JPWO2017026016A1 - Solar cell and method for manufacturing solar cell - Google Patents

Abstract

The back-side impurity diffusion layer (7) includes a back-side high-concentration impurity diffusion layer (7a) containing a first conductivity type impurity element at a first concentration and having a linear shape, and a back-side high-concentration impurity diffusion layer (7a). ) And a back-side low-concentration impurity diffusion layer (7b) containing an impurity element of the same conductivity type at a second concentration lower than the first concentration. The back surface side grid electrode (6a) protrudes from the side surface of the back surface side grid electrode (6a) in a direction intersecting with the extending direction of the back surface side grid electrode (6a) and extends in the extending direction of the back surface side grid electrode (6a). It has a plurality of connecting protrusions (6t) that are divided along the line. The plurality of connecting protrusions (6t) are protruding lengths from the side surface of the back surface side grid electrode (6a) as they are separated from a specific reference position on one surface side of the semiconductor substrate in the extending direction of the back surface side grid electrode (6a). Becomes longer.

Description

  The present invention relates to a solar battery cell having a grid electrode and a method for manufacturing the solar battery cell.

  Conventionally, as a structure of a solar cell having high photoelectric conversion efficiency, there is a structure in which the front and back surfaces of the solar cell are passivated to suppress carrier recombination on the front and back surfaces. In this case, it is important that the back surface field layer (BSF) is a selective diffusion layer. However, when the back surface field layer is a selective diffusion layer, the back side electrode and the back side high concentration must be formed unless an electrode is formed on the back side high concentration diffusion layer in which impurities are diffused to a high concentration in the back surface field layer. Insufficient electrical connection with the diffusion layer causes a decrease in the characteristics of the solar battery cell.

  As a solar cell for improving the electrical connection between the back surface side electrode and the back surface side high concentration diffusion layer, Patent Document 1 discloses a solar cell in which connection protrusions are formed on the finger electrodes. Patent Document 1 discloses a solar cell in which a back-side electrode includes a bus bar electrode, a finger electrode, and a connection protrusion that protrudes from the finger electrode in a direction intersecting the finger electrode. Such a connection protrusion of the solar cell of Patent Document 1 can be used even when the backside high-concentration diffusion layer and the finger electrode are displaced due to a process error or the like during alignment between the backside high-concentration diffusion layer and the finger electrode. It plays a role of electrically connecting the side high concentration diffusion layer and the finger electrode.

Japanese Patent Application Laid-Open No. 2014-216652

  However, in the solar cell disclosed in Patent Document 1, the finger electrode is partially provided with a protruding portion. The finger electrode is usually formed by printing and baking an electrode material paste containing a metal material. And the metal material which occupies most of the cost of a finger electrode is an expensive material in the material which comprises a photovoltaic cell. In particular, silver (Ag) is often used for finger electrodes, but silver is an expensive material among metal materials.

  For this reason, in order to reduce the cost of the solar battery cell, it is desired to reduce the amount of the metal material that occupies most of the cost of the finger electrode. However, there has been a problem that the reduction in the amount of metal material used is a limitation in the realization of the finger electrode having the connection protrusion shown in Patent Document 1.

  The present invention has been made in view of the above, and can reduce a decrease in photoelectric conversion efficiency due to electrical connection between an electrode and a high-concentration diffusion layer while reducing the amount of electrode material used. And it aims at obtaining the manufacturing method of a photovoltaic cell.

  In order to solve the above-described problems and achieve the object, the present invention provides a solar cell in which a first conductivity type semiconductor substrate and an impurity element of a first conductivity type or a second conductivity type on one surface side of the semiconductor substrate are provided. And a paste electrode disposed on one side and electrically connected to the impurity diffusion layer, extending in parallel at a first arrangement interval in a specific direction in the surface direction of the semiconductor substrate. A plurality of grid electrodes having a linear shape. The impurity diffusion layer includes a first conductive type or second conductive type impurity element at a first concentration in a lower region of the grid electrode and has a linear shape, and extends parallel to a specific direction in the plane direction of the semiconductor substrate. A plurality of first impurity diffusion layers, and a second impurity diffusion layer including an impurity element having the same conductivity type as that of the first impurity diffusion layer at a second concentration lower than the first concentration. The grid electrode protrudes from the side surface of the grid electrode in a direction intersecting with the extending direction of the grid electrode, and has a plurality of connecting protruding portions that are divided and arranged along the extending direction of the grid electrode. The plurality of connecting protrusions are characterized in that the protrusion length from the side surface of the grid electrode becomes longer as the distance from the specific reference position on the one surface side of the semiconductor substrate in the extending direction of the grid electrode is increased.

  The solar cell concerning this invention has an effect that the fall of the photoelectric conversion efficiency resulting from the electrical connection of an electrode and a high concentration diffusion layer can be suppressed, reducing the usage-amount of electrode material.

The upper surface schematic diagram which looked at the photovoltaic cell concerning embodiment of this invention from the light-receiving surface side. The lower surface schematic diagram which looked at the photovoltaic cell concerning embodiment of this invention from the back surface side facing a light-receiving surface FIG. 2 is a schematic cross-sectional view of a main part of a solar battery cell according to an embodiment of the present invention, and a main part cross-sectional view of the solar battery cell in the AA direction of FIG. 1. The principal part top view which expands and shows the back surface side grid electrode of the photovoltaic cell concerning embodiment of this invention. The principal part top view which expands and shows the back surface side high concentration impurity diffusion layer of the photovoltaic cell concerning embodiment of this invention The schematic diagram explaining the back surface side grid electrode of the photovoltaic cell concerning embodiment of this invention. The top view for demonstrating the principle of the electrical connection by the protrusion part for a connection in case the overlay error of the back surface side grid electrode with respect to a back surface side high concentration impurity diffusion layer generate | occur | produces in the photovoltaic cell concerning embodiment of this invention. The flowchart which showed the process flow of the manufacturing method of the photovoltaic cell concerning embodiment of this invention Sectional drawing which shows the principal part explaining the manufacturing process of the photovoltaic cell concerning embodiment of this invention Sectional drawing which shows the principal part explaining the manufacturing process of the photovoltaic cell concerning embodiment of this invention Sectional drawing which shows the principal part explaining the manufacturing process of the photovoltaic cell concerning embodiment of this invention Sectional drawing which shows the principal part explaining the manufacturing process of the photovoltaic cell concerning embodiment of this invention Sectional drawing which shows the principal part explaining the manufacturing process of the photovoltaic cell concerning embodiment of this invention Sectional drawing which shows the principal part explaining the manufacturing process of the photovoltaic cell concerning embodiment of this invention Sectional drawing which shows the principal part explaining the manufacturing process of the photovoltaic cell concerning embodiment of this invention Sectional drawing which shows the principal part explaining the manufacturing process of the photovoltaic cell concerning embodiment of this invention Sectional drawing which shows the principal part explaining the manufacturing process of the photovoltaic cell concerning embodiment of this invention The schematic diagram which shows the structure of the printing mask for printing Ag containing paste on the pattern of the back surface side grid electrode concerning embodiment of this invention. The schematic diagram which shows the pattern of the back surface side grid electrode used when the back surface side grid electrode concerning embodiment of this invention tends to produce the position shift of a formation position in the direction rotated left centering on the center position C The schematic diagram which shows the pattern of the back surface side grid electrode used when the back surface side grid electrode concerning embodiment of this invention tends to produce the position shift of a formation position in the direction rotated clockwise centering on the center position C The principal part cross-section schematic diagram of the photovoltaic cell which made the light-receiving surface side impurity diffusion layer concerning embodiment of this invention the selective diffusion layer structure

  Below, the solar cell concerning embodiment of this invention and the manufacturing method of a photovoltaic cell are demonstrated in detail based on drawing. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. In the drawings shown below, the scale of each member may be different from the actual scale for easy understanding. The same applies between the drawings.

Embodiment FIG. 1 is a schematic top view of a solar battery cell 1 according to an embodiment of the present invention as viewed from the light-receiving surface side. FIG. 2 is a schematic bottom view of the solar battery cell 1 according to the embodiment of the present invention as viewed from the back side facing the light receiving surface. FIG. 3 is a schematic cross-sectional view of the main part of the solar battery cell 1 according to the embodiment of the present invention, and is a cross-sectional view of the main part of the solar battery cell 1 in the AA direction of FIG.

  In the solar cell 1 according to the present embodiment, the p-type light-receiving surface side impurity diffusion layer 3 in which boron (B), which is a p-type impurity of the second conductivity type, is diffused is of the first conductivity type. A semiconductor substrate 11 having a pn junction is formed over the entire light-receiving surface of an n-type semiconductor substrate 2. An antireflection film 4 made of an insulating film is formed on the light receiving surface side impurity diffusion layer 3. In this solar battery cell 1, light L enters from the antireflection film 4 side.

  As the semiconductor substrate 2, an n-type single crystal silicon substrate is used. Hereinafter, the semiconductor substrate 2 made of an n-type single crystal silicon substrate may be referred to as an n-type silicon substrate 2. The semiconductor substrate 2 is not limited to an n-type single crystal silicon substrate, and an n-type polycrystalline silicon substrate may be used.

  A texture structure is formed on the light receiving surface side of the n-type silicon substrate 2, that is, on the light receiving surface side of the p-type light receiving surface side impurity diffusion layer 3. Since the fine unevenness of the texture structure is very fine, it is not shown as an uneven shape in FIG. 3 and the following drawings.

