JP6826542B2 - Conductive composition - Google Patents

Description

The present invention relates to conductive compositions. More specifically, it relates to a conductive composition that can be used to form an electrode pattern of a solar cell or the like.
It should be noted that this international application claims priority based on Japanese Patent Application No. 2016-003756 filed on January 12, 2016, and the entire contents of the application are incorporated herein by reference. ing.

In recent years, solar cells have rapidly become widespread from the viewpoint of increasing environmental awareness and energy saving, and along with this, solar cells with higher performance than before, that is, solar cells with good photoelectric conversion efficiency and high output. It has been demanded. One measure to realize this requirement is to increase the light receiving area per unit area of the solar cell. For example, in the light receiving surface of a solar cell, the portion where the light receiving surface electrode is formed becomes a light shielding portion (non-light receiving portion), so that a line formed on the light receiving surface is one means for expanding the light receiving area. It is desired to make the shape electrode thinner (fine line).

On the light receiving surface of the so-called crystalline silicon solar cell, which is currently the mainstream, a finger (current collector) electrode made of a thin wire formed of a conductor such as silver and a finer electrode are typically used. A bus bar electrode to be connected is provided. Hereinafter, these electrodes are also collectively referred to as a light receiving surface electrode. Such a light receiving surface electrode contains a conductive powder such as silver as a conductor component and an organic vehicle component composed of an organic binder and a solvent, and is prepared in a paste form (including a slurry form and an ink form). A material (hereinafter, also referred to as "conductive composition", simply "composition", etc.) is printed on a light receiving surface of a solar cell (cell) with a predetermined electrode pattern by a method such as a screen printing method, and then fired. Is formed of. As a prior art relating to a conductive composition used for forming a light receiving surface electrode of such a solar cell, for example, Patent Documents 1 to 3 can be mentioned.

Japanese Patent Application Publication No. 2007-19106 Japanese Patent Application Publication No. 2013-165506 Japanese Patent Application Publication No. 2011-66134

Since the conductive composition is printed on the light receiving surface by a method such as a screen printing method as described above, the viscosity has an appropriate range. For example, when printing is performed using a mask (screen mesh, etc.), it is required to have a viscosity characteristic that shows good fluidity and makes it easy for the composition to come off from the mask (and thus, defects such as disconnection are unlikely to occur). There is. Further, after printing in a predetermined pattern through a mask (that is, after being applied to the light receiving surface), it is possible to suppress undesired expansion (sagging) of the line width and realize thinning of the electrode. It is required to show viscosity.
The above-mentioned prior art document describes that a wiring having a narrow line width and a high aspect ratio is formed by devising the components contained in the conductive composition. However, even such a technique is not sufficient to sufficiently satisfy the recent demand level for defect suppression such as fine line and disconnection, and further improvement is expected.

The present invention has been made in view of such a situation, and a main object thereof is to provide a conductive composition for forming an electrode, which can realize thinning of an electrode pattern and is less likely to cause defects such as disconnection. Is to provide. Another object of the present invention is to provide a solar cell element having improved functions or performance, which can be realized by adopting this conductive composition.

In order to achieve the above object, the present invention provides a conductive composition that can be suitably used for forming an electrode (electrode pattern). This conductive composition contains a conductive powder, a cellulosic resin, a butyral resin, and a dispersion medium. The number-average molecular weight _{M x} of the cellulose-based resin is a 55000 ≦ _{M x,} the number-average molecular weight _{M y} of the butyral resin is an _{M y} ≦ 100000. Such a conductive composition has a viscosity property suitable for printing. Therefore, if the conductive composition is used, a fine wire-shaped electrode can be formed while suppressing defects such as disconnection.

In one preferred embodiment of the conductive composition disclosed herein, the ratio of the number average molecular weight M _y of the butyral resin to the number average molecular weight M _x of the cellulose-based resin (M y _{/ M x)} is 0.2 ≦ a _M y / _{M x} ≦ 1.2. By using the cellulosic resin and the butyral resin in combination so as to have the above-mentioned specific number average molecular weight ratio, it is possible to achieve both the thinning of the electrode and the effect of suppressing defects such as disconnection at a higher level.

In one preferred embodiment of the disclosed conductive composition where the number-average molecular weight M _x of the cellulose-based resin, the relationship between the number-average molecular weight M _y of the butyral resin following equation: 10000 ≦ M _{y <M x} ≤ 100,000 is satisfied. By smaller than the number-average molecular weight M _x cellulosic resin number-average molecular weight M _y butyral resin, and the effect of suppressing the thinning and defects such as disconnection of the electrode can be more preferably exhibited.

In a preferred embodiment of the conductive composition disclosed herein, the ratio (W _y / W _x ) of the content W _y of the butyral resin to the content W _x of the cellulosic resin is 0.2 ≦ W. _y / W _x ≦ 1.5. When the content ratio (W _y / W _x ) of the cellulosic resin and the butyral resin is within the range, the effect of using the cellulosic resin and the butyral resin in combination can be more exerted. it can.

In a preferred embodiment of the conductive composition disclosed herein, when the total content of the conductive composition is 100% by mass, the content W _x of the cellulosic resin and the content W _y of the butyral resin The total amount (W _x + W _y ) is 0.1% by mass or more and 1% by mass or less. In such an embodiment, the thinning of the electrode and the effect of suppressing defects such as disconnection can be compatible at a higher level.

A preferred embodiment of the conductive composition disclosed herein further comprises a silicone resin. With such a configuration, the effect of suppressing defects such as thinning of the electrode and disconnection can be more preferably exhibited as compared with the case where the silicone resin is not added.

In a preferred embodiment of the conductive composition disclosed herein, the metal species constituting the conductive powder is any one or two selected from the group consisting of nickel, platinum, palladium, silver, copper and aluminum. Contains more than a species of element. With such a configuration, it is possible to construct an electrode having excellent conductivity.

In a preferred embodiment of the conductive composition disclosed herein, the viscosity η _0.1 at a shear rate of 0.1 s ^-1 is η _0.1 ≤ 500 Pa · s and the shear rate is 10 s ^-1. The viscosity η _{10 at} the time of is 50 Pa · s ≦ η ₁₀ .
Here, as the viscosity, a value measured at 25 ° C. by a commercially available rotational viscometer is adopted. For example, by using a rotary viscometer (cone plate type) standard in the art, the degree can be measured under the conditions of the shear rate range as described above.

