JP6062383B2 - Manufacturing method of solar cell - Google Patents

Description

  The present invention relates to a method for manufacturing a solar cell including a step of forming an electrode pattern by printing.

  In recent years, solar cells (solar cells) have been rapidly spreading from the viewpoint of environmental awareness and energy saving, and accordingly, a cell structure with higher performance than before, that is, a cell structure with good photoelectric conversion efficiency and high output. There is a need for solar cells. One measure for realizing this requirement is to increase the light receiving area per unit cell area of the solar cell. For example, as one means for expanding the light receiving area, there is a thinning (fine line) of a linear electrode formed on the light receiving surface.

On the cell light-receiving surface of so-called silicon type solar cells which are currently mainstream, a grid consisting of linear bus bar (connecting) electrodes formed of a conductor such as silver, and a streaky thin line connected to the bus bar (For current collection) electrodes are provided. These electrodes are also collectively referred to as light receiving surface electrodes.
On the light receiving surface of the solar cell, a portion where such a light receiving surface electrode is formed becomes a light shielding portion (non-light receiving portion). For this reason, if the light-receiving surface electrode is made thinner than before, the light-shielding portion is reduced accordingly, the light-receiving area per cell unit area is expanded, and the output per cell unit area can be improved. However, at this time, if the electrode is not bulky (thickened) by the amount of thinning, the line resistance of the electrode increases, and the output characteristics of the solar cell decrease by that amount. Accordingly, for thinning the light-receiving surface electrode, an improvement in electrode thickness, that is, a high aspect ratio (increasing the ratio of thickness to line width (thickness / line width) in the electrode; the same shall apply hereinafter) is required at the same time.

  Such a conventional light-receiving surface electrode contains a metal powder such as silver as a conductor component and an organic vehicle component composed of a binder or a solvent, and is prepared in a paste form (including slurry form and ink form). Hereinafter, it is formed on the light receiving surface of the solar cell (cell) with a predetermined electrode pattern by screen printing using “electrode forming paste” or simply “paste”. As a conventional technique for forming such a linear electrode in a predetermined pattern on a semiconductor substrate using a technique such as screen printing, for example, Patent Document 1 is cited.

JP 2012-54517 A

  By the way, according to the screen printing technique using the above paste, typically, a predetermined electrode pattern is printed as follows. That is, first, a screen plate for screen printing (mesh plate) having a linear opening corresponding to a predetermined electrode pattern above a light receiving surface of a semiconductor substrate for a silicon solar cell, and a clearance (gap). Provide and arrange. Next, after supplying the paste onto the screen plate of the mesh plate making, the scraper is brought into contact with the surface of the screen plate, and the scraper is moved from one end to the other end along the surface of the screen plate. As a result, the paste is uniformly spread on the surface of the screen ridge, and the opening is filled while rolling (rolling). Thereafter, the squeegee is moved from the other end of the screen ridge to the one end while the screen ridge is pressed against the surface of the semiconductor substrate by the squeegee. As a result, the paste filled in the opening is pushed out to the surface of the substrate while excessive paste is rolled on the surface of the screen. At this time, in accordance with the movement of the squeegee, after the screen ridge contacts the substrate, it continuously releases the plate so as to follow the passage of the squeegee. Along with such separation, the paste can be printed (transferred) on the substrate with a predetermined electrode pattern. By repeating the above steps, electrode patterns can be sequentially printed on a plurality of semiconductor substrates.

That is, according to the conventional screen printing technique as described above, the printing direction of the electrode pattern is constant, and when the electrode pattern is printed once on one substrate, the supplied paste is screen-prescribed using a scraper and a squeegee. It was necessary to move up and down once.
Further, since the screen plate making is provided with a screen wrinkle (mesh) in the opening portion, if a high-viscosity paste is used, clogging is likely to occur, and printing using the high-viscosity paste could not be performed. For this reason, the printed electrode pattern is likely to have uneven thickness, and when printed in a bulky manner, the paste after printing is sagging and the line width is widened, so that sufficient thinning cannot be realized.
Therefore, the present invention has been made in view of such a situation, and a main object thereof is to provide a method for manufacturing a solar cell capable of printing a thinned electrode pattern with high productivity.

  In order to achieve the above object, the invention disclosed herein provides a method of manufacturing a solar cell including a semiconductor substrate and a linear electrode having a predetermined pattern printed on the surface of the semiconductor substrate. This manufacturing method corresponds to the predetermined pattern on the surface of the first semiconductor substrate by preparing an electrode forming paste (hereinafter sometimes simply referred to as “paste”) for forming the electrode. Disposing a plate making with a linear opening, the paste at the first end of the plate making, at the end of the region in which the opening is included in the width direction perpendicular to the printing direction Supplying the paste supplied from the first end of the plate making to the second end opposite to the plate making the first semiconductor substrate by moving the paste through the opening while passing through the opening. Performing the first printing. In this manufacturing method, the first printing plate making after the first printing is arranged on the surface of the second semiconductor substrate, and the moved paste is opposed to the first end from the second end. By moving the end portion by the squeegee while passing through the opening, the second printing is performed on the second semiconductor substrate, the printed paste is baked, and the electrode having the predetermined pattern is formed. It is included.

  In such a configuration, the paste is supplied to the end of the plate making and the region including the opening. And unlike the conventional screen printing technique, the process of homogenizing the paste with a scraper and filling the openings is not included. That is, when printing an electrode having a predetermined pattern, it is only necessary to pass the paste once through the opening of the plate making using a squeegee. Thereby, printing can be performed twice by reciprocation of the squeegee, and an electrode having a predetermined pattern can be efficiently formed. As a result, a solar cell can be manufactured with high productivity.

  In the present specification, “printing” refers to the target through the opening of the plate making in which the opening is formed in a pattern corresponding to the target pattern (that is, the electrode pattern desired to be formed on the surface of the semiconductor substrate). This means a printing technique in which an electrode-forming paste is supplied to the surface of a semiconductor substrate as a pattern, and is not limited to the material and configuration of the plate making used and the precision of the pattern to be formed. For example, the constituent material of the plate making provided with the opening may be various synthetic resin (for example, polyester) materials, metal materials (for example, stainless alloy), or the like. In the plate making, a mask plate making an opening of a predetermined pattern formed on the plate making original plate by etching or laser processing, or an emulsion was applied so as to form an opening of a predetermined pattern in a screen cage provided in the plate making frame. So-called screen plate making (mesh plate making) may be used.

  In a preferred aspect of the solar cell manufacturing method disclosed herein, the plate making is a mask plate that does not include a mesh in the opening. According to this configuration, an appropriate amount of paste can be printed on the substrate as the paste is moved once by the squeegee. Thereby, generation | occurrence | production of appearance defects, such as line thinning, line thickening, and bleeding, can be suppressed and the electrode of a solar cell can be formed.

In a preferred aspect of the solar cell manufacturing method disclosed herein, the printing direction is a direction parallel to the opening, and the paste has a surface height from the plate making of 0.5 mm to 10 mm. It is characterized by supplying in the width direction orthogonal to the said printing direction of the said supplied paste so that it may become.
According to such a configuration, the paste can be uniformly supplied onto the plate making, and even without using a scraper, the occurrence of poor appearance can be further suppressed and the electrode of the solar cell can be formed.

