JP6971769B2 - Solar cell element - Google Patents

Description

The present disclosure relates to a solar cell element (solar cell).

The solar cell element includes a PERC (Passivated Emitter and Rear Cell) type solar cell element (see, for example, the description of Patent Document 1 below). In this solar cell element, the passivation layer is located on the semiconductor substrate.

When manufacturing this PERC type solar cell element, a back electrode can be formed by applying a conductive paste on a passivation layer and firing it. During this firing, the passivation layer may be provided with a region that is not fired through by the conductive paste. Therefore, a protective layer such as silicon oxide, silicon nitride, or silicon oxynitride may be formed on the passivation layer by dry or wet treatment, and a back surface electrode may be formed on the protective layer. Here, as the dry process, for example, a CVD (Chemical Vapor Deposition) method or the like can be considered. As the wet treatment, for example, treatment by applying an insulating paste and drying can be considered (see, for example, the description of Patent Document 2 below).

Japanese Unexamined Patent Publication No. 2014-39018 International Publication No. 2014/126117

There is room for improvement in the PERC type solar cell element in that the passivation layer is less likely to deteriorate.

The solar cell element is disclosed.

One aspect of the solar cell element includes a semiconductor substrate, a passivation layer, a protective layer, and an electrode. The passivation layer is located on the semiconductor substrate. The protective layer is located above the passivation layer and contains a siloxane resin and chlorine in the form of hydrochloric acid or chloride. The electrode is located on the protective layer.

FIG. 1 is a flowchart showing an example of a method for producing an insulating paste according to an embodiment. FIG. 2 is a plan view showing an example of the appearance of the solar cell element according to the embodiment on the surface side of the first element. FIG. 3 is a plan view showing an example of the appearance of the solar cell element according to the embodiment on the surface side of the second element. FIG. 4 is an end view showing a cut surface of the solar cell element along the lines IV-IV of FIGS. 2 and 3. 5 (a) to 5 (e) are end views illustrating a state in which the solar cell element according to the embodiment is being manufactured. FIG. 5 (f) is an end view showing an example of a cut surface of the solar cell element according to the embodiment.

In the PERC type solar cell element, a passivation layer, a protective layer, and a back surface electrode are laminated on the back surface of the semiconductor substrate in the order described.

Then, when the conductive paste is applied to form the back surface electrode and then fired, the conductive paste may cause fire-through of the protective layer and the passivation layer depending on the state of the protective layer. Further, if the density of the protective layer is low, the moisture permeability of the protective layer is high. At this time, the passivation layer tends to deteriorate, and the characteristics of the solar cell element tend to deteriorate.

Therefore, the inventors of the present application have created a technique in which the passivation layer is less likely to deteriorate. Hereinafter, an embodiment will be described with reference to the drawings.

In the drawings, parts having the same structure and function are designated by the same reference numerals, and duplicate description is omitted in the following description. The drawings are schematically shown. A right-handed XYZ coordinate system is attached to FIGS. 2 to 5 (f). In this XYZ coordinate system, for example, the longitudinal direction of the output take-out electrode 6a located on the first element surface 10a side, which is the light receiving surface of the solar cell element 10 described later, is the + Y direction, and the output take-out electrode 6a is short. The hand direction is the + X direction, and the normal direction of the first element surface 10a is the + Z direction.

<1. Embodiment>
<1-1. Insulating paste>
The insulating paste of one embodiment contains chlorine. Further, the insulating paste has at least a siloxane resin, an organic solvent, and a filler.

The siloxane resin is a siloxane compound having a Si—O—Si bond (also referred to as a siloxane bond). The siloxane resin is, for example, a resin having a low molecular weight (for example, 15,000 or less in terms of molecular weight) obtained by hydrolyzing and conducting condensation polymerization of alkoxysilane, silazane, or the like. The siloxane resin may have at least one of Si—R bond, Si—OR bond and Si—OH bond in addition to the siloxane bond. "R" is one type of alkyl group _{(-C m H 2m + 1)} and a phenyl group such as a methyl group (-CH ₃₎ and ethyl group _{(-C 2 H 5) (-C} 6 H 5) in the binding It is selected from the above. Here, m is a natural number. Further, since the siloxane resin has a molecular weight of 15,000 or less, the siloxane resin and the silicone oil having a molecular weight of 50,000 or more can be clearly distinguished. The siloxane resin is also different from silicone oil in that it has a bonded state of oxygen and an alkyl group and a bonded state of oxygen and a phenyl group or the like.

Here, if the siloxane resin has at least one of a Si—OR bond and a Si—OH bond, the reactivity of the siloxane resin is high. In this case, a strong bonding force can be expected between the protective layer formed by using the insulating paste and the other portion of the solar cell element that is in contact with the protective layer. For example, when the siloxane resin has a Si—OH bond, a hydrogen atom is removed from the OH group, and the siloxane resin easily bonds with silicon, aluminum, or the like. Alternatively, the OH groups on the surface of silicon, aluminum, etc. react with the Si-OH bond of the siloxane resin to release water molecules, and the siloxane resin easily bonds with silicon, aluminum, or the like. Further, for example, when the siloxane resin has a Si-OR bond, if water and a catalyst used or generated in the manufacturing process of the insulating paste described later remain in the protective layer, these water and the catalyst are present. The Si-OR bond is hydrolyzed by a catalyst or the like, and an OH group is likely to be generated. Therefore, the siloxane resin tends to bond with silicon, aluminum, or the like, as in the case of having the Si—OH bond described above. As described above, if the binding force of the siloxane resin is increased, the adhesiveness between the protective layer formed by using the insulating paste and other portions (also referred to as adjacent portions) adjacent to the protective layer is improved. .. Other portions adjacent to the protective layer include, for example, a substrate under which the protective layer is formed (for example, a silicon substrate), a substrate such as another different insulating layer, and a metal layer formed on the protective layer. Can be considered.

For example, if three or four Si—O bonds are present for one Si atom constituting the siloxane resin, the adhesion between the protective layer and the adjacent portion is improved. Therefore, when producing an insulating paste, for example, a material in which three or four Si-OR bonds are present for one Si atom is used as a precursor of a siloxane resin. As a result, in the siloxane resin obtained by hydrolyzing the precursor of the siloxane resin and performing condensation polymerization, the number of bonds of at least one of the Si-OR bond and the Si-OH bond is increased, and the protective layer and the adjacent portion are formed. A strong bond between them is achieved. That is, high adhesion between the protective layer and the adjacent portion is realized. Further, when the siloxane resin is a resin obtained by condensation polymerization of a precursor of a siloxane resin having a Si—N bond to be hydrolyzed, an unhydrolyzed Si—H bond, a Si—N bond, or the like can be obtained. May have.

When the alkyl group contains a methyl group, the by-product produced by hydrolysis (for example, methyl alcohol) is likely to volatilize, and the by-product is unlikely to remain in the insulating paste. Therefore, when the insulating paste is printed by the screen printing method, the screen plate-making emulsion is less likely to be dissolved by the by-products, so that the screen plate-making pattern dimensions are less likely to fluctuate.

The concentration of the siloxane resin is, for example, 7% by mass to 92% by mass in the insulating paste (100% by mass). When the ratio of the siloxane resin occupying the insulating paste is within the above range, the protective layer formed by applying and drying the insulating paste becomes dense and can be a film having a high barrier property. Further, when the concentration of the siloxane resin in the insulating paste is within the above range, the insulating paste is less likely to gel and the viscosity of the insulating paste does not increase too much. Here, for example, if the insulating paste (100% by mass) contains 40% by mass to 90% by mass of a siloxane resin, the denseness of the protective layer and the difficulty of gelling the insulating paste can be easily realized. can do.

In addition, the insulating paste may further contain, for example, a non-condensation polylytic additive having a Si—O bond or a Si—N bond. Such an additive is represented by, for example, the following general formula 1.

(R1) _4-ab Si (OH) _a (OR2) _b ... General formula 1

R1 and R2 in the general formula 1 represent an alkyl group such as a methyl group or an ethyl group. Further, a in the general formula 1 is an integer of any of 1 to 4. b is an integer from 0 to 4. a + b is an integer of 1 to 4, for example, 3 or 4. R1 and R2 may be the same alkyl group or different alkyl groups.

Here, when the insulating paste contains a hydrolyzable additive which has a Si—O bond or a Si—N bond and is not condensation polymerized, it is compared with the case where the additive is not contained. As a result, the ratio of Si-OR bond or Si-OH bond in the siloxane resin increases. If the ratio of Si-OR bond or Si-OH bond in the siloxane resin is increased, high adhesion between the protective layer and the adjacent portion of the holding layer is likely to be realized. In addition, the insulating paste tends to gradually undergo condensation polymerization even during storage to thicken and gel. However, in the insulating paste according to one embodiment, by containing the above-mentioned additive, a condensation polymerization reaction can be exhibited between the hydrolyzed additive and the condensation-polymerized siloxane resin having a large molecular weight. Therefore, the condensation polymerization reaction between the siloxane resins having a large molecular weight is inhibited, the insulating paste is less likely to gel, and the viscosity of the insulating paste does not increase too much.

The filler has a surface covered with an organic coating containing a material different from the siloxane resin. This can reduce the number of unbonded hands on the surface of the filler. At this time, for example, since the surface of the filler is less likely to be charged, the fillers are less likely to repel each other. Further, at this time, it becomes difficult for the siloxane resin and the filler to bond with each other. As a result, the fillers can be appropriately aggregated while maintaining a certain distance from each other. As a result, the filler is less likely to be homoscedastic, and the insulating paste can be appropriately thickened. Further, since OH groups are less likely to be formed on the surface of the filler, the reaction between the OH groups on the surface of the filler and the OH groups of the siloxane resin is reduced, and the filler and the siloxane resin component are less likely to be bonded. This makes it difficult for the insulating paste to gel and prevents the viscosity of the insulating paste from increasing too much. Therefore, for example, the coatability and viscosity stability of the insulating paste can be improved. This can improve the function of protecting the passivation layer by the protective layer formed by using the insulating paste. Further, even when the insulating paste is stored or used for a long time, the insulating paste can be stably applied to a desired pattern. As a result, the deterioration of the quality of the passivation layer in the solar cell element with time is reduced, and the quality of the passivation layer can be improved.

