Tandem solar cell and manufacturing method thereof

Abstract

The present invention provides a tandem solar cell and a manufacturing method thereof, which can increase the horizontal resistance of the recombination layer connecting the upper and lower cells of the tandem solar cell, minimize the occurrence of shunt paths, prevent a decrease in recombination efficiency due to electron transfer problems, and have low absorbance in the short wavelength band, thereby improving the current value when applied to the tandem solar cell.

Description

[Technical Field]

[0001] The present invention relates to a tandem solar cell, and more particularly to a tandem solar cell and a method for manufacturing the same, which can reduce the horizontal resistance of a recombination layer connecting upper and lower cells of a tandem solar cell, minimize the occurrence of shunt paths, prevent a decrease in recombination efficiency due to electron migration problems, and have low absorbance in the short wavelength band, thereby improving current value when applied to a tandem solar cell.

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2022-0119088, filed on September 21, 2022, the entire contents of which are incorporated herein by reference. [Background technology]

[0003] Multi-junction (tandem) solar cells attempt to effectively utilize solar energy across a wide wavelength range and minimize thermalization loss by vertically stacking photoabsorption layers with different bandgaps. Specifically, tandem solar cells overcome the efficiency limitations of single-junction solar cells by using photoabsorption layers with different bandgaps to separate and absorb solar light by wavelength. This minimizes the loss of excess electron-hole energy as heat when photons with higher energy than the bandgap are absorbed by the photoabsorption layer in single-junction solar cells. Recently, interest in tandem solar cells as the most promising next-generation solar cells has been increasing, and a fierce global R&D race is underway to pioneer tandem solar cell technologies with various structures.

[0004] In addition, such tandem solar cells mainly use transparent conductive thin films (TCO) as the recombination layer that electrically connects the silicon lower cell and the perovskite upper cell. A TCO film has the characteristic that if the free charge concentration is low, the mobility of free charges can be significantly reduced due to the significant scattering of grain boundaries caused by the energy barriers formed by free charges trapped at the grain boundaries. On the other hand, if the free charge concentration is high, more free charges can overcome the energy barriers formed at the grain boundaries, increasing the mobility of free charges to a certain extent. However, if the free charge concentration increases beyond a certain level, the number of ionized impurities present in the film increases, causing scattering between the free charges and the ionized impurities, which can result in a decrease in the mobility of free charges.

[0005] To address this issue, various studies are being conducted to increase the concentration of free charges in the transparent conductive thin film used in the recombination layer of tandem solar cells by doping with cationic metal elements to generate free charges and controlling the concentration of free charges by adjusting the amount of doping. In typical tandem solar cells, ITO with a highly conductive ratio of 10 wt% SnO2 and 90 wt% In2O3 or IZO with a ratio of 10 wt% ZnO2 and 90 wt% In2O3 is used for the transparent conductive thin film of the recombination layer.

[0006] However, in the case of a recombination layer having such a ratio, although the electrical resistance is low and electrons can be efficiently transferred, there are limitations to improving the efficiency of the tandem solar cell due to the following problems.

[0007] First, in the case of a tandem solar cell in which a transparent conductive thin film having the above ratio is used as the recombination layer, a shunt path is formed, resulting in electrical losses. That is, in a tandem solar cell in which a lower silicon cell and an upper perovskite layer are connected in series via a recombination layer, if the horizontal electrical conductivity of the recombination layer is low, charges flow horizontally, forming a shunt path and inducing electrical losses. Such electrical losses limit the efficiency improvement of the solar cell.

[0008] Second, when ITO with a 10 wt% In2O3 content is used for the transparent conductive thin film of the recombination layer, there is a limit to minimizing optical loss due to increased light absorption caused by absorption in the visible light region due to ionized impurities and free carrier absorption in the long wavelength region of visible light and near infrared region. In other words, there is a limit to reducing optical loss in tandem solar cells, which have a structure in which the upper cell with a large bandgap absorbs solar energy in the short wavelength region and the lower cell with a low bandgap absorbs solar energy in the long wavelength region, resulting in the problem of not being able to use solar energy in a wide wavelength region.

