JP2002176186A - Solar cell and solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solar cell and a solar cell module in which a reaction can take place under a sufficiently stabilized state between silicon in an n-layer and a surface silver electrode while enhancing the electric characteristics and the lifetime. SOLUTION: The solar cell or the solar cell module is constituted such that the sheet resistance of the n-layer 3 is not higher than 80 Ω/(square) and the depth of the n-layer 3 being corroded by the surface silver electrode 10 is in the range of 5-40 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell and a solar cell module, and to improve the power generation efficiency and life of a silicon solar cell that controls the power generation of a solar cell system.
This relates to the state of the front electrode on the light receiving surface side of sunlight and the silicon substrate.

[0002]

2. Description of the Related Art In recent years, solar cell systems using a silicon substrate as a main material have become remarkably popular for use in houses and high-rise buildings in order to be environmentally friendly and effectively use energy. In the future, solar cell systems are expected to spread further, but the key technological development items include the development of low-cost manufacturing processes, improvement of power generation efficiency, and improvement of life.

When the installation area of the solar cell system is limited, a solar cell system having high power generation efficiency is effective. Also, from the viewpoint of purchase cost payback on the consumer side, it is important to reduce the price of the solar cell system itself and to extend its life.
Hereinafter, a conventional solar cell will be specifically described with reference to the drawings.

FIG. 10 is a schematic view of the front and back sides of a conventional silicon solar cell used for houses and the like.
(A) is a schematic diagram of the front side of the silicon solar cell, FIG.
0 (B) is a schematic view of the back side of the silicon solar cell. FIG. 11 is a sectional view of the silicon solar cell taken along the line A1-A2 shown in FIG. 10A, and FIGS. 12 and 13 are sectional structural views showing main manufacturing steps of the silicon solar cell shown in FIG.

[0005] In FIGS. 10 to 13, reference numeral 101 denotes a p-type silicon substrate, 102 denotes a texture formed on the p-type silicon substrate 101, and 103 denotes an n-type film formed between the p-type silicon substrate 101 and the texture 102. Layer. Reference numeral 104 denotes an anti-reflection film formed on the texture 102, and reference numeral 110 denotes a sintered surface silver grid electrode formed so as to be connected to the n-layer 103.

Reference numeral 111 denotes a surface silver grid electrode paste formed on the antireflection film 104 after screen printing, and 112 denotes a surface silver bus electrode formed so as to be connected to the n-layer 103. 120 is a p-type silicon substrate 101
A sintered back aluminum electrode formed on the back side,
Reference numeral 1 denotes a paste for the back aluminum electrode formed on the back surface of the p-type silicon substrate 101 after screen printing.

Reference numeral 122 denotes a p + layer formed between the p-type silicon substrate 101 and the back aluminum electrode 120, and 130 denotes a p + layer.
This is a back silver bus electrode after sintering formed so as to be connected to the + layer 122. Reference numeral 40 denotes solder formed on the surface of the surface silver grid electrode 110, t indicates the thickness of the n-layer 103, and d indicates the thickness of the n-layer 10 in the surface silver grid electrode 110.
3 shows the erosion depth.

On the front side of the solar cell shown in FIG.
In order to contribute as much sunlight as possible to power generation on the p-type silicon substrate 101, an antireflection film 104 is usually provided to suppress the reflection of incident light. Furthermore,
On the front side of the solar cell, a surface silver grid electrode 11 for locally collecting electricity generated in the silicon substrate 101.
0 and a surface silver bus electrode 112 for extracting electricity collected by the surface silver grid electrode 110.

Here, the surface silver grid electrode 110 and the surface silver bus electrode 112, which are the front electrodes of the solar cell, block sunlight incident on the front side of the solar cell. A smaller arrangement is desirable from the viewpoint of improving the power generation efficiency of the solar cell.

Therefore, considering that a large amount of sunlight is incident on the front side of the solar cell, for example, a comb-shaped grid electrode 110 and a bus electrode 112 as shown in FIG. In general, it is constituted by. Further, as the electrode material of the grid electrode 110 and the bus electrode 112, for example, it is general from the viewpoint of cost and performance that silver is used as a main component.

On the back side of the solar cell shown in FIG.
In order to prevent the electricity generated on the back side from being reduced by the loss due to the resistance, the back aluminum electrode 120 is provided in a wide range, and the back silver bus electrode 130 is provided for collecting the electricity generated by the back aluminum electrode 120. Are further arranged.

The back aluminum electrode 120 is made of BSF (Back Su
rface Field) effect to improve power generation capacity
Generally, aluminum materials are often used. When the back silver bus electrode 130 is made to function as an electric lead wire for drawing out the electric power generated by the back aluminum electrode 120, it is common to use a copper wire with solder.
For example, a silver electrode is used as the back bus electrode having good adhesion workability with the back aluminum electrode 120.

Next, the solar cell shown in FIG. 11 will be described. In the solar cell shown in FIG. 11, electrons and holes are generated in silicon by incident sunlight. Most of short-wavelength light is absorbed by the silicon surface layer, but long-wavelength light is transmitted deep into silicon. Has the property of being absorbed.
In addition, electrons generated in silicon tend to have a long distance in which they can diffuse and move in silicon, while holes generated in silicon tend to have a short distance in which they can diffuse and move in silicon.

In a solar cell, when electrons and holes are absorbed by impurities and defects in silicon, the power generation performance is reduced. In the case of a photovoltaic cell, a semiconductor having a pn junction is irradiated with light,
In contrast to the structure in which generated electrons and holes are separated, in the case of a solar cell, the structure must be adjusted so that the power generation efficiency is optimized on the semiconductor side in accordance with the spectrum of sunlight.

