Stacked solar cell and method for manufacturing a stacked solar cell

Abstract

The application provides a laminated solar cell and a preparation method of the laminated solar cell. The laminated solar cell comprises a bottom cell, a base of the bottom cell has a pyramid structure; a top cell is located above the pyramid structure, the top cell comprises a perovskite thin film, the perovskite thin film comprises a plurality of crystal grains, and the size of the crystal grains is 0.8-2.5 mu m. The application solves the problem of poor electrical performance caused by the small size of the crystal grains of the conformal perovskite thin film in the laminated solar cell in the prior art.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and more specifically, to a tandem solar cell and a method for fabricating a tandem solar cell. Background Technology

[0002] Crystalline silicon / perovskite tandem solar cells are considered one of the core directions of next-generation high-efficiency photovoltaic technology due to their complementary energy efficiency. Monocrystalline silicon materials possess excellent stability, a mature industrial foundation, and high absorption efficiency below a wide bandgap, while perovskite materials, with their high absorption coefficient, tunable bandgap, solution processability, and low defect tolerance, can effectively capture high-energy photons in the solar spectrum, achieving a breakthrough in photoelectric conversion efficiency. However, in existing technologies, conformal perovskite films in tandem solar cells typically have small grain sizes, resulting in generally poor electrical performance and limiting the efficiency stability and mass production feasibility of tandem solar cells.

[0003] The information disclosed above in the background section is only intended to enhance the understanding of the background art of the art described herein. Therefore, the background art may contain certain information that does not constitute prior art known to those skilled in the art in this country. Summary of the Invention

[0004] The main objective of this application is to provide a tandem solar cell and a method for fabricating a tandem solar cell, in order to solve the problem of poor electrical performance caused by the small grain size of conformal perovskite thin film in tandem solar cells.

[0005] To achieve the above objectives, according to one aspect of this application, a tandem solar cell is provided, comprising: a bottom cell having a pyramidal structure on its substrate; and a top cell located above the pyramidal structure, the top cell comprising a perovskite thin film having a plurality of grains having a size of 0.8 μm to 2.5 μm.

[0006] Optionally, the conformability of the perovskite film is 35%-85%, where conformability characterizes the ratio of the apex film thickness to the valley film thickness. The apex film thickness is the thickness of the perovskite film covering the apex of the pyramid structure, and the valley film thickness is the thickness of the perovskite film covering the valley of the pyramid structure. The thickness directions of the apex film thickness and the valley film thickness are parallel to the thickness direction of the bottom cell.

[0007] Optionally, the first film thickness is greater than the second film thickness. The first film thickness is the thickness of the perovskite film covering one of the slopes of the pyramid structure, and the second film thickness is the thickness of the perovskite film covering the other slope of the pyramid structure. The thickness direction of the first film thickness is perpendicular to the one slope of the pyramid structure, and the thickness direction of the second film thickness is perpendicular to the other slope of the pyramid structure.

[0008] Optionally, the difference between the first film thickness and the second film thickness is 3%-30% of the second film thickness.

[0009] Optionally, the material of the perovskite film includes at least one of urea molecules, biuret molecules, and thiourea molecules.

[0010] Optionally, the mass fraction of the impurity phase in the perovskite film is less than 0.5%, and the impurity phase includes lead iodide.

[0011] Optionally, the radius of curvature of the perovskite film covering the apex of the pyramid structure is 5 nm to 50 nm.

[0012] Optionally, the spacing between two adjacent grains is 5nm-50nm.

[0013] Optionally, the thickness of the perovskite film is 500nm-1500nm.

[0014] Optionally, the tandem solar cell further includes: a tunneling composite layer located between the bottom cell and the top cell; the top cell further includes: a first transparent conductive layer located between the perovskite film and the tunneling composite layer; a first carrier transport layer located between the perovskite film and the first transparent conductive layer; a second carrier transport layer located on the side of the perovskite film opposite to the bottom cell; a second transparent conductive layer located on the side of the second carrier transport layer opposite to the bottom cell; and a plurality of spaced-apart top electrodes located on the side of the second transparent conductive layer opposite to the bottom cell.

[0015] Optionally, the bottom battery includes any one of PERC battery, PERT battery, TOPCon battery, HJT battery and BC battery.

[0016] According to another aspect of this application, a method for fabricating a tandem solar cell is provided. The method is used to fabricate any of the tandem solar cells described above. The method includes: providing a bottom cell, the substrate of which has a pyramid structure; and forming a top cell above the pyramid structure, the top cell comprising a perovskite thin film, the perovskite thin film comprising a plurality of grains, the grains having a size of 0.8 μm to 2.5 μm.

[0017] Optionally, forming a top cell above the pyramid structure includes: forming a porous inorganic phase film layer above the pyramid structure, the inorganic phase film layer being made of PbI2 and CsBr; depositing an organic phase solution on the surface of the inorganic phase film layer opposite to the bottom cell, the organic phase solution including an additive, the additive including at least one of urea, biuret, and thiourea; post-processing the bottom cell with the deposited organic phase solution using a near-infrared radiation heating device and / or a vacuum drying device; and annealing the post-processed bottom cell to obtain the perovskite thin film.

[0018] Optionally, the mass concentration of the additive in the organic phase solution is 1 mg / ml to 5 mg / ml.

[0019] Optionally, the post-processed bottom battery is annealed, including annealing the bottom battery at a temperature of 100°C-130°C for 15-30 minutes.

[0020] Optionally, the organic phase solution further includes a solute and a solvent, the solute comprising an organic ammonium salt, and the solvent comprising a first solvent or a second solvent, the first solvent comprising n-butanol and isooctanol, and the second solvent comprising isopropanol and γ-valerolactone.

