JP5920130B2 - Manufacturing method of solar cell - Google Patents

Description

The present invention relates to how to produce good productivity solar cells with high long term reliability, more particularly by changing the mask pattern of the light-receiving surface electrode, without increasing the cost, the high conversion efficiency solar cells about the method capable of forming electrodes.

  As shown in FIG. 1 to FIG. 3, a general solar battery cell manufactured using a conventional technique diffuses an n-type dopant into a p-type semiconductor substrate 100 b such as silicon to form an n-type. By forming the diffusion layer 101, a pn junction is formed. On the n-type diffusion layer 101, an antireflection film 102 such as a SiNx film is formed. Also, an aluminum paste is applied to almost the entire surface on the back surface side (lower side in FIG. 1) of the p-type semiconductor substrate 100b, and a BSF (Back Surface Field) layer 103 and an aluminum electrode 104 are formed by baking. Furthermore, a conductive paste containing silver or the like is applied to the back surface as a thick electrode 106 called a bus bar electrode for current collection, and is formed by baking. On the other hand, on the light receiving surface side (upper side in FIG. 1, on the antireflection film 102), thick electrodes called a current collecting finger electrode 107 and a bus bar electrode 105 formed to collect current from the finger electrode are substantially. They are arranged in a comb shape so as to intersect at right angles.

  Here, the contact resistance (contact resistance) between the finger electrode 107 on the surface and the semiconductor substrate 100 and the wiring resistance of the electrode have a great influence on the conversion efficiency of the solar cell, and high efficiency (low cell series resistance, high fill factor FF). In order to obtain (curve factor)), the contact resistance and the wiring resistance value of the finger electrode 107 are required to be sufficiently low. In addition, the electrode area must be reduced on the light receiving surface of the solar cell so as to capture as much light as possible. In order to improve the short circuit current (Jsc) while maintaining such a high FF, as the finger electrode 107, an electrode having a narrow electrode line width and a large cross-sectional area, that is, a high aspect ratio electrode must be formed. Don't be.

  Examples of methods for forming electrodes for solar cells include vapor deposition, plating, printing, etc. As a method for forming a high aspect ratio, ultrafine wire, a method of forming grooves in cells and filling with paste (special Japanese Laid-Open Patent Publication No. 2006-54374 (Patent Document 1) and a printing method using an inkjet method are disclosed. However, since the former includes a step of forming a groove in the substrate, it is not preferable because it may damage the substrate. The latter ink-jet method is a method suitable for forming a thin line because it applies a pressure to eject droplets from a thin nozzle, but it is difficult to increase the height.

  On the other hand, the screen printing method is easy to create a printing pattern, can minimize damage to the substrate by adjusting the printing pressure, has a high working speed per cell, is low cost, and has excellent productivity. By using a conductive paste having high thixotropy, the shape can be maintained even after the transfer, and an electrode having a high aspect ratio can be formed.

That is, in the screen printing method, as shown in FIG. 4, a printing paste (not shown) filled in the pattern opening 409 c on the screen plate making 409 is transferred to the printing material by the movement of the spatula squeegee 408. In this way, the same pattern as the pattern opening 409c formed in the screen plate making 409 shown in FIG. 5A is formed on the printed material. Further, as the surface electrode material, generally, a conductive paste containing silver powder, glass frit, organic vehicle, and organic solvent as main components is used, and after applying this conductive paste by the screen printing method The surface electrode is formed by high-temperature sintering in a firing furnace. By using a highly thixotropic conductive paste, the shape is maintained even after coating on the substrate, and a high aspect ratio electrode can be formed. .
As described above, the screen printing method is cheaper than other printing methods and is a method suitable for forming a high aspect ratio electrode.

  However, when fine lines are printed using the screen printing method, the finger electrode ends are easily peeled off, resulting in a problem that the conversion efficiency is lowered. The cause is due to insufficient discharge amount at the finger electrode ends. That is, in a screen printing machine that moves a squeegee for printing, the squeegee starts to rise as soon as the squeegee moves to the end of the finger electrode and the printing operation ends. In other words, the time during which the squeegee presses the screen plate making is shorter than the other portions, so that the contact time between the screen plate making and the printing material cannot be sufficiently obtained, and the discharge amount becomes small.

  Here, since the main component of the conductive paste is metal, when the electrode in such a coated state is sintered at high temperature, the shrinkage amount of the portion with a large coating amount is large, and the portion with a small coating amount is a portion with a large coating amount. As a result, the electrode floats and a gap is formed between the semiconductor substrate and the electrode. The finger electrode that has become easy to peel off due to this gap can not withstand changes in temperature and humidity when the solar cell is exposed to the outdoor environment, and the finger electrode comes to peel from the end, The generated electricity could not be taken out and the conversion efficiency was lowered.

  In order to solve such a problem, a method as described in JP 2006-324504 A (Patent Document 2) has been proposed. This increases the electrode width (area) at the end of the finger electrode 107 'to increase the adhesion area and increase the adhesion strength (FIG. 6). However, in this method, peeling from the end of the finger electrode is not caused, but after a temperature history such as a temperature cycle test, one of the plurality of finger electrodes 107 ′ is shown as shown in a region B in FIG. Disconnection occurred in the finger electrode 107 ′ of the part, and the current generated in the solar cell in that region B could not be taken out, resulting in a problem that the output was reduced.

  In order to solve the above problem, Japanese Patent Laid-Open No. 2010-239167 (Patent Document 3) proposes a method of connecting the ends of the finger electrodes 107 with a linear auxiliary electrode 108 ′ (FIG. 7). . According to this method, the finger electrode 107 is not peeled off from the end portion, and even if a plurality of finger electrodes 107 are disconnected as shown in the region C, the other finger passes through the auxiliary electrode 108 ′. It is possible to take out the current generated in the solar cell from the electrode 107.

