JP2001015787A - Substrate with transparent conductive film, manufacturing method therefor, and solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a substrate with a transparent conductive film, having an uneven surface structure that can be manufactured using a sputtering method and is rich in productivity by laminating a zinc-oxide system transparent conductive film which is in contact with a titanium oxide film formed on a substrate. SOLUTION: A titanium oxide film is nearly a flat film without special, large uneven structures. The titanium oxide film affects the crystal growth of the zinc-oxide system transparent conductive film laminated on it, hence crystal growth is accelerated, and a zinc oxide crystal of large crystal grains is grown. The surface of the zinc-oxide system transparent conductive film becomes uneven due to the crystal grains. The crystal is orientated nearly vertical with respect to the substrate surface, and the crystal orientation is aligned, thus obtaining a recess and projection in nearly aligned shape. The zinc-oxide system transparent conductive film has roof-shaped uneven shape and is suited for the surface electrode of a solar battery and has high optical confinement effect. As a result, reliability of a solar cell using the substrate with the zinc-oxide system transparent conductive film is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a substrate with a transparent conductive film, a method for producing the same, and a solar cell.

[0002]

2. Description of the Related Art As a transparent conductive film for an amorphous silicon solar cell, a tin oxide-based film (for example, F-doped SnO ₂ ) or an indium oxide-based film (for example, Sn-doped In ₂
O ₃ ) has been put to practical use. On the other hand, in recent years, zinc oxide-based films, which are inexpensive materials, have attracted attention. It is said that the transparent conductive film for an amorphous silicon solar cell preferably has high transparency, high conductivity, and a surface unevenness structure for effectively utilizing sunlight. The conversion efficiency of the solar cell can be improved by the light confinement effect by the surface uneven structure.

In general, an amorphous silicon solar cell has a structure in which a transparent electrode on a glass substrate is provided with irregularities and light is incident from the substrate side (the side opposite to the transparent electrode) to exhibit a light confinement effect. I have. As a method of forming the uneven film, a tin oxide-based film is formed by using tin tetrachloride (SnCl ₄ ) or tetramethyltin (Sn (CH ₃ ) ₄ ) as a raw material,
It is formed by a VD method or a spray method. For a zinc oxide-based film, an MOCVD (organic metal chemical vapor deposition) method using diethyl zinc (Zn (C ₂ H ₅ ) ₂ ) and water as raw materials has been developed (The Technical Digest of the 5th Interna).
nation Photovoltaic Science and Engineering Confer
ence (1990) 1032).

In recent years, as the demand for a larger area of a solar cell has increased, a uniform film thickness and film quality can be easily obtained even in a large area, and a film can be formed at a relatively low temperature. Attention has been paid to the sputtering method.
For a zinc oxide-based film, a method of forming an uneven film by increasing the sputtering gas pressure has been proposed (JP-A-6-57410). However, in this method, it is necessary to set the sputtering pressure higher than the normal sputtering pressure (0.06 to 1.4 Pa), so that the film forming rate is low, the productivity is low, and the method is not practical.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and provides a substrate with a transparent conductive film having a surface irregularity structure, which can be formed at high speed by a sputtering method and has high productivity. And a method of manufacturing the same and a solar cell using the substrate with a transparent conductive film.

[0006]

According to the present invention, there is provided a transparent conductive material mainly composed of zinc oxide which is in contact with a film mainly composed of titanium oxide (hereinafter simply referred to as a titanium oxide film) formed on a substrate. Provided is a method for manufacturing a substrate with a transparent conductive film, which laminates a film (hereinafter, simply referred to as a zinc oxide-based transparent conductive film). The present invention also provides a substrate with a transparent conductive film in which a zinc oxide-based transparent conductive film is laminated on a titanium oxide film formed on the substrate.

[0007] The zinc oxide-based transparent conductive film of the present invention comprises:
The surface has an uneven structure. As the surface unevenness state,
Arithmetic mean roughness R _a as defined in JIS B0601 is 1
It is preferably from 5 to 150 nm. If it is smaller than 15 nm, the light confinement effect tends to be low. Also 15
If it is larger than 0 nm, the unevenness is too coarse, and the thickness of the photoelectric conversion layer (for example, an amorphous silicon layer) formed on the film becomes uneven, or a portion where the photoelectric conversion layer is not formed, and the efficiency of the battery is reduced. It tends to decrease.

