JPH06310739A - Solar cell element - Google Patents

Abstract

PURPOSE:To enhance output characteristics by forming a lightly doped impurity layer having large crystal particle size on the side of light receiving face. CONSTITUTION:Oxide 2 is deposited on the surface of a p-type Si wafer 1 heavily doped with B(boron) and microopenings 7 are made regularly in the oxide 2. An amorphous Si film is then formed thereon and annealed. Crystal growth of the amorphous Si film 2 takes place gradually from the opening 7 onto the surrounding oxide 2 with the crystallinity of the p-type Si wafer 1 as the speed. The crystal growth stops when the crystal comes into contact with a crystal part grown from an adjacent opening 7 thus forming a p-type lightly doped impurity layer 3 having a regular and square grain boundary 8. A light receiving face n-layer 4 doped with P(phosphorus) is then formed on the layer 3 followed by formation of a surface electrode 5 and a rear surface electrode 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell element using a substrate in which a non-single-crystal silicon layer is laminated on a single-crystal silicon substrate and non-single-crystal silicon is crystal-grown.

[0002]

2. Description of the Related Art Si (silicon) substrates used for solar cell elements include single crystal Si, polycrystalline Si and amorphous Si. By the way, as a method of improving the characteristics of a solar cell element using single crystal Si, there is a method of lengthening the carrier lifetime of a Si wafer. Usually, the Si wafer contains p-type or n-type impurities, and the life is improved as the amount of impurities is reduced, but the problem is that the electrical resistance increases and the characteristics deteriorate.
An impurity element of about 1 ppma is contained.

In order to solve the contradictory problem, a region having a small amount of impurities and a long lifetime is formed on a low resistance substrate having a large amount of impurities to improve the characteristics of a region near the surface side that absorbs more light. There is a technology to try.

[0004]

However, conventionally, when forming a Si layer region having good crystallinity on a Si substrate, it is necessary to carry out epitaxial growth, which is a high temperature process, and thermal strain defects are generated. There is a problem that the lifetime is reduced.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 4-177880, there is a method in which a polycrystalline Si film is formed on a substrate at a low temperature and then recrystallized by annealing.
In this method, random crystallization is performed using any part of the substrate as a nucleus, so that a large number of minute crystals are deposited, carrier movement is deteriorated, and it is difficult to form a solar cell element having good photoelectric conversion characteristics. It was

The properties required for the crystal growth layer on the light receiving surface are the following three points. (A) The impurity element concentration is low. (B) Long lifetime. (C) The crystallinity is good, and in the case of polycrystal, the crystal grain size is large.

However, conventionally, it was difficult to satisfy the above three points.

Therefore, an object of the present invention is to provide a solar cell element capable of forming a low impurity concentration layer having a large crystal grain size on the light receiving surface side and improving output characteristics.

[0009]

In the solar cell element of the present invention, a non-single-crystal silicon layer having a low impurity concentration is formed on the light-receiving surface side of a single-crystal silicon substrate, and the non-single-crystal silicon layer is crystal-grown. In the case of using a substrate, an intermediate layer having a minute opening is provided between the single crystal silicon substrate and the non-single crystal silicon layer, and the non-single crystal silicon is crystallized through the opening so that the non-single crystal silicon grows through the opening. The single crystal silicon substrate and the non-single crystal silicon layer are in contact with each other.

[0010]

In this solar cell element, the non-single-crystal silicon crystal grows from the opening of the intermediate layer provided between the single-crystal silicon substrate and the non-single-crystal silicon layer, and does not grow from other portions. The growing crystals do not collide with each other and the crystal grain size increases.

[0011]

EXAMPLES Examples of the present invention will be described in detail below.

FIG. 1 is a sectional view of a solar cell element according to the first embodiment of the present invention. As shown in this figure, in the solar cell element of this embodiment, a thermal oxide film 2 is formed on the surface of a p-type Si wafer 1 that is highly doped with B (boron), and the surface of this thermal oxide film 2 is formed. A p-type impurity low-concentration layer region 3 lightly doped with B (boron) is formed on the p-type impurity low-concentration layer region 3, and a light-receiving surface n-layer region doped with P (phosphorus) is formed on the p-type impurity low-concentration layer region 3. 4 is forming. Further, the surface comb-shaped electrode 5 is formed on the light receiving surface of the Si wafer processed as described above, and the back surface electrode 6 is formed on the back surface to form a solar cell element.