  However, this method has problems such as a decrease in the light receiving area due to blurring of the printed pattern by screen printing on the auxiliary electrode and its surroundings, disconnection of the electrode, and formation of finely patterned electrodes. This occurs because of the following.

  That is, in a method of printing solar cell electrodes by screen printing, generally, finger electrodes, bus bar electrodes, and auxiliary electrodes are printed simultaneously in order to reduce the number of steps of solar cells. The squeegee is moved so that the longitudinal direction of the finger electrode is parallel to the printing direction (squeegee moving direction) in order to print the electrodes and the like in a straight line without unevenness or disconnection on a thin line. At this time, since the longitudinal direction of the bus bar electrode and the auxiliary electrode becomes perpendicular to the printing direction, the paste tends to bleed and thicken in the direction of the end of printing, thereby reducing the light receiving area and the sun. The aesthetics of the battery began to be damaged. Further, as described above, the pattern opening in which the longitudinal direction is a fine line perpendicular to the printing direction has a tendency that the paste is difficult to be ejected, and the print pattern tends to be blurred or disconnected.

  Furthermore, while printing is repeatedly performed using the same screen plate making, the plate film (emulsion layer) 409b of the screen plate making 409 corresponding to the finger electrode ends is gradually peeled off, and the opening shape of the pattern opening 409c is broken. As a result, there is a problem that it becomes impossible to form electrodes with fine patterns. Specifically, in the screen plate making 409 near the end of the finger electrode (region A) for forming the conventional electrode pattern (FIG. 2), as shown in FIG. 5B, the plate film (emulsion layer) 409b is the finger electrode. Since the area outside the edge and the area between the finger electrodes are connected together and firmly adhered to the mesh material, it does not peel off even by repeated printing, but the edges of the finger electrodes 107 are linearly auxiliary. In the screen plate making 409 in the vicinity of the finger electrode end portion (region D) of the electrode pattern (FIG. 7) connected by the electrode 108 ′, as shown in FIG. 8, the plate film (emulsion layer) in the region outside the end portion of the finger electrode ) The plate film (emulsion layer) 409b2 in the region between 409b1 and the finger electrode is isolated in an island shape without being connected, and the area to be bonded to each mesh material 409a is small. Since there are many portions that are corners, particularly at right angles to the printing direction, hard portions with metal parts of the conductive paste and irregularities of the semiconductor substrate are used in the screen printing (emulsion layers) 409b1, 409b2. , The emulsion peeled off from the corners of the plate films (emulsion layers) 409b1 and 409b2, and the opening shape of the pattern opening 409c was broken.

JP 2006-54374 A JP 2006-324504 A JP 2010-239167 A

The present invention has been made in view of the above circumstances. Even when screen cells are repeatedly screen-printed when producing a solar cell with high conversion efficiency and low output loss even when part of the finger electrode is disconnected, the disconnection and shape are not lost. Kyosu Hisage manufacturing how capable of forming an electrode for the purpose of Rukoto.

The present invention, in order to achieve the above object, to provide a manufacturing how a solar cell below.
[1] A semiconductor substrate on which at least a pn junction is formed, a plurality of finger electrodes formed in a comb shape on at least one surface of the semiconductor substrate, and disposed perpendicular to the longitudinal direction of the finger electrodes. A bus bar electrode connected to a portion other than the end portion of the finger electrode, and at least a portion of adjacent finger electrodes of the finger electrodes that are adjacent to each other or projecting outward in the longitudinal direction of the finger electrode A method of manufacturing a solar cell comprising an arcuate or chevron-shaped auxiliary electrode comprising a mesh material and a plate film coated on the mesh material by a screen printing method. The finger electrode pattern opening and the portion other than the end of the finger electrode pattern opening are arranged orthogonal to the longitudinal direction of the finger electrode pattern opening. The bus bar electrode pattern opening and the finger electrode pattern opening that connects at least a part of the adjacent finger electrode pattern opening ends of the finger electrode pattern opening to the outside in the longitudinal direction of the finger electrode pattern opening A conductive paste is printed on the semiconductor substrate using a screen plate having a convex arc-shaped or chevron-shaped auxiliary electrode pattern opening, and the finger electrode, bus bar electrode, and auxiliary electrode are simultaneously formed. A method for manufacturing a solar cell.
[2] The method for manufacturing a solar cell according to [1], wherein the plate film is made of a photosensitive emulsion.
[3] The method for producing a solar cell according to [1] or [2], wherein a printing direction is parallel to a longitudinal direction of the finger electrode .

  According to the present invention, among the finger electrodes, by providing the auxiliary electrode that connects at least some of the adjacent or adjacent finger electrode ends, even if the finger electrode breaks during use, the auxiliary electrode Therefore, it is possible to obtain a solar cell with high long-term reliability. Moreover, since the auxiliary electrode is connected to the end portion of the finger electrode, adhesion at the end portion is strengthened and the electrode is difficult to peel off. In addition, since the pattern opening for the auxiliary electrode of the screen plate-making has an arc shape or a chevron shape protruding outward in the longitudinal direction of the finger electrodes connecting the ends of the finger electrodes, the electrode by screen printing method In the formation, the longitudinal direction of the pattern electrode opening for the auxiliary electrode has fewer straight portions perpendicular to the printing direction, the bleeding of the paste in the direction of the end of printing is reduced, and the printing pattern is prevented from being blurred or broken, In addition, because the plate film has few corners with respect to the printing direction, peeling of the plate film during repetitive printing is suppressed, so that a fine pattern of electrodes can be formed without reducing the light receiving area without increasing the manufacturing cost of solar cells. Capable of producing a solar cell having high conversion efficiency, and further providing a solar cell module using the solar cell. Kill.

