JP6405285B2 - Manufacturing method of solar cell - Google Patents

Description

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

  FIG. 3 shows an overview of a solar battery cell having a relatively high photoelectric conversion efficiency using a single crystal or polycrystalline semiconductor substrate. FIG. 3 is an external view showing the surface (light-receiving surface) shape of a general solar cell. As shown in FIG. 3, a solar cell 100 has a large number of electrodes having a width of several hundreds to several tens of μm called finger electrodes 102 on a substrate 101 such as a silicon substrate as a collecting electrode on a light receiving surface. It is common to have 1 to 4 bus bar electrodes 103 as current collecting electrodes for connecting battery cells. In the present specification, the collecting electrode means an electrode for taking out carriers generated in the substrate, and includes a finger electrode and a bus bar electrode.

  A schematic diagram of the cross-sectional structure of the cell is shown in FIG. FIG. 4 is a schematic cross-sectional view of a general solar cell. As shown in FIG. 4, the solar cell 200 is provided with an emitter layer 202 having a conductivity type opposite to the conductivity type of the substrate 201 on the light receiving surface side with respect to the substrate 201, and provided with a light receiving surface current collecting electrode 203 thereon. It is done. In order to reduce reflection loss, an antireflection film 204 such as a SiNx film or a silicon oxide film is often provided in the light receiving region.

  In addition, a back surface electric field layer 205 is provided on the surface (back surface) on the side opposite to the light receiving surface, and a back surface collecting electrode 206 is formed thereon, as in the light receiving surface, and no back surface collecting electrode 206 is provided. The non-electrode region is covered with a surface protective film 207 such as a SiNx film or a silicon oxide film.

  For electrode formation, methods such as vapor deposition and sputtering can be used, but screen printing is widely used from the viewpoint of cost. An Ag paste obtained by mixing Ag powder and glass frit with an organic binder is printed in a finger pattern on the surface of a substrate on which a SiNx film or the like is formed using a printing plate. Thereafter, Ag powder is passed through the SiNx film or the like by heat treatment (fire through), and the electrode and silicon are made conductive.

  The photoelectric conversion efficiency of the solar cell having such a structure is affected by the resistance (wiring resistance) of the finger electrodes on either the light receiving surface or the back surface. That is, if the finger electrode is thin and the sectional area is small or the distance to the bus bar electrode is long, the photoelectric conversion efficiency is lowered.

  As a method of reducing the wiring resistance in the finger electrode, it is easy to increase the finger electrode width, but this reduces the area of the non-electrode region, and the area of the region where the photogenerated carriers are likely to recombine. The conversion efficiency increases and the conversion efficiency decreases. That is, the reduction in the wiring electrode resistance due to the increase in the finger electrode width and the increase in recombination due to the decrease in the non-electrode region area are in a trade-off relationship, so that it is difficult to further improve the conversion efficiency.

  In addition, there is a method of expanding the electrode cross-sectional area by, for example, printing the finger electrode a plurality of times (for example, Patent Document 1). It is not always an effective method because an apparatus capable of adjustment is required.

International Publication No. WO2008 / 026415 Pamphlet

  The present invention has been made in view of the above problems, and a solar cell having a low wiring resistance of a collecting electrode and a small contact area between a substrate and the collecting electrode, and easily manufacturing such a solar cell. It aims at providing the manufacturing method of the solar cell which can do.

To achieve the above object, the present invention provides a method for producing a solar cell having a current collecting electrode on at least a first main surface of a semiconductor substrate, wherein the current collecting electrode is formed.
Forming a contact electrode portion by printing and baking a first conductive material on the first main surface of the semiconductor substrate; and
On the first main surface on which the contact electrode portion is formed, an insulating material is applied so that at least a part of the contact electrode portion is exposed, and cured to form an insulating film;
On the insulating film, a second conductive material is formed and cured so as to cover the portion where the contact electrode portion is formed and the second conductive material is in contact with the exposed portion of the contact electrode portion. And a step of forming the upper electrode portion to form the current collecting electrode comprising the contact electrode portion and the upper electrode portion.

