JPH0799776B2 - Method for manufacturing amorphous silicon solar cell - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an amorphous silicon solar cell, and more particularly to a method for manufacturing an amorphous silicon solar cell with high efficiency and high mass productivity. It is a thing.

[Conventional technology]

A solar cell can be illustrated as a typical electronic device utilizing the photovoltaic effect. This solar cell converts solar energy or other light energy into electric energy, and is attracting attention as a clean energy source as part of future energy measures. The above-mentioned energy conversion by a solar cell utilizes the photovoltaic effect, which is one of the basic characteristics of semiconductor heterojunctions, Pn or Pin junctions, Schottky junctions, etc. This is based on the mechanism that electron-hole pairs are generated and are taken out.

Amorphous semiconductors, such as amorphous silicon, can be made thin and have a large area, and have a large degree of freedom in composition.
Since it is possible to control electrical and optical characteristics in a wide range, it has recently attracted attention as a material for various devices. In particular, the absorption coefficient for light near the peak of the solar energy distribution is higher than that of Si crystals, the thin film formation temperature is low, direct film formation from raw materials by glow discharge is possible, and the formation of junctions is easy. It is attracting attention as a battery material.

Designing a photovoltaic element typified by such a solar cell
What is important in manufacturing is to thoroughly study the selection and combination of materials that can achieve high photoelectric conversion efficiency, and also devise to improve absorption efficiency over a wide wavelength range. Is. This makes it possible to realize a highly efficient and practicable product. Conventionally, amorphous silicon used in this solar cell has a transparent electrode.

Silane (SiH ₄ ) gas or disilane (Si ₂ H ₆ ) gas is used as the main raw material on the glass substrate, and it is produced by plasma decomposition method. 300Å, 1,000-7,000Å, 100-50
It was formed so as to have a thickness of 0Å, and a metal electrode was formed by a vapor deposition method to obtain a solar cell.

[Problems to be solved by the invention]

By the way, in order to obtain a solar cell with high conversion efficiency when forming amorphous silicon by the above-mentioned conventional method, a thick i-type layer is formed at a relatively slow rate of 0.5 to 2Å / sec. It had to be productive and unproductive. Again 10
When the film was deposited at a high speed of Å / sec or more, a solar cell with a high conversion efficiency and a low fill factor and output current was not obtained.

For solar cells, which are regarded as important as part of measures for new energy in the future, cost reduction and high performance are important issues for immediate research and development. Amorphous silicon is attracting attention as a solar cell material that achieves low prices, but it has come to be possible to obtain conversion efficiency that is quite high in terms of performance, but low prices are not yet sufficient. . One possible reason for this is that the above-mentioned film formation rate is low.

The p-i-n amorphous solar cell manufactured by the glow discharge decomposition method has conventionally been formed at a constant film formation rate in the film thickness direction of the i-type layer, for example, 0.1 to 2Å / sec. Therefore, it took about 30 minutes to 2 hours to complete the formation of the i-type film with a thickness of 4,000Å. Also 100% SiH ₄ gas and 100% Si ₂ H ₆
Attempts have been made to perform high-speed film formation of 5 to 100 Å / sec using gas, but the i-type layer in contact with the p-type layer (i at the p / i interface)
When the mold layer is formed at a high speed, the p / i interface characteristics are deteriorated as described above, and a solar cell having good output characteristics has not been obtained.

In the former case, the solar cell manufactured by the above-described two conventional methods has a high conversion efficiency, but on the other hand, it takes a long time to manufacture, which is unproductive. or,
The film formed at a low speed had a large amount of impurities, particularly oxygen atoms, incorporated into the film, and was largely deteriorated by light.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing an amorphous silicon solar cell with high efficiency and high mass productivity.

[Means for solving problems]

According to the present invention, when the i-type layer of the p-i-n type amorphous solar cell is formed, H ₂ is used for forming the i-type layer in contact with the p-type layer.
SiH ₄ gas diluted with is used to form a bulk i-type layer
By using 100% SiH ₄ gas, contact with the p-type layer i
A method for manufacturing an amorphous silicon solar cell, characterized in that film formation is performed at different film forming rates for a mold layer and a bulk i-type layer.

One particularly preferred embodiment of the present invention is the above method wherein the thickness of the i-type layer in contact with the p-type layer is about 30Å to 1000Å. In another particularly preferred embodiment, the film formation rate of the i-type layer in contact with the p-type layer is 0.1Å / sec to 2Å / sec, and the film formation rate of the bulk i-film layer is 2Å / sec to 50Å / s
ec is the above method.

The present invention will be specifically described below with reference to the drawings. FIG. 1 is a cross-sectional view showing the structure of an amorphous silicon solar cell according to the present invention, in which 1 is a glass substrate, 2 is a transparent conductive film, 3 is a p-type amorphous silicon layer, and 4 is a low-speed film forming i. Type amorphous silicon layer (i-type amorphous silicon in contact with p-type layer), 5 is an i-type amorphous silicon layer (bulk i-type amorphous silicon) formed at high speed, and 6 is n-type amorphous silicon The layer 7 represents a metal electrode, and light is incident from the glass substrate 1 side p-
It has an in structure.

When forming the i-type amorphous silicon layers 4 and 5 subsequent to the p-type amorphous silicon layer 3, 30 to 1000 Å, preferably 100 to 500 Å of the i-type layer 4 near the p-i interface is conventionally used. 0.1-2 used to get high conversion efficiency
The film is formed at a low rate of Å / sec, and the i-type bulk layer 5 toward the in-n interface is formed at a high rate of 2 to 50 Å / sec. Especially preferred is 0.5-1.5Å / sec for low-speed film formation and 10-30Å for high-speed film formation.
/ sec can be mentioned.