Therefore, in the solar cell, in consideration of optimizing the power generation efficiency on the semiconductor side corresponding to the spectrum of sunlight, the hole concentration on the p + layer 122 side is increased and the n layer 103 is increased.
The structure may be appropriately designed to increase the electron concentration on the side.
As a result, the solar cell has a p +
By the pn junction of the layer 122 and the n-layer 103 with an increased electron concentration, electrons and holes can be efficiently separated.

Generally, a low-cost solar cell uses a silicon substrate to generate sunlight by a simple pn junction, and a V-type substrate such as phosphorus (P) is applied to a p-type silicon substrate 101 having a thickness of about several hundred μm. An n layer 103 having a thickness of about several hundred nm is formed by performing diffusion or the like with a group element. Here, the p-type silicon substrate 101 may be either a single crystal or a polycrystal, but in the following description, a single crystal substrate having a (100) plane orientation will be described as an example.

In the solar cell shown in FIG. 11, the specific resistance is 0.1.
N layer 1 on the surface of p-type silicon 101 of about 5 Ω · cm.
03 and a texture 102 having a concavo-convex structure for confining light on the substrate 101 side are provided, and an antireflection film 104 is disposed on the texture 102. A back aluminum electrode 120 is arranged on the back side of the substrate 101, and a BSF (Back Surface Fiel)
d) The p + layer 122 is provided to
In order to prevent the electrons inside from disappearing, p +
The electron concentration of the layer 122 is increased.

The back aluminum electrode 120 is also expected to have a BSR (Back Surface Reflection) effect in which long-wavelength light passing through the silicon substrate 101 is reflected and reused for power generation. However, the back aluminum electrode 120 tends to significantly warp the silicon substrate 101, thereby inducing the substrate 101 to crack. For this reason, the back aluminum electrode 1
20 is often removed after forming the P + layer 22 by heat treatment in consideration of cracks in the substrate 101.

Here, the reason why the silicon substrate 101 is warped will be described. When an aluminum (Al) film for the back aluminum electrode 120 is formed on the back surface of the silicon substrate 101, the Al in the silicon substrate 101 and the Al in the Al film are used.
-Si alloying reaction occurs. Thereafter, re-solidification at about 577 ° C. is performed to sinter the Al film to form the back aluminum electrode 120. Due to this heat treatment, a difference in thermal expansion occurs between the silicon substrate 101 having a different coefficient of thermal expansion and the back aluminum electrode 120, and the silicon substrate 101 warps so as to be concave on the back aluminum electrode 120 side.

Next, a manufacturing process of the solar cell shown in FIG. 11 will be described with reference to FIGS. This figure 1
Processes 2 and 13 are technically said to have high hurdles, and exemplify a solar cell manufacturing process having a small number of manufacturing steps in consideration of cost reduction. Here, the surface silver grid electrode 110 and the surface silver bus electrode 112 are formed by applying a silver paste on the anti-reflection film 104 by a screen printing method and dried, and the back aluminum electrode 120 and the back silver bus electrode 130 are also applied by a screen printing method. dry.

Subsequently, the electrode paste for each of the electrodes 110, 112, 120, and 13 is fired by simultaneously firing the electrode pastes for the front and back sides.
0 is formed. By this baking, the surface silver electrodes 110, 11
2 stays in the n-layer 103 through the anti-reflection film 104. Also, the back aluminum electrode 120 and the silicon substrate 101
Is melted and re-solidified by this firing, so that the p + layer 12 is formed between the back aluminum electrode 120 and the silicon substrate 101.
Form 2 Hereinafter, a method for manufacturing the solar cell will be specifically described.

First, using a p-type silicon substrate 101 shown in FIG. 12 (A), a damaged layer on the surface of the silicon substrate 101 generated when slicing from a cast ingot is reduced to 10 to 20 wt% caustic soda or carbonated caustic soda. 2
After removing about 0 μm thickness, the same alkaline low concentration solution
Anisotropic etching of the surface of the silicon substrate 101 is performed with a solution to which PA (isopropyl alcohol) is added, and a texture 102 is formed on the surface of the silicon substrate 101 so that the silicon (111) surface is exposed (FIG. 12B).

Subsequently, for example, phosphorus oxychloride (POCl
3) 800-900 ° C in a mixed gas atmosphere of nitrogen and oxygen
By performing a heat treatment of about several tens of minutes, the n-layer 103 is formed uniformly over the entire surface of the silicon substrate 101. At this time, the range of the sheet resistance in the n-layer 103 formed on the surface of the silicon substrate 101 is about 30 to 80 Ω / □, and good electric characteristics as a solar cell can be obtained.

The depth of the silicon substrate 101 into which the phosphorus (P) has penetrated into the silicon substrate 101 from the surface of the silicon substrate 101 to a point where the phosphorus (P) concentration is 1E16 / cm 3. For (t), n
The layer 103 is formed by SIMS (Secondary-Ion-Mass-Spectroscop).
y) Analyzed and evaluated. As a result, the sheet resistance was 30, 6
The depth (t) of each of the n layers 103 of 0 and 80 Ω / □ is 450, 35 from the surface of the silicon substrate 101, respectively.
0, 250 nm.

Next, in order to protect the n-layer 103 on the light-receiving surface required as a light-receiving surface, the n-layer 103 on the light-receiving surface portion is protected.
A polymer resist paste is attached by a screen printing method so as to cover the substrate and dried. At this time, a resist mask is selectively formed so as to cover the n-layer 103 in the light-receiving surface portion, and the n-layer 103 in a portion other than the light-receiving surface portion is exposed.

