A solar cell and its preparation method, and a battery assembly

Abstract

The present invention relates to the technical field of solar cells, and specifically to a solar cell and a preparation method thereof, and a cell assembly. The solar cell is a cell after being cut and sliced, and the reflectivity of the cut surface after slicing is 10% to 90%, the roughness Ra is less than 1μm, and Rz is less than 2μm; a passivation layer is deposited on the cut surface. The preparation method of the solar cell comprises: non-destructively cutting the solar cell to obtain the cell after being cut and sliced; and depositing a passivation layer on the exposed cut surface of the cell after being cut by atomic layer deposition technology. The present invention repairs the damage caused by cutting by passivation, and at the same time, by limiting the cutting and passivation processes, standardizes the optimal value of mutual matching between cutting and passivation, realizes the state of completely repairing the cut damage, and greatly improves the power generation of the solar cell assembly.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a solar cell and a preparation method thereof, and a cell assembly. Background Art

[0002] With the development of photovoltaic technology, improving the conversion efficiency of solar cells has become a key goal. At present, the mainstream is to cut solar cells into half slices and then package them into half-cell modules. Half-cell cutting can reduce the current transmission distance inside the battery, reduce resistance loss, and thus increase the output power of the battery. At the same time, in the production process, cutting into half slices can make more efficient use of raw materials such as silicon wafers. When there are some edge defects or silicon wafers of inappropriate size, cutting into half slices can reduce waste, improve material utilization, and reduce costs. Since the heat generation of the half-cell module is reduced, the thermal stress is also reduced accordingly, which helps to reduce the risk of deformation and damage of the half-cell module during long-term use, improves the reliability and service life of the half-cell module, and in areas with large temperature differences, the stability advantage of the half-cell module is more prominent. The half-cell module also has a higher ability to resist shadows, because the parallel structure of the half-cell battery allows the current to continue to flow through other unshaded cells, reducing the power loss caused by shadows. In practical applications, such as building shading or dust accumulation, the performance of the half-cell module is more stable.

[0003] However, most of the current industry practices encapsulation directly after cutting solar cells, which will cause great damage and a significant drop in conversion efficiency. Therefore, the cut half-cell is passivated to reduce surface recombination; however, the existing cutting and passivation process fails to ensure the mutual matching of cutting and passivation, and cannot completely and stably repair the cutting damage, which has obvious drawbacks. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a solar cell and a preparation method thereof, and a battery assembly, which standardize the cutting and passivation processes to achieve a state of completely repairing the cut damage.

[0005] The present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a solar cell, wherein the solar cell is a cell after being split and sliced, the reflectivity of the cut surface after slicing is 10%~90%, the roughness Ra<1μm, Rz<2μm; a passivation layer is deposited on the cut surface, and the refractive index of the passivation layer is 1.52~1.78.

[0007] Furthermore, the thickness of the passivation layer is 10nm~100nm.

[0008] Furthermore, the width of the passivation layer plated around the cut surface is less than 10 mm.

[0009] In a second aspect, the present invention provides a method for preparing the above-mentioned solar cell, comprising the following steps:

[0010] (1) performing non-destructive cutting on the solar cell to obtain a cell after segmentation and slicing;

[0011] (2) A passivation layer is deposited on the exposed cut surface of the battery after segmentation and slicing using atomic layer deposition technology.

[0012] Furthermore, the non-destructive cutting includes laser grooving and then laser thermal cutting.

[0013] Furthermore, the power of the grooving laser of the laser grooving is 20W~200W, and the power of the thermal cracking laser of the laser thermal cracking is 50W~600W.

[0014] Furthermore, the laser wavelength of the laser grooving and the laser wavelength of the laser thermal cracking are both 500nm~1200nm.

[0015] Furthermore, the deposition temperature of the passivation layer deposition process is 120°C to 450°C.

[0016] Furthermore, an annealing process is also included after deposition, the annealing temperature is 120° C. to 400° C., and the annealing time is 10 min to 60 min.

[0017] In a third aspect, the present invention further provides a battery assembly, comprising the above-mentioned solar cell or the solar cell prepared by the above-mentioned process.