  In such a solar cell manufacturing method, a contact electrode part in contact with a substrate is formed, and then an insulating material is applied, cured to form an insulating film, and then an upper electrode part is formed, thereby collecting current electrodes An electrode structure in which only a part of the electrode is in contact with the substrate can be easily formed. Accordingly, it is possible to easily manufacture a solar cell having a low wiring resistance of the collecting electrode and a small contact area between the substrate and the collecting electrode.

  In addition, the insulating material is selected from one or more of silicone resin, polyimide resin, polyamideimide resin, fluorine resin, phenol resin, melamine resin, urea resin, polyurethane, epoxy resin, acrylic resin, polyester resin, and poval resin. It is preferably made of a material containing a resin.

  If it is the manufacturing method of the solar cell using such an insulating material, an insulating film can be formed easily and the solar cell which has an insulating film excellent in heat resistance can be manufactured.

Furthermore, in the present invention, a solar cell having a current collecting electrode on at least a first main surface of a semiconductor substrate,
The current collecting electrode is in contact with the first main surface of the semiconductor substrate and comprises a contact electrode portion having a pattern shape and an upper electrode portion formed so as to cover the contact electrode portion,
The upper electrode part is a part of the upper electrode part in contact with the contact electrode part, and a part other than the contact part is physically and electrically isolated from the semiconductor substrate by an insulating film containing a resin. A solar cell is provided.

  In such a solar cell, the wiring resistance of the collecting electrode is low, and the contact area between the substrate and the collecting electrode is small.

  The resin may be one or more selected from silicone resin, polyimide resin, polyamideimide resin, fluororesin, phenol resin, melamine resin, urea resin, polyurethane, epoxy resin, acrylic resin, polyester resin, and poval resin. Preferably there is.

  If it is such a solar cell, an insulating film can be formed easily and it can be set as the solar cell which has an insulating film excellent in heat resistance.

  In the method for manufacturing a solar cell of the present invention, the conductive material needs to be printed twice, but when the second conductive material is printed, an insulating film is formed on the main surface on which the contact electrode portion is formed. Therefore, the printing width of the second conductive material can be made relatively thick. Thereby, the condition of the alignment at the time of printing of the second conductive material can be relaxed. In addition, in order to reduce the wiring resistance of the current collecting electrode, it is sufficient if there is only one electrical contact location between the contact electrode portion and the upper electrode portion in the current collecting electrode (the contact electrode portion and the upper electrode portion are entirely connected to each other). This structure can be easily formed by the solar cell production method of the present invention.

  As a result, the collector electrode can greatly reduce the wiring resistance of the collector electrode while maintaining the minimum necessary contact area with the substrate. For this reason, a form factor improves without reducing an open circuit voltage, and photoelectric conversion efficiency improves.

It is a flowchart which shows an example of the formation process of the current collection electrode in the manufacturing method of the solar cell of this invention. It is a cross-sectional schematic diagram which shows an example of the solar cell of this invention. It is an external view which shows the surface (light-receiving surface) shape of a common solar cell. It is a cross-sectional schematic diagram of a general solar cell.

  Hereinafter, the present invention will be described in more detail.

  As described above, a solar cell having a low wiring resistance of a collecting electrode and a small contact area between a substrate and the collecting electrode and a method for producing such a solar cell capable of easily producing such a solar cell are desired. .

  The present inventors have intensively studied to achieve the above object. As a result, after forming the contact electrode portion in contact with the substrate, an insulating material is applied and cured to form an insulating film, and then a method for manufacturing a solar cell using the upper electrode portion as a current collecting electrode The present invention has been completed.

  In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention and how to implement it in specific embodiments. However, it will be understood that the invention may be practiced without these specific details. In the following description, well-known methods, procedures, and techniques are not shown in detail to avoid obscuring the present invention. The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto. The drawings included and described herein are schematic and are not limiting the scope of the invention. Also, in the drawings, the size of some of the elements is exaggerated for illustrative purposes and therefore is not to scale.

