JPH10190028A - High refractive index transparent conductive film and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high refractive index transparent conductive film for manufacturing a solar cell without reducing a converting efficiency of the cell by constituting it of an oxide film having specific refractive index and specific value or less of specific resistance. SOLUTION: A refractive index of a transparent electrode is desired to be generally 2.2 or more. Meanwhile, a transparent conductive film having 2.5 or more of refractive index is not obtained at present. Accordingly, the index of this high refractive index transparent conductive film is set to 2.2 to 2.5. Once a film thickness has been increased to obtain the electrode having a desired electric resistance, its light transmittance is reduced, and hence the smaller the specific resistance of the film is, the better the film is. Therefore, the specific resistance is set to 5×10<-4> Ωcm or less. This specific resistance is more preferably 4.5×10<-4> Ωcm or less, and still more preferably 4×10<-4> Ωcm. Thus, a solar cell can be, for example, manufactured with a low cost without reducing a conversion efficiency by using the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent conductive film made of an oxide and a solar cell using the transparent conductive film as a transparent electrode.

[0002]

2. Description of the Related Art A solar cell using silicon, a compound semiconductor or the like as a photoelectric conversion material and utilizing an electromotive force generated in the photoelectric conversion material when light such as sunlight enters the photoelectric conversion material is an inexhaustible solar cell. Since it is a clean power generation element using light as an energy source, it is widely used for various uses. These solar cells can be classified into several types, but thin-film solar cells represented by amorphous silicon solar cells do not require expensive silicon substrates used in single-crystal silicon solar cells and polycrystalline silicon solar cells. Because of the thin-film structure, it is expected that the material cost will be significantly reduced and the housing market will grow in the future.

On the other hand, thin-film solar cells include (1) lower conversion efficiency than single-crystal silicon solar cells and polycrystalline silicon solar cells, and (2) large deterioration in conversion efficiency after installation. There are problems, and various studies have been made to solve these problems. As a method of improving the conversion efficiency of the thin-film solar cell, (a) by providing irregularities on the substrate surface on the photoelectric conversion layer side, to increase the chance of multiple reflection of light transmitted through the photoelectric conversion layer, (b) It is known to form a light confinement layer and (c) increase the amount of light incident on the photoelectric conversion layer by forming an antireflection film.

It has already been found that by combining the methods (a) to (c), the conversion efficiency of a thin-film solar cell can be improved to the level of single-crystal silicon or polycrystalline silicon. Have been. However, the above (a) ~
Each of the methods (c) leads to an increase in the manufacturing cost of the thin-film solar cell.

[0005]

The method of (c) increasing the amount of light incident on the photoelectric conversion layer by forming the antireflection film is employed not only in thin-film solar cells but also in other solar cells. If a function as an anti-reflection film can be added to a transparent electrode used for a solar cell, it is possible to increase the manufacturing cost without lowering the conversion efficiency of the solar cell. It has the advantage that.

[0006] The wavelength of light that is photoelectrically converted in a solar cell with high efficiency varies according to the band gap of the material of the photoelectric conversion layer of the solar cell, the radiation energy of light, and the like.
When the conversion efficiency is to be improved by providing a single-layer anti-reflection film, it is desirable that the optical film thickness of the anti-reflection film be about ４ times the wavelength of the specific light. That is, it is desirable that the antireflection film be a λ / 4 film (λ is the wavelength of light whose reflection is to be prevented; hereinafter, it may be referred to as “design wavelength” of the antireflection film).
For example, when the photoelectric conversion layer is made of amorphous silicon, the wavelength of light that is photoelectrically changed by the amorphous silicon with high efficiency in sunlight is approximately 500 to 700.
Therefore, it is preferable that the optical film thickness of the single-layer antireflection film be １ ／ of the wavelength of specific light whose reflection is to be prevented from light having a wavelength of 500 to 700 nm or in the vicinity thereof.

However, ITO films, ZnO films, SnO ₂ films, In ₂
O ₃ film, Al-doped ZnO film, Sb-doped SnO ₂ film,
In the case of an F-doped SnO ₂ film or the like, its refractive index (wavelength 550 nm)
Is about 1.8 to 2.0,
When an attempt is made to add the function as an anti-reflection film to such a transparent electrode, the actual film thickness is generally increased as compared with a case where the function as an anti-reflection film is not added. For example, a conventional transparent electrode having a refractive index of 1.8 has a wavelength of 60.
In order to serve also as an anti-reflection film for light of 0 nm, the film thickness needs to be about 833 Å. When the thickness of the transparent electrode is increased, the light transmittance of the transparent electrode naturally decreases due to the absorption of the transparent electrode material, so that the conversion efficiency of the solar cell tends to decrease.

A first object of the present invention is to provide a high-refractive-index transparent conductive film which is useful for manufacturing a solar cell at lower cost without lowering the conversion efficiency of the solar cell.

It is a second object of the present invention to provide a solar cell which can be manufactured at lower cost without lowering the conversion efficiency.

[0010]

The high refractive index transparent conductive film of the present invention which achieves the first object has a refractive index of 2.2 to 2.2.
2.5, characterized by being made of an oxide having a specific resistance of 5 × 10 ⁻⁴ Ωcm or less.