Here, the material contained in the organic film covering the surface of the filler has a structure in which the number of carbon atoms in the main chain is 6 or more, or the number of carbon atoms and the number of silicon atoms in the main chain. If the structure has a total number of 6 or more, the hydrophobicity of the protective layer is improved by the components of the organic film. Specific materials for the organic coating covering the surface of the filler include, for example, an alkyl group having 6 or more carbon atoms in the main chain, or the number of carbon atoms and the number of silicon atoms in the main chain. Examples thereof include octylsilane having a total number of 6 or more. An alkyl group having 6 or more carbon atoms in the main chain, an octylsilane, or the like is less likely to generate polarity even when reacted with an OH group, and the hydrophobicity in the protective layer is likely to be maintained. Further, as a specific material of the organic film covering the surface of the filler, dimethylpolysiloxane having a total number of 6 or more carbon atoms and silicon atoms in the main chain may be adopted. Didimethylpolysiloxane has, for example, a hydrophobic structure because the main chain has a spiral structure and a methyl group is located on the surface of the dimethylpolysiloxane. As described above, if the protective layer has hydrophobicity, the film quality of the protective layer is unlikely to change due to moisture or the like, and the insulating property of the protective layer is maintained. Therefore, the function of protecting the passivation layer by the protective layer formed by using the insulating paste can be improved. As a result, the deterioration of the passivation layer in the solar cell element with time is reduced, and the quality of the passivation layer can be improved. Further, if the total number of carbon atoms and silicon atoms in the main chain in the organic film covering the surface of the filler is, for example, 10,000 or less, the particle size of the agglutinating filler does not become too large, and the insulating paste The thickness of the coating film is less likely to be uneven when the coating film is applied. That is, the coatability of the insulating paste is improved. This can also improve the function of protecting the passivation layer by the protective layer formed by using the insulating paste.

More specifically, as the material of the organic film covering the surface of the filler, for example, octylsilane represented by the following chemical formula 1, dodecyl group represented by the following chemical formula 2, and dimethylpoly represented by the following general formula 2. At least one material of siloxane is adopted.

C ₈ H ₂₀ Si ・ ・ ・ (Chemical formula 1)
-C ₁₂ H ₂₅ ... (Chemical formula 2)
-(O-Si (R3) ₂ ) _c -... (general formula 2)

R3 in the general formula 2 represents, for example, a methyl group. Further, a part of R3 may be hydrogen (H) or the like. Further, c is represented by an integer of 6 or more. Also, one of the dimethylpolysiloxanes is _{terminated with Si (CH 3} ) ₃ and the other is terminated with the surface of the filler. Further, the material of the organic coating having a structure containing 6 or more silicon atoms in the main chain and different from the siloxane resin may be methylphenylpolysiloxane or methylhydrogenpolysiloxane. May be good. Methylphenylpolysiloxane is a dimethylpolysiloxane in which a part of the methyl group is a phenyl group. Methylhydrogenpolysiloxane is a dimethylpolysiloxane in which a part of the methyl group is hydrogen (H).

Examples of the organic compound having a dodecyl group include dodecyltrimethoxysilane and dodecyltriethoxysilane.

Further, the filler may contain, for example, a plurality of fillers whose surfaces are covered with different types of organic coatings. In this case, for example, it is possible to reduce the sticking between the plate making and the substrate, which is considered to be caused by the decrease in surface tension when the insulating paste is applied on the substrate. Further, at this time, for example, it becomes easy to apply the insulating paste in an arbitrary pattern at the time of printing, and the printability of the insulating paste can be improved. In this case, for example, the surface is covered with a filler whose surface is covered with an organic film made of dimethylpolysiloxane represented by the general formula 2 and an organic film made of octylsilane represented by the chemical formula 1. It can be used with a broken filler.

Further, the total mass of the filler is set so that the concentration of the filler in the insulating paste is, for example, a value of 3% by mass to 30% by mass. In this case, the viscosity of the insulating paste can be adjusted to a viscosity suitable for a screen printing method or the like. At this time, in the insulating paste, the amount of the filler can be reduced to some extent and the proportion of the siloxane resin can be increased. As a result, a dense protective layer can be formed, and the barrier property of the protective layer can be improved. However, if the amount of the filler is too small, cracks are likely to occur when the siloxane resins are bonded to each other due to the progress of the condensation polymerization reaction in the firing step described later. Therefore, if the total mass of the filler is set so that, for example, the concentration of the filler in the insulating paste is set to a value of 5% by mass to 25% by mass, the barrier property of the protective layer can be easily improved. ..

Further, in the insulating paste, if the mass of the filler is smaller than the mass of the siloxane resin, the viscosity of the insulating paste can be adjusted to a viscosity suitable for a screen printing method or the like. In this case, in the insulating paste, the amount of the filler is small to some extent and the proportion of the siloxane resin is high. As a result, the protective layer becomes dense, so that the barrier property can be improved. For example, if a filler of 3 parts by mass to 60 parts by mass is contained in 100 parts by mass of the siloxane resin, a dense protective layer can be easily formed. Further, for example, if a filler of 25 parts by mass to 60 parts by mass is contained in 100 parts by mass of the siloxane resin, a dense protective layer can be formed more easily.

As the filler contained in the insulating paste according to the embodiment, for example, an inorganic filler made of silicon oxide, aluminum oxide, titanium oxide or the like is used. Here, for example, when a filler of silicon oxide is adopted, the compatibility is improved, so that the insulating paste is less likely to gel. Further, as the shape of the filler, a shape such as a particle shape, a layer shape, a flat shape, a hollow shape, or a fibrous shape is adopted. By using a filler having these shapes, it is possible to reduce a decrease in viscosity due to equal dispersion of the filler. Here, for example, a non-spherical filler such as a flattened filler has a larger surface area than a filler having a shape close to a true sphere, so that the fillers are more likely to aggregate with each other. As a result, the filler is less likely to be homoscedastic.

The average particle size of the filler is set to, for example, 1000 nm or less. The average particle size may be the average particle size of the primary particles or the average particle size of the secondary particles in which the primary particles are aggregated.

The organic solvent is a solvent that disperses the siloxane resin and the filler. Examples of the organic solvent include one or more of diethylene glycol monobutyl ether, methyl cellosolve, ethyl cellosolve, ethyl alcohol, 2- (4-methylcyclohexa-3-enyl) propan-2-ol or 2-propanol. Can be used.

Further, if the organic solvent is contained in the insulating paste at a concentration of 5% by mass to 90% by mass, the viscosity of the insulating paste can be adjusted to a viscosity suitable for a screen printing method or the like. Then, for example, if the insulating paste contains an organic solvent at a concentration of 5% by mass to 50% by mass, the viscosity of the insulating paste can be easily adjusted to a viscosity suitable for a screen printing method or the like.

Here, if the insulating paste contains chlorine, the protective layer containing chlorine can be formed when the insulating paste is applied to form the protective layer. The chlorine content in the insulating paste is set, for example, so that the concentration of chlorine in the insulating paste is a value of 1 ppm to 10000 ppm.

Further, the insulating paste may contain any one or more of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium. If the insulating paste contains these elements, one of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium can be applied to form a protective layer. A protective layer containing the above can be formed. The content of one or more elements of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium in the insulating paste is, for example, 1 ppm to 10,000 ppm in the concentration of the one or more elements in the insulating paste. Is set to be the value of.

Further, the insulating paste may contain fluorine. When the insulating paste contains fluorine, the protective layer containing fluorine can be formed by forming the protective layer by applying the insulating paste. The fluorine content in the insulating paste is set, for example, so that the concentration of fluorine in the insulating paste is a value of 1 ppm to 10 ppm.

Further, if the insulating paste does not substantially contain the organic binder, the generation of voids due to the decomposition of the organic binder or the like is reduced in the step of drying the insulating paste. As a result, the protective layer becomes dense, and the barrier property of the protective layer can be improved. However, less than 0.1 parts by mass of organic binder may be contained with respect to 100 parts by mass of the insulating paste.

Further, if the viscosity of the insulating paste ^{is set from 5 Pa · sec to 400 Pa · sec at a shear rate of 1 second -1} , when the insulating paste is applied to a desired pattern by using the screen printing method, the insulating paste is insulated. It is possible to reduce the bleeding of the sex paste. For example, the insulating paste can be easily applied to a shape having an opening having a width of about several tens of μm to several hundreds of μm. The viscosity of the insulating paste can be measured, for example, by using a viscosity-viscoelasticity measuring instrument or the like.

The number of alkyl groups and phenyl groups in the siloxane resin can be measured as follows. For example, first for identification of alkyl and phenyl groups, Infrared Spectroscopy (IR), Gas Chromatograph Mass Spectrometer (GC-MS) or High Performance Liquid Chromatography (High Performance Liquid Chromatography). HPLC) method is used. Further, the content of alkyl group and phenyl group in the siloxane resin can be measured by a nuclear magnetic resonance (NMR) method, a mass spectrometry (MS) method, or the like.

The molecular weight of the siloxane resin and the organic coating can be determined by, for example, Gel Permeation Chromatography (GPC) method, Static Light Scattering (SLS) method, Intrinsic Viscosity (IV) method or vapor pressure osmotic pressure. It can be measured by the (Vapor Pressure Osmometer: VPO) method or the like. The composition of the siloxane resin and the organic film can be measured by, for example, an NMR method, an IR method, a pyrolysis gas chromatography (PGC) method, or the like. By these measuring methods, the number of carbon atoms or silicon atoms in the main chain of the organic film can be measured. In the above measuring method, the siloxane resin and a large number of fillers whose surfaces are covered with an organic film may be separately measured. For example, after diluting the insulating paste with an organic solvent, the siloxane resin can be separated from a large number of fillers having a surface covered with an organic film by centrifugation.

<1-2. Manufacturing method of insulating paste>
A method for producing an insulating paste according to an embodiment will be described below with reference to FIG.

The insulating paste can be prepared by mixing a precursor of a siloxane resin, water for hydrolyzing the precursor of the siloxane resin, a catalyst, an organic solvent, and a large number of fillers.

First, a mixing step (step S1) is performed. Here, a mixed solution is prepared by mixing a precursor of a siloxane resin, water for hydrolyzing the precursor of a siloxane resin, a catalyst, and an organic solvent in a container.

