DE112012002354T5 - Solar cell and paste composition for forming an aluminum electrode of a solar cell - Google Patents

Abstract

There are provided a solar cell having an aluminum electrode which has improved bonding strength and a paste composition for forming the aluminum electrode. This paste composition contains a glass frit which (1) has a glass softening point of at least 400 ° C and not more than 600 ° C, (2) a coefficient of thermal expansion of at least 60 × 10-7 / ° C and not more than 80 × 10-7 / ° C and (3) comprises as essential components SiO2, B2O3, ZnO and / or PbO, Al2O3 and at least one alkali metal oxide.

Description

Technical area

The present invention relates to a solar cell and a method for the production thereof. The invention further relates to a paste composition for forming an aluminum electrode used in such a manufacturing method.

This application claims the priority of Japanese Patent Application No. 2011-125062 filed on 3 June 2011, the entire contents of which are hereby incorporated by reference.

The in the 7 shown unilateral solar cell 1000 has hitherto been known as a typical example of a solar cell composed primarily of silicon (semiconductor substrate) such as silicon. Crystalline silicon or amorphous silicon (hereinafter sometimes referred to as "silicon solar cell") (see, for example, Patent Documents 1 to 4).

This solar cell 1000 has a silicon semiconductor substrate (Si wafer) 111 in which an n-Si layer 116 by a pn-junction formation on the light-receiving surface side of a p-Si layer (p-type crystalline silicon) 118 has been trained. On a front surface of the n-Si layer 116 are an antireflection film 114 composed of titanium oxide or silicon nitride formed by chemical vapor deposition (CVD) or the like and front surface electrodes (light receiving surface electrodes) 112 , which are composed of silver and formed by screen printing and firing a paste composition, which is typically composed primarily of a silver (Ag) paste (hereinafter also referred to as "silver paste").

On the back surface of the p-Si layer 118 (Here and below, "back surface" refers to the surface on the side opposite to the light-receiving surface) are electrodes 122 for an external connection on the back surface side made of silver and by screen printing and firing a silver paste in the same manner as for the front surface electrodes 112 are formed, and an aluminum electrode 120 having a back surface field effect (BSF effect) provided.

The aluminum electrode 120 is formed substantially over the entire back surface by printing and firing a paste composition composed essentially of an aluminum (Al) powder (which composition is also referred to hereinafter as an "aluminum paste"). At the time of such firing, an Al-Si alloy film (not shown) is formed and the aluminum diffuses into the p-Si layer 118 , where a p ⁺ layer 124 is formed. Due to the formation of this p ⁺ layer 124 or BSF layer, photogenerated carriers are prevented from recombining near the back surface electrodes, causing e.g. B. an increase of the short-circuit current and the open circuit voltage (Voc) is achieved.

List of documents

Patent documents

• Patent Document 1: Japanese Patent Application Laid-Open No. 2010-10495
• Patent Document 2: Japanese Patent Application Laid-Open No. 2011-23598
• Patent Document 3: Japanese Patent Application Laid-Open No. 2010-192480
• Patent Document 4: Japanese Patent Application Laid-Open No. 2007-59380

As it is in the 7 Shown are in a conventional silicon solar cell 1000 Silver front surface electrodes (electrodes of the light-receiving surface) 112 for extracting a current formed on the light-receiving surface side, and a BSF layer 124 for preventing the recombination of electrons is formed on the back surface side. The silver front surface electrodes 112 and the aluminum electrode 120 for forming the BSF layer 124 are typically formed by screen printing and then simultaneous firing of both surfaces.

Further, lead wires (a terminal comb, not shown) for extracting current to the solar cell wafer are also 1000 soldered, in which electrodes ( 112 . 120 . 122 ) have been formed in this way on both surfaces. Using these leads, a plurality of solar cell wafers 1000 connected in series and thereby modularized, whereby in this modularized state, a specific electrical power can be delivered.

Here are the structure in the 7 is shown at the solder joints silver electrodes 122 formed because a solder is not on the aluminum electrode 120 , which is used on the back surface, can be used. The formation of such silver electrodes 122 disturbs the uniformity of the BSF layer 124 , Further, the fact that silver, which is a precious metal that is more expensive than aluminum, is also the conductive component in forming the silver electrodes 122 is used, a major factor that leads to high costs.

The inventors, in an effort to cover the entire back surface with an aluminum electrode, have investigated a technique for thermocompression bonding lead wires by means of an electroconductive adhesive film (ie, a film containing an adhesive and electroconductive particles) in place of a solder. In particular, bonding without the use of a solder is accomplished by thermocompression bonding of lead wires via an electroconductive adhesive film at the positions of electrodes 122 for external bonding made of aluminum.

However, techniques using this conductive adhesive film have found that with electrodes 122 , which are made of aluminum, no sufficient bond strength can be obtained. That is, according to research by the inventors, when the portions of lead wires (conductive tape wires) bonded using a conductive adhesive film are torn off, peeling occurs within the aluminum film on the electrodes 122 made of aluminum, which is considered to be the reason why a sufficient bonding strength can not be obtained. In fact, the aluminum film itself faces the electrodes 122 made of aluminum have a lack of strength, and it has been found that the cause thereof is the weakness of the bonding strength between the aluminum particles constituting the aluminum film after firing.

If it were possible to bond leads to the aluminum electrodes of a solar cell wafer, this would have the advantage of having a BSF layer 124 that would be formed on the entire surface would be enabled. In addition, it would no longer be necessary to use silver, which would allow a significant reduction in costs corresponding to the difference in material price of silver and aluminum.

Summary of the invention

This invention has been made in view of the above. An object of the invention is to provide a paste composition for forming an aluminum electrode (in particular, an external connection electrode on the back surface side) having an improved bonding strength. Another object is to provide a solar cell having an aluminum electrode (in particular, an electrode for external connection on the back surface side) formed by using such a paste composition, and a process for producing such a solar cell.

The paste composition (i.e., a composition prepared in the form of a paste) provided by this invention is a paste composition for forming an aluminum electrode for a solar cell.

• (1) einen Glaserweichungspunkt von mindestens 400°C und nicht mehr als 600°C aufweist,
• (2) einen Wärmeausdehnungskoeffizienten von mindestens 60 × 10^–7/°C und nicht mehr als 80 × 10^–7/°C aufweist und
• (3) als essentielle Bestandteile SiO₂, B₂O₃, ZnO und/oder PbO, Al₂O₃ und mindestens ein Alkalimetalloxid umfasst.

