JP2017069247A - Insulating paste, manufacturing method of the same, and manufacturing method of solar cell element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulating paste capable of forming a protective layer having good barrier properties and adhesiveness, a manufacturing method of the same, and a manufacturing method of a solar cell element.SOLUTION: The insulating paste includes: a siloxane resin; an organic solvent; and a filler in which peak positions of a particle size distribution measured by a particle size distribution measurement method appear at a plurality of places.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an insulating paste, a method for producing the same, and a method for producing a solar cell element.

  An insulating paste is used to form a protective layer of a solar cell element (see, for example, Patent Document 1 below).

International Publication No. 2014/126117

  The protective layer of the solar cell element is desired to be dense and excellent in barrier properties and adhesion.

  Accordingly, an object of the present invention is to provide an insulating paste capable of forming a dense protective layer having good adhesion, a method for manufacturing the same, and a method for manufacturing a solar cell element.

  In order to solve the above problems, an insulating paste according to one embodiment of the present invention includes a siloxane resin, an organic solvent, and a filler in which peak positions of a particle size distribution measured by a particle size distribution measurement method appear at a plurality of locations. .

  The insulating paste manufacturing method according to one embodiment of the present invention is measured by a hydrolyzing compound having Si—O bond or Si—N bond, water, an organic solvent, and a particle size distribution measurement method. A mixing step of mixing fillers in which the peak positions of the particle size distribution appear at a plurality of locations.

  In the method for manufacturing a solar cell according to one embodiment of the present invention, after forming a passivation layer over a semiconductor substrate, the insulating paste is applied onto the passivation layer, and the insulating paste is baked. And a protective layer forming step of forming a protective layer on the passivation layer.

  According to said insulating paste, its manufacturing method, and the manufacturing method of a solar cell element, the dense protective layer excellent in adhesiveness can be formed.

FIG. 1 is a flowchart showing a method for manufacturing an insulating paste according to an embodiment of the present invention. FIG. 2 is a plan view showing the appearance of the first principal surface side of the solar cell element according to one embodiment of the present invention. FIG. 3 is a plan view showing the appearance of the second principal surface side of the solar cell element according to one embodiment of the present invention. 4 is a cross-sectional view taken along line XX in FIGS. 2 and 3. FIGS. 5A to 5F are enlarged end views showing a method for manufacturing a solar cell element according to an embodiment of the present invention. FIG. 6 is a particle size distribution diagram of the example. FIG. 7 is a particle size distribution diagram of a comparative example.

  Hereinafter, embodiments of an insulating paste, a manufacturing method thereof, and a manufacturing method of a solar cell element according to the present invention will be described in detail with reference to the drawings. The drawings are schematically shown. In FIG. 4, a part of the electrodes is omitted.

<Insulating paste>
The insulating paste of this embodiment has a siloxane resin, an organic solvent, and a filler in which the peak positions of the particle size distribution measured by the particle size distribution measuring method appear at a plurality of locations. Here, the particle size distribution measuring method refers to a measuring method obtained from the result of the particle size distribution obtained by measuring the ratio of particles having several thousand to several hundred thousand particles. Specifically, it can be obtained from the result of measurement using, for example, a laser diffraction particle size distribution measuring device or a transmission electron microscope (TEM). For example, when the range of the particle size to be measured (minimum particle size: d ₁ , maximum particle size: d _{n + 1} ) is divided into n, the average particle size is the representative particle size Di of the particle size interval and each particle size interval. Can be obtained from the equation of the sum of products with the particle size distribution ratio Yi corresponding to, that is, Σ [i = 1, n] Di · Yi.

  Further, when a particle size distribution is measured by a measurement using a laser diffraction particle size distribution measuring device, a TEM, or the like for a sample including a plurality of particles having different average particle sizes, a peak corresponding to the average particle size of each particle appears.

  In addition, the peak positions appearing at the above-mentioned plurality of locations shall not overlap within a range of particle diameters within ± 5% with reference to the particle diameter at each peak position. When a plurality of peak positions exist within the above range, it is regarded as a single peak position having the highest peak.

  A siloxane resin is a siloxane compound having a Si—O—Si bond. The siloxane resin is made of, for example, a resin obtained by hydrolyzing alkoxysilane or silazane and performing condensation polymerization. In addition to the Si—O—Si bond, the siloxane resin also has a Si—R bond, a Si—OR bond, a Si—OH bond, and the like. However, R is a methyl group or an ethyl group. Among these bonds, a strong bonding force can be expected particularly by having a Si-OR bond or a Si-OH bond. Thus, the protective layer formed using the insulating paste is a base layer (for example, silicon) substrate on which the protective layer is formed or a base layer made of an insulating layer different from the base layer, or a metal layer formed on the protective layer. High adhesion is realized. In addition, when the siloxane resin is a resin obtained by hydrolysis and condensation polymerization of a compound having an Si—N bond, the siloxane resin may have an unhydrolyzed Si—H bond, an Si—N bond, and the like.

  Moreover, it is preferable that 30-70 mass% of siloxane resin is contained in the insulating paste. If it is the said range, since the protective layer formed by apply | coating and drying insulating paste becomes dense, it can be set as a film | membrane with high barrier property. Moreover, if it is the said range, it becomes difficult to gelatinize an insulating paste and it can prevent the viscosity of an insulating paste from increasing too much.

  The organic solvent is a solvent in which a siloxane resin or a filler described later is dispersed. As the organic solvent, for example, diethylene glycol monobutyl ether, methyl cellosolve, ethyl cellosolve, ethyl alcohol or 2-propanol can be used. Of these, diethylene glycol monobutyl ether is particularly preferable because it is difficult to volatilize and the viscosity hardly changes when the insulating paste is stored and when applied for a long time.

Moreover, it is preferable that 10-50 mass% of organic solvents are contained in the insulating paste. If it is in the said range, the viscosity of an insulating paste can be adjusted to the viscosity suitable for a screen printing method etc.

  The filler of the insulating paste of this embodiment can increase the viscosity of the insulating paste by containing fillers having different average particle diameters. Thereby, the insulating paste can be applied in a desired pattern provided with openings having an opening width of, for example, several tens of μm. When only the filler with a small average particle size is used, the insulating paste can be thickened with a small filler content, but a crack is generated in the protective layer formed by applying and drying the insulating paste. It becomes easy. The reason for this is considered to be that the filler having a small average particle size is likely to aggregate, so that the filler is aggregated and an internal stress is generated in the drying process of the protective layer. Therefore, by including a filler having a large average particle size, the internal stress due to the aggregation of the filler is reduced in the drying step of the protective layer, so that the aggregation of the filler can be improved and the generation of cracks can be reduced. In addition, when the content of the filler having a large average particle size is large in the insulating paste and the base layer or metal layer in contact with the protective layer is formed, the ratio of the siloxane resin in contact with the base layer or metal layer is reduced. As a result, the adhesion of the protective layer decreases. Then, the adhesiveness of a protective layer can be improved by using a filler with a small average particle diameter. This is because by using a filler having a small average particle size, the surface area of the entire filler can be increased, and the siloxane resin present around the filler increases. That is, the ratio of the siloxane resin in contact with the base layer on which the protective layer formed using the insulating paste is disposed, or the siloxane resin in contact with the metal layer formed on the protective layer can be increased.