[Solar cell]
Hereinafter, although the solar cell of this invention is demonstrated using FIG. 2, this invention is not limited to this.

  FIG. 2 is a schematic cross-sectional view showing an example of the solar cell of the present invention. As shown in FIG. 2, the solar cell 10 is provided with an emitter layer 12 having a conductivity type opposite to the conductivity type of the substrate on the light receiving surface side of the semiconductor substrate 11, and a light receiving surface collecting electrode 13 is provided thereon. It is done. An antireflection film 14 such as a SiNx film or a silicon oxide film can be provided in the light receiving region for the purpose of reducing reflection loss.

  Further, a back surface electric field layer 15 is provided on the back surface side, and a back surface collecting electrode 16 is formed on the back surface electric field layer 15 as well as a light receiving surface. The surface protective film 17 can be covered.

  Here, the back surface collecting electrode 16 is in contact with the back surface of the semiconductor substrate 11 and includes a back surface contact electrode portion 19 having a pattern shape and a back surface upper electrode portion 20 formed so as to cover the back surface contact electrode portion 19. Become. The light receiving surface collecting electrode 13 is in contact with the light receiving surface of the semiconductor substrate 11 and has a light receiving surface contact electrode portion 22 having a pattern shape and a light receiving surface upper electrode formed so as to cover the light receiving surface contact electrode portion 22. Part 23.

  The back surface upper electrode part 20 is physically and electrically isolated from the semiconductor substrate 11 by a back surface insulating film 18 containing a resin at a part other than the contacted part of the back surface upper electrode part 20 in contact with the back surface contact electrode part 19. Has been. Further, the light receiving surface upper electrode portion 23 is physically connected to the semiconductor substrate 11 by the light receiving surface insulating film 21 including a resin at a part of the light receiving surface upper electrode portion 23 that is in contact with the light receiving surface contact electrode portion 22 and a portion other than the contact portion. Is electrically and electrically isolated.

  As described above, only the light receiving surface contact electrode portion 22 and the back surface contact electrode portion 19 are in contact with the semiconductor substrate 11, and the back surface upper electrode portion 20 and the light receiving surface upper electrode portion 23 having a large cross-sectional area mainly serve as a path of electricity. Bear. That is, in the finger electrode portion, the back surface upper electrode portion 20 and the light receiving surface upper electrode portion 23 mainly play a role as an electrical path to the bus bar electrode. Since the back surface upper electrode portion 20 and the light receiving surface upper electrode portion 23 have large cross-sectional areas, they can function as resistance reduction electrodes. Therefore, the internal series resistance as a solar cell is reduced and the photoelectric conversion efficiency is improved. Further, since the back surface upper electrode portion 20 is separated from the semiconductor substrate 11 by the back surface insulating film 18, the surface protective film 17 is not unnecessarily damaged. That is, the recombination region area does not increase. In other words, the resistance of the back surface collecting electrode can be greatly reduced while maintaining the minimum necessary contact area with the substrate. Similarly, the resistance of the light receiving surface collecting electrode can be greatly reduced while maintaining the minimum necessary contact area with the substrate. A part of the collecting electrodes, for example, only the finger electrodes may have a two-layer structure including a contact electrode part and an upper electrode part, and the bus bar electrode may be a single layer, and this aspect is also included in the present invention. Since the finger electrode has a particularly small contact area with the substrate (that is, the wiring resistance is larger than that of the bus bar electrode) and is larger than that of the bus bar electrode, the effect of the two-layer structure of the present invention is great.

  The insulating film should just contain resin. If it is a solar cell provided with the insulating film containing resin, the electrode structure in which only a part of current collection electrode contacts a board | substrate can be simply formed without using a mask etc. at the time of manufacture. Specific examples of the resin include silicone resin, polyimide resin, polyamideimide resin, fluorine resin, phenol resin, melamine resin, urea resin, polyurethane, epoxy resin, acrylic resin, polyester resin, and poval resin. This resin may be used individually by 1 type, and may use 2 or more types together. Such a resin is more excellent in heat resistance.