In a preferred aspect of the solar cell manufacturing method disclosed herein, the paste is supplied by a nozzle discharge type paste dispenser.
According to such a configuration, the paste can be easily and uniformly supplied onto the plate making. Therefore, the electrodes of the solar cell can be formed with high yield while suppressing the occurrence of poor appearance. Moreover, as such a nozzle discharge type paste dispenser, for example, a hand gun type paste dispenser can be used, and the supply of the paste can be easily realized without preparing expensive equipment.

In a preferred embodiment of the solar cell manufacturing method disclosed herein, the paste includes a conductive powder and an organic vehicle component in which the powder is dispersed, and has a viscosity of 200 Pa · s or more and 400 Pa when the rotation speed is 20 rpm.・ It is characterized by being s or less.
Such a paste exhibits viscosity characteristics suitable for forming electrodes on the surface of a semiconductor substrate by printing. Therefore, it is possible to more suitably form a thin wire electrode (especially a grid electrode for current collection) having a desired aspect ratio with a predetermined electrode pattern.

In a preferred aspect of the solar cell manufacturing method disclosed herein, the linear electrode having a line width of 60 μm or less and a thickness of 15 μm or more is formed on the light receiving surface of the semiconductor substrate. Yes.
According to this configuration, by performing printing, for example, an electrode having a predetermined pattern having a line width of 60 μm or less (more preferably 55 μm or less, particularly 50 μm or less) and a thickness of 15 μm or more (more preferably 20 μm or more). It can be formed on the surface of a semiconductor substrate. Therefore, the manufacturing method disclosed herein can be preferably used to manufacture a solar cell that realizes thinning of the light-receiving surface electrode and a high aspect ratio.

It is process drawing explaining one Embodiment of the first half of the manufacturing process of the solar cell disclosed here. It is process drawing explaining one Embodiment of the latter half of the manufacturing process of the solar cell disclosed here. It is a top view explaining a mode of supply of paste for electrode formation in a manufacturing method of a solar cell indicated here. It is sectional drawing which shows an example of the structure of a solar cell typically. It is a top view which shows typically the pattern of the electrode formed in the light-receiving surface of a solar cell. It is a scanning electron microscope (SEM) image which shows the pattern of the grid electrode of (a) sample 3 and (b) sample 4 of the solar cell formed in the Example.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that technical matters other than the contents particularly mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters for those skilled in the art based on the prior art. The present invention can be carried out based on the technical contents disclosed in the present specification and the common general technical knowledge in the field.

FIG. 3 schematically illustrates an example of a solar cell (solar cell) 10 that can be suitably manufactured by the solar cell manufacturing method disclosed herein. This solar cell 10 is a so-called silicon type solar cell that uses a wafer made of single crystal, polycrystalline, or amorphous silicon (Si) as a semiconductor substrate 11. FIG. 3 exemplifies a general single-sided light receiving type solar cell 10, and the surface of the solar cell 10 is a light receiving surface 11 </ b> A.
Specifically, this type of solar cell 10 includes an n-Si layer 16 formed by pn junction formation on a light-receiving surface side 11A of a silicon substrate (p-Si layer) 11 made of p-type crystalline silicon. The surface is provided with an antireflection film 14 made of titanium oxide, silicon nitride or the like formed by CVD or the like, and a light receiving surface electrode 12 made of an electrode forming paste containing silver (Ag) powder or the like.

On the other hand, on the back surface 11B side of the silicon substrate 11, as with the light receiving surface electrode 12, a back surface side external connection electrode 22 formed of a predetermined paste material (typically a conductive paste whose conductive powder is Ag powder). And an aluminum electrode 20 having a so-called back surface field (BSF) effect. The aluminum electrode 20 is formed on substantially the entire back surface by printing and baking an aluminum paste mainly composed of aluminum powder. During this firing, an Al—Si alloy layer (not shown) is formed, and aluminum diffuses into the silicon substrate 11 to form the p ⁺ layer 24. By forming the p ⁺ layer 24, that is, the BSF layer, the photogenerated carriers are prevented from recombining in the vicinity of the back electrode, and for example, an improvement in short circuit current and open circuit voltage (Voc) is realized.

On the light receiving 11A surface side of the silicon substrate 11 of the solar cell 10, as shown in FIG. 4, several mutually parallel linear bus bar electrodes 12A and the bus bar electrodes 12A intersect as the light receiving surface electrodes 12. In this manner, parallel grid-like grid electrodes (also called current collecting electrodes, finger electrodes, etc.) 12B are formed.
A large number of grid electrodes 12B are formed to collect photogenerated carriers (holes and electrons) generated by light reception. The bus bar electrode 12A is a connection electrode for collecting carriers collected by the grid electrode 12B. Therefore, as described above, the bus bar electrode 12A and the grid electrode 12B (particularly the large number of grid electrodes 12B) provided on the light receiving surface 11A side are made as thin as possible, thereby increasing the photoelectric conversion efficiency of the solar cell 10 and increasing the output power. Can be achieved.
In addition, about this solar cell 10, about an essential structure, it is the same as that of the conventional solar cell. For this reason, the present invention is not characterized with respect to the same configuration as before, the use of the same material as that of the conventional method, and the manufacturing method of the solar cell as in the conventional method.

  The solar cell 10 as described above can be generally manufactured through the following process. That is, an appropriate silicon substrate 11 is prepared, and the n-Si layer 16 is formed by doping predetermined impurities by a general technique such as thermal diffusion or ion plantation. Next, an antireflection film 14 made of silicon nitride or the like is formed by a technique such as plasma CVD. Thereafter, on the back surface 11B side of the silicon substrate 11, first, a predetermined electrode forming paste (typically a conductive paste in which the conductive powder is Ag powder) is used for screen printing in a predetermined pattern and dried. As a result, a back-side conductor paste coating that will later become the back-side external connection electrode 22 is formed. Next, a paste containing aluminum powder as a conductor component is applied (supplied) by a screen printing method or the like on the entire back surface 11B side, and dried to form an aluminum film.

  Next, an electrode pattern as shown in FIG. 4 is typically formed on the antireflection film 14 formed on the surface 11A side of the silicon substrate 11 based on a printing method characteristic in the manufacturing method disclosed herein. The electrode forming paste is printed (supplied). Details of the printing method will be described later. The line width at the time of printing is not particularly limited, but the electrode pattern coating film (printed body) having a grid electrode having a line width of about 60 μm or less, preferably in the range of about 40 μm to 60 μm, more preferably in the range of about 40 μm to 50 μm. ). Thereafter, the substrate is dried in an appropriate temperature range (typically 100 ° C. to 200 ° C., for example, about 120 ° C. to 150 ° C.).

