HK1148608A - Solar cell - Google Patents

Description

Solar cell unit

The present application is a divisional application of an invention patent application having an application number of 200580017453.4, an application date of 28/11/2005, and an invention name of "solar cell".

Technical Field

The present invention relates to a solar cell, and more particularly, to a solar cell in which electrode peeling is prevented.

Background

Solar photovoltaic power generation is a clean power generation method that generates power using light energy as infinite energy and does not release harmful substances. In the solar power generation, a solar cell is used as a photoelectric conversion element that converts light energy from the sun into electric energy to generate electric power.

In general, an electrode on the back surface of the light-receiving surface of a commonly produced solar cell is formed by screen printing a silver paste and an aluminum paste on the back surface of a silicon substrate, drying, and firing. Here, aluminum formed on substantially the entire back surface of the silicon substrate functions as a positive electrode. However, when manufacturing a solar cell module, it is not possible to directly solder a lead wire for taking out an output to an aluminum electrode formed of aluminum. Therefore, a silver electrode is formed on the back surface of the silicon substrate, and the silver electrode and the aluminum electrode are partially overlapped with each other as an electrode for taking out an output (for example, see patent documents 1 and 2).

In this way, an aluminum electrode for realizing high output and a silver electrode for taking out output are formed on the back surface of the substrate of the solar cell so as to partially overlap each other. Further, in a portion where the aluminum electrode overlaps the silver electrode, three metals of silicon of the silicon substrate, aluminum of the aluminum electrode, and silver of the silver electrode are partially alloyed.

Patent document 1: japanese laid-open patent publication No. 2003-273378

Patent document 2: japanese unexamined patent publication Hei 10-335267

However, the overlapped portions are very fragile due to stress caused by the difference in thermal expansion coefficient between the respective members in rapid heating and cooling at the time of sintering. Therefore, for example, when a silver electrode is overlapped on an aluminum electrode after firing, the corner portions of the silver electrode may be peeled off in the overlapped portion.

In addition, in order to reduce the cost of the solar battery cell, it is necessary to further thin the silicon substrate having a high price ratio. However, if only the silicon substrate is thinned, the warpage of the silicon substrate due to the difference in thermal expansion coefficient between silicon and aluminum becomes larger in the thinned silicon substrate than in the case of the thick silicon substrate.

When the warpage of the silicon substrate occurs to a large extent as described above, there are problems that cracks occur in the silicon substrate in the manufacturing process after sintering, the production yield is lowered, and the manufacturing itself is impossible due to the cracks in the silicon substrate.

As a countermeasure against these problems, for example, a method of re-evaluating the material of the aluminum paste and improving the thermal shrinkage rate of the electrode material to suppress the warpage of the silicon substrate may be considered. However, even if the material of the aluminum paste is simply changed, depending on the material combination, peeling may occur in a part of the silver electrode due to the difference in thermal shrinkage rate between aluminum and silver.

In such a case, if the degree of silver electrode peeling is large, there is also a problem that the production yield is reduced due to the generation of cracks in the solar battery cell or the reduction in the characteristics of the solar battery cell caused by the stacking of the solar battery cells.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object of the present invention is to obtain a solar cell in which electrode peeling is effectively prevented.

In order to solve the above problems, a solar battery cell according to the present invention includes: a photoelectric conversion layer; a first electrode formed on one surface side of the photoelectric conversion layer; a second electrode formed on the other surface side of the photoelectric conversion layer; and a third electrode having an outer edge portion overlapping the second electrode in an in-plane direction of the photoelectric conversion layer on the other surface side of the photoelectric conversion layer, and having a rounded corner portion provided in a substantially quadrangular shape for taking out an output from the second electrode.

In the solar cell according to the present invention, the third electrode is provided in the solar cell including the photoelectric conversion layer, the first electrode formed on one surface side of the photoelectric conversion layer, and the third electrode for taking out an output from the second electrode provided on the other surface side of the photoelectric conversion layer, and the outer edge portion of the third electrode overlaps with the second electrode, and the corner portion thereof is rounded to be substantially quadrangular.

Further, the solar battery cell according to the present invention has the following effects: even when the silicon substrate is thinned in order to reduce the cost of the solar cell, it is possible to sufficiently cope with the situation that a plurality of substrate cracks are generated in the silicon substrate as in the conventional art, and the degree of freedom in selecting the type of usable material can be increased.

In the solar cell according to the present embodiment, the corner of the third electrode is rounded, so that the area of the third electrode can be reduced and the amount of electrode material used can be reduced. As a result, the solar cell according to the present embodiment has the effect of reducing material costs and realizing an inexpensive solar cell.

