CN116332500A

CN116332500A - Glass, conductive paste and solar cell

Info

Publication number: CN116332500A
Application number: CN202211681202.8A
Authority: CN
Inventors: 田村奈奈子
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 2021-12-27
Filing date: 2022-12-27
Publication date: 2023-06-27
Also published as: JP2023097203A; KR20230099683A

Abstract

The invention relates to glass, conductive paste and solar cells. The present invention relates to a glass, a glass powder containing the same, a conductive metal powder, a conductive paste containing an organic carrier, and a solar cell having an electrode formed using the conductive paste, the glass containing, in mol% in terms of oxide: 40% to 70% PbO, 4% to 20% SiO ₂ 1% to 10% of Al ₂ O ₃ B of 0% to 30% ₂ O ₃ And 1% to 20% Ga ₂ O ₃ 。

Description

Glass, conductive paste and solar cell

Technical Field

The present invention relates to a glass, a conductive paste, and a solar cell, and more particularly, to a glass suitable for use as an electrode for forming a solar cell, a conductive paste using glass powder containing the glass, and a solar cell having an electrode formed by the conductive paste.

Background

Conventionally, electronic devices in which a conductive layer serving as an electrode is formed on a semiconductor substrate of silicon (Si) or the like have been used for various purposes. The conductive layer to be an electrode is formed by: a conductive paste obtained by dispersing conductive metal powder such as aluminum (Al), silver (Ag), copper (Cu) and the like and glass powder in an organic vehicle is applied to a semiconductor substrate, and baked at a temperature necessary for electrode formation.

In forming an electrode on a semiconductor substrate in this manner, an insulating film may be formed over the entire surface of the semiconductor substrate where the electrode is formed, and a patterned electrode may be formed so as to partially penetrate the insulating film and come into contact with the semiconductor substrate.

For example, in a solar cell, an antireflection film is provided on a semiconductor substrate that becomes a light receiving surface, and electrodes are provided thereon in a pattern. The antireflection film is a film for improving light receiving efficiency by reducing surface reflectance while maintaining sufficient visible light transmittance, and is generally composed of an insulating material such as silicon nitride, titanium oxide, silicon dioxide, or aluminum oxide.

In the double-sided light receiving solar cell capable of receiving light also on the back surface side, a passivation film containing the same insulating material as the antireflection film is provided on the entire back surface, and an electrode is formed on the passivation film so as to be partially in contact with the semiconductor substrate.

Since the electrode needs to be formed in contact with the semiconductor substrate, the insulating film is removed according to the pattern of the electrode to be formed, and the electrode is formed at the portion where the insulating film is removed. As a method for removing the insulating film, a method of physically removing the insulating film by a laser or the like is exemplified, but this method involves an increase in manufacturing steps and an increase in equipment introduction cost. In recent years, therefore, a method of applying a conductive paste containing a conductive metal powder and a glass powder, that is, a paste-like electrode material, on an insulating film and performing a heat treatment to cause the conductive paste to penetrate through a fire-through (fire-through) of the insulating film has been employed.

The above-described technique of forming an electrode on a semiconductor substrate is also applicable to forming an electrode on a pn junction type semiconductor substrate in a solar cell.

Patent document 1 discloses, as a specific glass composition among glasses used in the electroconductive paste, the following composition: comprises 60 to 95 percent of PbO and 0 to 10 percent of B by mass percent ₂ O ₃ And 1 to 30 percent of SiO ₂ +Al ₂ O ₃ 。

Patent document 2 discloses lead glass used as a sealing material that can be sealed at a relatively low temperature, and discloses the following composition as a specific glass composition: contains 5 to 40 mass percent of B ₂ O ₃ 0 to 5 percent of Al ₂ O ₃ 0 to 60 percent of PbO, 2 to 20 percent of ZnO, 5 to 50 percent of BaO and 0 to 30 percent of V ₂ O ₅ 0 to 25 percent of Sb ₂ O ₃ 0 to 20 percent of SiO ₂ And 0 to 40% of Bi ₂ O ₃ 。

Prior art literature

Patent literature

Patent document 1: international publication No. 2013/103087

Patent document 2: chinese patent application publication No. 112786233 specification

Disclosure of Invention

Problems to be solved by the invention

As disclosed in patent documents 1 and 2, regarding glass used for forming electrodes of solar cells, a technique of improving the formability of the electrodes and reducing the contact resistance between the electrodes and a semiconductor substrate has been developed.

However, the glass disclosed in patent document 1 has a problem in that the glass fluidity at the time of baking is high, and the corrosion of the antireflection film is increased due to excessive burn-through, resulting in deterioration of open circuit voltage (Voc). In addition, the contact resistance is high, which causes a problem that the conversion efficiency of the solar cell is lowered. In addition, the glass described in patent document 2 has a problem in that reactivity with silicon nitride (SiN) used for a passivation film is high, burn-through proceeds excessively, and Voc is deteriorated.

In particular, in a solar cell such as TOPCon (tunnel oxide passivation contact), a technology for reducing contact resistance between an electrode and a semiconductor substrate and suppressing excessive burn-through to improve conversion efficiency of the solar cell has been developed.

The present invention aims to provide a glass for forming an electrode, which can improve the conversion efficiency of a solar cell by suppressing contact resistance between the electrode and a semiconductor substrate and suppressing excessive burn-through when the electrode is formed on the semiconductor substrate of the solar cell or the like via an insulating film. The present invention also aims to provide a conductive paste containing a glass powder containing the glass and a solar cell having improved conversion efficiency by using the conductive paste.

Means for solving the problems

The present inventors have found that the above problems can be solved by setting the glass composition within a specific range, and have completed the present invention. The invention provides a glass, a conductive paste and a solar cell which are formed as follows.

