Perovskite tandem cell substrate, perovskite tandem cell and preparation method thereof

Abstract

The application relates to a perovskite laminated battery substrate, a perovskite laminated battery and a preparation method thereof, and the substrate preparation method comprises the following steps: preparing a crystalline silicon substrate through a diamond wire cutting process; performing a front wet polishing treatment on the crystalline silicon substrate, cleaning residual on the surface of the crystalline silicon substrate, rounding sharp peaks and valleys generated in the cutting process, forming a pretreated surface; performing laser cold polishing on the pretreated surface, adopting a picosecond / femtosecond pulse laser to perform engraving on the surface cutting line mark, reducing the surface height difference and roughness, and forming a photochemical treatment surface; and performing a rear wet polishing treatment on the photochemical treatment surface, removing the laser melting layer and surface residual and modifying the morphology, and finally forming a textured surface after activation. Through the dry-wet combined preparation method, the diamond wire cutting silicon wafer is polished and engraved to be suitable for large-scale industrialized production of perovskite laminated battery substrates, the preparation cost of the substrate and the battery is reduced, and the production efficiency is improved.

Description

Technical Field

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

[0002] Dual-ended tandem solar cells combine a perovskite absorber layer and a crystalline silicon bottom cell. Using wide-bandgap perovskite as the top cell absorber and crystalline silicon as the bottom cell, they achieve a conversion efficiency as high as 31.3%, significantly exceeding that of single-junction silicon solar cells, thus becoming the future direction for high-efficiency solar cell production. Currently, most high-efficiency perovskite / crystalline silicon tandem cells are based on an N-type monocrystalline silicon bottom cell (approximately 250-300 µm thick), with a planar polished or sub-textured surface on the front side to ensure compatibility with solution-processed perovskite thin films. Detailed optical analysis of perovskite / crystalline silicon tandem solar cells reveals that their optical losses mainly originate from reflection and parasitic absorption losses. To further improve the current collection efficiency of tandem cells, the most direct approach is to reduce reflection from the front surface, which can be achieved through antireflection layers, increasing the gradient refractive index, and textured light-trapping structures. Therefore, while ensuring the matching of perovskite thin film deposition, and drawing on the technical route of crystalline silicon solar cells, the top of the perovskite / crystalline silicon tandem solar cell can be transformed from a planar structure to a pyramidal textured structure. This can reduce reflection and increase light capture, thereby improving the energy conversion efficiency of tandem solar cells.

[0003] However, due to the diamond wire cutting process, the surface of existing monocrystalline silicon wafers exhibits significant surface undulations in the cutting marks. The height difference between peaks and valleys within a 100μm range is typically around 4-5μm, resulting in a roughness of approximately 0.8-1.1μm. Such large surface height variations, even when using traditional alkaline texturing systems to prepare substrates, will result in significant height differences on the substrate surface due to these cutting mark variations, and the surface flatness is insufficient to meet the requirements of texturing and etching. While the existing chemical mechanical polishing (CMP) method can control the height difference of the cutting marks on the original diamond wire-cut silicon wafers to within the required range, this method is extremely time-consuming. For example, processing a single M6 (166mm*166mm) silicon wafer typically takes over 1 hour, and the cost per wafer is as high as 600 yuan, which cannot meet the needs of commercially viable low-cost perovskite / crystalline silicon tandem solar cells. Therefore, a low-cost, rapid substrate preparation method that meets the production requirements of perovskite tandem solar cells is needed. Summary of the Invention

[0004] This application provides a perovskite tandem solar cell substrate, a perovskite tandem solar cell, and a method for preparing the same, in order to solve the problems in the prior art where the height difference of the diamond wire cut substrate is too large, the ordinary alkaline polishing process cannot meet the requirements, and the CMP process is too time-consuming and costly.

[0005] According to the method for fabricating a perovskite tandem solar cell substrate provided in this application, the method includes:

[0006] Step S1: Fabricate a crystalline silicon substrate using a diamond wire cutting process;

[0007] Step S2: Perform pre-wet polishing on the crystalline silicon substrate to clean the residue on the surface of the crystalline silicon substrate and round the sharp peaks and valleys generated by cutting to form a pre-treated surface;

[0008] Step S3: Perform laser cold polishing on the pre-treated surface using picosecond / femtosecond pulsed lasers to sculpt the surface with a spot size that matches the surface cutting lines, thereby reducing surface height differences and roughness and forming a photochemically treated surface.

[0009] Step S4 involves post-wet polishing of the photochemically treated surface to remove the laser-melted layer and surface residues and modify the morphology, ultimately forming an activated textured surface.

[0010] In some embodiments, the peak-to-valley spacing of the cutting marks generated by diamond wire cutting in step S1 is 50-100 μm; in step S3, the laser beam spot conditions are set as follows: laser spot diameter 40-80 μm, laser spot overlap rate 29-100%, laser defocusing amount 0.5-1.5 mm, laser spot scanning line spacing 0.03-0.05 mm, and scanning speed 5000-6000 mm / s, to adapt to the surface cutting marks for engraving.

[0011] In some embodiments, step S3 further includes setting the laser beam energy conditions as follows: laser wavelength 342-532nm, average power 10-50W, repetition frequency 50KHz-20MHz, pulse width 10-20ps, single pulse energy 40-90μJ, and beam quality factor M. 2 ≤1.3, to control the depth of laser engraving.

