JP2000277768A - Method of forming solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar battery in which electrodes are mode dense, drastically improve contact resistance and optical transducing efficiency by electrolytically plating printed electrodes baked at a high temperature, because there is a problem that the electrodes have poor wettability for solder and contact resistance. SOLUTION: In a method of forming a solar battery, a diffused layer 1a of semiconductor impurities of one conductivity is provided at one main surface side of a semiconductor substrate 1 of another conductivity, and electrodes 4 and 5 connected to both main surface sides of the semiconductor substrate 1 are provided. In this case, after the electrode 4 of one main surface of the semiconductor substrate 1 is applied with silver paste to be baked, copper, nickel or tin is impregnated into the electrode 4 by an electrolytic plating method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for forming a solar cell.

[0002]

2. Description of the Related Art A general structure of a solar cell is shown in FIG. In FIG. 2, 1 denotes one conductivity type (for example, P
Semiconductor substrate, 1a is an n-type region in which phosphorus atoms are diffused at a high concentration in the surface portion of the semiconductor substrate 1, 2 is an antireflection film on one main surface side, 3 is a semiconductor junction, 4 is a back surface The electrodes 5 are surface electrodes.

The anti-reflection film 2 is formed by etching a portion corresponding to the surface electrode 5, or is formed by passing the anti-reflection film 2 from above the anti-reflection film 2. Conventionally, as a method for forming an electrode of this type of solar cell, a vacuum deposition method, a plating method, a printing method, or the like has been used. In the vacuum evaporation method, an electrode with sufficiently reduced contact resistance is formed, but it has a disadvantage that productivity is low and a manufacturing apparatus is expensive.

[0004] On the other hand, there are plating methods and printing methods as methods which can be formed at low cost. At present, the printing method is the mainstream from the viewpoint of mass productivity. As the paste used for the printing method, a conductive paste such as silver is used. Electrodes formed using conductive paste have strong adhesion strength to silicon,
Various characteristics such as low contact resistance (to make ohmic contact), low wire resistance, and good solder wettability are required.

However, the electrodes formed by the printing method sinter the conductive paste at a high temperature.
An oxide film is easily formed at the interface between the electrode and the electrode 5, and there is a limit in reducing the contact resistance. Furthermore, the electrode 5 fired at a high temperature
Since an oxide film is formed on itself, an acid treatment is required to improve the solder wettability.

As a method of reducing the contact resistance, Japanese Patent Application Laid-Open No. Sho 59-168668 discloses silver powder and at least one metal compound selected from carbides and nitrides of metals of the 4a or 5a group, and an organic binder. It is disclosed that a conductive paste comprising an organic solvent, an organic solvent, and glass powder added as needed is used. However, this method has a problem that it is difficult to obtain a contact resistance equivalent to that of a vapor deposition electrode and that solder wettability is poor.

As a method for improving solder wettability,
JP-A-59-84477 discloses that copper or nickel is deposited on an aluminum electrode or a silver electrode by an electroless plating method. However, this method has a problem that the contact resistance is large. in this way,
The printing method has a problem that it is difficult to obtain the same contact resistance and solder wettability as the vacuum evaporation method.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a method of forming a solar cell which has solved the conventional problems of poor contact resistance and poor solder wettability. And

[0009]

In order to achieve the above object, in a method for forming a solar cell according to the present invention, a semiconductor substrate exhibiting another conductivity type is provided on one principal surface side of a semiconductor substrate exhibiting one conductivity type. In the method for forming a solar cell, in which electrodes are connected to both main surfaces of the semiconductor substrate, a silver paste is applied and baked as an electrode on one main surface of the semiconductor substrate. This electrode is impregnated with copper, nickel or tin by electrolytic plating.

With this structure, the contact resistance at the interface between the semiconductor substrate and the electrode is improved, and an electrode having good contact resistance and good solder wettability can be formed at low cost. In other words, copper, nickel, tin or the like is deposited on the surface of the electrode by electrolytic plating to improve the solder wettability, but these metals are contained throughout the inside of the electrode to densify the inside of the fired electrode. This also improves the contact resistance.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing a method for forming a solar cell element of the present invention. First, a semiconductor substrate 1 is prepared (see FIG. 1A). This semiconductor substrate 1 is made of single crystal or polycrystalline silicon. This semiconductor substrate 1
Is to add 1 × 10 ¹⁶ p-type semiconductor impurities such as boron (B).
About 10 ¹⁸ atoms / cm ³ , specific resistance 1.5
The substrate is about Ωcm. In the case of a single crystal silicon substrate, it is formed by a pulling method or the like, and in the case of a polycrystalline silicon substrate, it is formed by a casting method or the like. Polycrystalline silicon substrates can be mass-produced and are more advantageous than single-crystal silicon substrates in terms of manufacturing cost. An ingot formed by a pulling method or a casting method is sliced into a thickness of about 300 to 500 μm, and 10 cm × 10 cm or 15 c
The semiconductor substrate is cut into a size of about mx 15 cm.