[1] A glass, wherein the glass comprises, in mole percent on an oxide basis:

40% to 70% of PbO,

4% to 20% SiO ₂ 、

1% to 10% of Al ₂ O ₃ 、

0% to 30% B ₂ O ₃ And (d) sum

1% to 20% Ga ₂ O ₃ 。

[2]Such as [1]]The glass comprises PbO+Bi in mol% in terms of oxide ₂ O ₃ +SiO ₂ +B ₂ O ₃ Represented PbO, bi ₂ O ₃ 、SiO ₂ 、B ₂ O ₃ The total content of (2) is 70% or more.

[3]Such as [1]]Or [2 ]]The glass comprises, in mole% in terms of oxide, ga ₂ O ₃ And B ₂ O ₃ Sum of the contents (Ga ₂ O ₃ +B ₂ O ₃ ) Relative to SiO ₂ 、Ga ₂ O ₃ And B ₂ O ₃ Sum of the contents (SiO) ₂ +Ga ₂ O ₃ +B ₂ O ₃ ) The ratio of (2) is 40% to 90%.

[4] The glass according to any one of claims 1 to 3, wherein the glass has a glass transition temperature of 280℃to 430 ℃.

[5] A conductive paste, wherein the conductive paste contains a glass powder, a conductive metal powder and an organic vehicle, and the glass powder contains the glass of any one of [1] to [4 ].

[6] A solar cell, wherein the solar cell has an electrode formed using the electroconductive paste of [5 ].

[7] A solar cell, the solar cell having:

a silicon substrate having a sunlight receiving surface;

a first insulating film provided on the sunlight receiving surface of the silicon substrate;

a second insulating film provided on a surface of the silicon substrate on a side opposite to the sunlight receiving surface;

a first electrode penetrating a portion of the first insulating film and contacting the silicon substrate; and

a second electrode penetrating a portion of the second insulating film and contacting the silicon substrate, wherein,

the first electrode comprises a metal and a glass,

the metal contains at least one selected from the group consisting of Al, ag, cu, au, pd and Pt,

the glass contains, in terms of mole% of oxide, pbO in an amount of 40% to 70% and SiO in an amount of 4% to 20% inclusive ₂ 1% to 10% of Al ₂ O ₃ B of 0% to 30% ₂ O ₃ And 1% to 20% Ga ₂ O ₃ 。

Effects of the invention

The glass of the present invention has a specific composition range, and contains a specific amount of Ga together with PbO having a high burn-through promoting effect ₂ O ₃ This can suppress excessive reaction between silicon nitride used for the passivation film and glass, and suppress excessive burn-through. In addition, by containing Ga ₂ O ₃ The Ga diffuses into the Si substrate, and the contact resistance can be reduced.

Therefore, the glass of the present invention can realize excellent burn-through properties by being used in the electroconductive paste together with the electroconductive component, and can reduce contact resistance between the electrode and the semiconductor substrate, thereby improving conversion efficiency of the solar cell.

Drawings

Fig. 1 is a schematic cross-sectional view of an example of an n-type Si substrate double-sided light-receiving solar cell in which an electrode is formed using the electroconductive paste according to the present embodiment.

Fig. 2 is a diagram showing an electrode pattern formed on a Si substrate used in evaluating contact resistance Rc [ Ω ].

Description of the reference numerals

10 … solar cell, 1 … n type Si semiconductor substrate, 1a … n ⁺ Layer 1b … p ⁺ Layer, 2a … antireflection film (silicon nitride/aluminum oxide), 2b … antireflection film (silicon nitride/aluminum oxide), 3a … Ag electrode, 3b … Ag-Al electrode, S1 … light receiving face, S2 … non light receiving face.

Detailed Description

Hereinafter, embodiments of the present invention will be described.

< glass >

The glass of the present embodiment contains, in terms of mole% in terms of oxide, 40% to 70% of PbO, 4% to 20% of SiO ₂ 1% to 10% of Al ₂ O ₃ B of 0% to 30% ₂ O ₃ And 1% to 20% Ga ₂ O ₃ . In the following description, unless otherwise specified, "%" of the content of each component of the glass indicates oxide conversionIn mole%. In the present specification, the term "to" indicating a numerical range includes upper and lower limits. In the present specification, "0% contained" means not contained.

The content of each component in the glass of the present embodiment can be determined from the results of inductively coupled plasma (ICP-AES: inductively Coupled Plasma-Atomic Emission Spectroscopy) analysis or electron beam microscopy analysis (EPMA: electron Probe Micro Analyzer) analysis of the obtained glass.

Hereinafter, in the description of the glass composition, "electroconductive paste" means "electroconductive paste containing the glass of the present invention". The "electrode" means an "electrode obtained by using the electroconductive paste containing the glass of the present invention".

PbO has reactivity with an insulating film and a silicon substrate, and has a function of improving softening fluidity of glass. In this way, for example, when an electrode is formed on a semiconductor substrate or the like using the electroconductive paste containing the glass of the present embodiment, the contact resistance between the electrode and the substrate or the like can be reduced, and the bonding strength can be improved.

The glass of the present embodiment contains PbO in a proportion of 40% to 70%. By setting the PbO content to 40% or more, burn-through is easy to occur, and sufficient contact between the electrode and the insulating film and the semiconductor substrate can be ensured. The content of PbO is preferably 45% or more, more preferably 48% or more, and still more preferably 55% or more. Further, by setting the PbO content to 70% or less, excessive burn-through can be prevented, and corrosion of the insulating film can be suppressed. The content of PbO is preferably 67% or less, more preferably 63% or less, and still more preferably 59% or less.

