Electrically conductive paste, solar cell and method for producing solar cell

Abstract

The present invention provides an electrically conductive paste which is suitable for the formation of an electrode by a laser process for the production of a crystalline silicon solar cell.　This electrically conductive paste is used for the purpose of forming an electrode on a passivation film which is disposed on the surface of a p-type semiconductor layer that is disposed on the surface of an n-type semiconductor substrate; and this electrically conductive paste contains (A) silver particles, (B) an organic vehicle and (C) glass frit. This electrically conductive paste additionally contains 0.5 part by weight or less of (D) aluminum particles relative to 100 parts by weight of the (A) silver particles; or alternatively, this electrically conductive paste does not contain the (D) aluminum particles.

Description

Conductive paste, solar cell, and method for manufacturing solar cell

[0001] The present invention relates to a conductive paste used for forming electrodes of semiconductor devices, etc. In particular, the present invention relates to a conductive paste for forming electrodes of solar cells. The present invention also relates to a solar cell manufactured using the conductive paste for forming electrodes, and a method for manufacturing a solar cell.

[0002] Semiconductor devices such as crystalline silicon solar cells, which use crystalline silicon substrates made by processing single-crystal silicon or polycrystalline silicon into flat plates, generally have electrodes formed on the surface of the silicon substrate using a conductive paste for electrode formation to ensure electrical contact with the outside of the device. Among semiconductor devices with electrodes formed in this manner, the production volume of crystalline silicon solar cells has increased significantly in recent years. These solar cells have an impurity diffusion layer, an anti-reflection film, and a light-incident surface electrode on one surface of the crystalline silicon substrate, and a back electrode on the other surface. The light-incident surface electrode and the back electrode allow the power generated by the crystalline silicon solar cell to be extracted to the outside.

[0003] Conventional electrodes for crystalline silicon solar cells are formed using a conductive paste containing conductive particles, glass frit, an organic binder, a solvent, and other additives. The conductive particles are mainly silver particles.

[0004] Patent Document 1 describes a conductive paste containing (i) 100 parts by weight of a conductive powder containing a metal selected from the group consisting of silver, nickel, copper, and mixtures thereof, (ii) 0.3 to 8 parts by weight of aluminum powder having a particle size of 3 to 11 μm, (iii) 3 to 22 parts by weight of glass frit, and (iv) an organic medium. Patent Document 1 also describes a method for producing a p-type electrode for an N-type base solar cell, the method comprising the steps of: preparing an N-type base semiconductor substrate including an n-base layer, a p-type emitter on the n-base layer, a first passivation layer on the p-type emitter, and a second passivation layer on the n-base layer; applying the above-mentioned conductive paste on the first passivation layer; and firing the conductive paste.

[0005] Patent Document 2 describes a method for improving the ohmic contact behavior between a contact grid and an emitter layer of a silicon solar cell. Specifically, Patent Document 2 describes the following: A silicon solar cell (1) is first provided with the emitter layer, the contact grid (5), and a back contact (3). The contact grid (5) is electrically connected to one pole of a voltage source. A contact device electrically connected to the other pole of the voltage source is connected to the back contact (3). The voltage source applies a voltage in the opposite direction to the forward direction of the silicon solar cell (1) that is lower than the breakdown voltage. During this voltage application, a point light source (13) is induced across the sun-facing side of the silicon solar cell (1). A small section of the sun-facing side is point-illuminated, inducing a current flowing in a partial area. This current acts on the small section for 1 ms to 100 ms. The current is equivalent to a reduction of 10 to 30 times the magnitude of the short-circuit current of the silicon solar cell (1) measured under standard test conditions, based on the ratio of the area of ​​the subsection to the area of ​​the silicon solar cell (1).

[0006] Patent Literature 3 describes a process for improving the ohmic contact behavior between a contact grid and an emitter layer in a silicon solar cell. Specifically, Patent Literature 3 describes a process for applying a predetermined voltage in a forward direction and a reverse direction to the silicon solar cell, and guiding a point light source to the solar surface side of the silicon solar cell, thereby irradiating a cross section of a subsection on the solar surface side.

[0007] Patent Document 4 describes a method for manufacturing a crystalline silicon solar cell using a conductive paste for forming an electrode of a crystalline silicon solar cell that contains an inorganic material. Patent Document 4 describes a conductive paste that contains conductive particles and glass frit as the inorganic material. The glass frit contained in the conductive paste of Patent Document 4 contains 70 to 90 wt % of PbO relative to 100 wt % of the glass frit, and Al ２ O ３ It is stated that it does not contain

[0008] Patent Document 5 describes a conductive composition containing silver powder, a glass powder containing PbO, and a vehicle made of an organic substance. Patent Document 5 also describes that the conductive composition is a conductive composition for forming an electrode that penetrates a silicon nitride layer and is conductive with an n-type semiconductor layer formed below the silicon nitride layer. Patent Document 5 also describes that the glass powder contained in the conductive composition has a basicity of 0.6 to 0.8 and a glass transition point of 300°C to 450°C.

[0009] JP 2014-515161 A JP 2019-525471 A JP 2021-513218 A JP 2011-86754 A JP 2009-231826 A

[0010] FIG. 5 shows an example of a cross-sectional schematic diagram of a typical crystalline silicon solar cell. As shown in FIG. 5 , a crystalline silicon solar cell generally includes an impurity diffusion layer 4 (e.g., a p-type impurity diffusion layer 4 in which p-type impurities are diffused) formed on the light-incident surface (light-incident surface) of a crystalline silicon substrate 1 (e.g., an n-type crystalline silicon substrate 1). An anti-reflection film 2 is formed on the impurity diffusion layer 4. The anti-reflection film 2 also functions as a passivation film, and is sometimes referred to as a passivation film. Furthermore, an electrode pattern for a light-incident surface electrode 20 (surface electrode) is printed on the anti-reflection film 2 using a conductive paste by screen printing or the like, followed by drying and firing at a predetermined temperature to form the light-incident surface electrode 20. In typical crystalline silicon solar cells, the conductive paste fires through the anti-reflection film 2 during firing at this predetermined temperature. This fire-through allows the light-incident surface electrode 20 to be formed so as to contact the impurity diffusion layer 4. Fire-through refers to etching the anti-reflection film 2, which is an insulating film, with glass frit or the like contained in a conductive paste, thereby establishing electrical continuity between the light-incident surface electrode 20 and the impurity diffusion layer 4. In the example shown in FIG. 5 , the electrode pattern fires through the anti-reflection film 2 during firing, causing the anti-reflection film 2 to disappear. This results in contact between the light-incident surface electrode 20 and the impurity diffusion layer 4. A p-n 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 entering a crystalline silicon solar cell is transmitted through the anti-reflection film 2 and the impurity diffusion layer 4. The transmitted incident light enters the n-type crystalline silicon substrate 1, where it is absorbed, generating electron-hole pairs. The electron-hole pairs are separated by the electric field created by the p-n junction. Specifically, electrons travel from the n-type crystalline silicon substrate 1 to the back electrode 15, and holes travel from the p-type impurity diffusion layer 4 to the light-incident surface electrode 20. The electrons and holes (carriers) are extracted to the outside via these electrodes as a current.

[0011] FIG. 2 shows an example of a schematic diagram of the light-incident side surface of a crystalline silicon solar cell. As shown in FIG. 2, a busbar electrode (light-incident side busbar electrode 20a) and a light-incident side finger electrode 20b (sometimes simply referred to as "finger electrode 20b") are arranged on the light-incident side surface of the crystalline silicon solar cell as a light-incident side surface electrode 20. In the example shown in FIGS. 5 and 2, electrons of electron-hole pairs generated by incident light entering the crystalline silicon solar cell are collected by the finger electrode 20b and then further collected by the light-incident side busbar electrode 20a. A metal ribbon for interconnection, the periphery of which is covered with solder, is soldered to the light-incident side busbar electrode 20a. This metal ribbon extracts current to the outside.

[0012] In order to obtain a crystalline solar cell with high conversion efficiency, the contact resistance between the light-incident side surface electrode 20 and the impurity diffusion layer 4 is required to be low.

[0013] A solar cell manufacturing method using a laser treatment process has been proposed to obtain low contact resistance between the light-incident surface electrode 20 and the impurity diffusion layer 4. Patent Documents 2 and 3 describe specific examples of the laser treatment process. In this specification, the laser treatment process refers to a technique for obtaining low contact resistance by forming the light-incident surface electrode 20, applying a predetermined voltage to the crystalline silicon solar cell so that a current flows in the reverse direction to the forward direction, and irradiating the light-incident surface of the solar cell with light from a point light source. Generally, the laser treatment process can improve the fill factor (FF) without reducing the open circuit voltage (Voc), which is one of the solar cell characteristics. When forming the light-incident surface electrode 20 before the laser treatment process, it is preferable that the conductive paste in the anti-reflection film 2 in contact with the electrode pattern does not fire through the anti-reflection film 2 when the electrode pattern made of conductive paste is fired at a predetermined temperature. Figure 1 shows an example of a cross-sectional schematic diagram illustrating a structure in which a light-incident surface electrode 20 is formed on the light-incident surface of a crystalline silicon solar cell using a laser treatment process. As shown in FIG. 1 , when the laser treatment process is used, the anti-reflection film 2 is present in most of the area between the light-incident side surface electrode 20 and the impurity diffusion layer 4. In the laser treatment process, a voltage is applied to the pn junction so that a current flows in the reverse direction to the forward direction. Light is irradiated from a point light source to generate carriers (electrons and holes). This causes a current to flow in a small area between the light-incident side surface electrode 20 and the impurity diffusion layer 4, resulting in localized heating. This localized heating creates a small area between the light-incident side surface electrode 20 and the impurity diffusion layer 4 where the impurity diffusion layer 4 is not present. As a result, as shown in FIG. 12 , a small electrically conductive area, an AgSi alloy 30, is thought to be formed between the light-incident side surface electrode 20 and the impurity diffusion layer 4. Note that the AgSi alloy 30 is formed locally in a limited area, and is therefore not shown in FIG. 1 . It is thought that this small electrically conductive area allows for good electrical conductivity between the light-incident side surface electrode 20 and the impurity diffusion layer 4.Therefore, it is considered that the AgSi alloy 30 is formed in an area of, for example, 1% or less (preferably 0.1% or less) of the area of ​​the region where the light-incident side surface electrode 20 and the impurity diffusion layer 4 contact each other. As a result, the fill factor (FF) can be improved without reducing the open-circuit voltage (Voc) of the solar cell. Therefore, the conductive paste used to form the light-incident side surface electrode 20 by the laser treatment process must have properties different from conventional conductive pastes (conductive pastes that can fire through the anti-reflection coating 2). The AgSi alloy 30 is a minute electrically conductive portion measuring 200 to 1800 nm or less in size, and the AgSi alloy 30 can be confirmed in an SEM photograph of a cross section of the AgSi region 30, as shown in FIG. 12 .

[0014] Furthermore, in the case of conventional crystalline silicon solar cells, when the light-incident side surface electrode 20 is formed, the electrode pattern made of conductive paste is fired, causing the conductive paste to fire through the anti-reflection film 2 and bring the electrode pattern into contact with the impurity diffusion layer 4. This fire-through process damages the impurity diffusion layer 4, resulting in a degradation of the performance of the crystalline silicon solar cell. In contrast, the laser treatment process does not generally fire through the anti-reflection film 2 when forming the light-incident side surface electrode 20. Therefore, the use of the laser treatment process can prevent damage to the impurity diffusion layer 4. Furthermore, because electrical conduction between the light-incident side surface electrode 20 and the impurity diffusion layer 4 is achieved through a very small region, the anti-reflection film 2, which functions as a passivation film, is present in most of the area between the light-incident side surface electrode 20 and the impurity diffusion layer 4. Therefore, carrier recombination on the surface of the impurity diffusion layer 4 where the light-incident side surface electrode 20 is present, can be prevented.

[0015] Generally, when an electrode is formed on an impurity diffusion layer (p-type impurity diffusion layer) containing boron (B) as a p-type impurity using a conductive paste containing aluminum particles, the contact resistance between the electrode and the impurity diffusion layer can be reduced. Therefore, a conductive paste for forming an electrode on a p-type impurity diffusion layer typically contains 1 part by weight or more of aluminum particles per 100 parts by weight of conductive particles such as silver particles. Meanwhile, the present inventors have discovered that the inclusion of aluminum particles in a conductive paste reduces the adhesion of the electrode to the p-type impurity diffusion layer, resulting in a problem in which the electrode is easily peeled off from the p-type impurity diffusion layer of a solar cell. In this specification, this electrode problem is sometimes referred to as a "reliability problem of the electrode." In other words, the inclusion of aluminum particles in a conductive paste significantly impairs the reliability of the electrode with respect to the p-type impurity diffusion layer.

[0016] Furthermore, to electrically connect multiple solar cells, metal ribbons for interconnection are soldered to the electrodes of the solar cells. When the conductive paste for forming the electrodes contains aluminum particles, there is a problem that the soldering strength of the metal ribbon to the electrodes decreases.

