Solar cell

Abstract

Provided is a highly efficient crystalline silicon solar cell having a high open circuit voltage (Voc) and a fill factor (FF). A solar cell according to the present invention comprises: a crystalline silicon substrate (1) including an impurity diffusion layer; a passivation film (2) disposed on at least a portion of the impurity diffusion layer of the substrate (1); the solar cell includes a substrate (1), a passivation film (2) including silver (Ag), and an electrode (20) including silver (Ag) and disposed on at least a portion of the passivation film (2), the solar cell further includes at least one AgSi region (30) disposed on at least a portion between the electrode (20) and the substrate (1), and the AgSi region (30) includes at least one AgSi region (30) having a depth of 100 nm or more. In a scanning electron microscope photograph of a 5.7 [mu] m * 3.9 [mu] m cross section including the AgSi region (30) of the solar cell, the remaining rate of the passivation film (2), which is the ratio of the remaining length of the passivation film (2), is 10-90%.

Description

Technical Field

[0001] The present invention relates to a crystalline silicon solar cell using a crystalline silicon substrate. Background Art

[0002] In semiconductor devices such as crystalline silicon solar cells that use crystalline silicon obtained by processing single-crystalline silicon or polycrystalline silicon into a flat plate as a substrate, in order to make electrical contact between the device and the outside, electrodes are usually formed on the surface of the silicon substrate using a conductive paste for electrode formation. In semiconductor devices formed with electrodes in this way, in recent years, the production volume of crystalline silicon solar cells has increased significantly. These solar cells have an impurity diffusion layer, an antireflection film (passivation film), and a light incident side surface electrode on one surface of the crystalline silicon substrate, and a back electrode on the other surface. Using the light incident side surface electrode and the back electrode, the electric power generated by the crystalline silicon solar cell can be taken out to the outside.

[0003] In the formation of electrodes for conventional crystalline silicon solar cells, a conductive paste containing conductive powder, glass frit, organic binder, solvent, and other additives is used. As the conductive powder, silver particles (silver powder) are mainly used.

[0004] In Patent Document 1, a manufacturing method of a crystalline silicon solar cell is described. Patent Document 1 describes that, for the formation of electrodes of a crystalline silicon solar cell, a conductive paste for electrode formation containing an inorganic material is used. Patent Document 1 describes that the inorganic material contains conductive particles and glass frit.

[0005] In Patent Document 2, a process for improving the ohmic contact behavior between the contact grid and the emitter layer in a silicon solar cell is described. Specifically, the process of Patent Document 2 is described as follows: a given voltage is applied in a direction opposite to the forward direction of the silicon solar cell, and a point light source is directed to the sun side of the silicon solar cell, thereby irradiating the cross section of the sub-segment on the sun side.

[0006] In Patent Document 3, a conductive composition for forming an electrode of a solar cell, which contains silver powder, glass powder containing PbO, and a carrier composed of an organic substance, is described. Patent Document 3 describes a conductive composition for forming an electrode that conducts through a silicon nitride layer and is in contact with an n-type semiconductor layer formed under the silicon nitride layer. In addition, Patent Document 3 describes that the basicity of the glass powder contained in the conductive composition is 0.6 or more and 0.8 or less, and the glass transition temperature is 300°C to 450°C.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Laid-Open No. 2011-86754

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2021-513218

[0011] Patent Document 3: Japanese Patent Laid-Open No. 2009-231826 Summary of the Invention

[0012] Figure 5 shows an example of a cross-sectional schematic diagram of a general crystalline silicon solar cell. As Figure 5 shown, in a general crystalline silicon solar cell, using a screen printing method or the like, an electrode pattern of a light incident side surface electrode 20 (surface electrode) is printed on a passivation film 2 that functions as a passivation film 2 using a conductive paste, the conductive paste is dried, and firing is performed at a given temperature, thereby forming the light incident side surface electrode 20. In a general crystalline silicon solar cell, during firing at the given temperature, the conductive paste burns through the passivation film 2. Through this burning through, the light incident side surface electrode 20 can be formed in contact with the impurity diffusion layer 4. It should be noted that the so-called burning through means etching the passivation film 2 that serves as an insulating film with the glass frit or the like contained in the conductive paste to make the light incident side surface electrode 20 conduct with the impurity diffusion layer 4. Figure 5 In the example shown, during firing of the electrode pattern, the electrode pattern burns through the passivation film 2, whereby the passivation film 2 disappears and the light incident side surface electrode 20 comes into contact with the impurity diffusion layer 4. A pn junction is formed at the interface between the n-type crystalline silicon substrate 1 and the impurity diffusion layer 4. Most of the incident light incident on the crystalline silicon solar cell passes through the passivation film 2 and the impurity diffusion layer 4 and then enters the n-type crystalline silicon substrate 1. In this process, light is absorbed in the n-type crystalline silicon substrate 1, generating electron-hole pairs. Due to the action of the electric field caused by the pn junction, electrons are separated from the n-type crystalline silicon substrate 1 to the back electrode 15, and holes are separated from the p-type impurity diffusion layer 4 to the light incident side surface electrode 20. Electrons and holes (carriers) are taken out to the outside in the form of an electric current via these electrodes.

[0013] Figure 2 shows an example of a schematic diagram of the light incident side surface of a crystalline silicon solar cell. As Figure 2 shown, on the light incident side surface of the crystalline silicon solar cell, as the light incident side surface electrode 20, a main grid electrode (light incident side main grid electrode 20a) and a light incident side sub-grid electrode 20b (sometimes simply referred to as "sub-grid electrode 20b") are arranged. Figure 5 and Figure 2In the example shown, electrons in electron-hole pairs generated by incident light incident on the crystalline silicon solar cell gather at the sub-grid electrode 20b and then at the light-incident side main-grid electrode 20a. At the light-incident side main-grid electrode 20a, a metal solder tape for interconnection covered with solder around it is welded, and the current is taken out to the outside using this metal solder tape.

[0014] The photoelectric conversion efficiency of a solar cell (sometimes simply referred to as "conversion efficiency") is expressed as the product of the fill factor (Fill Factor: FF), open circuit voltage (Open Circuit Voltage: Voc), and short circuit current (Short Circuit Current: Jsc). Basically, the fill factor (FF) and the open circuit voltage (Voc) are in an inverse relationship, and it is difficult to improve both the fill factor and the open circuit voltage simultaneously.

[0015] In order to obtain a crystalline silicon solar cell with high conversion efficiency, especially a high fill factor (FF), a low contact resistance between the light-incident side surface electrode 20 and the impurity diffusion layer 4 is required.

[0016] In addition, in the case of a conventional crystalline silicon solar cell, when forming the light-incident side surface electrode 20, the electrode pattern of the conductive paste is fired, thereby burning through the passivation film 2 and contacting the impurity diffusion layer 4. At the time of this burning through, damage occurs in the impurity diffusion layer 4, resulting in a problem that the performance of the crystalline silicon solar cell (especially the open circuit voltage (Voc)) decreases.

[0017] As described above, it is generally difficult to improve both the fill factor and the open circuit voltage simultaneously. On the other hand, if the structure between the electrode and the substrate necessary for obtaining a high-efficiency crystalline silicon solar cell with a high open circuit voltage (Voc) and fill factor (FF) is clarified, guidelines for manufacturing a high-efficiency crystalline silicon solar cell can be obtained.

[0018] Therefore, an object of the present invention is to provide a high-efficiency crystalline silicon solar cell having a high open circuit voltage (Voc) and fill factor (FF). In particular, for the purpose of obtaining a high-efficiency crystalline silicon solar cell having a high open circuit voltage (Voc) and fill factor (FF), the present invention aims to provide a crystalline silicon solar cell in which the structure between the electrode and the above substrate is a given structure.

[0019] In order to solve the above problems, the present invention has the following configuration.

[0020] (Configuration 1)

[0021] Configuration 1 is a solar cell, which includes:

[0022] A substrate, which includes crystalline silicon and has an impurity diffusion layer on at least one surface;

[0023] A passivation film, which is disposed on at least a part of the impurity diffusion layer of the above substrate; and

[0024] An electrode, which includes silver (Ag) and is disposed on at least a part of the above passivation film,

[0025] The above solar cell further includes at least one AgSi region disposed on at least a part between the above electrode and the above substrate,

[0026] The above AgSi region includes at least one AgSi region with a depth of 100 nm or more,

[0027] In a scanning electron microscope photograph of a 5.7 μm × 3.9 μm cross-section of the above solar cell including the above AgSi region, the ratio of the remaining length of the above passivation film, i.e., the remaining rate of the passivation film, is 10 to 90%.

[0028] (Constitution 2)

[0029] Constitution 2 is the solar cell of Constitution 1 as follows, that is, the ratio Db / Da of the film thickness Da just after the formation of the above passivation film to the film thickness Db of the above passivation film in a scanning electron microscope photograph of a 5.7 μm × 3.9 μm cross-section of the above solar cell formed with the above electrode on the surface and completed is 15% to 85%.

[0030] (Constitution 3)

[0031] Constitution 3 is the solar cell of Constitution 1 or 2 as follows, that is, the above electrode further includes 0.1 to 5.0 parts by weight of a glass frit with respect to 100 parts by weight of the silver (Ag) contained in the above electrode.

[0032] (Constitution 4)

[0033] Constitution 4 is the solar cell of Constitution 3 as follows, that is, the glass transition temperature of the above glass frit is 250 to 600 °C.

[0034] (Constitution 5)

[0035] Constitution 5 is the solar cell of Constitution 3 or 4 as follows, that is, the above glass frit contains a substance selected from SiO 2 、B 2 O 3 、V 2 O 5 、Bi 2 O 3 、TeO 2 、Li2 At least one of O and ZnO.

[0036] (Constitution 6)

[0037] Constitution 6 is a solar cell of any one of Constitutions 3 to 5 below, that is, the above-mentioned frit substantially does not contain PbO.

[0038] (Constitution 7)

[0039] Constitution 7 is a solar cell of any one of Constitutions 1 to 6 below, that is, the above-mentioned electrode substantially does not contain lead (Pb).

[0040] (Constitution 8)

[0041] Constitution 8 is a solar cell of any one of Constitutions 1 to 7 below, that is, the above-mentioned electrode substantially does not contain aluminum particles.

[0042] (Constitution 9)

[0043] Constitution 9 is a solar cell of any one of Constitutions 1 to 8 below, that is, the above-mentioned substrate is the above-mentioned crystalline silicon substrate of the first conductivity type,

[0044] The above-mentioned impurity diffusion layer is an impurity diffusion layer of the second conductivity type,

[0045] The above-mentioned electrode is a light incident side surface electrode disposed on the light incident side surface,

[0046] The above-mentioned solar cell further includes a back electrode disposed in a manner of being electrically connected to the surface of the above-mentioned crystalline silicon substrate opposite to the above-mentioned light incident side surface,

[0047] The above-mentioned light incident side surface electrode is the above-mentioned light incident side surface electrode that has been subjected to the following treatment, that is, while applying a voltage between the above-mentioned back electrode and the above-mentioned light incident side surface electrode so that a current flows in a direction opposite to the forward direction between the above-mentioned impurity diffusion layer of the second conductivity type and the above-mentioned crystalline silicon substrate of the first conductivity type, irradiating the above-mentioned light incident side surface of the above-mentioned solar cell with light from a point light source.

[0048] According to the present invention, it is possible to provide a highly efficient crystalline silicon solar cell having a high open circuit voltage (Voc) and fill factor (FF). In particular, according to the present invention, in order to obtain a highly efficient crystalline silicon solar cell having a high open circuit voltage (Voc) and fill factor (FF), it is possible to provide a crystalline silicon solar cell in which the structure between the electrode and the above-mentioned substrate is a given structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is an example of a cross-sectional schematic view of the crystalline silicon solar cell of the present embodiment.

[0050] Figure 2 This is an example of a schematic diagram of the light incident side surface of a crystalline silicon solar cell.

[0051] Figure 3 This is an example of a schematic diagram of the back surface of a crystalline silicon solar cell.

[0052] Figure 4 This is an example of a cross-sectional schematic diagram of a double-sided light receiving type crystalline silicon solar cell according to the present embodiment.

[0053] Figure 5 This is an example of a cross-sectional schematic diagram near the light incident side surface electrode (sub-grid electrode) of a normal crystalline silicon solar cell, and is a cross-sectional schematic diagram showing a state where the antireflection film (passivation film) between the electrode and the impurity diffusion layer has disappeared due to burning through.

[0054] Figure 6 This is a cross-sectional SEM (scanning electron microscope) photograph (magnification: 20,000 times) near the passivation film on the light incident side surface of the crystalline silicon solar cell of Example 3, and is a diagram for explaining the depth d of the AgSi region.

[0055] Figure 7 This is a cross-sectional SEM (scanning electron microscope) photograph (magnification: 20,000 times) near the passivation film on the light incident side surface of the crystalline silicon solar cell of Example 3, and is a diagram for explaining the residual ratio Lp / (Lp + Le) of the passivation film.

