JP2021144960A - Solar cell and method for manufacturing solar cell - Google Patents

Abstract

To provide a solar cell that can improve both the power generation characteristics and the carrier recovery performance, and a method for manufacturing the same.SOLUTION: A solar cell of the present disclosure is a solar cell having a crystalline silicon substrate of a first conductivity type and a first semiconductor layer of a second conductivity type formed on a first main surface side of the crystalline silicon substrate. The side surface extending in the thickness direction of the crystalline silicon substrate includes a side portion whose arithmetic mean roughness differs in the thickness direction, has a high-resistance region with a high sheet resistance on the first main surface side in the vicinity of the side portion, and has a high-resistance region on the first main surface side in the region between the side portion and the center of the first main surface as it moves away from the side portion in one direction starting from the high-resistance region.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a solar cell and a method for manufacturing the solar cell.

As exemplified in Patent Document 1, there is an example in which a solar cell is incorporated into a solar cell module after being processed so as to have a smaller area than that at the time of manufacture according to various requirements of a product. In this method of processing a solar cell, first, a large-area solar cell is formed. In a large-area solar cell, a p-type amorphous silicon layer and a transparent conductive layer are sequentially provided on the first main surface side of the n-type single crystal substrate, and an n-type solar cell is provided on the second main surface side of the n-type single crystal substrate. It is formed by sequentially providing an amorphous silicon layer and a transparent conductive layer. Next, by irradiating the transparent conductive layer on the n-type amorphous silicon side with laser light, a dividing groove is formed in the large-area solar cell. Then, the solar cell is divided into a plurality of parts from the dividing groove as a starting point. In this way, a solar cell having a small area smaller than the large area is formed.

Japanese Unexamined Patent Publication No. 2008-235521

The inventors of the present application provided a silicon substrate having a first conductive type, a first amorphous silicon having a second conductive type provided on the first surface of the silicon substrate, and a second surface of the silicon substrate. In a heterojunction type solar cell including a second amorphous silicon having a first conductive type, laser light is emitted from the outside of a transparent conductive layer further provided on the second amorphous silicon provided on a silicon substrate. When the solar cell is divided after irradiating and providing a dividing groove in the solar cell, the exposed end face generated by the division reduces the shunt resistance between the pn junctions, and the exposed end face has a low resistance. It has been found that a leak current path can occur. The leak current flowing through the leak current path may reduce the power generation characteristics of the solar cell. Further, the degree of reduction of the shunt resistance between the pn junctions becomes large when the transparent conductive layer is present on the side of the amorphous silicon layer having the second conductive type different from the conductive type of the silicon substrate. On the other hand, in order to avoid this problem, if the existing region of the transparent conductive layer provided on the second conductive type amorphous silicon layer side is reduced, the area of the transparent conductive layer from which the generated carriers are taken out is reduced, and as a result, the area of the transparent conductive layer is reduced. , The resistance of the transparent conductive layer on the side of the second conductive type amorphous silicon layer increases, and the power generation characteristics of the solar cell are lowered.

The same phenomenon as described above can be considered when forming a dividing groove by laser irradiation for a solar cell other than the heterojunction type solar cell. As an example, the formation region of the second conductive type region in the solar cell in which the second conductive type region is provided by thermal diffusion on the crystalline silicon substrate on the first conductive side is also established. If the existing region of the second conductive type region provided on the first conductive type crystalline silicon substrate is made smaller in consideration of the position of irradiating the laser, the carrier recovery performance is lowered and the power generation characteristics of the solar cell are lowered. On the other hand, if the second conductive type region is provided at the laser irradiation position, the power generation characteristic is greatly deteriorated due to the damage caused by the laser light irradiation when the solar cell is divided into small areas.

An object of the present disclosure relates to a manufacturing method for processing a large-area solar cell into a small-area solar cell using a laser. That is, (1) damage to the silicon substrate, etc. caused by laser light irradiation, and deterioration of power generation characteristics due to the influence of the unprotected end face generated in the processed small area cell, and (2) carrier recovery performance. It is an object of the present invention to provide a solar cell and a method for manufacturing a solar cell, which can suppress both the decrease and the power generation characteristics and improve the power generation characteristics.

The solar cell of the present disclosure for solving the above problems is formed on a first conductive type crystalline silicon substrate having a first main surface and a second main surface and on the first main surface side of the crystalline silicon substrate. It is a solar cell including a second conductive type first semiconductor layer. The solar cell has an edge including two sides parallel to each other, and the sheet resistance of the solar cell changes along the first direction orthogonal to both of the two sides. A portion is provided on one surface of the surface on the first main surface side or the surface on the second main surface side, and the first sheet resistance changing portion includes a resistance increasing portion in which the sheet resistance increases as it advances in the first direction. A resistance reducing portion for reducing the sheet resistance is provided in this order.

Further, the solar cell of the present disclosure includes a first conductive type crystalline silicon substrate and a second conductive type first semiconductor layer formed on the first main surface side of the crystalline silicon substrate. It is a cell. The side surface extending in the thickness direction of the crystalline silicon substrate includes a side surface portion in which the arithmetic mean roughness differs in the thickness direction, and has a high resistance region having a high sheet resistance on the first main surface side in the vicinity of the side surface portion. However, the region between the side surface portion and the center of the first main surface includes one direction in which the sheet resistance on the first main surface side monotonically decreases as the distance from the side surface portion increases in one direction starting from the high resistance region.

In addition, the method for manufacturing a solar cell of the present disclosure includes the following steps. That is, a first conductive type silicon substrate having a first main surface and a second main surface, a second conductive type first amorphous silicon layer located on the first main surface side of the crystalline silicon substrate, and a crystal. A heteropolar junction forming step of forming a heteropolar junction comprising a first conductive type second amorphous silicon layer located on the second main surface of the sex silicon substrate; after the heteropolar junction forming step. Arrangement step of arranging the heteropolar joint in the transparent conductive layer forming chamber; after the arrangement step, 1 mm outside at least one of the first amorphous silicon layer and the second amorphous silicon layer in the chamber. Mask placement step for placing a linear mask with the above width; after the mask placement step, transparent conductivity is placed on at least one of the first amorphous silicon layer and the second amorphous silicon layer via the mask. A transparent conductive layer forming step for laminating layers; a mask removing step for removing a mask after the transparent conductive layer forming step.

According to the solar cell of the present disclosure, the power generation characteristics due to the influence of the unprotected end face generated in the small area solar cell due to the damage caused by the laser light irradiation when forming the dividing groove and the formation of the dividing groove. It is possible to suppress both the deterioration of the carrier recovery performance and the deterioration of the carrier recovery performance, and the power generation characteristics can be improved. Further, according to the method for manufacturing a solar cell of the present disclosure, as described above, it is possible to manufacture a solar cell capable of suppressing both a decrease in power generation characteristics and a decrease in carrier recovery performance due to the formation of a dividing groove of the solar cell. ..