[0012] In some embodiments, in step S3, the surface roughness of the photochemically treated surface obtained after laser cold polishing is Ra<0.14μm, and the peak-to-valley height difference within a 100μm range is less than 1.5μm.

[0013] In some embodiments, the polishing conditions for the pre-wet polishing treatment are: time 200-400s, temperature 65-75℃; the polishing solution used in the pre-wet polishing treatment comprises: 3-5 volumes of 22-25wt% alkaline solution, 1-2 volumes of 2-4wt% working solution, and 182-186 volumes of pure water; wherein, the working solution comprises: oxidant, complexing agent, surfactant, corrosion inhibitor and solvent.

[0014] In some embodiments, the post-wet polishing treatment has the same polishing conditions and polishing liquid composition as the pre-wet polishing treatment. The textured surface of the perovskite tandem battery substrate finally prepared in step S4 has a peak-valley height difference of 0.4-0.8 μm within a range of 100 μm and a roughness Ra of 0.07-0.1 μm.

[0015] According to another aspect of this application, a perovskite tandem solar cell substrate is provided, characterized in that the perovskite tandem solar cell substrate is prepared by the perovskite tandem solar cell substrate preparation method described above.

[0016] According to another aspect of this application, a method for fabricating a perovskite tandem solar cell is provided, the method comprising:

[0017] Step S10: Fabricate a crystalline silicon substrate using the perovskite tandem solar cell substrate fabrication method described above;

[0018] Step S11: Clean and texturize the crystalline silicon substrate;

[0019] Step S12: Deposit an amorphous silicon passivation layer, a microcrystalline silicon doped layer, and an ITO conductive layer on a crystalline silicon substrate to form a crystalline silicon bottom cell;

[0020] Step S13: Fabricate a perovskite absorber layer on the crystalline silicon bottom cell to form a stacked cell substrate;

[0021] Step S14: Deposit a transparent conductive layer on the stacked battery substrate;

[0022] Step S15: Print metal electrodes on the transparent conductive layer to form a perovskite tandem solar cell.

[0023] In some embodiments, in step S12, the amorphous silicon passivation layer has a deposition thickness of 5-10 nm, the N-type / P-type microcrystalline doped layer has a deposition thickness of 15-30 nm, and the transparent conductive layer has a deposition thickness of 70-100 nm.

[0024] According to another aspect of this application, a perovskite tandem solar cell is provided, which is prepared by the perovskite tandem solar cell preparation method described above.

[0025] By applying the technical solution of this application, a diamond wire cutting process is used to fabricate crystalline silicon substrates, maintaining the advantages of large-scale, low-cost, and rapid production of diamond wire cutting. A combined wet and dry method is employed to planarize the diamond wire-cut substrates. This method overcomes the problem that traditional single wet processing cannot adequately plan the substrate surface by utilizing pre-wet polishing, ultrafast laser cold polishing, and post-wet polishing. This forms a substrate preparation method that can replace the high-cost CMP process. Specifically, the pre-wet polishing process can initially round sharp peaks and valleys, thereby improving the beam coverage uniformity of the laser engraving step and increasing engraving efficiency to quickly and preferentially process protrusions. Combined with a laser spot matching the characteristics of the cutting lines, the wire-cut features are efficiently and completely planarized. Finally, through the modification and activation effect of the post-wet polishing step, a substrate texture surface that meets the requirements for perovskite tandem solar cell production is obtained. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A schematic diagram of the perovskite tandem solar cell substrate fabrication method according to an embodiment of this application is shown;

[0029] Figure 2 It shows Figure 1 A schematic diagram of the process for fabricating the perovskite tandem solar cell substrate in the embodiment;

[0030] Figure 3 A schematic diagram of photochemical processes in laser cold polishing is shown.

[0031] Figure 4 This paper shows a diagram of the surface structure of the perovskite tandem solar cell substrate before processing, according to an embodiment of this application.

[0032] Figure 5 The diagram shows the surface structure of the substrate after processing by the perovskite tandem solar cell substrate preparation method according to an embodiment of this application.

[0033] Figure 6 A schematic flowchart of the perovskite tandem solar cell fabrication method according to an embodiment of this application is shown.

[0034] The above figures include the following reference numerals:

[0035] 1. Surface protrusion; 2. Cold polishing laser beam; 3. Finished surface. Detailed Implementation

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] 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.

[0038] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways, rotated 90 degrees, or in other orientations, and the spatial relative descriptions used herein will be interpreted accordingly.

[0039] In the current photovoltaic industry, surface texturing of crystalline silicon substrates mainly falls into the following categories: 1. Planar texture: The simplest surface structure, achieved by removing sawing damage using alkaline wet chemical etching technology to obtain a near-planar surface. However, the planar structure leads to significant light reflection loss and is unsuitable for high-efficiency cell production. 2. Micron-level pyramidal texture: Prepared using alkaline etching methods, commonly used in industrial single-junction silicon solar cells. This texture has good light-trapping and reflection loss reduction capabilities, but is not suitable for perovskite solution processing methods. 3. Submicron-level pyramidal texture: Achieved by adjusting the etching solution concentration and processing time. This texture is compatible with perovskite solution processing methods, but still suffers from tip current leakage issues. 4. Nanotexture: Widely designed and applied in recent years, with commercial compatibility, capable of perovskite solution processing, and possessing excellent light-trapping capabilities. Therefore, for the fabrication of high-efficiency perovskite tandem cells, crystalline silicon substrates with nanotextured textures are the most promising.

