JP2015082512A - Method of manufacturing solar cell, solar cell and conductive paste for forming bus bar electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a solar cell capable of forming a bus bar electrode having a small thickness easily so that the bus bar electrode is not peeled from a semiconductor substrate.SOLUTION: By coating the surface 1a of a semiconductor substrate 1 with a first conductivity paste, a bus bar electrode 21 consisting of a plurality of electrode wires 23 extending, respectively, in a first direction in the surface 1a and arranged in a second direction crossing the first direction is formed. In the method of manufacturing a solar cell, a finger electrode extending in a second direction in the surface 1a is formed by coating the surface 1a of a semiconductor substrate 1 with a second conductivity paste. The ratio of the thickness TH3 to the width WD3 of the electrode wire 23 is smaller than the ratio of the thickness to the width of the finger electrode.

Description

  The present invention relates to a method for manufacturing a solar cell, a solar cell, and a conductive paste for forming bus bar electrodes.

  The solar cell module has a plurality of solar cell elements, that is, solar cells. Each of these solar cells includes a semiconductor substrate having a pn junction formed therein, a light-receiving surface side of the semiconductor substrate, that is, a surface electrode formed on the surface side, and a side opposite to the light-receiving surface of the semiconductor substrate, that is, And a back electrode formed on the back side. The plurality of solar cells are electrically connected to each other by, for example, tab wires that are wiring members.

  Japanese Patent Laying-Open No. 2005-353851 (Patent Document 1) describes an example of a solar cell in which a surface electrode is formed on the surface of a semiconductor substrate and a back electrode is formed on the back surface of the semiconductor substrate. In addition, Patent Document 1 describes a method of forming a front electrode and a back electrode by screen printing.

  In JP 2011-198982 A (Patent Document 2), a paste-like coating liquid containing an electrode pattern material is continuously discharged from a nozzle onto a photoelectric conversion surface of a substrate included in a solar cell, to thereby form an electrode pattern. A method of forming is described. In the method described in Patent Document 2, nozzles each having a plurality of discharge ports that are respectively communicated with the liquid storage space and arranged in a direction intersecting the relative movement direction of the substrate are used. In the method described in Patent Document 2, the coating liquid stored in the liquid storage space is pressurized and discharged from each discharge port, so that they are parallel to each other by one relative movement between the nozzle and the substrate. A large number of linear electrode patterns are formed.

JP 2005-353851 A JP 2011-198982 A

  As described in Patent Document 1, when the electrode pattern is formed by screen printing, the semiconductor substrate may be broken by pressing the squeegee against the semiconductor substrate, the yield of the solar cell to be manufactured is reduced, and the manufacturing cost is reduced. May increase. In addition, it is necessary to periodically clean and replace the screen printing plate on which the pattern corresponding to the electrode pattern is formed, which may increase the manufacturing cost.

  On the other hand, as described in Patent Document 2, when an electrode pattern is formed by a method of pressurizing a coating liquid and discharging from a discharge port, the semiconductor substrate is compared with a case of forming an electrode pattern by a screen printing method. There is little risk of cracking. Further, an increase in manufacturing cost due to cleaning and replacement of consumables such as screen printing plates can be suppressed.

  The surface electrode includes a bus bar electrode and a finger electrode. The width of the bus bar electrode is larger than the width of the finger electrode. When the bus bar electrode has a large thickness, the bus bar electrode may be peeled off from the semiconductor substrate due to the stress generated when the formed bus bar electrode is heat-treated and then contracted. Therefore, it is necessary to reduce the thickness of the bus bar electrode and to reduce the stress generated when the bus bar electrode shrinks after the bus bar electrode is heat treated so that the bus bar electrode does not peel from the semiconductor substrate.

  Here, when the bus bar electrode is formed by a method in which the coating liquid is pressurized and discharged from the discharge port, the thickness of the formed bus bar electrode is approximately the same as the width of the formed bus bar electrode. Therefore, the thickness of the bus bar electrode having a width larger than the width of the finger electrode is larger than the thickness of the finger electrode, and the bus bar electrode is more easily peeled from the semiconductor substrate than the finger electrode.

  Therefore, the present invention provides a method for manufacturing a solar cell that can easily form a bus bar electrode having a small thickness such that the bus bar electrode does not peel from the semiconductor substrate. Alternatively, the present invention provides a solar cell capable of easily forming a bus bar electrode having a small thickness such that the bus bar electrode does not peel from the semiconductor substrate, and a bus bar used for forming the bus bar electrode of the solar cell. A conductive paste for electrode formation is provided.

  In a method for manufacturing a solar cell according to a representative embodiment, the first conductive paste is applied on the first main surface of the semiconductor substrate, thereby extending in the first direction within the first main surface, and The bus bar electrodes are formed of a plurality of electrode lines arranged in the second direction intersecting the first direction. Moreover, in the manufacturing method of the said solar cell, the finger electrode extended in a 2nd direction within a 1st main surface is formed by apply | coating a 2nd conductive paste on the 1st main surface of a semiconductor substrate. The ratio of the first thickness of each of the plurality of electrode lines to the first width of each of the plurality of electrode lines is equal to the second width of the finger electrode with respect to the second width of the finger electrode in the first direction. Less than the thickness ratio.

  Moreover, the solar cell by typical embodiment has the bus-bar electrode formed in the 1st main surface side of the semiconductor substrate, and the finger electrode formed in the 1st main surface side of the semiconductor substrate. The bus bar electrode includes a plurality of electrode lines extending in the first direction within the first main surface and arranged in the second direction intersecting the first direction. The finger electrode extends in the second direction within the first main surface. The ratio of the first thickness of each of the plurality of electrode lines to the first width of each of the plurality of electrode lines is equal to the second width of the finger electrode with respect to the second width of the finger electrode in the first direction. Less than the thickness ratio.

Furthermore, the conductive paste for bus bar electrode formation according to a representative embodiment includes a bus bar electrode formed on the first main surface side of the semiconductor substrate, a finger electrode formed on the first main surface side of the semiconductor substrate, It is the electrically conductive paste used in order to form a bus-bar electrode in the solar cell which has this. The bus bar electrode forming conductive paste forms bus bar electrodes each of which extends in the first direction within the first main surface and includes a plurality of electrode lines arranged in the second direction intersecting the first direction. Is to do. The ratio of the first thickness of each of the plurality of electrode lines to the first width of each of the plurality of electrode lines is equal to the second width of the finger electrode with respect to the second width of the finger electrode in the first direction. Less than the thickness ratio. The finger electrode extending in the second direction within the first main surface is formed by applying a finger electrode forming conductive paste on the first main surface of the semiconductor substrate. The temperature 25 ° C., and the viscosity of the bus bar electrode formation conductive paste at a shear rate of 2s ^-1, the temperature 25 ° C., and less than the viscosity of the finger electrodes forming conductive paste at a shear rate of 2s ^-1.

  According to a typical embodiment, a bus bar electrode having a small thickness such that the bus bar electrode does not peel from the semiconductor substrate can be easily formed.

It is the top view which looked at the solar cell of Embodiment 1 from the light-receiving surface side. It is the top view which looked at the solar cell of Embodiment 1 from the opposite side to the light-receiving surface. 3 is a cross-sectional view of the solar cell in the first embodiment. FIG. 3 is a plan view of a bus bar electrode in the solar cell of Embodiment 1. FIG. 2 is a cross-sectional view of a bus bar electrode in the solar cell of Embodiment 1. FIG. 3 is a cross-sectional view of finger electrodes in the solar cell of Embodiment 1. FIG. It is a top view which shows the structure of a bus-bar electrode formation apparatus. It is a side view which shows the structure of a bus-bar electrode formation apparatus. It is a figure which shows the arrangement | sequence of the ejection opening in the application nozzle of a bus-bar electrode formation apparatus. It is a top view which shows the structure of a finger electrode formation apparatus. It is the photograph which observed the bus-bar electrode of Example 1 with the optical microscope. It is the photograph which observed the bus-bar electrode of Example 2 with the optical microscope. It is the photograph which observed the bus-bar electrode of Example 3 with the optical microscope. It is the photograph which observed the bus-bar electrode of the comparative example with the optical microscope. It is the graph which measured the shape of the bus-bar electrode of Example 1 with the stylus type step meter. It is the graph which measured the shape of the bus-bar electrode of Example 2 with the stylus type level difference meter. It is the graph which measured the shape of the bus-bar electrode of Example 3 with the stylus type step meter. It is the graph which measured the shape of the bus-bar electrode of a comparative example with the stylus type level difference meter.

  In the following embodiments, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other. There are some or all of the modifications, details, supplementary explanations, and the like.

  Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number.

  Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say. Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted. In the following embodiments, the description of the same or similar parts will not be repeated in principle unless particularly necessary.

  Further, in the drawings used in the embodiments, hatching may be omitted even in a cross-sectional view for easy viewing of the drawings. Further, even a plan view may be hatched to make the drawing easy to see.

  In the following embodiments, when ranges are shown as A to B, A to B are shown unless otherwise specified.

(Embodiment 1)
<Configuration of solar cell>
First, the configuration of the solar cell of the first embodiment will be described with reference to FIGS. FIG. 1 is a plan view of the solar cell of Embodiment 1 viewed from the light receiving surface side. FIG. 2 is a plan view of the solar cell of Embodiment 1 viewed from the side opposite to the light receiving surface. FIG. 3 is a cross-sectional view of the solar cell of the first embodiment. FIG. 3 is a cross-sectional view taken along line AA in FIGS. 1 and 2.

  As shown in FIGS. 1 to 3, the solar cell includes a semiconductor substrate 1, a front electrode 2, and a back electrode 3. The surface electrode 2 is formed on the surface 1 a side which is the first main surface of the semiconductor substrate 1. The back electrode 3 is formed on the back surface 1 b side, which is the second main surface, on the side opposite to the front surface 1 a of the semiconductor substrate 1. The front surface 1 a is a light receiving surface on which light such as sunlight incident on the solar cell is received by the semiconductor substrate 1. The back surface 1b is a surface opposite to the light receiving surface.

  In the surface 1a of the semiconductor substrate 1, two directions intersecting each other, preferably perpendicular to each other, are defined as an X-axis direction and a Y-axis direction, respectively. A direction perpendicular to both the X-axis direction and the Y-axis direction, that is, a direction perpendicular to the surface 1a of the semiconductor substrate 1 is defined as a Z-axis direction.