As a result of having the viscosity characteristics as described above, the conductive composition disclosed here exhibits good fluidity when, for example, is applied (supplied) to the light receiving surface of a solar cell via a printing mask. The composition can be easily removed from the mask. Therefore, it is possible to suppress the occurrence of disconnection (that is, poor supply portion). Further, after printing in a predetermined pattern through a mask (that is, after being applied to the light receiving surface), high viscosity (shape maintaining performance) can be exhibited and undesired expansion of the line width can be suppressed. .. That is, since the shape of the electrode pattern applied to the light receiving surface is less likely to bleed before firing, a fine line-shaped electrode pattern can be formed. Therefore, according to the conductive composition having the above structure, a fine line-shaped electrode having a desired line width (for example, 45 μm or less, preferably 40 μm or less) can be stably formed.

The present invention provides a semiconductor device comprising an electrode formed by using the conductive composition according to any one of the above, in another aspect for achieving the above object. This semiconductor device can typically be a solar cell element including a light receiving surface electrode made of a fired product of the conductive composition.
Specifically, the conductive composition of the present invention stably forms an electrode pattern and an electrode having a finer line width, for example, when supplied on a light receiving surface of a semiconductor substrate by a screen printing method or the like. be able to. Therefore, for example, it is possible to realize further fine-line printing in printing electrode patterns of various semiconductor elements, and to realize a high-performance semiconductor element in which the semiconductor element is further miniaturized and highly integrated. Further, for example, by applying it to the formation of the light receiving surface electrode of the solar cell element, the amount of light received per unit area of the light receiving surface can be increased, which is particularly preferable because more electric power can be generated.

FIG. 1 is a cross-sectional view schematically showing an example of the structure of a solar cell. FIG. 2 is a plan view schematically showing a pattern of electrodes formed on a light receiving surface of a solar cell.

Hereinafter, preferred embodiments of the present invention will be described. It should be noted that technical matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of 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 art.

<Conductive composition>
The conductive composition disclosed here is typically a conductive composition capable of forming an electrode by firing. This conductive composition contains a conductive powder, a cellulosic resin, a butyral resin, and a dispersion medium. Hereinafter, each of these components will be described.

<Cellulose resin>
The conductive composition disclosed herein contains a cellulosic resin. Here, the cellulosic resin is a concept including cellulose and various cellulosic derivatives (modified products, etc.). Examples of the cellulose derivative include a derivative in which the hydroxy (OH) group of a glucose residue, which is a constituent unit of cellulose, is etherified or esterified. Examples of the cellulose ether include ethyl cellulose (EC), methyl cellulose (MC), hydroxyethyl cellulose, hydroxymethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl cellulose; and the like. Salts such as sodium carboxylmethyl cellulose salt may be used. Examples of the cellulose ester include cellulose phthalate acetate, cellulose nitrate, cellulose acetate, cellulose acetate-propionate, and cellulose acetate-butyrate. Among them, EC is exemplified as a particularly preferable cellulosic resin for the present invention from the viewpoint of realizing a viscosity characteristic capable of performing good printing. The cellulosic resin can function suitably as an organic binder and a viscosity (fluidity) adjusting agent.

The number average molecular weight M _x of the cellulosic resin is 55000 ≦ M _x . By setting the number average molecular weight M _x of the cellulosic resin to 55,000 or more, it is possible to achieve both the thinning of the electrode and the effect of suppressing defects such as disconnection at a higher level. The number average molecular weight _{M x} cellulosic resins, from the viewpoint of obtaining no defective thin wire-shaped electrode is preferably 60000 or more, more preferably 65000 or more, more preferably 70,000 or more. In a preferred embodiment, the number average molecular weight _{M x} cellulosic resin may be may be 75,000 or more, for example, 80,000 or more. The number average molecular weight M _x of the cellulosic resin is typically 200,000 or less, preferably 150,000 or less, more preferably 120,000 or less, and even more preferably 100,000 or less. The technique disclosed herein can be preferably carried out in an embodiment in which the number average molecular weight M _x of the cellulosic resin is 55,000 ≤ M _x ≤ 100,000. As the number average molecular weight M _x of the cellulosic resin, a value obtained by a chromatography method is adopted.

The weight average molecular weight Mw _x of the cellulose-based resin is not particularly limited as long as the number-average molecular weight M _x cellulosic resin satisfies the above range, typically at 10 × 10 ⁴ or more. The weight average molecular weight Mw _x of the cellulosic resin is preferably 13 × 10 ⁴ or more, more preferably 15 × 10 ⁴ or more, still more preferably 18 × 10 ⁴ or more, from the viewpoint of realizing a viscosity characteristic capable of performing good printing. Is. Further, the weight average molecular weight Mw _x cellulosic resins, preferably 30 × 10 ⁴ or less, more preferably 25 × 10 ⁴ or less, more preferably 20 × 10 ⁴ or less.

The relationship between the number average molecular weight M _{x of the} cellulosic resin and the weight average molecular weight M w _x is not particularly limited, but from the viewpoint of the stability of the composition, for example, the molecular weight distribution (Mw _x / M _x ) is 4.0 or less. (For example, 3.0 or less) can be preferably used. The Mw _x / M _x of the cellulosic resin is preferably 2.8 or less, more preferably 2.6 or less, still more preferably 2.5 or less (for example, 2.4 or less). In principle, Mw _x / M _x is 1.0 or more. From the viewpoint of easy availability of raw materials and ease of synthesis, a cellulosic resin having Mw _x / M _x of 1.1 or more (preferably 1.5 or more) can be preferably used.

The content W _x of the cellulosic resin in the conductive composition is not particularly limited, and can be, for example, 0.05% by mass or more. From the viewpoint of better exerting the effect of using the cellulosic resin, the preferable content W _x is 0.1% by mass or more, for example, 0.2% by mass or more. Further, the content W _x is preferably 5% by mass or less, and more preferably 1% by mass or less (for example, 0.5% by mass or less).

<Buchiral resin>
The conductive composition disclosed herein contains a butyral resin in addition to the cellulosic resin described above. Here, the butyral resin refers to a polymer obtained by reacting polyvinyl alcohol and butyraldehyde under acidic conditions (acetalization reaction), and the remaining hydroxy group is reacted with another compound to introduce an acid group or the like. It is a concept that also includes the polymer. The butyral resin can function as an organic binder and a viscosity (fluidity) adjusting agent together with the cellulosic resin described above.