It is sectional drawing which shows the structure of a common solar cell. It is a top view which shows the electrode pattern of the surface of a common solar cell. It is a top view which shows the electrode pattern of the back surface of a common solar cell. It is the schematic which shows the structure of the conventional screen printing method, (a) shows the state which has a squeegee on a plate film, (b) shows the state which has a squeegee on a pattern opening part. 3A and 3B are plan views showing an opening pattern of screen plate making used for electrode formation in FIG. 2, where FIG. 10 is a plan view showing an electrode pattern on the surface of a solar cell described in Patent Document 2. FIG. 10 is a plan view showing an electrode pattern on the surface of a solar cell described in Patent Document 3. FIG. It is an enlarged view which shows the opening pattern of the screen plate making used for electrode formation of FIG. It is a top view which shows the structural example (1) of the electrode pattern of the surface of the solar cell which concerns on this invention. It is a top view which shows the structural example (2) of the electrode pattern of the surface of the solar cell which concerns on this invention. It is a top view which shows the structural example (3) of the electrode pattern of the surface of the solar cell which concerns on this invention. It is a top view which shows the opening pattern of the screen plate making used for electrode formation of FIG. It is a top view which shows the opening pattern of the screen platemaking used for electrode formation of FIG. It is a top view which shows the opening pattern of screen platemaking used for electrode formation of FIG. It is a top view which shows the basic composition of the solar cell module which concerns on this invention. It is sectional drawing which shows the basic composition of the solar cell module which concerns on this invention.

  Below, the solar cell which concerns on this invention, its manufacturing method, and a solar cell module are demonstrated. However, the present invention is not limited to the solar cell and the manufacturing method thereof shown in the present embodiment.

  A solar cell according to the present invention includes a semiconductor substrate having at least a pn junction, a plurality of finger electrodes 107 formed in a comb shape on at least one surface of the semiconductor substrate, and the longitudinal direction of the finger electrodes 107. The bus bar electrode 105 that is arranged orthogonally and connected to the finger electrode 107 and the longitudinal direction of the finger electrode that connects at least a part of the finger electrodes 107 adjacent to or adjacent to each other among the finger electrodes 107 And an auxiliary electrode 108 having a circular arc shape or a mountain-shaped protrusion shape protruding outward (FIGS. 9 to 11). In addition, the solar cell of this invention has the characteristics in the electrode pattern of the surface, and other structures are as having shown, for example in FIG.

  Here, the auxiliary electrode 108 does not have a linear shape orthogonal to the longitudinal direction of the finger electrode 107, but has a curved shape that protrudes outward in the longitudinal direction of the finger electrode between the two finger electrodes 107 to be connected. Is preferred. That is, the auxiliary electrode 108 has a connection angle with at least the finger electrode 107 (the angle formed by the auxiliary electrode 108 and the finger electrode 107) is not a right angle, and a circle is formed between the ends of two adjacent finger electrodes 107. It is connected in an arc shape (arch shape) and a mountain-shaped protrusion shape (pseudo arc shape) consisting of a combination of short line segments.

  The line width of the auxiliary electrode 108 is preferably equal to or larger than the line width of the finger electrode 107 and less than the line width of the bus bar electrode 105. Specifically, it is preferably 40 μm or more and less than 500 μm, more preferably 40 μm or more and less than 100 μm. As will be described later, in order to perform screen printing so that the finger electrode 107 does not have unevenness and bleeding, generally, the printing direction is set parallel to the longitudinal direction of the finger electrode 107. In such a printing method, since the longitudinal direction of the auxiliary electrode 108 as a whole is a direction orthogonal to the printing direction, it becomes difficult to discharge paste when the line width is less than 40 μm, and an auxiliary electrode having an appropriate shape cannot be printed. There is a risk. In addition, when the line width of the auxiliary electrode 107 is equal to or larger than the line width of the bus bar electrode 105, the light receiving area may be reduced and the conversion efficiency of the solar cell may be reduced.

9 to 11 show configuration examples of the solar cell of the present invention.
FIG. 9 is a configuration example (1) of the electrode pattern on the surface of the solar cell according to the present invention.
In this configuration example, as shown in FIG. 9, the adjacent ends of all the finger electrodes 107 at both ends of the finger electrode 107 are connected by the auxiliary electrode 108. The auxiliary electrode 108 connects the ends of two adjacent finger electrodes 107 with an arc-shaped (arch-shaped) electrode line.

FIG. 10 is a configuration example (2) of the electrode pattern on the surface of the solar cell according to the present invention.
In this configuration example, as shown in FIG. 10, a part of the auxiliary electrode 108 in the configuration of FIG. 9 is thinned out, and a plurality of finger electrodes 107 are connected by one at each end of the finger electrode 107. In addition, the adjacent end portions are connected by the auxiliary electrode 108. In FIG. 10, all 17 finger electrodes 107 are connected by the auxiliary electrode 108 so as to be electrically connected to one. The auxiliary electrode 108 connects the ends of two adjacent finger electrodes 107 with arc-shaped (arched) electrode wires.

FIG. 11 is a configuration example (3) of the electrode pattern on the surface of the solar cell according to the present invention.
In this configuration example, as shown in FIG. 11, adjacent ends of the finger electrodes 107 are connected to each other by auxiliary electrodes 108 so that the plurality of finger electrodes 107 are connected by one. In FIG. 11, three or four finger electrodes 107 are connected so as to be electrically connected to one by the auxiliary electrode 108. In addition, the auxiliary electrode 108 connects the end portions of the two finger electrodes 107 adjacent to each other with the one finger electrode 107 interposed therebetween by an angled electrode wire.