The paste composition for forming an aluminum electrode for a solar cell disclosed herein comprises an aluminum powder, a glass frit, and an organic carrier. The glass frit is characterized in that it:

• (1) has a glass softening point of at least 400 ° C and not more than 600 ° C,
• (2) has a thermal expansion coefficient of at least 60 × 10 ^-7 / ° C and not more than 80 × 10 ^-7 / ° C, and
• (3) as essential constituents SiO ₂ , B ₂ O ₃ , ZnO and / or PbO, Al ₂ O ₃ and at least one alkali metal oxide.

By including in the above-mentioned paste composition (aluminum paste) a glass frit (glass powder) which satisfies the conditions mentioned above ( 1 ) to (3), the bonding strength of aluminum electrodes formed by applying this paste composition to a silicon semiconductor substrate can be increased. Consequently, the bond or compound between aluminum electrodes (eg, electrodes for external bonding on the back surface side) formed of the paste composition and other connecting members (e.g., an electroconductive adhesive film comprising an adhesive and electroconductive particles) are stably maintained. As a result, the conductive component can be used in places where silver electrodes have hitherto been used, such. As electrodes for an external connection to be replaced by aluminum, which is cheaper than precious metals, such as. Silver, which allows for cost reductions commensurate with the difference in material prices between silver and aluminum. Moreover, when it is possible to replace the silver electrodes for external connection on the back surface side with aluminum electrodes, a BSF layer can be uniformly formed on the entire back surface side of a silicon semiconductor substrate.

In a preferred embodiment of the paste composition (aluminum paste) disclosed herein, the paste composition is characterized in that the constituents of the glass frit have the following respective molar contents per 100 mol% of these combined constituents: SiO ₂ 20 to 35 mol%, B ₂ O ₃ 5 to 30 mol%, ZnO and / or PbO From 25 to 45 mol%, Al ₂ O ₃ 2 to 10 mol%, at least one of Li ₂ O, Na ₂ O and K ₂ O 5 to 15 mol%, at least one of CaO, SrO and BaO 0 to 10 mol% and Bi ₂ O ₃ 0 to 5 mol%, the sum of these constituents being at least 95 mol% (eg 100 mol%) of the total glass frit.

By using a thus-constructed glass frit, the bonding strength (peel strength) of aluminum electrodes (eg, electrodes for external compound on the back surface side) formed from the paste composition can be further increased.

In another preferred embodiment of the paste composition (aluminum paste) disclosed herein, the paste composition is characterized in that the constituents of the glass frit have the following respective molar contents per 100 mol% of these combined constituents: SiO ₂ 20 to 30 mol%, B ₂ O ₃ 20 to 30 mol%, ZnO From 25 to 35 mol%, Al ₂ O ₃ 3 to 7 mol%, at least one of Li ₂ O, Na ₂ O and K ₂ O 10 to 15 mol% and at least one of CaO, SrO and BaO 2 to 10 mol%, the sum of these constituents being at least 95 mol% (eg 100 mol%) of the total glass frit.

By using a glass frit thus constituted, the bonding strength (peel strength) of aluminum electrodes formed of the paste composition, such as, e.g. As electrodes for an external connection on the back surface side, further increased. Furthermore, this high bond strength can be achieved with a lead-free composition.

In another preferred embodiment of the paste composition (aluminum paste) disclosed herein, the paste composition is characterized in that the glass frit has a glass softening point of at least 500 ° C and not more than 600 ° C. By using a glass frit having a glass softening point in this temperature range, aluminum electrodes having a high bonding strength (peel strength) can be formed.

In a further preferred embodiment of the paste composition (aluminum paste) disclosed herein, the paste composition is characterized in that per 100% by weight of the total paste composition, the aluminum powder is included in an amount of 60 to 80 wt .-% and the glass frit is included in an amount of 2 to 10 wt .-%. By incorporating the solids of the paste composition in these amounts, it is easy to apply the paste composition containing these solids uniformly (typically in the form of a film) to a silicon semiconductor substrate. Moreover, by firing the substrate to which this paste composition has been applied, an aluminum electrode having a good appearance and a high bonding strength can be formed.

As described above, by using any of the paste compositions (aluminum pastes) disclosed herein, aluminum electrodes having a high bonding strength can be formed on a silicon semiconductor substrate.

• (1) einen Glaserweichungspunkt von mindestens 400°C und nicht mehr als 600°C aufweist,
• (2) einen Wärmeausdehnungskoeffizienten von mindestens 60 × 10^–7/°C und nicht mehr als 80 × 10^–7/°C aufweist und
• (3) als essentielle Bestandteile SiO₂, B₂O₃, ZnO und/oder PbO, Al₂O₃ und mindestens ein Alkalimetalloxid umfasst.

Therefore, according to the present invention, a solar cell having a silicon semiconductor substrate, an electrode of the light-receiving surface formed on a light-receiving surface side serving as one side of the substrate, and an aluminum electrode formed on a back surface side serving as the one is provided, is formed, wherein the solar cell is characterized in that at least a part of the aluminum electrode comprises a glass composition, the

• (1) has a glass softening point of at least 400 ° C and not more than 600 ° C,
• (2) has a thermal expansion coefficient of at least 60 × 10 ^-7 / ° C and not more than 80 × 10 ^-7 / ° C, and
• (3) as essential constituents SiO ₂ , B ₂ O ₃ , ZnO and / or PbO, Al ₂ O ₃ and at least one alkali metal oxide.

A solar cell constructed in this way can achieve a high bonding strength (peel strength) to aluminum electrodes containing the glass composition (glass components) having the above-described properties. Incidentally, in the solar cell (silicon solar cell) disclosed herein, the conductive component can be found in places where silver electrodes have hitherto been used, such as silver electrodes. As electrodes for an external connection to be replaced by aluminum, which is cheaper than precious metals, such as. Silver, whereby cost reductions in electrode fabrication (i.e., replacement of silver electrodes by aluminum electrodes) can be achieved.

Moreover, this invention can provide a solar cell in which a BSF layer has been formed on the entire back surface side of a silicon semiconductor substrate in which the silver electrodes for external connection on the back surface side have been replaced by aluminum electrodes.