[0056] Figure 8 This is a cross-sectional SEM (scanning electron microscope) photograph (magnification: 20,000 times) near the passivation film on the light incident side surface of the crystalline silicon solar cell of Comparative Example 1. Detailed Embodiment

[0057] Hereinafter, embodiments of the present invention will be specifically described. It should be noted that the following embodiments are the ways when the present invention is embodied, and do not limit the present invention within its scope.

[0058] <Solar Cell>

[0059] Figure 1 This shows an example of a cross-sectional schematic diagram of the solar cell of the present embodiment. The solar cell of the present embodiment includes: a substrate containing crystalline silicon (crystalline silicon substrate 1), a passivation film 2, and an electrode (for example, a light incident side surface electrode 20). In addition, the solar cell of the present embodiment further includes at least one AgSi region 30 disposed at least partially between the electrode and the substrate.

[0060] <<Substrate>>

[0061] The solar cell of the present embodiment includes a substrate. The substrate of the solar cell of the present embodiment is a crystalline silicon substrate 1. Therefore, the solar cell of the present embodiment is a crystalline silicon solar cell.

[0062] In this specification, "crystalline silicon" includes single crystal and polycrystalline silicon. In addition, the so-called "crystalline silicon substrate" refers to a material in which crystalline silicon is formed into a shape suitable for element formation, such as a flat plate shape, in order to form semiconductor devices such as electrical components or electronic components. Any method can be used for the manufacturing method of crystalline silicon. For example, the Czochralski method can be used in the case of single crystal silicon, and the casting method can be used in the case of polycrystalline silicon. In addition, polycrystalline silicon ribbons produced by other manufacturing methods, such as the ribbon pulling method, and polycrystalline silicon formed on a different substrate such as glass can also be used as the crystalline silicon substrate 1. In addition, the so-called "crystalline silicon solar cell" refers to a solar cell manufactured using the crystalline silicon substrate 1. In this specification, the crystalline silicon substrate 1 is sometimes simply referred to as the "substrate".

[0063] In a general solar cell, as the material of the semiconductor substrate of the solar cell, crystalline silicon, silicon carbide, germanium, gallium arsenide, etc. can be used. From the aspects of the safety and cost of the solar cell, the material of the semiconductor substrate is preferably crystalline silicon (such as single crystal silicon and polycrystalline silicon).

[0064] The crystalline silicon substrate 1 of the solar cell of the present embodiment is an n-type crystalline silicon substrate 1 or a p-type crystalline silicon substrate 1 containing n-type or p-type impurities. As the n-type impurities contained in the n-type crystalline silicon substrate 1, group 13 elements such as boron (B), aluminum (Al), and gallium (Ga) can be cited. As the p-type impurities contained in the p-type crystalline silicon substrate 1, group 15 elements such as phosphorus (P), arsenic (As), and antimony (Sb) can be cited.

[0065] As Figure 1 shown, the solar cell of the present embodiment includes an impurity diffusion layer 4 on at least a part of at least one surface of the crystalline silicon substrate 1. In the case of the solar cell of the present embodiment, the impurity diffusion layer 4 formed on the light incident side surface is a p-type or n-type impurity diffusion layer 4. It should be noted that in this specification, as Figure 1 shown, the part of the substrate where the impurity diffusion layer 4 is not formed is sometimes referred to as the "substrate main body 6".

[0066] In this specification, in crystalline silicon containing n-type or p-type impurities, one conductivity type (n-type or p-type) is referred to as the first conductivity type, and the other conductivity type (p-type or n-type), which is not the first conductivity type, is referred to as the second conductivity type. When the crystalline silicon substrate 1 is of the first conductivity type, the impurity diffusion layer 4 is an impurity diffusion layer 4 of the second conductivity type. Specifically, when the crystalline silicon substrate 1 is an n-type crystalline silicon substrate 1 containing n-type impurities, the impurity diffusion layer 4 formed on at least one surface of the crystalline silicon substrate 1 is a p-type impurity diffusion layer 4. In addition, when the crystalline silicon substrate 1 is a p-type crystalline silicon substrate 1 containing p-type impurities, the impurity diffusion layer 4 formed on at least one surface of the crystalline silicon substrate 1 is an n-type impurity diffusion layer 4. By selecting the first and second conductivity types in this way, a pn junction can be formed near the surface of the crystalline silicon substrate 1 on which the impurity diffusion layer 4 is formed.

[0067] The first conductivity type crystalline silicon substrate 1 of the solar cell of this embodiment is preferably an n-type crystalline silicon substrate 1. In addition, the second conductivity type impurity diffusion layer 4 of the solar cell of this embodiment is preferably a p-type impurity diffusion layer 4. Generally speaking, the mobility of electrons as carriers in the n-type crystalline silicon substrate 1 is higher than the mobility of holes as carriers in the p-type crystalline silicon substrate 1. Therefore, in order to obtain a solar cell with high conversion efficiency, it is advantageous to use an n-type crystalline silicon substrate 1.

[0068] The sheet resistance of the impurity diffusion layer 4 is preferably 30 to 300 Ω / □ (square), 40 to 160 Ω / □ (square), and more preferably 45 to 120 Ω / □. In addition, the depth at which the impurity diffusion layer 4 is formed can be 0.3 μm to 1.0 μm. It should be noted that the depth of the impurity diffusion layer 4 refers to the depth from the surface of the impurity diffusion layer 4 to the pn junction. The depth of the pn junction can be set to the depth from the surface of the impurity diffusion layer 4 to the depth at which the impurity concentration in the impurity diffusion layer 4 is the same as the impurity concentration of the substrate main body 6.

[0069] It should be noted that in this specification, the impurity diffusion layer 4 of the crystalline silicon solar cell of this embodiment is sometimes referred to as the "silicon emitter layer".

[0070] <<Passivation film 2>>

[0071] The solar cell of this embodiment includes a passivation film 2. The passivation film 2 is disposed on at least a part of the impurity diffusion layer 4 of the substrate.

[0072] The passivation film 2 can have the function of an antireflection film. In this specification, the passivation film 2 formed on the light incident side surface of the crystalline silicon substrate 1 is sometimes referred to as the antireflection film.

[0073] The passivation film 2 can be a film composed of a single layer or multiple layers. When the passivation film 2 is a single layer, from the aspect of being able to effectively passivate the surface of the silicon substrate, a thin film (SiN film) made of silicon nitride (SiN) is preferably used. Additionally, when the passivation film 2 is multiple layers, it can be a laminated film of a thin film made of silicon nitride and a thin film made of silicon oxide (SiN / SiO x film). It should be noted that when the SiN / SiO x film is the passivation film 2, from the aspect of being able to more effectively passivate the surface of the silicon substrate, it is preferable to form the SiO x film in a manner that the SiO x film contacts the silicon substrate 1, and form the SiN film on the SiO x film. The SiO x film can be the natural oxide film of the silicon substrate.

[0074] Figure 5 FIG. shows an example of a cross-sectional schematic diagram of a typical crystalline silicon solar cell. As Figure 5 shown, in a typical crystalline silicon solar cell, a passivation film 2 (antireflection film) is formed on the impurity diffusion layer 4. In addition, an electrode pattern of the light incident side surface electrode 20 (surface electrode) is printed on the passivation film 2 using a conductive paste such as the screen printing method, the conductive paste is dried, and fired at a given temperature, thereby forming the light incident side surface electrode 20. In a typical crystalline silicon solar cell, during firing at the given temperature, the conductive paste burns through the passivation film 2. In a typical crystalline silicon solar cell, by using this burn-through, the light incident side surface electrode 20 can be formed in electrical contact with the impurity diffusion layer 4. It should be noted that the so-called burn-through means etching the passivation film 2 that serves as an insulating film with the glass frit etc. contained in the conductive paste to make the light incident side surface electrode 20 conduct with the impurity diffusion layer 4. Figure 5 In the example of the typical crystalline silicon solar cell shown in FIG., during firing of the electrode pattern, the electrode pattern burns through the passivation film 2, thereby the passivation film 2 disappears and the light incident side surface electrode 20 contacts the impurity diffusion layer 4.

[0075] On the other hand, as Figure 1As shown, in the case of the crystalline silicon solar cell of the present embodiment, a passivation film 2 (antireflection film) exists in most of the region between the surface electrode 20 on the light incident side and the impurity diffusion layer 4. Therefore, in the case of the crystalline silicon solar cell of the present embodiment, most of the passivation film 2 in the portion in contact with the impurity diffusion layer 4 of the crystalline silicon substrate 1 can exist as it is in the portion other than the AgSi region 30 described later. Due to the presence of the passivation film 2, an increase in the surface defect density that causes carrier recombination can be prevented. As a result, the crystalline silicon solar cell of the present embodiment can obtain a high open-circuit voltage (Voc).

[0076] In the case of the crystalline silicon solar cell of the present embodiment, most of the passivation film 2 between the electrode and the impurity diffusion layer 4 also remains after firing for forming the electrode. In this specification, the degree of remaining of the passivation film 2 between the electrode after firing for forming the electrode and the crystalline silicon substrate 1 is expressed as the remaining rate of the passivation film 2. The remaining rate of the passivation film 2 will be described later.

[0077] <<Electrode>>

[0078] The solar cell of the present embodiment includes an electrode. The electrode of the solar cell of the present embodiment is disposed on at least a part of the passivation film 2. In addition, the electrode of the solar cell of the present embodiment contains silver (Ag).

[0079] As Figure 1 shown, on the light incident side surface of the crystalline silicon solar cell, a sub-grid electrode 20b is disposed as the light incident side surface electrode 20. Figure 1 In the example shown, holes in the electron-hole pairs generated by the incident light incident on the crystalline silicon solar cell gather at the sub-grid electrode 20b via the impurity diffusion layer 4 (for example, a p-type impurity diffusion layer 4). Therefore, a low contact resistance between the sub-grid electrode 20b and the impurity diffusion layer 4 is required.

[0080] It should be noted that Figure 1 shown, a back electrode 15 is disposed on the back surface of the crystalline silicon solar cell opposite to the light incident side surface. In this specification, the light incident side surface electrode 20 and the back electrode 15, which are electrodes for taking out current from the crystalline silicon solar cell to the outside, are sometimes simply referred to as "electrodes".

[0081] Figure 4 shows an example of a cross-sectional schematic view of the double-sided light-receiving type crystalline silicon solar cell (double-sided power generation type crystalline silicon solar cell) of the present embodiment. Figure 4 The crystalline silicon solar cell shown can generate electricity by incident light from two surfaces (the first and second light incident side surfaces).

[0082] Generally, the electrodes of crystalline silicon solar cells can be formed by printing a conductive paste using a method such as screen printing and then firing. In this specification, the conductive paste used to form the electrodes of the crystalline silicon solar cells of the present embodiment may be referred to as a given conductive paste. Generally, the conductive paste contains conductive particles and an organic carrier. In addition, the conductive paste may further contain a glass frit on the basis of the conductive particles and the organic carrier. The electrodes of the solar cells of the present embodiment contain silver (Ag). Therefore, the conductive particles contained in the given conductive paste need to contain silver (Ag). The organic carrier contained in the conductive paste burns out during the firing used to form the electrodes. Therefore, the fired electrodes contain the components contained in the conductive paste other than the organic carrier. Specifically, the fired electrodes contain a conductive component resulting from the conductive particles of the conductive paste. In addition, when the conductive paste contains a glass frit, the fired electrodes further contain a component resulting from the glass frit of the conductive paste.

[0083] From the aspect of obtaining low resistance and high reliability, the conductive component contained in the given electrodes of the crystalline silicon solar cells of the present embodiment is preferably composed only of silver. It should be noted that the conductive component composed only of silver may contain other metal elements as inevitably contained impurities.

[0084] In this specification, the glass frit is a substance mainly composed of various oxides, such as metal oxides, and is usually used in the form of glassy particles. During the firing used to form the electrodes, the glass frit softens and the particles bind to each other. In this specification, the component (oxide) resulting from the glass frit contained in the electrodes is also simply referred to as "glass frit".

[0085] In the solar cells of the present embodiment, the content of the glass frit contained in the electrodes is preferably 0.1 to 5.0 parts by weight, more preferably 0.2 to 4.0 parts by weight, further preferably 0.3 to 3.0 parts by weight, and particularly preferably 0.4 to 2.7 parts by weight with respect to 100 parts by weight of the content of silver (Ag) contained in the electrodes. By making the content of the glass frit within an appropriate range, the reactivity of the glass frit with the passivation film 2 can be made appropriate during the firing used to form the electrodes.

[0086] In the solar cells of the present embodiment, the glass transition temperature of the glass frit contained in the electrodes is preferably 250 to 600 °C, more preferably 270 to 500 °C, and further preferably 300 to 400 °C. By making the glass transition temperature (Tg) of the glass frit 250 °C or higher, the reactivity with the passivation film 2 can be suppressed. In addition, by making the glass transition temperature (Tg) 600 °C or lower, the contact resistance between the obtained electrodes (for example, the light incident side surface electrode 20) and the impurity diffusion layer 4 can be reduced.