[0040] However, based on existing alkaline texturing systems, the surface of the silicon substrate is subject to significant variations due to the diamond wire cutting process. The height difference of these cut lines within a 100μm range is typically around 4-5μm, resulting in a roughness of approximately 0.8-1.1μm. Therefore, such large surface height variations cannot be addressed by existing single wet alkaline polishing processes to achieve the required nano-textured surface. While chemical mechanical polishing (CMP) can control the cut line height difference to within 0.3-0.6μm, its time consumption per wafer is excessively long and costly, failing to meet the demands for commercially viable, low-cost perovskite tandem solar cell fabrication. Therefore, to reduce costs and improve fabrication efficiency, this application proposes a method for rapidly and cost-effectively producing perovskite tandem solar cell substrates with nano- or near-nano-textured surfaces by combining the wet processing method of the alkaline texturing system with dry laser cold polishing.

[0041] Figures 1 to 5 An embodiment of the method for fabricating a perovskite tandem solar cell substrate according to this application is illustrated schematically.

[0042] like Figure 1 and Figure 2 As shown, this application discloses a method for fabricating a perovskite tandem solar cell substrate, the method comprising:

[0043] Step S1: Fabricate a crystalline silicon substrate using a diamond wire cutting process.

[0044] Diamond wire cutting is a commonly used single-crystal silicon cutting technology, characterized by high efficiency and low cost, suitable for large-scale silicon wafer manufacturing, and can effectively control battery production costs and improve production efficiency. Diamond wire cutting creates a unique, highly undulating surface, which significantly impacts the performance of subsequent perovskite tandem solar cells. This application embodiment uses a combination of dry and wet methods to process this unique diamond wire-cut surface to obtain the crystalline silicon substrate surface structure required for perovskite deposition.

[0045] Step S2 involves pre-wetting polishing the crystalline silicon substrate to clean the residue on the surface of the substrate and round off the sharp peaks and valleys generated by the cutting process, thus forming a pre-treated surface.

[0046] The purpose of pre-wet polishing is to remove residual silicon powder and organic contaminants from the surface of the crystalline silicon substrate under the original diamond wire cutting process, and at the same time to initially smooth the surface of the crystalline silicon substrate, thereby providing a clean and smooth surface foundation for the subsequent dry laser cold polishing process, so that the laser beam can more evenly and effectively irradiate and cover the surface of the crystalline silicon substrate.

[0047] Step S3: Perform laser cold polishing on the pre-treated surface using picosecond / femtosecond pulsed lasers to sculpt the surface with a spot size that matches the surface cutting lines, thereby reducing surface height differences and roughness and forming a photochemically treated surface.

[0048] In step S3, dry laser cold polishing is used to perform surface scanning etching on the crystalline silicon substrate using an ultrafast picosecond / femtosecond pulsed laser. This flattens the surface of the crystalline silicon substrate, rapidly reduces peaks, and minimizes surface undulations to match the subsequent textured perovskite deposition technique.

[0049] Step S4 involves post-wet polishing of the photochemically treated surface to remove the laser-melted layer and surface residues and modify the morphology, ultimately forming an activated textured surface.

[0050] Since the high-energy laser beam generates a molten silicon layer, residue, and surface organic contaminants during the previous laser cold polishing process, this application embodiment adds a post-wet polishing process to remove the amorphous silicon layer and residue generated by the laser beam, modify the surface morphology of the laser-polished silicon substrate, and restore its surface chemical activity, ultimately forming a smooth and clean nano-textured silicon substrate.

[0051] Figure 2 The process diagram shown depicts, from top to bottom, the original diamond wire-cut silicon wafer, the result of pre-wet polishing, the result of ultrafast laser cold polishing, and the result of post-wet polishing.

[0052] Through the above-described method embodiments, the perovskite tandem solar cell substrate preparation method of this application uses diamond wire cutting technology to fabricate crystalline silicon substrates, maintaining the advantages of large-scale, low-cost, and rapid production of diamond wire cutting. It employs a combination of dry and wet methods to planarize the diamond wire-cut substrate, utilizing pre-wet polishing, ultrafast laser cold polishing, and post-wet polishing to overcome the problem that traditional single wet processing cannot adequately plan the substrate surface, forming a substrate preparation method that can replace the high-cost CMP process. Specifically, the pre-wet polishing process can initially round sharp peaks and valleys, thereby improving the beam coverage uniformity of the laser engraving step, increasing engraving efficiency to quickly and preferentially process protrusions, and, combined with a laser spot matching the characteristics of the cutting lines, efficiently and completely planarizing the wire-cut features. Finally, through the modification and activation effect of the post-wet polishing process, a substrate texture surface that meets the requirements for perovskite tandem solar cell production is obtained.