  On the light receiving surface side of the semiconductor substrate 2, a plurality of elongated light receiving surface side grid electrodes 5 a are arranged in parallel along a pair of side directions in the semiconductor substrate 11. In addition, a plurality of light receiving surface side bus electrodes 5b electrically connected to the light receiving surface side grid electrode 5a are arranged in parallel along the other pair of side directions in the semiconductor substrate 11 in a state orthogonal to the light receiving surface side grid electrode 5a. ing. The light-receiving surface side grid electrode 5a and the light-receiving surface-side bus electrode 5b are electrically connected to the p-type light-receiving surface-side impurity diffusion layer 3 at the bottom surface. The light receiving surface side grid electrode 5a and the light receiving surface side bus electrode 5b are made of an electrode material containing silver. The light-receiving surface side grid electrode 5a and the light-receiving surface-side bus electrode 5b constitute a light-receiving surface-side electrode 5 that is a first electrode having a comb shape.

  The light receiving surface side grid electrode 5a has a width of, for example, about 40 μm or more and 70 μm or less, and is arranged in parallel with a predetermined interval of 70 or more and 300 or less, and collects electricity generated inside the semiconductor substrate 11. Electricity. The light receiving surface side bus electrode 5b has a width of, for example, about 0.5 mm or more and 1.0 mm or less, and two or more and 5 or less are arranged per solar cell, and the light receiving surface side grid The electricity collected by the electrode 5a is taken out to the outside. The number of light receiving surface side grid electrodes 5a is more preferably 100 or more and 200 or less.

  On the other hand, the n-type backside impurity diffusion layer 7 in which phosphorus (P) is diffused is opposed to the light-receiving surface of the n-type semiconductor substrate 2 on the surface layer on the backside that is the surface facing the light-receiving surface in the semiconductor substrate 2. The BSF layer is formed on the entire back surface. On the backside impurity diffusion layer 7, a backside insulating film 8 made of an insulating film is formed.

  On the back surface side impurity diffusion layer 7, a plurality of elongated back surface side grid electrodes 6 a are arranged in parallel along a pair of side directions in the semiconductor substrate 11. In addition, a plurality of backside bus electrodes 6b electrically connected to the backside grid electrode 6a are arranged in parallel along the other pair of side directions in the semiconductor substrate 11 in a state orthogonal to the backside grid electrode 6a. The back-side grid electrode 6a and the back-side bus electrode 6b are formed on a back-side high-concentration impurity diffusion layer 7a of an n-type back-side impurity diffusion layer 7 to be described later, and each has an n-type back-side impurity diffusion at the bottom. The back surface side high concentration impurity diffusion layer 7a of the layer 7 is electrically connected. The back side grid electrode 6a and the back side bus electrode 6b are made of an electrode material containing silver. The back-side grid electrode 6a and the back-side bus electrode 6b constitute a back-side electrode 6 that is a second electrode having a comb shape.

  The back surface side grid electrode 6a has a width of, for example, about 40 μm or more and 70 μm or less, and 70 or more and 300 or less are arranged in parallel at predetermined intervals, and collects electricity generated inside the semiconductor substrate 11 To do. Further, the back-side bus electrode 6b has a width of, for example, about 0.5 mm or more and 1.0 mm or less, and two or more and 5 or less are arranged per solar cell, and the back-side grid electrode 6a. Take out the electricity collected at the outside. The number of backside grid electrodes 6a is more preferably 100 or more and 200 or less.

  The n-type backside impurity diffusion layer 7 is an n-type impurity diffusion layer in which phosphorus is diffused as an n-type impurity in the surface layer on the backside of the semiconductor substrate 2. In the solar battery cell 1, two types of layers are formed as the n-type backside impurity diffusion layer 7 to form a selective diffusion layer structure. That is, in the surface layer portion on the back surface side of the n-type silicon substrate 2, n-type impurities are diffused at a relatively high concentration in the back surface side impurity diffusion layer 7 in the lower region of the back surface side electrode 6 and its peripheral region. A back side high concentration impurity diffusion layer 7a which is a first impurity diffusion layer is formed. Further, in the surface layer portion on the back side of the n-type silicon substrate 2, n-type impurities are relatively low in the back-side impurity diffusion layer 7 in a region where the back-side high-concentration impurity diffusion layer 7 a is not formed. A back-side low-concentration impurity diffusion layer 7b, which is a second impurity diffusion layer that is uniformly diffused, is formed.

  The back side high concentration impurity diffusion layer 7a is a low resistance diffusion layer having a lower electrical resistance than the back side low concentration impurity diffusion layer 7b. The back side low concentration impurity diffusion layer 7b is a high resistance diffusion layer having a higher electrical resistance than the back side high concentration impurity diffusion layer 7a. The back-side impurity diffusion layer 7 is configured by the back-side high-concentration impurity diffusion layer 7a and the back-side low-concentration impurity diffusion layer 7b.

  Accordingly, when the impurity diffusion concentration of the back side high concentration impurity diffusion layer 7a is the first concentration and the impurity diffusion concentration of the back side low concentration impurity diffusion layer 7b is the second concentration, the second concentration is lower than the first concentration. Become. Further, if the electrical resistance value of the back side high concentration impurity diffusion layer 7a is the first electrical resistance value and the electrical resistance value of the back side low concentration impurity diffusion layer 7b is the second electrical resistance value, the second electrical resistance value is It becomes larger than the first electric resistance value.

  In solar cell 1 according to the present embodiment configured as described above, backside low-concentration impurity diffusion layer 7b suppresses carrier recombination on the backside of n-type silicon substrate 2 as a BSF layer. Therefore, a good open circuit voltage can be obtained. Moreover, since the back surface side high concentration impurity diffusion layer 7a reduces the contact resistance of the back surface side impurity diffusion layer 7 and the back surface side electrode 6, a favorable curve factor can be obtained.

  Next, the back surface side grid electrode 6a according to the present embodiment will be described. FIG. 4 is an enlarged plan view showing a main part of the back surface side grid electrode 6a of the solar battery cell 1 according to the embodiment of the present invention. FIG. 5 is an enlarged plan view showing a main part of the back surface side high-concentration impurity diffusion layer 7a of the solar battery cell 1 according to the embodiment of the present invention. FIG. 6 is a schematic diagram for explaining the back surface side grid electrode 6a of the solar battery cell 1 according to the embodiment of the present invention.

  As shown in FIG. 4, the back surface side grid electrodes 6 a have an elongated shape as a basic shape, and are arranged in parallel with each other at a predetermined first arrangement interval D <b> 1 along a pair of side directions of the semiconductor substrate 11. ing. The back surface side grid electrode 6a has a plurality of connecting projections 6t formed on both side surfaces of the back surface side grid electrode 6a. The connecting protrusion 6t protrudes from both side surfaces of the back surface side grid electrode 6a in a direction intersecting the longitudinal direction of the back surface side grid electrode 6a. In addition, a plurality of connection protrusions 6t are divided and arranged along the longitudinal direction of the back surface side grid electrode 6a at a predetermined second arrangement interval D2.

  In FIG. 4, the connecting protrusion 6 t protrudes in a direction perpendicular to the longitudinal direction of the back surface side grid electrode 6 a in the surface direction of the semiconductor substrate 11. Such a connecting protrusion 6t is formed on the backside high-concentration impurity diffusion when misalignment occurs during alignment between the backside high-concentration impurity diffusion layer 7a and the backside electrode 6 when the backside grid electrode 6a is formed. It has a function of assisting electrical connection between the layer 7a and the backside grid electrode 6a.

  The long and narrow back side high-concentration impurity diffusion layer 7a has the same width and the same shape as the long and slender shape part of the back side grid electrode 6a excluding the connecting protrusion 6t. That is, the width 6aW of the back surface side grid electrode is the same as the width 7W of the back surface high concentration impurity diffusion layer. And the elongate elongated shape part of the back surface side grid electrode 6a is overlapped and formed on the back surface side high concentration impurity diffusion layer 7a. In addition, the width 6aW of the back surface side grid electrode in this specification is the width of the long and narrow shape portion excluding the connection protrusion 6t in the back surface side grid electrode 6a, and includes the protrusion of the connection protrusion 6t. Not in. Therefore, the connecting protrusion 6t protrudes from the side surface of the back surface side high concentration impurity diffusion layer 7a and is formed on the back surface side low concentration impurity diffusion layer 7b.

  In the present embodiment, the width 7W of the backside high-concentration impurity diffusion layer to which the backside grid electrode 6a is electrically connected is set to the minimum necessary, that is, the same width as the width 6aW of the backside grid electrode. Thereby, the ratio of the area | region of the back surface side low concentration impurity diffusion layer 7b in the back surface side impurity diffusion layer 7 can be increased, and a back surface passivation effect can be increased.

  The protruding portion 6t for connection has a larger protruding amount from the side surface of the back surface side grid electrode 6a as it is away from the specific reference position in the longitudinal direction of the back surface side grid electrode 6a, that is, for connection from the side surface of the back surface side grid electrode 6a. The protrusion length 6tL of the protrusion 6t is longer. Therefore, the protruding portion 6t for connection has a smaller protruding amount as it is closer to a specific reference position in the longitudinal direction of the back surface side grid electrode 6a, that is, the protruding length 6t from the side surface of the back surface side grid electrode 6a is shorter.