  Moreover, it is preferable that 5-50 mass% of the total mass of a filler is contained in the insulating paste. The filler has a structure such as a particle shape, a layer shape, a flat shape, a hollow structure shape, or a fiber shape.

  Of the plural types of fillers having different average particle diameters, the filler having the largest average particle diameter preferably has an average particle diameter that is twice or more that of the filler having the smallest average particle diameter. By being in the above range, it is possible to improve the viscosity adjustment and adhesion of the insulating paste by containing a filler having a small average particle size, and to improve the effect of reducing cracks by containing a filler having a large average particle size. it can. For example, in the average particle size of the primary particles, the filler having the maximum average particle size may be 30 to 100 nm, and the filler having the minimum average particle size may be 5 to 20 nm. The average particle diameter may be the average particle diameter of the primary particles or the average particle diameter of the secondary particles in which the primary particles are aggregated.

  Further, the plurality of types of fillers having different average particle diameters may be such that the mass ratio of the filler having the largest average particle diameter and the filler having the smallest average particle diameter is 0.4: 1 to 18: 1. More preferably, it is set to 0.5: 1 to 16: 1. By adjusting the mass ratio of the filler having the largest average particle diameter and the filler having the smallest average particle diameter in the above range, the viscosity adjustment of the insulating paste and the improvement of the adhesiveness by containing the filler having a small average particle diameter, The effect of reducing cracks by containing a filler having a large average particle diameter can be enhanced.

  The filler is preferably an inorganic filler made of silicon oxide in at least one kind of filler. The siloxane bond constituting the siloxane resin has the same structure as silicon oxide. For this reason, by using silicon oxide as the filler, the adhesion between the filler and the siloxane resin becomes good, and the occurrence of cracks in the protective layer can be reduced.

The material of the filler is not particularly limited, but it is preferable to use aluminum oxide as a material other than silicon oxide. By using the inorganic filler made of aluminum oxide, the viscosity change of the insulating paste can be reduced even if the insulating paste is stored for a long time. Moreover, by mixing and using the said inorganic filler and silicon oxide, the viscosity of an insulating paste can be improved easily and also the spread (bleeding) of an insulating paste can be reduced.

  Moreover, although it is preferable that an insulating paste does not contain an organic binder substantially, if it is less than 0.1 mass%, it is thought that it may be contained. By substantially not including an organic binder in the insulating paste, in the step of drying the insulating paste, the generation of voids due to decomposition of the organic binder or the like is reduced, and the protective layer becomes dense, so that the barrier property can be improved. .

In addition, the viscosity of the insulating paste is adjusted to 5 to 400 Pa · s at a shear rate of 1 sec ⁻¹ in order to form a protective layer by applying and drying the insulating paste in a desired pattern using a screen printing method. It is preferable. By adjusting the viscosity to the above range, bleeding of the insulating paste can be reduced, and the insulating paste can be easily applied to a shape having an opening with a width of about several tens of μm. The viscosity of the insulating paste can be measured using a viscosity-viscoelasticity measuring instrument.

  As the filler, an inorganic filler coated with a resin component may be used. By the said structure, an inorganic filler becomes easy to mix and stir in an organic solvent, and the viscosity of a paste can be stabilized.

<Insulating paste manufacturing method>
Below, the manufacturing method of the insulating paste of this embodiment is demonstrated using FIG.

  The insulating paste comprises an organic compound having a Si—O bond or a compound having a Si—N bond, water for hydrolyzing the compound, an organic solvent, and a plurality of types of fillers having different average particle sizes. Prepare by mixing.

  First, a mixing process (step S1) is performed. An organic compound having an Si—O bond or a compound having an Si—N bond (hereinafter referred to as a siloxane raw material), water, and an organic solvent are mixed in a container to prepare a mixed solution.

  The organic compound having a Si—O bond is composed of at least one silicon-containing compound. The silicon-containing compound is selected from the group consisting of siloxane resins obtained by hydrolyzing at least one alkoxysilane represented by the following general formula 1 and performing condensation polymerization.

(R1) ₄ -nSi (OR2) n ... General formula 1
R1 and R2 in the general formula 1 represent a hydrocarbon group such as a methyl group (CH ₃ ) or an ethyl group (CH ₂ CH ₃ ), and n is represented by an integer of 2 to 4. R1 and R2 may be the same or different.

  As the compound having an Si—N bond, for example, polysilazane represented by the following chemical formula 1 is used for an inorganic compound, and hexamethyldisilazane represented by the following chemical formula 2 is used for an organic compound.

H ₂ SiNH ... Chemical formula 1
_{(CH 3) 3 SiNHSi (CH} 3) 3 ··· Formula 2
Water is a solution for hydrolyzing the siloxane raw material, for example, pure water is used.

  The organic solvent uses the above-described materials. As the organic solvent, for example, diethylene glycol monobutyl ether, methyl cellosolve, ethyl cellosolve, ethyl alcohol or 2-propanol is used.

  In the mixing step, the catalyst may be mixed in order to adjust the hydrolysis and condensation polymerization reaction rates. As the catalyst, for example, an inorganic acid or an organic acid such as hydrochloric acid, nitric acid, sulfuric acid, boric acid, phosphoric acid, hydrofluoric acid, and acetic acid can be used. As the catalyst, inorganic bases or organic bases such as ammonia, sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, and pyridine can be used. Furthermore, these inorganic acids or organic acids, or inorganic bases or organic bases can be used alone or in combination of two or more.

  Moreover, the ratio of each material mixed by a mixing process is 30-70 mass% of siloxane raw materials with respect to the total mass which mixed these materials, 5-40 mass% of water, More preferably, 10-20 mass%, A catalyst is 1-1000 ppm and an organic solvent is 5-50 mass%. By setting the content within the above range, the siloxane resin obtained by hydrolysis and condensation polymerization of the siloxane raw material can be contained in the insulating paste at an appropriate mass ratio. The viscosity may not be increased too much.

  Further, in the mixing step, the siloxane raw material and water react to start hydrolysis of the siloxane raw material. Further, the hydrolyzed siloxane raw material undergoes condensation polymerization, and siloxane resin begins to be generated.

  Next, a 1st stirring process (step S2) is performed. The mixed solution prepared in the mixing step is stirred by a method such as a mix rotor or a stirrer. By stirring the mixed solution, the siloxane raw material is further hydrolyzed, and almost all of the siloxane raw material is hydrolyzed. In addition, the hydrolyzed siloxane raw material undergoes condensation polymerization, and siloxane resin continues to be generated. For example, when agitation is performed with a mix rotor, the agitation is performed under agitation conditions of a rotational speed of 400 to 600 rpm and agitation time of 30 to 90 minutes. By stirring under the above stirring conditions, the siloxane raw material, water, catalyst and organic solvent can be uniformly mixed.

