Conductive paste, use of conductive paste, solar cell, and method for manufacturing solar cell

Abstract

In order to produce a crystalline silicon solar cell, a conductive paste is provided, which is suitable for the formation of an electrode by a laser treatment process, and which contains a lead-free glass frit. This conductive paste is used for forming an electrode of a solar cell, and contains (A) conductive particles, (B) an organic vehicle, and (C) a glass frit that does not substantially contain PbO, the product BGF * G of the alkalinity BGF of the glass frit (C) and the content G of the glass frit (C) in parts by weight in the conductive paste when the content of the conductive particles (A) in the conductive paste is taken as 100 parts by weight is in the range of 0.25-1.45.

Description

TECHNICAL FIELD

[0001] The present application relates to a conductive paste used in electrode formation of a semiconductor device or the like. In particular, the present application relates to a conductive paste for electrode formation of a solar cell. In addition, the present application relates to a solar cell manufactured using the conductive paste for electrode formation and a manufacturing method of a solar cell. BACKGROUND

[0002] In a semiconductor device such as a crystalline silicon solar cell using a crystalline silicon which is processed into a flat plate shape from a single crystal silicon or a polycrystal silicon as a substrate, an electrode is formed on the surface of the silicon substrate using a conductive paste for electrode formation in order to electrically contact the device with the outside. In the semiconductor device in which the electrode is formed like this, in recent years, the production amount of the crystalline silicon solar cell has greatly increased. These solar cells have a diffusion layer of impurities, an anti-reflection film, and a light incident side surface electrode on one surface of the crystalline silicon substrate, and a back surface electrode on the other surface. With the light incident side surface electrode and the back surface electrode, it is possible to take out the electric power emitted from the crystalline silicon solar cell to the outside.

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

[0004] The glass frit contained in the conductive paste generally contains lead (Pb). However, lead (Pb) can possibly cause adverse effects on the environment. Therefore, a lead-free glass frit which does not contain lead has been proposed.

[0005] As an example of a conductive paste containing a lead-free glass frit, Patent Literature 1 describes a conductive paste containing: (a) about 85 wt% to about 99.5 wt% of an electrically conductive metal or a derivative thereof based on the solid content, (b) about 0.5 wt% to 15 wt% of a lead-free glass frit containing tellurium-bismuth-selenium-lithium-oxide based on the solid content, and (c) an organic carrier. Note that in Patent Literature 1, the weight of the solid content is the total weight of (a) the electrically conductive metal or the derivative thereof and (b) the lead-free glass frit.

[0006] In Patent Literature 2, a process for improving the ohmic contact behavior between a contact grid and an emitter layer in a silicon solar cell is described. Specifically, as described in Patent Literature 2, a given voltage is applied in the 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 a sub-section on the sun side.

[0007] Patent Document 3 discloses a conductive composition comprising silver powder, PbO-containing glass powder, and an organic carrier. Patent Document 3 also discloses a conductive composition used to form an electrode that penetrates a silicon nitride layer and is conductive to an n-type semiconductor layer formed beneath the silicon nitride layer. Furthermore, Patent Document 3 discloses 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.

[0008] Existing technical literature

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent No. 5934411

[0011] Patent Document 2: Japanese Patent Publication No. 2021-513218

[0012] Patent Document 3: Japanese Patent Application Publication No. 2009-231826 Summary of the Invention

[0013] Figure 5 The image shows an example of a typical cross-sectional schematic diagram of a crystalline silicon solar cell. For example... Figure 5 As shown, in a crystalline silicon solar cell, an impurity diffusion layer 4 (e.g., a p-type impurity diffusion layer obtained by diffusing p-type impurities) is typically formed on the light-incident side surface (light-incident side surface) of a crystalline silicon substrate 1 (e.g., an n-type crystalline silicon substrate 1). An anti-reflective film 2 is formed on the impurity diffusion layer 4. The anti-reflective film 2 also functions as a passivation film, and is therefore sometimes referred to as a passivation film. Furthermore, an electrode pattern for the light-incident side surface electrode 20 (surface electrode) is printed on the anti-reflective film 2 using a conductive paste, such as by screen printing. The conductive paste is then 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 this given temperature, the conductive paste burns through the anti-reflective film 2. Through this burn-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 burn-through refers to etching the anti-reflective film 2, which serves as an insulating film, with glass frit contained in a conductive paste, so that the surface electrode 20 on the light incident side becomes electrically connected to the impurity diffusion layer 4. Figure 5In the example shown, during the firing of the electrode pattern, the electrode pattern burns through the antireflective film 2, causing the antireflective film 2 to disappear. As a result, the light-incident 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 antireflective film 2 and the impurity diffusion layer 4 before entering the n-type crystalline silicon substrate 1. During this process, light is absorbed in the n-type crystalline silicon substrate 1, generating electron-hole pairs. Due to 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 surface electrode 20. Electrons and holes (charge carriers) are extracted to the outside in the form of current through these electrodes.

[0014] Figure 2 This is an example of a schematic diagram showing the light-incident side surface of a crystalline silicon solar cell. For example... Figure 2 As shown, on the light-incident side surface of a crystalline silicon solar cell, 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 disposed as the light-incident side surface electrode 20. Figure 5 and Figure 2 In the example shown, electrons from the electron-hole pairs generated by incident light on the crystalline silicon solar cell converge at the sub-gate electrode 20b, and then converge at the light-incident side main gate electrode 20a. On the light-incident side main gate electrode 20a, interconnecting metal solder strips covered with solder are welded. Current is extracted to the outside using these metal solder strips.

[0015] To obtain a crystalline silicon solar cell with high conversion efficiency, a low contact resistance is required between the light incident side surface electrode 20 and the impurity diffusion layer 4.

[0016] As a component of the conductive paste, a glass frit containing lead oxide (PbO) (lead-containing glass frit) is typically used. This is because including lead-containing glass frit in the conductive paste used to form the electrodes of a crystalline silicon solar cell reduces the contact resistance between the light-incident surface electrode 20 and the impurity diffusion layer 4. However, lead has adverse effects on human health. When products are manufactured using lead-containing materials, lead may pollute the environment upon product disposal. Therefore, it is desirable to use lead-free materials that do not contain lead during product manufacturing. In the manufacturing process of solar cells, lead-free glass frit is preferred.

[0017] On the other hand, in order to obtain a low contact resistance between the light-incident side surface electrode 20 and the impurity diffusion layer 4, a method for manufacturing a solar cell using a laser processing technique has been proposed. A specific example of the laser processing technique is described in Patent Document 2. In this specification, the laser processing technique refers to a technique in which, after forming the light-incident side surface electrode 20, a given voltage is applied in such a way that a current flows in the opposite direction to the forward direction of the pn junction of the crystalline silicon solar cell, thereby irradiating the light-incident side surface of the solar cell with light from a point source (e.g., wavelength 400 nm to 1500 nm), thereby obtaining a low contact resistance. Generally speaking, by performing a laser processing technique, the fill factor (FF) can be increased without reducing the open circuit voltage (Voc) in the characteristics of the solar cell. It should be noted that, in the laser processing technique, when the electrode pattern of the conductive paste is fired at a given temperature, it is preferable that the conductive paste does not burn through the anti-reflective film 2 in most of the portion in contact with the electrode pattern. Figure 1 The figure shows an example of a cross-sectional schematic diagram, illustrating the structure of a light-incident side surface electrode 20 formed using a laser processing technique on the light-incident side surface of a crystalline silicon solar cell. For example... Figure 1 As shown, an antireflective film 2 exists in most of the area between the light-incident side surface electrode 20 and the impurity diffusion layer 4. In the laser processing, a given voltage is applied such that a current flows through the pn junction in the opposite direction to the forward direction, and light from a point source is irradiated to generate charge carriers (electrons and holes). Using this laser processing, a current flows through a small region between the light-incident side surface electrode 20 and the impurity diffusion layer 4, thereby causing localized heating. Through this localized heating, a small portion of the impurity diffusion layer 4 is locally formed between the light-incident side surface electrode 20 and the impurity diffusion layer 4, where the impurity diffusion layer 4 is absent. As a result, it is believed that... Figure 6 and 7 As shown, in the impurity diffusion layer 4 that contacts the light-incident side surface electrode 20, an AgSi alloy 30 (an alloy of silver and silicon) is locally formed as a tiny electrically conductive portion (local conductive section). It should be noted that because the AgSi alloy 30 is locally formed in a limited area, its electrical conductivity is limited. Figure 1 The illustrations are omitted. Additionally, Figure 6 and 7The dashed ellipse represents the approximate location of the AgSi alloy 30, but does not strictly represent its boundary. It can be considered that by utilizing this locally formed, small electrically conductive portion, good electrical conductivity can be achieved between the light-incident side surface electrode 20 and the impurity diffusion layer 4. Furthermore, an anti-reflective film 2 (passivation film) exists in most of the space between the light-incident side surface electrode 20 and the impurity diffusion layer 4, excluding the portion where the locally conductive portion is formed. As a result, the fill factor (FF) can be improved without reducing the open-circuit voltage (Voc) as a performance characteristic of the solar cell. Therefore, the conductive paste used in the formation of the light-incident side surface electrode 20 based on the laser processing technology needs to have properties different from conventional conductive pastes (conductive pastes capable of burning through the anti-reflective film 2).

[0018] Furthermore, in conventional crystalline silicon solar cells, during the formation of the light-incident side surface electrode 20, the conductive paste electrode pattern is sintered, thereby burning through the antireflective film 2 and bringing it into contact with the impurity diffusion layer 4. This burn-through causes damage to the impurity diffusion layer 4, resulting in a decrease in the performance of the crystalline silicon solar cell. In contrast, in the laser processing process, during the sintering used to form the light-incident side surface electrode 20, the conductive paste electrode pattern essentially does not burn through the antireflective film 2. Therefore, by using the laser processing process, damage to the impurity diffusion layer 4 can be suppressed.

[0019] Therefore, the present invention aims to provide a conductive paste suitable for the formation of electrodes based on laser processing technology, and comprising lead-free glass frit, for the manufacture of crystalline silicon solar cells.

[0020] Furthermore, an object of the present invention is to provide a method for manufacturing a high-performance crystalline silicon solar cell, which is suitable for electrode formation based on a laser processing process and uses a conductive paste comprising lead-free glass frit. Additionally, an object of the present invention is to provide a high-performance lead-free crystalline silicon solar cell manufactured using a manufacturing method comprising electrode formation based on a laser processing process.

[0021] To address the aforementioned issues, the present invention has the following configuration.

[0022] (Component 1)

[0023] Component 1 is a conductive paste used to form the electrode of a solar cell, comprising:

[0024] (A) Conductive particles,

[0025] (B) Organic carriers, and

[0026] (C) Glass material,

[0027] The glass material described above (C) does not actually contain PbO.

[0028] The basicity B of the above (C) glass frit GF B is the product of the content of the conductive paste (A) conductive particles in the conductive paste (in parts by weight) and the content of the conductive paste (C) glass frit in the conductive paste (in parts by weight) when the content of the 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.

[0029] (Component 2)

[0030] Composition 2 is a conductive paste according to Composition 1, wherein the glass material (C) above contains Bi2O3.

[0031] (Component 3)

[0032] Composition 3 is a conductive paste according to composition 1 or 2, wherein the content of Bi2O3 in the glass frit (C) described above, expressed in mol%, is (C Bi2O3 The product of (C) and the above-mentioned content G of the glass material is C Bi2O3 ·G is in the range of 10 to 200.

[0033] (Component 4)

[0034] Composition 4 is a conductive paste according to any one of Compositions 1 to 3, wherein the conductive particles in (A) above include silver particles.

[0035] (Component 5)

[0036] Composition 5 is a conductive paste according to any one of compositions 1 to 4, wherein the content G of the glass frit (C) is 0.1 to 5.0 parts by weight.

[0037] (Composition 6)

[0038] Composition 6 is a conductive paste according to any one of compositions 1 to 5, wherein the content G of the glass frit (C) is 0.3 to 3.0 parts by weight.

[0039] (Component 7)

[0040] Composition 7 is a conductive paste according to any one of compositions 1 to 6, wherein the glass transition temperature of the glass material (C) is 250 to 600°C.

[0041] (Composition 8)

[0042] Composition 8 is a conductive paste according to any one of Compositions 1 to 7, wherein the glass frit (C) above contains at least one selected from SiO2, B2O3, V2O5, Bi2O3, TeO2, BaO, CuO, Li2O and ZnO.

[0043] (Composition 9)

[0044] Composition 9 is a conductive paste according to any one of Compositions 1 to 8, wherein (B) the organic carrier comprises at least one selected from ethyl cellulose, rosin ester, acrylic resin and organic solvent.

[0045] (Composition 10)

[0046] Configuration 10 is a conductive paste according to any one of Configurations 1 to 9, used to form the electrodes of a solar cell.

[0047] Solar cells include:

[0048] Semiconductor substrate of the first conductivity type,

[0049] A second conductivity type semiconductor layer disposed on one surface of the semiconductor substrate of the first conductivity type.

[0050] The back electrode is configured to be electrically connected to another surface of the semiconductor substrate of the first conductivity type described above.

[0051] The passivation film disposed in contact with the surface of the semiconductor layer of the second conductivity type, and

[0052] At least a portion of the light incident side surface electrode is disposed on the surface of the passivation film.

[0053] The aforementioned light-incident side surface electrode is a light-incident side surface electrode that has undergone the following treatment: while applying a voltage between the back electrode and the light-incident side surface electrode to allow a current flowing in the opposite direction to the forward direction between the second conductivity type semiconductor layer and the first conductivity type semiconductor substrate, light from a point source is irradiated onto the light-incident side surface of the solar cell.

[0054] The aforementioned conductive paste is a conductive paste used to form the aforementioned light incident side surface electrode.

[0055] (Composition 11)

[0056] Configuration 11 is a solar cell that includes:

[0057] Semiconductor substrate of the first conductivity type,

[0058] A second conductivity type semiconductor layer disposed on one surface of the semiconductor substrate of the first conductivity type.

[0059] The back electrode is configured to be electrically connected to another surface of the semiconductor substrate of the first conductivity type described above.

[0060] The passivation film disposed in contact with the surface of the semiconductor layer of the second conductivity type, and

[0061] At least a portion of the light incident side surface electrode is disposed on the surface of the passivation film.

[0062] The aforementioned light-incident side surface electrode is a light-incident side surface electrode that has undergone the following treatment: while applying a voltage between the back electrode and the light-incident side surface electrode to allow a current flowing in the opposite direction to the forward direction between the second conductivity type semiconductor layer and the first conductivity type semiconductor substrate, light from a point source is irradiated onto the light-incident side surface of the solar cell.

[0063] The aforementioned light incident side surface electrode is a sintered body constituting the conductive paste described in any one of items 1 to 10.

[0064] Configuration 12 is a solar cell that includes:

[0065] First conductivity type crystalline silicon substrate,

[0066] A silicon emitter layer of the second conductivity type disposed on one surface of the crystalline silicon substrate of the first conductivity type described above,

[0067] The back electrode is electrically connected to the other surface of the crystalline silicon substrate of the first conductivity type described above.

[0068] The passivation film disposed in contact with the surface of the silicon emitter layer of the second conductivity type described above, and

[0069] A light-incident side surface electrode containing silver disposed on at least a portion of the surface of the passivation film.

[0070] The silicon emitter layer of the second conductivity type described above has a local conductive portion that is in direct contact with the light incident side surface electrode without being separated by a passivation film.

[0071] The aforementioned partial conductive portion comprises an alloy of silver and silicon.

[0072] The aforementioned light incident side surface electrode is a sintered body constituting the conductive paste described in any one of items 1 to 10.

