JP2009272405A - Solar battery element and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery element which allows grid and bus electrodes widely different in electrode width from each other to be formed without wire breaking by an inexpensive and simple process and provides superior conversion efficiency, and to provide a manufacturing method for the solar battery element. <P>SOLUTION: The solar battery element includes the bus electrode 4 formed by multilayer printing using a screen printing method and the grid electrode 7 having a width narrower than that of the bus electrode 4 on the light-receiving surface of a substrate. The solar battery element also includes an electrode connection portion 9 where the bus electrode 4 is connected to the grid electrode 7 to form an area where the width along the longitudinal direction of the bus electrode 4 is narrower than the width of the bus electrode 4 and is greater than the width of the grid electrode 7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solar cell element and a manufacturing method thereof.

  For example, a conventional solar cell element is a p-type silicon substrate having a thickness of 200 μm, and has a concavo-convex structure of 10 μm on the front side (light receiving surface side) in order to increase the light collection rate, and a silicon that is an antireflection film on the surface A nitride film is formed. On the silicon nitride film, a surface electrode that collects the photo-electron converted electrons is formed. Further, on the back surface, a back surface connection electrode is formed in contact with the back surface electrode and the external electrode. Here, as a method for improving the photo-electron conversion efficiency of the solar cell element, there is a method of making the surface area on the light receiving surface maximum and reducing the surface pole area.

  In general, the surface electrode is formed by printing a paste on a predetermined location of a silicon substrate by a printing method using a printing mask plate having a transmissive portion having a desired pattern, and performing high-temperature treatment in a baking furnace. A printing mask plate for forming a surface electrode in a desired pattern is obtained by attaching a mesh in which fine metal wires such as stainless steel having a wire diameter of about 10 to 100 μm are braided vertically and horizontally at a pitch of about 20 to 200 μm on a metal frame. A film-like photosensitive resin having a desired thickness is attached to the film, and a desired pattern is exposed and etched by photolithography. Such a printing mask plate is attached to a printing apparatus, and a silicon substrate is arranged in alignment with the printing mask plate. Then, the paste is placed on the printing mask plate and pushed in with a resin squeegee, and the paste is pushed out from the transmission part of the printing mask plate, so that the paste adheres to the silicon substrate side and a desired pattern is formed.

  There are various other methods for forming the thin wire electrode, such as a method in which a pressure is applied to a syringe and a paste is applied from a nozzle, a method using a roll coater, a method using an ink jet, and a method using a photoengraving method.

  Among these, the formation by the printing method that can be manufactured at the lowest cost is the main, and as an example of thinning the electrode, the grid electrode (thin electrode) is formed with a predetermined pattern on a thin metal plate without a mesh. There is a method of forming electrodes by multi-layer printing using a mesh mask using a mesh for forming orthogonal bus electrodes (thick electrodes) using a metal mask having an opening of (see Patent Document 1). reference). If this method is used, it is possible to prevent disconnection, printing blur, and the like that occur in an electrode formed using a printing mask plate made of mesh.

  An example using a mesh mask shows how to increase the light receiving area without reducing the current collection rate by making the grid electrode shape thicker on the bus electrode side and thinner toward the bus electrode. (For example, see Patent Document 2).

Japanese Patent Laid-Open No. 8-335711 JP-A-6-283737

  However, in the printing method using the mesh mask described above, in order to increase the light receiving area of the solar cell element and to improve the conversion efficiency, the grid electrode of the surface electrode is set to be very thin as 80 μm or less, and the bus electrode and the grid electrode When the multi-layer printing is performed in the same pattern, disconnection occurs between the bus electrode and the grid electrode during firing and cooling. The cause of this is that the bus electrode and the grid electrode are multilayer printed in the same pattern, thereby increasing the difference in film thickness between the bus electrode and the grid electrode, resulting in disconnection due to contraction during firing cooling. This is because the amount of paste proportional to the printing area is printed through the mesh mask, and the difference in film thickness between the bus electrode and the grid electrode is large because the printing area differs greatly between the bus electrode and the extremely thin grid electrode. Due to becoming. Furthermore, minute unevenness for efficiently condensing light is formed on the light receiving surface side of the solar cell element, and this further causes disconnection when the grid electrode is finely printed. Therefore, since the electrode width of the grid electrode cannot be reduced as much as possible, there is a problem that the light receiving area of the solar cell element cannot be increased and there is a limit to improving the conversion efficiency.

  In order to avoid such disconnection, in order to make the film thickness of the grid electrode and the bus electrode uniform, a method of reducing the aperture ratio of the printing mask plate by the bus electrode, a method of printing the bus electrode and the grid electrode separately A method such as a method of flattening the lower part of the electrode can be considered. However, such a method has a problem of an increase in production cost due to an additional process and a decrease in yield due to electrode alignment.