SiO ₂ The glass is a component for improving the stability and weather resistance of the glass, and is also a component for adjusting the reactivity with an insulating film and a silicon substrate. The glass of the present embodiment contains SiO in a proportion of 4% to 20% ₂ . By mixing SiO ₂ The content of (2) is set to 4% or more, and vitrification is easy to be performed, and an electrode is easy to be formed. SiO (SiO) ₂ The content of (2) is preferably 6% or more, more preferably 8% or more, and still more preferably 10% or more. In addition, by SiO ₂ The content of (2) is 20% or less, the rise of the glass transition temperature is suppressed, and the glass exhibits excellent fluidity during baking, and the reactivity with an insulating film and a silicon substrate is improved. SiO (SiO) ₂ The content of (2) is preferably 18% or less, more preferably 16% or less, and still more preferably 14% or less.

Al ₂ O ₃ A component for improving the weather resistance of the glass. The glass of the present embodiment contains Al in a proportion of 1% or more and 10% or less ₂ O ₃ . By mixing Al with ₂ O ₃ The content of (2) is set to 1% or more, so that the weather resistance can be improved and the glass can be stabilized. Al (Al) ₂ O ₃ The content of (2) is preferably 2% or more, more preferably 3% or more. In addition, by Al ₂ O ₃ The content of (2) is 10% or less, and the glass transition temperature is suppressed from rising, and the resin composition exhibits excellent fluidity when softened. Al (Al) ₂ O ₃ The content of (2) is preferably 8% or less, more preferably 6% or less, and still more preferably 5% or less.

B ₂ O ₃ Has the function of reducing contact resistance by diffusion of B into Si substrate, and B ₂ O ₃ The fluidity of the glass during softening is improved, and the bonding strength with a semiconductor substrate is improved. In addition, B ₂ O ₃ Is a network structure forming component of the glass and contributes to the stabilization of the glass. The glass of the present embodiment contains B in a proportion of 0% to 30% ₂ O ₃ . In the presence of B ₂ O ₃ In the case of (2), the content is preferably 4% or more, more preferably 8% or more, and still more preferably 10% or more. In addition, by mixing B ₂ O ₃ The content of (2) is set to 30% or less, and weather resistance can be improved. B (B) ₂ O ₃ The content of (2) is preferably 28% or less, more preferably 26% or less, and still more preferably 24% or less.

Ga ₂ O ₃ To suppress excessive reaction between glass and silicon nitride used for a passivation film and to suppress excessive burn-through. Furthermore, ga ₂ O ₃ The function of reducing contact resistance by diffusion of Ga into a Si substrate is provided. The glass of the present embodiment contains 1% to 20% of the glassGa ₂ O ₃ . By mixing Ga ₂ O ₃ The content of (2) is set to 1% or more, whereby excessive burn-through can be suppressed, contact resistance can be reduced, and conversion efficiency of the solar cell can be improved. In addition, the weather resistance can be improved and the glass can be stabilized. Ga ₂ O ₃ The content of (2) is preferably 1.5% or more, more preferably 2.5% or more. In addition, from the viewpoint of stabilization of glass, ga ₂ O ₃ The content of (2) is 20% or less, preferably 18% or less, more preferably 15% or less, and even more preferably 10% or less.

Bi ₂ O ₃ Similar to PbO, pbO has a function of improving the softening fluidity of glass, but has a weaker burn-through ability than PbO, and therefore, by substituting Bi for a part of PbO in the glass composition ₂ O ₃ Excessive burn-through can be suppressed, and the contact between the electrode and the insulating film and the semiconductor substrate can be improved. Therefore, the glass of the present embodiment may contain Bi ₂ O ₃ . In the presence of Bi ₂ O ₃ In the case of Bi ₂ O ₃ The content of (2) is preferably 2% or more, more preferably 4% or more. In addition, from the viewpoint of ensuring burn-through properties, bi ₂ O ₃ The content of (2) is preferably 15% or less, more preferably 10% or less.

TiO ₂ The composition for promoting crystallization during baking and suppressing excessive burn-through may contain TiO ₂ . In the presence of TiO ₂ In the case of (2), from the viewpoint of suppressing excessive burn-through, tiO ₂ The content of (2) is preferably 1% or more, more preferably 2% or more. In addition, from the viewpoint of securing fluidity of glass at the time of softening, tiO ₂ The content of (2) is preferably 12% or less, more preferably 10% or less.

La ₂ O ₃ In order to promote crystallization during baking and inhibit excessive burn-through, la may be contained ₂ O ₃ . In the presence of La ₂ O ₃ In the case of (2), la from the viewpoint of suppressing excessive burn-through ₂ O ₃ The content of (2) is preferably 0.5% or more, more preferably 1.0% or more, and still more preferably 1.5% or more. In addition, from ensuring burn-throughFrom the viewpoint of sex, la ₂ O ₃ The content of (2) is preferably 10% or less, more preferably 8% or less, and still more preferably 6% or less.

Nb ₂ O ₅ The composition may contain Nb for improving fluidity and reactivity of the glass and improving weather resistance ₂ O ₅ . In the presence of Nb ₂ O ₅ In the case of (2), the content is preferably 0.5% or more, more preferably 1.0% or more. In addition, nb is used to improve reactivity and electrical characteristics of the solar cell ₂ O ₅ The content of (2) is preferably 10% or less, more preferably 8% or less, and still more preferably 6% or less.

PbO and Bi in the glass of the present embodiment ₂ O ₃ 、SiO ₂ 、B ₂ O ₃ Total (PbO+Bi) content of ₂ O ₃ +SiO ₂ +B ₂ O ₃ ) Preferably 70% or more. By (PbO+Bi) ₂ O ₃ +SiO ₂ +B ₂ O ₃ ) In the above range, the glass can be stabilized. (PbO+Bi) ₂ O ₃ +SiO ₂ +B ₂ O ₃ ) More preferably 75% or more, and still more preferably 80% or more. In addition, (PbO+Bi) from the viewpoint of suppressing excessive burn-through ₂ O ₃ +SiO ₂ +B ₂ O ₃ ) Preferably 98% or less, more preferably 95% or less, and still more preferably 93% or less.