Drawings

Fig. 1-1 is a cross-sectional view showing a schematic structure of a solar battery cell according to embodiment 1 of the present invention.

Fig. 1-2 are plan views showing schematic configurations of the front surface side (light receiving surface side) of the solar battery cell according to embodiment 1 of the present invention.

Fig. 1 to 3 are plan views showing schematic configurations of the solar cell according to embodiment 1 of the present invention on the back surface side (the side opposite to the light-receiving surface side).

Fig. 1 to 4 are enlarged views showing the periphery of an alloy portion in which three metals, i.e., silicon, aluminum, and silver, are partially alloyed in a solar battery cell according to embodiment 1 of the present invention.

Fig. 1 to 5 are enlarged sectional views showing the peripheral portions of the region B and the region C in which the aluminum electrode and the rear silver electrode provided on the rear surface of the solar cell according to embodiment 1 of the present invention partially overlap.

Fig. 2 is a cross-sectional view showing in an enlarged manner the peripheral portions of a region B 'and a region C' in which an aluminum electrode and a rear silver electrode provided on the rear surface of a conventional solar cell partially overlap.

Fig. 3-1 is a sectional view illustrating a method for manufacturing a solar cell according to embodiment 1 of the present invention.

Fig. 3-2 is a sectional view illustrating a method for manufacturing a solar cell according to embodiment 1 of the present invention.

Fig. 3 to 3 are sectional views for explaining a method of manufacturing a solar cell according to embodiment 1 of the present invention.

Fig. 3 to 4 are sectional views for explaining a method of manufacturing a solar cell according to embodiment 1 of the present invention.

Fig. 3 to 5 are sectional views for explaining a method of manufacturing a solar cell according to embodiment 1 of the present invention.

Fig. 3 to 6 are sectional views for explaining a method of manufacturing a solar cell according to embodiment 1 of the present invention.

Fig. 3 to 7 are plan views showing an example of a screen mask used for printing silver paste in manufacturing a solar cell according to embodiment 1 of the present invention.

Fig. 3 to 8 are cross-sectional views showing an example of a screen mask used for printing silver paste in manufacturing a solar cell according to embodiment 1 of the present invention.

Fig. 3 to 9 are sectional views for explaining a method of manufacturing a solar cell according to embodiment 1 of the present invention.

Fig. 3 to 10 are sectional views for explaining a method of manufacturing a solar cell according to embodiment 1 of the present invention.

Fig. 4-1 is a plan view for explaining the dimensions of the back surface side (the side opposite to the light receiving surface side) of a specific solar battery cell to which embodiment 1 of the present invention is applied.

Fig. 4-2 is a plan view for explaining the shape and size of the rear silver electrode of the solar cell to which embodiment 1 of the present invention is applied.

Fig. 5-1 is a plan view showing a schematic configuration of the back surface side (the side opposite to the light-receiving surface side) of the solar battery cell according to embodiment 2 of the present invention.

Fig. 5-2 shows, in an enlarged manner, the periphery of the alloy portion in the solar cell according to embodiment 2 of the present invention after the three metals, i.e., silicon, aluminum, and silver, are partially alloyed.

Fig. 5 to 3 are enlarged sectional views showing peripheral portions of a region D and a region E in which an aluminum electrode and a rear silver electrode provided on the rear surface of a solar cell according to embodiment 2 of the present invention partially overlap.

Fig. 6-1 is a plan view for explaining the dimensions of the back surface side (the side opposite to the light receiving surface side) of a specific solar battery cell to which embodiment 2 of the present invention is applied.

Fig. 6-2 is a plan view for explaining the shape and size of the rear silver electrode of the solar cell to which embodiment 2 of the present invention is applied.

Description of the symbols

10 semiconductor layer part

11 silicon substrate

13n type diffusion layer

13an type diffusion layer

14p⁺Layer(s)

15 anti-reflection film

17 aluminum electrode

17a aluminum paste layer

19 back silver electrode

19a silver paste layer

21 surface silver electrode

21a silver paste layer

23 alloy part

25 mesh

27 emulsion

31 back silver electrode

33 alloy part

Detailed Description

Hereinafter, an embodiment of the solar cell according to the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following description, and can be appropriately modified within a range not departing from the gist of the present invention. In the drawings described below, for the sake of easy understanding, the scaling between the drawings and the scaling between the members may be different from the actual ones.

Embodiment 1.