In this way, the silicon substrate 11 on which the paste application (dried film-like application) is formed on both sides is subjected to an appropriate baking temperature (for example, using a baking furnace such as a near-infrared high-speed baking furnace) in an air atmosphere. 700-900 ° C).
By such firing, a fired aluminum electrode 20 is formed together with a light-receiving surface electrode (typically an Ag electrode) 12 and a back side external connection electrode (typically an Ag electrode) 22, and at the same time, an Al—Si (not shown) is formed. While the alloy layer is formed, aluminum diffuses into the silicon substrate 11 to form the p ⁺ layer (BSF layer) 24 described above, and the solar cell 10 is manufactured.
In addition, instead of simultaneous firing as described above, for example, firing for forming a light receiving surface electrode (typically an Ag electrode) 12 on the light receiving surface 11A side, an aluminum electrode 20 on the back surface 11B side, and an external connection electrode The firing for forming 22 may be performed separately.

  In the above solar cell manufacturing process, the electrodes (the light-receiving surface electrode 12 and the backside external connection electrode 22) are preferably printed by a printing method characteristic of the solar cell manufacturing method disclosed herein. be able to. 1A and 1B are process diagrams for explaining a method of manufacturing a solar cell disclosed herein. As described above, the method for manufacturing such a solar cell is, for example, a linear electrode (light receiving surface) having a predetermined pattern on the surface (light receiving surface) 11A of the semiconductor substrate 11 prepared up to the previous stage of the electrode printing process. Electrode) 12 can be printed. Such a manufacturing method includes the following steps.

(1) An electrode forming paste 50 for forming electrodes is prepared.
(2) A plate making 60 having a linear opening 60a corresponding to a predetermined pattern is arranged on the surface 11A of the first semiconductor substrate 11a.
(3) The paste 50 prepared in (1) above is the first end P1 of the plate making 60 at the end of the region in which the opening 60a is included in the width direction orthogonal to the printing direction D. Supply.
(4) By moving the paste 50 supplied in (3) above from the first end P1 of the plate making 60 to the second end P2 facing the squeegee 70 while passing the opening 60a, First printing is performed on the first semiconductor substrate 11a.
(5) The plate making 60 after the first printing is arranged on the surface 11A of the second semiconductor substrate 11b.
(6) The moved paste 50 is moved to the second semiconductor substrate 11b by moving the paste 50 from the second end P2 to the first end P1 facing the second end P2 by the squeegee 70 while passing through the opening 60a. Printing 2 is performed.
(7) The printed paste 50 is baked to form electrodes 12 having a predetermined pattern.

[1. Preparation of electrode forming paste]
The electrode forming paste disclosed here is made of a material mainly composed of conductive powder and an organic vehicle component for dispersing the powder, as in the conventional paste material (conductor paste) of this type. Can be used.
As the “conductive powder” that is the main component of the solid content of the paste, a powder made of a conductive material exhibiting conductivity suitable for forming an electrode of a solar cell can be used without particular limitation. Typically, a simple substance of a noble metal such as silver (Ag), platinum (Pt), palladium (Pd), gold (Au) or an alloy thereof (Ag—Pd alloy, Pt—Pd alloy, etc.), and the noble metal What consists of an alloy with another metal etc. is mentioned as a suitable example. From the viewpoints of cost, low electrical resistance, and the like, typically a powder made of silver or a silver-based alloy (hereinafter collectively referred to as “Ag powder”) is particularly preferably used.

As the Ag powder and other conductive powders, those having an average particle size of 5 μm or less are suitable, and those having an average particle size of 3 μm or less (typically 1 to 3 μm, for example 1 to 2 μm) are preferably used. In the present specification, the average particle size means a cumulative 50% particle size (D50) in a volume-based particle size distribution based on a laser scattering / diffraction method.
The shape of the particles constituting the conductive powder is not particularly limited, but typically, a spherical shape, a scaly shape, a conical shape, a rod shape, or the like can be preferably used. Of course, an indefinite shape can also be used. Spherical or scaly particles are preferably used for reasons such as easy formation of a fine light-receiving surface electrode with good filling properties. As the conductive powder to be used, those having a sharp (narrow) particle size distribution are preferable. For example, a conductive powder having a sharp particle size distribution that does not substantially contain particles having a particle diameter of 10 μm or more is preferably used. As this index, the ratio (D10 / D90) of the particle size (D10) at the time of accumulation 10% and the particle size (D90) at the time of accumulation 90% in the volume-based particle size distribution based on the laser scattering / diffraction method may be adopted. it can. When all the particle diameters constituting the conductive powder are equal, the value of D10 / D90 is 1, and conversely, the value of D10 / D90 approaches 0 as the particle size distribution becomes wider. It is preferable to use a powder having a relatively narrow particle size distribution such that the value of D10 / D90 is 0.2 or more (for example, 0.2 to 0.5).
The paste using the conductive powder having such an average particle diameter and particle shape has a good filling property of the conductive powder and can form a dense electrode. This is advantageous in forming a fine wiring pattern on the light receiving surface with high shape accuracy.

  The method for producing such conductive powder such as Ag powder is not particularly limited. For example, conductive powder (typically Ag powder) produced by a known wet reduction method, gas phase reaction method, gas reduction method or the like can be classified and used as necessary. Such classification can be performed using, for example, a classification device using a centrifugal separation method.

On the other hand, as the “organic vehicle component” in which the conductive powder is dispersed, those conventionally used in this type of paste material can be used without any particular limitation. Typically, the vehicle is composed of organic binders and organic solvents of various compositions.
Examples of the organic binder include cellulose polymers such as ethyl cellulose and hydroxyethyl cellulose, acrylic resins such as polybutyl methacrylate, polymethyl methacrylate, and polyethyl methacrylate, epoxy resins, phenol resins, alkyd resins, polyvinyl alcohol, and polyvinyl butyral. An organic binder based on is preferably used. In particular, a cellulosic polymer (for example, ethyl cellulose) is preferable, and a viscosity characteristic capable of performing particularly good screen printing can be realized.

Organic solvents include ester solvents such as butyl cellosolve acetate and butyl carbitol acetate (BCA: diethylene glycol monobutyl ether acetate), ether solvents such as butyl carbitol (BC: diethylene glycol monobutyl ether), ethylene glycol and diethylene glycol derivatives Organic solvents such as toluene, xylene, mineral spirit, terpineol and mentanol are preferably used.
A preferable solvent constituting the organic vehicle is an organic solvent having a boiling point of about 200 ° C. or higher (typically about 200 to 260 ° C.). An organic solvent having a boiling point of about 230 ° C. or higher (typically about 230 to 260 ° C.) is more preferably used. Particularly preferred solvent components include butyl carbitol (BC), butyl carbitol acetate (BCA), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and the like.