[0073] (Composition 13)

[0074] Configuration 13 is a method for manufacturing a solar cell, the method comprising:

[0075] Prepare a semiconductor substrate of the first conductivity type;

[0076] A semiconductor layer of the second conductivity type is formed on one surface of the semiconductor substrate of the first conductivity type described above;

[0077] A back electrode is formed in such a way that it is electrically connected to another surface of the semiconductor substrate of the first conductivity type described above;

[0078] A passivation film is formed in such a way that it contacts the surface of the semiconductor layer of the second conductivity type described above;

[0079] A light-incident side surface electrode is formed on at least a portion of the surface of the passivation film; and

[0080] While applying a voltage between the back electrode and the light-incident surface electrode to allow a current to flow in the opposite direction between the second conductivity type semiconductor layer and the first conductivity type semiconductor substrate, light from a point source is irradiated onto the light-incident surface of the solar cell.

[0081] The aforementioned light incident side surface electrode is a sintered body constituting the conductive paste described in any one of items 1 to 10.

[0082] Configuration 14 is the application of a conductive paste described in any one of configurations 1 to 10 for forming an electrode of a solar cell.

[0083] Configuration 15 is a solar cell according to Configuration 11 or 12, wherein the back electrode is a sintered body of a conductive paste for the back electrode.

[0084] The conductive paste for the back electrode described above comprises:

[0085] The second conductive particle,

[0086] The second organic carrier, and

[0087] Second glass material,

[0088] The second glass material mentioned above does not actually contain PbO.

[0089] The aforementioned second glass material comprises at least one selected from SiO2, B2O3, Bi2O3, P2O5, Li2O, Na2O, Al2O3, TeO2, TiO2, ZrO2 and ZnO.

[0090] Configuration 16 is a solar cell according to Configuration 15, wherein the second glass material mentioned above contains TeO2.

[0091] Configuration 17 is a method for manufacturing a solar cell as described in Configuration 13, wherein the back electrode is a sintered body of a conductive paste for the back electrode.

[0092] The conductive paste for the back electrode described above comprises:

[0093] The second conductive particle,

[0094] The second organic carrier, and

[0095] Second glass material,

[0096] The second glass material mentioned above does not actually contain PbO.

[0097] The aforementioned second glass material comprises at least one selected from SiO2, B2O3, Bi2O3, P2O5, Li2O, Na2O, Al2O3, TeO2, TiO2, ZrO2 and ZnO.

[0098] Configuration 18 is a method for manufacturing a solar cell as described in Configuration 17, wherein the second glass material mentioned above contains TeO2.

[0099] According to the present invention, in order to manufacture crystalline silicon solar cells, a conductive paste suitable for the formation of electrodes based on laser processing technology can be provided, and which contains lead-free glass frit.

[0100] Furthermore, according to the present invention, an objective is to provide a method for manufacturing a high-performance crystalline silicon solar cell, which uses a conductive paste suitable for forming electrodes based on laser processing technology and comprising lead-free glass frit. Additionally, the present invention can provide a high-performance lead-free crystalline silicon solar cell manufactured using a manufacturing method including forming electrodes based on laser processing technology. Attached Figure Description

[0101] Figure 1 This is an example of a cross-sectional schematic diagram showing the structure of a light-incident side surface electrode formed on the light-incident side surface of a crystalline silicon solar cell using the conductive paste of this embodiment via a laser processing process.

[0102] Figure 2 This is an example of a schematic diagram of the light-incident side surface of a crystalline silicon solar cell.

[0103] Figure 3 This is an example of a schematic diagram of the back side of a crystalline silicon solar cell.

[0104] Figure 4 This is an example of a cross-sectional schematic diagram of a double-sided light-receiving crystalline silicon solar cell formed using the conductive paste of this embodiment.

[0105] Figure 5 This is an example of a cross-sectional schematic diagram of the area near the light-incident surface electrode (sub-gate electrode) of a typical crystalline silicon solar cell, and it is a cross-sectional schematic diagram showing the state in which the anti-reflection film (passivation film) between the electrode and the impurity diffusion layer disappears due to burn-through.

[0106] Figure 6 This is a cross-sectional SEM (scanning electron microscope) image (magnification: 20,000x) of a solar cell with a light-incident side surface electrode formed using the conductive paste of Reference Example 1.

[0107] Figure 7 This is a cross-sectional SEM image (magnification: 20,000x) of a solar cell with a light-incident side surface electrode formed using the conductive paste of Example 1.

[0108] Figure 8 This is a cross-sectional SEM image (magnification: 20,000x) of a solar cell with a light-incident side surface electrode formed using the conductive paste of Comparative Example 1.

[0109] Figure 9 The image shown is a cross-sectional SEM (scanning electron microscope) photograph (magnification: 20,000x) of the passivation film on the light-incident side surface of the crystalline silicon solar cell of Reference Example 1, and is a diagram used to illustrate the depth d of the region of AgSi alloy.

[0110] Figure 10 The image shown is a cross-sectional SEM (scanning electron microscope) photograph (magnification: 20,000x) of the passivation film on the light-incident side surface of the crystalline silicon solar cell of Reference Example 1, and is a graph used to illustrate the passivation film retention rate Lp / (Lp+Le). Detailed Implementation

[0111] The embodiments of the present invention will now be described in detail. It should be noted that the following embodiments are merely illustrative of the present invention and do not limit the scope of the invention.

[0112] In this specification, "crystalline silicon" includes both monocrystalline silicon and polycrystalline silicon. Furthermore, the term "crystalline silicon substrate" refers to a material in which crystalline silicon is shaped into a planar or other form suitable for forming semiconductor devices such as electrical or electronic components. Crystalline silicon can be manufactured using any method. For example, the Chuklaski method can be used for monocrystalline silicon, and the casting method can be used for polycrystalline silicon. Additionally, polycrystalline silicon ribbons manufactured using other methods, such as those produced by the ribbon pulling process, or polycrystalline silicon formed on dissimilar substrates such as glass, can also be used as crystalline silicon substrates. Furthermore, the term "crystalline silicon solar cell" refers to a solar cell manufactured using a crystalline silicon substrate.

[0113] In this specification, the term "glass material" refers to a material made primarily of various oxides, such as metal oxides, and is typically used in the form of glassy particles.

[0114] In this specification, the term "lead-free glass" refers to glass that substantially does not contain lead (Pb). Since glass is manufactured using metal oxides as raw materials, lead-free glass means glass that substantially does not contain lead oxide (PbO). In manufacturing lead-free glass, materials containing lead (PbO) are not intentionally used. However, trace amounts of lead may unavoidably be present as impurities in lead-free glass. Specifically, the lead-free glass of this embodiment may contain less than 0.1% by weight of lead as an impurity per 100% of the glass.

[0115] like Figure 1 As shown, a sub-gate electrode 20b is disposed on the light-incident side surface of a crystalline silicon solar cell as a light-incident side surface electrode 20. Figure 1 In the example shown, holes from electron-hole pairs generated by incident light onto a crystalline silicon solar cell are collected at the sub-gate electrode 20b via an impurity diffusion layer 4 (e.g., a p-type impurity diffusion layer 4). Therefore, a low contact resistance between the sub-gate electrode 20b and the impurity diffusion layer 4 is required. The conductive paste of this embodiment is preferably used for forming the sub-gate electrode 20b.

[0116] It should be noted that, in this specification, the light-incident side surface electrode 20 and the back electrode 15, which are used as electrodes to extract current from a crystalline silicon solar cell to the outside, are sometimes referred to together as "electrodes".

[0117] This embodiment is a conductive paste for forming electrodes in a solar cell. The conductive paste of this embodiment comprises (A) conductive particles, (B) an organic carrier, and (C) a glass frit. The glass frit (C) contained in the conductive paste of this embodiment substantially does not contain PbO. That is, the glass frit (C) contained in the conductive paste of this embodiment is lead-free glass frit. Furthermore, in the conductive paste of this embodiment, the alkalinity of the glass frit (C) and the content of the glass frit (C) in the conductive paste are appropriately controlled.

[0118] The conductive paste of this embodiment contains (C) glass frit, which is substantially lead-free. Furthermore, the materials other than (C) glass frit in the conductive paste of this embodiment are also substantially lead-free. Therefore, the conductive paste of this embodiment is a lead-free conductive paste. Thus, solar cells manufactured using the conductive paste of this embodiment can prevent lead pollution of the environment when discarded.

[0119] The photoelectric conversion efficiency (sometimes simply called "conversion efficiency") of a solar cell is expressed as the product of the fill factor (FF), open circuit voltage (Voc), and short circuit current (Jsc). Basically, FF and Voc are inversely related. Therefore, it is difficult to simultaneously increase both FF and Voc. On the other hand, Patent Document 2 describes how, by employing a laser processing process during the manufacture of a crystalline silicon solar cell, the ohmic contact behavior between the grid-shaped electrode (serving as the light-incident side surface electrode 20) and the impurity diffusion layer 4 (emitter layer) can be improved. Furthermore, it describes how the contact resistance between the light-incident side surface electrode 20 and the impurity diffusion layer 4 can be significantly reduced. Therefore, by performing a laser processing process, FF can be increased without reducing Voc.

[0120] The inventors have discovered that when a laser processing process is applied to a solar cell that uses a conventional conductive paste (such as the conductive paste described in Patent Document 3) to form the light incident side surface electrode 20, it adversely affects the antireflective film 2 (passivation film) and the impurity diffusion layer 4 (and the substrate 1), resulting in a decrease in the conversion efficiency of the solar cell. Furthermore, the inventors have found that this is because the conventional conductive paste has excessively strong burn-through (reactivity) to the antireflective film 2 (passivation film). In addition, the inventors have discovered that by adjusting the alkalinity and content of the lead-free glass frit to an appropriate range, the reactivity of the glass frit to the antireflective film 2 (passivation film) can be appropriately adjusted. By using lead-free glass frit, lead pollution to the environment caused by lead discharge can be prevented. Furthermore, when using the conductive paste (lead-free glass frit) of this embodiment, the contact resistance of the resulting electrode can be reduced to the same extent as that of lead-containing glass frit. Having obtained the above insights, the inventors discovered a conductive paste that can be preferably used in the manufacture of crystalline silicon using a laser processing process, thus completing the present invention.

[0121] By using the conductive paste of this embodiment to form the electrodes of a crystalline silicon solar cell and performing a laser processing process, a low contact resistance can be obtained between the electrodes and the impurity diffusion layer 4 of the solar cell without compromising the function of the antireflective film 2 as a passivation film. Therefore, by using the conductive paste of this embodiment and performing a laser processing process, a crystalline silicon solar cell with high conversion efficiency can be obtained. The conductive paste of this embodiment is preferably used during the manufacture of a crystalline silicon solar cell for forming the light incident side surface electrode 20 using a laser processing process.

[0122] In the laser processing using the conductive paste of this embodiment, the antireflective film 2 (passivation film) is essentially not burned through when the light incident side surface electrode 20 is formed. Furthermore, even when the light incident side surface electrode 20 is subjected to laser processing, most of the antireflective film 2 (passivation film) in contact with the light incident side surface electrode 20 does not disappear. That is, the antireflective film 2 (passivation film) exists in most of the area between the light incident side surface electrode 20 and the impurity diffusion layer 4 (e.g., more than 90% of the interface area, preferably more than 95% of the area, more preferably more than 99%), except for the locally formed small electrically conductive portions (partially conductive portions). Therefore, by using a laser processing process when forming the light incident side surface electrode 20, damage to the impurity diffusion layer 4 can be suppressed.

[0123] One type of crystalline silicon solar cell is a bifacial crystalline silicon solar cell that generates electricity by incident light from two surfaces (the first and second light-incident surfaces). In this case, electrodes formed on the first and second light-incident surfaces using the conductive paste of this embodiment are preferably used.

[0124] The conductive paste of this embodiment is preferably used to form the light-incident side surface electrode 20, which is formed on the surface (light-incident side surface) of the anti-reflection film 2 (passivation film) formed on the impurity diffusion layer 4, but is not limited thereto. For example, the conductive paste of this embodiment can also be used to form the back electrode 15 on the surface (back side) opposite to the light-incident side surface. Sometimes a passivation film is formed on the back side of a crystalline silicon solar cell, and the back electrode 15 is formed on the passivation film. In the case of this solar cell structure, as described above, the conductive paste of this embodiment can be used to sandwich the passivation film on the back side to form an electrical contact between the back electrode 15 and the crystalline silicon substrate 1 of the solar cell.

[0125] The conductive paste of the present invention will be described below using the case of forming a light-incident side surface electrode 20 (surface electrode) of a crystalline silicon solar cell using an n-type crystalline silicon substrate 1 as an example. In the case of this crystalline silicon solar cell, the impurity diffusion layer 4 formed on the light-incident side surface is a p-type impurity diffusion layer 4. It should be noted that in this specification, the impurity diffusion layer 4 in the case of a solar cell using a crystalline silicon substrate 1 is sometimes referred to as a "silicon emitter layer". In addition, an anti-reflective film 2 is formed on the surface of the p-type impurity diffusion layer 4.

[0126] The passivation film (anti-reflective film 2) can be a single layer or multiple layers. When the passivation film is a single layer, from the perspective of effectively passivating the surface of the silicon substrate, the passivation film is preferably a thin film (SiN film) made of silicon nitride (SiN). Alternatively, when the passivation film is multiple layers, it can be a laminate of a thin film made of silicon nitride and a thin film made of silicon oxide (SiN / SiO). x (Membranes). It should be noted that in SiN / SiO... x When the film is a passivation film, from the perspective of more effectively passivating the surface of the silicon substrate, it is preferable to make SiO... x SiO is formed by contacting the film with the silicon substrate 1. x Membrane, and in SiO x A SiN film is formed on the membrane. SiO x The film can be the natural oxide film of the silicon substrate.

[0127] A crystalline silicon solar cell may have a light-incident side main grid electrode 20a and / or a back TAB electrode 15a. The light-incident side main grid electrode 20a has the function of electrically connecting a sub-grid electrode 20b for collecting current generated by the solar cell to an interconnecting metal solder strip. Similarly, the back TAB electrode 15a has the function of electrically connecting a back full-face electrode 15b for collecting current generated by the solar cell to an interconnecting metal solder strip. If the sub-grid electrode 20b contacts the crystalline silicon substrate 1, the surface defect density of the surface (interface) of the crystalline silicon substrate 1 at the contact point of the sub-grid electrode 20b increases, and the performance of the solar cell decreases. The conductive paste of the present invention, particularly as a conductive paste for the sub-grid electrode 20b, has low burn-through (reactivity) to the anti-reflective film 2, and therefore will not completely burn through the anti-reflective film 2. Therefore, when the sub-grid electrode 20b is formed using the conductive paste of the present invention, the passivation film at the contact point with the crystalline silicon substrate 1 can maintain its original state, and the increase in surface defect density, which is a cause of carrier recombination, can be prevented. Therefore, the conductive paste of this embodiment described above can be appropriately used as a conductive paste for forming the sub-gate electrode 20b of a crystalline silicon solar cell. It should be noted that the conductive paste of this embodiment, as... Figure 4 As shown, it can also be suitably used as the back electrode 15 (back sub-gate electrode 15c) of a bifacial light-receiving crystalline silicon solar cell. Alternatively, the conductive paste of this embodiment can be used to form the entire electrode 20.

[0128] In the laser processing, light from a point source is irradiated after applying the given voltage. Current flows through a small region between the surface electrode 20 on the light-incident side and the impurity diffusion layer 4 (silicon emitter layer), resulting in localized heating. The result is as follows: Figure 7As shown, an AgSi alloy 30 is formed as a local electrical conduction portion (local conduction section) in the impurity diffusion layer 4 (silicon emitter layer) that contacts the light incident side surface electrode 20. It can be considered that good electrical conduction between the light incident side surface electrode 20 and the impurity diffusion layer 4 (silicon emitter layer) can be achieved using this locally formed electrical conduction portion. Therefore, the conductive paste used in the formation of the light incident side surface electrode 20 based on the laser processing process of this embodiment has properties different from conventional conductive pastes (conductive pastes capable of burning through the antireflective film 2).