  The present invention has been made in view of the above, and it is possible to form a grid electrode and a bus electrode having greatly different electrode widths by preventing disconnection by an inexpensive and simple process, and reducing the electrode width of the grid electrode. Since it can be made as thin as possible, it aims at obtaining the solar cell element excellent in conversion efficiency, and its manufacturing method.

  In order to solve the above-described problems and achieve the object, the solar cell element according to the present invention includes a bus electrode formed by multilayer printing using a mask for screen printing and an electrode width narrower than the electrode width of the bus electrode. A grid electrode on the light receiving surface side of the substrate, wherein the bus electrode and the grid electrode are connected, and a width in the longitudinal direction of the bus electrode is narrower than an electrode width of the bus electrode, and An electrode connection portion having a region wider than the electrode width of the grid electrode is provided.

  According to the present invention, the grid electrode and the bus electrode having greatly different electrode widths are formed by preventing the disconnection by an inexpensive and simple process, and without increasing the cost of the solar cell element or reducing the yield, the solar cell element It is possible to improve the conversion efficiency.

  Embodiments of a solar cell element and a method for manufacturing the solar cell element according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably.

Embodiment 1 FIG.
FIGS. 1-1 and 1-2 are diagrams for explaining a schematic configuration of the solar cell element according to the first embodiment of the present invention, and FIG. 1-1 is a solar cell element viewed from the light receiving surface side. FIG. 1-2 is a cross-sectional view taken along line AA in FIG. 1-1.

  The solar cell element according to the first embodiment uses a p-type single crystal or polycrystalline silicon substrate (hereinafter referred to as silicon substrate 1) as a substrate. Note that the substrate is not limited to this, and an n-type silicon substrate may be used. On the surface on the light-receiving surface side of the silicon substrate 1 of the solar cell element, fine irregularities 2 having a height of 3 to 10 μm are formed. The minute unevenness 2 has a structure that increases the area for absorbing light from the outside on the light receiving surface, suppresses the reflectance on the light receiving surface, and confines light. An antireflection film 3 is provided on the minute unevenness 2 to suppress reflection of light from the outside and improve light absorption on the light receiving surface.

  Further, on the light receiving surface side of the silicon substrate 1, bus electrodes 4 (thick electrodes) and grid electrodes 7 (thin electrodes) are arranged as surface electrodes so as to intersect at substantially right angles, and are converted from light in the solar cell element. Collect electrons. On the back surface (surface opposite to the light receiving surface) of the silicon substrate 1, a back surface extraction electrode 5 and a back surface electrode 6 for extraction are formed.

In the solar cell element according to the first embodiment, the bus electrode 4 and the grid electrode 7 are connected, the width of the bus electrode 4 in the longitudinal direction is narrower than the electrode width of the bus electrode 4 and the electrode width of the grid electrode 7. The electrode connection portion having a wide area is also provided. That is, the solar cell element according to the first embodiment has an electrode width W in the longitudinal direction of the bus electrode 4 as shown in FIGS. 2-1 and 2-2 as an electrode connection portion between the bus electrode 4 and the grid electrode 7. and a grid electrode connecting portion 9 - _C bus electrodes 4 of the electrode width W and narrower than _B wider than the electrode width W _G of the grid electrode 7, the bus generally rectangular in shape. Here, FIG. 2A is a diagram for explaining the bus-grid electrode connecting portion 9, and is an enlarged view of a region B which is an intersection portion of the bus electrode 4 and the grid electrode 7 in FIG. is there. FIG. 2B is a diagram for explaining the bus-grid electrode connecting portion 9, and is a cross-sectional view along the longitudinal direction of the grid electrode 7 in the region B in FIG.

The cross-sectional shape of the electrode is such that the amount of paste that is proportional to the printing area is formed through the printing mask plate during electrode printing with a printing mask plate for electrode printing using a mesh. bus by selecting the electrode width W _C of the electrode connecting portions 9 - thickness T _C of the grid electrode connecting portion 9 and the values between the thickness T _G of the thickness T _B and the grid electrode 7 of the bus electrode 4 Become. As a result, the height difference in the height direction between the bus electrode 4 and the grid electrode 7 is relaxed, the difference in film thickness between the regions having different thicknesses adjacent to each other is reduced, and the bus electrode 4 and the grid electrode during firing cooling are reduced. The disconnection due to thermal contraction with 7 is prevented. That is, the amount of change in film thickness between the bus electrode 4 and the grid electrode 7 is reduced by the bus-grid electrode connecting portion 9, thereby causing a large film thickness difference between the bus electrode 4 and the grid electrode 7. Disconnection due to heat shrinkage is prevented.