[0087] In the solar cell of the present embodiment, the frit contained in the electrode preferably contains at least one selected from SiO 2 , B 2 O 3 , V 2 O 5 , Bi 2 O 3 , TeO 2 , BaO, CuO, Li 2 O and ZnO. In the solar cell of the present embodiment, the frit contained in the electrode more preferably contains at least one selected from SiO 2 , B 2 O 3 , V 2 O 5 , Bi 2 O 3 , TeO 2 , Li 2 O and ZnO. By including at least one of these oxides in the frit, the alkalinity of the frit can be adjusted to an appropriate range. By adjusting the alkalinity of the frit to an appropriate range, the reactivity of the frit with respect to the passivation film 2 can be made appropriate during firing for forming the electrode.

[0088] Although not particularly limited, in the solar cell of the present embodiment, the frit contained in the electrode may substantially not contain PbO. In addition, the electrode of the solar cell of the present embodiment may also substantially not contain lead (Pb). In the present specification, a lead-free frit means a frit that substantially does not contain lead (Pb). Since a frit is manufactured using metal oxides as raw materials, a lead-free frit means a frit that substantially does not contain lead oxide (PbO). When manufacturing a lead-free frit, materials containing lead (PbO) are not intentionally used. However, a lead-free frit may contain a trace amount of lead that is inevitably mixed in as an impurity. Specifically, the lead-free frit of the present embodiment may contain 0.1% by weight or less of lead as an impurity with respect to 100% by weight of the frit.

[0089] When manufacturing a conventional crystalline silicon solar cell, a glass frit contained in a conductive paste for forming an electrode is a glass frit containing lead oxide (PbO) (lead-containing glass frit). This is because, in the case of a conventional crystalline silicon solar cell, by making the conductive paste for forming an electrode contain a lead-containing glass frit, the contact resistance between the surface electrode 20 on the light incident side and the impurity diffusion layer 4 can be reduced. However, lead has an adverse effect on the human body. When using a lead-containing material to manufacture a product, lead may pollute the environment when the product is discarded. Therefore, when manufacturing a product, it is desirable to use a lead-free material that does not contain lead. Therefore, in the manufacturing process of a solar cell, it is preferable to use a lead-free glass frit. By using a lead-free glass frit, a solar cell having an electrode that substantially does not contain lead (Pb) can be manufactured. Therefore, pollution of the environment by lead can be suppressed.

[0090] In addition, in the present embodiment, materials other than the electrodes of the crystalline silicon solar cell of the present embodiment may also substantially not contain lead. In order to prevent lead from polluting the environment, the crystalline silicon solar cell of the present embodiment is preferably a lead-free solar cell.

[0091] The electrode of the solar cell of the present embodiment may further contain an aluminum component resulting from aluminum particles. The aluminum particles may be contained as particles different from (A) conductive particles. When the conductive paste for forming an electrode contains aluminum, the electrode also contains aluminum.

[0092] In the crystalline silicon substrate 1, aluminum has the property of being a p-type impurity. When the conductive paste printed on the crystalline silicon is fired, the aluminum in the conductive paste diffuses into the crystalline silicon and becomes a p-type impurity. Therefore, when forming an electrode on the surface of the p-type semiconductor layer of the crystalline silicon substrate 1, by making the conductive paste contain aluminum particles, a low contact resistance can be obtained between the electrode and the p-type semiconductor layer. Therefore, when forming an electrode on the surface of the p-type semiconductor layer of the crystalline silicon substrate 1, the conductive paste may contain aluminum particles.

[0093] On the other hand, since the conductive paste contains aluminum particles, the adhesiveness of the electrode to the p-type semiconductor layer is reduced, and there is a problem that the electrode is likely to peel off from the p-type semiconductor layer of the solar cell unit. That is, since the conductive paste contains aluminum particles, the reliability of the electrode with respect to the p-type semiconductor layer is greatly impaired.

[0094] In addition, in order to electrically connect a plurality of solar cell units, a metal solder strip for welding the electrodes of the solar cell is used. When the conductive paste for forming an electrode contains aluminum particles, there is a problem that the welding strength of the metal solder strip to the electrode is reduced.

[0095] According to the above description, the conductive paste of the present embodiment preferably contains aluminum particles in a given amount or less, or does not contain aluminum particles.

[0096] Specifically, the aluminum particles are as follows. In the conductive paste of the present embodiment, 0.5 parts by weight or less of aluminum particles are further contained relative to 100 parts by weight of the (A) silver particles, or no aluminum particles are contained. In addition, the upper limit of the content of the aluminum particles in the conductive paste of the present embodiment is preferably 0.3 parts by weight or less, more preferably less than 0.3 parts by weight, and further preferably contains 0.25 parts by weight or less relative to 100 parts by weight of the (A) silver particles. The conductive paste of the present embodiment may be a conductive paste that does not contain aluminum particles. It should be noted that the so-called "does not contain aluminum particles" means excluding the case of intentionally adding "aluminum particles", and does not exclude the case of containing aluminum components as inevitably mixed impurities.

[0097] In addition, in the present invention, when forming an electrode on the surface of the p-type semiconductor layer of the crystalline silicon substrate 1 by forming at least one AgSi region in at least a part between the electrode and the substrate, even if the electrode substantially does not contain aluminum, a low contact resistance can be obtained between the electrode and the p-type semiconductor layer.

[0098] On the other hand, when the conductive paste for forming an electrode contains aluminum, it has an impact from the viewpoint of reliability.

[0099] As Figure 2 and 3 shown, as an electrode of a crystalline silicon solar cell, it may have a light incident side main grid electrode 20a and / or a back surface TAB electrode 15a. The light incident side main grid electrode 20a has a function of electrically connecting the sub-grid electrode 20b for collecting the current emitted from the solar cell to the metal bonding wire for interconnection. Similarly, the back surface TAB electrode 15a has a function of electrically connecting the back surface full electrode 15b for collecting the current emitted from the solar cell to the metal bonding wire for interconnection. If the sub-grid electrode 20b contacts the crystalline silicon substrate 1, the surface defect density of the surface (interface) of the part of the crystalline silicon substrate 1 contacted by the sub-grid electrode 20b increases, and the performance of the solar cell decreases. In the crystalline silicon solar cell of the present embodiment, when forming the sub-grid electrode 20b, the passivation film 2 (antireflection film) is not completely burned through. Therefore, most of the passivation film 2 in the part contacting the crystalline silicon substrate 1 can be kept intact, and an increase in the surface defect density that causes carrier recombination can be prevented. As a result, a crystalline silicon solar cell with a high open circuit voltage (Voc) can be obtained.

[0100] Figure 1 The crystalline silicon solar cell shown may have Figure 3The back electrode 15 of the structure shown. The back electrode 15 is arranged so as to be electrically connected to the other surface of the semiconductor substrate of the first conductivity type. As Figure 3 shown, the back electrode 15 generally may include a back full-surface electrode 15b and a back TAB electrode 15a electrically connected to the back full-surface electrode 15b.

[0101] Figure 1 The main grid electrodes of the crystalline silicon solar cell shown include Figure 2 the light-incident side main grid electrode 20a shown and Figure 3 the back TAB electrode 15a shown. On the light-incident side main grid electrode 20a and the back TAB electrode 15a, a metal solder strip for interconnection covered with solder around is welded. Using this metal solder strip, the current generated by the solar cell is taken out to the outside of the crystalline silicon solar cell unit. Figure 4 The double-sided light-receiving type crystalline silicon solar cell shown may also have a light-incident side main grid electrode 20a and a back TAB electrode 15a having the same shape as the light-incident side main grid electrode 20a.

[0102] The width of the main grid electrodes (the light-incident side main grid electrode 20a and the back TAB electrode 15a) may be a width of the same degree as that of the metal solder strip for interconnection. In order to make the main grid electrode have a low resistance, a large width is preferred. On the other hand, in order to increase the incident area of light with respect to the light-incident side surface, it is preferable that the width of the light-incident side main grid electrode 20a is small. Therefore, the width of the main grid electrode may be set to 0.05 to 5 mm, preferably set to 0.08 to 3 mm, more preferably set to 0.1 to 2 mm, and further preferably set to 0.15 to 1 mm. In addition, the number of the main grid electrodes may be determined according to the size of the crystalline silicon solar cell. The number of the main grid electrodes is optional. Specifically, the number of the main grid electrodes may be set to 3 or 4, or more than that. The optimal number of the main grid electrodes can be determined by simulation of the operation of the solar cell so as to maximize the conversion efficiency of the crystalline silicon solar cell. It should be noted that since the crystalline silicon solar cells are connected in series with each other using the metal solder strip for interconnection, the number of the light-incident side main grid electrode 20a and the back TAB electrode 15a is preferably the same. For the same reason, the width of the light-incident side main grid electrode 20a and the back TAB electrode 15a is preferably the same.

[0103] In order to increase the incident area of light relative to the crystalline silicon solar cell, it is preferable that the area occupied by the light incident side surface electrode 20 on the light incident side surface be as small as possible. Therefore, the sub-grid electrode 20b on the light incident side surface is preferably as narrow as possible and preferably has as few numbers as possible. On the other hand, from the aspect of reducing electrical loss (ohmic loss), it is preferable that the width of the sub-grid electrode 20b be large and the number of roots be large. In addition, from the aspect of reducing the contact resistance between the sub-grid electrode 20b and the crystalline silicon substrate 1 (impurity diffusion layer 4), it is also preferable that the width of the sub-grid electrode 20b be large. According to the above description, the number of main grid electrodes can also be determined according to the size of the crystalline silicon solar cell and the width of the main grid electrode. The optimal width and number of the sub-grid electrodes 20b (the interval between the sub-grid electrodes 20b) can be determined by simulating the operation of the solar cell so as to maximize the conversion efficiency of the crystalline silicon solar cell. It should be noted that, regarding Figure 4 the width and number of the back sub-grid electrodes 15c of the back electrode 15 of the double-sided light-receiving type crystalline silicon solar cell shown, they can be determined in the same manner.

[0104] <<AgSi Region 30>>

[0105] The solar cell of the present embodiment includes at least one AgSi region 30. The AgSi region 30 is disposed in at least a part between the electrode and the substrate. Figure 6 An example of the AgSi region 30 is shown in the SEM photograph of Figure 6 The region indicated by the symbol 30 surrounded by a dotted line in the SEM photograph of can be set as the AgSi region 30 as long as the AgSi region 30 is disposed in at least a part between the electrode and the substrate.

[0106] When manufacturing the solar cell of the present embodiment, silver (Ag) contained in the electrode diffuses into silicon (Si) of the substrate, whereby a region of an alloy of silver (Ag) and silicon (Si) can be formed in at least a part between the electrode and the substrate. In this specification, the region of the alloy of silver (Ag) and silicon (Si) formed when manufacturing the solar cell of the present embodiment is referred to as "AgSi region 30". The AgSi region 30 can be determined as a region where both Ag and Si are detected when measuring the cross section of the solar cell of the present embodiment using an energy dispersive X-ray fluorescence spectrometer (hereinafter sometimes referred to as EDX).

[0107] One AgSi region 30 means an AgSi region 30 separated from other AgSi regions 30. In Figure 6In the SEM photograph, one AgSi region 30 is shown. The solar cell of the present embodiment preferably has a plurality of spot-like AgSi regions 30 in at least a part between the electrode and the substrate. The AgSi region 30 participates in the electric conduction between the electrode and the impurity diffusion layer 4 as a local conduction part.

[0108] In the crystalline silicon solar cell of the present embodiment, for example, when observing the cross section of 1 mm in length, which is a part of the sub-grid electrode, by SEM, about 1 to 3 spot-like AgSi regions 30 are included. Therefore, the part where the AgSi region 30 exists can be said to be an extremely minute part in the region where the electrode is formed.

[0109] The crystalline silicon solar cell of the present embodiment includes at least one AgSi region 30 having a depth d of 100 nm or more.

[0110] In this specification, the depth d of the AgSi region 30, in the SEM photograph obtained by observing the cross section of the AgSi region 30 as shown in Figure 6 is the length of the line segment with the largest length among the line segments connecting any one point ( Figure 6 B1) at the interface between the electrode and the AgSi region 30 to any one point ( Figure 6 B2) at the interface between the substrate and the AgSi region 30 (the length d of the line segment connecting Figure 6 B1 and B2). Specifically, for the AgSi region 30 determined by overlapping EDX measurement on the SEM photograph obtained by observing the cross section near the passivation film 2 at a magnification of 20,000 times, the above-mentioned given line segment is determined, and the length of the given line segment is measured, whereby the depth d of the AgSi region 30 can be obtained.

