Perovskite solar cell using single-walled carbon nanotube as transparent conductive electrode and method for manufacturing same

Abstract

Disclosed is a perovskite solar cell which uses one or more single-walled carbon nanotubes synthesized on protective glass sheets (1a, 1b) as transparent conductive electrodes, the single-walled carbon nanotubes being obtained by providing the protective glass sheets (1a, 1b) on the bottom of a vertical thermal CVD device, on the outer periphery of which an electric furnace (10) is installed, and spraying a mixed liquid (16) of an Fe-based element metal and an alcohol by means of a nebulizer device (11), while having the vertical thermal CVD device set the temperature of the electric furnace (10) to 800°C to 1000°C.

Description

Perovskite solar cells with single-walled carbon nanotubes as transparent conductive electrodes and their manufacturing method

[0001] The present invention relates to a perovskite solar cell in which single-walled carbon nanotubes are used as a transparent conductive electrode, and a method for manufacturing the same.

[0002] Perovskite solar cells are a new type of solar cell that uses perovskite crystalline structure materials. They are attracting attention because they are inexpensive to manufacture, do not require rare metals, are "light," "thin," "soft," and flexible, and can be adapted to a variety of shapes. They also achieve high conversion efficiency comparable to "silicon-based solar cells" and "compound solar cells."

[0003] The rare metal indium tin oxide (ITO) is used as the transparent conductive electrode for perovskite solar cells, but it is expensive, its supply is unstable, and there are problems with the flexibility of ITO conductive glass. ITO conductive glass, which contains the rare metal indium, has a resistance value of 2Ω / sq to 1000Ω / sq and a light transmittance of only 50% to 90%, making it difficult to achieve low resistance and high light transmittance. As it is difficult to achieve low resistance and high light transmittance, there is an urgent need to consider alternative materials.

[0004] Patent Publication No. 2022-181466

[0005] The objective of the present invention is to develop a transparent conductive electrode that can replace ITO and a perovskite solar cell equipped with the electrode.

[0006] Carbon nanostructures, which are structures with specific microstructures mainly composed of carbon, are known, including fullerenes, carbon nanotubes, carbon nanowalls, and graphene.

[0007] Among these, carbon nanotubes have a single-wall structure in which SP2 carbon atoms are bonded in a honeycomb pattern, forming a single-atom-thick carbon atom. They are flexible, with an electron mobility of 200,000 cm2V-1s-1 at room temperature, a resistance of only 1*10-4Ω / sq, and an optical transmittance of 90% to 92%.

[0008] Therefore, although carbon nanotubes are theoretically the most ideal transparent conductive material, they are not suitable as a conductive material because a uniform carbon nanotube thin film cannot be obtained using conventional synthesis methods using horizontal thermal CVD apparatus.

[0009] In contrast, research by the present inventors has revealed that by using a vertical thermal CVD apparatus with a quartz tube installed on top of the thermal CVD apparatus, atomized Fe / ethanol gas heated to a predetermined temperature (800°C to 1000°C) from a nebulizer device is sprayed onto a protective glass (set temperature of about 100°C) placed below, carbon nanotubes (SWNTs) can be uniformly synthesized onto the surface of the protective glass to form an extremely flat carbon nanotube net.

[0010] Based on the above findings, the present invention proposes a perovskite solar cell and a method for manufacturing the same, in which a protective glass is placed at the bottom of a vertical thermal CVD apparatus with an electric furnace installed on the outer periphery, the temperature of the electric furnace of the vertical thermal CVD apparatus is set to 800°C to 1000°C, and a mixed liquid of Fe-based element metal / alcohol is sprayed from a nebulizer device to synthesize one or more single-walled carbon nanotubes onto the protective glass, each of which serves as a transparent conductive electrode.

[0011] Here, examples of Fe-based element metals include Fe, Co, Ni, etc., with Fe being preferred.

[0012] The alcohol may be a lower alcohol such as methanol or ethanol, with ethanol being preferred.

[0013] Under the above conditions, a single-walled carbon nanotube net is synthesized on the protective glass placed at the bottom of the vertical thermal CVD apparatus by spraying a mixed solution of Fe / ethanol from a nebulizer device from the top of the apparatus.

[0014] The resulting single-walled carbon nanotube net has an extremely flat carbon nanotube net structure with few defects and large "holes" between the tubes, which allows for flexibility, low resistance, and high light transmittance. This effectively increases light absorption over a wide spectral range, thereby significantly improving the photoelectric conversion efficiency of perovskite solar cells, making it ideal as a transparent conductive electrode for perovskite solar cells.