Further, a solar cell according to the present invention that achieves the second object has a photoelectric conversion layer that generates an electromotive force by light irradiation, and a pair of positive and negative electrodes that are electrically connected to the photoelectric conversion layer. At least one of the pair of electrodes is formed on the light incident surface side, and the electrode formed on the light incident surface side is a transparent electrode made of the high refractive index transparent conductive film of the present invention. It is characterized by being.

[0012]

Embodiments of the present invention will be described below in detail. First, the high refractive index transparent conductive film of the present invention will be described. As described above, the high refractive index transparent conductive film has a refractive index of 2.2 to 2.5 and a specific resistance of 5 × 10 ^−4.
It is made of an oxide having a value of Ωcm or less. Here, the “transparent conductive film” in the present invention means a conductive film having a transmittance of light of 550 nm at a thickness of 500 angstroms of approximately 850 nm or more. The refractive index in the present invention is a wavelength of 5
It means the refractive index of 50 nm light.

The reason for setting the refractive index of the high refractive index transparent conductive film of the present invention to 2.2 to 2.5 is as follows. That is, when the transparent electrode also serves as an anti-reflection film, as described above, it is desired that the transparent electrode be a λ / 4 film or a film having a thickness close to the λ / 4 film. However, at this time, it is necessary to increase the actual film thickness as the refractive index of the transparent electrode is smaller. Therefore, for example, when the transparent electrode for the amorphous silicon solar cell element also serves as the anti-reflection film, in order to suppress the increase in the thickness of the transparent electrode caused by also serving as the anti-reflection film, the refractive index of the transparent electrode is required. Is desirably approximately 2.2 or more. On the other hand, a transparent conductive film having a refractive index of more than 2.5 has not been obtained at this stage even if its composition and film forming conditions are adjusted. Therefore, the refractive index of the high refractive index transparent conductive film of the present invention is set to 2.2 to 2.5.

The refractive index of the high-refractive-index transparent conductive film of the present invention can be appropriately selected within the range of 2.2 to 2.5 depending on the intended use of the high-refractive-index transparent conductive film. When the high refractive index transparent conductive film also has a function as an antireflection film, the higher the refractive index, the better. That is, the refractive index is more preferably from 2.3 to 2.5, and particularly preferably from 2.4 to 2.5.

If the specific resistance of the transparent conductive film is large, it is necessary to increase the thickness of the transparent conductive film in order to obtain a transparent electrode having a desired electric resistance (sheet resistance). When the thickness is large, the light transmittance is reduced, so that the specific resistance of the high refractive index transparent conductive film of the present invention is preferably as small as possible. Therefore, in the high refractive index transparent conductive film of the present invention, the specific resistance is set to 5 × 10 ⁻⁴ Ωcm or less. This specific resistance is more preferably 4.5 × 10 ⁻⁴ Ωcm or less, and particularly preferably 4 × 10 ⁻⁴ Ωcm or less.

As a specific example of the oxide satisfying the above conditions for the light transmittance, the refractive index, and the specific resistance, an In—Zn—O-based oxide formed under a specific condition, that is, indium ( Oxides containing In), zinc (Zn) and oxygen (O) as main constituent elements. This In-Zn-O-based oxide may be composed of only three elements of indium (In), zinc (Zn) and oxygen (O) except for unavoidable contaminants, or these constituent elements. In addition, gallium (Ga) may be contained as a constituent element. Gallium (Ga) as a constituent element
, An In-Zn-O-based oxide with improved light transmittance in the visible light region can be obtained. The In—Zn—O-based oxide may be one that satisfies the above conditions for the light transmittance, the refractive index, and the specific resistance. It is preferable that the film is amorphous (hereinafter, this amorphous film is referred to as “In—Zn—O-based amorphous oxide”).

The composition of the In—Zn—O-based amorphous oxide is not particularly limited as long as a film that satisfies the above conditions for light transmittance, refractive index, and specific resistance can be obtained. When the atomic ratio In / (total metal element) of indium (In) in In, Zn and Ga (including the case where Ga is not contained; the same applies hereinafter) is less than 0.5; Gallium (Ga) in elements
When the atomic ratio Ga / (all metal elements) exceeds 0.04, it becomes difficult to obtain films each having a specific resistance of 5 × 10 ⁻⁴ Ωcm or less. If the atomic ratio In / (all metal elements) of indium (In) in all metal elements exceeds 0.9, the stability of the electrical resistance of the film against moisture and heat decreases. A preferable atomic ratio In / (all metal elements) of In from the viewpoint of the electrical characteristics of the film and its stability is 0.55 to 5.
0.9, and particularly preferably 0.60 to 0.9. The preferable atomic ratio Ga / (all metal elements) of Ga is 0 to 0.03 in view of the electrical and optical characteristics of the film, and particularly preferably 0 to 0.025.

