JPH11189436A - Transparent electrode substrate, its preparation and production of photoelectromotive force element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a transparent electrode substrate having a good textural structure on the surface thereof even when the thickness of a transparent electroconductive film is reduced or under relatively low-temperature conditions. SOLUTION: (a) A crystalline film 2 of a microcrystalline silicon alloy is formed on a light transmitting substrate 1 made of a glass according to a plasma chemical vapor deposition(CVD) method. (b) A transparent electroconductive film 3 consisting essentially of any of tin oxide, zinc oxide and indium oxide is laminated and formed on the crystalline film 2 according to a thermal CVD method to prepare a transparent electrode substrate 4 having a textural structure on the surface thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent electrode substrate formed by forming a transparent conductive film on a transparent substrate, a method of manufacturing the same, and a photovoltaic device using such a transparent electrode substrate. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In a thin-film photovoltaic device having a structure in which light is incident from a substrate side to extract electric energy, a transparent substrate such as tin oxide, zinc oxide or indium oxide is formed on a transparent substrate such as a glass plate. A transparent electrode substrate formed by laminating a conductive film as a light incident side electrode is used. This transparent conductive film is usually formed into a thin film on a translucent substrate by thermal decomposition of a source gas based on a thermal CVD method.

At this time, when a transparent conductive film is formed under certain specific conditions, an uneven shape called a texture structure by crystal grain enlargement can be formed on the surface of the film. This texture structure plays an important role in terms of photoelectric conversion characteristics. In other words, light that has entered from the light-transmitting substrate side is scattered at the interface between the transparent conductive film having the uneven shape and the photoelectric conversion layer, and then enters the photoelectric conversion layer. When the light enters, the substantial optical path of the light is extended to increase the light absorption. As a result, the photoelectric conversion characteristics of the photovoltaic element are improved, and the output current is increased.

FIG. 7 is a configuration diagram of a conventional amorphous silicon photovoltaic device using a transparent electrode substrate having such a texture structure. In FIG. 7, reference numeral 31 denotes a light-transmitting substrate made of glass, and SnO ₂ :
F transparent conductive film 33 (thickness: 10000 °), p-type amorphous silicon layer 34, i-type amorphous silicon layer 35 and n-type amorphous silicon layer 36 constituting the photoelectric conversion layer, and the back surface of Ag The electrode films 37 are stacked in this order.

Next, a procedure for manufacturing a conventional amorphous silicon photovoltaic device having such a configuration will be described. Thermal CV
According to the D method, at a substrate temperature of 500 to 600 ° C., S
nCl ₄ gas, F type dopant gas such as HF, H ₂ O,
A gas such as O ₂ is used as a raw material gas, and a thermal decomposition and a chemical decomposition of the gas are performed on the light transmitting substrate 31 made of glass.
SnO ₂ : F film (transparent conductive film 33) having a thickness of 10,000
Deposit about 成膜. At this time, by adjusting the forming conditions, a texture structure can be obtained on the surface of the SnO ₂ : F film (transparent conductive film 33). Next, the amorphous silicon layers 34, 35 and 36 are laminated on the transparent conductive film 33 in the order of p-type, i-type and n-type by plasma CVD using SiH ₄ gas as a main raw material gas. Then, an Ag film (back surface electrode film 37) is formed thereon by a sputtering method.

A photovoltaic element using a transparent electrode substrate having a texture structure has a higher effective use of light than a photovoltaic element using a transparent electrode substrate having a transparent conductive film having a flat surface. The process of forming a texture structure is an indispensable technique for improving the photoelectric conversion efficiency of a thin-film solar cell that is being put to practical use. However, in order to obtain such a texture structure, a transparent conductive film must be formed under specific conditions as described above,
In particular, optimization of the film thickness is the most important condition.