  Next, a by-product removing step (step S3) is performed. In this step, a hydrolysis reaction between the siloxane raw material and water, and in this step, a by-product of an organic component such as alcohol generated by the reaction between the organic solvent and water is volatilized. By removing this by-product, when the insulating paste is stored or continuously applied, fluctuations in the viscosity of the insulating paste due to the volatilization of the organic component can be reduced. In addition, when the insulating paste is printed by the screen printing method, it is possible to reduce the fluctuation of the pattern size of the screen plate making by dissolving the emulsion of the screen plate making by the organic component. Also in the byproduct removal step, the hydrolyzed siloxane raw material undergoes condensation polymerization and siloxane resin continues to be produced.

  The by-product removing step is performed by, for example, using a hot plate or a drying furnace, a mixed solution after stirring under conditions of a processing temperature of room temperature to 90 ° C., more preferably 50 to 90 ° C., and a processing time of 10 to 600 minutes. Process. By-products can be removed when the processing temperature is within the above temperature range. Moreover, since the organic component which is a by-product is more easily volatilized within the above temperature range, the processing time can be shortened and the productivity can be improved.

  In the byproduct removal step, the remaining siloxane raw material may be hydrolyzed without being hydrolyzed in the first stirring step.

Next, a filler addition process (step S4) is performed. Plural kinds of fillers having different average particle diameters are added to the mixed solution from which the by-products have been removed. The above-mentioned material is used for the filler. For example, an inorganic filler made of silicon oxide is used. Thus, the viscosity of the mixed solution can be easily adjusted by performing the filler adding step after the first stirring step. Moreover, a filler is added so that 5-50 mass% may be contained in the insulating paste after preparation.

  Next, a 2nd stirring process (step S5) is performed. This agitation is performed on the mixed solution to which the filler has been added using, for example, a rotation / revolution mixer. For example, when stirring is performed with a rotating / revolving mixer, the rotation is performed at 800 to 1000 rpm and the stirring time is 1 to 10 minutes. By stirring under the above conditions, the filler can be uniformly dispersed in the mixed solution.

  Next, a viscosity stabilization process (step S6) is performed. By storing the mixed solution after stirring for about 2 to 24 hours at room temperature, for example, the viscosity of the mixed solution is stabilized. Further, by using silicon oxide for the filler, the filler is easily dispersed uniformly, so that the viscosity is stabilized in a short time and the productivity of the insulating paste can be improved.

  Through the above steps, an insulating paste can be manufactured.

  Moreover, although the filler addition process is performed after the first stirring process, the filler may be added simultaneously in the mixing process. Thereby, since a filler addition process and a 2nd stirring process become unnecessary, productivity improves.

  Further, the byproduct removal step may not be performed. The insulating paste produced without performing the byproduct removal step can be applied by a spray method or the like.

<Solar cell element>
A solar cell element 10 according to this embodiment is shown in FIGS. In the following, an embodiment in which the insulating paste of the present invention is applied to a PERC (Passivated Emitter Rear Cell) type solar cell element will be described.

  As shown in FIG. 4, the solar cell element 10 includes a first main surface 10a which is a light receiving surface on which light is mainly incident, and one main surface (back surface) located on the opposite side of the first main surface 10a. It has the 2nd main surface 10b and the side surface 10c. Moreover, the solar cell element 10 includes a silicon substrate 1 as a semiconductor substrate. The silicon substrate 1 also has a first main surface 1a, a second main surface 1b located on the opposite side of the first main surface 1a, and a side surface 1c. The silicon substrate 1 includes a first semiconductor layer 2 that is a one-conductivity type (for example, p-type) semiconductor region, and a reverse conductivity type (for example, n-type) semiconductor region that is provided on the first main surface 1a side in the first semiconductor layer 2. And the second semiconductor layer 3. Further, the solar cell element 10 includes a third semiconductor layer 4, an antireflection layer 5, a first electrode 6, a second electrode 7, a third electrode 8, a first passivation layer 9 and a protective layer 11.

  The silicon substrate 1 is, for example, a single crystal silicon or a polycrystalline silicon substrate. The silicon substrate 1 includes a first semiconductor layer 2 and a second semiconductor layer 3 provided on the first main surface 1a side of the first semiconductor layer 2. In addition, as long as the semiconductor substrate has the first semiconductor layer 2 and the second semiconductor layer 3 as described above, a material other than silicon may be used.

  Hereinafter, an example in which a p-type semiconductor is used as the first semiconductor layer 2 will be described. When a p-type semiconductor is used as the first semiconductor layer 2, a p-type silicon substrate is used as the silicon substrate 1. As the silicon substrate 1, a polycrystalline or single crystal substrate is used. For example, a substrate having a thickness of 250 μm or less, or a thin substrate having a thickness of 150 μm or less can be used. The shape of the silicon substrate 1 is not particularly limited, but when the solar cell module is manufactured from the solar cell element 10, the gap between the elements can be reduced as long as the shape is substantially rectangular in plan view. So convenient. When the first semiconductor layer 2 made of the polycrystalline silicon substrate 1 is p-type, an impurity such as boron or gallium is contained as a dopant element.

  The second semiconductor layer 3 is stacked on the first semiconductor layer 2. The second semiconductor layer 3 has a conductivity type opposite to that of the first semiconductor layer 2 (n-type in this embodiment), and is provided on the first main surface 1a side of the first semiconductor layer 2. . Thereby, the silicon substrate 1 has a pn junction at the interface between the first semiconductor layer 2 and the second semiconductor layer 3. The second semiconductor layer 3 can be formed, for example, by diffusing impurities such as phosphorus on the first main surface 1a side of the silicon substrate 1 as a dopant.

  As shown in FIG. 4, a fine uneven structure (texture) for reducing the reflectance of the irradiated light may be provided on the first main surface 1 a side of the silicon substrate 1. The height of the convex portions of the texture is about 0.1 to 10 μm, and the length between the apexes of the adjacent convex portions is about 0.1 to 20 μm. For example, the concave portion may have a substantially spherical shape, or the convex portion may have a pyramid shape. Note that the above-mentioned “height of the convex portion” refers to, for example, a straight line passing through the bottom surface of the concave portion in FIG. 4 as a reference line, and the top of the convex portion from the reference line in a direction perpendicular to the reference line. It is the distance to.

  The antireflection layer 5 has a function of reducing the reflectance of light irradiated on the first main surface 10 a of the solar cell element 10. The antireflection layer 5 is made of, for example, a silicon oxide, aluminum oxide, or silicon nitride layer. The refractive index and thickness of the antireflection layer 5 are appropriately selected from refractive indexes and thicknesses that can realize low reflection conditions for light in a wavelength range that can be absorbed by the silicon substrate 1 and contribute to power generation. That's fine. For example, the refractive index of the antireflection layer 5 can be about 1.8 to 2.5, and the thickness can be about 20 to 120 nm.