  Here, the shape of the contact electrode portion may be a pattern shape, and may be, for example, a linear continuous shape. In addition, since the upper electrode part is formed on the contact electrode part, the contact electrode part does not necessarily need to be continuous, and there is no problem even if it is disconnected somewhat. When the contact electrode portion is disconnected, the upper electrode portion may be formed in a linear continuous shape so that each contact electrode portion is electrically connected.

  In FIG. 2, a solar cell including a current collecting electrode composed of a contact electrode portion and an upper electrode portion on the light receiving surface and the back surface is illustrated, but the solar cell of the present invention is not limited to this. For example, it is also possible to make a solar cell including either the light receiving surface or the back surface as the first main surface and the current collecting electrode composed of the contact electrode portion and the upper electrode portion of the present invention only on the first main surface. it can. In this case, the electrode structure on the second main surface is not limited.

  FIG. 2 shows a solar cell including an insulating film on the entire surface of the light-receiving surface and the back surface (except for the portion where the upper electrode portion and the contact electrode portion are in contact), and the upper electrode portion on a part of the light-receiving surface and the back surface. However, the solar cell of the present invention is not limited to this. For example, a solar cell including an insulating film only around the contact electrode portion can be obtained. Moreover, it can also be set as the solar cell which provides an insulating film in the back surface whole surface (except the location which an upper electrode part and a contact electrode part contact | connect), and has a back surface current collection electrode in the whole surface on this insulating film.

[Method for manufacturing solar cell]
Hereinafter, although an example of the manufacturing method of the solar cell of this invention is demonstrated to the case of an N-type silicon substrate, this invention is not limited to this.

  High purity silicon is doped with a group V element such as phosphorus, arsenic, or antimony, and has a specific resistance of 0.1 to 5 Ω · cm. Etching using a high concentration alkali such as sodium hydroxide or potassium hydroxide or a mixed acid of hydrofluoric acid and nitric acid. The single crystal silicon substrate may be manufactured by either the CZ method or the FZ method. The substrate is not necessarily made of single crystal silicon, but may be polycrystalline silicon.

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

  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.

  On this substrate, an emitter layer is formed on the light receiving surface side, and a back surface electric field layer is formed on the back surface side. The emitter layer has a conductivity type opposite to that of the substrate (in this case P type) and a thickness of about 0.05 to 1 μm, and the back surface field layer has the same conductivity type as the substrate (in this case N type) and has a thickness of 0.1 to 2 μm. Degree.

A thermal diffusion method is suitable as a method for forming the emitter layer. Specifically, in addition to the vapor phase diffusion method using BBr ₃ or the like, a method in which a coating agent containing a boron source is applied to the entire light receiving surface and heat-treated at 950 to 1050 ° C. can be exemplified.

  A vapor phase diffusion method using phosphorus oxychloride can be used for forming the back surface electric field layer. The back surface electric field layer is formed by heat-treating the substrate at 830 to 950 ° C. in a mixed gas atmosphere of phosphorus oxychloride, nitrogen, and oxygen. In addition to the vapor phase diffusion method, the back surface electric field layer can also be formed by a method in which a phosphorus-containing material is spin-coated or printed and then heat-treated.

  After the formation of the diffusion layers (emitter layer and back surface field layer), the glass formed on the surface is removed with hydrofluoric acid or the like.

Next, an antireflection film is formed on the light receiving surface. As the antireflection film, a SiNx film or a silicon oxide film can be used. In the case of a SiNx film, a film is formed to a thickness of about 100 nm using a plasma CVD apparatus. As the reaction gas, monosilane (SiH ₄ ) and ammonia (NH ₃ ) are often mixed and used. However, 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. In the case of a silicon oxide film, a CVD method may be used, but a film obtained by a thermal oxidation method can provide higher cell characteristics.

  A SiNx film or a silicon oxide film can also be used on the back surface as a surface protective film. The film thickness is preferably 50 to 250 nm. Similar to the light receiving surface side, the SiNx film can be formed by the CVD method, and the silicon oxide film can be formed by the thermal oxidation method or the CVD method.