The high-refractive-index transparent conductive film of the present invention having the above-mentioned refractive index and specific resistance has a high refractive index of 2.2 to 2.5. The actual film thickness at that time is smaller than the same λ / 4 film made of a conventional transparent electrode material. For example, even when a λ / 4 film for light having a wavelength of 600 nm is used, the actual film thickness may be about 600 to 682 Å. When the high refractive index transparent conductive film is a λ / 4 film with respect to light having a wavelength of 500 to 700 nm, the transmittance of light having a wavelength of 550 nm is approximately 80% or more, so that it functions sufficiently as a transparent electrode. Further, since the high-refractive-index transparent conductive film of the present invention has a small specific resistance of 5 × 10 ⁻⁴ Ωcm or less, the sheet resistance becomes 100 Ω / □ or less even when the film thickness is 500 Å, for example.
Conductivity sufficient for use as a transparent electrode for a solar cell or the like can be obtained.

Therefore, by using the high refractive index transparent conductive film of the present invention, it is possible to form a thin transparent electrode having excellent light transmittance and conductivity and having a function as an antireflection film. Thereby, for example, in a solar cell, it is possible to omit the anti-reflection film conventionally formed as a separate member from the transparent electrode, so that the manufacturing cost can be reduced without lowering the conversion efficiency of the solar cell. Will be possible. When the high refractive index transparent conductive film of the present invention is used as a transparent electrode for a solar cell, particularly as a transparent electrode for an amorphous silicon solar cell, and when this transparent electrode also serves as an anti-reflection film, the thickness thereof is reduced. About 440
Preferably 700 Angstroms, 500
~ 650 Å is more preferable,
It is particularly preferred that the thickness be 500 to 600 Å.

The high-refractive-index transparent conductive film of the present invention is a film which is excellent in light transmittance and conductivity as described above, and which can easily obtain a material having excellent denseness as described later. Therefore, besides being used as a transparent electrode for a solar cell or its material, it is used for various purposes such as a transparent electrode for a liquid crystal panel, a transparent electrode for an organic EL element, and a transparent electrode for a coordinate input device represented by a touch panel. In addition to being suitable as a transparent electrode or its material, it is also suitable as an electromagnetic wave shielding material or its material. Note that whether or not the high refractive index transparent conductive film of the present invention also functions as an antireflection film can be appropriately selected.

The high refractive index transparent conductive film of the present invention having the above-mentioned characteristics can be formed, for example, by a sputtering method in which the influence of water is reduced as much as possible. As the sputtering method at this time, DC magnetron sputtering method, RF magnetron sputtering method, DC
An RF magnetron sputtering method or the like can be applied.

The sputtering target (including pellets; the same applies hereinafter) used in the above-mentioned sputtering method includes In ₂ O ₃ (ZnO) _m which is a hexagonal layered compound.
(M = 2 to 20) and with one or more selected from InGaZn ₂ O _5, an oxide sintered body target consisting of In ₂ O ₃ or ZnO is preferable. Here, the reason for limiting the value of m to 2 to 20 in the above formula representing a hexagonal layered compound is that a compound in which a hexagonal layered compound is not generated outside this range and the value of m is outside the above range. This is because the volume resistance of a sputtering target containing 増 加 increases, so that the discharge becomes unstable in ordinary DC sputtering or the like, and it becomes difficult to stably form a film.

As the sputtering target, In
Has an atomic ratio In / (all metal elements) of 0.45 to 0.85,
It is preferable that the atomic ratio of Ga / (all metal elements) is 0 to 0.04. If the atomic ratio In / (all metal elements) of In in the sputtering target is less than 0.45, the atomic ratio In / (all metal elements) of In in the obtained film tends to be less than 0.5. It becomes difficult to obtain a film having resistance. Further, when the atomic ratio In / (all metal elements) of In in the sputtering target exceeds 0.85, the atomic ratio In / (all metal elements) of In in the obtained film easily exceeds 0.9. The stability of the electrical resistance of the film against moisture and heat is likely to decrease. On the other hand, when the atomic ratio Ga / (all metal elements) of Ga in the sputtering target exceeds 0.04, the atomic ratio Ga / (all metal elements) of Ga in the obtained film tends to exceed 0.04. It becomes difficult to obtain a film having a desired specific resistance.

The atomic ratio In / (all metal elements) of In in the sputtering target is more preferably 0.50 to 0.85, and particularly preferably 0.55 to 0.85. The atomic ratio Ga / (all metal elements) of Ga in the sputtering target is 0 to 0.03.
Is more preferable, and particularly preferably 0 to 0.025.

The relative density of the above sputtering target is preferably 90% or more. 90 relative density
%, The film formation rate is lowered and the quality of the obtained film is lowered. The relative density of the sputtering target is 9
It is preferably at least 5%, particularly preferably at least 97%. And, the purity of the above sputtering target is preferably 99% or more. If the purity is less than 99%, the conductivity and chemical stability of the obtained film are reduced due to impurities. The purity of the sputtering target is more preferably 99.9% or more.
It is particularly preferably at least 9.99%.

In performing sputtering using the above-described sputtering target, first, a substrate for film formation (hereinafter, referred to as a "film formation substrate") and a sputtering target are mounted in a vacuum chamber of a sputtering apparatus. The moisture adsorbed on the film substrate, the sputtering target and the like is removed.