The butyral resin has a number average molecular weight _{M y} is 100,000 or less. By the number average molecular weight M _y butyral resin to 100,000, and the effect of suppressing the thinning and defects such as disconnection of the electrode can be compatible at a higher level. The number-average molecular weight _{M y} butyral resin is preferably 90000 or less, more preferably 70,000. In a preferred embodiment, the number average molecular weight _{M y} of butyral-based resin may be 40,000 or less, and may be for example, 20,000 or less. The number average molecular weight _{M y} butyral resin is typically 5000 or more, preferably 8000 or more, more preferably 12000 or more, more preferably 15000 or more. Here disclosed is technology has a number average molecular weight _{M y} butyral resin can be preferably carried out at 10000 ≦ _{M y} ≦ 100000 is a manner. As the number average molecular weight M _y butyral resin, a value obtained by chromatographic methods is employed.

Conductive composition disclosed herein, the number-average molecular weight _{M x} cellulosic resins, relationship equation between the number average molecular weight _{M y} butyral _{resin: 10000 ≦ M y <M x} ≦ 100000; meet Is preferable. By smaller than the number-average molecular weight M _x cellulosic resin number-average molecular weight M _y butyral resin, and the effect of suppressing the thinning and defects such as disconnection of the electrode can be compatible at a higher level.

In one preferred embodiment, the ratio of the number average molecular weight _{M y} butyral resin to the number average molecular weight _{M x} cellulosic resin _(M y / _{M x)} is a generally _M y / _{M x} ≦ 1.2, preferably _{M y} / M x <1.0, more preferably _M y / _{M x} ≦ 0.9. In a preferred _embodiment, it may be a _M y / M _x ≦ 0.8, for example may be a _M y / _{M x} ≦ 0.7. By using a cellulosic resin and a butyral resin in combination so as to have a specific number average molecular weight ratio, it is possible to achieve both the thinning of the electrode and the effect of suppressing defects such as disconnection at a higher level. The lower limit of M _y / _{M x} is not particularly limited, but is preferably 0.2 ≦ _M y / _{M x,} and more preferably 0.23 ≦ _M y / _{M x.}

Preferred examples of the electrically conductive composition disclosed herein, the number-average molecular weight _{M x} of the cellulose-based resin is 55000 ≦ _{M x} ≦ 200000, and the number-average molecular weight _{M y} butyral resin is 5000 ≦ _{M y} ≦ 100000 a is one; number-average molecular weight _{M x} of the cellulose-based resin is 60000 ≦ _{M x} ≦ 150000, and a number average molecular weight _{M y} butyral resin is 10000 ≦ _M y <60000; cellulosic resin the number-average molecular weight _{M x} is 70000 ≦ _{M x} ≦ 100000, and butyral based number average molecular weight _{M y} of the resin is 15000 ≦ _{M y} ≦ 40000; number-average molecular weight of the cellulose-based resin _{M x} is 80000 ≦ M an _x ≦ 90000, and a number average molecular weight _{M y} butyral resin is 18000 ≦ _{M y} ≦ 22000; and the like. When the number average molecular weight of the cellulosic resin and the butyral resin is within the range, the thinning of the electrode and the effect of suppressing the disconnection can be compatible at a higher level.

Butyralization degree of the butyral resin is not particularly limited as long as the number-average molecular weight M _y butyral resin satisfies the above range. From the viewpoint of realizing the viscosity characteristics capable of performing good printing, it may be, for example, 60 mol% or more, and typically 63 mol% or more, for example 65 mol% or more. The technique disclosed here can be preferably carried out in an embodiment in which the degree of butyralization of the cellulosic resin is, for example, 60 mol% or more and 80 mol% or less (typically 63 mol% or more and 74 mol% or less). The degree of butyralization refers to the ratio of the number of moles occupied by the constituent units constituting the butyral unit to the total number of moles of the constituent units constituting the butyral unit, the vinyl alcohol unit, and the vinyl ester unit.

The content W _y of butyral resin in the conductive composition is not particularly limited and may be, for example, 0.01% by mass or more. From the viewpoint of better exerting the effect of using the butyral resin, the preferable content _Wy is 0.02% by mass or more, for example 0.04% by mass or more. Further, the content W _x is preferably 3% by mass or less, and more preferably 0.7% by mass or less (for example, 0.3% by mass or less).

From the viewpoint of better exerting the effect of using the cellulosic resin and the butyral resin in combination, the ratio of the content W _y of the butyral resin to the content W _x of the cellulosic resin (W _y / W _x ) is determined. It is preferable that 0.2 ≦ W _y / W _x . By using a cellulosic resin and a butyral resin in combination so as to have a specific content ratio, it is possible to achieve both thinning of the electrode and suppression of defects such as disconnection at a higher level. The content ratio (W _y / W _x ) is preferably 0.4 or more, more preferably 0.6 or more. The upper limit of W _y / W _x is not particularly limited, but it is preferably W _y / W _x ≤ 1.5, more preferably W _y / W _x ≤ 1.2, and W _y / W _x. It is more preferable that ≦ 1.0. In the technique disclosed herein, for example, the relationship between W _x and W _y is 0.2 ≤ W _y / W _x ≤ 1.5 (for example, 0.5 ≤ W _y / W _x ≤ 1.0). It can be preferably carried out in certain embodiments.

When the total conductive composition is 100% by mass, the total amount (W _x + W _y ) of the cellulosic resin content W _x and the butyral resin content W _y is 0.02% by mass or more and 10% by mass. % Or less is preferable. The preferred total amount (W _x + W _y ) is 0.05% by mass or more, for example 0.1% by mass or more. Further, the total amount (W _x + W _y ) is preferably 10% by mass or less, more preferably 5% by mass or less, further preferably 1% by mass or less, and 0.5% by mass or less. Is particularly preferable.

