JPH08181342A - Solar cell - Google Patents

Abstract

PURPOSE: To make it possible to use effectively light incident on a semiconductor layer by installing a semiconductor layer having a semiconductor junction part on the front surface or the rear surface of a white-colored ceramic board which forms a large number of Via holes and installing an electrode on both the front and rear surfaces of the semiconductor layer. CONSTITUTION: On a light receiving surface side of a semiconductor layer 2 there are installed a light receiving surface electrode 3 which is made of silver (g), for example and a reflection preventive film 6 which comprises a nitriding silicon film, for example on the rear surface side of the semiconductor layer 2. On the rear surface side of the semiconductor layer 2, there is installed a silver-made rear surface electrode 4, to which aluminum is added, for example. Since a white colored-ceramic board 1 is used so as to support the semiconductor layer 2, almost all light penetrating the semiconductor layer 2 is not being absorbed in the white colored ceramic board 1, and it is reflected on the surface of the white colored ceramic board 1 and returns to the semiconductor layer 2 once again. It is, therefore, possible to use effectively the light which enters the semiconductor layer 2 in this solar cell, thereby producing a highly efficient solar cell.

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, and more particularly to a solar cell element provided with a semiconductor layer having a semiconductor junction on a white ceramic substrate.

[0002]

2. Description of the Related Art Recently, in order to obtain an inexpensive and highly efficient solar cell element, for example, a solar cell element having a monocrystalline or polycrystalline semiconductor layer formed on a ceramic substrate has been proposed.

Single crystal or polycrystalline semiconductor layers are formed by CVD.
Method, liquid phase growth method, solid phase growth method, or the like. Of these, the CVD method and the solid phase growth method can use a glass substrate because they can form a film at a low temperature, but the obtained crystal is of poor quality and a highly efficient solar cell element cannot be obtained.

On the other hand, according to the liquid phase growth method, a high quality semiconductor film can be obtained, and a highly efficient solar cell element can be expected.
A high melting point material such as ceramic must be used as the substrate.

For example, as a solar cell element using a ceramic substrate, a solar cell element as shown in FIG. 6 has been reported (for example, see 23rd IEEE PVSC, 1993. P214). In the solar cell element shown in FIG. 6, reference numeral 11 denotes a ceramic substrate which is formed by molding with a tape molding method and then firing.
Reference numeral 2 is a semiconductor layer formed on the ceramic substrate 11 and made of polycrystalline silicon or the like.

The semiconductor layer 12 is composed of a layer 12a containing p-type impurities and a layer 12b containing n-type impurities. Further, the semiconductor layer 12 is separated into small sections by the groove 13, and the adjacent semiconductors 12 include the layer 12a containing the p-type impurity and the layer 12 containing the n-type impurity.
b are connected by the connecting member 14. A barrier layer 15 for preventing impurities from being mixed into the semiconductor layer 12 from the ceramic substrate 11 is provided on the ceramic substrate 11. The barrier layer 15 is formed of, for example, a metal oxide.

[0007]

However, in this conventional solar cell element, the semiconductor layer 12 is formed on the ceramic substrate 11.
Although the above is divided into small sections, the pitch of this groove portion has an important influence on the characteristics. That is, if the pitch is narrowed to increase the contact area in order to reduce the series resistance, the short-circuit current is reduced due to the reduction of the photovoltaic region, which causes a problem that the characteristics are degraded.

As shown in FIG. 7, the p-layer side electrode 17 is formed on the surface of the ceramic substrate 11, and the semiconductor layer 12 having a semiconductor junction portion on the p-layer side electrode 17 and the light receiving surface side. Although it is possible to sequentially form the electrodes 16, if the electrode 17 on the p-layer side is formed before forming the semiconductor layer 12, the semiconductor layer 12 must be formed by a low temperature process such as a CVD method, which results in high efficiency. It is impossible to obtain a good solar cell element.

Further, as shown in FIG. 8, a conductive substrate 11 such as a semiconductor or a conductive ceramic is used as the substrate 11, and a liquid crystal growth method capable of obtaining a good quality semiconductor layer on the conductive substrate 11 is obtained. It is conceivable that the semiconductor layer 12 is formed and the electrodes 16 and 17 are formed on the back surface side of the conductive substrate 11 and on the semiconductor layer 12.
Exhibits a black color, has a low reflectance and absorbs light that has entered the semiconductor layer 12, and the utilization rate of light is poor, so that a highly efficient solar cell element cannot be obtained and the substrate 1
When a semiconductor substrate is used as No. 1, there is a problem that it becomes expensive.

[0010]

SUMMARY OF THE INVENTION The present invention has been invented in view of the above problems of the prior art, and an object of the present invention is to provide a highly efficient and inexpensive solar cell element.

[0011]

In order to achieve the above object, in the solar cell element according to claim 1, a semiconductor junction is formed from the front surface or the front surface to the back surface of a white ceramic substrate in which a large number of through holes are formed. Is provided, and electrodes are provided on the front and back surfaces of the semiconductor layer.

