Solar cell and preparation method therefor

Abstract

The present disclosure relates to the technical field of solar cells. Disclosed are a solar cell and a preparation method therefor. The solar cell comprises a cell substrate, and the cell substrate comprises a first surface and a second surface opposite to the first surface; the solar cell further comprises a TCO film layer located on the first surface and / or the second surface, and the TCO film layer comprises copper; and at least 95% of crystal grains in the TCO film layer have a size of 15 nm to 35 nm. Copper is doped in the TCO film layer, and at the same time, at least 95% of crystal grains in the TCO film layer are controlled to have a size of 15 nm to 35 nm, thereby achieving effective doping of copper in the TCO film layer, and avoiding excessive accumulation of copper at grain boundaries, thus effectively improving the bonding force between grid lines and the TCO film layer while ensuring that the TCO film layer has excellent overall performance, so that the solar cell can have both good photoelectric conversion efficiency and good conductivity.

Description

A solar cell and its preparation method Technical Field

[0001] This disclosure relates to the field of solar cell technology, and more specifically, to a solar cell and a method for its fabrication. Background Technology

[0002] In the field of solar cells, the adhesion between the grid lines and the transparent conductive oxide (TCO) film is poor, and the grid lines are prone to detachment. Therefore, a common method is to dope the TCO film with elements to improve the adhesion between the grid lines and the TCO film. However, different dopants have different degrees of difficulty in doping the TCO film; at the same time, the size of the grains in the TCO film also affects the diffusion of the dopants in the TCO film.

[0003] Specifically, the TCO film is a polycrystalline layer with a grain size of several hundred nanometers. The smaller the grain size in the TCO film, the more grain boundaries there are. Grain boundaries are fast channels for the diffusion of dopants. More grain boundaries may make it easier for dopants to be injected into the TCO film. However, this can also easily lead to the accumulation of dopants at the grain boundaries, affecting the overall performance of the TCO film (including electrical properties, optical properties, mechanical properties, and corrosion resistance).

[0004] In view of this, this disclosure is hereby made. Summary of the Invention

[0005] The purpose of this disclosure is to provide a solar cell and its fabrication method to solve or improve the above-mentioned technical problems. It achieves effective doping of copper in the TCO film layer, avoids excessive accumulation of copper at the grain boundaries, and thus effectively improves the bonding force between the grid line and the TCO film layer while ensuring the excellent overall performance of the TCO film layer. This is beneficial for the solar cell to have both better photoelectric conversion efficiency and conductivity.

[0006] This disclosure can be implemented as follows:

[0007] In a first aspect, this disclosure provides a solar cell, which includes a cell substrate, the cell substrate including a first surface and a second surface opposite to the first surface;

[0008] The solar cell also includes a TCO film layer located on the first surface and / or the second surface, the TCO film layer containing copper; at least 95% of the grains in the TCO film layer have a size of 15nm to 35nm.

[0009] In an optional embodiment, the TCO film layer contains at least [missing information - likely a specific ingredient or component]. <222> Grain orientation; and, in the TCO film layer, <222> The diffraction peaks corresponding to grain orientation have the strongest intensity.

[0010] In an optional implementation, in the TCO film layer, <222> The proportion of grains with grain orientation is 70wt% to 80wt%.

[0011] In an optional embodiment, the TCO film layer further contains <440> Grain orientation and <622> Grain orientation;

[0012] <222> Grain orientation, <440> Grain orientation and <622> The total proportion of grains corresponding to the grain orientation in the TCO film layer is not less than 90 wt%.

[0013] In an optional implementation, in the TCO film layer, <440> The diffraction peak intensity corresponding to grain orientation is <222> The intensity of the diffraction peaks corresponding to the grain orientation is 1 / 6 to 1 / 3;

[0014] or, <622> The diffraction peak intensity corresponding to grain orientation is <222> The intensity of the diffraction peak corresponding to the grain orientation is 1 / 6 to 1 / 3.

[0015] In an optional embodiment, the copper concentration is 1×10⁻⁶ within a 5nm depth range of the TCO film layer, along the direction from the surface of the TCO film layer to the battery substrate. 18 ions / cm 2 ~1×10 21 ions / cm 2 ;

[0016] Alternatively, along the direction from the surface of the TCO film to the battery substrate, within a depth range of 20nm to 25nm in the TCO film, the copper concentration is 1×10⁻⁶. 10 ions / cm 2 ~1×10 14 ions / cm 2 ;

[0017] Alternatively, along the direction from the surface of the TCO film to the battery substrate, within a depth range of 30nm to 50nm in the TCO film, the copper concentration is ≤1×10⁻⁶. 5 ions / cm 2 ;

[0018] Alternatively, along the direction from the surface of the TCO film to the battery substrate, the depth of copper in the TCO film does not exceed 50 nm.

[0019] In an optional embodiment, the surface roughness of the TCO film on the side away from the battery substrate is 20 nm to 30 nm.

[0020] In an alternative embodiment, at least the grain boundary gaps within the TCO film are bonded with copper through bonding.

[0021] In an optional embodiment, the thickness of the TCO film is 50 nm to 150 nm.

[0022] In an optional embodiment, a metal seed layer is provided on the side of the TCO film away from the battery substrate, corresponding to the grid line region.

[0023] In an optional embodiment, the solar cell further includes a doped layer disposed between the cell substrate and the TCO film layer, and grid lines connected to the metal seed layer.

[0024] In an optional embodiment, the solar cell includes a cell substrate;

[0025] The front side of the battery substrate is provided with a first passivation layer and a first doped layer; the front side of the first doped layer is provided with a first TCO film layer, and the front side of the first TCO film layer is provided with a first metal seed layer at the position corresponding to the gate line area; the front side of the first metal seed layer is connected to the first gate line.

[0026] A second passivation layer and a second doped layer are stacked on the back side of the battery substrate; a second TCO film layer is provided on the back side of the second doped layer, and a second metal seed layer is provided on the back side of the second TCO film layer at the position corresponding to the gate line region; a second gate line is connected to the back side of the second metal seed layer.

[0027] Secondly, this disclosure provides a method for preparing a solar cell as described in any of the foregoing embodiments, comprising the following steps:

[0028] A copper-containing TCO film layer is disposed on the first and / or second surfaces of the battery substrate.

[0029] In an optional implementation, the following steps are included:

[0030] A copper-containing TCO film layer is disposed on the first and / or second surfaces of the battery substrate;

[0031] A metal seed layer is disposed on the side of the TCO film away from the battery substrate.

[0032] In an optional implementation, the following steps are included:

[0033] A first passivation layer and a first doped layer are stacked on the first surface of the battery substrate; a first TCO film layer is disposed on the front side of the first doped layer, and a first metal seed layer is disposed on the front side of the first TCO film layer; a first gate line is connected to the front side of the first metal seed layer.

[0034] A second passivation layer and a second doped layer are stacked on the second surface of the battery substrate; a second TCO film layer is disposed on the back side of the second doped layer, and a second metal seed layer is disposed on the back side of the second TCO film layer; a second gate line is connected to the back side of the second metal seed layer.

[0035] The beneficial effects of this disclosure include:

[0036] In this disclosure, copper is doped into the TCO film. Firstly, copper's atomic size is moderate, which facilitates its diffusion within the solid material (TCO film). Secondly, copper's moderate electronegativity results in weaker chemical bonds with indium oxide, tin oxide, or other elements in the TCO film, making diffusion easier. In comparison, copper has a higher diffusion coefficient in the TCO film than other metallic elements (such as nickel, tungsten, titanium, and silver), allowing it to be doped not only on the surface but also further into the grain boundaries. Based on the ease with which copper diffuses in the TCO film compared to other dopants, this disclosure specifically controls that at least 95% of the grains in the TCO film have a size of 15 nm to 35 nm. This grain size and content ensures effective copper doping in the TCO film while preventing excessive accumulation at grain boundaries, thereby ensuring excellent overall performance of the TCO film while effectively improving the adhesion between the gate lines and the TCO film. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 is a schematic diagram of the structure of the solar cell (HJT cell) provided in Example 1.