The content of the conductive powder in the entire paste is suitably about 80% by mass or more (typically 80 to 90% by mass) when the entire paste is 100% by mass, for example, 85% by mass. It is preferable to set the degree. Increasing the content of the conductive powder is preferable from the viewpoint of forming a dense electrode pattern with good shape accuracy. On the other hand, if the content is too high, the handleability of the paste, the suitability for screen printing, and the like may decrease, which is not preferable.
Further, the content of the organic vehicle is suitably 5 to 20% by mass when the total paste is 100% by mass, and 10 to 20% by mass (particularly 10 to 15% by mass). preferable.
Moreover, it is preferable that an organic binder is contained in the ratio of 15 mass parts or less (typically 1-10 mass parts) with respect to 100 mass parts of electroconductive powder among organic vehicle components. Particularly preferably, it is contained at a ratio of 5 to 10 parts by mass with respect to 100 parts by mass of the conductive powder.
In addition, the said numerical range regarding the content rate of each component should not be interpreted exactly | strictly, As long as the objective of this invention can be achieved, slight deviation from this range is accept | permitted.

In addition to the main conductive powder and organic vehicle component, various inorganic and / or organic additives can be included as long as the object of the present invention can be achieved. Preferable examples of the inorganic additive include glass powder and other ceramic powders (ZnO ₂ , Al ₂ O ₃ , SiO _2, etc.) and fillers made of various other materials. Among these, addition of ceramic powder, particularly glass powder (glass frit) is preferable. The average particle size of this type of powder (filler) is typically adjusted to be equal to or less than that of the conductive powder. For example, glass powder or other powder (filler) having an average particle size of 3 μm or less, preferably 2 μm or less, and typically an average particle size of about 0.1 to 2 μm can be used.

The glass component to be added may be a crystallized glass as well as a normal amorphous material. Specific examples include those containing oxides such as lead, boron and silicon, such as lead silicate glass, lead aluminosilicate glass, lead borosilicate glass and lead aluminoborosilicate glass. Although a glass softening point is not specifically limited, It is preferable that it is about 300-600 degreeC (for example, 400-500 degreeC). When such a glass powder is added, an electrode having excellent adhesion to the electrode can be formed by welding the glass component to a substrate (typically a silicon substrate) when the pace coating material is baked. .
The content ratio of the glass powder and other ceramic powder is suitably 10% by mass or less when the entire paste is 100% by mass, and typically 5% by mass or less (eg, about 1 to 5% by mass). is there.

  In addition to the above components, various additive components can be added to the electrode forming paste as necessary. Examples thereof include additives such as surfactants, antifoaming agents, antioxidants, dispersants, polymerization inhibitors.

The electrode forming paste of the present invention suitably used in the solar cell manufacturing method disclosed herein has a viscosity (hereinafter “η ₂₀ ”) at a rotational speed of 20 rpm of 200 Pa · s or more and 400 Pa · s or less. . Such viscosity is typically a viscosity measured by a Brookfield type rotational viscometer by rotating the test paste material at any one of the above rotational speed conditions using an appropriate spindle (for example, No. 4 spindle). is there. When η _{20 of the} electrode forming paste is 200 Pa · s or more and 400 Pa · s or less, viscosity suitable for forming an electrode by the solar cell manufacturing method disclosed herein can be exhibited. By satisfying such eta _20, and leaving from a plate making or the like used during printing, while maintaining the slipping of the opening portion such as the ejection port or mesh, the occurrence of sagging and bleeding or the like on a substrate after printing Difficult prints can be formed. Therefore, when the electrode forming paste having such properties is used, it is possible to prevent occurrence of disconnection or thinning (that is, poor supply of paste). As a result, it is possible to form a uniform and bulky electrode although the line width is small. The η ₂₀ of the electrode forming paste is more preferably 250 Pa · s to 350 Pa · s.

Incidentally, the viscosity of the electrode forming paste, the viscosity at a rotation speed 10 rpm: viscosity eta ₁₀ and when the rotational speed of 50 rpm: The viscosity ratio of η _50: η ₁₀ / η ₅₀ is 2 to 4.5 More preferably, it is in the range. More preferably, η ₁₀ / η ₅₀ is in the range of 2.5-4. Hereinafter, this point will be described.
When the rotational speed: viscosity at 10 rpm: η ₁₀ is constant, the viscosity ratio: η ₁₀ / η ₅₀ increases as the viscosity η _{50 at the} rotational speed: 50 rpm decreases. Such a rotational speed: When the viscosity η _{50 at 50} rpm (that is, when the shearing speed is larger than that when the rotational speed is 10 rpm) is low, the shearing speed is increased when the paste is screen-printed. Indicates that the paste "spills out" or flows out from various screen printing masks (typically metal masks). In particular, when applying paste material to the light-receiving surface of a semiconductor substrate that constitutes a cell of a solar cell by using a screen printing method via a screen printing mask (specifically, using a squeegee to open the mask opening) Viscosity characteristics that are preferred when the paste material is filled in). This is because the paste exhibits good fluidity and “pull” of the paste from the mask is good.

On the other hand, assuming that the viscosity η _{50 at} a rotational speed of 50 rpm is constant, the value of the viscosity ratio (η ₁₀ / η ₅₀ ) increases as the viscosity η _{10 at the} rotational speed 10 rpm increases. Such a rotational speed: The viscosity η10 at ₁₀ rpm (that is, when the shearing speed is smaller than that at a rotational speed of 50 rpm) is high, which means that the paste printed on the light receiving surface of the substrate is difficult to flow (the paste dripping is small). ) From the viewpoint. As a result, after the screen printing method is executed and printed on the light receiving surface of the substrate in a predetermined pattern through various masks (that is, the shear rate after being applied to the light receiving surface is extremely low). , Good viscosity (shape maintaining performance) can be exhibited, and undesired expansion of the line width can be prevented.
That is, since the shape of the wiring pattern applied to the light receiving surface before baking is difficult to spread, an electrode pattern with high shape accuracy can be formed. In addition, when the value of the viscosity ratio (η ₁₀ / η ₅₀ ) is too large, the leveling property of the paste generally tends to decrease, which is not preferable.

Such viscosity (η ₁₀ , η ₂₀ , η ₅₀ ) and / or viscosity ratio (η ₁₀ / η ₅₀ ) is, for example, the content ratio of the conductive powder contained in the paste, the average particle diameter or the conductivity of the conductive powder. Although it can be adjusted by the particle size distribution of the powder, etc., preferably the kind of the solvent constituting the organic vehicle while maintaining the above-described suitable shape (outer shape and average particle size and particle size distribution) of the conductive powder, It can be set by adjusting the type of organic binder and the content ratio thereof.

  The electrode-forming paste disclosed here can be prepared typically by mixing the conductive powder and the organic vehicle component in the same manner as the conventional conductor paste of this type. At this time, an additive as described above (for example, an inorganic filler such as glass powder or an auxiliary component such as a viscosity modifier) can be added and mixed as necessary. For example, by using a three-roll mill or other kneader, the conductive powder and various additives are mixed together with the organic vehicle component at a predetermined blending ratio and kneaded with each other, thereby forming electrode forming pastes having various compositions. Can be prepared.