[0021] Using the technical solution of this application, the tandem solar cell includes a bottom cell and a top cell including a perovskite thin film. The bottom cell has a pyramid structure on its substrate, and the top cell is located on top of the pyramid structure. The perovskite thin film includes multiple grains with a grain size of 0.8 μm-2.5 μm. Compared to the poor electrical performance caused by the small grain size of conformal perovskite films in existing tandem solar cells, this application achieves conformal growth of large grains on the complex three-dimensional surface of perovskite films by forming perovskite films with a grain size of 0.8-2.5 μm on top of a bottom cell with a pyramidal structure. This reduces the electrical performance degradation caused by the small grain size of existing perovskite films. The optimized grain size effectively improves carrier migration efficiency and reduces grain boundary recombination losses, improving interface contact quality and charge transport continuity. At the same time, this grain size range can be highly matched with the pyramidal morphology of the bottom cell, achieving excellent conformal coverage, avoiding film breakage or void defects, enhancing interface contact stability, and realizing complete, dense, and large grain coverage of perovskite films on the three-dimensional structure, thereby improving the photoelectric conversion efficiency and long-term stability of the cell. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0023] Figure 1 A schematic SEM cross-sectional view of a tandem solar cell according to an embodiment of this application is shown;

[0024] Figure 2 A schematic SEM image of a tandem solar cell according to an embodiment of this application is shown.

[0025] Figure 3 A cross-sectional structural schematic diagram of a stacked solar cell according to an embodiment of this application is shown;

[0026] Figure 4 A schematic SEM cross-section of the perovskite thin film in a tandem solar cell prepared by a one-step solution method is shown.

[0027] Figure 5 A schematic SEM cross-sectional view of the tandem solar cell in Comparative Example 2 is shown.

[0028] Figure 6 A schematic SEM image of the tandem solar cell of Comparative Example 2 is shown.

[0029] The above figures include the following reference numerals:

[0030] 10. Bottom cell; 11. Top cell; 12. Perovskite thin film; 13. Grain; 14. Tunneling composite layer; 15. First transparent conductive layer; 16. First carrier transport layer; 17. Second carrier transport layer; 18. Second transparent conductive layer; 19. Top electrode. Detailed Implementation

[0031] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of the invention described herein. 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 comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0034] It should be understood that when an element (such as a layer, film, region, or substrate) is described as being "on" another element, the element may be directly on the other element, or there may be an intermediate element present. Furthermore, in the specification and claims, when an element is described as being "connected" to another element, the element may be "directly connected" to the other element, or "connected" to the other element via a third element.

[0035] As described in the background section, the electrical performance of conformal perovskite films in existing tandem solar cells is poor due to their small grain size. To address this issue, embodiments of this application provide a tandem solar cell and a method for fabricating a tandem solar cell.

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0037] This application provides a tandem solar cell, such as... Figures 1 to 3 As shown, it includes:

[0038] The bottom battery 10 has a pyramid structure (not shown) on its substrate (not shown).

[0039] Specifically, the bottom cell is a crystalline silicon bottom cell.

[0040] The top cell 11 is located above the pyramid structure. The top cell 11 includes a perovskite thin film 12, which includes a plurality of grains 13 with a size of 0.8 μm to 2.5 μm.

[0041] Specifically, grain size can be obtained by measuring the two-dimensional dimensions of the grain's outer surface. For example, if the grain's two-dimensional shape is circular or approximately circular, the grain size refers to the grain's diameter; if the grain's two-dimensional shape is square or approximately square, the grain size refers to the grain's side length or diagonal length; if the grain has other shapes, its grain size can also be obtained by measuring the two-dimensional shape of its surface. Of course, other methods can also be used to measure grain size, and this is not limited here. For example, Figure 2 In the diagram, the line segment with double arrows represents the size m of grain 13.

[0042] Specifically, the method for measuring the grain size of perovskite thin films can be as follows: take any consecutive n grains, or take random n grains, or take n grains within a unit area range, and then measure the size of these n grains respectively to obtain multiple sizes, and then take the average of these multiple sizes as the grain size of the perovskite thin film.

[0043] In this embodiment, the tandem solar cell includes a bottom cell and a top cell including a perovskite thin film. The bottom cell has a pyramid structure on its substrate, and the top cell is located on top of the pyramid structure. The perovskite thin film includes multiple grains with a grain size of 0.8 μm-2.5 μm. Compared to the poor electrical performance caused by the small grain size of conformal perovskite films in existing tandem solar cells, this application achieves conformal growth of large grains on the complex three-dimensional surface of perovskite films by forming perovskite films with a grain size of 0.8-2.5 μm on top of a bottom cell with a pyramidal structure. This reduces the electrical performance degradation caused by the small grain size of existing perovskite films. The optimized grain size effectively improves carrier migration efficiency and reduces grain boundary recombination losses, improving interface contact quality and charge transport continuity. At the same time, this grain size range can be highly matched with the pyramidal morphology of the bottom cell, achieving excellent conformal coverage, avoiding film breakage or void defects, enhancing interface contact stability, and realizing complete, dense, and large grain coverage of perovskite films on the three-dimensional structure, thereby improving the photoelectric conversion efficiency and long-term stability of the cell.

[0044] It should be noted that in the tandem solar cell of this application, the surface of the perovskite thin film is free of impurities (i.e., free of lead iodide) and has high color uniformity.