Although the p-type is selected for the Si wafer in this embodiment, the n-type low-concentration impurity layer region and the light-receiving surface p-layer are similarly formed in the n-type Si wafer to form a solar cell element. It is possible.

FIG. 2 shows the oxide film 2 as seen from the light receiving surface (front surface) side.
It is a top view showing the outline of. As shown in this figure, the oxide film 2 has regularly minute openings 7. Oxide film 2
The amorphous (amorphous) Si film formed above is crystallized by annealing and gradually grows on the surrounding oxide film 2 from the opening 7 using the crystallinity of the p-type Si wafer 1 as a seed. Then, the crystal growth is stopped by coming into contact with the crystal part grown from the adjacent opening 7, and the p-type impurity low concentration layer region 3 having the regular and square grain boundaries 8 is formed.

As described above, the amorphous Si film is formed through the oxide film 2 having the regularly formed openings 7 provided on the Si wafer 1 and is annealed to form a regular grain size. It is possible to form the p-type impurity low-concentration layer region 3 having a large area. This region is close to the light-receiving surface and has the largest amount of light absorption. By reducing the impurity concentration and improving the lifetime, the output of the solar cell element is greatly improved. Further, by increasing the concentration of impurities (boron) in the p-type Si wafer 1 to reduce the resistance, it is possible to reduce the series resistance of the solar cell element and further improve the output. Further, since the above process is performed at a relatively low temperature, it is possible to prevent deterioration of crystallinity due to thermal strain.

Next, with reference to FIG. 3, a method of manufacturing the solar cell element of this embodiment will be specifically described. First, as shown in (b), the surface of the p-type Si wafer 1 having a specific resistance range of about 0.05 to 1.0 Ω · cm doped with B (boron) at a high concentration as shown in (a) is shown in (b). Oxide film (Si
O ₂ ) 2 is formed to a thickness of about 400 nm. Next, as shown in (c), the oxide film 2 is processed by photolithography to form openings 7 of 3 μm square at 15 μm intervals. Next, as shown in (d), SiH ₄ (monosilane) gas containing a trace amount of B ₂ H ₆ (diborane) was added to
The p-type amorphous Si film 11 having a film thickness of about 5 μm is formed by decomposition and deposition by the plasma CVD method. By annealing this film 11 at 600 ° C., the Si wafer (crystal part) existing in the opening 7 of the oxide film 2 is used as a seed to grow epitaxially while dehydrogenating, and as shown in FIG. A p-type impurity low-concentration layer region 3 having uniform and regular crystal grains with a grain size of about 15 μm is formed in accordance with 15 μm.

Subsequently, a p ⁺ layer (not shown) heavily doped with B (boron) is formed on the back surface side, and P (phosphorus) is formed on the light receiving surface (p-type impurity low concentration layer region 3). After forming a heavily doped n layer 4 and subsequently forming an antireflection film (not shown) made of TiO ₂ , a front surface comb electrode 5 and a back surface electrode 6 are formed by silver paste screen printing. The solar cell element shown in FIG. 1 was completed.

Next, a second embodiment of the present invention will be described. In this embodiment, an oxide film (SiO ₂ ) 2 is formed on the surface of the p-type Si wafer 1 similar to that of the first embodiment to a thickness of about 400 nm. Next, the oxide film 2 is processed by photolithography to form openings 7 having a square shape of 3 μm at intervals of 30 μm. Next, S containing a small amount of B ₂ H ₆
iH ₄ gas is decomposed and deposited by the plasma CVD method,
A p-type amorphous Si film 11 having a film thickness of about 5 μm is formed. By annealing this film 11 at 600 ° C.,
Si wafer existing in opening 7 of oxide film 2 (crystal part)
Using as a seed, epitaxial growth is performed while dehydrogenating to form a p-type impurity low-concentration layer region 3 having uniform and regular crystal grains with a grain size of about 30 μm in accordance with an opening interval of 30 μm. Subsequently, the same processing as in Example 1 was performed to complete the solar cell element.

Next, a third embodiment of the present invention will be described. A solar cell element may employ a textured structure in which pyramid-shaped irregularities are formed on the entire surface in order to reduce surface reflection of incident light and improve output. In this example, the present invention is applied to a solar cell element having this texture structure.