Fig. 1-1 to 1-3 show a schematic structure of a solar battery cell according to embodiment 1 of the present invention, and fig. 1-1 is a cross-sectional view showing the schematic structure of the solar battery cell according to embodiment 1. Fig. 1-2 are plan views showing schematic configurations of the front side (light-receiving surface side) of the solar battery cell according to embodiment 1, and fig. 1-3 are plan views showing schematic configurations of the back side (opposite surface side to the light-receiving surface side) of the solar battery cell according to embodiment 1. Further, FIG. 1-1 is a cross-sectional view taken along line A-A of FIG. 1-3.

As shown in fig. 1-1 to 1-3, the solar cell according to the present embodiment includes: comprises a p-type layer 11 as a semiconductor substrate, an n-type diffusion layer 13 with inverted conductivity type on the surface of the p-type layer 11, and a p-type layer containing high concentration impurity⁺A semiconductor layer portion 10 as a photoelectric conversion layer composed of a layer (BSF layer: back surface field) 14; an antireflection film 15 provided on the light-receiving surface of the semiconductor layer portion 10 to prevent reflection of incident light; a front silver electrode 21 as a light-receiving-surface electrode portion formed in a substantially rod-like shape on the light-receiving surface of the semiconductor layer portion 10(ii) a An aluminum electrode 17 as a rear surface electrode portion provided on substantially the entire rear surface of the semiconductor layer portion 10 for the purpose of extracting power and reflecting incident light; and a rear silver electrode 19 as an extraction electrode section for extracting electric power from the aluminum electrode 17.

In the solar battery cell according to the present embodiment configured as described above, if sunlight is irradiated from the light receiving surface side (the antireflection film 15 side) of the solar battery cell and reaches the internal pn junction (the junction between the p-type layer 11 and the n-type diffusion layer 13), holes and electrons of electron-hole pairs on the pn junction are separated. The separated electrons move toward the n-type diffusion layer 13. On the other hand, the separated holes are directed toward p⁺The layer 14 moves. Thereby, the n-type diffusion layer 13 and p⁺A potential difference is generated between the layers 14 to p⁺The potential of layer 14 increases. As a result, surface silver electrode 21 connected to n-type diffusion layer 13 becomes a positive electrode, aluminum electrode 17 connected to n-type diffusion layer 13 becomes a negative electrode, and a current flows through an external circuit (not shown).

Next, the features of the solar battery cell according to the present embodiment will be described. As shown in FIGS. 1 to 3 and FIGS. 1 to 4, in the solar cell according to the present embodiment, p is⁺The aluminum electrode 17 on layer 14 partially overlaps the back silver electrode 19. Fig. 1 to 4 show the periphery of the rear silver electrode 19 in the plan views of fig. 1 to 3 in an enlarged manner, and show a portion where the aluminum electrode 17 provided on the rear surface of the solar cell unit partially overlaps the rear silver electrode 19 in an enlarged manner. In addition, fig. 1 to 5 are sectional views showing the periphery of the rear silver electrode 19 in the sectional view of fig. 1 to 1 in an enlarged manner, and showing the peripheral portions of the region B and the region C where the aluminum electrode 17 provided on the rear surface of the solar cell and the rear silver electrode 19 partially overlap.

In the regions B and C where the aluminum electrode 17 and the rear silver electrode 19 partially overlap, p of the silicon substrate⁺The three metals of silicon of layer 14, aluminum of aluminum electrode 17, and silver of back silver electrode 19 are partially alloyed, as shown in fig. 1-4 and 1-5, forming alloy portion 23. Furthermore, in FIGS. 1-1 and 1-5, for region B and region BThe boundaries of the domains C, the respective metals (silicon, aluminum, silver) are clear, but are certainly not clear in practice since the portions are partially alloyed.

Here, in the solar battery cell according to the present embodiment, as shown in fig. 1 to 3 and 1 to 4, the rear silver electrode 19 has a substantially rectangular shape (rectangle) in the in-plane direction of the silicon substrate. The rear silver electrode 19 is curved at the corner of a substantially rectangular shape. Specifically, the corner of the substantially rectangular shape of the rear silver electrode 19 is rounded.

Thus, in the solar cell unit relating to the present embodiment, as shown in fig. 1 to 5, the alloy portion 23 is reliably formed in the region B and the region C where the aluminum electrode 17 and the rear surface silver electrode 19 partially overlap, and the rear surface silver electrode 19 and the aluminum electrode 17 are reliably bonded even in the end portion of the rear surface silver electrode 19.

In the conventional solar cell, the rear silver electrode 19 has a substantially rectangular shape (rectangle) in the inner direction of the silicon substrate, and the corner of the substantially rectangular shape (rectangle) is formed substantially at a right angle. In addition, similar to the solar cell of the present embodiment, the conventional solar cell also has a region B 'and a region C' in which the aluminum electrode 17 and the rear silver electrode 19 partially overlap, as shown in fig. 2.