  Here, in the present embodiment, the specific reference position is a semiconductor substrate that is an alignment position at the time of alignment between the back-side high-concentration impurity diffusion layer 7a and the back-side electrode 6 when the back-side grid electrode 6a is formed. 11 is the center position C in the surface direction. The specific reference position is a position where the alignment accuracy between the back side high-concentration impurity diffusion layer 7a and the back side electrode 6 is the highest. In each of the plurality of back surface side grid electrodes 6a, a virtual line V passing through the center position C and orthogonal to the longitudinal direction of the back surface side grid electrode 6a can be considered as a specific reference position. Here, the alignment position at the time of alignment is the center position C in the surface direction of the semiconductor substrate 11, but the alignment position at the time of alignment is not limited to this, and an arbitrary position in the plane of the semiconductor substrate 11. Is possible. Also in this case, the alignment position at the time of alignment becomes a specific reference position.

  In this case, the projecting length 6tL of the connecting protrusions 6t in the plurality of back surface side grid electrodes 6a becomes longer as the distance from the center position C in the longitudinal direction of the back surface side grid electrode 6a increases. That is, the protrusion 6tL for connection in the plurality of back surface side grid electrodes 6a has a protrusion length 6tL that increases as the distance from the virtual line V orthogonal to each back surface side grid electrode 6a increases. Each of the connecting protrusions 6t in the back surface side grid electrode 6a has a protrusion length 6tL that is directly proportional to the center position C or the distance from the position corresponding to the center position C in the longitudinal direction of the back surface side grid electrode 6a. It is getting longer. Therefore, the protrusion 6t for connection in each back surface side grid electrode 6a has a protrusion length 6tL that is directly proportional to the distance from the position corresponding to the center position C in the longitudinal direction of the back surface side grid electrode 6a. .

  In other words, the protrusion 6t for connection in the plurality of back surface side grid electrodes 6a has a protrusion length 6tL that decreases in the longitudinal direction of the back surface side grid electrode 6a from the end of the solar cell 1 to the center position C. It has become. That is, the connecting protrusions 6t in the plurality of backside grid electrodes 6a are virtual lines V orthogonal to the respective backside grid electrodes 6a from the end of the solar cell 1 in the longitudinal direction of the backside grid electrode 6a. The protrusion length 6 tL is shortened as the distance from the point approaches.

  The center position C, which is a specific reference position in the surface direction of the semiconductor substrate 11, is used when aligning the formation position of the back surface side electrode 6 with respect to the back surface side high concentration impurity diffusion layer 7a when forming the back surface side grid electrode 6a. In some cases, the position where the back surface side grid electrode 6a is formed is displaced in the direction of rotation around the center. In this case, at the position close to the center position C, the overlay accuracy of the back surface side grid electrode 6a with respect to the back surface side high concentration impurity diffusion layer 7a becomes high. Hereinafter, the overlay accuracy of the back surface side grid electrode 6a on the back surface side high concentration impurity diffusion layer 7a may be referred to as overlay accuracy. That is, each back surface side grid electrode 6a has high overlay accuracy at a position near the virtual line V. For this reason, the connection protrusion 6t is almost unnecessary at a position near the virtual line V, and the protrusion length 6tL may be short.

  On the other hand, the overlay accuracy of each back-side grid electrode 6a is low at a position far from the virtual line V. That is, the shift amount of the back surface side grid electrode 6a located far from the virtual line V with respect to the back surface side high concentration impurity diffusion layer 7a is different from the back surface side high concentration impurity diffusion layer 7a of the back surface side grid electrode 6a located near the virtual line V. It becomes larger than the amount of deviation. Then, the shift amount of the end portion of the back surface side grid electrode 6a farthest from the virtual line V becomes the largest.

  In this case, as described above, the protrusion length 6tL of the connection protrusion 6t in the back surface side high concentration impurity diffusion layer 7a is increased as the distance from the virtual line V increases. The impurity diffusion layer 7a and the back surface side grid electrode 6a can be electrically connected by the connecting protrusion 6t. Thereby, the contact area of the back surface side grid electrode 6a and the back surface side high concentration impurity diffusion layer 7a reduced by having shifted the back surface side grid electrode 6a from the back surface side high concentration impurity diffusion layer 7a can be increased. The back side where the backside grid electrode 6a has a large shift amount with respect to the backside high concentration impurity diffusion layer 7a, and the elongated elongated portion of the backside grid electrode 6a is not in contact with the backside high concentration impurity diffusion layer 7a. Even in the vicinity of the end of the grid electrode 6a, the back-side high-concentration impurity diffusion layer 7a and the back-side grid electrode 6a can be electrically connected by the connecting protrusion 6t. FIG. 7 shows electrical connection by the connecting protrusion 6t when an overlay error of the back surface side grid electrode 6a with respect to the back surface side high concentration impurity diffusion layer 7a occurs in the solar cell 1 according to the embodiment of the present invention. It is a top view for demonstrating a principle.

  In FIG. 7, the region on the right side of the virtual line V in the back surface side grid electrode 6a is shown, but the same applies to the region on the left side of the virtual line V. However, in the region on the left side of the virtual line V in the case of FIG. 7, the back surface side grid electrode 6a is shifted to the lower side of the back surface side high concentration impurity diffusion layer 7a. And the back surface side high concentration impurity diffusion layer 7a and the back surface side grid electrode 6a can be electrically connected by the connection protrusion 6t protruding from the upper side surface of the back surface side grid electrode 6a.

  Therefore, in the solar battery cell 1 according to the present embodiment, even when the formation position of the back surface side grid electrode 6a is shifted from the back surface side high concentration impurity diffusion layer 7a in the direction of rotation about the center position C. Since the back side high-concentration impurity diffusion layer 7a and the back side grid electrode 6a can be electrically connected by the connecting protrusion 6t, the back side grid electrode 6a can be thinned. And the amount of the metal material used for the back surface side grid electrode 6a can be reduced by aiming at thinning of the back surface side grid electrode 6a, and the fall of the cost of the back surface side grid electrode 6a and the photovoltaic cell 1 is realizable.

  Thus, by appropriately setting the protrusion length 6tL of the connecting protrusion 6t according to the distance from the center position C or the virtual line V in the longitudinal direction of the back surface side grid electrode 6a, the back surface side grid electrode 6a The amount of the metal material used can be reduced, and the cost of the back side grid electrode 6a and the solar battery cell 1 can be reduced. The protrusion length 6tL of the connecting protrusion 6t according to the distance from the imaginary line V grasps the tendency of the position shift of the formation position of the back surface side grid electrode 6a in the direction of rotation about the center position C. Therefore, it can be set appropriately.

  Further, in the solar cell 1 according to the present embodiment, even when the formation position of the back surface side grid electrode 6a is shifted from the back surface side high concentration impurity diffusion layer 7a in the direction of rotation about the center position C. The backside high-concentration impurity diffusion layer 7a and the backside grid electrode 6a can be electrically connected by the connecting protrusion 6t. For this reason, the width 7W of the back-side high-concentration impurity diffusion layer can be made the minimum necessary, that is, the same width as the width 6aW of the back-side grid electrode. Thereby, the ratio of the area | region of the back surface side low concentration impurity diffusion layer 7b in the back surface side impurity diffusion layer 7 can be increased, and a back surface passivation effect can be increased.

  On the other hand, when the protruding lengths 6tL of all the connecting protruding portions 6t are made equal in the longitudinal direction of the back surface side grid electrode 6a, the above effect is very small. In FIG. 7, when the protrusion length 6tL of all the connection protrusions 6t is set to be small in accordance with the connection protrusion 6t on the virtual line V side, the protrusion length 6tL is short. On the end side of the back surface side grid electrode 6a where the deviation amount of the back surface side grid electrode 6a with respect to the concentration impurity diffusion layer 7a is large, the connection between the back surface side high concentration impurity diffusion layer 7a and the back surface side grid electrode 6a by the connecting protrusion 6t. The area becomes smaller or disappears.

  That is, in FIG. 7, the protruding lengths 6tL of all the connecting protrusions 6t are matched with the protruding length 6tL of the connecting protruding part 6t near the virtual line V, for example, and the position where the overlapping accuracy is high. If the distance is shorter than the imaginary line V, the connection area between the back-side high-concentration impurity diffusion layer 7a and the back-side grid electrode 6a by the connecting protrusion 6t is small on the end side where the overlay accuracy is low. Or disappear. In this case, the electrical connection between the back-side high-concentration impurity diffusion layer 7a and the back-side grid electrode 6a becomes insufficient, and the contact resistance increases.

  In FIG. 7, the protrusion length 6 tL of all the connection protrusions 6 t is large in accordance with the protrusion length 6 tL of the connection protrusion 6 t at the position on the end side that is far from the imaginary line V and has low overlay accuracy. In this case, the back-side high-concentration impurity diffusion layer 7a and the back-side grid electrode 6a can be electrically connected by the connecting protrusion 6t even in the vicinity of the end of the back-side grid electrode 6a. However, in this case, since the area of the connecting protrusion 6t increases, the recombination of carriers on the back surface of the semiconductor substrate 11 increases, and the amount of the metal material used for the connecting protrusion 6t increases. The cost of the back surface side grid electrode 6a and the photovoltaic cell 1 increases.