As the precursor of the siloxane resin, for example, a silane compound having a Si—O bond or a silazane compound having a Si—N bond can be adopted. These compounds have the property of causing hydrolysis (also referred to as hydrolyzable). Further, the precursor of the siloxane resin becomes a siloxane resin by hydrolysis and condensation polymerization.

The silane compound is represented by the following general formula 1.

(R4) _4-d Si (OR5) _d ... General formula 3

Here, d in the general formula 3 is, for example, an integer of any one of 1, 2, 3 and 4. Further, R4 and R5 in the general formula 3 represent a hydrocarbon group such as an alkyl group such as a methyl group and an ethyl group or a phenyl group.

Here, the silane compound includes, for example, a silane compound in which at least R4 contains an alkyl group (also referred to as an alkyl group-based silane compound). Specifically, examples of the alkyl-based silane compound include methyltrimethoxysilane (CH _3- Si- (OCH ₃ ) ₃ ) and dimethyldimethoxysilane ((CH ₃ ) _2- Si- (OCH _{3 ) 2} ). ), Triethoxymethylsilane (CH _3- Si- (OC ₂ H ₅ ) ₃ ), _{Diethoxydimethylsilane ((CH 3} ) _2- Si- (OC ₂ H ₅ ) ₂ ), Trimethoxypropylsilane ((CH 2 H 5) 2). ₃ O) _3- Si- (CH ₂ ) ₂ CH ₃ ), triethoxypropylsilane ((C ₂ H ₅ O) _3- Si- (CH ₂ ) ₂ CH ₃ ), hexyltrimethoxysilane ((CH ₃ O) ) _3- Si- (CH ₂ ) ₅ CH ₃ ), triethoxyhexylsilane ((C ₂ H ₅ O) _3- Si- (CH ₂ ) ₅ CH ₃ ), triethoxyoctylsilane ((C ₂ H ₅ O) ) _3- Si- (CH ₂ ) ₇ CH ₃ ) and decyltrimethoxysilane ((CH ₃ O) _3- Si- (CH ₂ ) ₉ CH ₃ ) and the like.

Here, for example, if the alkyl group is a methyl group, an ethyl group or a propyl group, alcohol as a by-product having a small number of carbon atoms and easily volatilizing can be produced when the precursor of the siloxane resin is hydrolyzed. This facilitates the removal of by-products in the by-product removing step described later. As a result, for example, when the protective layer 11 is formed, the generation of vacancies due to evaporation of by-products is less likely to occur, so that the protective layer 11 becomes dense and the barrier property of the protective layer 11 can be improved. Further, since the by-product produced by hydrolysis is a low-viscosity liquid, the mixed solution is less likely to gel in the insulating paste manufacturing process up to the by-product removing step. This does not increase the viscosity of the insulating paste too much.

Here, for example, when the precursor of the siloxane resin has a phenyl group, the precursor of the siloxane resin is hydrolyzed and condensation polymerized, and the by-products generated by the hydrolysis and condensation polymerization of the phenyl group are removed. It may be mixed in the state of being made into the said siloxane resin. This reduces, for example, fluctuations in the viscosity of the insulating paste due to the hydrolysis reaction of the siloxane resin, and makes it easier to stabilize the viscosity of the insulating paste. Further, for example, if an insulating paste is produced by mixing a siloxane resin, an organic solvent, and a filler with the by-products removed, the amount of by-products contained in the insulating paste is reduced. .. Therefore, if such an insulating paste is produced, for example, when the insulating paste is applied by a screen printing method, it is possible to reduce the dissolution of the screen plate-making emulsion by the by-products. As a result, the dimensions of the screen plate making pattern are less likely to fluctuate.

Further, the silane compound includes, for example, a silane compound in which R4 and R5 contain both a phenyl group and an alkyl group. Such silane compounds, for example, trimethoxyphenyl silane _{(C 6 H 5 -Si- (OCH} 3) 3), dimethoxy diphenyl silane _{((C 6 H 5) 2} -Si- (OCH 3) 2), Methoxytriphenylsilane ((C ₆ H ₅ ) ₃ -Si-OCH ₃ ), triethoxyphenylsilane (C ₆ H _5- Si- (OC ₂ H ₅ ) ₃ ), diethoxydiphenylsilane ((C ₆ H ₅₎₎ ) _2- Si- (OC ₂ H ₅ ) ₂ ), ethoxytriphenylsilane ((C ₆ H ₅ ) ₃ -Si-OC ₂ H ₅ ), triisopropoxyphenylsilane (C ₆ H ₅ -Si- (OC) ₃ H ₇ ) ₃ ), diisopropoxydiphenylsilane ((C ₆ H ₅ ) _2- Si- (OC ₃ H ₇ ) ₂ ) and isopropoxytriphenylsilane ((C ₆ H ₅ ) ₃ -Si-OC ₃₎ H ₇₎ and the like.

Among these silane compounds, for example, if a silane compound containing two or more OR bonds is adopted, a siloxane bond (Si-O-Si) formed by causing condensation polymerization after hydrolysis of the silane compound is adopted. The number of bonds) can increase. This can increase the network of siloxane bonds in the silicon oxide that constitutes the protective layer. As a result, the barrier property of the protective layer can be improved.

Further, the silazane compound may be either an inorganic silazane compound or an organic silazane compound. Here, examples of the inorganic silazane compound include polysilazane (-(H ₂ SiNH)-). Examples of the organic silazane compound include hexamethyldisilazane ((CH ₃ ) ₃ SiNHSi (CH ₃ ) ₃ ), tetramethylcyclodisilazane ((CH ₃ ) ₂ Si (NH) ₂ Si (CH ₃ ) ₂ ) or Examples thereof include tetraphenylcyclodisilazane ((C ₆ H ₅ ) ₂ Si (NH) ₂ Si (C ₆ H ₅ ) _2).

Water is a solution for hydrolyzing a precursor of a siloxane resin. For example, pure water is used as water. _{For example, water reacts with the bond of Si-OCH 3} of a silane compound to form a Si-OH bond and HO-CH ₃ (methyl alcohol).

The organic solvent is a solvent for producing a paste containing a siloxane resin from a precursor of the siloxane resin. In addition, the organic solvent can be a mixture of a precursor of a siloxane resin and water. The organic solvent can also serve to disperse the siloxane resin and the filler described later. As the organic solvent, for example, diethylene glycol monobutyl ether, methyl cellosolve, ethyl cellosolve, ethyl alcohol, 2- (4-methylcyclohexa-3-enyl) propan-2-ol, 2-propanol and the like are used. Here, any one of these organic solvents and an organic solvent in which two or more kinds of organic solvents are mixed may be used.

The catalyst can control the rate of reaction as the precursor of the siloxane resin undergoes hydrolysis and condensation polymerization. For example, Si-OR bond contained in the precursor of the siloxane resin (e.g., R represents an alkyl group) and cause hydrolysis and condensation polymerization, Si-O-Si bond from two or more Si-OH and _H 2 O The rate of reaction that causes (water) can be adjusted. As the catalyst, for example, one or more inorganic acids selected from hydrochloric acid, nitric acid, sulfuric acid, boric acid, phosphoric acid, hydrofluoric acid, acetic acid and the like, or one or more organic acids are used. Further, as the catalyst, for example, one or more inorganic bases such as ammonia, sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, pyridine and the like or one or more organic bases may be used. Further, the catalyst may be, for example, a combination of an inorganic acid and an organic acid, or a combination of an inorganic base and an organic base.

The ratio of each material to be mixed in the mixing step is 10% by mass to 90% by mass of the precursor of the siloxane resin and 5% by mass to 40% by mass of water with respect to the total mass (100% by mass) of these materials mixed. % (Or 10% to 20% by weight), 1 ppm to 1000 ppm for the catalyst, 5% to 50% by weight for the organic solvent. Within the above range, the siloxane resin obtained by hydrolyzing the precursor of the siloxane resin and performing condensation polymerization can be contained in the insulating paste in an appropriate mass ratio. In addition, the insulating paste may not gel and the viscosity of the insulating paste may not increase too much.

In such a mixing step, the precursor of the siloxane resin reacts with water, and hydrolysis of the precursor of the siloxane resin begins. Further, the precursor of the hydrolyzed siloxane resin undergoes condensation polymerization, and the siloxane resin begins to be produced.

Further, a chlorine compound may be mixed with the mixed solution. This chlorine compound is represented by, for example, the following general formula 4. When the chlorine compound is not mixed with the mixed solution in the mixing step, the chlorine compound may be added to the mixed solution in a step after the mixing step.

(R6) _4-e-f Si (OR7) _e (Cl) _f ... General formula 4

Here, R6 and R7 in the general formula 4 represent a hydrocarbon group such as an alkyl group such as a methyl group or an ethyl group or a phenyl group. Further, e in the general formula 4 is an integer of any one of 1, 2 and 3. f is an integer of any one of 1 and 2. e + f is an integer of any one of 2, 3 and 4. e + f is, for example, 3 or 4. R6 and R7 may be the same alkyl group or phenyl group, and may not be the same alkyl group or phenyl group. For example, a chlorine compound may be contained in the mixed solution in a state where it has a Si—Cl bond and no hydrolysis reaction has occurred.

Further, for example, chloride or the like may be mixed with the mixed solution. As the chloride, for example, zinc chloride (ZnCl ₂ ), magnesium chloride (MgCl ₂ ), tin chloride (SnCl ₂ ) and the like are adopted.

Also, the mixed solution is mixed with at least one of elemental elements, oxides and chlorides, for example, for any one or more of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium. May be good.

Further, for example, a fluorine compound may be mixed with the mixed solution. As the fluorine compound, for example, any one or more fluorides of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium are adopted.

Next, the first stirring step (step S2) is performed. The mixed solution prepared in the mixing step is stirred using, for example, a mix rotor, a stirrer, or the like. Here, when the mixed solution is stirred, the hydrolysis of the precursor of the siloxane resin further proceeds. In addition, the precursor of the hydrolyzed siloxane resin undergoes condensation polymerization, and the siloxane resin continues to be produced. For example, when stirring with a mix rotor, stirring conditions are adopted in which the rotation speed of the rotating roller of the mix rotor is about 400 rpm to 600 rpm and the stirring time is about 30 minutes to 90 minutes. When such stirring conditions are adopted, the precursor of the siloxane resin, water, the catalyst and the organic solvent can be uniformly mixed.