[0045] In one alternative, such as Figure 1 and Figure 2As shown, the conformability of the perovskite film 12 is 35%-85%. The conformability represents the ratio of the apex film thickness h1 to the valley film thickness h2. The apex film thickness h1 is the thickness of the perovskite film 12 covering the apex of the pyramid structure, and the valley film thickness h2 is the thickness of the perovskite film 12 covering the valley of the pyramid structure. The thickness directions of the apex film thickness h1 and the valley film thickness h2 are parallel to the thickness direction of the bottom cell (not shown). In this embodiment, by setting the conformability of the perovskite film to 35%-85%, the perovskite film achieves a synergistic effect of large grain growth and high conformability coverage on the surface of complex three-dimensional structures. This further reduces the electrical performance degradation caused by local film defects in existing perovskite films. The conformability limit ensures that the thickness distribution of the perovskite film is uniform in the pyramid apex and valley regions, thereby further improving the interface contact quality and charge transport continuity. It overcomes defects such as coverage breakage and material shortage in the valley caused by uneven film formation, and achieves complete and dense coverage of the perovskite layer on the three-dimensional structure, further improving the photoelectric conversion efficiency and long-term stability of the battery.

[0046] Specifically, the average conformability of the perovskite thin film is between 35% and 85%.

[0047] Specifically, if the thickness of the membrane at the top of the tower is 560 nm and the thickness of the membrane at the bottom of the tower is 800 nm, then the conformability is 70%.

[0048] Specifically, if there are multiple pyramid structures, the conformality of the perovskite thin film can be calculated as follows: 1) Any n consecutive pyramid structures, or n random pyramid structures, or n pyramid structures within a unit area can be selected. The average thickness of the apex of these n pyramid structures is taken as the apex thickness of the perovskite thin film, and the average thickness of the valley of these n pyramid structures is taken as the valley thickness of the perovskite thin film. The ratio of the apex thickness to the valley thickness of the perovskite thin film is calculated to obtain the conformality of the perovskite thin film; 2) Any n consecutive pyramid structures, or n random pyramid structures, or n pyramid structures within a unit area can be selected. The conformality of each pyramid structure in these n pyramid structures is calculated separately, resulting in n conformality values. The average of these n conformality values ​​is then taken as the conformality of the perovskite thin film. Both of these methods for calculating the conformality of the perovskite thin film are acceptable, and other methods are also possible. This application does not impose any specific restrictions on these methods.

[0049] In another alternative, the first film thickness is greater than the second film thickness. The first film thickness refers to the thickness of the perovskite film covering one of the slopes of the pyramid structure, and the second film thickness refers to the thickness of the perovskite film covering the other slope of the pyramid structure. The thickness direction of the first film thickness is perpendicular to one of the slopes of the pyramid structure, and the thickness direction of the second film thickness is perpendicular to the other slope of the pyramid structure. In this embodiment, when the first film thickness is greater than the second film thickness, compared to a symmetrical structure where both thicknesses are the same, this asymmetric film thickness design can effectively match the natural non-uniform deposition characteristics of the perovskite film on both sides of the pyramid textured surface caused by the difference in printing droplet spreading kinetics and solvent evaporation rate. This significantly reduces the pinhole defect density caused by excessively thin local film thickness while maintaining high overall conformability, and suppresses stress concentration and abnormal grain growth caused by excessive film thickness.

[0050] Specifically, if there are multiple pyramid structures, the measurement methods for the first and second thicknesses of the perovskite thin film can be as follows: 1) Any n consecutive pyramid structures, or n random pyramid structures, or n pyramid structures within a unit area can be selected. The average of the first thicknesses of these n pyramid structures is taken as the first thickness of the perovskite thin film, and the average of the second thicknesses of these n pyramid structures is taken as the second thickness of the perovskite thin film; 2) Any n consecutive pyramid structures, or n random pyramid structures, or n pyramid structures within a unit area can be selected, wherein at least 50% of these n pyramid structures satisfy the condition that the first thickness is greater than the second thickness. Both of these methods for measuring the first and second thicknesses of the perovskite thin film are acceptable. Of course, other measurement methods are also possible, and this application does not impose specific limitations on them.

[0051] In another alternative, the difference between the first film thickness and the second film thickness is 3%-30% of the second film thickness. In this embodiment, by making the thickness of the perovskite film covering one slope of the pyramid structure greater than the thickness on the other slope, and controlling the difference between the two thicknesses within the range of 3%-30% of the film thickness, while ensuring that the measurement directions of the two film thicknesses are perpendicular to the corresponding slopes, the stress distribution of the film in the asymmetric textured structure is actively guided while maintaining the overall conformity of the perovskite film at 35%-85% and the grain size at 0.8μm-2.5μm. This avoids the risk of local stress concentration or interface desorption caused by abrupt changes in thickness on both sides. The thickness gradient design and the thickness measurement method perpendicular to the slope work together to form a continuous transition layer on the pyramid slope that is adapted to the substrate morphology, significantly improving the interfacial bonding strength and mechanical stability. This achieves synergistic optimization of reliable coverage and long-term service performance of high conformability, large grain perovskite films in complex textured structures.