[0039] Figure 2 is an XRD pattern of the first TCO film layer in the solar cell provided in Example 1.

[0040] Figure 3 is an XRD pattern of the second TCO film layer in the solar cell provided in Example 1.

[0041] Figure 4 is a SEM image of the solar cell provided in Example 1.

[0042] Figure 5 is an enlarged view of the area within the box in Figure 4.

[0043] Figure 6 shows the corrosion resistance test results of the yellow film prepared in Example 7 of Experiment 2.

[0044] Icons: 100 - Battery substrate; 111 - First intrinsic amorphous silicon layer; 112 - N-type doped layer; 113 - First TCO film layer; 114 - First copper seed layer; 115 - First gate line; 116 - First protective layer; 121 - Second intrinsic amorphous silicon layer; 122 - P-type doped layer; 123 - Second TCO film layer; 124 - Second copper seed layer; 125 - Second gate line; 126 - Second protective layer. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0046] The solar cells and their fabrication methods disclosed herein are described in detail below.

[0047] The test methods involved in this disclosure include:

[0048] ① The concentration of copper doping was detected using secondary ion mass spectrometry (SIMS);

[0049] ② Layer structure was examined using a scanning electron microscope (SEM);

[0050] ③ Use an X-ray diffractometer to perform XRD analysis, including analyzing grain orientation, diffraction peak intensity, grain content, and size;

[0051] The grain size is calculated using the Scherrer formula, specifically: D = Kλ / βcosθ. Here, D is the grain size in nm; K is a constant determined by β, where K = 0.89 when β is the full width at half maximum (FWHM) of the diffraction peak, and K = 1 when β is the FWHM of the diffraction peak area integral; λ is the wavelength of the X-ray in nm; β is the FWHM of the diffraction peak in radians; and θ is the diffraction angle.

[0052] ④ Atomic force microscopy (AFM) is used to detect the surface morphology and roughness of the test material.

[0053] ⑤ The bonding force between the TCO film layer and the copper seed layer in the grid line region was tested using a thrust meter;

[0054] ⑥ Use an IV tester to test the electrical parameters of the solar cells.

[0055] This disclosure proposes a solar cell, which includes a cell substrate, the cell substrate including a first surface and a second surface opposite to the first surface, the solar cell further including a TCO film layer located on the first surface and / or the second surface, the TCO film layer containing copper; at least 95% of the grains in the TCO film layer have a size of 15nm to 35nm (such as 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm, 31nm, 32nm, 33nm, 34nm or 35nm, etc., or other values ​​in the range of 15nm to 35nm).

[0056] The aforementioned battery substrate can be, exemplarily, a silicon-based substrate.

[0057] The TCO film is a transparent conductive oxide film that can collect current generated by the photoelectric effect. The performance of the TCO film directly affects the efficiency and stability of the solar cell, such as transparency, conductivity, and durability. In this disclosure, the materials of the TCO film may include, but are not limited to, ZnO, SnO2, and ITO (such as silver indium oxide).

[0058] In this disclosure, a metal seed layer is disposed on the side of the TCO film away from the battery substrate, corresponding to the grid line region. The metal in the metal seed layer may, exemplarily, include at least one of silver, copper, nickel, titanium, tantalum, tungsten, and aluminum. In some typical embodiments, the metal seed layer may be a copper seed layer.

[0059] Metal seed layers provide excellent electrical conductivity in solar cells, which helps to form an efficient current collection network and improve the overall performance of solar cells.

[0060] Furthermore, the aforementioned solar cell also includes a doped layer disposed between the cell substrate and the TCO film layer, and grid lines connected to the metal seed layer.

[0061] Furthermore, solar cells also include protective layers for protecting the grid lines, such as tin protective layers. In addition, protective layers of other materials may be provided as needed.

[0062] In some embodiments, the first or second surface of the solar cell has a TCO film layer containing copper. In other embodiments, both the first and second surfaces of the solar cell have a TCO film layer containing copper.

[0063] In some embodiments, 95%, 96%, 97%, 98%, or 99% of the grains in the TCO film may have a size of 15 nm to 35 nm. Alternatively, other values ​​within the range of not less than 95% may correspond to grain sizes of 15 nm to 35 nm. In some optional embodiments, at least 95% of the grains in the TCO film have a size of 18 nm to 25 nm.

[0064] In this disclosure, copper is doped into the TCO film. Firstly, copper's atomic size is moderate, which facilitates its diffusion within the solid material (TCO film). Secondly, copper's moderate electronegativity results in weaker chemical bonds with indium oxide, tin oxide, or other elements in the TCO film, making diffusion within the TCO film easier. In comparison, copper has a higher diffusion coefficient in the TCO film than other metallic elements (such as nickel, tungsten, titanium, and silver), allowing it to be doped not only on the surface of the TCO film but also further incorporated into the grain boundaries and fissures. It should be noted that the surface of a TCO film typically has numerous pits and protrusions (i.e., the surface of the TCO film has a certain degree of roughness or gaps). In some embodiments of this disclosure, copper is mainly present in the gaps on the surface of the TCO film; in other embodiments, copper exists simultaneously on the surface and inside the TCO film. The bonding effect of copper atoms and / or copper ions with the chemical bonds within the TCO film further enhances the adhesion between the TCO film and the metal seed layer. In some alternative implementations, at least the grain boundary gaps within the TCO film are bonded with copper through bonding.

[0065] It should be noted that the grain size in the TCO film layer affects the copper implantation concentration, mainly in the following aspects:

[0066] ① Grain boundary effect: TCO films are polycrystalline layers with grain sizes of several hundred nanometers. The smaller the grain size, the more grain boundaries there are. Grain boundaries are fast channels for atomic diffusion, so copper atoms may be more easily injected into the TCO film through grain boundaries. However, this may also lead to the accumulation of copper atoms at the grain boundaries, affecting the overall performance of the TCO film.

[0067] The accumulation of copper atoms at grain boundaries has a significant impact on the overall performance of TCO films in the following aspects:

[0068] A. Electrical Properties: The accumulation of copper atoms at grain boundaries may cause changes in the resistivity of the TCO film, thus affecting its conductivity. The accumulated copper atoms may form conductive channels or produce electrochemical effects, leading to an increase in local current density and even causing short circuits.

[0069] B. Optical Performance: TCO films typically require high light transmittance, but the accumulation of copper atoms at grain boundaries can affect light transmittance. Accumulated copper atoms may absorb or scatter light, leading to a decrease in the optical performance of the TCO film.

[0070] C. Mechanical Properties: The accumulation of copper atoms at grain boundaries may also affect the mechanical properties of the TCO film. Grain boundaries are weak points in metallic materials, and the accumulation of copper atoms may exacerbate the brittleness of the grain boundaries, making the TCO film more prone to fracture or damage when subjected to external forces.

[0071] D. Corrosion Resistance: The accumulation of copper atoms at grain boundaries can also affect the corrosion resistance of the TCO film. The accumulated copper atoms may form a galvanic cell effect, making the TCO film more susceptible to corrosion damage in humid or corrosive environments.

[0072] Therefore, when preparing TCO films, it is necessary to reasonably control the amount and distribution of copper atoms to avoid excessive accumulation at the grain boundaries, thereby ensuring that the TCO film has excellent overall performance.

[0073] ② Carrier Transport: Grain size also affects carrier transport in the TCO film. Larger grains generally mean less grain boundary scattering, which is beneficial for carrier migration. If the injection of copper atoms leads to a significant decrease in carrier mobility, the conductivity of the TCO film may be affected.

[0074] ③ Thin film quality: Grain size is also an important indicator for evaluating the quality of TCO films. Smaller grains may lead to increased surface roughness of the film, thereby affecting the implantation efficiency and distribution uniformity of copper atoms.

[0075] As mentioned above, the grain size in the TCO film indirectly affects the concentration of copper injected into the TCO film by influencing the number of grain boundaries, carrier transport, and film quality. This disclosure specifically controls that at least 95% of the grains in the TCO film have a size of 15 nm to 35 nm. With this grain size and content, effective copper doping in the TCO film can be ensured while avoiding excessive copper accumulation at grain boundaries. This, in turn, effectively improves the adhesion between the gate line and the TCO film while ensuring excellent overall performance of the TCO film.