Here, the electrode width W _C of the bus-grid electrode connecting portion 9 is preferably set to a ratio of 30 to 80 with respect to the electrode width W _B : 100 of the bus electrode 4. Such bus - thickness of the film thickness T _B and the grid electrode 7 having a film thickness T _C of the grid electrode connecting portion 9 is reliably bus electrodes 4 - bus by selecting the electrode width W _C of the grid electrode connecting portion 9 The film thickness is between _TG and the cross-sectional shape is such that no disconnection occurs between the bus electrode 4 and the grid electrode 7.

For example, when forming a substantially rectangular bus-grid electrode connecting portion 9 as shown in FIGS. 2-1 and 2-2, the bus electrode 4 has an electrode width of 2 mm, an electrode film thickness of 60 μm, and the grid electrode 7 has an electrode width of 50 μm. and electrode thickness 40 [mu] m, bus connecting the bus electrode 4 and the grid electrode 7 - the film thickness by the electrode width W _C of the grid electrode connecting portion 9 to 800μm is 50 [mu] m.

  Here, if there is no bus-grid electrode connection part 9, the difference in film thickness between the bus electrode 4 and the grid electrode 7 which are adjacent areas having different film thicknesses is 20 μm. The difference in thickness between adjacent regions having different thicknesses is 10 μm between the bus electrode 4 and the bus-grid electrode connecting portion 9 and 10 μm between the bus-grid electrode connecting portion 9 and the grid electrode 7. Thereby, the film thickness difference between adjacent different film thickness regions is reduced, and disconnection due to the film thickness difference during firing cooling is eliminated.

  Below, the manufacturing method of the solar cell element concerning Embodiment 1 is demonstrated. A p-type silicon substrate is prepared as the silicon substrate 1, and the silicon substrate 1 is washed with hydrogen fluoride or pure water. Then, the micro unevenness | corrugation 2 formation process which forms the micro unevenness | corrugation 2 in the surface of the silicon substrate 1 is implemented. As the step of forming the minute irregularities 2 on the surface of the silicon substrate 1, for example, the silicon substrate 1 is immersed in a mixed solution of an alkaline solution (for example, NaOH solution) and isopropyl alcohol, and wet etching is performed until the surface irregularities become 10 μm. Further, the surface of the silicon substrate 1 may be formed into an uneven shape by a dry etching process such as reactive ion etching (RIE). In this case, a smaller protrusion shape with a height of 1 to 3 μm can be uniformly formed regardless of the plane orientation of the silicon crystal as in wet etching.

Next, diffusion is performed in which a silicon substrate 1 having minute irregularities 2 formed on the surface is thermally diffused at a high temperature in a phosphorus oxychloride (POCl ₃ ) gas by a vapor phase diffusion method to form an n-type layer on the surface layer of the silicon substrate 1 Perform the process. The concentration of phosphorus diffused at this time can be controlled by the concentration of phosphorus oxychloride gas, the temperature atmosphere, and the heating time. The sheet resistance of the silicon substrate 1 after diffusion is 50 to 65Ω / □.

  After the diffusion step, an antireflection film 3 is formed on one surface of the silicon substrate 1 on the light receiving surface side. For example, plasma CVD is used to form the antireflection film 3, and a silicon nitride film is formed as an antireflection film 3 with a thickness of 80 nm using a mixed gas of silane and ammonia.

  Next, a back electrode is formed on the back surface of the silicon substrate 1. The back electrode is formed on almost the entire back surface of the silicon substrate 1. As a method for forming the back electrode, a printing method, an ink jet method, a sputtering method, a vapor deposition method, or the like can be used, but a printing method is preferable from the viewpoint of ease of electrode formation and process time. In forming the back electrode by the printing method, first, a silver material paste is printed in the shape of the back surface extraction electrode 5, dried at a temperature of 150 ° C., and then the aluminum material paste is printed in the shape of the back electrode 6.

  After forming the back electrode, the front electrode is formed. For the surface electrode, methods such as a printing method, an ink jet method, a sputtering method, and a vapor deposition method can be used, but the printing method is preferable from the viewpoint of the ease of electrode formation and the process time. As a material for the surface electrode, a paste using silver is used. For printing the surface electrode, first, a printing mask plate is set in a printing apparatus, and the silicon substrate 1 is arranged so that the printing pattern is at a predetermined position. On the printing mask plate, patterns of shapes of substantially rectangular bus-grid electrode connecting portions 9, bus electrodes 4, and grid electrodes 7 as shown in FIGS. 2-1 and 2-2 are formed. Then, a paste is applied on the silicon substrate 1 by a printing process. As a result, the shapes of the bus-grid electrode connecting portion 9, the bus electrode 4, and the grid electrode 7 are simultaneously printed on the silicon substrate 1. Thereafter, by drying at a temperature of 150 ° C., the organic solvent in the paste is removed, and the paste becomes dry.