Then, using a resist mask covering the n-layer 103 in the light-receiving surface portion, the n-layer 103 formed on the surface of the silicon substrate 101 other than desired (other than the light-receiving surface portion) such as the back surface of the silicon substrate 101 is, for example, After immersion in a 20 wt% potassium hydroxide solution for several minutes to selectively remove the resist, the resist used as a mask is removed with an organic solvent (FIG. 12C). As a result, the n-layer 103 in the light-receiving surface portion remains, and the n-layer 103 other than the light-receiving surface portion is removed, exposing the silicon substrate 101.

Further, an antireflection film 104 made of a silicon oxide film, a silicon nitride film, a titanium oxide film, or the like is formed on the surface of the n-layer 103 in the remaining light-receiving surface portion with a uniform thickness (FIG. 13A). ). For example, when the anti-reflection film 104 is formed of a silicon oxide film, SiH
A silicon oxide film is formed at a temperature of 300 ° C. or more under reduced pressure using 4 gases and NH 3 gas as raw materials.

The antireflection film 104 made of a silicon oxide film formed here has a refractive index of about 2 to 2.2.
The optimum thickness of the antireflection film 104 is 70 to 90 n
m. The anti-reflection film 104 made of a silicon oxide film formed as described above functions as an insulator. Therefore, simply forming a surface electrode on the anti-reflection film 104 made of an insulator operates as a solar cell. I can't let it. Therefore, steps such as wiring connection described below are performed.

Next, silver paste for forming the surface silver grid electrode 110 and for forming the surface silver bus electrode 112 is attached to the antireflection film 104 by a screen printing method and dried. As a result, the surface silver grid electrode paste 111 and the surface silver bus electrode paste are selectively formed on the antireflection film 104. FIG. 13B shows that the surface silver grid electrode paste 111 is formed on the antireflection film 104. Note that the surface silver bus electrode paste is not shown in FIG.

Further, similarly, when forming the back aluminum electrode 120 and the back silver bus electrode 130, the aluminum paste for forming the back aluminum electrode 120 and the silver paste for forming the back silver bus electrode 130 are formed by screen printing. Substrate 101
Each is attached to the back surface and dried. Thus, the paste 121 for forming the back aluminum electrode and the paste for forming the back silver bus electrode are selectively formed on the back surface of the silicon substrate 101.

FIG. 13B shows that the back aluminum electrode paste 121 is formed on the back surface of the silicon substrate 101. The paste for the back silver bus electrode is not shown in FIG. In screen printing, usually, a mesh having a mesh count of 200 to 400 is used. Usually, the thickness of the paste before drying is about ten to several tens of μm, but the thickness of the paste is reduced by several percent due to drying or baking.

Finally, the front and back electrode paste including the front silver grid electrode paste 111, the front silver bus electrode paste, the back aluminum electrode paste 121, and the back silver bus electrode paste is simultaneously heated to 600 ° C. to 900 ° C. Bake for about several minutes. By this firing, the silicon substrate 1
On the front side of No. 01, the glass material contained in the surface silver paste including the surface silver grid electrode paste 111 and the surface silver bus electrode paste causes the glass paste contained in the silver paste while the anti-reflection film 104 is being melted. Silver material is silicon substrate 10
1. Re-solidify in contact with the silicon in the upper n-layer 103.

By the above-described firing step, the front and back electrode pastes are fired, and the front silver grid electrode 110, the front silver bus electrode 112, the back aluminum electrode 120, and the back silver bus electrode 1 are fired.
30 are formed. FIG. 13C shows that the front silver grid electrode 110 and the back aluminum electrode 120 are formed, and the front silver bus electrode 112 and the back silver bus electrode 130 are formed.
Is not shown in FIG. 13C due to the cross-sectional location.

Further, by the above-described firing step, conduction between the surface silver electrode and the silicon n-layer 103 by the surface silver grid electrode 110 / surface silver bus electrode 112 is ensured. Such a process is called a fire-through method. In this firing step, the back aluminum electrode paste 121 also reacts with silicon in the silicon substrate 101 to form the back aluminum electrode 120, and the p + layer 122 is formed between the silicon substrate 101 and the back aluminum electrode 120. Is done.

Here, what is important in the fire-through method is that the antireflection film 104 is formed with a thickness of about several
That is, the layer 103 is formed only with a thickness of about several hundred nm. During the firing, the glass in the silver paste becomes
Not only that, it also generally reacts with the silicon in the n-layer 103, and the firing temperature and time must be controlled so that the glass and silver electrodes 110 and 112 remain within the n-layer 103.

The anti-reflection film 104 is formed on the surface silver electrode 11.
Also in the manufacturing method in which only the area immediately below and near 0 and 112 is removed in advance and the manufacturing method in which the antireflection film 104 is formed later, the controllability at the time of firing is also important. If the firing temperature is low or the firing time is short, the silicon in the n-layer 103 and the silver electrodes 110 and 112 are insufficiently contacted with each other, resulting in an increase in contact resistance.

Conversely, when the firing temperature is high or the firing time is long, the n-layer 103 is made of a glass component or a silver electrode 11.
0, 112 penetrates, and the electrical characteristics of the solar cell are likely to deteriorate. In addition, if the area immediately below the surface silver electrodes 110 and 112 is not uniformly connected to the silicon in the n-layer 103, the initial electrical characteristics of the solar cell deteriorate.