[0018] The present invention has the following beneficial effects:

[0019] The present invention repairs the damage caused by cutting by passivation, and at the same time, by limiting the reflectivity and roughness of the cut surface after slicing and the refractive index of the passivation layer, standardizes the optimal value of mutual matching between cutting and passivation, achieves a state of complete repair of the cut damage, and greatly improves the power generation capacity of the solar cell module. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0021] In a first aspect, the present invention provides a solar cell, which is a cell after being split and sliced, wherein the reflectivity of the cut surface after slicing is 10%~90%, the roughness Ra<1μm, Rz<2μm; a passivation layer is deposited on the cut surface, and the refractive index of the passivation layer is 1.52~1.78.

[0022] The present invention repairs the damage caused by cutting by passivation, and at the same time, by limiting the cutting and passivation processes, standardizing the optimal value of mutual matching between cutting and passivation, achieving a state of complete repair of the cutting damage, and greatly improving the power generation of the solar cell module. For the cut surface, if its reflectivity and roughness are not within the above range, it means that the flatness of the cut surface is poor, which makes the deposited passivation layer uneven, resulting in reduced passivation performance. The limitation of the refractive index of the passivation layer also reflects the compactness of the passivation layer from the side. Only the passivation layer within the current refractive index range has a compactness that meets the passivation requirements. More specifically, the refractive index of the passivation layer is 1.52, 1.55, 1.58, 1.60, 1.62, 1.64, 1.67, 1.69, 1.70, 1.73, 1.75, 1.78 or a range value composed of any two of them.

[0023] Specifically, in some embodiments of the present invention, the position of the solar cell slice is the cutting surface formed by the cell slice. The present invention does not limit the specific morphology of the cutting surface, nor does it specifically limit the number of cutting surfaces. The present invention does not specifically limit the type of solar cell, which can be a double-sided cell, a back contact cell, etc. The passivation layer deposited on the cutting surface can be a conventional passivation layer such as an aluminum oxide passivation layer, a silicon oxide passivation layer or a silicon nitride passivation layer, and the present invention does not specifically limit it; preferably, the passivation layer is an aluminum oxide passivation layer.

[0024] Specifically, in some embodiments of the present invention, the roughness is measured by contact and non-contact profile testing methods for surface roughness and cutting marks of silicon wafers for solar cells specified in GB / T30860-2014.

[0025] Specifically, in some embodiments of the present invention, the thickness of the passivation layer is 10nm~100nm. More specifically, the thickness of the passivation layer is 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm or a range value composed of any two point values; preferably, the thickness of the passivation layer is 40nm~80nm. By limiting the reflectivity, roughness, etc. of the cut surface before passivation, the thickness of the passivation layer deposited at different positions of the cut surface in the subsequent deposition process is not much different, basically within ±2nm; and at the current passivation layer thickness, it can have a good passivation effect; if the thickness is thin, it will deteriorate the battery performance.

[0026] Wrap-coating means that a cut surface passivation layer is formed on the remaining surfaces of the cell except the cut surface. The solar cell of the present invention also includes a first side surface and a second side surface intersecting with the cut surface, and during the passivation process of the cut surface, a passivation layer is wrapped around the first side surface and the second side surface near the cut surface.

[0027] Specifically, in some embodiments of the present invention, the width of the passivation layer plated around the cut surface is less than 10 mm.

[0028] In the present invention, the width of the plated passivation layer is less than 10 mm, and the passivation layer on the cut surface does not cover the effective area of ​​the battery. Although there is a carrier transport layer on the edge of the battery cell, there is no metal contact on this area and the current cannot be conducted outward. Therefore, the passivation layer on the cut surface does not affect the operation of the battery and the photoelectric conversion efficiency.

[0029] The solar cell of the present invention, before the deposition of the passivation layer, the cells to be deposited are stacked and clamped by a clamping device to control the passivation edge plating width, so as to ensure that the passivation edge plating has no negative impact on the conversion efficiency of the cell. Since the refractive index of the passivation layer, especially the aluminum oxide passivation layer itself, is relatively low, the impact on the cell performance is relatively small under the current plating width. More specifically, the width of the passivation layer plated on the cut surface is 10mm, 8mm, 6mm, 4mm, 2mm, 1mm, 0.5mm, 0.3mm, 0.2mm, 0.1mm, 0.05mm. The width of the passivation layer plated on the cut surface referred to in the present invention is the maximum size of the passivation layer of the cut surface plated on the first side or the second side in the direction perpendicular to the cutting edge on the first side or the second side. If the cutting edge is a curve, it is perpendicular to its tangent. Preferably, the width of the passivation layer plated on the cut surface is 0.05mm~0.3mm.