[0009] As a result, the recombination layer connecting the upper and lower cells of a tandem solar cell exhibits higher sheet resistance, lower electrical conductivity, and lower electron mobility than conventional materials, thereby minimizing efficiency reduction due to shunt paths and preventing recombination reduction and efficiency reduction due to restrictions on horizontal electron movement. Furthermore, since it has low absorption in the short wavelength band, it is expected to improve current values ​​when applied to tandem solar cells. Therefore, there is an urgent need for research into tandem solar cells that can improve the efficiency of tandem solar cells. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made to overcome the above-mentioned problems, and an object of the present invention is to provide a tandem solar cell and a manufacturing method thereof that can increase horizontal resistance and minimize efficiency reduction due to shunt paths by using a transparent conductive thin film element having a specific ratio in the recombination layer that connects the upper and lower cells of the tandem solar cell.

[0011] Another object of the present invention is to provide a tandem solar cell and a manufacturing method thereof that can prevent a decrease in recombination and efficiency due to restriction of electron movement, and that has low absorbance in the short wavelength band, thereby enabling an improvement in current value when applied to a tandem solar cell and improving the efficiency of the tandem solar cell. [Means for solving the problem]

[0012] In order to solve the above-mentioned problems, the present invention provides a tandem solar cell including a silicon lower cell, a perovskite upper cell, and a recombination layer connecting the silicon lower cell and the perovskite upper cell, wherein the recombination layer is ITO, which is a transparent conductive thin film, and the weight ratio of SnO2 and In2O3 is 18-21:79-82.

[0013] According to one embodiment of the present invention, the transparent conductive thin film has a thickness of 5 to 50 nm.

[0014] The transparent conductive thin film is characterized in that the sheet resistance is 50 ohm / sq to 1M ohm / sq.

[0015] The silicon lower cell is characterized by being any one selected from the group consisting of Al-BSF, PERC, PERT, PERL, and TOPCon structures.

[0016] It is also characterized by having an electrical conductivity of 600 1 / ohm·cm to 1200 1 / ohm·cm.

[0017] Also, 60cm3 / Vs~120cm 3 It is characterized by having an electron mobility of / Vs.

[0018] The present invention also provides a method for manufacturing a tandem solar cell, comprising: a first step of forming a recombination layer on an upper surface of a silicon lower cell, the recombination layer including a compound represented by Chemical Formula 1 below; and a second step of forming a perovskite upper cell connected to the silicon lower cell via the recombination layer, wherein the recombination layer is ITO, a transparent conductive thin film, and has a weight ratio of SnO2 and In2O3 of 18-21:79-82.

[0019] The present invention was researched with the support of the following Korean research and development project.

[0020] 1. [National research and development project that supported this invention] [Project unique number]1415174234 [Project number] 20203040010320 [Department name] Ministry of Industry, Trade and Industry and Energy [Name of issue management (specialized organization)] Korea Energy Technology Evaluation Institute [Research Project Name] Core Technology Development for New Renewable Energy [Research title] Development of manufacturing technology for 6-inch perovskite / crystalline silicon tandem solar cells with 26% efficiency to increase power generation [Contribution rate] 1 / 2 [Name of organization performing the task] Hanwha Solutions Co., Ltd. [Research Period] 2022.01.01~2022.12.31 2. [National research and development project that supported this invention] [Project unique number]1415176482 [Project number] 20213030010400 [Department name] Ministry of Industry, Trade and Industry and Energy [Name of issue management (specialized organization)] Korea Energy Technology Evaluation Institute [Research Project Name] New and Renewable Energy Core Technology Development (R&D) [Research title] Development of process technology for highly efficient and durable perovskite / crystalline silicon tandem solar modules [Contribution rate] 1 / 2 [Name of organization performing the task] Hanwha Solutions Co., Ltd. [Research Period] 2022.05.01~2022.12.31 [Effects of the Invention]

[0021] The present invention exhibits higher sheet resistance, lower electrical conductivity, and lower electron mobility than conventional recombination layers connecting the upper and lower cells of a tandem solar cell, thereby increasing horizontal resistance, minimizing efficiency reduction due to shunt paths, and preventing recombination reduction and efficiency reduction due to electron mobility restriction. Furthermore, the present invention has low absorbance in the short wavelength band, which is expected to improve current value when applied to a tandem solar cell, thereby improving the efficiency of the tandem solar cell. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram showing a tandem solar cell element according to one embodiment of the present invention. [Figure 2] FIG. 2 is a graph showing the transparent conductive thin film characteristics of the recombination layer according to an example of the present invention and a comparative example. [Figure 3] FIG. 3 is a graph showing the cell efficiency of tandem solar cell elements according to an example of the present invention and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: FIG. 1 is a block diagram of a semiconductor device according to an embodiment of the present invention;

[0024] As mentioned above, conventional tandem solar cells have limitations in improving their efficiency due to electrical / optical losses in the transparent conductive thin film used in the recombination layer connecting the upper and lower cells.