The above-mentioned water is removed, for example, when the degree of vacuum in the vacuum chamber is 1 × 10 ⁻⁴ Pa or less (low pressure of 1 × 10 ⁻⁴ Pa or less).
It can be performed by evacuating until the pressure becomes. Heating is preferably performed during the evacuation. This heating makes it possible to more reliably remove moisture and shorten the evacuation time. The degree of vacuum at this time exceeds 1 × 10 ⁻⁴ Pa (1 ×
When the pressure is higher than 10 ⁻⁴ Pa), the moisture adsorbed on the apparatus, the film-forming substrate, the sputtering target, and the like tends to be insufficiently removed. It becomes difficult to obtain a high refractive index transparent conductive film of 0.2 to 2.5. The evacuation is more preferably performed until the partial pressure of the water gas in the atmosphere in the vacuum chamber becomes approximately 1 × 10 ⁻⁵ Pa or less, particularly preferably until the partial pressure becomes approximately 1 × 10 ⁻⁶ Pa or less. Note that the exhaust system of the sputtering device to be used preferably has a trap or a getter for removing moisture.

After the evacuation is performed, a target high refractive index transparent conductive film is formed. The degree of vacuum during film formation is 1 ×
The pressure is preferably set to 10 ⁻² to 1 × 10 ⁰ Pa. The vacuum degree is less than 1 × 10 ^-2 Pa (lower pressure than 1 × 10 ^-2 Pa)
In decreases the discharge stability during film becomes 1 × 10 ⁰ exceeds Pa (higher pressures than 1 × 10 ⁰ Pa) and difficult to increase the voltage applied to the sputtering target. The degree of vacuum during film formation is more preferably be ^{1 × 10 -2 ~5 × 10 -1} Pa, and particularly preferably to ^{1 × 10 -2 ~2 × 10 -2} Pa.

The output during film formation is preferably 3 W / cm ² or less. If this output exceeds 3 W / cm ² , the resulting film will have a reduced denseness and a refractive index of 2.2 to 2.2.
It becomes difficult to obtain a high refractive index transparent conductive film of 2.5.
The output at the time of film formation, more preferably to 2W / cm ² or less, and particularly preferably 1W / cm ² or less. The voltage during film formation is preferably 100 to 400 V, more preferably 100 to 300 V,
It is particularly preferable to set the voltage to 100 to 200 V.

As an atmosphere gas during film formation, a mixed gas of an argon gas (Ar gas) and an oxygen gas (O ₂ gas) is usually used. The mixing ratio of the Ar gas and the O ₂ gas varies depending on the oxidation state of the sputtering target to be used, the degree of vacuum during the film formation and the output, but when the volume concentration of the O ₂ gas in the ambient gas exceeds 5%, the mixing ratio is increased. The conductivity of the resulting film tends to decrease. Therefore, the volume concentration of the O ₂ gas in the atmosphere gas during film formation is preferably 5% or less, more preferably 4% or less, and more preferably 3% or less.
% Is particularly preferable. The purity of the atmosphere gas is preferably 99.991% or more.
It is more preferably at least 9.995%, and 99.9% or more.
It is particularly preferred that the content be 99% or more.

The substrate temperature at the time of film formation can be appropriately selected from the range of 50 ° C. to the heat-resistant temperature of the film-formed substrate. However, when the substrate temperature exceeds 200 ° C., the heat-resistant temperature of many resin substrates is reduced. Therefore, the types of substrates that can be used are strongly limited. On the other hand, if the substrate temperature is lower than 50 ° C., the denseness of the obtained film decreases, and it becomes difficult to obtain a high refractive index transparent conductive film having a refractive index of 2.2 to 2.5. The substrate temperature during film formation is preferably 50 to 200 ° C, and 80 to 200 ° C.
The temperature is more preferably set to 100 to 200 ° C.

The film-forming substrate can be appropriately selected according to the intended use of the high refractive index transparent conductive film and the like.
There is no particular limitation on a metal substrate, a heat-resistant resin substrate, a solar cell (under fabrication), and the like. Specific examples of the glass substrate include soda-lime glass, lead glass, borosilicate glass,
Glass substrates made of high silicate glass, non-alkali glass, etc., and SiO ₂ , SiO _x (1 ≦
x <2), TiO _x (1 ≦ x ≦ 2) or the like. Specific examples of the metal substrate include metal foils such as stainless steel foil, copper foil, and aluminum foil, as well as metal plates and metal sheets of the same quality as these metal foils. And as a specific example of the heat resistant resin substrate,
Polyester resin such as polyethylene terephthalate, polycarbonate resin, polyarylate resin, polyether sulfone resin, amorphous polyolefin resin, polystyrene resin, acrylic resin, etc.
Examples include molded articles, films, sheets, and the like made of a resin at 0 ° C. or higher, and those formed with a gas barrier layer, a solvent-resistant layer, a hard coat layer, and the like on the surface thereof.