[0129] The conductive paste of this embodiment will be described in detail.

[0130] <(A) Conductive particles>

[0131] The conductive paste of this embodiment contains (A) conductive particles.

[0132] In the conductive paste of this embodiment, metal particles or alloy particles can be used as conductive particles. Examples of metals included in the metal or alloy particles include silver, gold, copper, nickel, zinc, and tin. Silver particles (Ag particles) can be used as the metal particles. It should be noted that the conductive paste of this embodiment may contain metals other than silver, such as gold, copper, nickel, zinc, and tin. From the perspective of obtaining low resistance and high reliability, the conductive particles are preferably silver particles composed of silver. It should be noted that silver particles composed of silver may contain other metallic elements as unavoidable impurities. Furthermore, multiple silver particles (Ag particles) are sometimes referred to as silver powder (Ag powder). The same applies to other particles.

[0133] There are no particular limitations on the shape and size (also called particle size or particle diameter) of the conductive particles. For example, spherical and flake-like shapes can be used as particle shapes. The particle size can be defined using the cumulative size of 50% of all particles (D50). 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 determined by measuring particle size distribution using the Microtrac method (laser diffraction scattering method) and based on the results of the particle size distribution measurement.

[0134] 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 keeping the average particle diameter (D50) of the conductive particles within a given range, the reactivity of the conductive paste to the passivation film can be suppressed during the firing of the conductive paste. It should be noted that if the average particle diameter (D50) is greater than the above range, problems such as clogging may occur during screen printing.

[0135] Alternatively, the size of silver particles can be expressed as their BET specific surface area (also simply referred to as "specific surface area"). The preferred BET specific surface area of ​​silver particles is 0.1–1.5 m². 2 / g, more preferably 0.2 to 1.2m 2 / g. BET specific surface area can be measured, for example, using a fully automated specific surface area measuring device such as Macsoeb (manufactured by MOUNTEC).

[0136] <(B) Organic Carrier>

[0137] The conductive paste of this embodiment includes (B) an organic carrier.

[0138] As an organic carrier, it can contain organic binders and solvents. The organic binders and solvents serve functions such as adjusting the viscosity of the conductive paste, and there are no particular limitations. Alternatively, the organic binder can be dissolved in a solvent before use.

[0139] In the conductive paste of this embodiment, (B) the organic carrier preferably comprises at least one selected from ethyl cellulose, rosin ester, acrylic resin, and organic solvent. By including at least one selected from ethyl cellulose, rosin ester, acrylic resin, and organic solvent in the (B) organic carrier, the conductive paste can be screen printed appropriately, and the shape of the printed pattern can be made into a suitable shape.

[0140] As an organic binder, cellulose-based resins (such as ethyl cellulose and nitrocellulose) and (meth)acrylic resins (such as polymethyl acrylate and polymethyl methacrylate) can be selected. The organic carrier contained in the conductive paste of this embodiment preferably includes at least one selected from ethyl cellulose, rosin ester, butyral, acrylic resins, and organic solvents. The amount of organic binder added relative to 100 parts by weight of silver particles is typically 0.1 to 30 parts by weight, preferably 0.2 to 5 parts by weight.

[0141] As an organic solvent, one or more can be selected from alcohols (such as terpineol, α-terpineol, and β-terpineol) and esters (such as hydroxyl-containing esters, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and diethylene glycol monobutyl ether acetate (butyl carbitol acetate)). The amount of solvent added is typically 0.5 to 30 parts by weight relative to 100 parts by weight of silver particles, preferably 2 to 25 parts by weight. A specific example of an organic solvent is diethylene glycol monobutyl ether acetate (butyl carbitol acetate).

[0142] <(C) Glass Material>

[0143] The conductive paste of this embodiment includes (C) glass frit.

[0144] The conductive paste of this embodiment contains lead-free glass frit. Therefore, the glass frit in the conductive paste of this embodiment does not substantially contain lead (Pb). However, the glass frit used in this embodiment may contain trace amounts of lead as an impurity. Specifically, the glass frit used in this embodiment may contain less than 0.1% by weight of lead as an impurity per 100% of the glass frit.

[0145] In the conductive paste of this embodiment, (C) the alkalinity of the glass frit B GF B is the product of (A) the content of conductive particles in the conductive paste (with the content of (C) glass frit in the conductive paste in parts by weight, when the content of (A) conductive particles in the conductive paste is set to 100 parts by weight. GF The basicity B of the glass frit is in the range of 0.05 to 1.5, preferably in the range of 0.1 to 1.4, and more preferably in the range of 0.15 to 1.35. GF The product of B and the content G GF • G is within an appropriate range, which allows the glass frit to have appropriate reactivity to the antireflective film 2 (passivation film). Therefore, when manufacturing crystalline silicon using a laser processing process, the conductive paste of the embodiment can be preferably used.

[0146] The basicity of the glass powder can be calculated using the method described in Patent Document 3 (Japanese Patent Application Publication No. 2009-231826). Specifically, regarding "basicity," the basicity of the glass powder can be defined using the formula shown in "K. Morinaga, H. Yoshida And H. Takebe: J. AmCerm. Soc., 77, 3113 (1994)". Specifically, it is as follows.

[0147] Oxide M i O of M i The bonding force between -O ions, as the attraction Ai between cations and oxygen ions, is given by the following equation.

[0148] A i =Z i ·Z 02- / (r i +r 02- ) 2 =Zi·2 / (r) i +1.40) 2

[0149] Z i The valence of the cation is 2, and the oxygen ion is 2.

[0150] r i Ionic radius (Å) of a cation

[0151] The ionic radius r of oxygen ions i It is 1.40 nm. The A in the above formula... i The reciprocal of B i (=1 / A) i Let M be a single-component oxide. i Oxygen supply capacity.

[0152] B i ≡1 / A i

[0153] If this B i Standardized as B CaO =1, B SiO2 =0, then give the B of each single-component oxide. i -Indicators. If the B of each component... i - By extending the index to multi-component systems using the percentage of cations, the basicity (=B) of a melt of glass oxide (glass frit) with any composition can be calculated. GF ).

[0154] B GF =Σn i ·B i

[0155] n i : Cation percentage

[0156] Alkalinity (B) specified like this GF As mentioned above, alkalinity indicates oxygen supply capacity; a higher value indicates easier oxygen supply and easier oxygen exchange with other metal oxides. In other words, "alkalinity" can represent the degree of dissolution in the glass melt.

[0157] Since the content G of glass frit (C) is a ratio relative to the content of conductive particles (A), it is a dimensionless number. Furthermore, as mentioned above, since B... i It is standardized as B CaO =1, B SiO2 =0, therefore (C) the alkalinity of the glass frit B GF (=Σn) i ·B i ( ) is a dimensionless number. Therefore, (C) the basicity of the glass frit B GF The product of B and the content G GF G is also a dimensionless number.

[0158] The alkalinity (B) of the glass frit in this embodiment GF The preferred alkalinity is 0.10–1.5, more preferably 0.15–1.3, and even more preferably 0.20–1.1. At alkalinity (B... GFWithin such a range, by adjusting the amount of glass frit added to the conductive paste, the reactivity of the glass frit to the passivation film can be made appropriate.

[0159] The glass frit content G in the conductive paste of this embodiment is preferably 0.1 to 5.0 parts by weight relative to 100 parts by weight of conductive particles, more preferably 0.2 to 4.0 parts by weight, even more preferably 0.3 to 3.0 parts by weight, and particularly preferably 0.4 to 2.7 parts by weight. The glass frit content G in the conductive paste is related to the alkalinity (B). GF By appropriately adjusting the glass frit, the reactivity of the glass frit to the passivation film can be made appropriate. More specifically, in order to prepare a conductive paste suitable for forming electrodes using laser processing, the glass frit content is reduced compared to the past, and the basicity of the glass frit is made within an appropriate range, thereby suppressing the reactivity to the passivation film and increasing Voc.

[0160] The conductive paste of this embodiment preferably contains one or more glass frits selected from SiO2, B2O3, V2O5, Bi2O3, TeO2, BaO, CuO, Li2O, and ZnO. By including at least one of these oxides in the glass frit, the basicity of the glass frit can be adjusted to an appropriate range.

[0161] The glass frit preferably contains Bi2O3. The content of Bi2O3 in the glass frit (100 mol%) is preferably 10 to 80 mol%, more preferably 15 to 75 mol%, and even more preferably 20 to 70 mol%. By including Bi2O3 in the glass frit, even without lead, the reactivity with the passivation film can be adjusted to an appropriate range, while the contact resistance can be reduced.

[0162] In this embodiment, the conductive paste preferably contains (C) a Bi₂O₃ content in the glass frit in mol% (C Bi2O3 The product of (C) and (C) the content of glass frit G, C Bi2O3 • G is in the range of 10 to 200, more preferably in the range of 13 to 170, and even more preferably in the range of 15 to 150. This is achieved by multiplying C by the content of glass frit G (C). Bi2O3 • G is within the above range. Even without lead, the reactivity with the passivation film can be adjusted to an appropriate range, while reducing contact resistance.

[0163] The glass frit may contain SiO2 within a range that does not adversely affect the conductive paste of this embodiment. When the glass frit contains SiO2, the SiO2 content in the glass frit (100 mol%) is preferably 10 to 60 mol%, more preferably 15 to 40 mol%. By including an appropriate amount of SiO2 in the glass frit, the reactivity with the passivation film can be controlled.

[0164] The glass frit may contain B2O3 within a range that does not adversely affect the conductive paste of this embodiment. When the glass frit contains B2O3, the content of B2O3 in the glass frit (100 mol%) is preferably 3 to 60 mol%, more preferably 4 to 50 mol%. By including an appropriate amount of B2O3 in the glass frit, the reactivity with the passivation film can be controlled.

[0165] The glass frit can contain V2O5 within a range that does not adversely affect the conductive paste of this embodiment. When the glass frit contains V2O5, the V2O5 content in the glass frit (100 mol%) is preferably less than 8 mol%, more preferably less than 5 mol%. By including V2O5 in the glass frit, the basicity of the glass frit can be reduced. Therefore, when the basicity of the glass frit is high, by including an appropriate amount of V2O5, the basicity of the glass frit can be adjusted to an appropriate range.

[0166] The glass frit can contain TeO2 within a range that does not adversely affect the conductive paste of this embodiment. When the glass frit contains TeO2, the TeO2 content in the glass frit (100 mol%) is preferably less than 80 mol%, more preferably less than 50 mol%. By including TeO2 in the glass frit, the basicity of the glass frit can be reduced. Therefore, when the basicity of the glass frit is high, by including an appropriate amount of TeO2, the basicity of the glass frit can be adjusted to an appropriate range.

[0167] The glass frit may contain BaO within a range that does not adversely affect the conductive paste of this embodiment. When the glass frit contains BaO, the BaO content in the glass frit (100 mol%) is preferably 3 to 20 mol%, more preferably 5 to 10 mol%. By including an appropriate amount of BaO in the glass frit, the reactivity with the passivation film can be adjusted to an appropriate range.

[0168] The glass frit may contain CuO within a range that does not adversely affect the conductive paste of this embodiment. When the glass frit contains CuO, the CuO content in the glass frit (100 mol%) is preferably 10 to 40 mol%, more preferably 20 to 30 mol%. By including an appropriate amount of CuO in the glass frit, the reactivity with the passivation film can be adjusted to an appropriate range.

[0169] The glass frit may contain Li2O within a range that does not adversely affect the conductive paste of this embodiment. When the glass frit contains Li2O, the Li2O content in the glass frit (100 mol%) is preferably 3 to 40 mol%, more preferably 5 to 30 mol%. By including an appropriate amount of Li2O in the glass frit, the reactivity with the passivation film can be adjusted to an appropriate range.

[0170] The glass frit may contain ZnO within a range that does not adversely affect the conductive paste of this embodiment. When the glass frit contains ZnO, the ZnO content in the glass frit (100 mol%) is preferably 5 to 70 mol%, more preferably 15 to 60 mol%. By including ZnO in the glass frit, the basicity of the glass frit can be adjusted to an appropriate range.

[0171] The glass transition temperature (Tg) of the (C) glass frit in this embodiment is preferably 250–600°C, more preferably 270–500°C, and even more preferably 300–470°C. By setting the glass transition temperature (Tg) of the (C) glass frit to 250°C or higher, reactivity with the passivation film can be suppressed. Furthermore, by setting the glass transition temperature (Tg) to 600°C or lower, the contact resistance between the resulting electrode (e.g., the light incident side surface electrode 20) and the impurity diffusion layer 4 can be reduced.

[0172] The glass transition temperature (Tg) can be determined as follows. First, a differential calorimeter (MACScience Co., Ltd. TG-DTA2000S) is used, with the glass powder (sample) and reference material set up. Then, the temperature is increased from room temperature to 900°C at a heating rate of 10°C / min as the measurement conditions, and a curve (DTA curve) is obtained by plotting the temperature difference between the glass powder (sample) and the reference material against temperature. The first inflection point of the DTA curve obtained in this way can be set as the glass transition temperature Tg.

[0173] The shape of the glass particles is not particularly limited; for example, spherical or amorphous shapes can be used. Furthermore, the particle size is not particularly limited. From a workability perspective, the average particle diameter (D50) is preferably in the range of 0.1 to 10 μm, more preferably in the range of 0.5 to 5 μm.

[0174] The glass frit particles can be a single type of particle containing a given amount of each of the required multiple oxides. Alternatively, particles composed of a single oxide can be used as particles that differ for each of the required multiple oxides. Furthermore, multiple particles with different compositions of the required multiple oxides can be used in combination. To synergistically obtain the effects of different types of oxides, the glass frit particles are preferably a single type of particle containing a given amount of each of the required multiple oxides.

[0175] <Other Ingredients>

[0176] The conductive paste of this embodiment may include additives and additives other than those mentioned above, within a range that does not adversely affect the solar cell characteristics of the resulting solar cell.

[0177] In the conductive paste of this embodiment, as an additive, substances selected from plasticizers, defoamers, dispersants, leveling agents, stabilizers, and adhesion promoters may be further incorporated as needed. Among these, at least one plasticizer selected from phthalates, glycolates, phosphate esters, sebacic acid esters, adipates, and citrate esters may be used.

[0178] The conductive paste of this embodiment may include additives other than those described above within a range that does not adversely affect the characteristics of the resulting solar cell. For example, the conductive paste of this embodiment may further include at least one additive selected from titanium resin, titanium oxide, cobalt oxide, cerium oxide, silicon nitride, copper manganese tin, aluminosilicate, and aluminum silicate. By including these additives, the adhesion strength of the electrode to the passivation film can be improved. These additives may be in the form of particles (additive particles). The amount of additive added relative to 100 parts by weight of silver particles is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 2 parts by weight. To obtain higher adhesion strength, the additive is preferably copper manganese tin, aluminosilicate, or aluminum silicate. The additive may include both aluminosilicate and aluminum silicate.

[0179] <Method for manufacturing conductive paste>

[0180] The method for manufacturing the conductive paste according to this embodiment will now be described. The conductive paste of this embodiment can be manufactured by adding silver particles, glass frit, and other additives and / or additives as needed to an organic binder and solvent, and then mixing and dispersing them.

[0181] Mixing can be performed, for example, using a planetary mixer. Dispersion can be performed using a three-roll mill. Mixing and dispersion are not limited to these methods; various known methods can be used.