It is a schematic cross-sectional view of the solar cell which concerns on 1st Embodiment of this disclosure. It is a schematic cross-sectional view explaining the manufacturing method of the said solar cell, and is the schematic cross-sectional view which shows the state in the process of manufacturing the said solar cell. It is a schematic cross-sectional view explaining the manufacturing method of the said solar cell, and is the schematic cross-sectional view which shows the state in the process of manufacturing the said solar cell. It is a schematic cross-sectional view explaining the manufacturing method of the said solar cell, and is the schematic cross-sectional view which shows the state in the process of manufacturing the said solar cell. It is a schematic cross-sectional view explaining the manufacturing method of the said solar cell, and is the schematic cross-sectional view which shows the state in the process of manufacturing the said solar cell. It is a schematic cross-sectional view explaining the manufacturing method of the said solar cell, and is the schematic cross-sectional view which shows the state in the process of manufacturing the said solar cell. It is a schematic diagram which shows the relationship between the change of the film thickness of the transparent conductive layer of the said solar cell, and the arrangement position of a mask in one test example. It is a schematic cross-sectional view of the solar cell of a modification. It is a schematic cross-sectional view explaining the manufacturing method of the solar cell of 2nd Embodiment, and is the schematic cross-sectional view which shows the state in the process of manufacturing the solar cell. It is a schematic cross-sectional view explaining the manufacturing method of the solar cell of 2nd Embodiment, and is the schematic cross-sectional view which shows the state in the process of manufacturing the solar cell. It is a schematic cross-sectional view explaining the manufacturing method of the solar cell of 2nd Embodiment, and is the schematic cross-sectional view which shows the state in the process of manufacturing the solar cell. It is a schematic cross-sectional view of the solar cell of the 2nd Embodiment. It is a schematic plan view which shows the position of the laser light split part in the plan view in the solar cell of a modification. It is a schematic plan view explaining the manufacturing method of the solar cell used in a small device.

Hereinafter, embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. When a plurality of embodiments and modifications are included in the following, it is assumed from the beginning that a new embodiment is constructed by appropriately combining the characteristic portions thereof. Further, in the following description and drawings, the X direction indicates one direction, the Y direction indicates the extending direction of the grooves 19, 219 described later, and the Z direction indicates the solar cell 50,150,250, The thickness direction of 350 is shown. The X, Y, and Z directions are orthogonal to each other.

(First Embodiment)
FIG. 1 is a schematic cross-sectional view of the solar cell 50 according to the first embodiment of the present disclosure. Further, FIGS. 2 to 6 are schematic cross-sectional views for explaining the manufacturing method of the solar cell 50, and are schematic cross-sectional views showing a state in which the solar cell 50 is in the process of being manufactured. Hereinafter, first, the structure of the solar cell 50 will be described with reference to FIG.

As shown in FIG. 1, in the solar cell 50, the first i-type amorphous silicon is placed on the first main surface of an n-type crystalline silicon substrate (hereinafter, simply referred to as a silicon substrate) 1 as an example of the first conductive type. Quality silicon layer (first amorphous silicon layer) 2a, p-type first amorphous silicon layer 3a as an example of the second conductive type, first transparent conductive layer 4a, and first main surface side collecting electrode 5a are laminated in this order. Further, in the solar cell 50, the second i-type amorphous silicon layer (second intrinsic amorphous silicon layer) 2b and the n-type second amorphous silicon layer 3b are placed on the second main surface of the silicon substrate 1. , The second transparent conductive layer 4b, and the second main surface side collecting electrode 5b are laminated in this order.

The silicon substrate 1 is a single crystal silicon substrate to which conductivity is added. In this embodiment, the case where the first conductive type is n type will be described. For example, the silicon substrate 1 is formed by incorporating a phosphorus atom that introduces an electron into a Si atom (silicon atom) into a single crystal silicon substrate as an impurity. The n-type single crystal silicon substrate of this example has, for example, a thickness of 50 μm to 300 μm, a specific resistance of 0.5 Ω · cm to 30 Ω · cm, and an n-type impurity concentration of 1 × 10 ^-16 cm ^-3 to 1 × 10. ^It is preferably -14 cm- ³ , and more preferably 100 μm to 200 μm in thickness and 1 Ω · cm to 10 Ω · cm in specific resistance. The n-type single crystal silicon substrate may have a high-concentration impurity layer having a thickness of about 50 nm to 500 nm on the front surface and the back surface, respectively, and may be provided with an n-type high-concentration impurity layer in the present embodiment.

The silicon substrate 1 may have a texture structure on at least one of the front surface and the back surface thereof. In this embodiment, the silicon substrate 1 has a random texture structure in which a large number of pyramid shapes are irregularly arranged and their heights (sizes) are irregular. The pyramid-shaped unevenness has, for example, a width of several μm to several tens of μm and a height of several μm to several tens of μm. The vertices and valleys of each pyramid shape may be rounded.

The first and second i-type amorphous silicon layers 2a and 2b are preferably composed of i-type hydrogenated amorphous silicon containing silicon and hydrogen. The first and second type amorphous silicon layers 2a and 2b may be omitted. The first amorphous silicon layer 3a is preferably composed of p-type hydrogenated amorphous silicon containing silicon, hydrogen and boron, and the second amorphous silicon layer 3b is preferably silicon, hydrogen and phosphorus. It is composed of n-type hydride amorphous silicon containing.

The first and second transparent conductive layers 4a and 4b preferably contain a conductive oxide as a main component. As the conductive oxide, for example, indium oxide, tin oxide, zinc oxide and the like can be used alone or in combination. As the conductive oxide, an indium-based oxide containing indium oxide as a main component is preferable from the viewpoint of conductivity, optical properties, and long-term reliability. For example, indium oxide (IWO) or tin doped with tungsten is used. Dopeed indium tin oxide (ITO) or the like can be used. The first and second transparent conductive layers 4a and 4b may be a single layer or a laminated structure composed of a plurality of layers.

The first and second transparent conductive layers 4a and 4b of this embodiment are from the first and second type amorphous silicon layers 2a and 2b, the first amorphous silicon layer 3a and the second amorphous silicon layer 3b. It has low resistance and high conductivity. For example, the specific resistances of the first and second transparent conductive layers 4a and 4b may be 3 × 10 ^-4 Ω · cm to 4 × 10 ^-3 Ω · cm, and the thickness is 50 nm to 200 nm.

The first and second main surface side collecting electrodes 5a and 5b include a conductive material such as silver, copper, or aluminum. It may be composed of only a conductive material such as metal, or may be a mixture of a powder of the conductive material or the like and an insulating material such as a resin. The first and second main surface side collecting electrodes 5a and 5b of this embodiment are a mixture of metal particles and a resin formed by curing an insulating resin paste material containing silver fine particles by sintering or drying. Consists of.

The side surface 8 extending substantially along the Z direction includes a side surface portion 8a including a plurality of types of side surface portions 8b and 8c whose arithmetic mean roughness differs in the Z direction. More specifically, the side surface portion 8a is a first region 8b in which the material is melted and then solidified from the outer end portion of the second amorphous silicon layer 3b to a part of the silicon substrate 1 on the second main surface side in the Z direction. Has. Further, the side surface portion 8a has a second region 8c that exists at a position (thickness position) in the Z direction different from the first region and has no trace of melting of the material. The surface roughness of the first region 8b is larger than the surface roughness of the second region 8c. In the following description, when the arithmetic mean roughness is referred to as a side surface portion different in the Z direction (different in the thickness direction), the side surface portion includes a first region having a trace of solidification after the material is melted. It includes a second region that exists at a position (thickness position) in the Z direction different from the first region and has no trace of melting of the material.

In FIG. 1, the first region 8b is schematically shown in a sawtooth shape. The first region 8b extends in the Z direction from the second amorphous silicon layer 3b to a part of the silicon substrate 1. The first region 8b preferably has a depth of 20% or more and 70% or less of the thickness of the silicon substrate 1 and does not reach the non-polar joint portion. However, the first region 8b may reach a depth of less than 20% of the thickness of the silicon substrate 1, and is larger than 70% of the thickness of the silicon substrate 1 in a range not reaching the heteropolar junction 20. It may reach deep depths.