[0052] Specifically, if there are multiple pyramid structures, the calculation method for the difference between the first and second film thicknesses of the perovskite thin film, expressed as d% of the second film thickness, can be as follows: 1) Any consecutive n pyramid structures can be selected, or n random pyramid structures can be selected, or n pyramid structures within a unit area range can be selected. Then, the average of the first film thicknesses of these n pyramid structures is taken as the first film thickness *a* of the perovskite thin film, and the average of the second film thicknesses of these n pyramid structures is taken as the second film thickness *b* of the perovskite thin film. The difference *b* between the first film thickness *a* and the second film thickness of the perovskite thin film is calculated, yielding the difference *c*. The ratio of *c* to *b* is then calculated to obtain d%; 2) Any consecutive n pyramid structures can be selected, or... 1) Select n random pyramid structures, or n pyramid structures within a unit area. Then, calculate the difference between the first membrane thickness and the second membrane thickness for each of these n pyramid structures, obtaining n differences. Then, calculate the percentage of each of these n differences to the second membrane thickness of the corresponding pyramid structure, obtaining n percentages. Finally, take the average of these n percentages as d%. 2) Select any n consecutive pyramid structures, or randomly select n pyramid structures, or select n pyramid structures within a unit area. Among these n pyramid structures, at least 50% of the pyramid structures satisfy the condition that the difference between the first membrane thickness and the second membrane thickness is 3%-30% of the second membrane thickness. All three methods for calculating d% are acceptable. Of course, other methods for calculating d% are also possible, and this application does not impose specific restrictions on them.

[0053] In other embodiments, the material of the perovskite film includes at least one of urea molecules, biuret molecules, and thiourea molecules. In this embodiment, introducing at least one of urea molecules, biuret molecules, or thiourea molecules as a functional additive into the perovskite film can effectively regulate crystallization kinetics at the molecular structure level: these molecules have strong coordination ability and can interact with Pb²⁻. + The formation of reversible intermediate coordination complexes slows down the nucleation rate of perovskite crystals and promotes preferred orientation growth of crystals, thereby significantly increasing the grain size. At the same time, it suppresses the residue of impurity phases such as lead iodide. In addition, these molecules are low in toxicity, low in cost, and environmentally friendly. They can achieve the controllable preparation of perovskite films with high conformability, high uniformity, and no impurity phases without introducing precious metals or complex processes.

[0054] Specifically, the main component of the perovskite thin film is perovskite, and the minor components are at least one of urea molecules, biuret molecules, and thiourea molecules.

[0055] According to some exemplary embodiments of this application, the mass fraction of the impurity phase in the perovskite thin film is less than 0.5%, and the impurity phase includes lead iodide. In this embodiment, by stably controlling the mass fraction of the impurity phase in the thin film to be below 0.5%, the number of non-radiative recombination centers at the interface can be reduced, and the carrier lifetime and mobility can be improved, thereby effectively enhancing the open-circuit voltage and photoelectric conversion efficiency of the solar cell.

[0056] According to some exemplary embodiments of this application, the radius of curvature of the perovskite thin film covering the apex of the pyramid structure is 400nm-550nm. In this embodiment, the perovskite thin film covering the apex of the pyramid structure has a smaller radius of curvature (i.e., a sharper surface morphology), which can significantly improve the geometric conformability of the thin film and the pyramid textured surface of the bottom cell, effectively avoiding stress concentration and interface voids in the apex region caused by excessive film thickness or rounding passivation, thereby enhancing the interface contact quality and carrier transport efficiency. At the same time, the sharp apex coating can more completely cover the high curvature region, reduce grain boundary exposure and defect density, suppress nonradiative recombination, improve the open-circuit voltage and fill factor of the cell, and ultimately achieve a high-efficiency and high-stability perovskite / crystalline silicon tandem solar cell structure.

[0057] Figure 4 This is a schematic SEM cross-section of the perovskite thin film in a tandem solar cell fabricated using a one-step solution method. Figure 4 As can be seen, in the perovskite films prepared by the one-step solution method, the perovskite film covering the apex of the pyramid structure is relatively rounded and smooth, with a larger radius of curvature; compared to... Figure 4 ,like Figure 1 and Figure 2As shown, in the perovskite film 12 of this application, the perovskite film 12 covering the top of the pyramid structure is sharper and less rounded, with a smaller radius of curvature, and the perovskite film 12 has greater geometric conformity with the pyramid textured surface of the bottom cell.

[0058] According to some exemplary embodiments of this application, the spacing between two adjacent grains is 5nm-50nm. In this embodiment, by limiting the spacing between two adjacent grains to 5nm-50nm, combined with the perovskite film grain size of 0.8μm-2.5μm and the conformality of 35%-85%, the grains form a uniform and controllable micro-gap distribution on the surface of the bottom cell pyramid structure. This avoids the accumulation of grain boundary defects and the aggravation of charge recombination caused by excessive grain density, and also prevents the film continuity breakage and poor interface contact caused by excessive spacing. Thus, while maintaining excellent conformal coverage, an efficient and continuous charge transport channel is constructed, significantly reducing interface nonradiative recombination loss and improving carrier collection efficiency. Ultimately, this achieves high integrity, low defect, and high performance integration of perovskite films on complex three-dimensional structures, effectively solving the problem of electrical performance degradation caused by disordered grain arrangement and uncontrollable spacing in the prior art.

[0059] Specifically, there is a gap of 5-50 nm or a pinhole with a diameter of 5-50 nm between two adjacent grains.

[0060] Specifically, the method for measuring the spacing between adjacent grains of a perovskite thin film can be as follows: take any consecutive n grains, or take random n grains, or take n grains within a unit area, and then measure the spacing between adjacent grains in these n grains respectively to obtain multiple spacings. Then take the average of these multiple spacings as the spacing between adjacent grains of the perovskite thin film.

[0061] According to some other exemplary embodiments of this application, the thickness of the perovskite thin film is 500nm-1500nm. In this embodiment, by limiting the thickness of the perovskite thin film to 500nm-1500nm, combined with its structural characteristics of covering a bottom cell with a pyramid structure, a grain size of 0.8μm-2.5μm, and a conformality of 35%-85%, it is effectively ensured that the film maintains a minimum thickness of not less than 500nm in both the pyramid apex and valley regions. This achieves high conformality and large grain growth while avoiding problems such as electrical continuity disruption, increased series resistance, or increased leakage current caused by excessively thin local films. It ensures efficient carrier transport in the vertical direction and interface contact stability, ultimately achieving high-quality coverage of the perovskite thin film on complex three-dimensional structures and simultaneous optimization of device performance.