[0017] The present invention aims to provide a conductive paste that solves the above-mentioned problems. That is, the present invention aims to provide a conductive paste suitable for forming electrodes by a laser treatment process for manufacturing crystalline silicon solar cells. Another aim of the present invention is to provide a conductive paste for forming electrodes for solar cells that can suppress the occurrence of electrode reliability problems, such as the tendency for the electrodes to peel off from the p-type impurity diffusion layer of the solar cell.

[0018] Another object of the present invention is to provide a method for manufacturing a high-performance crystalline silicon solar cell that uses a conductive paste suitable for forming electrodes by a laser treatment process, and that can suppress the occurrence of electrode reliability problems. Another object of the present invention is to provide a high-performance crystalline silicon solar cell that can suppress the occurrence of electrode reliability problems and that is manufactured by a manufacturing method that includes forming electrodes by a laser treatment process.

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

[0020] (Configuration 1) Configuration 1 is a conductive paste for forming an electrode formed on a passivation film disposed on the surface of a p-type semiconductor layer disposed on the surface of an n-type semiconductor substrate, the conductive paste comprising: (A) silver particles; (B) an organic vehicle; and (C) a glass frit, wherein the conductive paste further comprises 0.5 parts by weight or less of (D) aluminum particles relative to 100 parts by weight of the (A) silver particles, or the conductive paste does not comprise the (D) aluminum particles.

[0021] (Configuration 2) In Configuration 2, the glass frit (C) is a glass frit containing ZnO, V ２ O ５ , W.O. ３ and Nb ２ O ３ 2. The conductive paste of claim 1, comprising at least one selected from:

[0022] (Configuration 3) Configuration 3 is the conductive paste of Configuration 1 or 2, wherein the conductive paste contains 0.3 parts by weight or less of the (D) aluminum particles per 100 parts by weight of the (A) silver particles, or does not contain the (D) aluminum particles.

[0023] (Configuration 4) Configuration 4 is the conductive paste of any one of configurations 1 to 3, wherein the conductive paste contains 0.5 to 3.0 parts by weight of the (C) glass frit per 100 parts by weight of the (A) silver particles.

[0024] (Configuration 5) Configuration 5 is the conductive paste of any one of configurations 1 to 4, in which the glass frit (C) has a glass transition temperature of 350 to 450°C.

[0025] (Configuration 6) Configuration 6 is the (C) glass frit basicity B ＧＦ and the product B of the content G of the (C) glass frit in parts by weight in the conductive paste when the content of the (A) silver particles in the conductive paste is taken as 100 parts by weight, ＧＦ The conductive paste of any one of configurations 1 to 5, wherein G is in the range of 0.3 to 2.

[0026] (Configuration 7) Configuration 7 is the (C) content C of PbO in mol% in the glass frit ＰｂＯ and the product C of the content G of the glass frit (C) ＰｂＯ The conductive paste of any one of configurations 1 to 6, wherein G is in the range of 26 to 105.

[0027] (Configuration 8) Configuration 8 is the conductive paste of any one of Configurations 1 to 7, in which the ratio D / G of the content G of the (C) glass frit in parts by weight in the conductive paste to the content D of the (D) aluminum particles in parts by weight in the conductive paste, when the content of the (A) silver particles in the conductive paste is taken as 100 parts by weight, is 0.4 or less.

[0028] (Configuration 9) Configuration 9 is the conductive paste of any of Configurations 1 to 8, wherein the solar cell includes: the n-type semiconductor substrate; the p-type semiconductor layer disposed on one surface of the n-type semiconductor substrate; a second electrode disposed so as to be electrically connected to the other surface of the n-type semiconductor substrate; a passivation film disposed in contact with the surface of the p-type semiconductor layer; and a first electrode disposed on at least a portion of the surface of the passivation film, wherein the first electrode is the first electrode that has been treated to irradiate light from a point light source onto the surface of the solar cell on which the first electrode is formed while applying a voltage between the second electrode and the first electrode so that a current flows between the p-type semiconductor layer and the n-type semiconductor substrate in a direction opposite to the forward direction, and the conductive paste is a conductive paste for forming the first electrode of the solar cell.

[0029] (Configuration 10) Configuration 10 is a solar cell including: an n-type semiconductor substrate; a p-type semiconductor layer disposed on one surface of the n-type semiconductor substrate; a second electrode disposed so as to be electrically connected to the other surface of the n-type semiconductor substrate; a passivation film disposed in contact with the surface of the p-type semiconductor layer; and a first electrode disposed on at least a portion of the surface of the passivation film, wherein the first electrode is the first electrode that has been treated by irradiating light from a point light source onto the surface of the solar cell on which the first electrode is formed while applying a voltage between the second electrode and the first electrode so that a current flows in a direction opposite to the forward direction between the p-type semiconductor layer and the n-type semiconductor substrate, and the first electrode is a fired body of the conductive paste of any of Configurations 1 to 9 of the solar cell.

[0030] (Configuration 11) Configuration 11 is the solar cell of Configuration 10, further including an AgSi alloy disposed in at least a portion between the first electrode and the p-type semiconductor layer so as to be in contact with the first electrode and the p-type semiconductor layer.

[0031] (Configuration 12) Configuration 12 is a method for manufacturing a solar cell, comprising: preparing an n-type semiconductor substrate; forming a p-type semiconductor layer on one surface of the n-type semiconductor substrate; forming a second electrode so as to be electrically connected to the other surface of the n-type semiconductor substrate; forming a passivation film so as to be in contact with the surface of the p-type semiconductor layer; forming a first electrode on at least a part of the surface of the passivation film; and irradiating the surface of the solar cell on the side where the first electrode is formed with light from a point light source while applying a voltage between the second electrode and the first electrode so that a current flows between the p-type semiconductor layer and the n-type semiconductor substrate in a direction opposite to the forward current;

[0032] (Configuration 13) Configuration 13 is the solar cell of Configuration 12, further including: by irradiating the light from the point light source onto the surface of the solar cell on which the first electrode is formed, while applying the voltage between the second electrode and the first electrode, an AgSi alloy is formed in at least a portion between the first electrode and the p-type semiconductor layer so as to be in contact with the first electrode and the p-type semiconductor layer.

[0033] According to the present invention, a conductive paste suitable for forming electrodes by a laser treatment process for manufacturing crystalline silicon solar cells can be provided. Also, according to the present invention, a conductive paste for forming electrodes of solar cells can be provided that can suppress the problem of electrode reliability, such as the tendency for the electrodes to peel off from the p-type impurity diffusion layer of the solar cell.

[0034] Furthermore, according to the present invention, it is possible to provide a method for manufacturing a high-performance crystalline silicon solar cell that uses a conductive paste suitable for forming electrodes by a laser treatment process, and that can prevent electrode reliability problems from occurring. Furthermore, according to the present invention, it is possible to provide a high-performance crystalline silicon solar cell that is manufactured by a manufacturing method that includes forming electrodes by a laser treatment process, and that can prevent electrode reliability problems from occurring.

[0035] 1 is an example of a cross-sectional schematic diagram showing a structure in which a light-incident side surface electrode is formed on the light-incident side surface of a crystalline silicon solar cell by a laser treatment process using the conductive paste of this embodiment. FIG. 2 is an example of a schematic diagram of the light-incident side surface of a crystalline silicon solar cell. FIG. 3 is an example of a schematic diagram of the back surface of a crystalline silicon solar cell. FIG. 4 is an example of a cross-sectional schematic diagram of a bifacial crystalline silicon solar cell using the conductive paste of this embodiment. FIG. 5 is an example of a cross-sectional schematic diagram of the vicinity of the light-incident side surface electrode (finger electrode) of a general crystalline silicon solar cell, showing a state in which the anti-reflection film (passivation film) between the electrode and the impurity diffusion layer has disappeared due to fire-through. FIG. 6 is a plan view schematic diagram showing a resistivity measurement pattern for an electrode formed using the conductive paste. FIG. 7 is a plan view schematic diagram showing a contact resistance measurement pattern and a tape peeling test pattern for an electrode formed using the conductive paste. FIG. 8 is a plan view schematic diagram showing a photoluminescence imaging (PL) measurement pattern for an electrode formed using the conductive paste. 10 is an image of the photoluminescence intensity measured by the photoluminescence imaging method (PL method) for the sample of Example 1. 11 is an image of the photoluminescence intensity measured by the photoluminescence imaging method (PL method) for the sample of Comparative Example 2. 12 is a cross-sectional SEM photograph (magnification: 20,000 times) of the vicinity of the passivation film on the light-incident side surface of a sample in which the light-incident side surface electrode is formed using the same conductive paste as the sample shown in FIG. 10. 13 is a cross-sectional SEM photograph (magnification: 2 times) showing that an AgSi alloy, which is a minute electrically conductive portion, is formed locally between the light-incident side surface electrode and the impurity diffusion layer of a sample prepared under the same conditions as in Example 1.

[0036] Hereinafter, embodiments of the present invention will be described in detail. Note that the following embodiments are forms for realizing the present invention, and are not intended to limit the scope of the present invention.

[0037] In this specification, "crystalline silicon" includes both single crystal and polycrystalline silicon. Furthermore, "crystalline silicon substrate" refers to a material obtained by forming crystalline silicon into a shape suitable for element formation, such as a flat plate, for the formation of semiconductor devices such as electric or electronic elements. Any method may be used to manufacture crystalline silicon. For example, the Czochralski method can be used for single crystal silicon, and the casting method can be used for polycrystalline silicon. Other manufacturing methods, such as polycrystalline silicon ribbons manufactured by the ribbon pulling method, and polycrystalline silicon formed on heterogeneous substrates such as glass, can also be used as crystalline silicon substrates. Furthermore, "crystalline silicon solar cell" refers to a solar cell manufactured using a crystalline silicon substrate.

[0038] In this specification, glass frit is a material containing multiple types of oxides, for example, metal oxides as main materials, and is generally used in the form of glassy particles.

[0039] This embodiment is a conductive paste for forming an electrode of a solar cell. The conductive paste of this embodiment includes (A) silver particles, (B) an organic vehicle, and (C) glass frit. The conductive paste of this embodiment may further include 0.5 parts by weight or less of (D) aluminum particles per 100 parts by weight of the (A) silver particles, or may not include (D) aluminum particles.

[0040] The photoelectric conversion efficiency of a solar cell (sometimes simply referred to as "conversion efficiency") is expressed as the product of the fill factor (FF), open circuit voltage (Voc), and short circuit current (Jsc). Basically, FF and Voc are in a trade-off relationship, and it is difficult to simultaneously increase both FF and Voc. For example, Patent Documents 2 and 3 describe that employing a laser treatment process during the manufacture of a crystalline silicon solar cell can improve the ohmic contact behavior between a grid-shaped electrode, which is the light-incident surface electrode, and an impurity diffusion layer (emitter layer), thereby significantly reducing the contact resistance between the light-incident surface electrode and the impurity diffusion layer. Therefore, by performing a laser treatment process, FF can be improved without reducing Voc.

[0041] The present inventors have found that the inclusion of aluminum particles in a conductive paste reduces the adhesion of the electrode to the p-type semiconductor layer (p-type impurity diffusion layer 4), resulting in a problem of the electrode easily peeling off from the p-type semiconductor layer (p-type impurity diffusion layer 4) of the solar cell (a problem of "electrode reliability"). In other words, the inclusion of aluminum particles in a conductive paste significantly impairs the reliability of the electrode with respect to the p-type semiconductor layer (p-type impurity diffusion layer 4). On the other hand, the conductive paste of this embodiment either further contains 0.5 parts by weight or less of (D) aluminum particles per 100 parts by weight of (A) silver particles, or does not contain (D) aluminum particles. Therefore, by using the conductive paste of this embodiment, a highly reliable electrode can be obtained.

[0042] The present inventors have found that when a laser treatment process is applied to a solar cell having a light-incident surface electrode formed using a conventional conductive paste (e.g., the conductive paste described in Patent Document 4), it adversely affects the anti-reflection film (passivation film) and the impurity diffusion layer (and substrate), resulting in a decrease in the conversion efficiency of the solar cell. The present inventors have also found that this is due to the conventional conductive paste having excessively strong fire-through (reactivity) with the anti-reflection film (passivation film). Furthermore, the present inventors have found that by adjusting the basicity and content of the glass frit within an appropriate range, the reactivity of the glass frit with the anti-reflection film (passivation film) can be made appropriate. The conductive paste of this embodiment can be preferably used in the production of crystalline silicon using a laser treatment process.

[0043] FIG. 1 shows a cross-sectional schematic diagram of an example of a crystalline silicon solar cell in which a light-incident-side surface electrode 20 is formed using the conductive paste of this embodiment. In this specification, the electrode formed using the conductive paste of this embodiment is referred to as the "first electrode." In FIG. 1, the light-incident-side surface electrode 20 is the first electrode. By forming an electrode for a crystalline silicon solar cell using the conductive paste of this embodiment and performing a laser treatment process, low contact resistance can be obtained between the first electrode (light-incident-side surface electrode 20) and the impurity diffusion layer 4 of the solar cell without impairing the function of the anti-reflection film 2 as a passivation film. Therefore, by performing a laser treatment process using the conductive paste of this embodiment, a crystalline silicon solar cell with high conversion efficiency can be obtained. The conductive paste of this embodiment can be preferably used to form the first electrode (light-incident-side surface electrode 20) by a laser treatment process when manufacturing a crystalline silicon solar cell.