[0053] In some embodiments of this application, the peak-to-valley spacing of the cutting marks generated by diamond wire cutting in step S1 is 50-100 μm. In step S3, the laser beam spot conditions are set as follows: laser spot diameter 40-80 μm, laser spot overlap rate 29-100%, laser defocusing amount 0.5-1.5 mm, laser spot scanning line spacing 0.03-0.05 mm, and scanning speed 5000-6000 mm / s, to adapt to the surface cutting marks for engraving. During laser etching in this application, the spot size diameter is 40-80 μm, matching the peak-to-valley spacing of the cutting marks at 50-100 μm. When the spot covers multiple peaks and valleys, the overlapping scanning overlap rate of 29-100% prioritizes the removal of surface protrusions, thereby achieving rapid and efficient planarization of the crystalline silicon substrate and reducing height differences and roughness. Moreover, in the embodiments of this application, the laser scanning line spacing is 0.03-0.05 mm, which ensures full coverage and avoids omissions. By establishing the correspondence between the laser spot size and the wire cutting mark size, this embodiment enables the laser to efficiently smooth the wire cutting features. The laser spot overlap rate is 29%–100% to ensure scanning continuity; it should not be too large or too small. If the overlap rate is <29%, unpolished stripes are likely to appear; if the overlap rate is >100%, efficiency decreases, and over-polishing may occur. A scanning speed of 5000–6000 mm / s improves efficiency. If the scanning speed is <5000 mm / s, the thermal risk increases; if the scanning speed is >6000 mm / s, insufficient pulse overlap results in an uneven surface. The scanning line spacing is 0.03–0.05 mm to match the laser spot diameter and ensure full coverage. A spacing >0.05 mm results in missed areas; a spacing <0.03 mm increases time costs. The laser defocusing amount is 0.5–1.5 mm to control the spot size and energy density appropriately. If the defocusing amount is less than 0.5mm, the energy density is too high and ablation may occur; if the defocusing amount is greater than 1.5mm, the energy is dispersed and the polishing effect is poor.

[0054] When lasers polish material surfaces, both thermal and photochemical effects occur simultaneously. However, in this application embodiment, short-wavelength, ultrafast lasers are used to polish crystalline silicon substrates, where photochemical effects play a dominant role. Specifically, the laser cold polishing process selects short-pulse-width, short-wavelength lasers as the laser source, such as picosecond-level or femtosecond-level pulsed lasers. Different surfaces are suitable for different laser polishing mechanisms, and these mechanisms are closely related to material surface properties, laser characteristics, process parameters, and the processing environment. The laser cold polishing mechanism has almost no limitations on the processed materials and is suitable for hard and brittle materials such as single-crystal silicon, as well as some materials with poor thermophysical properties, achieving true "cold polishing."

[0055] Specifically, in some embodiments of this application, step S3 further includes setting the laser beam energy conditions as follows: laser wavelength 342-532nm, average power 10-50W, repetition frequency 50KHz-20MHz, pulse width 10-20ps, single pulse energy 40-90μJ, and beam quality factor M. 2 ≤1.3, through the above parameter design, the laser engraving depth is controlled and the laser thermal effect is reduced, so that photochemical action is dominant, achieving cold polishing. Its photochemical action is as follows: Figure 3 As shown.

[0056] refer to Figure 3 A cold-polishing laser beam 2 irradiates the surface of a crystalline silicon substrate, and the irradiated area absorbs laser photon energy. Since the laser wavelength of 342-532nm corresponds to photon energy of 3.6-2.3eV, which is higher than the bond energy of silicon (1.1eV), it can directly break Si-Si bonds to achieve photochemical decomposition. The cold-polishing laser beam 2 instantly destroys the crystal lattice structure, and the chemical bond breaking rate is greater than the bonding rate, causing material expansion. This leads to the photochemical decomposition and peeling off of the protrusion 1 on the crystalline silicon substrate surface. The photochemical decomposition causes the material in the etched area to expand rapidly, and the local gas pressure increases rapidly. The expanded material detaches from the substrate in the form of a Coulomb explosion, and the excess energy is carried away through photolytic peeling, ultimately achieving cold polishing and forming a smooth etched surface 3. During this process, the heat-affected zone is less than 1μm, avoiding melting and resolidification. The laser generator uses a picosecond pulsed laser PX50-2-G with a laser wavelength of 342-532nm. The short wavelength and high photon energy enhance the photochemical decomposition. If the wavelength is >532nm, the energy is insufficient, resulting in a low removal rate; if the wavelength is <342nm, excessive absorption by the surface may cause thermal damage. An average power of 10-50W balances removal efficiency and thermal effects. Power <10W results in slow polishing; power >50W may lead to heat accumulation and microcracks on the surface. A repetition frequency of 50kHz-20MHz allows for high-speed scanning. A frequency <50kHz results in long pulse intervals and surface inhomogeneity; a frequency >20MHz may result in insufficient pulse energy and incomplete polishing. A pulse width of 10-20ps reduces heat diffusion with ultrashort pulses. Pulses >20ps exhibit significant thermal effects, similar to nanosecond lasers; pulses <10ps result in high equipment costs and limited benefits. A single pulse energy of 40-90μJ ensures effective photolytic ablation. Energy <40μJ results in insufficient material removal; energy >90μJ may cause excessive Coulomb explosions, forming pits on the surface. Beam quality factor M. 2 ≤1.3, ensuring accurate beam focusing and uniform processing. M 2 If the value is greater than 1.3, the light spot will deform and the roughness will increase.

