Perovskite tandem solar cells

Abstract

This application provides a perovskite tandem solar cell, comprising a first solar cell unit and a second solar cell unit. The first solar cell unit absorbs front-side light, and the second solar cell unit absorbs back-side light. The first and second solar cell units are connected by a first encapsulating film. The difference between the refractive index of the first encapsulating film and the refractive index of the first lower electrode and the second upper electrode is greater than a first preset value. Therefore, in this application, the second solar cell unit is connected to the back-side of the first solar cell unit via the first encapsulating film. The second solar cell unit absorbs and converts back-side light, improving the utilization of back-side light in the perovskite tandem solar cell. Furthermore, the refractive index of the first encapsulating film differs significantly from the refractive indices of the two electrodes at its junction, enhancing the secondary utilization of reflected light and further improving the power generation efficiency of the second solar cell unit.

Description

Technical Field

[0001] This application relates to the field of solar cells, and more particularly to a perovskite tandem solar cell. Background Technology

[0002] Both perovskite and crystalline silicon solar cells are carriers for generating electricity using solar energy. To achieve higher power generation efficiency, perovskite and crystalline silicon solar cells are combined in a tandem configuration to form a crystalline silicon-perovskite tandem cell. Currently, photovoltaic modules are generally installed at an optimal tilt angle, with one side being the light-facing side and the other the back-facing side. However, because crystalline silicon solar cells typically only absorb and convert light from the front side, the light resources on the back side cannot be utilized, resulting in lower cell efficiency. Summary of the Invention

[0003] This application provides a perovskite tandem solar cell, in which a second solar cell is connected to the backlight side of a first solar cell unit via a first encapsulating film. The second solar cell unit absorbs and converts backlight, thereby improving the utilization of backlight in the perovskite tandem solar cell. Furthermore, the refractive index of the first encapsulating film differs significantly from the refractive indices of the two electrodes at its junction, thereby enhancing the secondary utilization of reflected light and further improving the power generation efficiency of the second solar cell unit.

[0004] In a first aspect, this application provides a perovskite tandem solar cell, comprising: a first solar cell unit including a first sub-cell, the first sub-cell including a first upper electrode, a first light-absorbing layer, and a first lower electrode, the first solar cell unit being used to absorb front light from the perovskite tandem solar cell; and a second solar cell unit including a second sub-cell, the second sub-cell including a second upper electrode, a second light-absorbing layer, and a second lower electrode, the second solar cell unit being used to absorb back light from the perovskite tandem solar cell; wherein the first lower electrode and the second upper electrode are connected by a first encapsulating film, the difference between the refractive index of the first encapsulating film and the refractive index of the first lower electrode, and the difference between the refractive index of the first encapsulating film and the refractive index of the second upper electrode are both greater than a first preset value, such that the reflectivity of a portion of the back light passing through the second light-absorbing layer when passing through a first interface and a second interface is greater than the first preset reflectivity, so that the portion of the back light is reflected back into the second light-absorbing layer; the first interface is the interface between the second upper electrode and the first encapsulating film, and the second interface is the interface between the first encapsulating film and the first lower electrode.

[0005] In some embodiments, the first sub-cell is a crystalline silicon cell; or, the first sub-cell is a thin-film cell, and the first light-absorbing layer includes a perovskite thin film or a CIGS thin film.

[0006] In some embodiments, the second sub-cell is a thin-film cell, and the second light-absorbing layer includes a perovskite thin film or a CIGS thin film; the band gap width of the second sub-cell is 0.9-1.2 eV.

[0007] In some embodiments, the refractive index of the first encapsulating film is 1.4-1.6, and the refractive indices of the first lower electrode and the second upper electrode are 1.8-2.1.