By setting it as the above electrode pattern, the following effects are acquired.
First, even if a part of the finger electrodes 107 is disconnected through a temperature history such as a temperature cycle test, the ends of the disconnected finger electrodes 107 are connected to the other finger electrodes 107 by the auxiliary electrode 108. Since it is connected to the end portion, current can be taken out via the other finger electrode 107, so there is no power loss. Second, since the auxiliary electrode 108 is connected to the end of the finger electrode 107, the contact area with the semiconductor substrate is increased at the end of the finger electrode 107, and the adhesive strength at the end of the finger electrode 107 is improved. In addition, the finger electrode 107 can be prevented from peeling even for long-term use. Third, it is possible to prevent the end portion of the finger electrode 107 from being peeled off from the semiconductor substrate due to thermal contraction during firing. Fourth, the auxiliary electrode 108 reduces the wiring resistance, increases the fill factor, and improves the conversion efficiency. Fifth, by providing the auxiliary electrode 108, the loss of Jsc and the increase of the fill factor due to the decrease in the light receiving area are offset, so that high conversion efficiency can be maintained. In the configuration examples of FIGS. 10 and 11, even if the auxiliary electrode 108 is thinned out, an increase in the short circuit current due to an increase in the light receiving area and a decrease in the fill factor due to an increase in the wiring resistance are offset, so that high conversion efficiency is maintained. As a result, costs can be reduced.

  Next, the manufacturing method of the solar cell concerning this invention is demonstrated. In addition, this invention is not limited to the following manufacturing method.

(Preparation of substrate)
First, an ingot crystal is sliced by a general wire saw to prepare a p-type semiconductor substrate 100b having a substrate thickness of 100 to 200 μm. The p-type semiconductor substrate 100b is, for example, a high-purity silicon doped with a group III element such as boron or gallium. The silicon single crystal may be produced by any of the Czochralski (CZ) method and the float zone (FZ) method. The specific resistance of the p-type semiconductor substrate 100b is preferably, for example, 0.1 to 20 Ω · cm, more preferably 0.1 to 5.0 Ω · cm, and still more preferably 0.5 to 2.0 Ω · cm. When the specific resistance of the p-type semiconductor substrate 100b is less than 0.1 Ω · cm and more than 20 Ω · cm, it becomes unsuitable for making a high-performance solar cell.

(Damage etching)
Next, the p-type semiconductor substrate 100b is immersed in an aqueous sodium hydroxide solution, and the damaged layer is removed by etching. For removing damage from the substrate, a strong alkaline aqueous solution such as potassium hydroxide may be used. The same object can be achieved with an acid aqueous solution such as a mixed acid of hydrofluoric acid and nitric acid.

(Texture formation)
Subsequently, minute unevenness called texture is formed on the substrate surface. Texture is an effective way to reduce solar cell reflectivity. The texture should be immersed for about 10 to 30 minutes in an alkali solution (concentration: 1 to 10% by mass, temperature: 60 to 100 ° C.) such as heated sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium hydrogen carbonate, etc. Easy to make. In many cases, a predetermined amount of 2-propanol is dissolved in the solution to promote the reaction.

(Washing)
After texture formation, washing is performed in an acidic aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, or the like, or a mixture thereof. From an economic and efficient standpoint, washing in hydrochloric acid is preferred. In order to improve the cleanliness, 0.5 to 5% by mass of hydrogen peroxide may be mixed in a hydrochloric acid solution and heated to 60 to 90 ° C. for washing.

(Pn junction formation)
Next, the n-type diffusion layer 101 is formed on the light receiving surface of the substrate by heat treatment. Specifically, the n-type diffusion layer 101 is formed on the light receiving surface by performing heat treatment in a phosphorus oxychloride (POCl ₃ ) gas atmosphere. Common silicon solar cell, it is necessary to form only on the light receiving surface of the PN junction, or diffused in a state superimposed two substrates to each other in order to achieve this, SiO ₂ film Ya on the back surface before spreading It is necessary to devise such that a pn junction cannot be formed on the back surface by forming a SiNx film or the like as a diffusion mask. The dopant diffusion in the heat treatment step described above may be performed by not only a vapor phase diffusion method but also a coating diffusion method using a coating agent containing a dopant.

(Joining separation)
Next, junction separation is performed using a plasma etching apparatus. In this process, the sample is stacked so that plasma and radicals do not enter the light receiving surface and back surface of the substrate, and the end surface is shaved by several microns in this state. Thereby, the leakage current at the time of using a solar cell can be prevented.
Thereafter, the glass formed on the substrate surface is removed with hydrofluoric acid or the like.

(Antireflection film formation)
Next, a silicon nitride antireflection film 102 is formed on the light receiving surface. Specifically, a SiNx film having a thickness of about 100 nm is formed using a plasma CVD apparatus. As the reaction gas, monosilane (SiH ₄ ) and ammonia (NH ₃ ) are often mixed and used, but nitrogen can be used instead of NH ₃ , and the process pressure can be adjusted and the reaction gas diluted. Furthermore, when polycrystalline silicon is used for the substrate, hydrogen may be mixed into the reaction gas in order to promote the bulk passivation effect of the substrate. The other antireflection film 102 includes a silicon oxide film, a titanium dioxide film, a zinc oxide film, a tin oxide film, and the like, and can be replaced with a silicon nitride film. In addition to the above, the formation method includes a remote plasma CVD method, a coating method, a vacuum deposition method, and the like. From the economical viewpoint, it is preferable to form the nitride film by the plasma CVD method.