<Conductive powder>
The conductive composition disclosed herein contains a conductive powder in addition to the above-mentioned cellulosic resin and butyral resin. The conductive powder is a component that mainly forms the solid content of the conductive composition. As the conductive powder, a powder made of various metals or alloys thereof having desired conductivity and other physical properties according to the application can be considered. As an example of the material constituting such a conductive powder, gold (Au), silver (Ag), copper (Cu), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium ( Metals such as Ir), osmium (Os), nickel (Ni) and aluminum (Al) and their alloys, carbonaceous materials such as carbon black, LaSrCoFeO ₃ oxides (eg LaSrCoFeO ₃ ), LaMnO ₃ oxides (eg LaSrCoFeO ₃ ) For example, conductive ceramics typified by transition metal perovskite type oxides represented as LaSrGaMgO ₃ ), LaFeO ₃ type oxide (for example, LaSrFeO ₃ ), LaCoO ₃ type oxide (for example, LaSrCoO ₃ ) and the like are exemplified. Among them, a conductive powder consisting of a single noble metal such as platinum, palladium or silver, an alloy thereof (Ag-Pd alloy, Pt-Pd alloy, etc.), nickel, copper, aluminum and an alloy thereof is particularly preferable. It is mentioned as a material which constitutes. From the viewpoints of relatively low cost and high electrical conductivity, a powder made of silver and an alloy thereof (hereinafter, also simply referred to as “Ag powder”) is particularly preferably used. Hereinafter, the conductive composition of the present invention will be described by taking the case of using Ag powder as the conductive powder as an example.

The particle size of Ag powder and other conductive powders is not particularly limited, and various particle sizes depending on the intended use can be used. Typically, one having an average particle diameter of 5 μm or less based on a laser / scattering diffraction method is suitable, and one having an average particle diameter of 3 μm or less (typically 1 to 3 μm, for example 1 to 2 μm) is preferably used. Be done.

The shape of the particles constituting the conductive powder is not particularly limited. Typically, a spherical shape, a flake shape, a conical shape, a rod shape, or the like can be preferably used. It is preferable to use spherical or scaly particles because of good filling property and easy formation of a dense light receiving surface electrode. As the conductive powder to be used, one having a sharp (narrow) particle size distribution is 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 cumulative volume of 10% and the particle size (D90) at the cumulative volume of 90% in the particle size distribution based on the laser scattering diffraction method can be adopted. When all the particle sizes constituting the powder are the same, the value of D10 / D90 becomes 1, and conversely, the wider the particle size distribution, the closer the value of D10 / D90 approaches 0. 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 or more and 0.5 or less).
A conductive composition using a conductive powder having such an average particle size and a particle shape has good filling property of the conductive powder and can form a dense electrode. This is advantageous in forming a fine electrode pattern with high shape accuracy.

The conductive powder such as Ag powder is not particularly limited depending on the production method and the like. For example, a conductive powder (typically Ag powder) produced by a well-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 carried out by using, for example, a classification device using a centrifugation method or the like.

It is appropriate that the content ratio of the conductive powder in the conductive composition is about 70% by mass or more (typically 70% by mass to 95% by mass) when the whole composition is 100% by mass. It is more preferably about 85% by mass to 95% by mass, for example, about 90% by mass. Increasing the content ratio of the conductive powder is preferable from the viewpoint of forming a dense electrode pattern with good shape accuracy. On the other hand, if this content ratio is too high, the handleability of the paste, suitability for various printability, and the like may deteriorate.

<Dispersion medium>
The conductive composition disclosed herein typically contains a dispersion medium in addition to the cellulosic resin, butyral resin and conductive powder described above. A preferred dispersion medium 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. Examples of such an organic solvent 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. Organic solvents such as derivatives, toluene, xylene, mineral spirit, tarpineol, mentanol, and texanol can be preferably used. Particularly preferable solvent components include butyl carbitol (BC), butyl carbitol acetate (BCA), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and the like.

The conductive composition disclosed herein has, for example, a non-volatile content (NV) of 70% by mass to 99% by mass, and the balance is a dispersion medium (typically an organic solvent). It can be preferably carried out in a form that is a form. The form in which the NV is 90% by mass to 95% by mass is more preferable.

<Other ingredients>
The conductive composition disclosed herein may contain various inorganic additives and / or organic additives other than the above, as long as the object does not deviate from the object of the present invention. Preferable examples of the inorganic additive include glass frit, ceramic powders other than the above (ZnO ₂ , Al ₂ O _3, etc.), and various other fillers. Further, as a preferable example of the organic additive, additives such as a surfactant, a defoaming agent, an antioxidant, a dispersant, and a viscosity modifier can be mentioned.

The glass frit is a component that can function as an inorganic binder of the conductive powder, and enhances the bondability between the conductive particles constituting the conductive powder and between the conductive particles and the substrate (the object on which the electrode is formed). To work. Further, when this conductive composition is used for forming, for example, a light receiving surface electrode of a solar cell, the presence of the glass frit may cause the conductive composition to penetrate the antireflection film as a lower layer during firing. This makes it possible to achieve good adhesion and electrical contact with the substrate.
It is preferable that such a glass frit is adjusted to a size equal to or smaller than that of the conductive powder. For example, the average particle size based on the laser / scattering diffraction method is preferably 4 μm or less, preferably 3 μm or less, and typically 0.1 μm or more and 2 μm or less.

The composition of the glass frit is not particularly limited, and glass having various compositions can be used. For example, as an approximate glass composition, so-called lead-based glass, lead-lithium-based glass, zinc-based glass, borate-based glass, borosilicate-based glass, alkaline-based glass, which are commonly expressed by those skilled in the art. It may be lead-free glass, tellurium glass, glass containing barium oxide, bismuth oxide, or the like. Needless to say, these glasses have Si, Pb, Zn, Ba, Bi, B, Al, Li, Na, K, Rb, Te, Ag, Zr, Sn in addition to the main glass constituent elements appearing in the above names. , Ti, W, Cs, Ge, Ga, In, Ni, Ca, Cu, Mg, Sr, Se, Mo, Y, As, La, Nd, Co, Pr, Gd, Sm, Dy, Eu, Ho, Yb , Lu, Ta, V, Fe, Hf, Cr, Cd, Sb, F, Mn, P, Ce and Nb may contain one or more elements selected from the group. Such a glass frit may be, for example, a general amorphous glass or a crystallized glass containing a part of crystals. Further, as the glass frit, the glass frit having one kind of composition may be used alone, or the glass frit having two or more kinds of compositions may be mixed and used.