[0111] The depth d of the AgSi region 30 is preferably 100 to 4000 nm, more preferably 120 to 3000 nm, further preferably 130 to 2500 nm, and particularly preferably 150 to 2000 nm. By making the depth d of the AgSi region 30 within this range, the contact resistance is reduced, and a high-efficiency crystalline silicon solar cell with a fill factor (FF) can be obtained.

[0112] The solar cell of the present embodiment preferably has the above-mentioned AgSi region 30 formed by a laser treatment process. The laser treatment process refers to a process of treating the light incident side surface electrode 20 as follows: while applying a voltage between the back electrode 15b and the light incident side surface electrode 20 so that a current flows in a direction opposite to the forward direction between the second conductivity type impurity diffusion layer 4 and the first conductivity type crystalline silicon substrate 1, light from a point light source is irradiated onto the light incident side surface of the solar cell. In this case, the solar cell further includes a back electrode 15b disposed in electrical connection with the surface of the crystalline silicon substrate 1 opposite to the light incident side surface. By using the laser treatment process, an appropriate AgSi region 30 can be formed.

[0113] Details of the laser treatment process will be described later.

[0114] Figure 4 shows an example of a cross-sectional schematic view of a double-sided light-receiving crystalline silicon solar cell. Figure 4 The double-sided light-receiving crystalline silicon solar cell shown has an impurity diffusion layer 4, a passivation film 2 (antireflection film), and a back passivation film 14. A given structure of the electrode including the AgSi region 30 is as Figure 4 shown, and can also be suitably applied as the structure of the back electrode 15 (back sub-grid electrode 15c) of the double-sided light-receiving crystalline silicon solar cell. Therefore, in the double-sided light-receiving crystalline silicon solar cell, when forming the light incident side surface electrode 20 (especially the sub-grid electrode 20b) on the light incident side surface and the back electrode 15 (back sub-grid electrode 15c), a given AgSi region 30 can be formed both near the light incident side surface and near the back surface.

[0115] <<Survival rate of the passivation film 2>>

[0116] In this specification, the survival rate of the passivation film 2 can be used to represent the degree to which the passivation film 2 between the fired electrode for forming the electrode of the solar cell of the present embodiment and the impurity diffusion layer 4 of the crystalline silicon substrate 1 exists. It should be noted that in the portion where the AgSi region 30 is formed, the passivation film 2 disappears. Since the AgSi region 30 is not formed in the portion where the passivation film 2 exists, the so-called survival rate of the passivation film 2 can be considered as the ratio of the region where the AgSi region 30 is not formed near the AgSi region 30.

[0117] Use Figure 7An example of an SEM photograph of a cross-section of the solar cell shown is used to explain a method for measuring the survival rate of the passivation film 2. First, in order to obtain the survival rate of the passivation film 2, an SEM observation is first performed on the cross-section including the passivation film 2 and the AgSi region 30 at a magnification of 20,000 times, thereby obtaining an SEM photograph. It should be noted that the length of the SEM photograph in the horizontal direction (the direction parallel to the substrate surface) is 5.7 μm, and the length in the vertical direction (the direction perpendicular to the substrate surface) is 3.9 μm. Then, the total length Lp of the cross-section of the passivation film 2 in the SEM photograph is measured. Figure 7 In the example shown, the total length Lp of the cross-section of the passivation film 2 in the SEM photograph is the total length of Lp1, Lp2, Lp3, and Lp4. Then, in the SEM photograph, the total length Le of the cross-section of the interface between the AgSi region 30 and the electrode in the portion where the AgSi region 30 is formed is measured. The length Le corresponds to the length at which the passivation film 2 disappears in the manufacturing process of the solar cell. Figure 7 In the example shown, the total length Le of the cross-section of the interface between the AgSi region 30 and the electrode in the portion where the AgSi region 30 is formed is the total length of Le1 and Le2. The survival rate of the passivation film 2 can be obtained as Lp / (Lp + Le). It should be noted that the portion where the passivation film 2 disappears in the manufacturing process of the solar cell can be determined by EDX-based measurement. In addition, the lengths such as Le1 can be measured by approximating the passivation film 2 as a straight line.

[0118] In the crystalline silicon solar cell of the present embodiment, the survival rate of the passivation film 2 is 10 to 90%, preferably 30% or more and less than 90%, more preferably 50% or more and less than 90%, and further preferably 70% to 89%. By making the survival rate of the passivation film 2 within an appropriate range, a high-efficiency crystalline silicon solar cell having a high open-circuit voltage (Voc) and a fill factor (FF) can be obtained.

[0119] <<Ratio of film thickness of the passivation film 2 before and after firing>>

[0120] In this specification, the ratio of the film thickness of the passivation film 2 before and after firing refers to the ratio (Db / Da) of the film thickness Da before firing for forming the electrode of the passivation film 2 to the film thickness Db after firing (after the solar cell is completed) for forming the electrode. In this specification, the ratio of the film thickness before and after firing is sometimes simply referred to as "film thickness ratio (Db / Da)".

[0121] In the solar cell of the present embodiment, the film thickness ratio (Db / Da) is preferably 15% to 85%, more preferably 20% to 70%, and still more preferably 30% to 60%. By setting the film thickness ratio (Db / Da) of the passivation film 2 within a given range, an increase in the surface defect density that causes carrier recombination during power generation of the solar cell of the present embodiment can be prevented.

[0122] In this specification, the film thickness Da of the passivation film 2 before firing refers to the film thickness of the passivation film 2 when the passivation film 2 is formed on a given substrate. The film thickness Da immediately after film formation can be measured by SEM observation of a cross section near the passivation film 2 before forming the electrode.

[0123] In this specification, the film thickness Db after the solar cell is completed refers to the film thickness of the passivation film 2 in a scanning electron microscope photograph of a 5.7 μm × 3.9 μm cross section of the solar cell including the AgSi region 30 after the electrode is formed by firing on the surface of the solar cell.

[0124] In this specification, the film thickness Db of the passivation film 2 in a scanning electron microscope photograph of a 5.7 μm × 3.9 μm cross section of the solar cell including the AgSi region 30 after the electrode is formed on the surface of the solar cell refers to the film thickness of the passivation film 2 near the AgSi region 30 of the solar cell after performing given processes such as forming an electrode pattern using a given conductive paste on the passivation film 2 formed on a given substrate, and performing given firing to form the electrode and the AgSi region 30. Sometimes the film thickness Db is referred to as the "film thickness Db after the solar cell is completed". By performing SEM observation on a 5.7 μm × 3.9 μm image range of a cross section of the solar cell including the passivation film 2 and the AgSi region 30 after the electrode and the AgSi region 30 are formed, the film thickness Db after the solar cell is completed can be measured. That is, the film thickness Db after the solar cell is completed is the film thickness Db of the passivation film 2 in a scanning electron microscope photograph of a 5.7 μm × 3.9 μm cross section of the completed solar cell including the AgSi region 30. Specifically, by performing SEM observation on a cross section including the passivation film 2 and the AgSi region 30 at a magnification of 20,000 times, an SEM photograph (SEM image range: 5.7 μm × 3.9 μm) is obtained, and the cross section of the SEM photograph is divided into six equal parts longitudinally, and the film thicknesses (at five locations) of the passivation film 2 at the five intersections of the six equal parts are measured, and the film thickness Db after the solar cell is completed of the passivation film 2 can be obtained as the average value of the film thicknesses at the five locations.

[0125] <Manufacturing method of solar cell>

[0126] Next, a method for manufacturing a crystalline silicon solar cell of the present embodiment will be described.

[0127] The manufacturing method of the solar cell according to this embodiment includes a step of forming an electrode (light incident side surface electrode 20) by printing a given conductive paste on the surface of the passivation film 2 (antireflection film) on the second conductive type semiconductor layer (impurity diffusion layer 4) and drying and firing it. The given conductive paste will be described later.

[0128] The manufacturing method of the solar cell according to this embodiment includes a step of preparing a first conductive type (p-type or n-type) crystalline silicon substrate 1. As the first conductive type semiconductor substrate, an n-type crystalline silicon substrate 1 or a p-type crystalline silicon substrate 1 can be used. In the solar cell according to this embodiment, since a higher efficiency solar cell may be obtained, it is preferable to use the n-type crystalline silicon substrate 1.

[0129] It should be noted that, from the viewpoint of obtaining a high conversion efficiency, the surface on the light incident side of the crystalline silicon substrate 1 preferably has a pyramidal texture structure.

[0130] Subsequently, the manufacturing method of the solar cell according to this embodiment includes a step of forming a second conductive type impurity diffusion layer 4 on one surface of the first conductive type semiconductor substrate.

[0131] In the case of using the n-type crystalline silicon substrate 1 as the crystalline silicon substrate 1, as the impurity diffusion layer 4, for example, a p-type impurity diffusion layer 4 formed by diffusing B (boron) or the like as a p-type impurity can be formed. It should be noted that a crystalline silicon solar cell can also be manufactured using the p-type crystalline silicon substrate 1. In this case, as the impurity diffusion layer 4, an n-type impurity diffusion layer 4 formed by diffusing P (phosphorus) or the like as an n-type impurity is formed.

[0132] When forming the impurity diffusion layer 4, it can be formed such that the sheet resistance of the impurity diffusion layer 4 is 30 to 300 Ω / □ (square), preferably 40 to 150 Ω / □, and more preferably 45 to 120 Ω / □. In addition, in the manufacturing method of the crystalline silicon solar cell according to this embodiment, the depth of the impurity diffusion layer 4 can be set to 0.3 μm to 1.0 μm. The sheet resistance and depth of the impurity diffusion layer 4 can be controlled by adjusting conditions such as the concentration of the dopant coated on the crystalline silicon substrate 1 and the temperature and / or time for the diffusion of the impurity element.

[0133] The manufacturing method of the solar cell according to this embodiment includes a step of forming a back electrode 15 in a manner of being electrically connected to the other surface of the semiconductor substrate of the first conductivity type (n-type crystalline silicon substrate 1). It should be noted that the back electrode 15 can be either before or after forming the light incident side surface electrode 20. In addition, the firing for forming the back electrode 15 can be carried out simultaneously with or separately from the firing for forming the light incident side surface electrode 20.

[0134] Specifically, in the manufacturing method of the crystalline silicon solar cell according to this embodiment, the back electrode 15 is formed by printing a conductive paste on the other surface (back surface) of the crystalline silicon substrate 1 and then firing it.

[0135] It should be noted that, in the case of manufacturing a double-sided light-receiving type crystalline silicon solar cell as Figure 4 shown, a second impurity diffusion layer 16 can be formed. On the other hand, a given conductive paste (conductive composition) can be used to form the back electrode 15, and the above-mentioned AgSi region 30 can be formed between the back electrode 15 and the crystalline silicon substrate 1. Therefore, in the case of a double-sided light-receiving type crystalline silicon solar cell, it is preferable to use a given conductive paste to form the back electrode 15. In this case, the back electrode 15 is a fired body of the given conductive paste.

[0136] Subsequently, the manufacturing method of the solar cell according to this embodiment includes an operation of forming a passivation film 2 in a manner of being in contact with the surface of the semiconductor layer of the second conductivity type (impurity diffusion layer 4). The passivation film 2 can have the function of an antireflection film.

[0137] Specifically, in the manufacturing method of the crystalline silicon solar cell according to this embodiment, an antireflection film having the function of the passivation film 2 is formed on the surface of the impurity diffusion layer 4 formed in the above-mentioned step. As the passivation film 2 (antireflection film), a silicon nitride film (SiN film) can be formed. When using a silicon nitride film as the passivation film 2, the layer of the silicon nitride film also has the function of the passivation film 2 on the light incident side surface. Therefore, when using a silicon nitride film as the passivation film 2, a high-performance crystalline silicon solar cell can be obtained. In addition, by making the passivation film 2 a silicon nitride film, the antireflection function for incident light can be exerted. The silicon nitride film can be formed by a method such as PECVD (Plasma Enhanced Chemical Vapor Deposition).

[0138] The manufacturing method of the solar cell according to this embodiment includes a step of forming a light incident side surface electrode 20 on at least a part of the surface of the passivation film 2 (anti-reflection film). In the manufacturing method of this embodiment, in order to form the light incident side surface electrode 20, a given conductive paste described later is used. Therefore, the light incident side surface electrode 20 is a fired body of the given conductive paste.

[0139] In the manufacturing method of the crystalline silicon solar cell according to this embodiment, the light incident side surface electrode 20 is formed by printing a given conductive paste on the surface of the passivation film 2 (anti-reflection film) and firing it. It should be noted that when firing for forming the light incident side surface electrode 20, the firing for forming the back electrode 15 can be carried out simultaneously.

[0140] Specifically, first, the pattern of the light incident side surface electrode 20 printed with the given conductive paste is dried at a temperature of about 100 to 150 °C for several minutes (for example, 0.5 to 5 minutes). It should be noted that at this time, the given conductive paste can be used to form the light incident side main grid electrode 20a and the light incident side sub-grid electrode 20b of the light incident side surface electrode 20.

