current of 25.12mA / cm. 2 The fill factor is 83.2%, and the battery conversion efficiency is 23.75%.

[0071] Comparative Example 2

[0072] The tin oxide modification method in this embodiment is the same as that in Example 1, except that the molar ratio of tin oxide nanoparticles to ammonium chromate in step (1) is 10:1.

[0073] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this comparative example (according to Application Example 2) has an open-circuit voltage of 1.141 V and a short-circuit current of 25.14 mA / cm². 2 The fill factor is 82.3%, and the battery conversion efficiency is 23.61%.

[0074] Comparative Example 3

[0075] The preparation method of the metal oxide electron transport layer in this comparative example is the same as that in Example 1, except that the annealing temperature in step (2) is 90°C.

[0076] The perovskite solar cell device fabricated using the tin oxide electron transport layer prepared in this comparative example (according to Application Example 2) has an open-circuit voltage of 1.121 V and a short-circuit current of 24.14 mA / cm². 2 The fill factor is 80.3%, and the battery conversion efficiency is 21.73%.

[0077] Test Example 1

[0078] The AFM patterns of the tin oxide electron transport layer films prepared in Example 1 and Comparative Example 1 were tested respectively, as follows: Figure 1 and Figure 2 As shown, from Figure 1 and Figure 2 As can be seen, the introduction of ammonium chromate reduces surface roughness, improves film morphology, and enhances film quality.

[0079] Test Example 2

[0080] The conductivity, Raman spectrum, and X-ray photoelectron spectrum of the tin oxide electron transport layer films obtained in Example 1 and Comparative Example 1 were tested respectively, as shown below. Figure 3 , Figure 4 and Figure 5 As shown.

[0081] from Figure 3 As can be seen, the tin oxide film modified with ammonium chromate exhibits higher conductivity. Figure 4 It can be seen from the Raman shift that the peak height corresponding to the OH dangling bond decreases, from Figure 5 The results show that the peak area corresponding to oxygen defects in the X-ray photoelectron spectrum is smaller, indicating that the defects on the surface are reduced, non-radiative recombination is suppressed, and the quality of the transport layer film is greatly improved.

[0082] Test Example 3

[0083] The high-resolution transmission electron microscopy (HRTEM) image of the product after the redox reaction of ammonium chromate with tin oxide surface defects in Example 1 is shown below. Figure 6 As shown.

[0084] Application Example 1

[0085] The fabricated device structure, from bottom to top, is FTO / ETL / FAPbI3 perovskite / Spiro-OMeTAD / MoO x / Ag forward perovskite solar cells

[0086] The ETL used in this application example is Cr2O3 / SnO2 prepared in Example 1.

[0087] The specific fabrication method of the solar cell in this application example is as follows:

[0088] (1) Cleaning of FTO glass substrate: FTO was ultrasonically cleaned for 20 minutes with cleaning solution, deionized water, acetone and isopropanol respectively. After cleaning, the FTO substrate was immersed in isopropanol for use. When using, it was dried with nitrogen and treated with ultraviolet UVO for 30 minutes for use.

[0089] (2) Preparation of SnO2 electron transport layer: The method is the same as in Example 1. It is prepared on FTO substrate and treated with UVO for 30 minutes before use.

[0090] (3) Preparation of FAPbI3 perovskite thin film: 922 mg lead iodide, 344 mg formamidin hydroiodide and 47.3 mg methylamine hydrochloride were added to a mixed solvent of N,N-dimethylformamide and dimethyl sulfoxide and stirred until homogeneous to obtain a precursor solution. The volume ratio of N,N-dimethylformamide to dimethyl sulfoxide was 8:1 and the concentration of perovskite in the perovskite precursor solution was 1.8 mol / L. The mixed solution was dropped onto an FTO / SnO2 substrate and spin-coated at 5000 rpm for 20 seconds with an acceleration of 3000 rpm. At the 10th second, 800 μL of antisolvent diethyl ether was spin-coated to remove excess solvent. The solution was then transferred to a hot plate and annealed at 120 °C for 60 minutes to obtain a perovskite thin film.