  Subsequently, current collecting electrodes are formed on the light receiving surface and the back surface of the substrate. The method for forming the current collecting electrode will be described with reference to FIG. 1, but the present invention is not limited to this. FIG. 1 is a flowchart showing an example of a collecting electrode forming step in the method for manufacturing a solar cell of the present invention.

  Through the steps from the etching to the formation of the surface protective film, an emitter layer 12 and an antireflection film 14 are formed on the light receiving surface side of the semiconductor substrate 11 as shown in FIG. A back surface electric field layer 15 and a surface protective film 17 are formed on the back surface side. Note that the texture is not shown in FIG.

  A first conductive material (first conductive material for the back electrode) is printed in a pattern on the back surface of the semiconductor substrate 11, and the first conductive material (first for the light receiving surface electrode) is printed on the light receiving surface. The back surface contact electrode portion 19 and the light receiving surface contact electrode portion 22 are formed by printing a conductive material) in a pattern and firing them (FIG. 1A). Specifically, the back contact electrode portion 19 and the light receiving surface contact electrode portion 22 can be formed as follows.

  First, the first conductive material is printed on the back surface by, for example, a screen printing method. For example, a plate making in which a portion corresponding to a finger electrode has an opening width of 30 to 100 μm and a parallel line pattern with an interval of 1 to 2 mm is prepared, and Ag powder and glass frit are used as a first conductive material (first conductive paste). An Ag paste mixed with an organic binder is printed. The back contact electrode portion obtained by firing the first conductive material does not necessarily have to be continuous because there is a subsequent second electrode formation step, and there is no problem even if it is somewhat disconnected.

  Next, a first conductive material is formed on the light receiving surface. A screen printing method can also be used when printing a conductive material on the light receiving surface. For example, a plate making in which the part corresponding to the finger electrode has an opening width of 20 to 70 μm and a parallel line pattern with an interval of 1 to 2 mm can be used. Using this plate making, the above Ag paste is printed on the light receiving surface. Also in this case, the light-receiving surface contact electrode portion obtained by firing the first conductive material does not necessarily have to be continuous because there is a second electrode formation step later, and may be somewhat disconnected. no problem. Further, the printing order of the first conductive material on the back surface and the first conductive material on the light receiving surface may be reversed. The composition of the first conductive material for the back electrode and the first conductive material for the light receiving surface electrode may be different or the same.

  After the printing of the first conductive material on the light receiving surface and the back surface, Ag powder is passed through the SiNx film by heat treatment (fire through), and the electrode and silicon are made conductive. The first conductive material on the back surface and the first conductive material on the light receiving surface can be fired separately. Firing is usually performed by treating at a temperature of 700 to 850 ° C. for 5 to 30 minutes. By this baking, the back contact electrode portion 19 and the light receiving surface contact electrode portion 22 are formed.

  Next, an insulating material is applied on the back surface on which the back contact electrode portion 19 is formed so that at least a part of the back contact electrode portion 19 is exposed and cured to form the back surface insulating film 18 (FIG. 1). (B)). In addition, an insulating material is applied onto the light receiving surface on which the light receiving surface contact electrode portion 22 is formed so that at least a part of the light receiving surface contact electrode portion 22 is exposed and cured to form the light receiving surface insulating film 21. (FIG. 1 (c)). Specifically, the back surface insulating film 18 and the light receiving surface insulating film 21 can be formed as follows.

  First, an insulating material is applied to the back surface. As the coating method, screen printing or spin coating can be used. It may be applied so that at least a part of the back contact electrode portion 19 is exposed, may be applied so as to cover the back contact electrode portion 19 formed earlier, or may be applied to the entire back surface. As the insulating material, a material that is liquid at normal temperature and normal humidity and is cured by heating, humidification, drying, or the like is preferable. Specifically, what consists of a material containing 1 or more types of resin described in the item of the above-mentioned solar cell is preferable. Note that fluidity can also be imparted by adding a solvent to the insulating material.