The first transparent conductive layer 4a has a layer thickness increasing portion 6a in which the layer thickness increases in the direction away from the side surface portion 8a in the X direction (the width direction of the paper surface in FIG. 1). The layer thickness increasing portion 6a is a resistance decreasing portion in which the thickness of the first transparent conductive layer 4a monotonically increases in the direction away from the side surface portion 8a in the X direction, and the resistivity per unit area decreases monotonically accordingly. It has become. Further, the second transparent conductive layer 4b also has a layer thickness increasing portion 6b in which the layer thickness increases in the direction away from the side surface portion 8a in the X direction. The length of each of the layer thickness increasing portions 6a and 6b in the X direction is preferably 0.5 mm or more and 1.5 mm or less, but other lengths may be used. Further, among the layer thickness increasing portions 6a and 6b, the thickness of the end portion (thinnest portion) on the side closer to the side surface portion 8a is the thinnest, and the thickness of this portion is the standard thickness of the first transparent conductive layer 4a. It is preferably 20% or less, more preferably 15% or less of the maximum value, and may be 10% or less of the maximum value. Since the sheet resistance per unit area of the first and second transparent conductive layers 4a and 4b decreases as the thickness increases, it can be said that the layer thickness increasing portions 6a and 6b are resistance decreasing portions. On the contrary, since the sheet resistance per unit area increases as the thickness decreases, it can be said that the layer thickness decreasing portions 7a and 7b are resistance increasing portions. Further, among the first and second transparent conductive layers 4a and 4b, the thicknesses of the portions excluding the layer thickness increasing portions 6a and 6b and the layer thickness decreasing portions 7a and 7b are substantially uniform in the plane.

Here, the term "monotonically increasing" will be described. This indicates that when the thicknesses of the first and second transparent conductive layers 4a and 4b are measured by the measuring method described later, the thicknesses change in one direction. Therefore, for example, the change in thickness in a very local range, which can be measured by cross-sectional observation using an optical microscope, an electron microscope, or the like, does not necessarily have to increase monotonically in one direction.

As shown in FIG. 1, most of the first main surface side collecting electrode 5a is provided on a portion of the first transparent conductive layer 4a having a constant thickness. However, as shown in FIG. 1, when viewed from the Z direction, the first main surface side collecting electrode 5a may be provided at a position where it overlaps with the layer thickness increasing portion 6a of the first transparent conductive layer 4a. , Peripheral portion 13a that does not overlap with the first transparent conductive layer 4a may be included.

Similarly, most of the second main surface side collecting electrode 5b is provided on a portion of the second transparent conductive layer 4b having a constant thickness. However, as shown in FIG. 1, when viewed from the Z direction, the second main surface side collecting electrode 5b may be provided at a position where it overlaps with the layer thickness increasing portion 6b of the second transparent conductive layer 4b. 2 The peripheral portion 13b on which the main surface side collecting electrode 5b does not overlap the second transparent conductive layer 4b may be included.

Next, an example of a method for manufacturing the solar cell 50 will be described with reference to FIGS. 2 to 6. In the following description, a case where the solar cell 40 (see FIG. 5) is regarded as a large-area cell and the solar cell 40 (see FIG. 5) is divided into two small-area solar cells 50 (see FIG. 1) will be described.

First, the original substrate of the n-type crystalline silicon substrate 1 is immersed in an HF aqueous solution for several minutes to remove the silicon oxide film on the surface, and rinse with ultrapure water. Next, the original substrate is sufficiently immersed in a KOH (potassium hydroxide aqueous solution) / isopropyl alcohol aqueous solution at a predetermined temperature, and the surface of the substrate is etched to form the original substrate having a random texture structure on the surface. Then, the original substrate is rinsed with ultrapure water and dried with warm air to form an n-type crystalline silicon substrate 1. As a method for forming a random texture structure on the surface of the substrate, a chemical other than the above may be used, or a dry etching method using an etching gas may be used. The texture structure may be formed on both sides of the silicon substrate 1, or may be formed on only one side. Further, it is not necessary to form a texture structure on the crystalline silicon substrate.

Next, a first i-type amorphous silicon layer 2a having a film thickness of several nm is formed on the first main surface of the silicon substrate 1. _{SiH 4} and H ₂ are used as raw materials for the first type amorphous silicon layer 2a. Subsequently, a p-type first amorphous silicon layer 3a having a film thickness of several nm is formed on the first i-type amorphous silicon layer 2a. A general CVD (Chemical Vapor Deposition) device may be used to form these films. _{SiH 4} and B ₂ H ₆ are used as raw materials for the first amorphous silicon layer 3a. As the B ₂ H ₆ gas, _{a gas obtained by diluting the B 2} H ₆ concentration with H ₂ to several thousand ppm is used.

Next, a second i-type amorphous silicon layer 2b having a film thickness of several nm is formed on the second main surface of the silicon substrate 1. _{SiH 4} and H ₂ are used as raw materials for the second type amorphous silicon layer 2b. Subsequently, an n-type second amorphous silicon layer 3b having a film thickness of several nm is formed on the second i-type amorphous silicon layer 2b. A general CVD apparatus may be used for forming these films. _{SiH 4} and PH ₃ are used as raw materials for the second amorphous silicon layer 3b. As the PH ₃ gas, _{a gas obtained by diluting the pH 3} concentration with H ₂ to several thousand ppm is used.

After forming the first i-type amorphous silicon layer 2a and the p-type first amorphous silicon layer 3a on the first main surface side of the silicon substrate 1 in order, the second main surface side of the silicon substrate 1 is formed. The second i-type amorphous silicon layer 2b and the n-type second amorphous silicon layer 3b were formed in this order. However, the film may be formed first from the second main surface side, and the order of film formation is arbitrary.

Further, the i-type amorphous silicon of the present embodiment may contain a trace amount of boron or phosphorus. In this case, the trace amount means that the concentration is sufficiently thinner than the dopant concentration contained in each of the first amorphous silicon layer and the second amorphous silicon layer. Further, instead of the first type amorphous silicon layer 2a and the second type amorphous silicon layer 2b, a tunnel layer that passesivates the surface of the silicon substrate 1 may be provided. The tunnel layer is made of a thin layer such as _{silicon oxide (SiO 2).} In this way, a laminated body (FIG. 2) having the different polarity joint portion 20 was produced. In the present embodiment, the heteropolar junction 20 is the pn junction of the solar cell.

Next, the first transparent conductive layer 4a is formed on the first amorphous silicon layer 3a. More specifically, a method of forming a film using a sputtering apparatus can be mentioned. First, the laminate having the different polarity joint portion 20 is introduced into the sputtering apparatus. Then, as shown in FIG. 3, the outer peripheral side metal mask 10a is arranged over the entire circumference of the outer peripheral portion on the first amorphous silicon layer 3a, and the linear metal mask 11a is placed on the first amorphous silicon layer 3a. It is arranged at an arbitrary position on the silicon layer 3a. In this embodiment, it is arranged at a substantially central portion in the X direction (the width direction of the paper surface in FIG. 3). The linear metal mask 11a has a length (width) in the X direction of, for example, 1.0 mm or more and 2.5 mm or less, and extends in the Y direction (direction perpendicular to the paper surface of FIG. 3). One side and the other side of the linear metal mask 11a in the Y direction are connected to, for example, the outer peripheral side metal mask 10a, and in the present embodiment, the outer peripheral side metal mask 10a and the linear metal mask 11a are integrally configured. There is.

Then, as shown in FIG. 4, a first transparent conductive layer 4a having a diameter of several tens of nm is formed on the first amorphous silicon layer 3a by using, for example, a sputtering device. In the present embodiment, a transparent conductive layer made of indium tin oxide (ITO) is formed by using a sintered body of indium oxide and tin oxide as a sputter target. Then, the second transparent conductive layer 4b is formed on the second amorphous silicon layer 3b by the same method as the method for forming the first transparent conductive layer 4a. Since the order of formation of the first transparent conductive layer 4a and the second transparent conductive layer 4b is arbitrary, after forming the second transparent conductive layer 4b on the second amorphous silicon layer 3b, the first non-transparent conductive layer 4b is formed. The first transparent conductive layer 4a may be formed on the crystalline silicon layer 3a. Further, the length (width) of the linear metal mask 11a in the X direction may be less than 1.0 mm or longer than 2.5 mm. Further, the first and second transparent conductive layers may be formed by a method other than the sputtering method, for example, a chemical vapor deposition method (MOCVD). In this way, the cell laminate 30 shown in FIG. 4 is produced.