[0007]

Essentially, the function of the transparent conductive film is to have the optical characteristics of efficiently introducing light into the photoelectric conversion layer as much as possible and the loss of generated current as much as possible. It is important to have an electrical characteristic of taking out to the outside without any change. In consideration of such optical characteristics, it is desirable that the film thickness be as small as possible in order to reduce light loss due to light absorption or the like in the transparent conductive film as much as possible.
On the other hand, in view of such electrical characteristics, it is desirable that the thickness of the transparent conductive film be as large as possible. In order to obtain a good texture structure, a certain film thickness is required. Therefore, the conventional transparent electrode substrate requires a transparent conductive film having a thickness larger than the optimum thickness that can obtain a certain degree of optical characteristics and sufficient electrical characteristics in a portion excluding the texture structure. Was.

The present invention has been made in view of the above-mentioned circumstances, and provides a transparent electrode substrate capable of obtaining a good texture structure on the surface of a transparent conductive film having a small thickness, and a method of manufacturing the same. The purpose is to provide.

Another object of the present invention is to provide a transparent electrode substrate capable of forming a transparent conductive film having a good texture structure at a relatively low temperature, and a method of manufacturing the same.

It is still another object of the present invention to provide a method for manufacturing a photovoltaic element capable of forming a transparent conductive film having a good texture structure and improving photoelectric conversion characteristics.

[0011]

According to a first aspect of the present invention, there is provided a method of manufacturing a transparent electrode substrate, comprising forming a transparent conductive film on a transparent substrate. The method includes a first step of forming a crystalline film thereon and a second step of forming a transparent conductive film on the crystalline film.

According to a second aspect of the present invention, in the method of manufacturing a transparent electrode substrate according to the first aspect, the first step is a step of forming an amorphous film on the translucent substrate; Subjecting the crystalline film to an energy beam irradiation or a heat treatment to crystallize the crystalline film.

A transparent electrode substrate according to a third aspect of the present invention is a transparent electrode substrate comprising a transparent substrate and a transparent conductive film formed thereon, wherein a crystalline film is provided between the transparent substrate and the transparent conductive film. It is characterized by having.

According to a fourth aspect of the present invention, there is provided the transparent electrode substrate according to the third aspect.
, Wherein the crystalline film contains impurities.

According to a fifth aspect of the present invention, there is provided the transparent electrode substrate according to the third aspect.
The thickness of the crystalline film is 50 to 200
Å.

According to a sixth aspect of the present invention, in the method for manufacturing a photovoltaic element, a step of forming a crystalline film on the translucent substrate, and a step of forming a transparent conductive film on the crystalline film. Forming a conductive film, forming an amorphous semiconductor layer on the transparent conductive film, and forming a back electrode on the amorphous semiconductor layer.

FIG. 1 is a view showing the concept of a method for manufacturing a transparent electrode substrate according to the present invention. For example, a crystalline film 2 having crystallinity such as microcrystal, polycrystal, or single crystal is formed on a glass translucent substrate 1. For example, a microcrystalline silicon film is formed as the crystalline film 2 by a plasma CVD method (FIG. 1A). Instead of this, an amorphous film made of, for example, amorphous silicon is formed on the translucent substrate 1, and the amorphous film is irradiated with an energy beam or subjected to a heat treatment to be crystallized. Alternatively, a polycrystalline or single-crystalline crystalline film 2 may be obtained. Any material may be used as the material of the crystalline film 2 as long as it has crystallinity. For example, microcrystalline, polycrystalline, or single crystal made of silicon, silicon nitride, silicon carbide, silicon oxide, or a mixture thereof is used. Is preferred. Further, impurities such as P and B may be added to these materials.

Next, a transparent conductive film 3 containing, for example, any one of tin oxide, zinc oxide and indium oxide as a main component is formed on the crystalline film 2 by, for example, a thermal CVD method. A transparent electrode substrate 4 having a texture structure is manufactured (FIG. 1B). In this case, even when the thickness of the transparent conductive film is reduced as compared with the conventional example in which the transparent conductive film is formed directly on the light-transmitting substrate, a good texture structure can be obtained on the surface.

In the case where a crystalline film is used as a base layer and a transparent conductive film is formed thereon, crystal growth of the transparent conductive film is promoted and a transparent electrode substrate having a good texture structure even with a relatively thin film thickness. Can be produced. Further, since the crystal growth of the transparent conductive film is promoted, a better texture structure can be obtained even at a lower temperature condition (500 ° C. or lower) than in the past.