[0182] Solar cells

[0183] The solar cell of this embodiment will now be described. The conductive paste of this embodiment described above is preferably used to form the electrode of the solar cell. That is, the conductive paste of this embodiment described above is preferably used to form a given electrode of a crystalline silicon solar cell, and its manufacturing process includes a laser processing process on the given electrode.

[0184] This embodiment is a solar cell that uses the above-described conductive paste to form at least a portion of the electrode. Figure 1 and Figure 4 The diagram shows a cross-sectional view of a crystalline silicon solar cell. The conductive paste in this embodiment is substantially lead-free. Furthermore, in the crystalline silicon solar cell of this embodiment, materials other than the conductive paste can also be substantially lead-free. Therefore, the crystalline silicon solar cell of this embodiment can be a lead-free solar cell.

[0185] In the solar cell of this embodiment, crystalline silicon, silicon carbide, germanium, and gallium arsenide can be used as the semiconductor substrate material. From the perspective of safety and cost of the solar cell, crystalline silicon (monocrystalline silicon and polycrystalline silicon, etc.) is preferred as the semiconductor substrate material.

[0186] The solar cell of this embodiment includes a first conductivity type semiconductor substrate, a second conductivity type semiconductor layer disposed on one surface of the first conductivity type semiconductor substrate, a passivation film (anti-reflection film 2) disposed in contact with the surface of the second conductivity type semiconductor layer, and a light incident side surface electrode 20 disposed on at least a portion of the surface of the passivation film. Additionally, the solar cell of this embodiment may include a back electrode 15 disposed in electrical connection with the other surface of the first conductivity type semiconductor substrate. Figure 1 In the example, the semiconductor substrate of the first conductivity type is a crystalline silicon substrate 1, the semiconductor layer of the second conductivity type is an impurity diffusion layer 4, and the passivation film is an anti-reflection film 2.

[0187] The semiconductor substrate of the first conductivity type is either an n-type or a p-type semiconductor substrate. The semiconductor layer of the second conductivity type is either a p-type or an n-type semiconductor layer. When the semiconductor substrate is an n-type semiconductor substrate, a p-type semiconductor layer (p-type impurity diffusion layer 4) is disposed on one surface of the semiconductor substrate. When the semiconductor substrate is a p-type semiconductor substrate, an n-type semiconductor layer (n-type impurity diffusion layer 4) is disposed on one surface of the semiconductor substrate. The interface between the semiconductor substrate of the first conductivity type and the semiconductor layer of the second conductivity type corresponds to a pn junction. The semiconductor substrate material is preferably silicon. Therefore, a crystalline silicon substrate is preferred.

[0188] The passivation film can be an anti-reflective film 2. The passivation film is preferably a thin film made of silicon nitride.

[0189] The light-incident side surface electrode 20 of the solar cell in this embodiment can be a sintered body of the conductive paste of this embodiment. The conductive paste of this embodiment can be used to manufacture a solar cell with this structure.

[0190] The conductive paste of this embodiment is preferably used for forming the light-incident side surface electrode 20 of a crystalline silicon solar cell using a laser processing process. The laser processing process refers to irradiating the light-incident side surface of the solar cell with light from a point source while applying a voltage to the back electrode 15 and the light-incident side surface electrode 20 to allow current to flow in the pn junction between the second conductivity type semiconductor layer and the first conductivity type semiconductor substrate in the opposite direction to the forward direction. Using the light from the point source, charge carriers (electron-hole pairs) can be generated inside the semiconductor substrate. The application of voltage enables the movement of these charge carriers, i.e., the flow of current. The voltage is applied in such a way that the direction of current flow 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 in such a way that 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, a voltage is applied to the back electrode 15 and the light incident side surface electrode 20 in such a way that current flows from the n-type semiconductor layer to the p-type semiconductor substrate.

[0191] It should be noted that, in crystalline silicon solar cells, as... Figure 4 In the case of the bifacial solar cell shown, light can be incident from two surfaces (the light-incident side surface and the back surface). Therefore, by irradiating at least one surface of the bifacial solar cell with light from a point source, an AgSi alloy can be formed as a local conductive portion in the impurity diffusion layer that contacts at least one electrode (the light-incident surface electrode 20 or the back electrode 15). Furthermore, by irradiating at least one surface of the bifacial solar cell with light from a point source, an AgSi alloy can be formed near the electrodes (the light-incident surface electrode 20 and the back electrode 15) on both surfaces of the bifacial solar cell.

[0192] The semiconductor substrate of the solar cell of this embodiment with respect to the first conductivity type is preferably an n-type semiconductor substrate, and more preferably an n-type crystalline silicon substrate 1. Furthermore, the semiconductor layer of the solar cell of this embodiment with respect to the second conductivity type is preferably a p-type semiconductor layer, and more preferably a p-type impurity diffusion layer 4 made of crystalline silicon. Generally, the electron mobility as a charge carrier in the n-type crystalline silicon substrate 1 is higher than the hole mobility as a charge carrier in the p-type crystalline silicon substrate 1. Therefore, using an n-type crystalline silicon substrate 1 is advantageous for obtaining a solar cell with high conversion efficiency.

[0193] In the following description, a solar cell with an n-type crystalline silicon substrate 1 as the semiconductor substrate of the first conductivity type and a p-type impurity diffusion layer 4 (sometimes simply referred to as "impurity diffusion layer 4") as the semiconductor layer of the second conductivity type will be used as an example.

[0194] like Figure 1 As shown, in the case of using a laser processing technique, an anti-reflection film 2 (passivation film) exists in most of the area between the light-incident surface electrode 20 and the impurity diffusion layer 4. In the laser processing, the given voltage is applied in such a way that a current flows through the pn junction in the opposite direction to the forward direction, and light from a point source (e.g., a laser) is irradiated. This causes a current to flow through a small region between the light-incident surface electrode 20 and the impurity diffusion layer 4, resulting in localized heating. As a result, as... Figure 6 and 7 As shown, an AgSi alloy 30 (an alloy of silver and silicon) is locally formed as an electrically conductive portion (partially conductive portion) between the light-incident side surface electrode 20 and the impurity diffusion layer 4. That is, the locally conductive portion contains an alloy of silver and silicon. In addition, in the locally conductive portion, the impurity diffusion layer 4 (the silicon emitter layer of the second conductivity type) is in direct contact with the light-incident side surface electrode 20 without the anti-reflection film 2 (passivation film) in between. By utilizing this locally formed electrically conductive portion (partially conductive portion), good electrical conductivity between the light-incident side surface electrode 20 and the impurity diffusion layer 4 can be achieved. Compared with conventional conductive pastes, the conductive paste of this embodiment has low reactivity to the anti-reflection film 2 and has reactivity with the anti-reflection film 2 (passivation film) suitable for laser processing. Therefore, the conductive paste of this embodiment is preferably used for forming the light-incident side surface electrode 20 of a crystalline silicon solar cell using a laser processing process.

[0195] Figure 1 The crystalline silicon solar cell shown can have Figure 3 The back electrode 15 of the structure shown is configured to be electrically connected to another surface of the semiconductor substrate of the first conductivity type. Figure 3As shown, the back electrode 15 may typically include a back full electrode 15b and a back TAB electrode 15a electrically connected to the back full electrode 15b.

[0196] Figure 4 The diagram shows an example of a cross-sectional schematic of a bifacial crystalline silicon solar cell. Figure 4 The illustrated bifacial light-receiving crystalline silicon solar cell has an impurity diffusion layer 4 and an anti-reflection film 2 (passivation film and back passivation film). In this bifacial light-receiving crystalline silicon solar cell, a conductive paste of this embodiment can be used to form the light-incident side surface electrode 20 (partially the sub-gate electrode 20b) and the back electrode 15 (back sub-gate electrode 15c) on the light-incident side surface. Therefore, an electrically conductive portion (partially conductive portion) can be formed on the passivation film (anti-reflection film 2) on the light-incident side surface and the back passivation film (anti-reflection film 2) using a laser processing process.

[0197] Therefore, the conductive paste of this embodiment described above can be suitably used as a conductive paste for forming the sub-gate electrode 20b of a crystalline silicon solar cell. Furthermore, the conductive paste of this embodiment can also be used as a conductive paste for forming the back electrode 15 of a bifacial light-receiving crystalline silicon solar cell.

[0198] Figure 1 The main grid electrode of the crystalline silicon solar cell shown contains Figure 2 The light incident side main gate electrode 20a and shown Figure 3 The back TAB electrode 15a is shown. Interconnect metal ribbons, covered with solder, are soldered onto the light-incident side main grid electrode 20a and the back TAB electrode 15a. These metal ribbons are used to extract the current generated by the solar cell to the exterior of the crystalline silicon solar cell. Figure 4 The bifacial light-receiving crystalline silicon solar cell shown can also have a light-incident side main grid electrode 20a and a back TAB electrode 15a with the same shape as the light-incident side main grid electrode 20a.

[0199] The width of the main grid electrodes (light-incident side main grid electrode 20a and back TAB electrode 15a) can be the same as the width of the interconnect metal solder strips. To ensure low resistance of the main grid electrodes, a large width is preferred. On the other hand, to increase the incident area of ​​light relative to the light-incident side surface, a small width of the light-incident side main grid electrode 20a is preferable. Therefore, the width of the main grid electrodes can be set to 0.05–5 mm, preferably 0.08–3 mm, more preferably 0.1–2 mm, and even more preferably 0.15–1 mm. Furthermore, the number of main grid electrodes can be determined according to the size of the crystalline silicon solar cell. The number of main grid electrodes is optional. Specifically, the number of main grid electrodes can be 3 or 4, or more. The optimal number of main grid electrodes can be determined by simulating the operation of the solar cell to maximize the conversion efficiency of the crystalline silicon solar cell. It should be noted that since the crystalline silicon solar cells are interconnected in series using interconnect metal solder strips, the number of light-incident side main grid electrodes 20a and back TAB electrodes 15a is preferably the same. For the same reason, the widths of the light incident side main gate electrode 20a and the back TAB electrode 15a are preferably the same.

[0200] To increase the incident area of ​​light on the crystalline silicon solar cell, the area occupied by the light-incident surface electrode 20 on the light-incident side surface is preferably as small as possible. Therefore, the sub-gate electrode 20b on the light-incident side surface is preferably as narrow as possible and preferably has as few electrodes as possible. On the other hand, from the perspective of reducing electrical losses (ohmic losses), it is preferable that the sub-gate electrode 20b has a large width and a large number of electrodes. In addition, from the perspective of reducing the contact resistance between the sub-gate electrode 20b and the crystalline silicon substrate 1 (impurity diffusion layer 4), it is also preferable that the sub-gate electrode 20b has a large width. According to the above explanation, 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 sub-gate electrodes 20b (the spacing of the sub-gate electrodes 20b) can be determined by simulating the operation of the solar cell 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-gate electrodes 15c of the back electrode 15 of the bifacial light-receiving crystalline silicon solar cell shown can also be determined in the same way.

[0201] <Methods for Manufacturing Solar Cells>

[0202] The manufacturing method of the solar cell according to this embodiment will now be described. The solar cell can be a crystalline silicon solar cell. In the following description, an example of a crystalline silicon solar cell will be described.

[0203] The method for manufacturing a solar cell according to this embodiment includes a process of forming an electrode (light incident side surface electrode 20) by printing the aforementioned conductive paste onto the surface of an antireflective film 2 on a second conductivity type semiconductor layer (impurity diffusion layer 4), drying, and firing. The method for manufacturing a solar cell according to this embodiment will be further described in detail below.

[0204] The method for manufacturing a solar cell according to this embodiment includes a step of preparing a semiconductor substrate of a first conductivity type (p-type or n-type) (e.g., a crystalline silicon substrate 1). As the semiconductor substrate of the first conductivity type, an n-type crystalline silicon substrate 1 is preferably used. Hereinafter, an example will be described using an n-type crystalline silicon substrate 1 to manufacture a crystalline silicon solar cell.

[0205] It should be noted that, from the viewpoint of obtaining high conversion efficiency, the surface of the light incident side of the crystalline silicon substrate 1 preferably has a pyramid-shaped textured structure.

[0206] Subsequently, the method for manufacturing a solar cell according to this embodiment includes a step of forming a semiconductor layer of a second conductivity type on one surface of a semiconductor substrate of a first conductivity type.

[0207] The method for manufacturing a crystalline silicon solar cell according to this embodiment includes a step of forming a second conductivity type semiconductor layer (impurity diffusion layer 4) on one surface of a crystalline silicon substrate 1 prepared in the above-described steps. When using an n-type crystalline silicon substrate 1 as the crystalline silicon substrate 1, the impurity diffusion layer 4 can be, for example, a p-type impurity diffusion layer 4 formed by diffusing elements such as boron (B), which are p-type impurities. It should be noted that a p-type crystalline silicon substrate 1 can also be used to manufacture a crystalline silicon solar cell. In this case, an n-type impurity diffusion layer 4 is formed by diffusing elements such as phosphorus (P), which are n-type impurities.

[0208] When forming the impurity diffusion layer 4, it can be formed in such a way that the sheet resistance of the impurity diffusion layer 4 is 40 to 150 Ω / □ (square), preferably 45 to 120 Ω / □.

[0209] Furthermore, in the manufacturing method of the crystalline silicon solar cell of this embodiment, the depth of the impurity diffusion layer 4 can be set to 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 a depth where the impurity concentration in the impurity diffusion layer 4 is equal to the impurity concentration of the substrate.

[0210] The method for manufacturing a solar cell according to this embodiment includes a step of forming a back electrode 15 in a manner electrically connected to another surface of a semiconductor substrate of the first conductivity type (n-type crystalline silicon substrate 1). It should be noted that the back electrode 15 can be formed either before or after the formation of the light-incident side surface electrode 20. Furthermore, the firing for forming the back electrode 15 can be performed simultaneously with or separately from the firing for forming the light-incident side surface electrode 20.

[0211] Specifically, in the manufacturing method of the crystalline silicon solar cell of this embodiment, a back electrode 15 is formed by printing a conductive paste on another surface (back side) of the crystalline silicon substrate 1 and firing it.

[0212] It should be noted that in manufacturing such as Figure 4 In the case of the bifacial light-receiving crystalline solar cell shown, a second impurity diffusion layer 16 can be formed. Alternatively, the back electrode 15 can be formed using the conductive paste (conductive composition) of this embodiment, and a laser processing process can be performed, thereby forming a low-resistance electrically conductive portion (partially conductive portion) between the back electrode 15 and the crystalline silicon substrate 1. Therefore, in the case of the bifacial light-receiving crystalline solar cell, it is preferable to use the conductive paste of this embodiment to form the back electrode 15. In this case, the back electrode 15 is a sintered body of the conductive paste of this embodiment.

[0213] Subsequently, the method for manufacturing a solar cell according to this embodiment includes forming a passivation film in a manner that brings it into contact with the surface of a semiconductor layer (impurity diffusion layer 4) of the second conductivity type. The passivation film may be an anti-reflective film 2.

[0214] Specifically, in the manufacturing method of the crystalline silicon solar cell of this embodiment, an anti-reflective film 2, which also functions as a passivation film, is formed on the surface of the impurity diffusion layer 4 formed in the above-described process. The anti-reflective film 2 can be a silicon nitride film (SiN film). When using a silicon nitride film as the anti-reflective film 2, the silicon nitride film layer also functions as a passivation film on the light incident side surface. Therefore, when using a silicon nitride film as the anti-reflective film 2, a high-performance crystalline silicon solar cell can be obtained. Furthermore, by making the anti-reflective film 2 a silicon nitride film, it is possible to provide anti-reflection functionality against incident light. The silicon nitride film can be formed using methods such as PECVD (Plasma Enhanced Chemical Vapor Deposition).