[0141] After the printing and drying of the pattern of the light incident side surface electrode 20, then the conductive paste for forming the back electrode 15 is printed and dried. In order to form electrodes (the light incident side surface electrode 20 and the back electrode 15 as the case may be) of a solar cell such as a crystalline silicon solar cell, the given conductive paste can be preferably used.

[0142] Thereafter, the material obtained by drying the printed conductive paste is fired in the atmosphere in a firing furnace such as a tubular furnace under given firing conditions. As the firing conditions, the firing atmosphere is in the atmosphere, the firing temperature is 500 to 1000 °C, more preferably 600 to 1000 °C, further preferably 500 to 900 °C, and particularly preferably 700 to 900 °C. The firing is preferably carried out in a short time, and the temperature distribution (temperature-time curve) during firing is preferably in a peak shape. For example, it is preferable to use the above temperature as the peak temperature, and the inlet and outlet time of the firing furnace is 10 to 100 seconds, more preferably fired for 20 to 80 seconds, and further preferably fired for 40 to 60 seconds.

[0143] During firing, it is preferable to simultaneously fire the conductive paste for forming the light incident side surface electrode 20 and the back electrode 15 to form the two electrodes simultaneously. By printing the given conductive paste on the light incident side surface and the back surface and firing simultaneously in this way, the firing for electrode formation can be only 1 time. Therefore, the crystalline silicon solar cell can be manufactured at a lower cost.

[0144] The manufacturing method of the solar cell according to this embodiment includes a step of forming the above-described AgSi region 30. In the manufacturing method of the solar cell according to this embodiment, in order to form the above-described AgSi region 30, for example, a laser treatment process can be performed.

[0145] The so-called laser treatment process refers to the following treatment: between the second-conductive-type semiconductor layer and the first-conductive-type semiconductor substrate, while applying a voltage to the back electrode 15 and the light incident-side surface electrode 20 so that a current flows in a direction opposite to the forward direction in the pn junction, light from a point light source is irradiated onto the light incident-side surface of the solar cell. Due to the action of the light from the point light source, carriers (electron-hole pairs) are generated inside the semiconductor substrate, and the movement of the carriers, that is, the flow of current, can be achieved due to the application of the voltage. The voltage is applied in such a way that the direction of the current flowing in the pn junction is opposite to the forward direction. Therefore, when the semiconductor substrate is an n-type semiconductor substrate and the semiconductor layer is a p-type semiconductor layer, the voltage is applied to the back electrode 15 and the light incident-side surface electrode 20 so that the current flows from the n-type semiconductor substrate to the p-type semiconductor layer. In addition, when the semiconductor substrate is a p-type semiconductor substrate and the semiconductor layer is an n-type semiconductor layer, the voltage is applied to the back electrode 15 and the light incident-side surface electrode 20 so that the current flows from the n-type semiconductor layer to the p-type semiconductor substrate.

[0146] In the following description, a solar cell in which the first-conductive-type semiconductor substrate is an n-type crystalline silicon substrate 1 and the second-conductive-type semiconductor layer is a p-type impurity diffusion layer 4 (sometimes simply referred to as "impurity diffusion layer 4") will be described as an example.

[0147] As Figure 1 shown, when the laser treatment process is used, a passivation film 2 (antireflection film) exists in most of the region between the light incident-side surface electrode 20 and the impurity diffusion layer 4. In the laser treatment process, the above-mentioned given voltage is applied in such a way that a current flows in a direction opposite to the forward direction in the pn junction, and light from a point light source (such as a laser) is irradiated, whereby a current flows in a minute region between the light incident-side surface electrode 20 and the impurity diffusion layer 4 and is locally heated. As a result, as Figure 6 and 7As shown, a region of an alloy of silver and silicon, which is a portion (local conduction portion) for locally electrically conducting, is formed between the surface electrode 20 on the light incident side and the impurity diffusion layer 4. In this specification, a region of an alloy of silver (Ag) and silicon (Si) formed by performing a laser treatment process or the like is referred to as an "AgSi region 30". The AgSi region 30 can be determined by measurement using an energy dispersive X-ray fluorescence spectrometer (hereinafter sometimes referred to as EDX) as a region in which both Ag and Si are detected. In addition, the passivation film 2 does not exist in the portion where the AgSi region 30 is formed. That is, in the portion where the AgSi region 30 is formed, the impurity diffusion layer 4 (the second conductivity type silicon emitter layer) is electrically conducted to the surface electrode 20 on the light incident side via the AgSi region 30. Since the locally formed AgSi region 30 is an electrically conducting portion (local conduction portion), good electrical conduction between the surface electrode 20 on the light incident side and the impurity diffusion layer 4 can be achieved.

[0148] Generally, by performing a laser treatment process, the fill factor (Fill Factor: FF) can be increased without reducing the open circuit voltage (Open Circuit Voltage: Voc), which is a characteristic of the solar cell characteristics. By forming a given AgSi region 30, a higher open circuit voltage (Voc) and a higher fill factor (FF) can be obtained.

[0149] The crystalline silicon solar cell of the present embodiment can be manufactured as described above.

[0150] The crystalline silicon solar cell of the present embodiment obtained as described above is electrically connected using a metal solder tape for interconnection, and laminated using a glass plate, a sealing material, a protective sheet, etc., whereby a solar cell module can be manufactured. As the metal solder tape for interconnection, a metal solder tape (for example, a tape made of copper) covered with solder can be used. As the solder, a solder mainly composed of tin can be used. Specifically, a commercially available solder such as a lead-containing solder or a lead-free solder can be used. In order to obtain a lead-free solar cell, it is preferable to use a lead-free solder as the solder.

[0151] <Conductive paste>

[0152] A given conductive paste that can be used to form the electrodes of the crystalline silicon solar cell of the present embodiment will be described. The given conductive paste is a conductive paste suitable for forming the above-mentioned AgSi region 30. Hereinafter, the given conductive paste may sometimes be referred to as the conductive paste of the present embodiment.

[0153] The conductive paste of the present embodiment has a lower reactivity with the passivation film 2 (anti-reflection film) than conventional conductive pastes, and has a reactivity with the passivation film 2 (anti-reflection film) suitable for the laser processing process. Therefore, the conductive paste of the present embodiment can be preferably used for forming the light incident side surface electrode 20 of the crystalline silicon solar cell using the laser processing process.

[0154] The inventors of the present invention have found that, when applying the laser processing process to a solar cell in which the light incident side surface electrode 20 is formed using a conventional conductive paste, it has an adverse effect on the passivation film 2 (anti-reflection film) and the impurity diffusion layer 4 (and the substrate), and the conversion efficiency of the solar cell is reduced. In addition, the inventors of the present invention have found that the reason is that the burn-through property (reactivity) of the conventional conductive paste with respect to the passivation film 2 (anti-reflection film) is too strong.

[0155] The conductive paste that can be used for forming the light incident side surface electrode 20 based on the laser processing process needs to have properties different from those of conventional conductive pastes (conductive pastes that can burn through the passivation film 2).

[0156] In addition, the inventors of the present invention have found that by making the alkalinity and content of the lead-free frit within an appropriate range, the reactivity of the frit with respect to the passivation film 2 (anti-reflection film) can be made appropriate. Since a lead-free frit is used as the frit, it is possible to prevent lead pollution caused by the discharge of lead into the environment. In addition, even when a lead-free frit is used, the contact resistance can be reduced to the same extent as that of a lead-containing frit. The inventors of the present invention who obtained the above insights have found a conductive paste that can be preferably used in the manufacture of crystalline silicon using the laser processing process.

[0157] When forming an electrode of a crystalline silicon solar cell using the conductive paste of the present embodiment and performing a laser processing process to form a given AgSi region 30, it is possible to obtain a low contact resistance between the electrode and the impurity diffusion layer 4 of the solar cell without impairing the function of the passivation film 2. Therefore, by using the conductive paste of the present embodiment to perform a laser processing process to form a given AgSi region 30, a crystalline silicon solar cell with high conversion efficiency can be obtained. When manufacturing a crystalline silicon solar cell, the conductive paste of the present embodiment can be preferably used to form a given AgSi region 30 using the laser processing process.

[0158] Specific descriptions will be given of the components contained in the conductive paste of the present embodiment.

[0159] <<(A) Conductive particles>>

[0160] The conductive paste of the present embodiment contains (A) conductive particles.

[0161] In the conductive paste of the present embodiment, metal particles or alloy particles can be used as the conductive particles. Examples of the metal contained in the metal particles or alloy particles include silver, gold, copper, nickel, zinc, and tin. As the metal particles, silver particles (Ag particles) can be used. It should be noted that in the conductive paste of the present embodiment, metals other than silver, such as gold, copper, nickel, zinc, and tin, can be included. From the aspect of obtaining low resistance and high reliability, the conductive particles are preferably silver particles composed of silver. It should be noted that in the silver particles composed of silver, other metal elements may be contained as inevitably contained impurities. In addition, a large amount of silver particles (Ag particles) is sometimes referred to as silver powder (Ag powder). The same applies to other particles.

[0162] The particle shape and particle size (also referred to as particle diameter or particle size) of the conductive particles are not particularly limited. As the particle shape, for example, spherical and flaky shapes can be used. The particle size of the conductive particles can be defined by the particle size (D50) of the cumulative value of all particles at 50%. In this specification, D50 is also referred to as the average particle diameter. It should be noted that the average particle diameter (D50) can be measured by the Microtrac method (laser diffraction scattering method) for particle size distribution and calculated based on the results of the particle size distribution measurement.

[0163] The average particle diameter (D50) of the conductive particles is preferably 0.5 to 2.5 μm, more preferably 0.8 to 2.2 μm. By making the average particle diameter (D50) of the conductive particles within a given range, the reactivity of the conductive paste with respect to the passivation film 2 can be suppressed during the firing of the conductive paste. It should be noted that when the average particle diameter (D50) is greater than the above range, there may be problems such as clogging during screen printing.

[0164] In addition, the size of the silver particles can be expressed as the BET specific surface area (also simply referred to as "specific surface area"). The BET specific surface area of the silver particles is preferably 0.1 to 1.5 m 2 / g, more preferably 0.2 to 1.2 m 2 / g. The BET specific surface area can be measured, for example, using a fully automatic specific surface area measuring device Macsoeb (manufactured by MOUNTEC).

[0165] <<(B) Organic carrier>>

[0166] The conductive paste of the present embodiment contains (B) an organic carrier.

[0167] As the organic carrier, an organic binder and a solvent can be included. The organic binder and the solvent play roles in adjusting the viscosity of the conductive paste and the like, and are not particularly limited. The organic binder can also be dissolved in the solvent and then used.

[0168] In the conductive paste of the present embodiment, the (B) organic carrier preferably contains at least one selected from ethyl cellulose, rosin ester, acrylic resin, and organic solvent. By making the (B) organic carrier contain at least one selected from ethyl cellulose, rosin ester, acrylic resin, and organic solvent, screen printing of the conductive paste can be appropriately performed, and the shape of the printed pattern can be made into an appropriate shape.

[0169] As the organic binder, it can be selected and used from cellulose-based resins (such as ethyl cellulose, nitrocellulose, etc.), (meth)acrylic-based resins (such as polymethyl acrylate, polymethyl methacrylate, etc.). The organic carrier contained in the conductive paste of the present embodiment preferably contains at least one selected from ethyl cellulose, rosin ester, butyraldehyde, acrylic resin, and organic solvent. The addition amount of the organic binder is usually 0.1 to 30 parts by weight, preferably 0.2 to 5 parts by weight, relative to 100 parts by weight of the silver particles.

[0170] As the organic solvent, one or more can be selected and used from alcohols (such as terpineol, α-terpineol, β-terpineol, etc.), esters (such as hydroxy-containing esters, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, diethylene glycol monobutyl ether acetate (butyl carbitol acetate), etc.). The addition amount of the solvent is usually 0.5 to 30 parts by weight, preferably 2 to 25 parts by weight, relative to 100 parts by weight of the silver particles. As a specific example of the organic solvent, diethylene glycol monobutyl ether acetate (butyl carbitol acetate) can be cited.

[0171] <<(C) frit>>

[0172] The conductive paste of the present embodiment contains (C) frit.

[0173] In the conductive paste of the present embodiment, the basicity B of the (C) frit GF The product B of the content G of the (C) frit in the conductive paste in parts by weight when the content of the (A) conductive particles in the conductive paste is set to 100 parts by weight GF ·G is in the range of 0.25 to 1.45, preferably in the range of 0.3 to 1.4, and more preferably in the range of 0.3 to 1.2. By making the product B of the basicity B of the frit GF and the content G GF ·G be in an appropriate range, the reactivity of the frit to the passivation film 2 (antireflection film) can be made appropriate. Therefore, when manufacturing crystalline silicon using a laser processing technique, the conductive paste of the embodiment can be preferably used.