Furthermore, even if the solar cell is sealed with a resin, glass or the like to form a module, the moisture permeating the sealing resin reaches the solar cell during long-term use, and the surface silver electrode 11
In some cases, the interface between 0 and 112 and the silicon is deteriorated by a reaction such as oxidation, thereby shortening the life of the solar cell.

Therefore, as one of the countermeasures, a silver electrode 1
In order to improve the moisture resistance of 10 and 112, 200 to 25
The solar cell was immersed in a lead / tin eutectic solder melting tank at about 0 ° C., as shown in FIG.
A coating process is performed on the solder 112 with solder 140. Thereby, the moisture resistance of the surface silver electrodes 110 and 112 can be improved.

[0040]

In the conventional silicon solar cell as described above, the reaction between the surface silver electrodes 110 and 112 and the silicon in the n layer 103 formed on the silicon substrate 101 is sufficiently considered. No surface silver electrode 11
When the glass layers 0 and 112 and a part of the glass material erode more than necessary into the n-layer 103 by silicon, the glass component and the silver electrodes 110 and 112 penetrate the n-layer 103, and the electrical characteristics of the solar cell deteriorate. There was a problem that there was. Conversely, there is a problem that the contact between the silicon in the n-layer 103 and the silver electrodes 110 and 112 is insufficient and the contact resistance increases, which may shorten the life of the solar cell.

Further, in the conventional silicon solar cell as described above, if the erosion reaction occurs only under the surface silver electrodes 110 and 112 unevenly, the surface silver electrodes 110 and 112 become
There has been a problem that electrical conductivity with the silicon in the cell No. 03 cannot be uniformly obtained, and the electrical characteristics of the solar cell may be deteriorated.

Accordingly, the present invention provides a solar cell and a solar cell module that can perform the reaction between silicon in the n-layer and the surface silver electrode in a sufficiently stable state, and can improve electrical characteristics and life. The purpose is to do.

[0043]

A solar cell according to the present invention comprises: a silicon substrate of a first conductivity type; a semiconductor layer of a second conductivity type formed on a light receiving surface of the silicon substrate of the first conductivity type; A metal electrode formed so as to erode the second conductive type semiconductor layer and come into contact with the second conductive type semiconductor layer, wherein the second conductive type semiconductor layer has a sheet resistance of 80 Ω / □ and the depth at which the metal electrode erodes the second conductivity type semiconductor layer is 5 n
m and 40 nm or less.

In the above solar cell, the area where the metal electrode erodes the semiconductor layer of the second conductivity type is 30% or more of the area of the metal electrode.

The solar cell module according to the present invention has a first
A conductive type silicon substrate, a second conductive type semiconductor layer formed on a light receiving surface of the first conductive type silicon substrate, and the second conductive type semiconductor layer by eroding the second conductive type semiconductor layer. In a solar cell module including a plurality of solar cells having a metal electrode formed so as to be in contact with a layer, the sheet resistance of the semiconductor layer of the second conductivity type is 80Ω /
And the depth at which the metal electrode erodes the semiconductor layer of the second conductivity type is in the range of 5 nm or more and 40 nm or less.

In the solar cell module, the area where the metal electrode erodes the second conductivity type semiconductor layer is:
It is 30% or more of the area of the metal electrode.

[0047]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. FIG. 1 is a sectional structural view showing a silicon solar cell according to Embodiment 1 of the present invention. In FIG. 1, 1 is a p-type silicon substrate, 2 is a texture formed on the p-type silicon substrate 1, and 3 is an n-layer formed between the p-type silicon substrate 1 and the texture 2.

Reference numeral 4 denotes an anti-reflection film formed on the texture 2. Reference numeral 10 denotes a sintered surface silver grid electrode formed so as to penetrate the anti-reflection film 4 and be connected to the n-layer 3. The surface silver bus electrode is not shown in FIG. 1 due to the cross-sectional location, as in the above-described conventional example. 20 is a sintered back aluminum electrode formed on the back side of the p-type silicon substrate 1, and 22 is a p-type silicon substrate 1 and the back aluminum electrode 2
This is a p + layer formed between zero.

The back silver bus electrode is similar to the above-described conventional example.
It is not shown in FIG. 1 due to the cross section. Reference numeral 40 denotes solder formed on the surface of the surface silver grid electrode 10,
t indicates the thickness of the n-layer 3, and d indicates the maximum erosion depth of the surface silver grid electrode 10 into the n-layer 3. The front silver grid electrode 10, the front silver bus electrode, and the back aluminum electrode 20
The back silver bus electrode is formed by selectively forming a paste of silver and aluminum by a printing technique and then baking the same, as in the above-described conventional example.

The surface silver grid electrode 10 and the surface silver bus electrode
It is formed so as to penetrate the anti-reflection film 4 and erode the n-layer 3 to come into contact with the n-layer 3. N in the present embodiment
The sheet resistance of the layer 3 is 80Ω / □ or less. here,
The reason why the sheet resistance of the n-layer 3 is set to 80 Ω / □ or less is that if the sheet resistance is larger than 80 Ω / □, the cell characteristics of the solar cell (such as a decrease in cell factor) are deteriorated, which is not practically preferable. / □ or less.

Surface silver grid electrode 1 in the present embodiment
0, the depth of erosion of the n-layer 3 by the surface silver bus electrode is 5n
The range is from m to 40 nm. Here, the lower limit of the erosion depth of the n-layer 3 by the silver electrode is set to 5 nm.
This is because the erosion of the silver electrode becomes insufficient, and the silver electrode is easily peeled off from the n-layer 3, which is not preferable in practical use.