Further, in the first stirring step, for example, if the mixed solution is heated, hydrolysis and condensation polymerization of the precursor of the siloxane resin are likely to proceed. This makes it easier for the viscosity of the mixed solution to stabilize, for example, in the steps after the first stirring step. Further, for example, since hydrolysis and condensation polymerization of the precursor of the siloxane resin are likely to proceed, productivity can be improved by shortening the stirring time.

Next, a by-product removing step (step S3) is performed. In this step, by-products are removed from the mixed solution stirred in the first stirring step (step S2). Here, for example, by-products of organic components such as alcohol, water and a catalyst generated by the reaction between a precursor of an organic solvent and a siloxane resin and water are volatilized. This removal of by-products reduces changes in the viscosity of the insulating paste due to volatilization of organic components as by-products when the insulating paste is stored or when the insulating paste is applied continuously. Can be done. Further, when the insulating paste is applied by using the screen printing method, the screen plate-making emulsion is less likely to be dissolved by the organic component as a by-product. This can reduce the dimensional variation of the screen plate making pattern. Further, also in the by-product removing step, the precursor of the hydrolyzed siloxane resin undergoes condensation polymerization, and the siloxane resin continues to be produced. Further, in the by-product removing step, since water and the catalyst are volatilized, the reaction of condensation polymerization of the precursor of the siloxane resin can be reduced. This can reduce the variation in viscosity of the mixed solution.

In the by-product removing step, for example, using a hot plate or a drying oven, the treatment temperature is about 90 ° C. (or about 50 ° C. to 90 ° C.) and the treatment time is about 10 to 600 minutes. Under the above conditions, the mixed solution after stirring is treated. By-products can be removed if the treatment temperature is within the above temperature range. Further, within the above temperature range, the organic component which is a by-product tends to volatilize. As a result, productivity can be improved by shortening the processing time.

In the by-product removing step, for example, not only organic components such as methyl alcohol produced by the reaction of hydrolysis but also added catalysts and the like are removed by volatilization. In one embodiment, in the by-product removing step, the catalyst added in the mixing step volatilizes, so that chlorine is also removed when hydrochloric acid is used as the catalyst. Therefore, after the by-product removing step, chlorine is contained in the mixed solution by adding hydrochloric acid or a compound containing chlorine in a part of the above-mentioned alkoxysilane represented by the general formula 4 to the mixed solution. You may. Further, a chloride such as zinc, magnesium or tin may be mixed with the mixed solution.

When fluorine is contained in the mixed solution, the catalyst added in the mixing step volatilizes in the by-product removing step, so that the fluorine is removed. Therefore, after the by-product removing step, fluorine may be contained in the mixed solution by adding fluoride such as hydrofluoric acid or zinc, magnesium or tin to the mixed solution.

If the by-product removing step is performed under reduced pressure, the organic components and catalysts, which are by-products, are likely to volatilize. As a result, productivity can be improved by shortening the processing time.

Further, for example, in the by-product removing step, the precursor of the siloxane resin remaining without being hydrolyzed in the first stirring step may be further hydrolyzed.

Next, a filler addition step (step S4) is performed. Here, a large number of fillers are added to the mixed solution from which the by-products have been removed in the by-product removing step (step S3). As the filler material, for example, an inorganic material such as silicon oxide is adopted. Further, here, as the filler, for example, a filler having a surface covered with an organic film is used. The material of this organic coating has a structure in which the number of carbon atoms in the main chain is 6 or more, or the total number of carbon atoms and silicon atoms in the main chain is 6 or more, and the siloxane. A material different from the resin is applied. As described above, the viscosity of the mixed solution can be easily adjusted by performing the filler addition step after the first stirring step. Further, the filler is added so as to be contained in, for example, 3% by mass to 30% by mass (may be 5% by mass to 25% by mass) in the insulating paste after preparation.

Next, a second stirring step (step S5) is performed. Here, for the mixed solution to which the filler is added, for example, a rotation / revolution mixer or the like is used. For example, when stirring with a rotation / revolution mixer, the rotation speed of the rotation part and the revolution part is 800 rpm to 1000 rpm, and the stirring time is 1 minute to 10 minutes. By stirring under the above conditions, the filler can be uniformly dispersed in the mixed solution.

Next, a viscosity stabilizing step (step S6) is performed. Here, the viscosity of the mixed solution is stabilized by storing the mixed solution after stirring at room temperature for about 2 hours to 24 hours, for example. If the viscosity of the mixed solution is stable in the second stirring step, the viscosity stabilizing step can be omitted.

By the above steps, an insulating paste can be produced.

Further, although the filler addition step is performed after the first stirring step, for example, the filler may be added at the same time in the mixing step. This eliminates the need for the filler addition step and the second stirring step, so that the productivity is improved.

Moreover, it is not necessary to perform the by-product removing step. The insulating paste prepared without performing the by-product removing step can be applied by a spray method or the like.

Further, for example, a siloxane resin having an alkyl group may be produced in the mixing step, and the siloxane resin having a phenyl group may be added in the filler addition step.

<1-3. Solar cell element ＞
The solar cell element according to one embodiment has a semiconductor substrate, a passivation layer, a protective layer, and an electrode. The passivation layer is located on the semiconductor substrate. The protective layer is located above the passivation layer and contains chlorine. The electrodes are located above the protective layer. Hereinafter, a schematic configuration of the PERC type solar cell element 10 according to the embodiment will be described with reference to FIGS. 2 to 4.

As shown in FIG. 4, the solar cell element 10 has a first element surface 10a, a second element surface 10b, and a side surface 10c. The first element surface 10a is a light receiving surface on which light is mainly incident. The second element surface 10b is a back surface located on the opposite side of the first element surface 10a. The side surface 10c is located in a state where the first element surface 10a and the second element surface 10b are connected to each other.

The solar cell element 10 includes a semiconductor substrate 1, an antireflection layer 5, a first electrode 6, a second electrode 7, a third electrode 8, a passivation layer (hereinafter, also referred to as a first passivation layer) 9, and a protective layer 11. There is.

The semiconductor substrate 1 has a first surface 1a, a second surface 1b, and a side surface 1c. The second surface 1b is located on the opposite side of the first surface 1a. The side surface 1c is located in a state where the first surface 1a and the second surface 1b are connected to each other. The semiconductor substrate 1 has a first semiconductor layer 2 and a second semiconductor layer 3. The first semiconductor layer 2 is a monoconductive type (for example, p-type) semiconductor region. The second semiconductor layer 3 is a reverse conductive type (for example, n type) semiconductor region located on the first surface 1a side of the first semiconductor layer 2. For example, a single crystal silicon or a polycrystalline silicon substrate is applied to the semiconductor substrate 1. The semiconductor substrate 1 may be a semiconductor substrate using a material other than silicon as long as it is a semiconductor substrate having the first semiconductor layer 2 and the second semiconductor layer 3 as described above.

Here, for example, it is assumed that a p-type semiconductor is used as the first semiconductor layer 2. In this case, as the semiconductor substrate 1, for example, a polycrystalline or single crystal p-type silicon substrate is adopted. The silicon substrate is, for example, a thin substrate having a thickness of 250 μm or less or 150 μm or less. The shape of the semiconductor substrate 1 is not particularly limited, but if it has a substantially square shape in a plan view, there is a gap between the solar cell elements 10 when a plurality of solar cell elements 10 are arranged side by side to manufacture a solar cell module. Can be small. For example, when the first conductive type is p-type and the second conductive type is n-type, the p-type silicon substrate is a polycrystal or single crystal silicon crystal, and boron or gallium is used as a dopant element. It can be manufactured by containing the impurities of.

The second semiconductor layer 3 is located so as to be laminated on the first semiconductor layer 2. The second semiconductor layer 3 has a conductive type (n type in one embodiment) opposite to that of the first semiconductor layer 2, and is located on the first surface 1a side of the first semiconductor layer 2. As a result, the semiconductor 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 an impurity such as phosphorus as a dopant in the region on the first surface 1a side of the p-type semiconductor substrate.

As shown in FIG. 4, the first surface 1a of the semiconductor substrate 1 may have, for example, a fine uneven structure (texture) for reducing the reflectance of the irradiated light. At this time, the height of the convex portion of the texture is, for example, about 0.1 μm to 10 μm. Here, the distance between the vertices of the adjacent convex portions is about 0.1 μm to 20 μm. As for the texture, for example, the concave portion may have a substantially spherical shape, or the convex portion may have a pyramid shape. The above-mentioned "height of the convex portion" is, for example, in FIG. 4, a straight line passing through the bottom surface of the concave portion is used as a reference line, and from this reference line in a direction perpendicular to the reference line (here, the + Z direction). It is the distance to the apex of the convex part.

The antireflection layer 5 has a function of reducing the reflectance of the light irradiated to the first element surface 10a of the solar cell element 10. As the material of the antireflection layer 5, for example, silicon oxide, aluminum oxide, silicon nitride layer, or the like can be adopted. The refractive index and thickness of the antireflection layer 5 realize a condition in which the reflectance is low (also referred to as a low reflection condition) with respect to light in a wavelength range that can be absorbed by the semiconductor substrate 1 and contribute to power generation among sunlight. The refractive index and thickness that can be set can be appropriately set. For example, it is conceivable that the refractive index of the antireflection layer 5 is about 1.8 to 2.5, and the thickness of the antireflection layer 5 is about 20 nm to 120 nm.

Further, the semiconductor substrate 1 has a third semiconductor layer 4. The third semiconductor layer 4 is located on the surface layer portion on the second surface 1b side of the semiconductor substrate 1. The conductive type of the third semiconductor layer 4 is the same as the conductive type of the first semiconductor layer 2 (p type in one 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. In other words, the dopant element is present in the third semiconductor layer 4 at a concentration higher than the concentration of the dopant element doped in the first semiconductor layer 2 in order to make it a monoconductive type. The third semiconductor layer 4 forms an internal electric field on the second surface 1b side of the semiconductor substrate 1. As a result, recombination of minority carriers caused by photoelectric conversion in response to light irradiation is less likely to occur in the vicinity of the second surface 1b of the semiconductor substrate 1. As a result, the photoelectric conversion efficiency is less likely to decrease. The third semiconductor layer 4 can be formed, for example, by diffusing a dopant element such as boron or aluminum on the surface layer portion on the second surface 1b side of the semiconductor substrate 1. At this time, the concentration of the dopant element contained in the first semiconductor layer 2 is set to about 5 × 10 ¹⁵ atoms / cm ³ to about 1 × 10 ¹⁷ atoms / cm ^3, and the concentration of the dopant element contained in the third semiconductor layer 4 is set. It can be about 1 × 10 ¹⁸ atoms / cm ³ to 5 × 10 ²¹ atoms / cm ^3. The third semiconductor layer 4 may be present at a contact portion between the third electrode 8 and the semiconductor substrate 1, which will be described later.