[2. Arrangement of plate making on first semiconductor substrate]
Next, as shown in FIG. 1A (a), a plate making 60 having a linear opening 60a corresponding to a predetermined pattern is arranged on the surface 11A of the first semiconductor substrate 11a.
As the plate making 60, various kinds of plate making conventionally used by this kind of printing can be used. For example, various types of plate making such as screen plate making (mesh plate) and mask plate making used in a so-called screen printing technique, which is a typical electrode pattern forming technique, can be used.
Screen platemaking is essentially a structure in which screen meshes (mesh) are stuck in a platemaking frame, and emulsion is applied to such screen cells leaving an opening (mesh) corresponding to a desired printing pattern. Is. When the electrode forming paste passes through this mesh and adheres to the surface of the substrate, a printed body can be formed. In the present invention, printing can be carried out using a screen with a relatively large opening.

The mask plate making is a configuration in which an opening corresponding to a desired printing pattern is cut out with high accuracy in a plate-like plate making material. The electrode forming paste passes through the opening and adheres to the surface of the substrate, whereby a printed body can be formed. The material constituting these plate making (frame, mesh, plate material, etc.) is not particularly limited, and is appropriately selected from various resin materials typified by polyester, various metal materials typified by stainless steel, etc. Can be configured.
Although not particularly limited, in the manufacturing method disclosed herein, as a preferred example, a metal mask plate making in which openings corresponding to electrode patterns are formed in an accurate shape by etching or laser processing is used. To do. In the following, a case where non-contact printing is performed using a relatively thin and flexible metal mask plate making will be described as a main example.

The opening width of the opening 60a of the plate making 60 to be used can be set to a size that can realize thinning of the light-receiving surface electrode 12, and can be appropriately set according to the properties of the paste to be used. For example, when a grid electrode having a line width of about 60 μm is formed, an opening width corresponding to the size, typically about 60 μm or less (for example, about 35 to 55 μm) plate making 60 (mask plate making or screen plate making) Can be used). Alternatively, when a grid electrode having a line width of about 50 μm is formed, a plate making 60 having an opening width corresponding to the size, typically about 50 μm or less (for example, about 25 to 45 μm) can be used. For example, when a grid electrode having a line width of about 40 μm is formed, a plate making 60 having an opening width corresponding to the size, typically about 40 μm or less (for example, about 2 to 35 μm) can be used. Since it depends on the target line width as described above, it is not particularly limited. For example, plate making with an opening width narrower by about 10 to 50% (for example, about 2 to 40%) than the line width of the target grid electrode. 60 (for example, if an electrode having a line width of about 45 μm is intended), it may be preferable to use plate making 60 having an opening width of about 25 ± 5 μm. Further, as the plate making 60 to be used, both the grid electrode line forming opening and the bus bar electrode line forming opening are formed, or only the grid electrode line opening is formed. It may be a thing. When using the plate making 60 in which only the opening for forming the grid electrode line is used, the bus bar electrode can be formed using another plate making 60.
When the plate making 60 is screen plate making, the plate making 60 can be arranged above the first semiconductor substrate 11a by providing a predetermined clearance on the surface 11A of the first semiconductor substrate 11a according to a conventional method. . Further, when the plate making 60 is a mask plate making, the plate making 60 may be arranged so as to contact the surface 11A of the first semiconductor substrate 11a (that is, contact printing), and a predetermined clearance is provided similarly to the screen plate making. May be arranged (that is, non-contact printing). In the case of arranging with clearance, the mask plate making may be configured to be highly flexible so that the contact between the mask plate making and the substrate 11 and the plate can be separated by movement of the squeegee 70 described later. preferable.

[3. Paste supply]
Here, for example, as shown in FIG. 2, the paste 50 prepared above includes the opening 60 a in the width direction perpendicular to the printing direction D, which is the first end P <b> 1 of the plate making 60. Supply to the end of the area. Such a paste supply area may be an area where the paste 50 can pass over all the openings 60a in the subsequent printing process. Here, the first end P <b> 1 is an end on the near side in the printing direction D of the plate making 60.

  Here, the paste 50 is preferably supplied to the first end portion P1 of the plate making 60 with a thickness such that the surface height from the plate making is 0.5 mm or more and 10 mm or less. By doing in this way, in the printing of the next process, the amount of the paste 50 filled in the opening 60a can be controlled uniformly and precisely. The surface height of the paste 50 is preferably 1 mm or more and 9 mm or less, for example, 2 mm or more and 8 mm or less. The surface height of the paste is not particularly limited, but can be measured by using, for example, a laser-type surface roughness analyzer or a nondestructive X-ray inspection device.

The method of supplying the paste 50 is not particularly limited, and for example, an operator uses a spatula (can be a spatula or the like) to use a spatula or the like as conventionally used in this type of manufacturing method. The paste 50 may be scooped and supplied to the first end P1 of the plate making 60. Alternatively, for example, an appropriate amount of paste 50 may be supplied to the first end P <b> 1 of the plate making 60 using an automatic paste supply device using power such as electric power.
However, according to these methods, it may be difficult to keep the surface height of the supplied paste 50 within the above range. This is because, for example, the paste 50 that satisfies the viscosity η ₂₀ as described above has a relatively high viscosity. Therefore, supplying the paste 50 using a spatula may be difficult to maintain accuracy depending on the skill level of the operator. Further, for example, in a general-purpose paste automatic supply device used for display printing or solder printing of a television or a personal computer, such a high-viscosity paste 50 is supplied while appropriately controlling the paste supply amount. This is because it is difficult. Further, such an automatic paste supplying apparatus is relatively expensive, and electric power for driving the apparatus is required.

  Therefore, in a more preferable embodiment, the paste 50 is supplied to the first end P1 of the plate making 60 by a nozzle discharge type paste dispenser. By using such a nozzle discharge type paste dispenser, even if the paste 50 is highly viscous, an appropriate amount of paste 50 is simply supplied to the first end P1 of the plate making 60 while appropriately controlling the amount of paste supplied. be able to. Such a nozzle discharge type paste dispenser may be configured such that the paste can be automatically discharged under a preset condition by electric power or the like, or manually by an operator manually driving the paste dispenser. It may be configured so that the paste can be discharged (by human power). By using such a dispenser, for example, it becomes possible to suitably supply the paste onto the substrate regardless of the skill level of the operator. For example, a hand gun-type paste dispenser can be cited as a suitable example of the latter nozzle discharge type paste dispenser that is manually supplied.

  In such a nozzle discharge type paste dispenser, the shape of the discharge port of the nozzle is not particularly limited, and may be, for example, a circle or a rectangle. For example, when the shape of the discharge port is circular, the diameter of the discharge port is 2 mm or more and 15 mm or less considering that the light receiving surface electrode 12 is formed on the substrate 11 of a typical 5-6 inch solar cell. It is preferable to be in the order (for example, about 3 mm or more and 10 mm or less). In addition, when the shape of the discharge port is other than a circle, it is preferable that the area of the discharge port is an area corresponding to the circle having the diameter. According to a nozzle discharge-type paste dispenser having discharge ports of such dimensions, for example, an operator can supply the paste 50 onto the plate making 60 while easily controlling the surface height. Thereby, for example, the light-receiving surface electrode 12 having a good cross-sectional shape can be formed.

