Perovskite solar cell based on fulleropyrrolidine electron transport layer

Abstract

The application discloses a perovskite solar cell based on fulleropyrrolidine electron transport layer and belongs to the solar cell field. The application adopts fulleropyrrolidine (FMG) as a functionalized electron transport layer material, forms a gradient heterojunction structure with a perovskite thin film photosensitive layer, and prepares a high-performance perovskite solar cell based on the fulleropyrrolidine electron transport layer. The electron transport layer material FMG in the solar cell has good solution processing and surface infiltration capacity on the surface of the halogenated lead perovskite, can form a dense and smooth fullerene film, blocks the migration of the metal electrode, and at the same time, part of the FMG molecules penetrates into the perovskite thin film to form a gradient heterojunction structure, realizes efficient electron extraction and grain boundary passivation, improves the energy conversion efficiency and illumination stability of the solar cell device, and the energy conversion efficiency can reach 23.8%.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of solar cells, and particularly relates to a perovskite solar cell based on a fullerene pyrrolidine electron transport layer. BACKGROUND

[0002] It is of great significance to convert solar energy into electricity by photoelectric conversion devices to provide enough clean energy for human beings. Therefore, efficient conversion of solar energy into electricity has become a focus and research hotspot in the academic and industrial fields. Among all the solar cells, inorganic solar cells dominated by silicon-based solar cells are the most mature, and have high energy conversion efficiency. However, the production and manufacturing process is costly and causes serious pollution. Therefore, it is an inevitable choice to develop new solar cells with low cost and environmental friendliness.

[0003] Organic-inorganic hybrid halide lead perovskite materials have excellent photoelectric properties such as high extinction coefficient, long carrier diffusion distance, and high defect tolerance, so that the perovskite solar cells have become the focus of emerging photovoltaic technology. The energy conversion efficiency of the perovskite solar cell has exceeded 25%, and the stability research and large component preparation of the perovskite solar cell have become the focus direction, which also represents that the perovskite solar cell technology is further commercialized.

[0004] However, ion migration significantly restricts the efficiency and stability of the perovskite solar cell. Ion migration not only leads to the decrease of the efficiency of the perovskite solar cell device, but also accelerates the degradation of the perovskite, greatly shortening the service life. In the existing technology, small molecule passivation reagents are added to the perovskite precursor solution or the perovskite film is subjected to surface post-treatment to passivate the grain boundary defects of the perovskite, inhibit ion migration, and improve the efficiency of the battery. In the existing technology, defect passivation functions are also integrated into the existing functional layer, but this method will weaken the original function or passivation effect. Fullerene materials have good electron extraction and transmission capacity, and the passivation function can achieve the dual functions of electron extraction and defect passivation. Therefore, fullerene materials can be used as electron transport layer materials to develop high-efficiency and stable perovskite solar cells. SUMMARY

[0005] The application aims to overcome the shortcomings of the prior art, and a high-performance perovskite solar cell is prepared by a method of forming a gradient heterojunction structure of a functionalized fullerene electron transport material and a perovskite. Specifically, a perovskite solar cell based on a fullerene electron transport layer is provided.

[0006] The application adopts fulleropyrrolidine molecules (FMG) containing three ethoxyl monomethyl ether groups as an electron transport layer material, forms a dense and smooth fullerene film on the perovskite surface by means of solution processing and surface infiltration capacity of the FMG on the perovskite surface, and realizes efficient electron extraction and grain boundary passivation by means of partial penetration of the FMG molecules into the perovskite film photoactive layer to form a gradient heterojunction structure, so that a high-efficiency and stable perovskite solar cell is developed.

[0007] The specific technical scheme adopted in the application is as follows:

[0008] The application provides a perovskite solar cell based on a fulleropyrrolidine electron transport layer.

[0009] The material of the photoactive layer is perovskite; the electron transport layer material adopts fulleropyrrolidine FMG, and the specific chemical structural formula is as follows:

[0010] The electron transport layer is a dense and smooth film, and there is no mutual penetration between the electron transport layer and the metal electrode layer, and part of the fulleropyrrolidine molecules in the electron transport layer penetrate into the photoactive layer along the grain boundary of the perovskite to form a gradient heterojunction structure in which the content of the fulleropyrrolidine molecules decreases along the penetration direction.