In order to fabricate such a transparent electrode substrate, an optimal thickness range (50 ° to 200 °) of the crystalline film is required.
Å) exists. If the crystalline film becomes too thick,
The amount of light absorbed by the crystalline film is increased, and the amount of transmitted light is reduced, so that the crystalline film cannot function as a transparent electrode substrate. On the other hand, if the crystalline film is too thin, it is not possible to realize a good texture structure with a thin transparent conductive film.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments.

FIG. 2 is a configuration diagram of an amorphous silicon photovoltaic device using the transparent electrode substrate of the present invention. In FIG. 2, reference numeral 11 denotes a transparent substrate made of glass. Translucent substrate 1
1, a microcrystalline silicon thin film 12 (thickness: about 100
Å), a transparent conductive film 13 of SnO ₂ : F having a texture structure on the surface (thickness: about 5000 Å), a p-type amorphous silicon layer 14 and an i-type amorphous silicon layer 15 constituting a photoelectric conversion layer The n-type amorphous silicon layer 16 and the back electrode film 17 of Ag are laminated in this order.

Next, the procedure for manufacturing the amorphous silicon photovoltaic device of the present invention having such a structure will be described with reference to FIG.
This will be described with reference to FIG. First, a mixed gas obtained by mixing a SiH ₄ gas and a H ₂ gas at a gas flow ratio of SiH ₄ : H ₂ = 1: 200 was used as a raw material gas, and the substrate temperature was 250 ° C. and the RF power was 50 mW / cm ² by plasma CVD. Then, a microcrystalline silicon thin film 12 having a thickness of about 100 ° is formed on the light transmitting substrate 11 made of glass (FIG. 3A).

Next, at a substrate temperature of 400 ° C., an F-based dopant gas such as SnCl ₄ gas, HF, or a gas such as H ₂ O or O ₂ is used as a raw material gas by a thermal CVD method. A SnO ₂ : F film (transparent conductive film 13) having a thickness of about 5000 ° is formed on the microcrystalline silicon thin film 12 by chemical decomposition (FIG. 3B).

Next, using the SiH ₄ gas as a main raw material gas, the respective amorphous silicon layers 14, p-type, i-type and n-type are formed on the transparent conductive film 13 in order of plasma CVD.
15 and 16 are formed by lamination (FIG. 3C). Finally, an Ag film (back electrode film 17) is formed on the n-type amorphous silicon layer 16 by a sputtering method (FIG. 3D).

Hereinafter, the optimum ranges of the thicknesses of the microcrystalline silicon thin film 12 and the transparent conductive film 13 in the transparent electrode substrate of the present invention will be considered.

FIG. 4 shows the haze ratio and total transmittance of the transparent electrode substrate when the thickness of the transparent conductive film 13 is constant (6000 °) and the thickness (horizontal axis) of the microcrystalline silicon thin film 12 is changed. It is a graph which shows the change of (vertical axis). In FIG.
The change in the haze ratio (%) of the transparent electrode substrate is indicated by △, and the change in the total transmittance (%) of the transparent electrode substrate is indicated by ○. The haze ratio (%) representing the degree of the light scattering effect is defined by the following equation (1), and the total transmittance (%) is in the visible region (400 to 700 n).
m).

Haze rate = {(light scattering transmittance) / (total light transmittance)} × 100 (1) where light scattering transmittance: (total transmittance) − (linear transmittance) Total transmittance: transmittance for all transmitted light measured using an integrating sphere

The thickness of the microcrystalline silicon thin film 12 is 200 °
If it exceeds, the total transmittance is too low to function as a transparent electrode substrate. On the other hand, the microcrystalline silicon thin film 12
When the film thickness is less than 50 °, the haze ratio decreases and a sufficient light scattering effect cannot be obtained. Therefore, the optimum range of the thickness of the microcrystalline silicon thin film 12 is 50 ° to 200 °.