The first electrode 6 is an electrode located on the first surface 1a side of the semiconductor substrate 1. As shown in FIGS. 2 and 4, the first electrode 6 has an output take-out electrode 6a and a plurality of linear current collector electrodes 6b. However, in FIG. 4, the current collector electrode 6b is omitted.

The output take-out electrode 6a is for taking out the carrier obtained by photoelectric conversion in response to the irradiation of light on the semiconductor substrate 1 to the outside of the solar cell element 10. As the output take-out electrode 6a, for example, a bus bar electrode having an elongated rectangular shape is adopted when the first element surface 10a is viewed in a plan view. The length (also referred to as the width) of the output take-out electrode 6a in the lateral direction is, for example, about 1.3 mm to 2.5 mm. At least a part of the output take-out electrode 6a is in a state of being electrically connected to the current collector electrode 6b so as to intersect with the current collector electrode 6b.

The current collector electrode 6b can collect carriers obtained by photoelectric conversion in response to light irradiation on the semiconductor substrate 1. Each current collecting electrode 6b is, for example, a linear electrode having a width of about 50 μm to 200 μm. As described above, the width of the current collector electrode 6b is smaller than the width of the output extraction electrode 6a. The plurality of current collector electrodes 6b are located so as to be arranged at intervals of, for example, about 1 mm to 3 mm from each other.

The thickness of the first electrode 6 is, for example, about 10 μm to 40 μm. The first electrode 6 can be formed, for example, by applying a metal paste (also referred to as silver paste) containing silver as a main component to a desired shape by screen printing or the like and then firing the paste. In one embodiment, the main component means a component having the largest (highest) content ratio (also referred to as a content rate) among the contained components. Further, for example, since the auxiliary electrode 6c having the same shape as the current collecting electrode 6b is located along the peripheral edge of the semiconductor substrate 1, the current collecting electrodes 6b may be electrically connected to each other.

The second electrode 7 and the third electrode 8 are located on the second surface 1b side of the semiconductor substrate 1 as shown in FIGS. 3 and 4.

The second electrode 7 is an electrode for taking out the carrier obtained by photoelectric conversion in response to light irradiation in the solar cell element 10 to the outside of the solar cell element 10. The thickness of the second electrode 7 is, for example, about 10 μm to 30 μm. The width of the second electrode 7 is about 1.3 mm to 7 mm. When the second electrode 7 contains silver as a main component, for example, a metal paste containing silver as a main component (also referred to as silver paste) is applied to the second electrode 7 in a desired shape by screen printing or the like. After being made, it can be formed by firing.

The third electrode 8 is an electrode for collecting carriers obtained by photoelectric conversion in the semiconductor substrate 1 in response to light irradiation on the second surface 1b side of the semiconductor substrate 1. The third electrode 8 is located in a state of being electrically connected to the second electrode 7. Here, it is sufficient that at least a part of the second electrode 7 is located in a state of being connected to the third electrode 8. The thickness of the third electrode 8 is, for example, about 15 μm to 50 μm.

When the third electrode 8 contains aluminum as a main component, for example, a metal paste containing aluminum as a main component (also referred to as aluminum paste) is applied to the third electrode 8 in a desired shape. It can later be formed by firing.

The first passivation layer 9 is located on at least the second surface 1b of the semiconductor substrate 1. The first passivation layer 9 has a function of reducing recombination of minority carriers generated by photoelectric conversion in response to light irradiation in the semiconductor substrate 1. As the material of the first passivation layer 9, for example, aluminum oxide or the like is adopted. In this case, the first passivation layer 9 can be formed, for example, by an atomic layer deposition (ALD) method. Here, when the first passivation layer 9 contains aluminum oxide, the aluminum oxide has a negative fixed charge. Therefore, the minority carriers (electrons in this case) generated on the second surface 1b side of the semiconductor substrate 1 due to the electric field effect are the interface between the p-type first semiconductor layer 2 and the first passivation layer 9 (second surface 1b). ). As a result, recombination of minority carriers in the vicinity of the second surface 1b of the semiconductor substrate 1 can be reduced. As a result, the photoelectric conversion efficiency of the solar cell element 10 can be improved. The thickness of the first passivation layer 9 is, for example, about 10 nm to 200 nm.

The first passivation layer 9 may contain, for example, chlorine or fluorine. In this case, the output characteristics of the solar cell element 10 are less likely to deteriorate due to the PID (Potential Induced Degradation) phenomenon. The reason for this can be explained as follows. Sodium ion is considered as one of the causes of the PID phenomenon. When sodium ions are diffused into the first passivation layer 9, the interfacial recombination of minority carriers increases due to the decrease in the electric field passivation effect. Further, when sodium ions are diffused in the semiconductor substrate 1, recombination of minority carriers is further increased. Therefore, the output characteristics of the solar cell element 10 are deteriorated. However, when the first passivation layer 9 contains at least one element of chlorine and fluorine, at least one element of chlorine and fluorine easily reacts with sodium ion. It is presumed that this makes it difficult for sodium ions to diffuse into the first passivation layer 9 and the semiconductor substrate 1. The first passivation layer 9 containing at least one element of chlorine and fluorine can be formed, for example, by introducing a gas containing at least one of chlorine and fluorine in the step of forming the first passivation layer 9 by the ALD method. .. The concentration of chlorine contained in the first passivation layer 9 is, for example, 1 ppm to 5000 ppm. The concentration of fluorine contained in the first passivation layer 9 is, for example, 1 ppm to 10 ppm.

The presence and concentration of chlorine and fluorine contained in the first passion layer 9 can be determined, for example, by secondary ion mass spectrometry (SIMS) or ICP-Atomic Emission Spectrometry (ICP-AES). ) Can be measured by method or the like.

The protective layer 11 is located on the first passivation layer 9 located on the second surface 1b of the first semiconductor layer 2. The protective layer 11 can protect the first passivation layer 9. As the material of the protective layer 11, for example, silicon oxide or the like is adopted. The protective layer 11 is located on the first passivation layer 9 in a state of having a desired pattern. The protective layer 11 has a gap penetrating the protective layer 11 in the thickness direction (here, the + Z direction). This gap may be, for example, a hole having a closed through hole around the second surface 1b, or at least a part of the periphery along the second surface 1b is opened. It may be a slit-shaped hole. For example, when the protective layer 11 is viewed in a plan view, it is assumed that the protective layer 11 has a plurality of holes 12. Here, when the protective layer 11 is viewed in a plan view, each hole portion 12 may have a dot shape or a band shape. The diameter or width of the hole 12 is about 10 μm to 500 μm. The pitch of the holes 12 is, for example, about 0.3 mm to 3 mm. The pitch of the hole portions 12 is, for example, the distance between the centers of the hole portions 12 adjacent to each other when the protective layer 11 is viewed in a plan view.

By the way, when the third electrode 8 is formed on the protective layer 11, for example, an aluminum paste is applied so as to have a desired shape and fired. At this time, the aluminum paste directly applied on the first passivation layer 9 in the hole 12 of the protective layer 11 is fire-through (also referred to as firing penetration) of the first passivation layer 9 to form the second surface 1b of the semiconductor substrate 1. The third electrode 8 is directly connected to the. Further, at this time, for example, the aluminum in the Al paste diffuses into the surface layer portion on the second surface 1b side of the semiconductor substrate 1, so that the third semiconductor layer 4 is formed. Further, in the portion of the first passivation layer 9 covered with the protective layer 11, the aluminum paste does not cause fire-through of the first passivation layer 9. As a result, in the solar cell element 10, the first passivation layer 9 can be present on the second surface 1b of the semiconductor substrate 1 in a pattern corresponding to the desired pattern of the protective layer 11. As a result, the passivation effect of the first passivation layer 9 is unlikely to be reduced. The thickness of the protective layer 11 is, for example, about 0.5 μm to 10 μm. The thickness of the protective layer 11 includes the composition of the insulating paste, the size of the uneven shape of the second surface 1b of the semiconductor substrate 1, the type or content of the glass frit contained in the aluminum paste, and the formation of the third electrode 8. It is changed as appropriate depending on the firing conditions and the like. The protective layer 11 can be formed by applying the above-mentioned insulating paste by a screen printing method and drying it.

The protective layer 11 is, for example, coated on the first passivation layer 9 formed on the second surface 1b of the semiconductor substrate 1 so that the insulating paste has a desired pattern by a coating method such as a screen printing method. It is formed by being dried above. The protective layer 11 may be formed, for example, directly on the side surface 1c of the semiconductor substrate 1 or also on the antireflection layer 5 formed on the first passivation layer 9. At this time, the presence of the protective layer 11 can reduce the leakage current in the solar cell element 10.

Here, for example, the protective layer 11 may contain chlorine in the form of hydrochloric acid (HCl) or chloride. As the chloride, for example, zinc chloride (ZnCl ₂ ), magnesium chloride (MgCl ₂ ), tin chloride (SnCl ₂ ) and the like can be considered. For example, if the protective layer 11 contains chlorine, a hydrolysis and condensation polymerization reaction occurs in a region containing a low molecular weight component of the siloxane resin remaining in the protective layer 11, and the siloxane resin becomes a polymer. Easy to become an ingredient.

Here, for example, when hydrochloric acid is contained in the protective layer 11, it is assumed that the following reaction occurs. In this case, for example, in the protective layer 11, there is a portion where the siloxane resin is terminated with a methoxy group (-OCH ₃ ), and if water and hydrochloric acid are present, the concentration of hydrogen ions is high. A condition arises. At this time, for example, hydrogen ions are bonded to the oxygen at the end of the siloxane resin, which is terminated by the methoxy group, so that the methyl group at the end is removed from the oxygen, and the silicon present at the end of the siloxane resin. Is terminated with a hydroxy group (-OH). Further, at this time, for example, methyl alcohol is generated by the bond between the methyl group deviated from the terminal portion of the siloxane resin and the hydroxide ion. In this way, the hydrolysis of the siloxane resin is promoted.