[0174] The basicity of the frit can be calculated by the method described in Patent Document 3 (Japanese Patent Application Laid-Open No. 2009-231826). That is, regarding the "basicity", the basicity of the glass powder can be defined by the formula shown in "K. Morinaga, H. Yoshida And H. Takebe: J. AmCerm. Soc., 77, 3113 (1994)". Specifically, it is as follows.

[0175] Oxide M i The bond force between M of O i -O is given by the following formula as the cation-oxygen ion attraction Ai.

[0176] A i =Z i ·Z 02- / (r i +r 02- ) 2 =Zi·2 / (r i +1.40) 2

[0177] Z i : Valence of the cation, oxygen ion is 2

[0178] r i : Ionic radius of the cation (Å)

[0179] Ionic radius r of the oxygen ion i is 1.40 nm. Let the reciprocal B i of A in the above formula ( = 1 / A i ) be the oxygen supply ability of the single-component oxide M i O. i O.

[0180] B i ≡1 / A i

[0181] If this B i is normalized to B CaO =1, B SiO2 =0, then the B i -index of each single-component oxide is given. If the B i -index of each component is extended to a multi-component system using the cation percentage, the basicity ( = B GF ) of the melt of the glass oxide (frit) with any composition can be calculated.

[0182] B GF =Σn i ·B i

[0183] n i: Cation percentage

[0184] The basicity (B) defined in this way GF represents the oxygen supply capacity as described above. The larger the value, the easier it is to supply oxygen, and the easier it is to have the transfer of oxygen with other metal oxides. That is, the so-called "basicity" can represent the degree of dissolution in the glass melt.

[0185] Since the content G of the glass frit (C) is the ratio relative to the content of the conductive particles (A), it is a dimensionless number. In addition, as described above, since B i is normalized to the value of B CaO = 1 and B SiO2 = 0, the basicity B GF (= Σn i ·B i ) of the glass frit (C) is a dimensionless number. Therefore, the product B GF ·G of the basicity B GF of the glass frit (C) and the content G is also a dimensionless number.

[0186] The basicity (B GF ) of the glass frit of this embodiment is preferably 0.10 to 1.5, more preferably 0.15 to 1.3, and further preferably 0.20 to 1.1. When the basicity (B GF ) is in such a range, by adjusting the addition amount of the glass frit in the conductive paste, the reactivity of the glass frit with respect to the passivation film 2 can be made appropriate.

[0187] The content G of the glass frit in the conductive paste of this embodiment is preferably 0.1 to 5.0 parts by weight, more preferably 0.2 to 4.0 parts by weight, further preferably 0.3 to 3.0 parts by weight, and particularly preferably 0.4 to 2.7 parts by weight with respect to 100 parts by weight of the conductive particles. By appropriately adjusting the content G of the glass frit in the conductive paste together with the basicity (B GF ), the reactivity of the glass frit with respect to the passivation film 2 can be made appropriate. More specifically, in order to prepare a conductive paste suitable for forming an electrode using a laser processing process, by reducing the content of the glass frit compared with the prior art and making the basicity of the glass frit in an appropriate range, the reactivity with respect to the passivation film 2 can be suppressed and Voc can be improved.

[0188] The glass transition temperature (Tg) of the glass frit (C) in the conductive paste of the present embodiment is preferably 250 to 600 °C, more preferably 270 to 500 °C, and still more preferably 300 to 400 °C. By setting the glass transition temperature (Tg) of the glass frit (C) to 250 °C or higher, the reactivity with the passivation film 2 can be suppressed. In addition, by setting the glass transition temperature (Tg) to 600 °C or lower, the contact resistance between the obtained electrode (e.g., the light incident side surface electrode 20) and the impurity diffusion layer 4 can be reduced.

[0189] The glass transition temperature (Tg) can be measured as follows. That is, using a differential thermal balance (TG-DTA2000S manufactured by MACScience Co., Ltd.), glass powder as a sample and a reference substance are set in the differential thermal balance. As measurement conditions, the temperature is raised from room temperature to 900 °C at a heating rate of 10 °C / minute, and a curve (DTA curve) is obtained by plotting the temperature difference between the glass powder as the sample and the reference substance against the temperature. The first inflection point of the DTA curve obtained in this way can be set as the glass transition temperature Tg.

[0190] The shape of the glass frit particles is not particularly limited, and for example, spherical, amorphous, or other shapes can be used. In addition, the particle size is not particularly limited. From the viewpoint of operability and the like, the average particle diameter (D50) of the particles is preferably in the range of 0.1 to 10 μm, and more preferably in the range of 0.5 to 5 μm.

[0191] As the glass frit contained in the conductive paste of the present embodiment, glass frits (first glass frit and second glass frit) having different compositions can be independently used.

[0192] First, the first glass frit will be described.

[0193] The first glass frit contained in the conductive paste of the present embodiment preferably contains one or more selected from SiO 2 , B 2 O 3 , V 2 O 5 , Bi 2 O 3 , TeO 2 , BaO, CuO, Li 2 O and ZnO. The first glass frit contained in the conductive paste of the present embodiment more preferably contains one or more selected from SiO 2 , B 2 O 3 , V 2 O 5 , Bi 2 O 3 , TeO 2 , Li2 One or more of O and ZnO. By including at least one of these oxides in the first frit, the alkalinity of the first frit can be adjusted to an appropriate range.

[0194] The first frit preferably contains Bi 2 O 3 . The content of Bi 2 O 3 in the first frit (100 mol%) is preferably 10 to 80 mol%, more preferably 15 to 75 mol%, and further preferably 20 to 70 mol%. By including Bi 2 O 3 in the first frit, the reactivity with respect to the passivation film 2 can be adjusted to an appropriate range while reducing the contact resistance.

[0195] In the conductive paste of the present embodiment, the product C 2 O 3 of the content (C Bi2O3 ) of Bi Bi2O3 ·G of the content G of the first frit is preferably in the range of 10 to 200, more preferably in the range of 13 to 170, and further preferably in the range of 15 to 150. By making the product C Bi2O3 ·G with the content G of the frit be in the above range, the reactivity with respect to the passivation film can be adjusted to an appropriate range while reducing the contact resistance.

[0196] The first frit may contain SiO 2 within a range that does not adversely affect the conductive paste of the present embodiment. When the first frit contains SiO 2 , the content of SiO 2 in the first frit (100 mol%) is preferably 10 to 60 mol%, more preferably 15 to 40 mol%. By including an appropriate content of SiO 2 in the first frit, the reactivity with respect to the passivation film 2 can be controlled.

[0197] The first frit may contain B 2 O 3 within a range that does not adversely affect the conductive paste of the present embodiment. When the first frit contains B 2 O 3 , the content of B 2 O 3 in the first frit (100 mol%) is preferably 3 to 60 mol%, more preferably 4 to 50 mol%. By including an appropriate content of B 2 O 3, which can control the reactivity with respect to the passivation film 2.

[0198] The first frit may contain V within a range that does not adversely affect the conductive paste of the present embodiment. 2 O 5 . When the first frit contains V 2 O 5 , the content of V 2 O 5 in the first frit (100 mol%) is preferably less than 8 mol%, more preferably 5 mol% or less. By including V 2 O 5 in the first frit, the alkalinity of the first frit can be reduced. Thus, when the alkalinity of the first frit is high, by including an appropriate content of V 2 O 5 , the alkalinity of the first frit can be adjusted to an appropriate range.

[0199] The first frit may contain TeO within a range that does not adversely affect the conductive paste of the present embodiment. 2 . When the first frit contains TeO 2 , the content of TeO 2 in the first frit (100 mol%) is preferably less than 80 mol%, more preferably 50 mol% or less. By including TeO 2 in the first frit, the alkalinity of the first frit can be reduced. Thus, when the alkalinity of the first frit is high, by including an appropriate content of TeO 2 , the alkalinity of the first frit can be adjusted to an appropriate range.

[0200] The first frit may contain BaO within a range that does not adversely affect the conductive paste of the present embodiment. When the first frit contains BaO, the content of BaO in the first frit (100 mol%) is preferably 3 to 20 mol%, more preferably 5 to 10 mol%. By including an appropriate content of BaO in the first frit, the reactivity with respect to the passivation film 2 can be adjusted to an appropriate range.

[0201] The first frit may contain CuO within a range that does not adversely affect the conductive paste of the present embodiment. When the first frit contains CuO, the content of CuO in the first frit (100 mol%) is preferably 10 to 40 mol%, more preferably 20 to 30 mol%. By including an appropriate content of CuO in the first frit, the reactivity with respect to the passivation film 2 can be adjusted to an appropriate range.

[0202] The first frit may contain Li within a range that does not adversely affect the conductive paste of the present embodiment. 2 O. When the first frit contains Li 2 O, the content of Li 2 O in the first frit (100 mol%) is preferably 3 to 40 mol%, more preferably 5 to 30 mol%. By making the first frit contain an appropriate content of Li 2 O, the reactivity with respect to the passivation film 2 can be adjusted to an appropriate range.

[0203] The first frit may contain ZnO within a range that does not adversely affect the conductive paste of the present embodiment. When the first frit contains ZnO, the content of ZnO in the first frit (100 mol%) is preferably 5 to 70 mol%, more preferably 15 to 60 mol%. By making the first frit contain ZnO, the alkalinity of the first frit can be adjusted to an appropriate range.

[0204] The first frit contained in the conductive paste of the present embodiment is preferably a lead-free frit. In this case, the first frit contained in the conductive paste of the present embodiment substantially does not contain lead (Pb). However, a trace amount of lead that is inevitably mixed in may be contained as an impurity in the lead-free first frit used in the present embodiment. Specifically, the lead-free first frit used in the present embodiment may contain 0.1% by weight or less of lead as an impurity. By manufacturing a solar cell using a conductive paste containing a lead-free first frit, lead pollution to the environment can be prevented when the solar cell is discarded.

[0205] Next, the second frit will be described. The second frit is a frit containing PbO.

[0206] The second frit contained in the conductive paste of the present embodiment preferably contains one or more selected from PbO, SiO 2 , Al 2 O 3 , B 2 O 3 , ZnO, V 2 O 5 , WO 3 and Nb 2 O 3 . The second frit contained in the conductive paste of the present embodiment more preferably contains PbO, SiO 2 , Al 2 O 3 , B 2 O 3 and ZnO.

[0207] In the conductive paste of this embodiment, the second frit preferably contains at least one selected from ZnO, V 2 O 5 , WO 3 and Nb 2 O 3 . By making the second frit contain at least one of these oxides, the basicity of the second frit can be adjusted to an appropriate range.

[0208] The second frit preferably contains PbO. The content of PbO in the second frit (100 mol%) is preferably 25 to 60 mol%, more preferably 30 to 55 mol%, and further preferably 40 to 55 mol%. By making the second frit contain PbO, the contact resistance can be reduced while suppressing the reactivity with the passivation film 2.

[0209] The second frit preferably contains SiO 2 . The content of SiO 2 in the second frit (100 mol%) is preferably 20 to 65 mol%, more preferably 25 to 60 mol%. By making the second frit contain SiO 2 , the reactivity with the passivation film 2 can be suppressed.

[0210] The second frit preferably contains Al 2 O 3 . The content of Al 2 O 3 in the second frit (100 mol%) is preferably 3.0 to 6.8 mol%, more preferably 3.5 to 6 mol%. By making the second frit contain Al 2 O 3 , the reactivity with the passivation film 2 can be suppressed.

[0211] The second frit preferably contains B 2 O 3 . The content of B 2 O 3 in the second frit (100 mol%) is preferably 3.0 to 15 mol%, more preferably 3.5 to 12 mol%.

[0212] The second frit preferably contains ZnO. The content of ZnO in the second frit (100 mol%) is preferably 5 to 20 mol%, more preferably 8 to 15 mol%. By making the second frit contain ZnO, the basicity of the second frit can be adjusted to an appropriate range.

[0213] In the conductive paste of this embodiment, the product C of the content C of PbO in the second frit in mol% and the content G of the second frit is preferably PbO the product C ofPbO ·G ranges from 20 to 139, more preferably from 22 to 130, and still more preferably from 26 to 105. In the product C PbO ·When G is greater than 139, the reactivity between the second frit and the passivation film 2 is too high. Also, in the product C PbO ·When G is less than 20, the contact resistance between the obtained electrode and the impurity diffusion layer 4 is too high.

[0214] In the first and second frits, the frit particles can be one kind of particles respectively containing a given amount of various necessary oxides. Alternatively, particles composed of a single oxide can be used as particles different for each of the various necessary oxides. Alternatively, a plurality of particles with different compositions of the various necessary oxides can be used in combination. In order to synergistically obtain the effects of different types of oxides, the frit particles of the first and second frits are preferably one kind of particles respectively containing a given amount of various necessary oxides.

[0215] <Other components>

[0216] The conductive paste of the present embodiment can contain additives and additives other than the above examples within a range that does not adversely affect the solar cell characteristics of the obtained solar cell.

