JPS6235680A - Amorphous silicon solar battery and manufacture of the same - Google Patents

Abstract

PURPOSE:To improve an open-circuit voltage significantly by a method wherein an n1-layer is made of amorphous Si and an n2-layer contains fine-crystallized silicon and the thickness of the n1-layer is selected to be not less than 60Angstrom and not more than 400Angstrom . CONSTITUTION:An amorphous silicon solar battery is constituted by junctions composed of a substrate 1, a transparent conductive film 2, a p-layer 3, an i-layer 4 and an n1-layer 5 and an n2-layer 6 and by a metal electrode 7. The n1-layer is produced in a material gas such as silane, disilane or silicon fluoride which contains at least one of nitrogen compound such as ammonia, fluorine compound, carbon compound such as methane, oxygen compound or compound such as nitrogen monoxide or carbon monoxide and is practically in an amorphous condition. The silicon source is diluted by 10-60 times with hydrogen. The n2-layer is fine-crystallized by a conventional method. Moreover, the n1-layer is formed to have the thickness of 60-400Angstrom and the n2-layer is formed to have the thickness of 10-80Angstrom .

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an amorphous silicon (hereinafter abbreviated as a-Si) solar cell and a method for manufacturing the same.
Specifically, the present invention relates to a pin type solar cell in which the n-layer is composed of two layers, an a-Si layer and a microcrystalline silicon layer having different electrical conductivities, and a method for manufacturing the solar cell using a plasma CVD method.

(Prior Art) In recent years, solar energy has attracted attention as a clean and limitless energy source, and the development of solar cells for photoelectric conversion of solar energy has been actively promoted.

Ideally, a solar cell would be able to convert 100% of the energy emitted by the sun that can reach the ground into electrical energy, but currently those using a-St have a conversion efficiency of just over 10%. It remains possible to achieve this.

A-S, i' solar cells are made by forming pin junctions on a substrate such as glass, stainless steel, or polyimide through electrodes, and because they can be manufactured with large area and at low cost, they are expected to be used in future solar cells. It is said to be the mainstream.

The open circuit voltage of an a-Si solar cell is such that the bandgap of a-St is 1.7eV and the Fermi level of the Sp layer is 0.3eV.
, and the Fermi level of the n layer is 0.2 eV, so an open circuit voltage of 1.2 .mu. is theoretically supposed to be obtained. However, in reality, the open circuit voltage of an a-Si solar cell has only been measured to be 0.80 to 0.87 V.

As a result of various studies conducted, this difference between the theoretical value and the measured value is thought to be due to the fact that the bonding state at the p/i interface and n/i interface is far from the ideal state and the actual solar cell. It is being

A-Si solar cells are manufactured by glow discharge plasma CVD method, sputtering method, etc., but in these manufacturing methods, high-energy reactive species generated by plasma hit the p/i interface and n/i interface. This is thought to be due to the formation of areas with high density of states at defects and interfaces.

Therefore, mild conditions such as lowering the plasma power are adopted at the p/i interface and the i/n interface. The reason why the open circuit voltage of an actual solar cell is much lower than the ideal is due to the physicochemical differences such as the atomic density of the compounds constituting the p, i, and n layers at the p/i interface and the i/n interface. It is also conceivable that this could cause the occurrence of , or increase the density of states. For this reason, consideration is being given to gradually changing the structure at the joint portion.

Recently, a pin-n type a-Si solar cell has been proposed in which the portion corresponding to the n-layer in the pin type a-Si solar cell is made into two layers.

In order to suppress the drop in open circuit voltage at the i/n interface, the dopant concentration is lowered before forming the n layer to form an a-St n layer.

On the other hand, from a similar point of view, an a-Si solar cell has also been proposed in which a microcrystalline silicon layer different from the n layer is inserted at the n/metal electrode interface (Japanese Patent Laid-Open No. 59-83774).

This involves forming a microcrystalline silicon layer of 608 or more by increasing the glow discharge power after forming the n-layer.
In particular, when metal electrodes are formed by screen printing and firing, contact resistance can be reduced and output power can be increased.

(Problems to be Solved by the Invention) In a conventional pin-n type solar cell, each of the n-layer and the n-layer is composed of a-St, but compared to the pin type, there is less openness at the I/N interface. Although the power drop is improved, n/
The reduction in open-circuit power at the metal electrode interface has still not been overcome.

In addition, among the solar cells that have already been proposed, which consist of two n-layers, one n-layer is made of a-St, and the other n-layer on the metal electrode side is made of microcrystalline silicon, the manufacturing cost is low. There was a problem in that the output power was low even though the power was high. That is, in this type of solar cell, a first n-layer is formed using a plasma CVD method, a second n-layer is formed by increasing the plasma power, and finally a silver paste or the like is screen printed and fired. by n1ili)
A metal electrode is provided on top.

Therefore, not only are relatively expensive raw materials used, but also firing conditions may require high temperatures (e.g., over 600°C), which creates unfavorable atomic states at the interface with the n-layer, resulting in A satisfactory open circuit voltage as a battery cannot be obtained.