FIG. 5 shows the thickness (horizontal axis) of the transparent conductive film 13 with the thickness of the microcrystalline silicon thin film 12 being constant (100 °).
6 is a graph showing a change in the haze ratio and the total transmittance (vertical axis) of the transparent electrode substrate in the case where is changed. Also in FIG. 5, a change in the haze ratio (%) of the transparent electrode substrate is indicated by a triangle, and a change in the total transmittance (%) of the transparent electrode substrate is indicated by a circle.

If the thickness of the transparent conductive film 13 exceeds 8000 °, the total transmittance is so reduced that it cannot function as a transparent electrode substrate. On the other hand, when the thickness of the transparent conductive film 13 is 4
If the thickness is less than 000 °, the haze ratio decreases, and a sufficient light scattering effect cannot be obtained. Therefore, the optimal range of the thickness of the transparent conductive film 13 is 4000 to 8000 °.

Next, the result of comparing the characteristics of the transparent electrode substrate of the present invention (hereinafter, referred to as the present invention) and the conventional transparent electrode substrate (hereinafter, referred to as the conventional example) will be described. In addition,
In both the present invention example and the conventional example, the alkali diffusion preventing film (SiO ₂
A non-alkali glass which does not require a film) is used as the light-transmitting substrate. In the present invention, the microcrystalline silicon thin film and the SnO ₂ : F film (film forming temperature 400
C.), and the conventional example has a configuration in which an SnO ₂ : F film (film formation temperature 550 ° C.) is directly formed on such a translucent substrate.

When the total transmittance of the present invention example and the conventional example was measured and evaluated, it was 85% in the example of the present invention and 80% in the conventional example, and the light transmittance was also obtained by inserting a microcrystalline silicon thin film. Has not deteriorated, but it can be proved that it can be improved.

Further, the haze ratios of the present invention example and the conventional example were measured. A transparent electrode substrate (hereinafter referred to as a comparative example) having a configuration in which a SnO ₂ : F film is directly formed at a film forming temperature of 400 ° C. on a translucent base made of an alkali-free glass similar to the present invention example and the conventional example is used. The haze ratio of this comparative example was also measured. The measurement results of the haze ratio were 17.0%, 16.0%, and 5.0% in the present invention example, the conventional example, and the comparative example, respectively. The example of the present invention has a light scattering effect equal to or more than that of the conventional example.
However, it was proved that a good texture structure equivalent to or higher than that of the conventional example under the high temperature condition (550 ° C.) was obtained. In the comparative example, the haze ratio was extremely low, and the microcrystalline silicon thin film was not inserted.
It is considered that the texture structure could not be formed due to the low temperature condition (400 ° C.).

Next, the electromotive force characteristics of the photovoltaic device of the present invention having the structure shown in FIG. 2 and the conventional photovoltaic device having the structure shown in FIG. 7 were measured. The measurement results are shown in Table 1 below. The measurement conditions for both photovoltaic elements are as follows:
AM 1.5, sun, 100 mW / cm ² , 25 ° C.

[0036]

[Table 1]

As shown in the results of Table 1, it can be seen that the photovoltaic device of the present invention is superior in current value as compared with the conventional photovoltaic device. This is because, despite the relatively thin film thickness of the transparent conductive film in the photovoltaic element of the present invention, a good texture structure can be formed, and a light confinement effect equal to or higher than that of the conventional photovoltaic element can be obtained. It was because he was able to demonstrate.

Hereinafter, another embodiment of the method for producing a transparent electrode substrate of the present invention will be described. FIG. 6 is a diagram showing this manufacturing process. First, an amorphous silicon thin film 21 having a thickness of 50 to 200 ° is formed on a transparent substrate 11 made of glass (FIG. 6A). Next, the amorphous silicon thin film 21 is irradiated with an energy beam such as an excimer laser to be microcrystallized to form a microcrystalline silicon thin film 12 (FIG. 6).
(B)). Next, at a substrate temperature of 400 ° C., a gas such as SnCl ₄ gas, an F-based dopant gas such as HF, or a gas such as H ₂ O or O ₂ is used as a raw material gas by a thermal CVD method. On the microcrystalline silicon thin film 12, SnO ₂ : F having a thickness of 4000-8000 °
A film (transparent conductive film 13) is formed (FIG. 6C).