[0025] Therefore, in order to solve the above-mentioned problems, the present invention provides a tandem solar cell including a silicon lower cell, a perovskite upper cell, and a recombination layer connecting the silicon lower cell and the perovskite upper cell, wherein the recombination layer is ITO, which is a transparent conductive thin film, and the weight ratio of SnO2 and In2O3 is 18-21:79-82.

[0026] As a result, the present invention exhibits higher sheet resistance, lower electrical conductivity, and lower electron mobility than conventional recombination layers connecting the upper and lower cells of a tandem solar cell, thereby increasing horizontal resistance, minimizing efficiency reduction due to shunt paths, and preventing recombination reduction and efficiency reduction due to electron mobility restriction. Furthermore, the present invention has low absorbance in the short wavelength band, which is expected to improve current value when applied to a tandem solar cell, thereby improving the efficiency of the tandem solar cell.

[0027] In this specification, the lower cell refers to a silicon solar cell formed at the bottom of a tandem solar cell, and the upper cell refers to a perovskite solar cell formed at the top of a tandem solar cell.

[0028] In addition, in this specification, a silicon lower cell refers to a solar cell containing silicon as a light absorbing layer, and a perovskite upper cell refers to a solar cell containing a material having a perovskite structure as a light absorbing layer.

[0029] The tandem solar cell element according to the present invention will be specifically described below with reference to the drawings.

[0030] The tandem solar cell device 100 according to the present invention includes a silicon lower cell 200, a perovskite upper cell 400, and a recombination layer 300 connecting the silicon lower cell 200 and the perovskite upper cell 400.

[0031] The silicon lower cell 200 may be formed on the upper surface of the front electrode as shown in FIG. 1 and may include a silicon layer 210 and an emitter layer 220 disposed on the silicon layer 210 .

[0032] The silicon layer 210 may have one of the structures of known silicon solar cells and is not limited to a specific structure. For example, the silicon layer 210 may include a crystalline silicon substrate (not shown), a p-type amorphous or crystalline silicon layer (not shown), an n-type amorphous or crystalline silicon layer (not shown), or an amorphous intrinsic silicon layer (not shown), and may further include additional layers, if necessary, although not shown.

[0033] According to such a preferred embodiment of the present invention, the silicon lower cell 200 structure has an n-type silicon layer on the surface of the p-type silicon. ++ Al-BSF (Aluminum Back Surface Field), PERC (Passivated Emitter and Rear Cell), PERT (Passivated Emitter Rear Totally Diffused) and PERL (Passivated Emitter and Rear Locally Diffused) structures through the formation of emitters or SiOx tunneling layer / n ++ Examples include a TOPCon (Tunnel oxide passivated contact) structure through the formation of poly-Si, but there is no particular limitation.

[0034] In addition, at least a portion of one or the other surface of the silicon layer 210 may be textured to improve light efficiency. That is, an uneven surface (not shown) is formed in the direction of light incidence, and the light path of the light incident on the silicon layer 210 is increased through the light scattering effect of the light incident through the uneven surface, thereby improving light collection and increasing the solar light absorption rate.

[0035] Next, the recombination layer 300 serves as an intermediate layer that physically combines and electrically connects the silicon lower cell 200 and the perovskite upper cell 400, and can perform charge recombination between the upper and lower cells.

[0036] Conventional tandem solar cells have attempted to improve the electrical and mechanical stability of tandem solar cells by improving the interfacial properties of the recombination layer. To achieve this, the recombination layer has traditionally been made of a transparent conductive material, such as TCO-based materials such as ITO (Indium Tin Oxide), ICO (Indium Cerium Oxide), IWO (Indium Tungsten Oxide), ZITO (Zinc Indium Tin Oxide), ZIO (Zinc Indium Oxide), ZTO (Zinc Tin Oxide), GITO (Gallium Indium Tin Oxide), GIO (Gallium Indium Oxide), GZO (Gallium Zinc Oxide), AZO (Aluminum-doped Zinc Oxide), FTO (Fluorine Tin Oxide), and ZnO, or an nc-Si:H material layer.