[0008] In some embodiments, the first upper electrode, the first lower electrode, and the second upper electrode are metal oxides, including at least one of FTO, ITO, AZO, and ZnO; the second lower electrode is the metal oxide, and the perovskite tandem solar cell further includes a third encapsulating film and a first photovoltaic substrate, the third encapsulating film being connected to the second lower electrode and the first photovoltaic substrate respectively; the first photovoltaic substrate is a glass substrate or a polymer material coated with metal oxide, and the refractive index of the first photovoltaic substrate is less than or equal to 1.55; or, the second lower electrode is a second photovoltaic substrate, and the second photovoltaic substrate has a different thickness than the first photovoltaic substrate.

[0009] In some embodiments, the first solar cell unit further includes a third sub-cell, the third sub-cell including a third upper electrode, a third light-absorbing layer and a third lower electrode; the third lower electrode and the first upper electrode are connected by a second encapsulating film; the difference between the refractive index of the second encapsulating film and the refractive index of the third lower electrode, and the difference between the refractive index of the second encapsulating film and the refractive index of the first upper electrode are both less than a second preset value; such that the reflectivity of some front light passing through the third light-absorbing layer when passing through the third interface and the fourth interface is less than the second preset reflectivity, the third interface being the interface between the third lower electrode and the second encapsulating film, and the fourth interface being the interface between the second encapsulating film and the first upper electrode.

[0010] In some embodiments, the third sub-cell is a thin-film cell, and the third light-absorbing layer includes a perovskite thin film; the band gap width of the first sub-cell is 0.9-1.3 eV, and the band gap width of the third sub-cell is 1.7-1.8 eV; the third sub-cell is used to absorb short-wavelength light in the front light, and the second sub-cell is used to absorb long-wavelength light in the front light, wherein the wavelength of the short-wavelength light is less than 720 nm, and the wavelength of the long-wavelength light is greater than 720 nm.

[0011] In some embodiments, the refractive index of the second encapsulating film is 1.6-1.9; the refractive indices of the third lower electrode and the first upper electrode are 1.6-1.9.

[0012] In some embodiments, the third lower electrode is a metal oxide, including at least one of FTO, ITO, AZO, and ZnO; the third upper electrode is a third photovoltaic substrate, which is a glass substrate or a polymer material coated with metal oxide; and the refractive index of the second upper electrode is less than 1.55.

[0013] In some embodiments, the reflectivity of the first interface is calculated using the following formula: R = (n1 - n2) 2 / (n1+n2) 2 Where R is the reflectivity, and n1 and n2 represent the refractive index of the second upper electrode and the refractive index of the first encapsulating film, respectively.

[0014] As can be seen from the embodiments of this application, the perovskite tandem solar cell includes a first solar cell unit, which includes a first sub-cell. The first sub-cell includes a first upper electrode, a first light-absorbing layer, and a first lower electrode. The first solar cell unit is used to absorb the front light of the perovskite tandem solar cell. The second solar cell unit includes a second sub-cell, which includes a second upper electrode, a second light-absorbing layer, and a second lower electrode. The second solar cell unit is used to absorb the back light of the perovskite tandem solar cell. The first lower electrode and the second upper electrode are connected by a first encapsulating film. The difference between the refractive index of the first encapsulating film and the refractive index of the first lower electrode, and the difference between the refractive index of the first encapsulating film and the refractive index of the second upper electrode are both greater than a first preset value. This makes the reflectivity of some back light passing through the second light-absorbing layer greater than the first preset reflectivity when passing through the first interface and the second interface, so that some back light is reflected back into the second light-absorbing layer again. The first interface is the interface between the second upper electrode and the first encapsulating film, and the second interface is the interface between the first encapsulating film and the first lower electrode. Therefore, in this application, a second solar cell unit is connected to the backlight side of the first solar cell unit through a first encapsulating film. The second solar cell unit absorbs and converts the backlight, thereby improving the utilization of the backlight of the perovskite tandem cell. Furthermore, the refractive index of the first encapsulating film differs significantly from the refractive index of the two electrodes at its junction, thereby enhancing the secondary utilization of reflected light and further improving the power generation efficiency of the second solar cell unit. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of a two-terminal stacked perovskite solar cell provided in an embodiment of this application;