[0030] In a second aspect, the present invention provides a method for preparing the above-mentioned solar cell, comprising the following steps:

[0031] (1) Perform non-destructive cutting of solar cells to obtain cells after segmentation and slicing;

[0032] (2) Atomic layer deposition technology is used to deposit aluminum oxide on the exposed cut surface of the battery after segmentation to form a passivation layer.

[0033] Specifically, in some embodiments of the present invention, the non-destructive cutting includes laser grooving and then laser thermal cracking cutting. The present invention performs laser pre-grooving on both sides of the solar cell cutting line to isolate the cutting line and prevent the cutting damage left on the cutting cross section during the silicon wafer cutting process from causing a decrease in the photoelectric conversion efficiency of the cell slice.

[0034] Specifically, in some embodiments of the present invention, the power of the slotting laser is 20W-200W, and the power of the thermal cracking laser is 50W-600W. More specifically, the power of the slotting laser is 20W, 30W, 40W, 50W, 60W, 80W, 90W, 100W, 120W, 140W, 150W, 160W, 180W, 200W, or a range value consisting of any two point values; preferably, the power of the slotting laser is 50-150W. The power of the thermal cracking laser is 50W, 80W, 100W, 120W, 140W, 150W, 160W, 180W, 200W, 240W, 260W, 300W, 320W, 360W, 400W, 420W, 450W, 480W, 500W or a range value consisting of any two point values; preferably, the power of the thermal cracking laser is 200W~400W.

[0035] Specifically, in some embodiments of the present invention, the laser wavelength of laser grooving and the laser wavelength of laser thermal cracking are both 500nm~1200nm. More specifically, the laser wavelength of laser grooving and the laser wavelength of laser thermal cracking are both 532nm~1064nm; preferably, the laser wavelength of laser grooving and the laser wavelength of laser thermal cracking are 532nm, 798nm, and 1064nm.

[0036] Specifically, in some embodiments of the present invention, the laser used for laser grooving is a green picosecond laser or an ultraviolet picosecond laser.

[0037] More specifically, in some embodiments of the present invention, the resistivity of the silicon wafer in the solar cell used for slicing is 0.3Ω / cm~1.8Ω / cm, and the base height of the pyramid after the front and back of the silicon wafer are textured is 6μm~25μm. For the silicon wafer resistivity and the base height of the pyramid of conventional solar cells, they basically meet the above ranges, further illustrating that the cutting passivation process of the present invention is basically applicable to conventional solar cell structures and has a wide range of applications.

[0038] Specifically, in some embodiments of the present invention, lossless cutting may be carried out by water lossless cutting or waterless lossless cutting. The present invention does not make any specific limitation. As long as the lossless cutting method that can achieve the roughness and reflectivity of the cutting surface in the present invention is achieved, it belongs to the protection scope of the present invention.

[0039] More specifically, as an embodiment, the present invention adopts waterless and lossless cutting, including the following steps: the cutting path of the solar cell is preset, and when cutting, the spot center of the thermal cracking laser coincides with the spot center of the slotting laser or follows the spot center of the slotting laser, the slotting laser moves along the cutting path and briefly cuts two short cracking grooves at both ends of the solar cell or near the edges of both ends, the thermal cracking laser moves along the cutting path and scans the solar cell, dividing the solar cell into two along the cutting path to complete the cutting.

[0040] Specifically, in some embodiments of the present invention, before the atomic layer deposition technology is used to deposit the passivation layer, a plurality of losslessly cut battery cells are stacked and clamped using special tooling, and then deposition is performed on the exposed cut surfaces. This can ensure that the plating area around the passivation edge is extremely small and has no negative impact on the conversion efficiency.