The reason why the upper limit of the erosion depth of the n-layer 3 by the silver electrode is set to 40 nm is that when the erosion depth is larger than 40 nm, the erosion of the n-layer 3 by the silver electrode proceeds extremely, This is because the cell characteristics of the solar cell deteriorate due to penetration through the n-layer 3 and are not practically preferable.

Therefore, the erosion of the n-layer 3 by the silver electrode becomes insufficient to prevent the silver electrode from peeling off the n-layer 3 and the erosion of the n-layer 3 by the silver electrode proceeds extremely. In consideration of preventing the silver electrode from penetrating the n-layer 3 and deteriorating the cell characteristics of the solar cell, the depth at which the electrode erodes the n-layer 3 is in the range of 5 nm to 40 nm. I just need. This erosion depth will be described later based on experimental results.

The surface silver grid electrode 10 and the surface silver bus electrode are n
It is preferable that the area for eroding the layer 3 is 30% or more of the area of the silver electrode. It is preferable that the eroded area of the n-layer 3 by the silver electrode be 30% or more of the area of the silver electrode. The eroded area of the n-layer 3 by the silver electrode is smaller than 30% of the area of the silver electrode. N layer 3 in
This is because the contact area with the metal becomes small, the resistance component becomes large, and the cell characteristics of the solar cell are likely to deteriorate, which is not preferable. The relationship between the contact areas will be described later based on experimental results.

It is preferable that the surface silver grid electrode 10 and the surface silver bus electrode are eroded so as to be uniform with respect to the n-layer 3. As described above, when the n-layer 3 is uniformly eroded by the silver electrode, the silver electrode can uniformly conduct with the n-layer 3, so that the deterioration of the cell characteristics of the solar cell can be suppressed.

Generally, the glass material in the silver paste is S
i, Pb, B, O elements as main components, and Bi, Zn,
A small amount of Ti, Al, Mg, etc. is contained, and the softening temperature can be freely adjusted by changing the composition. Usually, the glass softening temperature is 400 to 650 ° C., and its amount is also several wt%.
It is. The glass softening temperature and the glass amount are determined by matching with the material immediately below the surface silver electrode, that is, the material of the antireflection film 4 in FIG.

FIG. 2 is a diagram showing the relationship among the cell characteristics, the glass erosion depth and the erosion area ratio for the four types of pastes for the surface silver electrode actually examined. Hereinafter, the four types of surface silver electrode pastes A to D actually examined will be described with reference to FIG. The main component changes in each of the pastes A to D are the amount of the glass material and the softening temperature.

The surface silver paste C of the comparative example is a conventional product having a glass softening temperature of 550 ° C. and a glass amount of 7 wt%.
A structure equivalent to that of the silver paste in the conventional solar cell shown in FIG. 11 described above and corresponding to FIG. 11 is formed. According to the surface silver paste C of this comparative example, the silicon maximum erosion depth d of the n-layer 3 is 75 nm, and the erosion of the glass component and silver in the paste on the n-layer 3 is extremely advanced.
Penetration of the layer 3 is likely to occur.

The surface silver paste D of the comparative example was compared with the surface silver paste C of the comparative example by 7 wt% without changing the glass amount.
And the glass softening temperature was lowered to 350 ° C. According to the surface silver paste D of this comparative example, the silicon maximum erosion depth d of the n-layer 3 is 150 nm, which is further smaller than that of the surface silver paste C of the comparative example (75 nm). The layer 3 is eroded to form a structure in which the silver electrode penetrates the n-layer 3.

On the other hand, the surface silver paste B of the present invention comprises:
Compared with the surface silver paste C of the comparative example, the composition is changed so as to match the composition with the antireflection film 4, and the glass softening temperature is set to 500 ° C. Further, the surface silver paste B of the present invention is obtained by changing the lower limit glass amount at which the fire through can be performed to 1 wt% or less.

According to the surface silver paste B of the present invention, compared to the surface silver pastes C and D of the comparative example, n by the silver electrode
The erosion depth d into the layer 3 is as small as 40 nm,
It was found that no penetration into the n-layer 3 by the silver electrode occurred. Moreover, since the erosion depth d was 40 nm, the silver electrode did not peel off due to insufficient erosion. The surface silver paste B of the present invention has a lower glass limit of 1% by weight or less at which the fire through can be performed, so that the reaction during sintering is somewhat unstable,
It is easy to have a structure in which the portion directly below the surface silver electrode is electrically connected to silicon only locally.

The surface silver paste A of the present invention is a paste obtained by optimizing the glass amount of the paste B to 3 wt% and increasing the glass softening temperature to 500 ° C., the same as the paste B. According to the surface silver paste A of the present invention, as compared with the surface silver pastes C and D of the comparative example, the erosion depth d into the n-layer 3 by the silver electrode is reduced to 35 nm, and It was found that no penetration into the n-layer 3 occurred. Moreover, since the erosion depth d was 35 nm, the silver electrode did not peel off due to insufficient erosion.

FIG. 3 is a diagram showing electrical characteristics of a solar cell at the time of light irradiation. In FIG. 3, V indicates a voltage, and J indicates a current density. The current density indicates
It is commonly used to compare electrical characteristics side by side, excluding the effect of the size (area) of the solar cell. A solar cell that can achieve normal performance, when the voltage is swept,
And a thin line passing through point Q. An intersection between the curve and the J axis is represented by a short circuit current: Jsc, and an intersection with the V axis is represented by an open voltage: Voc.