[0057] In some embodiments of this application, in step S3, the surface roughness of the photochemically treated surface obtained after laser cold polishing is Ra < 0.14 μm, and the peak-to-valley height difference within a 100 μm range is less than 1.5 μm. This surface smoothing index ensures that the desired nanotextured crystalline silicon substrate surface is obtained after post-wet polishing to match the perovskite thin film deposition technology in the subsequent battery production process.

[0058] In some embodiments of this application, the polishing conditions for the pre-wet polishing treatment are: time 200-400s, temperature 65-75℃. The polishing solution used in the pre-wet polishing treatment comprises: 3-5 volumes of 22-25wt% alkaline solution, 1-2 volumes of 2-4wt% working solution, and 182-186 volumes of pure water. The working solution comprises: an oxidant, a complexing agent, a surfactant, a corrosion inhibitor, and a solvent. The working solution can be a commercially available existing wet alkaline polishing working solution, such as the commercial ST-02 series. In some embodiments of this application, the oxidant in the working fluid includes hydrogen peroxide and / or organic peroxides (such as peracetic acid); the complexing agent includes one or more of EDTA (sodium ethylenediaminetetraacetate), DTPA (diethyltriaminepentaacetic acid), NTA (nitrotriacetic acid), and citrate; the surfactant includes alcohol ethers and / or polyether compounds (such as fatty alcohol polyoxyethylene ether, polyoxyethylene lauryl ether); the corrosion inhibitor includes pyrrolidones (such as N-methylpyrrolidone), specific organic compounds, etc. The polishing principle of the working fluid is: Si + 2NaOH + H2O = Na2SiO3 + 2H2, the chemical corrosion reaction of alkali with silicon; R-X + NaOH = R-OH + NaX, Ar-X + 2NaOH = Ar-ONa + NaX + H2O, where R, Ar, and X represent alkyl, aryl, and halogen, respectively, representing the chemical corrosion reaction of alkali with organic matter.

[0059] In some embodiments of this application, a pre-wet polishing working fluid is provided with the following specific components: oxidant – hydrogen peroxide (H2O2) 27–35 wt%; complexing agent – ​​EDTA-4Na (ethylenediaminetetraacetic acid tetrasodium) 0.05–0.2 wt%, NTA-3Na (trisodium triacetate) 0.05–0.3 wt%; nonionic surfactant – AEO-9 (fatty alcohol polyoxyethylene ether) 0.01–0.05 wt%, Brij-35 (polyoxyethylene lauryl ether) 0.01–0.03 wt%; corrosion inhibitor – NMP (N-methylpyrrolidone) 0.01–0.1 wt%, with the balance being solvent.

[0060] In some embodiments of this application, the post-wet polishing treatment uses the same polishing conditions and polishing solution composition as the pre-wet polishing treatment, but their functions differ. The post-wet polishing treatment is mainly used to remove laser-generated amorphous silicon layer residues and restore surface chemical activity. The textured surface of the perovskite tandem solar cell substrate finally prepared in step S4 has a peak-to-valley height difference of 0.4-0.8 μm within a 100 μm range and a roughness Ra of 0.07-0.1 μm, thereby transforming the uniquely undulating surface formed by diamond wire cutting into a nano-substrate textured surface that meets the production requirements of perovskite tandem solar cells.

[0061] In this embodiment, the unique surface structure formed by diamond wire cutting on the silicon substrate is mainly a sharp peak-valley structure, with a peak-valley spacing of approximately 50-100 μm and a height difference of 4-5 μm. The surface contains microcracks and silicon powder residue. The pre-wet polishing treatment in this application primarily aims to remove residues, round the sharp peaks and valleys, reduce the height difference, and form a smoother surface that still has slight undulations. Therefore, using pre-wet polishing before laser etching results in a cleaner surface, preventing light absorption caused by residue interference during laser action. Simultaneously, the micro-undulation structure allows the laser spot to cover the surface evenly, without being blocked by sharp, curved peaks. Thus, during overlapping scanning, the protruding parts of the silicon substrate surface are preferentially removed, thereby rapidly reducing the surface height difference.

[0062] Using M6 specification (silicon wafer area 274.15cm²) 2 Taking diamond wire cutting of a single-crystal silicon wafer as an example, the height difference of the cutting line within a 100μm range is 4.26μm, and the roughness is 1.03μm. The following verification was performed:

[0063] Example 1

[0064] Process: Diamond wire cutting of raw silicon wafers — pre-wet polishing — laser cold polishing — post-wet polishing. Alkaline polishing formula: 22wt% NaOH solution, 3L; 2wt% ST-02 series alkaline polishing working solution, 1L; pure water, 186L; time, 200s; temperature, 70℃; reaction tank volume, 190L; laser polishing parameters: average power, 50W; repetition frequency, 615KHz; pulse width, 10ps; single pulse energy, 50μJ; beam quality factor, M. 2 ≤1.3, wavelength 532nm, laser spot overlap rate 55%, laser spot scanning speed 5000mm / s, laser spot scanning line spacing 0.03mm, laser defocusing amount 1mm, laser spot diameter 60μm.