[0015] As described above, the transparent conductive electrode of the perovskite solar cell used in the present invention can be replaced with single-walled carbon nanotubes, which have superior flexibility, conductivity, and light transparency compared to commonly used ITO glass. As a result, the present invention can provide perovskite solar cells that have low production costs, excellent flexibility, conductivity, and light transparency, and are also thin, lightweight, and have excellent bending and deformation resistance.

[0016] Figure 1 shows an example of a perovskite solar cell according to the present invention, in which a single-walled carbon nanotube (SWNTs) net synthesized in a vertical thermal CVD apparatus is used as a transparent conductive electrode. Figure 2 shows another example of a perovskite solar cell according to the present invention, in which a single-walled carbon nanotube (SWNTs) net synthesized in a vertical thermal CVD apparatus is used as a transparent conductive electrode. Figure 3 shows the synthesis of a single-walled carbon nanotube thin film in a vertical thermal CVD apparatus. Figure 4 shows the manufacturing process of the perovskite solar cell shown in Figure 2. SEM image of a single-walled carbon nanotube net. TEM image of a single-walled carbon nanotube net. Raman spectroscopy image of a single-walled carbon nanotube net. Figure 5 shows the purification of a single-walled carbon nanotube net attached to a protective glass.

[0017] A protective glass is placed at the bottom of a vertical thermal CVD apparatus with an electric furnace installed around its periphery. The temperature of the electric furnace in the vertical thermal CVD apparatus is set to 800-1000°C, and a mixed solution of Fe / ethanol is sprayed from a nebulizer device onto the protective glass to synthesize one or more single-walled carbon nanotubes, each of which serves as a transparent conductive electrode, resulting in a perovskite solar cell.

[0018] (Synthesis of Single-Walled Carbon Nanotubes) Figure 3 shows a vertical thermal CVD apparatus using a quartz tube for producing a single-walled carbon nanotube (SWNTs) net 2 (2a, 2b), in which an electric furnace 10 is installed around the quartz tube, protective glass 1 (1a, 1b) is placed on a table 19 installed at the bottom of the apparatus below the electric furnace 10, and a nebulizer device 11 is installed inside the tank containing a mixture of iron-based metal and lower alcohol, preferably a mixture 16 of Fe / ethanol.

[0019] To produce a single-walled carbon nanotube (SWNT) net 2 (2a, 2b), a vacuum pump 14 is started to draw a vacuum, and then the N2 gas valve 13 is turned on to remove the air from the thermal CVD chamber. The temperature is raised to the synthesis temperature (800°C to 1000°C), and finally the nebulizer device 11 is turned on to evaporate the Fe / ethanol mixture 16. This atomizes the Fe / ethanol mixture 16 and passes through the heating section of the electric furnace 10, synthesizing the SWNT net 2 on the protective glass 1 (at about 100°C).

[0020] Figure 1 shows an example of a perovskite solar cell in which a single-walled carbon nanotube (SWNT) net synthesized in a vertical thermal CVD apparatus is used as a transparent conductive electrode. Figure 1 shows a perovskite solar cell according to one embodiment of the present invention, in which synthesized SWNTs 2 are attached to a protective glass 1 to form a transparent conductive electrode. Next, a hole transition layer (conductive polymer: PEDOT:PSS) 3, a conductive layer (Poly TPD) 4 that allows holes to flow and blocks electrons, a perovskite layer 5, a conductive layer (PCBM) 6 that allows electrons to flow and blocks holes, and a metal electrode 7 are layered in this order. Finally, the SWNTs 2 and the metal electrode 7 are connected using wiring 8 to complete the structure of the perovskite solar cell.

[0021] In the solar cell manufacturing process of FIG. 1, a single-walled carbon nanotube (SWNTs) net 2 is synthesized on a protective glass 1 as described above.

[0022] Next, a hole transition layer (conductive polymer: PEDOT:PSS) 3, a conductive layer (Poly TPD) 4 that allows holes to flow and blocks electrons, and a perovskite layer 5 are coated.

[0023] The perovskite layer 5 is coated with a conductive layer (PCBM) 6 that allows surface electrons to flow and blocks holes, and then a metal electrode 7 is layered on top of it. Finally, the single-walled carbon nanotube (SWNT) net 2 and the metal electrode 7 are connected using wiring 8 to form the structure of the perovskite solar cell.

[0024] When exposed to sunlight 9, electrons and holes are excited in the perovskite layer 5, and the hole transition layer 3 has a low carrier transition rate, which increases the diffusion distance and lifetime of the carriers.

[0025] The electron-hole pairs that do not recombine are collected in the electron conducting layer (PCBM) 6 and the hole conducting layer (Poly TPD) 4, and finally flow into the conductive electrode, generating a current.