[0044] In the laser treatment process using the conductive paste of this embodiment, the antireflection film 2 (passivation film) is not essentially fired through when the first electrode (light-incident side surface electrode 20) is formed. Furthermore, when the laser treatment process is performed on the first electrode (light-incident side surface electrode 20), most of the antireflection film 2 (passivation film) in contact with the light-incident side surface electrode 20 is not lost. Therefore, by using the laser treatment process when forming the first electrode (light-incident side surface electrode 20), damage to the impurity diffusion layer 4 can be suppressed.

[0045] As shown in Fig. 1, finger electrodes 20b are arranged on the light-incident surface of a crystalline silicon solar cell as light-incident surface electrodes 20. In the example shown in Fig. 1, the holes of electron-hole pairs generated by incident light entering the crystalline silicon solar cell are collected in the finger electrodes 20b via the impurity diffusion layer 4 (e.g., the p-type impurity diffusion layer 4). Therefore, low contact resistance is required between the finger electrodes 20b and the impurity diffusion layer 4. The conductive paste of this embodiment can be preferably used to form the finger electrodes 20b.

[0046] In this specification, the light-incident side surface electrode 20 and the back surface electrode 15, which are electrodes for extracting current from a crystalline silicon solar cell to the outside, may be collectively referred to simply as "electrodes." As described above, the electrode formed using the conductive paste of this embodiment is the "first electrode." Furthermore, the other electrode different from the first electrode may be referred to as the "second electrode." When the light-incident side surface electrode 20 is the first electrode, the back surface electrode 15 is the second electrode. Furthermore, when the back surface electrode 15 is the first electrode, the light-incident side surface electrode 20 is the second electrode. Furthermore, when referring to FIG. 1 , the surface of the solar cell on which the first electrode is formed may be referred to as the light-incident side surface.

[0047] One type of crystalline silicon solar cell is a bifacial power generation crystalline silicon solar cell that generates electricity by receiving light from two surfaces (first and second light-incident surfaces) (see FIG. 4 ). In this case, the conductive paste of this embodiment can be used to form an electrode (first electrode) that is formed on the light-incident surface on which a p-type impurity diffusion layer (p-type semiconductor layer) is formed.

[0048] The conductive paste of this embodiment can be preferably used to form a light-incident-side surface electrode 20 formed on the surface (light-incident surface) of an anti-reflection film 2 (passivation film) formed on an impurity diffusion layer 4, but is not limited thereto. For example, the conductive paste of this embodiment may be used to form a back surface electrode 15 on the surface (back surface) opposite the light-incident surface. A passivation film may be formed on the back surface of a crystalline silicon solar cell, and the back surface electrode 15 may be formed on the passivation film. For solar cells with this structure, the conductive paste of this embodiment can be used to form electrical contact between the back surface electrode 15 and the crystalline silicon substrate 1 of the solar cell via the back surface passivation film, as described above. In this case, the back surface electrode 15 is the first electrode.

[0049] The conductive paste of this embodiment will be described below using an example in which it is used to form a light-incident-side surface electrode 20 (surface electrode) of a crystalline silicon solar cell using an n-type crystalline silicon substrate 1. In this case, the light-incident-side surface electrode 20 is the first electrode. 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. An anti-reflection film 2 is formed on the surface of the p-type impurity diffusion layer 4.

[0050] The passivation film (anti-reflection film 2) can be a film consisting of a single layer or multiple layers. When the passivation film is a single layer, it is preferably a thin film (SiN film) made of silicon nitride (SiN) because it can effectively passivate the surface of the silicon substrate. When the passivation film is a multiple layer, it is preferably a laminated film (SiN / SiO ｘIt should be noted that SiN / SiO ｘ When the film is a passivation film, the surface of the silicon substrate can be passivated more effectively. ｘ The SiN / SiO ｘ It is preferable to form a film of SiO ｘ The film can be a native oxide film of a silicon substrate. ｘ The x of the film can range from 1 to 2.

[0051] The crystalline silicon solar cell can have a light-incident busbar electrode 20a and / or a backside TAB electrode 15a. The light-incident busbar electrode 20a functions to electrically connect the finger electrodes 20b for collecting current generated by the solar cell to the metal ribbon for interconnection. Similarly, the backside TAB electrode 15a functions to electrically connect the full-surface backside electrode 15b for collecting current generated by the solar cell to the metal ribbon for interconnection. If the finger electrodes 20b come into contact with the crystalline silicon substrate 1, the surface defect density on the surface (interface) of the crystalline silicon substrate 1 where the finger electrodes 20b come into contact increases, resulting in a decrease in solar cell performance. The conductive paste of this embodiment has low fire-through (reactivity) to the anti-reflection film 2 and therefore does not completely fire-through the anti-reflection film 2. Therefore, when the finger electrodes 20b are formed using the conductive paste of this embodiment, the portion of the passivation film in contact with the crystalline silicon substrate 1 can be maintained intact, preventing an increase in the surface defect density that causes carrier recombination. Therefore, the conductive paste of this embodiment described above can be suitably used as a conductive paste for forming the finger electrodes 20b of a crystalline silicon solar cell. The entire electrode 20 can also be formed using the conductive paste of this embodiment. However, the light-incident side busbar electrode 20a can be formed using a different conductive paste from the finger electrodes 20b, which are the first electrodes. In this case, of the light-incident side surface electrode 20, only the finger electrodes 20b are the first electrodes. The same applies to the back surface electrode 15.

[0052] A laser treatment process can be performed on an electrode (light-incident side surface electrode 20) formed using the conductive paste of this embodiment. In the laser treatment process, a voltage is applied and light from a point light source is irradiated, causing a current to flow in a small region between the light-incident side surface electrode 20 and the impurity diffusion layer 4, resulting in localized heating. As a result, as shown in FIG. 12 , an AgSi alloy 30, which serves as a localized electrically conductive portion, is formed between the light-incident side surface electrode 20 and the impurity diffusion layer 4. Note that, because the AgSi alloy 30 is formed locally in a limited area, it is not shown in FIG. 1 . It is believed that this locally formed electrically conductive portion enables good electrical conduction between the light-incident side surface electrode 20 and the impurity diffusion layer 4. Therefore, the conductive paste used to form the light-incident side surface electrode 20 by the laser treatment process must have properties different from those of conventional conductive pastes (conductive pastes that can fire through the anti-reflection coating 2).

[0053] The conductive paste of this embodiment will be specifically described.

[0054] <(A) Silver Particles> The conductive paste of this embodiment contains (A) silver particles.

[0055] In the conductive paste of this embodiment, the silver particles (Ag particles) may be silver particles or silver alloy particles, or silver-coated particles (those in which a metal other than silver is used as a core material and the core material is coated with silver). The conductive paste of this embodiment may contain metals other than silver, such as gold, copper, nickel, zinc, and tin. To obtain an electrode with low electrical resistance and high reliability, the silver particles are preferably silver particles with a silver content of 90% by weight or more. A large number of silver particles (Ag particles) may be referred to as silver powder (Ag powder). The same applies to other particles.

[0056] The particle shape and particle size (also referred to as particle diameter or particle size) of the silver particles are not particularly limited. Examples of particle shapes that can be used include spherical and scale-like particles. The particle size of the silver particles can be defined as the particle size (D50) of 50% of the total particle size. In this specification, D50 is also referred to as the average particle size. The average particle size (D50) can be determined from the results of particle size distribution measurement performed using the Microtrack method (laser diffraction scattering method).

[0057] The average particle size (D50) of the silver particles is preferably 0.5 to 2.5 μm, and more preferably 0.8 to 2.2 μm. By ensuring that the average particle size (D50) of the silver particles is within the specified range, the reactivity of the conductive paste with the passivation film during firing of the conductive paste can be suppressed. Note that if the average particle size (D50) is larger than the above range, problems such as clogging may occur during screen printing.

[0058] The size of silver particles can also be expressed as a BET specific surface area (also simply referred to as "specific surface area"). The BET specific surface area of ​​silver particles is preferably 0.1 to 1.5 m ２ / g, more preferably 0.2 to 1.2 m ２ The BET specific surface area can be measured using, for example, a fully automatic specific surface area measuring device Macsoeb (manufactured by MOUNTEC).

[0059] <(B) Organic Vehicle> The conductive paste of this embodiment contains (B) an organic vehicle.

[0060] The organic vehicle may contain an organic binder and a solvent. The organic binder and the solvent serve to adjust the viscosity of the conductive paste, and are not particularly limited. The organic binder may be dissolved in a solvent before use.

[0061] In the conductive paste of this embodiment, the (B) organic vehicle preferably contains at least one selected from ethyl cellulose, rosin ester, acrylic, and an organic solvent. By containing at least one selected from ethyl cellulose, rosin ester, acrylic, and an organic solvent, the (B) organic vehicle can be suitably screen-printed, and the shape of the printed pattern can be made appropriate.

[0062] The organic binder can be selected from cellulose-based resins (e.g., ethyl cellulose, nitrocellulose, etc.) and (meth)acrylic resins (e.g., polymethyl acrylate, polymethyl methacrylate, etc.). The organic binder contained in the conductive paste of this embodiment preferably contains at least one selected from ethyl cellulose, rosin ester, butyral, and acrylic. The amount of organic binder added is typically 0.1 to 30 parts by weight, and preferably 0.2 to 5 parts by weight, per 100 parts by weight of silver particles.

[0063] The organic solvent can be at least one selected from alcohols (e.g., terpineol, α-terpineol, β-terpineol, etc.) and esters (e.g., hydroxy group-containing esters, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and diethylene glycol monobutyl ether acetate (butyl carbitol acetate)). The amount of the solvent added is typically 0.5 to 30 parts by weight, and preferably 2 to 25 parts by weight, per 100 parts by weight of silver particles. A specific example of the organic solvent is diethylene glycol monobutyl ether acetate (butyl carbitol acetate).

[0064] <(C) Glass Frit> The conductive paste of the present embodiment contains (C) glass frit.

[0065] The glass frit contained in the conductive paste of this embodiment is PbO, SiO ２ , Al ２ O ３ , B ２ O ３ , ZnO, V２ O ５ , W.O. ３ and Nb ２ O ３ It may include at least one selected from:

[0066] By including at least one of these oxides in the glass frit, the basicity of the glass frit, which will be described later, can be adjusted to an appropriate range.

[0067] The glass frit preferably contains PbO. The content of PbO in the glass frit (100 mol%) is preferably 25 to 60 mol%, more preferably 30 to 55 mol%, and even more preferably 40 to 55 mol%. By including PbO, reactivity with the passivation film can be suppressed and contact resistance can be reduced.

[0068] The glass frit is SiO ２ The glass frit (100 mol%) preferably contains SiO ２ The content of SiO is preferably 20 to 65 mol %, and more preferably 25 to 60 mol %. ２ By including the compound, the reactivity with the passivation film can be suppressed.

[0069] The glass frit is Al ２ O ３ The glass frit (100 mol%) preferably contains Al. ２ O ３ The content of Al is preferably 3.0 to 6.8 mol %, and more preferably 3.5 to 6 mol %. ２ O ３ By including the compound, the reactivity with the passivation film can be suppressed.

[0070] The glass frit is B ２ O ３ It is preferable that the glass frit (100 mol%) contains B. ２ O ３ The content is preferably 3.0 to 15 mol %, more preferably 3.5 to 12 mol %.

[0071] The glass frit (C) contained in the conductive paste of this embodiment further contains ZnO, V in addition to the above components. ２ O ５ , W.O. ３ and Nb ２ O ３ It is preferable that the composition contains at least one selected from the following:

[0072] The glass frit preferably contains ZnO. The content of ZnO in the glass frit (100 mol%) is preferably 5 to 20 mol%, and more preferably 8 to 15 mol%. By including ZnO, the basicity of the glass frit can be adjusted to an appropriate range and also contributes to reliability.

[0073] The glass frit is V ２ O ５ , W.O. ３ and Nb ２ O ３ It is preferable that the glass frit contains at least one selected from the following. The content of each of these oxides in the glass frit (100 mol %) is preferably 0.2 to 5 mol %, and more preferably 0.5 to 2 mol %. By containing these oxides, the basicity of the glass frit can be adjusted to an appropriate range and also contributes to reliability.

[0074] In the conductive paste of this embodiment, the glass transition temperature (Tg) of the (C) glass frit is preferably 300 to 600°C, more preferably 320 to 500°C, and even more preferably 350 to 450°C. By setting the glass transition temperature (Tg) of the (C) glass frit to be equal to or higher than the lower limit of the above temperature range, reactivity with the passivation film can be suppressed. Furthermore, by setting the glass transition temperature (Tg) to be equal to or lower than the upper limit of the above temperature range, contact resistance between the resulting electrode and the p-type semiconductor layer can be reduced.