[0017] Figure 2 This is a schematic diagram of the structure of a four-terminal stacked perovskite solar cell provided in an embodiment of this application;

[0018] Figure 3 A simplified structural diagram of a perovskite tandem solar cell provided in this application embodiment;

[0019] Figure 4 This is one of the structural schematic diagrams of the perovskite tandem solar cell provided in the embodiments of this application;

[0020] Figure 5 This is a schematic diagram of the back-side illumination optical path provided in an embodiment of this application;

[0021] Figure 6 One of the structural schematic diagrams of the second sub-battery is provided for an embodiment of this application;

[0022] Figure 7 This is a second schematic diagram of the structure of the second sub-battery provided in the embodiments of this application;

[0023] Figure 8 The second schematic diagram of the perovskite tandem solar cell provided in the embodiments of this application;

[0024] Figure 9 This is a schematic diagram of the front illumination optical path provided in an embodiment of this application.

[0025] Explanation of reference numerals in the attached figures:

[0026] 1-Perovskite tandem solar cell, 10-First solar cell unit, 20-Second solar cell unit, 30-First encapsulating film, 40-Second encapsulating film, 11-First sub-cell, 111-First upper electrode, 112-First light-absorbing layer, 113-First lower electrode, 21-Second sub-cell, 211-Second upper electrode, 212-Second light-absorbing layer, 213-Second lower electrode, 214-Hole transport layer, 215-Electron transport layer, 216-Third encapsulating film, 217-First photovoltaic substrate, 218-Second photovoltaic substrate, 31-Third sub-cell, 311-Third upper electrode, 312-Third light-absorbing layer, 313-Third lower electrode. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0028] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0029] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0030] In the embodiments of this application, "and / or" describes the relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone; A and B exist simultaneously; B exists alone. Among them, A and B can be singular or plural.

[0031] In this embodiment, the symbol " / " can indicate that the preceding and following objects are in an "or" relationship. Alternatively, the symbol " / " can also represent a division sign, i.e., performing a division operation. For example, A / B can mean A divided by B.

[0032] In the embodiments of this application, "at least one item" or its similar expression refers to any combination of these items, including any combination of a single item or a plurality of items. "One or more" means one or more, while "multiple" means two or more. For example, "at least one item" of a, b, or c can represent the following seven cases: a, b, c; a and b; a and c; b and c; a, b, and c. Each of a, b, and c can be an element or a set containing one or more elements.

[0033] In the embodiments of this application, "equal to" can be used with "greater than" and is applicable to technical solutions used when "greater than" is used; it can also be used with "less than" and is applicable to technical solutions used when "less than" is used. When "equal to" is used with "greater than", it is not used with "less than"; when "equal to" is used with "less than", it is not used with "greater than".

[0034] A perovskite tandem solar cell structure comprises a top electrode layer, an electron transport layer, a perovskite layer, a hole transport layer, and a bottom electrode layer. After laser scribing, these layers form independently segmented sub-cell regions. Because the bandgap of perovskite material is adjustable, it can be stacked with other photovoltaic technologies to form a tandem cell. By utilizing the different spectral ranges of natural light absorption by the materials in different photovoltaic technologies, the bandgap width of the solar cell can be adjusted, thereby improving the power generation efficiency of the tandem cell. Common tandem cell technologies include perovskite-crystalline silicon, perovskite-organic materials, perovskite-thin films, and perovskite-perovskite. As a novel solar cell technology, compared to single-junction solar cells, tandem cells can better utilize different wavelengths of the solar spectrum, solving the absorption and heat losses of single-junction cells, thereby improving photon utilization efficiency and energy conversion efficiency, overcoming the theoretical efficiency limit of single-junction cells.