By forming a film under the above-described conditions, a refractive index of 2.2 to 2.5 on the above-mentioned film-forming substrate is obtained.
The high refractive index transparent conductive film of the present invention having a specific resistance of 5 × 10 ⁻⁴ Ωcm or less can be formed.

Next, the solar cell of the present invention will be described. As described above, the solar cell of the present invention includes a photoelectric conversion layer that generates an electromotive force by light irradiation, and a pair of positive and negative electrodes electrically connected to the photoelectric conversion layer. At least one is formed on the light incident surface side, and the electrode formed on the light incident surface side is a transparent electrode made of the high refractive index transparent conductive film of the present invention described above. Things.

The solar cell of the present invention can take various forms such as a thin-film solar cell, a single-crystal silicon solar cell, and a polycrystalline silicon solar cell. The above-mentioned photoelectric conversion layer constituting the solar cell is made of a photoelectric conversion material that generates an electromotive force by light irradiation. As the photoelectric conversion material, a pn junction is formed as in a conventional solar cell. Amorphous silicon (hereinafter referred to as “pn-type amorphous silicon”), amorphous silicon having a pin junction formed (hereinafter referred to as “pin-type amorphous silicon”), n-type CdS / p-type CdTe, GaAl
Various materials such as a heterojunction type compound semiconductor such as As / GaAs, single crystal silicon having a pn junction formed (hereinafter referred to as “pn single crystal silicon”), and polycrystalline silicon having a pn junction formed are used. Can be used.

The pair of positive and negative electrodes constituting the solar cell of the present invention is for electrically connecting the above-mentioned photoelectric conversion layer and an external circuit. In the case of being formed of amorphous silicon or pn-type single crystal silicon, p of the photoelectric conversion layer
The positive electrode of the pair of electrodes is formed so as to be electrically connected to the mold region, and the negative electrode of the pair of electrodes is formed so as to be electrically connected to the n-type region of the photoelectric conversion layer. You.

Of the pair of electrodes, the electrode formed at least on the light incident surface side when viewed from the photoelectric conversion layer includes:
A transparent electrode is used so as not to prevent light from entering the photoelectric conversion layer. And in the solar cell of the present invention, the above-mentioned transparent electrode is formed by the above-mentioned high refractive index transparent conductive film of the present invention.

As described above, the transparent conductive film having a high refractive index of the present invention is a film which is excellent in light transmittance and conductivity, and can easily obtain a material having excellent denseness. It is suitable as a material for an electrode. Since the high refractive index transparent conductive film of the present invention has a high refractive index of 2.2 to 2.5, the high refractive index transparent conductive film has a wavelength of, for example, 500 to 700 nm.
Even when the λ / 4 film is used for the above-mentioned light, the transmittance of light having a wavelength of 550 nm is approximately 80% or more, and the film sufficiently functions as a transparent electrode. Further, since the high-refractive-index transparent conductive film of the present invention has a small specific resistance of 5 × 10 ⁻⁴ Ωcm or less, the sheet resistance becomes 100 Ω / □ or less even when the film thickness is set to 500 Å, for example. Conductivity sufficient for use as a transparent electrode is obtained.

Therefore, when forming the above-mentioned transparent electrode with the high refractive index transparent conductive film of the present invention as described above, if the transparent electrode is a λ / 4 film or a film having a thickness close to the λ / 4 film, Since the transparent electrode can also serve as an anti-reflection film, it is possible to omit the anti-reflection film conventionally formed as a separate member from the transparent electrode,
The manufacturing cost can be reduced without lowering the conversion efficiency of the solar cell. Whether or not the above-mentioned transparent electrode also serves as an antireflection film can be appropriately selected.

In order to supply a solar cell at a low cost, it is desirable that the solar cell is an amorphous silicon solar cell. Therefore, the solar cell of the present invention is also preferably an amorphous silicon solar cell. An amorphous silicon solar cell has a substrate, a photoelectric conversion layer composed of an amorphous silicon layer, and a transparent electrode. When the substrate side is not a light incident surface, the amorphous silicon layer and the transparent electrode are viewed from the substrate side. Are formed in this order,
The transparent electrode side becomes the light incident surface. When the substrate side is used as a light incident surface, a transparent electrode and an amorphous silicon layer are formed in this order when viewed from the substrate side, and a pair of positive and negative electrodes is formed on the amorphous silicon layer together with the transparent electrode. Another electrode to be formed is formed of a conductive metal or the like. In order to obtain a solar cell with high conversion efficiency, the transparent electrode side is used as the light incident surface instead of the substrate side as the light incident surface, that is, the amorphous silicon layer and the transparent electrode are formed in this order when viewed from the substrate side. Is preferred.

The type of the substrate can be appropriately selected depending on the intended use of the solar cell, such as a glass substrate, a metal substrate, a heat-resistant resin substrate, and the like. Specific examples of these substrates are described above. The same materials as those described in the description of the high refractive index transparent conductive film of the present invention are exemplified.

When an amorphous silicon solar cell is obtained by using a transparent substrate or a substrate having poor conductivity and forming an amorphous silicon layer and a transparent electrode in this order when viewed from the substrate side, the above-mentioned substrate is used. A back electrode made of a conductive metal or the like having a high light reflectance is interposed between the amorphous silicon layer and the amorphous silicon layer. In the case where a substrate having excellent conductivity is used as the substrate, the substrate can be used as an electrode, so the back electrode is not necessarily required, but the back electrode is provided if necessary. You may.