  The semiconductor substrate 1 has a first conductivity type. A semiconductor region 11 of the second conductivity type opposite to the first conductivity type is formed on the surface 1a side portion of the semiconductor substrate 1 having the first conductivity type. At this time, if a portion of the semiconductor substrate 1 where the semiconductor region 11 is not formed is a semiconductor region 12, the first conductivity type semiconductor region 12 and the second conductivity type semiconductor region are inside the semiconductor substrate 1. A pn junction is formed at the interface with the electrode 11.

  When the first conductivity type is p-type and the second conductivity type is n-type, a single-crystal silicon substrate which is a p-type semiconductor into which a p-type impurity such as boron is introduced is used as the semiconductor substrate 1. Can do. At this time, by introducing an n-type impurity such as phosphorus or arsenic from the surface 1a side of the single crystal silicon substrate, the n-type semiconductor is formed on the surface 1a side portion of the single crystal silicon substrate which is a p-type semiconductor. The semiconductor region 11 can be formed. The first conductivity type described above may be n-type, and the second conductivity type may be p-type.

  The surface electrode 2 includes a bus bar electrode 21 and finger electrodes 22. The bus bar electrode 21 and the finger electrode 22 are electrically connected to each other. The bus bar electrode 21 extends in the X-axis direction within the surface 1a. The finger electrode 22 extends in the Y-axis direction within the surface 1a. Therefore, the bus bar electrode 21 and the finger electrode 22 intersect within the surface 1a.

  The bus bar electrode 21 is an electrode for extracting output from the surface 1 a of the semiconductor substrate 1. The finger electrode 22 is an electrode for collecting the output from the surface 1 a of the semiconductor substrate 1 at a part away from the bus bar electrode 21 to the bus bar electrode 21. Accordingly, the width WD1 of the bus bar electrode 21 in the Y-axis direction is larger than the width WD2 of the finger electrode 22 in the X-axis direction. Preferably, the surface electrode 2 has a plurality of bus bar electrodes 21 extending in the X-axis direction within the surface 1a and arranged at intervals in the Y-axis direction. Preferably, the surface electrode 2 has a plurality of finger electrodes 22 extending in the Y-axis direction within the surface 1a and arranged at intervals in the X-axis direction.

  The back electrode 3 has a bus bar electrode 31 and a current collecting electrode 32. The bus bar electrode 31 and the current collecting electrode 32 are electrically connected to each other. The bus bar electrode 31 extends in the X-axis direction within the back surface 1b. The current collecting electrode 32 is formed on the back surface 1 b side of the semiconductor substrate 1 where the bus bar electrode 31 is not formed.

  The bus bar electrode 31 is an electrode for extracting output from the back surface 1 b of the semiconductor substrate 1. The current collecting electrode 32 is an electrode for collecting the output from the back surface 1 b of the semiconductor substrate 1 at a portion away from the bus bar electrode 31 to the bus bar electrode 31. Preferably, the back surface electrode 3 includes a plurality of bus bar electrodes 31 that extend in the X axis direction within the back surface 1b and are arranged at intervals in the Y axis direction.

  A plurality of solar cells as shown in FIGS. 1 to 3 are arranged in a plane, the bus bar electrode 21 of the surface electrode 2 of a certain solar cell, and the bus bar electrode 31 of the back electrode 3 of the solar cell adjacent to the solar cell. Are electrically connected to each other by a tab wire which is a wiring member. By such a method, these several solar cells can be connected in series. And a solar cell module is formed by sealing a plurality of solar cells connected in series with a sealing material between two support plates arranged on both sides of the light receiving surface and the opposite side of the light receiving surface. The

<Configuration of bus bar electrode>
Next, with reference to FIGS. 4-6, the structure of the bus-bar electrode in the solar cell of Embodiment 1 is demonstrated. FIG. 4 is a plan view of the bus bar electrode in the solar cell of the first embodiment. FIG. 5 is a cross-sectional view of the bus bar electrode in the solar cell of the first embodiment. FIG. 6 is a cross-sectional view of the finger electrode in the solar cell of the first embodiment. 5 is a cross-sectional view perpendicular to the X-axis direction, and FIG. 6 is a cross-sectional view perpendicular to the Y-axis direction.

  As shown in FIGS. 4 and 5, the bus bar electrode 21 includes a plurality of electrode lines 23 extending in the X-axis direction within the surface 1a and arranged in the Y-axis direction. 4 and 5 show a bus bar electrode 21 including six electrode lines 23 as an example. At this time, the thickness of the bus bar electrode 21 is set to thickness TH1, the thickness of the finger electrode 22 is set to thickness TH2 (see FIG. 6), and the thickness of each of the plurality of electrode wires 23 is set to thickness TH3. The width in the Y-axis direction of each of the plurality of electrode lines 23 is defined as a width WD3. As shown in FIG. 5, the thickness TH1 of the bus bar electrode 21 is defined as the maximum thickness of the bus bar electrode 21, and as shown in FIG. 6, the thickness TH2 of the finger electrode 22 is defined as the maximum thickness of the finger electrode 22. As shown in FIG. 5, the thickness TH3 of each of the plurality of electrode lines 23 is defined as the maximum thickness of each electrode line 23. At this time, the thickness TH1 of the bus bar electrode 21 and the thickness TH3 of each of the plurality of electrode lines 23 are equal to each other. Further, the width WD2 in the X-axis direction of the finger electrode 22 is defined as the maximum width of the finger electrode 22, and the width WD3 in the Y-axis direction of each of the plurality of electrode lines 23 is defined as the maximum width of each electrode line 23. To do.

  In such a case, the aspect ratio (TH3 / WD3) which is the ratio of the thickness TH3 of each of the plurality of electrode lines 23 to the width WD3 of each of the plurality of electrode lines 23 in the Y-axis direction is X It is smaller than the aspect ratio (TH2 / WD2) that is the ratio of the thickness TH2 of the finger electrode 22 to the width WD2 in the axial direction. Accordingly, even when the bus bar electrode 21 having the width WD1 larger than the width WD2 of the finger electrode 22 is formed, the thickness TH1 of the bus bar electrode 21 is prevented from becoming larger than the thickness TH2 of the finger electrode 22. Or it can be suppressed. Therefore, the thickness TH1 of the bus bar electrode 21 can be easily reduced, and peeling of the bus bar electrode 21 from the semiconductor substrate 1 can be easily prevented or suppressed.

  Further, when there is a magnitude relationship of the aspect ratio as described above, it is possible to prevent or suppress the formation of irregularities having a large difference between the height position of the concave portion and the height position of the convex portion on the surface of the bus bar electrode 21. it can. Therefore, when a solar cell module is formed by a plurality of solar cells, even if the tab wire and the bus bar electrode 21 are joined using solder, the solder easily spreads over the entire upper surface of the bus bar electrode 21. The bonding area between the wire and the bus bar electrode 21 increases and the bonding strength increases. Therefore, when the solar cell module is manufactured or after the solar cell module is manufactured, it is possible to prevent or suppress the tab wire from peeling off from the bus bar electrode 21.

  Note that the thickness TH2 of the finger electrode 22 may be defined as an average value of the thickness of the finger electrode 22 instead of the above-described maximum thickness. In this case, similarly to the finger electrode 22, the thickness TH3 of each of the plurality of electrode lines 23 may be defined as an average value of the thickness of each of the plurality of electrode lines 23 instead of the maximum thickness described above. .

  In FIG. 4 and FIG. 5, a plurality of electrode lines 23 are integrated by connecting adjacent electrode lines 23, and the bus bar electrode 21 is composed of a plurality of integrated electrode lines 23. Show. However, the aspect ratio (TH3 / WD3), which is the ratio of the thickness TH3 of each of the plurality of electrode lines 23 to the width WD3 of each of the plurality of electrode lines 23 in the Y-axis direction, is the X-axis direction of the finger electrode 22 What is necessary is just to be smaller than the aspect ratio (TH2 / WD2) which is the ratio of the thickness TH2 of the finger electrode 22 to the width WD2. Therefore, the adjacent electrode lines 23 are not connected to each other, the plurality of electrode lines 23 are not integrated, and the surface 1 a of the semiconductor substrate 1 may be exposed between the adjacent electrode lines 23. .

  Preferably, in the region where the bus bar electrode 21 is formed, the coverage of the surface 1a of the semiconductor substrate 1 by the plurality of electrode lines 23 is 90% or more. Here, the region where the bus bar electrode 21 is formed refers to the region where the electrode line 23 located at one end of the array of the plurality of electrode lines 23 is formed on the surface 1a of the semiconductor substrate 1 and the plurality of electrodes. It includes a region where the electrode line 23 located at the other end of the array of the lines 23 is formed and a region sandwiched between the electrode lines 23 located at both ends. Thereby, when a solar cell module is formed by a plurality of solar cells, the bonding area between the tab wire, which is a wiring member bonded to the bus bar electrode 21, and the bus bar electrode 21 is increased, and the bonding strength is increased. The tab wires can be prevented or suppressed from peeling off from the bus bar electrode 21.

  More preferably, in the region where the bus bar electrode 21 is formed, the coverage of the surface 1a of the semiconductor substrate 1 by the plurality of electrode lines 23 is 100%, and the bus bar electrode with respect to the maximum thickness TH11 of the bus bar electrode 21 The ratio (TH12 / TH11) of the minimum thickness TH12 of the portion other than the outer peripheral portion of 21 is larger than 0.2. That is, the plurality of electrode wires 23 are integrated, and the bus bar electrode 21 includes the integrated electrode wires 23, and the bus bar electrode 21 has a thickness other than the outer peripheral portion with respect to the maximum thickness TH11 of the bus bar electrode 21. The ratio of the minimum thickness TH12 of the portion (TH12 / TH11) is greater than 0.2.

  Thereby, when forming a solar cell module with a plurality of solar cells, the bonding area between the tab wire, which is a wiring member bonded to the bus bar electrode 21, and the bus bar electrode 21 is increased, and the bonding strength is increased. . Therefore, it is possible to more reliably prevent or suppress the separation of the tab wire from the bus bar electrode 21. Even if the ratio of the minimum thickness TH12 to the maximum thickness TH11 is 0.2 or less, if the plurality of electrode wires 23 are integrated, the plurality of electrode wires 23 are not integrated. Further, it is possible to prevent or suppress the tab wire from peeling off from the bus bar electrode 21 more reliably.