(Means for Solving the Problems) The present inventors have conducted extensive research aimed at significantly increasing the open-circuit voltage of a pini solar cell consisting of two n-layers, and have developed a solar cell with high performance. The present invention has been completed by establishing a technology for manufacturing the product at low cost and efficiently.

The present invention provides a solar cell that has a transparent conductive film, a junction consisting of pin layers, and a metal electrode on a substrate, and the n layer is composed of an n1 layer and an n2 layer having different electric type conductivities.
The 01 layer is a-8t, the n2 layer contains microcrystalline silicon, and the thickness of the 01 layer is 60 Å or more and 400 Å or more.
This is a solar cell characterized in that the solar cell has a thickness of Å or less.

The present invention also provides a method for manufacturing a solar cell using a plasma CVD method using glow discharge, in which a transparent conductive film, a p layer and an i layer are sequentially formed on a substrate, and then a
A characterized by forming an I layer, then forming a microcrystalline 02 layer by changing the temperature of the substrate, and finally forming a metal electrode by sputtering or vacuum evaporation.
-It relates to a method for manufacturing a Si solar cell.

The structure of the A-3T solar cell of the present invention is as shown in Part 1.

That is, a substrate (1), a transparent conductive film (2), a p-layer (3),
It is composed of an i layer (4), a junction consisting of an n1 layer (5) and an n2 layer (6), and a metal electrode (7).

The substrate is selected from materials such as glass, thin metal plates such as stainless steel and aluminum, and heat-resistant plastics such as polyimide, with glass being particularly preferred.

The transparent conductive film is mainly composed of tin oxide and/or indium, and contains a small amount of additives, and it is preferable to use tin oxide.

In the p layer, an element of group 1 of the periodic table of elements, such as boron, is stored as a dopant in a-3i.

The i-layer is a-3i with no dopant.

The above-described bonding from the substrate to the i-layer has a conventionally known structure.

The n-layer has a relatively low concentration (0.01-0.1%) in a-5i.
) contains an element from group Ⅰ of the periodic table of elements such as phosphorus as a dopant, and in addition to the dopant, it also contains one or more elements selected from the group of fluorine, nitrogen, oxygen, and carbon as an impurity. be able to. Particularly preferred are nitrogen and/or oxygen. The content of impurities is n
In the case of a single layer, the amount of nitrogen and oxygen is preferably within the range of 0.1 to 5 atomic percent, since microcrystalization is inhibited.

The thickness of the 01 layer is preferably thicker than the 02 layer;
The number of layers or more is preferably 608 to 4008. More preferably, it is 100-300A.

The 02 layer is a microcrystalline silicon layer, which is thinner than the n1 layer and preferably has a thickness of 1008 or less, particularly an IOA of 808 or less.

The metal electrode is a thin layer of a conductive metal abrasive, such as aluminum, and is formed on the 02 layer by sputtering or vacuum deposition in the present invention.

Next, a method for manufacturing the a-Si solar cell of the present invention will be explained.

In the a-3i solar cell of the present invention, the pin junction is manufactured using a plasma CVD apparatus. The plasma CVD apparatus may be any known one, but in order to continuously and stably manufacture each layer of pins, an apparatus is used that has reaction chambers that can be separated by partitions and is configured so that the substrate is transported by a belt conveyor. It is preferable to do so. With this plasma CVD apparatus, a p layer and an i layer are formed on a transparent electrode on a substrate by a known method.

Next, n1+ and n2 layers are formed. nl.

There are two methods for producing the n2 layer, but both are devised so that the n1 layer is an amorphous layer and the 02 layer is a microcrystalline layer.

First, in the first method, the n1 layer contains nitrogen compounds such as ammonia, fluorine compounds, carbon compounds such as methane, oxygen compounds, -compounds such as nitrogen oxide and carbon monoxide in the raw material gas such as silane, disilane, and silicon fluoride. It is manufactured so as to contain any one or more of the following, and is made into a substantially amorphous state. The silicon source is diluted 10-60 times with hydrogen. The 02 layer is microcrystallized by a conventionally known method. Furthermore, the n1 layer is 60 to 400A.

The n2 layer is prepared to have a thickness of 10 to 808. The power density is 0.05~0, 4W/cd is adopted.

In the second method, the raw material gas compositions of the n1 layer and the 02 layer are the same, but the substrate temperature during the n1 fabrication is set to 180 to 220° C., and crystallization is suppressed by controlling the substrate temperature. At the time of 02 production? The temperature is set at 220 to 250°C to form microcrystals. These utilize the characteristic that microcrystalization does not occur when the U plate temperature is low. In this case as well, the n1 layer is made to have 60 to 300 A, and the n2 layer is made to have 10 to 80 people. This change in substrate temperature may be rapid or may be changed gradually over time. Although the 02 layer can be manufactured by changing the plasma power, a better quality N2 layer can be formed by changing the substrate temperature without changing the plasma power. Is the thickness of the n2 layer thinner than the n'1 layer?<100A or less,
In particular, the plasma conditions are set to be in the range of 108 to 80^.