  When the grid electrode is a thin wire having a width of 100 μm or less, it is necessary to increase the electrode film thickness in order to secure a cross-sectional area so that current can easily flow. For this reason, in order to form a grid electrode having an electrode width of 100 μm or less, it is necessary to print the paste several times. Therefore, the silicon substrate 1 on which the paste has been dried is attached again to the printing apparatus, and alignment is performed so that it is the same as the previously printed position. Then, the electrode is printed, and then the paste is dried. At this time, the pattern of the bus-grid electrode connection portion 9 in the printing mask plate has a value that the electrode width is smaller than the electrode width of the bus electrode 4 pattern and larger than the electrode width of the grid electrode 7 pattern. Such a printing-drying process is performed a plurality of times until the required electrode height is obtained. Next, in order to bake an electrode, it bakes in an air | atmosphere atmosphere of 750 to 800 degreeC, and a solar cell element is completed.

  Here, it demonstrates compared with the manufacturing method of the conventional solar cell element. In a conventional solar cell element, when a surface electrode is formed by a printing method on a silicon substrate on which fine irregularities are formed on the surface and further an antireflection film is formed, for example, the electrode width of the grid electrode is 0.06 mm, the electrode width of the bus electrode An electrode is printed on a silicon substrate using a printing mask plate having a 2.0 mm pattern, and further dried at 150 ° C. in a drying furnace. And this printing process-drying process is repeated 4 times, for example, and electrode formation is performed.

  The specifications of the printing mask plate are, for example, 400 mesh (wire diameter 20 μm, aperture ratio 50%) and emulsion thickness 20 μm. The formed surface electrode has a bus electrode height of 60 μm and a grid electrode height of 40 μm, and has a structure having a large difference in film thickness between the bus electrode 4 and the grid electrode 7.

  When the electrode formed in this manner was baked in the atmosphere at 750 to 800 ° C., cracks occurred between the bus electrode 4 and the grid electrode 7, thereby breaking the wire. This is because the width and film thickness of the bus electrode 4 and the grid electrode 7 which are adjacent areas having different film thicknesses are greatly different from each other, and are thus disconnected due to distortion caused by thermal contraction. As described above, in the case of thin line printing, multi-layer printing that increases the cross-sectional area so as to flow current efficiently is indispensable. However, when the grid electrode 7 is thinned, the grid electrode 7 and the bus electrode 4 are formed in the multi-layer printing. A difference in film thickness occurs, and disconnection occurs during subsequent baking and cooling.

  Here, the large difference in film thickness between the bus electrode 4 and the grid electrode 7 occurs in the multi-layer printing because the grid electrode 7 is printed with a fine mesh printing mask plate for fine line printing. This is because there is a difference between the paste transmittance of this and the paste transmittance of the printed portion of the bus electrode 4.

However, in the present embodiment, the paste transmittance in the printing mask plate is controlled by changing the electrode width of the connection portion between the bus electrode 4 and the grid electrode 7, and a large film between adjacent regions having different film thicknesses. The thickness difference is eliminated to prevent disconnection. Since the transmittance of the paste decreases when the printed pattern area is reduced, a bus-grid electrode connecting portion 9 for connecting the bus electrode 4 and the grid electrode 7 is provided, and the electrode width W _C of the bus-grid electrode connecting portion 9 is set to be smaller. by wider than the electrode width W _G of and narrower than the electrode width W _B of the bus electrode 4 grid electrode 7, the bus - thickness T _B and the grid electrode of the film thickness T _C of the grid electrode connecting portion 9 bus electrode 4 7 between the film thicknesses _TG . Thereby, the film thickness difference between adjacent areas having different film thicknesses is reduced, and disconnection between adjacent areas having different film thicknesses during firing cooling can be prevented. In other words, disconnection that has conventionally occurred between the bus electrode 4 and the grid electrode 7 can be prevented.

  Such a change in the electrode shape can be easily realized by only changing the design of the printing mask plate without using a complicated process, and thus can be applied without increasing the production cost.