<Method for manufacturing solar cell>
Next, with reference to FIGS. 1-3 and FIGS. 7-10, the manufacturing method of the solar cell of Embodiment 1 is demonstrated. FIG. 7 is a plan view showing the configuration of the bus bar electrode forming apparatus. FIG. 8 is a side view showing the configuration of the bus bar electrode forming apparatus. FIG. 9 is a diagram showing an array of ejection openings in the application nozzle of the bus bar electrode forming apparatus. FIG. 10 is a plan view showing the configuration of the finger electrode forming apparatus.

  First, as shown in FIG. 3, a semiconductor substrate 1 is prepared. In the step of preparing the semiconductor substrate 1, first, the semiconductor substrate 1 having the first conductivity type is prepared. Then, a second conductivity type semiconductor region 11 opposite to the first conductivity type is formed on the surface 1a side portion of the semiconductor substrate 1 having the first conductivity type. That is, a semiconductor substrate 1 is prepared in which a semiconductor region 11 of a second conductivity type opposite to the first conductivity type is formed in a portion on the surface 1a side of the semiconductor substrate 1 having the first conductivity type. At this time, if a portion of the semiconductor substrate 1 where the semiconductor region 11 is not formed is a semiconductor region 12, the first conductivity type semiconductor region 12 and the second conductivity type semiconductor region are inside the semiconductor substrate 1. A pn junction is formed at the interface with 11.

  When the first conductivity type is p-type and the second conductivity type is n-type, a p-type single crystal silicon substrate into which a p-type impurity such as boron is introduced can be used as the semiconductor substrate 1. . At this time, by introducing an n-type impurity such as phosphorus or arsenic from the surface 1a side of the single crystal silicon substrate, the n-type semiconductor region 11 is formed on the surface 1a side portion of the p-type single crystal silicon substrate. Can be formed. The first conductivity type described above may be n-type, and the second conductivity type may be p-type.

  Next, as shown in FIGS. 1 and 3, the surface electrode 2 is formed. The step of forming the surface electrode 2 includes a step of forming the bus bar electrode 21 and a step of forming the finger electrode 22.

  Among these, in the step of forming the bus bar electrode 21, the bus bar electrode 21 is formed on the surface 1 a side of the semiconductor substrate 1. Below, the method to form the bus-bar electrode 21 using the bus-bar electrode formation apparatus shown in FIGS. 7-9 is demonstrated. The bus bar electrode forming apparatus is used to form bus bar electrodes.

  The bus bar electrode forming apparatus includes a substrate mounting table 41, a substrate transfer stage 42, and a coating unit 43. The substrate mounting table 41 is a holding unit that holds the semiconductor substrate 1. The semiconductor substrate 1 is mounted such that the back surface 1 b opposite to the front surface 1 a of the semiconductor substrate 1 faces the surface of the substrate mounting table 41. The substrate mounting table 41 is attached to the substrate transfer stage 42 so that it can be transferred in the same plane as the surface 1a of the semiconductor substrate 1 held on the substrate mounting table 41 in the same direction as the X-axis direction of the surface 1a. . The substrate transfer stage 42 extends in the same direction as the X-axis direction of the surface 1a, and is a transfer unit that transfers the substrate mounting table 41 in the X-axis direction.

  The application unit 43 includes an application nozzle 44, a nozzle lifting / lowering stage 45, a nozzle support frame 46, a tank 47, a valve 48, and a regulator 49.

  The coating nozzle 44 is located on the first side (upper side in FIG. 8) in the Z-axis direction, which is the direction perpendicular to the surface 1a of the semiconductor substrate 1, rather than the semiconductor substrate 1 held on the substrate mounting table 41. The conductive paste for forming the bus bar electrode is discharged. The bus bar electrode forming conductive paste is used to form a bus bar electrode 21 composed of a plurality of electrode wires 23 by applying the bus bar electrode forming conductive paste on the surface 1 a of the semiconductor substrate 1. is there.

  As shown in FIG. 9, a conductive paste for forming bus bar electrodes is discharged onto the surface of the coating nozzle 44 facing the surface 1a of the semiconductor substrate 1 held on the substrate mounting table 41 (the lower surface in FIG. 8). A plurality of discharge ports 50 are formed for this purpose. FIG. 9 shows an example in which twelve discharge ports 50 are formed. FIG. 9 shows a state in which the ejection port 50 is seen through from above the coating nozzle 44 when the ejection port 50 is formed on the lower surface of the coating nozzle 44.

  The nozzle raising / lowering stage 45 is a moving part that extends in the Z-axis direction and moves the application nozzle 44 up and down in the Z-axis direction. The nozzle support frame 46 is a support unit that supports the nozzle lifting stage 45. The nozzle support frame 46 and the semiconductor substrate 1 transported while being held by the substrate mounting table 41 in the middle of the transporting section of the substrate mounting table 41 along the X-axis direction that is the extending direction of the substrate transport stage 42. It is provided at a position where it does not touch.

  The tank 47 is provided so that it can be connected to the application nozzle 44 via a pipe 51, and the bus bar electrode forming conductive paste 52 is stored inside the tank 47. The valve 48 is provided on the pipe 51 between the tank 47 and the application nozzle 44, and connects the application nozzle 44 to the inside of the tank 47 or blocks the application nozzle 44 from the inside of the tank 47. The regulator 49 is provided on a pipe 53 that supplies high-pressure gas to the inside of the tank 47, controls the pressure that pressurizes the inside of the tank 47, and conducts bus bar electrode formation from the inside of the tank 47 to the coating nozzle 44. The supply speed of the functional paste 52 is controlled. That is, the regulator 49 is a control unit that controls the pressure inside the tank 47.

  The semiconductor substrate 1 held on the substrate mounting table 41 is transferred in the X-axis direction by the substrate transfer stage 42. Then, while the semiconductor substrate 1 is transported and the application nozzle 44 is connected to the inside of the tank 47 by the valve 48, the pressure inside the tank 47 is adjusted by the regulator 49 and stored in the tank 47. The bus bar electrode forming conductive paste 52 is discharged from the coating nozzle 44. In this manner, the bus bar electrode forming conductive paste 52 is applied onto the surface 1a of the semiconductor substrate 1, whereby a plurality of electrode wires 23 are formed on the surface 1a side of the semiconductor substrate 1 (see FIGS. 4 and 5). Form. Thereafter, the bus bar electrode forming conductive paste 52 is dried, for example, at a temperature of about 200 ° C., and then the bus bar electrode forming conductive paste 52 is baked at a temperature of, eg, about 800 ° C. By performing these steps, a bus bar electrode 21 (see FIGS. 4 and 5) including a plurality of electrode lines 23 is formed.

  As shown in FIG. 9, as shown in FIG. 9, the conductive paste 52 for forming bus bar electrodes is formed on the surface of the coating nozzle 44 that faces the surface 1 a of the semiconductor substrate 1 held on the substrate mounting table 41. A plurality of discharge ports 50 for discharging the liquid is formed. The plurality of discharge ports 50 are arranged in the Y-axis direction. The diameter DM1 of the discharge port 50 can be set to, for example, about 50 μm.

  In this case, the semiconductor substrate 1 held on the substrate mounting table 41 is transported in the X-axis direction by the substrate transport stage 42. Then, while the semiconductor substrate 1 is transported and the application nozzle 44 is connected to the inside of the tank 47 by the valve 48, the pressure inside the tank 47 is adjusted by the regulator 49 and stored in the tank 47. The bus bar electrode forming conductive paste 52 is discharged from the coating nozzle 44. In this way, the bus bar electrode-forming conductive paste 52 is arranged on the surface 1a of the semiconductor substrate 1 so as to extend in the X-axis direction within the surface 1a and at intervals in the Y-axis direction. Apply in multiple lines. Then, the bus bar electrode forming conductive paste 52 applied in a plurality of lines is made to flow and spread to extend to the surface 1a side of the semiconductor substrate 1 in the X-axis direction within the surface 1a, and A plurality of electrode lines 23 arranged in the Y-axis direction are formed. Thereafter, the bus bar electrode forming conductive paste 52 is dried, for example, at a temperature of about 200 ° C., and then the bus bar electrode forming conductive paste 52 is baked at a temperature of, eg, about 800 ° C. By performing these steps, a bus bar electrode 21 (see FIGS. 4 and 5) including a plurality of electrode lines 23 is formed.

  In the first embodiment, the bus bar electrode forming conductive paste 52 may be a base material made of a conductive paste containing a conductive material, the viscosity of which is adjusted by adding an organic solvent.

  As the conductive material contained in the substrate, for example, silver, copper, aluminum, gold, platinum, or the like can be used. Thereby, the conductivity of the bus bar electrode 21 can be improved.

  As an organic solvent, the viscosity of the conductive paste for forming the bus bar electrode is reduced below the viscosity of the base material made of the conductive paste containing the conductive material, and after applying the conductive paste for forming the bus bar electrode In this step, for example, in the step of drying the conductive paste for forming bus bar electrodes, a material that volatilizes can be used. Examples of such an organic solvent include α-terpineol, texanol, butyl carbitol, butyl carbitol acetate, ethylene glycol ethyl ether, ethylene glycol monoethyl ether, benzyl alcohol, or 2,2,4-trimethyl-1, 3-pentanediol monoisobutyrate or the like can be used.

  The organic solvent to be added to the base material made of a conductive paste containing a conductive material may be the same type of organic solvent originally contained in the conductive paste, that is, the same type of organic solvent, or The organic solvent originally contained in the conductive paste may be a different type, that is, a different organic solvent.

  The aspect ratio (TH3 / WD3), which is the ratio of the thickness TH3 of each of the plurality of electrode lines 23 to the width WD3 of each of the plurality of electrode lines 23 in the Y-axis direction, is the width WD2 of the finger electrode 22 in the X-axis direction. Is smaller than the aspect ratio (TH2 / WD2), which is the ratio of the thickness TH2 of the finger electrode 22. Accordingly, even when the bus bar electrode 21 having the width WD1 larger than the width WD2 of the finger electrode 22 is formed, the thickness TH1 of the bus bar electrode 21 is prevented from becoming larger than the thickness TH2 of the finger electrode 22. Or it can be suppressed. Therefore, the thickness TH1 of the bus bar electrode 21 can be easily reduced, and peeling of the bus bar electrode 21 from the semiconductor substrate 1 can be easily prevented or suppressed.