The solar cell according to a preferred embodiment disclosed herein is characterized in that the constituents of the glass composition have the following respective molar contents per 100 mol% of these combined constituents: SiO ₂ 20 to 35 mol%, B ₂ O ₃ 5 to 30 mol%, ZnO and / or PbO From 25 to 45 mol%, Al ₂ O ₃ 2 to 10 mol%, at least one of Li ₂ O, Na ₂ O and K ₂ O 5 to 15 mol%, at least one of CaO, SrO and BaO 0 to 10 mol% and Bi ₂ O ₃ 0 to 5 mol%, the sum of these constituents being at least 95 mol% (typically 100 mol%) of the total glass composition.

Alternatively, the glass composition may be characterized in that the constituents of the glass composition have the following respective molar contents per 100 mol% of these combined constituents: SiO ₂ 20 to 30 mol%, B ₂ O ₃ 20 to 30 mol%, ZnO From 25 to 35 mol%, Al ₂ O ₃ 3 to 7 mol%, at least one of Li ₂ O, Na ₂ O and K ₂ O 10 to 15 mol% and at least one of CaO, SrO and BaO 2 to 10 mol%, the sum of these constituents being at least 95 mol% (typically 100 mol%) of the total glass composition.

Preferably, the glass composition has a glass softening point of at least 500 ° C and not more than 600 ° C.

An advantage of this invention is that aluminum electrodes having a bonding strength (peel strength) identical to or larger than that of conventional silver electrodes can be formed as electrodes for external connection on a silicon semiconductor substrate.

Therefore, a particularly preferred embodiment of the solar cell disclosed herein is characterized in that an external connection electrode is formed on the back surface side of the silicon semiconductor substrate, and this external connection electrode is formed of the above-described aluminum electrode containing the glass composition ,

Further, in a preferred embodiment, an electroconductive adhesive film is provided on the aluminum electrode containing the glass composition and forming the electrode for external connection.

In addition, as another aspect for achieving the above-mentioned objects, the invention provides a method of manufacturing a solar cell including a silicon semiconductor substrate, an electrode of the light-receiving surface provided on a light-receiving surface side serving as a side of the substrate. is formed and has an aluminum electrode formed on a back surface side serving as another side of the substrate.

The method of manufacturing a solar cell disclosed herein is characterized in that at least a part of the aluminum electrode formed on the back surface side is formed by using one of the paste compositions provided by this invention.

Brief description of the drawings

1 Fig. 13 is a sectional view schematically showing an example of the structure of a solar cell 100 according to an embodiment of the invention,

2A and 2 B respectively, are a plan view and a sectional view schematically showing the structure on a back surface side of a substrate 11 in the solar cell 100 demonstrate,

3 FIG. 15 is a perspective view schematically showing a structure in which electroconductive adhesive films. FIG 30 on aluminum electrodes 22 for an external connection on a back surface side of the solar cell 100 have been arranged

4A and 4B are each sectional views of a structure in which a lead wire (contact wire) 35 by means of an electrically conductive adhesive film 30 on an aluminum electrode 22 has been arranged for an external connection,

5 is a sectional view schematically illustrating the structure of a strength measuring device 300 shows are performed with the bond strength tests,

6 is a graph showing the relationship between the bond strength and the softening point of a glass frit and

7 Fig. 10 is a sectional view schematically showing an example of the structure of a conventional solar cell 1000 shows.

Description of embodiments

Hereinafter, a preferred embodiment of the invention will be described. Features not specifically mentioned in the specification (eg, the shapes, compositions, blending proportions, etc., of the aluminum powder and the glass frit), however, which are required to practice the invention (e.g., the method of making the Paste and the general production process for solar cells, none of which is an essential feature of the invention) are considered as a matter of design by a person skilled in the art based on the prior art in the field. This invention may be accomplished on the basis of details described in the specification as well as on the basis of common technical knowledge in the field.

First, the paste composition constituting the aluminum electrode will be described in detail.

The paste composition disclosed herein which forms the aluminum electrode is an aluminum paste which can be used in applications where an aluminum electrode is formed on a solar cell, and is an electrode-forming material prepared in the form of a paste ( including cases where the material is described as "inky") containing an aluminum powder, a glass frit, and an organic vehicle. With respect to the other components, there is no particular limitation provided that the objects of the invention can be achieved.

In this specification, "aluminum powder" refers to a collection of particles composed predominantly of aluminum (Al), typically an aggregate of particles composed only of aluminum. Even if small amounts of impurities other than aluminum and alloys consisting essentially of aluminum are contained, it may be comprised of what is referred to herein as "aluminum powder" as long as the aggregate as a whole consists of particles which are composed mainly of aluminum. The aluminum powder itself may be one prepared by a known manufacturing method, and it does not require special manufacturing facilities. The particles that form the aluminum powder that is used are typically spherical, but need not be completely spherical. Particles in the form of scales or having an irregular shape may also be included.

The aluminum powder used is preferably a powder having a relatively narrow particle size distribution (that is, having a uniform particle diameter). As an indicator, the ratio (D10 / D90) of the particle diameter at 10% of the cumulative volume (D10) to the particle diameter at 90% of the cumulative volume (D90) in a particle size distribution based on a laser diffraction method can be used , When the diameters of the particles forming a powder are all the same, the value of D10 / D90 is 1; On the other hand, if the particle size distribution becomes wider, the value of this ratio D10 / D90 approaches zero (0). The use of a powder having a relatively narrow particle size distribution such that the value of D10 / D90 is 0.2 or more (for example, from 0.2 to 0.5) is preferred.

With respect to the aluminum powder used in the paste composition disclosed herein which forms the aluminum electrode, it is desirable that it has an average particle diameter of not more than 20 μm. For example, an aluminum powder having an average particle diameter of about 1 μm to about 10 μm may be preferably used.

In this specification, "average particle diameter" refers to the particle diameter at 50% of the sum volume in the particle size distribution of the powder, i. h., D50 (the median value of the diameter). This D50 value can be easily measured with a particle size analyzer based on a laser diffraction method.

Although not particularly limited, the aluminum powder is preferably included in an amount of 55 to 85% by weight, and more preferably 60 to 80% by weight, per 100% by weight of the total paste composition. In this aluminum powder content, an aluminum electrode having an increased density (eg, an aluminum electrode for an external compound having a film thickness of not more than 100 μm, such as 10 μm to 100 μm) may be advantageously formed on the silicon semiconductor substrate be formed.

Of the solids in the paste composition disclosed herein, which forms the aluminum electrode, the glass frit (glass powder) is an inorganic additive which increases the bonding strength of the glass frit Aluminum electrode increased. In particular, in the paste composition (aluminum paste) provided by the invention, the glass frit, by satisfying the above-mentioned conditions (1) to (3), can impart high bond strength (peel strength) to the aluminum electrodes being formed.