[0037] In particular, to control the concentration of free charges and improve the efficiency of tandem solar cells, ITO with a ratio of 10 wt% SnO2 and 90 wt% In2O3 or IZO with a ratio of 10 wt% ZnO2 and 90 wt% In2O3 doped with cationic metal elements and the doping amount adjusted is mainly used for the transparent conductive thin film of the recombination layer.

[0038] However, in the case of a tandem solar cell in which a transparent conductive thin film having the above ratio is used as the recombination layer, there is a problem that a shunt path is generated, resulting in loss. Furthermore, there is a limit to minimizing optical loss because free carrier absorption occurs in the long wavelength region of visible light and the near infrared region, increasing light absorption.

[0039] Therefore, in the present invention, the recombination layer 300 is formed of a transparent conductive thin film of ITO having a weight ratio of SnO2 and In2O3 of 18-21:79-82, thereby solving the above-mentioned problems.

[0040] More specifically, referring to Table 2 and Figure 2, Example 1, which was fabricated using a transparent conductive thin film falling within the aforementioned numerical range, had higher sheet resistance and lower conductivity and electron mobility than the Comparative Example, which was fabricated using a transparent conductive thin film with a conventional weight ratio. Also, referring to Table 3 and Figure 3, it can be seen that Example 1, which was fabricated using a transparent conductive thin film falling within the preferred numerical range of the present invention, had improved JSC and FF at the same thickness compared to the Comparative Example, which was fabricated using a transparent conductive thin film with a conventional weight ratio.

[0041] Therefore, it can be seen that the recombination layer 300 according to the present invention can efficiently function as a recombination layer of a tandem solar cell that physically and electrically connects the upper and lower cells and recombines charges only when it is embodied as ITO, a transparent conductive thin film, and SnO2 and In2O3 in a weight ratio of 18-21:79-82.

[0042] In this case, if a transparent conductive thin film containing SnO2 at a weight ratio of less than 18 or more than 21 of SnO2 and In2O3 in the weight ratio of ITO, which is the recombination layer 300, is used as the recombination layer 300 of a tandem solar cell, the carrier concentration and electron mobility of the recombination layer 300 will be significantly reduced, making it difficult to transport electrons generated in the lower cell, and there may be a problem that the recombination layer cannot efficiently perform its role.

[0043] The transparent conductive thin film forming the recombination layer 300 may have a thickness of 5 to 50 nm, and more preferably 10 to 30 nm. If the thickness of the transparent conductive thin film forming the recombination layer 300 exceeds 50 nm, problems may occur, such as current loss due to increased parasitic absorption and reduced efficiency due to shunt paths caused by reduced horizontal resistance. Furthermore, if the thickness of the transparent conductive thin film forming the recombination layer 300 is less than 5 nm, reduced recombination and reduced efficiency may occur due to limited electron mobility.

[0044] The transparent conductive thin film forming the recombination layer 300 has a sheet resistance of 50 ohm / sq to 1M ohm / sq, preferably 100 ohm / sq or more. If the sheet resistance of the transparent conductive thin film forming the recombination layer 300 is less than 50 ohm / sq, a decrease in horizontal resistance may increase shunt paths, resulting in a decrease in efficiency, as is clear from FIG. 2 and Table 1 below. Furthermore, if the sheet resistance of the thin film exceeds 1M ohm / sq, the vertical electrical conductivity may decrease significantly, restricting electron movement and resulting in a decrease in recombination and a decrease in efficiency.

[0045] That is, by implementing the recombination layer 300 of the tandem solar cell with a transparent conductive thin film having the above-mentioned specific weight ratio, the present invention can manufacture a transparent conductive thin film having a low electrical conductivity of 600 1 / ohm·cm to 1200 1 / ohm·cm, more preferably 700 1 / ohm·cm to 1100 1 / ohm·cm. Due to the effect of such low electrical conductivity, the present invention can manufacture a transparent conductive thin film having a low electrical conductivity of 600 1 / ohm·cm to 1200 1 / ohm·cm. 3 / Vs~120cm 3 / Vs, more preferably 70 cm 3 / Vs~110cm 3 It is characterized by realizing a transparent conductive thin film having low electron mobility / Vs.

[0046] As a result, the present invention can increase horizontal resistance to minimize efficiency reduction due to shunt paths, prevent recombination reduction and efficiency reduction due to electron mobility restriction, and exhibit low absorption in the short wavelength band, which can be expected to improve the current value of tandem solar cells and improve the efficiency of tandem solar cells.