Examples of the zinc oxide-based transparent conductive film include a film obtained by doping ZnO with another component (for example, at least one selected from the group consisting of B, Al, Ga, In, Si and Ti) as a dopant. Can be Particularly, from the viewpoint of conductivity, the dopant is preferably Ga or Al, particularly Ga. The content ratio of the dopant in the transparent conductive film is preferably such that the total amount of the dopant with respect to the total amount of the dopant and zinc (Zn) is 0.01 to 10 atomic%. Particularly, from the viewpoint of conductivity, the content is preferably 0.2 to 8 atomic%, more preferably 0.3 to 7 atomic%.

The thickness of the zinc oxide-based transparent conductive film is 100 to 3
000 nm is preferred. If it is thinner than 100 nm, the uneven structure is less likely to appear. On the other hand, if the thickness exceeds 3000 nm, it takes a long time to form a film, which is not practical. In particular, the film thickness is 100
It is preferably from 1000 to 1000 nm. As the form of the zinc oxide-based transparent conductive film, a continuous film (a film having a film thickness that is considered to be apparently continuous from an electron microscope) is used.
It is preferable that

The titanium oxide film of the present invention has a high conversion efficiency.
From the viewpoint of obtaining a solar cell with high
That is, it is a transparent film having an extinction coefficient of 0.1 or less, particularly almost 0.
Is preferred. For example, TiO_TwoFilm and TiO_TwoBeside
Another component of the crab (eg SiO 2 _Two, Al_TwoO_Three, Fe_TwoO_Three)
And the like. Thickness of titanium oxide film
Is preferably 0.5 to 200 nm. Thinner than 0.5 nm
And the uneven structure of the zinc oxide-based transparent conductive film hardly appears. Ma
If it exceeds 200 nm, it takes a long time to form a film and it is practical.
Absent. In particular, the thickness is preferably 1 to 10 nm. Oxidation
The form of the titanium film can be either a continuous film or a discontinuous film.
Is also good.

The substrate with a transparent conductive film of the present invention is produced, for example, as follows. On a glass substrate, a TiO ₂ film is formed in a thickness of 0.5 to 200 nm (the film thickness is a geometric film thickness, and the same applies hereinafter) using a Ti target by an oxidation reactive sputtering method. Then, sputtering is performed in an argon gas using a conductive oxide target containing zinc oxide as a main component to form a zinc oxide-based transparent conductive film in contact with the TiO ₂ film. .

The titanium oxide film is formed on an oxide target (Ti
A film can also be formed using O ₂ or TiO _2-x (1 <x <2). TiO ₂ targets are limited to radio frequency (RF) sputtering because they are not conductive. TiO _2-x (1 <x <
2) Direct current (DC) because the target has conductivity
It can be used for either sputtering or RF sputtering. T
A film formed by DC sputtering using an iO _2-x (1 <x <2) target can be formed at a higher speed than a film formed by DC sputtering using a Ti target.

Examples of the conductive oxide target containing zinc oxide as a main component include a ZnO target doped with at least one selected from the group consisting of B, Al, Ga, In, Si and Ti as a dopant. . The content ratio of the dopant in the target is such that the total amount of the dopant with respect to the total amount of the dopant and the total amount of zinc (Zn) is:
It is preferably 0.01 to 10 atomic%. From the viewpoint of conductivity, the dopant is preferably Ga or Al, particularly Ga. In particular, from the viewpoint of conductivity, 0.2
Preferably, it is ８8 atomic%. The conductive oxide target containing zinc oxide as a main component is DC sputtering or R
It can be used for any of F sputtering. From the viewpoint of productivity, it is preferable to form a film by DC sputtering at a high film formation rate.

The temperature of the substrate during the formation of the titanium oxide film and the sputtering of the zinc oxide-based transparent conductive film is 0 to 600 ° C.
It is preferable that If the temperature is lower than 0 ° C., it becomes difficult to form an uneven structure. As the base, a glass substrate is preferably used. If the temperature exceeds 600 ° C., the glass substrate is deformed, or the zinc oxide-based transparent conductive film is peeled off due to a difference in thermal expansion coefficient between the glass substrate and the zinc oxide-based transparent conductive film. It will be easier.
From the viewpoint of productivity, the temperature is preferably 20 ° C. or higher, and more preferably 400 ° C. or lower. As the substrate used in the present invention, a surface-treated substrate such as a glass substrate on which a film (for example, a silicon oxide film) for preventing diffusion of an alkali component in the glass substrate may be used.

The sputtering pressure at the time of forming the zinc oxide-based transparent conductive film by sputtering is not particularly limited, and is generally preferably 0.01 to 2 Pa at which stable discharge can be performed. In particular, from the viewpoints of discharge stability and deposition rate, 0.06
It is preferable that it is -1.4 Pa.