[0062] Specifically, there are multiple pyramid structures. The method for measuring the thickness of the perovskite film can be as follows: take any n consecutive pyramid structures, or take n random pyramid structures, or take n pyramid structures within a unit area. Then, measure the thickness of each of these n pyramid structures to obtain multiple thicknesses. Finally, take the average of these multiple thicknesses as the thickness of the perovskite film.

[0063] Specifically, such as Figure 3 As shown, the aforementioned tandem solar cell further includes: a tunneling composite layer 14 located between the bottom cell 10 and the top cell 11. The top cell 11 further includes: a first transparent conductive layer 15 located between the perovskite thin film 12 and the tunneling composite layer 14; a first carrier transport layer 16 located between the perovskite thin film 12 and the first transparent conductive layer 15; a second carrier transport layer 17 located on the side of the perovskite thin film 12 facing away from the bottom cell 10; a second transparent conductive layer 18 located on the side of the second carrier transport layer 17 facing away from the bottom cell 10; and a plurality of spaced-apart top electrodes 19 located on the side of the second transparent conductive layer 18 facing away from the bottom cell 10. If the first carrier transport layer is a hole transport layer, then the second carrier transport layer is an electron transport layer; if the first carrier transport layer is an electron transport layer, then the second carrier transport layer is a hole transport layer.

[0064] Specifically, the aforementioned bottom cell includes any one of the following: PERC cell (Passivated Emitter and Rear Cell), PERT cell (Passivated Emitter and Rear Totally diffused cell), TOPCon cell (Tunnel Oxide Passivated Contact), HJT cell (Heterojunction Technology), and BC cell (BackContact).

[0065] The tandem solar cell of this application will be described in detail below with reference to specific embodiments and comparative examples.

[0066] Example 1

[0067] The tandem solar cell includes: a bottom cell with a pyramidal structure on its substrate; and a top cell located above the pyramidal structure, the top cell comprising a perovskite thin film, the perovskite thin film comprising multiple grains with a grain size of 0.8 μm and an average conformability of 60%.

[0068] Example 2

[0069] The tandem solar cell includes: a bottom cell with a pyramidal structure on its substrate; and a top cell located above the pyramidal structure, the top cell comprising a perovskite thin film, the perovskite thin film comprising multiple grains with a grain size of 2.5 μm and an average conformability of 35%.

[0070] Example 3

[0071] The tandem solar cell includes: a bottom cell with a pyramidal structure on its substrate; and a top cell located above the pyramidal structure, the top cell comprising a perovskite thin film, the perovskite thin film comprising multiple grains with a grain size of 1.6 μm and a conformability of 85%.

[0072] Comparative Example 1

[0073] The tandem solar cell includes: a bottom cell with a pyramidal structure on its substrate; and a top cell located above the pyramidal structure, the top cell comprising a perovskite thin film, the perovskite thin film comprising multiple grains with a grain size of 0.3 μm and a conformability of 30%.

[0074] The performance of the tandem solar cells in Examples 1-3 and Comparative Example 1 was tested, and the test results are shown in Table 1:

[0075] Table 1 Comparison of parameters for perovskite-crystalline silicon tandem solar cells

[0076]

[0077] This application also provides a method for fabricating a tandem solar cell, the method comprising the following steps:

[0078] Step S101: Provide a bottom battery, wherein the substrate of the bottom battery has a pyramid structure;

[0079] Specifically, a pyramid-shaped velvety structure can be formed through etching.

[0080] In step S102, a top cell is formed above the pyramid structure. The top cell includes a perovskite thin film, which includes multiple grains with a size of 0.8 μm to 2.5 μm.

[0081] In this embodiment, a bottom cell with a pyramid structure is first provided, and then a top cell including a perovskite thin film is formed on top of the pyramid structure. The perovskite thin film includes multiple grains with a grain size of 0.8 μm-2.5 μm. Compared to the poor electrical performance caused by the small grain size of conformal perovskite films in existing tandem solar cells, this application achieves conformal growth of large grains on the complex three-dimensional surface of perovskite films by forming perovskite films with a grain size of 0.8-2.5 μm on top of a bottom cell with a pyramidal structure. This reduces the electrical performance degradation caused by the small grain size of existing perovskite films. The optimized grain size effectively improves carrier migration efficiency and reduces grain boundary recombination losses, improving interface contact quality and charge transport continuity. At the same time, this grain size range can be highly matched with the pyramidal morphology of the bottom cell, achieving excellent conformal coverage, avoiding film breakage or void defects, enhancing interface contact stability, and realizing complete, dense, and large grain coverage of perovskite films on the three-dimensional structure, thereby improving the photoelectric conversion efficiency and long-term stability of the cell.