The third semiconductor layer 4 is disposed on the second main surface 1b side of the silicon substrate 1 and may have the same conductivity type as the first semiconductor layer 2 (p-type in the present embodiment). The concentration of the dopant contained in the third semiconductor layer 4 is higher than the concentration of the dopant contained in the first semiconductor layer 2. That is, the dopant element is present in the third semiconductor layer 4 at a concentration higher than the concentration of the dopant element that is doped to make the first semiconductor layer 2 have one conductivity type. The third semiconductor layer 4 forms an internal electric field on the second main surface 1 b side of the silicon substrate 1. Thereby, in the vicinity of the surface of the second main surface 1b of the silicon substrate 1, it has a role of making it difficult for the photoelectric conversion efficiency to decrease due to recombination of minority carriers. The third semiconductor layer 4 can be formed, for example, by diffusing a dopant element such as boron or aluminum on the second main surface 1b side of the silicon substrate 1. The concentrations of the dopant elements contained in the first semiconductor layer 2 and the third semiconductor layer 4 are about 5 × 10 ¹⁵ to 1 × 10 ¹⁷ atoms / cm ³ and about 1 × 10 ^{18 to} 5 × 10 ²¹ atoms / cm ³ , respectively. can do. The third semiconductor layer 4 is preferably present at a contact portion between a third electrode 8 and a silicon substrate 1 described later.

  The first electrode 6 is an electrode provided on the first main surface 1 a side of the silicon substrate 1. Moreover, the 1st electrode 6 has the output extraction electrode 6a and the some linear current collection electrode 6b, as shown in FIG. The output extraction electrode 6a is an electrode for extracting electricity obtained by power generation to the outside, and the length in the short direction (hereinafter referred to as width) is, for example, about 1.3 to 2.5 mm. At least a part of the output extraction electrode 6a intersects with the current collecting electrode 6b and is electrically connected. The collector electrode 6 b is an electrode for collecting electricity generated from the silicon substrate 1. Moreover, the current collection electrode 6b is a some linear form, These widths are about 50-200 micrometers, for example. Thus, the width of the current collecting electrode 6b is smaller than the width of the output extraction electrode 6a. A plurality of current collecting electrodes 6b are provided with an interval of about 1 to 3 mm. The thickness of the first electrode 6 is about 10 to 40 μm. The first electrode 6 can be formed, for example, by applying a metal paste containing silver as a main component into a desired shape by screen printing or the like and then baking it. In addition, in this embodiment, a main component means that the ratio contained with respect to the whole component is 50% or more. Note that an auxiliary electrode 6c having the same shape as the current collecting electrode 6b may be provided on the peripheral edge of the silicon substrate 1 so that the current collecting electrodes 6b are electrically connected to each other.

  As shown in FIGS. 3 and 4, the second electrode 7 and the third electrode 8 are provided on the second main surface 1 b side of the silicon substrate 1. The second electrode 7 is an electrode for taking out electricity obtained by power generation by the solar cell element 10 to the outside. The thickness of the 2nd electrode 7 is about 10-30 micrometers, and the width | variety is about 1.3-7 mm.

  The second electrode 7 contains silver as a main component. Such a second electrode 7 can be formed, for example, by applying a metal paste containing silver as a main component into a desired shape by screen printing or the like and then baking it.

  As shown in FIGS. 3 and 4, the third electrode 8 is an electrode for collecting electricity generated by the silicon substrate 1 on the second main surface 1 b side of the silicon substrate 1. It is provided so that it may connect. It is sufficient that at least a part of the second electrode 7 is connected to the third electrode 8. The thickness of the third electrode 8 is about 15 to 50 μm.

  The third electrode 8 contains aluminum as a main component. The third electrode 8 can be formed by, for example, applying a metal paste containing aluminum as a main component into a desired shape and baking it.

The first passivation layer 9 is disposed on at least the second main surface 1b of the silicon substrate 1 and has a function of reducing minority carrier recombination. As the first passivation layer 9, for example, aluminum oxide formed by an ALD (Atomic Layer Deposition) method is employed. Since aluminum oxide has a negative fixed charge, minority carriers (electrons in this case) on the second main surface 1b side of the silicon substrate 1 are converted into p-type first semiconductor layer 2 and first passivation by this electric field effect. It is kept away from the interface with the layer 9 (surface of the substrate 1). Thereby, since recombination of minority carriers on the second main surface 1b side of the silicon substrate 1 is reduced, the photoelectric conversion efficiency of the solar cell element 10 can be improved. The thickness of the first passivation layer 9 is about 10 to 200 nm.

  The protective layer 11 is disposed in a desired pattern on the first passivation layer 9 including aluminum oxide, which is disposed on the first semiconductor layer 2. The pattern when viewed in plan is provided with a plurality of openings, and the openings may be in the form of dots (dots) or in the form of bands (lines). In this case, the diameter or width of the opening may be about 10 to 500 μm. The pitch of the openings (the distance between the centers of the openings adjacent to each other in plan view) may be about 0.3 to 3 mm. A metal paste applied on the first passivation layer 9 in the opening where the protective layer 11 is not formed when a metal paste containing aluminum as a main component is applied to the protective layer 11 in a desired shape and fired. Forms a third semiconductor layer 4 by firing through the first passivation layer 9 and electrically connecting it to the silicon substrate 1 during firing. Further, in the region where the protective layer 11 is formed on the first passivation layer 9, the passivation effect is not reduced because the first passivation layer 9 is not fired through with the metal paste. The thickness of the protective layer 11 is about 0.5 to 10 μm. In addition, the thickness of the protective layer 11 is the components contained in the insulating paste and the respective contents, the size of the uneven shape of the second main surface 1b of the silicon substrate 1, the type or content of the glass frit contained in the metal paste. Depending on the firing conditions at the time of forming the third electrode 8, it is appropriately changed. The protective layer 11 is formed by applying the above-described insulating paste by a screen printing method and drying it.

  The protective layer 11 is not only on the first passivation layer 9 formed on the second main surface 1b side of the silicon substrate 1, but also on the side surface 10c of the solar cell element 10 or the periphery of the first main surface 1a. It may also be formed on the formed antireflection layer 5. The arrangement of the protective layer 11 in this case can reduce the leakage current of the solar cell element 10.

  In addition, a second passivation layer containing silicon oxide may be formed between the p-type semiconductor region (first semiconductor layer 2 in this embodiment) and the first passivation layer 9 containing an aluminum oxide layer. Thereby, the passivation performance can be improved. In particular, the thickness of the second passivation layer is preferably about 0.1 to 1 nm. Since the thickness of the second passivation layer made of silicon oxide is within the above range, even if the second passivation layer has a positive fixed charge, the passivation effect of the passivation layer 9 is obtained due to the presence of the second passivation layer. It becomes difficult to decrease.

  Further, the third electrode 8 may be formed on the second main surface 1 b of the solar cell element 10 in a shape like the current collecting electrode 6 a and connected to the second electrode 7. With such a structure, reflected light from the ground or the like incident on the back surface side of the solar cell module can also contribute to power generation and improve the output of the solar cell module.

<Method for producing solar cell element>
Next, each process of the manufacturing method of the solar cell element 10 is demonstrated in detail using FIG.

  First, a silicon substrate 1 is prepared as shown in FIG. The silicon substrate 1 is formed by, for example, an existing CZ method or a casting method. Hereinafter, an example in which a p-type polycrystalline silicon substrate is used as the silicon substrate 1 will be described.