That is, the glass frit (glass composition) included in the paste composition forming the aluminum electrode disclosed herein is preferably a glass frit having a thermal expansion coefficient (linear thermal expansion coefficient) of at least 60 × 10 ^-7 / ° C and not more as 80 x 10 ^-7 / ° C, and more preferably at least 65 x 10 ^-7 / ° C and not more than 75 x 10 ^-7 / ° C.

In this specification, the thermal expansion coefficient is calculated as the average value of measurements between room temperature (25 ° C) and a temperature at the glass transition point or below the glass transition point (e.g., 400 ° C or 500 ° C) with a thermomechanical analyzer (TMA) on the Calculated based on an ordinary differential expansion method.

The glass frit included in the paste composition forming the aluminum electrode disclosed herein is preferably a glass frit having a glass softening point (a glass softening point) by measurement with a conventional thermomechanical analyzer (TMA) in the same manner as the aforementioned coefficient of thermal expansion calculated) of at least 400 ° C and not more than 600 ° C. The glass softening point is more preferably at least 500 ° C and not more than 600 ° C.

The glass frit (glass composition) having the aforesaid preferred thermal expansion coefficient and the preferred glass softening point mentioned above preferably comprises SiO ₂ , B ₂ O ₃ , ZnO and / or PbO, Al ₂ O ₃ and at least one alkali metal oxide (selected from e.g. Li ₂ O, Na ₂ O and K ₂ O) as essential components.

Preferred examples of the glass frit (glass composition) included in the paste composition disclosed herein which forms the aluminum electrode are glass frits having the following respective molar contents per 100 mol% of these combined components: SiO ₂ 20 to 35 mol%, B ₂ O ₃ 5 to 30 mol%, ZnO and / or PbO From 25 to 45 mol%, Al ₂ O ₃ 2 to 10 mol%, at least one of Li ₂ O, Na ₂ O and K ₂ O 5 to 15 mol%, at least one of CaO, SrO and BaO 0 to 10 mol% and Bi ₂ O ₃ 0 to 5 mol%, the sum of these constituents being at least 95 mol% (typically 100 mol%) of the total glass frit.

Particularly preferred examples of the glass frit include those having the following respective molar contents per 100 mol% of these combined components: SiO ₂ 20 to 30 mol%, B ₂ O ₃ 20 to 30 mol%, ZnO From 25 to 35 mol%, Al ₂ O ₃ 3 to 7 mol%, at least one of Li ₂ O, Na ₂ O and K ₂ O 10 to 15 mol% and at least one of CaO, SrO and BaO 2 to 10 mol%, the sum of these constituents being at least 95 mol% (typically 100 mol%) of the total glass frit.

By incorporating a glass frit having the above-described structure, the bonding strength (peel strength) of the formed aluminum electrode can be further increased.

For example, the SiO ₂ serving as an essential ingredient is a main component constituting the glass skeleton. Too high a SiO ₂ content is undesirable because the glass softening point becomes too high. On the other hand, too low an SiO ₂ content leads to less chemical resistance and lower water resistance and is therefore undesirable.

B ₂ O ₃ is a component showing significant effects of lowering the softening point as well as the glass frit melting temperature. If the B ₂ O ₃ content is too low, effects for lowering the glass softening point and the melting temperature are not obtained. On the other hand, too high a B ₂ O ₃ content is undesirable because it may lead to a reduction in water resistance.

ZnO and PbO are components that can reduce the softening point of the glass frit (glass composition) or that can be used to adjust the thermal expansion coefficient. It is preferable that either ZnO or PbO or both be included in the above content range. If the content of these ingredients is too high, the glass softening point becomes too low, which is undesirable. PbO-free glass frits are preferred.

Al ₂ O ₃ is a component that controls the flow properties of the glass frit when molten, and it provides a deposition stability during the formation of the aluminum electrode. If the Al ₂ O ₃ content is too low, the deposition stability decreases, which is undesirable. On the other hand, if the Al ₂ O ₃ content is too high, the chemical durability of the glass may decrease, which is undesirable.

Alkalimetalloxidbestandteile, such as. As Li ₂ O, Na ₂ O and K ₂ O, are components that increase the thermal expansion coefficient. If the content of these alkali metal oxide components is too low, the thermal expansion coefficient may become too low. On the other hand, if the content of these alkali metal oxide components is too high, the thermal expansion coefficient may become too high, which is undesirable.

In addition to the essential ingredients mentioned above, optional ingredients may be included in the glass frit.

For example, it is preferred that alkaline earth metal oxide components, such as. As CaO, SrO and BaO, are included in a content of not more than 10 mol%. The incorporation of at least one alkaline earth metal oxide is desirable because the adjustment of the coefficient of thermal expansion can be more easily performed, and in addition the chemical resistance and other properties are improved by the diversification of the glass composition (greater diversity of the metal constituent elements), whereby the glass stability can be increased. It is preferred that alkaline earth metal oxide components, such as. CaO, SrO and BaO, in a content of at least 1 mol% and not more than 10 mol% (for example, from 2 to 10 mol% and especially from 5 to 10 mol%).

Bi ₂ O ₃ may be included in an appropriate amount, such as. B. in a proportion of not more than 10 mol% (preferably not more than 5 mol%), so that the stability of the glass frit after firing (and concomitantly the stability of the aluminum electrode after firing) is increased.

In addition, oxides of zirconium (Zr), titanium (Ti), vanadium (V), niobium (Nb), lanthanum (La), cerium (Ce), tin (Sn), phosphorus (P) and the like may be contained in a proportion of not more than 5 mole% (eg, from about 0.1 to about 5 mole%) of the total glass composition.

In order to stably burn and affix the paste composition (coated film) deposited on the silicon semiconductor substrate, it is preferable that the glass frit included in the paste composition has a specific surface area formed by the BET method is at least about 0.5 m ² / g and not more than about 50 m ² / g and has a median particle diameter (D50) of not more than 2 μm (and more preferably about 1 μm or smaller). having.

The content of such a glass powder in the paste composition is not particularly limited, though the amount per 100 wt% of the total paste composition is typically from about 1 to about 15 wt%, and preferably from about 2 to about 10 wt%. With a paste composition containing a glass frit having the above-described elemental structure in approximately this amount, aluminum electrodes (e.g., aluminum electrodes for external connection on the back surface side) having a high bonding strength can be easily formed.