[0035] For perovskite / crystalline silicon double-junction tandem solar cells, they generally consist of a perovskite transparent top cell and a crystalline silicon bottom cell. The two-terminal double-junction tandem cell structure involves directly growing the perovskite cell on the crystalline silicon cell, see... Figure 1 Two sub-cells are connected in series via a composite layer or tunnel junction. This type of cell requires only one transparent electrode, which helps reduce parasitic absorption and lower costs. However, stacked cells at both ends face greater technological challenges, especially in the process of preparing perovskite thin films on crystalline silicon surfaces. Issues such as current matching need to be addressed, and the preparation processes for stacked cells using different crystalline silicon routes vary.

[0036] The four-terminal double-junction tandem solar cell structure is made by stacking crystalline silicon cells and perovskite cells, which avoids the complex stacking process problems of stacking at both ends. See Figure 2 The perovskite solar cell with the highest bandgap is placed on the top layer, and the crystalline silicon solar cell with the second highest bandgap is placed on the layer below. When sunlight shines on the stacked device, the wide-bandgap solar cell absorbs short-wavelength sunlight. For long-wavelength sunlight, since its photon energy is lower than the bandgap of the wide-bandgap solar cell, it cannot be absorbed by the wide-bandgap solar cell. Therefore, long-wavelength sunlight passes through the wide-bandgap solar cell and enters the narrow-bandgap solar cell, where it is absorbed. In this combined structure, each solar cell acts as a filter to block high-energy photons, rationally distributing sunlight to each solar cell.

[0037] In a multi-terminal tandem solar cell architecture, the individual cells are connected by insulating layers or even air layers. Each cell is independent and electrically unaffected by the others; therefore, this type of tandem solar cell is also called a mechanically stacked tandem solar cell. Besides not being limited by current matching, adjustments to a single cell in a mechanically stacked tandem solar cell do not affect the performance of other cells except for optical performance. However, because the cell connection points in a mechanically stacked tandem solar cell have relatively thick insulating layers, sunlight experiences significant optical loss in these areas, and the backlight of the tandem solar cell cannot be utilized.

[0038] To address the aforementioned issues, this application provides a perovskite tandem solar cell. A second solar cell unit is connected to the backlight side of a first solar cell unit via a first encapsulating film. The second solar cell unit absorbs and converts backlight, thereby improving the utilization of backlight in the perovskite tandem solar cell. Furthermore, the refractive index of the first encapsulating film differs significantly from the refractive indices of the two electrodes at its interface, enhancing the secondary utilization of reflected light and further improving the power generation efficiency of the second solar cell unit.

[0039] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will be described below with reference to the accompanying drawings.

[0040] Please see Figure 3 , Figure 3 This is a simplified structural diagram of a perovskite tandem solar cell provided in an embodiment of this application. The perovskite tandem solar cell 1 includes a first solar cell unit 10 and a second solar cell unit 20. The first solar cell unit 10 is used to absorb front light from the perovskite tandem solar cell 1, and the second solar cell unit 20 is used to absorb back light from the perovskite tandem solar cell 1. The first solar cell unit 10 and the second solar cell unit 20 are stacked together by a first encapsulating film 30. Specifically, the first solar cell unit 10 includes a first sub-cell 11, and the second solar cell unit 20 includes a second sub-cell 21. The first sub-cell 11 and the second sub-cell 21 are connected by the first encapsulating film 30.

[0041] Among them, see Figure 4 The first sub-cell 11 includes a first upper electrode 111, a first light-absorbing layer 112, and a first lower electrode 113. The second sub-cell 21 includes a second upper electrode 211, a second light-absorbing layer 212, and a second lower electrode 213. The first lower electrode 113 and the second upper electrode 211 are connected by a first encapsulating film 30.

[0042] The first lower electrode 113 and the second upper electrode 211 are made of one or more metal oxides (TCOs) such as FTO / ITO / AZO / ZnO. Both the first lower electrode 113 and the second upper electrode 211 have a certain refractive index, and the first encapsulating film 30 also has a certain refractive index.