As a specific example of the material of the back electrode,
A simple metal such as aluminum (Al), copper (Cu), silver (Ag), platinum (Pt), and gold (Au) can be used. Further, a back electrode may be formed by further forming a layer of TiAg (alloy), titanium (Ti), or the like on the layer composed of the above-mentioned metal simple substance (on the side of the amorphous silicon layer). The thickness of the back electrode is preferably 0.01 to 10 μm. If the thickness is less than 0.01 μm, the moisture resistance of the back electrode is reduced, and if it exceeds 10 μm, it is not economical. The thickness of the back electrode is more preferably 0.1 to 0.5 μm, and particularly preferably 0.3 to 1 μm. The back electrode can be formed by a vacuum evaporation method, a sputtering method, or the like.

In the above case, an amorphous silicon solar cell is obtained by forming an amorphous silicon layer and a transparent electrode in this order when viewed from the substrate side. It is preferable to form irregularities such that the surface roughness ( _Rmax ) of this surface is 1 μm or more. By forming the unevenness, the amorphous silicon layer is formed directly on the substrate by the unevenness, and the back electrode and the amorphous silicon layer are sequentially formed on the substrate by the unevenness. Due to the irregularities generated on the back electrode, it is possible to increase the chance of multiple reflection of light transmitted through the amorphous silicon layer, respectively.
As a result, the conversion efficiency of the solar cell can be improved. When the irregularities are less than 1 μm, the chance of multiple reflection of light transmitted through the amorphous silicon layer does not increase so much. The unevenness is more preferably one having a surface roughness of 5 μm or more, and particularly preferably one having a surface roughness of 10 μm or more.

The amorphous silicon layer serving as the photoelectric conversion layer in the amorphous silicon solar cell may be formed of pn type amorphous silicon or pin type amorphous silicon. In order to obtain a solar cell with high conversion efficiency, it is preferable that the amorphous silicon layer serving as the photoelectric conversion layer is formed of pin-type amorphous silicon, and in particular, a two-layer repeating structure of pin-type amorphous silicon or pin-type amorphous silicon
It is preferably formed by a three-layer repeating structure of type amorphous silicon.

The photoelectric conversion layer made of single-layer pin type amorphous silicon is made of, for example, a-Si: H, a-S
a p-layer composed of iC: H or a-SiN: H or the like and a group III element such as boron (B) or gallium (Ga) added thereto as an acceptor; And an i-layer formed by adding substantially equal amounts of a donor and an n-layer formed by adding a group V element such as phosphorus (P) or arsenic (As) to a-Si: H or the like as a donor. In the order of p-layer-i-layer,
Alternatively, it can be obtained by laminating in order of n layer-i layer-p layer.

Further, the photoelectric conversion layer made of pin-type amorphous silicon having a two-layer repeating structure includes, for example, the above-mentioned p-layer and an acceptor and a donor as necessary in a-SiGe: H or a-SiSn: H. A first i-layer made up of substantially equal amounts, and the above-mentioned n-layer,
a-Si: H, Si: H, a-SiC: H or a-S
a second i composed of iN: H or the like to which an acceptor and a donor are added, if necessary, in substantially equal amounts;
Layers, a p-layer-first i-layer-n-layer-p-layer-second i-layer-
It can be obtained by laminating in the order of n layers, or in the order of n layer-first i layer-p layer-n layer-second i layer-p layer.

The photoelectric conversion layer made of pin-type amorphous silicon having a three-layer repeating structure includes, for example, the above-mentioned p-layer, first i-layer, n-layer and second i-layer, and aS
i: H, Si: H, a-SiC: H or a-SiN:
And a third i-layer made up of H and the like, to which acceptors and donors are added, if necessary, in substantially equal amounts, to form a p-layer-first i-layer-n-layer-p-layer-second i Layer-n-layer-p-layer-third i-layer-n-layer or n-layer-first i-layer-p-layer-n-layer-second i-layer-p-layer-n-layer-third I
It can be obtained by laminating in order of layer-p layer.

The p-layer, the i-layer, the first i-layer, the second i-layer, the third i-layer, and the n-layer are formed by a plasma CVD method using a predetermined source gas, light, CVD method, EC
Each of them can be formed by an R plasma CVD method or the like.

When an amorphous silicon solar cell is obtained by forming an amorphous silicon layer and a transparent electrode (consisting of the aforementioned high refractive index transparent conductive film of the present invention) in this order when viewed from the substrate side, and In view of the above, in any case where an amorphous silicon solar cell is obtained by forming a transparent electrode (comprising the high refractive index transparent conductive film of the present invention described above) and an amorphous silicon layer in this order, the transparent electrode is It may be formed in direct contact with the above-mentioned amorphous silicon layer, but from the viewpoint of obtaining a solar cell with high conversion efficiency, a light confinement layer having a texture structure between the transparent electrode and the amorphous silicon layer Is preferably interposed.