  First, an ingot of polycrystalline silicon is produced by, for example, a casting method. Next, the silicon substrate 1 is manufactured by slicing the ingot to a thickness of, for example, 250 μm or less. Thereafter, in order to remove the mechanical damage layer and the contamination layer on the cut surface of the silicon substrate 1, the surface of the silicon substrate 1 may be etched by a very small amount with an aqueous solution such as NaOH, KOH, hydrofluoric acid or hydrofluoric acid.

  Next, as shown in FIG. 5B, a texture is formed on the first main surface 1 a of the silicon substrate 1. As a texture forming method, a wet etching method using an alkali solution such as NaOH or an acid solution such as hydrofluoric acid, or a dry etching method using an RIE (Reactive Ion Etching) method or the like can be used.

  Next, as shown in FIG. 5C, a step of forming the second semiconductor layer 3 which is an n-type semiconductor region on the first main surface 1a of the silicon substrate 1 having the texture formed by the above steps. To do. Specifically, the n-type second semiconductor layer 3 is formed on the surface layer of the textured silicon substrate 1 on the first main surface 1a side.

Such a second semiconductor layer 3 is formed by applying a coating thermal diffusion method in which paste-like P ₂ O ₅ is applied to the surface of the silicon substrate 1 to thermally diffuse, or gaseous POCl ₃ (phosphorus oxychloride) as a diffusion source. The gas phase thermal diffusion method is used. The second semiconductor layer 3 is formed to have a depth of about 0.1 to 2 μm and a sheet resistance value of about 40 to 200Ω / □. For example, in the vapor phase thermal diffusion method, the silicon substrate 1 is heat-treated for about 5 to 30 minutes at a temperature of about 600 to 800 ° C. in an atmosphere having a diffusion gas composed of POCl ₃ or the like, and the phosphor glass is formed on the surface of the silicon substrate 1 To form. Then, phosphorus is diffused from phosphorus glass to the silicon substrate 1 by heat-treating the silicon substrate 1 for about 10 to 40 minutes at a high temperature of about 800 to 900 ° C. in an inert gas atmosphere such as argon or nitrogen. A second semiconductor layer 3 is formed on the first main surface 1 a side of the silicon substrate 1.

  Next, in the step of forming the second semiconductor layer 3, when the second semiconductor layer is also formed on the second main surface 1b side, only the second semiconductor layer formed on the second main surface 1b side is used. Etch away. Thereby, the p-type conductivity type region is exposed on the second main surface 1b side. For example, the second semiconductor layer formed on the second main surface 1b side is removed by immersing only the second main surface 1b side of the silicon substrate 1 in a hydrofluoric acid solution. Thereafter, the phosphorus glass adhering to the first main surface 1a side of the silicon substrate 1 when the second semiconductor layer 3 is formed is removed by etching.

  In this way, the phosphorous glass remains on the first main surface 1a side, and the second semiconductor layer formed on the second main surface 1b side is removed by etching. Thereby, it can reduce that the 2nd semiconductor layer 3 by the side of the 1st main surface 1a is removed or damaged. At this time, the second semiconductor layer formed on the side surface 1c of the silicon substrate 1 may also be removed.

  Further, in the step of forming the second semiconductor layer 3, a diffusion mask is formed in advance on the second main surface 1b side, the second semiconductor layer 3 is formed by a vapor phase thermal diffusion method, and then the diffusion mask is formed. It may be removed. A similar structure can be formed by such a process. In that case, since the second semiconductor layer is not formed on the second main surface 1b side, the step of removing the second semiconductor layer on the second main surface 1b side becomes unnecessary.

  As described above, the polycrystalline silicon substrate 1 including the first semiconductor layer 2 in which the second semiconductor layer 3 as the n-type semiconductor layer is disposed on the first main surface 1a side and the texture is formed on the surface is prepared. it can.

  Next, as shown in FIG. 5 (d), a first passivation layer made of aluminum oxide is formed on the first main surface 1 a of the first semiconductor layer 2 and the second main surface 1 b of the second semiconductor layer 3. 9 is formed. Further, an antireflection layer 5 made of a silicon nitride film is formed on the first passivation layer 9.

  As a method for forming the first passivation layer 9, for example, an ALD method is used. Thus, the first passivation layer 9 can be formed around the entire periphery including the side surface 1c of the silicon substrate 1. In the formation of the first passivation layer 9 by the ALD method, first, the silicon substrate 1 on which the second semiconductor layer 3 is formed is placed in the chamber of the film forming apparatus. Then, in a state where the silicon substrate 1 is heated to a temperature range of 100 to 250 ° C., the following steps A to D are repeated a plurality of times to form the first passivation layer 9 made of aluminum oxide. Thereby, the first passivation layer 9 having a desired thickness is formed.

  Even when a second passivation layer containing silicon oxide is formed by the ALD method between the first semiconductor layer 2 and the first passivation layer 9 containing an aluminum oxide layer, silicon is kept in the same temperature range as above. While the substrate 1 is heated, the following steps A to D are repeated a plurality of times to form a second passivation layer made of silicon oxide.

  The contents of steps A to D are as follows.

  [Step A] A silicon raw material such as bisdiethylaminosilane (BDEAS) for forming a silicon oxide layer or an aluminum raw material such as trimethylaluminum (TMA) for forming aluminum oxide is a carrier such as Ar gas or nitrogen gas. Together with the gas, it is supplied onto the silicon substrate 1. Thereby, the silicon raw material or the aluminum raw material is adsorbed on the entire periphery of the silicon substrate 1. The time for supplying BDEAS or TMA may be, for example, about 15 to 3000 milliseconds.

  At the start of step A, the surface of the silicon substrate 1 is preferably terminated with an OH group. That is, it is preferable that the surface of the silicon substrate 1 has a Si—O—H structure. This structure can be formed, for example, by treating the silicon substrate 1 with dilute hydrofluoric acid and then washing with pure water.

  [Step B] By purifying the inside of the chamber of the film forming apparatus with nitrogen gas, the silicon material or aluminum material in the chamber is removed. Further, silicon raw materials or aluminum raw materials other than components chemically adsorbed at the atomic layer level are removed from the silicon raw materials or aluminum raw materials physically adsorbed and chemically adsorbed on the silicon substrate 1. The time for purifying the inside of the chamber with nitrogen gas may be about 1 to several tens of seconds, for example.

  [Step C] By supplying an oxidizing agent such as water or ozone gas into the chamber of the film forming apparatus, the alkyl group contained in BDEAS or TMA is removed and replaced with an OH group. Thereby, an atomic layer of silicon oxide or aluminum oxide is formed on the silicon substrate 1. The time for supplying the oxidizing agent into the chamber is preferably about 750 to 1100 milliseconds. Further, for example, by supplying H together with the oxidizing agent into the chamber, hydrogen atoms are more easily contained in silicon oxide or aluminum oxide.

  [Step D] By purifying the inside of the chamber of the film forming apparatus with nitrogen gas, the oxidizing agent in the chamber is removed. At this time, for example, an oxidant that has not contributed to the reaction during the formation of silicon oxide or aluminum oxide at the atomic layer level on the silicon substrate 1 is removed. In addition, the time for purifying the inside of the chamber with nitrogen gas may be about 1 to several tens of seconds, for example.

  Thereafter, a series of steps A to D are repeated a plurality of times, thereby forming a silicon oxide layer or an aluminum oxide layer having a desired film thickness.