(Back electrode printing / drying)
Next, the aluminum electrode 104 paste and the bus bar electrode 106 paste are printed on the back side of the substrate by screen printing, and then dried. For example, on the back surface of the substrate, a paste in which silver powder and glass frit are mixed with an organic binder is screen-printed in a bus bar electrode shape, and then a paste in which aluminum powder is mixed with an organic binder is screen-printed in an area other than the bus bar electrode. After these printings, the back electrode is formed by baking at a temperature of 700 to 800 ° C. for 5 to 30 minutes. The back electrode is preferably formed by a printing method, but can also be formed by a vapor deposition method, a sputtering method, or the like.

(Surface electrode printing / drying)
Next, the conductive paste for the bus bar electrode 105, the finger electrode 107, and the auxiliary electrode 108 is screen printed in a predetermined pattern on the light receiving surface (front surface) side of the substrate by a screen printing method and dried. For example, the surface of the substrate has a comb-shaped printing pattern in which a paste obtained by mixing silver powder, glass frit, and an organic binder is designed with a finger electrode width of 30 to 80 μm and a finger electrode interval of 0.5 to 4.0 mm. Print using screen plate making. This screen printing process forms the basis of the present invention, and details will be described later.

(Baking)
Finally, firing is performed in a firing furnace to form the aluminum electrode 104 and the bus bar electrode 106 on the back surface side of the substrate, the bus bar electrode 105, the finger electrode 107, and the auxiliary electrode 108 on the light receiving surface side, thereby obtaining the solar cell of the present invention. Firing is performed, for example, by heat treatment at 700 to 800 ° C. for 5 to 30 minutes in the air. The firing for forming the aluminum electrode 104 and the bus bar electrode 106 on the back surface side of the substrate and the firing for forming the bus bar electrode 105, the finger electrode 107 and the auxiliary electrode 108 on the light receiving surface side may be performed separately. . Moreover, the BSF layer 103 formed at the time of electrode firing contributes to the improvement of the open circuit voltage of the solar cell.

Next, the screen printing method used for electrode formation of the substrate light-receiving surface (front surface) in the method for manufacturing a solar cell of the present invention will be described.
First, as shown in FIG. 4, a screen plate making 409 for screen printing used in the present invention is coated with a photosensitive emulsion on a mesh material 409a in which warp and weft perpendicular to each other are knitted, and this emulsion is exposed. A plate film (emulsion layer) 409b having a pattern opening 409c opened in a desired pattern shape (for example, a substantially rectangular shape for an electrode) is formed by removing a part thereof.

  In the screen printing method, this screen plate making 409 is placed on an object to be printed (here, a semiconductor substrate on which a pn junction and an antireflection film 102 are formed), and a printing paste (or ink or non-printing material) placed on the screen plate making 409 is used. The flat squeegee (also referred to as a flat squeegee) 408, which is a spatula having appropriate hardness (rubber hardness; 60 to 90 degrees) and flexibility, is spread on the pattern opening 409c. Inclined at a predetermined angle (squeegee angle; 60 to 80 degrees) and pressed at the tip with a predetermined pressure (printing pressure; 0.2 to 0.5 MPa), a predetermined moving speed (printing speed; 20) (100 mm / sec), the paste is attached to the printing material through the pattern opening 409c of the screen plate making 409. Cormorant. The rubber hardness is a value measured using an A hardness durometer (JIS K 6253).

Specifically, when the squeegee 408 is moved on the screen plate 409, the paste is pressed against the screen plate 409 with a predetermined pressure at the tip of the squeegee 408, and when entering the pattern opening 409c, the mesh in the pattern opening 409c is obtained. Through the opening where the material 409a does not exist, the material 409a is pushed out to the opposite side of the screen plate-making 409, and drops and adheres to the substrate. At this time, immediately after adhering to the printing material, the paste does not adhere to the portion immediately below the warp and weft in the pattern opening 409c, so that the paste film has a non-uniform thickness. Thereafter, the mesh material 409a Since the paste adhering to the portion immediately below the opening flows on the printing material, a paste film having a uniform pattern with a uniform thickness is obtained.
Next, the paste film is dried, and the screen printing process is completed.

  As described above, the screen printing method is the same as the pattern opening 409c formed on the screen plate 409 by the paste on the screen plate 409 being pushed out of the pattern opening 409c by the moving squeegee 408 and ejected onto the substrate 410. This is a technique for forming a pattern on a substrate. When this screen printing method is used for forming an electrode of a solar cell, a shape corresponding to the pattern opening 409c can be obtained even after being printed on the semiconductor substrate (antireflection film 102) by using a highly thixotropic conductive paste. It is possible to form a high aspect ratio electrode.

  Here, in the conventional screen plate making (FIGS. 5 and 8), when the plate film (emulsion layer) 409b has an angle, particularly a right angle, with respect to the printing direction, the screen plate making is repeated. When electrode printing is performed, there is a problem that the emulsion is gradually peeled off from the corners of the plate-making plate (emulsion layer) 409b of the screen plate making, and the opening shape of the pattern opening 409c is broken, so that a fine pattern cannot be drawn. Further, in the screen plate making 409 of FIG. 8, blurring or disconnection of the printing or bleeding of the paste toward the end of the printing has occurred in the pattern opening 409c for the auxiliary electrode 108 '.

The inventor diligently studied to solve these problems, and based on the knowledge that it can be improved by the shape of the pattern opening 409c of the screen plate making, the present inventor has been made.
That is, the present invention employs a screen printing method in at least the light receiving surface (front surface) side electrode forming step in the solar cell manufacturing process described above, and includes the finger electrode 107, the bus bar electrode 105, and the auxiliary electrode. A conductive paste is printed on a semiconductor substrate by a screen printing method using a predetermined screen plate making (FIGS. 12 to 14) having openings corresponding to 108 patterns (FIGS. 9 to 11), and the above-mentioned predetermined Pattern finger electrodes 107, bus bar electrodes 105, and auxiliary electrodes 108 are formed.