The present invention also provides a solar cell in which a photoelectric conversion layer and an electrode layer are formed in this order on the zinc oxide-based transparent conductive film of the substrate with a transparent conductive film. An example of the photoelectric conversion layer is an amorphous silicon layer. The amorphous silicon layer is formed by, for example, a plasma CVD method. The thickness of the layer is preferably between 200 and 800 nm. 20
If the thickness is smaller than 0 nm, the conversion efficiency decreases. 800n
If it is thicker than m, it takes a long time to form a film, the cost increases, and the conversion efficiency also decreases.

Examples of the electrode layer include a metal film or a laminated film in which a metal film (for example, an Ag film or an Al film) and a zinc oxide-based transparent conductive film are laminated. Specifically, a film formed by forming a zinc oxide-based transparent conductive film and a metal film on amorphous silicon in this order can be given. The electrode layer is formed by, for example, a sputtering method. The metal film preferably has a thickness of 50 to 500 nm. If it is less than 50 nm, the reflectance will decrease and the conversion efficiency will decrease. The thickness of the zinc oxide-based transparent conductive film is preferably from 5 to 500 nm. If it is smaller than 5 nm, the conversion efficiency is reduced, and if it is larger than 500 nm, the film stress increases and the film is easily peeled. Examples of the solar cell include an amorphous silicon solar cell and a compound semiconductor solar cell such as a Cu-In-Se type.

[0018]

The titanium oxide film is a substantially flat film without a particularly large uneven structure. The titanium oxide film has an effect on the crystal growth of a zinc oxide-based transparent conductive film that is stacked on the titanium oxide film, and as a result, the crystal growth is promoted and zinc oxide crystals having large crystal grains grow. The surface of the zinc oxide-based transparent conductive film becomes uneven due to the crystal grains. The crystals are oriented in a direction substantially perpendicular to the substrate surface, and the crystal orientations are uniform, so that unevenness having a substantially uniform shape is obtained. The zinc oxide-based transparent conductive film has a roof-like uneven shape, is suitable as an incident light side electrode (so-called surface electrode) of a solar cell, and has a high light confinement effect. In addition, since the inclination is a relatively gentle roof type, when an amorphous silicon layer is stacked on the transparent conductive film, the portion where the amorphous silicon layer is not formed is extremely small, and a continuous cell suitable as a solar cell is obtained. It becomes an amorphous silicon layer.

Further, the zinc oxide-based transparent conductive film can be used also for the back electrode of a solar cell, and it is expected that the light confinement effect can be further enhanced by using it for the back electrode. The titanium oxide film also has an effect of preventing diffusion of alkali components and moisture from the substrate glass, and can prevent deterioration of the zinc oxide-based transparent conductive film. As a result, the reliability of the solar cell using the substrate with a transparent conductive film of the present invention is improved.

[0020]

[Example 1] TiO produced by plasma spraying
_{A 2-x} (x = 0.06) target was set in a magnetron DC sputtering apparatus. On a glass substrate, a mixed gas of argon gas (Ar) and oxygen gas (O ₂ ) (Ar: O ₂ =
4: 1 (volume ratio)) and a sputtering pressure of 0.4 Pa
A TiO ₂ film was formed to a thickness of 3 nm on a silica glass substrate having a thickness of 1 mm.

Subsequently, ZnO (Ga / (Zn + Ga) =
3 atomic%) using a sintered target (hereinafter referred to as a GZO target), introducing Ar, and applying a sputtering pressure of 0.4
As a Pa, a ZnO film to which 3 atomic% of Ga was added (hereinafter, referred to as a GZO film) was formed in a thickness of 700 nm in contact with the TiO ₂ film to obtain a glass substrate with a transparent conductive film. The substrate temperature of the TiO ₂ film and the GZO film were 25
0 ° C.

The specific resistance of the obtained glass substrate with a transparent conductive film was 8 × 10 ⁻⁴ Ω · cm. The total transmittance (T _t ) measured using an integrating sphere at a wavelength of 550 nm was 85% including the substrate. The haze ratio (H) was 10%.
Incidentally, the haze (H) _{is, H = ((T t -T} p) / T t)
× 100, preferably 2% or more, and the upper limit is not particularly limited, but is preferably 30% or less for practical use. T _p is the transmittance on the optical path.