Ga in the glass of the present embodiment ₂ O ₃ And B ₂ O ₃ Sum of the contents (Ga ₂ O ₃ +B ₂ O ₃ ) Relative to SiO ₂ 、Ga ₂ O ₃ And B ₂ O ₃ Sum of the contents (SiO) ₂ +Ga ₂ O ₃ +B ₂ O ₃ ) The ratio of (2) is preferably 40% to 90%. By the ratio being 40% or more, p in the semiconductor wafer can be promoted ⁺ Diffusion of B and Ga, which can function as acceptors in the layer, into the Si substrate can reduce contact resistance. The proportion is more preferably 45% or more, and still more preferably 50% or more. In addition, when the ratio is set to 90% or less,the glass can be stabilized. The proportion is more preferably 85% or less, and still more preferably 80% or less. Ga ₂ O ₃ And B ₂ O ₃ Sum of the contents (Ga ₂ O ₃ +B ₂ O ₃ ) Relative to SiO ₂ 、Ga ₂ O ₃ And B ₂ O ₃ Sum of the contents (SiO) ₂ +Ga ₂ O ₃ +B ₂ O ₃ ) The ratio of (C) is that in the process of mixing SiO ₂ 、Ga ₂ O ₃ And B ₂ O ₃ Sum of the contents (SiO) ₂ +Ga ₂ O ₃ +B ₂ O ₃ ) Assuming 100%, ga ₂ O ₃ And B ₂ O ₃ Sum of the contents (Ga ₂ O ₃ +B ₂ O ₃ ) Is a ratio of (2).

In the glass of the present embodiment, ga capable of suppressing excessive reaction with silicon nitride used in the passivation film is added together with PbO having high burnthrough property ₂ O ₃ . This can form the electrode while suppressing excessive burn-through and erosion of the insulating film such as the antireflection film, and can improve Voc. Further, ga is added to the glass of the present embodiment ₂ O ₃ Can be moved from glass to p by promoting impurities ⁺ Diffusion of the layer reduces contact resistance. For this reason, it is considered that the wafer is p-type when manufacturing a semiconductor wafer ⁺ Ga, which is a group 13 element used for forming the layer, acts as a acceptor, and Ga diffuses into the Si substrate as an impurity, whereby contact resistance can be reduced. Since B is also a group 13 element similar to Ga, B is considered to function as a receptor, and contact resistance can be reduced. Therefore, it is preferable to use Ga ₂ O ₃ Together contain B ₂ O ₃ 。

The glass of the present embodiment may contain other optional components in addition to the above components. As other optional ingredients, specifically, P may be mentioned ₂ O ₅ 、As ₂ O ₃ 、Sb ₂ O ₅ 、Na ₂ O、K ₂ O、Fe ₂ O ₃ 、CuO、Sb ₂ O ₃ 、SnO ₂ 、MnO、MnO ₂ 、CeO ₂ And the like are commonly used for various oxide components of glass.

The other components may be used singly or in combination according to purposes.

The content of the other optional components is preferably 20% or less, more preferably 15% or less, further preferably 10% or less, and still further preferably 5% or less. The total content of the other components is preferably 20% or less, more preferably 10% or less.

The glass of the present embodiment preferably has a glass transition temperature (Tg) of 280℃to 430 ℃. By having a glass transition temperature of 280 ℃ or higher, excessive burn-through can be suppressed and Voc can be improved. The glass transition temperature is more preferably 290℃or higher, and still more preferably 300℃or higher. Further, since the glass transition temperature is 430 ℃ or lower, the fluidity is excellent in softening, the reaction between the electrode and the semiconductor substrate proceeds, the contact resistance is reduced, and the contact property between the electrode and the insulating film can be improved. The glass transition temperature is more preferably 420℃or lower, and still more preferably 410℃or lower.

In the present specification, the glass transition temperature (Tg) is obtained by determining, as Tg, the first inflection point of a Differential Thermal Analysis (DTA) chart obtained by measuring a DTA device Tg8110 manufactured by the phylogenetic company at a temperature increase rate of 10 degrees/min.

The method for producing the glass of the present embodiment is not particularly limited. Specifically, the composition can be produced by the following method, for example.

First, a raw material mixture is prepared. The raw material is not particularly limited as long as it is a raw material used in the production of a usual oxide-based glass, and oxides, carbonates, and the like can be used. In the obtained glass, the kinds and proportions of raw materials are appropriately adjusted to reach the above-mentioned composition ranges, thereby producing a raw material mixture.

Subsequently, the raw material mixture is heated by a known method to obtain a melt. The temperature of the heating and melting (melting temperature) is preferably 800 to 1400 ℃, more preferably 900 to 1300 ℃. The time for the heating and melting is preferably 30 minutes to 300 minutes.

Then, the melt was cooled and solidified, whereby the glass of the present embodiment was obtained. The cooling method is not particularly limited. For example, a method of quenching by dropping into a rolling mill (roll mill), a pressing machine, a cooling liquid, or the like can be cited. The glass obtained is preferably completely amorphous, i.e. has a crystallinity of 0%. However, the crystallized portion may be contained as long as the effect of the present invention is not impaired.

The shape of the glass obtained above is not particularly limited, and may be, for example, a block, a plate, a thin plate (sheet), a powder, or the like.

The glass of the present embodiment has a function as a binder and conductivity, and is preferably used for a conductive paste. The conductive paste containing the glass of the present embodiment has high conductivity, and is suitable for forming an electrode of a solar cell, for example. In the case where the glass of the present embodiment is contained in the conductive paste, the glass is preferably contained in the form of glass powder.