Points P and Q are values obtained by multiplying J and V of each curve,
That is, the point at which the power is maximized is shown. The fill factor: FF shown in FIG. 3 indicates that the maximum power is (Jsc × Vo).
The ratio to c) is shown. In FIG. 3, the thick line is superior to the thin line in terms of the electrical characteristics of the solar cell. Generally, increase the glass amount of the optimal surface silver electrode,
When the glass softening temperature is lowered, the line shifts from a thick line to a thin line. It tends to be noticeable in the open circuit voltage Voc and FF.

The erosion depth at which the surface silver electrode and its glass component erode the silicon of the n-layer 3 is shown in FIG. 1 as a flat structure sample having no texture 2 structure.
The silver electrode and the glass were etched with a 50% nitric acid solution for 1 minute, the antireflection film 4 was further etched with a 50% hydrofluoric acid solution for 5 minutes, and the silicon step was evaluated by observing with a cross-sectional SEM or the like.

FIGS. 4 and 5 are schematic views of photographs of the surface silver pastes A and B according to the present invention as observed from above by an optical microscope. FIG. 4 shows the surface silver paste A of the present invention, and FIG. 5 shows the surface silver paste B of the present invention. 4 and 5, reference numeral 60 denotes a portion having no silver electrode pattern, 61 denotes a portion having a silver electrode pattern and is removed by etching, and 62 denotes a portion where the silver electrode erodes silicon and is etched to the depth thereof. It is the part that was done.

FIG. 6 shows the silicon erosion depth and the open-circuit voltage Vo after removing the surface silver electrode when each of the surface silver pastes A to D was used.
It is a relationship diagram with c. As described above, by varying the composition of the paste, the maximum erosion depth (d) of the surface silver electrode and the n-layer 3 of glass into silicon and the open-circuit voltage Voc have a strong correlation. I understood.

From FIG. 6, it can be seen that as the erosion depth d of the n-layer 3 by the silver electrode becomes smaller, the open-circuit voltage Voc becomes larger, and the erosion depth d of the n-layer 3 by the silver electrode becomes larger. , The open circuit voltage Voc was found to be small. In addition, in the surface silver pastes A and B of the present invention in which the erosion depth is smaller than the surface silver pastes C and D of the comparative example, it was found that the open-circuit voltage was higher than that of the comparative example.

From the image data of the portion immediately below the convex surface silver electrode shown in FIGS. 4 and 5, the area of silicon in the three portions of the n layer immediately below the surface silver electrode can be determined by a simple binary method using a 50% threshold method. The silicon erosion area ratio was determined by the conversion treatment. As shown in FIG. 2, the silicon erosion area ratio was 80% for the silver paste A of the present invention and 30% for the silver paste B of the present invention.

According to the silver pastes A and B of the present invention,
Since the erosion area ratio was set to 80% and 30%, it was found that the contact area between the silver electrode and the n-layer 3 was sufficient and the resistance component could be reduced. Further, the difference in the constitution of the silver pastes A and B of the present invention between the two is the amount of glass as can be seen from FIG.

The silver paste A of the present invention has a glass content of 3 watts.
t% and the silver paste B of the present invention (less than 1 wt%)
It is configured to be larger than that. Silver paste A of the present invention,
B and B had a maximum silicon erosion depth of 40 nm or less, as shown in FIGS. 2 and 6, and both were good as pastes for obtaining initial electrical characteristics of a solar cell.

Further, even when the silver paste A according to the present invention is used, the maximum silicon erosion depth d can be changed with good controllability by changing the solar cell formation conditions. For example, the firing conditions of the silver paste A are changed from a maximum temperature of 850 ° C. and a holding time of 60 seconds to a maximum temperature of 750 ° C. and a holding time of 5 seconds.
By changing to, the maximum silicon erosion depth d can be suppressed from 35 nm to 5 nm. It was confirmed that even when the silicon erosion maximum depth d was 5 nm, the electrical characteristics and reliability of the solar cell could be secured.

Next, the result of examining the moisture resistance of the solar cell will be described. Using the silver pastes A and B according to the present invention, a structure shown in FIG. 1 and a corresponding solar cell were respectively constructed.
A coating of solder 40 is also provided on the surface silver grid electrode 10 using silver pastes A and B and the surface silver bus electrode. FIG. 7 is a diagram showing the results of a moisture resistance test performed in a naked state in accordance with “JIS C 8917”.

In the JIS test, deterioration from the initial characteristics is defined as 5% or less after the test for 1000 hours. The silver paste B in the present invention was on the border between the pass and the reject, but the silver paste A in the present invention was found to be pass. Further, as a result of performing a moisture resistance test by changing the amount of the intermediate glass between the silver pastes A and B in the present invention, it was found that the silicon erosion area ratio passed the JIS test at 30% or more.

Embodiment 2 In Embodiment 1 described above, the case of a solar cell alone was described as shown in FIG. 1. However, a plurality of solar cells using silver pastes A and B in the present invention were used. Thus, if a solar cell module is configured, the same effect as in the first embodiment can be obtained in the solar cell module. In the first embodiment, for example,
Although the result of the moisture resistance test performed in a high-temperature and high-humidity atmosphere has been described, the present embodiment is directed to a solar cell manufactured by using a plurality of solar cells as shown in FIG. The results of the moisture resistance test of the module will be described below.

FIG. 8 is a diagram showing a solar cell module according to Embodiment 2 of the present invention, and FIG.
It is sectional drawing of the solar cell module in the B2 line. 8 and 9, reference numeral 51 denotes a solar cell; 52, a moisture-resistant back sheet (for example, PVF) disposed on the back side of the solar cell 51; and 53, a solar cell for interconnecting the solar cells 51. Interconnect tab wiring. Solar cell 51 has a structure equivalent to that of FIG. 1 using silver pastes A, B, and the like in the present invention described in the first embodiment.