[0065] Test results (high magnification 3D microscope): maximum profile height difference within 100μm range is 0.53μm, surface roughness is -0.079μm.

[0066] Comparative Example 1

[0067] Process: Diamond wire cutting of raw silicon wafers — pre-wet polishing treatment — laser cold polishing. Alkaline polishing formula: 22wt% NaOH solution, 3L; 2wt% ST-02 series alkaline polishing working solution, 1L; pure water, 186L; time, 200s; temperature, 70℃; reaction tank volume, 190L; laser polishing parameters: average power, 50W; repetition frequency, 615KHz; pulse width, 10ps; single pulse energy, 50μJ; beam quality factor, M. 2 ≤1.3, wavelength 532nm, laser spot overlap rate 55%, laser spot scanning speed 5000mm / s, laser spot scanning line spacing 0.03mm, laser defocusing amount 1mm, laser spot diameter 60μm.

[0068] Test results (high magnification 3D microscope): maximum profile height difference within 100μm range is 1.47μm, surface roughness is -0.138μm.

[0069] Comparative Example 2

[0070] Process: Diamond wire cutting of raw silicon wafers — laser cold polishing — post-wet polishing treatment. Alkaline polishing formula: 22wt% NaOH solution, 3L; 2wt% ST-02 series alkaline polishing working solution, 1L; pure water, 186L; time, 200s; temperature, 70℃; reaction tank volume, 190L; laser polishing parameters: average power, 50W; repetition frequency, 615KHz; pulse width, 10ps; single pulse energy, 50μJ; beam quality factor, M. 2 ≤1.3, wavelength 532nm, laser spot overlap rate 55%, laser spot scanning speed 5000mm / s, laser spot scanning line spacing 0.03mm, laser defocusing amount 1mm, laser spot diameter 60μm.

[0071] Test results (high magnification 3D microscope): maximum profile height difference within 100μm range is 1.63μm, surface roughness is -0.492μm.

[0072] Comparative Example 3

[0073] Process: Diamond wire cutting of raw silicon wafers — single wet polishing treatment. Alkaline polishing formula: 22wt% NaOH solution, 3L; 2wt% ST-02 series alkaline polishing working solution, 1L; pure water, 186L; time, 200s; temperature, 70℃; reaction tank volume, 190L.

[0074] Test results (high magnification 3D microscope): maximum profile height difference within 100μm range is 2.17μm, surface roughness is -0.82μm.

[0075] Comparative Example 4

[0076] Process: Diamond wire cutting of raw silicon wafers — outsourced CMP polishing.

[0077] Test results (high magnification 3D microscope): maximum profile height difference within 100μm range is 0.31μm, surface roughness is -0.047μm.

[0078] As can be seen from the above embodiments and comparative examples, this application achieves effective preparation of the surface of diamond wire-cut silicon wafers through a combined wet and dry polishing and carving method, employing a process flow of pre-wet polishing + ultrafast laser cold polishing + post-wet polishing. This results in a nano-textured crystalline silicon substrate similar to the CMP process, reducing the production cost of large-scale crystalline silicon substrates and improving the production efficiency of substrates and perovskite tandem solar cells. Specifically, compared to the existing single wet alkaline polishing process, this application improves the performance of a maximum contour height difference of 2-4 μm and a roughness of 0.6-0.9 μm to a maximum contour height difference of 0.4-0.8 μm and a roughness of 0.07-0.1 μm, with performance parameters similar to the CMP process. Regarding production costs and time consumption, this application is suitable for large-scale industrial production. The pre- and post-wet polishing processes can adopt mature equipment solutions such as existing tank cleaning or chain cleaning in the photovoltaic field. The laser polishing equipment is also easy to cooperate with laser manufacturers in the photovoltaic field to develop mass production. Laboratory results show that, compared with the high-cost and time-consuming CMP process, taking M6 silicon wafers as an example, the wet processing + laser cold polishing + post-wet processing method of this application has a single-wafer polishing efficiency of about 50-60 seconds (time consumption is amortized through batch processing), and a single-wafer processing cost (chemical and auxiliary material costs such as water, electricity and gas) of about 0.6 yuan. These figures can be even lower for mass production, thus overcoming the cost and efficiency problems of existing perovskite tandem cell substrate preparation.

[0079] According to another aspect of this application, a perovskite tandem solar cell substrate is disclosed, which is prepared by the perovskite tandem solar cell substrate preparation method as described in the above embodiments. (Reference) Figure 4 and Figure 5 As shown in the images, the surface morphology of the crystalline silicon substrate before and after processing by the perovskite tandem solar cell substrate preparation method of this application demonstrates that this application effectively flattens the unique surface morphology of the diamond wire-cut crystalline silicon substrate, making it more suitable for perovskite tandem solar cell preparation. This is used to match the perovskite thin film deposition process, reduce reflection, increase light-harvesting ability, and meet the production requirements of high-efficiency perovskite tandem solar cells.

[0080] According to another aspect of this application, this application discloses a method for fabricating perovskite tandem solar cells, such as... Figure 6 As shown, the method includes:

[0081] Step S10 involves fabricating a crystalline silicon substrate using the perovskite tandem solar cell substrate fabrication method described in the above embodiment. Through step S10, a nanotextured crystalline silicon substrate meeting the production requirements of perovskite tandem solar cells is obtained.