In this state, the thickness of the cell laminate 30 decreases to the thinnest thin layer portion 9a as it goes to one side in the X direction in the cross section of the first transparent conductive layer 4a including the X direction and the Z direction. After the layer thickness decreasing portion 7a appears, the layer thickness increasing portion 6a whose thickness increases as compared with the thin layer portion 9a appears. The layer thickness decreasing portion 7a and the layer thickness increasing portion 6a are arranged with a slight gap with respect to the silicon substrate 1 in the film forming process of the first transparent conductive layer 4a, and are linear metals having a constant thickness. It is formed by performing a vapor deposition process such as a sputtering method via the mask 11a. Similarly, in the cross section of the second transparent conductive layer 4b including the X direction and the Z direction, the cell laminate 30 decreases to the thinnest thin layer portion 9b toward one side in the X direction. After the layer thickness decreasing portion 7b appears, the layer thickness increasing portion 6b whose thickness increases as compared with the thin layer portion 9a appears. It is preferable that the thicknesses of the layer thickness increasing portions 6a and 6b and the layer thickness decreasing portions 7a and 7b change monotonically, respectively. That is, it is preferable that the thickness of the layer thickness increasing portions 6a and 6b increases monotonically from the thin layer portions 9a and 9b toward the unidirectional side in the X direction, and that of the layer thickness decreasing portions 7a and 7b, the thin layer portions 9a and 9b It is preferable that the thickness decreases monotonically toward 9b.

In the above embodiment, the layer thickness decreasing portions 7a and 7b and the layer thickness increasing portions 6a and 6b are formed by undergoing a vapor deposition step using a metal mask and a sputtering apparatus. However, after forming the first and second transparent conductive layers 4a and 4b on the entire surfaces of the first main surface and the second main surface of the silicon substrate 1, the layers are partially etched by a desired method. The thickness decreasing portions 7a and 7b and the layer thickness increasing portions 6a and 6b may be formed. For partial etching, an etching paste or a chemical solution such as hydrochloric acid may be used. In addition, after forming the first and second transparent conductive layers 4a and 4b on the entire surfaces of the first main surface and the second main surface of the silicon substrate 1, the thicknesses of the first and second transparent conductive layers 4a and 4b are increased. The layer thickness decreasing portions 7a and 7b and the layer thickness increasing portions 6a and 6b may be formed by irradiating the portion to be thinned with, for example, an excimer laser.

In the present embodiment, the thin layer portion 9a, which is the region where the linear metal mask 11a is arranged when the first transparent conductive layer 4a is formed, may be a portion where the first transparent conductive layer 4a does not exist. , It may be a very thin portion. Similarly, the thin layer portion 9b may be a portion where the second transparent conductive layer 4b does not exist, or may be a portion having a very thin thickness. The thin portion is, for example, about 10% to 15% thicker than the thickness of the first transparent conductive layer 4a and the second transparent conductive layer 4b in the vicinity of the central portion of the solar cell 40. means. In other words, the thin portion is a region of the first transparent conductive layer 4a and the second transparent conductive layer 4b that does not include the layer thickness increasing portions 6a and 6b and the layer thickness decreasing portions 7a and 7b. It is about 10% to 15% thicker than the average thickness. Further, in the thin layer portions 9a and 9b, the transparent conductive layer may be formed discontinuously, and in that case, a region in which the transparent conductive layer is thinly formed and a region in which the transparent conductive layer is hardly formed coexist. , The transparent conductive layer may be formed in an island shape.

Subsequently, the first main surface side collecting electrode 5a is formed on the first transparent conductive layer 4a. Specifically, a silver paste is screen-printed on the first transparent conductive layer 4a so as to have the shape of a comb-shaped electrode, and heated at a temperature of about 180 ° C. for about 1 hour to form the first main surface side collecting electrode 5a. do. As the silver paste, a silver paste in which fine silver particles are dispersed in an insulating resin may be used. At this time, the first main surface side collecting electrode 5a is preferably formed at a position where it does not overlap with the layer thickness increasing portion 6а and the layer thickness decreasing portion 7a, but a part thereof is formed at the layer thickness increasing portion 6a and the layer thickness decreasing portion. It may be arranged at a position overlapping with 7a. Further, when viewed from the Z direction, the peripheral portion 13а, which is a part of the first main surface side collecting electrode 5а, may be provided at a position where it does not overlap with the first transparent conductive layer 4a.

Similarly to this, the second main surface side collecting electrode 5b is formed on the second transparent conductive layer 4b. Specifically, a silver paste is screen-printed on the second transparent conductive layer 4b so as to have the shape of a comb-shaped electrode, and heated at a temperature of about 180 ° C. for about 1 hour to obtain the second main surface side collecting electrode 5b. Form. At this time, it is preferable that the second main surface side collecting electrode 5b is formed at a position where it does not overlap with the layer thickness increasing portion 6b and the layer thickness decreasing portion 7b. However, at least a part 12b of the second main surface side collecting electrode 5b may be arranged at a position where it overlaps with the layer thickness increasing portion 6b and the layer thickness decreasing portion 7b. Further, when viewed from the Z direction, the peripheral portion 13b, which is a part of the second main surface side collecting electrode 5b, may be provided at a position where it does not overlap with the second transparent conductive layer 4b.

In the present embodiment, the case where the silver paste is applied by the screen printing method to form the first and second main surface side collecting electrodes 5a and 5b has been described. However, the first and second main surface side collecting electrodes 5a and 5b may be manufactured by an inkjet method, a lead wire bonding method, a spray method, a vacuum vapor deposition method, a sputtering method, a plating method or the like. However, from the viewpoint of productivity, production by a screen printing method using a silver paste or a plating method using copper is preferable. Further, other materials such as aluminum may be used as the material of the first and second main surface side collecting electrodes 5a and 5b.

In this way, the large-area solar cell 40 shown in FIG. 5 is produced. In the solar cell 40, in the cross section of the first transparent conductive layer 4a including the X direction and the Z direction, a layer thickness reducing portion 7a that monotonically decreases to the thinnest thin layer portion 9a toward the X direction is provided. After appearing, a layer thickness increasing portion 6a whose thickness monotonically increases from the thin layer portion 9a appears. Further, in the solar cell 40, in the cross section of the second transparent conductive layer 4b including the X direction and the Z direction, the layer thickness decreasing portion monotonically decreases to the thinnest thin layer portion 9b toward the X direction. After the appearance of 7b, a layer thickness increasing portion 6b whose thickness monotonically increases from the thin layer portion 9b appears.

Next, the large-area solar cell 40 is divided into the small-area solar cells 50 shown in FIG. In FIG. 6, in the first transparent conductive layer 4a, where the layer thickness increasing portion 6a and the layer thickness decreasing portion 7a face each other, the thickest portion of the layer thickness increasing portion 6a and the layer thickness decreasing portion 7a The width with the thickest part is T _4a . The laser light L is emitted from the n-type second amorphous silicon layer 3b side at a place where the laser light overlaps in the Z direction with respect to an arbitrary place within 0.5 mm on both sides from the vicinity of the center of _{the width T 4a.} Irradiate. A groove 19 that reaches a depth of 20% or more and 70% or less of the thickness of the silicon substrate 1 by irradiation with this laser beam, and extends in the Y direction is provided. The groove 19 preferably has a depth that does not reach the heteropolar junction 20 of the solar cell 40.