The paste composition disclosed herein comprises, as the solid material, the aluminum powder and the glass frit (glass powder) described above, and also comprises a liquid medium (an organic vehicle) for dispersing these solids.

The organic solvent within this carrier should be an organic solvent which can appropriately disperse the aluminum powder and the glass frit; Organic solvents heretofore used in this type of paste can be used here without any particular limitation. Illustrative examples of the organic solvent within the carrier include one or a combination of a plurality of high boiling organic solvents, such as e.g. For example, ethylene glycol and diethylene glycol derivatives (glycol ether type solvents), toluene, xylene, butylcarbitol (BC), butyldiglycol acetate (BDGA) and terpineol. In addition, various resin components can be included as organic binders in the carrier. Such resin components may be those which have heretofore been used in this kind of paste, and are not particularly limited, provided that they can impart a good viscosity and a good film forming ability to the paste composition disclosed herein (a capability of depositing and adhering a silicon substrate). Illustrative examples include resin components composed primarily of an acrylic resin, an epoxy resin, a phenolic resin, an alkyd resin, a cellulose-containing polymer, polyvinyl alcohol or rosin. Of these, a cellulose-containing polymer, such as. For example, ethyl cellulose, preferably.

Although not particularly limited, the content of the organic carrier is preferably about 10 to 30% by weight, and more preferably about 15 to 25% by weight of the entire paste.

The paste composition disclosed herein, like conventional aluminum pastes for solar cells, can be easily prepared by typically mixing together the aluminum powder, the glass frit (glass powder) and a suitable organic carrier. For example, with a three-roll mill or other mixer, the aluminum powder and the glass frit mixed in a given proportion may be mixed and stirred together with an organic vehicle in a predetermined mixing ratio.

The paste composition disclosed herein can be handled in the same manner as aluminum pastes heretofore used to form an aluminum electrode as a back surface electrode on a substrate (and thus as a p ⁺ layer, ie, a BSF layer), and methods of Those known in the art may be used without particular limitation. Typically, the paste composition is applied (coated) to the silicon semiconductor substrate by screen printing, spray coating, dip coating, or the like to obtain a desired film thickness and film structure. The thickness of this substrate can be adjusted after factors such. For example, the size of the desired solar cell, the film thickness of the aluminum electrode to be formed on the substrate, and the strength of the substrate (eg, the breaking strength) have been taken into consideration. Although not particularly limited, a thickness of about 5 μm to about 300 μm is suitable, and a thickness of about 5 μm to about 200 μm (more preferably about 10 μm to about 100 μm) is preferable.

Next, the applied paste is dried at a suitable temperature (eg, at least room temperature, and typically about 100 ° C). After drying, the dried film is dried by heating in a suitable kiln (e.g., a high speed kiln) under suitable heating conditions (e.g., at least 600 ° C and not more than 900 ° C and preferably at least 700 ° C and not more than 800 ° C) for a given period of time. The applied paste is thereby anchored to the substrate, whereby the formation of the subsequently described aluminum electrodes 22 for an external connection, such as B. those in the 1 are shown is possible.

The 1 is a sectional view showing the structure of a solar cell 100 according to an embodiment of the invention. The solar cell 100 in this embodiment, a silicon semiconductor substrate (Si wafer) 11 , the electrodes of the light-receiving surface 12 on one side (front surface side) of the substrate 11 are formed, and aluminum electrodes ( 20 . 22 ), on the other side (back surface side) of the substrate 11 are trained on.

The silicon semiconductor substrate 11 This embodiment is made of silicon, such as. As crystalline silicon or amorphous silicon, composed. In this embodiment, an n-Si layer 16 formed by pn junction formation on the light-receiving surface side of a p-Si layer (p-type crystalline silicon) 18 of the substrate 11 educated. An antireflection film 14 that through An ordinary chemical vapor deposition (CVD) or the like formed and composed of titanium oxide or silicon nitride is formed on the front surface of the n-Si layer 16 arranged. In addition, front surface electrodes (electrodes of the light-receiving surface) are typically used. 12 made of silver and formed by screen printing and firing a silver paste on the surface of the antireflection film 14 provided.

In this embodiment, aluminum electrodes 22 formed from the paste composition disclosed herein which forms the aluminum electrode (hereinafter sometimes referred to as "the first aluminum paste" for convenience) on the back surface side of the p-Si layer 18 provided. These aluminum electrodes 22 correspond to the electrodes 22 for an external connection on the back surface side, wherein the electrodes are connected to other elements for an external connection, such. B. lead wires (conductive tape wires), are electrically connected.

The aluminum electrodes 22 For an external interconnection of this embodiment, as in cases where conventional electrodes of this electrode type are formed (for example, in cases where silver electrodes for external connection are formed by using a silver paste as the material), by screen-printing and firing the first one Aluminum paste formed with a given composition.

An aluminum electrode 20 made of another aluminum paste (hereinafter sometimes referred to as "the second aluminum paste" for convenience) is used together with the aluminum electrodes 22 for an external connection on the back surface side of the p-Si layer 18 educated. Such an aluminum electrode 20 becomes on substantially the entire back surface of the p-Si layer 18 and is an aluminum electrode having a back surface field (BSF) effect (hereinafter referred to as a "wide area backside aluminum electrode"). In this embodiment, the aluminum electrodes are 22 for an external connection as lines on the back surface side of the p-Si layer 18 formed and the back surface aluminum electrode with a wide area 20 is over substantially the entire back surface side of the p-Si layer 18 formed in areas different from those where the aluminum electrodes 22 have been designed for an external connection.

Also in this embodiment, the back surface aluminum electrode is a wide area 20 designed to have sections of aluminum electrodes 22 covered for an external connection (especially both edges of the linear structure), and making them openings 23 comprising the aluminum electrodes 22 for an external connection. Except that the back surface aluminum electrode has a wide area 20 both edges of the aluminum electrodes 22 For an external connection, it is also possible that the side walls of the back surface aluminum electrode have a wide area 20 the side walls of the aluminum electrodes 22 contact for an external connection.

Moreover, in this embodiment, the back surface aluminum electrode having a wide area 20 may be made of an ordinary aluminum paste comprising an aluminum powder, a glass frit, and an organic carrier used to form aluminum electrodes in conventional solar cells, and is not particularly limited in their construction. Since this is not an essential feature of the invention, a detailed description is omitted here.