[0076] In some alternative embodiments, the TCO film layer contains at least [missing information]. <222> Grain orientation; and, in the TCO film layer, <222> The diffraction peaks corresponding to grain orientation have the strongest intensity.

[0077] It should be noted that the grain orientation of the TCO film mainly grows towards the orientation that consumes the least energy; <222> The oriented grains and the metal seed layer bombard the battery substrate in a direction perpendicular to each other, meaning that metal ions or metal atoms bombard the substrate directly and perpendicularly. <222> On the crystal plane, this can suppress excessive copper accumulation, thereby limiting copper diffusion and forming uniform copper doping. In the TCO film, the higher the proportion of grains, the stronger the corresponding diffraction peaks. In this disclosure, in the TCO film... <222> The diffraction peaks corresponding to grain orientation have the strongest intensity, which can ensure the effective formation of uniform copper doping.

[0078] In some alternative implementations, in the TCO film layer, <222> The grain orientation has a grain percentage of 70wt% to 80wt%, such as 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 78wt%, 79wt%, or 80wt%, or other values ​​within the range of 70wt% to 80wt%.

[0079] In order to achieve uniform copper doping in the TCO film, this disclosure describes the method of doping the TCO film with copper. <222> The orientation of the grains is set to be the maximum; specifically, the TCO film layer... <222> The grain proportion of the grain orientation is set to 70wt% to 80wt%. On the one hand, this can improve the uniformity of copper doping, and on the other hand, it can minimize the damage to the light transmittance of TCO. In addition, it is also beneficial to improve the conductivity of TCO film.

[0080] In some alternative embodiments, the TCO film layer also contains <440> Grain orientation and <622> Grain orientation; <222> Grain orientation, <440> Grain orientation and <622> The total proportion of grains corresponding to the grain orientation in the TCO film layer is not less than 90 wt%. In other words, except... <222> Grain orientation, <440> Grain orientation and <622> The total proportion of grains other than the grains corresponding to the grain orientation in the TCO film layer does not exceed 10 wt%, such as 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, or 1 wt%, or other values ​​within the range not exceeding 10 wt%.

[0081] The above <440> Grain orientation and <622> Grain orientation and <222> Grain orientation and co-growth <222> During the growth of oriented grains, mainly incidental growth occurs. <440> and <622> In addition to the oriented grains, other grains with smaller proportions (such as...) may also be present or coexist with them. <211> Oriented grains, <332> Oriented grains and <400> Oriented grains).

[0082] because <440> , <622> and <222> The orientations of the grains are relatively similar, so grains with the above-mentioned orientations can all play a role in inhibiting copper diffusion. Grains with other orientations are similar to... <440> as well as <222> As the differences in orientation gradually increase, the corresponding inhibitory effect also gradually decreases.

[0083] This disclosure will... <222> Grain orientation, <440> Grain orientation and <622> The total proportion of grains corresponding to the grain orientation in the TCO film layer is controlled to be no less than 90 wt%, which is conducive to copper implantation. At the same time, it is also helpful to prevent and improve the possible reduction of TCO optical performance after copper implantation and avoid the reduction of short-circuit current of the cell.

[0084] In some alternative implementations, in the TCO film layer, <440> The diffraction peak intensities corresponding to grain orientation are <222> The intensity of the diffraction peak corresponding to the grain orientation is 1 / 6 to 1 / 3, such as 1 / 6, 1 / 5, 1 / 4 or 1 / 3, or other values ​​in the range of 1 / 6 to 1 / 3.

[0085] In some alternative implementations, <622> The diffraction peak intensities corresponding to grain orientation are <222> The intensity of the diffraction peak corresponding to the grain orientation is 1 / 6 to 1 / 3, such as 1 / 6, 1 / 5, 1 / 4, or 1 / 3, or other values ​​within the range of 1 / 6 to 1 / 3. In some typical embodiments, <622> The diffraction peak corresponding to the grain orientation is the third most intense diffraction peak.

[0086] For ease of distinction, the following definition applies to TCO film layers. <222> The diffraction peak corresponding to the grain orientation is the first X-ray diffraction peak. <440> The diffraction peak corresponding to the grain orientation is the second X-ray diffraction peak. <211> The diffraction peak corresponding to the grain orientation is the third X-ray diffraction peak. <400> The diffraction peak corresponding to the grain orientation is the fourth X-ray diffraction peak. <332> The diffraction peak corresponding to the grain orientation is the fifth X-ray diffraction peak. <431> The diffraction peak corresponding to the grain orientation is the sixth X-ray diffraction peak. <622> The diffraction peak corresponding to the grain orientation is the seventh X-ray diffraction peak.

[0087] In some embodiments, a first TCO film layer is provided on the front side of the battery substrate, in which the intensity of the seventh X-ray diffraction peak is greater than the intensity of the fourth X-ray diffraction peak. In some embodiments, a second TCO film layer is provided on the back side of the battery substrate, in which the intensity of the seventh X-ray diffraction peak is less than the intensity of the fourth X-ray diffraction peak.

[0088] It should be noted that, if <440> grains and <622> The intensity of the radial peak corresponding to any one of the grain orientations exceeds <222> If the intensity of the line radiation peak corresponding to the grain orientation is 1 / 6 to 1 / 3, then it indicates that... <222> When grains undergo reconstruction, stacking, misalignment, or other anomalies, not only can copper not be diffused uniformly, but the permeability and conductivity of the TCO film will also be affected.

[0089] Continuing from the above, the TCO film in this disclosure exhibits high crystallinity, with distinct, sharp, and high-intensity diffraction peaks, and a relatively large grain size (15nm–35nm), which facilitates effective copper implantation. Furthermore, the higher crystallinity helps prevent and mitigate the potential reduction in TCO optical performance after copper implantation, avoiding a decrease in the short-circuit current of the solar cell. In addition, the higher crystallinity and larger grain size also improve the process window for copper electroplating, preventing the TCO film from being corroded by the acid solutions used in the copper electroplating process.

[0090] In some optional embodiments, the thickness of each TCO film layer (e.g., the first TCO film layer and / or the second TCO film layer) can be 50nm to 150nm, such as 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, 105nm, 110nm, 115nm, 120nm, 125nm, 130nm, 135nm, 140nm, 145nm or 150nm, or other values ​​within the range of 50nm to 150nm. In some optional embodiments, the thickness of each TCO film layer is 70nm to 120nm, such as 70nm, 72nm, 75nm, 78nm, 80nm, 82nm, 85nm, 88nm, 90nm, 92nm, 95nm, 98nm, 100nm, 102nm, 105nm, 108nm, 110nm, 112nm, 115nm, 118nm, or 120nm, or other values ​​within the 70nm to 120nm range. In some optional embodiments, the thickness of each TCO film layer is 80nm to 100nm.

[0091] In some optional embodiments, the surface roughness of the side of each TCO film layer away from the battery substrate is 20nm to 30nm, such as 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, or 30nm, or other values ​​within the range of 20nm to 30nm. It should be noted that the smaller the roughness of the TCO film layer, the larger the grain size. If the surface roughness of the side of the TCO film layer away from the battery substrate is less than 20nm, especially less than 2nm, there will be obvious gaps and large grain boundaries between grains, which can easily cause copper atoms or ions to aggregate, ultimately leading to a decrease in the overall performance of the TCO film layer.

[0092] In some optional embodiments, the copper concentration is 1×10⁻⁶ within a 5 nm depth range of the TCO film layer, along the direction from the surface of the TCO film layer to the battery substrate. 18 ions / cm 2 ~1×10 21 ions / cm 2 , such as 1×10 18 ions / cm 2 5×10 18 ions / cm 2 1×10 19 ions / cm 2 5×10 19 ions / cm 2 1×10 20 ions / cm 2 5×10 20 ions / cm 2 Or 1×10 21 ions / cm 2 Etc. can also be 1×10 18 ions / cm 2 ~1×10 21 ions / cm 2 Other values ​​within the range.