[0047] That is, referring to FIG. 3, according to a preferred embodiment of the present invention, the recombination layer 300 is ++ In the case of a TOP Perc / perovskite tandem device fabricated by depositing a 20wt% SnO2:80wt% In2O3 ITO thin film on the emitter layer and electrically connecting the upper and lower devices, it was found to have improved JSC and FF at the same thickness compared to the existing structure in which a 10wt% SnO2:90wt% In2O3 ITO thin film was applied to the recombination layer.

[0048] Next, the perovskite upper cell 400 is an upper cell that contacts the silicon lower cell 200, and a perovskite absorption layer 410, an electron transport layer 420, and a transparent conductive oxide electrode layer 430 may be sequentially stacked on top of the recombination layer 300.

[0049] The perovskite absorption layer 410 may be formed such that hole-electron pairs generated by receiving light energy from the sun are separated into electrons or holes. In one embodiment, electrons formed in the perovskite absorption layer 410 may be transferred to the electron transport layer 420, and holes formed in the perovskite absorption layer 410 may be transferred to the hole transport layer.

[0050] In this case, the perovskite absorption layer 410 may include an organic halide perovskite such as methyl ammonium iodide (MAI) or formamidinium iodide (FAI), or a metal halide perovskite such as lead iodide (PbI), bromine iodide (PbBr), or lead chloride (PbCl). That is, the perovskite absorption layer 410 may have a multilayer structure including at least one of an organic halide perovskite or a metal halide perovskite. More specifically, the perovskite absorption layer 410 may be represented by AMX3 (where A is a monovalent organic ammonium cation or metal cation; M is a divalent metal cation; and X is a halogen anion). Non-limiting examples of this include CH3NH3PbI3, CH3NH3PbI x Cl 3-x , CH3NH3PbI x Br 3-x , CH3NH3PbCl x Br 3-x , HC(NH2)2PbI3, HC(NH2)2PbI x Cl 3-x , HC(NH2)2PbI x Br 3-x , HC(NH2)2PbCl x Br 3-x , (CH3NH3)(HC(NH2)2) 1-y PbI3, (CH3NH3)(HC(NH2)2) 1-y PbI x Cl 3-x , (CH3NH3)(HC(NH2)2) 1-y PbI x Br 3-x , or (CH3NH3)(HC(NH2)2) 1-y PbCl x Br 3-x etc. may be used (0=x, y=1).

[0051] The electron transport layer 420 serves to separate and transport electrons formed in the perovskite absorber layer 410 and may be formed of any known material as long as it satisfies the objectives of the present invention. Non-limiting examples of the electron transport layer 420 include Ti oxide, Zn oxide, In oxide, Sn oxide, W oxide, Nb oxide, Mo oxide, Mg oxide, Zr oxide, Sr oxide, Yr oxide, La oxide, V oxide, Al oxide, Y oxide, Sc oxide, Sm oxide, Ga oxide, In oxide, and SrTi oxide.

[0052] The tandem solar cell element according to the present invention has been described above, but this is merely an example, and the tandem solar cell element may further include an additional stack structure that can improve the efficiency of the solar cell.

[0053] The present invention will be described in more detail below with reference to examples. However, it should be understood that the following examples are not intended to limit the scope of the present invention, but are intended to aid in understanding the present invention.

[0054] Example 1 - Production of tandem solar cell element The bottom solar cell is made by doping p-type impurities on a silicon substrate with a bottom passivation layer and bottom electrode made by Hanwha Q CELLS through a POCl process. ++ A cell with a PERC structure in which an emitter layer was formed was used.

[0055] Next, n ++ An ITO (Indium Tin Oxide) layer was formed to a thickness of 50 nm on the emitter layer as a recombination layer using a sputtering system.

[0056] Then, ++ A 20 wt% SnO2:80 wt% In2O3 ITO thin film was deposited on the emitter layer to form a 20 nm thick recombination layer that electrically connects the upper and lower elements. xThe above was performed under high vacuum conditions using E-beam deposition to form a hole transport layer, and then a 100 nm thick layer of IZO (Indium doped Zinc Oxide) was formed on top of the hole transport layer using sputtering equipment.

[0057] Next, silver (Ag) was formed on the transparent electrode layer to a thickness of 200 nm using a thermal evaporation machine under high vacuum conditions to fabricate a TOPPerc / perovskite tandem device.