Further, in the solar cell element according to the second aspect, a semiconductor layer having a semiconductor junction is provided on the surface of the white ceramic substrate having a large number of through holes, and the light receiving surface is provided on the surface side of the semiconductor layer. An electrode is provided, and a back electrode is provided in the through hole portion of the white ceramic substrate.

[0013]

With the above structure, a white ceramic substrate which is inexpensive and has a large reflectance can be used as the substrate for forming the semiconductor layer. Further, with the above configuration, since the electrode can be formed after the semiconductor layer is formed, the semiconductor layer can be formed by liquid phase growth to obtain a high quality semiconductor layer, and a white ceramic substrate having a large reflectance is used. It is possible to obtain a highly efficient solar cell.

[0014]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing an embodiment of the solar cell element according to the invention described in claim 1, 1 is a white ceramic substrate, 2 is a semiconductor layer, 3 is a light receiving surface electrode, and 4 is a back surface electrode. .

The white ceramic substrate 1 is formed in a thin plate shape, and has a through hole 1a which is communicated from the front surface side to the back surface side over substantially the entire surface. This ceramic substrate 1
It is only for maintaining the semiconductor layer 2 in a predetermined shape, and has a thickness of, for example, about 1 to several mm. Through hole 1
In consideration of carrier movement in the semiconductor layer 2, a is provided so as to correspond to, for example, about 1 to 8% of the total area. Further, in consideration of carrier movement in the semiconductor layer 2, the layers are provided at a pitch of, for example, several tens μm to several hundreds μm.

The white ceramic substrate 1 is composed of, for example, a ceramic substrate containing alumina (Al ₂ O ₃ ) as a main component. That is, with alumina as the main component,
The ceramic substrate 1 contains a small amount of a sintering aid such as silica (SiO ₂ ), magnesia (MgO), and calcia (CaO). Such a thin plate-shaped white ceramic substrate 1 is formed into a thin plate-shaped molding die by, for example, a pressure molding method or a tape molding method, and then 1400 to 150
It is formed by sintering at about 0 ° C.

When the green body is formed by the pressure molding method,
The through holes 1a are formed at the same time as the pressure molding, and when formed by the tape molding method, the through holes 1a are formed after being molded into a tape shape. A white ceramic substrate 1 composed mainly of alumina, for example 3000 Kg / cm ² of about flexural ^{strength, 3.8 × 10 6 Kg / cm} 2 of about Young's modulus, and 10 ¹⁴ Ω · cm or more volume Have resistance.

A semiconductor layer 2 is formed on the surface of the white ceramic substrate 1. Further, the semiconductor layer 2 is formed so that the semiconductor material is filled also in the through hole 1a portion of the white ceramic substrate 1. The semiconductor layer 2 is made of, for example, polycrystalline silicon or the like, and is formed by a liquid phase growth method or the like. That is, the white ceramic substrate 1 is dipped in a melt of silicon and gradually cooled while being pulled up to form the semiconductor layer 2 in which the semiconductor material is also filled in the through holes 1a. In this case, p-type impurities such as boron (B) are contained in the molten silicon. Such a semiconductor layer 2 is formed to have a thickness of, for example, about 5 to 100 μm.

On the light-receiving surface side of the semiconductor layer 2, an n layer 2a containing an n-type impurity such as phosphorus (P) is formed with a thickness of about 0.3 to 1 μm. Further, on the back surface side of the semiconductor layer 2,
P ⁺ layer 2b containing a large amount of p-type impurities is formed.

The n layer 2a containing n-type impurities diffuses phosphorus (P) to a depth of 0.3 to 1 μm in the semiconductor layer 2 by a gas phase reaction using phosphorus oxychloride (POCl ₃ ) as a diffusion source. It is formed by Also, p ⁺ layer 2
b is formed by diffusing aluminum to a depth of 1 to 10 μm in the semiconductor layer 2 by applying a metal paste containing aluminum powder as a main component to the back surface side of the semiconductor layer 2 and baking it.

On the light-receiving surface side of the semiconductor layer 2, for example, silver (A
g) and the anti-reflection film 5 made of, for example, a silicon nitride film, and the back surface electrode 4 made of, for example, silver doped with aluminum is provided on the back surface side of the semiconductor layer 2. Is provided. The back surface electrode 4 may be provided not only on the p ⁺ layer portion but also on the entire back surface side of the white ceramic substrate 1.

The state of current collection in the solar cell element is shown in FIG. When the light incident from the light-receiving surface side reaches the pn junction (semiconductor junction), an electron-hole pair is generated, reaches the depletion layer region without recombination, and is attracted to a strong electric field, so that the electron is n layer. 2a and holes flow into the p-layer 2b. At this time, if the light-receiving surface electrode 3 and the back surface electrode 4 are short-circuited, the n-layer 2
The electrons flowing into a reach the light-receiving surface electrode 3, and the holes flowing into the p layer 2 reach the back surface electrode 4 via the through hole 1a formed in the ceramic substrate 1 of the semiconductor layer 2 and the p ⁺ layer. Then
A photocurrent proportional to the amount of incident light flows through an external circuit (not shown).