FIG. 4 is a sectional view of the solar cell element of this embodiment. In the regular texture structure using the photolithography process, as shown in FIG. 5, an oxide film 2 is formed on a p-type Si wafer 1, and an opening is formed in the center of the wall surface of the pyramid with respect to this oxide film 2. Form 7. Then, an amorphous Si film is formed on the oxide film 2 and annealed to gradually grow crystals on the surrounding oxide film 2 using the crystallinity of the p-type wafer 1 as a seed. Then, the crystal growth is stopped by coming into contact with the crystal part grown from the adjacent opening 7, and the p-type impurity low concentration layer region 3 having the regular and triangular grain boundaries 8 is formed. Other configurations are similar to those of the first embodiment.

As described above, the S having the texture structure is formed.
Also in the i-wafer 1, it is possible to form the p-type impurity low-concentration layer region 3 having a regular and large grain size, and it is possible to greatly improve the output similarly to the solar cell element having the structure of FIG. .

Next, the method for manufacturing the solar cell element of this embodiment will be specifically described. In the present embodiment, a uniform pyramid-shaped texture structure having a base of 20 μm and a regular square pyramid is formed on the p-type Si wafer 1 similar to the first embodiment by using a photolithography process and an alkali selective etching method. The oxide film 2 is formed here with a thickness of about 400 nm. Next, as shown in FIG. 5, triangular openings 7 having a side length of 3 μm are processed and formed at intervals of 10 μm on the oxide film 2 by a photolithography process. Next, B ₂ H
SiH ₄ gas containing a small amount of ₆ is decomposed and deposited by a plasma CVD method to form a p-type amorphous Si film 11 having a film thickness of about 5 μm. By annealing this film 11 at 600 ° C., the Si existing in the opening 7 of the oxide film 2
A p-type impurity low-concentration layer region 3 having uniform and regular crystal grains with a gap between openings of 10 μm and a grain size of about 10 μm in accordance with the square pyramid shape of the texture structure is epitaxially grown using a wafer (crystal portion) as a seed.
To form. Then, the same processing as in the first embodiment is performed,
The solar cell element was completed.

Table 1 shows the device structure having the p-type impurity low concentration layer region in the first to third embodiments and the device structure of the conventional example not having the region, and the output characteristics are also compared. It is a thing.

[0024]

[Table 1] As can be seen from Table 1, in the conventional example, the substrate specific resistance varies from 2.0 Ω · cm in the conventional example 1 to 0.
The output characteristic was greatly reduced from 1.33 W to 1.08 W by reducing the voltage to 08 Ω · cm. However, in the first embodiment of the present invention, by providing the impurity low concentration layer region, conversely, the output characteristics are improved to 1.48 W. Furthermore, in the second embodiment in which the particle size is expanded, 1.52 W
The output characteristics were further improved, and the effectiveness of the present invention was confirmed. It was also confirmed that in the third example in which the texture structure was formed on the substrate, the output characteristics were greatly improved to 1.75W.

[0025]

As described above, according to the present invention, an intermediate layer having a minute opening is provided between the single crystal silicon substrate and the non-single crystal silicon layer, and the non-single layer is opened from the opening of the intermediate layer. Since the crystalline silicon is allowed to grow into crystals, it is possible to form an impurity low-concentration layer having a large crystal grain size on the light-receiving surface side, and it is possible to improve the output characteristics of the solar cell element.

[Brief description of drawings]

FIG. 1 is a sectional view of a solar cell element according to a first embodiment of the present invention.

FIG. 2 is a plan view showing an oxide film in FIG.

FIG. 3 is an explanatory view showing a method for manufacturing the solar cell element of FIG.

FIG. 4 is a sectional view of a solar cell element according to a third embodiment of the present invention.

5 is a perspective view showing an oxide film in FIG.

[Explanation of symbols]

 1 p-type Si wafer 2 oxide film 3 p-type impurity low-concentration layer region 4 light-receiving surface n layer 5 front surface comb-type electrode 6 back electrode 7 opening 8 crystal grain boundary

Claims (1)

[Claims] 1. A solar cell element using a substrate in which a non-single-crystal silicon layer having a low impurity concentration is formed on a light-receiving surface side of a single-crystal silicon substrate, and the non-single-crystal silicon layer is crystal-grown. An intermediate layer having a minute opening is provided between the substrate and the non-single crystal silicon layer, and the single crystal silicon substrate is provided through the opening so that the non-single crystal silicon grows through the opening. A solar cell element, which is in contact with a non-single crystal silicon layer.