[0041] Specifically, in some embodiments of the present invention, the deposition temperature of the aluminum oxide deposition process is 120° C. to 450° C. More specifically, the deposition temperature is 120° C., 150° C., 180° C., 200° C., 220° C., 240° C., 250° C., 270° C., 300° C., 320° C., 350° C., 360° C., 380° C., 400° C., 420° C., 450° C., or a range of any two point values; preferably, the deposition temperature is 200° C. to 400° C.

[0042] Furthermore, after deposition, an annealing process is also included, the annealing temperature is 120°C to 400°C, and the annealing time is 10min to 60min. Specifically, in some embodiments of the present invention, the annealing temperature is 120°C, 150°C, 180°C, 200°C, 220°C, 240°C, 250°C, 270°C, 300°C, 320°C, 350°C, 360°C, 380°C, 400°C or a range consisting of any two point values; preferably, the annealing temperature is 200°C to 350°C. The annealing time is 10 min, 12 min, 15 min, 18 min, 20 min, 22 min, 25 min, 28 min, 30 min, 32 min, 35 min, 38 min, 40 min, 42 min, 45 min, 48 min, 50 min, 53 min, 55 min, 57 min, 60 min or a range value composed of any two point values; preferably, the annealing time is 25 min to 40 min.

[0043] In a third aspect, the present invention further provides a battery assembly, comprising the above-mentioned solar cell or the solar cell prepared by the above-mentioned process.

[0044] Specifically, in some embodiments of the present invention, the battery assembly includes a plurality of battery strings electrically connected to each other, and the battery strings can be connected in series or in parallel, which is not specifically limited by the present invention. For example, the battery assembly is obtained by connecting and packaging the above solar cells in series.

[0045] The solar cell of the present invention will be further described below in conjunction with specific embodiments.

[0046] Example 1

[0047] The present embodiment provides a solar cell, which is a cell after being split and sliced. The reflectivity of the cut surface after slicing is 70%, the roughness Ra=0.8μm, Rz=1.6μm; an aluminum oxide passivation layer is deposited on the cut surface, and the thickness of the passivation layer is 60nm; the width of the passivation layer plated on the cut surface is 5mm, and the refractive index is 1.62.

[0048] The method for preparing a solar cell of this embodiment comprises the following steps:

[0049] (1) Perform non-destructive cutting of solar cells. The power of the slotting laser is 50W, the power of the thermal splitting laser is 300W, and the wavelength of the slotting laser and the thermal splitting laser is 1064nm to obtain the cells after segmentation and slicing.

[0050] (2) Atomic layer deposition technology is used to deposit aluminum oxide on the exposed cut surface of the split battery to form a passivation layer at a deposition temperature of 200°C; after deposition, annealing treatment is performed at an annealing temperature of 300°C and an annealing time of 30 minutes.

[0051] Example 2

[0052] The present embodiment provides a solar cell, which is a cell after being split and sliced. The reflectivity of the cut surface after slicing is 10%, the roughness Ra=0.8μm, Rz=1.6μm; an aluminum oxide passivation layer is deposited on the cut surface, and the thickness of the passivation layer is 10nm; the width of the passivation layer plated on the cut surface is 2mm, and the refractive index is 1.78.

[0053] The method for preparing a solar cell of this embodiment comprises the following steps:

[0054] (1) Perform non-destructive cutting of solar cells. The power of the slotting laser is 20 W, the power of the thermal splitting laser is 50 W, and the wavelength of the slotting laser and the thermal splitting laser is 798 nm to obtain the cells after segmentation and slicing.

[0055] (2) Atomic layer deposition technology is used to deposit aluminum oxide on the exposed cut surface of the split battery to form a passivation layer at a deposition temperature of 120°C; after deposition, annealing treatment is performed at an annealing temperature of 120°C and an annealing time of 60 minutes.

[0056] Example 3

[0057] The present embodiment provides a solar cell, which is a cell after being split and sliced. The reflectivity of the cut surface after slicing is 90%, the roughness Ra=0.8μm, Rz=1.6μm; an aluminum oxide passivation layer is deposited on the cut surface, and the thickness of the passivation layer is 100nm; the width of the passivation layer plated on the cut surface is 9mm, and the refractive index is 1.52.