[0043] During the process of light passing through the second sub-cell 21 from the back side, see Figure 5 The back light E0 is reflected at the interface between the air and the second lower electrode 213, generating reflected light E1. The back light passing through the second lower electrode 213 enters the second light-absorbing layer 212, where it absorbs and converts part of the back light. The remaining back light passes through the second upper electrode 211. Within each individual cell, light reflection is minimal due to the relatively uniform refractive index. Reflection occurs at the interface between the second upper electrode 211 and the first encapsulating film 30, generating reflected light E2. The back light passing through the first encapsulating film 30 is reflected again at the interface between the first encapsulating film 30 and the first lower electrode 113, generating reflected light E3. Both reflected light E2 and E3 re-pass through the second light-absorbing layer 212 and are absorbed and converted again. Part of the reflected light E4 passes through the second lower electrode 213 and returns to the air.

[0044] The intensity of reflected light is determined by the refractive index of the material through which the light passes. A higher refractive index results in higher reflectivity and more reflected light; a lower refractive index results in lower reflectivity and less reflected light. Furthermore, the greater the difference in refractive indices between adjacent materials, the stronger the reflection. In some implementations, the formula for calculating reflectivity is as follows:

[0045] R = (n1 - n2) 2 / (n1+n2) 2 Formula (1)

[0046] Where R is the reflectivity, and n1 and n2 are the refractive indices of the two adjacent materials.

[0047] exist Figure 5Since the first sub-cell 11 can only absorb and convert front light, the utilization rate of back light can only be enhanced by the second sub-cell 21. One solution is to increase the light absorption rate of the second light-absorbing layer 212. Specifically: for back light E0, it is necessary to minimize the reflected light E1 and increase the back light transmitted through the second lower electrode 213. Therefore, the second lower electrode 213 needs to be set with a smaller refractive index. For reflected light E2 and reflected light E3, the stronger the reflected light E2 and reflected light E3, the more back light the second light-absorbing layer 212 can absorb and utilize. Therefore, the second upper electrode 211 and the first lower electrode 113 need to be set with a higher refractive index. Based on this, according to the above formula (1), the greater the difference between the refractive index of the first encapsulating film 30 and the refractive index of the second upper electrode 211, and the greater the difference between the refractive index of the first encapsulating film 30 and the refractive index of the first lower electrode 113, the higher the reflectivity, and the stronger the reflected light E2 and reflected light E3.

[0048] In some embodiments, the refractive indices of the first lower electrode 113 and the second upper electrode 211 are substantially the same, the refractive indices of the first lower electrode 113 and the second upper electrode 211 are 1.8-2.1, and the refractive index of the first encapsulating film 30 is 1.4-1.6.

[0049] In some embodiments, the second sub-cell 21 is a thin-film cell, and the second light-absorbing layer 212 includes a perovskite thin film or a CIGS thin film; the band gap width of the second sub-cell 21 is 0.9-1.2 eV. The second light-absorbing layer 212 mainly absorbs scattered light from natural light, ground radiation, and secondary reflected light, which can help improve the photoelectric efficiency of the entire perovskite tandem cell 1.

[0050] In some embodiments, see Figure 6 The second lower electrode 213 is a metal oxide (TCO), including at least one of FTO, ITO, AZO, and ZnO. The perovskite tandem solar cell 1 also includes a third encapsulating film and a first photovoltaic substrate. The third encapsulating film is used to connect the second lower electrode 213 and the first photovoltaic substrate. The first photovoltaic substrate is a glass substrate or a polymer material coated with a metal oxide, including but not limited to polycarbonate (PC) and polymethyl methacrylate (PMMA). The refractive index of the first photovoltaic substrate is less than or equal to 1.55. The structural sequence of the second sub-cell 21 is as follows: second upper electrode 211, hole transport layer 214, second light-absorbing layer 212, electron transport layer 215, second lower electrode 213, third encapsulating film 216, and first photovoltaic substrate 217.

[0051] In some embodiments, see Figure 7The second lower electrode 213 is directly the second photovoltaic substrate 218. The structural sequence of the second sub-cell 21 is as follows: second upper electrode 211, electron transport layer 215, second light-absorbing layer 212, hole transport layer 214, and second photovoltaic substrate 218.