< glass powder >)

The glass powder of the present embodiment includes the glass of the present embodiment, D ₅₀ Preferably from 0.3 μm to 3.0 μm. Through D ₅₀ When the particle size is 0.3 μm or more, the dispersibility is further improved when the conductive paste is prepared. In addition, through D ₅₀ Since the thickness is 3.0 μm or less, a portion where no glass powder is present is less likely to occur around the conductive metal powder, and thus the adhesiveness between the electrode and the semiconductor substrate or the like is further improved. D (D) ₅₀ More preferably 0.5 μm or more. In addition, D ₅₀ More preferably 2.7 μm or less, and still more preferably 2.0 μm or less.

In the present specification, "D ₅₀ "represents the 50% particle size by volume in the cumulative particle size distribution, specifically, the particle size when the cumulative amount thereof occupies 50% by volume in the cumulative particle size curve of the particle size distribution measured using the laser diffraction/scattering particle size distribution measuring apparatus.

The glass powder according to the present embodiment can be obtained by, for example, pulverizing the glass produced in the above manner to have the above-described specific particle size distribution by a dry pulverizing method or a wet pulverizing method.

For example, a method of dry-pulverizing glass having an appropriate shape and then wet-pulverizing the glass is preferable as the glass pulverizing method for obtaining the glass powder of the present embodiment. The dry grinding and wet grinding may be performed using a grinder such as a roller mill, a ball mill, a jet mill, or the like. The particle size distribution can be adjusted by adjusting the pulverizer such as the pulverizing time in each pulverization and the ball size of the ball mill. In the case of wet pulverization, water is preferably used as a solvent. After wet pulverization, moisture is removed by drying or the like, thereby obtaining glass powder. In order to adjust the particle size of the glass powder, classification may be performed as needed in addition to pulverization of the glass.

< conductive paste >)

The glass of the present embodiment can be applied to a conductive paste in the form of glass powder. The conductive paste formed of the glass of the present embodiment contains the glass powder of the present embodiment described above, conductive metal powder, and organic vehicle.

The conductive metal powder contained in the conductive paste of the present embodiment is not particularly limited, and metal powder generally used for an electrode formed on a circuit board (including a laminated electronic component) such as a semiconductor substrate or an insulating substrate can be used. Specifically, the conductive metal powder includes a powder such as Ag, al, cu, au, pd, pt, and among them, ag powder and Al powder are preferable from the viewpoint of productivity. From the viewpoint of suppressing aggregation and obtaining uniform dispersibility, the particle diameter D of the conductive metal powder ₅₀ Preferably from 0.3 μm to 10 μm.

The content of the conductive metal powder in the conductive paste is preferably set to 63.0 mass% or more and 97.9 mass% or less with respect to the total mass of the conductive paste. When the content of the conductive metal powder is 63.0 mass% or more, further sintering of the conductive metal powder can be suppressed, and occurrence of glass floating or the like can be suppressed. Further, by setting the content of the conductive metal powder to 97.9 mass% or less, it is easy to sufficiently cover the periphery of the conductive metal powder with glass precipitates. In addition, the adhesiveness between the electrode and the circuit board such as a semiconductor board or an insulating board can be improved. The content of the conductive metal powder is more preferably 95.0 mass% or less with respect to the total mass of the conductive paste.

The content of glass in the conductive paste is preferably set to, for example, 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the conductive metal powder. By setting the content of glass to 0.1 part by mass or more, it is easier to sufficiently cover the periphery of the conductive metal powder with glass precipitates.

In addition, the adhesiveness between the electrode and the circuit board such as a semiconductor board or an insulating board can be improved. Further, by setting the content of the glass powder to 10 parts by mass or less, further sintering of the conductive metal powder can be suppressed, and occurrence of glass floating or the like can be suppressed. The content of the glass powder is more preferably 0.5 parts by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the conductive metal powder.

Examples of the organic resin binder used for the organic vehicle include: cellulose resins such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, benzyl cellulose, propyl cellulose, and nitrocellulose; and an organic resin such as an acrylic resin obtained by polymerizing one or more acrylic monomers such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, butyl acrylate, and 2-hydroxyethyl acrylate.

As the solvent used in the organic vehicle, for example, in the case of a cellulose-based resin, there can be preferably mentioned: terpineol, diethylene glycol butyl ether acetate, diethylene glycol diethyl ether acetate, propylene glycol diacetate and other solvents. In addition, for example, in the case of an acrylic resin, it is preferable to list: methyl ethyl ketone, terpineol, diethylene glycol butyl ether acetate, diethylene glycol diethyl ether acetate, propylene glycol diacetate and the like.

The ratio of the organic resin binder to the solvent in the organic vehicle is not particularly limited, and is selected so that the resulting organic resin binder solution becomes a viscosity capable of adjusting the viscosity of the conductive paste. Specifically, to a binder made of an organic resin: the mass ratio of solvent representation is preferably about 3:97 to about 15:85.

the content of the organic vehicle in the electroconductive paste is preferably 2 mass% or more and 30 mass% or less with respect to the total amount of the electroconductive paste. By setting the content of the organic vehicle to 2 mass% or more, it is possible to suppress an increase in viscosity of the conductive paste, improve coatability of the conductive paste such as printing, and facilitate formation of a good conductive layer (electrode). Further, by setting the content of the organic vehicle to 30 mass% or less, the reduction in the content of the solid content of the electroconductive paste can be prevented, and a sufficient coating film thickness can be obtained.