[0011] Preferably, the thickness of the electron transport layer is 2-200 nm.

[0012] Preferably, the substrate material is one of glass, quartz, flexible polyethylene terephthalate (PET) or flexible polyethylene naphthalate (PEN).

[0013] Preferably, the transparent electrode layer material is indium tin oxide or fluorine-doped tin oxide.

[0014] Preferably, the material of the hole transport layer is one of PTAA or nickel oxide nanoparticles or a combination of both.

[0015] Preferably, the material of the photoactive layer adopts one of methylammonium lead bromide, formamidinium lead iodide or a mixture thereof, the chemical structural general formula of the methylammonium lead bromide is CH3NH3PbI3, the chemical structural general formula of the formamidinium lead iodide is HC(NH2)2PbI3, and the chemical structural general formula of the mixture of the methylammonium lead bromide and the formamidinium lead iodide can be represented as (CH3NH3PbBr3) x ·(HC(NH2)2PbI3) 1-x , wherein 0≤x≤1.

[0016] Preferably, the metal electrode layer material is one of silver, aluminum, magnesium, copper, gold, indium tin oxide or fluorine-doped tin oxide.

[0017] Preferably, the thickness of the metal electrode layer is 50-300 nm.

[0018] In a second aspect, the present application provides a method for preparing the perovskite solar cell of the first aspect, which specifically comprises the following steps:

[0019] S1: Preparation of a substrate and a transparent electrode layer:

[0020] The ITO glass substrate (i.e. substrate + transparent electrode layer) is sequentially cleaned with a cleaning agent, deionized water, acetone and isopropanol by ultrasonic oscillation for 15 minutes, dried by nitrogen flow, and then treated with oxygen plasma for 20 minutes.

[0021] S2: Preparation of a hole transport layer:

[0022] Nickel (II) nitrate hexahydrate and ethylenediamine are dissolved in ethylene glycol at a molar ratio of 1:1 at a concentration of 1 mol / L, and then 5% of a molar amount of potassium chloride aqueous solution is added, and stirred at room temperature, and filtered with an organic filter head with a pore size of 22 microns to obtain a nickel oxide precursor solution.

[0023] Subsequently, the above nickel oxide precursor solution is spin-coated on the treated ITO glass substrate at a speed of 4000 rpm for 40 seconds, and then heated at 120°C for 10-15 minutes for pretreatment, and then an annealing process is performed at a hot stage of 300°C for 1 hour to prepare a hole transport layer containing a nickel oxide substrate. A PTAA solution with a concentration of 1 mg / mL is spin-coated on the above hole transport layer containing a nickel oxide substrate at a speed of 5000 rpm, and then annealed at 100°C for 10 minutes to complete the modification of the hole transport layer containing a nickel oxide substrate.

[0024] S3: Preparation of a perovskite thin film photoactive layer:

[0025] A perovskite precursor solution is prepared by mixing 1.5M methylammonium lead bromide solution and 1.5M formamidinium lead iodide solution at a molar ratio of 3:97. The methylammonium lead bromide solution is prepared by dissolving methylammonium bromide and lead bromide at a molar ratio of 1:1 in a mixed solvent of dimethylformamide and dimethyl sulfoxide at a concentration of 1.5M, and the formamidinium lead iodide solution is prepared by dissolving formamidinium iodide, lead iodide and methylammonium chloride at a molar ratio of 1:1:0.3 in a mixed solvent of dimethylformamide and dimethyl sulfoxide at a concentration of 1.5M. The volume ratio of dimethylformamide and dimethyl sulfoxide is 4:1.

[0026] 30 μL of the perovskite precursor solution is dropped on the substrate prepared in step S2 at a speed of 4000 rpm for 40 seconds, and then 120 μL of isopropanol is added after about 20 seconds of spin coating, and then annealed at 100°C for 30 minutes to obtain a perovskite thin film photoactive layer.

[0027] S4: electron transport layer preparation:

[0028] Fulleropyrrolidine (FMG) was dissolved in chlorobenzene solution to obtain a FMG / chlorobenzene solution with a concentration of 15 mg / mL. The solution was spin-coated on the above-mentioned perovskite thin film photoactive layer at a rotation speed of 3000 rpm for 30 seconds, and annealed at 100℃ for 5 minutes to obtain a fulleropyrrolidine-based electron transport layer.