[0052] Figure 6 and Figure 7 The difference between the two perovskite tandem solar cells shown is that the second photovoltaic substrate has a different thickness than the first photovoltaic substrate. Figure 7 The photovoltaic substrate shown is typically 3mm thick. This type of module is relatively weak and can only be used in centralized power plants or BIPV products on the ground floor, limiting its application scenarios. Figure 6 The perovskite tandem cell 1 structure shown encapsulates the second sub-cell 21 and the photovoltaic substrate together through a third encapsulation film. At this time, the first photovoltaic substrate can be selected as a 5mm, 6mm or thicker photovoltaic substrate, which can greatly improve the strength of the module product, but also increases the cost.

[0053] In some embodiments, the first sub-cell 11 is a crystalline silicon cell; or, the first sub-cell 11 is a thin-film cell, and the first light-absorbing layer 112 includes a perovskite thin film or a CIGS thin film.

[0054] The first sub-cell 11 can be a crystalline silicon cell technology such as HJT or Topcon, or a thin-film cell technology such as perovskite or CIGS.

[0055] In some embodiments, the first solar cell unit 10 includes a first sub-cell 11, and may also include other sub-cells other than the first sub-cell 11.

[0056] When the first solar cell unit 10 includes only the first sub-cell 11, the band gap width of the first sub-cell 11 can be determined according to the required range of light wavelengths to be absorbed.

[0057] When the first solar cell unit 10 includes multiple sub-cells, by segmenting the solar spectrum, a stacked structure of two or more sub-cells in series is used to collect light of a specific spectrum to achieve absorption and utilization of the entire solar spectrum. The bandgap widths of the multiple sub-cells decrease sequentially, with the sub-cell with the largest bandgap width placed on the top layer, the sub-cell with the second largest bandgap width placed on the next layer, and so on.

[0058] In some embodiments, the first solar cell unit 10 further includes a third sub-cell 31, see Figure 8 The third sub-cell 31 includes a third upper electrode 311, a third light-absorbing layer 312, and a third lower electrode 313; the third lower electrode 313 and the first upper electrode 111 are connected by a second encapsulation film 40.

[0059] The third lower electrode 313 is one or more of metal oxides (TCO) such as FTO / ITO / AZO / ZnO, and both the third lower electrode 313 and the second encapsulating film 40 have a certain refractive index.

[0060] During the process of frontal light passing through the first solar cell unit 10, see Figure 9 The front light E5 is reflected at the interface between the air and the third upper electrode 311, producing reflected light E6. The front light passing through the third upper electrode 311 enters the third light-absorbing layer 312, where part of the front light is absorbed and converted. The remaining front light passes through the third lower electrode 313. It is reflected at the interface between the third lower electrode 313 and the second encapsulating film 40, producing reflected light E7. The back light passing through the second encapsulating film 40 is reflected again at the interface between the second encapsulating film 40 and the first upper electrode 111, producing reflected light E8. The remaining front light E9 passes through the first upper electrode 111 and enters the first light-absorbing layer 112, where it is absorbed and converted.

[0061] exist Figure 9 In this structure, the third light-absorbing layer 312 absorbs short-wavelength light from the front light source, while the first light-absorbing layer 112 absorbs long-wavelength light from the front light source. The short-wavelength light has a wavelength less than 720 nm, and the long-wavelength light has a wavelength greater than 720 nm. In this combined structure, each solar cell acts as a filter to block high-energy photons, rationally distributing sunlight to each solar cell and improving the photoelectric efficiency of the perovskite tandem solar cell 1.