The softening point of the glass constituting the glass frit is not particularly limited, but is preferably about 300 to 600 ° C. (for example, 400 to 500 ° C.). Specific examples of the glass whose softening point can be adjusted within the range of 300 ° C. or higher and 600 ° C. or lower include glass containing a combination of the following elements. B-Si-Al-based glass, Pb-B-Si-based glass, Si-Pb-Li-based glass, Si-Al-Mg-based glass, Ge-Zn-Li-based glass, B-Si-Zn-Sn-based glass, B-Si-Zn-Ta glass, B-Si-Zn-Ta-Ce glass, B-Zn-Pb glass, B-Si-Zn-Pb glass, B-Si-Zn-Pb-Cu Glass, B-Si-Zn-Al glass, Pb-B-Si-Ti-Bi glass, Pb-B-Si-Ti glass, Pb-B-Si-Al-Zn-P glass, Pb- Li-Bi-Te glass, Pb-Si-Al-Li-Zn-Te glass, Pb-B-Si-Al-Li-Ti-Zn glass, Pb-B-Si-Al-Li-Ti- P-Te-based glass, Pb-Si-Li-Bi-Te-based glass, Pb-Si-Li-Bi-Te-W-based glass, P-Pb-Zn-based glass, P-Al-Zn-based glass, P- Si-Al-Zn-based glass, P-B-Al-Si-Pb-Li-based glass, P-B-Al-Mg-FK-based glass, Te-Pb-based glass, Te-Pb-Li-based glass, VP-Ba-Zn-based glass, VP-Na-Zn-based glass, AgI-Ag ₂ O-BP-based glass, Zn-B-Si-Li-based glass, Si-Li-Zn-Bi- Mg-W-Te glass, Si-Li-Zn-Bi-Mg-Mo-Te glass, Si-Li-Zn-Bi-Mg-Cr-Te glass, etc. When a conductive composition containing a glass frit having such a softening point is used, for example, when forming a light receiving surface electrode of a solar cell element, it exhibits good fire-through characteristics and can form a high-performance electrode. Preferred to contribute.

Examples of organic additives include silicone resins. By containing the silicone resin, it is possible to better realize the viscosity characteristics capable of performing good printing (for example, screen printing). As the silicone resin (which may also be simply called silicone), an organic compound containing silicon (Si) can be used without particular limitation, and for example, it has a main skeleton composed of a siloxane bond (Si—O—Si). Organic compounds can be preferably used. For example, it may be a linear silicone in which an alkyl group, a phenyl group or the like is introduced into an unbonded hand (side chain, terminal) in the main skeleton. Further, it may be a linear modified silicone in which other substituents such as a polyether group, an epoxy group, an amine group, a carboxyl group, an aralkyl group and a hydroxyl group are introduced into a side chain, a terminal, or both, or a polyether may be used. It may be a linear block copolymer bonded alternately with silicone. Specifically, as the silicone resin, for example, polydimethylsiloxane and / or polyether-modified siloxane can be preferably used.

Such silicone resins tend to be formed an electrode having a high aspect ratio as the weight-average molecular weight Mw _z increases. From the viewpoint of realizing a high aspect ratio, weight average molecular weight Mw _z of the silicone resin may be, for example, 1000 or more, preferably at least 3,000, more preferably 5,000 or more, 8000 or more, for example 10000 The above is particularly preferable. The upper limit of Mw _z is not particularly limited, but from the viewpoint of suppressing defects such as disconnection and low resistance, Mw _z is preferably 150,000 or less, more preferably 120,000 or less, and more preferably 100,000 or less. It is more preferably 80,000 or less, and particularly preferably 80,000 or less.

The content W _z of the silicone resin is not particularly limited, the total conductive composition excluding the silicone resin can be is 100% by weight, for example 0.01% by mass or more. From the viewpoint of better exerting the effect of using the silicone resin, the preferable content W _z is 0.05% by mass or more, for example, 0.01% by mass or more. Further, the content W _z is preferably 3% by mass or less, and more preferably 1% by mass or less (for example, 0.5% by mass or less).

<Viscosity>
The conductive composition disclosed here has a viscosity of η _{0.1 at} a shear rate of 0.1 s ^-1 and η _0.1 ≤ 500 Pa · s (for example, 100 Pa · s ≤ η _0.1 ≤ 500 Pa · s. s), preferably η _0.1 <500 Pa · s, more preferably η _0.1 ≤ 450 Pa · s, still more preferably η _0.1 ≤ 300 Pa · s, and particularly preferably η _0.1 ≤ 250 Pa · s ( For example, 200 Pa · s ≦ η _0.1 ≦ 250 Pa · s). Shear velocity: A conductive composition in which the viscosity η _0.1 at _0.1 s ^-1 is η _0.1 ≤ 500 Pa · s is applied (supplied) to, for example, the light receiving surface of a solar cell via a printing mask. When it is used, it shows good fluidity and the composition can be easily removed from the mask. Therefore, it is possible to suppress the occurrence of defects such as disconnection (that is, poor supply portion).

Further, in the conductive composition disclosed here, the viscosity η _{10 at} a shear rate of 10s ^-1 is 50 Pa · s ≦ η ₁₀ (for example, 50 Pa · s ≦ η ₁₀ ≦ 100 Pa · s), preferably 52 Pa. S ≦ η ₁₀ ≦ 80 Pa · s, more preferably 55 Pa · s ≦ η ₁₀ ≦ 70 Pa · s. The conductive composition disclosed here has a viscosity characteristic of 50 Pa · s ≦ η ₁₀ and thus is printed in a predetermined pattern through the mask (that is, after being applied to the light receiving surface). In the state of), it is possible to exhibit high viscosity (shape maintenance performance) and suppress undesired expansion of the line width. That is, since the shape of the electrode pattern applied to the light receiving surface is less likely to bleed before firing, a fine line-shaped electrode pattern can be formed. Therefore, according to the conductive composition having the above structure, a fine line-shaped electrode having a desired line width (for example, 45 μm or less, preferably 40 μm or less) can be stably formed.