[0029] S5: Bathocuproin (BCP) was dissolved in ethanol to obtain a BCP / ethanol solution with a concentration of 1 mg / mL. The solution was spin-coated on the above-mentioned electron transport layer at a rotation speed of 3000 rpm for 20 seconds. Then, 5×10 -4 A 100 nm thick silver electrode was deposited under high vacuum conditions to obtain a perovskite solar cell based on a fulleropyrrolidine electron transport layer.

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

[0031] (1) The present application uses fulleropyrrolidine molecules as electron transport layer materials, wherein the fullerene shell determines that the entire molecule has high conductivity, electron mobility, and basic functions of electron extraction and transport. The three ethoxymethyl ether flexible side chains have good solution processing properties and surface wetting properties, etc., so that they form a dense and smooth film on the rough surface of the photoactive layer, block the mutual diffusion of metal atoms and halogen ions, and improve the stability of the device. The oxygen atoms in the flexible chain are associated with ammonium salt cations and lead ions in the perovskite layer in the form of hydrogen bonding and Lewis acid-base interaction, which can well passivate the perovskite grain boundaries and surface defects, and improve the photovoltaic performance of the device. The perovskite solar cell prepared from the material has higher energy conversion efficiency and better light stability.

[0032] (2) The perovskite solar cell device based on the fulleropyrrolidine FMG molecule prepared in the present application has an energy conversion efficiency of up to 23.8%, while the perovskite solar cell device based on the fullerene derivative PCBM molecule in the comparative example has an energy conversion efficiency of up to 21.1%. Through 60 days of light aging test, it is found that the perovskite solar cell device based on the fulleropyrrolidine FMG molecule retains 85% of the initial efficiency, while the perovskite solar cell device based on the fullerene derivative PCBM molecule in the comparative example only retains 74% of the initial efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structural schematic diagram of the perovskite solar cell provided by the present application;

[0034] Figure 2is a current density-voltage curve of a perovskite solar cell based on FMG provided by the embodiment;

[0035] Figure 3 is a current density-voltage curve of a perovskite solar cell based on PCBM provided by the comparative example;

[0036] Figure 4 is a time-of-flight secondary ion mass spectrometer test experimental result of the perovskite solar cell prepared by the embodiment and the comparative example: wherein (a) and (b) are respectively relative intensity-sputtering time curves of the perovskite solar cells prepared by the embodiment and the comparative example, and (c) is a structural schematic diagram of the distribution of the silver electrode, the electron transport layer and the perovskite photoactive layer;

[0037] Figure 5 is an energy conversion efficiency-aging time curve of the perovskite solar cell based on FMG and PCBM provided by the embodiment and the comparative example. DETAILED DESCRIPTION

[0038] The present application will be further described and illustrated below in conjunction with the drawings and specific embodiments. The technical features of each embodiment in the present application can be combined accordingly without conflict.

[0039] EMBODIMENT

[0040] The present embodiment provides a perovskite solar cell based on fulleropyrrolidine FMG electron transport layer material, and the specific preparation method is as follows:

[0041] (1) Substrate and transparent electrode layer preparation:

[0042] The ITO glass substrate (i.e. substrate + transparent electrode layer) is sequentially cleaned with cleaning agent, deionized water, acetone and isopropanol for 15 minutes, dried with nitrogen flow, and then treated with oxygen plasma for 20 minutes.

[0043] (2) Hole transport layer preparation:

[0044] Nickel (II) nitrate hexahydrate and ethylenediamine are dissolved in ethylene glycol at a molar ratio of 1:1 at a concentration of 1 mol / L, and then 5% of the molar ratio of potassium chloride aqueous solution is added, and stirred at room temperature. The nickel oxide precursor solution is obtained by filtering with an organic filter head with a pore size of 22 microns.

[0045] Subsequently, the above nickel oxide precursor solution was spin-coated on the treated ITO glass substrate at a rotation speed of 4000 rpm for 40 seconds, and then preheated at 120°C for 10-15 minutes, and then annealed at 300°C for 1 hour to prepare a hole transport layer containing a nickel oxide substrate. A PTAA solution with a concentration of 1 mg / mL was spin-coated on the above hole transport layer containing a nickel oxide substrate at a rotation speed of 5000 rpm, and then annealed at 100°C for 10 minutes to complete the modification of the hole transport layer containing a nickel oxide substrate.