[0093] By doping with a concentration of 10 within a 5 nm depth range of the TCO film along the direction from the surface of the TCO film to the battery substrate. 18 ions / cm 2 ~1×10 21 ions / cm 2The copper doping (primarily in atomic and / or ionic form) can form copper compounds or alloy phases, enhancing chemical bonding, improving interface structure, and increasing the bonding strength between the TCO film layer and the metal seed layer in the grid line region, thereby improving the adhesion between the grid line and the battery substrate. The chemical bonds involved in "bonding" in this disclosure include ionic and covalent bonds, for example, copper ions (Cu... 2+ It can react with oxygen atoms (O) in the TCO film. 2- Ionic bonds are formed between copper ions and oxygen atoms. This is because copper ions carry a positive charge, while oxygen atoms in oxides typically carry a negative charge; they form stable ionic bonds through electrostatic attraction. This bonding effect is particularly significant when copper ions replace some indium or tin ions in ITO, maintaining charge balance. For example, copper atoms exist in a lower valence state (such as Cu). + When Cu is used, it can share electron pairs with indium or tin atoms to form covalent bonds.

[0094] In addition, copper penetrating into the TCO film can increase the density of the internal structure of the TCO film, and copper located on the surface of the TCO film can play a protective role, blocking corrosive substances from eroding the TCO film and improving the corrosion resistance of the TCO film.

[0095] Continuing from the above, along the direction from the surface of the TCO film to the battery substrate, this disclosure controls the concentration of copper in the TCO film at a depth range of 5 nm to be 1 × 10⁻⁶. 18 ions / cm 2 ~1×10 21 ions / cm 2 This approach can largely maintain the integrity of the TCO film or grains (i.e., it will not damage the integrity of the TCO film structure) while improving the adhesion between the TCO film and the metal seed layer in the gate region. If the copper doping concentration within a 5nm depth range of the TCO film is less than 1×10⁻⁶... 18 ions / cm 2 It is difficult to effectively improve the bonding force between the TCO film and the copper seed layer in the gate region; if the copper doping concentration within a 5nm depth range of the TCO film is higher than 1×10 21 ions / cm 2 On the one hand, the process is difficult to achieve, and on the other hand, it is difficult to maintain the integrity of the TCO film and grains, which may reduce the performance of the battery.

[0096] The effects of copper on the bonding force between the TCO film and the metal seed layer in the gate region under the aforementioned doping depth and concentration conditions include: First, it can enhance chemical bonding. During copper doping, copper atoms and / or copper ions penetrate into the interface region between the TCO film and the metal seed layer in the gate region, forming new chemical bonds with adjacent atoms. The formation of these chemical bonds enhances the interaction force between the TCO film and the metal seed layer in the gate region, thereby improving the bonding force between the TCO film and the metal seed layer in the gate region. Second, it can improve the interface structure. The doping of copper atoms and / or copper ions changes the microstructure of the film interface, reducing unfavorable factors such as porosity and defects at the interface. Third, the doping of copper atoms and / or copper ions introduces copper elements into the film layer, forming copper compounds or alloy phases (such as copper-tin alloys, copper-indium alloys, or copper-indium-tin alloys), which helps to increase the interface area, improve the interface energy, and thus enhance the bonding force between the film layers. Fourth, the doping of copper atoms and / or copper ions can promote the interdiffusion of elements between the TCO film layer and the metal seed layer in the gate region. This diffusion process helps to form a more uniform alloy layer or compound layer and enhances the bonding strength between the film layers.

[0097] In some optional embodiments, the copper concentration is 1×10⁻⁶ within a depth range of 20 nm to 25 nm of the TCO film layer, along the direction from the surface of the TCO film layer to the battery substrate. 10 ions / cm 2 ~1×10 14 ions / cm 2 , such as 1×10 10 ions / cm 2 5×10 10 ions / cm 2 1×10 11 ions / cm 2 5×10 11 ions / cm 2 1×10 12 ions / cm 2 5×10 12 ions / cm 2 1×10 13 ions / cm 2 5×10 13 ions / cm 2 Or 1×10 14 ions / cm 2 Etc. can also be 1×10 10 ions / cm 2 ~1×10 14 ions / cm 2 Other values ​​within the range.

[0098] In some optional embodiments, the copper concentration is ≤1×10⁻⁶ within a depth range of 30nm to 50nm in the TCO film layer along the direction from the surface of the TCO film layer to the battery substrate. 5 ions / cm 2 , such as 1×10 5 ions / cm 2 5×10 4 ions / cm 2 1×10 4 ions / cm 2 5×10 3 ions / cm 2 1×10 3 ions / cm 2 5×10 2 ions / cm 2 1×10 2 ions / cm 2 5×10 1 ions / cm 2 1×10 1 ions / cm 2 0.5 ions / cm 2 Or 0.1 ions / cm 2 Etc., can also be ≤1×10 5 ions / cm 2 Other values ​​within the range.

[0099] In some optional embodiments, the concentration of copper in the depth range of 25 nm to 30 nm along the direction from the surface of the TCO film to the battery substrate can be 1 × 10⁻⁶. 5 ions / cm 2 ~1×10 14 ions / cm 2 , such as 1×10 5 ions / cm 2 5×10 5 ions / cm 2 1×10 6 ions / cm 2 5×10 6 ions / cm 2 1×10 7 ions / cm 2 5×10 7 ions / cm 2 1×10 8 ions / cm 2 5×10 8 ions / cm 2 1×109 ions / cm 2 5×10 9 ions / cm 2 1×10 10 ions / cm 2 5×10 10 ions / cm 2 1×10 11 ions / cm 2 5×10 11 ions / cm 2 1×10 12 ions / cm 2 5×10 12 ions / cm 2 1×10 13 ions / cm 2 5×10 13 ions / cm 2 Or 1×10 14 ions / cm 2 Etc. can also be 1×10 5 ions / cm 2 ~1×10 14 ions / cm 2 Other values ​​within the range; in some other embodiments, and in some optional embodiments, the concentration of copper in the depth range of 25 nm to 30 nm is ≤1 × 10⁻⁶. 5 ions / cm 2 , such as 1×10 5 ions / cm 2 5×10 4 ions / cm 2 1×10 4 ions / cm 2 5×10 3 ions / cm 2 1×10 3 ions / cm 2 5×10 2 ions / cm 2 1×10 2 ions / cm 2 5×10 1 ions / cm 2 1×10 1 ions / cm 2 0.5 ions / cm 2 Or 0.1 ions / cm 2 Etc., can also be ≤1×10 5 ions / cm2 Other values ​​within the range.

[0100] In some optional embodiments, the depth of copper in the TCO film layer does not exceed 50 nm along the direction from the surface of the TCO film layer to the battery substrate. In other embodiments, it is not excluded that the depth of copper in the TCO film layer exceeds 50 nm, but no obvious signal of copper element can be detected after the depth exceeds 50 nm.

[0101] In some optional embodiments, the depth of copper in the TCO film layer along the direction from the surface of the TCO film layer to the battery substrate does not exceed 50 nm, and the concentration of copper in the 5 nm depth range is 1 × 10⁻⁶. 18 ions / cm 2 ~1×10 21 ions / cm 2 The concentration in the depth range of 20nm to 25nm is 1×10 10 ions / cm 2 ~1×10 14 ions / cm 2 The concentration in the depth range of 30nm to 50nm is <1×10 5 ions / cm 2 .

[0102] As mentioned above, the copper doping form and concentration in the TCO film layer disclosed herein can improve the conductivity and photoelectric response characteristics of the film layer while maintaining high light transmittance, which is beneficial for enabling solar cells to have both better photoelectric conversion efficiency and conductivity.