  The width 6tW of the connection protrusions is the same in all the connection protrusions 6t, and is equal to or less than the width 6aW of the back surface side grid electrode. As an example, the ratio of the width 6tW of the connecting protrusion to the width 6aW of the back surface side grid electrode: 6tW / 6aW is set to 0.3 or more and 1 or less. When the ratio: 6tW / 6aW is less than 0.3, since the width 6tW of the connecting protrusion is small, the electrical connection between the back-side high-concentration impurity diffusion layer 7a and the back-side grid electrode 6a by the connecting protrusion 6t. There is a risk that the target connection area will be insufficient. Further, when the ratio: 6tW / 6aW is larger than 1, the connecting protrusion 6t has a large width 6tW, so that the area of the connecting protrusion 6t increases, and carriers are recombined on the back surface of the semiconductor substrate 11. May increase and the characteristics of the solar battery cell 1 may deteriorate. The ratio: 6tW / 6aW depends on various conditions such as the size of the solar cell 1, the type of the solar cell 1, the constituent material of the back side grid electrode 6a, the impurity concentration of the back side high concentration impurity diffusion layer 7a, and the like. It can be set appropriately as appropriate.

  The protruding length 6tL of the connecting protrusion 6t from the side surface of the back surface side grid electrode 6a is set to be smaller than the first arrangement interval D1 that is the arrangement interval between the adjacent back surface side grid electrodes 6a. Further, the projecting lengths 6tL of the two connecting projecting parts 6t facing each other across the long and narrow shaped part are the same. The ratio of the projection length 6 tL to the first arrangement interval D1: 6 tL / D1 is 0.6 or less. When the ratio: 6tL / D1 is larger than 0.6, the connecting protrusions 6t of the adjacent back surface side grid electrodes 6a may be connected to each other. In addition, since the length of the connecting protrusion 6t is long, the area of the connecting protrusion 6t is increased, and the recombination of carriers on the back surface of the semiconductor substrate 11 is increased, which may deteriorate the characteristics of the solar battery cell 1. There is. There exists a possibility that the characteristic of the photovoltaic cell 1 may fall. In addition, the 1st arrangement | positioning space | interval D1 shall be about 0.5 mm or more and 2.0 mm or less.

  The second arrangement interval D2 is about 0.5 mm or more and 2.0 mm or less. When the second arrangement interval D2 is less than 0.5 mm, the connecting protrusions 6t are densely positioned in the longitudinal direction of the back surface side grid electrode 6a, and the area of the back surface side grid electrode 6a is increased. The characteristics of the solar battery cell 1 may be deteriorated. When the second arrangement interval D2 is larger than 2.0 mm, the electrical connection area between the back-side high-concentration impurity diffusion layer 7a and the back-side grid electrode 6a by the connecting protrusion 6t may be insufficient. .

  As an example, the ratio: 6 tL / D1 is 0.05 or more and 0.3 or less. When the ratio: 6tL / D1 is less than 0.05, the protruding length 6tL is small, so that the connecting protruding portion against the overlay error of the back side grid electrode 6a with respect to the back side high concentration impurity diffusion layer 7a. There is a possibility that the back side high concentration impurity diffusion layer 7a and the back side grid electrode 6a cannot be electrically connected by 6t. When the ratio: 6tL / D1 is larger than 0.3, the protruding length 6tL becomes unnecessarily long, and the area of the connecting protruding portion 6t may become unnecessarily large. The ratio: 6 tL / D1 is appropriate according to the distance from the imaginary line V by grasping the tendency of the position shift of the formation position of the back surface side grid electrode 6a in the direction of rotation about the center position C. Can be set.

  A plurality of connection protrusions 6t are arranged along the longitudinal direction of the back surface side grid electrode 6a at a predetermined second arrangement interval D2. The plurality of connecting protrusions 6t are arranged at the second arrangement interval D2 from the imaginary line V side toward the both end parts across the imaginary line V in the back surface side grid electrode 6a. By providing a plurality of connection protrusions 6t in the longitudinal direction of the back surface side grid electrode 6a, the back surface side is shifted when the position of the back surface side grid electrode 6a is shifted in the direction of rotation about the center position C. It is possible to assist electrical connection between the back-side high-concentration impurity diffusion layer 7a and the back-side grid electrode 6a over the entire region in the longitudinal direction of the grid electrode 6a.

  The second arrangement interval D2 is set larger than the width 6tW of the back surface side grid electrode. When the second arrangement interval D2 is smaller than the width 6tW of the back surface side grid electrode, the connecting protrusions 6t are densely positioned in the longitudinal direction of the back surface side grid electrode 6a. There is a possibility that the area is increased and the characteristics of the solar battery cell 1 are deteriorated.

  In increasing the output of the solar cell 1 having the back-side impurity diffusion layer 7 as the BSF layer on the back side, the concentration of the back-side low-concentration impurity diffusion layer 7b is reduced and the back-side low concentration of the back-side impurity diffusion layer 7 is reduced. It is important to increase the ratio of the impurity diffusion layer 7b. In other words, the reduction in the ratio of the region of the back-side high-concentration impurity diffusion layer 7 a in the back-side impurity diffusion layer 7 greatly contributes to the output improvement of the solar battery cell 1. This is due to carrier recombination in the surface layer on the back surface of the semiconductor substrate 11. The back surface side high concentration impurity diffusion layer 7a corresponding to the back surface side grid electrode 6a, that is, the back surface side high concentration impurity diffusion layer to which the back surface side grid electrode 6a is electrically connected has a minimum width 7W, that is, the back surface side grid electrode. The structure of the solar cell 1 that secures the electrical connection between the back-side high-concentration impurity diffusion layer 7a and the back-side grid electrode 6a by the connecting protrusion 6t is substantially equivalent to the width 6aW of large. Further, in the longitudinal direction of the back surface side grid electrode 6a, the protrusion length 6tL is changed in direct proportion to the distance from the virtual line V orthogonal to the back surface side high concentration impurity diffusion layer 7a as described above. It is possible to reduce the thickness of the electrode 6a, and further contribute to reducing the width 7W of the back-side high-concentration impurity diffusion layer.

  Note that the width 7W of the back-side high-concentration impurity diffusion layer does not have to be exactly the same width as the width 6aW of the back-side grid electrode, and may be slightly larger than the width 6aW of the back-side grid electrode. However, the back-side high-concentration impurity diffusion layer 7a that protrudes from the back-side grid electrode 6a causes the characteristics of the solar battery cell 1 to deteriorate, so it is desirable to make it narrow as much as possible. From the viewpoint of improving the output of the solar cell 1 by reducing the ratio of the region of the back-side high-concentration impurity diffusion layer 7a in the back-side impurity diffusion layer 7 described above, the width 7W of the back-side high-concentration impurity diffusion layer is The width can be increased up to about twice the width 6aW of the electrode. In this case, substantially the same output improvement effect can be obtained as compared with the case where the width 7W of the backside high-concentration impurity diffusion layer is the same as the width 6aW of the backside grid electrode. In this specification, including this range, the width 7W of the backside high-concentration impurity diffusion layer is assumed to be the same as the width 6aW of the backside grid electrode.

  When the width 7W of the back-side high-concentration impurity diffusion layer is wider than the width 6aW of the back-side grid electrode in the above range, the position where the back-side grid electrode 6a is formed in the direction of rotation about the center position C. Even when the positional deviation occurs, the back surface side high concentration impurity diffusion layer 7a and the back surface side grid electrode 6a are compared with the case where the width 6aW of the back surface side grid electrode is the same as the width 7W of the back surface side high concentration impurity diffusion layer. The area of electrical connection with is increased. Therefore, the protrusion length 6tL may be shortened as a whole.

  Next, a method for manufacturing the solar battery cell 1 according to the present embodiment will be described with reference to FIGS. FIG. 8 is a flowchart showing a process flow of the method for manufacturing the solar battery cell 1 according to the embodiment of the present invention. 9 to 17 are cross-sectional views of relevant parts for explaining the manufacturing process of the solar battery cell 1 according to the embodiment of the present invention.

  FIG. 9 is an explanatory diagram of step S10 in FIG. In step S10, an n-type silicon substrate 2 is prepared as the semiconductor substrate 2, and cleaning and formation of a texture structure are performed. The n-type silicon substrate 2 is manufactured by cutting and slicing the single crystal silicon ingot obtained in the single crystal pulling step into a desired size and thickness using a cutting device such as a band saw or a multi-wire saw. The damage layer at the time of slicing remains. Therefore, the damage layer existing near the surface of the n-type silicon substrate 2 is generated by etching the surface of the n-type silicon substrate 2 to remove the damaged layer, and is generated when the silicon substrate is cut out by surface contamination during slicing. Cleaning to remove is performed. Cleaning is performed, for example, by immersing the n-type silicon substrate 2 in an alkaline solution in which sodium hydroxide of about 1 wt% or more and 10 wt% or less is dissolved.

  Then, after the damage layer is removed, a textured structure is formed by forming minute irregularities on the surface of the first main surface serving as the light receiving surface in the n-type silicon substrate 2. Since the minute unevenness is very fine, it is not expressed as an uneven shape in FIGS. For the formation of the texture structure, for example, a chemical solution in which an additive such as isopropyl alcohol or caprylic acid is mixed in an alkaline solution of about 0.1 wt% or more and 10 wt% or less is used. By immersing the n-type silicon substrate 2 in such a chemical solution, the surface of the n-type silicon substrate 2 is etched, and a texture structure is obtained on the entire surface of the n-type silicon substrate 2. The texture structure may be formed not only on the light receiving surface of the n-type silicon substrate 2 but also on the back surface of the n-type silicon substrate 2. Note that the surface contamination and damage layer removal during slicing and the formation of the texture structure may be performed simultaneously.