[0046] (3) Perovskite thin film photoactive layer preparation:

[0047] A perovskite precursor solution was prepared by mixing a 1.5M methylammonium lead bromide solution and a 1.5M formamidinium lead iodide solution at a molar ratio of 3:97. The methylammonium lead bromide solution was prepared by dissolving methylammonium bromide and lead bromide at a molar ratio of 1:1 at a concentration of 1.5M in a mixed solvent of dimethylformamide and dimethyl sulfoxide. The formamidinium lead iodide solution was prepared by dissolving formamidinium iodide, lead iodide, and methylammonium chloride at a molar ratio of 1:1:0.3 at a concentration of 1.5M in a mixed solvent of dimethylformamide and dimethyl sulfoxide. The volume ratio of dimethylformamide and dimethyl sulfoxide was 4:1.

[0048] 30 μL of the perovskite precursor solution was dropped onto the substrate prepared in step (2) at a rotation speed of 4000 rpm for 40 seconds. After about 20 seconds of spin coating, 120 μL of isopropanol was added, and then annealed at 100°C for 30 minutes to obtain a perovskite thin film photoactive layer.

[0049] (4) Electron transport layer preparation:

[0050] Fulleropyrrolidine (FMG) was dissolved in chlorobenzene to obtain a FMG / chlorobenzene solution with a concentration of 15 mg / mL. The solution was spin-coated on the above perovskite thin film photoactive layer at a rotation speed of 3000 rpm for 30 seconds, and then annealed at 100°C for 5 minutes to obtain a fulleropyrrolidine-based electron transport layer.

[0051] Bathocuproin (BCP) was dissolved in ethanol to obtain a BCP / ethanol solution with a concentration of 1 mg / mL. The solution was spin-coated on the above electron transport layer at a rotation speed of 3000 rpm for 20 seconds. Then, a 100 nm thick silver electrode was deposited in a vacuum chamber at a pressure of 5x10 -4 Pa to obtain a perovskite solar cell based on a fulleropyrrolidine electron transport layer. The area of the perovskite solar cell device was 0.06 cm 2 , which was determined by the area of the test mask.

[0052] The short-circuit current density (Jsc) of the perovskite solar cell was 15.6 mA / cm 2The current density-voltage curve of the perovskite solar cell based on the fullerene pyrrolidine electron transport layer prepared in this embodiment was tested under AM 1.5G simulated sunlight irradiation, and the results are shown in Figure 2 The open-circuit voltage of the device was 1.15 V, the short-circuit current density was 24.9 mA / cm 2 , the fill factor was 0.833, and the energy conversion efficiency was 23.8%.

[0053] Comparative Example

[0054] This embodiment provides a perovskite solar cell based on a fullerene derivative PCBM electron transport layer material, and the specific preparation method is as follows:

[0055] (1) Preparation of substrate and transparent electrode layer:

[0056] The ITO glass substrate (i.e. substrate + transparent electrode layer) was sequentially cleaned with cleaning agent, deionized water, acetone and isopropanol for 15 minutes, dried with nitrogen flow, and then treated with oxygen plasma for 20 minutes.

[0057] (2) Preparation of hole transport layer:

[0058] Nickel (II) nitrate hexahydrate and ethylenediamine were dissolved in ethylene glycol at a molar ratio of 1:1 at a concentration of 1 mol / L, and then 5% molar potassium chloride aqueous solution was added, and stirred at room temperature. The nickel oxide precursor solution was obtained by filtering with an organic filter head with a pore size of 22 microns.

[0059] Subsequently, the above nickel oxide precursor solution was spin-coated on the treated ITO glass substrate at a speed of 4000 rpm for 40 seconds, and then heated at 120°C for 10-15 minutes for pretreatment. A hole transport layer containing nickel oxide substrate was prepared by using a 300°C hot stage and annealing for 1 hour. A PTAA solution with a concentration of 1 mg / mL was spin-coated on the above hole transport layer containing nickel oxide substrate at a speed of 5000 rpm, and then annealed at 100°C for 10 minutes to complete the modification of the nickel oxide substrate hole transport layer.