[0082] In one alternative embodiment, forming a top cell above the pyramid structure includes: forming a porous inorganic phase film layer above the pyramid structure, the inorganic phase film layer being made of PbI2 and CsBr; depositing an organic phase solution on the surface of the inorganic phase film layer facing away from the bottom cell, the organic phase solution including additives, the additives including at least one of urea, biuret, and thiourea; post-processing the bottom cell with the deposited organic phase solution using a near-infrared radiation heating device and / or a vacuum drying device, the vacuum drying device including a vacuum flash evaporation device and / or a vacuum crystallizer; and annealing the post-processed bottom cell to obtain the perovskite thin film. In this embodiment, a porous inorganic phase film composed of PbI2 and CsBr is formed on a bottom cell with a pyramidal structure, constructing a three-dimensional framework structure conducive to organic phase penetration. Then, an organic phase solution containing at least one additive selected from urea, biuret, or thiourea is deposited on its surface. These additives are used to regulate crystallization kinetics at the interface, promoting uniform diffusion and full reaction of organic and inorganic components at the complex three-dimensional morphology interface. This effectively suppresses the formation of residual lead iodide phase, effectively inhibits excessive nucleation of crystal nuclei, and promotes directional grain growth. Near-infrared radiation heating is employed. Equipped with and / or vacuum drying equipment, the solvent evaporation rate and reaction temperature gradient are precisely controlled to avoid film rupture or impurity phase residue caused by localized rapid drying. Ultimately, during the annealing process, the perovskite grain size is uniformly expanded to 0.8μm-2.5μm, and the film completely covers the apex and valley regions of the pyramid structure, improving the conformability to 35%-85%. This effectively overcomes the film quality defects caused by small grains, numerous impurities, and poor conformability in the wet-dry two-step method, significantly improving the coverage integrity and photoelectric performance stability of perovskite films on complex microstructure substrates.

[0083] Specifically, a loose and porous inorganic phase film layer was prepared using a vacuum thermal evaporation equipment, with an evaporation rate ratio of PbI2:CsBr=4:0.8 and a thickness of 400nm-600nm for the inorganic phase film layer.

[0084] Specifically, vacuum drying equipment includes post-processing equipment such as vacuum flash evaporators and vacuum crystallizers, which accelerate solvent evaporation based on low vacuum levels.

[0085] In one embodiment, a top cell is formed above the pyramid structure, specifically including: forming a tunneling composite layer on one side of the bottom cell with the pyramid structure; forming a first transparent conductive layer on the side of the tunneling composite layer opposite to the bottom cell; forming a first carrier transport layer on the side of the first transparent conductive layer opposite to the bottom cell; forming a porous inorganic phase film layer on the side of the first carrier transport layer opposite to the bottom cell, the inorganic phase film layer being made of PbI2 and CsBr; and depositing an organic phase solution on the surface of the inorganic phase film layer opposite to the bottom cell, the organic phase solution including additives. The agent includes at least one of urea, biuret, and thiourea. A near-infrared radiation heating device and / or a vacuum drying device are used to post-process the bottom cell on which the organic phase solution is deposited. The vacuum drying device includes a vacuum flash evaporation device and / or a vacuum crystallizer. The post-processed bottom cell is annealed to obtain a perovskite film. A second carrier transport layer is formed on the side of the perovskite film opposite to the bottom cell. A second transparent conductive layer is formed on the side of the second carrier transport layer opposite to the bottom cell. Multiple spaced-apart top electrodes are formed on the side of the second transparent conductive layer opposite to the bottom cell.

[0086] According to some exemplary embodiments of this application, the mass concentration of the additive in the organic phase solution is 1 mg / ml-5 mg / ml. In this embodiment, by limiting the mass concentration of the additive in the organic phase solution to 1 mg / ml-5 mg / ml, the additive is distributed at a suitable concentration on the surface of the inorganic phase film during the deposition process. This effectively suppresses the non-uniform nucleation tendency during perovskite nucleation and avoids solvent evaporation imbalance or aggravated side reactions caused by excessive concentration. This synergistically promotes the directional growth of grains on the pyramid structure surface and the complete conversion of PbI2, significantly increasing the grain size to 0.8 μm-2.5 μm and maintaining a conformity of 35%-85%. At the same time, it ensures that the lead iodide impurity phase is stably and reproducibly eliminated. This overcomes the technical defects of uncontrolled film quality fluctuations and uncontrollable impurity phase residues caused by uncontrolled additive concentration in the traditional wet-dry two-step method. Ultimately, it achieves the preparation of perovskite films with high reproducibility, high conformity, and no impurity phases, significantly improving the photoelectric conversion efficiency and device stability of solar cells.

[0087] According to some other exemplary embodiments of this application, the post-processed bottom battery is annealed, including annealing the bottom battery at a temperature of 100°C-130°C for 15-30 minutes. In this embodiment, after forming a porous inorganic phase film layer and depositing an organic phase solution containing additives on a pyramidal bottom cell, preliminary post-treatment is performed using near-infrared radiation heating equipment and / or vacuum drying equipment to remove most of the volatile components and induce a preliminary reaction. Subsequently, a precise annealing treatment is performed at a temperature range of 100℃-130℃ for 15-30 minutes. This heat treatment condition, in conjunction with the complexation and nucleation regulation effect of the additives, effectively promotes the complete evaporation of residual solvents, the full conversion of unreacted PbI2 and organic ammonium salts, and drives the perovskite grains to grow oriented and uniformly on the pyramidal structure surface. This ensures that the grain size is stably controlled within the range of 0.8μm-2.5μm, while ensuring that the thickness ratio of the film in the pyramidal region is stably maintained at a high conformability level of 35%-85%. This effectively eliminates impurity phases, improves the film density and carrier transport performance, and ultimately solves the technical problems of insufficient grain growth, uneven film structure, and fluctuations in electrical performance after post-treatment. This achieves high-quality conformal coverage of efficient and stable perovskite films on three-dimensional bottom cells.