A YAG laser can be preferably used as the type of laser used when forming the groove 19, a basic wavelength may be used as the wavelength of the laser light, and a second harmonic or a third harmonic may be used. good. By irradiating the laser beam, a groove having a depth of 20% or less of the thickness of the silicon substrate may be provided, or a groove having a depth of 70% or more may be provided. Then, the solar cell 40 is folded along the groove 19 to produce the solar cell 50 having a small area shown in FIG. In addition to the method of folding along the groove 19, the solar cell 40 may be divided by using a rod, or the solar cell 40 may be divided by applying stress to the left and right sides of the groove 19. Alternatively, the solar cell 40 may be scanned for a heat source to cause thermal expansion to grow and divide the cracks.

When the solar cell 40 is divided by using the laser light in this way, traces of forming the groove by using the laser light appear on the divided surface. Specifically, the surface state of the divided surface (side surface portion 8a in FIG. 1) changes from the side of the surface irradiated with the laser beam toward the surface not irradiated with the laser beam. Specifically, the laser irradiation region in which the silicon substrate 1 is mainly melted and resolidified by the laser light, the fracture region in which the silicon substrate 1 begins to crack from the laser, and the cleavage region cracked along the cleavage surface of the crystalline silicon wafer are formed. Appears in this order. From the viewpoint of average arithmetic roughness, the arithmetic mean roughness of the cleavage region is smaller than that of the laser irradiation region. Further, since the laser irradiation region, the fracture region, and the cleavage region appear in this order, by observing the side surface portion 8a of the solar cell 50 having a small area, which of the two main surfaces of the solar cell 40 has can be observed. It can be determined whether the laser is irradiated from the surface. In the first embodiment, the above-mentioned laser light irradiation region exists on the second main surface side. Further, the structure of such a cross section can be confirmed by observing the divided surface (side surface portion 8a in FIG. 1) of the solar cell 50 using a microscope, SEM, or the like.

According to the first embodiment, the solar cell 50 includes a second transparent portion 6b including a layer thickness increasing portion 6b in which the film thickness monotonously increases in one direction in the X direction from the laser light irradiation position which is the side surface portion 8a. A conductive layer 4b is provided. With this configuration, the sheet resistance of the solar cell 50 near the laser beam irradiation position can be increased, and the influence of the split portion shunt caused by the side surface portion 8a can be reduced. Therefore, the generation of the leak current path can be suppressed, and the output decrease of the solar cell 50 can be suppressed. Further, since the second transparent conductive layer 4b includes the layer thickness increasing portion 6b, the second transparent conductive layer 4b can be provided as close as possible to the laser light irradiation position. Therefore, the power extraction performance of the second transparent conductive layer 4b can be made good, and the output decrease of the solar cell 50 can be suppressed. With such a configuration, the solar cell 50 can suppress both the output decrease due to the formation of the groove 19 using the laser light and the output decrease due to the decrease in the power extraction performance, and can improve the power generation performance. ..

Further, according to the first embodiment, the solar cell 50 is a region of the first and second transparent conductive layers 4a and 4b that overlaps the layer thickness increasing portions 6a and 6b and the layer thickness decreasing portions 7a and 7b. The first and second main surface side collecting electrodes 5a and 5b provided in the above may be included. With this configuration, the area where the first and second main surface side collecting electrodes 5a and 5b can be formed can be widened, so that the power extraction performance of the solar cell 50 can be further improved, and the power generation performance can be improved. ..

Further, according to the first embodiment, the large-area solar cell 40 is irradiated with laser light to have a depth of 20% or more and 70% or less of the thickness of the silicon substrate and having a different polarity. A groove 19 having a depth that does not reach the joint portion 20 is provided, and then the groove 19 is divided. By creating the solar cell 50 having a small area in this way, the influence of the laser light on the heteropolar junction 20 can be reduced, and the output decrease of the solar cell 50 can be suppressed, so that the solar cell can be suppressed. The power generation performance of 50 can be improved.

Further, according to the first embodiment, the second transparent conductive layer 4b of the solar cell 50 includes a layer thickness increasing portion 6b whose film thickness monotonously increases toward one side in the X direction. However, in order to reduce the influence of the shunt generated on the side surface portion 8a, the sheet resistance of the second transparent conductive layer 4b is high at least one place on the way from the side surface portion 8a toward the central portion along one direction in the X direction. It suffices if there is a place, that is, a thin layer portion 9b. Therefore, the effect can be obtained even when the thin layer portion 9b does not exist in the vicinity of the side surface portion 8a, that is, when the thin layer portion exists on the central portion side of the solar cell 50 with respect to the side surface portion 8a. That is, in the immediate vicinity of the side surface portion 8a, the thickness of the second transparent conductive layer 4b is thicker than that of the thin layer portion 9b, and the thin layer portion 9b goes toward the center of the solar cell 50 along one direction in the X direction. And the layer thickness increasing portion 6b may have a form in which they appear in this order.

Next, the relationship between the metal mask and the shape of the second transparent conductive layer 4b after formation will be described by taking the formation of the second transparent conductive layer 4b of the solar cell 50 as an example. FIG. 7 is a schematic view showing the relationship between the change in the film thickness of the second transparent conductive layer 4b of the solar cell 50 and the arrangement position of the linear metal mask 11b in one test example. As shown in FIG. 7, in one test example, when viewed from the Z direction, a part of the layer thickness increasing portion 6b is present at a portion that does not overlap the linear metal mask 11b, and the other layer thickness increasing portion 6b is present. A part is present at a position overlapping the linear metal mask 11b.

As shown in FIG. 7, at the position where the linear metal mask 11b is provided, it is possible to make it difficult to form the second transparent conductive layer 4b directly under the linear metal mask 11b. Further, even in a portion overlapping the linear metal mask 11b when viewed from the Z direction, when the second transparent conductive layer 4b is formed, a part of the raw material of the second transparent conductive layer 4b is formed with the linear metal mask 11b. It penetrates between the second amorphous silicon layer 3b and the second amorphous silicon layer 3b. In this way, the layer thickness increasing portion 6b whose film thickness increases monotonically toward the X direction can be formed on the second transparent conductive layer 4b.

When the cross section of the second transparent conductive layer 4b in the sample prepared by using the linear metal mask 11b having an arbitrary width was observed, a film thickness change region was observed in a region wider than the width of the linear metal mask 11b. .. On the other hand, the second transparent conductive layer 4b was slightly detected even in the vicinity of the linear metal mask 11b immediately below the center in the X direction, and there was almost no region where the second transparent conductive layer 4b did not exist. That is, the end portion of the arrangement position of the linear metal mask 11b is a portion of the second transparent conductive layer 4b that corresponds to the boundary between the portion having a certain thickness and the layer thickness increasing portion 6b or the layer thickness decreasing portion 7b. Did not match, and a film thickness change region was observed in a wider range than the region where the linear metal mask 11b was provided.

This is due to the fact that the linear metal mask 11b has a thickness and that the linear metal mask 11b is arranged with a very small gap between the laminated body before the second transparent conductive layer 4b is provided. .. The thicker the thickness of the linear metal mask 11b and the larger the gap between the linear metal mask 11b and the laminate, the wider the width of the region where the thickness of the second transparent conductive layer 4b changes, and the layer thickness increasing portion 6b And the width of the layer thickness reduction portion 7b are increased. For example, when the thickness of the metal mask 11b is about 1.5 mm and a gap of about 0.5 mm is provided between the metal mask 11b and the laminated body, the width of the layer thickness increasing portion 6b is about 2.5 mm. But this is just an example. The size of the gap between the linear metal mask 11b and the laminated body affects the width of the portion of the layer thickness increasing portion 6b covered by the linear metal mask 11b. The thickness of the linear metal mask 11b affects the width of the region of the layer thickness increasing portion 6b that is not covered by the linear metal mask. The influence of the arrangement position of the metal mask and the thickness of the metal mask on the change in the thickness of the second transparent conductive layer 4b is not limited to this. A similar relationship can be seen with respect to changes in the thickness of the peripheral portion of the peripheral portion metal mask 10b and the second transparent conductive layer 4b.