[0058] The method for preparing a solar cell of this embodiment comprises the following steps:

[0059] (1) Perform non-destructive cutting of solar cells. The power of the slotting laser is 200 W, the power of the thermal cracking laser is 600 W, and the wavelength of the slotting laser and the thermal cracking laser is 532 nm to obtain the cells after segmentation and slicing.

[0060] (2) Atomic layer deposition technology is used to deposit aluminum oxide on the exposed cut surface of the split battery to form a passivation layer at a deposition temperature of 450°C; after deposition, annealing treatment is performed at an annealing temperature of 400°C and an annealing time of 10 minutes.

[0061] Comparative Example 1

[0062] The comparative example provides a solar cell, which is a cell after being split and sliced. The reflectivity of the cut surface after slicing is 50%, the roughness Ra=2.4μm, Rz=3.6μm; an aluminum oxide passivation layer is deposited on the cut surface, and the thickness of the passivation layer is 10nm; the width of the passivation layer plated on the cut surface is 5mm, and the refractive index of the passivation layer is 1.62.

[0063] The method for preparing the solar cell of this comparative example comprises the following steps:

[0064] (1) Perform non-destructive cutting of solar cells. The power of the slotting laser is 10W, the power of the thermal splitting laser is 30W, and the wavelength of the slotting laser and the thermal splitting laser is 1064nm to obtain the cells after segmentation and slicing.

[0065] (2) Atomic layer deposition technology is used to deposit aluminum oxide on the exposed cut surface of the split battery to form a passivation layer at a deposition temperature of 300°C; after deposition, annealing treatment is performed at an annealing temperature of 120°C and an annealing time of 60 minutes.

[0066] Comparative Example 2

[0067] The comparative example provides a solar cell, which is a cell after being split and sliced. The reflectivity of the cut surface after slicing is 70%, the roughness Ra=0.8μm, and Rz=1.6μm; an aluminum oxide passivation layer is deposited on the cut surface, and the thickness of the passivation layer is 8nm; the width of the passivation layer plated on the cut surface is 5mm, and the refractive index of the passivation layer is 1.50.

[0068] The method for preparing the solar cell of this comparative example comprises the following steps:

[0069] (1) Perform non-destructive cutting of solar cells. The power of the slotting laser is 100 W, the power of the thermal cracking laser is 300 W, and the wavelength of the slotting laser and the thermal cracking laser is 1064 nm to obtain the cells after segmentation and slicing.

[0070] (2) Atomic layer deposition technology is used to deposit aluminum oxide on the exposed cut surface of the split battery to form a passivation layer at a deposition temperature of 300°C; after deposition, annealing treatment is performed at an annealing temperature of 120°C and an annealing time of 60 minutes.

[0071] Comparative Example 3

[0072] The comparative example provides a solar cell, which is a cell after being split and sliced. The reflectivity of the cut surface after slicing is 70%, the roughness Ra=0.8μm, and Rz=1.6μm; an aluminum oxide passivation layer is deposited on the cut surface, and the thickness of the passivation layer is 105nm; the width of the passivation layer plated on the cut surface is 5mm, and the refractive index of the passivation layer is 1.80.

[0073] The method for preparing the solar cell of this comparative example comprises the following steps:

[0074] (1) Perform non-destructive cutting of solar cells. The power of the slotting laser is 100 W, the power of the thermal cracking laser is 300 W, and the wavelength of the slotting laser and the thermal cracking laser is 1064 nm to obtain the cells after segmentation and slicing.

[0075] (2) Atomic layer deposition technology is used to deposit aluminum oxide on the exposed cut surface of the split battery to form a passivation layer at a deposition temperature of 300°C; after deposition, annealing treatment is performed at an annealing temperature of 120°C and an annealing time of 60 minutes.

[0076] Comparative Example 4

[0077] This comparative example provides a solar cell, which is a cell after being split and sliced. The reflectivity of the cut surface after slicing is 70%, the roughness Ra=0.8μm, Rz=1.6μm; an aluminum oxide passivation layer is deposited on the cut surface, and the thickness of the passivation layer is 7mm; the width of the passivation layer plated on the cut surface is 5mm, and the refractive index is 1.62.