As described above, according to the solar cell element according to the first embodiment, the bus-grid electrode connecting portion 9 that connects the bus electrode 4 and the grid electrode 7 is provided between the bus electrode 4 and the grid electrode 7. , the bus - is set wider than the electrode width W _G of the electrode width W _B than narrow and the grid electrode 7 of the electrode width of the grid electrode connecting portion 9 bus electrode 4. Thus, the bus electrode formation - for the thickness T _C of the grid electrode connecting portion 9 becomes a value between the thickness T _G of the thickness T _B and the grid electrode 7 of the bus electrode 4, and the bus electrode 4 There is no large step between adjacent regions with different film thicknesses with respect to the grid electrode 7, the difference in film thickness between adjacent regions with different film thicknesses is reduced, and disconnection due to the difference in film thickness during firing cooling is caused. Is prevented.

  Therefore, according to the solar cell element according to the first embodiment, disconnection between the bus electrode 4 and the grid electrode 7 having greatly different electrode widths is prevented, and a solar cell element excellent in productivity and cost is realized. Yes. Moreover, since the electrode width of the grid electrode can be made as small as possible without causing disconnection, the light receiving area of the solar cell element can be expanded to improve the conversion efficiency.

  Moreover, according to the manufacturing method of the solar cell element according to the first embodiment, the bus electrode 4 and the grid electrode 7 having greatly different electrode widths are formed by preventing the disconnection by an inexpensive and simple process. A solar cell element excellent in conversion efficiency can be produced without causing an increase in cost or a decrease in yield.

Embodiment 2. FIG.
In the second embodiment, another shape of the bus-grid electrode connecting portion 9 will be described. FIGS. 3A and 3B are diagrams for explaining the configuration of the bus-grid electrode connecting portion 9 of the solar cell element according to the second embodiment, and FIGS. FIG. 3B is a cross-sectional view of the main part showing the peripheral part of the bus-grid electrode connecting part 9 in the cross section in the longitudinal direction of the grid electrode 7. In addition, the solar cell element concerning Embodiment 2 has the same structure as the solar cell element of Embodiment 1 except the bus-grid electrode connection part 9. FIG.

In the first embodiment, substantially rectangular bus having an electrode width W wider electrode width W _C than _G electrode width W _B than narrow and the grid electrode 7 of the bus electrode 4 in the longitudinal direction of the bus electrodes 4 - grid electrode connecting portion 9 as an example, as shown in FIG. 3A, the electrode width of the bus-grid electrode connection portion 9 is changed from the connection portion D between the bus-grid electrode connection portion 9 and the bus electrode 4 to the grid electrode 7. You may make it change gradually to the electrode width of the grid electrode 7 toward the front-end | tip direction.

In other words, the bus-grid electrode connecting portion 9 may be tapered such that the connecting portion D becomes narrower toward the tip of the grid electrode 7. At this time, the bus - electrode width W _D of the connecting portion D to the grid electrode connecting portion 9 is joined to the bus electrode 4, the electrode width of the bus electrode 4 W and _B and equal to or less than the bus electrode 4 and the bus - a grid electrode The difference in film thickness from the connection portion 9 is not increased. In the example shown in Figure 3-1, the bus - the grid electrode connecting portion 9, the direction from the connection portion between the bus electrode 4 to the connecting portion between the grid electrode 7, the electrode width W _C is the electrode width W _B of the bus electrode 4 It is changed to the electrode width W _G of the grid electrode 7.

For example, the bus - the grid electrode connecting portion 9 and 2mm electrode width W _D of the connecting portion D to be bonded to the bus electrode 4, the linearly varying the electrode width W _G of the grid electrode 7 as 60 [mu] m, the bus - a grid electrode the cross-sectional shape of the connecting portion 9, the bus as shown in Figure 3-2 - a slowly changing shape 40μm film thickness T _C of the grid electrode connecting portion 9 is 60 [mu] m. This is because the cross-sectional shape of the electrode is formed by passing an amount of paste in proportion to the printing area through the printing mask plate for electrode printing, so that the electrode width W _C of the bus-grid electrode connecting portion 9 -Electrode printing of paste by gradually changing the electrode width of the grid electrode 7 from the connection portion D between the grid electrode connection portion 9 and the bus electrode 4 to the bus-grid electrode connection portion 9, the grid electrode 7 and the connection portion E. This is because the transmission amount of the printing mask plate for use is gradually changing.

Thus bus - by a shape having a thickness T _C of the grid electrode connecting portion 9 changes gradually, there is no large change in electrode thickness, the electrode formation disconnection due to heat shrinkage during subsequent sintering cooling does not occur Can be realized. And by making the shape of the bus-grid electrode connection part 9 into such a shape, while preventing the disconnection between the bus electrode 4 and the grid electrode 7, the thinning of the electrode reduces the light receiving area compared to the conventional case. A wide solar cell element can be realized.