[0088] In other embodiments, the organic phase solution further includes a solute and a solvent, wherein the solute includes an organic ammonium salt, and the solvent includes a first solvent or a second solvent, wherein the first solvent includes n-butanol and isooctanol, and the second solvent includes isopropanol and γ-valerolactone. In this embodiment, the solute in the organic phase solution includes an organic ammonium salt, and the solvent adopts either a first solvent system (a mixture of n-butanol and isooctanol) or a second solvent system (a mixture of isopropanol and γ-valerolactone). This combination significantly improves the wettability and volatile kinetic controllability of the solution: the synergistic effect of n-butanol and isooctanol can slow down the solvent evaporation rate and promote the deep penetration and uniform distribution of organic ammonium salt in the porous inorganic framework, while the combination of isopropanol and γ-valerolactone has both high polarity and high boiling point characteristics, effectively inhibiting microcracks and impurity phase precipitation caused by excessively rapid crystallization. Both can work with additives to achieve preferential growth of perovskite grains, ultimately obtaining a high-quality perovskite film with a grain size of 0.8μm-2.5μm, conformability of 35-85%, and no PbI2 residue on the surface.

[0089] Specifically, in preparing the organic phase solution, the solvent system is divided into two categories: In the first solvent system, the volume ratio of n-butanol (NBA) to isooctanol (2EH) can be 95:5, 90:10, 85:15, or 80:20, and this application does not impose specific limitations on this; In the second solvent system, the volume ratio of isopropanol (IPA) to γ-valerol (GVL) can be 98:2, 97:3, 96:4, 95:5, 94:6, or 90:10, and this application does not impose specific limitations on this. The concentration of the organic ammonium salt in the organic phase solution is 0.6-0.8 mol / L.

[0090] Specifically, an organic phase solution is printed on the surface of the inorganic phase film layer of the back cell using an inkjet printer, wherein the grayscale of the inkjet printer is 70%-100%.

[0091] It should be noted that inkjet printing deposition technology has advantages such as fine patterning, large-size processing, precise and controllable deposition volume, and high material utilization (close to 100%). Inkjet printing technology is used in various industrial applications, including printing posters, signs, textiles, labels, and photographs of different sizes. Currently, inkjet printing technology is also used to deposit thin-film resist patterns in the manufacturing process of electronic liquid crystal display panels, and even in decorations and seasonings in the food industry. In recent years, academia and industry have shown interest in the application of inkjet printing technology in the field of tandem solar cells. The general chemical formula of lead halide perovskite is APbX3, where A represents a monovalent cation and X represents a monovalent halide anion. In existing technologies, perovskite thin films are typically prepared using a two-step dry-wet method (dry (evaporation) + wet (spin coating)). Compared with the one-step solution method, the perovskite grain size prepared by the dry-wet two-step method is significantly smaller, which is a common technical drawback in the two-step method field. The perovskite thin film grain size obtained by existing technical solutions is relatively small (100-400nm). Small grain size means more grain boundaries, more grain boundaries mean more interface defects, and more interface defects mean poorer film electrical properties. The method for fabricating tandem solar cells disclosed in this application achieves perovskite grain size comparable to that of a one-step solution method in a two-step dry-wet process, and promotes the full reaction between the organic and inorganic phases, thereby eliminating residual lead iodide. Based on the combined dry-wet two-step route and using an additive containing urea, this application obtains grain size (800-2500 nm) comparable to that of the one-step solution method. Urea has the advantages of low toxicity, safety, environmental friendliness, and ultra-low cost. At the same time, it eliminates the impurity phase (i.e., lead iodide) on the surface of the perovskite film, and can obtain perovskite films with highly reproducible grain size (800-2500 nm), high conformability, and no impurity phases.

[0092] The preparation method of the tandem solar cell of this application will be described in detail below with reference to specific embodiments and comparative examples.

[0093] Example 4

[0094] The first step involves preparing a porous inorganic phase film using a vacuum thermal evaporation system. The evaporation rate ratio is PbI2:CsBr = 4:0.8, and the thickness of the inorganic phase film is 500 nm. The second step involves preparing an organic phase solution. The solvent system is the first solvent system, in which the volume ratio of n-butanol (NBA) to isooctanol (2EH) is 85:15. Urea at a concentration of 1.5 mg / ml is added to the solution to obtain the organic phase solution. The concentration of the organic ammonium salt in the organic phase solution is 0.7 mol / L. The organic phase solution is then printed onto the surface of the bottom cell opposite to the inorganic phase film using an inkjet printer with a grayscale of 85%. The third step involves post-processing the bottom cell with the printed organic phase solution using a near-infrared radiation heating device or a vacuum drying device. The fourth step involves annealing the post-processed bottom cell at 110°C for 15 minutes.

[0095] Comparative Example 2

[0096] The first step involves preparing a porous inorganic phase film using a vacuum thermal evaporation device. The evaporation rate ratio is PbI2:CsBr = 4:0.8, and the thickness of the inorganic phase film is 500 nm. The second step involves preparing an organic phase solution. The solvent system is the first solvent system, in which the volume ratio of n-butanol (NBA) to isooctanol (2EH) is 85:15. The concentration of the organic ammonium salt in the organic phase solution is 0.7 mol / L. The organic phase solution is then printed onto the surface of the bottom cell opposite to the inorganic phase film using an inkjet printer with a grayscale of 85%. The third step involves post-processing the bottom cell with the printed organic phase solution using a near-infrared radiation heating device or a vacuum drying device. The fourth step involves annealing the post-processed bottom cell at 110°C for 15 minutes. (Comparative Example 2 is an example where, under the same conditions, urea is not added during the preparation of the organic phase solution.)