As one embodiment of the conductive paste of the present embodiment, there is exemplified a conductive paste containing 63.0 to 97.9 mass% of a metal containing at least one selected from the group consisting of Ag, al, cu, au, pd and Pt, relative to 100 parts by mass of the metal, the conductive paste containing 0.1 to 10 parts by mass of glass, and the conductive paste containing 2 to 30 mass% of an organic vehicle, relative to the total mass of the conductive paste, in terms of mole% in terms of oxide, the glass including: 40% to 70% PbO, 4% to 20% SiO ₂ 1% to 10% of Al ₂ O ₃ B of 0% to 30% ₂ O ₃ And 1% to 20% Ga ₂ O ₃ 。

In the electroconductive paste of the present embodiment, a known additive may be blended as needed and within a limit not to violate the purpose of the present embodiment, in addition to the above-described glass, electroconductive metal powder, and organic vehicle.

Examples of such additives include various inorganic oxides. Specific examples of the inorganic oxide include: b (B) ₂ O ₃ 、ZnO、SiO ₂ 、Al ₂ O ₃ 、TiO ₂ 、MgO、ZrO ₂ And Sb (Sb) ₂ O ₃ And their composite oxides. These inorganic oxides have an effect of moderating sintering of the conductive metal powder at the time of baking of the conductive paste, thereby having an effect of adjusting the bonding strength after baking. The size of the additive containing these inorganic oxides is not particularly limited, and for example, D can be preferably used ₅₀ Is an additive of 10 μm or less.

The content of the inorganic oxide in the conductive paste is appropriately set according to the purpose, and is preferably 10 mass% or less, more preferably 7 mass% or less, with respect to the glass powder. When the content of the inorganic oxide relative to the glass powder is 10 mass% or less, the decrease in fluidity of the conductive paste at the time of electrode formation can be suppressed, and sufficient bonding strength between the electrode and a circuit board such as a semiconductor substrate or an insulating substrate can be ensured. In order to obtain a practical blending effect (adjustment of the bonding strength after baking), the lower limit value of the content is preferably 0.5 mass% or more, more preferably 1.0 mass% or more.

Additives known in the conductive paste, such as an antifoaming agent and a dispersing agent, may be added to the conductive paste. The organic vehicle and these additives are usually components that disappear during the electrode formation process. In the preparation of the conductive paste, a known method using a rotary mixer having stirring blades, a masher, a roll mill, a ball mill, or the like can be used.

The application and baking of the conductive paste to the circuit board such as the semiconductor board and the insulating board can be performed by the same method as the application and baking in the conventional electrode formation. Examples of the coating method include screen printing and dispensing (dispensing) method. The baking temperature depends on the type and surface state of the conductive metal powder contained, and may be exemplified by a temperature of about 500 to about 1000 ℃. The baking time may be appropriately adjusted according to the shape, thickness, and the like of the electrode to be formed. In addition, a drying treatment at about 80 to about 200 ℃ may be provided between the application and baking of the conductive paste.

< solar cell >)

The solar cell of the present embodiment has an electrode formed using the conductive paste described in the above < conductive paste > and specifically an electrode printed on a semiconductor substrate. In the solar cell of the present embodiment, at least one of the electrodes is preferably an electrode provided so as to partially penetrate the insulating film by burning through the conductive paste and to be in contact with the semiconductor substrate.

Examples of such an electrode penetrating through an insulating film included in a solar cell include: an electrode provided as an electrode on a light receiving surface of a solar cell using a pn junction type semiconductor substrate, and partially penetrating an insulating film serving as an antireflection film and contacting the semiconductor substrate. As an insulating material constituting the insulating film as the antireflection film, silicon nitride, titanium oxide, silicon dioxide, aluminum oxide, or the like can be cited, and the insulating material preferably contains two layers. In this case, the light receiving surface may be one surface or both surfaces of the semiconductor substrate, and the semiconductor substrate may be either n-type or p-type, but in order to further improve the efficiency of the solar cell, both surfaces are preferable, and the semiconductor substrate is preferably n-type. Such an electrode provided on the light receiving surface of the solar cell may be formed by firing through using the above-described conductive paste.

The following describes a configuration example of the solar cell of the present embodiment, but the configuration of the solar cell of the present embodiment is not limited to this configuration example. The solar cell of this configuration example comprises: a silicon substrate having a solar light receiving surface (hereinafter also simply referred to as a "light receiving surface" or a "surface"); a first insulating film provided on a light receiving surface of the silicon substrate; a second insulating film provided on a surface (hereinafter also simply referred to as "back surface") of the silicon substrate on the opposite side of the light-receiving surface; a first electrode penetrating a portion of the first insulating film and contacting the silicon substrate; and a second electrode penetrating a portion of the second insulating film and contacting the silicon substrate.

More specifically, as shown in fig. 1, for example, a solar cell 10 on the light receiving surface S1 of the n-type Si semiconductor substrate 1, p is provided ⁺ Layer 1b. An antireflection film (silicon nitride/aluminum oxide) 2b is also formed on the surface thereof, in a part of the region, to penetrate the antireflection film (silicon nitride/aluminum oxide) 2b and to communicate with p ⁺ The layer 1b is formed with an ag—al electrode 3b in contact.

N is also provided on the non-light receiving surface S2 of the n-type Si semiconductor substrate 1 in the same manner ⁺ A layer 1a further having an antireflection film (silicon nitride/aluminum oxide) 2a formed on the surface thereof, in a part of the region so as to penetrate the antireflection film (silicon nitride/aluminum oxide) 2a and communicate with n ⁺ The layer 1a is formed with an Ag electrode 3a in contact therewith.

The ag—al electrode 3b and the Ag electrode 3a may be formed by coating and baking a partial region on the surface of the antireflection film (silicon nitride/aluminum oxide) 2b, 2a with the above-mentioned conductive paste.

In this configuration example, the first electrode is an electrode formed by firing through using the conductive paste of the present embodiment, and preferably includes a metal including at least one selected from the group consisting of Al, ag, cu, au, pd and Pt, and the glass of the present embodiment.