The light confinement layer has a refractive index of about 1.6, such as ZnO, Al-doped ZnO, and fluorine-doped SnO _2.
It is preferably formed of a transparent material having a size of from 2.0 to 2.0.
The surface roughness (R _max ) of the light confinement layer on the transparent electrode side is preferably 0.1 to 100 μm. When the surface roughness is less than 0.1 μm or more than 100 μm, the effect of confining light decreases. The surface roughness is more preferably from 0.2 to 50 μm, particularly preferably from 0.5 to 20 μm. The above-described light confinement layer can be formed by a plasma CVD method or the like as in the related art.

When an amorphous silicon solar cell is obtained by forming an amorphous silicon layer and a transparent electrode in this order when viewed from the substrate side, the entire shape in plan view is formed on the transparent electrode. The auxiliary electrode layer having a lattice shape or the like may be formed of a conductive thin wire having a line width of 10 to 100 μm. Since the electrode resistance can be reduced by forming the auxiliary electrode layer,
It is possible to deal with a large area.

Specific examples of the material of the auxiliary electrode layer (the material of the conductive thin wire) include aluminum (Al), copper (C
u), silver (Ag), platinum (Pt), gold (Au) and the like. Further, the auxiliary electrode layer may be formed by coating the above-mentioned layer (thin wire) made of a single metal with titanium nitride (TiN), titanium (Ti) or the like. The thickness of the auxiliary electrode layer (the thickness of the conductive thin wire) is 0.01 to 10
It is preferably set to μm. When the thickness is less than 0.01 μm, the moisture resistance of the auxiliary electrode layer is reduced, and when it exceeds 10 μm, it is not economical. The thickness of the auxiliary electrode layer is 0.1 to
More preferably 0.5 μm, 0.3-1 μm
It is particularly preferred that The auxiliary electrode layer can be formed by a vacuum deposition method, a sputtering method, a screen printing method, or the like.

Even when the solar cell of the present invention is the above-mentioned amorphous silicon solar cell, the transparent electrode is formed of a λ / 4 film or a film when the transparent electrode is formed by the high refractive index transparent conductive film of the present invention. If the thickness of the film is a value close to the λ / 4 film, the transparent electrode can also serve as an antireflection film, so that the antireflection film conventionally formed as a separate member from the transparent electrode is omitted. It is possible to reduce the manufacturing cost of the amorphous silicon solar cell without lowering the conversion efficiency.

[0055]

Embodiments of the present invention will be described below. Using non-alkali glass substrate (Corning # 7059) having a thickness of 1mm as film substrate made in Example 1, hexagonal layered compound represented by In ₂ O ₃ (ZnO) ₃ as a sputtering target and In ₂ O ₃ [The relative density is 97%. As shown in Table 1, indium (In)
Has an atomic ratio In / (all metal elements) of 0.50. To form a high-refractive-index transparent conductive film in the following manner.

First, the above-mentioned glass substrate and sputtering target were mounted in a DC magnetron sputtering apparatus equipped with a turbo molecular pump as an exhaust system, and the inside of the vacuum chamber was evacuated to 5 × 10 ⁻⁴ Pa or less. Thereafter, the mixture was heated to 120 ° C. and evacuated continuously for further 6 hours. The pressure (total pressure) in the vacuum chamber after evacuation is 1 × 1
0 ^-4 Pa and the partial pressure of water gas were 5 × 10 ^-6 Pa. Next, a mixed gas of Ar gas (purity: 99.999%) and O ₂ gas (purity: 99.999%) (volume concentration of O ₂ gas: 3%) was introduced into the vacuum chamber, and the pressure in the vacuum chamber was increased. To 0.
After setting the pressure to 1 Pa, the DC output was 2 W / cm ² and the substrate temperature was 10
A high refractive index transparent conductive film having a thickness of 520 Å was formed by sputtering at 0 ° C.

Table 1 shows excerpts of the film forming conditions. The thickness, composition (excluding oxygen), crystallinity, transmittance of light having a wavelength of 550 nm (hereinafter abbreviated as “light transmittance”), and refractive index (measurement light) of the obtained high refractive index transparent conductive film are obtained. Has a wavelength of 5
50 nm. same as below. ), Sheet resistance and specific resistance are shown in Table 2.

The above film thickness was measured by the stylus method [device used: D
EKTAK3030 (manufactured by Sloan)], and the composition is determined by inductively coupled plasma emission spectroscopy [used equipment:
SPS-1500VR (manufactured by Seiko Instruments Inc.)], the crystallinity is determined by X-ray diffraction [used equipment: Rotaflex RU-200B (manufactured by Rigaku Corporation)], and the light transmittance is measured by spectroscopy [used equipment: U- 3210 (manufactured by Hitachi, Ltd.)], the refractive index is determined by the ellipso method [device used: DVA-36L (manufactured by Mizojiri Optical Industrial Co., Ltd.)], and the sheet resistance is the four probe method [device used: LORESTA FP]
(Manufactured by Mitsubishi Yuka) and the specific resistance was calculated by taking the product of the film thickness and the sheet resistance.