FIG. 3 is a diagram showing how light is confined in the solar cell element according to the present invention.

The solar cell element according to the present invention comprises a semiconductor layer 2
Since the white ceramic substrate 1 is used as a substrate for supporting the light, most of the light that has entered the semiconductor layer 2 is not absorbed by the white ceramic substrate 1 and the surface of the white ceramic substrate 1 is not absorbed. The semiconductor layer 2 is reflected again
Return to inside. Therefore, in the solar cell element of the present invention, the light incident on the semiconductor layer can be effectively used, and the solar cell element has high efficiency.

A transparent insulating film made of, for example, a silicon nitride film or a silicon dioxide film may be inserted between the ceramic substrate 1 and the semiconductor layer 2. In this way, when the transparent insulating film is inserted between the ceramic substrate 1 and the semiconductor layer 2, the reflectance at the bottom portion of the semiconductor layer 2 can be increased, and light can be more effectively confined.

FIG. 4 is a diagram showing another embodiment. This embodiment is similar to the previous embodiment in that a large number of through holes 1a are formed in the white ceramic substrate 1 and the semiconductor layer 2 is formed on the surface of the white ceramic substrate 1, but this embodiment is the same. In the example, the semiconductor layer 2 is provided not only on the front surface side of the white ceramic substrate 1 but also on the back surface side. Therefore, even with the solar cell element according to this example, a highly efficient solar cell element can be obtained as in the previous example, but in this example, the p ⁺ layer 2b is provided on the entire back surface side of the semiconductor layer 2. Therefore, the accuracy of forming the back surface electrode 4 can be increased.

FIG. 5 is a view showing an embodiment of the solar cell element according to the invention described in claim 3.

Also in this solar cell element, a large number of through holes 1a are formed in the white ceramic substrate 1 and the semiconductor layer 2 is formed on the surface of the white ceramic substrate 1, so that the solar cell according to claim 1 is formed. Similar to the battery element, in the present invention, the semiconductor layer 2 is formed only on the front surface side of the white ceramic substrate 1, and the p ⁺ layer 2b is formed in the vicinity of the through hole 1a of the white ceramic substrate 1 to form a transparent layer. The back surface electrode 4 is formed in the hole 1a. Such a solar cell element is formed so that the semiconductor layer is not filled in the through hole 1a portion of the white ceramic substrate 1 by the surface tension of the silicon melt, and aluminum is diffused from this through hole 1a portion to p ⁺ The layer 2b is formed, and the back surface electrode 4 is embedded in the through hole 1a portion of the ceramic substrate 1.

[0029]

As described in detail above, according to the solar cell element described in claim 1, a semiconductor having a semiconductor junction portion from the front surface or the front surface to the back surface of the white ceramic substrate in which a large number of through holes are formed. Since the layers are provided and the electrodes are provided on the front and back surfaces of the semiconductor layer, the light applied to the inside of the semiconductor layer can be effectively utilized, resulting in an inexpensive and highly efficient solar cell element.

Also in the solar cell element according to claim 3, a semiconductor layer having a semiconductor junction is provided on the surface of the white ceramic substrate having a large number of through holes, and the light receiving surface is provided on the surface side of the semiconductor layer. Since the electrode is provided and the back electrode is provided in the through hole portion of the white ceramic substrate, the light applied to the inside of the semiconductor layer can be effectively used, and the solar cell element is inexpensive and highly efficient.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the solar cell element according to claim 1.

FIG. 2 is a diagram showing a state of current collection in the solar cell element according to claim 1.

FIG. 3 is a diagram showing a state of optical confinement in the solar cell element according to claim 1.

FIG. 4 is a cross-sectional view showing another embodiment of the solar cell element according to claim 1.

FIG. 5 is a cross-sectional view showing an embodiment of the solar cell element described in claim 3.

FIG. 6 is a cross-sectional view showing a conventional solar cell element.

FIG. 7 is a cross-sectional view showing another conventional solar cell.

FIG. 8 is a cross-sectional view showing another conventional solar cell.

[Explanation of symbols]

1 ... White ceramic substrate, 2 ... Semiconductor layer, 3
... Light-receiving surface electrode, 4 ... Back surface electrode

Claims (3)

[Claims] 1. A solar cell element comprising a white ceramic substrate on which a large number of through holes are formed, or a semiconductor layer having a semiconductor junction from the front surface to the back surface, and electrodes provided on the front and back surfaces of the semiconductor layer. 2. The solar cell element according to claim 1, wherein a through hole portion of the white ceramic substrate is filled with a semiconductor material forming the semiconductor layer. 3. A semiconductor layer having a semiconductor junction is provided on the surface of a white ceramic substrate on which a large number of through holes are formed,
A solar cell element comprising a light-receiving surface electrode provided on the front surface side of this semiconductor layer, and a back surface electrode provided at a through hole portion of the white ceramic substrate.