  Next, the surface of the n-type silicon substrate 2 on which the texture structure is formed is cleaned. For cleaning the surface of the n-type silicon substrate 2, for example, a cleaning method called RCA cleaning is used. In the RCA cleaning, a mixed solution of sulfuric acid and hydrogen peroxide, a hydrofluoric acid aqueous solution, a mixed solution of ammonia and hydrogen peroxide, and a mixed solution of hydrochloric acid and hydrogen peroxide are prepared as cleaning solutions. The organic substance, the metal and the oxide film are removed by combining the cleaning with the cleaning liquid.

  Moreover, you may combine the washing | cleaning by one or several washing | cleaning liquids of said washing | cleaning liquid, without using all the washing | cleaning liquids of said washing | cleaning liquid kind. In addition to the cleaning liquid, a mixed solution of hydrofluoric acid and hydrogen peroxide water and water containing ozone may be included as the cleaning liquid.

  In addition, each cleaning solution itself does not cause contamination of other cleaning solutions or unintentional reaction between cleaning solutions or silicon, and to ensure safety after removal from the cleaning device. The n-type silicon substrate 2 is washed with pure water or the like at an arbitrary timing such as during the process or before the n-type silicon substrate 2 is dried.

FIG. 10 is an explanatory diagram of step S20 of FIG. Step S20 is a process of forming a pn junction by forming a p-type impurity diffusion layer 3a on the surface of the n-type silicon substrate 2. The p-type impurity diffusion layer 3a is formed by placing the n-type silicon substrate 2 having a textured structure in a thermal diffusion furnace and in the presence of boron tribromide (BBr ₃ ) vapor or boron trichloride (BCl ₃ ). Realized by heat treatment in the presence of steam.

  On the front and back surfaces of the n-type silicon substrate 2 after the formation of the p-type impurity diffusion layer 3a, a p-type impurity diffusion layer 3a in which boron is diffused at a uniform concentration in the surface direction of the n-type silicon substrate 2, and an oxide film And a boron-containing glass layer (not shown) which is an impurity-containing glass layer containing boron.

  FIG. 11 is an explanatory diagram of step S30 of FIG. Step S30 is a step of forming the oxide film 21 on the surface of the n-type silicon substrate 2 by thermal oxidation. The purpose of the step S30 is to incorporate a boron-containing glass layer, which is a boron-rich layer formed at the interface between silicon and the oxide film on the surface of the n-type silicon substrate 2, into the oxide film, There is an object to form a diffusion protective film when forming the BSF layer on the back surface of the silicon substrate 2. As a result of the thermal oxidation in step S30, an oxide film 21 is formed on the surface of the n-type silicon substrate 2 by incorporating the boron-containing glass layer on the surface of the n-type silicon substrate 2.

  FIG. 12 is an explanatory diagram of step S40 in FIG. Step S40 is a step of removing the oxide film 21 and the p-type impurity diffusion layer 3a, which is an impurity-containing layer, formed on the back surface opposite to the light receiving surface of the n-type silicon substrate 2. The removal of the oxide film 21 and the p-type impurity diffusion layer 3a can be performed by single-sided etching in which only the back surface of the n-type silicon substrate 2 is brought into contact with the hydrofluoric acid aqueous solution using, for example, a single-sided etching apparatus. As a result, the p-type impurity diffusion layer 3 a formed on the light-receiving surface side of the n-type silicon substrate 2 becomes the p-type impurity diffusion layer 3. A semiconductor substrate 11 in which a pn junction is formed by an n-type silicon substrate 2 made of n-type single crystal silicon and a p-type impurity diffusion layer 3 formed on the light-receiving surface side of the n-type silicon substrate 2 is formed. can get.

Thereafter, n-type impurities are diffused into the back surface of the semiconductor substrate 11, that is, the back surface of the n-type silicon substrate 2, thereby forming a selective diffusion layer. Here, as an example, a case of using a phosphorus paste step using a doping paste for forming the backside high-concentration impurity diffusion layer 7a and phosphorus oxychloride (POCl ₃ ) for forming the backside low-concentration impurity diffusion layer 7b is used. Will be described.

  FIG. 13 is an explanatory diagram of step S50 of FIG. Step S50 is a process of selectively printing the phosphorus-containing doping paste 22 on the back surface of the semiconductor substrate 11, that is, on the back surface of the n-type silicon substrate 2, as a doping paste that is an n-type impurity diffusion source. Here, a phosphorus-containing doping paste 22 that is a resin paste containing a phosphorus oxide is selectively printed on the back surface of the n-type silicon substrate 2 as a doping paste using a screen printing method. The printing pattern of the phosphorus-containing doping paste 22 is a region that forms the back surface side electrode 6 formation region and its peripheral region on the back surface of the n-type silicon substrate 2. That is, the phosphorus-containing doping paste 22 is printed in the formation region of the back surface side grid electrode 6a, the formation region of the back surface side bus electrode 6b, and the peripheral region thereof. The printing pattern of the phosphorus-containing doping paste 22 includes, for example, a pattern in which linear patterns having a line width of 150 μm are arranged in parallel at intervals of 1.5 mm and a pattern in which two linear patterns having a line width of 2.0 mm are arranged in parallel. This is a comb-shaped pattern. After printing, the phosphorus-containing doping paste 22 is dried. In addition, in the principal part sectional drawing of FIG. 13, only the printing pattern of the phosphorus containing doping paste 22 for forming the back side high concentration impurity diffusion layer 7a is shown.

FIG. 14 is an explanatory diagram of step S60 of FIG. Step S60 is a process of forming a BSF layer having a selective diffusion layer structure by heat-treating the semiconductor substrate 11 on which the phosphorus-containing doping paste 22 is printed. In step S60, the semiconductor substrate 11 on which the phosphorus-containing doping paste 22 is printed is placed in a thermal diffusion furnace, and heat treatment is performed in the presence of phosphorus oxychloride (POCl ₃ ) vapor.

  Specifically, a boat on which the semiconductor substrate 11 is placed in a horizontal furnace is charged, and the semiconductor substrate 11 is heat-treated at about 1000 ° C. or more and about 1100 ° C. or less for 30 minutes. By this heat treatment, phosphorus as a dopant component in the phosphorus-containing doping paste 22 is thermally diffused into the n-type silicon substrate 2 immediately below the phosphorus-containing doping paste 22. As a result, the back-side high-concentration impurity diffusion layer 7 a is formed in the surface layer on the back surface of the n-type silicon substrate 2 immediately below the phosphorus-containing doping paste 22. The back-side high-concentration impurity diffusion layer 7 a is formed in the same comb-shaped pattern as the printing pattern of the phosphorus-containing doping paste 22.

On the other hand, in the surface layer on the back surface side of the n-type silicon substrate 2, the dopant component of the phosphorus-containing doping paste 22 does not diffuse in the region other than the region immediately below the phosphorus-containing doping paste 22. However, phosphorus in phosphorus oxychloride (POCl ₃ ) vapor is thermally diffused in the surface layer of the region other than the region immediately below the phosphorus-containing doping paste 22 in the surface layer on the back surface side of the n-type silicon substrate 2. Then, a back-side low-concentration impurity diffusion layer 7b in which phosphorus is diffused at a uniform concentration in the surface direction of the n-type silicon substrate 2 is formed. Thereby, the back side impurity diffusion layer 7 having the back side high concentration impurity diffusion layer 7a and the back side low concentration impurity diffusion layer 7b, which is a BSF layer having a selective diffusion layer structure, is formed.

  Here, the semiconductor substrate 11 is overlapped with the light receiving surface side of the two semiconductor substrates 11 facing each other so that the light receiving surface side of the semiconductor substrate 11 is not directly exposed to the atmosphere in the thermal diffusion furnace. Is charged. Thereby, the film formation of phosphorous glass on the light receiving surface side of the semiconductor substrate 11 is greatly restricted. Further, an oxide film 21 is formed on the surface of the semiconductor substrate 11 on the light receiving surface side. Since the oxide film 21 functions as a diffusion barrier, it is possible to prevent phosphorus from entering the n-type silicon substrate 2 from the light receiving surface side of the semiconductor substrate 11 from the furnace atmosphere. That is, phosphorus is diffused into the n-type silicon substrate 2 selectively on the back surface, and an n-type impurity diffusion layer is formed on the back surface.

  Next, in step S70 of FIG. 8, the oxide film 21 and the phosphorus-containing doping paste 22 are removed. The removal of the oxide film 21 and the phosphorus-containing doping paste 22 can be performed by immersing the semiconductor substrate 11 in a hydrofluoric acid aqueous solution.

  Next, in step S80 of FIG. 8, the p-type impurity diffusion layer 3 formed on the light receiving surface side of the n-type silicon substrate 2 and the back-side impurity diffusion layer 7 formed on the back surface side of the n-type silicon substrate 2. A pn separation step for electrically separating the two is performed. Specifically, for example, about 50 to 300 semiconductor substrates 11 that have undergone the processes up to step S70 are stacked, and end face etching is performed in which the side surface is etched by plasma discharge. Alternatively, laser separation may be performed in which the n-type silicon substrate 2 is exposed by melting the vicinity of the side edge of the light receiving surface side or the back surface side of the semiconductor substrate 11 or the side surface of the semiconductor substrate 11 by laser irradiation.