In such a solar cell, the overlapping portions are very fragile due to stress caused by a difference in thermal expansion coefficient between the respective members, which is generated in a rapid heating step and a cooling step during sintering in the manufacturing process. Therefore, after sintering, in the region B ' and the region C ' where the aluminum electrode 17 and the back silver electrode 19 partially overlap, as shown in the region C ' of fig. 2, in the corner portion of the back silver electrode 19, the back silver electrode 19 is sometimes peeled off from the aluminum electrode 17. Further, the stress is likely to concentrate on the sharp corner of the rear silver electrode 19. That is, due to the concentration of the stress, the alloy portion 23 cannot be formed normally in the sharp corner portion of the rear surface silver electrode 19, and the rear surface silver electrode 19 tends to be peeled off from the right-angled corner portion.

Therefore, in the solar battery cell according to the present embodiment, the corner portions are rounded in order to eliminate the sharp corner portions of the rear silver electrode 19, so that stress is not concentrated on the corner portions of the rear silver electrode 19. Thus, in the solar battery cell according to the present embodiment, stress concentrated on the corner portion of the rear silver electrode 19 can be relaxed, and as shown in fig. 1 to 5, the alloy portion 23 is reliably formed in the region B and the region C where the aluminum electrode 17 and the rear silver electrode 19 partially overlap, and the bonding force between the aluminum electrode 17 and the rear silver electrode 19 and the substrate bonding force of the aluminum electrode 17 and the rear silver electrode 19 are improved. Therefore, according to the solar cell of the present embodiment, the rear surface silver electrode 19 and the aluminum electrode 17 are reliably bonded to each other even at the corner portion of the rear surface silver electrode 19, and the peeling of the rear surface silver electrode 19 can be effectively prevented.

When the fillet dimension R is larger than the dimension of the alloy portion 23, the alloy portion of the aluminum electrode 17 and the rear silver electrode 19 cannot be partially formed, and it is not suitable as the rear silver electrode 19. Thus, as shown in fig. 1 to 4, it is necessary to determine the values of the dimensions L1, L3 of the portions of the aluminum electrode 17 and the rear surface silver electrode 19 overlapping in the longitudinal direction of the rear surface silver electrode 19 and the dimensions L5, L7 of the portions of the aluminum electrode 17 and the rear surface silver electrode 19 overlapping in the short side direction of the rear surface silver electrode 19, which determine the dimensions of the alloy portion 23, in such a manner that the alloy portion 23 can be reliably formed. The aluminum electrode 17 and the rear silver electrode 19 are formed by screen printing as described later, and the dimensions are determined in consideration of the positional shift during printing of the aluminum paste and the silver paste.

In addition, in the conventional solar cell, when the silicon substrate is thinned in order to reduce the cost of the solar cell, the warp of the silicon substrate due to the difference in thermal expansion coefficient between silicon and aluminum is increased as compared with the case where a thick silicon substrate is used. Further, when the warpage of the silicon substrate is largely generated, there are problems that the production yield is lowered due to the generation of cracks in the silicon substrate in the production process after sintering, and the production itself is impossible due to the cracks in the silicon substrate.

Even when the material of the aluminum electrode is changed and the thermal shrinkage rate of the electrode material is improved to suppress the warpage of the silicon substrate as a countermeasure against these problems, depending on the material combination, the peeling occurs in a part of the rear surface silver electrode due to the difference in thermal shrinkage rate between aluminum and silver. In addition, when the degree of peeling of the rear surface silver electrode is large, there is a problem that the production yield is lowered due to the generation of cracks in the solar battery cell or the deterioration of the characteristics of the solar battery cell caused by the stacking of the solar battery cell.

However, in the solar cell according to the present embodiment, as described above, the bonding force between the aluminum electrode 17 formed on the back surface of the silicon substrate and the back surface silver electrode 19 and the bonding force between the aluminum electrode 17 and the back surface silver electrode 19 and the silicon substrate are improved, and the peeling of the back surface silver electrode 19 and the peeling of the aluminum electrode 17 can be effectively prevented. This ensures bonding between the aluminum electrode 17 and the rear silver electrode 19 and the substrate.

Therefore, according to the solar battery cell according to the present embodiment, the following effects are exhibited: even when the silicon substrate is thinned in order to reduce the cost of the solar battery cell, a large number of substrate cracks are not generated in the silicon substrate as in the conventional technique, and the method can sufficiently cope with the substrate cracks, and can increase the degree of freedom in selecting the type of silver paste that can be used.