[0078] The method for preparing the solar cell of this comparative example comprises the following steps:

[0079] (1) Perform non-destructive cutting of solar cells. The power of the slotting laser is 50W, the power of the thermal splitting laser is 300W, and the wavelength of the slotting laser and the thermal splitting laser is 1064nm to obtain the cells after segmentation and slicing.

[0080] (2) Atomic layer deposition technology is used to deposit aluminum oxide on the exposed cut surface of the split battery to form a passivation layer at a deposition temperature of 300°C; after deposition, annealing treatment is performed at an annealing temperature of 120°C and an annealing time of 60 minutes.

[0081] The solar cells of each embodiment and comparative example were tested for cell performance before and after cutting and passivation, and the results are shown in Table 1. Cutting passivation gain refers to the optimization size of the cell performance after passivation compared with the performance before passivation.

[0082] Table 1

[0083] ;

[0084] It can be seen from the test results in Table 1 that the solar cell of the present invention repairs the damage caused by cutting by passivation. At the same time, by limiting the cutting and passivation processes, the optimal value of mutual matching between cutting and passivation is standardized, and the state of complete repair of cutting damage is achieved, which greatly improves the performance of the solar cell. It can be seen from the test results of Example 1 and Comparative Example 1 that when the roughness of the cut surface is too large, the flatness of the cut surface is poor, resulting in uneven deposited passivation layer and poor passivation performance improvement effect. It can be seen from the test results of Example 1 and Comparative Examples 2-4 that when the refractive index of the passivation layer is too large or too small, or the thickness of the passivation layer is too thin, the density of the passivation layer cannot meet the passivation requirements, which will lead to the performance degradation of the battery after passivation.

[0085] The present invention is further described above with the aid of specific embodiments. However, it should be understood that the specific description here should not be construed as limiting the essence and scope of the present invention. Various modifications made to the above embodiments by ordinary technicians in the field after reading this specification are all within the scope of protection of the present invention.

Claims

1. A solar cell, characterized in that: The solar cell is a cell after being cut and sliced, and the reflectivity of the cut surface after slicing is 10% to 90%, the roughness Ra is less than 1 μm, and Rz is less than 2 μm; a passivation layer is deposited on the cut surface, and the refractive index of the passivation layer is 1.52 to 1.78; The thickness of the passivation layer is 10nm~100nm; The solar cell comprises a first side surface and a second side surface intersecting with the cutting surface, and a passivation layer is plated around the first side surface and the second side surface near the cutting surface; The width of the passivation layer plated around the cut surface is the maximum dimension of the passivation layer plated around the cut surface located on the first side surface or the second side surface in a direction perpendicular to the cut edge on the first side surface or the second side surface; if the cut edge is a curve, it is perpendicular to its tangent; The width of the passivation layer plated around the cut surface is less than 10 mm.

2. The method for preparing a solar cell according to claim 1, characterized in that: The following steps are involved: (1) performing non-destructive cutting on the solar cell to obtain a cell after segmentation and slicing; (2) A passivation layer is deposited on the exposed cut surface of the battery after segmentation and slicing using atomic layer deposition technology.

3. The method for preparing a solar cell according to claim 2, characterized in that: The non-destructive cutting includes laser grooving and then laser thermal cutting.

4. The method for preparing a solar cell according to claim 3, characterized in that: The power of the grooving laser of the laser grooving is 20W~200W, and the power of the thermal cracking laser of the laser thermal cracking is 50W~600W.

5. The method for preparing a solar cell according to claim 3, characterized in that: The laser wavelength of the laser grooving and the laser wavelength of the laser thermal cracking are both 500nm~1200nm.

6. The method for preparing a solar cell according to claim 2, characterized in that: The deposition temperature of the passivation layer deposition process is 120°C to 450°C.

7. The method for preparing a solar cell according to claim 2, characterized in that: After deposition, an annealing process is also included, with an annealing temperature of 120°C to 400°C and an annealing time of 10min to 60min.

8. A battery assembly, characterized in that: A solar cell comprising the solar cell according to claim 1 or a solar cell prepared by the method for preparing a solar cell according to any one of claims 2 to 7.