  In the above description, a preferred method for performing pn separation has been described. However, the separation state between the p-type impurity diffusion layer 3 and the back-side impurity diffusion layer 7, that is, the magnitude of leakage current, the final power generation product, Depending on the arrangement of the solar cells in the solar cell module, the pn separation step in step S80 can be omitted.

  Next, the silicon oxide film formed on the light receiving surface side surface of the semiconductor substrate 11, that is, the surface of the p-type impurity diffusion layer 3 is, for example, using an aqueous hydrofluoric acid solution of 5% to 25%. Removed. Then, the hydrofluoric acid aqueous solution adhering to the surface of the semiconductor substrate 11 is removed by washing with water. At this time, an oxide film formed by washing with water, generally called a natural oxide film, may be used as a passivation layer described later or a part thereof. For the same purpose, an oxide film obtained by cleaning the semiconductor substrate 11 with water containing ozone may be used as a passivation layer described later or a part thereof.

  FIG. 15 is an explanatory diagram of step S90 of FIG. Step S90 is a step of forming the back surface side insulating film 8 and the antireflection film 4. First, a silicon nitride film is formed on the back surface of the semiconductor substrate 11, that is, on the back surface side impurity diffusion layer 7 by using, for example, plasma CVD, and a back surface side insulating film 8 made of an insulating film is formed on the back surface of the semiconductor substrate 11. Is done. Note that a passivation layer may be formed between the silicon nitride film of the back-side insulating film 8 and the back-side impurity diffusion layer 7. In this case, the passivation layer is preferably a silicon oxide film, and in addition to general thermal oxidation, an oxide film obtained by washing with water or washing with ozone-containing water as described above may be used.

  Subsequently, an antireflection film 4 made of a silicon nitride film is formed on the light receiving surface side of the semiconductor substrate 11, that is, on the p-type impurity diffusion layer 3 by using, for example, plasma CVD. Note that a passivation layer may be formed between the silicon nitride film of the antireflection film 4 and the p-type impurity diffusion layer 3. In this case, the passivation layer is preferably a silicon oxide film or an aluminum oxide film, or a laminated film of a silicon oxide film and an aluminum oxide film. When a silicon oxide film is used for the passivation layer, an oxide film obtained by washing with water or washing with ozone-containing water as described above may be used in addition to a general thermal oxide film. When an aluminum oxide film is used, the aluminum oxide film is formed by, for example, plasma CVD or ALD (Atomic Layer Deposition). In this case, a fixed charge included in the film formation is more preferable because it has an effect of enhancing the passivation ability.

  Further, the order of formation of the backside insulating film 8, the antireflection film 4 and the passivation layer formed on the front and back surfaces of the semiconductor substrate 11 is not necessarily limited to the above order. You may select and form suitably.

  FIG. 16 is an explanatory diagram of step S100 in FIG. Step S100 is a step of printing the electrodes to form the light-receiving surface side electrode 5 and the back surface side electrode 6 in a dry state. As the electrode material, for example, copper, silver, aluminum, and a mixture thereof are used. For example. An electrode material paste prepared by mixing a metal powder of copper, silver, aluminum, and a mixture thereof, a glass or ceramic component powder, and an organic solvent into a paste shape, for example, by screen printing, has a desired shape and Printed on the pattern.

  First, an Ag-containing paste 5p, which is an electrode material paste containing, for example, Ag and glass frit, is formed on the light receiving surface side grid electrode 5a and the light receiving surface side bus electrode 5b on the antireflection film 4 on the light receiving surface side of the semiconductor substrate 11. The shape is applied by screen printing. Thereafter, the Ag-containing paste 5p is dried, whereby the light-receiving surface side electrode 5 in a dry state having a comb shape is formed.

  Next, an Ag-containing paste 6p which is an electrode material paste containing Ag and glass frit is formed on the back-side grid electrode 6a and the back-side bus electrode 6b on the back-side high concentration impurity diffusion layer 7a on the back side of the semiconductor substrate 11. The shape is applied by screen printing. Thereafter, the Ag-containing paste 6p is dried to form the back-side electrode 6 in a dry state having a comb shape. Here, the shape of the back surface side grid electrode 6a is applied to the shape having the connecting protrusions 6t as shown in FIG. Thereby, it is not necessary to separately form only the connection protrusion 6t, and the back-side grid electrode 6a having the connection protrusion 6t can be formed without adding a process. Here, the line width of the elongated elongated portion of the back surface side grid electrode 6a is a linear pattern having the same 150 μm width as that of the back surface side high concentration impurity diffusion layer 7a, and the same 1.5 mm as that of the back surface side high concentration impurity diffusion layer 7a. The back surface side grid electrode 6a having the connecting protrusions 6t is formed in a pattern arranged in parallel at intervals.

  The Ag-containing paste 6p for forming the back surface side electrode 6 is printed on the back surface side high concentration impurity diffusion layer 7a by using an alignment mechanism. For example, a state in which infrared rays are irradiated on the back surface side of the semiconductor substrate 11 is photographed with an infrared camera. Thereby, it becomes possible to distinguish the back side high concentration impurity diffusion layer 7a and the back side low concentration impurity diffusion layer 7b. In this way, by recognizing the position of the region of the back-side high-concentration impurity diffusion layer 7a and determining the printing position of the Ag-containing paste 6p, the Ag-containing paste 6p is printed on the back-side high-concentration impurity diffusion layer 7a. It becomes possible.

  Here, when the back surface side grid electrode 6a is shifted from the back surface side high concentration impurity diffusion layer 7a, the back surface side grid electrode 6a is different from the back surface side grid electrode 6a in the region where the back surface side grid electrode 6a is shifted from the region of the back surface side high concentration impurity diffusion layer 7a. Contact with the back side high concentration impurity diffusion layer 7a cannot be made. For this reason, the electrical resistance between the back surface side grid electrode 6a and the back surface side high concentration impurity diffusion layer 7a increases, resistance loss arises, and the characteristic deterioration of the photovoltaic cell 1 is caused. However, an increase in the area of the back-side high-concentration impurity diffusion layer 7a and an increase in the electrode width of the back-side grid electrode 6a are not effective because they cause a decrease in photoelectric conversion efficiency and an increase in cost. Further, the alignment accuracy between the back surface side grid electrode 6a and the back surface side high concentration impurity diffusion layer 7a has a limit.

  Therefore, in the present embodiment, as shown in FIG. 4, the print mask 31 having the opening patterns 32 corresponding to the pattern of the back surface side grid electrode 6 a having the connection protrusions 6 t in parallel at the same interval is provided on the semiconductor substrate 2. The Ag-containing paste 6p is printed in alignment with the back surface side of the semiconductor substrate 2 at the center position C in the surface direction of the semiconductor substrate 11 which is a specific reference position on one surface side. FIG. 18 is a schematic diagram showing the configuration of the print mask 31 for printing the Ag-containing paste 6p on the pattern of the back surface side grid electrode 6a according to the embodiment of the present invention. Thereby, the back surface side grid electrode 6a in a dry state can be formed. By printing the Ag-containing paste 6p with the pattern shown in FIG. 4, even if the printing position of the back surface side grid electrode 6a with respect to the back surface high concentration impurity diffusion layer 7a is slightly shifted, the connecting protrusion 6t causes the back surface side High-concentration impurity diffusion layer 7a and backside grid electrode 6a can be electrically connected. Thereby, the increase in resistance loss resulting from the rotational position shift of the back surface side grid electrode 6a with respect to the back surface side high concentration impurity diffusion layer 7a can be suppressed.

  FIG. 17 is an explanatory diagram of step S110 in FIG. Step S110 is a step of simultaneously baking the electrode material paste printed and dried on the light receiving surface side and the back surface side of the semiconductor substrate 11. Specifically, the semiconductor substrate 11 is introduced into a firing furnace, and a short-time heat treatment is performed at a peak temperature of about 600 ° C. to 900 ° C., for example, 800 ° C. for 3 seconds in an air atmosphere. Thereby, the resin component in the electrode material paste disappears. On the light receiving surface side of the semiconductor substrate 11, the silver material contacts the silicon of the p-type impurity diffusion layer 3 while the glass material contained in the Ag-containing paste 5 p is melted and penetrates the antireflection film 4. Then re-solidify. Thereby, the light receiving surface side grid electrode 5a and the light receiving surface side bus electrode 5b are obtained, and electrical conduction between the light receiving surface side electrode 5 and the silicon of the semiconductor substrate 11 is ensured.

  Further, on the back surface side of the semiconductor substrate 11, while the glass material contained in the Ag-containing paste 6 p is melted and penetrates through the back surface insulating film 8, the silver material is bonded to the silicon in the back surface high concentration impurity diffusion layer 7 a. Contact and re-solidify. Thereby, the back surface side grid electrode 6a and the back surface side bus electrode 6b are obtained, and electrical conduction between the back surface side electrode 6 and the silicon of the semiconductor substrate 11 is ensured.