In the solar cell according to the present embodiment, the sharp corner portions that are supposed to be present in the rear silver electrode of the conventional solar cell are rounded, so that the area of the rear silver electrode 19 is reduced, and the amount of silver paste used for the rear silver electrode 19 is reduced. Therefore, according to the solar battery cell according to the present embodiment, the material cost can be reduced, and an inexpensive solar battery cell can be realized. The specific reduction effect of the silver paste will be described later.

Next, a method for manufacturing the solar cell according to the present embodiment configured as described above will be described. In order to manufacture the solar cell according to the present embodiment, first, as shown in fig. 3-1, a p-type silicon substrate 11' is obtained by slicing a p-type single crystal silicon ingot manufactured by a czochralski method or a polycrystalline silicon ingot manufactured by a casting method, for example. Then, for example, a thickness of about 10 to 20 μm is removed by etching with about several to 20 wt% of sodium hydroxide or sodium hydrogencarbonate oxide, and a damaged layer and contamination on the silicon surface generated at the time of dicing are removed.

If necessary, the substrate is washed with a mixed solution of hydrochloric acid and hydrogen peroxide to remove heavy metals such as iron adhering to the surface of the substrate. Thereafter, anisotropic etching is performed using a solution in which IPA (isopropyl alcohol) is added to the same alkaline low-concentration solution, and for example, texture (texture) is formed so that the silicon (111) surface is exposed.

Next, an n-type diffusion layer 13a is formed to form a pn junction. In the step of forming the n-type diffusion layer 13a, for example, phosphorus oxychloride (POCl) is used₃) The diffusion treatment is performed in a mixed gas atmosphere of nitrogen and oxygen at 800 to 900 ℃, and as shown in fig. 3-2, phosphorus is thermally diffused to form an n-type diffusion layer 13a having an inverted conductivity type on the entire surface of the silicon substrate 11'. The sheet resistance of the n-type diffusion layer 13a is about several tens (30 to 80. omega./□, for example, and the depth of the n-type diffusion layer 13a is about 0.3 μm to 0.5. mu.m, for example.

Next, in order to protect the n-type diffusion layer 13a on the light receiving surface side, a polymer resist paste is printed by a screen printing method and dried to form a resist. Then, the n-type diffusion layer 13a formed on the back surface and the side surface of the silicon substrate 11' is removed by immersing in, for example, a 20 wt% potassium hydroxide solution for several minutes. Thereafter, the resist is removed with an organic solvent, and as shown in fig. 3 to 3, a silicon substrate 11' having the n-type diffusion layer 13 formed on the entire surface (light-receiving surface) is obtained.

Next, as shown in FIGS. 3-4, in the n-type diffusion layer 13An antireflection film 15 such as a silicon oxide film, a silicon nitride film, or a titanium oxide film is formed on the surface of the substrate with a uniform thickness. For example, in the case of a silicon oxide film, SiH is used as a material by plasma CVD₄Gas and NH₃The gas is a raw material, and the antireflection film 15 is formed at a heating temperature of 300 ℃ or higher and under reduced pressure. The refractive index is, for example, about 2.0 to 2.2, and the optimal thickness of the antireflection film 15 is about 70 to 90 nm.

Next, an aluminum paste containing glass is printed and dried as shown in fig. 3 to 5 on the entire surface of the back surface (surface opposite to the light-receiving surface) of the silicon substrate 11 'by a screen printing method, and an aluminum paste layer 17a is formed on the entire surface of the back surface of the silicon substrate 11'. In the aluminum paste layer 17a, openings are provided corresponding to the formation portions of the rear silver electrodes 19. The thickness of the aluminum paste applied can be adjusted by the wire diameter of the screen mask and the thickness of the emulsion.

Next, a silver paste for the rear surface silver electrode 19 was printed and dried on the rear surface (the surface opposite to the light-receiving surface) of the silicon substrate 11' on which the aluminum electrode 17 was formed by a screen printing method as shown in fig. 3 to 6, thereby forming a silver paste layer 19 a. At this time, as shown in fig. 1 to 3, the silver paste layer 19a is formed into a substantially rectangular shape (rectangle) having rounded corners. Here, for example, as shown in fig. 3 to 7 and 3 to 8, printing of silver paste may be performed using a screen mask in which the mesh 25 is patterned with the emulsion 27.