  In the solar cell element according to the second embodiment having the bus-grid electrode connecting portion 9 described above, the bus-grid electrode connecting portion 9 is connected from the connecting portion D to the connecting portion E as shown in FIGS. It can be formed in the same manner as in the first embodiment except that it is printed in a tapered shape that becomes narrower toward.

  Further, when the bus-grid electrode connection portion 9 as shown in FIGS. 3A and 3B is formed, the light receiving area is increased as compared with the conventional case due to the thinning of the grid electrode 7, but the bus-grid electrode connection portion. Since the area of 9 is slightly increased, the effect of increasing the light receiving area may be reduced.

  Therefore, as shown in FIG. 4A and FIG. 4B, the electrode width in the vicinity of the joint portion of the bus electrode 4 with the bus-grid electrode connection portion 9 is made narrower than the electrode width of other portions of the bus electrode 4. By adopting such a shape, the light receiving area is increased, and at the same time, a large difference in film thickness between the bus electrode 4 and the grid electrode 7 is eliminated, and an electrode can be formed in which disconnection is prevented. FIGS. 4-1 and FIGS. 4-2 are figures for demonstrating the other structure of the bus-grid electrode connection part 9 of the solar cell element concerning Embodiment 2, FIGS. 4-1 is a bus-grid electrode connection. FIG. 4B is a cross-sectional view of the main portion showing the peripheral portion of the bus-grid electrode connecting portion 9 in the cross section in the longitudinal direction of the grid electrode 7. .

Bus in the bus electrode 4 - electrode width W _F of the junction F between the grid electrode connecting portion 9, is preferably 20% to 80% of the width of the electrode width W _B of the bus electrode 4. Decrease in efficiency because current is limited by the electrode width W _B of the electrode width W _F of the junction F is the extremely narrow bus electrode 4 also becomes extremely narrow place. Therefore, To prevent disconnection of and electrodes increase the light receiving area, the bus in the bus electrode 4 - electrode width W _F of the junction F between the grid electrode connecting portion 9 is preferably in the range as described above.

  Such a change in the electrode shape can be easily realized by only changing the design of the printing mask plate without using a complicated process, and thus can be applied without increasing the production cost.

  As described above, according to the solar cell element according to the second embodiment, as in the solar cell element according to the first embodiment, disconnection between the bus electrode 4 and the grid electrode 7 having greatly different electrode widths is prevented. Thus, a solar cell element excellent in productivity, cost and conversion efficiency is realized.

Embodiment 3 FIG.
FIG. 5 is a cross-sectional view of the grid electrode 7, which is a thin line electrode formed by a printing method, along the longitudinal direction of the grid electrode 7. When a fine line electrode is formed as the grid electrode 7 by a printing method, as shown in FIG. 5, a concave portion 11 (mesh mark) is formed on the surface of the grid electrode 7 by the mesh 10 of the printing mask plate, and the surface of the grid electrode 7 is uneven. Shape is possible. Although depending on the characteristics of the paste used for printing the grid electrode 7, since the paste for thin line printing has a relatively high viscosity and a high thixotropy, this tendency is strong because the leveling characteristics are poor. In multilayer printing, the concave and convex portions are printed with the concave portions overlapped with the concave portions and the convex portions overlapped with the convex portions, so that the unevenness difference is further increased.

  The uneven shape on the electrode surface greatly affects the flow of electrons, resulting in a decrease in current collection efficiency, which causes deterioration of the characteristics of the solar cell element. Since the concavo-convex shape by the mesh 10 is determined by the mesh pitch, a printing mask plate having a different mesh pitch can be used for each printing. However, in this case, the cost increases and the printing process steps become complicated.

  Therefore, at the time of multilayer printing of the electrodes, the printing mask plate (mesh mask) and the silicon substrate 1 are simultaneously placed on the silicon substrate 1 with the bus electrode 4, the grid electrode 7, and the bus-grid electrode connection portion 9 on the silicon substrate 1. A first step of printing, and a second relative position between the silicon substrate 1 and the printing mask plate (mesh mask) displaced by a predetermined amount from the first relative position in a direction substantially parallel to the longitudinal direction of the grid electrode 7 The second step of simultaneously printing the bus electrode 4, the grid electrode 7, and the bus-grid electrode connecting portion 9 on the silicon substrate 1 is executed. Thereby, the formation positions of the recesses 11 (mesh marks) are averaged, the size of the recesses 11 is reduced, the surface of the grid electrode 7 is made flat, and the sun caused by the recesses 11 due to the mesh 10 of the printing mask plate It is possible to prevent the deterioration of the characteristics of the battery element.