^{Further, for example, a hydrogen ion (H +} ) derived from hydrochloric acid (HCl) is bonded to the oxygen (O) of the silanol bond (Si—OH bond) at the terminal portion of the first siloxane resin. At this time, chlorine ions (Cl ⁻ ) derived from hydrochloric acid (HCl) are present. Further, at this time, at the silanol bond portion at the terminal portion of the first siloxane resin, the oxygen bonded by the hydrogen ion robs the silicon electron, the bond between the silicon and the oxygen is broken, and water (H ₂ O). ) Is generated. ^{Here, silicon (Si +} ), to which one electron has been deprived, is unstable and tries to bond with surrounding molecules. On the other hand, at the terminal portion of the second siloxane resin, hydrogen (H) in the silanol bond becomes hydrogen ion (H ⁺ ) and is separated from the terminal portion of the second siloxane resin, and Si − in which oxygen is bonded to silicon. O ^- is generated. At this time, the hydrogen ion (H ⁺ ) disengaged from the silanol bond binds to the chloride ion (Cl ⁻ ) to generate hydrochloric acid (HCl). ^{Then, the silicon (Si +} ) at the end of the first siloxane resin ^{and the Si—O − at} the end of the second siloxane resin are bonded to form a siloxane bond (Si—O—Si bond). Such a reaction promotes condensation polymerization of the siloxane resin. Therefore, for example, when the protective layer 11 contains chlorine, hydrolysis and condensation polymerization reactions easily occur in the region containing the low molecular weight component of the siloxane resin remaining in the protective layer 11, and the protective layer 11 tends to become a high molecular weight component. .. As a result, the low molecular weight component of the siloxane resin is unlikely to remain, and the low molecular weight component of the siloxane resin in the protective layer 11 is unlikely to volatilize. Therefore, the formation of voids due to the volatilization of the small molecule component remaining in the protective layer 11 is reduced, and the moisture permeability of the protective layer 11 tends to decrease. As a result, the first passivation layer 9 can be sufficiently protected by the protective layer 11, and the first passivation layer 9 is less likely to deteriorate. As a result, the passivation effect of the first passivation layer 9 is less likely to decrease.

Further, here, for example, in the case where the protective layer 11 has a portion where the terminal portion of the siloxane resin is terminated by a silanol bond, and the protective layer 11 contains zinc chloride (ZnCl ₂ ) as a chloride. Is expected to cause the following reactions. In this case, for example, the portion of two chlorine elements in _{zinc chloride (ZnCl 2} ^{) becomes two chlorine ions (2Cl −} ), and the portion of zinc element (Zn) becomes zinc ions (Zn ²⁺ ). .. At this time, the zinc ion (Zn ²⁺ ) is unstable. Therefore, the zinc ion (Zn ²⁺ ) binds to the hydroxyl group of the silanol bond in the first siloxane resin. ^{At this time, silicon (Si +} ) as a terminal portion of the first siloxane resin, monovalent zinc hydroxide (ZnOH ⁺ ), and two chlorine ions (2Cl ⁻ ) are generated. Next, hydrogen ions (H ⁺ ) are released from the unstable monovalent zinc hydroxide (ZnOH ⁺ ) to generate zinc oxide (ZnO). At this time, hydrogen ion (H ⁺ ) and two chlorine ions (Cl ⁻ ) function as catalysts to form a silanol bond in the second siloxane resin and silicon (Si ⁺ ) as a terminal portion of the first siloxane resin. Reacts with. This results in a siloxane bond (Si—O—Si bond), zinc oxide (ZnO), two hydrogen ions (2H ⁺ ) and two chlorine ions (2Cl ⁻ ). At this time, if hydrogen ions (H ⁺ ) are excessively present, two hydrogen ions (2H ⁺ ) and a part of two chlorine ions (2Cl ⁻ ) react appropriately to generate hydrochloric acid (HCl). NS. Such a reaction promotes condensation polymerization of the siloxane resin. Therefore, for example, in the protective layer 11, the low molecular weight component of the siloxane resin tends to become the high molecular weight component of the siloxane resin. As a result, the low molecular weight component of the siloxane resin is unlikely to remain, and the low molecular weight component of the siloxane resin in the protective layer 11 is unlikely to volatilize. Therefore, the formation of voids due to the volatilization of the low molecular weight component of the siloxane resin remaining in the protective layer 11 is reduced, and the moisture permeability of the protective layer 11 tends to decrease.

Further, here, for example, by promoting the condensation polymerization of the siloxane resin, the high molecular weight component of the siloxane resin and the low molecular weight component of the siloxane resin, which are located at intervals from each other, are continuously formed by forming a siloxane bond. It tends to be a polymer component of siloxane resin. At this time, the protective layer 11 becomes a dense layer, and the moisture permeability of the protective layer 11 tends to decrease. In addition, the protective layer 11 is less likely to be fired through. As a result, the first passivation layer 9 can be sufficiently protected by the protective layer 11, and the passivation effect of the first passivation layer 9 is less likely to decrease. Further, when the protective layer 11 contains chlorine, this chlorine easily reacts with sodium ions. Therefore, sodium ions that can cause the PID phenomenon are less likely to diffuse into the first passivation layer 9 and the semiconductor substrate 1. As a result, the PID phenomenon is less likely to occur. Therefore, for example, when the protective layer 11 contains chlorine, the output characteristics of the solar cell element 10 can be maintained.

Here, the chlorine content concentration in the protective layer 11 may be, for example, 1 ppm to 10000 ppm. In this case, the above-mentioned effect can be obtained. The presence and concentration of chlorine contained in the protective layer 11 can be measured by, for example, the SIMS method or the ICP-AES method.

In the protective layer 11, for example, the chlorine content in the portion located on the third electrode 8 side may be higher than the chlorine content in the portion located on the first passivation layer 9 side. In this case, if the concentration of chlorine in the protective layer 11 is higher in the portion located on the third electrode 8 side than in the portion located on the first passivation layer 9 side, the protective layer 11 is included. The polymer component of the siloxane resin tends to increase at the portion on the 8th side of the third electrode. At this time, voids are less likely to occur in the portion of the protective layer 11 located on the third electrode 8 side. As a result, the first passivation layer 9 can be sufficiently protected by the protective layer 11, and the first passivation layer 9 is less likely to deteriorate. As a result, the output characteristics of the solar cell element 10 can be maintained. Further, in a situation where the small molecule component of the siloxane resin remaining in the protective layer 11 volatilizes, the siloxane remaining in the protective layer 11 is affected by the portion of the protective layer 11 on the third electrode 8 side. The phenomenon that the small molecule component of the resin volatilizes and flows out to the outside is less likely to occur. As a result, the small molecule component of the siloxane resin that does not flow out to the outside is likely to undergo hydrolysis and condensation polymerization due to the chlorine in the protective layer 11. As a result, the barrier property of the protective layer 11 is likely to be improved. In other words, the first passivation layer 9 can be sufficiently protected by the protective layer 11, and the first passivation layer 9 is less likely to deteriorate.

Further, the protective layer 11 may contain any one or more of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium. When the protective layer 11 contains these components, one or more of these components in the protective layer 11 and the metal particles and the glass component in the third electrode 8 are likely to react with each other. As a result, the adhesion between the protective layer 11 and the third electrode 8 can be improved. Any one or more of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium in the protective layer 11 may be contained in the protective layer 11 in the form of, for example, these oxides.

Here, the content concentration of any one or more of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium in the protective layer 11 may be, for example, 1 ppm to 10000 ppm. In this case, the above-mentioned effect can be obtained.

Further, in the protective layer 11, the portion located on the first passivation layer 9 side is more boron, vanadium, iron, zinc, bismuth, lead, tin and the portion located on the first passivation layer 9 side than the portion located in the center in the thickness direction (also referred to as the central portion). The concentration of any one or more of magnesium may be high. In this case, even if voids are likely to occur in the protective layer 11, one or more components of boron, vanadium, iron, zinc, bismuth, lead, tin, and magnesium are contained in the first passivation layer 9. On the side, it easily binds to the component of the protective layer 11. Therefore, voids are less likely to occur in the portion of the protective layer 11 on the first passivation layer 9 side. As a result, the reaction between the glass component contained in the third electrode 8 and the first passivation layer 9 is reduced, and the thickness of the first passivation layer 9 can be easily secured. In other words, the first passivation layer 9 is less likely to deteriorate. As a result, the passivation effect is less likely to decrease, and the output characteristics of the solar cell element 10 are more likely to be maintained. Here, for example, the concentration of one or more of boron, vanadium, iron, zinc, bismuth, lead, tin, and magnesium increases toward the third electrode 8 side from the central portion in the thickness direction of the protective layer 11. May be.

Further, the protective layer 11 may contain, for example, fluorine. For example, the protective layer 11 may contain fluorine in the form of hydrofluoric acid (HF) or fluoride. As the fluoride, for example, zinc fluoride (ZnF ₂ ), magnesium fluoride (MgF ₂ ), tin fluoride (SnF ₂ ) and the like can be considered. When the protective layer 11 contains fluorine, the low molecular weight component of the siloxane resin causes a reaction of hydrolysis and condensation polymerization in the region of the protective layer 11 containing the low molecular weight component of the residual siloxane resin. It becomes easy to become a polymer component. Therefore, since the moisture permeability of the protective layer 11 tends to decrease, the first passivation layer 9 can be sufficiently protected by the protective layer 11, and the first passivation layer 9 is less likely to deteriorate. As a result, the passivation effect of the first passivation layer 9 is less likely to decrease. Thereby, the initial characteristics of the output of the solar cell element 10 can be maintained for a long period of time. Further, even when sodium ions diffuse toward the semiconductor substrate 1 and the first passivation layer 9, which is considered to be one of the causes of the PID phenomenon, the fluorine in the protective layer 11 reacts with the sodium ions, so that the sodium ions react with the sodium ions. Sodium ions are less likely to diffuse into the semiconductor substrate 1 and the first passivation layer 9. Thereby, the initial characteristics of the output of the solar cell element 10 can be maintained for a long period of time.

Here, the concentration of fluorine contained in the protective layer 11 may be, for example, 1 ppm to 10 ppm. In this case, the above-mentioned effect can be obtained. The presence and concentration of fluorine, boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium contained in the protective layer 11 can be measured by, for example, the SIMS method or ICP-AES.