[0075] The glass transition point (Tg) can be measured as follows. That is, a differential thermobalance (TG-DTA2000S manufactured by Mac Science Co., Ltd.) is used, and a glass powder sample and a reference material are set on the differential thermobalance. The temperature is increased from room temperature to 900°C at a temperature increase rate of 10°C / min as a measurement condition, and a curve (DTA curve) is obtained by plotting the temperature difference between the glass powder sample and the reference material against the temperature. The first inflection point of the DTA curve obtained in this way can be determined as the glass transition point Tg.

[0076] The shape of the glass frit particles is not particularly limited, and for example, spherical, irregular, etc. may be used. The particle size is also not particularly limited. From the viewpoint of workability, the average particle diameter (D50) of the particles is preferably in the range of 0.1 to 10 μm, more preferably in the range of 0.5 to 5 μm.

[0077] The glass frit particles can be one type of particles containing a predetermined amount of each of the required oxides. Alternatively, particles made of a single oxide can be used as different particles for each of the required oxides. Alternatively, a combination of multiple types of particles with different compositions of the required oxides can be used.

[0078] The conductive paste of this embodiment has (C) a basicity B of the glass frit ＧＦ and the product B of the content G of (C) glass frit in parts by weight in the conductive paste when the content of (A) silver particles in the conductive paste is taken as 100 parts by weight. ＧＦ G is preferably in the range of 0.3 to 2, more preferably in the range of 0.4 to 1.6, and even more preferably in the range of 0.5 to 1.4. ＧＦ and the product B of the content G ＧＦ By setting G in an appropriate range, the reactivity of the glass frit with the anti-reflection film 2 (passivation film) can be made appropriate. Therefore, the conductive paste of the embodiment can be preferably used when manufacturing crystalline silicon using a laser treatment process.

[0079] The basicity of the glass frit can be calculated by the method described in Patent Document 5 (JP 2009-231826 A). That is, the basicity of the glass powder can be defined using the formula shown in "K. Morinaga, H. Yoshida and H. Takebe: J. Am Cerm. Soc., 77, 3113 (1994)". Specifically, the formula is as follows.

[0080] Oxide M ｉ O's M ｉ The bonding force between -O is given by the following equation as the attractive force Ai between a cation and an oxygen ion:

[0081] A ｉ =Z ｉ ・Z ０２－ / (r ｉ +r ０２－ ) ２ = Zi 2 / (r ｉ +1.40) ２ Z ｉ : valence of cation, oxygen ion is 2r ｉ : Ionic radius of cation (Å)

[0082] Ionic radius r of oxygen ion ｉ is 1.40 nm. ｉ Reciprocal B ｉ (= 1 / A ｉ ) as a single component oxide M ｉ The oxygen donating capacity of O is ｉ ≡1 / A ｉ

[0083] This B ｉ BCaO = 1, BSiO ２ When normalized as = 0, the B of each single component oxide ｉ -index is given. B of each component ｉ - When the index is expanded to a multi-component system using the cation fraction, the basicity (= B ＧＦ ) can be calculated. ＧＦ =Σn ｉ ・B ｉ n ｉ : cation fraction

[0084] The basicity B thus defined ＧＦ represents the oxygen donating ability as described above, and the larger the value, the easier it is to donate oxygen and the easier it is to exchange oxygen with other metal oxides. ＧＦ It can be said that the degree of dissolution in the glass melt is expressed.

[0085] The content G of (C) glass frit is a dimensionless number because it is the ratio to the content G of (A) silver particles. ｉ is BCaO = 1, BSiO ２ = 0, so (C) the basicity B of the glass frit ＧＦ (B ＧＦ =Σn ｉ ・B ｉ ) is a dimensionless number. Therefore, (C) the basicity B of the glass frit ＧＦ and the product B of the content G ＧＦ ・G is also a dimensionless number.

[0086] Basicity B of the glass frit of this embodiment ＧＦ is preferably 0.30 to less than 0.80, more preferably 0.32 to 0.75, and even more preferably 0.35 to 0.70. ＧＦ When the amount of glass frit added to the conductive paste is within this range, the reactivity of the glass frit with the passivation film can be made appropriate.

[0087] The conductive paste of this embodiment has (C) a PbO content C in the glass frit in units of mol%. ＰｂＯ and (C) the product C of the glass frit content G ＰｂＯ G is preferably in the range of 26 to 105, more preferably in the range of 35 to 104, and even more preferably in the range of 45 to 103. ＰｂＯ If G exceeds 105, the reactivity between the glass frit and the passivation film becomes too high. ＰｂＯ If G is less than 26, the contact resistance between the resulting electrode and the p-type semiconductor layer becomes too high.

[0088] The conductive paste of this embodiment preferably contains 0.5 to 3.0 parts by weight of (C) glass frit per 100 parts by weight of (A) silver particles. The conductive paste of this embodiment more preferably contains 0.5 parts by weight or more but less than 3 parts by weight of (C) glass frit per 100 parts by weight of (A) silver particles, even more preferably 0.7 parts by weight or more but less than 2.5 parts by weight, and particularly preferably 0.9 parts by weight or more but less than 2.2 parts by weight. By appropriately adjusting the content G of glass frit in the conductive paste, the reactivity of the glass frit with the passivation film can be made appropriate.

[0089] <(D) Aluminum Particles> The conductive paste of this embodiment may further contain (D) aluminum particles. The (D) aluminum particles may be contained as particles separate from the (A) silver particles.

[0090] In the crystalline silicon substrate 1, aluminum has properties as a p-type impurity. When the conductive paste printed on the crystalline silicon is fired, the aluminum in the conductive paste diffuses into the crystalline silicon and becomes a p-type impurity. Therefore, when an electrode is formed on the surface of the p-type semiconductor layer of the crystalline silicon substrate 1, the conductive paste containing aluminum particles can provide low contact resistance between the electrode and the p-type semiconductor layer. Therefore, when an electrode is formed on the surface of the p-type semiconductor layer of the crystalline silicon substrate 1, the conductive paste can contain aluminum particles.

[0091] On the other hand, the present inventors have found that when the conductive paste contains aluminum particles, the adhesion of the electrode to the p-type semiconductor layer decreases, causing the electrode to easily peel off from the p-type semiconductor layer of the solar cell (a problem of "electrode reliability"). In other words, when the conductive paste contains aluminum particles, the reliability of the electrode with respect to the p-type semiconductor layer is significantly impaired.

[0092] Furthermore, to electrically connect multiple solar cells, metal ribbons for interconnection are soldered to the electrodes of the solar cells. If the conductive paste for forming the electrodes contains aluminum particles, there is a problem that the soldering strength of the metal ribbon to the electrodes decreases.

[0093] In view of the above, it is preferable that the conductive paste of this embodiment contains (D) aluminum particles in a predetermined amount or less, or does not contain (D) aluminum particles.

[0094] Specifically, the (D) aluminum particles are as follows: The conductive paste of this embodiment further contains 0.5 parts by weight or less of (D) aluminum particles per 100 parts by weight of (A) silver particles, or does not contain (D) aluminum particles. The upper limit of the content of (D) aluminum particles in the conductive paste of this embodiment is preferably 0.3 parts by weight or less per 100 parts by weight of (A) silver particles, more preferably less than 0.3 parts by weight, and even more preferably 0.25 parts by weight or less. The conductive paste of this embodiment may be a conductive paste that does not contain (D) aluminum particles. Note that "not containing (D) aluminum particles" means that the intentional addition of "(D) aluminum particles" is excluded, and does not exclude the inclusion of aluminum components as unavoidable impurities.

[0095] When the conductive paste contains a predetermined amount of aluminum particles, low contact resistance may be obtained between the electrode and the p-type semiconductor layer. Therefore, the lower limit of the content of the (D) aluminum particles in the conductive paste of this embodiment can be 0.01 parts by weight, preferably 0.1 parts by weight, and more preferably 0.2 parts by weight per 100 parts by weight of the (A) silver particles. However, as described above, if the conductive paste contains more aluminum particles than the predetermined amount, the reliability of the electrode relative to the p-type semiconductor layer may be impaired. Therefore, the upper limit of the content of the (D) aluminum particles in the conductive paste of this embodiment is as described above.

[0096] In the conductive paste of this embodiment, when the content of (A) silver particles in the conductive paste is taken as 100 parts by weight, the ratio D / G of the content G of (C) glass frit in the conductive paste in parts by weight to the content D of (D) aluminum particles in the conductive paste in parts by weight is preferably 0.4 or less, more preferably 0.35 or less, and even more preferably 0.32 or less. When the D / G of the conductive paste of this embodiment is a predetermined amount or less, the reliability of an electrode formed using the conductive paste of this embodiment can be improved.

[0097] When an electrode is formed on the surface of an n-type semiconductor layer or an n-type crystalline silicon substrate, aluminum in the conductive paste diffuses into the n-type semiconductor layer or the n-type crystalline silicon substrate, adversely affecting the solar cell characteristics. Therefore, when an electrode is formed on the surface of an n-type semiconductor layer or an n-type crystalline silicon substrate, it is preferable that the conductive paste of this embodiment does not contain (D) aluminum particles (the content of (D) aluminum particles is zero).

[0098] The aluminum particles mainly contain aluminum elements. The purity of aluminum in the aluminum particles is, for example, preferably 99.7% or more, more preferably 99.9% or more. The aluminum particles may contain impurities other than aluminum, for example, other metal elements that are inevitably contained. The aluminum particles may also contain alloys of aluminum and other metal elements, aluminum oxides, etc. The aluminum particles may contain components other than aluminum as unavoidably mixed impurities.

[0099] The shape of the aluminum particles is exemplified by, but not limited to, a spherical shape or an oval spherical shape. From the viewpoints of good printability and good reactivity with a semiconductor substrate, the shape of the aluminum particles is preferably spherical.

[0100] The average particle size (D50) of the aluminum particles is not particularly limited. It is preferable for the average particle size (D50) of the aluminum particles to be 1 μm or more and 20 μm or less in terms of improving the printability of the paste composition and improving the reactivity with the semiconductor substrate. A more preferable average particle size (D50) of the aluminum particles is 2 to 4 μm.

[0101] <Other Components> The conductive paste of this embodiment may contain additives other than those described above, as long as they do not adversely affect the solar cell characteristics of the resulting solar cell.

[0102] The conductive paste of this embodiment may further contain, as necessary, one or more additives selected from the group consisting of plasticizers, antifoaming agents, dispersants, leveling agents, stabilizers, and adhesion promoters. Among these, the plasticizer may be selected from the group consisting of phthalates, glycolates, phosphates, sebacates, adipic acids, and citrates.

[0103] The conductive paste of this embodiment may contain additives other than those described above, provided that they do not adversely affect the solar cell characteristics of the resulting solar cell. For example, the conductive paste of this embodiment may further contain at least one additive selected from titanium resinate, titanium oxide, cobalt oxide, cerium oxide, silicon nitride, copper manganese tin, aluminosilicate, and aluminum silicate. The inclusion of these additives can improve the adhesive strength of the solder ribbon to the passivation film via the electrode. These additives may be in the form of particles (additive particles). The amount of additive added per 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 achieve higher adhesive strength, the additive is preferably copper manganese tin, aluminosilicate, or aluminum silicate. The additive may include both aluminosilicate and aluminum silicate.

[0104] The conductive paste of the present embodiment preferably does not contain inorganic carbon powder such as graphite, graphene, or carbon nanotubes, because if inorganic carbon powder is contained in the electrode, the resistivity of the electrode may increase, which may reduce the efficiency of the solar cell.

[0105] <Method for manufacturing conductive paste> Next, a method for manufacturing the conductive paste of this embodiment will 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 a solvent, mixing them, and dispersing them.

[0106] Mixing can be performed, for example, using a planetary mixer, and dispersion can be performed using a three-roll mill. The mixing and dispersion methods are not limited to these, and various known methods can be used.

[0107] <Solar Cell> Next, a solar cell of the present embodiment will be described. This embodiment is a solar cell in which at least a portion of an electrode is formed using the conductive paste described above. Figures 1 and 4 show schematic cross-sectional views of a crystalline silicon solar cell.

[0108] In the solar cell of this embodiment, the material of the semiconductor substrate can be crystalline silicon, silicon carbide, germanium, gallium arsenide, etc. From the viewpoints of safety and cost as a solar cell, the material of the semiconductor substrate is preferably crystalline silicon (single crystal silicon, polycrystalline silicon, etc.).

[0109] The solar cell of this embodiment shown in Figure 1 includes an n-type semiconductor substrate, a p-type semiconductor layer disposed on one surface of the n-type semiconductor substrate, a passivation film (anti-reflection film 2) disposed in contact with the surface of the p-type semiconductor layer, and a light-incident side surface electrode 20 (first electrode) that is an electrode disposed on at least a portion of the surface of the passivation film. The solar cell of this embodiment may also include a back surface electrode 15 (second electrode) disposed so as to be electrically connected to the other surface of the n-type semiconductor substrate. In the example of Figure 1, the n-type semiconductor substrate is a crystalline silicon substrate 1 containing n-type impurities, the p-type semiconductor layer is an impurity diffusion layer 4, and the passivation film is the anti-reflection film 2.

[0110] The material of the semiconductor substrate is preferably silicon, and therefore the semiconductor substrate is preferably a crystalline silicon substrate 1.

[0111] The passivation film can be an anti-reflection film 2. The passivation film is preferably a thin film (SiN film) made of silicon nitride (SiN).