Here, according to the findings of the present inventors, cellulose resin and a butyral resin containing no or cellulose resin and a butyral-based number average molecular weight including resin M _x, M _y conventional that does not satisfy the range If the amount of the resin added is increased in order to suppress the expansion of the line width, the viscosity of the conductive composition in the high shear rate range tends to increase, but the viscosity in the low shear rate range also tends to increase accordingly. .. Therefore, if the amount of resin added is simply increased, the viscosity at a shear rate of 0.1 s- ¹ exceeds 500 Pa · s, resulting in printing defects, and as a result, fine linear electrodes may not be stably formed. there were.
In contrast, the conductive compositions disclosed herein, the cellulose resin and the butyral resin and a specific number average molecular weight M _x, by using a combination such that the M _y, regardless of the amount of resin However, the viscosity near the shear rate: 0.1s ^-1 can be specifically reduced. The reason why such effects are obtained, but are not particularly limiting sense, butyral-based resin and is compatible with a cellulose-based resin and the number average molecular weight M _y having the number average molecular weight M _x It is thought that this is because it plays a role in alleviating mutual aggregation. As a result, the viscosity η _0.1 when the shear rate: 0.1 s ^-1 is η _0.1 ≤ 500 Pa · s, and the viscosity η ₁₀ when the shear rate: 10 s ^-1 is 50 Pa · s. An optimum conductive composition capable of better realizing a conductive composition having a viscosity characteristic of ≤η ₁₀ and satisfying both thinning of electrodes and suppression of defects such as disconnection, which could not be obtained in the past. can do.

Since the conductive composition disclosed here has viscosity characteristics suitable for printing as described above, it is a printing composition applied to, for example, screen printing, gravure printing, offset printing, inkjet printing and the like. (It may also be referred to as paste, slurry, ink, etc.). Then, when forming an electrode pattern that requires fine line formation and defect suppression such as disconnection, it can be particularly preferably adopted when such a general-purpose printing means is used. Therefore, for example, a solar cell element as an example of a semiconductor element is taken as an example, and the semiconductor element disclosed here is shown by showing an example of forming a comb-shaped electrode pattern including finer finger electrodes on the light receiving surface by screen printing. The solar cell element as a device will be described. The solar cell element may be the same as that of the conventional solar cell except for the configuration of the light receiving surface electrode that characterizes the present invention, and the present invention describes the same configuration as the conventional one and the part related to the use of the same material as the conventional one. Since it does not characterize, detailed description is omitted.

1 and 2 schematically show an example of a solar cell element (cell) 10 that can be suitably manufactured by carrying out the present invention, from single crystal, polycrystalline or amorphous silicon (Si). This is a so-called silicon type solar cell element 10 that uses the wafer as the semiconductor substrate 11. The cell 10 shown in FIG. 1 is a general single-sided light receiving type solar cell element 10. Specifically, this type of solar cell element 10 is an n-Si layer 16 formed by pn junction formation on the light receiving surface side of the p-Si layer (p-type crystalline silicon) 18 of the silicon substrate (Si wafer) 11. The surface thereof is provided with an antireflection film 14 made of titanium oxide or silicon nitride formed by CVD or the like, and light receiving surface electrodes 12 and 13 formed of a conductive composition mainly containing Ag powder or the like. ..

On the other hand, on the back surface side of the p—Si layer 18, the outside of the back surface side formed by a predetermined conductive composition (typically, a conductive paste in which the conductive powder is Ag powder) like the light receiving surface electrode 12. A connecting electrode 22 and a back surface aluminum electrode 20 that exhibits a so-called back surface electric field (BSF) effect are provided. The aluminum electrode 20 is formed on substantially the entire back surface of the back surface by printing and firing a conductive composition mainly composed of aluminum powder. During this firing, an Al—Si alloy layer (not shown) is formed, and aluminum diffuses into the p—Si layer 18 to form the p ⁺ layer 24. By forming the p ⁺ layer 24, that is, the BSF layer, the photogenerated carriers are prevented from being recombined in the vicinity of the back electrode, and for example, the short circuit current and the open circuit voltage (Voc) are improved.

As shown in FIG. 2, on the light receiving surface 11A side of the silicon substrate 11 of the solar cell element 10, several (for example, about 1 to 3) light receiving surface electrodes 12 and 13 are linearly parallel to each other. Bus bar (connection) electrode 12 and a large number of parallel (for example, about 60 to 90) streak-shaped finger (collection) electrodes 13 connected to the bus bar electrode 12 so as to intersect with each other. It is formed.
A large number of finger electrodes 13 are formed to collect light-generating carriers (holes and electrons) generated by light reception. The bus bar electrode 12 is a connecting electrode for collecting current from the carrier collected by the finger electrode 13. The portion where the light receiving surface electrodes 12 and 13 are formed forms a non-light receiving portion (light shielding portion) on the light receiving surface 11A of the solar cell element. Therefore, by making the bus bar electrode 12 and the finger electrode 13 (particularly a large number of finger electrodes 13) provided on the light receiving surface 11A side as fine as possible, the non-light receiving portion (light shielding portion) corresponding to this is reduced. The light receiving area per cell unit area is expanded. This can be extremely simple to improve the output per unit area of the solar cell element 10.

At this time, if sagging or denting occurs in a part of the thinned electrode, the sagging or dented portion causes an increase in resistance, and loin is generated in current collection. Further, if a wire break occurs even in a part of the thinned electrodes, it becomes difficult to collect the generated current through the broken wire (a state in which a current collector loin is generated as a current flowing through a high-resistance substrate). Will be collected at). Therefore, in order to form the light receiving surface electrode of the solar cell element, a conductive composition having not only high electrical characteristics but also excellent shape stability by printing is required.

Such a solar cell element 10 is generally manufactured through the following process.
That is, the silicon is prepared by preparing an appropriate silicon wafer and doping it with a predetermined impurity by a general technique such as a thermal diffusion method or an ion plantation to form the p-Si layer 18 and the n-Si layer 16. A substrate (semiconductor substrate) 11 is manufactured. Next, the antireflection film 14 made of silicon nitride or the like is formed by a technique such as plasma CVD.
Then, on the back surface 11B side of the silicon substrate 11, first, a predetermined conductive composition (typically, a conductive composition in which the conductive powder is Ag powder) is screen-printed in a predetermined pattern and dried. By doing so, a back surface side conductor coating material that becomes the back surface side external connection electrode 22 (see FIG. 1) after firing is formed. Next, an aluminum film is formed by applying (supplying) a conductive composition containing aluminum powder as a conductor component to the entire surface on the back surface side by a screen printing method or the like and drying the mixture.

Next, the conductive composition of the present invention is printed (supplied) on the antireflection film 14 formed on the surface side of the silicon substrate 11 with a wiring pattern as shown in FIG. 2, typically based on a screen printing method. ). The line width to be printed is not particularly limited, but by adopting the conductive composition of the present invention, the line width is about 45 μm or less (preferably in the range of about 30 μm to 45 μm, more preferably about 30 μm to 40 μm, and more. A coating film (printed matter) of an electrode pattern including finger electrodes (preferably less than 40 μm) is formed. Then, the substrate is dried in an appropriate temperature range (typically 100 ° C. to 200 ° C., for example, about 120 ° C. to 150 ° C.). The contents of a suitable screen printing method will be described later.