[0058] In this case, in the case of a 20 wt% SnO2:80 wt% In2O3 ITO thin film, the Sn / In ratio can be 18 wt% to 21 wt% depending on the formation atmosphere, formation method, and post-treatment method.

[0059] Comparative Example 1 A TOPPerc / perovskite tandem device was fabricated in the same manner as in Example 1, except that a thin film was deposited with 10 wt% SnO2:90 wt% In2O3ITO, which is a conventional range of values, and a recombination layer electrically connecting the upper and lower devices was formed to a thickness of 20 nm.

[0060] Experimental Example 1: Evaluation of transparent conductive thin film properties The thin film composition ratios of the recombination layers of Examples 1 and 2 were evaluated using an XPS analysis device, and are shown in Table 1 below.

[0061] Referring to Table 1 below, it can be seen that in the case of a 20 wt% SnO2:80 wt% In2O3 ITO thin film according to Example 1 of the present invention, the Sn / In ratio can be 18 wt% to 21 wt% depending on the thin film formation atmosphere, formation method, and post-treatment method.

[0062] [Table 1]

[0063] Experimental Example 2: Evaluation of transparent conductive thin film properties The thin film properties of Example 1 and Comparative Example 1 were evaluated and are shown in Table 2 below and FIG. 2 (the vertical axis n in FIG. 2 represents the refractive index, and k represents the absorption coefficient).

[0064] Referring to Table 2 and FIG. 2 below, Example 1, which is fabricated using a transparent conductive thin film that falls within the preferred range of the present invention, has a higher sheet resistance (ohm / sq), a lower conductivity (1 / ohm cm), and a lower electron mobility (cm) than the comparative example, which is fabricated using a transparent conductive thin film with a conventional weight ratio. 3 / Vs).

[0065] [Table 2]

[0066] Experimental Example 3 - Evaluation of solar cell efficiency The photoelectric efficiency of the tandem solar cell devices according to Example 1 and Comparative Example 1 was measured under AM1.5G light conditions using a solar simulator, and the results are shown in Table 3 and FIG.

[0067] Referring to Table 3 and FIG. 3 below, in the case of the examples manufactured using transparent conductive thin films corresponding to the preferred numerical ranges of the present invention, the short circuit current density (J) was improved at the same thickness compared to the comparative example corresponding to a transparent conductive thin film with a conventional weight ratio. SC ) and fill factor (FF).

[0068] [Table 3]

[0069] Taking these results into consideration, the present invention exhibits higher sheet resistance, lower electrical conductivity, and lower electron mobility than conventional recombination layers connecting the upper and lower cells of a tandem solar cell, thereby increasing horizontal resistance, minimizing efficiency reduction due to shunt paths, and preventing recombination reduction and efficiency reduction due to electron mobility restriction. Furthermore, the present invention has low absorbance in the short wavelength band, which is expected to improve current value when applied to a tandem solar cell, thereby improving the efficiency of the tandem solar cell.

Claims

1. a silicon bottom cell; a perovskite top cell; a recombination layer connecting the silicon bottom cell and the perovskite top cell; The recombination layer includes ITO, which is a transparent conductive thin film, and the ITO is SnO ２ and In ２ O ３ A tandem solar cell comprising:

2. 2. The tandem solar cell according to claim 1, wherein the transparent conductive thin film has a thickness of 5 to 50 nm.

3. 2. The tandem solar cell according to claim 1, wherein the transparent conductive thin film has a sheet resistance of 50 ohm / sq to 1 M ohm / sq.

4. 2. The tandem solar cell of claim 1, wherein the silicon lower cell has one selected from the group consisting of Al-BSF, PERC, PERT, PERL, and TOPCon structures.

5. 2. The tandem solar cell according to claim 1, wherein the transparent conductive thin film has an electrical conductivity of 600 1 / ohm·cm to 1200 1 / ohm·cm.

6. The transparent conductive thin film has a thickness of 60 cm ３ / Vs~120cm ３ 2. The tandem solar cell according to claim 1, wherein the tandem solar cell has an electron mobility of 1 / Vs.

7. a first step of forming a recombination layer on the top surface of the silicon lower cell; a second step of forming a perovskite upper cell connected to the silicon lower cell via the recombination layer; The recombination layer is a transparent conductive thin film made of ITO and SnO ２ and In ２ O ３ in a weight ratio of 18-21:79-82.

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