With such a configuration, the resistance per area near the center of the solar cell 50 can be made higher than the resistance per area at the end of the solar cell 50. Taking the second transparent conductive layer 4b as an example, the sheet resistance as the transparent conductive layer is 40 to 200 Ω / □ (ohm) in the vicinity of the central portion of the solar cell 50 in which the thickness of the second transparent conductive layer 4b is substantially uniform. While it is about per square), it is 40 to 10 ⁴ Ω / □ in the thin layer portion 9b, and when the transparent conductive layer is present in an island shape in the thin layer portion 9b, the sheet as the transparent conductive layer. It was found that the resistance ^{increased to about 10 4} to 10 ^{8 Ω / □.}

The thickness of the second transparent conductive layer 4b included in the large-area solar cell 50 and the small-area solar cell 40 can be measured by measuring the film thickness with a spectroscopic ellipsometer, measuring the resistance value with a resistance measuring device (tester), or measuring the resistance value. It can be confirmed by surface observation and cross-sectional observation using an electron microscope or the like. In either method, the thickness is individually measured at a plurality of observation / measurement points including the second transparent conductive layer 4b, the layer thickness increasing portion 6b, the layer thickness decreasing portion 7b, the thin layer portion 9b, and the like. The change in thickness is measured by repeating the thickness measurement at each measurement point. This also applies to the first transparent conductive layer 4a.

That is, the large-area solar cell 40 includes an n-type crystalline silicon substrate 1 and a p-type first amorphous silicon layer 3a provided on the first main surface side of the silicon substrate 1 in the Z direction. , An n-type second amorphous silicon layer 3b provided on the second main surface side of the silicon substrate 1 in the Z direction. Further, the solar cell 40 is on the side opposite to the silicon substrate 1 side in the Z direction of the first amorphous silicon layer 3a and the side opposite to the silicon substrate 1 side in the Z direction of the second amorphous silicon layer 3b. The first and second transparent conductive layers 4a and 4b provided on at least one side of the above are provided. Further, in the cross sections of the first and second transparent conductive layers 4a and 4b including the X direction and the Z direction which are the extending directions of the straight line, the thinnest thin layer portions 9a and 9b are reached in the X direction. Layer thickness reduction portions 7a and 7b appear monotonically decreasing. After that, in the cross section, there is an X direction in which the layer thickness increasing portions 6a and 6b whose thickness monotonically increases from the thin layer portions 9a and 9b appear in the X direction.

Here, _{similarly to the width T 4a} , the portion of the second transparent conductive layer 4b that is thinner than the typical thickness is referred to as T _4b . The width of the T _4a may be the same as the width of the T _4b, it may be provided such that the width of the T _4b becomes wider than the width of the T _4a. In manufacturing the solar cell 40, it may be difficult to completely match the position where _{the T 4a} is provided and the position where the T _{4b is provided. In this case, by increasing the width of T 4a} on the surface side that is not irradiated with the laser beam as compared with _{T 4b} provided on the surface side that is directly irradiated with the laser beam, the first and second positions are irradiated with the laser beam. Neither of the transparent conductive layers can be present or can be present in a very thin film thickness. With such a configuration, the influence of the shunt caused by the side surface portion 8a of the solar cell 50 can be reliably reduced on both the first main surface side and the second main surface side. That is, since the decrease in the output of the solar cell 50 can be suppressed, the power generation performance of the solar cell 50 can be improved.

The solar cell manufacturing method includes an n-type crystalline silicon substrate 1, a p-type first amorphous silicon layer 3a located on the first main surface side of the silicon substrate 1 in the Z direction, and a silicon substrate. A heteropolar junction forming step of forming a heteropolar junction comprising an n-type second amorphous silicon layer 3b located on the second main surface side in the Z direction of 1 is included. Further, the solar cell manufacturing method is opposite to the side of the first amorphous silicon layer 3a opposite to the silicon substrate 1 side in the Z direction and the side of the second amorphous silicon layer 3b opposite to the silicon substrate 1 side in the Z direction. A mask placement step is included in which a linear metal mask 11a or 11b having a width of 1 mm or more and 2.5 mm or less is placed on the outside of at least one side of the side. Further, the solar cell manufacturing method is a transparent conductive layer forming step of forming the first and second transparent conductive layers 4a and 4b from the side of the linear metal mask 11a or 11b opposite to the silicon substrate 1 side in the Z direction. including. Further, the solar cell manufacturing method includes a mask removing step of removing the linear metal mask 11a or 11b after the transparent conductive layer forming step.

Further, in the solar cell manufacturing method, after the mask removing step, the linear metal mask 11a is arranged in the Z direction with respect to the vicinity of the center in the width direction (corresponding to the X direction) of the first place where the linear metal mask 11a is arranged. A groove forming step of forming a groove 19 by irradiating a second overlapping portion with a laser beam is included.

According to this manufacturing method, with respect to the manufactured solar cell 50, the output is reduced due to the formation of the groove 19 using laser light irradiation and the cell division starting from the groove 19, and the output is reduced due to the deterioration of the power extraction performance. Can be suppressed together, and the power generation performance can be improved.

In the first embodiment, the first transparent conductive layer 4a having the layer thickness increasing portion 6a whose film thickness monotonically increases in the direction away from the side surface portion 8a in the X direction is the first amorphous silicon layer 3a. A case where the second transparent conductive layer 4b having the layer thickness increasing portion 6b in the direction away from the side surface portion 8a in the X direction is provided on the outside of the second amorphous silicon layer 3b has been described. However, as shown in FIG. 8, that is, a schematic cross-sectional view of the solar cell 150 of the modified example, the substantially planar side surface portion 108a having different arithmetic average roughness in the Z direction is divided by using laser light. A transparent first transparent conductive layer 104a having a layer thickness increasing portion 106a whose thickness increases monotonically as the distance from the side surface portion 108a increases in the X direction is provided on the outside of the first amorphous silicon layer 103a. 2. A transparent conductive layer 104b having a constant cross section may be provided on the outside of the amorphous silicon layer 103b. Alternatively, the layer thickness is a substantially planar side surface portion in which the arithmetic mean roughness differs in the Z direction, and the film thickness monotonically increases in the direction away from the side surface portion divided by using the laser beam in the X direction. A transparent conductive layer having an increasing portion may be provided on the outside of the second amorphous silicon layer, while a transparent conductive layer having a constant film thickness may be provided on the outside of the first amorphous silicon layer. In FIG. 8, reference number 101 is a silicon substrate, and reference numbers 102a and 102b are i-type amorphous silicon layers.

According to the present embodiment, since the power extraction performance of the transparent conductive layer 104b can be improved by providing the transparent conductive layer 104b having a constant film thickness, the output caused by the formation of the groove 19 using the laser light irradiation. It is possible to manufacture a small-area solar cell 50 having good power generation performance by suppressing both the decrease and the output decrease due to the result of the power extraction performance.

Further, a part of the first main surface side collecting electrode 5a is present on the side of the layer thickness increasing portion 6a opposite to the silicon substrate 1 side in the Z direction, and the layer thickness increasing portion 6b is on the silicon substrate 1 side in the Z direction. Described the case where a part of the second main surface side collecting electrode 5b is present on the opposite side. However, the first main surface side collecting electrode may not be present on the side opposite to the silicon substrate side in the Z direction in the layer thickness increasing portion of the first transparent conductive layer. Further, the second main surface side collecting electrode may not be present on the side opposite to the silicon substrate side in the Z direction in the layer thickness increasing portion of the second transparent conductive layer.