In this embodiment, the first aluminum paste is typically applied to the silicon semiconductor substrate (wafer). 11 z. By screen printing, spray coating, dip coating or the like, to obtain a desired thickness and a desired film structure. Next, the applied material is dried at a suitable temperature (from room temperature to about 100 ° C). Moreover, the second aluminum paste becomes so on the silicon semiconductor substrate 11 applied that openings 23 which are the aluminum electrodes 22 for an external connection. This applied material is then dried at a suitable temperature (from room temperature to about 100 ° C). The dried films are then fired by heating for a given period of time in a suitable kiln (e.g., a high speed kiln) under suitable heating conditions (e.g., 700 to 800 ° C). The deposited materials are anchored to the substrate in this manner, with aluminum electrodes 22 for an external connection and a back surface aluminum electrode with a wide area 20 in the in the 1 be formed manner shown. In this embodiment, along with the burning of the aluminum electrodes 22 for an external connection and the back surface aluminum electrode with a wide area 20 also a p ⁺ -layer (BSF-layer) 24 be formed.

The 2A and 2 B FIG. 12 is a plan view and a sectional view, respectively, schematically illustrating the structure on the back surface side of the substrate. FIG 11 in the silicon solar cell 100 show this embodiment. In the 2A and 2 B For convenience, it is the back surface side of the substrate 11 shown above.

The aluminum electrodes 22 for an external connection are formed in places where in the in the 7 shown arrangement electrodes 122 are positioned for an external connection on the back surface side (silver electrodes). In the in the 2A and 2 B As shown, the aluminum electrodes 22 function for an external connection as electrodes having a width of z. B. 2 to 6 mm. Bonding aluminum and a solder is generally difficult. Therefore, in this embodiment, an electrically conductive adhesive film 30 so attached to the aluminum electrodes 22 is compression-bonded for an external connection (cf the one described below 3 ). The leading film of detention 30 ( 3 ) is typically an anisotropic, electrically conductive adhesive film. For example, an epoxy resin, a phenoxy resin, an acrylic resin, a polyimide resin, a polyamide resin, a polycarbonate resin, or other thermosetting resin or thermoplastic resin may be used as the adhesive component. The leading film of detention 30 contains various electrically conductive particles (typically metal particles of nickel, copper, a noble metal or the like) dispersed within the resin component (adhesive component). When exposed to heat and pressure, the conductive adhesive film may 30 be attached to predetermined locations and an electrical connection can be ensured by the conductive particles. The conductive adhesive film used for this purpose is not particularly limited; it can be used any of commercial conductive adhesive films for such applications without particular limitation.

The 3 FIG. 12 is a perspective view schematically showing electroconductive adhesive films. FIG 30 shows on aluminum electrodes 22 for an external connection on a back surface side of the solar cell 100 are arranged. As it is in the 3 are shown, the conductive adhesive films 30 on the front surface of the aluminum electrode 22 arranged for an external connection and then connecting wires 35 , also called "contact wires" (conductive band wires) 35 are known on the front surface of the conductive adhesive film 30 arranged.

The 4A and B show sectional views of a structure in which a contact wire 35 via a conductive adhesive film 30 on an aluminum electrode 22 for an external connection (a bus bar electrode).

First, as it is in the 4A is shown, an electrically conductive adhesive film 30 on an aluminum electrode 22 arranged for an external connection on a substrate 11 has been formed, and a contact wire 35 will be on the senior detention film 30 arranged. The leading film of detention 30 is made of electrically conductive particles 31 (eg, gold-plated nickel particles) which are uniform in an adhesive component 32 are dispersed, the z. B. made of a thermosetting epoxy-based resin.

Next connect as it is in the 4B is shown, wherein the conductive adhesive film 30 serves as the contact wire-bonding material when heat and pressure (see the arrow 50 ) on a laminate of the aluminum electrode 22 for an external connection, the conductive adhesive film 30 and the contact wire 35 applied or exercised, the conductive particles 31 within the conductive adhesive film 30 electrically (see the arrow 55 ) the aluminum electrode 22 for an external connection with the contact wire 35 , At the same time takes place in the adhesive component (here, a thermosetting resin) 32 within the conductive adhesive film 30 thermosetting, which makes it possible to achieve an electrical connection that is as reliable as a solder joint. If contact wires 35 be bound by a solder, an elevated temperature of at least 200 ° C must be used. In contrast, when bonded to the conductive adhesive film 30 a low temperature bonding can be achieved at about 180 ° C. Therefore, the influence of heating (such as the generation of a voltage due to the heat) to the solar cell 100 be reduced or prevented in advance.

In the embodiment described above, a structure has been described in which aluminum electrodes 22 for an external connection composed of a first aluminum paste and a back surface aluminum electrode having a wide area 20 which is composed of a second aluminum paste when the back surface aluminum electrodes were used. However, the invention is not limited in this regard.

For example, it is possible to use all the back surface aluminum electrodes, including the wide area back surface aluminum electrode 20 to form from the first aluminum paste.

Several test examples concerning the invention are described below, although the invention should not be limited to these test examples.

The differences in bond strengths, as the properties of the glass frits, which serve as an integral part in the paste compositions forming the aluminum electrode (aluminum pastes), were evaluated in the following tests.

In these tests, a total of eight types of glass samples (Sample 1 to Sample 8) were used with the glass compositions (mole%), glass softening points (° C), and thermal expansion coefficients shown in Table 1.

In this way, a total of eight types of aluminum pastes were prepared (Test Examples 1 to 8) containing the respective glass frits (Samples 1 to 8) shown in Table 1.

The aluminum pastes in these test examples differed only in the properties of the above glass frits. The other ingredients (aluminum powder, organic carrier) and the mixing ratios were identical.

That is, the contents of the aluminum pastes in the respective test examples were as follows.

(1) Aluminum powder:

An aluminum powder having an average particle diameter of 6 μm was incorporated in an amount corresponding to 66% by weight of the entire paste.

(2) Organic carrier:

Terpineol as an organic solvent was included in an amount corresponding to 26% by weight of the total paste.

In addition, ethyl cellulose was included as an organic binder in an amount corresponding to about 2% by weight of the total paste.

(3) glass frit:

A glass frit having the properties of any of the above-mentioned samples 1 to 8 was incorporated in an amount corresponding to 6% by weight of the entire paste.