  By performing the steps as described above, the solar battery cell 1 according to the present embodiment shown in FIGS. 1 to 3 can be manufactured. Note that the order of arrangement of the paste, which is an electrode material, on the semiconductor substrate 11 may be switched between the light receiving surface side and the back surface side.

  In addition, when it is possible to grasp the tendency of displacement of the formation position of the back surface side grid electrode 6a in the direction of left rotation or right rotation about the center position C, the shape of the back surface side grid electrode 6a is changed. May be. That is, as shown in FIGS. 19 and 20, in the two regions of the back surface side grid electrode 6a facing each other across the center position C or the virtual line V in the extending direction of the back surface side grid electrode 6a, the back surface side grid electrode 6a. The connecting protrusions 6t may be formed only on different side surfaces of the two side surfaces. FIG. 19 shows a pattern of the back surface side grid electrode 6a used when the back surface side grid electrode 6a according to the embodiment of the present invention tends to cause a displacement of the formation position in a direction in which the back surface side grid electrode 6a rotates counterclockwise around the center position C. It is a schematic diagram which shows. FIG. 20 shows a pattern of the back surface side grid electrode 6a used in the case where the back surface side grid electrode 6a according to the embodiment of the present invention tends to be displaced in the formation position in the direction in which the back surface side grid electrode 6a rotates clockwise around the center position C. It is a schematic diagram which shows.

  In the above description, the case where the BSF layer has a selective diffusion layer structure has been described. However, the light receiving surface side impurity diffusion layer has a selective diffusion layer structure, and the light receiving surface side grid electrode 5a has the same pattern as the back surface side grid electrode. It is also possible to do. In this case, as shown in FIG. 21, the light receiving surface side impurity diffusion layer 3 is constituted by the light receiving surface side high concentration impurity diffusion layer 3b and the light receiving surface side low concentration impurity diffusion layer 3c. If the impurity diffusion concentration of the light receiving surface side high concentration impurity diffusion layer 3b is the third concentration and the impurity diffusion concentration of the light receiving surface side low concentration impurity diffusion layer 3c is the fourth concentration, the fourth concentration is lower than the third concentration. Become. FIG. 21 is a schematic cross-sectional view of a relevant part of a solar battery cell in which the light-receiving surface side impurity diffusion layer according to the embodiment of the present invention has a selective diffusion layer structure.

  The light receiving surface side high concentration impurity diffusion layer 3b has the same shape and dimensions as the light receiving surface side grid electrode 5a, and the light receiving surface side grid electrode 5a is printed on the light receiving surface side high concentration impurity diffusion layer 3b. . Also in this case, similarly to the case where the back surface side grid electrode 6a is used, even when the printing position is slightly shifted in the rotation direction when the light receiving surface side grid electrode 5a is printed, the light receiving surface side grid electrode 5a is provided. The light receiving surface side high-concentration impurity diffusion layer 3b and the light receiving surface side grid electrode 5a can be electrically connected by the connecting protrusion. Thereby, it is possible to suppress an increase in resistance loss due to a rotational position shift of the light receiving surface side grid electrode 5a with respect to the light receiving surface side high concentration impurity diffusion layer 3b.

  In the above description, the connection protrusion 6t protrudes in a direction perpendicular to the longitudinal direction of the back surface side grid electrode 6a. However, the connection protrusion 6t extends in the longitudinal direction of the back surface side grid electrode 6a. And may protrude in an inclined direction.

  In the above description, the back side high-concentration impurity diffusion layer 7a has a long and narrow shape that does not have a connecting protrusion. However, the back side high-concentration impurity diffusion layer 7a has a back-side grid electrode 6a. It may be made into the shape provided with the protrusion part for a connection which has the same shape and dimension. In this case, the shape and size of the back surface side grid electrode 6a are the same as the shape and size of the back surface side high concentration impurity diffusion layer 7a.

  In the above description, the case where an n-type single crystal silicon substrate is used as the semiconductor substrate 2 has been described. However, the semiconductor substrate 2 is not limited to this. That is, as long as it functions as a solar cell substrate, the semiconductor substrate 2 may be an n-type polycrystalline silicon substrate. Further, a p-type silicon substrate may be used as the semiconductor substrate 2. Further, the diffusion layers formed on the light receiving surface side and the back surface side of the semiconductor substrate 2 may be appropriately determined depending on the conductivity type of the semiconductor substrate 2. Further, the impurity elements that form the diffusion layers on the light receiving surface side and the back surface side of the semiconductor substrate 2 may be selected as appropriate.

  As described above, in the solar battery cell 1 according to the present embodiment, the back surface side grid electrode 6a includes the connection protrusion 6t. Thereby, even when the rotational position shift of the light receiving surface side grid electrode 5a with respect to the light receiving surface side high concentration impurity diffusion layer 3b occurs, the back surface side high concentration impurity diffusion layer 7a and the back surface side grid electrode 6a are caused by the connecting protrusion 6t. Can be electrically connected. For this reason, the back side high concentration impurity diffusion in the case where the rotational position shift of the light receiving surface side grid electrode 5a with respect to the light receiving surface side high concentration impurity diffusion layer 3b becomes a problem when the back side grid electrode 6a is thinned. Insufficient electrical connection between the layer 7a and the backside grid electrode 6a can be suppressed, and an increase in resistance loss between the backside high-concentration impurity diffusion layer 7a and the backside grid electrode 6a can be suppressed.

  Therefore, in the solar cell 1, the width 7W of the back-side high-concentration impurity diffusion layer can be set to the necessary minimum, that is, the same width as the width 6aW of the back-side grid electrode. By increasing the ratio of the region of the backside low-concentration impurity diffusion layer 7b, the backside passivation effect can be increased.

  Moreover, in the photovoltaic cell 1, the amount of the metal material used for the back surface side grid electrode 6a can be reduced by thinning the back surface side grid electrode 6a, and the back surface side grid electrode 6a and the photovoltaic cell 1 cost can be reduced. A reduction can be realized.

  Therefore, according to the solar battery cell 1 according to the present embodiment, it is possible to reduce the cost by reducing the amount of electrode material used by thinning the back surface side grid electrode 6a, and the back surface side high concentration impurity diffusion layer. A solar battery cell capable of suppressing a decrease in photoelectric conversion efficiency due to electrical connection between 7a and the back surface side grid electrode 6a is obtained.

  The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

  DESCRIPTION OF SYMBOLS 1 Solar cell, 2 Semiconductor substrate, 3 Light-receiving surface side impurity diffusion layer, 3a P-type impurity diffusion layer, 4 Antireflection film, 5 Light-receiving surface side electrode, 5a Light-receiving surface side grid electrode, 5b Light-receiving surface side bus electrode, 5p Ag-containing paste, 6 back side electrode, 6a back side grid electrode, 6aW back side grid electrode width, 6b back side bus electrode, 6p Ag containing paste, 6t connecting projection, 6tW connecting projection width, 7 Backside impurity diffusion layer, 7W Width of backside high concentration impurity diffusion layer, 7a Backside high concentration impurity diffusion layer, 7b Backside low concentration impurity diffusion layer, 8 Backside insulating film, 11 Semiconductor substrate, 21 Oxide film, 22 Phosphorus-containing doping paste, D1 arrangement interval, D2 arrangement interval, V virtual line.

In order to solve the above-described problems and achieve the object, the present invention provides a solar cell in which a first conductivity type semiconductor substrate and an impurity element of a first conductivity type or a second conductivity type on one surface side of the semiconductor substrate are provided. And a paste electrode disposed on one side and electrically connected to the impurity diffusion layer, extending in parallel at a first arrangement interval in a specific direction in the surface direction of the semiconductor substrate. A plurality of grid electrodes having a linear shape. The impurity diffusion layer includes a first conductive type or second conductive type impurity element at a first concentration in a lower region of the grid electrode and has a linear shape, and extends parallel to a specific direction in the plane direction of the semiconductor substrate. A plurality of first impurity diffusion layers, and a second impurity diffusion layer including an impurity element having the same conductivity type as that of the first impurity diffusion layer at a second concentration lower than the first concentration. Grid electrode has a plurality of collision detecting portion which is placed along the extending direction of the grid electrode with protruding in a direction crossing the side surface of the grid electrode and the extending direction of the grid electrode. The plurality of connecting protrusions are characterized in that the protrusion length from the side surface of the grid electrode becomes longer as the distance from the specific reference position on the one surface side of the semiconductor substrate in the extending direction of the grid electrode is increased.

The protruding portion 6t for connection has a larger protruding amount from the side surface of the back surface side grid electrode 6a as it is away from the specific reference position in the longitudinal direction of the back surface side grid electrode 6a. The protrusion length 6tL of the protrusion 6t is longer. Therefore, the protrusion 6t for connection has a smaller protrusion amount as it is closer to a specific reference position in the longitudinal direction of the back surface side grid electrode 6a, that is, the protrusion length 6t L from the side surface of the back surface side grid electrode 6a is shorter. .