[0103] In some optional embodiments, the thickness of the metal seed layer can be from 30 nm to 250 nm, such as 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm. m, 145nm, 150nm, 155nm, 160nm, 165nm, 170nm, 175nm, 180nm, 185nm, 190nm, 195nm, 200nm, 205nm, 210nm, 215nm, 220nm, 225nm, 230nm, 235nm, 240nm, 245nm, or 250nm, etc., or other values ​​in the range of 30nm to 250nm. In some optional embodiments, the thickness of the metal seed layer is 50nm to 150nm, such as 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, 105nm, 110nm, 115nm, 120nm, 125nm, 130nm, 135nm, 140nm, 145nm, or 150nm, or other values ​​within the range of 50nm to 150nm.

[0104] In some optional embodiments, an alloy layer exists between the metal seed layer and the corresponding TCO film layer. The alloy contained in the alloy layer may include at least one of copper-tin alloy, copper-indium alloy, and copper-indium-tin alloy, depending on the circumstances.

[0105] In some embodiments, the solar cell provided in this disclosure includes a cell substrate;

[0106] The front side of the battery substrate is provided with a first passivation layer and a first doped layer; the front side of the first doped layer is provided with a first TCO film layer, and the front side of the first TCO film layer is provided with a first metal seed layer at the position corresponding to the gate line area; the front side of the first metal seed layer is connected to the first gate line.

[0107] A second passivation layer and a second doped layer are stacked on the back side of the battery substrate; a second TCO film layer is provided on the back side of the second doped layer, and a second metal seed layer is provided on the back side of the second TCO film layer at the position corresponding to the gate line region; a second gate line is connected to the back side of the second metal seed layer.

[0108] In some more specific embodiments, the solar cell includes a cell substrate;

[0109] The front side of the battery substrate is stacked with a first intrinsic amorphous silicon layer and an N-type doped layer; the front side of the N-type doped layer is provided with a first TCO film layer, and the front side of the first TCO film layer is provided with a first copper seed layer at the position corresponding to the gate line region; the front side of the first copper seed layer is connected to the first gate line.

[0110] The back side of the battery substrate is stacked with a second intrinsic amorphous silicon layer and a P-type doped layer; the back side of the P-type doped layer is provided with a second TCO film layer, and the back side of the second TCO film layer is provided with a second copper seed layer at the position corresponding to the gate line region; the back side of the second copper seed layer is connected to the second gate line.

[0111] Furthermore, the first copper grid line may be provided with a first protective layer, and the second grid line may be provided with a second protective layer.

[0112] It should be noted that in the actual design and fabrication process, the structure of the solar cell can be added to, subtracted from, and reasonably adjusted as needed. As long as the TCO film layer contains copper and at least 95% of the grains in the TCO film layer have a size of 15nm to 35nm, the solar cell structure is within the scope of this disclosure.

[0113] The solar cell provided in this disclosure has higher conversion efficiency, short-circuit current, and fill factor than conventional solar cells. It has lower contact resistance between the grid lines and the substrate, and can improve the conductivity and photoelectric response characteristics of the film while maintaining high light transmittance, thus achieving the effect of having both better photoelectric conversion efficiency and conductivity.

[0114] Accordingly, this disclosure also provides a method for preparing the above-mentioned solar cell, comprising the following steps: depositing a copper-containing TCO film layer on a first surface and / or a second surface of a cell substrate.

[0115] In some optional embodiments, the method for fabricating a solar cell includes the following steps: depositing a copper-containing TCO film layer on a first surface and / or a second surface of a cell substrate;

[0116] A metal seed layer is disposed on the side of the TCO film away from the battery substrate; the copper seed layer is connected to the grid line.

[0117] Furthermore, a protective layer is provided on the surface of the grid lines.

[0118] In some alternative embodiments, the method for fabricating a solar cell includes the following steps:

[0119] A first passivation layer and a first doped layer are stacked on the first surface of the battery substrate; a first TCO film layer is disposed on the front side of the first doped layer, and a first metal seed layer is disposed on the front side of the first TCO film layer; a first gate line is connected to the front side of the first metal seed layer.

[0120] A second passivation layer and a second doped layer are stacked on the second surface of the battery substrate; a second TCO film layer is disposed on the back side of the second doped layer, and a second metal seed layer is disposed on the back side of the second TCO film layer; a second gate line is connected to the back side of the second metal seed layer.

[0121] In some specific embodiments, the method for fabricating a solar cell includes the following steps:

[0122] A first intrinsic amorphous silicon layer and an N-type doped layer are stacked on the front side of the battery substrate; a first TCO film layer is disposed on the front side of the N-type doped layer; a first copper seed layer is disposed on the front side of the first TCO film layer; and a first gate line is connected on the front side of the first copper seed layer.

[0123] A second intrinsic amorphous silicon layer and a P-type doped layer are stacked on the back side of the battery substrate; a second TCO film layer is disposed on the back side of the P-type doped layer, and a second copper seed layer is disposed on the back side of the second TCO film layer; a second gate line is connected to the back side of the second copper seed layer.

[0124] Furthermore, a first protective layer is provided on the surface of the first copper grid line; and a second protective layer is provided on the surface of the second grid line.

[0125] It should be noted that any method that can achieve the TCO film layer containing copper and at least 95% of the grains in the TCO film layer having a size of 15nm to 35nm is within the protection scope of this disclosure. This disclosure does not impose special limitations on specific preparation conditions and methods. The following are just some examples of its implementation methods.

[0126] In some alternative embodiments, the preparation of the TCO film includes depositing the TCO film using physical vapor deposition (PVD) magnetron sputtering, followed by annealing.

[0127] The deposition power density used to prepare the TCO film can be from 2.5 kW / m to 5.0 kW / m, such as 2.5 kW / m, 3.0 kW / m, 3.5 kW / m, 4.0 kW / m, 4.5 kW / m, or 5.0 kW / m, or other values ​​within the range of 2.5 kW / m to 5.0 kW / m. In some optional embodiments, the deposition power density used to prepare the TCO film is from 3.0 kW / m to 4.0 kW / m.

[0128] During the deposition of the TCO film, the temperature of the battery substrate can be between 170°C and 220°C, such as 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, or 220°C, or other values ​​within the range of 170°C to 220°C. In some optional embodiments, the temperature of the battery substrate is between 190°C and 210°C, such as 190°C, 192°C, 195°C, 198°C, 200°C, 202°C, 205°C, 208°C, or 210°C.

[0129] The annealing temperature used to prepare the TCO film can be between 180℃ and 230℃, such as 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, or 230℃, or other values ​​within the range of 180℃ to 230℃. In some optional embodiments, the annealing temperature used to prepare the TCO film is 220℃.

[0130] The annealing time used to prepare the TCO film can be from 5 min to 25 min, such as 5 min, 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, 22 min, or 25 min, or other values ​​within the range of 5 min to 25 min. In some optional embodiments, the annealing time used to prepare the TCO film is 15 min.

[0131] Under the above conditions, a TCO film with higher crystallinity and larger grain size can be obtained, which is more conducive to preventing and improving the potential reduction in TCO optical performance after copper implantation and avoiding a decrease in the short-circuit current of the solar cell. In addition, it is also more conducive to improving the process window of copper electroplating and preventing the TCO film from being corroded by the acid solution in the copper electroplating process.

[0132] In some alternative implementations, the preparation of the metal seed layer includes depositing a copper seed layer using PVD magnetron sputtering followed by annealing.

[0133] The copper implantation energy for preparing the metal seed layer can be between 300 keV and 1000 keV, such as 300 keV, 350 keV, 400 keV, 450 keV, 500 keV, 550 keV, 600 keV, 650 keV, 700 keV, 750 keV, 800 keV, 850 keV, 900 keV, 950 keV, or 1000 keV, or other values ​​within the range of 300 keV to 1000 keV. In some optional embodiments, the copper implantation energy is between 500 keV and 800 keV, such as 500 keV, 520 keV, 550 keV, 580 keV, 600 keV, 620 keV, 650 keV, 680 keV, 700 keV, 720 keV, 750 keV, 780 keV, or 800 keV.