[0082] Step S11 involves cleaning and texturing the crystalline silicon substrate. Cleaning and texturing the crystalline silicon substrate further forms a pyramidal textured surface structure, which is used to fabricate crystalline silicon solar cells. The morphology is progressively transferred to the top surface of the crystalline silicon solar cell, providing a surface structure that meets the requirements and is compatible with perovskite thin film deposition technology.

[0083] Step S12: An amorphous silicon passivation layer, a microcrystalline silicon doped layer, and a transparent conductive layer are deposited on a crystalline silicon substrate to form a crystalline silicon bottom cell. To ensure that the surface features of the crystalline silicon substrate can be conducted to the transparent conductive layer to match the perovskite thin film deposition, the amorphous silicon passivation layer, the microcrystalline silicon doped layer, and the transparent conductive layer should all be prepared as thin as possible to avoid completely covering and reshaping the texture structure of the crystalline silicon substrate.

[0084] Step S13 involves fabricating a perovskite absorber layer on a crystalline silicon base cell to form a tandem cell substrate. The perovskite layer needs to form a dense, uniform, and well-adhered thin film on top of the crystalline silicon base cell without damaging the passivation / transport layer. Common methods for depositing the perovskite absorber layer include spin coating, thermal evaporation, evaporation-solution mixing, and blade coating and slot coating. This application preferably uses the evaporation-solution mixing method, as well as blade coating and slot coating. The evaporation-solution mixing method combines the advantages of vacuum and solution technologies, making it suitable for large-scale manufacturing, particularly for micron-level pyramidal textures. It can obtain dense films at low temperatures and is also suitable for perovskite tandem cells to protect the crystalline silicon base cell. Blade coating and slot coating are suitable for micron- and submicron-level pyramidal textures, possessing the potential for large-scale manufacturing and high material utilization, making them more suitable for commercial production. Of course, other perovskite deposition methods can also be applied to this application embodiment as long as they meet the requirements. For example, the perovskite absorber layer in this application is MAPbI3.

[0085] Step S14: A transparent conductive layer is deposited on the tandem battery substrate. This transparent conductive layer is used for lateral transport of photogenerated carriers.

[0086] Step S15: Print metal electrodes on the transparent conductive layer to form a perovskite tandem solar cell.

[0087] By applying the above method to prepare a nanotextured crystalline silicon substrate and depositing it to form a perovskite tandem solar cell, the cell manufacturing process is optimized, the production cost of the cell is reduced, and the process time is shortened. It can replace the existing high-cost and time-consuming chemical mechanical etching process, and significantly improve the production efficiency and effectiveness of perovskite tandem solar cells.

[0088] In the perovskite tandem solar cell fabrication method of this application, the surface characteristics of the crystalline silicon substrate (i.e., roughness / smoothness, texture scale) are not directly transferred 1:1 to the layer below the perovskite film. Instead, they are weakened and conducted to that layer after being stacked and filtered through an "amorphous silicon passivation layer + microcrystalline silicon doped layer + transparent conductive layer." Therefore, they statistically affect the characteristics of the final perovskite absorber layer, such as the bonding ability and nucleation density of the perovskite absorber layer. Thus, to ensure that the nanotexture structure of the crystalline silicon substrate is continuously conducted to the perovskite film deposition surface and to prevent the surface properties of the crystalline silicon substrate from being reshaped and smoothed out, the preferred embodiment of this application has certain thickness requirements for each layer of the deposited crystalline silicon substrate solar cell.

[0089] Specifically, in some preferred embodiments of this application, in step S12, the amorphous silicon passivation layer has a thickness of 5-10 nm and is deposited using a PECVD process, requiring high-quality passivation and low light absorption; the N-type / P-type microcrystalline doped layer has a thickness of 15-30 nm and is deposited using a PECVD process, serving as a carrier transport and collection layer to form a PN junction; the transparent conductive layer has a thickness of 70-100 nm and is deposited using a PVD process, serving as an anti-reflection layer and a lateral conductive electrode. These three layers are grown in thin layers on a crystalline silicon substrate, transferring the nanotexture structure of the crystalline silicon substrate to the deposition surface of the perovskite thin film to match the perovskite deposition technology. Preferably, the transparent conductive layer is an ITO layer to ensure high carrier transport rate and high light transmittance.

[0090] In some other embodiments of this application, step S12 may also include depositing a thin interface protection layer, such as an ultrathin inorganic interface layer like Al2O3 or SnO2, on the transparent conductive layer on top of the crystalline silicon bottom cell, to improve wettability, increase the film density of the perovskite layer, and prevent the perovskite deposition solution from damaging the passivation layer of the crystalline silicon bottom cell.

[0091] In other embodiments of this application, the method for preparing a perovskite tandem solar cell further includes: testing and encapsulating the perovskite tandem solar cell formed in step 15 to achieve battery encapsulation protection.

[0092] According to another aspect of this application, a perovskite tandem solar cell is disclosed, which is prepared by the perovskite tandem solar cell preparation method described above.