Also in such an embodiment, it is possible to manufacture a transparent electrode substrate in which a good texture structure is formed on the surface of the transparent conductive film 13. In the above-described example, the amorphous silicon thin film 21 is microcrystallized by irradiation with an energy beam, but may be microcrystallized by a heat treatment.

In the above-described example, a microcrystalline silicon alloy film was used as an underlayer for forming a transparent conductive film. However, even when a polycrystalline silicon alloy film was used, a good texture structure was formed on the surface. Can be formed under a thin-film and low-temperature condition, and P, P is added to these microcrystalline silicon alloys or polycrystalline silicon alloys.
The same effect can be obtained even with a doped film to which an impurity such as B is added.

Examples of such a microcrystalline silicon alloy and a polycrystalline silicon alloy include silicon hydride, silicon nitride,
A single substance of silicon carbide or silicon oxide or a mixture thereof can be used.

Further, in the above example, SnO ₂ as a transparent conductive film: was used the F layer, in addition to SnO _2, Zn
A material containing O or In ₂ O ₃ as a main component may be used.

[0043]

As described above, according to the present invention, a crystalline film is formed on a translucent substrate, and a transparent conductive film is further formed thereon. In addition, a transparent electrode substrate having a good texture structure on the surface of the transparent conductive film can be produced even under low temperature conditions. As described above, a textured transparent conductive film can be formed even under low-temperature conditions, so that it is possible to expand the types of materials that can be used as a light-transmitting substrate, particularly, the types of tempered glass.

Further, by applying such a method for producing a transparent electrode substrate to a method for producing a photovoltaic element, the effect of confining incident light by the texture structure of the transparent conductive film is increased, and the photoelectric conversion characteristics are improved. It is possible to manufacture a photovoltaic element that can achieve the above.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a method for manufacturing a transparent electrode substrate of the present invention.

FIG. 2 is a configuration diagram of a photovoltaic device according to the present invention.

FIG. 3 is a diagram showing steps of a method for manufacturing a photovoltaic device according to the present invention.

FIG. 4 is a graph showing the relationship between the thickness of a microcrystalline silicon thin film and the haze ratio and total transmittance of a transparent electrode substrate.

FIG. 5 is a graph showing the relationship between the thickness of a transparent conductive film and the haze ratio and total transmittance of a transparent electrode substrate.

FIG. 6 is a diagram showing steps of a method for manufacturing a transparent electrode substrate of the present invention.

FIG. 7 is a configuration diagram of a conventional photovoltaic element.

[Explanation of symbols]

 Reference Signs List 1,11 Transparent substrate 2 Crystal film 3,3 Transparent conductive film 4 Transparent electrode substrate 12 Microcrystalline silicon thin film 14 P-type amorphous silicon layer 15 i-type amorphous silicon layer 16 n-type amorphous Silicon layer 17 Back electrode film 21 Amorphous silicon thin film

Claims (6)

[Claims] 1. A method for manufacturing a transparent electrode substrate comprising a transparent conductive film formed on a transparent substrate, a first step of forming a crystalline film on the transparent substrate, and the crystalline film And a second step of forming a transparent conductive film thereon. 2. The method according to claim 1, wherein the first step is a step of forming an amorphous film on the light-transmitting substrate, and the step of irradiating the formed amorphous film with an energy beam or a heat treatment to crystallize the crystal. Forming a conductive film.
The method for producing the transparent electrode substrate described in the above. 3. A transparent electrode substrate formed by forming a transparent conductive film on a transparent substrate, wherein a transparent film is provided between the transparent substrate and the transparent conductive film. Electrode substrate. 4. The transparent electrode substrate according to claim 3, wherein said crystalline film contains impurities. 5. The crystalline film has a thickness of 50 ° to 200 °.
The transparent electrode substrate according to claim 3, wherein 6. A method for manufacturing a photovoltaic device, comprising:
Forming a crystalline film on the transparent substrate, forming a transparent conductive film on the crystalline film, forming an amorphous semiconductor layer on the transparent conductive film, Forming a back electrode on the crystalline semiconductor layer.