[0134] The deposition power density of the metal seed layer can be from 3.0 kW / m to 6.0 kW / m, such as 3.0 kW / m, 3.5 kW / m, 4.0 kW / m, 4.5 kW / m, 5.0 kW / m, 5.5 kW / m, or 6.0 kW / m, or other values ​​within the range of 3.0 kW / m to 6.0 kW / m. In some optional embodiments, the deposition power density of the copper seed layer can be from 4.0 kW / m to 5.0 kW / m, such as 4.0 kW / m, 4.1 kW / m, 4.2 kW / m, 4.3 kW / m, 4.4 kW / m, 4.5 kW / m, 4.6 kW / m, 4.7 kW / m, 4.8 kW / m, 4.9 kW / m, or 5.0 kW / m.

[0135] During the copper seed layer deposition process, the temperature of the battery substrate can be between 160℃ and 230℃, such as 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, or 230℃, or other values ​​within the range of 160℃ to 230℃. In some optional embodiments, the temperature of the battery substrate is between 170℃ and 190℃, such as 170℃, 172℃, 175℃, 178℃, 180℃, 182℃, 185℃, 188℃, or 190℃.

[0136] During the metal seed layer deposition process, the temperature of the battery substrate can be between 160℃ and 230℃, such as 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, or 230℃, or other values ​​within the range of 160℃ to 230℃. In some optional embodiments, the temperature of the battery substrate is between 170℃ and 190℃, such as 170℃, 172℃, 175℃, 178℃, 180℃, 182℃, 185℃, 188℃, or 190℃.

[0137] The annealing temperature of the metal seed layer can be 170℃~250℃, such as 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃ or 250℃, or other values ​​within the range of 170℃~250℃.

[0138] The annealing time for the metal seed layer can be 5 min to 25 min, such as 5 min, 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, 22 min or 25 min, or other values ​​within the range of 5 min to 25 min.

[0139] The annealing of the aforementioned metal seed layer is carried out under vacuum conditions. High-temperature vacuum annealing can eliminate the internal stress between the TCO film and the metal seed layer, ensuring a direct and tight bond between them. Furthermore, the annealing process of the metal seed layer allows metal atoms and / or metal ions to diffuse uniformly within the TCO film and implant into deeper locations, improving bonding ability; it also helps prevent oxidation of the metal seed layer.

[0140] In some of the embodiments proposed in this disclosure, by first depositing a TCO film layer and then depositing a metal seed layer, and by setting the relevant preparation conditions for the TCO film layer and the metal seed layer, a better metal atom and / or metal ion doping effect can be obtained in the TCO film layer. However, the method of directly doping the metal in the TCO target material for film deposition is not excluded. However, when the metal is directly doped in the TCO target material for film deposition, the metal in the target material mainly exists in the form of metal oxides, and when it is deposited on the silicon wafer surface, the metal inside the entire film layer also mainly exists in the form of metal oxides. In this method, the metal concentration is uniformly distributed, and the effect of forming a specific structure with the top layer gate lines is worse, and the effect of improving the gate line adhesion is worse than that of first depositing the TCO film layer and then depositing the metal seed layer.

[0141] It should be noted that the conventional processes not described or explained in further detail above can be referred to in relevant existing technologies, and will not be elaborated on here.

[0142] The following is a specific embodiment provided as an example. The preparation of the solar cell involved in this embodiment can be carried out with reference to the following steps:

[0143] (1) Texturing and cleaning: Texturing and cleaning the battery substrate to form a positive pyramid structure on the silicon wafer surface (the size of the pyramid structure can be, for example, 2μm to 8μm, and in some embodiments, 3μm to 6μm);

[0144] (2) Amorphous silicon film is deposited on the battery substrate after texturing and cleaning using PECVD plasma deposition equipment (the thickness of the intrinsic amorphous silicon layer on the front side can be 3nm to 6nm, the thickness of the intrinsic amorphous silicon layer on the back side can be 5nm to 10nm, the thickness of the N-type doped layer on the front side can be 5nm to 10nm, and the thickness of the P-type doped layer on the back side can be 5nm to 15nm).

[0145] (3) PVD-TCO deposition: A TCO film is deposited on the surface of an amorphous silicon film using a PVD magnetron sputtering device (the thickness of the TCO film can be 50nm to 150nm, 70nm to 120nm in some embodiments, and 80nm to 100nm in some embodiments). The deposition power density of the TCO film is 2.5kw / m to 5.0kw / m (3.0kw / m to 4.0kw / m in some embodiments). During the deposition process, the temperature of the battery substrate is maintained at 170℃ to 220℃ (190℃ to 210℃ in some embodiments). After deposition, the substrate is annealed at 180℃ to 230℃ (220℃ in some embodiments) for 5min to 25min (15min in some embodiments).

[0146] (4) PVD-Cu (copper seed layer) deposition: A copper seed layer (the thickness of the copper seed layer can be 30nm to 250nm, and in some embodiments 50nm to 150nm) is deposited on the surface of the TCO film using a PVD magnetron sputtering device. The copper implantation energy is 300keV to 1000keV (in some embodiments 500keV to 800keV), and the deposition power density is 3.0kw / m to 6.0kw / m (in some embodiments 4.0kw / m to 5.0kw / m). During the deposition process, the temperature of the battery substrate is maintained at 160℃ to 230℃ (in some embodiments 170℃ to 190℃). After deposition, the substrate is annealed at 170℃ to 250℃ and 0.1mbar to 2.0mbar for 5min to 25min to obtain a yellow film.

[0147] (5) Coating: Coating the surface of the yellow film with photosensitive ink to completely cover the copper seed layer (the coating thickness of the photosensitive ink can be 10μm~15μm);

[0148] (6) Laser printing: The predetermined pattern is printed onto the photosensitive film by laser according to the designed grid pattern. The photosensitive film is photosensitive and changes in color, thus distinguishing it from the unexposed areas.

[0149] (7) Development: The photosensitive ink area is cleaned and removed using an alkaline solution (such as sodium carbonate solution), forming a groove on the battery surface and exposing the underlying copper seed layer.

[0150] (8) Electroplating: Copper grid lines are electroplated in the first electroplating solution (such as copper sulfate solution, etc.), and the height of the copper grid lines can be 6μm to 12μm; a tin protective layer is electroplated in the second electroplating solution (such as tin methanesulfonate solution, etc.), and the height of the tin protective layer can be 2μm to 6μm.

[0151] (9) Removal and Etching: First, remove all the photosensitive ink in an alkaline solution (such as NaOH solution and / or KOH solution, etc.), then remove the copper seed layer in the non-grid area in an acidic solution (such as dilute sulfuric acid solution, etc.), and finally leave grid lines on the surface of the TCO film.

[0152] (10) Perform light injection treatment on the solar cells after the film removal and re-etching (the light injection temperature can be 200℃~220℃, and the time can be 60s~120s).

[0153] (11) Complete the fabrication of the battery cells and conduct IV tests on their electrical performance.

[0154] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0155] Example 1

[0156] This embodiment provides a solar cell. Please refer to Figures 1, 4 and 5. The solar cell includes a cell substrate 100 (silicon wafer).

[0157] The front side of the battery substrate 100 is provided with a first intrinsic amorphous silicon layer 111 and an N-type doped layer 112. The front side of the N-type doped layer 112 is provided with a first TCO film layer 113, and the front side of the first TCO film layer 113 is provided with a first copper seed layer 114. The front side of the first copper seed layer 114 is connected to a first gate line 115 (copper gate line). The surface of the first gate line 115 is provided with a first protective layer 116 (tin protective layer).

[0158] A second intrinsic amorphous silicon layer 121 and a P-type doped layer 122 are stacked on the back side of the battery substrate 100; a second TCO film layer 123 is disposed on the back side of the P-type doped layer 122, and a second copper seed layer 124 is disposed on the back side of the second TCO film layer 123; a second gate line 125 (copper gate line) is connected to the back side of the second copper seed layer 124; a second protective layer 126 (tin protective layer) is disposed on the surface of the second gate line 125.