The first electrode contains 90 mass% or more and 99.9 mass% or less of the metal, and more preferably contains 0.1 mass% or more and 10 mass% or less of the glass of the present embodiment. Further, the first electrode more preferably contains at least Ag.

In this configuration, the first electrode and the second insulating film more preferably have a metal oxide film in contact with both surfaces of the silicon substrate and a silicon nitride film on the metal oxide film. The metal oxide film more preferably contains alumina or silica.

Examples

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples. Examples 1 to 11 are examples, and examples 12 to 21 are comparative examples.

Examples 1 to 20

Glass is produced into a sheet glass by the following method, and glass powder is produced from the sheet glass. The particle size distribution of the glass powder was measured, and the glass transition temperature of the glass was measured using the glass powder.

< manufacturing of glass (sheet glass) >)

Raw material powders were mixed and mixed in accordance with compositions shown in tables 1 and 2 in terms of mole% based on oxides, and melted in an electric furnace at 1000 to 1600 ℃ using a crucible for 30 minutes to 1 hour, to form a sheet-like glass comprising glasses having compositions shown in tables 1 and 2.

< production of glass powder >

In each example, the obtained sheet-like glass was pulverized by a combination of dry pulverization and wet pulverization in the following manner, thereby adjusting the particle size distribution. The particle size distribution of the obtained glass powder was measured, and the glass transition temperature was measured using the glass powder.

Dry grinding was performed for 6 hours by a ball mill, and coarse particles were removed by a 150 mesh sieve. Next, coarse glass powder was removed after the dry pulverization obtained above to give D ₅₀ The glass powder having a desired particle size distribution is produced by wet-pulverizing with a ball mill and water so as to fall within a predetermined range. In the wet grinding, a predetermined D is obtained ₅₀ Balls of alumina having a diameter of 5mm were used. Then, the slurry obtained by wet grinding was filtered, and dried at 130 ℃ by a dryer to remove moisture, thereby producing glass powder.

< evaluation >

For each glass, the glass powder D was evaluated by the following method ₅₀ And glass transition temperature. The results are shown in tables 1 and 2 together with the composition.

(D ₅₀ )

0.02g of glass powder was mixed with 60 cubic centimeters of isopropyl alcohol (IPA) and dispersed by ultrasonic dispersion for 1 minute. The sample was put into a Microtrack measuring machine (laser diffraction/scattering type particle size distribution measuring apparatus), whereby D was obtained ₅₀ Is a value of (2).

(glass transition temperature)

The obtained glass powder was placed in an aluminum pan, and measured at a temperature rise rate of 10 ℃/min by using a differential thermal analyzer TG8110 manufactured by the company of science. The first inflection point of the DTA plot obtained by the measurement was taken as the glass transition temperature (denoted "Tg" in tables 1 and 2).

< manufacturing of conductive paste >)

The conductive pastes for forming Ag-Al electrodes, each containing the glass powder of examples 1 to 21, were prepared by the following method.

First, 85 parts by mass of diethylene glycol butyl ether acetate was mixed with 15 parts by mass of ethyl cellulose, and stirred at 85 ℃ for 2 hours, thereby preparing an organic vehicle. Next, 15 parts by mass of the obtained organic vehicle was mixed with 84.5 parts by mass of Ag powder (manufactured by DOWA Electronics Co., ltd., spherical silver powder: AG-4-8F) and 0.5 parts by mass of Al powder (atomized aluminum powder manufactured by Minalco Co.: # 600F), followed by kneading for 10 minutes by a masher. Then, the glass powders of examples 1 to 21 were blended in a proportion of 2 parts by mass with respect to 100 parts by mass of the metal powder (Ag powder and Al powder), and kneaded for 90 minutes by a masher, thereby obtaining an electroconductive paste for ag—al electrode formation.

< evaluation >

(measurement of contact resistance Rc)

Using the above-prepared conductive pastes for ag—al electrode formation, ag—al electrodes were formed on a semiconductor substrate via an insulating film (two-layer film including a silicon nitride layer and an aluminum oxide layer) in the following manner, and the contact resistance at this time was evaluated.

A method for measuring contact resistance will be described with reference to fig. 1 and 2. Fig. 1 is a schematic cross-sectional view of an example of an n-type Si substrate double-sided light-receiving solar cell in which an electrode is formed using the electroconductive paste according to the present embodiment. Fig. 2 is a diagram showing an electrode pattern formed on a Si substrate used in evaluating contact resistance Rc [ Ω ].

An n-type crystalline Si semiconductor substrate cut to a thickness of 160 μm is used, and first, etching treatment of a very small amount of the front and back surfaces is performed with hydrofluoric acid in order to clean the cut surface of the Si semiconductor substrate. Then, a concave-convex structure reducing light reflectance is formed on the light receiving surface of the Si semiconductor substrate using a wet etching method.

Next, p is formed on the light receiving surface of the Si semiconductor substrate by diffusion ⁺ A layer. B (boron) is used as the doping element for the p-type. In this way, a mixture having p is obtained ⁺ An n-type Si semiconductor substrate of a layer. Next, a light-receiving surface (p ⁺ The surface of the layer) is formed with an antireflection film. An aluminum oxide layer of 10nm thickness was formed by ALD (atomic layer deposition) and then a silicon nitride layer of 80nm thickness was formed on the upper layer by plasma CVD, mainly using silicon nitride and aluminum oxide as materials of the antireflection film. Next, p for the semiconductor substrate ⁺ And a layer on the back surface (back surface of the n-type Si substrate) of which an insulating film is formed. A thickness of 80nm was formed by plasma CVD mainly using silicon nitride as a material of the antireflection film.