[0112] The light-incident side surface electrode 20 (first electrode) of the solar cell of this embodiment can be a fired 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.

[0113] The conductive paste of this embodiment can be preferably used to form the light-incident-side surface electrode 20 of a crystalline silicon solar cell using a laser treatment process. The laser treatment process refers to a process in which light from a point light source is applied to the surface (light-incident surface) on which the light-incident-side surface electrode 20 (first electrode) of the solar cell is formed, while a voltage is applied to the back electrode 15 and the light-incident-side surface electrode 20 so that a current flows in the opposite direction to the forward direction at the p-n junction between the p-type semiconductor layer (impurity diffusion layer 4) and the n-type semiconductor substrate (substrate 1). The light from the point light source generates carriers (electron-hole pairs) inside the semiconductor substrate, and the application of voltage enables the carriers to move, i.e., current to flow. The voltage is applied so that the direction of current flow at the p-n 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, a voltage is applied to the back electrode 15 and the light-incident-side surface electrode 20 so that a current flows from the n-type semiconductor substrate to the p-type semiconductor layer.

[0114] The n-type semiconductor substrate of the solar cell of this embodiment is preferably an n-type crystalline silicon substrate 1. The p-type semiconductor layer of the solar cell of this embodiment is preferably a p-type impurity diffusion layer 4 in which crystalline silicon contains p-type impurities. Generally, the mobility of electrons, which are carriers in the n-type crystalline silicon substrate 1, is higher than the mobility of holes, which are carriers in the p-type crystalline silicon substrate 1. Therefore, in order to obtain a solar cell with high conversion efficiency, it is advantageous to use an n-type crystalline silicon substrate 1.

[0115] The conductive paste of this embodiment is preferably a conductive paste for forming the light-incident side surface electrode 20 (first electrode) of the solar cell described above.

[0116] In the following explanation, a solar cell in which the n-type semiconductor substrate is an n-type crystalline silicon substrate 1 and the p-type semiconductor layer is a p-type impurity diffusion layer 4 (sometimes simply referred to as the "impurity diffusion layer 4") will be used as an example for more specific explanation.

[0117] In the example shown in FIG. 1 , an anti-reflection film 2 (passivation film) is present in most of the area between the light-incident-side surface electrode 20 (first electrode) and the impurity diffusion layer 4. In the example shown in FIG. 1 , a laser treatment process is performed on the light-incident-side surface electrode 20 (first electrode). In the laser treatment process, a voltage is applied to the pn junction so that a current flows in the reverse direction to the forward direction. Light (e.g., laser light) is irradiated from a point light source. This causes a current to flow in a small area between the light-incident-side surface electrode 20 and the impurity diffusion layer 4, resulting in localized heating. As a result, as shown in FIG. 12 , an AgSi alloy 30, which serves as a localized electrically conductive portion, is formed between the light-incident-side surface electrode 20 and the impurity diffusion layer 4. Because the AgSi alloy 30 is formed locally in a limited area, it is not shown in FIG. 1 . It is believed that this locally formed electrically conductive portion enables good electrical conductivity between the light-incident-side surface electrode 20 and the impurity diffusion layer 4. The conductive paste of this embodiment has lower reactivity with the anti-reflection film 2 than conventional conductive pastes, and has reactivity with the anti-reflection film 2 (passivation film) suitable for the laser treatment process. 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 the laser treatment process.

[0118] The crystalline silicon solar cell shown in Fig. 1 can have a back electrode 15 having a structure shown in Fig. 3. The back electrode 15 is arranged so as to be electrically connected to the other surface of the n-type semiconductor substrate. As shown in Fig. 3, the back electrode 15 can generally include an entire back electrode 15b and a back TAB electrode 15a electrically connected to the entire back electrode 15b.

[0119] FIG. 4 shows an example of a cross-sectional schematic diagram of a bifacial crystalline silicon solar cell. The bifacial crystalline silicon solar cell shown in FIG. 4 has an impurity diffusion layer 4, an anti-reflection film 2, and a back surface passivation film (back surface anti-reflection film 14). In the case of the bifacial crystalline silicon solar cell shown in FIG. 4, when the front surface impurity diffusion layer 4 is a p-type impurity diffusion layer (p-type semiconductor layer), the light-incident side front surface electrode 20 (first electrode) can be formed using the conductive paste of this embodiment, as in the crystalline silicon solar cell shown in FIG. 1 described above. Furthermore, in the bifacial crystalline silicon solar cell shown in FIG. 4, when the back surface impurity diffusion layer (second impurity diffusion layer 16) is a p-type impurity diffusion layer (p-type semiconductor layer), the back surface electrode 15 (first electrode) can be formed using the conductive paste of this embodiment. In this case, as in the solar cell shown in FIG. 1 described above, a laser treatment process can be used to form an electrically conductive portion in the back surface passivation film (back surface anti-reflection film 14). In a bifacial crystalline silicon solar cell, light is also incident from the back surface, and the impurity diffusion layer on the back surface (second impurity diffusion layer 16) is a diffusion layer of p-type impurities (p-type semiconductor layer), so the back surface electrode 15 of the bifacial crystalline silicon solar cell can be considered to be an electrode (first electrode) similar to the light-incident surface electrode 20 of the solar cell shown in Fig. 1. Also, the light-incident surface electrode 20 shown in Fig. 4 can be considered to be a second electrode.

[0120] The conductive paste of this embodiment described above can be suitably used as a conductive paste for forming finger electrodes 20b (first electrodes) of crystalline silicon solar cells. The conductive paste of this embodiment can also be suitably used as a conductive paste for forming back electrode 15 (back finger electrode 15c, first electrode) of bifacial crystalline solar cells.

[0121] The busbar electrodes of the crystalline silicon solar cell shown in Figure 1 include a light-incident side busbar electrode 20a shown in Figure 2 and a backside TAB electrode 15a as shown in Figure 3. Metal ribbons for interconnection, the periphery of which is covered with solder, are soldered to the light-incident side busbar electrode 20a and the backside TAB electrode 15a. This metal ribbon allows current generated by the solar cell to be extracted to the outside of the crystalline silicon solar cell. The bifacial crystalline solar cell shown in Figure 4 can also have the light-incident side busbar electrode 20a and the backside TAB electrode 15a having a shape similar to that of the light-incident side busbar electrode 20a.

[0122] The width of the busbar electrodes (light-incident side busbar electrode 20a and backside TAB electrode 15a) can be approximately the same as that of the metal ribbon used for interconnection. A wider width is preferable for the busbar electrodes to have low electrical resistance. On the other hand, a narrower width of the light-incident side busbar electrode 20a is preferable to increase the area of ​​light incident on the light-incident side surface. Therefore, the busbar electrode width can be 0.05 to 5 mm, preferably 0.08 to 3 mm, more preferably 0.1 to 2 mm, and even more preferably 0.15 to 1 mm. The number of busbar electrodes can be determined depending on the size of the crystalline silicon solar cell. The number of busbar electrodes is optional, but can be three, four, or more. The optimal number of busbar electrodes can be determined by simulating solar cell operation so as to maximize the conversion efficiency of the crystalline silicon solar cell. Since the crystalline silicon solar cells are connected in series with each other by the interconnect metal ribbons, it is preferable that the number of light-incident side busbar electrodes 20a and the backside TAB electrodes 15a are the same. For the same reason, it is preferable that the widths of the light-incident side busbar electrodes 20a and the backside TAB electrodes 15a are the same.

[0123] To increase the area of ​​light incident on the crystalline silicon solar cell, it is preferable that the area occupied by the light-incident surface electrode 20 on the light-incident surface be as small as possible. Therefore, it is preferable that the finger electrodes 20b on the light-incident surface be as narrow as possible and as few as possible in number. On the other hand, from the viewpoint of reducing electrical loss (ohmic loss), it is preferable that the finger electrodes 20b be wide and numerous. Furthermore, from the viewpoint of reducing contact resistance between the finger electrodes 20b and the crystalline silicon substrate 1 (impurity diffusion layer 4), it is also preferable that the finger electrodes 20b be wide. From the above, the number of busbar electrodes can be determined depending on the size of the crystalline silicon solar cell and the width of the busbar electrodes. The optimal width and number of finger electrodes 20b (the spacing between the finger electrodes 20b) can be determined by simulating solar cell operation so as to maximize the conversion efficiency of the crystalline silicon solar cell. The width and number of back finger electrodes 15c of the back electrode 15 of the bifacial crystalline silicon solar cell shown in FIG. 4 can also be determined in a similar manner.

[0124] <Solar Cell Manufacturing Method>

[0125] Next, a method for manufacturing a solar cell according to this embodiment will be described. The solar cell can be a crystalline silicon solar cell. In the following description, an example in which the solar cell is a crystalline silicon solar cell will be described.

[0126] The method for manufacturing a solar cell according to this embodiment includes preparing an n-type semiconductor substrate. As the n-type semiconductor substrate, an n-type crystalline silicon substrate 1 is preferably used. The following describes an example in which a crystalline silicon solar cell is manufactured using the n-type crystalline silicon substrate 1.

[0127] From the viewpoint of obtaining high conversion efficiency, it is preferable that the surface of the crystalline silicon substrate 1 on the light incident side has a pyramidal texture structure.

[0128] Next, the method for manufacturing a solar cell according to this embodiment includes a step of forming a p-type semiconductor layer (impurity diffusion layer 4) on one surface of the crystalline silicon substrate 1 (n-type semiconductor substrate) prepared in the above step. When an n-type crystalline silicon substrate 1 is used, the impurity diffusion layer 4 can be formed by diffusing p-type impurities (Group 13 elements) such as B (boron), Al (aluminum) and / or Ga (gallium).

[0129] When the impurity diffusion layer 4 is formed, it can be formed so that the sheet resistance of the impurity diffusion layer 4 is 40 to 150 Ω / □ (square), preferably 45 to 120 Ω / □.

[0130] Furthermore, in the method for manufacturing a crystalline silicon solar cell of this embodiment, the depth to which the impurity diffusion layer 4 is formed can be 0.3 μm to 1.0 μm. 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 the depth from the surface of the impurity diffusion layer 4 to the point where the impurity concentration in the impurity diffusion layer 4 becomes the impurity concentration of the substrate.

[0131] The method for manufacturing a solar cell according to this embodiment includes forming a second electrode so as to be electrically connected to the other surface of the n-type semiconductor substrate. In the example shown in FIG. 1 , the second electrode is a back surface electrode 15. In the method for manufacturing a solar cell according to this embodiment, a conductive paste is printed on the other surface (back surface) of the crystalline silicon substrate 1, followed by firing to form the second electrode (back surface electrode 15). The second electrode can be formed either before or after the light-incident side surface electrode 20 is formed. The firing to form the second electrode can be performed simultaneously with or separately from the firing to form the light-incident side surface electrode 20.

[0132] Next, the method for manufacturing a solar cell of this embodiment includes forming a passivation film so as to be in contact with the surface of the p-type semiconductor layer (impurity diffusion layer 4). The passivation film can be an anti-reflection film 2.

[0133] Specifically, in the method for manufacturing a crystalline silicon solar cell of this embodiment, an anti-reflection film 2 that also functions as a passivation film is formed on the surface of the impurity diffusion layer 4 formed in the above-described process. A silicon nitride film (SiN film) can be formed as the anti-reflection film 2. When a silicon nitride film is used as the anti-reflection film 2, the silicon nitride film layer also functions as a passivation film on the light-incident surface. Therefore, when a silicon nitride film is used as the anti-reflection film 2, a high-performance crystalline silicon solar cell can be obtained. Furthermore, since the anti-reflection film 2 is a silicon nitride film, it can exhibit an anti-reflection function against incident light. The silicon nitride film can be formed by a method such as PECVD (Plasma Enhanced Chemical Vapor Deposition).

[0134] The method for manufacturing a solar cell according to this embodiment includes forming a light-incident-side surface electrode 20 (first electrode) on at least a portion of the surface of the passivation film (anti-reflection film 2). In the manufacturing method according to this embodiment, the above-described conductive paste is used to form the light-incident-side surface electrode 20. Therefore, the light-incident-side surface electrode 20 is a fired body of the above-described conductive paste.

[0135] The method for manufacturing a crystalline silicon solar cell of this embodiment includes a step of printing a conductive paste on the surface of the anti-reflection film 2 and firing the paste to form the light-incident side surface electrode 20. Note that firing to form the back electrode 15 can be performed simultaneously with firing to form the light-incident side surface electrode 20.

[0136] Specifically, first, the pattern of the light-incident side surface electrode 20 printed using the conductive paste of this embodiment is dried for several minutes (e.g., 0.5 to 5 minutes) at a temperature of about 100 to 150° C. At this time, the light-incident side busbar electrodes 20 a and the light-incident side finger electrodes 20 b of the light-incident side surface electrode 20 can be formed using the conductive paste of this embodiment.

[0137] If the back electrode 15 has not been printed and dried, a conductive paste for forming the back electrode 15 can be printed and dried thereafter.