  Further, when there is a magnitude relationship of the aspect ratio as described above, it is possible to prevent or suppress the formation of irregularities having a large difference between the height position of the concave portion and the height position of the convex portion on the surface of the bus bar electrode 21. it can. Therefore, when a solar cell module is formed by a plurality of solar cells, even if the tab wire and the bus bar electrode 21 are joined using solder, the solder easily spreads over the entire upper surface of the bus bar electrode 21. The bonding area between the wire and the bus bar electrode 21 increases and the bonding strength increases. Therefore, when the solar cell module is manufactured or after the solar cell module is manufactured, it is possible to prevent or suppress the tab wire from peeling off from the bus bar electrode 21.

  Preferably, the bus bar electrode forming conductive paste is applied in a plurality of lines extending in the X-axis direction within the surface 1a and arranged at intervals in the Y-axis direction, As shown in FIGS. 4 and 5, the plurality of electrode wires 23 are integrated by flowing and spreading the conductive paste for forming bus bar electrodes applied in a plurality of lines. Then, the bus bar electrode forming conductive paste constituting the electrode wire 23 is dried and then fired to form the bus bar electrode 21 including a plurality of integrated electrode wires 23. Thereby, when a solar cell module is formed by a plurality of solar cells, the bonding area between the tab wire, which is a wiring member bonded to the bus bar electrode 21, and the bus bar electrode 21 is increased, and the bonding strength is increased. The tab wires can be prevented or suppressed from peeling off from the bus bar electrode 21.

Preferably, the viscosity of the bus bar electrode forming conductive paste 52 at a temperature of 25 ° C. and a shear rate of 2 s ⁻¹ is such that the finger electrode forming conductive paste for forming the finger electrode 22 has a temperature of 25 ° C. Less than the viscosity at a shear rate of 2 s ⁻¹ . Thereby, when apply | coating to the surface 1a of the semiconductor substrate 1, the conductive paste 52 for bus-bar electrode formation becomes easy to flow compared with the conductive paste for finger electrode formation, and becomes easy to spread. Therefore, it is possible to easily reduce the thickness TH3 (see FIG. 5) of each of the plurality of electrode lines 23 and easily increase the width WD3 (see FIG. 5) of each of the plurality of electrode lines 23 in the Y-axis direction. it can. Therefore, even when the bus bar electrode 21 having the width WD1 larger than the width WD2 of the finger electrode 22 is formed, it is more certain that the thickness TH1 of the bus bar electrode 21 is larger than the thickness TH2 of the finger electrode 22. Can be prevented or suppressed.

  Preferably, the bus bar electrode forming conductive paste 52 and the finger electrode forming conductive paste contain the same type of organic solvent, and the content of the organic solvent in the bus bar electrode forming conductive paste is It is larger than the content of the organic solvent in the electrode forming conductive paste. Thereby, the viscosity of the conductive paste 52 for bus bar electrode formation can be easily reduced as compared with the viscosity of the conductive paste for finger electrode formation.

Specifically, for example, the viscosity of the conductive paste for forming a bus bar electrode at a temperature of 25 ° C. and a shear rate of 2 s ⁻¹ is 0.1 Pa · s to 300 Pa · s, that is, 0.1 to 300 Pa · s. Preferably there is. When the viscosity of the conductive paste for forming a bus bar electrode at a temperature of 25 ° C. and a shear rate of 2 s ⁻¹ is less than 0.1 Pa · s, the conductive paste for forming a bus bar electrode spreads too much, and each of the plurality of electrode wires 23 There is a risk that the uniformity of the shape of the film will be reduced. When the viscosity of the bus bar electrode forming conductive paste at a temperature of 25 ° C. and a shear rate of 2 s ⁻¹ exceeds 300 Pa · s, the bus bar electrode forming conductive paste sufficiently spreads in each of the plurality of electrode wires 23. Therefore, the width WD3 of each of the plurality of electrode lines 23 may not be sufficiently widened.

Or even if it is the conductive paste for bus bar electrode formation with a comparatively large viscosity in a steady state, the shear rate after passing the discharge port 50 is small from the state where the shear rate when passing the discharge port 50 is large. What is necessary is just to have a small speed | rate at which a viscosity increases when changing to a state. Specifically, for example, at a temperature of 25 ° C., the viscosity of the conductive paste for forming a bus bar electrode after 1 second after changing the shear rate from 1000 s ⁻¹ to 2 s ⁻¹ is 300 Pa · s or less. Is preferred. In such a case, the conductive paste for forming the bus bar electrode is discharged through the discharge port 50 and then the surface of the semiconductor substrate 1 until the viscosity increases when reaching the surface 1a of the semiconductor substrate 1. It spreads on 1a. Therefore, the thickness TH3 (see FIG. 5) of each of the plurality of electrode lines 23 can be reduced, and the width WD3 (see FIG. 5) of each of the plurality of electrode lines 23 in the Y-axis direction can be increased.

  Preferably, the interval DS1 as the center-to-center distance in the Y-axis direction of the plurality of discharge ports 50 arranged in the Y-axis direction is larger than the diameter DM1 of the discharge port 50 and 4 of the diameter DM1 of the discharge port 50. Smaller than twice.

  When the interval DS1 is less than or equal to the diameter DM1, the bus bar electrode forming conductive paste 52 discharged from the discharge port 50 is formed from the adjacent discharge port 50 before the bus bar electrode forming conductive paste 52 reaches the surface 1a of the semiconductor substrate 1. There is a risk of bonding with the conductive paste 52. As a result, the discharge amount of the bus bar electrode forming conductive paste 52 varies, and any one of the electrode wires 23 may be disconnected in the middle thereof.

  Further, when the distance DS1 is four times or more the diameter DM1, the area of the semiconductor substrate 1 exposed between the adjacent electrode lines 23 increases. That is, in the region where the bus bar electrode 21 is formed, the coverage of the surface 1a of the semiconductor substrate 1 by the plurality of electrode wires 23 is reduced. As a result, after the solar cell is manufactured, the bonding area between the tab wire and the bus bar electrode 21 is reduced when the tab wire as the wiring member is bonded to the bus bar electrode 21 in the process of manufacturing the solar cell module. As a result, the bonding strength is weakened, and the tab wire may be peeled off from the bus bar electrode 21.

  The aspect ratio (TH3 / WD3), which is the ratio of the thickness TH3 of each of the plurality of electrode lines 23 to the width WD3 of each of the plurality of electrode lines 23 in the Y-axis direction, is the X axis direction of the finger electrode 22 in the X-axis direction. What is necessary is just to be smaller than the aspect ratio (TH2 / WD2) which is the ratio of the thickness TH2 of the finger electrode 22 to the width WD2. Therefore, as described above, the adjacent electrode lines 23 may not be connected to each other, and the surface 1 a of the semiconductor substrate 1 may be exposed between the adjacent electrode lines 23.

  On the other hand, in the step of forming the finger electrode 22, the finger electrode 22 is formed on the surface 1 a side of the semiconductor substrate 1. The finger electrode 22 can be formed using the finger electrode forming apparatus shown in FIG.

  The finger electrode forming device is the same device as the bus bar electrode forming device (see FIGS. 7 to 9). However, in the finger electrode forming apparatus, unlike the bus bar electrode forming apparatus described with reference to FIGS. 7 to 9, the substrate transfer stage 42 transfers the semiconductor substrate 1 held on the substrate mounting table 41 in the Y-axis direction. To do. Although not shown, in the finger electrode forming device, a plurality of discharge ports corresponding to the plurality of discharge ports 50 in the bus bar electrode forming device are arranged in the X-axis direction. In the finger electrode forming apparatus, the intervals as the center-to-center distances in the X-axis direction of the plurality of discharge ports (not shown) arranged in the X-axis direction are the intervals between the plurality of finger electrodes 22 arranged in the X-axis direction. It is equal to the distance DS2 (see FIG. 1) as the distance between the centers.

  Furthermore, in the finger electrode forming apparatus, unlike the bus bar electrode forming apparatus described with reference to FIGS. 7 to 9, the finger electrode forming conductive paste 54 is stored inside the tank 47. The finger electrode forming conductive paste 54 is used to form the finger electrode 22 by applying the finger electrode forming conductive paste onto the surface 1 a of the semiconductor substrate 1.

  In the step of forming the finger electrodes 22, the semiconductor substrate 1 held on the substrate mounting table 41 is transferred in the Y-axis direction by the substrate transfer stage 42. Then, while the semiconductor substrate 1 is transported and the application nozzle 44 is connected to the inside of the tank 47 by the valve 48, the pressure inside the tank 47 is adjusted by the regulator 49 and stored in the tank 47. The finger electrode forming conductive paste 54 is discharged from the coating nozzle 44. In this way, the finger electrode forming conductive paste 54 is applied on the surface 1a of the semiconductor substrate 1 in a linear shape extending in the Y-axis direction within the surface 1a. Thereafter, the finger electrode forming conductive paste 54 is dried, for example, at a temperature of about 200 ° C., and then the finger electrode forming conductive paste 54 is baked at a temperature of, for example, about 800 ° C. By performing these steps, the finger electrode 22 (see FIG. 1) extending in the Y-axis direction within the surface 1a is formed on the surface 1a side of the semiconductor substrate 1.

  In addition, after apply | coating and drying the conductive paste for bus bar electrode formation, before conducting the main baking of the conductive paste for bus bar electrode formation, the conductive paste for finger electrode formation is applied and dried, and then the bus bar electrode The main baking of the forming conductive paste and the main baking of the finger electrode forming conductive paste may be performed in the same step.

  In the first embodiment, as the finger electrode forming conductive paste 54, a base material made of a conductive paste containing a conductive material to which no organic solvent is added can be used. Alternatively, as the finger electrode forming conductive paste 54, a base material made of a conductive paste containing a conductive material and an organic solvent added thereto can be used. Moreover, as a base material which consists of an electrically conductive paste, the same kind of base material as the base material contained in the electrically conductive paste 52 for bus bar electrode formation (refer FIG. 7) can be used. Furthermore, as the organic solvent, an organic solvent of the same type as the organic solvent contained in the bus bar electrode forming conductive paste 52 can be used.