[0215] The method for manufacturing a solar cell according to this embodiment includes a step of forming a light-incident side surface electrode 20 on at least a portion of the surface of a passivation film (anti-reflection film 2). In the manufacturing method of this embodiment, the conductive paste described above is used to form the light-incident side surface electrode 20. Therefore, the light-incident side surface electrode 20 is a sintered body of the conductive paste described above.

[0216] In the manufacturing method of the crystalline silicon solar cell of this embodiment, the light incident side surface electrode 20 is formed by printing a conductive paste onto the surface of the antireflective film 2 and then firing it. It should be noted that the firing for forming the light incident side surface electrode 20 can be performed simultaneously with the firing for forming the back electrode 15.

[0217] Specifically, firstly, the pattern of the light incident side surface electrode 20 printed using the conductive paste of this embodiment is dried at a temperature of approximately 100–150°C for several minutes (e.g., 0.5–5 minutes). It should be noted that, at this time, the conductive paste of this embodiment can be used to form the light incident side main gate electrode 20a and the light incident side sub-gate electrode 20b of the light incident side surface electrode 20.

[0218] After the pattern of the light-incident side surface electrode 20 is printed and dried, a conductive paste for forming the back electrode 15 is then printed and dried. The conductive paste of this embodiment is preferably used to form the electrodes (light-incident side surface electrode 20 and, depending on the situation, back electrode 15) of a solar cell such as a crystalline silicon solar cell.

[0219] Subsequently, the material obtained by drying the printed conductive paste is fired in an atmosphere under given firing conditions using a firing furnace such as a tubular furnace. The firing atmosphere is atmospheric, and the firing temperature is 500–1000°C, more preferably 600–1000°C, even more preferably 500–900°C, and particularly preferably 700–900°C. Firing is preferably performed within a short time, and the temperature distribution (temperature-time curve) during firing is preferably peak-shaped. For example, it is preferable to use the above-mentioned temperature as the peak temperature, and the furnace entry / exit time is 10–100 seconds, more preferably 20–80 seconds, and even more preferably 40–60 seconds.

[0220] During firing, it is preferable to fire the conductive paste used to form the light-incident side surface electrode 20 and the back electrode 15 simultaneously, thus forming both electrodes at the same time. By printing a given conductive paste onto the light-incident side surface and the back surface in this way and firing it simultaneously, the firing process for electrode formation can be completed in only one step. Therefore, crystalline silicon solar cells can be manufactured at a lower cost.

[0221] The method for manufacturing a solar cell according to this embodiment includes performing the laser processing process described above. Specifically, the method includes the following operation: while applying a voltage between the back electrode 15 and the light-incident side surface electrode 20 to allow a current flowing in the opposite direction between the second conductivity type semiconductor layer (p-type impurity diffusion layer 4) and the first conductivity type semiconductor substrate (n-type crystalline silicon substrate 1), light (e.g., a laser) from a point source is irradiated onto the light-incident side surface of the solar cell. Using the laser processing process, good electrical conductivity between the light-incident side surface electrode 20 and the impurity diffusion layer 4 can be achieved.

[0222] The crystalline silicon solar cell of this embodiment can be manufactured by operating as described above.

[0223] The crystalline silicon solar cell of this embodiment, obtained as described above, is electrically connected using interconnecting metal solder strips. A solar cell module is then obtained by laminating a glass plate, a sealing material, and a protective sheet. The interconnecting metal solder strips can be metal solder strips covered with solder (e.g., copper-based strips). The solder can be tin-based, specifically commercially available leaded solder or lead-free solder. To obtain a lead-free solar cell, lead-free solder is preferred.

[0224] In the crystalline silicon solar cell of this embodiment, a given electrode of the solar cell is formed using the conductive paste of this embodiment, and a laser processing process is performed, thereby obtaining a high-performance crystalline silicon solar cell.

[0225] The conductive paste of this embodiment contains lead-free glass frit. Therefore, the electrodes formed on the surface of the solar cell are also lead-free. Thus, when a solar cell manufactured using the conductive paste of this embodiment is discarded, lead pollution to the environment can be prevented. In other words, by using the conductive paste of this embodiment, lead-free solar cells can be manufactured.

[0226] <Depth d of the region in AgSi alloy 30>

[0227] In this specification, the depth d of the region referred to as AgSi alloy 30 (sometimes simply referred to as "AgSi alloy 30") is as follows: Figure 9 The SEM image shown, obtained by SEM observation of the cross-section of AgSi alloy 30, refers to any one point at the interface connecting the electrode and AgSi alloy 30. Figure 9 Any point from B1 to the interface between the substrate and AgSi alloy 30 ( Figure 9 The length of the longest line segment in line segment B2) Figure 9The length d of the line segment connecting B1 and B2. Specifically, in the region of AgSi alloy 30 determined by SEM image superimposed with EDX measurement obtained from SEM observation of the cross section near the passivation film 2 at a magnification of 20,000, the given line segment is determined, and the length of the given line segment is measured, thereby obtaining the depth d of AgSi alloy 30.

[0228] The depth d of the AgSi alloy 30 is preferably 100–4000 nm, more preferably 120–3000 nm, even more preferably 130–2500 nm, and particularly preferably 150–2000 nm. By making the depth d of the AgSi alloy 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.

[0229] <Residual rate of passivation film 2>

[0230] In this specification, the degree to which the passivation film 2 (anti-reflection film 2) exists between the electrode and the impurity diffusion layer 4 of the crystalline silicon substrate 1 after firing for forming the electrode in the solar cell of this embodiment is present is expressed as the passivation film 2 retention rate. It should be noted that the passivation film 2 disappears in the areas where the AgSi alloy 30 is formed. Since the AgSi alloy 30 is not formed in the areas where the passivation film 2 exists, the so-called passivation film 2 retention rate can be considered as the proportion of the area near the AgSi alloy 30 where the AgSi alloy 30 is not formed.

[0231] use Figure 10 The example of a SEM image of a cross-section of a solar cell illustrates the method for determining the retention rate of the passivation film 2. First, to obtain the retention rate of the passivation film 2, a cross-section containing the passivation film 2 and AgSi alloy 30 is observed using SEM at a magnification of 20,000, thus obtaining an SEM image. It should be noted that the transverse (horizontal direction) length of this SEM image is 5.7 μm, and the longitudinal (perpendicular direction) length is 3.9 μm. Then, the total length Lp of the cross-section of the passivation film 2 in this SEM image is measured. Figure 10 In the example shown, the total length Lp of the cross-section of the passivation film 2 in the SEM image is the sum of the lengths of Lp1, Lp2, Lp3, and Lp4. Then, in this SEM image, the total length Le of the cross-section of the interface between the AgSi alloy 30 and the electrode in the portion where the AgSi alloy 30 is formed is measured. Length Le corresponds to the length by which the passivation film 2 disappears during the solar cell manufacturing process. Figure 10In the example shown, the total length Le of the cross-section of the interface between AgSi alloy 30 and the electrode in the portion where AgSi alloy 30 is formed is the total length of Le1 and Le2. The retention rate of the passivation film 2 can be obtained as Lp / (Lp+Le). It should be noted that the portion of the passivation film 2 that disappears during the solar cell manufacturing process can be determined using EDX-based measurements. Furthermore, the lengths of Le1, etc., can be measured by approximating the passivation film 2, etc., as a straight line.

[0232] In the crystalline silicon solar cell of this embodiment, the residual 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 even more preferably 70% to 89%. By making the residual rate of the passivation film 2 within an appropriate range, a high-efficiency crystalline silicon solar cell with high open-circuit voltage (Voc) and fill factor (FF) can be obtained.

[0233] <Thickness ratio of passivation film 2 before and after firing>

[0234] In this specification, the 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 for forming the electrode to the film thickness Db of the passivation film 2 after firing for forming the electrode (after the solar cell is completed). In this specification, the film thickness ratio before and after firing is sometimes simply referred to as "film thickness ratio (Db / Da)".

[0235] In the solar cell of this embodiment, the film thickness ratio (Db / Da) is preferably 15% to 85%, more preferably 20% to 70%, and even more preferably 30% to 60%. By setting the film thickness ratio (Db / Da) of the passivation film 2 to a given range, it is possible to prevent the increase in surface defect density, which is a cause of carrier recombination, during power generation in the solar cell of this embodiment.

[0236] In this specification, the pre-firing thickness Da of the passivation film 2 refers to the thickness of the passivation film 2 when it is formed on a given substrate. The thickness Da immediately after film formation can be measured by SEM observation of a cross-section near the passivation film 2 before electrode formation.

[0237] In this specification, the so-called film thickness Db after the solar cell is completed refers to the thickness of the passivation film 2 in a scanning electron microscope image of a 5.7 μm × 3.9 μm cross section containing AgSi alloy 30 after the electrodes are formed on the surface of the solar cell by firing.

[0238] In this specification, the thickness Db of the passivation film 2 in a 5.7 μm × 3.9 μm cross-section of the solar cell containing AgSi alloy 30, as seen in a scanning electron microscope image of the completed solar cell after electrodes are formed on the surface of the solar cell, refers to the thickness of the passivation film 2 near AgSi alloy 30 in the completed solar cell after electrode and AgSi alloy 30 are formed by forming an electrode pattern on the passivation film 2 formed on a given substrate using a given conductive paste and undergoing given processing such as firing. Sometimes, the film thickness Db is referred to as the "film thickness Db after the solar cell is completed." The film thickness Db after the solar cell is completed can be determined by observing a 5.7 μm × 3.9 μm image area of ​​the cross-section containing the passivation film 2 and AgSi alloy 30 in the completed solar cell after electrode and AgSi alloy 30 formation using SEM. That is, the final film thickness Db of the completed solar cell is the film thickness Db of the passivation film 2 in a scanning electron microscope image of a 5.7μm × 3.9μm cross-section containing AgSi alloy 30 of the completed solar cell. Specifically, the cross-section containing the passivation film 2 and AgSi alloy 30 is observed by SEM at a magnification of 20,000, thereby obtaining an SEM image (SEM image range: 5.7μm × 3.9μm). The SEM image is divided into 6 equal parts along the longitudinal direction, and the film thickness of the passivation film 2 at 5 intersections of the 6-part image is measured (5 locations). The average of the film thicknesses at the 5 locations can be used to obtain the final film thickness Db of the passivation film 2 of the completed solar cell.

[0239] <Conductive paste for back electrode>

[0240] A conductive paste (conductive paste for back electrode) that can be used to form the back electrode of the solar cell of this embodiment will be described.

[0241] In this specification, the term "back electrode" refers to the surface opposite to the surface on which the electrode is formed using the conductive paste of this embodiment described above. In this specification, the conductive paste used to form the back electrode is specifically referred to as "conductive paste for back electrode." It should be noted that the conductive paste for back electrode, like the conductive paste of this embodiment described above, is a lead-free conductive paste.

[0242] It should be noted that, as such Figure 4The bifacial solar cell shown can be exemplified by a bifacial solar cell using an n-type Si substrate. In the case of the bifacial solar cell using an n-type Si substrate, the surface electrode (light-incident side surface electrode 20) is the electrode on the surface where a p-type diffusion layer is formed, and the back electrode 15, formed using a conductive paste for the back electrode, is the electrode on the surface where an n-type diffusion layer is formed. Alternatively, a conductive paste for the back electrode can be used to form the surface electrode (light-incident side surface electrode 20) of the bifacial solar cell using a p-type Si substrate. In this case, the surface electrode (light-incident side surface electrode 20) is the electrode on the surface where an n-type diffusion layer is formed, and the back electrode 15 is the electrode on the surface where a p-type diffusion layer is formed (the electrode formed using the conductive paste of this embodiment described above).

[0243] The back electrode can be formed using a conductive paste. Figure 4 The back electrode 15 (back sub-gate electrode 15c) of the bifacial light-receiving crystalline silicon solar cell shown is preferably used. Furthermore, a conductive paste for the back electrode can be used to form... Figure 1 The back electrode 15 of the crystalline silicon solar cell shown is preferably used. It should be noted that in the crystalline silicon solar cell of this embodiment, a light incident side surface electrode 20 formed using the conductive paste of this embodiment is disposed on the surface opposite to the back electrode formed using the conductive paste for the back electrode.

[0244] The conductive paste for the back electrode is described below. The conductive paste for the back electrode comprises (A2) conductive particles, (B2) organic carrier, and (C2) glass frit, as described below.

[0245] <(A2) Conductive particles>

[0246] The conductive paste for the back electrode contains (A2) conductive particles. The (A2) conductive particles contained in the conductive paste for the back electrode can be the same conductive particles as the (A) conductive particles contained in the conductive paste of this embodiment described above. In this specification, the conductive particles contained in the conductive paste for the back electrode are sometimes referred to as "second conductive particles".

[0247] <(B2) Organic Carrier>

[0248] The conductive paste for the back electrode contains an organic carrier (B2). The same organic carrier as the organic carrier (B) described above can be used as the (B2) organic carrier. In this specification, the organic carrier contained in the conductive paste for the back electrode is sometimes referred to as the "second organic carrier".

[0249] <(C2) Glass Material>

[0250] The conductive paste for the back electrode contains (C2) glass frit. The (C2) glass frit in the conductive paste for the back electrode preferably contains Te. By including Te in the (C2) glass frit, even though it is a lead-free glass frit that does not contain lead (Pb), it is possible to reduce the contact resistance between the electrode and the impurity diffusion layer 4 (or the second impurity diffusion layer 16) of the crystalline silicon substrate 1 while adjusting the reactivity with the passivation film to an appropriate range, and to prevent lead pollution to the environment. It should be noted that, from the viewpoint of reducing contact resistance, it is preferable that the conductive paste used in the electrode on the side where the n-type diffusion layer is formed contains a glass frit containing Te.

[0251] In this specification, the glass frit contained in the conductive paste for the back electrode is sometimes referred to as "second glass frit".

[0252] The (C2) glass frit contained in the conductive paste for the back electrode is lead-free. Therefore, the (C2) glass frit contained in the conductive paste for the back electrode does not substantially contain lead (Pb). However, the (C2) glass frit used in the conductive paste for the back electrode may contain trace amounts of lead as an unavoidable impurity. Specifically, the (C2) glass frit used in the conductive paste for the back electrode may contain less than 0.1% by weight of lead as an impurity relative to 100% by weight of the (C2) glass frit.

[0253] In the conductive paste used for the back electrode, the basicity B of the glass frit (C2) GF B is the product of (A2) conductive particles in the conductive paste for the back electrode (where the content of conductive particles in the back electrode is set to 100 parts by weight) and (C2) glass frit content in the conductive paste for the back electrode (in parts by weight). GF • G is preferably in the range of 1 to 3, more preferably in the range of 1.2 to 2.5, and even more preferably in the range of 1.5 to 2.3. This is achieved by adjusting the basicity B of the (C2) glass frit. GF The product of B and the content G GF • G is within an appropriate range, and a crystalline silicon solar cell with appropriate performance can be obtained by combining it with the light incident side surface electrode 20 formed using the conductive paste of this embodiment.

[0254] The alkalinity (B) of the glass frit (C2) in this embodiment GF The preferred alkalinity is 0.10–1.5, more preferably 0.15–1.3, and even more preferably 0.20–1.1. At alkalinity (B... GF Within such a range, by adjusting the amount of (C2) glass frit added to the conductive paste for the back electrode, the reactivity of the (C2) glass frit to the passivation film can be adjusted to an appropriate value.

[0255] The content G2 of (C2) glass frit in the conductive paste for the back electrode is preferably 0.1 to 5.0 parts by weight relative to 100 parts by weight of (A2) conductive particles, more preferably 0.5 to 4.0 parts by weight, even more preferably 0.3 to 3.5 parts by weight, and particularly preferably 1.0 to 3.0 parts by weight. The content G2 of (C2) glass frit in the conductive paste for the back electrode is related to the alkalinity (B...) GF By adjusting them appropriately, the reactivity of the (C2) glass frit to the passivation film can be made appropriate.