[0217] In the conductive paste of the present embodiment, as additives, substances selected from plasticizers, defoamers, dispersants, leveling agents, stabilizers, adhesion promoters, etc. can be further blended as needed. Among them, as plasticizers, at least one selected from phthalates, glycolates, phosphates, sebacates, adipates, citrate esters, etc. can be used.

[0218] The conductive paste of the present embodiment can contain additives other than the above examples within a range that does not adversely affect the solar cell characteristics of the obtained solar cell. For example, the conductive paste of the present embodiment can further contain at least one additive selected from titanium resin acid, titanium oxide, cobalt oxide, cerium oxide, silicon nitride, copper manganese tin, aluminosilicate, and aluminum silicate. By containing these additives, the adhesion strength of the electrode to the passivation film 2 can be improved. These additives can be in the form of particles (additive particles). The addition amount of the additive relative to 100 parts by weight of the silver particles is preferably from 0.01 to 5 parts by weight, more preferably from 0.05 to 2 parts by weight. In order to obtain a higher adhesion strength, the additive is preferably copper manganese tin, aluminosilicate, or aluminum silicate. The additive can contain both aluminosilicate and aluminum silicate.

[0219] <Manufacturing method of the conductive paste>

[0220] Next, a method for manufacturing the conductive paste of the present embodiment will be described. The conductive paste of the present embodiment can be manufactured by adding silver particles, glass frit, and other additives and / or additives used as needed to an organic binder and a solvent, and mixing and dispersing them.

[0221] Mixing can be performed, for example, using a planetary mixer. In addition, dispersion can be performed using a three-roll mill. Mixing and dispersion are not limited to these methods, and various known methods can be used.

[0222] Examples

[0223] Hereinafter, the present embodiment will be specifically described using examples, but the present invention is not limited to them.

[0224] <Solar cells of Examples 1 to 7 and Comparative Examples 1 and 2>

[0225] In the examples and comparative examples, monocrystalline silicon solar cells were fabricated, and the electrical characteristics of the monocrystalline silicon solar cells were measured to evaluate the performance of the solar cells in the examples and comparative examples.

[0226] <<Materials and preparation ratios of conductive paste>>

[0227] In Tables 1 and 2, the blending amounts of (A) conductive particles and (C) glass frit of the conductive paste in the examples and comparative examples are shown. The blending amounts shown in Tables 1 and 2 and the blending amounts of the following respective components are shown as the weight parts of the respective components when (A) conductive particles are 100 parts by weight. The respective components contained in the conductive paste are as follows.

[0228] (A) Silver particles

[0229] In Table 3, the model numbers, manufacturing companies, shapes, average particle diameters (D50), TAP densities, and BET specific surface areas of silver particles A1 and A2 used in the conductive paste of the examples and comparative examples are shown. In Tables 1 and 2, the blending amounts of silver particles A1 and A2 of the conductive paste in the examples and comparative examples are shown. It should be noted that the average particle diameter (D50) was obtained by measuring the particle size distribution using the Microtrac method (laser diffraction scattering method) and obtaining the value of the median diameter (D50) from the results of the particle size distribution measurement. The same applies to the average particle diameter (D50) of other components. In addition, the measurement of the BET specific surface area was performed using a fully automatic specific surface area measurement device Macsoeb (manufactured by MOUNTEC). Regarding the BET specific surface area, pre-drying was performed at 100 °C, and after flowing nitrogen for 10 minutes, measurement was performed using the BET one-point method based on nitrogen adsorption.

[0230] (B) Organic carrier

[0231] As the organic carrier, an organic binder and a solvent are used. As the organic binder, ethyl cellulose having an ethoxy content of 48 to 49.5% by weight (0.4 part by weight) is used. As the solvent, diethylene glycol monobutyl ether acetate (butyl carbitol acetate) (3 parts by weight) is used.

[0232] (C) Glass frit

[0233] In Table 4, the compositions, basicities and glass transition temperatures of the glass frits GF1 to GF6 used in the conductive pastes of the examples and comparative examples are shown. It should be noted that the average particle size (D50) of the glass frits GF1 to GF6 is set to 2 μm. In Tables 1 and 2, the types and contents G (parts by weight) of the (C) glass frit of the conductive pastes of the examples and comparative examples are shown.

[0234] The glass transition temperatures of the glass frits GF1 to GF6 were measured. The measured values of the glass transition temperatures of the glass frits GF1 to GF6 are shown in Table 4. The measurement of the glass transition temperature of the glass frit was carried out as follows. That is, about 50 mg of the glass frits GF1 to GF6 were added as samples to a platinum cell, alumina powder was used as a standard sample, and in an air atmosphere, using a differential thermal analyzer (manufactured by Rigaku Corporation, TG-8120), the temperature was raised from room temperature to 800 °C at a heating rate of 20 °C / minute to obtain a DTA curve. The first endothermic start point (extrapolated point) of the DTA curve was set as the glass transition temperature.

[0235] The glass frits GF1 to GF6 were manufactured as follows. That is, first, the powders of the oxides that are raw materials were weighed, mixed, and put into a crucible. The crucible was placed in a heated oven, and the contents of the crucible were heated to the melting temperature (Melttemperature), and the raw materials were maintained at the melting temperature until they were sufficiently melted. Then, the crucible was taken out of the oven, and the melted contents were stirred evenly. Then, the contents of the crucible were rapidly cooled at room temperature using a stainless steel double roll to obtain plate-shaped glass. Finally, the plate-shaped glass was uniformly dispersed while being ground in a mortar and sieved using a sieve with a mesh, whereby a glass frit having a desired particle size could be obtained. The glass frit that passed through a 100-mesh sieve but remained on a 200-mesh sieve was sieved out, whereby a glass frit having an average particle size (D50) of 149 μm could be obtained. This glass frit was further ground, whereby a glass frit having an average particle size (D50) of 2 μm could be obtained.

[0236] Then, the above-mentioned given types and amounts of (A) conductive particles, (B) organic carrier, and (C) glass frit were mixed using a planetary mixer, and further dispersed using a three-roll mill to make a paste, whereby the conductive pastes of the examples and comparative examples were manufactured.

[0237] <<Manufacture of Monocrystalline Silicon Solar Cells>>

[0238] Manufacture a double-sided light-receiving type monocrystalline silicon solar cell as exemplified in Figure 4 . An n-type monocrystalline silicon substrate doped with P (phosphorus) (substrate thickness: 200 μm) was used as the substrate.

[0239] First, after forming a silicon oxide layer of about 20 μm by dry oxidation on the above substrate, etching was performed using a solution mixed with hydrogen fluoride, pure water, and ammonium fluoride to remove the damage on the substrate surface. In addition, heavy metal cleaning was performed using an aqueous solution containing hydrochloric acid and hydrogen peroxide.

[0240] Then, textures (concave-convex shapes) were formed on both sides of the substrate by wet etching. Specifically, a pyramidal texture structure was formed on both sides (the main light incident side surface and the back surface) by the wet etching method (aqueous sodium hydroxide solution). Thereafter, cleaning was performed using an aqueous solution containing hydrochloric acid and hydrogen peroxide.

[0241] Then, boron was implanted into one surface (light incident side surface) of the above substrate having a texture structure to form a p-type diffusion layer with a depth of about 0.5 μm. The sheet resistance of the p-type diffusion layer is 150 Ω / □.

[0242] In addition, phosphorus was implanted into the other surface (back surface) of the above substrate having a texture structure to form an n-type diffusion layer with a depth of about 0.5 μm. The sheet resistance of the n-type diffusion layer is 20 Ω / □. At the same time, boron and phosphorus implantation were performed using the thermal diffusion method.

[0243] Then, a passivation film 2 was formed on the surface (light incident side surface) of the substrate on which the p-type diffusion layer was formed and the surface (back surface) of the substrate on which the n-type diffusion layer was formed. Specifically, first, a thin oxide film layer of 1 - 2 nm was formed on the light incident side surface and the back surface, and then a silicon nitride film was formed with a thickness of about 60 nm using silane gas and ammonia gas by plasma CVD method. Specifically, glow discharge decomposition was performed on a mixed gas of NH 3 / SiH 4 = 0.5 at 1 Torr (133 Pa), and thus a silicon nitride film (antireflection film) with a film thickness of about 70 nm was formed by plasma CVD method.

[0244] For the electrode formation of the surface (light incident side surface) of the substrate of the monocrystalline silicon solar cell in the examples and comparative examples where the p-type diffusion layer was formed, a conductive paste with the blending amounts shown in Tables 1 and 2 was used.

[0245] The conductive paste is printed using the screen printing method. On the passivation film 2 of the above substrate, a pattern composed of a main gate electrode 20a on the light incident side with a width of 1.5 mm and a sub-gate electrode 20b on the light incident side with a width of 60 μm is printed so that the film thickness is about 20 μm. Then, it is dried at 150 °C for about 1 minute.

[0246] As the back electrode 15 (the electrode on the surface where the n-type diffusion layer is formed), the same Ag paste is printed using the screen printing method. It should be noted that the electrode pattern of the back electrode 15 is the same as the electrode pattern shape of the surface electrode 20 on the light incident side. Then, it is dried at 150 °C for about 60 seconds. The film thickness of the conductive paste for the dried back electrode 15b is about 20 μm. Then, using a belt furnace (firing furnace) CDF7210 manufactured by Despatch Industries, Inc., double-sided simultaneous firing is performed under the conditions of a peak temperature of 720 °C and a furnace entry and exit time of 50 seconds. The single-crystalline silicon solar cell is fabricated as described above.

[0247] <<Laser treatment process>>

[0248] The laser treatment process is performed on the light incident side surface of the single-crystalline silicon solar cells of the above embodiments and comparative examples to form the AgSi region 30. That is, while applying a negative voltage to the back electrode 15 and a positive voltage to the surface electrode 20 on the light incident side of the pattern shown so that a current flows in the direction opposite to the forward direction between the p-type impurity diffusion layer 4 and the n-type crystalline silicon substrate 1 of the solar cell unit, laser light is irradiated onto the light incident side surface of the solar cell. The applied voltage during the laser treatment process is 20 V, and the intensity of the irradiated laser is 100 W / cm Figure 2 The voltage application and laser irradiation time are set to 2 seconds. 2 The solar cells of the embodiments and comparative examples are fabricated as described above.

[0249] The electrical characteristics of the solar cells after the laser treatment process are measured as follows. That is, the current-voltage characteristics of the fabricated solar cells are measured using a solar simulator SS-150XIL manufactured by EIH Corporation under the conditions of 25 °C and AM1.5 of simulated sunlight (energy density 100 mW / cm

[0250] <Measurement of electrical characteristics of solar cells after laser treatment process>

[0251] The electrical characteristics of the single-crystalline silicon solar cells after the laser treatment process are measured as follows. That is, the current-voltage characteristics of the fabricated solar cells are measured using a solar simulator SS-150XIL manufactured by EIH Corporation under the conditions of 25 °C and AM1.5 of simulated sunlight (energy density 100 mW / cm 2Measurements were carried out under the irradiation of [[ID=]], and the fill factor (Fill Factor: FF), open circuit voltage (Open Circuit Voltage: Voc), and conversion efficiency (%) were calculated based on the measurement results. It should be noted that two monocrystalline silicon solar cells with the same manufacturing conditions were fabricated, and the measured values were obtained as the average of the two. The electrical characteristics (fill factor (FF), open circuit voltage (Voc), and conversion efficiency (%)) of the solar cells after the laser treatment process were measured. The measurement results are shown in Tables 1 and 2.

[0252] As clearly seen from Table 1, the electrical characteristics of the solar cells of Examples 1 to 7 fabricated using the given conductive paste are high after the laser treatment process. For example, the conversion efficiency ranges from 21.3% to 24.4%. In contrast, the electrical characteristics of the solar cells fabricated using the conductive paste of Comparative Example 1 are low after the laser treatment process. For example, the conversion efficiency ranges from 7.3 to 20.2. Therefore, it is obvious that the solar cells of Examples 1 to 7 of the present embodiment having the given AgSi region 30 have excellent electrical characteristics after the laser treatment process compared to the solar cells of Comparative Examples 1 and 2.

[0253] <SEM photographs>

[0254] The cross-section near the passivation film 2 (antireflection film) of the solar cells of the examples and comparative examples was observed using a scanning electron microscope (SEM). Figure 6 and 7 are the cross-section SEM photographs of the solar cell of Example 3. Additionally, Figure 8 are the cross-section SEM photographs of the solar cell of Comparative Example 1.