However, preferably, the temperature 25 ° C., and the viscosity of the finger electrode formation conductive paste 54 at a shear rate of ^{2s -1,} the temperature 25 ° C., and a shear rate of ^2s busbar electrode formation conductivity in ^-1 paste 52 Greater than the viscosity of Thereby, when apply | coating to the surface 1a of the semiconductor substrate 1, compared with the conductive paste 52 for bus bar electrode formation, the conductive paste 54 for finger electrode formation becomes difficult to flow, and becomes difficult to spread. Therefore, the finger electrode 22 can be formed with high shape accuracy.

  Further, when the finger electrode forming conductive paste 54 and the bus bar electrode forming conductive paste 52 contain the same type of organic solvent, the content of the organic solvent in the finger electrode forming conductive paste 54 is preferred. Is smaller than the content of the organic solvent in the conductive paste 52 for forming busbar electrodes. Thereby, the viscosity of the conductive paste 54 for finger electrode formation can be easily made larger than the viscosity of the conductive paste 52 for bus bar electrode formation.

  Note that either the step of forming the bus bar electrode 21 or the step of forming the finger electrode 22 may be performed first.

  Next, as shown in FIGS. 2 and 3, the back electrode 3 is formed. The step of forming the back electrode 3 includes a step of forming the bus bar electrode 31 and a step of forming the current collecting electrode 32.

  Among these, in the step of forming the bus bar electrode 31, the bus bar electrode 31 is formed on the back surface 1 b side of the semiconductor substrate 1. For example, the bus bar electrode 31 can be formed using a forming apparatus similar to the bus bar electrode forming apparatus described with reference to FIGS.

  On the other hand, in the step of forming the current collecting electrode 32, the current collecting electrode 32 can be formed on the back surface 1b side of the semiconductor substrate 1 by, for example, a screen printing method. In this way, a solar cell as shown in FIGS. 1 to 3 is formed.

  Note that either the step of forming the bus bar electrode 31 or the step of forming the current collecting electrode 32 may be performed first. Further, any one of the step of forming the front surface electrode 2 and the step of forming the back surface electrode 3 may be performed first.

  Thereafter, a plurality of solar cells as shown in FIGS. 1 to 3 are arranged in a plane, and the bus bar electrode 21 of the surface electrode 2 of a certain solar cell and the bus bar electrode 31 of the back electrode 3 of the solar cell adjacent to the solar cell. Are electrically connected to each other by a tab wire as a wiring member. By such a method, these several solar cells can be connected in series. And a solar cell module is formed by sealing a plurality of solar cells connected in series with a sealing material between two support plates arranged on both sides of the light receiving surface and the opposite side of the light receiving surface. The

<About peeling of bus bar electrode>
In a solar cell, a thin semiconductor substrate that is hard and easily broken, such as a single crystal silicon substrate, is used as a semiconductor substrate included in the solar cell. Therefore, as described in Patent Document 1, when the electrode pattern is formed by screen printing, the semiconductor substrate may be broken by pressing the squeegee against the semiconductor substrate, which decreases the yield of the manufactured solar cell. The manufacturing cost may increase. In addition, it is necessary to periodically clean and replace the screen printing plate on which the pattern corresponding to the electrode pattern is formed, which may increase the manufacturing cost.

  On the other hand, as described in Patent Document 2, when an electrode pattern is formed by, for example, a method of pressurizing a coating liquid that is a conductive paste and ejecting it from an ejection port, the semiconductor substrate included in the solar cell The electrode pattern can be formed without bringing the nozzle into contact with the surface. Therefore, the semiconductor substrate is less likely to crack compared to the case where the electrode pattern is formed by the screen printing method. Further, an increase in manufacturing cost due to cleaning and replacement of consumables such as screen printing plates can be suppressed.

  As described above, the width of the bus bar electrode is larger than the width of the finger electrode. When the bus bar electrode has a large thickness, the bus bar electrode may be peeled off from the semiconductor substrate due to stress generated when the bus bar electrode is contracted after being heat treated. Therefore, by reducing the thickness of the bus bar electrode and reducing the stress generated when the bus bar electrode shrinks after being heat-treated, for example, during the main firing, the bus bar electrode is prevented from peeling from the semiconductor substrate. There is a need. Specifically, in order to prevent the bus bar electrode from being peeled off from the semiconductor substrate, the average thickness of the bus bar electrode needs to be 20 μm or less, for example.

  Here, for example, when the bus bar electrode is formed by a method in which a coating liquid that is a conductive paste is pressurized and discharged from the discharge port, the coating liquid is applied using the nozzle in which the discharge port is formed. At this time, the thickness of the applied coating liquid is approximately the same as the opening width of the discharge port. That is, the thickness of the formed bus bar electrode is approximately the same as the width of the formed bus bar electrode. Therefore, the thickness of the bus bar electrode having a width larger than the width of the finger electrode is larger than the thickness of the finger electrode, and the bus bar electrode is more easily peeled from the semiconductor substrate than the finger electrode.

  Moreover, when forming a solar cell module with a plurality of solar cells, the tab wire and the bus bar electrode are joined using solder. At this time, if unevenness having a large difference between the height position of the concave portion and the height position of the convex portion is formed on the surface of the bus bar electrode, the solder does not wet and spread to the concave portion of the bus bar electrode, and the tab wire and the bus bar electrode The bonding area between the two decreases and the bonding strength decreases. Accordingly, when the solar cell module is manufactured or after the solar cell module is manufactured, there is a possibility that the tab wire is peeled off from the bus bar electrode.

  In particular, when a bus bar electrode having a width larger than the width of the finger electrode is formed, the thickness of the recess is formed on the surface of the bus bar electrode because the thickness of the bus bar electrode is larger than the thickness of the finger electrode. And unevenness having a large difference between the height of the protrusion and the height position of the protrusion is easily formed.

<Main features and effects of the present embodiment>
In the first embodiment, by applying a conductive paste for forming busbar electrodes on the surface 1a of the semiconductor substrate 1, each extends in the X-axis direction within the surface 1a and is arranged in the Y-axis direction. A bus bar electrode 21 including a plurality of electrode lines 23 is formed. Thereby, the thickness TH1 of the bus bar electrode 21 can be reduced to the same level as the thickness TH3 of each of the plurality of electrode lines 23 constituting the bus bar electrode 21.

  The aspect ratio (TH3 / WD3), which is the ratio of the thickness TH3 of each of the plurality of electrode lines 23 to the width WD3 of each of the plurality of electrode lines 23 in the Y-axis direction, is the X-axis direction of the finger electrode 22 It is smaller than the aspect ratio (TH2 / WD2) that is the ratio of the thickness TH2 of the finger electrode 22 to the width WD2. Thereby, the thickness TH3 of each of the plurality of electrode lines 23 can be easily reduced as compared with the thickness TH2 of the finger electrode 22 having the width WD2 smaller than the width WD1 of the bus bar electrode 21. Therefore, even when the bus bar electrode 21 having the width WD1 larger than the width WD2 of the finger electrode 22 is formed, the thickness TH1 of the bus bar electrode 21 is prevented from becoming larger than the thickness TH2 of the finger electrode 22. Can be suppressed. Therefore, the thickness TH1 of the bus bar electrode 21 can be easily reduced, and peeling of the bus bar electrode 21 from the semiconductor substrate 1 can be easily prevented or suppressed. Specifically, the average thickness of the bus bar electrode 21 can be set to 20 μm or less, for example, and peeling of the bus bar electrode 21 from the semiconductor substrate 1 can be easily prevented or suppressed.

  Furthermore, according to the first embodiment, when there is the above-described aspect ratio relationship, the surface of the bus bar electrode 21 is formed with unevenness having a large difference between the height position of the concave portion and the height position of the convex portion. Can be prevented or suppressed. Therefore, when a solar cell module is formed by a plurality of solar cells, even if the tab wire and the bus bar electrode 21 are joined using solder, the solder easily spreads over the entire upper surface of the bus bar electrode 21. The bonding area between the wire and the bus bar electrode 21 increases and the bonding strength increases. Therefore, when the solar cell module is manufactured or after the solar cell module is manufactured, it is possible to prevent or suppress the tab wire from peeling off from the bus bar electrode 21.

  In the first embodiment, it is only necessary that the thickness TH1 of the bus bar electrode 21 can be easily reduced. Therefore, the aspect ratio (TH3 / WD3) that is the ratio of the thickness TH3 of each of the plurality of electrode lines 23 to the width WD3 of each of the plurality of electrode lines 23 in the Y-axis direction is It may not be smaller than the aspect ratio (TH2 / WD2) that is the ratio of the thickness TH2 of the finger electrode 22 to the width WD2. For example, the bus bar electrode forming conductive paste is applied to a plurality of lines extending in the X-axis direction within the surface 1a and arranged at intervals in the Y-axis direction. The plurality of electrode wires 23 may be integrated by flowing and spreading the bus bar electrode forming conductive paste applied to the electrode. Thereafter, the bus bar electrode forming conductive paste is dried, and then the bus bar electrode forming conductive paste is baked to form the bus bar electrode 21 including a plurality of integrated electrode wires 23.

<Example of Embodiment 1>
Next, an example of the bus bar electrode of the surface electrode in the solar cell of the first embodiment will be described in comparison with a comparative example.

  The bus bar electrodes of Examples 1 to 3, which are examples of the first embodiment, were produced in the same manner as the bus bar electrode 21 of the surface electrode 2 in the solar cell described in the first embodiment. Specifically, first, a semiconductor substrate 1 made of a p-type single crystal silicon substrate and having an n-type semiconductor region formed in a portion on the surface 1a side was prepared. Next, a conductive paste for forming a bus bar electrode is applied on the surface 1a which is a light receiving surface of the semiconductor substrate 1 by using the bus bar electrode forming apparatus described with reference to FIGS. 23 was formed. Thereafter, the bus bar electrode forming conductive paste was dried, and then the bus bar electrode forming conductive paste was baked to form a bus bar electrode 21 including a plurality of electrode wires 23.