The low-rate film forming region near the pi interface is not sufficient to maintain high conversion efficiency at 30 Å or less, and 1000 Å does not lead to improvement in productivity. In the present invention, i that is in contact with the p-type layer
SiH ₄ gas diluted with H ₂ is used for low speed film formation of the mold layer, and 100% SiH ₄ gas is used for high speed film formation of the bulk i-type layer thereon to control the film formation speed.

[Operation] By forming the i-type layer in contact with the p-type layer at a low speed, p-
Light generation carrier near the interface (i
An electron-hole pair generated in the mold layer. The larger this amount, the larger the generated current. ) Is trapped, the rate of recombination and carrier disappearance is small, a good interface state can be maintained, and the output current and fill factor of the solar cell characteristics can be kept high, resulting in high conversion efficiency. Since a solar cell can be obtained and the bulk of the i-type layer is formed by high-speed film formation, the film formation cannot be completed in a shorter time than in the past, which is suitable for mass production.

〔Example〕

An amorphous silicon solar cell having the structure shown in FIG. 1 was prepared as follows. A glass substrate 1 having a transparent conductive film 2 which functions as an antireflection film and an electrode is set in a plasma reaction chamber, and a p-type amorphous silicon film 3 is formed by a plasma reaction using a mixed gas of SiH ₄ and B ₂ H ₆ to 120Å. After being deposited to a thickness, i-type amorphous silicon films 4 and 5 were formed using only SiH ₄ gas. As the film forming method, SiH ₄ gas diluted to 10% was used to form the i-type layer 4 at a film forming speed of 1 Å / sec to a thickness of 100 Å, and then the gas was changed to 100% SiH ₄ gas.
An i-type amorphous silicon layer 5 was formed in a thickness of 4500Å using a gas at a film forming rate of 20Å / sec.

Further, subsequently, an n-type amorphous silicon film 6 having a thickness of 500 Å is formed by using a mixed gas of SiH ₄ and PH ₃ , and then Ag is formed as a back surface electrode 7 by a vapor deposition method. An in-type amorphous silicon solar cell was completed (Example).

For comparison, an amorphous silicon solar cell having the cross-sectional view shown in FIG. 2 was prepared in which the i-type amorphous silicon layer was formed at a low speed of 1 Å / sec to a thickness of 4500 Å in the above-mentioned example (comparison). Example A). In addition, in the above-mentioned embodiment, the i-type amorphous silicon layer is formed at a high speed of 20 Å / s.
A comparative example B was prepared by forming a film of ec with a thickness of 4500Å and having a sectional view shown in FIG. The meanings of the reference numerals in FIGS. 2 and 3 are the same as those in FIG.

The output characteristics of the pin type amorphous silicon solar cells obtained in Examples of the present invention and Comparative Examples A and B are shown in the table below.

As is apparent from the table, the present invention provides a highly efficient amorphous silicon solar cell. Although this example and the comparative example A have almost the same characteristics,
In this example, the entire i-type layer can be formed in a time that is 20 times shorter than the time required for forming the i-type layer in the case of Comparative Example A. Therefore, the amorphous silicon having high efficiency and high mass productivity can be formed. Solar cells can be obtained. Comparative example B
Are obviously inferior in their properties.

FIG. 4 shows the light irradiation test results of the amorphous silicon solar cells according to this example and Comparative example A.
Conversion efficiency (η / η) standardized by the initial value (η ₀ ) of conversion efficiency (η) when light is irradiated under the light source of (Air mass one)
₀ %). In FIG. 4, "a" represents this embodiment and "b" represents comparative example A. In the 100-hour test, the conversion efficiency was reduced to 60% in Comparative Example A, but 90% in this Example.
It can be seen that a solar cell having high reliability with respect to light can be manufactured according to the present invention.

〔The invention's effect〕

As described above, according to the present invention, when forming the thickest i-type layer among the layers constituting the amorphous silicon solar cell, the film formation rate of the i-type layer in contact with the p-type layer is set to the i-type layer. By making the deposition rate lower than that in the bulk region, the characteristics of the p / i interface are improved, so an amorphous silicon solar cell with high conversion efficiency can be obtained, and high-speed deposition is performed in the bulk region. Therefore, it is possible to perform mass-production, and it is possible to reduce the cost and improve the reliability of the amorphous silicon solar cell.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of an amorphous silicon solar cell of the present invention, and FIGS. 2 and 3 are sectional views showing the structure of a conventional amorphous silicon solar cell. FIG. 4 is a graph showing the light irradiation test results of the product of the present invention and the conventional product, showing the relationship of the conversion efficiency (η / η ₀ %) with respect to the light irradiation time (hours).

Claims (3)

[Claims] 1. A p-i-n type amorphous solar cell i
For forming the i-type layer in contact with the p-type layer when forming the mold layer,
SiH ₄ gas diluted with H ₂ is used, and 100% SiH ₄ gas is used for film formation of the bulk i-type layer, so that the film formation rate for the i-type layer in contact with the p-type layer and the bulk i-type layer A method of manufacturing an amorphous silicon solar cell, characterized in that the film is formed by changing the temperature. 2. The thickness of the i-type layer in contact with the p-type layer is about 30Å
The method for producing an amorphous silicon solar cell according to claim 1, wherein the amorphous silicon solar cell is from 1000 to 1000Å. 3. The deposition rate of the i-type layer in contact with the p-type layer is 0.
The production of the amorphous silicon solar cell according to claim 1 or 2, wherein the deposition rate of the bulk i-type layer is from 1 Å / sec to 2 Å / sec and from 2 Å / sec to 50 Å / sec. Method.