[0159] Specifically, along the direction from the surface of the TCO film to the battery substrate 100, within a 5nm depth range of the TCO film (the depth region ① in Figure 5), the copper concentration is 1×10⁻⁶. 18 ions / cm 2 ~1×10 21 ions / cm 2 The copper concentration is 1×10⁻⁶ within the 20nm–25nm depth range of the TCO film (depth region ② in Figure 5). 10 ions / cm 2 ~1×10 14 ions / cm 2 Within a depth range of 30nm to 50nm in the TCO film (as shown in depth region ③ in Figure 5), the copper concentration is ≤1×10⁻⁶. 5 ions / cm 2 No obvious signal was detected when the depth of copper in the TCO film exceeded 50 nm.

[0160] Please refer to Figures 2 and 3. Both the first TCO film layer 113 and the second TCO film layer 123 simultaneously possess... <222> , <211> , <400> , <332> , <440> as well as <622> Grain orientation. Among them, <222> The intensity of the first diffraction peak corresponding to the grain orientation is the strongest. <622> The intensity of the seventh diffraction peak corresponding to the grain orientation is third. In the first TCO film layer 113, <440> The intensity of the fourth X-ray diffraction peak corresponding to the grain orientation is approximately <222> The intensity of the first X-ray diffraction peak corresponding to the grain orientation is 1 / 3. <622> The intensity of the seventh X-ray diffraction peak corresponding to the grain orientation is approximately <222> The intensity of the first X-ray diffraction peak corresponding to the grain orientation is 1 / 6. In the first TCO film 113, the intensity of the seventh X-ray diffraction peak is greater than that of the fourth X-ray diffraction peak; in the second TCO film 123, the intensity of the seventh X-ray diffraction peak is less than that of the fourth X-ray diffraction peak. More than 99% of the grains in the first TCO film 113 and the second TCO film 123 have a size of 18 nm to 25 nm. <222> The proportion of grains with grain orientation is approximately 75 wt%, except <222> , <440> as well as <622> The total proportion of grains other than the grains corresponding to the grain orientation in each TCO film layer is approximately 2 wt%.

[0161] The thickness of the first TCO film layer 113 and the second TCO film layer 123 is 100 nm, the thickness of the first copper seed layer 114 and the second copper seed layer 124 is 100 nm, the surface roughness of the side of the first TCO film layer 113 away from the battery substrate 100 is 25 nm, and the surface roughness of the side of the second TCO film layer 123 away from the battery substrate 100 is also 25 nm.

[0162] Example 2

[0163] The difference between this embodiment and Embodiment 1 is that: in the first TCO film layer, <440> The intensity of the fourth X-ray diffraction peak corresponding to the grain orientation is approximately <222> The intensity of the first X-ray diffraction peak corresponding to the grain orientation is 1 / 5. <622> The intensity of the seventh X-ray diffraction peak corresponding to the grain orientation is approximately <222> The intensity of the first X-ray diffraction peak corresponding to the grain orientation is 1 / 6. More than 97% of the grains in both the first and second TCO films have a size of 18 nm to 25 nm. <222> The proportion of grains with grain orientation is approximately 70 wt%, except <222> , <440> as well as <622> The total proportion of grains other than the grains corresponding to the grain orientation in each TCO film layer is approximately 10 wt%.

[0164] Example 3

[0165] The difference between this embodiment and Embodiment 1 is that: in the first TCO film layer, <440> The intensity of the fourth X-ray diffraction peak corresponding to the grain orientation is approximately <222> The intensity of the first X-ray diffraction peak corresponding to the grain orientation is 1 / 6. <622> The intensity of the seventh X-ray diffraction peak corresponding to the grain orientation is approximately <222> The intensity of the first X-ray diffraction peak corresponding to the grain orientation is 1 / 6. More than 98% of the grains in both the first and second TCO films have a size of 18 nm to 25 nm. <222> The proportion of grains with grain orientation is approximately 80 wt%, except <222> , <440> as well as <622> The total proportion of grains other than the grains corresponding to the grain orientation in each TCO film layer is approximately 5 wt%.

[0166] Example 4

[0167] The difference between this embodiment and Embodiment 1 is that: in the TCO film layer, <222> The proportion of grains with grain orientation is 60 wt%.

[0168] Example 5

[0169] The difference between this embodiment and Embodiment 1 is that: in the TCO film layer, <222> The proportion of grains with grain orientation is 90 wt%.

[0170] Example 6

[0171] The difference between this embodiment and Embodiment 1 is that: <222> Grain orientation, <440> Grain orientation and <622> The total proportion of grains corresponding to the grain orientation in the TCO film is 80 wt%.

[0172] Example 7

[0173] This embodiment provides a method for preparing a solar cell according to Embodiment 1, including the following steps:

[0174] (1) Texturing and cleaning: The silicon wafer substrate is texturized and cleaned to form a positive pyramid structure on the surface of the silicon wafer (the size of the pyramid structure is 4μm);

[0175] (2) A first intrinsic amorphous silicon layer and an N-type doped layer are deposited on the front side of the battery substrate after texturing and cleaning using a PECVD plasma deposition equipment, and a second intrinsic amorphous silicon layer and a P-type doped layer are deposited on the back side of the battery substrate (where the thickness of the first intrinsic amorphous silicon layer is 6 nm, the thickness of the second intrinsic amorphous silicon layer is 9 nm, the thickness of the N-type doped layer is 10 nm, and the thickness of the P-type doped layer is 15 nm).

[0176] (3) PVD-TCO deposition: A first TCO film was deposited on the surface of the N-type doped layer and a second TCO film was deposited on the surface of the P-type doped layer using a PVD magnetron sputtering device (the thickness of each TCO film was 100 nm). The deposition power density of each TCO film was 4.0 kW / m. The temperature of the battery substrate was kept at 210 °C during the deposition process. After the deposition was completed, the substrate was annealed at 220 °C for 15 min.

[0177] (4) PVD-Cu (copper seed layer) deposition: A first copper seed layer was deposited on the surface of the first TCO film using a PVD magnetron sputtering device, and a second copper seed layer was deposited on the surface of the second TCO film (the thickness of each copper seed layer was 100 nm). The copper injection energy was 800 keV and the deposition power density was 4.0 kW / m. The temperature of the battery substrate was kept at 180 °C during the deposition process. After deposition, the substrate was annealed at 250 °C and a vacuum of 1.0 mbar for 15 min to obtain a yellow film.

[0178] (5) Coating: Coating the surface of the yellow film with photosensitive ink to completely cover the copper seed layer (the coating thickness of the photosensitive ink is 12μm);

[0179] (6) Laser printing: The predetermined pattern is printed onto the photosensitive film by laser according to the designed grid pattern. The photosensitive film is photosensitive and changes in color, thus distinguishing it from the unexposed areas.

[0180] (7) Development: The photosensitive ink area is cleaned and removed using an alkaline solution (sodium carbonate solution), forming a groove on the battery surface and exposing the underlying copper seed layer.

[0181] (8) Electroplating: Copper grid lines are electroplated in the first electroplating solution (copper sulfate solution) with a height of 9 μm; a tin protective layer is electroplated in the second electroplating solution (tin methanesulfonate solution) with a height of 4 μm.

[0182] (9) Removal and Etching: First, remove all the photosensitive ink in an alkaline solution (NaOH solution), then remove the copper seed layer in the non-grid area in an acidic solution (dilute sulfuric acid solution), and finally leave grid lines on the surface of the TCO film.

[0183] (10) The solar cells after the film removal and re-etching are subjected to light injection treatment (the light injection temperature is 210℃ and the time can be 90s) to complete the solar cell fabrication.

[0184] Comparative Example 1

[0185] The difference between this embodiment and Embodiment 1 is that 95% of the grains in each TCO film layer have a size of less than 15 nm.

[0186] Comparative Example 2

[0187] The difference between this embodiment and Embodiment 1 is that 95% of the grains in each TCO film layer have a size greater than 35 nm.

[0188] Experimental Example 1

[0189] The performance of the solar cells prepared in Examples 1-6 and Comparative Examples 1-2 was tested. The test results are shown in Tables 1 and 2. The data are the average values ​​obtained from 5 parallel experiments.