In Examples 1 to 3, a conductive paste for forming busbar electrodes in which α-terpineol was added as an organic solvent to a silver paste PV16A manufactured by DuPont was used. On the other hand, in the comparative example, the bus bar electrode forming conductive paste to which no organic solvent was added was used for the silver paste PV16A manufactured by DuPont. About the conductive paste for bus bar electrode formation of Examples 1 to 3 and Comparative Example thus adjusted, the viscosity of the conductive paste for bus bar electrode formation at a temperature of 25 ° C. and a shear rate of 2 s ⁻¹ was measured. In the conductive paste for forming busbar electrodes of Examples 1 to 3 and Comparative Example, the content of the silver paste and α-terpineol, and the conductive paste for forming busbar electrodes at a temperature of 25 ° C. and a shear rate of 2 s ⁻¹ The viscosities are shown in Table 1 below. In Table 1, the contents of the silver paste and α-terpineol are shown by mass%.

  Next, the bus bar electrode forming conductive pastes of Examples 1 to 3 and the comparative example are formed on the surface 1a which is the light receiving surface of the semiconductor substrate 1 using the bus bar electrode forming apparatus described with reference to FIGS. Applied. At this time, the distance between the discharge port 50 formed in the coating nozzle 44 and the surface 1a of the semiconductor substrate 1 was 200 μm, and the transport speed of the semiconductor substrate 1 by the substrate transport stage 42 was 250 mm / s. Moreover, the pressure inside the tank 47 in Example 1 is 0.45 MPa, the pressure inside the tank 47 in Example 2 is 0.45 MPa, and the pressure inside the tank 47 in Example 3 is The pressure inside the tank 47 in the comparative example was 0.75 MPa. And in any case of Examples 1-3 and a comparative example, after apply | coating the electrically conductive paste for bus bar electrode formation, the electrically conductive paste for bus bar electrode formation is dried for 10 minutes at the temperature of 200 degreeC, and this baking is carried out. Thus, the bus bar electrode 21 including the plurality of electrode wires 23 was formed.

  Next, the shape of the bus bar electrode 21 formed on the surface 1a side of the semiconductor substrate 1 in Examples 1 to 3 and the comparative example was evaluated using an optical microscope and a stylus step meter. Specifically, the bus bar electrode 21 was observed using an optical microscope. Moreover, the surface shape of the bus bar electrode 21 was measured using a stylus type step meter.

  The photograph which observed the bus-bar electrode 21 of Example 1- Example 3 and the comparative example with the optical microscope is shown in FIGS. FIG. 11 shows a photograph in Example 1, FIG. 12 shows a photograph in Example 2, FIG. 13 shows a photograph in Example 3, and FIG. 14 shows a photograph in a comparative example.

  As shown in FIGS. 11 to 14, in Examples 1 to 3, the width WD <b> 3 (see FIG. 5) of each of the plurality of electrode lines 23 is increased as compared with the comparative example, and between the adjacent electrode lines 23. The area of the exposed semiconductor substrate 1 was reduced. In other words, in Examples 1 to 3, the coverage by the plurality of electrode lines 23 on the surface 1a of the semiconductor substrate 1 increased in the region where the bus bar electrode 21 was formed, as compared with the comparative example. In particular, when the content of α-terpineol is 1.5% by mass or more, that is, in Examples 2 and 3, adjacent electrode wires 23 are connected to each other, and a plurality of electrode wires 23 are integrated and adjacent to each other. The semiconductor substrate 1 was not exposed between the electrode lines 23.

  On the other hand, the graph which measured the shape of the bus-bar electrode 21 of Example 1- Example 3 and a comparative example with the stylus type level difference meter is shown in FIGS. Each of FIGS. 15 to 18 is a direction orthogonal to the direction in which the bus bar electrode 21 extends, that is, each position in the Y-axis direction (see FIG. 1) in each of Examples 1 to 3 and the comparative example. The height of the surface of the bus bar electrode 21 from the surface 1a of the semiconductor substrate 1, that is, the thickness of the bus bar electrode 21 is shown. FIG. 15 shows the result in Example 1, FIG. 16 shows the result in Example 2, FIG. 17 shows the result in Example 3, and FIG. 18 shows the result in the comparative example.

  As shown in FIGS. 15 to 18, in Examples 1 to 3, the thickness TH <b> 3 (see FIG. 5) of each of the plurality of electrode lines 23 is reduced compared to the comparative example, and each of the plurality of electrode lines 23 is reduced. The width WD3 (see FIG. 5) in the Y-axis direction has increased. When the content of α-terpineol is 1% by mass or more, that is, in Examples 1 to 3, adjacent electrode wires 23 are connected to each other. In addition, when the content of α-terpineol is 1% by mass or more, that is, in Examples 1 to 3, the connection is a portion where adjacent electrode wires 23 are connected to each other as the content of α-terpineol increases. The thickness of the part increased. The thickness of the connecting portion, which is a portion where the adjacent electrode lines 23 are connected to each other, is the minimum thickness TH12 of the portion other than the outer peripheral portion of the bus bar electrode 21 (see FIG. 5). As a result, in Examples 1 to 3, the difference between the maximum thickness TH11 (see FIG. 5) and the minimum thickness TH12 (see FIG. 5) of the bus bar electrode 21 was smaller than in the comparative example. That is, in Examples 1 to 3, the ratio of the minimum thickness TH12 to the maximum thickness TH11 of the bus bar electrode was larger than that in the comparative example.

(Embodiment 2)
Next, in Embodiment 2, an example in which the conductive paste for forming a bus bar electrode contains a plurality of particles made of a material that softens or melts at a temperature higher than room temperature will be described.

<Configuration of solar cell>
About the structure of the solar cell of this Embodiment 2, it is the same as that of the structure of the solar cell of Embodiment 1 mentioned above using FIGS. 1-3, The description is abbreviate | omitted.

<Configuration of bus bar electrode>
The configuration of the bus bar electrode according to the second embodiment is the same as the configuration of the bus bar electrode according to the first embodiment described above with reference to FIGS.

<Method for manufacturing solar cell>
Next, the manufacturing method of the solar cell of Embodiment 2 is demonstrated. The method for manufacturing the solar cell according to the second embodiment will be described with reference to FIGS. 1 to 3 and FIGS. 7 to 9 used to describe the method for manufacturing the solar cell according to the first embodiment.

  First, the semiconductor substrate 1 is prepared. The step of preparing the semiconductor substrate 1 can be the same as the step of preparing the semiconductor substrate 1 described with reference to FIG. 3 in the solar cell manufacturing method of the first embodiment.

  Next, the surface electrode 2 is formed. The step of forming the surface electrode 2 is a step of forming the bus bar electrode 21 in the same manner as the step of forming the surface electrode 2 described with reference to FIGS. 1 and 3 in the method for manufacturing the solar cell of the first embodiment. And a step of forming the finger electrode 22.

  Among these, in the step of forming the bus bar electrode 21, the bus bar electrode 21 is formed on the surface 1 a side of the semiconductor substrate 1. Also, in the solar cell manufacturing method of the second embodiment, the same bus bar electrode forming apparatus as that described with reference to FIGS. 7 to 9 in the solar cell manufacturing method of the first embodiment is used. The bus bar electrode 21 can be formed by using this. In this case, the semiconductor substrate 1 held on the substrate mounting table 41 is transported in the X-axis direction by the substrate transport stage 42. Then, while the semiconductor substrate 1 is transported and the coating nozzle 44 is connected to the inside of the tank 47 by the valve 48, the pressure inside the tank 47 is adjusted by the regulator 49 and stored in the tank 47. The bus bar electrode forming conductive paste 52 is discharged from the application nozzle 44. In this way, the bus bar electrode-forming conductive paste 52 is arranged on the surface 1a of the semiconductor substrate 1 so as to extend in the X-axis direction within the surface 1a and at intervals in the Y-axis direction. Apply in multiple lines. As a result, a plurality of electrode lines 23 are formed on the surface 1a side of the semiconductor substrate 1 so as to extend in the X-axis direction within the surface 1a and are arranged at intervals in the Y-axis direction. Thereafter, the bus bar electrode forming conductive paste 52 is dried, for example, at a temperature of about 200 ° C., and then the bus bar electrode forming conductive paste 52 is baked at a temperature of, eg, about 800 ° C. By performing these steps, a bus bar electrode 21 (see FIGS. 4 and 5) including a plurality of electrode lines 23 is formed.

  In the second embodiment, unlike the first embodiment, the bus bar electrode forming conductive paste 52 is softened or melted at a temperature T1 higher than room temperature on a base material made of a conductive paste containing a conductive material. What added the some particle | grains which consist of material can be used.

  As the conductive material contained in the substrate, for example, silver, copper, aluminum, gold, platinum, or the like can be used. Thereby, the conductivity of the bus bar electrode 21 can be improved.

  The material that is softened or melted at a temperature T1 higher than room temperature is softened or melted when the semiconductor substrate 1 is subjected to a heat treatment, for example, in the main baking after the bus bar electrode forming conductive paste is applied to form the plurality of electrode wires 23. Any material that melts, flows and spreads and can change the shape of each of the plurality of electrode wires 23 may be used. As such a material that softens or melts at a temperature T1 higher than room temperature, a thermoplastic material that softens at a temperature T1 can be used. As the thermoplastic material that softens at the temperature T1, for example, an acrylic resin such as poly (methyl methacrylate) (PMMA), a thermoplastic resin such as polypropylene, polycarbonate, or polyethylene terephthalate is used. it can.

  Alternatively, as a material that softens or melts at a temperature T1 higher than room temperature, an insulating material that melts at a temperature T1 can be used. As an insulating material that melts at this temperature T1, tin phosphate glass that is glass containing tin phosphate, bismuth glass that is glass containing bismuth, borosilicate glass, zinc glass that is glass containing zinc, Alternatively, low melting point glass such as lead glass can be used.

  Alternatively, as a material that softens or melts at a temperature T1 higher than room temperature, a conductive material that melts at a temperature T1 can be used. This conductive material is a conductive material different from the conductive material contained in the base material. As the conductive material that melts at this temperature T1, a metal having a melting point lower than 600 ° C., such as a tin-based solder that is a solder containing tin or a lead-based solder containing lead, can be used. Thereby, the conductivity of the bus bar electrode 21 can be improved as compared with the case where the material that melts at the temperature T1 is not a conductive material but an insulating material.