Further, when viewed from the Z direction, the first main surface side collecting electrode 5a includes a peripheral portion 13a that does not overlap with the first transparent conductive layer 4a, and the peripheral portion 13a includes the silicon substrate 1 and the first amorphous silicon layer 3a. , And the case where it does not come into contact with all of the second amorphous silicon layer 3b has been described. Further, when viewed from the Z direction, the second main surface side collecting electrode 5b includes a peripheral portion 13b that does not overlap with the first transparent conductive layer 4b, and the peripheral portion 13b includes the silicon substrate 1 and the first amorphous silicon layer 3a. , And the case where it does not come into contact with all of the second amorphous silicon layer 3b has been described. However, when viewed from the Z direction, the peripheral portion where the first main surface side collecting electrode does not overlap with the first transparent conductive layer may not be included. When viewed from the Z direction, the peripheral portion where the second main surface side collecting electrode does not overlap with the second transparent conductive layer may not be included.

According to the present embodiment, a small-area solar cell 50 having good power generation performance by suppressing both an output decrease due to the formation of a groove 19 using laser light irradiation and an output decrease due to a decrease in power extraction performance. Can be manufactured.

In the present embodiment, an example in which the first conductive type is n-type and an n-type crystalline silicon substrate is used has been described. The first conductive type may be a p-type, and in this case, the crystalline silicon substrate is, for example, a boron atom that introduces holes (also referred to as holes) into Si atoms (silicon atoms) in a single crystal silicon substrate. Can be used as an impurity.

In the present embodiment, an example has been described in which the linear metal mask 11a has a linear form in which both ends thereof are connected to the peripheral metal mask 10a. However, the form of the linear metal mask 11a is not limited to this, and may be a stitch shape in which a plurality of straight lines intersect. The shape of the metal mask for forming the second transparent conductive layer 4b is similar to this. Further, the shapes of the metal mask for forming the first transparent conductive layer 4a and the metal mask for forming the second transparent conductive layer 4b are the same in the present embodiment, but they do not necessarily have to be the same. It may be different.

A plurality of the solar cell 50 of the present embodiment can be prepared and used as a solar cell module by a general method. The general method includes a step of electrically connecting a plurality of solar cell 50s to form a solar cell string. Further, the step of protecting the solar cell string from the front and back with a sealing material such as a thermosetting resin sheet or a thermoplastic resin sheet, and a highly weather resistant sheet such as a tempered glass plate or a resin film is included.

(Second Embodiment)
Next, the application of the technical idea of the present application to a solar cell in which a second conductive type region is provided by thermal diffusion on a first conductive type crystalline silicon substrate will be described with reference to FIGS. 9 to 12. 9 to 11 show a schematic cross-sectional view of the solar cell of the second embodiment during manufacturing, and FIG. 12 shows a schematic cross-sectional view of the solar cell 250 of the second embodiment.

The solar cell 250 can be formed, for example, by the following method. For details, with reference to FIG. 9, first, a p-type crystalline silicon substrate (hereinafter, simply referred to as a silicon substrate) 201 as an example of the first conductive type is prepared. Then, if necessary, a texture shape is formed on at least one of the surfaces on the first and second main surface sides of the silicon substrate 201 by a known method.

Subsequently, the silicon substrate 201 is placed in a diffusion furnace _{and heated in phosphorus oxychloride (POCl 3} ) or the like to form a surface layer portion on the first main surface side of the silicon substrate 201 as an example of the second conductive side. The n-type n-type region 202 of the above is formed to form the heteropolar junction 203 which is a semiconductor junction. Next, in the n-type region 202 formed, an etching mask is formed so that the position to be divided is exposed by laser light irradiation, and a part of the n-type region is etched. In this way, the thin portion 202a having a relatively thin thickness (depth from the surface of the silicon substrate 201) is formed in the n-type region 202. The size of the region protected by the etching mask can be, for example, about the same as the region covered by the outer peripheral metal mask 10a of the first embodiment.

The silicon substrate 201 on which the different polarity joint portion 203 is formed further has the following configuration. An antireflection film 204 is formed on the first main surface side of the silicon substrate 201 so as to overlap the n-type region 202. The antireflection film 204 is made of a silicon nitride film or the like, and is formed by, for example, a plasma CVD method using a mixed gas of _{silane (SiH 4} ) and ammonia (NH _4). In addition, SiO, AlO and the like may be used. Further, a back surface side electrode 205 is provided on the second main surface side of the silicon substrate 201. The back surface electrode is a thin film electrode made of a metal thin film layer such as aluminum and covering almost the entire surface of the second main surface side of the silicon substrate 201, or formed in a comb shape using a highly conductive material such as silver or copper. It is a grid electrode. As shown in FIG. 9, it is preferable that the electrode 205 is not provided at a position overlapping the thin portion 202a in the thickness direction. Following the formation of the back surface side electrode, the comb-shaped electrode 206 is formed on the antireflection film 204 by screen printing or the like. The comb-shaped electrode 206 is preferably made of silver or the like. In this way, the large-area solar cell 240 shown in FIG. 9 is manufactured.

Next, as shown in FIG. 10, the solar cell 240 is irradiated with laser light L from the outside on the second main surface side that overlaps the thin portion 202a in the Z direction, and as shown in FIG. 11, the silicon substrate 201 is irradiated. A groove 219 is formed on the second main surface side of the above. The depth direction of the groove 219 substantially coincides with the Z direction, and the extending direction substantially coincides with the Y direction. Subsequently, the large-area solar cell 240 in which the groove 219 is formed is, for example, manually folded to produce a small-area solar cell 250 as shown in FIG.

As shown in FIG. 12, the solar cell 250 includes a side surface portion 208a whose side surface extending substantially parallel to the Z direction has an arithmetic mean roughness different in the Z direction. The side surface portion 208a is formed due to the irradiation of laser light. Further, the solar cell 250 has one direction in which a resistance reducing portion 202b in which the resistivity per unit area decreases monotonically toward a direction away from the side surface portion 208a in one direction (corresponding to the X direction) appears. The resistance reducing portion 202b corresponds to a layer thickness increasing portion in which the thickness of the n-type region 202 monotonically increases in a direction away from the side surface portion 208a in one direction.

As described in the first embodiment, even if the etching mask is applied, the effect of the mask is insufficient at the end portion in the width direction of the etching mask. The layer thickness increasing portion is formed due to this. In the heat diffusion type solar cell 250, the thickness of the n-type region 202 affects the recovery of carriers, and varying the thickness of the n-type region 202 of the second embodiment is the first transparency of the first embodiment. This corresponds to varying the thickness of the conductive layer 4a. Then, by increasing the thickness of the n-type region 202 in the direction away from the side surface portion 208a in one direction, the thickness of the first transparent conductive layer 4a in the first embodiment is increased in the direction away from the side surface portion 8a in one direction. The same effect as increasing toward can be obtained.

The present invention is not limited to the first and second embodiments described above, and modifications thereof, and various improvements and modifications are made in the matters described in the claims of the present application and in an equivalent range thereof. Is possible. For example, the solar cell used may be of a type different from that illustrated, and includes so-called PERC cells and the like.

Further, in the first embodiment, the case where the first conductive type is n type and the second conductive type is p type has been described, but the first conductive type is p type and the second conductive type is n type. But it may be. Further, in the second embodiment, the case where the first conductive type is the p type and the second conductive type is the n type has been described, but the first conductive type is the n type and the second conductive type is the p type. But it may be.

A plurality of solar cell 50s formed as described above may be prepared, and a solar cell module may be formed and used by a general method. A general method for forming a solar cell module is a step of connecting a plurality of solar cell cells 50 in series or in parallel to form a solar cell string, and a sealing material and a protective member for forming the solar cell module. It includes a step of laminating to prepare a laminated body and a step of heating and crimping the laminated body to seal the solar cell string. Further, the laminate includes, for example, a tempered glass plate corresponding to a protective material on the surface side of the solar cell module, a first resin sheet arranged on the tempered glass plate, and the sun arranged on the first resin sheet. A battery string, a second resin sheet arranged so as to cover the solar cell string, and a backside protective material such as a resin sheet or a glass plate having high heat resistance and water resistance provided on the second resin sheet. ,including.