  For example, when the electrode is multilayer printed, the silicon substrate 1 or the printing mask plate is offset in a direction substantially parallel to the longitudinal direction of the grid electrode 7 by a value X that is ½ of the mesh opening size or n times (nX) thereof (silicon By changing the relative position of the substrate 1 and the printing mask plate), the formation positions of the recesses 11 (mesh marks) can be averaged, the size of the recesses 11 can be reduced, and the surface of the grid electrode 7 can be made flat. it can. When the silicon substrate 1 or the printing mask plate is offset in this way, the electrode width of the bus electrode 4 is increased by X or n times (nX) the number of times of printing, so that the light receiving area is not reduced. The bus electrode 4 is designed to be narrow in advance by a distance for shifting the line width.

  Further, there is an effect of reducing the difference in film thickness as in the case of changing the shape by performing multi-layer printing with offset as described above. FIG. 6 is a diagram for explaining the configuration of the electrodes when the multi-layer printing is performed by offsetting the silicon substrate 1 or the printing mask plate, and the peripheral portion of the bus electrode 4 in the cross section in the longitudinal direction of the grid electrode 7. It is principal part sectional drawing which shows these.

  Since printing is performed by changing the position of the silicon substrate 1 or the printing mask plate, a difference in film thickness can be produced around the pattern. For example, as shown in FIG. The film thickness is gradually reduced in the direction (the tip direction of the grid electrode 7). This eliminates a large step between the bus electrode 4 and the grid electrode 7, thereby reducing the difference in film thickness between the two and preventing disconnection due to thermal contraction between the bus electrode 4 and the grid electrode 7. it can.

  The inventor of the present application conducted the following experiment using a p-type polycrystalline silicon substrate having an outer dimension of 150 mm × 150 mm and a thickness of 0.2 mm. This p-type polycrystalline silicon substrate has a fine uneven shape formed by etching on the light receiving surface side, and a surface electrode was formed on the fine uneven shape by a printing method.

The electrode shape of the surface electrode is the shape shown in FIG. 4A and FIG. 4B shown in the second embodiment, and the bus width of the bus electrode 4 is 2 mm and the electrode width of the grid electrode 7 is 0.05 mm as design values. , buses in the longitudinal direction of the grid electrode 7 - electrode width W _C of the central portion of the grid electrode connecting portion 9 is shaped to connect 0.5 mm. In the longitudinal direction of the grid electrode 7, the bus-grid electrode connection portion 9 has an electrode width W _C that gradually increases toward the bus electrode 4 and gradually decreases toward the tip end of the grid electrode 7. It has a shape.

For the printing mask plate, Stained Mesh No. 325 having a wire diameter of 16 μm was used as the mesh. The offset amount of the printing mask plate at the multi-layered printed, a half of 40μm mesh opening 80μm per printing once, electrode width _{W B} of the bus electrode 4 was set to 1.84mm design. Electrode width _{W G} of the grid electrode is 0.03mm design.

  The printing was performed while shifting in a direction substantially parallel to the longitudinal direction of the grid electrode 7 by 40 μm per printing on the basis of the outer shape of the substrate. Between printing, the paste was dried in a drying furnace at 150 ° C. as a drying process. Such a printing-drying process was repeated 5 times to form a surface electrode.

  On the back surface of the substrate, an electrode was formed by printing an aluminum paste in a 148 mm × 148 mm square region by a printing method, and the electrode was baked at 820 ° C. The sample of an Example was obtained by the above process. The connection part (bus-grid electrode connection part 9) and the grid electrode 7 of the bus electrode 4 and the grid electrode 7 of the sample of an Example did not have a disconnection, and the unevenness | corrugation of the surface of the grid electrode 7 also decreased.

  Further, as a comparative sample, an electrode width of 2 mm for the bus electrode and an electrode width of 100 μm for the grid electrode without performing offset at the time of multilayer printing on the same p-type polycrystalline silicon substrate as described above, the bus-grid electrode connecting portion 9 A conventional solar cell element not including the above was produced.

And about the sample of the Example and the sample of the comparative example, the characteristic was measured using the apparatus which simulates sunlight. When the sample of the example and the comparative sample are compared, the current density J of the solar cell element of the comparative sample is 33.2 mA / cm ² whereas the current density J of the sample of the example is 34.0 mA / cm ^2. As a result, an increase in current density of 2.5% was confirmed.

  Thus, by performing multi-layer printing of the electrodes by changing the relative position between the silicon substrate and the printing mask plate, the solar cell element caused by the recesses 11 due to the mesh 10 of the printing mask plate is brought close to the surface of the grid electrode 7. It was confirmed that the deterioration of the characteristics can be prevented.