[4. First print]
Here, the paste 50 supplied as described above is moved by the squeegee 70 while passing through the opening 60a from the first end P1 of the plate making 60 to the second end P2 facing the first end P1. The semiconductor substrate 11a is printed. As the squeegee 70, various commonly used ones can be used. For example, a squeegee 70 having a hardness of about 60 to 90 degrees (for example, about 60 to 80 degrees) and made of urethane rubber, silicon rubber, synthetic rubber, metal, plastic, or the like can be used. . The tip shape of the squeegee 70 is not particularly limited, and a flat shape, a square shape, a sword shape, or the like can be used.
Here, as shown in FIG. 1A (A), the squeegee 70 is brought into contact with a position P11 outside the plate making 60 rather than the paste 50 supplied to the first end P1 of the plate making 60. Then, as shown in (B) of FIG. 1A, the first end P1 is moved to the second end P2 that faces the first end P1 and passes through the opening 60a. At the time of such movement, since the plate making 60 and the substrate 11a are in contact in the case of contact printing, the squeegee 70 may move the surface of the plate making 60 horizontally. In the case of non-contact printing, the squeegee 70 is moved to the end portion P2 while pressing the plate making 60 with the squeegee 70 to bring the plate making 60 into contact with the substrate 11a. At this time, the paste 50 is conveyed while rotating (rolling) between the plate making 60 and the squeegee 70. By this rolling, an appropriate amount of paste 50 is filled in the opening 60a and attached to the surface of the first semiconductor substrate 11a. Thereby, the electrode pattern of the first semiconductor substrate 11a can be printed. The squeegee 70 is disposed at a position P21 inside the plate making 60 with respect to the paste 50.

The moving speed and printing pressure (pressure applied to the squeegee) of the squeegee 70 are not particularly limited. For example, as an example, by appropriately moving the squeegee 70 having an appropriate shape at a moving speed of 100 to 300 mm / second (for example, 150 to 250 mm / second), an appropriate filling action is given to the paste 50, and the opening of the plate making 60 An appropriate amount of paste 50 can be filled in 60a. Further, the printing pressure of the squeegee 70 can be determined based on a conventional method according to the printing method. For example, the printing pressure of the squeegee 70 is not particularly limited because it can be appropriately changed depending on the material and structure of the squeegee 70 itself, but typically can be about 0.05 MPa to 0.3 MPa, Can be about 0.1 to 0.2 MPa.
By such a smooth movement of the squeegee, the paste can be efficiently printed with an accurate size (line width).

[5. Arrangement of plate making on second semiconductor substrate]
After the first printing, as shown in FIG. 1A (C), the plate making 60 after the first printing is arranged on the surface 11A of the second semiconductor substrate 11b.
At this time, in the case of non-contact printing, the plate making 60 is located above the surface 11A of the first semiconductor substrate 11a while maintaining a clearance by half separation, so that the first semiconductor substrate 11a is removed from below the plate making 60. It is only necessary to move the second semiconductor substrate 11b under the plate making 60.
In the case of contact printing, the plate making 60 is moved upward from the surface 11A of the first semiconductor substrate 11a, and in this state, the first semiconductor substrate 11a is moved from the bottom of the plate making 60, and the second plate 60 is placed under the plate making 60. The second semiconductor substrate 11b is transported. Thereafter, the plate making 60 may be installed on the surface 11A of the second semiconductor substrate 11b.

[6. Second printing]
Next, the paste 50 moved to the second end P2 is moved by the squeegee 70 while passing through the opening 60a from the second end P2 to the first end P1 facing the second end P2. Second printing is performed on the second semiconductor substrate 11b. Here, as shown in FIG. 1A (B), the squeegee 70 is disposed at the position P21 inside the plate making 60 rather than the paste 50, as shown in FIG. 1A (B). As shown in FIG. 3, the plate is lifted upward and moved to a position P22 outside the plate making 60 with respect to the paste 50. Thereafter, as shown in FIG. 1B (e), the squeegee 70 is moved to the first end P1. The movement of the squeegee 70 at this time can be performed in the same manner except that it is in the reverse direction to the first printing. Thereby, the paste 50 is conveyed while rotating (rolling) between the plate making 60 and the squeegee 70. By this rolling, an appropriate amount of paste 50 is filled in the opening 60a and attached to the surface of the second semiconductor substrate 11b. Then, the electrode pattern of the second semiconductor substrate 11b can be printed. The squeegee 70 is disposed at a position P12 inside the plate making 60 with respect to the paste 50. Accordingly, as shown in FIG. 1B (f) to FIG. 1A (b), the squeegee 70 can be lifted upward and moved to a position P11 outside the plate making 60 with respect to the paste 50 at an appropriate time.

[7. Paste firing]
By baking the paste 50 printed on the semiconductor substrate 11, the electrode 12 having a predetermined pattern can be obtained. The conditions for such firing are as described above. The paste 50 printed in this way may be fired simultaneously with the paste for forming the aluminum electrode 20 and the external connection electrode 22 printed on the back surface 11B side of the semiconductor substrate 11 as described above. good.

[Continuous printing]
As described above, while the squeegee 70 is reciprocated between the first end portion P1 and the second end portion P2 of the plate making 60, the first semiconductor substrate 11a and the second semiconductor substrate 11b. The electrode pattern can be continuously printed on the sheet.
In addition, a desired number of new semiconductor substrates are prepared as the first semiconductor substrate 11a and the second semiconductor substrate 11b, and the above steps (4) to (6) are repeatedly performed. Electrode patterns can be continuously printed on a number of semiconductor substrates 11. When the amount of paste on the plate making 60 is reduced, the above step (3) is appropriately performed to add the paste.

  According to the solar cell manufacturing method disclosed herein, the electrode pattern can be printed easily and with good productivity by, for example, reciprocal printing using the above-described metal mask plate making or screen plate making. The electrode pattern manufactured by such a method can be bulky and formed with high quality in a state in which the occurrence of line thinning and disconnection is greatly reduced. Therefore, according to this manufacturing method, a high-performance solar cell with high conversion efficiency can be manufactured with high productivity.

Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.
(Embodiment 1)
[Preparation of electrode forming paste]
An electrode forming paste was prepared by the following procedure. That is, as the conductive powder, Ag powder having an average particle diameter of 2 μm was used. As the organic vehicle component, a vehicle containing ethyl cellulose as a resin component was used. Further, as the glass frit, a general lead borosilicate glass powder (average particle diameter: 0.5 to 1.6 μm) often used in the preparation of electrode forming pastes in the field of electronic materials was used. And the compounding ratio of these materials is blended at a ratio of 85% by mass of Ag powder, 3% by mass of glass frit and 12% by mass of organic vehicle, and kneaded well using a three-roll mill, did.
The average particle size of the Ag powder is an integrated 50% particle size in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measuring device (Horiba, Ltd. product: LA-920).