  Even if the insulating material is applied so as to cover the printed part of the back contact electrode part 19, the printed part of the back contact electrode part 19 is raised from the surroundings, so that the top of the electrode printed part is completely covered with the insulating material. Is not covered.

  In addition, as with the back surface, an insulating material is also applied to the light receiving surface. As with the back surface, the light receiving surface contact electrode portion 22 that has been printed and baked previously is raised from the surroundings, so that the top portion of the electrode print portion is not completely covered with the insulating material.

  Thus, since the contact electrode portion is raised from the non-electrode forming portion, the apex of the contact electrode portion is exposed from the insulating material. By curing this insulating material by heating, humidification, drying, or the like, the back surface insulating film 18 and the light receiving surface insulating film 21 are formed. If the second conductive material is formed in a pattern or the like on this, the wiring resistance of the current collecting electrode can be lowered while keeping the contact area between the substrate and the current collecting electrode to the minimum necessary.

  Next, on the back surface insulating film 18, the second conductive material (second conductive material for the back surface electrode) covers the portion where the back surface contact electrode portion 19 is formed, and the second conductive material is the back surface. It forms so that it may contact the exposed location of the contact electrode part 19, and it hardens | cures, and the back surface upper electrode part 20 is formed (FIG.1 (d)). Thereby, the back surface collecting electrode 16 which consists of the back surface contact electrode part 19 and the back surface upper electrode part 20 is formed. In addition, on the light-receiving surface insulating film 21, a second conductive material (second conductive material for the light-receiving surface electrode) covers the portion where the light-receiving surface contact electrode portion 22 is formed, and the second conductive material Is formed so as to be in contact with the exposed portion of the light receiving surface contact electrode portion 22 and hardened to form the light receiving surface upper electrode portion 23 (FIG. 1E). As a result, the light receiving surface collecting electrode 13 including the light receiving surface contact electrode portion 22 and the light receiving surface upper electrode portion 23 is formed. The printing order of the second conductive material on the back surface and the second conductive material on the light receiving surface may be reversed. Moreover, the composition of the second conductive material for the back electrode and the second conductive material for the light receiving surface electrode may be different or the same. Specifically, the back surface upper electrode portion 20 and the light receiving surface upper electrode portion 23 can be formed as follows.

  First, a second conductive material (second conductive paste) is formed on the back surface insulating film 18. Specifically, a low temperature curing type conductive paste is printed in a pattern or on the entire surface. In the case of a pattern, a plate making in which a portion corresponding to the finger electrode has a parallel line pattern with an opening width of 100 to 400 μm and an interval of 1 to 2 mm can be used. Using this plate making, the second conductive material is printed so as to cover the back contact electrode portion 19 in accordance with the back contact electrode portion 19 that has been printed and baked previously, and is cured at 100 to 400 ° C. . At this time, that the upper electrode portion covers the contact electrode portion means that at least the contact electrode portion and the upper electrode portion are made to coincide with each other, and the upper electrode portion may be wider than the width of the contact electrode portion. Thereby, the back surface upper electrode part 20 is formed. As the conductive carrier of the conductive paste, any one of Ag, Al, Ni, Cu or a mixture thereof is preferable. Examples of the second conductive material include a material containing such a conductive carrier and one or more kinds of resins selected from an epoxy resin, an acrylic resin, a polyester resin, a phenol resin, and a silicone resin.

  Next, a second conductive material is formed on the light receiving surface insulating film 21. In the case of an electrode formed on the light receiving surface, it is preferable to use a plate making in which a portion corresponding to a finger electrode has an opening width of 40 to 100 μm and a parallel line pattern with an interval of 1 to 2 mm. By setting the opening width within the above range, the light receiving area of the solar cell can be sufficient while increasing the cross-sectional area of the light receiving surface upper electrode portion in the manufactured solar cell. Using the plate making, the second conductive material is printed according to the light-receiving surface contact electrode portion 22 that has been printed and baked in advance, and is cured at 100 to 400 ° C. Thereby, the light receiving surface upper electrode part 23 is formed.