<Bond strength test (1)>

Next, bond strength tests were conducted on the aluminum electrodes prepared on silicon semiconductor substrates using the respective aluminum pastes of Test Examples 1 to 8 prepared in the manner described above. The following procedure has been to form aluminum electrodes on a surface (the back surface) of the silicon semiconductor substrate 11 using the respective aluminum pastes in Test Examples 1 to 8.

A commercially available p-type single crystal silicon substrate for use in a solar cell and having a size of 125 mm square (substrate thickness 200 μm) was provided, and the front surface was subjected to alkaline etching with an aqueous sodium hydroxide solution. Next, a phosphorus-containing solution was applied to the light-receiving surface of the silicon substrate on which a textured structure was formed by the etching treatment, and a heat treatment was performed, whereby an n-Si layer (n ⁺ layer) with a thickness of about 0.5 μm was formed on the light-receiving surface of the silicon substrate.

Next, on the n-Si layer, an antireflection film (titanium oxide film) having a thickness of at least about 50 nm and not more than about 100 nm was formed by plasma CVD (PECVD). Moreover, a coating (thickness of at least 20 μm and not more than 50 μm) to serve as a front surface electrode (silver electrode) was screen-printed on the antireflection film using a specific silver paste to form a front surface electrode (silver electrode).

In a separate operation, one of the paste compositions of the above Test Examples 1 to 8 was screen-printed (using a stainless steel mesh (SUS # 165)) on the back surface side of the silicon semiconductor substrate (coated), thereby forming a coating having a film thickness of about 30 microns in the form of 5 mm wide lines was formed. The substrate was then fired, creating linear aluminum electrodes 28 were formed for testing and evaluation. In particular, the substrate was fired at a temperature of at least about 700 ° C and not more than about 800 ° C in the air using a near infrared high speed firing furnace.

Using the thus obtained cells for testing and evaluation (solar cells), tests for evaluating the bonding strength were carried out and the bonding strengths of those from the Paste compositions for forming aluminum electrode formed aluminum electrodes in the respective test examples were measured.

The bonding strengths (peel strengths) of the aluminum electrodes formed in the above-described manner (ie, the peeling strength evaluation) were measured by a strength measuring device 300 like the one in the 5 shown is determined.

In particular, a glass substrate 41 on a holder 40 in the strength measuring device 300 in the 5 shown by fastening screws 43 and a fixing plate 44 appropriate. The light-receiving surface side of the silicon semiconductor substrate 11 for testing, obtained in the manner described above, was then treated with an epoxy adhesive 42 on the glass substrate 41 mounted and attached.

A commercial conductive adhesive film 30 was made by thermocompression bonding to the aluminum electrode 28 mounted on the exposed front surface side of the silicon semiconductor substrate 11 has been formed, which on the glass substrate 41 was attached, and in addition was a contact wire 35 on the conductive adhesive film 30 appropriate.

Next, as it was in the 5 is shown, the strength measuring device 300 so inclined to the bottom of the holder 40 was set at an angle of 135 °, and the bonding strength of contact wire 35 / senior detention film 30 /Electrode 28 was by pulling an already trained extension 35e of the contact wire 35 vertically upwards (see the arrow 45 ).

The results are shown in the corresponding columns of Table 2. The bond strength evaluation tests (peel strength tests) were performed on a plurality (two) of aluminum electrodes formed from the aluminum pastes obtained in the respective test examples. The average of the test results (measurement results) for the two aluminum electrodes (n = 2) was used as the bond strength.

The graph in the 6 Fig. 14 shows the relationship between the bond strength obtained in these tests and the softening point of the glass frit in the aluminum paste. Table 2 Al paste Glass Softening point (° C) Thermal expansion coefficient (× 10 ^-7 / ° C) Bond strength (N) dates average Test Example 1 Sample 1 644 45 0.3386 0.6147 0.48 Test Example 2 Sample 2 690 67 0.6873 0.6921 0.69 Test Example 3 Sample 3 716 66 0.3822 0.4156 0.40 Test Example 4 Sample 4 530 86 0.01 0.01 0.01 Test Example 5 Sample 5 570 63 0.8 0.7 0.75 Test Example 6 Sample 6 548 70 1.6822 1.2724 1.48 Test Example 7 Sample 7 568 70 0.9712 0.9297 0.95 Test Example 8 Sample 8 445 77 0.977 1.0775 1.03

As shown in Table 2 and in the 6 has been found to have a high bond strength at a glass softening point within the aluminum paste in the range of at least 400 ° C and not more than 600 ° C (especially at least 500 ° C and not more than 600 ° C) occurs. In particular, a very high bonding strength was found when the aluminum paste of Test Example 6 having a glass softening point near 550 ° C was used.

It has also been found that aluminum pastes having a thermal expansion coefficient of the glass frit of at least 60 × 10 ^-7 / ° C and not more than 80 × 10 ^-7 / ° C (at least 65 × 10 ^-7 / ° C and not more than 75 × 10 ^-7 / ° C) have a high bonding strength.

<Bond strength test (2)>

According to the same method as in the above-described peel strength test ( 1 ) was the aluminum paste of Test Example 6 to form linear aluminum electrodes having a film thickness of about 30 microns and a width of about 2 mm on the silicon semiconductor substrate 11 and a corresponding peel strength test was performed. As shown in the column "working example" in Table 3, a bonding strength of 3.25 N / 2 mm was found as the average value (n = 2).

As a control for comparison, linear silver electrodes having a film thickness of about 30 μm and a width of about 2 mm were formed on the aforementioned silicon semiconductor substrate 11 formed using a conventional silver paste in place of the aluminum paste of Test Example 6. The above-described contact wire 35 was applied to the surface with a solder and the same peel strength test was conducted. As shown in the column "Comparative Example A" in Table 3, a bonding strength of 3.5 N / 2 mm was found as the average value (n = 2).

Comparative Example B in Table 3 shows the result obtained when the aluminum paste of Test Example 1 was used instead of the aluminum paste of Test Example 6. Table 3 Comparative Example A Comparative Example B working example Bond strength (N / 2 mm) 3.50 0.50 3.25

As is apparent from Table 3, it was confirmed that the aluminum electrode formed of the aluminum paste of Test Example 6 could attain a good bond strength comparable to that of the solder-bonded silver electrode in Comparative Example A. It was also confirmed that the bonding strength of the aluminum electrode formed from the aluminum paste of Test Example 6 was considerably increased as compared with the bonding strength of the aluminum electrode in Comparative Example B.