[0256] The (C2) glass frit contained in the conductive paste for the back electrode preferably comprises at least one selected from SiO2, B2O3, Bi2O3, P2O5, Li2O, Na2O, Al2O3, TeO2, TiO2, ZrO2, and ZnO. By including at least one of these oxides in the (C2) glass frit, the basicity of the (C2) glass frit can be adjusted to an appropriate range.

[0257] The (C2) glass frit preferably contains TeO2. When the (C2) glass frit contains TeO2, the TeO2 content in the (C2) glass frit (100 mol%) is preferably less than 80 mol%, more preferably less than 60 mol%. Furthermore, the TeO2 content in the (C2) glass frit (100 mol%) is preferably 30 mol% or more, more preferably 40 mol% or more. By including TeO2 in the (C2) glass frit, even though it is lead-free, it is possible to reduce the contact resistance while adjusting the reactivity with the passivation film to an appropriate range.

[0258] In the conductive paste for the back electrode, the content of TeO2 in the glass frit (C2) is expressed in mol% (C TeO2 The product of the content of (C2) glass frit G2 and (C2) glass frit C TeO2 • G2 is preferably in the range of 10 to 200, more preferably in the range of 50 to 170, and even more preferably in the range of 80 to 150. This is achieved by increasing the product C2 with the content of the (C2) glass frit. TeO2 • G2 is within the above range. Although it is lead-free, it can reduce contact resistance while adjusting the reactivity with the passivation film to an appropriate range.

[0259] The (C2) glass frit preferably contains Bi2O3 within a range that does not adversely affect the conductive paste used for the back electrode. When the (C2) glass frit contains Bi2O3, the Bi2O3 content in the (C2) glass frit (100 mol%) is preferably 10–80 mol%, more preferably 15–75 mol%, and even more preferably 20–70 mol%. By including Bi2O3 in the (C2) glass frit, even though it is lead-free, it is possible to reduce the contact resistance while adjusting the reactivity with the passivation film to an appropriate range.

[0260] The (C2) glass frit may contain SiO2 within a range that does not adversely affect the conductive paste used for the back electrode. When the (C2) glass frit contains SiO2, the SiO2 content in the (C2) glass frit (100 mol%) is preferably 10 to 60 mol%, more preferably 15 to 40 mol%. By including an appropriate amount of SiO2 in the (C2) glass frit, the reactivity with the passivation film can be controlled.

[0261] (C2) The glass frit may contain B2O3 within a range that does not adversely affect the conductive paste used for the back electrode. When the (C2) glass frit contains B2O3, the content of B2O3 in the (C2) glass frit (100 mol%) is preferably 3 to 60 mol%, more preferably 4 to 50 mol%. By including an appropriate amount of B2O3 in the (C2) glass frit, the reactivity with the passivation film can be controlled.

[0262] The (C2) glass frit may contain P2O5 within a range that does not adversely affect the conductive paste used for the back electrode. When the (C2) glass frit contains P2O5, the P2O5 content in the (C2) glass frit (100 mol%) is preferably 1 to 10 mol%, more preferably 2 to 5 mol%. By including an appropriate amount of P2O5 in the (C2) glass frit, the reactivity with the passivation film can be controlled.

[0263] The (C2) glass frit may contain Li2O within a range that does not adversely affect the conductive paste used for the back electrode. When the (C2) glass frit contains Li2O, the Li2O content in the (C2) glass frit (100 mol%) is preferably 3 to 40 mol%, more preferably 5 to 30 mol%. By including an appropriate amount of Li2O in the (C2) glass frit, the reactivity with the passivation film can be adjusted to an appropriate range.

[0264] The (C2) glass frit may contain Na2O3 within a range that does not adversely affect the conductive paste used for the back electrode. When the (C2) glass frit contains Na2O3, the Na2O3 content in the (C2) glass frit (100 mol%) is preferably 5 to 15 mol%, more preferably 7 to 13 mol%. By including an appropriate amount of Na2O3 in the (C2) glass frit, the reactivity with the passivation film can be controlled.

[0265] The (C2) glass frit may contain Al2O3 within a range that does not adversely affect the conductive paste used for the back electrode. When the (C2) glass frit contains Al2O3, the Al2O3 content in the (C2) glass frit (100 mol%) is preferably 1 to 10 mol%, more preferably 3 to 8 mol%. By including an appropriate amount of Al2O3 in the (C2) glass frit, the reactivity with the passivation film can be controlled.

[0266] The (C2) glass frit can contain TiO2 within a range that does not adversely affect the conductive paste used for the back electrode. When the (C2) glass frit contains TiO2, the TiO2 content in the (C2) glass frit (100 mol%) is preferably 0.5 to 8 mol%, more preferably 1 to 4 mol%. By including an appropriate amount of TiO2 in the (C2) glass frit, the reactivity with the passivation film can be controlled.

[0267] (C2) The glass frit may contain ZrO2 within a range that does not adversely affect the conductive paste used for the back electrode. When the (C2) glass frit contains ZrO2, the ZrO2 content in the (C2) glass frit (100 mol%) is preferably 0.5 to 8 mol%, more preferably 1 to 4 mol%. By including an appropriate amount of ZrO2 in the (C2) glass frit, the reactivity with the passivation film can be controlled.

[0268] (C2) The glass frit may contain ZnO within a range that does not adversely affect the conductive paste used for the back electrode. When (C2) glass frit contains ZnO, the ZnO content in (C2) glass frit (100 mol%) is preferably 2 to 20 mol%, more preferably 5 to 15 mol%. By including ZnO in (C2) glass frit, the basicity of (C2) glass frit can be adjusted to an appropriate range.

[0269] The (C2) glass frit preferably contains Li2O, TeO2, and ZnO. Alternatively, the (C2) glass frit preferably contains SiO2, B2O3, Bi2O3, P2O5, Na2O, Al2O3, TiO2, and ZrO2. By including the given components in the (C2) glass frit of the conductive paste for the back electrode, a high-performance solar cell can be obtained.

[0270] In the conductive paste for the back electrode, the glass transition temperature (Tg) of the (C2) glass frit is preferably 250–600°C, more preferably 270–500°C, and even more preferably 300–470°C. By setting the glass transition temperature (Tg) of the (C2) glass frit to 250°C or higher, reactivity with the passivation film can be suppressed. Furthermore, by setting the glass transition temperature (Tg) to 600°C or lower, the contact resistance between the resulting electrode (e.g., the light incident side surface electrode 20) and the second impurity diffusion layer 16 can be reduced.

[0271] (C2) The shape of the glass particles is not particularly limited; for example, spherical or amorphous shapes can be used. Furthermore, the particle size is not particularly limited. From the perspective of operability, the average particle diameter (D50) is preferably in the range of 0.1 to 10 μm, more preferably in the range of 0.5 to 5 μm.

[0272] (C2) The glass frit particles may be a single type of particle containing a given amount of each of the required multiple oxides. Alternatively, particles composed of a single oxide may be used as particles that differ for each of the required multiple oxides. Furthermore, multiple particles with different compositions of the required multiple oxides may be used in combination. To synergistically obtain the effects of different types of oxides, (C2) the glass frit particles are preferably a single type of particle containing a given amount of each of the required multiple oxides.

[0273] <Other Ingredients>

[0274] The conductive paste for the back electrode in this embodiment can contain additives and additives other than those in the examples described above, within the range that does not adversely affect the characteristics of the resulting solar cell.

[0275] <Method for manufacturing conductive paste for back electrode>

[0276] The conductive paste for the back electrode can be manufactured using the same method as the conductive paste of this embodiment described above.

[0277] <Lead-free solar cells>

[0278] The lead-free crystalline silicon solar cell of this embodiment has lead-free electrodes and partial conductive portions. A lead-free electrode is an electrode formed using a lead-free conductive paste. Generally, the portions of a crystalline silicon solar cell other than the electrodes can be formed using a lead-free material. Therefore, in this specification, a crystalline silicon solar cell having lead-free electrodes is referred to as a lead-free crystalline silicon solar cell.

[0279] Specifically, the lead-free crystalline silicon solar cell of this embodiment comprises: a crystalline silicon substrate of a first conductivity type, a silicon emitter layer of a second conductivity type disposed on one surface of the crystalline silicon substrate of the first conductivity type, a back electrode disposed in electrical connection with the other surface of the crystalline silicon substrate of the first conductivity type, a passivation film disposed in contact with the surface of the silicon emitter layer of the second conductivity type, and a light-incident side surface electrode containing silver disposed on at least a portion of the surface of the passivation film. The silicon emitter layer of the second conductivity type has a partially conductive portion that is in direct contact with the light-incident side surface electrode without being separated by the passivation film. The partially conductive portion comprises an alloy of silver and silicon. The light-incident side surface electrode is a sintered body of the conductive paste of this embodiment described above. The back electrode is preferably a sintered body of the conductive paste for the back electrode described above. The crystalline silicon substrate, silicon emitter layer, passivation film, and partially conductive portion of the lead-free solar cell are the same as those of the solar cell of this embodiment described above.

[0280] The light-incident side surface electrode and the back electrode of a lead-free solar cell are lead-free electrodes that do not contain lead. Therefore, the aforementioned light-incident side surface electrode and the aforementioned back electrode are electrodes formed using a lead-free conductive paste.

[0281] In the lead-free crystalline silicon solar cell of this embodiment, a given electrode of the solar cell is formed using the conductive paste of this embodiment described above, and a laser processing process is performed, thereby forming a local conductive portion (AgSi alloy). By giving the lead-free crystalline silicon solar cell of this embodiment a local conductive portion (AgSi alloy), a high-performance crystalline silicon solar cell can be obtained.

[0282] The conductive paste of this embodiment and the conductive paste for the back electrode described above contain lead-free glass frit. Therefore, the electrodes formed on the surface of the solar cell are also lead-free. Thus, when a solar cell manufactured using the conductive paste of this embodiment is discarded, lead pollution to the environment can be prevented.

[0283] Example

[0284] The present invention will be specifically described below using examples; however, the present invention is not limited to these examples.

[0285] <Examples 1-8 and Comparative Examples 1 and 2>

[0286] In Examples 1-8 and Comparative Examples 1 and 2, monocrystalline silicon solar cells were fabricated, and the electrical characteristics of the monocrystalline silicon solar cells were measured, thereby evaluating the performance of the conductive paste of Examples 1-8 and Comparative Examples 1 and 2 of this embodiment.

[0287] <<Materials and Preparation Ratios of Conductive Paste>>

[0288] Table 1 shows the composition of the conductive pastes of Examples 1-8 and Comparative Examples 1 and 2. The composition shown in Table 1 and the composition of each component below are expressed as the weight parts of each component when (A) conductive particles are set to 100 parts by weight. The components contained in the conductive paste are shown below.

[0289] (A) Silver particles

[0290] Table 2 shows the type, manufacturer, shape, average particle diameter (D50), TAP density, and BET specific surface area of ​​the silver particles A1 and A2 used in the conductive pastes of Examples 1-8 and Comparative Examples 1 and 2. Table 1 shows the proportions of silver particles A1 and A2 in the conductive pastes of Examples 1-8 and Comparative Examples 1 and 2. It should be noted that the average particle diameter (D50) was determined by measuring the particle size distribution using the Microtrac method (laser diffraction scattering method) and obtaining the median diameter (D50) based on the particle size distribution measurement results. The same applies to the average particle diameter (D50) of other components. Furthermore, the BET specific surface area was measured using a fully automated specific surface area measuring device, Macsoeb (manufactured by MOUNTEC). Regarding the BET specific surface area, it was measured using the BET 1-point method based on nitrogen adsorption after pre-drying at 100°C and passing nitrogen gas through it for 10 minutes.

[0291] (B) Organic carrier

[0292] Organic carriers and solvents are used. As the organic binder, 0.4 parts by weight of ethyl cellulose with an ethoxylated content of 48–49.5% by weight is used. As the solvent, 3 parts by weight of diethylene glycol monobutyl ether acetate (butyl carbitol acetate) is used.

[0293] (C) Glass material

[0294] Table 3 shows the composition, basicity, and glass transition temperature of the glass frits GF1 to GF6 used in the conductive pastes of Examples 1 to 8 and Comparative Examples 1 and 2. It should be noted that the average particle size (D50) of glass frits GF1 to GF6 was set to 2 μm. Table 1 shows the type and content (G, parts by weight) of the (C) glass frits in the conductive pastes of Examples 1 to 8 and Comparative Examples 1 and 2. Glass frits GF1 to GF6 were lead-free glass frits.

[0295] The glass transition temperatures (DTAs) of glass frits GF1 to GF6 were determined. Table 3 shows the measured DTA values ​​for glass frits A to G. The determination of the glass transition temperatures of the glass frits was performed as follows: Approximately 50 mg of glass frits A to G were added as samples to a platinum bath, and alumina powder was used as a standard sample. Under atmospheric conditions, a differential thermal analysis (DTA) apparatus (RIGAKU Corporation, TG-8120) was used to heat the sample from room temperature to 800°C at a heating rate of 20°C / min to obtain the DTA curve. The starting point of the first endothermic reaction (extrapolation point) of the DTA curve was set as the glass transition temperature. It should be noted that the starting point of the first endothermic reaction of the DTA curve for glass frit GF4 could not be clearly determined. Therefore, it was marked as "unknown" in the "Glass Transition Temperature" column for glass frit GF4 in Table 3.

[0296] Glass frits GF1 to GF6 are manufactured as follows: First, powdered oxides used as raw materials are measured, mixed, and added to a crucible. The crucible is placed in a heated oven, and the contents are heated to the melt temperature and maintained at the melt temperature until the raw materials are fully melted. Then, the crucible is removed from the oven, and the molten contents are stirred evenly. Next, the contents of the crucible are rapidly cooled at room temperature using a stainless steel double roller to obtain plate-shaped glass. Finally, the plate-shaped glass is pulverized and evenly dispersed in a mortar, and sieved using a mesh sieve to obtain glass frit with the desired particle size. Glass frit that passes through a 100-mesh sieve but remains on a 200-mesh sieve is sieved, resulting in a glass frit with an average particle diameter (D50) of 149 μm. This glass frit is further pulverized to obtain a glass frit with an average particle diameter (D50) of 2 μm.

[0297] Then, the above-mentioned types and proportions of (A) conductive particles, (B) organic carrier and (C) glass frit are mixed using a planetary mixer and further dispersed using a three-roll mill to paste them, thereby producing the conductive pastes of Examples 1 to 8 and Comparative Examples 1 and 2.

[0298] <<Manufacturing of Monocrystalline Silicon Solar Cells>>

[0299] Manufacturing such as Figure 4 The example shown is a bifacial light-receiving monocrystalline silicon solar cell. The substrate used is a phosphorus-doped n-type monocrystalline silicon substrate (substrate thickness 200 μm).

[0300] First, after forming a silicon oxide layer of approximately 20 μm on the substrate using dry oxidation, etching is performed using a solution obtained from a mixture of hydrogen fluoride, pure water, and ammonium fluoride to remove damage to the substrate surface. Furthermore, heavy metals are removed using an aqueous solution containing hydrochloric acid and hydrogen peroxide.

[0301] Then, a texture (convex-concave shape) is formed on both sides of the substrate using wet etching. Specifically, a pyramid-shaped texture structure is formed on both sides (the main light-incident side surface and the back side) using wet etching (sodium hydroxide aqueous solution). Subsequently, it is cleaned with an aqueous solution containing hydrochloric acid and hydrogen peroxide.