Next, the viscosity of the obtained paste was measured at rotation speeds of 10 rpm, 20 rpm and 50 rpm, and viscosity: η ₁₀ , η ₂₀ , η ₅₀ and viscosity ratio: η ₁₀ / η ₅₀ were obtained. As a result, the paste prepared above had η ₂₀ of 300 Pa · s and η ₁₀ / η ₅₀ of 3.0.
The viscosity of the paste was measured with a rotational viscometer (HBT type DV III +) manufactured by Brookfield using a No. 4 spindle (spindle “SC-4-14”) at each rotational speed (10, 20) at 25 ° C. , 50 rpm).
For comparison, a silver paste (NP-4694A1 manufactured by Noritake Co., Ltd.) for forming a grid electrode for a commercially available solar cell was prepared. The viscosity of this comparative paste was measured at rotational speeds of 10 rpm, 20 rpm and 50 rpm, and viscosity: η ₁₀ , η ₂₀ , η ₅₀ and viscosity ratio: η ₁₀ / η ₅₀ were obtained. As a result, η _{20 of the} comparative paste was 230 Pa · s, and η ₁₀ / η ₅₀ was 3.4.

[Production of test solar cell element (light-receiving surface electrode)]
Using the electrode forming paste obtained above and the comparative paste, a light receiving surface electrode of the solar cell element (that is, a comb electrode composed of a grid electrode and a bus bar electrode) was formed by screen printing.
That is, a commercially available 156 mm square (6 inch square) p-type single crystal silicon wafer substrate (plate thickness: 200 μm) for solar cells is prepared, and the surface (light receiving surface) is alkali-etched with an aqueous NaOH solution to remove the damaged layer. In addition, an uneven texture structure was formed. Next, a phosphorus-containing solution is applied to the texture structure surface, and thermal diffusion treatment is performed, whereby an n-Si layer (n ⁺ layer) having a thickness of about 0.3 μm to 0.4 μm is formed on the light receiving surface of the substrate. ) Was formed. Next, a silicon nitride film having a thickness of about 50 nm to 100 nm was formed on the n-Si layer by a plasma CVD (PECVD) method to obtain an antireflection film.

Thereafter, the electrode forming paste prepared above was used for the substrates of samples 1 to 3, and the comparative paste was used for the substrate of sample 4 in the air at room temperature under the following conditions: The electrode pattern for the light-receiving surface electrode (Ag electrode) was printed on the antireflection film under the three printing conditions shown in Table 1.
Specifically, as shown in FIG. 4, an electrode pattern comprising three mutually parallel linear busbar electrodes and 67 grid electrodes parallel to each other so as to be orthogonal to the busbar electrodes. It was formed by printing. As shown in Table 1 below, the grid electrode was formed by printing using a plate making whose design line width was set to 25 to 45 μm. The bus bar electrode was printed so that the target line width was 1.5 mm.

  For printing plate making used for printing the grid electrodes of Samples 1 to 3, special mask plate making (no screen mesh) in which an opening portion having a predetermined design line width was formed on a metallic thin plate was used. Further, as the printing plate making used for printing the sample 4, a screen plate making (with screen mesh) provided with an opening having a predetermined design line width used for conventional general screen printing was used.

  In printing samples 1 to 3, this mask plate was placed on the light receiving surface of the first substrate, and an electrode forming paste was supplied onto the mask plate. For supplying the paste, a manual hand gun type paste dispenser was used. The paste contact portion of the paste dispenser is made of polypropylene (PP) or polyethylene (PE), the nozzle discharge port size is about 5 mm × 10 mm, and the paste capacity is about 100 to 800 g. . The paste was supplied so as to enclose the electrode pattern in the width direction of the plate making at the end on the near side (one side) in the printing direction of the mask plate making, and to have a uniform average height of 5 mm.

  The paste supplied on the mask plate is made of silicon rubber (or urethane rubber, etc.) squeegee (hardness 70 degrees) with an attack angle of 45 degrees and a printing pressure of 0.2 MPa. Passing on the mask plate making by rotating at a speed of 200 mm / sec from the front side (one side) end of the plate making to the back side (the other side) end. I let you. Thus, the first substrate was printed by filling the opening in the mask plate making and then lifting the mask plate making. Subsequently, the mask plate making is placed on the light receiving surface of the second substrate, the squeegee is placed on the outer side of the paste, and this time, the edge from the back side (the other side) to the near side (the one side) The second substrate was printed by moving while rotating to the same position.

  In the printing of Sample 4, printing was performed using a screen printing method using a conventional screen mesh plate making. That is, in the printing of the sample 4, the screen plate making is arranged with a clearance (gap) provided above the light receiving surface of the first substrate, and the electrode forming paste is applied on the screen plate making like the above samples 1 to 3. Supplied to. Next, the supplied paste is moved along the surface of the plate making from the front side (one side) end to the back side (the other side) of the plate making using the scraper, so that the opening of the screen ridge The paste was filled. Next, as in the above samples 1 to 3, a silicon rubber squeegee was pressed against the screen printing plate outward at an attack angle of 45 degrees and a printing pressure of 0.2 MPa, and the plate making and substrate The plate was moved at a high speed of 200 mm / sec from the back end (the other) end to the front end (the other end) on the plate making. As a result, the paste was passed while rotating on the screen plate making, the paste at the opening of the screen plate making was adhered to the substrate, and the screen plate making was released to print the first substrate. Subsequently, the mask plate making was placed on the light receiving surface of the second substrate, and the second substrate was printed in the same procedure as described above. These printing conditions are general and do not include special conditions or operations.

The substrates of Samples 1 to 4 printed above are dried at 120 ° C., and then fired in a firing temperature range of 700 to 800 ° C. using a near-infrared high-speed firing furnace in the air atmosphere. Electrode and bus bar electrode).
Then, the printing accuracy was evaluated by examining the shape of the formed grid electrode. Specifically, in the cross section of a grid electrode having a length of 100 μm, the width and height were measured with a laser microscope at positions where the grid electrode was divided every 10 μm. The results are shown in Tables 2 to 4, and the average values and standard deviations of width and height are shown in Table 1.

FIG. 5 illustrates scanning electron microscope (SEM) images of the grid electrodes of (a) Sample 3 and (b) Sample 4 formed by printing using a plate making having a design line width of 45 μm. As shown in FIG. 5 and Table 1, when the shapes of the grid electrodes of Sample 3 and Sample 4 formed by printing using a plate making with a design line width of 45 μm are compared, Sample 3 has a width and height that are higher. It was confirmed that it was uniform and small in variation and formed with high printing accuracy. That is, according to the method disclosed herein, grid lines can be formed with higher printing accuracy than conventional screen printing methods using conventional pastes, and further, reciprocal printing is possible and grid printing can be formed with high productivity. I was able to confirm that it was possible.
In addition, from the comparison of the shapes of the grid electrodes of Samples 1 to 3, by using a mask plate making with a thinner design line width in the method disclosed herein, the grid is thinner, more bulky, and has a higher aspect ratio. It was confirmed that the electrodes can be formed with high accuracy. For example, the average line width is about 43 μm (its standard deviation is 1.80 μm), the average height is about 18 μm (its standard deviation is 0.63 μm), and the aspect ratio is about 0.42 (its standard deviation is 0). .03) grid lines could be formed.

(Embodiment 2)
When the grid electrode of the solar cell is formed by printing, as shown in Table 6 below, there are various methods for supplying the electrode forming paste onto the plate making, the printing method, and the skill level of the operator. 200 substrates each having a grid electrode formed thereon were printed. The influence on the appearance of the grid electrode formed by this was examined.