[0138] The printed, dried conductive paste is then fired in air under specified firing conditions using a firing furnace such as a tubular furnace. The firing conditions are as follows: the firing atmosphere is air, and the firing temperature is 500 to 1000°C, more preferably 600 to 1000°C, even more preferably 500 to 900°C, and particularly preferably 700 to 900°C. The firing is preferably carried out for a short period of time, and the temperature profile (temperature-time curve) during firing preferably has a peak. For example, the peak temperature is preferably the above-mentioned temperature, and the in-out time of the firing furnace is preferably 10 to 100 seconds, more preferably 20 to 80 seconds, and even more preferably 40 to 60 seconds.

[0139] During firing, it is preferable to simultaneously fire the conductive pastes for forming the light-incident-side surface electrode 20 and the back surface electrode 15, thereby simultaneously forming both electrodes. By printing a predetermined conductive paste on the light-incident-side surface and the back surface and firing them simultaneously, firing to form the electrodes can be performed only once. This allows crystalline silicon solar cells to be manufactured at lower cost.

[0140] The method for manufacturing a solar cell of this embodiment includes performing the laser treatment process described above. That is, the method for manufacturing a solar cell of this embodiment includes irradiating the surface of the solar cell on which the first electrode is formed (the light-incident surface) with light (e.g., laser light) from a point light source while applying a voltage between the second electrode (rear electrode 15) and the first electrode (light-incident surface electrode 20) so that a current flows in a direction opposite to the forward direction between the p-type semiconductor layer (p-type impurity diffusion layer 4) and the n-type semiconductor substrate (n-type crystalline silicon substrate 1). The laser treatment process enables good electrical conduction between the light-incident surface electrode 20 and the impurity diffusion layer 4.

[0141] When manufacturing a bifacial crystalline solar cell as shown in FIG. 4 , a second impurity diffusion layer 16 can be formed. By forming a back electrode 15 (first electrode) using the conductive paste of this embodiment and performing a laser treatment process, a low-resistance conductive portion can be formed between the back electrode 15 (first electrode) and the crystalline silicon substrate 1. Therefore, in the case of a bifacial solar cell, the back electrode 15 can be formed using the conductive paste of this embodiment. In this case, the back electrode 15 (first electrode) is a fired body of the conductive paste of this embodiment.

[0142] In the manner described above, the crystalline silicon solar cell of this embodiment can be manufactured.

[0143] The crystalline silicon solar cells of this embodiment obtained as described above can be electrically connected with metal ribbons for interconnection and laminated with glass plates, sealing materials, protective sheets, etc. to obtain a solar cell module. Metal ribbons covered with solder (e.g., copper ribbons) can be used as the metal ribbons for interconnection. Commercially available solders, such as those containing tin as a main component, specifically lead-containing solders and lead-free solders, can be used as the solder.

[0144] In the crystalline silicon solar cell of this embodiment, a high-performance crystalline silicon solar cell can be obtained by forming a predetermined electrode of the solar cell using the conductive paste of this embodiment and performing a laser treatment process.

[0145] The present embodiment will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0146] In the examples and comparative examples, the performance of the conductive pastes of the examples and comparative examples of this embodiment was evaluated by using a measurement substrate simulating a single-crystal silicon solar cell to evaluate the degree of deterioration of the passivation film using the photoluminescence imaging method (PL method), as well as the contact resistance and specific resistance of the formed electrodes.

[0147] <Materials and Preparation Proportions of Conductive Paste> Tables 1 to 3 show the compositions of the conductive pastes of Examples 1 to 12 and Comparative Examples 1 and 2. The compositions shown in Tables 1 to 3 and the compositions of each component below are shown in parts by weight of each component when the (A) silver particles are taken as 100 parts by weight. The components contained in the conductive paste are as follows.

[0148] (A) Silver Particles Table 4 shows the product number, manufacturer, shape, average particle diameter (D50), tap density, and BET specific surface area of ​​silver particles A1 and A2 used in the conductive pastes of the Examples and Comparative Examples. Tables 1 to 3 show the blending amounts of silver particles A1 and A2 in the conductive pastes of the Examples and Comparative Examples. The average particle diameter (D50) was determined by measuring particle size distribution using the Microtrac method (laser diffraction scattering method) and obtaining the median diameter (D50) from the particle size distribution measurement results. The same applies to the average particle diameters (D50) of the other components. The BET specific surface area was measured using a fully automatic specific surface area analyzer, Macsoeb (manufactured by MOUNTEC). The BET specific surface area was measured by the single-point BET method using nitrogen gas adsorption after pre-drying at 100°C and flowing nitrogen gas through it for 10 minutes.

[0149] (B) Organic Vehicle An organic binder and a solvent were used as the organic vehicle. Ethyl cellulose (0.4 parts by weight) with an ethoxy content of 48 to 49.5% by weight was used as the organic binder. Diethylene glycol monobutyl ether acetate (butyl carbitol acetate) (3 parts by weight) was used as the solvent.

[0150] (C) Glass Frit Table 5 shows the composition, basicity, and glass transition point of the glass frits GF1 to GF4 used in the conductive pastes of the Examples and Comparative Examples. The average particle diameter (D50) of the glass frits GF1 to GF4 is 2 μm. Tables 1 to 3 show the type of (C) glass frit (any of GF1 to GF4) and the content G (parts by weight) of the glass frit in the conductive pastes of the Examples and Comparative Examples.

[0151] The glass transition points of glass frits GF1 to GF4 were measured. Table 5 shows the measured glass transition points of glass frits GF1 to GF4. The glass transition points of the glass frits were measured as follows. That is, approximately 50 mg of glass frits GF1 to GF4 were placed in a platinum cell as a sample. Alumina powder was used as a standard sample. A DTA curve of the sample was obtained in an air atmosphere using a differential thermal analyzer (TG-8120, manufactured by Rigaku Corporation) at a heating rate of 20°C / min from room temperature to 800°C. The onset point (extrapolated point) of the first endotherm in the DTA curve was taken as the glass transition point.

[0152] Glass frits GF1 to GF4 were produced as follows. First, the raw oxide powders were weighed, mixed, and placed in a crucible. This crucible was then placed in a heated oven. The contents of the crucible were heated to the melting temperature. The temperature was maintained at the melting temperature until the raw materials were fully melted. Next, the crucible was removed from the oven, and the molten contents were uniformly stirred. The contents of the crucible were then quenched at room temperature using two stainless steel rollers to obtain a plate-shaped glass. Finally, the plate-shaped glass was crushed and uniformly dispersed in a mortar and sieved through a mesh sieve to obtain glass frit with the desired particle size. By sieving the glass that passed through a 100-mesh sieve and remained on a 200-mesh sieve, a glass frit with an average particle size (D50) of 149 μm was obtained. Further crushing of this glass frit yielded a glass frit with an average particle size (D50) of 2 μm.

[0153] (D) Aluminum particles Table 6 shows the product number, manufacturer, shape, and average particle diameter (D50) of aluminum particles D1 and D2 used in the conductive pastes of Examples and Comparative Examples. Tables 1 to 3 show the blending amounts (parts by weight) of aluminum particles D1 and D2 in the conductive pastes of Examples and Comparative Examples.

[0154] Next, materials in the weight proportions shown in Tables 1 to 3 were mixed in a planetary mixer, and then dispersed in a three-roll mill to form a paste, thereby preparing conductive pastes for the examples and comparative examples.

[0155] <Evaluation of the Reactivity of Conductive Paste with Passivation Films by Photoluminescence Imaging (PL)> The reactivity of conductive pastes with passivation films was evaluated using the photoluminescence imaging method (referred to as the "PL method"). PL is a non-destructive, non-contact method that allows for rapid evaluation of the reactivity of conductive pastes with passivation films. Specifically, PL is a method in which a sample is irradiated with light with energy greater than the forbidden band width to cause light emission, and the state of defects within the crystal and surface / interface defects is evaluated based on the state of the light emission. When a sample contains defects within a single-crystal silicon substrate and surface / interface defects, the defects act as recombination centers for electron-hole pairs generated by light irradiation, correspondingly reducing the band-edge emission intensity of photoluminescence. In other words, when the passivation film is eroded by a printed / fired electrode, forming surface defects at the interface between the passivation film and the single-crystal silicon substrate (i.e., the surface of the single-crystal silicon substrate), the photoluminescence intensity of the area where the surface defects are formed (i.e., the area of ​​the electrode formed on the sample) decreases. The reactivity of the conductive paste with the passivation film can be evaluated based on the intensity of this photoluminescence.

[0156] The method for preparing a substrate for evaluation by the PL method is as follows.

[0157] The substrate used was an n-type single crystal silicon substrate (substrate thickness: 200 μm).

[0158] First, a silicon oxide layer of approximately 20 μm was formed on the substrate by dry oxidation, and then the substrate surface was etched with a solution containing hydrogen fluoride, pure water, and ammonium fluoride to remove damage.Furthermore, heavy metals were removed using an aqueous solution containing hydrochloric acid and hydrogen peroxide.

[0159] Next, textured structures (concave and convex shapes) were formed on both surfaces of the substrate by wet etching. Specifically, pyramidal textured structures were formed on both surfaces (the main light-incident surface and the back surface) by wet etching (sodium hydroxide aqueous solution). The substrate was then washed with an aqueous solution containing hydrochloric acid and hydrogen peroxide. Next, boron was implanted into one surface (the light-incident surface) of the substrate having the textured structure to form a p-type impurity diffusion layer 4 to a depth of approximately 0.5 μm. The sheet resistance of the p-type impurity diffusion layer 4 was 60 Ω / □. Furthermore, phosphorus was implanted into the other surface (the back surface) of the substrate having the textured structure to form an n-type impurity diffusion layer to a depth of approximately 0.5 μm. The sheet resistance of the n-type impurity diffusion layer was 20 Ω / □. The boron and phosphorus implantations were simultaneously performed by thermal diffusion.

[0160] Next, a thin oxide film of 1 to 2 nm was formed on the surface (light incident surface) of the substrate on which the p-type impurity diffusion layer 4 was formed, and on the surface (rear surface) of the substrate on which the n-type impurity diffusion layer was formed. After the oxide film was formed, a silicon nitride film was formed to a thickness of about 60 nm by plasma CVD using silane gas and ammonia gas. Specifically, NH ３ / SiH ４ A silicon nitride film (anti-reflection film 2) having a thickness of about 70 nm was formed by plasma CVD using glow discharge decomposition of a mixed gas of SiO 2 =0.5 at 1 Torr (133 Pa).

[0161] The substrate thus obtained was cut into a square of 25 mm x 25 mm to prepare substrate 1.

[0162] Next, as shown in FIG. 8, a square electrode pattern 22 of 13 mm×13 mm was printed on the surface of the substrate 1 using a conductive paste for forming electrodes, and then dried.

[0163] The substrate 1, on whose surface the electrode pattern 22 was printed using the conductive paste as described above, was fired using a belt furnace (firing furnace) CDF7210 manufactured by Despatch Industries, Inc., at a peak temperature of 720°C and an in-out time of the firing furnace of 50 seconds.

[0164] In this manner, a substrate (sample) for PL measurement was prepared.

[0165] Measurements using the PL method were carried out using a Photoluminescence Imaging System (model number LIS-R2) manufactured by BT Imaging Co., Ltd. Light from an excitation light source (wavelength 650 nm, output 3 mW) was irradiated onto the back surface of the substrate (the surface on which the electrode pattern 22 of the light-incident surface electrode 20 was not formed), and an image of the photoluminescence emission intensity was obtained.

[0166] 9 and 10 show images of the photoluminescence intensity measured by the PL method.

[0167] FIG. 9 shows an image of the photoluminescence intensity measured by the PL method for a sample on which an electrode pattern 22 was formed using the conductive paste of Example 1. As is clear from FIG. 9 , the image of the portion on which the electrode pattern 22 was formed is brighter than that shown in FIG. 10 (described later). This indicates that the decrease in the photoluminescence intensity in the portion on which the electrode pattern 22 of the light-incident side surface electrode 20 was formed was suppressed. Therefore, in the case of the sample shown in FIG. 9 , the passivation function of the passivation film was maintained by forming the electrode pattern 22 of the light-incident side surface electrode 20. Therefore, in the case of the sample using the conductive paste of Example 1 shown in FIG. 9 , it can be said that the surface defect density on the surface of the single-crystal silicon substrate did not increase.

[0168] On the other hand, the sample shown in Fig. 10 was fabricated using the conductive paste of Comparative Example 2 to form the light-incident side surface electrode 20. As is clear from Fig. 10, the image of the portion of the light-incident side surface electrode 20 where the electrode pattern 22 is formed is darker than that of the sample shown in Fig. 9. This indicates that the photoluminescence intensity of the portion of the light-incident side surface electrode 20 where the electrode pattern 22 is formed is reduced. Therefore, in the case of the sample shown in Fig. 10 using the conductive paste of Comparative Example 2, the formation of the electrode pattern 22 of the light-incident side surface electrode 20 impaired the passivation function of the passivation film, and the surface defect density of the surface of the single-crystal silicon substrate increased.