  As described above, according to the method for manufacturing the solar cell element according to the third embodiment, the disconnection between the bus electrode 4 and the grid electrode 7 having greatly different electrode widths is prevented, and the print mask at the time of multilayer printing A solar cell element excellent in productivity, cost, and conversion efficiency in which deterioration of the characteristics of the solar cell element due to the concave portion 11 due to the mesh 10 of the plate is prevented can be produced.

  As described above, the solar cell element according to the present invention is useful for a solar cell element having a grid electrode and a bus electrode having greatly different electrode widths.

It is the top view which looked at the solar cell element concerning Embodiment 1 of this invention from the light-receiving surface side. It is sectional drawing in line segment AA of FIGS. 1-1. It is a figure for demonstrating the bus-grid electrode connection part of the solar cell element concerning Embodiment 1 of this invention, and expands the area | region B which is an intersection part of the bus electrode and grid electrode in FIGS. 1-1. FIG. It is a figure for demonstrating the bus-grid electrode connection part of the solar cell element concerning Embodiment 1 of this invention, and is sectional drawing along the longitudinal direction of the grid electrode in the area | region B in FIGS. 1-1. It is a figure for demonstrating the bus-grid electrode connection part of the solar cell element concerning Embodiment 2 of this invention, and is the principal part top view which looked at the peripheral part of the bus-grid electrode connection part from the light-receiving surface side. . It is a figure for demonstrating the bus-grid electrode connection part of the solar cell element concerning Embodiment 2 of this invention, and is the principal part which shows the peripheral part of a bus-grid electrode connection part among the cross sections in the longitudinal direction of a grid electrode. It is sectional drawing. It is a figure for demonstrating the other bus-grid electrode connection part of the solar cell element concerning Embodiment 2 of this invention, and the principal part top view which looked at the peripheral part of the bus-grid electrode connection part from the light-receiving surface side It is. It is a figure for demonstrating the other bus-grid electrode connection part of the solar cell element concerning Embodiment 2 of this invention, and shows the peripheral part of a bus-grid electrode connection part among the cross sections in the longitudinal direction of a grid electrode. It is principal part sectional drawing. It is sectional drawing along the longitudinal direction of the grid electrode which is a thin wire electrode formed by the printing method. It is a figure for demonstrating the structure of the electrode at the time of performing multilayer printing by offsetting a silicon substrate or a printing mask plate, and is principal part sectional drawing which shows the peripheral part of a bus electrode among the cross sections in the longitudinal direction of a grid electrode. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Micro unevenness 3 Antireflection film 4 Bus electrode 5 Electrode 6 Back surface electrode 7 Grid electrode 9 Grid electrode connection part 10 Mesh of mask printing plate 11 Concave part

Claims (6)

A solar cell element having a bus electrode formed by multilayer printing using a screen printing method and a grid electrode having an electrode width narrower than the electrode width of the bus electrode on the light receiving surface side of the substrate,
Connecting the bus electrode and the grid electrode, and having an electrode connection portion having a region in which the width in the longitudinal direction of the bus electrode is narrower than the electrode width of the bus electrode and wider than the electrode width of the grid electrode;
A solar cell element characterized by the above. The electrode connecting portion has a substantially rectangular shape in which the width in the longitudinal direction of the bus electrode is narrower than the electrode width of the bus electrode and wider than the electrode width of the grid electrode in the in-plane direction of the substrate;
The solar cell element according to claim 1. The electrode connection portion has an electrode width that changes from an electrode width of the bus electrode to an electrode width of the grid electrode from a connection portion with the bus electrode toward a connection portion with the grid electrode.
The solar cell element according to claim 1. The bus electrode has a width in a short direction of the bus electrode in a connection portion with the electrode connection portion, which is narrower than a width in a portion other than the connection portion with the electrode connection portion,
The solar cell element according to claim 1. As a process of printing and forming bus electrodes and grid electrodes on a substrate by multilayer printing using a screen printing mask,
When printing the bus electrode and the grid electrode, the bus electrode is connected to the grid electrode and the width of the bus electrode in the longitudinal direction is smaller than the electrode width of the bus electrode and the electrode width of the grid electrode Including a printing step of printing an electrode connection portion having a wider area simultaneously with the bus electrode and the grid electrode,
The manufacturing method of the solar cell element characterized by these. The printing step comprises:
A first step of simultaneously printing the bus electrode, the grid electrode, and the electrode connection portion on the substrate at a first relative position between the mask and the substrate;
In the second relative position of the mask and the substrate displaced from the first relative position in a direction substantially parallel to the longitudinal direction of the grid electrode, the bus electrode, the grid electrode, and the electrode connection portion are A second step of simultaneously printing on the substrate;
The manufacturing method of the solar cell element of Claim 5 characterized by the above-mentioned.

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