Further, silver paste for the front surface silver electrode 21 is printed and dried on the front surface (light receiving surface) of the silicon substrate 11' on which the antireflection film 15 is formed by a screen printing method, and as shown in fig. 3 to 9, a silver paste layer 21a is formed. The thickness of the silver paste applied can also be adjusted by the wire diameter of the mesh forming the screen mask, the thickness of the emulsion, and the like.

Then, in the sintering step for forming the electrode, the front and back electrode paste layers are simultaneously sintered at 600 to 900 ℃ for several minutes to ten and several minutes. On the surface (light-receiving surface) side of the silicon substrate 11 ', the silver paste layer is sintered to become the surface silver electrode 21 as shown in fig. 3 to 10, and while the antireflection film 15 is melted, the silver material is in contact with the silicon of the silicon substrate 11' through the glass material contained in the silver paste, and the antireflection film 15 is again solidified. Thereby ensuring the conduction between the surface silver electrode 21 and silicon. Such a process is generally referred to as a fire-through process.

On the other hand, on the back surface side (the surface opposite to the light-receiving surface) of the silicon substrate 11', the aluminum paste layer is sintered to become the aluminum electrode 17 as shown in fig. 3 to 10, and the silver paste layer is sintered to become the back surface silver electrode 19 as shown in fig. 3 to 10. Here, aluminum of the aluminum paste reacts with silicon of the silicon substrate 11' to form p directly under the aluminum electrode 17⁺Layer 14. This layer is generally called a BSF (back surface field) layer, and contributes to improvement of energy conversion efficiency of the solar cell. Furthermore, the silicon substrate 11' is covered with an n-type diffusion layer 13 and p⁺The region sandwiched by the layers 14 becomes the p-type layer 11.

In addition, in the portion where the silver paste directly contacts the silicon substrate 11 ', the silver paste directly reacts with silicon of the silicon substrate 11 ', and in the portion contacting the aluminum paste, three metals of silicon of the silicon substrate 11 ', aluminum of the aluminum paste (aluminum electrode 17), and silver of the rear surface silver electrode 19 are partially alloyed. Using the above procedure, the cell is completed using the solar cell manufacturing process. In the module manufacturing step after the cell manufacturing step, a copper wire for taking out an output to the outside is arranged on the silver electrode 3.

Further, the solar cell described above can be realized only by changing the shape of the back silver electrode, and the solar cell described above can be realized only by changing the mask shape in screen printing of the silver paste for the back silver electrode without changing the existing equipment.

Next, a description will be given of a specific example of the reduction of the area of the rear silver electrode and the reduction of the amount of silver paste. Here, as shown in fig. 4-1 and 4-2, a case where a solar cell in which rear silver electrodes 19 adjacent to each other are arranged in 2 rows in the vertical direction is configured under the following conditions will be described as an example.

Length L1 of long side of back silver electrode 19 is 9.8mm

The short side length L5 of the rear silver electrode 19 is 7.8mm

Distance L9 between the rear silver electrode rows was 75mm

The distance L11 between the rear silver electrodes 19 at both ends of the rear silver electrode row was 135mm

The distance L13 between the rear silver electrodes 19 adjacent to each other in the rear silver electrode row is 22.5mm

Table 1 shows the area of the back silver electrode 19 reduced and the silver paste reduction rate when the radius of curvature R of the rounded portion of the back silver electrode 19 is changed from 1.0mm to 3.0mm at a pitch of 0.5mm in the solar cell having the above dimensions.

[ Table 1 ]

s

R(mm)	Area (mm) reduction of back silver electrode2)	Reduction ratio (%)
			3.0	7.7	10.1
2.5	5.4	7.0
			2.0	3.4	4.5
1.5	1.9	2.5
			1.0	0.9	1.1

As shown in Table 1, as the radius of curvature R of the rounded portion of the rear silver electrode 19 is increased from 1.0mm to 3.0mm, the cut surface of the rear silver electrode 19 is reducedVolume (mm)²) From 0.9mm²Increased to 7.7mm². Further, the reduction rate (%) of the silver paste, i.e., the reduction effect of the silver paste, increased from 1.1% to 10.1%. Thus, by applying the present invention, the amount of silver paste for the rear silver electrode 19 can be reduced, and the material cost can be reduced in the solar battery cell according to the present embodiment, and it can be said that an inexpensive solar battery cell can be realized.

Embodiment 2.

In embodiment 2, another embodiment of the solar battery cell according to the present invention will be described. The basic configuration of the solar cell according to embodiment 2 is the same as that of the solar cell according to embodiment 1 described above. Therefore, only the differences between the solar battery cell according to embodiment 2 and the solar battery cell according to embodiment 1 will be described below. In the following drawings, the same members as those of the solar battery cell according to embodiment 1 are denoted by the same reference numerals as those of embodiment 1.