[0169] Tables 1 to 3 show the measured photoluminescence intensity (PL value) values ​​for the examples and comparative examples. The PL value is the average value of the photoluminescence intensity near the electrode. The PL value is a numerical value that varies depending on the spectrum and intensity of the irradiated light from the excitation light source, the optical system used for measurement, and other factors, and is expressed in arbitrary units. When the conditions for measuring the PL value, such as the spectrum and intensity of the irradiated light and the optical system used for measurement, are the same, the degree of carrier recombination (the degree of degradation of the passivation function) in each sample can be evaluated by comparing the magnitude of the PL value of each sample. The higher the PL value, the better the passivation function provided by the passivation film.

[0170] For confirmation, the cross section of the sample shown in FIG. 9 was observed using a scanning electron microscope (SEM). FIG. 11 shows a cross-sectional SEM photograph (magnification: 20,000 times) of the vicinity of the passivation film of a sample (corresponding to Example 1) in which the light-incident-side surface electrode 20 was formed using the same conductive paste as the sample shown in FIG. 9 under the same conditions. As is clear from FIG. 11 , in the case of samples with high PL values, the antireflection film 2 (passivation film) maintained its shape almost unchanged even after the light-incident-side surface electrode 20 was formed, and the antireflection film 2 (passivation film) was not eroded by the glass frit. Furthermore, FIG. 12 shows a high-magnification SEM photograph (magnification: 20,000 times) of the cross section of a sample fabricated under the same conditions as Example 1, observed using a scanning electron microscope (SEM) at high magnification. As shown in FIG. 12 , it can be seen that a small electrically conductive AgSi alloy was formed locally between the light-incident-side surface electrode and the impurity diffusion layer of the sample fabricated under the same conditions as Example 1. On the other hand, in the case of samples with low PL values, it is believed that the anti-reflection film 2 (passivation film) has been eroded by the glass frit, and most of the anti-reflection film 2 (passivation film) has disappeared. Such conductive pastes are believed to be conductive pastes that are capable of firing through the passivation film. From the above, it is clear that the reactivity of a conductive paste with respect to the anti-reflection film 2 (passivation film) can be evaluated by measuring the PL value using the above-mentioned PL method.

[0171] As is clear from Tables 1 to 3, the PL values ​​of the samples obtained using the conductive pastes of Examples 1 to 12 of this embodiment were 5113 (Example 5) or higher. The PL value of Comparative Example 1 was 9868, and the PL value of Comparative Example 2 was 5520. In the case of this measurement method, if the PL value is 5000 or higher, it can be said that there is no problem with the reactivity of the conductive paste with the anti-reflection film 2 (passivation film). Therefore, it can be said that there is no problem with the reactivity of the conductive paste with the anti-reflection film 2 (passivation film) when the conductive pastes of Examples 1 to 12 and Comparative Examples 1 and 2 are used.

[0172] It was confirmed that the PL value did not change significantly before and after the laser treatment process, which is thought to be because the laser treatment process is a process for forming a small localized electrically conductive portion and does not affect the majority of the anti-reflection film 2 (passivation film).

[0173] <Measurement of Contact Resistance Before Laser Treatment Process> In the same manner as the sample for measurement by the PL method, a p-type impurity diffusion layer 4 was formed on one surface of an n-type crystalline silicon substrate 1 (substrate thickness: 200 μm), and further, a silicon nitride film (anti-reflection film 2 serving as a passivation film) having a thickness of approximately 60 nm was formed on the p-type impurity diffusion layer 4, thereby obtaining a substrate for measuring contact resistance.

[0174] For the monocrystalline silicon solar cells of the Examples and Comparative Examples, the conductive pastes used for forming the electrodes (conductive pastes for forming the first electrodes) on the surfaces (light incident side surfaces) of the substrates on which the p-type impurity diffusion layer 4 was formed were those shown in Tables 1 to 3.

[0175] The conductive paste was printed by screen printing onto the anti-reflection film 2 of the substrate in a pattern consisting of 1.5 mm wide light-incident side busbar electrodes 20a and 60 μm wide light-incident side finger electrodes 20b so as to have a film thickness of approximately 20 μm, and then dried at 150° C. for approximately 1 minute.

[0176] A commercially available Ag paste was printed by screen printing as the back electrode 15 (the electrode on the surface on which the n-type diffusion layer was formed). The electrode pattern of the back electrode 15 was the same as that of the light-incident side surface electrode 20. It was then dried at 150°C for approximately 60 seconds. After drying, the film thickness of the conductive paste for the back electrode 15 was approximately 20 μm. It was then simultaneously fired on both sides using a belt furnace (firing furnace) CDF7210 manufactured by Despatch Industries, Inc., at a peak temperature of 720°C with an in-out time of the furnace of 50 seconds. In this manner, a single-crystal silicon solar cell was fabricated.

[0177] The solar cell thus obtained was cut into a 15 mm × 15 mm square to obtain a contact resistance measurement sample, as shown in Figure 7 . As shown in Figure 7 , light-incident side finger electrodes 20b, each 60 μm wide and 15.0 mm long, were arranged at 1.5 mm intervals on the light-incident side surface of the cut solar cell (contact resistance measurement sample). These light-incident side finger electrodes 20b (first electrodes) were used as contact resistance measurement patterns. The contact resistances of the contact resistance measurement patterns of the examples and comparative examples before the laser treatment process were determined by the TLM (Transfer Length Method) method using a GP 4 TEST Pro manufactured by GP Solar.

[0178] Three samples were prepared under the same conditions for measuring the contact resistance, and the measured value was calculated as the average value of the three samples.

[0179] The contact resistance before the laser treatment process was 500 mΩ cm ２ If the contact resistance before the laser treatment is 300 Ω cm or less, the electrode can be used as a solar cell electrode by subjecting it to a laser treatment process. ２ If the thickness is below 1000 nm, the material can be more preferably used as an electrode for a solar cell by subjecting it to a laser treatment process.

[0180] As is clear from Tables 1 to 3, the contact resistance of the samples obtained using the conductive pastes of Examples 1 to 12 of this embodiment before the laser treatment process was 447 mΩ cm ２(Example 9) or less. Therefore, when the conductive pastes of the examples of this embodiment are used to form electrodes of solar cells, they can be used as electrodes of solar cells by subjecting them to a laser treatment process. Furthermore, the contact resistance of the samples obtained using the conductive pastes of Examples 5, 6 and 8 of this embodiment before the laser treatment process was 251 mΩ cm ２ The contact resistance before the laser treatment process of the samples obtained using the conductive pastes of Comparative Examples 1 and 2 was 300 mΩ cm or less. ２ was a lower value.

[0181] <Measurement of Contact Resistance After Laser Treatment Process> Similar to the measurement of contact resistance before the laser treatment process described above, a single-crystal silicon solar cell was fabricated, and a laser treatment process was performed on the light-incident surface of this solar cell. That is, laser light was irradiated onto the light-incident surface of the solar cell while applying a negative voltage to the back electrode 15 (second electrode) and a positive voltage to each of the light-incident surface electrodes 20 (first electrodes) formed on the light-incident surface in the pattern shown in Figure 2 so that a current flowed in the reverse direction to the forward direction between the p-type impurity diffusion layer 4 of the solar cell and the n-type crystalline silicon substrate 1. The applied voltage during the laser treatment process was 20 V, and the irradiated laser light intensity was 100 W / cm. ２ The voltage application and laser light irradiation time were set to 2 seconds.

[0182] The solar cell thus obtained was cut into a square of 15 mm x 15 mm as shown in Figure 7, and the contact resistance after the laser treatment process was measured in the same manner as in the contact resistance measurement before the laser treatment process.

[0183] The contact resistance after the laser treatment process is 20 mΩ cm ２ Since the contact resistance after the laser treatment process is 9 mΩ cm or less, it can be preferably used as the electrode 20 of a solar cell. ２ When the thickness is equal to or less than 100 nm, the electrode can be more preferably used as an electrode for a solar cell.

[0184] As is clear from Tables 1 to 3, the contact resistance after the laser treatment process of the samples obtained using the conductive pastes of Examples 1 to 12 of this embodiment was 16 mΩ cm ２ (Example 7) or less. Therefore, when the conductive paste of the example of this embodiment is used to form an electrode of a solar cell, it can be said that it can be preferably used as the electrode 20 of the solar cell. Furthermore, the contact resistance after the laser treatment process of the samples obtained using the conductive paste of Examples 3 to 6 and 12 of this embodiment was 9 mΩ cm ２ Therefore, when the conductive pastes of Examples 3 to 6 and 12 of this embodiment are used to form electrodes of solar cells, they can be more preferably used as electrodes of solar cells. The contact resistance after the laser treatment process of the samples obtained using the conductive pastes of Comparative Examples 1 and 2 was 9 mΩ cm ２ was a lower value.

[0185] <Solar Cell Characteristics After Laser Treatment Process> Using the conductive pastes of Examples 1 to 12 and Comparative Examples 1 and 2, single-crystal silicon solar cells were fabricated in the same manner as in the measurement of contact resistance before the laser treatment process described above, and a laser treatment process was performed on the light-incident surface of the solar cell. When the solar cell characteristics after the laser treatment process were measured, the conversion efficiency of the solar cells of the Examples and Comparative Examples was found to be satisfactory. Therefore, it can be said that the solar cells obtained using the conductive pastes of Examples 1 to 12 and Comparative Examples 1 and 2 have satisfactory solar cell characteristics.

[0186] <Measurement of Resistivity> The resistivity of the conductive film patterns for resistivity measurement obtained by firing the conductive pastes of the Examples and Comparative Examples was measured.

[0187] The resistivity of the examples and comparative examples was measured by the following procedure. A silicon substrate measuring 15 mm in width, 15 mm in length, and 180 μm in thickness was prepared. A pattern made of conductive paste as shown in FIG. 6 was printed on the substrate using a 325-mesh stainless steel screen.

[0188] Next, the silicon substrates on whose surfaces the patterns of the examples and comparative examples were printed were 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 an in-out time of the furnace of 50 seconds. In this manner, samples for resistivity measurement were prepared.

[0189] The resistivity of the conductive film patterns of the resistivity measurement samples obtained by firing the conductive pastes of the Examples and Comparative Examples was measured. First, the resistance value was measured using a four-terminal method using a Toyo Corporation Model 2001 multimeter. The cross-sectional area of ​​the conductive film pattern was measured using a Lasertec Corporation OPTELICS H1200 confocal microscope and a Lasertec Corporation 1500SD2 surface roughness and shape measuring instrument. Measurements were taken at 50 locations over a 1.6 mm range, and the average value was calculated. The resistivity was calculated using the cross-sectional area and the measured resistance value.

[0190] Four samples were prepared under the same conditions for measuring the resistivity, and the measured value was calculated as the average of the four values. The measurement results are shown in Tables 1 to 3.

[0191] As is clear from Tables 1 to 3, the resistivity of the samples obtained using the conductive pastes of Examples 1 to 12 of this embodiment was 5 to 6 μΩ cm. Therefore, when the conductive pastes of the Examples of this embodiment are used to form electrodes for solar cells, it can be said that there is no problem with the resistivity of the electrodes. The resistivity of the samples obtained using the conductive pastes of Comparative Examples 1 and 2 was 6 μΩ cm.

[0192] <Tape Peeling Test (Electrode Reliability Test)> As one of the evaluations of the conductive paste of this embodiment, a sample for a tape peeling test simulating a solar cell was produced using the prepared conductive paste, and a tape peeling test was performed.

[0193] Similar to the sample for measurement by the PL method, a p-type impurity diffusion layer 4 was formed on one surface of an n-type crystalline silicon substrate 1 (substrate thickness: 200 μm), and further, a silicon nitride film (anti-reflection film 2 serving as a passivation film) having a thickness of about 60 nm was formed on the p-type impurity diffusion layer 4, thereby obtaining a substrate for a tape peel test.

[0194] The conductive pastes used to form electrodes on the surface (light incident surface) of the substrate on which the p-type impurity diffusion layer 4 was formed in the monocrystalline silicon solar cells of the Examples and Comparative Examples were those shown in Tables 1 to 3.

[0195] The conductive paste was printed by screen printing. As with the sample for measuring contact resistance, a pattern consisting of 1.5 mm wide light-incident side busbar electrodes 20a and 60 μm wide light-incident side finger electrodes 20b was printed on the anti-reflection film 2 of the above-mentioned substrate to a film thickness of approximately 20 μm, and then dried at 150° C. for approximately 60 seconds.

[0196] Next, the silicon substrates on whose surfaces the patterns of the examples and comparative examples were printed were baked using a belt furnace (baking furnace) CDF7210 manufactured by Despatch Industries, Inc. at a peak temperature of 720°C and an in-out time of the baking furnace of 50 seconds.

[0197] The electrode-attached substrate thus obtained was cut into a 15 mm x 15 mm square as shown in Figure 7 to obtain a sample for a tape peeling test.

[0198] Next, the sample for the tape peeling test was immersed in a 1% aqueous solution of acetic acid at room temperature for 1 hour. After immersion, the sample was removed from the acetic acid solution, washed with pure water, and dried. Six electrodes (finger electrodes) were selected from the electrodes for the tape peeling test, and Scotch (registered trademark) Mending Tape 810 (12 mm wide) was attached to the six electrodes and peeled off. The number of electrodes that peeled off during the peeling was confirmed. Tables 1 to 3 show the results of the tape peeling test. "Good" indicates that none of the six electrodes peeled off. "Usable" indicates that one to five electrodes peeled off. "Poor" indicates that all six electrodes peeled off.