Next, the semiconductor substrate 1 is placed in a diffusion furnace and heated in phosphorus oxychloride (POCl ₃ ) or the like to diffuse phosphorus atoms into the surface of the semiconductor substrate 1 so that n-type is formed. A region 1a is formed, and a semiconductor junction 3 is formed (see FIG. 1B). The n-type region 1a is formed at a depth of about 0.2 to 0.5 μm and has a sheet resistance of 40Ω / □ or more. Due to this thermal diffusion, an n-type region 1 a and a phosphorus glass layer (not shown) containing phosphorus atoms are formed on the entire outer surface of the semiconductor substrate 1.
The remaining portion except for the n-type region 1a on one main surface side of the semiconductor substrate 1 is removed by dipping in an etching solution containing hydrofluoric acid and nitric acid as main components, and then washed with pure water (FIG. 1
(C)).

Next, an antireflection film 2 is formed on one main surface side of the semiconductor substrate 1 (see FIG. 1D). This antireflection film 2
Is formed of, for example, a silicon nitride film by a plasma CVD method using a mixed gas of silane and ammonia. The antireflection film 2 is provided to prevent light from being reflected on the surface of the semiconductor substrate 1 and to effectively take in light into the semiconductor substrate 1. The antireflection film 2 is formed by etching a portion corresponding to an electrode, applying a paste, and firing the paste. Alternatively, a paste is directly applied on the antireflection film 2 and baked. In the application and baking, after the back electrode material 4 is applied and dried, the front electrode material 5 is applied and dried. The electrode materials 4 and 5 were prepared by adding glass frit to silver powder and an organic vehicle in an amount of 0.1 to 100 parts by weight of silver.
The paste is added by about 5 parts by weight, and the paste is printed by a screen printing method and baked at 600 to 800 ° C. for about 1 to 30 minutes. This glass frit is
It is made of a material having a softening point of at least 500 ° C. containing at least one of PbO, B ₂ O ₃ and SiO ₂ .

Thereafter, the element 1 was immersed in a copper plating solution comprising CuSO ₄ (pentahydrate), sulfuric acid, a brightener, and the like.
A DC current of 0.03 mA per cm ^{2 is} applied for 20 minutes. The electrodes formed on one main surface side and the other main surface side are energized with the negative side and metal copper or the like on the positive side. When such electrolytic plating is performed, the plating metal adheres to the surface of the electrode and impregnates the inside of the electrode (FIG. 1 (f)). Therefore, these metals are impregnated into the porous portion inside the electrode and are denser. As the plating solution, the above CuSO ₄
Nickel chloride, tin chloride or the like may be used instead of (pentahydrate). The brightener may be added as needed.

[0015]

EXAMPLE A phosphorous (P) was diffused at 1 × 10 ¹⁷ atoms / cm ³ on one principal surface side of a silicon substrate having a resistance of 1.5 Ωcm to form a silicon nitride film having a thickness of 850 ° and then 100 parts by weight of silver After printing a silver paste consisting of a silver powder containing 3 parts by weight of glass frit and an organic vehicle and baking at 750 ° C. for 15 minutes, CuSO ₄ (pentahydrate) 64 g / liter, sulfuric acid 40 ml / liter, gloss A direct current of 0.03 mA per cm ² of the device was applied for 20 minutes in a copper plating solution of 5 ml / liter of the agent.

For comparison, two-layer printing was performed when no current was supplied, when a nitride was added to the printing paste, and in order to confirm the effect of line resistance. Table 1 shows the obtained electrical characteristics.

[0017]

[Table 1]

As is clear from Table 1, in the case of copper plating, a current density of 30.1 mA / cm ² , a voltage of 0.582 V, an FF of 0.782 and a conversion efficiency of 13.7% were obtained. On the other hand, when the copper plating was not performed, the current density was 30.4 / cm ² , the voltage was
F0.730, conversion efficiency 12.87%, two-layer printing, current density 30.2 / cm ² , voltage 0.580
V, FF 0.731, conversion efficiency 12.80%, and a paste obtained by adding 10% by weight of TiN as a nitride to the paste has a current density of 30.3 / cm ² and a voltage of 0.580.
V, FF 0.740, and conversion efficiency 13.00%.
Thus, the effect of reducing the contact resistance by the copper plating treatment was confirmed.

[0019]

As described above in detail, according to the method for forming a solar cell according to the present invention, a silver paste is applied and baked as an electrode on one main surface side of a semiconductor substrate, and then the electrode is applied to the electrode. Since copper, nickel, or tin is impregnated by the plating method, the printed electrodes fired at a high temperature are subjected to electrolytic plating, so that the electrodes become denser and the contact resistance can be greatly improved. Is greatly improved. In addition, the solder wettability is also improved, and wiring in a later step is facilitated.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a method for forming a solar cell according to the present invention.

FIG. 2 is a diagram showing a conventional solar cell.

[Explanation of symbols]

1 ... Semiconductor substrate, 1a ... N-type diffusion layer, 2 ...
Antireflection film, 3 ... Semiconductor junction, 4 ... Back electrode, 5 ... Surface electrode

Claims (1)

[Claims] 1. A solar cell provided with a diffusion layer of a semiconductor impurity having another conductivity type on one main surface side of a semiconductor substrate having one conductivity type and electrodes connected to both main surface sides of the semiconductor substrate. In the method of forming a solar cell, after applying and baking a silver paste as an electrode on one main surface side of the semiconductor substrate, the electrode is impregnated with copper, nickel, or tin by an electrolytic plating method. Forming method.