[0190] Table 1 Test Results

[0191] As can be seen from Table 1:

[0192] The solar cells prepared in Examples 1-3 showed better bonding strength and electrical parameters than those in Examples 4-6 and Comparative Examples 1-2. Examples 4-6 were even better than Comparative Examples 1-2. This indicates that the grain characteristics of the TCO film layer affect the bonding strength between the TCO film layer and the copper seed layer in the grid line region, as well as the electrical parameters of the solar cell. It is not possible to achieve both good bonding strength and electrical parameters simply by setting the parameters.

[0193] As can be seen from the comparison between Example 1 and Comparative Examples 1 and 2, inappropriate grain size in the TCO film layer significantly affects the adhesion and electrical parameters of the solar cell. This is because the grain size in the TCO film layer indirectly affects the concentration of copper injected into the TCO film layer by influencing the number of grain boundaries, carrier transport, and film quality. By controlling at least 95% of the grains in the TCO film layer to have a grain size of 15nm to 35nm, effective copper doping in the TCO film layer can be ensured while avoiding excessive copper accumulation at grain boundaries. This effectively improves the adhesion between the grid lines and the TCO film layer while ensuring excellent overall performance of the TCO film layer.

[0194] A comparison of Examples 1 and 4-5 shows that in the TCO film layer, <222> Both excessively low and excessively high proportions of grains in the grain orientation can affect the bonding strength and electrical parameters of solar cells; when... <222> When the grain proportion of the oriented grains is within the range of 70wt% to 80wt%, the solar cell can exhibit higher bonding strength and better overall electrical parameters. This is due to factors including: the TCO film layer... <222> When the grain proportion of the grain orientation meets the condition of 70wt% to 80wt%, it can improve the uniformity of copper doping, minimize the damage to the light transmittance of TCO, and also help improve the conductivity of TCO film.

[0195] A comparison of Examples 1 and 6 shows that, in the TCO film layer, <222> Grain orientation, <440> Grain orientation and <622> The total proportion of grains corresponding to different grain orientations in the TCO film also affects the adhesion and electrical parameters of the solar cell; when the total proportion of the above three grain orientations in the TCO film is not less than 90 wt%, the solar cell can have higher adhesion and better overall electrical parameters. The reasons include: by... <222> Grain orientation, <440> Grain orientation and <622> The total proportion of grains corresponding to the grain orientation in the TCO film layer is controlled to be no less than 90 wt%, which is conducive to copper implantation. At the same time, it is also helpful to prevent and improve the possible reduction of TCO optical performance after copper implantation and avoid the reduction of short-circuit current of the cell.

[0196] Experimental Example 2

[0197] Taking the yellow film prepared in Example 7 as an example, the yellow film sample was immersed in an acidic solution (prepared from water and sulfuric acid, with a sulfuric acid concentration of 5%) for 10 minutes. The results after immersion are shown in Figure 6. As can be seen from Figure 6, the yellow film prepared in the present invention did not show any corrosion after being immersed in the above-mentioned acidic solution, and the TCO film layer did not fall off, indicating that the solution provided in this disclosure can improve the corrosion resistance of the TCO film layer.

[0198] In summary, the solar cell provided by this disclosure can improve the corrosion resistance, conductivity and photoelectric response characteristics of the film while maintaining high light transmittance, which is beneficial for the solar cell to have both better photoelectric conversion efficiency and conductivity.

[0199] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A solar cell, characterized in that, The solar cell includes a cell substrate, the cell substrate including a first surface and a second surface opposite to the first surface; It also includes a TCO film layer located on the first surface and / or the second surface, the TCO film layer containing copper; at least 95% of the grains in the TCO film layer have a size of 15nm to 35nm.

2. The solar cell according to claim 1, characterized in that, At least 95% of the grains in the TCO film have a size of 18nm to 25nm.

3. The solar cell according to claim 1 or 2, characterized in that, The TCO film layer contains at least <222> Grain orientation; and, in the TCO film layer, the <222> The diffraction peaks corresponding to grain orientation have the strongest intensity; Preferably, in the TCO film layer, the <222> The proportion of grains with grain orientation is 70wt% to 80wt%.

4. The solar cell according to claim 3, characterized in that, The TCO film layer also contains <440> Grain orientation and <622> Grain orientation; The <222> Grain orientation, the <440> Grain orientation and the <622> The total proportion of grains corresponding to the grain orientation in the TCO film layer is not less than 90 wt%.

5. The solar cell according to claim 4, characterized in that, In the TCO film layer, the <440> The diffraction peak intensity corresponding to the grain orientation is the <222> The intensity of the diffraction peaks corresponding to the grain orientation is 1 / 6 to 1 / 3; And / or, the <622> The diffraction peak intensity corresponding to the grain orientation is the <222> The intensity of the diffraction peak corresponding to the grain orientation is 1 / 6 to 1 / 3.

6. The solar cell according to any one of claims 1 to 5, characterized in that, Along the direction from the surface of the TCO film to the battery substrate, within a 5 nm depth range of the TCO film, the copper concentration is 1 × 10⁻⁶. 18 ions / cm 2 ~1×10 21 ions / cm 2 ; Alternatively, along the direction from the surface of the TCO film to the battery substrate, within a depth range of 20nm to 25nm of the TCO film, the copper concentration is 1×10⁻⁶. 10 ions / cm 2 ~1×10 14 ions / cm 2 ; Alternatively, along the direction from the surface of the TCO film to the battery substrate, within a depth range of 30nm to 50nm of the TCO film, the copper concentration is ≤1×10⁻⁶. 5 ions / cm 2 ; Alternatively, along the direction from the surface of the TCO film to the battery substrate, the depth of copper in the TCO film does not exceed 50 nm.

7. The solar cell according to any one of claims 1 to 6, characterized in that, The surface roughness of the TCO film on the side away from the battery substrate is 20 nm to 30 nm.

8. The solar cell according to any one of claims 1 to 7, characterized in that, At least the grain boundary gaps within the TCO film are bonded with copper through bonding.

9. The solar cell according to any one of claims 1 to 8, characterized in that, The thickness of the TCO film is 50nm to 150nm; preferably 70nm to 120nm; more preferably 80nm to 100nm.

10. The solar cell according to any one of claims 1 to 9, characterized in that, A metal seed layer is provided on the side of the TCO film away from the battery substrate, corresponding to the grid line region; Preferably, the thickness of the metal seed layer is 30 nm to 250 nm; more preferably, it is 50 nm to 150 nm.

11. The solar cell according to claim 10, characterized in that, The solar cell further includes a doped layer disposed between the cell substrate and the TCO film layer, and grid lines connected to the metal seed layer.

12. The solar cell according to claim 11, characterized in that, The solar cell includes the cell substrate; The front side of the battery substrate is provided with a first passivation layer and a first doped layer; the front side of the first doped layer is provided with a first TCO film layer, and the front side of the first TCO film layer is provided with a first metal seed layer at the position corresponding to the gate line area; the front side of the first metal seed layer is connected to the first gate line. The back side of the battery substrate is provided with a second passivation layer and a second doped layer; a second TCO film layer is provided on the back side of the second doped layer, and a second metal seed layer is provided on the back side of the second TCO film layer at the position corresponding to the gate line region; a second gate line is connected to the back side of the second metal seed layer.

13. A method for preparing a solar cell according to any one of claims 1 to 12, characterized in that, Includes the following steps: A copper-containing TCO film layer is disposed on the first and / or second surfaces of the battery substrate.

14. The preparation method according to claim 13, characterized in that, Includes the following steps: A copper-containing TCO film layer is disposed on the first surface and / or the second surface of the battery substrate; A metal seed layer is disposed on the side of the TCO film away from the battery substrate.

15. The preparation method according to claim 13 or 14, characterized in that, Includes the following steps: A first passivation layer and a first doped layer are stacked on the first surface of the battery substrate; a first TCO film layer is disposed on the front side of the first doped layer, and a first metal seed layer is disposed on the front side of the first TCO film layer; a first gate line is connected to the front side of the first metal seed layer. A second passivation layer and a second doped layer are stacked on the second surface of the battery substrate; a second TCO film layer is disposed on the back side of the second doped layer, and a second metal seed layer is disposed on the back side of the second TCO film layer; a second gate line is connected to the back side of the second metal seed layer.

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