The antireflection layer 5 is formed by using, for example, PECVD method or sputtering method. If the PECVD method is used, the silicon substrate 1 is heated in advance at a temperature higher than the temperature during film formation. Thereafter, a mixed gas of silane (SiH ₄ ) and ammonia (NH ₃ ) is diluted with nitrogen (N ₂ ) on the heated silicon substrate 1, and the reaction pressure is set to 50 to 200 Pa to be plasmatized by glow discharge decomposition and deposited. Thus, the antireflection layer 5 is formed. The film formation temperature at this time is set to about 350 to 650 ° C., and the preheating temperature is set to about 50 ° C. higher than the film formation temperature. Further, a frequency of 10 to 500 kHz is used as the frequency of the high frequency power source necessary for glow discharge.

  The gas flow rate is appropriately determined depending on the size of the reaction chamber and the like. For example, the gas flow rate is preferably in the range of 150 to 6000 ml / min (sccm), and the silane flow rate A and ammonia flow rate B. The flow rate ratio B / A may be 0.5-15.

  Next, as shown in FIG. 5 (e), a protective layer 11 is formed on at least a part of the first passivation layer 9. The protective layer 11 is formed in a desired pattern by applying the insulating paste of the present invention to at least a part of the first passivation layer 9 using, for example, a screen printing method or the like. After the application, the protective paste 11 is dried on the first passivation layer 9 by drying the insulating paste using a hot plate or a drying furnace at a maximum temperature of 150 to 350 ° C. and a heating time of 1 to 10 minutes. To form a desired pattern. When the protective layer 11 is formed under the above-described formation conditions, the through-through is not performed when the third electrode described later is formed, and the passivation effect is hardly reduced. In addition, the adhesion between the protective layer 11 and the first passivation layer 9 and the third electrode 8 is difficult to be reduced.

  The protective layer 11 is preferably formed at a position other than the position where the third electrode 8 contacts on the second main surface 1b side of the silicon substrate 1. By forming the protective layer 11 in a desired pattern having a plurality of openings on the first passivation layer 9, a step of removing the protective layer 11 by laser beam irradiation or the like becomes unnecessary, and productivity can be improved. it can.

  The application amount of the insulating paste is the size of the uneven shape of the second main surface 1b of the silicon substrate 1, the type or content of glass frit contained in the metal paste mainly composed of aluminum described later, and third. It changes suitably according to the baking conditions at the time of electrode 8 formation.

  Next, as shown in FIG. 5F, the first electrode 6, the second electrode 7, and the third electrode 8 are formed as follows.

  The first electrode 6 is manufactured using, for example, a metal paste containing silver as a main component, an organic vehicle, and a glass frit (first metal paste). First, this first metal paste is applied to the first main surface 1 a of the silicon substrate 1. Then, the 1st electrode 6 is formed by baking a 1st metal paste on the conditions whose maximum temperature is 600-850 degreeC and heating time is about several dozen seconds-several tens of minutes in a baking furnace. As the coating method, a screen printing method or the like can be used. And after application | coating, you may evaporate a solvent at predetermined temperature and dry it. The first electrode 6 includes the output extraction electrode 6a and the current collection electrode 6b, but the output extraction electrode 6a and the current collection electrode 6b can be formed in one step by using screen printing.

  The second electrode 7 is manufactured using a metal paste (second metal paste) containing metal powder containing silver as a main component, an organic vehicle, glass frit, and the like. As a method for applying the second metal paste to the silicon substrate 1, for example, a screen printing method or the like can be used. After this application, the solvent may be evaporated and dried at a predetermined temperature. Thereafter, the second electrode 7 is made of the silicon substrate 1 by firing the second metal paste in a firing furnace under conditions where the maximum temperature is 600 to 850 ° C. and the heating time is about several tens of seconds to several tens of minutes. It is formed on the second main surface 1b side.

  The third electrode 8 is manufactured using a metal paste (third metal paste) containing a metal powder containing aluminum as a main component, an organic vehicle, and glass frit. This third metal paste is applied onto the second main surface 1b of the silicon substrate 1 so as to be in contact with a part of the second metal paste previously applied. At this time, you may apply | coat to the substantially whole surface of the 2nd main surface 1b except for a part of site | part in which the 2nd electrode 7 is formed. As the coating method, a screen printing method or the like can be used. After this application, the solvent may be evaporated and dried at a predetermined temperature. By firing the third metal paste in a firing furnace under the conditions that the maximum temperature is 600 to 850 ° C. and the heating time is about several tens of seconds to several tens of minutes, the third electrode 8 becomes the second electrode of the silicon substrate 1. It is formed on the main surface 1b side. By this firing, the third metal paste fires through the first passivation layer 9 and is connected to the first semiconductor layer 2 to form the third electrode 8. Along with the formation of the third electrode 8, the third semiconductor layer 4 is also formed. However, since the third metal paste on the protective layer 11 is blocked by the protective layer 11, there is almost no adverse effect due to the firing temperature on the first passivation layer 9 when the third metal paste is fired.

  Through the above steps, the solar cell element 10 can be manufactured.

  Note that the second electrode 7 may be formed after the third electrode 8 is formed. Further, the second electrode 7 does not need to be in direct contact with the silicon substrate 1, and the passivation layer 9 does not have to exist between the second electrode 7 and the silicon substrate 1, and the second electrode 7 is directly in contact with the silicon substrate 1. You may touch. The second electrode 7 may be provided on the protective layer 11.

  Further, the first electrode 6, the second electrode 7 and the third electrode 8 may be formed by applying each metal paste and then firing at the same time. Thereby, productivity can be improved, the thermal history of the silicon substrate 1 can be reduced, and the output characteristics of the solar cell element 10 can be improved.

<Insulating paste>
Below, the manufacturing method of the insulating paste of Examples 1-6 is demonstrated.

  First, in the mixing step, 55% by mass of methyltrimethoxysilane as an organic compound having an Si—O bond, 25% by mass of water, 20% by mass of diethylene glycol monobutyl ether as an organic solvent, and 50 ppm of hydrochloric acid as a catalyst are mixed. Thus, a mixed solution was prepared.

  Next, in the first stirring step, the mixed solution was stirred using a mix rotor under the conditions of a rotation speed of 550 rpm and a stirring time of 45 minutes.

  Next, in the by-product removing step, methyl alcohol as an organic component, which is a by-product generated by hydrolysis of methyltrimethoxysilane, was volatilized using a drying furnace at a processing temperature of 85 ° C. and a processing time of 180 minutes. .

  Next, in the filler addition step, the insulating pastes of Examples 1 to 8 have an average particle diameter of 20 nm as a filler in which the peak positions of the particle size distribution measured by the particle size distribution measurement method appear in a plurality of locations in the mixed solution. A filler made of silicon oxide, a filler made of silicon oxide having an average particle diameter of 40 nm, and a filler made of aluminum oxide having an average particle diameter of 20 nm were added so as to have a filler content shown in Table 1. In addition, content of the filler shown in Table 1 is content of each filler with respect to the insulating paste after preparation, It added so that the total mass of the filler in an insulating paste might be 25 mass% in total. In addition, the average particle diameter of said filler is an average particle diameter obtained from the peak position of the particle size distribution by the particle size distribution measurement which measured about 50,000 particles by image processing using TEM.