The silicon substrate 11 on which the paste coating material (dry film-like coating material) is formed on both sides in this way is used in an air atmosphere using a firing furnace such as a near-infrared high-speed firing furnace, and an appropriate firing temperature (for example, Bake at 700-900 ° C).
By such firing, a fired aluminum electrode 20 is formed together with the light receiving surface electrodes (typically Ag electrodes) 12 and 13 and the back surface side external connection electrode (typically Ag electrode) 22, and at the same time, Al (not shown) is formed. As the −Si alloy layer is formed, aluminum diffuses into the p—Si layer 18 to form the above-mentioned p + layer (BSF layer) 24, and the solar cell element 10 is manufactured.
Instead of firing at the same time as described above, for example, firing for forming the light receiving surface electrodes (typically Ag electrodes) 12 and 13 on the light receiving surface 11A side, and the aluminum electrode 20 on the back surface 11B side and the external connection. The firing for forming the electrode 22 may be performed separately.

According to the conductive composition disclosed here, for example, the conductive composition can be supplied (printed) on the silicon substrate 11 in a desired electrode pattern by screen printing. Since such a conductive composition has the above-mentioned viscosity characteristics, for example, with respect to the electrode obtained after firing, the finger electrode 13 having a line width of 45 μm or less (preferably 40 μm or less) is significantly thickened or broken. It can be formed with high quality in a reduced state. As for the bus bar electrode, for example, a bus bar electrode having a line width of about 1000 to 3000 μm can be formed with high quality. When the electrode wires are thinned in this way, a solar cell element having high photoelectric conversion efficiency can be provided by designing the width and the number of finger electrodes 13 as an optimum combination. ..

Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

<Conductive composition>
A conductive composition for forming an electrode was prepared by the procedure shown below. That is, were prepared as the number-average molecular weight M _x is different types of cellulose as cellulose-based resin (EC), and a number average molecular weight M _y is different kinds of polyvinyl butyral as a butyral resin (PVB). These EC and PVB, silver powder as a conductive powder, Pb-based glass as a glass frit, polydimethylsiloxane as a silicone resin, and butyl diglycol acetate as a dispersion medium are mixed to form a silver powder. The conductive compositions of Examples 1 to 24 containing 90 parts by mass, 2 parts by mass of glass frit, 0.5 parts by mass of the total amount of EC and PVB, and 7.5 parts by mass of the dispersion medium were prepared. The conductive composition of each example, the number-average molecular weight M _y of PVB _used, butyralization degree, the number-average molecular weight M _x of _EC, polymerization degree, the content ratio of PVB / EC, the content of the silicone resin (mass Part) is summarized in Table 1. In Example 17, polyvinyl alcohol (PVA) was used instead of PVB.

The number average molecular weight M _x, M _y cellulosic resins and butyral resins each example is determined under the following conditions using a Shimadzu Corporation Size exclusion chromatography (SEC) system.
(1) Number average molecular weight of cellulosic resin M _x
Column: GPC KF-806L (manufactured by Showa Denko KK)
Eluent: THF (tetrahydrofuran)
Flow rate: 1 ml / min Column temperature: 40 ° C
Standard substance: PS (polystyrene)
(2) Number-average molecular weight of butyral resin M _y
Column: GPC KF-806L (manufactured by Showa Denko KK)
Eluent: THF (tetrahydrofuran)
Flow rate: 1 ml / min Column temperature: 40 ° C
Standard substance: PS (polystyrene)

<Viscosity>
For the viscosities of the conductive compositions according to Examples 1 to 5, 11 and 16, a commercially available Hake Mars rheometer viscometer manufactured by Thermo Scientific Co., Ltd. was used, and the shear rate was 0.01 s ^{-1 to} 100 s ^-1 at a liquid temperature of 25 ° C. It was measured in the range of. The results are shown in Table 2.

As shown in Table 2, the EC number average molecular weight _{M x} is 55000 ≦ _{M x,} the number-average molecular weight _{M y} conductive compositions of Examples 1 to 3 in combination with PVB for _{M y} ≦ 100000 is Example 4 The viscosity in the high shear rate range was higher than that of 5, 11 and 16, and an extremely high viscosity of 50 Pa · s ≦ η ₁₀ could be realized. Further, the conductive compositions of Examples 1 to 3 had a lower viscosity in the low shear rate range than those of Examples 5, 11 and 16, and could realize an extremely low viscosity of η _0.1 ≤ 500 Pa · s or less.

<Manufacturing of test solar cell element (light receiving surface electrode)>
The solar cell elements of Examples 1 to 24 are produced by forming a light receiving surface electrode (that is, a comb-shaped electrode composed of a finger electrode and a busbar electrode) using the conductive compositions of Examples 1 to 24 obtained above. did.
Specifically, first, a commercially available p-type single crystal silicon substrate (thickness 180 μm) for a solar cell having a size of 156 mm square (6 inch square) is prepared, and its surface (light receiving surface) is a mixed acid of hydrofluoric acid and nitric acid. By etching with, the damaged layer was removed and an uneven texture structure was formed. Next, a phosphorus-containing solution was applied to the textured structural surface and heat-treated to form an n—Si layer (n ⁺ layer) having a thickness of about 0.5 μm on the light receiving surface of the silicon substrate. Next, a silicon nitride film having a thickness of about 80 nm was formed on the n—Si layer by a plasma CVD (PECVD) method to obtain an antireflection film.

Next, on the back surface side of the silicon substrate, a predetermined silver electrode forming paste was used, screen-printed with a predetermined pattern so as to become an electrode for external connection on the back surface side, and dried to form a back surface electrode pattern. .. Then, the aluminum electrode forming paste was screen-printed on the entire surface on the back surface side and dried to form an aluminum film.

Then, using the conductive compositions of each example, an electrode pattern for a light receiving surface electrode (Ag electrode) was printed on the antireflection film by a screen printing method in an air atmosphere and at room temperature, and at 120 ° C. It was dried. Specifically, as shown in FIG. 2, an electrode pattern consisting of three linear bus bar electrodes parallel to each other and 90 finger electrodes parallel to each other so as to be orthogonal to the bus bar electrodes is formed. Formed by screen printing.
The target finger electrode pattern has a line width of 35 μm to 40 μm after firing. Further, the bus bar electrode was set so that the line width after firing was about 1.5 mm.
Then, the substrate on which the electrode patterns were printed on both sides in this way was fired in an air atmosphere using a near-infrared high-speed firing furnace at a firing temperature of 700 to 800 ° C. to produce a solar cell for evaluation.