Next, the conductive paste for ag—al electrode formation obtained using the glass powders of examples 1 to 21 above was applied in a line pattern on the surface of the light receiving surface side of the obtained Si semiconductor substrate with an antireflection film by screen printing, and dried at 120 ℃.

Then, baking was performed for 100 seconds at a peak temperature of 740 ℃ using an infrared light heating furnace to form a surface ag—al electrode, thereby completing a single-sided battery for measuring contact resistance. By baking, p penetrating the antireflection film and contacting the Si semiconductor substrate ⁺ The layer contact forms an Ag-Al electrode.

The contact resistance of a single-sided battery fabricated using the conductive paste for ag—al electrode formation containing the glass powder of each example was measured by TLM (transfer length method). For the above obtained at p ⁺ Contact resistance Rc [ omega ] between an n-type Si semiconductor substrate having Ag-Al electrode formed on the layer side via an insulating film (two-layer film comprising a silicon nitride layer and an aluminum oxide layer) and the Ag-Al electrode]Evaluation was performed. Contact resistance Rc [ omega ]]The method is as follows: the contact resistance Rc [ Ω ] was obtained by fixing the anode side of the tester to the pattern P1 of FIG. 2, and by measuring the resistance by placing the cathode side of the tester at each position of the patterns P2, P3, P4, P5]. Will beThe results are shown in tables 1 and 2. N/D in tables 1 and 2 indicates that the paste was thickened and was not printed or that the contact resistance Rc [ Ω ] could not be measured due to a large resistance value]。

(residual Rate of silicon nitride layer (SiN residual Rate))

In order to evaluate the reactivity of each paste with the silicon nitride layer as one of the insulating films using the n-type Si semiconductor substrate after measuring the contact resistance Rc, the residual ratio of the silicon nitride layer was measured.

To remove the ag—al electrode from the n-type Si semiconductor substrate, the substrate was immersed in a 50% aqueous nitric acid solution for 2 hours, then the substrate and a 1% aqueous hydrofluoric acid solution were put into a vial and sealed, and immersed for 5 minutes while applying ultrasonic waves. Next, the substrate was cleaned with ion-exchanged water. The nitrogen (N1) on the electrode and the nitrogen (N2) outside the electrode were quantified by an analytical scanning electron microscopy (SEM-EDS), and the ratio (N1/N2) of the nitrogen on the electrode to the nitrogen outside the electrode was calculated as the residual ratio of the silicon nitride layer. The N/D in table 2 indicates that the paste was thickened and was not printable.

/>

As shown in tables 1 and 2, it is found that the SiN residual ratios of examples 1 to 11 as examples are higher than those of examples 12 to 21 as comparative examples, and crystallization can be promoted to suppress flow of glass at the time of high-temperature baking and excessive burn-through can be suppressed. Examples 12 to 17 contain no Ga ₂ O ₃ In example 18, the alloy contains no Al ₂ O ₃ 、SiO ₂ And Ga ₂ O ₃ And B is ₂ O ₃ In the case where the content of (C) is more than 30%, example 19 is a composition containing no Al ₂ O ₃ And Ga ₂ O ₃ In the case where the PbO content is more than 70%, example 20 contains no Ga ₂ O ₃ And Al ₂ O ₃ Is large in content of (2)In the case of 10%, example 21 is Ga-free ₂ O ₃ And PbO content less than 40% and SiO ₂ An example of the content of (2) is more than 30%.

In addition, the contact resistance Rc of examples 1 to 11 as examples was lower than that of comparative examples, and the penetration of the insulating film, that is, the burn-through was excellent. From the results, it is found that by using the glass of the present invention in the formation of a solar cell, the Voc can be improved by suppressing excessive burn-through, and the conversion efficiency can be improved by reducing the contact resistance between the electrode and the semiconductor substrate.

The present application is based on japanese patent application 2021-213436 filed on 12/27 of 2021, the contents of which are incorporated herein by reference.

Claims

1. A glass, wherein the glass comprises, in mole percent on an oxide basis:

40% to 70% of PbO,

4% to 20% SiO ₂ 、

1% to 10% of Al ₂ O ₃ 、

0% to 30% B ₂ O ₃ And (d) sum

1% to 20% Ga ₂ O ₃ 。

2. The glass according to claim 1, wherein the glass is composed of PbO+Bi in mol% in terms of oxide ₂ O ₃ +SiO ₂ +B ₂ O ₃ Represented PbO, bi ₂ O ₃ 、SiO ₂ 、B ₂ O ₃ The total content of (2) is 70% or more.

3. The glass according to claim 1 or 2, wherein the glass is composed of Ga in mol% in terms of oxide ₂ O ₃ +B ₂ O ₃ Ga of the representation ₂ O ₃ And B ₂ O ₃ The sum of the contents of (2) relative to SiO ₂ +Ga ₂ O ₃ +B ₂ O ₃ Represented SiO ₂ 、Ga ₂ O ₃ And B ₂ O ₃ The total content ratio of (2) is 40% to 90%.

4. The glass according to any one of claims 1 to 3, wherein the glass further comprises 1% to 12% by mol of TiO in terms of oxide ₂ 。

5. The glass according to any one of claims 1 to 4, wherein the glass further comprises 0.5% to 10% of La in terms of mol% in terms of oxide ₂ O ₃ 。

6. The glass of any one of claims 1-5, wherein the glass has a glass transition temperature of from 280 ℃ to 430 ℃.

7. A conductive paste, wherein the conductive paste contains a glass powder, a conductive metal powder, and an organic vehicle, the glass powder comprising the glass of any one of claims 1 to 6.

8. A solar cell, wherein the solar cell has an electrode formed using the conductive paste of claim 7.

9. A solar cell, the solar cell having:

a silicon substrate having a sunlight receiving surface;

the first electrode comprises a metal and a glass,