The method described so far, that is, the method of irradiating a large-area solar cell 40 with a laser to process a small-area solar cell 50 into a small-area solar cell 50 can be used for applications other than those described in the embodiments. .. For example, as shown in FIG. 13, in a solar cell 350 having a substantially octagonal shape with chamfered four corners of a square, the portion 351 corresponding to the chamfered portion may be removed by the above method. Further, as shown in FIG. 14, the solar cell 440 may be used for processing the solar cell 450 having a plurality of small areas. In this case, a plurality of solar cell 450s may be connected in series or in parallel, protected by a well-known method such as resin, and used as a power feeding member for a small electronic device.

1,101,201 Silicon substrate, 3a, 103a 1st amorphous silicon layer, 3b, 103b 2nd amorphous silicon layer, 4a, 104a 1st transparent conductive layer, 4b 2nd transparent conductive layer, 5a, 105a 1 Main surface side collecting electrode, 5b, 105b 2nd main surface side collecting electrode, 6a, 6b, 106a Layer thickness increasing part, 8 side surface, 8a, 208a side surface part, 9a, 9b thin layer part, 19,219 groove, 40 , 240,440 Large area (before division) solar cell, 50,150,250,450 Small area (after division) solar cell, 202a thin part, 202b resistance reduction part, X direction unidirectional, Y direction groove Extending direction, Z direction Solar cell thickness direction.

Claims (19)

A first conductive type crystalline silicon substrate having a first main surface and a second main surface,
A second conductive type first semiconductor layer formed on the first main surface side of the crystalline silicon substrate, and
It is a solar cell equipped with
The solar cell has a first edge portion including two sides parallel to each other, and the sheet resistance of the solar cell changes along a first direction orthogonal to both of the two sides. A sheet resistance changing portion is provided on one surface of the surface on the first main surface side or the surface on the second main surface side.
The first sheet resistance changing portion is a solar cell including a resistance increasing portion in which the seat resistance increases as it advances in the first direction and a resistance decreasing portion in which the sheet resistance decreases in this order. A second semiconductor layer of the same conductive type as the first conductive type provided on the second main surface corresponding to the opposite surface of the crystalline silicon substrate on the first main surface side, and
A first transparent conductive layer provided in contact with either the first semiconductor layer or the second semiconductor layer is further provided.
In the resistance increasing portion of the first sheet resistance changing portion, the thickness of the first transparent conductive layer decreases, and the thickness of the first transparent conductive layer decreases.
The solar cell according to claim 1, wherein the thickness of the first transparent conductive layer is increased in the resistance reducing portion of the first sheet resistance changing portion. The first semiconductor layer is a second conductive type first amorphous silicon layer provided on the first main surface side of the crystalline silicon substrate, and the first transparent conductive layer is the first semiconductor layer. The solar cell according to claim 2, which is provided above. A second transparent conductive layer provided on the second semiconductor layer is further provided.
The solar cell according to claim 2, further comprising a second sheet resistance changing portion on the second main surface side, which changes the sheet resistance of the solar cell. The solar cell according to claim 2 or 3, wherein the minimum value of the thickness of the first transparent conductive layer in the resistance increasing portion is 10% or less of the maximum thickness of the first transparent conductive layer in the resistance increasing portion. .. The claim that the second transparent conductive layer provided on the second semiconductor layer is further provided, and the second sheet resistance changing portion for changing the sheet resistance of the solar cell is not provided on the second main surface side. 2. The solar cell according to 2. The first semiconductor layer of the second conductive type is a conductive impurity diffusion layer formed on the first main surface side of the crystalline silicon substrate.
The solar cell has a first edge portion including two sides parallel to each other, and the sheet resistance of the solar cell changes along a first direction orthogonal to both of the two sides. A seat resistance changing portion is provided on the first main surface side.
The solar cell according to claim 1, wherein the first sheet resistance changing portion includes a resistance increasing portion in which the seat resistance increases as it advances in the first direction and a resistance decreasing portion in which the sheet resistance decreases in this order. .. A solar cell including a first conductive type crystalline silicon substrate and a second conductive type first semiconductor layer formed on the first main surface side of the crystalline silicon substrate.
The side surface extending in the thickness direction of the crystalline silicon substrate includes a side surface portion in which the arithmetic mean roughness differs in the thickness direction.
A high resistance region having a high sheet resistance on the first main surface side is provided in the vicinity of the side surface portion.
In the region between the side surface portion and the center of the first main surface, the sheet resistance on the first main surface side monotonically decreases as the distance from the side surface portion in one direction starts from the high resistance region. Including solar cells. The side surface portion has a first region in which a trace of solidification after melting of the crystalline silicon substrate exists and a trace of melting of the crystalline silicon substrate existing at a position different from the first region in the thickness direction. The solar cell according to claim 8, which has a second region that does not. The solar cell according to claim 8 or 9, wherein the sheet resistance in the high resistance region is 10 times or more the sheet resistance in the central portion on the first main surface side. The solar cell according to any one of claims 8 to 10, wherein the first region exists on the second main surface side of the side surface portion. A first conductive amorphous silicon layer provided on the second main surface side of the crystalline silicon substrate, and
The first transparent conductive layer laminated on the first semiconductor layer and
The second transparent conductive layer laminated on the amorphous silicon layer and
Further prepare
The first semiconductor layer is a second conductive type amorphous silicon layer.
8. The resistance reducing portion includes a layer thickness increasing portion in which the thickness of at least one of the first transparent conductive layer and the second transparent conductive layer monotonously increases as the distance from the side surface portion in one direction increases. The solar cell according to any one of 11. Any one of claims 8 to 12, wherein the layer thickness of the portion having the minimum thickness in the layer thickness increasing portion is 10% or less of the layer thickness of the portion having the maximum thickness in the layer thickness increasing portion. The solar cell described in the section. The solar cell according to any one of claims 8 to 13, wherein the layer thickness increasing portion is provided on the first transparent conductive layer. The sun according to any one of claims 8 to 14, wherein a collecting electrode is formed so as to overlap the layer thickness increasing portion in at least one of the first transparent conductive layer and the second transparent conductive layer. Battery cell. When viewed from the thickness direction, the collecting electrode includes a peripheral portion that does not overlap with the second transparent conductive layer.
Claim that the peripheral portion is not in electrical contact with all of the crystalline silicon substrate, the first conductive type amorphous silicon layer, and the second conductive type amorphous silicon layer. The solar cell according to any one of 12 to 15. A first conductive type silicon substrate having a first main surface and a second main surface, a second conductive type first amorphous silicon layer located on the first main surface side of the silicon substrate, and the silicon substrate. A heteropolar junction forming step for forming a heteropolar junction comprising a first conductive type second amorphous silicon layer located on the second main surface.
After the non-polar joint forming step, an arrangement step of arranging the non-polar joint in the transparent conductive layer forming chamber, and
After the arrangement step, a mask arrangement step of arranging a linear mask on the outside of at least one of the first amorphous silicon layer and the second amorphous silicon layer in the chamber,
After the mask placement step, a transparent conductive layer film forming step in which a transparent conductive layer is laminated on at least one of the first amorphous silicon layer and the second amorphous silicon layer via the mask.
A method for manufacturing a solar cell, comprising: a mask removing step of removing the mask after the transparent conductive layer forming step. After the mask removing step, in the second region located within 0.5 mm in the width direction from the center of the width direction of the first region where the mask was placed in the mask placement step, the thickness direction of the silicon substrate. The method for manufacturing a solar cell according to claim 17, further comprising a groove forming step of forming a groove by irradiating a third region overlapping the second region with a laser beam. A solar cell module including a plurality of solar cells according to any one of claims 8 to 16.

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