After forming the pin junction in this way, a metal electrode is finally formed. Metal electrodes are usually formed by sputtering or vacuum evaporation.

A metal such as aluminum or silver is selected as the raw material, and a thin film is formed on the 02 layer under known conditions.

Another known method for forming metal electrodes is to use screen printing and firing, but if the firing temperature is high, defects may occur in the contact area with the N2 layer. However, the low temperature method using silver epoxy paste is economically problematic.

(Function) The reason why the a-8′> solar cell having the ptnln2 structure of the present invention exhibits a high open circuit voltage is not completely clear, but it can be roughly considered as follows.

First, in the A-3T solar cell of the present invention, since the i layer is an amorphous layer and the 01 layer is also an amorphous layer,
The i/n1 interface has good consistency, and the generation of interface states can be reduced.

In addition, the n2 layer is microcrystalline, and the electrical conductivity is n2
The layer is higher than the 01 layer. This means that the position of the Fermi level is 0.2 eV in the 01 layer and 0.2 eV in the n2 layer. l
This is because it is less than eV. In other words, by utilizing this n2 layer, the open circuit voltage can be improved.

However, in a p/i/n2 type solar cell without the 01 layer,
The matching of the L/n2 interface is poor, the open circuit voltage is not improved, and the effect of the n2 layer cannot be fully utilized unless the structure of the present invention is adopted.

Furthermore, regarding the film thicknesses of the 01 and 02 layers, if the n2 layer is made thicker, the leakage current may increase. In order to prevent this, it is desirable that the thickness of the n2 layer be 10 to 80A, and in this case, the thickness of the 01 layer should be 60 to 40A.
08 is preferable.

Furthermore, in the a-Si solar cell of the present invention, since the n2 layer is made of microcrystalline silicon, it is thought that the electrical conductivity is high at the n2/metal electrode interface.

In addition, as in the present invention, a solar cell with good performance can be obtained by forming the N1 layer by plasma CVD and then changing the temperature of the substrate to form the O2 layer. Since the crystal state of microcrystalline silicon is better than that of n 1 / n 2
It is thought that the bonding condition at the interface and the n2/metal interface is improved.

Example 1 After forming a 5n02 transparent conductive film, p layer and i layer on a glass substrate, an a-3i layer of about 2008 was formed as an 01 layer at low power, and then microcrystalline silicon was formed as an n2 layer at high power. A layer of approximately 60A was deposited. As a result, the open circuit voltage is
The voltage was improved to 0.88 V.

Example 2 An a-8i layer was formed as the 01 layer at a substrate temperature of 200°C, and a crystallized silicon layer was formed as the n2 layer at a substrate temperature of 250°C. As a result, an open circuit voltage of 0.89 V was obtained. In this case, the same effect was obtained even when the substrate temperature was continuously raised from 200 to 250°C.

Example 3 A solar cell was manufactured by the method of Example 2 using the raw material gases shown in the following table.

As an impurity, N from NH3 is mixed into the film. X
Linear diffraction revealed that the 01 layer was not microcrystalline, and the N2 layer was microcrystallized. The solar cell using this n1 layer and n2 layer had an open circuit voltage GJ (l V. Also, F
Similar results were obtained using , Co, and NO.

Example 4 TI (nt layer strength), T2 (n2 layer strength)
The sum of 71 + T2 - 200 people (Thus, we looked at the thickness dependence. The fabrication of the 01 and 12 layers is the same as in Example 2. When 40 < 72 < TI, a high open circuit voltage can be obtained. This can be seen from the table.

(Effects of the Invention) The a-3i solar cell of the present invention is a high-performance solar cell that exhibits a significantly improved open circuit voltage than conventional solar cells. Further, according to the plasma CVD method of the present invention, high performance solar cells can be produced stably and efficiently, so the present invention is extremely useful industrially.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram illustrating the structure of the solar cell of the present invention.

Claims (1)

[Claims] 1) In an amorphous silicon solar cell having a transparent conductive film, a junction consisting of pin layers, and a metal electrode on a substrate, and the n layer consisting of two layers, an n1 layer and an n2 layer, An amorphous silicon solar cell characterized in that the n1 layer is amorphous silicon, the n2 layer is amorphous silicon containing microcrystallized silicon, and the thickness of the n1 layer is 60 Å or more and 400 Å or less. 2) Fluorine, nitrogen,
The solar cell according to claim 1, which contains one or more impurities selected from the group of oxygen and carbon. 3) In a method of manufacturing an amorphous silicon solar cell by a plasma CVD method using glow discharge, after forming a transparent conductive film, a p-layer and an i-layer of amorphous silicon on a substrate, an n1 layer of amorphous silicon is formed, and then the substrate A method for producing an amorphous silicon solar cell, which comprises forming an N2 layer of amorphous silicon at least partially microcrystallized by changing the temperature of the amorphous silicon, and finally forming a metal electrode by sputtering or vacuum evaporation.