  Note that the finger electrode 107, the bus bar electrode 105, and the auxiliary electrode 108 are desirably formed simultaneously by a screen printing method. In this way, the printing process can be performed once, the cost can be reduced, and the number of processes applied to the semiconductor substrate can be reduced, so that cracks are not easily generated and the yield is improved. There is an advantage of doing. At this time, the longitudinal direction of the finger electrode 107 is preferably the printing direction.

FIGS. 12 to 14 show examples of opening patterns of screen plate making used in the method for manufacturing a solar cell of the present invention.
FIG. 12 shows an example of the screen plate making 409 used for forming the finger electrode 107, bus bar electrode 105, and auxiliary electrode 108 having the electrode pattern shown in FIG.
As shown in FIG. 12, the plate film 409b1 in the region outside the end of the finger electrode and the plate film 409b2 in the region between the finger electrodes are in an island-like state without being connected, but the plate film 409b1, None of 409b2 has a corner with respect to the printing direction (left-right direction in the figure), and in particular, the end of the plate film 409b2 has an arc shape to form the pattern opening 409c1 for the auxiliary electrode 108. Therefore, the emulsion is difficult to peel off due to repeated printing. The opening shape of the pattern opening 409c1 for the auxiliary electrode 108 is not a linear shape orthogonal to the printing direction, but an arc shape including a component having a certain width and parallel to the printing direction. It is also possible to suppress fading and disconnection of the auxiliary electrode 108 formed by the above and bleeding of the paste toward the end of printing.

FIG. 13 shows an example of the screen plate making 409 used for forming the finger electrode 107, bus bar electrode 105, and auxiliary electrode 108 having the electrode pattern shown in FIG.
As shown in FIG. 13, there is an island-like part where the plate film 409b1 in the region outside the end of the finger electrode and the plate film 409b2 in the region between the finger electrodes are not connected, but the plate films 409b1 and 409b2 None of them have a corner portion with respect to the printing direction (left and right direction in the drawing), and in particular, the end portion of the plate film 409b2 has an arc shape for forming the pattern opening 409c1 for the auxiliary electrode 108. Therefore, the emulsion is difficult to peel off due to repeated printing. Further, since the pattern opening 409c1 for the auxiliary electrode 108 is thinned out from the pattern of FIG. 12, the plate film in the region between some finger electrodes is the plate film 409b1 in the region outside the end of the finger electrode. Since the portion is more firmly bonded to the mesh material 409a, the portion is difficult to peel off. Further, the opening shape of the pattern opening portion 409c1 for the auxiliary electrode 108 is not a linear shape orthogonal to the printing direction, but an arc shape including a component having a certain width and parallel to the printing direction. It is also possible to suppress fading and disconnection of the auxiliary electrode 108 formed by the above and bleeding of the paste toward the end of printing.

FIG. 14 shows an example of the screen plate making 409 used for forming the finger electrode 107, bus bar electrode 105, and auxiliary electrode 108 having the electrode pattern shown in FIG.
As shown in FIG. 14, there is an island-like part where the plate film 409b1 in the region outside the end of the finger electrode 107 and the plate film 409b2 in the region between the finger electrodes 107 are not connected, but the plate film 409b1, None of 409b2 has a portion that is at least perpendicular to the printing direction (the left-right direction in the figure), and in particular, the end of the plate film 409b2 has a chevron shape to form a pattern opening 409c1 for the auxiliary electrode 108. Therefore, the emulsion is difficult to peel off due to repeated printing. Further, since the pattern opening 409 c 1 for the auxiliary electrode 108 is thinned out from the pattern of FIG. 12, the plate film in the region between some finger electrodes 107 is a plate in the region outside the end of the finger electrode 107. The portion is connected to the film 409b1, and the portion is more firmly bonded to the mesh material 409a and thus is difficult to peel off. Further, the plate film 409b2 is an area surrounded by the pattern opening for two finger electrodes 107 and the pattern opening 409c1 for the auxiliary electrode 108 that are adjacent to each other with the one finger electrode 107 interposed therebetween. Since it is an area wider than the plate film 409b2 of FIG. 13, it is more firmly bonded to the mesh material 409a and is difficult to peel off. Further, the opening shape of the pattern opening 409c1 for the auxiliary electrode 108 is a chevron-like projection including a component having a certain width and parallel to the printing direction, with fewer straight portions perpendicular to the printing direction than in the past. For this reason, it is possible to suppress fading and disconnection of the auxiliary electrode 108 formed by screen printing and bleeding of the paste in the direction of the end of printing.

  Thus, in the method of manufacturing a solar cell having finger electrodes and bus bar electrodes on the light-receiving surface, as described above, the screen plate opening pattern is partially changed without significantly changing it as a general solar cell pattern. Only by doing so, it is possible to manufacture a solar cell with high long-term reliability while maintaining the conversion efficiency without increasing the manufacturing cost of the solar cell with the conventional screen printing method. In addition, this invention is applicable also when forming a finger electrode and a bus-bar electrode in the back surface side of a solar cell, ie, the case of a double-sided light reception type solar cell.

The effect of the present invention can be sufficiently obtained as a solar cell module.
That is, when the solar cell itself is exposed to an outdoor environment, the current collecting electrode is damaged by temperature, humidity, pressure, etc., and conversion efficiency is lowered. In addition, when foreign matter such as dust that does not transmit light adheres to the light receiving surface, sunlight cannot be taken in, and conversion efficiency is significantly reduced. Therefore, conventionally, it is made of a transparent surface side cover such as white plate tempered glass / filler such as ethylene vinyl acetate (EVA) / filler such as solar cell / EVA / resin film such as polyethylene terephthalate (PET). The solar cell module is configured so as to prevent a decrease in conversion efficiency as much as possible by heat-pressing in a state where the back side covers are sequentially laminated. However, even if such a solar cell module is exposed to a severe outdoor environment for many years, the conversion efficiency tends to gradually decrease. Among them, in particular, the electrode may be peeled off due to corrosion due to moisture or metal particles eluting due to moisture, resulting in weak adhesion to the semiconductor substrate.
If the solar cell of this invention is used, since the adhesive strength of a finger electrode edge part will increase, it is possible to solve the above problems.