Fig. 5-1 to 5-3 show a schematic configuration of a solar battery cell according to embodiment 2 of the present invention, and fig. 5-1 is a plan view showing a schematic configuration of a rear surface side (a side opposite to a light receiving surface side) of the solar battery cell according to embodiment 2, corresponding to fig. 1-3. Further, fig. 5-2 corresponds to fig. 1-4, and shows the periphery of the rear silver electrode 31 in the plan view of fig. 5-1 in an enlarged manner, and shows a portion where the aluminum electrode 17 provided on the rear surface of the solar cell unit partially overlaps the rear silver electrode 31 in an enlarged manner.

Fig. 5 to 3 are cross-sectional views corresponding to fig. 1 to 5, showing the periphery of the rear silver electrode 31 in an enlarged manner, and showing the periphery of the regions D and E where the aluminum electrode 17 provided on the rear surface of the solar cell and the rear silver electrode 31 partially overlap. The cross-sectional structure of the solar battery cell and the schematic structure of the light-receiving surface side (front surface side) of the solar battery cell in embodiment 1 are the same as those in embodiment 1, and therefore, reference is made to fig. 1-1 and 1-2.

Here, the rear silver electrode 31 in the present embodiment corresponds to the rear silver electrode 19 in embodiment 1, and is different from the case of embodiment 1 in that the corner portions are chamfered instead of rounded as shown in fig. 5-1 and 5-2.

Here, in the solar battery cell according to the present embodiment, as shown in fig. 5-1 and 5-2, the rear silver electrode 31 has a substantially rectangular shape (rectangle) in the in-plane direction of the silicon substrate. The corner of the rear silver electrode 31 is chamfered to have a substantially rectangular shape.

Further, although the shape of the corner portion of the rear surface silver electrode is different from that in embodiment 1, in the region D and the region E where the aluminum electrode 17 and the rear surface silver electrode 31 partially overlap, p of the silicon substrate is made to be the same⁺The three metals of silicon of the layer 14, aluminum of the aluminum electrode 17, and silver of the back silver electrode 31 are partially alloyed, as shown in fig. 5-2 and 5-3, forming an alloy portion 33. In fig. 5 to 3, the boundaries of the respective metals (silicon, aluminum, silver) are clear in the region D and the region E, but the portions are partially alloyed, so that the portions are actually not clear.

Thus, in the solar cell unit relating to the present embodiment, as shown in fig. 5-3, the alloy portion 33 is reliably formed in the region D and the region E where the aluminum electrode 17 and the rear surface silver electrode 31 partially overlap, and the rear surface silver electrode 31 and the aluminum electrode 17 are reliably bonded even in the end portion of the rear surface silver electrode 31.

In the solar cell according to the present embodiment, the corners are chamfered to avoid concentration of stress on the corners of the rear silver electrode 31 in order to eliminate sharp corners of the rear silver electrode 31. Thus, in the solar battery cell according to the present embodiment, stress concentrated on the corner portion of the rear silver electrode 31 can be relaxed, and as shown in fig. 5-3, the alloy portion 33 is reliably formed in the region D and the region E where the aluminum electrode 17 and the rear silver electrode 31 partially overlap, and the bonding force between the aluminum electrode 17 and the rear silver electrode 31 and the substrate bonding force of the aluminum electrode 17 and the rear silver electrode 31 are improved. Therefore, according to the solar cell of the present embodiment, the rear surface silver electrode 19 and the aluminum electrode 17 are reliably bonded to each other even at the corner portion of the rear surface silver electrode 19, and the peeling of the rear surface silver electrode 19 can be effectively prevented.

When the chamfer dimension C is larger than the dimension of the alloy portion 33, the alloy portion of the aluminum electrode 17 and the rear silver electrode 31 cannot be partially formed, and it is not suitable as the rear silver electrode 31. Thus, as shown in fig. 5-2, it is necessary to determine the values of the dimensions L21, L23 of the portions of the aluminum electrode 17 and the rear surface silver electrode 31 that overlap in the longitudinal direction of the rear surface silver electrode 31 and the dimensions L25, L27 of the portions of the aluminum electrode 17 and the rear surface silver electrode 31 that overlap in the short side direction of the rear surface silver electrode 31 in such a manner that the alloy portion 33 can be reliably formed. The aluminum electrode 17 and the rear silver electrode 31 are formed by screen printing as described later, and the dimensions are determined in consideration of the positional shift during printing of the aluminum paste and the silver paste.