  In addition, although the example which forms an upper electrode part in a light-receiving surface and a back surface after forming an insulating film in a light-receiving surface and a back surface was demonstrated in FIG. 1, the manufacturing method of the solar cell of this invention is not limited to this. For example, after the back surface insulating film 18 is formed on the back surface (FIG. 1B) and the back surface upper electrode portion 20 is formed (FIG. 1C ′), the light receiving surface insulating film 21 is formed on the light receiving surface. (FIG. 1 (d ′)), the light receiving surface upper electrode portion 23 can also be formed (FIG. 1 (e)).

  Moreover, in FIG. 1, although the manufacturing method of the solar cell provided with the current collection electrode which consists of a contact electrode part and an upper electrode part on a light-receiving surface and a back surface was illustrated, the manufacturing method of the solar cell of this invention is not limited to this. For example, a solar cell (for example, a figure) having either one of the light receiving surface and the back surface as a first main surface, and a collecting electrode composed of the contact electrode portion and the upper electrode portion of the present invention only on the first main surface. 1 (c ′)) can also be manufactured. In this case, the electrode structure on the second main surface is not limited.

  In this way, the solar cell shown in FIG. 2 can be manufactured. According to the above method, although the printing of the conductive material is indispensable, when the second conductive material is printed, the insulating film is formed on the main surface on which the contact electrode portion is formed. The printing width of the biconductive material can be made relatively thick. Thereby, the condition of the alignment at the time of printing of the second conductive material can be relaxed. In addition, in order to reduce the wiring resistance of the current collecting electrode, it is sufficient if there is only one electrical contact location between the contact electrode portion and the upper electrode portion in the current collecting electrode (the contact electrode portion and the upper electrode portion are entirely connected to each other). This structure can be easily formed by the solar cell production method of the present invention.

  Further, in the method for manufacturing a solar cell of the present invention, after forming a contact electrode portion in contact with a substrate, an insulating material is applied and cured to form an insulating film, and then an upper electrode portion is formed, thereby forming a mask. The electrode structure in which only a part of the collecting electrode is in contact with the substrate can be easily formed without using the like. Further, it is not necessary to use a device that can adjust the position with high accuracy. Therefore, a solar cell having such an electrode structure can be manufactured at low cost.

  As described above, the case of the N-type substrate has been described as an example. However, in the case of the P-type substrate, phosphorus, arsenic, antimony, etc. may be diffused when the emitter layer is formed, and boron, Al, etc. may be diffused when the back surface field layer is formed. The effect of reducing the wiring resistance of the collecting electrode is manifested and the conversion efficiency is improved.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to the following Example.

(Examples 1, 2 and comparative examples)
In order to confirm the effectiveness of the present invention, solar cells were manufactured and the solar cell characteristics were compared.

  After removing the damaged layer with a hot concentrated potassium hydroxide aqueous solution on 24 phosphorous-doped {100} N-type as-cut silicon substrates having a thickness of 200 μm and a specific resistance of 1 Ω · cm, a 72 ° C. potassium hydroxide / 2-propanol aqueous solution is removed. It was immersed in and textured, and then washed in a hydrochloric acid / hydrogen peroxide mixed solution heated to 75 ° C.

  Next, a 2% boric acid aqueous solution was spin-coated on the light-receiving surface, and heat treatment was performed at 1000 ° C. for 18 minutes to form a boron diffusion layer. As a result of measurement by the 4-probe method, the sheet resistance was 50Ω.

  Next, in a phosphorus oxychloride atmosphere, heat treatment was performed for 40 minutes with the light receiving surfaces overlapped at 870 ° C. to form a phosphorus diffusion layer on the back surface.

  Thereafter, the surface glass was removed by immersion in hydrofluoric acid having a concentration of 12%.

  After the above processing, SiNx films were formed on both sides using a plasma CVD apparatus. The film thickness was 100 nm on both the light receiving surface and the back surface.