  The solar cell module according to the present invention uses the solar cell according to the present invention, and electrically solders the plurality of solar cells by soldering a wiring material (interconnector 201) to each bus bar electrode of the plurality of solar cells. It is set as the structure which connects automatically. 15 and 16 show the basic configuration of the solar cell module of the present invention. Here, a configuration in which an interconnector 201 is connected to each of the bus bar electrodes 105 and 106 on the front and back surfaces of the solar cell 100 of the present invention via solder 202 is shown.

  In the solar cell module of the present invention, a plurality of solar cells 100 having such a configuration are arranged along the length direction of the bus bar electrode 105 with the light receiving surface facing in the same direction. It is obtained by connecting the interconnector 201 to the bus bar electrode 105 and the bus bar electrode 106 on the back surface of the other solar cell 100 adjacent to the solar cell 100. In addition, the connection number of a photovoltaic cell is 2-60 normally.

  Moreover, generally, in a solar cell module, since it is necessary to protect the surface and back surface of a solar cell, as a solar cell module product, a plurality of solar cells including the above-described interconnector 201 are used as a transparent substrate such as a glass plate. And a back cover (back sheet). In this case, for example, the light receiving surface of the solar cell is sandwiched between the transparent substrate and the back cover, facing the transparent substrate, and PVB (polyvinyl butyrol) with a low light transmittance decrease or EVA ( In general, a super straight system in which a plurality of solar cells 100 provided with an interconnector 201 are sealed with a transparent filling material such as ethylene vinyl acetate and external terminals are connected is generally used. At this time, an external extraction interconnector connected to the back surface bus bar electrode 106 of the solar cell 100 was connected to one external terminal, and the other external terminal was connected to the front surface bus bar electrode 105 of the solar cell 100. External take-out interconnector is connected.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these.

[Example 1]
In order to confirm the effectiveness of the present invention, the following steps were performed on 1000 semiconductor substrates to produce the solar cell 100 shown in FIG.
First, a boron-doped {100} p-type as-cut silicon substrate 100 having a 15 cm square, a thickness of 250 μm, and a specific resistance of 2.0 Ω · cm is prepared, and the damaged layer is removed with a concentrated potassium hydroxide aqueous solution to form a texture. An n-type diffusion layer 101 heat-treated at 850 ° C. in a phosphorus chloride atmosphere was formed, and the phosphorus glass was removed with hydrofluoric acid, washed and dried. Next, after a SiNx film is formed as an antireflection film 102 using a plasma CVD apparatus, and a paste in which silver powder and glass frit are mixed with an organic binder is screen printed on the back surface in a bus bar shape for the back surface bus bar electrode 106 Then, a paste obtained by mixing aluminum powder with an organic binder was screen-printed for the aluminum electrode 104 in a region other than the region printed in the bus bar shape, and the organic solvent was dried to prepare a semiconductor substrate on which a back electrode was formed.
Next, a conductive paste containing silver powder, glass frit, an organic vehicle, and an organic solvent as main components and a metal oxide as an additive is formed on the semiconductor substrate with an opening pattern shown in FIG. It was applied on the antireflection film 102 formed on the semiconductor substrate with a squeegee rubber hardness of 70 degrees, a squeegee angle of 70 degrees, a printing pressure of 0.3 MPa, and a printing speed of 50 mm / sec. After printing, the organic solvent was dried in a clean oven at 150 ° C. and then baked in an air atmosphere at 800 ° C. to obtain a solar cell 100.
The screen plate making 409 in FIG. 12 has an opening pattern shown in FIG. 12 by an exposure process on a screen material coated with a stainless mesh coated with a photosensitive agent (trade name MDX-100, manufactured by Mino Group Co., Ltd.). Formed. At this time, the line width of the pattern opening 409c for the finger electrode 107 was set to 80 μm, 66 lines were provided at an adjacent interval of 2.4 mm, and the line width of the pattern opening 409c for the auxiliary electrode 108 was set to 90 μm.

[Example 2]
In Example 1, solar cell 100 was produced in the same manner as in Example 1 except that screen plate making 409 for surface electrode formation was replaced with the screen plate making 409 shown in FIG. .
In the screen plate making 409 of FIG. 13, the line width of the pattern opening 409c for the finger electrode 107 is set to 80 μm, and 66 lines are provided at an interval of 2.4 mm, and the line width of the pattern opening 409c for the auxiliary electrode 108 is set to 90 μm. It was.

[Comparative Example 1]
In Example 1, instead of the screen plate making 409 for forming electrodes on the surface, instead of the one shown in FIG. 12, the screen plate making 409 shown in FIG. Produced.
In the screen plate making 409 of FIG. 5, 66 pattern openings 409c for the finger electrodes 107 were provided with a line width of 80 μm and an adjacent interval of 2.4 mm.

[Comparative Example 2]
In Example 1, instead of the screen plate making 409 for forming electrodes on the surface, the screen plate making 409 shown in FIG. 8 is used instead of the one shown in FIG. FIG. 7) was produced.
In the screen plate making 409 of FIG. 8, the line width of the pattern opening 409c for the finger electrode 107 is set to 80 μm, and 66 lines are provided at an interval of 2.4 mm, and the line width of the pattern opening for the auxiliary electrode 108 ′ is set to 90 μm. It was.