[0097] A schematic diagram of the SEM (Scanning Electron Microscope) image of the tandem solar cell prepared in Example 4 is shown below. Figure 1 and Figure 2 As shown, Figure 1 This is a SEM cross-sectional view of a tandem solar cell. Figure 2 This is a tilted SEM image of a tandem solar cell (i.e., an SEM surface image of a perovskite thin film). Figure 1The perovskite film 12 exhibits excellent conformal coverage on a bottom cell with multiple pyramidal structures, and the surface of the perovskite film 12 is essentially free of impurities. The thickness of the valley of one pyramidal structure is 1180 nm, the first film thickness of one pyramidal structure is 688 nm, the second film thickness of one pyramidal structure is 487 nm, the first film thickness of another pyramidal structure is 640 nm, and the second film thickness of another pyramidal structure is 544 nm. Figure 2 The perovskite thin film 12 exhibits large grain size 13 and smooth grain boundaries.

[0098] SEM image of the tandem solar cell prepared in Comparative Example 2 is shown below. Figure 5 and Figure 6 As shown, Figure 5 This is a SEM cross-sectional view of a tandem solar cell. Figure 6 This is a SEM image of the perovskite film with an angle (i.e., an SEM surface image of the perovskite film). Figure 5 and Figure 6 As can be seen, compared with Example 4, the perovskite film has a smaller grain size and obvious PbI2 impurity particles (white dots) on the film surface.

[0099] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0100] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A tandem solar cell, characterized in that, include: A bottom battery, wherein the base of the bottom battery has a pyramid structure; A top cell, located above the pyramid structure, comprises a perovskite thin film, the perovskite thin film comprising multiple grains, the grains having a size of 0.8 μm-2.5 μm.

2. The tandem solar cell according to claim 1, characterized in that, The conformability of the perovskite film is 35%-85%, which characterizes the ratio of the apex film thickness to the valley film thickness. The apex film thickness is the thickness of the perovskite film covering the apex of the pyramid structure, and the valley film thickness is the thickness of the perovskite film covering the valley of the pyramid structure. The thickness directions of the apex film thickness and the valley film thickness are parallel to the thickness direction of the bottom cell.

3. The tandem solar cell according to claim 1, characterized in that, The first film thickness is greater than the second film thickness. The first film thickness is the thickness of the perovskite film covering one of the slopes of the pyramid structure, and the second film thickness is the thickness of the perovskite film covering the other slope of the pyramid structure. The thickness direction of the first film thickness is perpendicular to the one slope of the pyramid structure, and the thickness direction of the second film thickness is perpendicular to the other slope of the pyramid structure.

4. The tandem solar cell according to claim 3, characterized in that, The difference between the first film thickness and the second film thickness is 3%-30% of the second film thickness.

5. The tandem solar cell according to claim 1, characterized in that, The perovskite film includes at least one of urea molecules, biuret molecules, and thiourea molecules.

6. The tandem solar cell according to claim 1, characterized in that, The mass fraction of impurity phases in the perovskite film is less than 0.5%, and the impurity phases include lead iodide.

7. The tandem solar cell according to claim 1, characterized in that, The radius of curvature of the perovskite film covering the apex of the pyramid structure is 400 nm-550 nm.

8. The tandem solar cell according to claim 1, characterized in that, The spacing between two adjacent grains is 5nm-50nm.

9. The tandem solar cell according to claim 1, characterized in that, The thickness of the perovskite film is 500nm-1500nm.

10. The tandem solar cell according to claim 1, characterized in that, The tandem solar cell further includes a tunneling composite layer located between the bottom cell and the top cell. The top cell further includes: a first transparent conductive layer located between the perovskite thin film and the tunneling composite layer; a first carrier transport layer located between the perovskite thin film and the first transparent conductive layer; a second carrier transport layer located on the side of the perovskite thin film opposite to the bottom cell; a second transparent conductive layer located on the side of the second carrier transport layer opposite to the bottom cell; and a plurality of spaced-apart top electrodes located on the side of the second transparent conductive layer opposite to the bottom cell.

11. The tandem solar cell according to claim 1, characterized in that, The base battery includes any one of PERC battery, PERT battery, TOPCon battery, HJT battery, and BC battery.

12. A method for fabricating a tandem solar cell, characterized in that, The method is used to prepare a tandem solar cell according to any one of claims 1 to 11, the method comprising: A bottom battery is provided, wherein the base of the bottom battery has a pyramid structure; A top cell is formed above the pyramid structure. The top cell includes a perovskite thin film, which comprises multiple grains with a size of 0.8 μm to 2.5 μm.

13. The method for preparing a tandem solar cell according to claim 12, characterized in that, A top battery is formed above the pyramid structure, comprising: A porous inorganic phase film layer is formed above the pyramid structure, and the materials of the inorganic phase film layer include PbI2 and CsBr; An organic phase solution is deposited on the surface of the inorganic phase film layer away from the bottom cell. The organic phase solution includes an additive, which includes at least one of urea, biuret, and thiourea. The bottom cell on which the organic phase solution is deposited is post-treated using near-infrared radiation heating equipment and / or vacuum drying equipment, wherein the vacuum drying equipment includes a vacuum flash evaporator and / or a vacuum crystallizer. The post-processed bottom cell is annealed to obtain the perovskite thin film.

14. The method for preparing a tandem solar cell according to claim 13, characterized in that, In the organic phase solution, the mass concentration of the additive is 1 mg / ml to 5 mg / ml.

15. The method for preparing a tandem solar cell according to claim 13, characterized in that, The post-processed bottom cell is annealed, including: The bottom battery is annealed at a temperature of 100℃-130℃ for 15-30 minutes.

16. The method for preparing a tandem solar cell according to claim 13, characterized in that, The organic phase solution further includes a solute and a solvent, the solute comprising an organic ammonium salt, and the solvent comprising a first solvent or a second solvent, the first solvent comprising n-butanol and isooctanol, and the second solvent comprising isopropanol and γ-valerolactone.

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