As is apparent from the above description of the embodiments and test examples, in the solar cell provided by this invention, aluminum electrodes can be used as the electrodes for external connection on the back surface side. As a result, it has become possible to perform bonding with an electroconductive adhesive film which has low bonding strength in conventional aluminum electrodes and thus can not be used. Moreover, as compared with a conventional structure in which a silver electrode is used as the electrode for external connection on the back surface side, it is possible to uniformly form a BSF layer on the entire back surface of a silicon semiconductor substrate (wafer). Furthermore, a cost reduction according to the difference in material prices between silver and aluminum can be achieved.

Further, since the aluminum electrode for external connection having improved aluminum film bonding strength (peel strength) enables the use of bonding by means of an electroconductive adhesive film, a structure without electrode portions for solder joints can be constructed. As a result, the use of aluminum on the entire back surface of the substrate (wafer) enables an increase in the power generation efficiency of the solar cell due to uniform formation of the BSF layer to be achieved, as well as the further increase in the power generation efficiency of the solar cell due to the omission of a bus bar electrode structure.

The invention has been described above in detail, although these examples are given by way of illustration only. The invention may be embodied in other forms and various modifications may be made with the invention without departing from the spirit and scope of the invention. For example, at least a part of the electrodes of the light-receiving surface (eg, bus bar electrodes or grid lines forming an electrode of the light-receiving surface) may be formed by using the paste composition disclosed herein which forms the aluminum electrode.

LIST OF REFERENCE NUMBERS

11

Silicon semiconductor substrate (Si wafer)

12

Electrode of light-receiving surface

14

Anti-reflection film

16

n-Si layer

18

p-Si layer

20

Rear surface aluminum electrode with wide area

22

Aluminum electrode for external connection

23

opening

24

BSF layer

30

Conductive film

31

Conductive particles

32

Adhesive component

35

Contact wire (connecting wire)

35e

Contact extension

40

holder

41

glass substrate

100, 200,

1000 Lötzellen

300

Strength measuring device

Claims (12)

A paste composition for forming an aluminum electrode for a solar cell, the composition comprising: an aluminum powder, a glass frit and an organic vehicle, wherein the glass frit (1) has a glass softening point of at least 400 ° C and not more than 600 ° C, (2) a Has thermal expansion coefficients of at least 60 × 10 ^-7 / ° C and not more than 80 × 10 ^-7 / ° C and (3) as essential components SiO ₂ , B ₂ O ₃ , ZnO and / or PbO, Al ₂ O ₃ and at least one alkali metal oxide. A paste composition according to claim 1, wherein the constituents of the glass frit have the following respective molar contents per 100 mol% of the combined ingredients: SiO ₂ 20 to 35 mol%, B ₂ O ₃ 5 to 30 mol%, ZnO and / or PbO From 25 to 45 mol%, Al ₂ O ₃ 2 to 10 mol%, at least one of Li ₂ O, Na ₂ O and K ₂ O 5 to 15 mol%, at least one of CaO, SrO and BaO 0 to 10 mol% and Bi ₂ O ₃ 0 to 5 mol%, the sum of the constituents being at least 95 mol% of the total glass frit. A paste composition according to claim 2, wherein the constituents of the glass frit have the following respective molar contents per 100 mol% of the combined ingredients: SiO ₂ 20 to 30 mol%, B ₂ O ₃ 20 to 30 mol%, ZnO From 25 to 35 mol%, Al ₂ O ₃ 3 to 7 mol%, at least one of Li ₂ O, Na ₂ O and K ₂ O 10 to 15 mol% and at least one of CaO, SrO and BaO 2 to 10 mol%, the sum of the constituents being at least 95 mol% of the total glass frit. A paste composition according to any one of claims 1 to 3, wherein the glass frit has a glass softening point of at least 500 ° C and not more than 600 ° C. A paste composition according to any one of claims 1 to 4, wherein per 100% by weight of the total paste composition, the aluminum powder is included in an amount of 60 to 80% by weight and the glass frit is included in an amount of 2 to 10% by weight , A solar cell having a silicon semiconductor substrate, an electrode of the light-receiving surface formed on a light-receiving surface side which is one side of the substrate, and an aluminum electrode formed on a back surface side which is the other side of the substrate wherein at least a part of the aluminum electrode is formed to comprise a glass composition, and the glass composition (1) has a glass softening point of at least 400 ° C and not more than 600 ° C, (2) a thermal expansion coefficient of at least 60 × 10 ^{- 7} / ° C and not more than 80 × 10 ^-7 / ° C and (3) as essential components SiO ₂ , B ₂ O ₃ , ZnO and / or PbO, Al ₂ O ₃ and at least one alkali metal oxide. A solar cell according to claim 6, wherein the constituents of the glass composition have the following respective molar contents per 100 mol% of the combined constituents: SiO ₂ 20 to 35 mol%, B ₂ O ₃ 5 to 30 mol%, ZnO and / or PbO From 25 to 45 mol%, Al ₂ O ₃ 2 to 10 mol%, at least one of Li ₂ O, Na ₂ O and K ₂ O 5 to 15 mol%, at least one of CaO, SrO and BaO 0 to 10 mol% and Bi ₂ O ₃ 0 to 5 mol%, the sum of the constituents being at least 95 mol% of the total glass composition. A solar cell according to claim 7, wherein the constituents of the glass composition have the following respective molar contents per 100 mol% of the combined components: SiO ₂ 20 to 30 mol%, B ₂ O ₃ 20 to 30 mol%, ZnO From 25 to 35 mol%, Al ₂ O ₃ 3 to 7 mol%, at least one of Li ₂ O, Na ₂ O and K ₂ O 10 to 15 mol% and at least one of CaO, SrO and BaO 2 to 10 mol%, the sum of the constituents being at least 95 mol% of the total glass composition. A solar cell according to any one of claims 6 to 8, wherein the glass composition has a glass softening point of at least 500 ° C and not more than 600 ° C. A solar cell according to any one of claims 6 to 9, wherein an electrode for external connection is formed on the back surface side, the electrode for external connection being formed of an aluminum electrode containing the glass composition. A solar cell according to claim 10, wherein an electroconductive adhesive film is provided on the aluminum electrode containing the glass composition and forming the external connection electrode. A method of manufacturing a solar cell comprising a silicon semiconductor substrate, an electrode of the light-receiving surface formed on a light-receiving surface side serving as a side of the substrate, and an aluminum electrode disposed on a back surface side as the other side of the substrate, the method comprising forming at least a part of the aluminum electrode formed on the back surface side using the paste composition according to any one of claims 1 to 5.

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