Reference numeral 54 denotes a horizontal tab wire for interconnecting the solar cells 51, 55 denotes a positive electrode of the solar cell module, and 56 denotes a negative electrode of the solar cell module. Reference numeral 57 denotes a reinforced cover glass disposed on the front side of the solar cell 51, and reference numeral 58 denotes a solar cell sealing material (EVA: Ethyle) disposed between the moisture-resistant back sheet 52 and the reinforced cover glass 57 so as to protect the solar cell 51.
ne-Vinyl-Acetate).

Since the solar cell 51 is configured such that the light receiving surface side is a negative electrode and the rear surface side is a positive electrode, FIG.
In this example, the upper and lower sides of the solar cells 51 adjacent to each other in the horizontal direction are interconnected by tab wirings 53 mainly composed of copper. Similarly, the solar cell arrays connected in the horizontal direction are also electrically connected by the horizontal tab wires 54, and finally, the positive and negative extraction electrodes 55 and 56 can be configured to extract electricity.

Since the solar cell module is required to have long-term reliability, as shown in FIGS. 8 and 9, the solar cell array prevents the penetration of rain and the like while allowing sunlight to pass through the outermost surface. It is configured to be covered with a strengthened cover glass 57 having a function of absorbing the impact of a falling object or the like.

On the back side of the solar cell array, a back sheet 52 having excellent water resistance and the like is provided. The gap between the solar cell 51 and the reinforced cover glass 57 or the back sheet 52 is filled with a sealing material 58 to improve the moisture resistance.
The sealing material 58 is generally made of EVA (Ethylene-Vinyl-Ace).
tate) is used. The EVA agent is preferably a sheet having good workability.

Here, the manufacturing process of the solar cell module according to the present embodiment will be described. First, the interconnection tab wire 53 is connected to the solar cell 51 to produce a lateral solar cell array. Next, the horizontal tab wiring 54 and the plus and minus extraction electrodes 55 and 56 are connected to the solar cell array.

Finally, the solar cell 51 is connected to two sheets of E
Inserting with a sheet of VA or the like, further inserting with a tempered glass 57 arranged above and below the solar cell 51 and a back sheet 52, and heating simultaneously with defoaming, there is no gap as shown in FIG. A solar cell module having a structure can be obtained.

A reliability test was carried out using the manufactured solar cell module.
As shown in FIG. 2, the pastes A and B according to the present invention, and any paste having an intermediate composition between A and B, obtained results sufficiently clearing the JIS test as in the first embodiment.

From these results and the results of the first embodiment, in the silicon solar cell having the surface silver electrode surface coated with solder, the process conditions, the presence or absence of the antireflection film immediately below the surface silver electrode material, and the type of the antireflection film material The composition, amount, and composition of the surface silver electrode material are intricately entangled with each other, and there are many combinations of optimal materials and processes. However, the depth at which the surface silver electrode and its glass erode the silicon n-layer 3 and the It has been found that the following optimum range exists for the area ratio.

(A) Considering that the silver electrode can be prevented from peeling off from the n-layer 3 and the silver electrode can be prevented from penetrating through the n-layer 3, the silicon surface can be suppressed. The sheet resistance of the n-layer 3 is 80Ω / □ or less, and the maximum depth at which the surface silver electrode diffuses and erodes the n-layer 3 is:
What is necessary is just to comprise in the range of 5 nm or more and 40 nm or less.

(B) It is possible to prevent the contact area of the silver electrode with the n-layer 3 from becoming small and the resistance component from becoming large, and to prevent the oxidation at the silicon interface from easily occurring. Considering the points,
The area ratio at which the silver electrode erodes the n-layer 3 on the silicon surface is 30.
% Is preferable.

In the first and second embodiments, a single crystal substrate having a (100) plane orientation has been described as an example. However, a single crystal substrate having another plane orientation or polycrystalline silicon having various plane orientation grains may be used. Has been confirmed to have the same effect. Further, although the n-layer is arranged on the light-receiving surface side of the p-type substrate, a structure in which the p-layer is arranged on the n-type substrate may be used.

Further, in the first and second embodiments, the case where the antireflection film 4 is provided between the silicon and the electrode before firing in the formation of the light receiving surface side electrode has been described.
It has been confirmed that the optimum range of the maximum silicon erosion depth and the erosion area ratio of the electrode is the same as the above-mentioned range even in a structure without the above.

[0089]

According to the solar cell of the present invention, a silicon substrate of the first conductivity type, a semiconductor layer of the second conductivity type formed on the light receiving surface of the silicon substrate of the first conductivity type, A metal electrode formed so as to erode the conductive semiconductor layer and come into contact with the second conductive semiconductor layer, wherein the sheet resistance of the second conductive semiconductor layer is 8
With the configuration of 0 Ω / □ or less, deterioration of the cell characteristics of the solar cell (such as a decrease in cell factor) can be suppressed. Further, by configuring the depth at which the second conductive type semiconductor layer is eroded by the metal electrode within a range of 5 nm or more and 40 nm or less, the metal electrode is not sufficiently eroded by the metal electrode, and the metal electrode is separated from the semiconductor layer. In addition, it is possible to prevent the metal electrode from eroding the semiconductor layer extremely and the metal electrode from penetrating the semiconductor layer to deteriorate the cell characteristics of the solar cell. Therefore, it is possible to obtain a solar cell having a stable connection state in which the metal electrode is hardly peeled off from the semiconductor layer and excellent cell characteristics.