[0062] However, during this process, reflected rays such as E6, E7, and E8 are still generated. To further increase the photoelectric efficiency of the perovskite tandem solar cell 1, one solution is to reduce the generation of reflected rays. Specifically: for the front light E5, it is necessary to minimize the reflected ray E6 and maximize the front light passing through the third upper electrode 311. Therefore, the third upper electrode 311 needs to be designed with a smaller refractive index. For the reflected rays E7 and E8, the weaker the reflected light, the stronger the light reaching the first light-absorbing layer 112, and the more front light the first light-absorbing layer 112 can absorb and utilize. Therefore, the third lower electrode 313 and the first upper electrode 111 need to be set with a smaller refractive index. Based on this, according to the above formula (1), the smaller the difference between the refractive index of the second encapsulating film 40 and the refractive index of the third lower electrode 313, and the smaller the difference between the refractive index of the second encapsulating film 40 and the refractive index of the first upper electrode 111, the smaller the reflectivity, and the weaker the reflected rays E7 and E8.

[0063] In some embodiments, the refractive indices of the third lower electrode 313, the second encapsulating film 40, and the first upper electrode 111 are substantially the same, and the second preset threshold is a value close to 0, determined based on the level achievable by actual technology. The second preset reflectivity is a value close to 0.

[0064] In some embodiments, the refractive index of the second encapsulating film 40 is 1.6-1.9; the refractive indexes of the third lower electrode 313 and the first upper electrode 111 are 1.6-1.9.

[0065] In some embodiments, the third sub-cell 31 is a thin-film cell, and the third light-absorbing layer 312 includes a perovskite thin film; the band gap width of the first sub-cell 11 is 0.9-1.3 eV, and the band gap width of the third sub-cell 31 is 1.7-1.8 eV.

[0066] In some embodiments, the third lower electrode 313 is a metal oxide, including at least one of FTO, ITO, AZO, and ZnO; the third upper electrode 311 is a second photovoltaic substrate, which is a glass substrate or a polymer material coated with a metal oxide; the refractive index of the second upper electrode 311 is less than 1.55. The polymer material includes, but is not limited to, polycarbonate (PC) and polymethyl methacrylate (PMMA).

[0067] As can be seen from the embodiments of this application, the perovskite tandem solar cell includes a first solar cell unit, which includes a first sub-cell. The first sub-cell includes a first upper electrode, a first light-absorbing layer, and a first lower electrode. The first solar cell unit is used to absorb the front light of the perovskite tandem solar cell. The second solar cell unit includes a second sub-cell, which includes a second upper electrode, a second light-absorbing layer, and a second lower electrode. The second solar cell unit is used to absorb the back light of the perovskite tandem solar cell. The first lower electrode and the second upper electrode are connected by a first encapsulating film. The difference between the refractive index of the first encapsulating film and the refractive index of the first lower electrode, and the difference between the refractive index of the first encapsulating film and the refractive index of the second upper electrode are both greater than a first preset value. This makes the reflectivity of some back light passing through the second light-absorbing layer greater than the first preset reflectivity when passing through the first interface and the second interface, so that some back light is reflected back into the second light-absorbing layer again. The first interface is the interface between the second upper electrode and the first encapsulating film, and the second interface is the interface between the first encapsulating film and the first lower electrode. Therefore, in this application, a second solar cell unit is connected to the backlight side of the first solar cell unit through a first encapsulating film. The second solar cell unit absorbs and converts the backlight, thereby improving the utilization of the backlight of the perovskite tandem cell. Furthermore, the refractive index of the first encapsulating film differs significantly from the refractive index of the two electrodes at its junction, thereby enhancing the secondary utilization of reflected light and further improving the power generation efficiency of the second solar cell unit.