<Line width>
The line width of the light receiving surface electrode (finger electrode) of the solar cell produced as described above was measured by the following procedure. As for the line width of the electrodes, the line width at an arbitrary position of the light receiving surface electrode of the solar cell of each example was measured with a shape analysis laser microscope (manufactured by KEYENCE CORPORATION). The results are shown in the corresponding columns of Table 1 as the average value of the values measured at 30 locations. Here, the line width of less than 40 μm was evaluated as “⊚”, the line width of 40 μm or more and less than 45 μm was evaluated as “◯”, and the line width of 45 μm or more was evaluated as “x”.

<Disconnection>
In addition, the number of disconnections was measured for the light receiving surface electrode (finger electrode) of the solar cell. The number of broken wires was measured by identifying the broken parts of the electrodes per substrate using a solar cell electroluminescence (EL) inspection device. Specifically, a bias was applied to the solar cell to cause the conductive portion of the electrode to emit light. At this time, in the EL emission image, the non-conducting portion of the electrode is displayed in black due to shading, so the number of the non-conducting portion was measured with the number of light-shielding portions as the disconnection points. The results are shown in the corresponding columns of Table 1. Here, those with less than 10 disconnections were evaluated as "◯", those with 10 or more and less than 45 were evaluated as "Δ", and those with 45 or more were evaluated as "x".

As shown in Table 1, Examples 4 and 5, the number-average molecular weight _{M x} of EC is less than 55000, and a number average molecular weight _{M y} of PVB is 100,000 or less. Further, Example 10, the number-average molecular weight _{M x} of EC is 55,000 or more and a number average molecular weight _{M y} of PVB is 100,000 or more. It was confirmed that the electrode formed by using these conductive compositions had a significantly thicker line width than Examples 1 to 3 and 6 to 9. That is, the print of the conductive composition using a conductive composition the number average molecular weight M _x was used EC is less than 55000 and a number average molecular weight M _y is 100000 or more PVB (coating) is cause to sag It was found that a fine wire-shaped electrode could not be formed.

Further, in Example 11 in which EC having a number average molecular weight M _x of 55,000 or more was used alone, the line width was significantly thicker than in Examples 1 to 3 and 6 to 9, and the composition from the mask at the time of printing was used. It was difficult to pull out, and there were many disconnections. Further, Example 16 using a PVB number average molecular weight M _y is 100,000 or less alone, although able to narrow the line width, poor omission of the composition from the mask at the time of printing, disconnection occurred frequently. Further, in Example 17 in which EC and PVA having a number average molecular weight M _x of 55,000 or more were used in combination, the line width could be narrowed, but the composition was poorly removed from the mask during printing, and disconnection occurred frequently. ..

In contrast, the number and EC-average molecular weight _{M x} is 55000 or more and a number-average molecular weight _{M y} conductive composition of Example 1～3,6～9 using a combination of the PVB is 100,000 or less, said It was possible to form an electrode having a line width narrower than that of Examples 4, 5, 10 and 11. That is, it was confirmed that the unfavorable spread of the coating film was suppressed and a fine line-shaped electrode could be formed. In addition, the conductive compositions of Examples 1 to 3 and 6 to 9 were able to reduce the number of wire breaks as compared with Examples 11, 16 and 17 described above. That is, it was confirmed that the composition can be easily removed from the mask during printing to form an electrode having few defects such as disconnection.

In the case of the conductive composition tested here, in Examples 4 and 13 to 15 in which the PVB / EC content ratio was 0.5 or more and 1.5 or less, the electrodes were thinner than in Example 12. was gotten. Further, in Examples 22 to 24 in which the content of the silicone resin was 0.1 to 0.5 parts by mass, a finer wire electrode was obtained as compared with Examples 18 to 21.

Although the present invention has been described above in terms of preferred embodiments, such a description is not a limitation, and of course, various modifications can be made.

According to the present invention, it is possible to provide a conductive composition capable of thinning the electrode pattern and suppressing disconnection of the electrode pattern.

Claims (8)

A conductive composition for forming electrodes.
With conductive powder
Cellulose resin and
Butyral resin and
Silicone resin and
Dispersion medium and
Including
The number average molecular weight M _{x of the} cellulosic resin is 55000 ≦ M _x .
The number-average molecular weight _{M y} of the butyral resin is, Ri _{M y} ≦ 100000 der,
When the entire conductive composition excluding the silicone resin is 100 mass%, the content W _z of the silicone resin is 3 wt% or less than 0.01 wt%, the conductive composition. The ratio of the number average molecular weight _{M y} of the butyral resin to the number average molecular weight _{M x} of the cellulose-based resin _(M y / _{M x)} is a _{0.2 ≦ M y / M x ≦} 1.2, claims The conductive composition according to 1. The number average molecular weight M _x of the cellulose-based resin, the relationship between the number-average molecular weight M _y of the butyral resin is the formula:
_{10000 ≦ M y <M x ≦} 100000
The conductive composition according to claim 1 or 2. Claims 1 to that the ratio (W _y / W _x ) of the content W _y of the butyral resin to the content W _x of the cellulosic resin is 0.2 ≦ W _y / W _x ≦ 1.5. The conductive composition according to any one of 3. When the entire conductive composition is 100% by mass, the total amount (W _x + W _y ) of the cellulosic resin content W _x and the butyral resin content W _y is 0.1% by mass. The conductive composition according to any one of claims 1 to 4, which is 1% by mass or less. Shear velocity: The viscosity η _0.1 when 0.1 s ^-1 is η _0.1 ≤ 500 Pa · s.
The conductive composition according to any one of claims 1 to 5 , wherein the viscosity η ₁₀ when the shear rate is 10 s ^-1 is 50 Pa · s ≦ η ₁₀ . Any one of claims 1 to 6 , wherein the metal species constituting the conductive powder contains any one or more elements selected from the group consisting of nickel, platinum, palladium, silver, copper and aluminum. The conductive composition according to one. A solar cell element comprising a light receiving surface electrode made of a fired product of the conductive composition according to any one of claims 1 to 7 .

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