The following evaluation was performed on 3000 solar cells manufactured as described above.
(1) Electrical characteristics As a measurement of the electrical characteristics of the solar cell, using a solar simulator (manufactured by Yamashita Denso Co., Ltd., model YSS-160A), the light of the solar simulator (substrate temperature 25 ° C., irradiation intensity: 1 kW / m) ² , spectrum: AM1.5 global) was irradiated to the solar cell sample, the current-voltage characteristics of the solar cell sample were measured, and the fill factor, current density, and conversion efficiency were determined from the measurement results. In addition, the measured value was calculated | required as an average value of 1000 solar cells.
(2) Emulsion peeling The plate film of the screen plate after use was magnified 50 times with an optical microscope, and the presence or absence of peeling of the emulsion was confirmed. At this time, as a state of peeling of the emulsion, a state having an influence on the degree to which the shape of the formed electrode is clearly broken is regarded as being peeled, and a case having no influence is regarded as not peeling.
(3) Separation of edge part Ten pieces were randomly extracted from 1000 solar cells, and the finger electrode edge part was observed with an optical microscope, and the presence or absence of peeling of the finger electrode edge part was confirmed. At this time, there were 132 finger electrode end portions per solar cell, and the ratio of the occurrence of peeling to the entire end portion was determined.

The above table results are shown in Table 1.
In Examples 1 and 2, the fill factor improved dramatically. This is because the wiring electrode resistance is reduced by connecting the ends of the finger electrodes, the pattern is not thickened due to the absence of the emulsion peeling of the screen plate, and the disconnection is eliminated.
In Comparative Example 1, peeling of the emulsion and peeling of the edge of the finger electrode were observed in the screen plate making, but none of Examples 1 and 2 was confirmed.

[Example 3]
Next, the solar cells produced in Examples 1 and 2 and Comparative Example 1 were used to make a module in the following manner.
Using a linear interconnector 201 having a width of 2 mm and a thickness of 0.2 mm, as shown in FIGS. 15 and 16, a flux is applied in advance to a location where the interconnector 201 and the bus bar electrode 105 are connected, The interconnector 201 and the bus bar electrode 105 on the light receiving surface of the solar cell were connected by solder. Similarly, the interconnector 201 was soldered to the bus bar electrode 106 on the back side of the solar cell.
Next, solar cell 100 / EVA / polyethylene terephthalate (PET) in order of white plate tempered glass / ethylene vinyl acetate (EVA) / wiring material is laminated in this order, and the surroundings are evacuated, then at a temperature of 150 ° C. for 10 minutes. After thermocompression bonding, it was completely cured by heating at 150 ° C. for 1 hour. Here, four solar cells were connected to each other by an interconnector 201 and sealed.
The solar cell module was manufactured through the above steps.

A temperature cycle test (JIS C8917) was performed on each of the solar cell modules manufactured using the solar cells of Examples 1 and 2 and Comparative Example 1, and the output of the solar cell module before and after the test was compared. In the temperature cycle test, a test of 400 cycles was performed under the condition conforming to the JIS C8917 standard. Moreover, the output of the solar cell module was measured under the light irradiation of AM 1.5 and 100 mW / cm ² by the solar simulator, and the output reduction rate (= (output after test / output before test) × 100 (%)) Asked.

As a result, the output of the solar cell module using the solar cell of Comparative Example 1 was reduced to 77% after 400 temperature cycles. On the other hand, the output decrease rate of the solar cell module using the solar cell of Example 1 was 99%, the output decrease rate of the solar cell module using the solar cell of Example 2 was 97%, and any decrease in output was observed. There wasn't.
As described above, in the solar cell produced by the conventional screen plate making, the finger electrode ends peeled off, and the output could not be maintained over a long period of time.In the present invention, with a slight change in the printing pattern of the screen plate making, A solar cell having high long-term reliability could be manufactured without increasing the number of steps and without reducing the conversion efficiency.

100 solar cell 100b p-type semiconductor substrate 101 n-type diffusion layer 102 antireflection film 103 BSF layer 104 aluminum electrode 105 bus bar electrode 106 back bus bar electrode 107, 107 'finger electrode 108, 108' auxiliary electrode 408 squeegee 409 screen plate making 409a mesh material 409b, 409b1, 409b2 Plate film (emulsion layer)
409c, 409c1 Pattern opening 201 Interconnector 202 Solder

Claims (3)

  A semiconductor substrate on which at least a pn junction is formed, a plurality of finger electrodes formed in a comb shape on at least one surface of the semiconductor substrate, and arranged perpendicular to the longitudinal direction of the finger electrodes. A bus bar electrode connected to a portion other than the end, and an arc shape that protrudes outward in the longitudinal direction of the finger electrode that connects at least a portion of adjacent finger electrodes of the finger electrodes. Or a method of manufacturing a solar cell comprising a chevron-shaped auxiliary electrode, comprising a mesh material and a plate film coated on the mesh material by a screen printing method, and comb-like fingers on the plate film An electrode pattern opening and a portion other than the end of the finger electrode pattern opening are arranged orthogonal to the longitudinal direction of the finger electrode pattern opening. Convex outwards in the longitudinal direction of the finger electrode pattern opening connecting the ends of the finger electrode pattern opening adjacent to or adjacent to each other among the sub electrode pattern opening and the finger electrode pattern opening. The finger electrode, the bus bar electrode, and the auxiliary electrode are simultaneously formed by printing a conductive paste on the semiconductor substrate using a screen plate having an arc-shaped or chevron-shaped auxiliary electrode pattern opening formed thereon. A method for manufacturing a solar cell.   2. The method for manufacturing a solar cell according to claim 1, wherein the plate film is made of a photosensitive emulsion. The method for manufacturing a solar cell according to claim 1, wherein a printing direction is parallel to a longitudinal direction of the finger electrodes .

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