[0199] As is clear from Tables 1 to 3, in the tape peeling test of samples obtained using the conductive pastes of Examples 1 to 12 of this embodiment, none of the samples showed peeling of all six electrodes. In contrast, in the tape peeling test of samples obtained using the conductive pastes of Comparative Examples 1 and 2, all six electrodes peeled off. Therefore, it was revealed that by using the conductive pastes of Examples 1 to 12 of this embodiment, it is possible to suppress a decrease in the adhesion of the electrode to the p-type impurity diffusion layer 4 and reduce the occurrence of the problem of the electrode easily peeling off from the p-type impurity diffusion layer 4 of the solar cell. Therefore, by using the conductive pastes of Examples 1 to 12 of this embodiment, it is possible to improve the reliability of the electrode with respect to the p-type impurity diffusion layer 4.

[0200] <Measurement of soldering adhesion strength> As one of the evaluations of the conductive paste of this embodiment, a substrate for measuring soldering adhesion strength simulating a solar cell was fabricated using the prepared conductive paste, and the soldering adhesion strength was measured. The substrate for measuring soldering adhesion strength had a light-incident side bus bar electrode 20a formed thereon.

[0201] The method for preparing the measurement substrate is as follows.

[0202] The substrate used was a p-type Si single crystal silicon substrate (substrate thickness: 200 μm).

[0203] First, a silicon oxide layer of approximately 20 μm was formed on the substrate by dry oxidation, and then the substrate surface was etched with a solution containing hydrogen fluoride, pure water, and ammonium fluoride to remove damage.Furthermore, heavy metals were removed using an aqueous solution containing hydrochloric acid and hydrogen peroxide.

[0204] Next, a textured structure was formed on the light-incident surface by wet etching (using a sodium hydroxide solution).

[0205] Next, a silicon nitride film was formed as a back surface passivation film to a thickness of about 60 nm on the entire surface of the substrate by plasma CVD using silane gas and ammonia gas. ３ / SiH ４A silicon nitride film (rear surface passivation film) having a thickness of about 60 nm was formed by glow discharge decomposition of a mixed gas of SiO 2 =0.5 at 1 Torr (133 Pa) using plasma CVD.

[0206] The solar cell substrate thus obtained was cut into a square of 15 mm x 15 mm for use.

[0207] The conductive paste for forming the light-incident-side busbar electrode 20a was printed by screen printing. Using the conductive pastes of Examples and Comparative Examples containing glass frit and silver particles shown in Tables 1 to 3, a pattern of the light-incident-side busbar electrode 20a, 1.3 mm long and 2 mm wide, was printed on the passivation film of the above-mentioned substrate to a film thickness of approximately 20 μm, and then dried at 150° C. for approximately 1 minute.

[0208] In addition, the back surface electrode 15 is not necessary for measuring the adhesive strength of the light-incident side bus bar electrode 20a, and therefore the back surface electrode 15 was not formed.

[0209] The substrates with the conductive paste printed on their surfaces as described above were fired in the atmosphere under specified conditions using a near-infrared firing furnace (NGK Insulators, Ltd., high-speed firing test furnace for solar cells) with a halogen lamp as the heating source. The firing conditions were a peak temperature of 775°C, firing in the atmosphere, and a 30-second in-out time in the firing furnace. In this way, substrates for measuring solder adhesion strength were prepared.

[0210] A sample for measuring the adhesive strength of the soldered metal ribbon was prepared and measured as follows. A copper ribbon (1.5 mm wide x 0.16 mm thick, coated with a eutectic solder [tin:lead = 64:36 by weight] to a thickness of approximately 40 μm) was used as an interconnect metal ribbon and soldered to the light-incident-side busbar electrode 20a of the 15 mm square solder adhesive strength measurement substrate described above. The sample for adhesive strength measurement was obtained by soldering the copper ribbon (1.5 mm wide x 0.16 mm thick, coated with a eutectic solder [tin:lead = 64:36 by weight] to a thickness of approximately 40 μm) onto the soldering pad using flux at 250 °C for 3 seconds. The ring-shaped portion at one end of the ribbon was then pulled at a 90-degree angle relative to the substrate surface using a digital tensile gauge (Digital Force Gauge AD-4932-50N, manufactured by A&D Corporation). The fracture strength of the adhesive was measured to measure the solder adhesive strength. Ten samples were prepared, and the measured value was calculated as the average of the 10 samples.

[0211] Note that when the adhesive strength of the metal ribbon is 1.5 N / mm or more, it can be said that the adhesive strength is sufficient for practical use. Furthermore, when the adhesive strength of the metal ribbon is 0.5 N / mm or more, it can be said that the adhesive strength is sufficient for use in specific applications. A possible specific application is, for example, a case in which the light-incident side finger electrodes 20b are formed using the conductive paste of this embodiment and the light-incident side busbar electrodes 20a are formed using another type of conductive paste. In this case, the adhesive strength of the metal ribbon to the light-incident side finger electrodes 20b is not particularly required, so even if the adhesive strength of the metal ribbon is 0.5 N / mm, no particular problem will arise.

[0212] As is clear from Tables 1 to 3, the adhesive strength of the metal ribbon of the electrode obtained using the conductive paste of Example 4 of this embodiment was 0.5 N / mm. Therefore, it can be said that the electrode formed using the conductive paste of Example 4 has adhesive strength that can be used for specific applications. Furthermore, the adhesive strength of the metal ribbon of the electrodes obtained using the conductive pastes of Examples 1 to 3 and 5 to 12 of this embodiment was 1.5 N / mm or more. Therefore, it can be said that the electrodes obtained using the conductive pastes of Examples 1 to 3 and 5 to 12 of this embodiment have good adhesive strength that can withstand use. In addition, the adhesive strength of the metal ribbon of the electrodes obtained using the conductive pastes of Comparative Examples 1 and 2 was 0.6 to 1.3 N / mm, which was adhesive strength that can be used for specific applications.

[0213]

[0214]

[0215]

[0216]

[0217]

[0218]

[0219] REFERENCE SIGNS LIST 1 crystalline silicon substrate 2 anti-reflection film (passivation film) 4 impurity diffusion layer 14 rear surface anti-reflection film (passivation film) 15 rear surface electrode 15a rear surface TAB electrode (rear surface bus bar electrode) 15b full rear surface electrode 15c rear surface finger electrode 16 second impurity diffusion layer 20 light incident side surface electrode (surface electrode) 20a light incident side bus bar electrode 20b light incident side finger electrode 22 electrode pattern 30 AgSi alloy

Claims

1. A conductive paste for forming electrodes on a passivation film placed on the surface of a p-type semiconductor layer placed on the surface of an n-type semiconductor substrate, (A) Silver particles and (B) Organic vehicle and (C) Glass frit and Includes, A conductive paste wherein the conductive paste further contains 0.5 parts by weight or less of (D) aluminum particles per 100 parts by weight of (A) silver particles, or a conductive paste which does not contain the (D) aluminum particles.

2. The (C) glass frit is ZnO, V ２ O ５ WO ３ and Nb ２ O ３ A conductive paste according to claim 1, comprising at least one selected from the following.

3. The conductive paste according to claim 1 or 2, wherein the conductive paste contains 0.3 parts by weight or less of the (D) aluminum particles per 100 parts by weight of the (A) silver particles, or does not contain the (D) aluminum particles.

4. The conductive paste according to claim 1 or 2, wherein the conductive paste contains 0.5 to 3.0 parts by weight of (C) glass frit per 100 parts by weight of (A) silver particles.

5. (C) The conductive paste according to claim 1 or 2, wherein the glass transition temperature of the glass frit is 350 to 450°C.

6. Basicity B of the glass frit (C) ＧＦ The product B of the content G of the glass frit (C) in the conductive paste, expressed in units of parts by weight, when the content of the silver particles (A) in the conductive paste is 100 parts by weight. ＧＦ - The conductive paste according to claim 1 or 2, wherein G is in the range of 0.3 to 2.

7. The content C of PbO in terms of mol% in the (C) glass frit ＰｂＯ and the product C ＰｂＯ ·G of the content G of the (C) glass frit is in the range of 26 to 105, the conductive paste according to claim 1 or 2.

8. The conductive paste according to claim 1 or 2, wherein the ratio D / G, which is the content G of the glass frit (C) in the conductive paste in parts by weight, and the content D of the aluminum particles (D) in the conductive paste in parts by weight, is 0.4 or less, when the content of silver particles (A) in the conductive paste is 100 parts by weight.

9. Solar cells, The aforementioned n-type semiconductor substrate, The p-type semiconductor layer disposed on one surface of the n-type semiconductor substrate, A second electrode is arranged to be electrically connected to the other surface of the n-type semiconductor substrate, A passivation film is disposed in contact with the surface of the p-type semiconductor layer, The first electrode, which is the electrode, is disposed on at least a portion of the surface of the passivation film. Includes, The first electrode is the first electrode which has been subjected to a process in which light from a point light source is shone onto the surface of the solar cell on the side where the first electrode is formed, while applying a voltage between the second electrode and the first electrode so that a current flows in the opposite direction to the forward direction between the p-type semiconductor layer and the n-type semiconductor substrate. The conductive paste according to claim 1 or 2, wherein the conductive paste is a conductive paste for forming the first electrode of the solar cell.

10. n-type semiconductor substrate and A p-type semiconductor layer disposed on one surface of the n-type semiconductor substrate, A second electrode is arranged to be electrically connected to the other surface of the n-type semiconductor substrate, A passivation film is disposed in contact with the surface of the p-type semiconductor layer, The first electrode, which is the electrode, is disposed on at least a portion of the surface of the passivation film. A solar cell that includes, The first electrode is the first electrode which has been subjected to a process in which light from a point light source is shone onto the surface of the solar cell on the side where the first electrode is formed, while applying a voltage between the second electrode and the first electrode, such that a current flows between the p-type semiconductor layer and the n-type semiconductor substrate in the opposite direction to the forward direction. The first electrode is a fired body of conductive paste, The conductive paste, (A) Silver particles and (B) Organic vehicle and (C) Glass frit and Includes, A solar cell wherein the conductive paste further contains 0.5 parts by weight or less of (D) aluminum particles per 100 parts by weight of (A) silver particles, or does not contain the (D) aluminum particles.

11. The solar cell according to claim 10, further comprising an AgSi alloy disposed in contact with the first electrode and the p-type semiconductor layer in at least a portion between the first electrode and the p-type semiconductor layer.

12. The conductive paste according to claim 10 or 11, wherein the (C) glass frit comprises at least one selected from ZnO, V2O5, WO3, and Nb2O3.

13. The conductive paste according to claim 10 or 11, wherein the conductive paste contains 0.3 parts by weight or less of the (D) aluminum particles per 100 parts by weight of the (A) silver particles, or does not contain the (D) aluminum particles.

14. The conductive paste according to claim 10 or 11, wherein the conductive paste contains 0.5 to 3.0 parts by weight of (C) glass frit per 100 parts by weight of (A) silver particles.

15. The conductive paste according to claim 10 or 11, wherein (C) the glass transition temperature of the glass frit is 350 to 450°C.

16. The conductive paste according to claim 10 or 11, wherein the product BGF of the basicity of the (C) glass frit and the content G of the (C) glass frit in the conductive paste, in units of parts by weight when the content of the (A) silver particles in the conductive paste is 100 parts by weight, is in the range of 0.3 to 2.

17. The conductive paste according to claim 10 or 11, wherein the product C PbO content in the (C) glass frit, in units of mol%, and G content of the (C) glass frit, C PbO·G, is in the range of 26 to 105.

18. The conductive paste according to claim 10 or 11, wherein the ratio D / G, which is the content G of the glass frit (C) in the conductive paste in units of parts by weight and the content D of the aluminum particles (D) in the conductive paste in units of parts by weight, is 0.4 or less, when the content of the silver particles (A) in the conductive paste is 100 parts by weight.

19. A method for manufacturing solar cells, To prepare an n-type semiconductor substrate, A p-type semiconductor layer is formed on one surface of the n-type semiconductor substrate. A second electrode is formed so as to be electrically connected to the other surface of the n-type semiconductor substrate, A passivation film is formed so as to be in contact with the surface of the p-type semiconductor layer, Forming a first electrode on at least a portion of the surface of the passivation film, The method includes irradiating the surface of the solar cell on the side where the first electrode is formed with light from a point light source, while applying a voltage between the second electrode and the first electrode, such that a current flows between the p-type semiconductor layer and the n-type semiconductor substrate in the opposite direction to the forward direction. A method for manufacturing a solar cell, wherein the first electrode is a fired body of the conductive paste described in claim 1 or 2.

20. A method for manufacturing a solar cell according to claim 19, further comprising applying the voltage between the second electrode and the first electrode, and irradiating the surface of the solar cell on the side where the first electrode is formed with light from the point light source, thereby forming an AgSi alloy in at least a portion between the first electrode and the p-type semiconductor layer so as to be in contact with the first electrode and the p-type semiconductor layer.