[0255] In the case of using the laser treatment process, the passivation film 2 (antireflection film) exists in most of the region between the surface electrode 20 on the light incident side and the impurity diffusion layer 4. In the laser treatment process, the above-mentioned given voltage is applied in such a way that a current flows in the direction opposite to the forward direction in the pn junction, and light (such as a laser) from a point light source is irradiated. As a result, a current flows in a minute region between the surface electrode 20 on the light incident side and the impurity diffusion layer 4, and it is locally heated. As a result, as Figure 6 and 7As shown, an AgSi region 30 (an alloy of silver and silicon), which serves as a locally electrically conductive portion (local conduction portion), is formed between the light incident side surface electrode 20 and the impurity diffusion layer 4. That is, the local conduction portion contains an alloy of silver and silicon. Further, in the local conduction portion, the impurity diffusion layer 4 (the second conductivity type silicon emitter layer) is in direct contact with the light incident side surface electrode 20 without being separated by the passivation film 2 (antireflection film). By using this locally formed electrically conductive portion (local conduction portion), good electrical conduction between the light incident side surface electrode 20 and the impurity diffusion layer 4 can be achieved. A given conductive paste for manufacturing the solar cell of the present embodiment has low reactivity with the passivation film 2 (antireflection film) and has reactivity with the passivation film 2 (antireflection film) suitable for the laser processing process. Therefore, the conductive paste of the present embodiment can be preferably used for forming the light incident side surface electrode 20 of the crystalline silicon solar cell using the laser processing process.

[0256] <Depth d of AgSi region 30>

[0257] The depth d of the AgSi region 30 of Examples 1 to 7 and Comparative Examples 1 and 2 was measured as follows. The measurement results are shown in Tables 1 and 2.

[0258] Figure 6 The depth d of the AgSi region 30 is illustrated. The depth d of the AgSi region 30 was measured as follows. That is, in the SEM photograph obtained by observing the cross section of the AgSi region 30 by SEM, any one point ( Figure 6 B1) of the interface connecting the electrode and the AgSi region 30 to any one point ( Figure 6 B2) of the interface between the substrate and the AgSi region 30, the length of the line segment with the maximum length among the line segments ( Figure 6 the length d of the line segment connecting B1 and B2) was measured. The cross section of the completed solar cell including the passivation film 2 and the AgSi region 30 was observed by SEM at a magnification of 20,000 times, and thus the Figure 6 shown SEM photograph was obtained.

[0259] <Survival rate of passivation film 2>

[0260] The survival rate of the passivation film 2 of Examples 1 to 7 and Comparative Examples 1 and 2 was measured as follows. The measurement results are shown in Tables 1 and 2.

[0261] Specifically, first, the cross-section of the completed solar cell including the passivation film 2 and the AgSi region 30 was observed by SEM at a magnification of 20,000 times, and an SEM photograph was thus obtained (SEM image range: 5.7 μm × 3.9 μm). It should be noted that the length of the SEM photograph in the horizontal direction (the direction parallel to the substrate surface) is 5.7 μm, and the length in the vertical direction (the direction perpendicular to the substrate surface) is 3.9 μm. Then, as Figure 7 illustrated in the example, the total length Lp of the cross-section of the passivation film 2 in the SEM photograph was measured. Figure 7 In the example shown, the total length Lp of the cross-section of the passivation film 2 in the SEM photograph is the sum of the lengths of Lp1, Lp2, Lp3, and Lp4. Then, in the SEM photograph, the total length Le of the cross-section of the interface between the AgSi region 30 and the electrode in the portion where the AgSi region 30 is formed was measured. The length Le corresponds to the length by which the passivation film 2 disappears in the manufacturing process of the solar cell. Figure 7 In the example shown, the total length Le of the cross-section of the interface between the AgSi region 30 and the electrode in the portion where the passivation film 2 disappears is the sum of the lengths of Le1 and Le2. The survival rate of the passivation film 2 can be obtained as Lp / (Lp + Le). It should be noted that lengths such as Lp1 were measured by approximating the passivation film 2 as a straight line.

[0262] <Film thickness and film thickness ratio before and after firing of the passivation film 2>

[0263] The film thickness Da before firing and the film thickness Db after completion of the solar cell of the passivation film 2 of the solar cells of Examples 1 to 7 and Comparative Examples 1 and 2 were measured. The measurement results are shown in Tables 1 and 2. Tables 1 and 2 show the film thickness ratio before and after firing of the passivation film 2.

[0264] The film thickness Da before firing of the passivation film 2 was measured by SEM observation of the cross-section of the passivation film 2 just after film formation. That is, the passivation film 2 was formed on the surface of the given crystalline silicon substrate 1 under the same conditions as in the examples and comparative examples, and the cross-section of the passivation film 2 was observed by SEM, whereby the film thickness Da before firing of the passivation film 2 of the examples and comparative examples was obtained.

[0265] Regarding the film thickness Db of the passivation film after the completion of the solar cell, it is the passivation film 2 of the completed solar cell after forming electrodes on the surface of the solar cell and performing a given laser treatment process as needed. Specifically, first, the cross-section of the completed solar cell including the passivation film 2 and the AgSi region 30 is observed by SEM at a magnification of 20,000 times, thereby obtaining an SEM photograph (SEM image range: 5.7 μm × 3.9 μm). Then, the SEM photograph is divided into six equal parts longitudinally, and the film thicknesses (at five locations) of the passivation film 2 at the five junctions of the six equal parts of the image are measured. The film thickness Db after the completion of the solar cell is set as the average value of the film thicknesses of the passivation film 2 at the five locations.

[0266] The so-called film thickness ratio before and after firing of the passivation film 2 is the ratio (Db / Da) of the film thickness Da of the passivation film 2 before firing measured as described above to the film thickness Db after the completion of the solar cell.

[0267] <Evaluation>

[0268] As shown in Tables 1 and 2, in the solar cells of Examples 1 to 7, the depth d of the AgSi region 30 obtained from the SEM photograph of the cross-section is in the range of 200 to 1800 nm. In addition, in the solar cells of Examples 1 to 7, it can be confirmed that a given AgSi region 30 is formed. In addition, the film thickness ratio before and after firing of the passivation film 2 of the solar cells of Examples 1 to 7 is in the range of 17 to 78%, and the survival rate of the passivation film 2 is in the range of 10 to 90%. Therefore, it can be confirmed that after the manufacture of the solar cells of Examples 1 to 7 manufactured by performing a given firing and laser treatment process, a given passivation film 2 also remains. As a result, the electrical characteristics after the laser treatment process of the solar cells of Examples 1 to 7 manufactured using the conductive paste containing GF1 to 3, GF5, and GF6 are high. For example, the conversion efficiency is in the range of 21.3% to 24.4%. In addition, in the solar cells of Examples 1 to 7, since the passivation film 2 having a given passivation function remains, the open circuit voltage (Voc) is high, in the range of 0.69 to 0.72 V. It should be noted that the fill factor (FF) of the solar cells of Examples 1 to 7 is in the range of 72.7 to 82.6%, which is a good value.

[0269] It should be noted that the survival rate of the passivation film 2 of the solar cells of Examples 1 to 5 is in the range of 76 to 88%, and the conversion efficiency is in the range of 23.4% to 24.4%. That is, the conversion efficiency of the solar cells of Examples 1 to 5 is higher than that of the solar cells of Example 6 (the survival rate of the passivation film 2 is 10%) and the solar cells of Example 7 (the survival rate of the passivation film 2 is 90%). Therefore, it can be said that when the survival rate of the passivation film 2 is 30% or more and less than 90%, a solar cell with a higher conversion efficiency can be obtained.

[0270] In addition, the film thickness ratio of the passivation film 2 of the solar cells of Examples 1 to 5 before and after firing is in the range of 36 to 51%, and the conversion efficiency is in the range of 23.4% to 24.4%. That is, the conversion efficiency of the solar cells of Examples 1 to 5 is higher than that of the solar cell of Example 6 (film thickness ratio: 78%) and the solar cell of Example 7 (film thickness ratio: 17%). Therefore, it can be said that when the film thickness ratio of the passivation film 2 before and after firing is in the range of 20 to 70%, a solar cell with a higher conversion efficiency can be obtained.

[0271] On the other hand, as shown in Table 2, in the solar cell of Comparative Example 1, the AgSi region 30 could not be observed from the SEM photograph of the cross section. In addition, the film thickness ratio of the passivation film 2 of the solar cell of Comparative Example 1 before and after firing was 91%, and the survival rate of the passivation film 2 was 100%. Therefore, it was confirmed that in the solar cell of Comparative Example 1 manufactured by performing a given firing and laser treatment process, the given passivation film 2 remained substantially unchanged after just being formed, and the AgSi region was not formed. Thus, the electrical characteristics after the laser treatment process of the solar cell manufactured using the conductive paste containing GF4 were low, for example, the conversion efficiency was 7.3%. In particular, in the solar cell of Comparative Example 1, since the passivation film 2 as an insulating film remained, the fill factor (FF) was as low as 35.7%.

[0272] In the solar cell of Comparative Example 2, the AgSi region 30 was observed in the SEM photograph of the cross section. As shown in Table 2, in the solar cell of Comparative Example 2, the depth d of the AgSi region 30 obtained from the SEM photograph of the cross section was 1200 nm. It should be noted that the film thickness ratio of the passivation film 2 of the solar cell of Comparative Example 2 before and after firing was 5%, and the survival rate of the passivation film 2 was 5%. Therefore, it was obvious that compared with the solar cells of Examples 1 to 7, the presence of the passivation film 2 in the solar cell of Comparative Example 2 manufactured by performing a given firing and laser treatment process was less. As a result, the conversion efficiency of the solar cell of Comparative Example 2 manufactured using the conductive paste containing GF3 after the laser treatment process was 20.2%, which was lower than that of the solar cells of Examples 1 to 7. In addition, in the solar cell of Comparative Example 2, since the presence of the passivation film 2 was less and the passivation function was reduced, the open circuit voltage (Voc) was 0.64 V, which was a low value. It is considered that in the solar cell of Comparative Example 2, when the electrode formed using the conductive paste containing GF3 was fired, the passivation film 2 was burned through.

[0273] In addition, since the solar cells of Embodiments 1, 2, and 4 to 7 are fabricated using a conductive paste containing a lead-free glass frit (the glass frits of GF1 to 5), lead pollution to the environment can be prevented when the solar cells are discarded.

[0274]

[0275]

[0276]

[0277]

[0278] Description of Reference Numerals

[0279] 1 Crystalline silicon substrate, 2 Passivation film, 4 Impurity diffusion layer, 6 Substrate main body, 14 Back surface passivation film, 15 Back surface electrode, 15a Back surface TAB electrode (back surface main grid electrode), 15b Back surface full electrode, 15c Back surface sub-grid electrode, 16 Second impurity diffusion layer, 20 Light incident side surface electrode (surface electrode), 20a Light incident side main grid electrode, 20b Light incident side sub-grid electrode, 30 AgSi region.

Claims

1. A solar cell, comprising: a substrate comprising crystalline silicon and having an impurity diffusion layer on at least one surface; a passivation film disposed on at least a part of the impurity diffusion layer of the substrate; and an electrode comprising silver (Ag) and disposed on at least a part of the passivation film, the solar cell further comprising at least one AgSi region disposed on at least a part between the electrode and the substrate, the AgSi region comprising at least one AgSi region having a depth of 100 nm or more, in a scanning electron microscope photograph of a 5.7 μm × 3.9 μm cross-section of the solar cell including the AgSi region, the ratio of the remaining length of the passivation film, i.e., the remaining rate of the passivation film, is 10% to 90%.

2. The solar cell according to claim 1, wherein, the ratio Db / Da of the film thickness Db of the passivation film in a scanning electron microscope photograph of a 5.7 μm × 3.9 μm cross-section of the solar cell including the AgSi region after the formation of the electrode on the surface of the solar cell to the film thickness Da of the passivation film just after film formation is 15% to 85%.

3. The solar cell according to claim 1 or 2, wherein, the electrode further comprises 0.1 to 5.0 parts by weight of a glass frit with respect to 100 parts by weight of the silver (Ag) contained in the electrode.

4. The solar cell according to claim 3, wherein, the glass transition temperature of the glass frit is 250°C to 600°C.

5. The solar cell according to claim 3 or 4, wherein, The frit contains at least one selected from SiO 2 , B 2 O 3 , V 2 O 5 , Bi 2 O 3 , TeO 2 , Li 2 O, and ZnO.

6. The solar cell according to any one of claims 3 to 5, wherein, the glass frit substantially does not contain PbO.

7. The solar cell according to any one of claims 1 to 6, wherein, the electrode substantially does not contain lead (Pb).

8. The solar cell according to any one of claims 1 to 7, wherein, the electrode substantially does not contain aluminum particles.

9. The solar cell according to any one of claims 1 to 8, wherein, the substrate is a crystalline silicon substrate of the first conductivity type, the impurity diffusion layer is an impurity diffusion layer of the second conductivity type, the electrode is a light incident side surface electrode disposed on the light incident side surface, the solar cell further comprises a back electrode disposed in a manner of being electrically connected to the surface of the crystalline silicon substrate opposite to the light incident side surface, the light incident side surface electrode is the light incident side surface electrode that has been subjected to the following treatment: while applying a voltage between the back electrode and the light incident side surface electrode so that a current flows in a direction opposite to the forward direction between the impurity diffusion layer of the second conductivity type and the crystalline silicon substrate of the first conductivity type, irradiating the light incident side surface of the solar cell with light from a point light source.

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