[0060] (3) Preparation of perovskite thin film photoactive layer:

[0061] A perovskite precursor solution was prepared by mixing 1.5M methylammonium lead bromide solution and 1.5M formamidinium lead iodide solution at a molar ratio of 3:97. The methylammonium lead bromide solution was prepared by dissolving methylammonium bromide and lead bromide at a molar ratio of 1:1 in a mixed solvent of dimethylformamide and dimethyl sulfoxide at a concentration of 1.5M. The formamidinium lead iodide solution was prepared by dissolving formamidinium iodide, lead iodide and methylammonium chloride at a molar ratio of 1:1:0.3 in a mixed solvent of dimethylformamide and dimethyl sulfoxide at a concentration of 1.5M. The volume ratio of dimethylformamide and dimethyl sulfoxide was 4:1.

[0062] 30 μL perovskite precursor solution was dropped on the substrate prepared in step (2) at a rotation speed of 4000 rpm for 40 seconds; 120 μL of isopropanol was added after about 20 seconds of the start of the spin coating, and then the perovskite thin film photoactive layer was obtained by annealing at 100 °C for 30 minutes.

[0063] (4) Preparation of the electron transport layer:

[0064] A fullerene derivative PCBM was dissolved in chlorobenzene solution to obtain a PCBM / chlorobenzene solution with a concentration of 15 mg / mL, and the solution was spin-coated on the perovskite thin film photoactive layer described above at a rotation speed of 3000 rpm for 30 seconds, and then annealed at 100 °C for 5 minutes to obtain an electron transport layer based on the fullerene derivative PCBM.

[0065] Bathocuproin (BCP) was dissolved in ethanol to obtain a BCP / ethanol solution with a concentration of 1 mg / mL, and the solution was spin-coated on the electron transport layer described above at a rotation speed of 3000 rpm for 20 seconds. Then, a 100 nm thick silver electrode was deposited in a vacuum chamber at a pressure of 5 x 10 -4 Pa to obtain a perovskite solar cell based on the fullerene derivative PCBM electron transport layer. The area of the perovskite solar cell device was 0.06 cm 2 , which was determined by the area of the test mask.

[0066] The current density-voltage curve of the perovskite solar cell based on the fullerene derivative PCBM electron transport layer material prepared in the present comparative example was tested under irradiation of simulated sunlight with an intensity of 100 mW / cm 2 AM 1.5G, and the results are shown in Figure 3 . From the results, the open circuit voltage of the device was 1.14 V, the short circuit current density was 23.6 mA / cm 2 , the fill factor was 0.786, and the energy conversion efficiency was 21.1%.

[0067] The vertical distribution of each layer material in the perovskite solar cell prepared in the examples and comparative examples was tested by a time-of-flight secondary ion mass spectrometer, and the relative intensity-sputtering time curve of each layer material was obtained, as shown in Figure 4(a) and (b) are shown. It is found from the figures that the silver electrode of the example is obviously layered with the fulleropyrrolidine FMG, while there is more overlapping area between the FMG layer and the perovskite layer, indicating that the FMG molecules have penetrated along the perovskite grain boundaries, but the distribution content of the FMG molecules gradually decreases along the penetration direction (i.e. the thickness direction of the perovskite layer from the side close to the FMG layer to the side close to the hole transport layer). In contrast, the silver electrode in the comparative example partially diffuses into the fullerene derivative PCBM and the perovskite layer, and there is less overlapping area between the PCBM layer and the perovskite layer. Based on the test results, a schematic diagram of the distribution structure of the silver electrode, the fullerene electron transport layer and the perovskite photoactive layer is proposed, as shown in Figure 4 (c). The fulleropyrrolidine FMG forms a dense and smooth electron transport layer film, and there is no mutual penetration between the electron transport layer and the metal electrode layer. At the same time, part of the FMG molecules in the electron transport layer penetrate into the perovskite film of the photoactive layer along the perovskite grain boundaries to form a gradient heterojunction structure with the FMG content decreasing along the penetration direction. While the fullerene derivative PCBM gets a rough and void electron transport layer film, and does not penetrate into the perovskite film.