[0093] In summary, this application uses diamond wire cutting to fabricate crystalline silicon substrates, maintaining the advantages of large-scale, low-cost, and rapid production. A combined wet and dry approach is employed to planarize the diamond wire-cut substrate. By utilizing pre-wet polishing, ultrafast laser cold polishing, and post-wet polishing, the problem of traditional single wet processing failing to adequately plan the substrate surface is overcome, forming a substrate preparation method that can replace the high-cost CMP process. Specifically, pre-wet polishing can initially round sharp peaks and valleys, thereby improving the beam coverage uniformity of the laser engraving step, increasing engraving efficiency to quickly and preferentially process protrusions. Combined with a laser spot matching the characteristics of the cutting lines, the wire-cut features are efficiently and completely planarized. Finally, the modification and activation effect of post-wet polishing results in a substrate texture surface that meets the requirements for perovskite tandem solar cell production.

[0094] 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.

[0095] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application 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 so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or 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.

[0096] The above are merely preferred embodiments of this application and are 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 method for preparing a perovskite tandem solar cell substrate, characterized in that, include: Step S1: Fabricate a crystalline silicon substrate using a diamond wire cutting process; Step S2: Perform pre-wet polishing on the crystalline silicon substrate to clean the residue on the surface of the crystalline silicon substrate and round the sharp peaks and valleys generated by cutting to form a pre-treated surface; Step S3: Perform laser cold polishing on the pre-treated surface using picosecond / femtosecond pulsed lasers to sculpt the surface with a spot size that matches the surface cutting lines, thereby reducing the surface height difference and roughness and forming a photochemically treated surface. Step S4: Perform post-wet polishing on the photochemically treated surface to remove the laser molten layer and surface residue and modify the morphology, ultimately forming an activated textured surface.

2. The method for preparing a perovskite tandem solar cell substrate according to claim 1, characterized in that, In step S1, the peak-to-valley spacing of the cutting marks produced by diamond wire cutting is 50-100 μm; in step S3, the laser beam spot conditions are set as follows: laser spot diameter 40-80 μm, laser spot overlap rate 29-100%, laser defocusing amount 0.5-1.5 mm, laser spot scanning line spacing 0.03-0.05 mm, and scanning speed 5000-6000 mm / s, to adapt to the surface cutting marks for engraving.

3. The method for preparing a perovskite tandem solar cell substrate according to claim 2, characterized in that, Step S3 further includes setting the laser beam energy conditions as follows: laser wavelength 342-532nm, average power 10-50W, repetition frequency 50KHz-20MHz, pulse width 10-20ps, single pulse energy 40-90μJ, and beam quality factor M. 2 ≤1.3, to control the depth of laser engraving.

4. The method for preparing a perovskite tandem solar cell substrate according to claim 3, characterized in that, In step S3, the surface roughness of the photochemically treated surface obtained after laser cold polishing is Ra<0.14μm, and the peak-to-valley height difference within a 100μm range is less than 1.5μm.

5. The method for preparing a perovskite tandem solar cell substrate according to claim 1, characterized in that, The polishing conditions for the pre-wet polishing treatment are: time 200-400s, temperature 65-75℃; the polishing solution used in the pre-wet polishing treatment includes: 3-5 volumes of 22-25wt% alkaline solution, 1-2 volumes of 2-4wt% working solution, and 182-186 volumes of pure water; wherein, the working solution includes: oxidant, complexing agent, surfactant, corrosion inhibitor and solvent.

6. The method for preparing a perovskite tandem solar cell substrate according to claim 1, characterized in that, The post-wet polishing process has the same polishing conditions and polishing liquid composition as the pre-wet polishing process. The perovskite tandem solar cell substrate finally prepared in step S4 has a textured surface with a peak-valley height difference of 0.4-0.8 μm within a range of 100 μm and a roughness Ra of 0.07-0.1 μm.

7. A perovskite tandem solar cell substrate, characterized in that, The perovskite tandem solar cell substrate is prepared by the perovskite tandem solar cell substrate preparation method according to any one of claims 1 to 6.

8. A method for fabricating a perovskite tandem solar cell, characterized in that, include: Step S10: Fabricate a crystalline silicon substrate using the perovskite tandem solar cell substrate fabrication method as described in any one of claims 1 to 6; Step S11: Clean and texturize the crystalline silicon substrate; Step S12: Deposit an amorphous silicon passivation layer, a microcrystalline silicon doped layer, and an ITO conductive layer on the crystalline silicon substrate to form a crystalline silicon bottom cell; Step S13: A perovskite absorber layer is fabricated on the crystalline silicon bottom cell to form a stacked cell substrate; Step S14: Deposit a transparent conductive layer on the stacked battery substrate; Step S15: Print metal electrodes on the transparent conductive layer to form a perovskite tandem battery.

9. The method for preparing a perovskite tandem solar cell according to claim 8, characterized in that, In step S12, the amorphous silicon passivation layer has a deposition thickness of 5-10 nm, the N-type / P-type microcrystalline doped layer has a deposition thickness of 15-30 nm, and the transparent conductive layer has a deposition thickness of 70-100 nm.

10. A perovskite tandem solar cell, characterized in that, The perovskite tandem solar cell is prepared by the perovskite tandem solar cell preparation method as described in claim 8 or 9.

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