  Next, in the second stirring step, the mixed solution was stirred using a rotation / revolution mixer under the conditions of a rotation speed of 850 rpm and a stirring time of 8 minutes.

  Next, in the viscosity stabilization step, the mixed solution was stored at room temperature for a certain time. The insulating pastes of Examples 1 to 5 were stored at room temperature for 6 hours. Moreover, the insulating paste of Example 6 was stored at room temperature for 10 hours.

  Insulating paste in which siloxane resin hydrolyzed and condensation-polymerized by the above steps is 50% by mass, butyl carbitol is 25% by mass, and the total of plural kinds of fillers having different average particle diameters is 25% by mass. Was made.

  The insulating pastes of Examples 1 to 5 are made of silicon oxide having a particle size distribution peak position (average particle size) of 20 nm measured by a particle size distribution measurement method using TEM, as shown in FIG. It was confirmed that it contained a filler and a filler made of silicon oxide having a peak position (average particle diameter) of 40 nm.

  Moreover, the mass ratio of the filler of the insulating paste in Examples 1-5 is 1: 0.4 in Example 1, 1: 0.5 in Example 2, 1: 4 in Example 3, and Example 4 1:16, Example 5 was 1:18. Here, the mass ratio was determined using a dielectrophoretic grating (IG) method. However, the calculation was performed based on the range of the particle size of plus or minus 10% of the minimum average particle size obtained by the particle size distribution measurement method. That is, for example, if the minimum average particle size is 20 nm, the mass is estimated using a particle size in the range of 18 to 22 nm, and if the average particle size is 40 nm, the particle size is 38 to 42 nm. The mass was estimated and used. The mass ratios of other examples and comparative examples were measured in the same manner.

  Insulating paste of Example 6 is a filler made of aluminum oxide having a peak position of 20 nm which appears by performing particle size distribution measurement using TEM in addition to silicon oxide at the same peak position as in Examples 1 to 5. It was confirmed that the material further contained. In Example 6, the mass ratio of the filler made of silicon oxide and aluminum oxide having an average particle diameter of 20 nm to the filler made of silicon oxide having an average particle diameter of 40 nm was 1:16.

  Moreover, the insulating paste of Example 7 contains a filler made of 20 nm silicon oxide and a filler made of aluminum oxide having a peak of 40 nm, which appears when particle size distribution measurement using TEM is performed. there were. In Example 7, the mass ratio of the filler made of silicon oxide having an average particle diameter of 20 nm and the filler made of aluminum oxide having an average particle diameter of 40 nm was 1:16.

  It was confirmed that the insulating paste of Example 8 contained a filler composed of 20 nm aluminum oxide and a filler composed of 40 nm aluminum oxide at a peak position appearing by performing particle size distribution measurement using TEM. In Example 8, the mass ratio of the filler content made of aluminum oxide having an average particle size of 20 nm and the filler made of aluminum oxide having an average particle size of 40 nm was 1:16.

  In Comparative Examples 1 to 7, an insulating paste having a filler content of 25% by mass was produced using the same steps as in Examples 1 to 8 except for the filler addition step. As shown in FIG. 7, the particle size distribution measurement using TEM confirmed that the insulating paste of the comparative example 1 contained only the filler which consists of a silicon oxide with an average particle diameter of 20 nm. Further, it was confirmed by performing particle size distribution measurement using TEM that the insulating paste of Comparative Example 2 contains only a filler made of silicon oxide having an average particle size of 40 nm.

  The insulating paste of Comparative Example 3 is composed of a filler made of silicon oxide having a peak position (average particle diameter) of 20 nm and a peak position (average particle diameter) of 20 nm measured by the particle size distribution measuring method. It was confirmed that it contains a filler. In Comparative Example 3, the mass ratio of the filler made of silicon oxide having an average particle diameter of 20 nm and the filler made of aluminum oxide having an average particle diameter of 20 nm was 1: 1.

  The insulating paste of Comparative Example 4 is composed of a filler made of silicon oxide having a peak position (average particle diameter) of 40 nm and a peak position (average particle diameter) of 40 nm measured by a particle size distribution measuring method. It was confirmed that it contains a filler. In Comparative Example 4, the mass ratio of the filler made of silicon oxide having an average particle diameter of 40 nm and the filler made of aluminum oxide having an average particle diameter of 40 nm was 1: 1.

It was confirmed that Comparative Example 5 was an insulating paste containing 2% by mass of an organic binder that was isobornylcyclohexanol with respect to Example 3. Confirmation of organic binder is differential heat
This was carried out with a simultaneous thermogravimetric analyzer (Simultaneous Thermogravimetry-Differential Thermal Analysis Apparatus).

  Comparative Example 6 was confirmed to be an insulating paste containing 2% by mass of an organic binder with respect to Example 6.

  Comparative Example 7 was confirmed to be an insulating paste containing 0.1% by mass of an organic binder with respect to Example 6.

<Solar cell element>
First, as the silicon substrate 1 having the p-type first semiconductor layer 2, a polycrystalline silicon substrate having a square side of about 156 mm and a thickness of about 200 μm in plan view was prepared. The silicon substrate 1 was etched with an aqueous NaOH solution to remove the damaged layer on the surface. Thereafter, the silicon substrate 1 was cleaned. And the texture was formed in the 1st main surface 1a side of the silicon substrate 1 using RIE method.

Next, phosphorus was diffused into the silicon substrate 1 by vapor phase thermal diffusion using phosphorus oxychloride (POCl ₃ ) as a diffusion source. Thus, the n-type second semiconductor region 3 having a sheet resistance of about 90Ω / □ was formed. Although the second semiconductor layer 3 was also formed on the side surface 1c and the first main surface 1a side of the silicon substrate 1, the second semiconductor layer 3 was removed with a hydrofluoric acid solution. Thereafter, the phosphorus glass remaining on the silicon substrate 1 was removed with a hydrofluoric acid solution.

  Next, an aluminum oxide layer was formed as a first passivation layer 9 on the entire surface of the silicon substrate 1 using the ALD method.

  The ALD method was performed under the following conditions. The silicon substrate 1 was placed in the chamber of the film forming apparatus, and the surface temperature of the silicon substrate 1 was maintained at about 200 ° C. Then, TMA was used as an aluminum raw material, and a first passivation layer 9 made of aluminum oxide having a thickness of about 30 nm was formed.

  Thereafter, an antireflection layer 5 made of a silicon nitride film was formed on the first passivation layer 9 on the first main surface 1a side by PECVD.

  Next, the insulating pastes of Examples 1 to 6 and Comparative Examples 1 to 3 are applied to a pattern having a plurality of openings on the first passivation layer 9 formed on the second main surface 1b by screen printing. Thus, a protective layer 11 having a thickness of 10 μm was formed. Drying after the application of the insulating paste was performed in a drying furnace at a drying temperature of 300 ° C. and a drying time of 10 minutes.