  In the second embodiment, in the step of forming the bus bar electrode 21, first, as in the first embodiment, by applying a conductive paste for bus bar electrode formation onto the surface 1 a of the semiconductor substrate 1, the inner surface 1 a A plurality of electrode lines 23 extending in the X-axis direction and arranged in the Y-axis direction are formed.

  Thereafter, the bus bar electrode forming conductive paste is dried, for example, at a temperature of about 200 ° C., and then the bus bar electrode forming conductive paste is baked at a temperature of, eg, about 800 ° C. Assuming that the temperature at which the bus bar electrode forming conductive paste is finally fired is temperature T2, in the second embodiment, after forming the plurality of electrode wires 23, the semiconductor substrate 1 is heat-treated at a temperature T2 higher than the temperature T1. It will be. By this heat treatment, the bus bar electrode forming conductive paste is caused to flow in each of the plurality of electrode lines 23, the width WD 3 of each of the plurality of electrode lines 23 is expanded, and the width WD 3 is expanded from each of the plurality of electrode lines 23. A bus bar electrode 21 is formed.

  In addition, before the step of firing the conductive paste for forming busbar electrodes, a heat treatment for flowing the conductive paste for forming busbar electrodes is performed separately from the step of firing the conductive paste for forming busbar electrodes. Also good.

  Here, as the conductive paste for finger electrode formation, a material in which a plurality of particles made of a material that softens or melts at a temperature higher than room temperature is added to a base material made of a conductive paste containing a conductive material is used. May be. However, for example, the content of a material that softens or melts at a temperature higher than room temperature in the finger electrode forming conductive paste is softened or melted at a temperature T1 in the bus bar electrode forming conductive paste that is higher than room temperature. It can be made smaller than the content of the material. Thereby, for example, after the conductive paste for forming the bus bar electrode is dried at a temperature of about 200 ° C., for example, the conductive paste for forming the bus bar electrode is finally baked at a temperature of about 800 ° C. Compared with the conductive paste for finger electrode formation, the paste can be easily flowed and can be easily spread.

  Therefore, also in the second embodiment, as in the first embodiment, the ratio of the thickness TH3 of each of the plurality of electrode lines 23 to the width WD3 of each of the plurality of electrode lines 23 in the Y-axis direction is the finger electrode. 22 is smaller than the ratio of the thickness TH2 of the finger electrode 22 to the width WD2 in the X-axis direction. Accordingly, even when the bus bar electrode 21 having the width WD1 larger than the width WD2 of the finger electrode 22 is formed, the thickness TH1 of the bus bar electrode 21 is prevented from becoming larger than the thickness TH2 of the finger electrode 22. Or it can be suppressed. Therefore, the thickness TH1 of the bus bar electrode 21 can be easily reduced, and peeling of the bus bar electrode 21 from the semiconductor substrate 1 can be easily prevented or suppressed.

  Also, in the case of the above-described aspect ratio, the difference between the height position of the concave portion and the height position of the convex portion on the surface of the bus bar electrode 21 is also the same as in the first embodiment. Can be prevented or suppressed. Therefore, when a solar cell module is formed by a plurality of solar cells, even if the tab wire and the bus bar electrode 21 are joined using solder, the solder easily spreads over the entire upper surface of the bus bar electrode 21. The bonding area between the wire and the bus bar electrode 21 increases and the bonding strength increases. Therefore, when the solar cell module is manufactured or after the solar cell module is manufactured, it is possible to prevent or suppress the tab wire from peeling off from the bus bar electrode 21.

  Further, in the second embodiment, after forming the plurality of electrode wires 23, for example, when heat treatment is performed in the main firing, the bus bar electrode forming conductive paste is caused to flow in each of the plurality of electrode wires 23 to thereby form the plurality of electrodes. The width WD3 of each line 23 can be increased. Therefore, when forming the plurality of electrode lines 23, the bus bar electrode forming conductive paste is flowed to form the plurality of electrode lines 23 with higher shape accuracy than when the width WD3 of each of the plurality of electrode lines 23 is increased. can do.

  Preferably, in the conductive paste for forming a bus bar electrode, the content of a plurality of particles made of a material that softens or melts at a temperature T1 higher than room temperature is 1 to 50% by mass. When the content of the plurality of particles is less than 1% by mass, the bus bar electrode forming conductive paste is formed in each of the plurality of electrode lines 23 when, for example, heat treatment is performed in the main baking after the plurality of electrode lines 23 are formed. There is a possibility that the width WD3 of each of the plurality of electrode lines 23 is not sufficiently widened. On the other hand, when the content of the plurality of particles exceeds 50% by mass, after forming the plurality of electrode wires 23, for example, when heat treatment is performed in the main firing, each of the plurality of electrode wires 23 has a bus bar electrode forming conductivity. There is a possibility that the paste spreads too much and the uniformity of the shape of each of the plurality of electrode wires 23 after the heat treatment is lowered.

  More preferably, when the conductive paste for forming a bus bar electrode contains a plurality of particles made of a material that is a thermoplastic resin that softens at a temperature T1, the thermoplastic material softens at a temperature T1 that is higher than room temperature, In addition, the material burns at a temperature T2 higher than the temperature T1. In such a case, for example, by heat-treating the semiconductor substrate 1 at the temperature T2 in the main firing, the plurality of particles made of the thermoplastic resin contained in the conductive paste for forming the bus bar electrode are softened, and the plurality of electrode wires After the width WD3 of each of 23 is expanded, a plurality of particles made of a thermoplastic material are burned and removed. Then, the bus bar electrode 21 including the plurality of electrode wires 23 in which the width WD3 is expanded and the plurality of particles made of the thermoplastic material are removed is formed. Thereby, the several particle | grains which consist of the thermoplastic material contained in the electrically conductive paste for bus-bar electrode formation do not remain after heat processing, such as this baking, for example. Therefore, the conductivity of the bus bar electrode 21 to be formed is improved to the same degree as the conductivity of the bus bar electrode 21 formed by applying a bus bar electrode forming conductive paste not containing a thermoplastic material. Can do.

  On the other hand, the process of forming the finger electrode 22 can be made the same as the process of forming the finger electrode 22 in the solar cell manufacturing method of the first embodiment. In addition, after apply | coating and drying the conductive paste for bus bar electrode formation, before conducting the main baking of the conductive paste for bus bar electrode formation, the conductive paste for finger electrode formation is applied and dried, and then the bus bar electrode The main baking of the forming conductive paste and the main baking of the finger electrode forming conductive paste may be performed in the same step. Further, any one of the step of forming the bus bar electrode 21 and the step of forming the finger electrode 22 may be performed first.

  Next, the back electrode 3 is formed. The step of forming the back electrode 3 can be the same as the step of forming the back electrode 3 described with reference to FIGS. 2 and 3 in the method for manufacturing the solar cell of the first embodiment. In this way, a solar cell as shown in FIGS. 1 to 3 is formed. Then, similarly to Embodiment 1, a solar cell module can be formed by connecting a plurality of solar cells in series.

<Main features and effects of the present embodiment>
Also in the second embodiment, as in the first embodiment, by applying the conductive paste for forming the bus bar electrode on the surface 1a of the semiconductor substrate 1, each extends in the X-axis direction within the surface 1a, and A bus bar electrode 21 composed of a plurality of electrode lines 23 arranged in the Y-axis direction is formed. The aspect ratio (TH3 / WD3), which is the ratio of the thickness TH3 of each of the plurality of electrode lines 23 to the width WD3 of each of the plurality of electrode lines 23 in the Y-axis direction, is the X axis direction of the finger electrode 22 in the X-axis direction. It is smaller than the aspect ratio (TH2 / WD2) that is the ratio of the thickness TH2 of the finger electrode 22 to the width WD2.

  As a result, as in the first embodiment, the thickness TH3 of each of the plurality of electrode lines 23 is easily made smaller than the thickness TH2 of the finger electrode 22 having the width WD2 smaller than the width WD1 of the bus bar electrode 21. can do. Therefore, similarly to the first embodiment, the thickness TH1 of the bus bar electrode 21 can be easily reduced, and peeling of the bus bar electrode 21 from the semiconductor substrate 1 can be easily prevented or suppressed.

  Also in the second embodiment, as in the first embodiment, when there is a magnitude relationship of the aspect ratio as described above, the difference between the height position of the concave portion and the height position of the convex portion on the surface of the bus bar electrode 21 It is possible to prevent or suppress the formation of large irregularities. Therefore, when a solar cell module is formed by a plurality of solar cells, even if the tab wire and the bus bar electrode 21 are joined using solder, the solder easily spreads over the entire upper surface of the bus bar electrode 21. The bonding area between the wire and the bus bar electrode 21 increases and the bonding strength increases. Therefore, when the solar cell module is manufactured or after the solar cell module is manufactured, it is possible to prevent or suppress the tab wire from peeling off from the bus bar electrode 21.

  Furthermore, in the second embodiment, the bus bar electrode forming conductive paste contains particles made of a material that softens or melts at a temperature T1 higher than room temperature. Thus, after forming the plurality of electrode lines 23, for example, when heat treatment is performed in the main baking, the bus bar electrode forming conductive paste is caused to flow in each of the plurality of electrode lines 23, and the width of each of the plurality of electrode lines 23 is determined. Each WD3 can be expanded. For example, the amount by which the width WD3 of each of the plurality of electrode wires 23 is increased can be accurately controlled by controlling the rate of temperature rise during heat treatment in the main firing. Therefore, when forming the plurality of electrode lines 23, the bus bar electrode forming conductive paste is flowed to form the plurality of electrode lines 23 with higher shape accuracy than when the width WD3 of each of the plurality of electrode lines 23 is increased. be able to.