In the solar cell according to the present embodiment, as described above, the bonding between the aluminum electrode 17 and the rear silver electrode 31 and the substrate can be secured. Therefore, the solar battery cell according to the present embodiment also exhibits the following effects: even when the silicon substrate is thinned in order to reduce the cost of the solar battery cell, a large number of substrate cracks are not generated in the silicon substrate as in the conventional technique, and the method can sufficiently cope with the substrate cracks, and can increase the degree of freedom in selecting the type of silver paste that can be used.

In the solar cell according to the present embodiment, the sharp corner portion which should be present in the rear silver electrode of the conventional solar cell is formed as the chamfered portion, so that the area of the rear silver electrode is reduced, and the amount of silver paste used for the rear silver electrode 31 is reduced. Therefore, the solar cell according to the present embodiment also has the effect of reducing the material cost and realizing an inexpensive solar cell.

Note that, in addition to the substantially rectangular shape (rectangle) in which the corner portion is chamfered as shown in fig. 5-1 when screen printing the silver paste layer, the solar cell according to the present embodiment can be manufactured by the same process as in the case of embodiment 1. Further, the solar cell according to the present embodiment can be realized only by changing the shape of the rear silver electrode, and the solar cell can be realized only by changing the shape of the mask used in screen-printing the silver paste for the rear silver electrode without changing the existing equipment.

Next, a description will be given of a specific example of the reduction of the area of the rear silver electrode and the reduction of the amount of silver paste. Here, as shown in fig. 6-1 and 6-2, a case where a solar cell in which rear silver electrodes 31 adjacent to each other are arranged in 2 rows in the vertical direction is configured under the following conditions will be described as an example.

Length L21 of long side of back silver electrode 31 is 9.8mm

The short side length L25 of the rear silver electrode 31 is 7.8mm

Distance L9 between the rear silver electrode rows was 75mm

The distance L11 between the rear silver electrodes 31 at both ends of the rear silver electrode row was 135mm

The distance L13 between the rear silver electrodes 31 adjacent to each other in the rear silver electrode row was 22.5mm

Table 2 shows the reduction area and the silver paste reduction rate of the rear surface silver electrode 31 when the chamfer dimension C of the chamfer portion of the rear surface silver electrode 31 is changed from 1.0mm to 3.0mm at a pitch of 0.5mm in the solar cell having the above dimensions.

[ Table 2 ]

C(mm)	Area (mm) reduction of back silver electrode2)	Reduction ratio (%)
			3.0	18.0	23.5
2.5	12.5	16.4
			2.0	8.0	10.5
1.5	4.5	5.9
			1.0	2.0	2.6

As shown in table 2, as the chamfer dimension C of the chamfer portion of the rear silver electrode 31 is made larger from 1.0mm to 3.0mm, the area of the rear silver electrode 31 is reduced (mm)²) From 2.0mm²Increase to 18.0mm². Further, the silver paste reduction rate (%), that is, the reduction effect of the silver paste, was increased from 2.6% to 23.5%. Thus, by applying the present invention, the amount of silver paste for the rear silver electrode 31 can be reduced, which is related to the present embodimentThe material cost of the solar cell of (4) can be reduced, and it can be said that an inexpensive solar cell can be realized.

In either of embodiments 1 and 2, in order to obtain a greater reduction effect of the silver paste, it is necessary to increase the radius of curvature or the chamfer size, but if the radius is too large, an alloy portion of aluminum and silver cannot be formed. When actually selecting the radius of curvature and the chamfer dimension, it is necessary to take into account positional displacement occurring when printing pastes for aluminum electrodes and silver electrodes, and it is necessary to determine the radius of curvature and the chamfer dimension so that the alloy portion can be reliably formed.

The solar battery cells according to embodiments 1 and 2 are examples of the embodiments of the present invention, and the present invention is not limited to the above description, and can be appropriately modified within a range not departing from the gist of the present invention.

Industrial applicability

As described above, the solar cell according to the present invention is useful for a solar cell having a structure in which an aluminum electrode and a silver electrode for taking out an output are partially overlapped with each other.

Claims (2)

1. A solar battery cell is provided with:

a photoelectric conversion layer having a first surface and a second surface;

a first electrode provided on the first surface;

a second electrode provided on the second surface; and

a third electrode provided on the second surface, the third electrode having an overlapping portion overlapping with the second electrode in an in-plane direction of the photoelectric conversion layer and being for taking out an output from the second electrode,

wherein a rounded corner portion is provided for relaxing stress concentrated at the corner portion of the third electrode.

2. The solar cell unit as defined in claim 1, wherein:

the second electrode is an aluminum electrode, and

the third electrode is a silver electrode.