In the above solar cell, the area where the metal electrode erodes the semiconductor layer of the second conductivity type is set to be 30% or more of the area of the metal electrode. Can increase the contact area, reduce the resistance component, reduce the fill factor, and improve the cell characteristics of the solar cell. Moreover,
Oxidation at the interface of the semiconductor can be suppressed, and the reliability of the solar cell can be improved.

According to the solar cell module of the present invention, the first conductive type silicon substrate, the second conductive type semiconductor layer formed on the light receiving surface of the first conductive type silicon substrate, and the second conductive type silicon substrate And a metal electrode formed so as to erode the semiconductor layer of the second conductivity type and come into contact with the semiconductor layer of the second conductivity type, wherein the sheet resistance of the semiconductor layer of the second conductivity type is 80Ω / □ or less. By doing so, it is possible to suppress deterioration of the cell characteristics of the solar cell (such as a decrease in cell factor). Further, by configuring the depth at which the second conductive type semiconductor layer is eroded by the metal electrode within a range of 5 nm or more and 40 nm or less, the metal electrode is not sufficiently eroded by the metal electrode, and the metal electrode is separated from the semiconductor layer. In addition, it is possible to prevent the metal electrode from eroding the semiconductor layer extremely and the metal electrode from penetrating the semiconductor layer to deteriorate the cell characteristics of the solar cell. Therefore, it is possible to obtain a solar cell having a stable connection state in which the metal electrode is hardly peeled off from the semiconductor layer and excellent cell characteristics.

Further, in the above solar cell module,
By making the area where the metal electrode erodes the second conductivity type semiconductor layer 30% or more of the area of the metal electrode, the contact area of the metal electrode with the semiconductor layer is increased, and the resistance component is increased. And the fill factor can be reduced to improve the cell characteristics of the solar cell.
Moreover, oxidation at the interface of the semiconductor can be suppressed, and the reliability of the solar cell can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional structural view showing a silicon solar cell according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing the relationship among cell characteristics, glass erosion depth, and erosion area ratio for four types of pastes for a surface silver electrode actually examined.

FIG. 3 is a diagram showing electrical characteristics of a solar cell at the time of light irradiation.

FIG. 4 is a schematic view of an upper observation photograph of the surface silver paste A (the state of the silicon surface after the removal of the surface silver electrode) according to the present invention observed by an optical microscope.

FIG. 5 is a schematic view of an upper observation photograph of the surface silver paste B (the surface state of the silicon after the removal of the surface silver electrode) in the present invention observed by an optical microscope.

FIG. 6 is a graph showing the relationship between the silicon erosion depth from which a surface silver electrode has been removed and the open-circuit voltage Voc when each of the surface silver pastes A to D is used.

FIG. 7 is a diagram showing the results of a reliability test on the surface silver electrodes A and B.

FIG. 8 is a diagram showing a solar cell module according to Embodiment 2 of the present invention.

9 is a diagram illustrating a cross-sectional structure of the solar cell module taken along line B1-B2 illustrated in FIG.

FIG. 10 is a schematic view of a front side (A) and a back side (B) of a conventional silicon solar cell used for a house or the like.

FIG. 11 is a cross-sectional view of the silicon solar cell taken along the line A1-A2 shown in FIG.

FIG. 12 is a sectional structural view showing main manufacturing steps of the silicon solar cell shown in FIG.

FIG. 13 is a sectional structural view showing main manufacturing steps of the silicon solar cell shown in FIG.

[Explanation of symbols]

1 p-type silicon, 2 textures, 3 n layers, 4
Anti-reflection film, 10 front silver grid electrode, 20 back aluminum electrode, 22 p + layer, 40 solder, 51 solar cell,
52 Backsheet, 53 Solar cell interconnection tough wiring, 54 Horizontal tab wiring, 55 Plus extraction electrode, 5
6 minus extraction electrode, 57 reinforced cover glass,
58 Solar cell sealing material.

Continued on the front page (72) Inventor Satoshi Arimoto 2-3-3 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 5F051 AA03 BA17 CB27 CB29 FA10 FA13 FA30 GA04 HA03 HA07

Claims (4)

[Claims] A first conductivity type silicon substrate; and a first conductivity type silicon substrate.
A second conductive type semiconductor layer formed on the light receiving surface of the conductive type silicon substrate; and a metal formed so as to erode the second conductive type semiconductor layer and come into contact with the second conductive type semiconductor layer. A sheet resistance of the second conductivity type semiconductor layer is 80 Ω / □ or less, and a depth at which the metal electrode erodes the second conductivity type semiconductor layer is 5 nm or more and 40 nm or less. A solar cell characterized by the following range. 2. The solar cell according to claim 1, wherein an area of the metal electrode eroding the semiconductor layer of the second conductivity type is 30% or more of an area of the metal electrode. battery. 3. A silicon substrate of a first conductivity type;
A second conductive type semiconductor layer formed on the light receiving surface of the conductive type silicon substrate; and a metal formed so as to erode the second conductive type semiconductor layer and come into contact with the second conductive type semiconductor layer. In a solar cell module including a plurality of solar cells having electrodes, the second conductive type semiconductor layer has a sheet resistance of 80 Ω / □ or less, and the metal electrode erodes the second conductive type semiconductor layer. A solar cell module having a depth of 5 nm or more and 40 nm or less. 4. The solar cell module according to claim 3, wherein an area in which the metal electrode erodes the semiconductor layer of the second conductivity type is 30% or more of an area of the metal electrode. Solar cell module.