  In the second embodiment, it is sufficient that the thickness TH1 of the bus bar electrode 21 can be easily reduced as in the first embodiment. Therefore, the aspect ratio (TH3 / WD3) that is the ratio of the thickness TH3 of each of the plurality of electrode lines 23 to the width WD3 of each of the plurality of electrode lines 23 in the Y-axis direction is It may not be smaller than the aspect ratio (TH2 / WD2) that is the ratio of the thickness TH2 of the finger electrode 22 to the width WD2. For example, the conductive paste for forming bus bar electrodes is applied in a plurality of lines extending in the X-axis direction within the surface 1a and arranged at intervals in the Y-axis direction, and dried. The plurality of electrode wires 23 may be integrated only by heat-treating during the main firing and flowing and spreading the bus bar electrode-forming conductive paste applied in a plurality of lines. At this time, a bus bar electrode 21 composed of a plurality of integrated electrode wires 23 is formed.

<Example of Embodiment 2>
Next, examples of the bus bar electrode of the surface electrode in the solar cell of the second embodiment will be described.

  The bus bar electrode of Example 4, which is an example of the second embodiment, was produced in the same manner as the bus bar electrode 21 of the surface electrode 2 in the solar cell described in the second embodiment. Specifically, first, a semiconductor substrate 1 made of a p-type single crystal silicon substrate and having an n-type semiconductor region formed in a portion on the surface 1a side was prepared. Next, a conductive paste for forming a bus bar electrode is applied on the surface 1a which is a light receiving surface of the semiconductor substrate 1 by using the bus bar electrode forming apparatus described with reference to FIGS. 23 was formed. Thereafter, the conductive paste for bus bar electrode formation is dried, and then the conductive paste for bus bar electrode formation is heat treated in the main firing, and the conductive paste for bus bar electrode formation is made to flow, thereby comprising a plurality of electrode wires 23. A bus bar electrode 21 was formed.

  In Example 4, a plurality of particles made of an acrylic resin were used as the plurality of particles made of a thermoplastic material. And the conductive paste for bus-bar electrode formation in which the bridge | crosslinking PMMA type | system | group fine particle FH-S005 by Toyobo Co., Ltd. was added to silver paste PV16A by DuPont as a particle | grain made from an acrylic resin was used.

  Next, a bus bar electrode 21 composed of a plurality of electrode wires 23 was formed under the same conditions as in Example 1 of the first embodiment. However, unlike Example 1, Example 4 differs from Example 1 in that the semiconductor substrate 1 is applied at a temperature at which the acrylic resin burns when the semiconductor substrate 1 is heat-treated in the main firing after being applied and dried. 1 was heat treated. Therefore, in Example 4, when the semiconductor substrate 1 is heat-treated in the main baking, the plurality of particles made of acrylic resin are softened to increase the width WD3 of each of the plurality of electrode lines 23, and then the plurality of pieces made of acrylic resin. The particles were removed by burning.

  As a result, also in Example 4, as in Examples 1 to 3 of the first embodiment, each width WD3 (see FIG. 5) of each of the plurality of electrode lines 23 is larger than that of the comparative example described in the first embodiment. As a result, the area of the semiconductor substrate 1 exposed between adjacent electrode lines 23 decreased. Further, in Example 4, as in Examples 1 to 3 of the first embodiment, each thickness TH3 (see FIG. 5) of each of the plurality of electrode lines 23 is smaller than that of the comparative example described in the first embodiment. As a result, the width WD3 (see FIG. 5) in the Y-axis direction of each of the plurality of electrode lines 23 increased.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  The present invention is effective when applied to a solar cell manufacturing method and a solar cell.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 1a Front surface 1b Back surface 2 Front surface electrode 3 Back surface electrodes 11 and 12 Semiconductor area | region 21 Bus bar electrode 22 Finger electrode 23 Electrode line 31 Bus bar electrode 32 Current collection electrode 41 Substrate mounting stage 42 Substrate conveyance stage 43 Application part 44 Application nozzle 45 Nozzle Lifting stage 46 Nozzle support frame 47 Tank 48 Valve 49 Regulator 50 Discharge port 51, 53 Piping 52 Conductive paste for bus bar electrode formation 54 Conductive paste for finger electrode formation DM1 Diameter DS1, DS2 Distance TH1-TH3 Thickness TH11 Maximum thickness TH12 Minimum thickness WD1 to WD3 Width

Claims (15)

(A) preparing a semiconductor substrate;
(B) forming a bus bar electrode on the first main surface side of the semiconductor substrate;
(C) forming a finger electrode on the first main surface side of the semiconductor substrate;
Have
The bus bar electrode and the finger electrode are electrically connected to each other,
In the step (b), a first conductive paste is applied on the first main surface of the semiconductor substrate, thereby extending in the first direction within the first main surface, and the first Forming the bus bar electrode comprising a plurality of electrode lines arranged in a second direction intersecting the direction,
In the step (c), the finger electrode extending in the second direction within the first main surface is formed by applying a second conductive paste on the first main surface of the semiconductor substrate. ,
The ratio of the first thickness of each of the plurality of electrode lines to the first width of each of the plurality of electrode lines in the second direction is the finger with respect to the second width of the finger electrode in the first direction. The manufacturing method of a solar cell smaller than ratio of the 2nd thickness of an electrode. In the manufacturing method of the solar cell of Claim 1,
Temperature 25 ° C., and the viscosity of the first conductive paste, temperature 25 ° C., and less than the viscosity of said second conductive paste at a shear rate of 2s ^-1, the manufacture of solar cells at a shear rate of 2s ^-1 Method. In the manufacturing method of the solar cell of Claim 2,
The method for manufacturing a solar cell, wherein the viscosity of the first conductive paste at a temperature of 25 ° C. and a shear rate of 2 s ⁻¹ is 300 Pa · s or less. In the manufacturing method of the solar cell of Claim 2,
The first conductive paste contains a first organic solvent,
The second conductive paste contains a second organic solvent of the same type as the first organic solvent,
The method for manufacturing a solar cell, wherein the content of the first organic solvent in the first conductive paste is larger than the content of the second organic solvent in the second conductive paste. In the manufacturing method of the solar cell of Claim 2,
The method for producing a solar cell, wherein the viscosity of the first conductive paste is 300 Pa · s or less after 1 second from changing the shear rate from 1000 s ⁻¹ to 2 s ^{−1 at a} temperature of 25 ° C. In the manufacturing method of the solar cell of Claim 1,
The first conductive paste contains a plurality of first particles made of a first material that softens or melts at a first temperature higher than room temperature,
The step (b)
(B1) forming the plurality of electrode lines by applying the first conductive paste on the first main surface of the semiconductor substrate;
(B2) After the step (b1), by heat-treating the semiconductor substrate at a second temperature higher than the first temperature, the first width of each of the plurality of electrode lines is expanded, and the first Forming the bus bar electrode comprising the plurality of electrode lines each having a widened width;
A method for manufacturing a solar cell, comprising: In the manufacturing method of the solar cell of Claim 6,
The first conductive paste contains the plurality of first particles made of the first material, which is a thermoplastic material that softens at the first temperature,
The first material burns at the second temperature;
In the step (b2), the semiconductor substrate is heat-treated at the second temperature to increase the first width of each of the plurality of electrode lines, and then burn and remove the plurality of first particles. A method for manufacturing a solar cell. In the manufacturing method of the solar cell of Claim 7,
The method for manufacturing a solar cell, wherein the first material is made of an acrylic resin. In the manufacturing method of the solar cell of Claim 6,
The method for manufacturing a solar cell, wherein the first conductive paste contains the plurality of first particles made of the first material that is a conductive material that melts at the first temperature. In the manufacturing method of the solar cell of Claim 1,
In the step (b), the first conductive paste is extended in the first direction within the first main surface, and is arranged in a plurality of lines arranged at intervals in the second direction. And then spreading the first conductive paste applied in a plurality of lines to unify the plurality of electrode lines to form the bus bar electrode comprising the plurality of integrated electrode lines. A method for manufacturing a solar cell. In the manufacturing method of the solar cell of Claim 1,
The method for manufacturing a solar cell, wherein a third width of the bus bar electrode in the second direction is larger than the second width of the finger electrode. A semiconductor substrate;
A bus bar electrode formed on the first main surface side of the semiconductor substrate;
Finger electrodes formed on the first main surface side of the semiconductor substrate;
Have
The bus bar electrode and the finger electrode are electrically connected to each other,
The bus bar electrode includes a plurality of electrode lines extending in the first direction in the first main surface and arranged in a second direction intersecting the first direction,
The finger electrode extends in the second direction within the first main surface,
The ratio of the first thickness of each of the plurality of electrode lines to the first width of each of the plurality of electrode lines in the second direction is the finger with respect to the second width of the finger electrode in the first direction. A solar cell smaller than the ratio of the second thickness of the electrodes. The solar cell according to claim 12, wherein
In the region where the bus bar electrode is formed, a solar cell in which the coverage of the first main surface of the semiconductor substrate by the plurality of electrode wires is 90% or more. The solar cell according to claim 12, wherein
The plurality of electrode wires are integrated,
The bus bar electrode is composed of the plurality of integrated electrode wires,
A solar cell in which a ratio of a minimum thickness of a portion other than an outer peripheral portion of the bus bar electrode to a maximum thickness of the bus bar electrode is larger than 0.2. The bus bar electrode is formed in a solar cell having a semiconductor substrate, a bus bar electrode formed on the first main surface side of the semiconductor substrate, and a finger electrode formed on the first main surface side of the semiconductor substrate. A conductive paste for forming a bus bar electrode used to
The bus bar electrode and the finger electrode are electrically connected to each other,
The bus bar electrode includes a plurality of electrode lines extending in the first direction in the first main surface and arranged in a second direction intersecting the first direction,
The finger electrode extends in the second direction within the first main surface,
The bus bar electrode forming conductive paste is formed on the first main surface of the semiconductor substrate by applying the bus bar electrode forming conductive paste to form the bus bar electrode including the plurality of electrode lines. Used for
The ratio of the first thickness of each of the plurality of electrode lines to the first width of each of the plurality of electrode lines in the second direction is the finger with respect to the second width of the finger electrode in the first direction. Smaller than the ratio of the second thickness of the electrodes,
The finger electrode is formed on the first main surface of the semiconductor substrate by applying a finger electrode forming conductive paste;
Temperature 25 ° C., and the viscosity of the bus bar electrode formation conductive paste at a shear rate of 2s ^-1, the temperature 25 ° C., and less than the viscosity of the finger electrode formation conductive paste at a shear rate of 2s ^-1, Conductive paste for busbar electrode formation.