[0068] In order to explore the light stability of the perovskite solar cell, an aging experiment was carried out. The perovskite solar cell based on the fullerene derivative PCBM electron transport layer material prepared in the comparative example and the perovskite solar cell based on the fulleropyrrolidine FMG electron transport layer material prepared in the example were simply packaged with 8mmx15mm glass using AB glue, and then the two packaged perovskite solar cells were placed in an open circuit state under the simulated sunlight of a white LED with an intensity of 100mW / cm 2 The current density-voltage curves of the two devices were tested every interval of time (1st, 2nd, 5th, 8th, 10th, 15th, 20th, 30th, 40th, 50th, 60th day), and the energy conversion efficiency-aging time curves were obtained, as shown in Figure 5

[0069] It can be seen that compared with the photovoltaic performance (energy conversion efficiency of 21.1%) of the commercialized material fullerene derivative PCBM, the perovskite solar cell based on the FMG electron transport layer provided in the example has higher open circuit voltage, higher short circuit current and higher fill factor, and obtains higher energy conversion efficiency and better light stability, and the efficiency can be as high as 23.8%.

[0070] After 60 days of light aging test, it is found that the perovskite solar cell based on the FMG electron transport layer in the example has better light stability and can maintain 85% of the initial efficiency. While the perovskite solar cell based on the PCBM electron transport layer in the comparative example only maintains 74% of the initial efficiency.

[0071] ​The fulleropyrrolidine FMG electron transport layer material used in the application has multiple flexible ethoxymethyl ether side chains, which can provide multiple passivation sites to passivate perovskite grain boundary defects through hydrogen bonding and Lewis acid-base interaction; meanwhile, FMG has good solution processing and surface wetting ability on the perovskite surface, can form a smooth and dense fullerene electron transport layer film on the perovskite surface, and form a gradient heterojunction structure with the perovskite layer. Thus, the extraction and transmission efficiency of electrons is improved, the perovskite grain boundary defects are passivated, the migration of halogen ions and silver electrode is inhibited, and finally the device efficiency and light stability are improved.

[0072] The above-described embodiments are only a preferred scheme of the application, and are not intended to limit the application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the application. Therefore, any technical scheme obtained by equivalent replacement or equivalent transformation falls within the protection scope of the application.

Claims

1. A perovskite solar cell based on fulleropyrrolidine electron transport layer, characterized in that, The perovskite solar cell comprises, from bottom to top, a substrate (1), a transparent electrode layer (2), a hole transport layer (3), a light-sensitive layer (4), an electron transport layer (5) and a metal electrode layer (6). The material of the photosensitive layer (4) is perovskite; the material of the electron transport layer (5) adopts fulleropyrrolidine, and the specific chemical structural formula is: ; The electron transport layer (5) is a dense and smooth film, and there is no mutual penetration between the electron transport layer (5) and the metal electrode layer (6), while part of the fulleropyrrolidine molecules in the electron transport layer (5) penetrate into the light-sensitive layer (4) along the grain boundaries of the perovskite, forming a gradient heterojunction structure with the content of the fulleropyrrolidine molecules decreasing along the penetration direction. The material of the hole transport layer (3) is one of PTAA or nickel oxide nanoparticles or a combination of both. The material of the light-sensitive layer (4) is one of methylammonium lead bromide or formamidinium lead iodide or a mixture thereof, the chemical structure of the methylammonium lead bromide is CH3NH3PbI3, and the chemical structure of the formamidinium lead iodide is HC(NH2)2PbI3.

2. The perovskite solar cell based on fulleropyrrolidine electron transport layer according to claim 1, characterized in that, The thickness of the electron transport layer (5) is 2-200 nm. 3.The perovskite solar cell based on fulleropyrrolidine electron transport layer according to claim 1, characterized in that, The material of the substrate (1) is one of glass, quartz, flexible polyethylene terephthalate or flexible polyethylene naphthalate. 4.The perovskite solar cell based on fulleropyrrolidine electron transport layer according to claim 1, characterized in that, The material of the transparent electrode layer (2) is indium tin oxide or fluorine-doped tin oxide.

5. The perovskite solar cell based on fulleropyrrolidine electron transport layer according to claim 1, characterized in that, The material of the metal electrode layer (6) is one of silver, aluminum, magnesium, copper, gold, indium tin oxide or fluorine-doped tin oxide, and the thickness of the metal electrode layer (6) is 50-300 nm.

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