[0302] Then, boron is implanted into one surface (the light-incident side surface) of the substrate with the textured structure to form a p-type diffusion layer to a depth of approximately 0.5 μm. The sheet resistance of the p-type diffusion layer is 60 Ω / □.

[0303] In addition, phosphorus was implanted into another textured surface (back side) of the aforementioned substrate to form an n-type diffusion layer to a depth of approximately 0.5 μm. The sheet resistance of the n-type diffusion layer was 20 Ω / □. Boron and phosphorus were implanted simultaneously using a thermal diffusion method.

[0304] Then, thin oxide films of 1-2 nm are formed on the surface of the substrate with the p-type diffusion layer (light incident side surface) and the surface of the substrate with the n-type diffusion layer (back side). Subsequently, a silicon nitride film with a thickness of approximately 60 nm is formed using plasma CVD with silane gas and ammonia gas. Specifically, glow discharge decomposition is performed on a mixed gas of NH3 / SiH4 = 0.5 at 1 Torr (133 Pa), thereby forming a silicon nitride film (antireflective film 2) with a thickness of approximately 70 nm using plasma CVD.

[0305] The conductive paste used for electrode formation on the surface (light incident side surface) of the substrate on which the p-type diffusion layer is formed in Examples 1 to 8 and Comparative Examples 1 and 2 of monocrystalline silicon solar cells uses the conductive pastes shown in Table 1.

[0306] The conductive paste was printed using screen printing. On the antireflective film 2 of the substrate described above, an electrode pattern consisting of a 1.5 mm wide light-incident side main gate electrode 20a and a 60 μm wide light-incident side sub-gate electrode 20b was printed to make the film thickness approximately 20 μm. After that, it was dried at 150°C for about 1 minute.

[0307] As the back electrode 15 (the electrode on the surface where the n-type diffusion layer is formed), a commercially available Ag paste was screen-printed. It should be noted that the electrode pattern of the back electrode 15 is the same as that of the light-incident side surface electrode 20. It was then dried at 150°C for approximately 60 seconds. The thickness of the conductive paste used for the dried back electrode was approximately 20 μm. Subsequently, it was simultaneously fired on both sides using a belt furnace (firing furnace) CDF7210 manufactured by Despatch Industries, Inc., at a peak temperature of 720°C and a furnace in-and-out time of 50 seconds. A monocrystalline silicon solar cell was fabricated as shown above.

[0308] <<Determination of Electrical Characteristics of Solar Cells Before Laser Processing>>

[0309] The electrical characteristics of the monocrystalline silicon solar cell were measured as follows. Specifically, the current-voltage characteristics of the prototype solar cell were measured using a solar simulator SS-150XIL manufactured by Eiko Seiki Co., Ltd., under simulated sunlight conditions of 25°C and AM 1.5 (energy density 100 mW / cm²). 2 The measurements were taken under irradiation, and the fill factor (FF), open circuit voltage (Voc), and conversion efficiency (%) were calculated based on the results. It should be noted that two monocrystalline silicon solar cells manufactured under identical conditions were fabricated, and the average value of the two was used to calculate the measured values.

[0310] <<Laser Processing Technology>>

[0311] The light-incident surface of the monocrystalline silicon solar cells of Examples 1-8 and Comparative Examples 1 and 2 described above was subjected to a laser processing process. Specifically, a negative voltage was applied to the back electrode 15, and the surface formed on the light-incident surface was laser-processed. Figure 2 The light-incident surface electrodes 20 of the pattern shown are each subjected to a positive voltage, causing a current flowing in the opposite direction to the positive current between the p-type impurity diffusion layer 4 and the n-type crystalline silicon substrate 1 of the solar cell, while irradiating the light-incident surface of the solar cell with laser light. The applied voltage during the laser processing is 20V, and the intensity of the irradiated laser is 100W / cm². 2 The voltage application and laser irradiation time were set to 2 seconds.

[0312] <<Determination of Electrical Characteristics of Solar Cells After Laser Processing>>

[0313] The electrical characteristics of the solar cells after laser processing were measured in the same manner as those of the solar cells before laser processing.

[0314] As can be clearly seen from Table 1, the solar cells fabricated using the conductive pastes of Examples 1 to 8 of this embodiment exhibit low electrical characteristics before the laser processing process, for example, a conversion efficiency in the range of 0.5 to 1.6%. In contrast, the solar cells fabricated using the conductive pastes of Comparative Examples 1 and 2 also exhibited similarly low electrical characteristics before the laser processing process, for example, a conversion efficiency in the range of 0.8 to 1.0.

[0315] As can be clearly seen from Table 1, the basicity B of the conductive paste ((C) glass frit) used in Examples 1-8 of this embodiment is... GF B is the product of (C) glass frit content G when the content of (A) conductive particles is set to 100 parts by weight. GF The electrical characteristics of solar cells fabricated using the conductive pastes of Comparative Examples 1 and 2 after laser processing are significantly higher than those of solar cells before laser processing. Specifically, the fill factor (FF) of the examples ranges from 77.8% to 82.4%, the open-circuit voltage (Voc) ranges from 0.630% to 0.717V, and the conversion efficiency ranges from 21.3% to 24.2%. In contrast, the electrical characteristics of solar cells fabricated using the conductive pastes of Comparative Examples 1 and 2 after laser processing are lower than those of Examples 1 to 8. Specifically, the basicity B of the glass frit in Comparative Example 1 (C) is significantly higher than that of the examples before laser processing. GF B is the product of (C) glass frit content G when the content of (A) conductive particles is set to 100 parts by weight. GF The fill factor (FF) of Comparative Example 1 (G = 0.11) is 31.9%, and the conversion efficiency is 6.4%. Although the open-circuit voltage (Voc) of the solar cell in Comparative Example 1 is 0.700V, the conversion efficiency is low due to the low fill factor (FF). Furthermore, the basicity B of the glass frit in Comparative Example 2 (C) is... GF B is the product of (C) glass frit content G when the content of (A) conductive particles is set to 100 parts by weight. GF The fill factor (FF) of Comparative Example 2 is in the range of 77.1% (G = 2.04), the open-circuit voltage (Voc) is in the range of 0.620V, and the conversion efficiency is in the range of 19.7%. Therefore, the electrical characteristics of the solar cell in Comparative Example 2 are lower than those of the solar cells in Examples 1-8. It is thus clear that the solar cells fabricated using the conductive paste of Examples 1-8 of this embodiment exhibit superior electrical characteristics after the laser processing process compared to the solar cells fabricated using the conductive paste of Comparative Examples 1 and 2.

[0316] <Reference Examples 1-4>

[0317] In Examples 1-8 and Comparative Examples 1 and 2, monocrystalline silicon solar cells were fabricated using a conductive paste containing lead glass frit, and the electrical characteristics of the monocrystalline silicon solar cells were measured.

[0318] Table 4 shows the composition of the conductive pastes of Reference Examples 1 to 4. The composition shown in Table 4 and the composition of each component below are expressed as the weight parts of each component when (A) conductive particles are set at 100 parts by weight. The components contained in the conductive paste are shown below.

[0319] (A) Conductive particles

[0320] Silver particles A1, as shown in Table 2, were used as the conductive particles. The proportions of the conductive particles are shown in Table 4.

[0321] (B) Organic carrier

[0322] As an organic carrier, the same organic binder and solvent as in Examples 1-8 and Comparative Examples 1 and 2 were used in the same proportions.

[0323] (C) Glass material

[0324] Table 5 shows the composition, basicity, and glass transition temperature of glass frits GF11 and GF12 used in the conductive pastes of Reference Examples 1-4. Both glass frits GF11 and GF12 contain PbO. It should be noted that the average particle size (D50) of glass frits GF11 and GF12 is set to 2 μm. Table 4 shows the type and content G (parts by weight) of (C) glass frits in the conductive pastes of Examples 1-8 and Comparative Examples 1 and 2. It should be noted that the glass transition temperatures of glass frits GF11 and GF12 were measured in the same manner as those of glass frits GF1-GF6 described above. Furthermore, glass frits GF11 and GF12 were manufactured in the same manner as those of glass frits GF1-GF6 described above.

[0325] As shown in Table 4, aluminum (Al) particles were added as component (D) in the conductive pastes of Reference Examples 2-4. The Al particles used were Al particles manufactured by Toyo Aluminum Co., Ltd. (model: TFH-A02P, spherical, average particle diameter (D50): 2 μm). Table 4 shows the amount (parts by weight) of the Al particles in the conductive pastes of Reference Examples 2-4. It should be noted that no Al particles were added to the conductive paste of Reference Example 1.

[0326] Then, in the same manner as Examples 1-8 and Comparative Examples 1 and 2 above, the given types and proportions of (A) conductive particles, (B) organic carrier, (C) glass frit and (D) Al particles used as needed were mixed in a planetary mixer, further dispersed using a three-roll mill, and pasted, thereby producing the conductive pastes of Reference Examples 1-4.

[0327] <Manufacturing of Monocrystalline Silicon Solar Cells>

[0328] Solar cells of Reference Examples 1-4 were manufactured in the same manner as those of Examples 1-8 and Comparative Examples 1 and 2 described above, and the electrical characteristics of the solar cells before and after the laser processing were measured. Table 4 shows the measurement results of the electrical characteristics of Reference Examples 1-4.

[0329] As can be clearly seen from Tables 1 and 4, the electrical characteristics of solar cells fabricated using the conductive paste of Examples 1-8 of this embodiment after laser processing are to the same extent as those of solar cells fabricated using the conductive paste of Reference Examples 1-4 after laser processing. Therefore, it is clear that when laser processing is performed on solar cells fabricated using the conductive paste with lead-free glass frit of Examples 1-8 of this embodiment, solar cells with the same performance as those using conductive paste with lead-containing glass frit can be manufactured.

[0330] <SEM Photos>

[0331] The cross-section near the antireflective film 2 (passivation film) of the solar cells of Reference Example 1, Example 1 and Comparative Example 1, which underwent laser processing, was observed using a scanning electron microscope (SEM). Figure 6 This is a cross-sectional SEM image of a solar cell with a light-incident side surface electrode 20 formed using the conductive paste of Reference Example 1. Additionally, Figure 7 This is a cross-sectional SEM image of a solar cell with a light-incident side surface electrode 20 formed using the conductive paste of Example 1. Figure 8 This is a cross-sectional SEM image of a solar cell with a light-incident side surface electrode 20 formed using the conductive paste of Comparative Example 1.

[0332] When a laser processing technique is used, an antireflective film 2 (passivation film) exists in most of the area between the light-incident surface electrode 20 and the impurity diffusion layer 4. In the laser processing technique, a given voltage is applied such that a current flows in the pn junction in the opposite direction to the forward direction, and light from a point source (e.g., a laser) is irradiated. This causes a current to flow through a small region between the light-incident surface electrode 20 and the impurity diffusion layer 4, resulting in localized heating. As a result, as... Figure 6 and 7As shown, an AgSi alloy 30 (an alloy of silver and silicon) is locally formed as an electrically conductive portion (partially conductive portion) between the light-incident side surface electrode 20 and the impurity diffusion layer 4. That is, the locally conductive portion contains an alloy of silver and silicon. In addition, in the locally conductive portion, the impurity diffusion layer 4 (the silicon emitter layer of the second conductivity type) is in direct contact with the light-incident side surface electrode 20 without the anti-reflection film 2 (passivation film) in between. By utilizing this locally formed electrically conductive portion (partially conductive portion), good electrical conductivity between the light-incident side surface electrode 20 and the impurity diffusion layer 4 can be achieved. The conductive paste of this embodiment, which contains lead-free glass frit, has low reactivity to the anti-reflection film 2, similar to the conductive paste containing a given lead-containing glass frit, and has reactivity with the anti-reflection film 2 (passivation film) suitable for laser processing. Therefore, the conductive paste of this embodiment can be preferably used for forming the light-incident side surface electrode 20 of a crystalline silicon solar cell using a laser processing process. Furthermore, since the conductive paste in this embodiment is a conductive paste containing lead-free glass frit, lead pollution to the environment can be prevented when the solar cell is discarded.

[0333] On the other hand, such as Figure 8 As shown, when a solar cell with a light-incident side surface electrode 20 is formed using the conductive paste of Comparative Example 1, after the laser processing process, no AgSi alloy 30 (an alloy of silver and silicon) is formed locally between the light-incident side surface electrode 20 and the impurity diffusion layer 4 as an electrically conductive portion (locally conductive portion). Therefore, it is clear that the conductive paste of Comparative Example 1 cannot be considered a suitable conductive paste for the formation of electrodes based on laser processing processes.

[0334] Furthermore, the fill factor (FF) of the solar cell using the conductive paste of Comparative Example 2 to form the light-incident side surface electrode 20 before laser processing was 62.4%. The fill factor (FF) of the solar cell of Comparative Example 2 before laser processing was higher than that of the solar cell of the embodiment. This can be attributed to the fact that, in the solar cell using the conductive paste of Comparative Example 2 to form the light-incident side surface electrode 20, the electrode pattern burned through the passivation film during the firing of the conductive paste (electrode pattern). As a result, the passivation film disappeared in the solar cell using the conductive paste of Comparative Example 2, and therefore the open-circuit voltage (Voc) after laser processing was low. Therefore, it is clear that the conductive paste of Comparative Example 2 cannot be considered a suitable conductive paste for forming electrodes based on laser processing.

[0335] <Examples 9-14 and Reference Example 5>

[0336] In Examples 9-14 and Reference Example 5, bifacial light-receiving monocrystalline silicon solar cells were fabricated, and the electrical characteristics of the monocrystalline silicon solar cells were measured, thereby evaluating the performance of the conductive paste of Examples 9-14 and Reference Example 5 of this embodiment.

[0337] It should be noted that in Examples 9-14 and Reference Example 5, the case of forming electrodes for a double-sided light-receiving solar cell using an n-type Si substrate using the conductive paste of this embodiment is described as an example. That is, the surface electrode (light-incident side surface electrode 20) in Examples 9-14 and Reference Example 5 is the electrode on the surface where a p-type impurity diffusion layer 4 is formed, and the back electrode 15 is the electrode on the surface where an n-type second impurity diffusion layer 16 is formed.

[0338] Table 6 shows the composition of the conductive paste for forming the surface electrode and the conductive paste for forming the back electrode in Examples 9-14 and Reference Example 5. The composition shown in Table 6 and the composition of each component below are expressed as the weight parts of each component when (A) conductive particles are set to 100 parts by weight.

[0339] <<Conductive Paste for Surface Electrode Formation>>

[0340] The conductive paste used for forming the surface electrode in Examples 9-11 and Reference Example 5 is the same as the conductive paste used for forming the surface electrode in Example 1. The conductive paste used for forming the surface electrode in Example 12 is the same as the conductive paste used for forming the surface electrode in Example 7. The conductive paste used for forming the surface electrode in Example 13 is the same as the conductive paste used for forming the surface electrode in Example 2. The conductive paste used for forming the surface electrode in Example 14 is the same as the conductive paste used for forming the surface electrode in Example 8. It should be noted that, here, the electrode formed using the conductive paste for forming the surface electrode is referred to as "surface electrode 20".

[0341] <<Materials and Preparation Ratios of Conductive Paste for Back Electrode Formation>>

[0342] The conductive paste used for forming the back electrode in Examples 9-14 and Reference Example 5 is shown below. It should be noted that, here, the electrode formed using the conductive paste for forming the back electrode is referred to as "back electrode 15".

[0343] (A) Silver particles

[0344] Table 6 shows the proportions of silver particles A1 and A2 in the conductive paste used for forming the back electrode in Examples 9-14 and Reference Example 5. It should be noted that silver particles A1 and A2 are the same as those used in the conductive paste used for forming the light-incident side surface electrode in Examples 1-8. Table 2 shows the type, manufacturer, shape, average particle diameter (D50), TAP density, and BET specific surface area of ​​the silver particles A1 and A2 used in the conductive paste used for forming the back electrode in Examples 9-14 and Reference Example 5.