[0091] (4) Preparation of Spiro-OMeTAD hole transport layer: Preparation of Spiro-OMeTAD solution: Dissolve 90 mg Spiro-OMeTAD in 1 mL of chlorobenzene, then add 39 μL of 4-tert-butylpyridine, 22 μL of LiTFSI acetonitrile solution (520 mg / mL) and 12 μL of FK209 acetonitrile solution (300 mg / mL), mix well and spin coat at 5000 rpm for 30 seconds.

[0092] (5)MoO x Preparation of the layer: MoO x It was prepared by vapor deposition and has a thickness of 10 nanometers.

[0093] (5) Preparation of Ag electrode: The Ag electrode was prepared by vapor deposition and the thickness was 100 nanometers.

[0094] The solar cell obtained in this application example was tested at AM1.5G, 100mW / cm². 2 The photovoltaic performance parameters under illumination conditions are shown in Table 1.

[0095] Table 1 Performance of Solar Cells

[0096]

[0097] Application Example 2

[0098] The solar cell in this application example is prepared using the same method as in application example 1, except that the tin oxide electron transport layer is prepared using the method described in comparative example 1.

[0099] The solar cell obtained in this comparative test was tested at AM1.5G, 100mW / cm². 2 The photovoltaic performance parameters under illumination conditions are shown in Table 2.

[0100] Table 2 Performance of Solar Cells

[0101]

[0102] Compared to Application Example 2, Application Example 1 exhibits a higher open-circuit voltage and fill factor, resulting in higher device efficiency. This demonstrates that the addition of ammonium chromate can effectively improve device efficiency. On one hand, ammonium chromate reduces interfacial carrier recombination due to the modification of surface defects on tin oxide. On the other hand, the chromium trioxide product of the redox reaction between ammonium chromate and tin oxide effectively fills the gaps between nanoparticles, reducing the roughness of the carrier transport layer, thereby enabling the epitaxial growth of high-quality, stress-negligible perovskite films.

[0103] In summary, the introduction of ammonium chromate can significantly improve carrier transport and induce the growth of high-quality perovskite thin films, thereby obtaining more efficient perovskite solar cell devices.

Claims

1. A tin oxide electron transport layer, which is a Cr2O3 / SnO2 nanoheterojunction formed by chromium trioxide distributed on the surface of tin oxide nanoparticles; The method for preparing the tin oxide electron transport layer includes the following steps: Ammonium chromate was added to a tin oxide nanoparticle precursor solution to form a tin oxide precursor film on a substrate; the film was then annealed to obtain the precursor.

2. The tin oxide electron transport layer according to claim 1, characterized in that: The tin oxide nanoparticle precursor solution is obtained by dispersing tin oxide nanoparticles in a solvent; The solvent is one or more of water, alcohols, esters, ethers, nitriles, alkanes, chlorinated hydrocarbons, aromatic hydrocarbons, and halogenated aromatic hydrocarbons.

3. The tin oxide electron transport layer according to claim 1 or 2, characterized in that: The tin oxide nanoparticle precursor solution has a mass concentration of 1%-15% for tin oxide nanoparticles.

4. The tin oxide electron transport layer according to claim 1 or 2, characterized in that: The amount of ammonium chromate added is 0.1-5% of the molar amount of the tin oxide nanoparticles.

5. The tin oxide electron transport layer according to claim 1 or 2, characterized in that: The processing methods include spin coating, blade coating, slot coating, inkjet printing, or chemical bath growth.

6. The tin oxide electron transport layer according to claim 1 or 2, characterized in that: The annealing process is carried out at a temperature of 100-400℃ for 5-90 minutes.

7. The use of the tin oxide electron transport layer according to any one of claims 1-6 in the fabrication of perovskite solar cells.

8. A perovskite solar cell, wherein the electron transport layer is the tin oxide electron transport layer as described in any one of claims 1-6.

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