  Next, as the first conductive material, an Ag paste was printed on the light receiving surface and the back surface and dried. The finger spacing on the back surface was 1.2 mm, and the finger spacing on the light receiving surface was 2.0 mm. When observed with a microscope, the line width was about 100 μm on the back surface and about 70 μm on the light receiving surface. This was baked in an air atmosphere at 780 ° C. to form a back contact electrode part and a light receiving surface contact electrode part. Eight of them were directly used as solar cells (comparative example).

  After that, about 8 out of 16 sheets except for the comparative example, room temperature curing type silicone (one-pack type RTV rubber; manufactured by Shin-Etsu Chemical Co., Ltd.) was printed on the entire back surface and cured at room temperature. An insulating film was obtained. At this time, silicone resin was printed on the entire back surface, but a part of the back contact electrode portion was exposed.

  Next, a thermosetting Ag paste (containing Ag powder and epoxy resin) was printed and cured at 300 ° C. to form a back upper electrode portion. The line width of the portion corresponding to the finger electrode was 300 μm. Thus, what the back electrode consists of a contact electrode part and an upper electrode part was obtained, and it was set as the solar cell (Example 1).

  For the other eight sheets, room temperature curable silicone was printed on the entire light receiving surface and cured at room temperature to form a light receiving surface insulating film. Thereafter, a thermosetting Ag paste was printed on the light receiving surface and cured at 300 ° C. to form a light receiving surface upper electrode portion. The line width was 80 μm. Thus, what the light-receiving surface electrode consists of a contact electrode part and an upper electrode part was obtained, and it was set as the solar cell (Example 2).

  About the solar cell obtained by Example 1, 2 and the comparative example, the current-voltage characteristic was measured under pseudo-sunlight. The average value of each condition is shown in Table 1 below.

  As shown in Table 1, since the wiring resistance of the finger electrode was reduced on the back surface in Example 1 and on the light receiving surface in Example 2, the shape factor was greatly improved. Further, since there is no unnecessary contact area with the substrate, no decrease in the open circuit voltage is observed. As a result, the conversion efficiency was greatly improved. On the other hand, in the comparative example in which the upper electrode portion is not formed, the cross-sectional area of the current collecting electrode is small, so that the wiring resistance of the finger electrode is not reduced, and the shape factor is low compared to the first and second embodiments. As a result, the conversion efficiency is also low compared to Examples 1 and 2.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

10, 100, 200 ... solar cell 11, 101, 201 ... substrate (semiconductor substrate),
12, 202 ... emitter layer, 13, 203 ... light receiving surface collecting electrode,
14, 204 ... antireflection film, 15, 205 ... back surface electric field layer,
16, 206 ... back current collecting electrode, 17, 207 ... surface protective film, 18 ... back surface insulating film,
19 ... back contact electrode part, 20 ... back upper electrode part, 21 ... light receiving surface insulating film,
22 ... Light-receiving surface contact electrode part, 23 ... Light-receiving-surface upper electrode part,
102: finger electrodes, 103: bus bar electrodes.

Claims (2)

A method for producing a solar cell having a current collecting electrode on at least a first main surface of a semiconductor substrate, wherein the current collecting electrode is formed,
Forming a contact electrode portion by printing and baking a first conductive material on the first main surface of the semiconductor substrate; and
On the first main surface on which the contact electrode portion is formed, an insulating material is applied so that at least a part of the contact electrode portion is exposed, and cured to form an insulating film;
On the insulating film, the second conductive material is printed and cured so as to cover the portion where the contact electrode portion is formed and the second conductive material is in contact with the exposed portion of the contact electrode portion. And forming the upper electrode part by forming the current collecting electrode comprising the contact electrode part and the upper electrode part.   The insulating material is a resin selected from one or more of silicone resin, polyimide resin, polyamideimide resin, fluorine resin, phenol resin, melamine resin, urea resin, polyurethane, epoxy resin, acrylic resin, polyester resin, and poval resin. It consists of material to contain, The manufacturing method of the solar cell of Claim 1 characterized by the above-mentioned.

Images