[0345] (B) Organic carrier

[0346] The types and amounts of organic carriers used in the conductive pastes for forming the back electrode in Examples 9-14 and Reference Example 5 are the same as those used in the (B) organic carriers used in the conductive pastes for forming the light incident side surface electrode in Examples 1-8 and Comparative Examples 1 and 2.

[0347] (C) Glass material

[0348] Table 7 shows the composition, basicity, and glass transition temperature of the glass frits GFA, GFB, and GFC used in the conductive paste for forming the back electrode in Examples 9-14 and Reference Example 5. It should be noted that the average particle size (D50) of the glass frits GFA, GFB, and GFC is set to 2 μm. Table 6 shows the type and content (G2, parts by weight) of the (C) glass frits in the conductive paste for forming the back electrode in Examples 9-14 and Reference Example 5. Glass frits GFA and GFB are lead-free glass frits. Glass frit GFC is a lead-containing glass frit.

[0349] The methods for determining the glass transition temperatures of glass frits GFA, GFB, and GFC are the same as those for glass frits A to G described above. Table 7 shows the measured values ​​of the glass transition temperatures of glass frits GFA, GFB, and GFC.

[0350] The manufacturing methods for glass frits GFA, GFB, and GFC are the same as those for glass frits A to G mentioned above.

[0351] Then, the above-mentioned conductive particles (A), organic carrier and glass frit of the given type and amount are mixed in a planetary mixer, further dispersed in a three-roll mill and pasted, thereby producing the conductive paste for forming the back electrode of Examples 9 to 14 and Reference Example 5.

[0352] <<Manufacturing of Monocrystalline Silicon Solar Cells>>

[0353] Solar cells were manufactured as Examples 9-14 and Reference Example 5, similar to Examples 1-8, Comparative Examples 1 and 2.Figure 4 The example shown is a bifacial light-receiving monocrystalline silicon solar cell. However, the conductive paste used for forming the electrode on the surface (light-incident side surface) of the substrate on which the p-type diffusion layer is formed and the conductive paste used for forming the back electrode 15 (the electrode on the surface on which the n-type diffusion layer is formed) of the monocrystalline silicon solar cell in Examples 9 to 14 and Reference Example 5 are the conductive pastes for forming the surface electrode and the back electrode shown in Table 6 above.

[0354] <<Determination of Electrical Characteristics of Solar Cells Before Laser Processing>>

[0355] The electrical characteristics of the solar cells of Examples 9-14 and Reference Example 5 before the laser processing were measured in the same manner as those of Examples 1-8 and Comparative Examples 1 and 2.

[0356] <<Laser Processing Technology>>

[0357] The laser processing process of Examples 9 to 14 and Reference Example 5 was performed in the same manner as that of the solar cells of Examples 1 to 8 and Comparative Examples 1 and 2 described above.

[0358] <<Determination of Electrical Characteristics of Solar Cells After Laser Processing>>

[0359] The electrical characteristics of the solar cells after laser processing in Examples 9 to 14 and Reference Example 5 were measured in the same manner as those in Examples 1 to 8 and Comparative Examples 1 and 2.

[0360] <<Depth d of AgSi alloy 30>>

[0361] The depth d of the AgSi alloy 30 of the surface electrode 20 in Examples 9-14 and Reference Example 5 was measured as shown below. The measurement results are shown in Table 6.

[0362] Figure 9 The example shows the depth d of the AgSi alloy 30 of the surface electrode 20. Regarding the depth d of the AgSi alloy 30, in an SEM image obtained by observing the cross-section of the AgSi alloy 30, any one point ( ) is taken as the interface connecting the electrode and the AgSi alloy 30. Figure 9 Any point from B1 to the interface between the substrate and AgSi alloy 30 ( Figure 9 The length of the longest line segment in line segment B2) Figure 9 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 AgSi alloy 30, was observed at a magnification of 20,000 using SEM, thereby obtaining... Figure 9 The SEM image shown.

[0363] <<Residual rate of passivation film 2>>

[0364] The retention rates of the passivation film 2 near the surface electrode 20 in Examples 9-14 and Reference Example 5 were measured as shown below. The results of the retention rate measurements of the passivation film 2 near the surface electrode 20 are shown in the "Retention Rate" column of "Evaluation of Surface Electrode" in Table 6.

[0365] Specifically, firstly, a cross-section containing the passivation film 2 and AgSi alloy 30 near the surface electrode 20 of the completed solar cell was observed using SEM at a magnification of 20,000, resulting in an SEM image (SEM image range: 5.7 μm × 3.9 μm). It should be noted that the transverse (horizontal direction) length of this SEM image is 5.7 μm, and the longitudinal (perpendicular direction) length is 3.9 μm. Then, as... Figure 10 As illustrated, the total length Lp of the cross-section of the passivation film 2 in the SEM image was measured. Figure 10 In the example shown, the total length Lp of the cross-section of the passivation film 2 in the SEM image is the sum of the lengths of Lp1, Lp2, Lp3, and Lp4. Then, in this SEM image, the total length Le of the cross-section of the interface between the AgSi alloy 30 and the electrode in the portion where the AgSi alloy 30 has formed is measured. Length Le corresponds to the length by which the passivation film 2 disappears during the solar cell manufacturing process. Figure 10 In the example shown, the total length Le of the cross-section of the interface between AgSi alloy 30 and the electrode in the portion where the passivation film 2 disappears is the total length of Le1 and Le2. The retention rate of the passivation film 2 can be obtained as Lp / (Lp+Le). It should be noted that the lengths Lp1, etc., are determined by approximating the passivation film 2 as a straight line.

[0366] <Thickness and thickness ratio of passivation film 2 before and after firing>

[0367] The thickness Da of the passivation film 2 near the surface electrode 20 of the solar cells in Examples 9-14 and Reference Example 5 before firing and the thickness Db after solar cell completion were measured. The measured value of the thickness Da of the passivation film 2 near the surface electrode 20 before firing is shown in the "Film Thickness (Da)" column of "Evaluation of Surface Electrode" in Table 6. The measured value of the thickness Db of the passivation film 2 near the surface electrode 20 after solar cell completion is shown in the "Film Thickness (Db)" column of "Evaluation of Surface Electrode" in Table 6. The film thickness ratio (Db / Da) of the passivation film 2 before and after firing is shown in the "Film Thickness Ratio (Db / Da)" column of "Evaluation of Surface Electrode" in Table 6.

[0368] The pre-firing thickness Da of the passivation film 2 was determined by SEM observation of the cross-section of the passivation film 2 near the surface electrode 20 after it was formed. That is, the passivation film 2 was formed on the surface of a given crystalline silicon substrate 1 under the same conditions as in Examples 9 to 14 and Reference Example 5, and the cross-section of the passivation film 2 was observed by SEM to obtain the pre-firing thickness Da of the passivation film 2 in Examples 9 to 14 and Reference Example 5.

[0369] The finished film thickness Db of a solar cell refers to the thickness of the passivation film 2 after electrodes are formed on the surface of the solar cell and a given laser processing process is performed as required. Specifically, firstly, a cross-section of the finished solar cell containing the passivation film 2 and AgSi alloy 30 is observed at a magnification of 20,000 using SEM, resulting in an SEM image (SEM image range: 5.7 μm × 3.9 μm). Then, the SEM image is divided into 6 equal parts along the longitudinal direction, and the film thickness of the passivation film 2 at 5 intersections of the 6-part image is measured (5 locations). The finished film thickness Db of the solar cell is set as the average of the film thicknesses of the passivation film 2 at the 5 locations.

[0370] The so-called film thickness ratio before and after firing of passivation film 2 is the ratio of the film thickness Da of passivation film 2 before firing to the film thickness Db of solar cell after completion (Db / Da), as measured as above.

[0371] As can be clearly seen from the results shown in Table 6, by using the conductive paste of this embodiment to form the surface electrode 20 and using the given conductive paste for forming the back electrode 15, a crystalline silicon solar cell with appropriate performance can be obtained.

[0372] To form the back electrode 15 of the crystalline silicon solar cell of Reference Example 5, a conductive paste containing lead-containing glass frit was used. Conversely, to form the back electrode 15 of the crystalline silicon solar cells of Examples 9-14, a conductive paste containing lead-free glass frit was used. Since the crystalline silicon solar cells of Examples 9-14 have the same level of performance as the crystalline silicon solar cell of Reference Example 5, it is clear that by using the conductive paste of this embodiment to form the surface electrode 20 and using a given conductive paste for back electrode formation to form the back electrode 15, a lead-free crystalline silicon solar cell with excellent performance can be manufactured.

[0373] In particular, it is clear that by using the conductive paste of this embodiment to form the surface electrode 20, and using a glass frit containing Te as the conductive paste for forming the back electrode to form the back electrode 15, and using a laser processing process to form the local conductive portion, even when using a conductive paste made of a lead-free material to form the electrodes of the two surfaces of the solar cell, it is possible to obtain a bifacial light-receiving crystalline silicon solar cell with the same high solar cell characteristics as when using a lead-containing glass frit, and which is also environmentally friendly.

[0374]

[0375]

[0376]

[0377]

[0378]

[0379]

[0380]

[0381] Explanation of reference numerals in the attached figures

[0382] 1 Crystalline silicon substrate, 2 Anti-reflective film (passivation film), 4 Impurity diffusion layer, 15 Back electrode, 15a Back TAB electrode (back main gate electrode), 15b Back electrode (back full electrode), 15c Back sub-gate electrode, 16 Second impurity diffusion layer, 20 Light incident side surface electrode (surface electrode), 20a Light incident side main gate electrode, 20b Light incident side sub-gate electrode, 22 Electrode pattern, 30 AgSi alloy (partial conductive section).

Claims

1. A conductive paste used to form electrodes for a solar cell, The conductive paste comprises: (A) Conductive particles, (B) Organic carriers, and (C) Glass material, The glass frit (C) does not substantially contain PbO. The alkalinity B of the glass frit (C) GF B is the product of the content of (C) glass frit in the conductive paste in parts by weight when the content of (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.

2. The conductive paste according to claim 1, wherein, The (C) glass material contains Bi2O3.

3. The conductive paste according to claim 1 or 2, wherein, The content of Bi2O3 in the glass frit (C) in mol% is C Bi2O3 The product C with the content G of the glass frit (C) Bi2O3 ·G is in the range of 10 to 200.

4. The conductive paste according to any one of claims 1 to 3, wherein, The conductive particles in (A) contain silver particles.

5. The conductive paste according to any one of claims 1 to 4, wherein, The content G of the glass material in (C) is 0.1 parts by weight to 5.0 parts by weight.

6. The conductive paste according to any one of claims 1 to 5, wherein, The content G of the glass material in (C) is 0.3 parts by weight to 3.0 parts by weight.

7. The conductive paste according to any one of claims 1 to 6, wherein, The glass transition temperature of the (C) glass material is 250℃~600℃.

8. The conductive paste according to any one of claims 1 to 7, wherein, The (C) glass material comprises at least one selected from SiO2, B2O3, V2O5, Bi2O3, TeO2, BaO, CuO, Li2O and ZnO.

9. The conductive paste according to any one of claims 1 to 8, wherein, (B) The organic carrier includes at least one selected from ethyl cellulose, rosin ester, acrylic resin and organic solvent.

10. The conductive paste according to any one of claims 1 to 9, used to form the electrode of a solar cell, Solar cells include: Semiconductor substrate of the first conductivity type, A second conductivity type semiconductor layer disposed on one surface of the first conductivity type semiconductor substrate, The back electrode is configured to be electrically connected to another surface of the semiconductor substrate of the first conductivity type. A passivation film disposed in contact with the surface of the semiconductor layer of the second conductivity type, and At least a portion of the light incident side surface electrode is disposed on the surface of the passivation film. The light-incident side surface electrode is a light-incident side surface electrode that has undergone the following treatment: while applying a voltage between the back electrode and the light-incident side surface electrode to allow a current to flow in the opposite direction between the second conductivity type semiconductor layer and the first conductivity type semiconductor substrate, light from a point source is irradiated onto the light-incident side surface of the solar cell. The conductive paste is a conductive paste used to form the light incident side surface electrode.

11. A solar cell comprising: Semiconductor substrate of the first conductivity type, A second conductivity type semiconductor layer disposed on one surface of the first conductivity type semiconductor substrate, The back electrode is configured to be electrically connected to another surface of the semiconductor substrate of the first conductivity type. A passivation film disposed in contact with the surface of the semiconductor layer of the second conductivity type, and At least a portion of the light incident side surface electrode is disposed on the surface of the passivation film. The light-incident side surface electrode is a light-incident side surface electrode that has undergone the following treatment: while applying a voltage between the back electrode and the light-incident side surface electrode to allow a current to flow in the opposite direction between the second conductivity type semiconductor layer and the first conductivity type semiconductor substrate, light from a point source is irradiated onto the light-incident side surface of the solar cell. The light incident side surface electrode is a sintered body of the conductive paste according to any one of claims 1 to 10.

12. A solar cell comprising: First conductivity type crystalline silicon substrate, A silicon emitter layer of the second conductivity type disposed on one surface of the first conductivity type crystalline silicon substrate, The back electrode is electrically connected to the other surface of the crystalline silicon substrate of the first conductivity type. A passivation film disposed in contact with the surface of the silicon emitter layer of the second conductivity type, and A light-incident side surface electrode containing silver disposed on at least a portion of the surface of the passivation film. The silicon emitter layer of the second conductivity type has a local conductive portion that is in direct contact with the light incident side surface electrode without being separated by a passivation film. The local conductive portion comprises an alloy of silver and silicon. The light incident side surface electrode is a sintered body of the conductive paste according to any one of claims 1 to 10.

13. A method for manufacturing a solar cell, the method comprising: Prepare a semiconductor substrate of the first conductivity type; A semiconductor layer of a second conductivity type is formed on one surface of the semiconductor substrate of the first conductivity type; A back electrode is formed in such a way that it is electrically connected to another surface of the semiconductor substrate of the first conductivity type; A passivation film is formed in such a way that it contacts the surface of the semiconductor layer of the second conductivity type; A light incident side surface electrode is formed on at least a portion of the surface of the passivation film; as well as While applying a voltage between the back electrode and the light-incident surface electrode to allow a current to flow in the opposite direction between the second conductivity type semiconductor layer and the first conductivity type semiconductor substrate, light from a point source is irradiated onto the light-incident surface of the solar cell. The light incident side surface electrode is a sintered body of the conductive paste according to any one of claims 1 to 10.

14. The use of the conductive paste according to any one of claims 1 to 10 in the electrode forming a solar cell.

15. The solar cell according to claim 11 or 12, wherein, The back electrode is a sintered body made of conductive paste for the back electrode. The conductive paste used for the back electrode comprises: The second conductive particle, The second organic carrier, and Second glass material, The second glass frit does not actually contain PbO. The second glass material comprises at least one selected from SiO2, B2O3, Bi2O3, P2O5, Li2O, Na2O, Al2O3, TeO2, TiO2, ZrO2 and ZnO.

16. The solar cell according to claim 15, wherein, The second glass material contains TeO2.

17. The method for manufacturing a solar cell according to claim 13, wherein, The back electrode is a sintered body made of conductive paste for the back electrode. The conductive paste used for the back electrode comprises: The second conductive particle, The second organic carrier, and Second glass material, The second glass frit does not actually contain PbO. The second glass material comprises at least one selected from SiO2, B2O3, Bi2O3, P2O5, Li2O, Na2O, Al2O3, TeO2, TiO2, ZrO2 and ZnO.

18. The method for manufacturing a solar cell according to claim 17, wherein, The second glass material contains TeO2.

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