[0068] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various locations throughout the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A perovskite tandem solar cell, characterized in that, include: The first solar cell unit includes a first sub-cell, the first sub-cell including a first upper electrode, a first light-absorbing layer and a first lower electrode, and the first solar cell unit is used to absorb the front light of the perovskite tandem solar cell. The second solar cell unit includes a second sub-cell, the second sub-cell includes a second upper electrode, a second light-absorbing layer, and a second lower electrode, and the second solar cell unit is used to absorb the back light of the perovskite tandem solar cell; The first lower electrode and the second upper electrode are connected by a first encapsulating film. The difference between the refractive index of the first encapsulating film and the refractive index of the first lower electrode, and the difference between the refractive index of the first encapsulating film and the refractive index of the second upper electrode are both greater than a first preset value. This makes the reflectivity of a portion of the back light passing through the second light-absorbing layer greater than the first preset reflectivity when passing through the first interface and the second interface, so that the portion of the back light is reflected back into the second light-absorbing layer again. The first interface is the interface between the second upper electrode and the first encapsulating film, and the second interface is the interface between the first encapsulating film and the first lower electrode. The first solar cell unit further includes a third sub-cell, which includes a third upper electrode, a third light-absorbing layer, and a third lower electrode. The third lower electrode and the first upper electrode are connected by a second encapsulating film. The difference between the refractive index of the second encapsulating film and the refractive index of the third lower electrode, and the difference between the refractive index of the second encapsulating film and the refractive index of the first upper electrode are both less than a second preset value. This makes the reflectivity of some front light passing through the third light-absorbing layer less than the second preset reflectivity when passing through the third interface and the fourth interface. The third interface is the interface between the third lower electrode and the second encapsulating film, and the fourth interface is the interface between the second encapsulating film and the first upper electrode.

2. The perovskite tandem solar cell according to claim 1, characterized in that, The first sub-cell is a thin-film cell, and the first light-absorbing layer includes a perovskite thin film.

3. The perovskite tandem solar cell according to claim 1, characterized in that, The second sub-cell is a thin-film cell, and the second light-absorbing layer includes a perovskite thin film; The band gap width of the second sub-cell is 0.9-1.2 eV.

4. The perovskite tandem solar cell according to claim 1, characterized in that, The refractive index of the first encapsulating film is 1.4-1.6, and the refractive indices of the first lower electrode and the second upper electrode are 1.8-2.

1.

5. The perovskite tandem solar cell according to claim 1, characterized in that, The first upper electrode, the first lower electrode, and the second upper electrode are metal oxides, and the metal oxides include at least one of FTO, ITO, AZO, and ZnO; The second lower electrode is the metal oxide, and the perovskite tandem solar cell further includes a third encapsulating film and a first photovoltaic substrate. The third encapsulating film is connected to the second lower electrode and the first photovoltaic substrate, respectively. The first photovoltaic substrate is a glass substrate or a polymer material coated with metal oxide, and the refractive index of the first photovoltaic substrate is less than or equal to 1.55; or... The second lower electrode is a second photovoltaic substrate, and the second photovoltaic substrate has a different thickness than the first photovoltaic substrate.

6. The perovskite tandem solar cell according to claim 1, characterized in that, The third sub-cell is a thin-film cell, and the third light-absorbing layer includes a perovskite thin film. The first sub-cell has a bandgap width of 0.9-1.3 eV, and the third sub-cell has a bandgap width of 1.7-1.8 eV. The third sub-cell is used to absorb short-wavelength light in the front light, and the second sub-cell is used to absorb long-wavelength light in the front light. The short-wavelength light has a wavelength of less than 720 nm, and the long-wavelength light has a wavelength of greater than 720 nm.

7. The perovskite tandem solar cell according to claim 1, characterized in that, The refractive index of the second encapsulating film is 1.6-1.9; The refractive index of the third lower electrode and the first upper electrode is 1.6-1.

9.

8. The perovskite tandem solar cell according to claim 1, characterized in that, The third lower electrode is a metal oxide, which includes at least one of FTO, ITO, AZO, and ZnO. The third upper electrode is a third photovoltaic substrate, which is a glass substrate or a polymer material coated with metal oxides; the refractive index of the second upper electrode is less than 1.

55.

9. The perovskite tandem solar cell according to claim 1, characterized in that, The reflectivity of the first interface is calculated using the following formula: R=(n1-n2) 2 / (n1+n2) 2 Where R is the reflectivity, and n1 and n2 represent the refractive index of the second upper electrode and the refractive index of the first encapsulating film, respectively.

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