When the surface of the transparent conductive film of the obtained glass substrate with a transparent conductive film was observed with an electron microscope, it was confirmed that the surface had a roof-shaped uneven structure. Further, when the obtained glass substrate with a transparent conductive film was cut and the cross section was observed with an electron microscope, it was confirmed that the GZO film was a continuous film. When the transparent conductive film is analyzed by X-ray diffraction,
Most of the peaks originated from the (002) plane, and it was confirmed that the film was oriented vertically from the substrate. Moreover, as a result of measuring the surface roughness using an AFM (atomic force microscope), _Ra was 30 nm. At this time, the cutoff value was set to one third of the evaluation length. The used Ti
In order to examine the optical characteristics of the O ₂ film, a TiO ₂ film having a thickness of about 100 nm was separately formed in the same manner as described above. As a result, the refractive index at a wavelength of 550 nm was 2.4, and the extinction coefficient was 1 × 10 ⁻⁴ .

[Example 2] The TiO _2-x (x =
0.06) Instead of the target, a Ti metal target was used, a mixed gas of Ar and O ₂ (Ar: O ₂ = 1: 4 (volume ratio)) was introduced, and the other conditions were the same as in Example 1. Ti
An O ₂ film was formed to a thickness of 5 nm. The film formation rate of the TiO ₂ film was 5 in the case of Example 1, assuming that the case of Example 2 was 1.

Next, a 700 nm-thick GZO film was laminated on the TiO ₂ film in the same manner as in Example 1 to obtain a glass substrate with a transparent conductive film. The obtained glass substrate with a transparent conductive film was measured in the same manner as in Example 1, and as a result, the specific resistance was 8
× 10 ⁻⁴ Ω · cm, _Tt is 85% including the substrate, H is 10
%Met. The surface irregularity structure of the transparent conductive film and the continuity and orientation of the GZO film were the same as in Example 1. R _a as measured in the same manner as in Example 1 was 28nm.

Example 3 (Comparative Example) Ar was introduced on a silica glass substrate having a thickness of 1 mm using a GZO target at a sputtering pressure of 0.4 Pa.
A GZO film was formed to a thickness of 700 nm to obtain a glass substrate with a transparent conductive film. The substrate temperature at this time is 250
° C. The specific resistance of the obtained glass substrate with a transparent conductive film was 8 × 10 ⁻⁴ Ω · cm. _Tt is 8 including substrate
5% and H was about 0%.

When the surface of the transparent conductive film of the obtained glass substrate with a transparent conductive film was observed by an electron microscope, almost no uneven structure was observed on the surface. Further, when the transparent conductive film was analyzed by X-ray diffraction, most of the peaks originated from the (002) plane, and it was confirmed that the film was oriented vertically from the substrate. Furthermore, R _a is 5 as measured in the same manner as in Example 1
nm.

Example 4 On the transparent conductive film of the glass substrate with a transparent conductive film obtained in Example 2, p-i was formed as a photoelectric conversion layer.
Plasma CVD of amorphous Si layer with -n junction
400 nm was laminated by the method. The substrate temperature at this time is 3
The temperature was set to 00 ° C. Next, on the photoelectric conversion layer, the GZ
Using an O target, Ar was introduced, the sputtering pressure was set to 0.4 Pa, and 50 nm GZO was formed by sputtering.
A film was formed. Finally, using a Ag target as the back electrode, Ar was introduced, a sputtering pressure of 0.4 Pa was applied, and a 200 nm Ag film was stacked by a sputtering method.
An amorphous silicon solar cell A was produced.

On the other hand, except that the glass substrate with a transparent conductive film obtained in Example 3 was used instead of the glass substrate with a transparent conductive film obtained in Example 2 in the production of the amorphous silicon solar cell A, Each layer was laminated in the same manner as described above to produce an amorphous silicon solar cell B. The obtained solar cells A and B are supplied with AM (air mass) using a solar simulator.
1 was irradiated, and the photoelectric conversion efficiency was determined from the measurement results of the short-circuit current, open-end voltage, and fill factor. As a result, when the photoelectric conversion efficiency of the amorphous silicon solar cell B is 1.00, the photoelectric conversion efficiency of the amorphous silicon solar cell A is 1.1.
It was 5.

[0030]

The substrate with a transparent conductive film of the present invention has a concavo-convex structure on the surface of the transparent conductive film, and thus exhibits a good light confinement effect when used as a transparent electrode of an amorphous silicon solar cell. Thus, an amorphous silicon solar cell having high photoelectric conversion efficiency can be obtained.

Claims (3)

[Claims] 1. A method of manufacturing a substrate with a transparent conductive film, comprising laminating a transparent conductive film mainly containing zinc oxide on a film mainly containing titanium oxide formed on the substrate. 2. A substrate with a transparent conductive film in which a transparent conductive film mainly containing zinc oxide is laminated on a film mainly containing titanium oxide formed on the substrate. 3. A solar cell in which a photoelectric conversion layer and an electrode layer are formed in this order on a transparent conductive film containing zinc oxide as a main component of the substrate with a transparent conductive film according to claim 2.