[0026] Figure 2 shows another example of a perovskite solar cell in which a single-walled carbon nanotube (SWNTs) net synthesized in a vertical thermal CVD apparatus is used as a transparent conductive electrode. The single-walled carbon nanotube (SWNTs) net 2 synthesized in the vertical thermal CVD apparatus forms a transparent conductive electrode coated on a protective glass 1. Next, perovskite material 5, single-walled carbon nanotube (SWNTs) net 2, perovskite material 5, and metal (Au) electrode 7 are layered in this order, and finally SWNTs 2 and metal (Au) electrode 7 are connected using wiring 8.

[0027] The manufacturing process of the perovskite solar cell shown in FIG. 2 using the single-walled carbon nanotube (SWNTs) net 2 (2a, 2b) manufactured using the vertical thermal CVD apparatus described above will be described with reference to FIG.

[0028] [Step shown in Figure 4A] First, two protective glasses 1a and 1b are prepared on a liftable table 19. Protective glasses 1a and 1b are used in the structure of this perovskite solar cell to prevent impurities such as dirt and dust from entering. Meanwhile, protective glass 1b is used when transferring to the perovskite layer 5a.

[0029] [Step shown in Figure 4B] A transparent and conductive electrode is formed by coating SWNT nets 2a on a protective glass 1a using a vertical thermal CVD apparatus. For example, the electron mobility of SWNTs with a diameter of 1.5 nm is approximately 36,000 cm2 / Vs at room temperature, achieving an optical transmittance of 92%.

[0030] [Step shown in FIG. 4C] The SWNTs net 2a synthesized on the protective glass 1a is washed with water vapor generated by a nebulizer device, dried, and then a perovskite layer 5a is applied thereon.

[0031] [Step shown in FIG. 4D] The protective glass 1b with the SWNTs net is immersed in purified water 12 to oxidize the surface 1b of the protective glass, thereby reducing the adhesion to the SWNTs net 2b.

[0032] [Step shown in FIG. 4E] A thermal peeling tape 17 is pressed onto the synthesized SWNTs 2b on the protective glass 1b.

[0033] [Step shown in FIG. 4F] The SWNTs net 2b is peeled off from the protective glass 1b with a thermal peeling tape 17.

[0034] [Step shown in FIG. 4G] The peeled SWNTs net 2b is transferred to the perovskite layer 5a.

[0035] [Step shown in FIG. 4H] The adhesive strength of the tape 17 is weakened.

[0036] [Step shown in FIG. 4I] The heated thermal peeling tape 17 is removed by the protective glass 1b.

[0037] [Step shown in FIG. 4J] The SWNTs net is transferred to the perovskite layer 5a.

[0038] [Step shown in FIG. 4K] A perovskite layer 5b is applied to the transferred SWNTs net.

[0039] [Step shown in FIG. 4L] Metal (Au) 7 is coated onto the perovskite layer 5b.

[0040] [Step shown in Figure 4G] Metal conductors 8 are wired between the transparent conductive electrode SWNT nets 2a, 2b and the Au metal electrode 7. The multilayer perovskite solar cell constructed as above is activated by light irradiation 9. The multilayer perovskite solar cell is activated by light irradiation.

[0041] The above embodiment shows an example in which the perovskite solar cell structure according to the present invention is a multilayer structure as shown in Figure 2. However, in the present invention, the single-walled carbon nanotube (SWNTs) net (2) is very thin and has excellent light transmission properties, so in principle it can be made into a multilayer laminated structure, which can significantly improve the photoelectric conversion rate of the perovskite solar cell.

[0042] However, the present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the claims.

[0043] (Purification of Single-Walled Carbon Nanotubes) The problem of amorphous carbon and dust generated during the synthesis of single-walled carbon nanotubes can be addressed by moving the protective glass 1 placed on the table 19 to the electric furnace 7 as shown in Figures 8(a) and 8(b), spraying purified water from a nebulizer onto the protective glass 1, and then drying it at 100 to 150°C about three times. As shown in Figures 8(c), 8(d), and 8(e), the amorphous carbon and dust are completely removed from the CNTs net (2), and the spaces between the nanotubes in the CNTs net (2) are naturally greatly expanded, which also increases the light transmittance of this transparent conductive electrode (6).

[0044] (Verification of single-walled carbon nanotubes) Figure 5. (a) and (b) are SEM images of the SWNTs net. A thin SWNTs net is observed on the protective glass, and it is clear that a very large amount of SWNTs has been synthesized in a net-like form.