The protective layer 11 is formed not only on the first passivation layer 9 located on the second surface 1b side of the semiconductor substrate 1, but also on the side surface 1c of the semiconductor substrate 1 and on the peripheral edge portion of the first surface 1a. It may also be located on at least one of the antireflection layers 5 provided. In this case, the presence of these protective layers 11 can reduce the leakage current of the solar cell element 10.

Further, for example, a second passivation layer containing silicon oxide is located between the p-type semiconductor region (first semiconductor layer 2 in one embodiment) and the first passivation layer 9 including the aluminum oxide layer. May be good. This can improve the passivation performance. Here, for example, if the thickness of the second passivation layer is about 0.1 nm to 1 nm, even if the second passivation layer has a positive fixed charge, the presence of the second passivation layer causes the first passivation layer 9 to be present. Passivation effect is less likely to decrease.

Further, for example, a third passivation layer containing silicon oxide may be located between the first passivation layer 9 and the protective layer 11. In this case, since the third passivation layer functions as a buffer layer for joining the protective layer 11 and the first passivation layer, the adhesion between the protective layer 11 and the passivation layer is improved. When the thickness of the third passivation layer is, for example, about 5 nm to 15 nm, even if the third passivation layer has a positive fixed charge, the passivation effect of the first passivation layer 9 is less likely to decrease.

Further, for example, the third electrode 8 may be located on the second surface 1b of the solar cell element 10 in a state having the same shape as the current collector electrode 6b, and may be connected to the second electrode 7. .. If such a structure is adopted, the reflected light from the ground or the like incident on the back surface side of the solar cell module can also contribute to the power generation in the solar cell element 10. This can improve the output of the solar cell module.

<1-4. Manufacturing method of solar cell element>
An example of a method for manufacturing the solar cell element 10 will be described with reference to FIGS. 5 (a) to 5 (f).

First, for example, as shown in FIG. 5A, the semiconductor substrate 1 is prepared. The semiconductor substrate 1 is formed by, for example, an existing CZ method or a casting method. Here, an example in which a p-type polycrystalline silicon substrate is used as the semiconductor substrate 1 will be described.

First, for example, an ingot of polycrystalline silicon is produced by a casting method. Next, the ingot is sliced to a thickness of, for example, 250 μm or less to prepare the semiconductor substrate 1. Then, in order to remove the mechanically damaged layer and the contaminated layer on the cut surface of the semiconductor substrate 1, the surface of the semiconductor substrate 1 is subjected to an aqueous solution such as sodium hydroxide, potassium hydroxide, hydrofluoric acid or nitric acid. It may be etched in a very small amount.

Next, as shown in FIG. 5B, a texture is formed on the first surface 1a of the semiconductor substrate 1. The texture can be formed by wet etching using an alkaline aqueous solution such as sodium hydroxide or an acidic aqueous solution such as fluorinated nitric acid, or dry etching using a reactive ion etching (RIE) method or the like.

Next, for example, as shown in FIG. 5 (c), the second semiconductor layer 3 which is an n-type semiconductor region is formed on the first surface 1a of the semiconductor substrate 1 having the texture formed by the above step. Form. Specifically, the n-type second semiconductor layer 3 is formed on the surface layer portion on the first surface 1a side of the textured semiconductor substrate 1.

The second semiconductor layer 3 is, for example, _{a coating heat diffusion method in which a paste-like diphosphorus pentoxide (P 2} O ₅ ) is applied to the surface of the semiconductor substrate 1 to thermally diffuse phosphorus, and a gaseous phosphorus oxychloride. It can be formed by using a vapor phase heat diffusion method or the like using (POCl _{3) as a diffusion source.} The second semiconductor layer 3 is formed so as to have, for example, a depth of about 0.1 μm to 2 μm and a sheet resistance value of about 40 Ω / □ to 200 Ω / □. Here, for example, in the vapor phase thermal diffusion method, first, the semiconductor substrate 1 is heat-treated for about 5 to 30 minutes at a temperature of about 600 ° C. to 800 ° C. in an atmosphere having a diffusion gas mainly containing _{POCl 3 or the like.} This is applied to form phosphorous glass on the surface of the semiconductor substrate 1. Then, the semiconductor substrate 1 is heat-treated for about 10 to 40 minutes at a relatively high temperature of about 800 ° C. to 900 ° C. in an atmosphere of an inert gas such as argon or nitrogen. As a result, phosphorus is diffused from the phosphorus glass to the semiconductor substrate 1, and the second semiconductor layer 3 is formed on the surface layer portion on the first surface 1a side of the semiconductor substrate 1.

Here, when the second semiconductor layer 3 is formed, the second semiconductor layer may also be formed on the second surface 1b side. In this case, the second semiconductor layer formed on the second surface 1b side is removed by etching. For example, by immersing the portion of the semiconductor substrate 1 on the second surface 1b side in an aqueous solution of fluorine nitric acid, the second semiconductor layer formed on the second surface 1b side can be removed. As a result, the region having the p-type conductive mold can be exposed on the second surface 1b side of the semiconductor substrate 1. Then, when the second semiconductor layer 3 is formed, the phosphorus glass adhering to the first surface 1a side of the semiconductor substrate 1 is removed by etching.

In this way, if the second semiconductor layer formed on the second surface 1b side is removed by etching with the phosphorus glass remaining on the first surface 1a side, the second semiconductor layer 3 on the first surface 1a side is removed. Removal and damage can be reduced. At this time, the second semiconductor layer formed on the side surface 1c of the semiconductor substrate 1 may also be removed.

Further, for example, a diffusion mask may be formed in advance on the second surface 1b side of the semiconductor substrate 1, a second semiconductor layer 3 may be formed by a vapor phase thermal diffusion method or the like, and then the diffusion mask may be removed. In this case, since the second semiconductor layer is not formed on the second surface 1b side, the step of removing the second semiconductor layer formed on the second surface 1b side of the semiconductor substrate 1 becomes unnecessary.

By the above processing, the polycrystal containing the first semiconductor layer 2 in which the second semiconductor layer 3 which is an n-type semiconductor layer is located on the first surface 1a side and has a texture on the first surface 1a. The semiconductor substrate 1 can be prepared.

Next, for example, as shown in FIG. 5D, aluminum oxide is mainly contained on the first surface 1a of the first semiconductor layer 2 and on the second surface 1b of the second semiconductor layer 3. The first passivation layer 9 is formed. Further, the antireflection layer 5 is formed on the first passivation layer 9. The antireflection layer 5 is made of, for example, a silicon nitride film.

The first passivation layer 9 can be formed by, for example, the ALD method. According to the ALD method, for example, the first passivation layer 9 can be formed all around the semiconductor substrate 1 including the side surface 1c. In the formation of the first passivation layer 9 by the ALD method, first, the semiconductor 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 semiconductor substrate 1 is heated to a temperature range of about 100 ° C. to 250 ° C., the following steps A to D are repeated a plurality of times to form the first passivation layer 9 mainly containing aluminum oxide. As a result, the first passivation layer 9 having a desired thickness is formed.

Further, a second passivation layer containing silicon oxide may be formed between the first semiconductor layer 2 and the first passivation layer 9 including the aluminum oxide layer by an ALD method or the like. Also in this case, the second step, which mainly contains silicon oxide, is repeated a plurality of times from the next steps A to D with the semiconductor substrate 1 heated in the temperature range of about 100 ° C. to 250 ° C. in the same manner as described above. Form a passivation layer. The contents of each process from the process A to the process D are as follows.

[Step A] A silicon raw material such as bisdiethylaminosilane (BDEAS) for forming a layer of silicon oxide, or an aluminum raw material such as trimethylaluminum (TMA) for forming a layer of aluminum oxide is an argon gas or a nitrogen gas. It is supplied on the semiconductor substrate 1 together with the carrier gas such as. As a result, the silicon raw material or the aluminum raw material is adsorbed all around the semiconductor substrate 1. The time for supplying BDEAS or TMA is, for example, about 15 ms to 3000 ms.

Here, at the start of step A, the surface of the semiconductor substrate 1 may be terminated with an OH group. In other words, the surface of the semiconductor substrate 1 may have a Si—O—H structure. This structure can be formed, for example, by treating the semiconductor substrate 1 with dilute hydrofluoric acid and then washing it with pure water.

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

[Step C] When an oxidizing agent such as water or ozone gas is supplied into the chamber of the film forming apparatus, the alkyl group contained in BDEAS or TMA is removed and replaced with an OH group. As a result, an atomic layer of silicon oxide or aluminum oxide is formed on the semiconductor substrate 1. The time for supplying the oxidant into the chamber is, for example, about 750 ms to 1100 ms. Further, for example, if hydrogen is supplied to the chamber together with an oxidizing agent, hydrogen atoms are more likely to be contained in silicon oxide or aluminum oxide.

[Step D] The oxidant in the chamber is removed by purifying the inside of the chamber of the film forming apparatus with nitrogen gas. At this time, for example, an oxidizing agent or the like that did not contribute to the reaction at the time of forming the atomic layer level silicon oxide or aluminum oxide on the semiconductor substrate 1 is removed. Here, the time for purifying the inside of the chamber by the nitrogen gas is, for example, about 1 second to several tens of seconds.

After that, by repeating a series of steps in which step A, step B, step C, and step D are performed in the order described in this manner a plurality of times, a layer of silicon oxide or a layer of aluminum oxide having a desired film thickness is formed.

The antireflection layer 5 is formed by using, for example, a PECVD (Plasma-Enhanced Chemical Vapor Deposition) method or a sputtering method. When the PECVD method is used, the semiconductor substrate 1 is preheated to a temperature higher than the temperature during film formation of the antireflection layer 5. After that, the mixed gas of _{silane (SiH 4} ) and ammonia (NH _{3 ) was diluted with nitrogen (N 2} ) gas, the reaction pressure was changed from 50 Pa to 200 Pa, and the gas was converted into plasma by glow discharge decomposition. It is deposited on the heated semiconductor substrate 1. As a result, the antireflection layer 5 is formed on the semiconductor substrate 1. At this time, the film forming temperature is set to about 350 ° C. to 650 ° C., and the preheating temperature of the semiconductor substrate 1 is set to be about 50 ° C. higher than the film forming temperature. Further, a frequency of about 10 kHz to 500 kHz is adopted as the frequency of the high frequency power supply required for glow discharge. Further, the gas flow rate is appropriately determined depending on the size of the reaction chamber and the like. For example, the flow rate of the gas is in the range of about 150 ml / min (sccm) to 6000 ml / min (sccm). At this time, the value (B / A) obtained by dividing the flow rate B of the ammonia gas by the flow rate A of the silane gas is in the range of 0.5 to 15.