That is, as the electrode forming paste, the electrode forming paste of Sample 1 prepared in Embodiment 1 above, which enables formation of a bulky electrode, was used.
The method of supplying the electrode forming paste onto the plate making is indicated as “dispenser” in the “paste supply” column of Table 6 when the operator supplies the paste using the dispenser as in the first embodiment. The case where the operator scraped the electrode forming paste with a spatula and supplied it on the plate and then made it uniform was indicated as “scalar”.
The method of printing the electrode forming paste is the same as the sample 1 of the first embodiment described above, when printing is performed according to the method disclosed herein, the “printing method” column of Table 6 shows “present invention”. A case where printing was performed according to a conventional screen printing method in the same manner as in the sample 4 of the first embodiment was indicated as “conventional method”.
Also, the worker selected A with high skill level, B with low skill level, and C with intermediate skill level.

In addition, regarding the appearance of the electrode, it is judged that the appearance is poor when the number of line thicknesses more than twice the formed line width is included in one substrate is two or more of the formed line width. When the thickness of the line was less than 3 on one substrate, the appearance was judged to be good. And the ratio of the appearance defect to the sum total of appearance defect and favorable was shown in Table 6 as an appearance defect rate.
Regarding the evaluation, Table 6 shows a case where the appearance defect rate is 20% or more, x, a case where the appearance defect rate is 5% or more and less than 20%, and a case where the appearance defect rate is less than 5%. It was shown to.

As shown in Table 6, according to the conventional method, even if the highly skilled worker A formed the electrodes, an appropriate amount of paste could not be supplied to the substrate by printing. As a result, it has been found that unprinted portions due to insufficient paste, paste sagging and bleeding due to excessive paste occur, and the appearance defect rate increases.
On the other hand, by printing in accordance with the method disclosed herein, the amount of paste passing through the plate making can be suitably controlled, and a thin and bulky electrode can be formed without causing sagging or bleeding. Therefore, it was confirmed that the appearance defect rate of the formed grid electrode can be kept low.
In the method disclosed herein, the amount of paste passing through the plate making can be controlled more precisely by supplying the paste using a dispenser, and printing with extremely high printing accuracy can be performed. It was found that a grid electrode can be formed. Moreover, according to this method, it was also confirmed that there was almost no variation in the skill level of the operator.

(Embodiment 3)
When the grid electrode of the solar cell is formed by printing, the diameter of the dispenser used when supplying the electrode forming paste onto the plate making is changed, and the grid electrode is formed in the same manner as in Sample 1 of Embodiment 1. 200 sheets of each substrate were printed. The influence on the appearance of the grid electrode formed by this was examined.
That is, as the electrode forming paste, the electrode forming paste of Sample 1 prepared in Embodiment 1 was used. Then, as shown in Table 7 below, the aperture of the dispenser used when supplying the electrode forming paste onto the platemaking was changed. Table 7 shows the diameter of the elliptical dispenser as “minor axis × major axis”. In addition, the surface height of the paste supplied on the plate making from the plate making was measured, and the results are shown in Table 7.

As for the appearance of the electrode, as in the second embodiment, it is determined that the appearance is poor when the thickness of the line is twice or more of the formed line width is included in one substrate in three or more places. When the thickness of two or more formed line widths was less than three on one substrate, the appearance was judged good. And the ratio of the appearance defect to the sum total of appearance defect and favorable was shown in Table 7 as an appearance defect rate.
Further, regarding the productivity, when the electrode pattern was printed on 2000 pieces of 6-inch solar cell substrates, the number of times the electrode forming paste was supplied onto the plate making with a dispenser was examined. Table 7 shows the case where the number of times of supply is 8 times or more, x, the case where the number of times of supply is 5 times or more and 7 times or less, and the case where the number of supply times is 1 time or more and 4 times or less. In this embodiment, there was no example in which the productivity was x.

  As shown in Table 7, it was found that the paste can be supplied while maintaining a low appearance defect rate by using a dispenser regardless of the diameter of the discharge port. (It was also confirmed that the surface height of the paste from the plate can be suitably adjusted by using a dispenser.) As shown in FIG. 1, when the diameter of the discharge port is reduced, the electrode appearance defect rate can be sufficiently reduced, but the number of paste supply increases and the productivity is lowered. No. As shown in FIG. 4, although the productivity is good when the diameter of the discharge port is increased, the amount of paste supplied from the mask plate to the substrate tends to increase, and the rate at which the appearance of the electrode is defective is slightly increased. Therefore, the diameter of the dispenser is preferably a circle having a diameter of about 2 mm to 15 mm or a size (area) corresponding to this, and in such a case, the appearance defect rate can be further reduced and the productivity is improved. It was confirmed that an electrode pattern could be formed.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

10 Solar cell 11 Semiconductor substrate (silicon substrate)
11A Photosensitive surface (surface)
11B Rear surface 12 Light-receiving surface electrode 12A Bus bar electrode 12B Grid electrode 14 Antireflection film 16 n-Si layer 20 Aluminum electrode 22 External connection electrode 24 p ⁺ layer

Claims (4)

A method of manufacturing a solar cell comprising a semiconductor substrate and a linear grid electrode having a predetermined pattern with a line width of 60 μm or less printed on the semiconductor substrate,
Preparing an electrode forming paste for forming the grid electrode;
Here, the electrode forming paste is
Comprising an electrically conductive powder and an organic vehicle component in which the powder is dispersed;
The viscosity when the rotational speed is 20 rpm is 200 Pa · s or more and 400 Pa · s or less,
On the first semiconductor substrate , the opening width corresponding to the predetermined pattern is 60 μm or less and 10% to 50% narrower than the line width of the grid electrode, and the opening length is the opening width. Placing a plate making with a longer linear opening, wherein the printing direction by the plate making is parallel to the linear opening,
The paste has a surface height from the plate making at a first end portion along the printing direction of the plate making and at an end portion of the region in which the opening is included in the width direction orthogonal to the printing direction. Supply so that the thickness becomes 0.5 mm or more and 10 mm or less,
The supplied paste is moved by a squeegee while passing through the opening to a second end facing the first end of the plate making, to the first semiconductor substrate. Printing,
Disposing the first post-print plate making on the second semiconductor substrate;
The moved paste is moved by the squeegee while passing through the opening from the second end to the first end facing the second end, whereby the second printing is performed on the second semiconductor substrate. What to do,
Firing the printed paste to form the grid electrode of the predetermined pattern having a line width of 60 μm or less and a thickness of 15 μm or more ;
A method for producing a solar cell, comprising:   The method for manufacturing a solar cell according to claim 1, wherein the plate making is a mask plate having no mesh in the opening.   The manufacturing method of the solar cell of Claim 1 or 2 which supplies the said paste with a nozzle discharge type paste dispenser. The method for producing a solar cell according to any one of claims 1 to 3 , wherein the squeegee is moved at a moving speed of 100 mm / sec or more and 300 mm / sec or less.