[0045] Figures 6(a) and (b) are TEM images of the SWNT net. Planar TEM observation was performed to confirm the distribution of SWNTs. Numerous CNTs extending in a net-like fashion from the SWNTs are clearly observed. It is believed that this net plays a role in imparting conductivity.

[0046] Figure 7 shows the Raman spectrum of a single-walled carbon nanotube net. The Raman spectrum of single-walled carbon nanotubes reveals a vibrational mode called the D-band near 1,340 cm-1. This mode is not Raman-active in highly crystalline graphite, but when the symmetry is disrupted by the introduction of defects, it becomes visible as a Raman peak. Therefore, the peak intensity ratio (G / D ratio) between the D-band and the G-band, a vibrational mode similar to the Raman-active mode of graphite, can be used to evaluate the amount of defects. A higher G / D ratio indicates fewer defects and higher quality. Figure 6 shows the D-band near 1,340 cm-1 and the G-band near 1,600 cm-1, accompanied by a Fano-type spectrum due to metallic resonance. By separating each peak and calculating the peak intensities of the G-band and D-band near 1,590 cm-1, the G / D ratio (G-band intensity / D-band intensity) was calculated to be 3.286. From this, it is thought that the G / D ratio indicates a small number of defects, and that the number of defects in the nanotubes produced by this process is also small.

[0047] As explained above, the transparent conductive electrode used in the solar cell of the present invention can be replaced with a carbon nanotube thin film, which has excellent flexibility, conductivity, and light transmittance compared to the commonly used ITO glass, and is significantly thinner and more resistant to bending and deformation. Therefore, not only does it have the advantages of low resistance and high light transmittance, but it also reduces the weight of the entire solar cell.

[0048] According to the present invention, by constructing a transparent conductive electrode from single-walled carbon nanotubes, it is possible to provide a perovskite solar cell that has advantages such as excellent flexibility, conductivity, and light transparency, as well as being thin, lightweight, and resistant to bending and deformation.

[0049] 1 (1a, 1b) Protective glass 2 (2a, 2b) Single-walled carbon nanotube net 3 Transparent conductive polymer (PEDOT:PSS) 5 (5a, 5b) Perovskite layer 6 PCBM 7 Metal (Au) 8 Wiring 9 Light 10 Electric furnace 11 Nebulizer 12 Purified water 13 N2 gas valve 14 Vacuum pump 15 Water vapor 16 Fe / ethanol mixture 17 Thermal release tape 18 Ultraviolet heating 19 Table

Claims

1. A protective glass is placed at the bottom of a vertical thermal CVD apparatus with an electric furnace installed around its periphery. The temperature of the electric furnace in the vertical thermal CVD apparatus is set to 800°C to 1000°C, and a mixed liquid of Fe-based element metal / alcohol is sprayed from a nebulizer device to synthesize single-walled carbon nanotubes onto the protective glass. This results in a perovskite solar cell in which one or more of the synthesized single-walled carbon nanotubes serve as a transparent conductive electrode.

2. The perovskite solar cell according to claim 1, which is constructed by coating a layer of perovskite material on each of two or more transparent conductive electrodes made of single-walled carbon nanotubes.

3. A perovskite solar cell according to claim 1, in which the single-walled carbon nanotubes synthesized on the protective glass are sprayed and washed with purified water from a nebulizer device in a vertical thermal CVD apparatus, and then dried.

4. The perovskite solar cell according to claim 1, wherein the mixed solution of Fe-based element metal / alcohol is an Fe / ethanol mixed solution.

5. A method for producing a perovskite solar cell as described in claim 2, comprising the steps of: providing a protective glass and one or more transfer protective glasses at the bottom of a vertical thermal CVD apparatus having an electric furnace installed around its periphery; setting the temperature of the electric furnace of the vertical thermal CVD apparatus to 800°C to 1000°C; spraying a mixture of Fe-based element metal / alcohol from a nebulizer device and letting it flow down from the top of the vertical thermal CVD apparatus to form single-walled carbon nanotubes on the protective glass or the transfer protective glass; coating the single-walled carbon nanotubes formed on the protective glass with a perovskite material layer; peeling off the single-walled carbon nanotubes formed on the transfer protective glass and transferring them to the perovskite material layer; and coating the transferred single-walled carbon nanotubes with a perovskite layer, repeated two or more times.

6. The method according to claim 5, wherein the single-walled carbon nanotubes formed on the protective glass or the transfer protective glass are washed by spraying purified water from a nebulizer device in a vertical thermal CVD apparatus, and then dried.

7. The method according to claim 5, wherein the mixed solution of Fe-based element metal / alcohol is a mixed solution of Fe / ethanol.

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