Next, for example, as shown in FIG. 5 (e), the protective layer 11 is formed on at least a part of the first passivation layer 9. For example, first, the above-mentioned insulating paste is applied to at least a part of the first passivation layer 9 so as to have a desired pattern by using a screen printing method or the like. Next, the coated insulating paste is dried using a hot plate, a drying oven, or the like under the conditions that the maximum temperature is about 150 ° C. to 350 ° C. and the heating time is about 1 minute to 10 minutes. As a result, the protective layer 11 having a desired pattern is formed on the first passivation layer 9. If the protective layer 11 is formed under such conditions, the first passivation layer 9 covered with the protective layer 11 will not be fired through at the time of forming the third electrode 8 described later, and the passivation effect will not be easily reduced. ..

Here, if the low molecular weight component of the siloxane resin remains in the protective layer 11, the low molecular weight component of the siloxane resin volatilizes in the firing step of the metal paste for forming the third electrode 8 described later. It's easy to do. At this time, the small molecule component of the volatilized siloxane resin adheres between the metal powders for forming the third electrode 8 and inhibits the sintering of the metal powders. Therefore, the electric resistance of the third electrode 8 formed by firing may increase. Further, when the small molecule component of the siloxane resin volatilizes, voids may occur in the protective layer 11. On the other hand, if the protective layer 11 is produced by using the insulating paste containing chlorine, the step of drying the insulating paste for forming the protective layer 11 and the step for forming the third electrode 8 can be achieved. In the step of firing the metal paste, the low molecular weight component of the siloxane resin remaining in the protective layer 11 tends to cause a reaction of condensation polymerization. As a result, the small molecule component of the siloxane resin remaining in the protective layer 11 is reduced. As a result, in the solar cell element 10 according to the embodiment, the electric resistance of the third electrode 8 is less likely to increase, and voids are less likely to be generated in the protective layer 11.

Further, the protective layer 11 may be prepared by using an insulating paste containing any one or more of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium.

Further, the protective layer 11 may be produced by using an insulating paste containing fluorine. In this case, the siloxane resin remaining in the protective layer 11 in the step of drying the insulating paste for forming the protective layer 11 and the step of firing the metal paste for forming the third electrode 8. Low molecular weight components are likely to cause a condensation polymerization reaction. As a result, the small molecule component of the siloxane resin remaining in the protective layer 11 is reduced. As a result, the electric resistance of the third electrode 8 is less likely to increase, and voids are less likely to be formed in the protective layer 11.

Further, after applying the first insulating paste containing chlorine, a second insulating paste having a higher chlorine content than the first insulating paste may be applied. As a result, in the protective layer 11, the chlorine content may be higher in the portion located on the third electrode 8 side than in the portion located on the first passivation layer 9 side. In this case, since the chlorine content is high in the portion of the protective layer 11 on the third electrode 8 side, voids due to volatilization of the low molecular weight component of the siloxane resin are unlikely to occur. This makes it difficult for the protective layer 11 and the first passivation layer 9 to be fired through, for example, when the aluminum paste is fired. As a result, the output characteristics of the solar cell element 10 are unlikely to deteriorate. Further, even if the small molecule component of the siloxane resin remaining in the protective layer 11 is likely to volatilize, it remains in the protective layer 11 due to the portion of the protective layer 11 on the third electrode 8 side. The phenomenon that the small molecule component of the siloxane resin volatilizes and flows out to the outside is less likely to occur. Then, the low molecular weight component of the siloxane resin that does not flow out to the outside of the solar cell element 10 is likely to undergo hydrolysis and condensation polymerization due to the chlorine in the protective layer 11. As a result, the barrier property of the protective layer 11 is likely to be improved.

Further, here, for example, the first insulating paste contains more than one or more of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium than the second insulating paste. You may. In this case, in the protective layer 11, in the portion located on the first passivation layer 9 side, boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium are more than those located on the third electrode 8 side. The content of any one or more may be high. Therefore, for example, even in a situation where voids are likely to occur in the protective layer 11, boron, vanadium, iron, zinc, bismuth, lead, and the like can be found in the portion of the protective layer 11 located on the first passivation layer 9 side. One or more components of tin and magnesium are likely to bind to the components of the protective layer 11. As a result, voids are less likely to occur in the portion of the protective layer 11 on the first passivation layer 9 side. As a result, the first passivation layer 9 is less likely to be fired through.

The protective layer 11 may be formed on the second surface 1b side of the semiconductor substrate 1 at a position other than the position where the third electrode 8 comes into contact with the second surface 1b. If the protective layer 11 is formed according to a desired pattern having a plurality of holes 12 on the first passivation layer 9, the step of removing the protective layer 11 by irradiation with a laser beam or the like becomes unnecessary, and the solar cell element 10 becomes unnecessary. Productivity can be improved.

Here, the coating amount of the insulating paste is, for example, the size of the uneven shape of the second surface 1b of the semiconductor substrate 1, the type or content of the glass frit contained in the aluminum paste for forming the third electrode 8. And, it is appropriately changed depending on the firing conditions at the time of forming the third electrode 8.

Next, for example, as shown in FIG. 5 (f), the first electrode 6, the second electrode 7, and the third electrode 8 are formed.

The first electrode 6 is made by using, for example, a metal powder containing silver as a main component, an organic vehicle, and a first metal paste (silver paste) containing glass frit. First, this first metal paste is applied to the first surface 1a side of the semiconductor substrate 1. After that, for example, the first metal paste is fired under the condition that the maximum temperature is about 600 ° C. to 850 ° C. and the heating time is about several tens of seconds to several tens of minutes in the firing furnace. The electrode 6 is formed. Here, the application of the first metal paste can be realized by, for example, screen printing. Then, after the application of the first metal paste, the solvent in the first metal paste may be evaporated and dried at a predetermined temperature. If the first metal paste is applied by screen printing, for example, the output take-out electrode 6a and the current collector electrode 6b included in the first electrode 6 can be formed in one step.

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

The third electrode 8 is produced, for example, by using a metal powder containing aluminum as a main component, an organic vehicle, and a third metal paste (aluminum paste) containing glass frit. Here, first, the third metal paste is applied to the second surface 1b side of the semiconductor substrate 1 so as to come into contact with a part of the second metal paste applied in advance. At this time, the third metal paste may be applied to almost the entire surface of the second surface 1b of the semiconductor substrate 1 except for a part of the portion where the second electrode 7 is formed. Here, the application of the third metal paste can be realized by, for example, screen printing. Here, after the third metal paste is applied, the solvent in the third metal paste may be evaporated and dried at a predetermined temperature. After that, for example, the third electrode 8 is fired under the condition that the maximum temperature is set to 600 ° C. to 850 ° C. and the heating time is set to about several tens of seconds to several tens of minutes in the firing furnace. Is formed on the second surface 1b side of the semiconductor substrate 1. At this time, by firing, the third metal paste fires through the first passivation layer 9 and connects to the first semiconductor layer 2. As a result, the third electrode 8 is formed. Further, with the formation of the third electrode 8, the third semiconductor layer 4 is also formed. However, at this time, the third metal paste on the protective layer 11 is blocked by the protective layer 11. Therefore, when the third metal paste is fired, the first passivation layer 9 blocked by the protective layer 11 is less likely to deteriorate.

By the above steps, the solar cell element 10 can be manufactured. As described above, according to the method for manufacturing the insulating paste and the solar cell element according to the embodiment, the protective layer 11 is less likely to be fired through. As a result, for example, the first passivation layer 9 is less likely to deteriorate. As a result, it is possible to provide a highly reliable solar cell element 10.

<2. Others>
In the above embodiment, for example, the second electrode 7 may be formed after the third electrode 8 is formed. The second electrode 7 does not need to be in direct contact with, for example, the semiconductor substrate 1. Further, for example, the first passivation layer 9 does not need to be present between the second electrode 7 and the semiconductor substrate 1, and the second electrode 7 may be in direct contact with the semiconductor substrate 1. Further, for example, the second electrode 7 may be located on the protective layer 11.

Further, in the above embodiment, for example, the first electrode 6, the second electrode 7, and the third electrode 8 may be formed by applying a metal paste for forming each of them and then firing them at the same time. As a result, the productivity of the solar cell element 10 can be further improved, and the output characteristics of the solar cell element 10 can be improved by reducing the thermal history of the semiconductor substrate 1.

Further, in the above embodiment, for example, the protective layer 11 may be formed by a film forming method such as a sputtering method or a CVD method. In this case, for example, a gas containing chlorine may be introduced into the atmosphere for forming the protective layer 11. Further, for example, the atmosphere for forming the protective layer 11 contains a gas containing one or more of boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium, or fluorine. Gas may be introduced.

1 Semiconductor substrate 1a 1st surface 1b 2nd 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 2nd electrode 8 3rd electrode 9 1st passivation layer 10 Solar cell element 11 Protective layer 12 Holes

Claims (6)

With a semiconductor substrate,
The passivation layer located on the semiconductor substrate,
A protective layer located above the passivation layer and containing a siloxane resin and chlorine in the form of hydrochloric acid or chloride.
A solar cell element comprising an electrode located on the protective layer. The solar cell element according to claim 1, wherein the concentration of chlorine in the portion of the protective layer located on the electrode side is higher than the concentration of chlorine in the portion located on the passivation layer side. The solar cell element according to claim 1 or 2, wherein the passivation layer contains chlorine or fluorine. One of claims 1 to 3, wherein the protective layer contains one or more elements selected from boron, vanadium, iron, zinc, bismuth, lead, tin and magnesium. The solar cell element described in. The solar cell according to claim 4, wherein the portion of the protective layer located on the passivation layer side has a higher concentration of one or more elements than the portion located at the center in the thickness direction of the protective layer. element. The solar cell element according to any one of claims 1 to 5, wherein the protective layer further contains fluorine.

Images