FIG. 12 is an explanatory diagram of step S40 in FIG. Step S40 is a step of removing the oxide film 21 and the p-type impurity diffusion layer 3a, which is an impurity-containing layer, formed on the back surface opposite to the light receiving surface of the n-type silicon substrate 2. The removal of the oxide film 21 and the p-type impurity diffusion layer 3a can be performed by single-sided etching in which only the back surface of the n-type silicon substrate 2 is brought into contact with the hydrofluoric acid aqueous solution using, for example, a single-sided etching apparatus. As a result, the p-type impurity diffusion layer 3 a formed on the light-receiving surface side of the n-type silicon substrate 2 becomes the p-type light-receiving surface side impurity diffusion layer 3. A semiconductor in which a pn junction is formed by an n-type silicon substrate 2 made of n-type single crystal silicon and a p-type light-receiving surface side impurity diffusion layer 3 formed on the light-receiving surface side of the n-type silicon substrate 2 A substrate 11 is obtained.

Next, in step S80 of FIG. 8, the p-type light-receiving surface side impurity diffusion layer 3 formed on the light-receiving surface side of the n-type silicon substrate 2 and the back-side impurities formed on the back surface side of the n-type silicon substrate 2. A pn separation step for electrically separating the diffusion layer 7 is performed. Specifically, for example, about 50 to 300 semiconductor substrates 11 that have undergone the processes up to step S70 are stacked, and end face etching is performed in which the side surface is etched by plasma discharge. Alternatively, laser separation may be performed in which the n-type silicon substrate 2 is exposed by melting the vicinity of the side edge of the light receiving surface side or the back surface side of the semiconductor substrate 11 or the side surface of the semiconductor substrate 11 by laser irradiation.

In the above description, a preferable method for performing pn separation has been described. However, the separation state between the p-type light-receiving surface side impurity diffusion layer 3 and the back surface side impurity diffusion layer 7, that is, the magnitude of the leakage current, the final Depending on the arrangement of the solar battery cells in the solar battery module to be a power generation product, the pn separation step in step S80 can be omitted.

Next, the hydrofluoric acid aqueous solution in which the silicon oxide film formed on the surface of the semiconductor substrate 11 on the light receiving surface side, that is, on the surface of the p-type light receiving surface side impurity diffusion layer 3 is, for example, 5% or more and 25% or less. Is removed. Then, the hydrofluoric acid aqueous solution adhering to the surface of the semiconductor substrate 11 is removed by washing with water. At this time, an oxide film formed by washing with water, generally called a natural oxide film, may be used as a passivation layer described later or a part thereof. For the same purpose, an oxide film obtained by cleaning the semiconductor substrate 11 with water containing ozone may be used as a passivation layer described later or a part thereof.

Subsequently, an antireflection film 4 made of a silicon nitride film is formed on the light receiving surface side of the semiconductor substrate 11, that is, on the p-type light receiving surface side impurity diffusion layer 3 by using, for example, plasma CVD. Note that a passivation layer may be formed between the silicon nitride film of the antireflection film 4 and the p-type light-receiving surface side impurity diffusion layer 3. In this case, the passivation layer is preferably a silicon oxide film or an aluminum oxide film, or a laminated film of a silicon oxide film and an aluminum oxide film. When a silicon oxide film is used for the passivation layer, an oxide film obtained by washing with water or washing with ozone-containing water as described above may be used in addition to a general thermal oxide film. When an aluminum oxide film is used, the aluminum oxide film is formed by, for example, plasma CVD or ALD (Atomic Layer Deposition). In this case, a fixed charge included in the film formation is more preferable because it has an effect of enhancing the passivation ability.

Figure 17 is an explanatory diagram of step S110 in FIG. 8. Step S110 is a step of simultaneously baking the electrode material paste printed and dried on the light receiving surface side and the back surface side of the semiconductor substrate 11. Specifically, the semiconductor substrate 11 is introduced into a firing furnace, and a short-time heat treatment is performed at a peak temperature of about 600 ° C. to 900 ° C., for example, 800 ° C. for 3 seconds in an air atmosphere. Thereby, the resin component in the electrode material paste disappears. On the light receiving surface side of the semiconductor substrate 11, the silver material contacts the silicon of the p-type impurity diffusion layer 3 while the glass material contained in the Ag-containing paste 5 p is melted and penetrates the antireflection film 4. Then re-solidify. Thereby, the light receiving surface side grid electrode 5a and the light receiving surface side bus electrode 5b are obtained, and electrical conduction between the light receiving surface side electrode 5 and the silicon of the semiconductor substrate 11 is ensured.

In the above description, the BSF layer has a selective diffusion layer structure. However, the light receiving surface side impurity diffusion layer 3 has a selective diffusion layer structure, and the light receiving surface side grid electrode 5a is the same as the back surface side grid electrode 6a . A pattern is also possible. In this case, as shown in FIG. 21, the light receiving surface side impurity diffusion layer 3 is constituted by the light receiving surface side high concentration impurity diffusion layer 3b and the light receiving surface side low concentration impurity diffusion layer 3c. If the impurity diffusion concentration of the light receiving surface side high concentration impurity diffusion layer 3b is the third concentration and the impurity diffusion concentration of the light receiving surface side low concentration impurity diffusion layer 3c is the fourth concentration, the fourth concentration is lower than the third concentration. Become. FIG. 21 is a schematic cross-sectional view of a relevant part of a solar battery cell in which the light-receiving surface side impurity diffusion layer according to the embodiment of the present invention has a selective diffusion layer structure.

Claims (13)

A first conductivity type semiconductor substrate;
An impurity diffusion layer in which an impurity element of the first conductivity type or the second conductivity type is diffused on one surface side of the semiconductor substrate;
A plurality of paste electrodes arranged on the one surface side and electrically connected to the impurity diffusion layer and extending in parallel at a first arrangement interval in a specific direction in the surface direction of the semiconductor substrate A grid electrode,
With
The impurity diffusion layer includes a first conductive type or second conductive type impurity element at a first concentration in a lower region of the grid electrode, and has a linear shape in the specific direction in the plane direction of the semiconductor substrate. A plurality of first impurity diffusion layers extending in parallel; and a second impurity diffusion layer including the impurity element having the same conductivity type as the first impurity diffusion layer at a second concentration lower than the first concentration. And
The grid electrode has a plurality of connecting protrusions that protrude from a side surface of the grid electrode in a direction intersecting with the extending direction of the grid electrode and that are divided and arranged along the extending direction of the grid electrode,
The plurality of connection protrusions have a longer protrusion length from the side surface of the grid electrode as they move away from a specific reference position on one surface side of the semiconductor substrate in the extending direction of the grid electrode.
A solar cell characterized by. The specific reference position is a position having the highest alignment accuracy between the first impurity diffusion layer and the grid electrode;
The solar battery cell according to claim 1. The plurality of connecting protrusions have a length that is longer in direct proportion to the distance from the specific reference position in the extending direction of the grid electrode;
The solar battery cell according to claim 2. The connecting protrusion is symmetrical about the specific reference position in the extending direction of the grid electrode;
The solar battery cell according to claim 3. The connection protrusions are disposed on different side surfaces of at least both side surfaces of the grid electrode in two regions of the grid electrode facing each other across the specific reference position in the extending direction of the grid electrode. Being
The solar battery cell according to claim 3. The first impurity diffusion layer has the same width as the grid electrode;
The solar battery cell according to any one of claims 1 to 5, wherein: The ratio of the width of the connecting protrusion to the width of the grid electrode is 0.3 or more and 1 or less,
The solar battery cell according to claim 1. The protrusion length is smaller than the first arrangement interval;
The solar battery cell according to claim 1. A ratio of the protruding length to the first arrangement interval is 0.6 or less;
The solar battery cell according to claim 8. The ratio of the protruding length to the first arrangement interval is 0.05 or more and 0.3 or less,
The solar battery cell according to claim 8. A plurality of the connecting protrusions are distributed and arranged at second arrangement intervals in the extending direction of the grid electrode,
The second arrangement interval is larger than a width of the grid electrode;
The solar battery cell according to claim 1. A second conductivity type impurity diffusion layer in which a second conductivity type impurity element is diffused on the other surface side of the semiconductor substrate;
A light-receiving surface side electrode electrically connected to the second conductivity type impurity diffusion layer;
Have
The impurity diffusion layer is a back surface electric field layer in which an impurity element of the first conductivity type is diffused on the back surface facing the light receiving surface side of the semiconductor substrate;
The grid electrode is a back electrode;
The solar battery cell according to claim 1. One surface side of the first conductivity type semiconductor substrate has a linear shape containing a first conductivity type or second conductivity type impurity element at a first concentration, and is parallel to a specific direction in the surface direction of the semiconductor substrate. Impurity diffusion comprising a plurality of first impurity diffusion layers extending and a second impurity diffusion layer containing the impurity element having the same conductivity type as the first impurity diffusion layer at a second concentration lower than the first concentration. A first step of forming a layer;
A plurality of linear grid electrodes extending in parallel to the specific direction and electrically connected to the first impurity diffusion layer are formed on the first impurity diffusion layer by printing an electrode material paste by screen printing. A second step of
Including
In the extending direction of the grid electrode, the grid electrode has a protruding length from the side surface of the grid electrode that increases from the specific reference position on the one surface side of the semiconductor substrate. Having a pattern that protrudes in a direction intersecting with the extending direction of the electrode and includes a plurality of connecting protruding portions arranged along the extending direction of the grid electrode;
In the second step, an electrode material paste is provided on one surface side of the semiconductor substrate at a specific reference position on one surface side of the semiconductor substrate with a print mask having parallel opening patterns corresponding to the grid electrode pattern at the same interval. Forming on the plurality of first impurity diffusion layers in alignment with each other;
The manufacturing method of the photovoltaic cell characterized by these.

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