  Then, a silver paste was applied to the pattern of the first electrode 6 on the first main surface 1a side, and a silver paste was applied to the pattern of the second electrode 7 on the second main surface 1b side. In addition, an aluminum paste was applied to the pattern of the third electrode 8 on the second main surface 1b side. And the 3rd semiconductor region 4, the 1st electrode 6, the 2nd electrode 7, and the 3rd electrode 8 were formed by baking these conductive pastes, and the solar cell element 10 was produced.

  In each of Examples and Comparative Examples, the barrier property and adhesiveness, which are indicators of printability and denseness, were evaluated as follows.

  Printability: Insulating paste was applied using a screen plate having a slit pattern with an opening width of 80 μm at a location where a rectangular opening was formed in plan view. At this time, the case where the average opening width of the openings of the protective layer 11 was 35 μm or more was judged good, and the case where the average opening width of the openings was less than 35 μm was determined as NG.

Barrier property: The protective layer 11 formed by applying and drying an insulating paste was observed with an optical microscope. At this time, the case where the occurrence of cracks was not confirmed was judged good, and the case where the occurrence of cracks was confirmed was judged as NG. Further, although the generation of cracks was not confirmed, the third electrode 8 was removed in the region where the protective layer 11 was formed, and the effective lifetime of minority carriers was measured. At this time, when the same decrease as that in the contact portion with the third electrode 8 was observed, it was similarly determined as NG.

  Adhesiveness: A 3.27 N / cm tape was attached to the third electrode 8 and a tensile test was performed. At this time, the case where peeling of the 3rd electrode 8 was not seen was made favorable, and the case where peeling of the 3rd electrode 8 was seen was determined as NG. Further, the case where the protective layer 11 peeled off at the interface with the first passivation layer 9 was also determined as NG.

  100 solar cell elements 10 each having the protective layer 11 formed using the insulating pastes of Examples 1 to 8 and Comparative Examples 1 to 7 were produced. And evaluation was performed about said printability, barrier property, and adhesiveness, respectively. An NG ratio of less than 2% was evaluated as ◯, an NG ratio of 2% or more and less than 10% as Δ, and an NG ratio of 10% or more as x. The results are shown in Table 1.

  As can be seen from Table 1, in Example 1, the barrier property was evaluated as Δ. This is presumably because the mass ratio of the filler made of silicon oxide having a small average particle diameter of 20 nm is excessively increased. Moreover, it is thought that in the drying process for forming the protective layer 11, internal stress was generated due to aggregation of fillers having a small average particle diameter.

  In Example 5, the printability determination was Δ. This is thought to be because the mass ratio of the filler made of silicon oxide having a large average particle diameter of 40 nm is excessively increased. Further, the judgment of adhesion was Δ. This is considered to be because the adhesiveness between the protective layer 11 and the first passivation layer 9 and the third electrode 8 is lowered due to the decrease in the ratio of the siloxane resin in contact with the first passivation layer 9 and the third electrode 8. .

  In Examples 2 to 4, the bleeding in the coating process or the drying process of the insulating paste and the occurrence of cracks in the protective layer 11 were reduced. Thereby, the adhesiveness of the protective layer 11 and the 1st passivation layer 9 or the 3rd electrode 8 improved, and was (circle) determination in any evaluation.

In the solar cell element 10 in which the protective layer 11 is formed using the insulating pastes of Examples 6 to 8,
Compared with the case where the protective layer 11 was formed using the insulating paste of Example 4, the paste viscosity was slightly improved. For this reason, printability improved compared with the case where only the filler which has a silicon oxide as a main component is contained. Moreover, compared with Comparative Examples 1-4, Example 1 and Example 5 reduced the generation | occurrence | production of the bleeding in the application | coating process and drying process of an insulating paste, and the crack of the protective layer 11. FIG. Thereby, the adhesiveness of the protective layer 11 and the 1st passivation layer 9 or the 3rd electrode 8 improved. Examples 6 to 8 were judged as “good” in any evaluation.

  In Comparative Example 1, the barrier property was evaluated as x. This is probably because the filler having a small average particle diameter was cracked due to the aggregation of the filler and the generation of internal stress in the protective layer 11 in the drying process of the protective layer 11.

  In Comparative Example 2, the printability determination was x. This is considered to be because the effect of thickening the insulating paste was reduced by not including a filler having a small average particle size. Moreover, determination of adhesiveness was x. This is because, at the interface between the first passivation layer 9 and the third electrode 8, the Si—OH bond or the Si—OR bond, which is thought to contribute to adhesion, is reduced, so that the protective layer 11 and the first passivation layer 9 and This is probably because the adhesion with the third electrode 8 was lowered.

  In the solar cell element 10 in which the protective layer 11 was formed using the insulating pastes of Comparative Examples 3 and 4, the filler was made of aluminum oxide which is a different material, but the average particle diameter was the same, Results similar to those of Comparative Examples 1 and 2 were obtained.

  In Comparative Examples 5 to 7, the determination of the barrier property due to the occurrence of cracks was good. However, when the third electrode 8 is removed and the effective lifetime of minority carriers is measured by the microwave photoconductive decay method (μ-PCD), the effective lifetime is similar to the region in contact with the third electrode 8. The barrier property was evaluated as x. Moreover, determination of adhesiveness was x. This is because when the organic binder is contained, voids that appear to be due to decomposition of the organic binder are generated in the protective layer 11 in the drying step of forming the protective layer 11, and the protective layer is formed in the firing step of the third electrode 8. This is probably because 11 was fire-through. Moreover, since the density of the protective layer 11 decreased due to the voids in the protective layer 11, it is considered that the third electrode 8 was peeled from the protective layer 11 in the tensile test.

1: Silicon substrate 1a: 1st main surface 1b: 2nd main surface 2: 1st semiconductor layer 3: 2nd semiconductor layer 4: 3rd semiconductor layer 5: Antireflection layer 6: 1st electrode 6a: Output extraction electrode 6b : Current collecting electrode 6c: Auxiliary electrode 7: Second electrode 8: Third electrode 9: First passivation layer 10: Solar cell element 11: Protective layer

Claims (6)

A siloxane resin;
An organic solvent,
An insulating paste comprising a filler in which peak positions of a particle size distribution measured by a particle size distribution measuring method appear at a plurality of locations.   The mass ratio A: B between the mass A of the filler having the largest average particle size determined by the peak position of the particle size distribution and the mass B of the filler having the smallest average particle size is 0.5: 1 to 16: The insulating paste according to claim 1, which is within a range of 1.   The insulating paste according to claim 1, wherein the organic binder is substantially not contained.   The manufacturing method of an insulating paste including the mixing process which mixes the compound which has a Si-O bond or a Si-N bond, hydrolyzes, water, an organic solvent, and several fillers from which an average particle diameter differs.   The manufacturing method of the insulating paste of Claim 4 which has a volatilization process which volatilizes the organic component produced | generated by the hydrolysis reaction after the said mixing process.   After forming a passivation layer on a semiconductor substrate, the insulating paste according to any one of claims 1 to 3 is applied on the passivation layer, and the insulating paste is baked to form a top surface of the passivation layer. The manufacturing method of a solar cell which has a protective layer formation process which forms a protective layer in a.

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