Examples 2 to 5 Under the same conditions as in Example 1 except that a sputtering target composed of an oxide sintered body having the composition (excluding oxygen) shown in Table 1 was used, a high refractive index transparent conductive material was used. Each membrane was formed. The physical properties and the like of these high refractive index transparent conductive films were determined in the same manner as in Example 1. Table 2 shows the results.

Comparative Examples 1 and 2 Except that a sputtering target composed of an oxide sintered body having the composition shown in Table 1 (excluding oxygen) was used, and the film forming conditions were changed to the conditions shown in Table 1. In the same manner as in Example 1, transparent conductive films were formed. The physical properties and the like of these transparent conductive films were determined in the same manner as in Example 1. Table 2 shows the results
Shown in

[0061]

[Table 1]

[0062]

[Table 2]

As shown in Table 2, Examples 1 to 5
Each of the high refractive index transparent conductive films obtained in the above has a refractive index of 2.41 to
Since it is as high as 2.50, wavelengths 501 to 5
Antireflection film (λ = 501 to 539) for light of 39 nm
Λ / 4 film). Further, these high refractive index transparent conductive films have a specific resistance of 3.30 × 10 ^−4.
~ 3.54 × 10 ^-4 Ωcm and light transmittance of 81.2
Since it is as high as 81.5%, it can be used also as a transparent electrode.

Therefore, when a transparent electrode for a solar cell, particularly a transparent electrode for an amorphous silicon solar cell is formed using the high refractive index transparent conductive film obtained in Examples 1 to 5, the transparent electrode Since the anti-reflection film can also serve as the anti-reflection film, it is not necessary to form the anti-reflection film again, and as a result, the solar cell can be manufactured at lower cost without lowering the conversion efficiency of the solar cell. Will be possible.

On the other hand, the ITO film having a thickness of 600 Å obtained in Comparative Example 1 has a specific resistance of 6.16 × 10 ⁻⁴ Ωc.
Since the light transmittance at m is 78.1%, it can be used as a transparent electrode, but the refractive index of this ITO film is as low as 1.83. For this reason, when the ITO film also serves as an anti-reflection film, the peak wavelength of light that can prevent reflection is 439 nm or its vicinity. Therefore, in order to form an antireflection film for light having a wavelength of 500 to 700 nm, which is a problem in amorphous silicon solar cells, with this ITO film, it is necessary to increase the film thickness to at least about 683 angstroms.
Since the light transmittance decreases with the increase in the film thickness, it is presumed that the conversion efficiency of the solar cell decreases.

The 600-Å-thick In—Zn—O-based amorphous oxide film obtained in Comparative Example 2 also has a specific resistance of 6.26 × 10 ⁻⁴ Ωcm and a light transmittance of 78.2%. Therefore, it can be used as a transparent electrode, but the refractive index of this In—Zn—O-based film is as low as 1.85. For this reason, for example, when an anti-reflection film for light having a wavelength of 500 to 700 nm, which is a problem in an amorphous silicon solar cell, is formed of this In—Zn—O-based amorphous oxide film, the ITO film of Comparative Example 1 is not used. As if you used it,
It is assumed that the conversion efficiency of the amorphous silicon solar cell decreases.

Example 6 A stainless steel substrate having an uneven surface (surface roughness R _max : 5)
0 μm) was used as a substrate, and an amorphous silicon layer (photoelectric conversion layer) made of pin type amorphous silicon was formed on the stainless steel substrate by the RF-plasma CVD method in the following manner.

First, the stainless steel substrate was placed on a susceptor in a reaction chamber of an RF-plasma CVD apparatus, and SiH ₄ gas (1 sccm) and H ₂ gas (48
sccm), and PH diluted to 1 vol% with H ₂ gas.
_{Using 3} gases (0.5 sccm), pressure during film formation (atmospheric pressure; the same applies hereinafter) 1 × 10 ⁻² Pa, RF power 18
W, a film is formed under the condition of a substrate temperature of 200 ° C., and a 400 angstrom thick a-S film is formed on the stainless steel substrate.
i: An n layer composed of an H layer (having phosphorus (P) added as a donor) was formed.

Next, SiH ₄ gas (4
0 sccm), GeH ₄ gas (40 sccm) and H
_{Using 2} gases (150 sccm), pressure during film formation 4 × 1
A film was formed under the conditions of 0 ⁻³ Pa, RF power of 20 W, and a substrate temperature of 200 ° C., and an i-layer made of an a-SiGe: H layer having a thickness of 5000 angstrom was formed on the n-layer.

[0070] Finally, SiH ₄ gas diluted to 10 vol% with H ₂ gas (0.25sccm), H ₂ gas (34s
ccm), and B ₂ H ₆ diluted to 2 vol% with H ₂ gas.
Using gas as source gas, pressure at the time of film formation 1 × 10 ^-2
A film was formed under the conditions of Pa, RF power of 42 W, and substrate temperature of 200 ° C., and was formed of an a-Si: H layer having a thickness of 200 Å (to which boron (B) was added as an acceptor) on the i-layer. A p-layer was formed. By sequentially forming the n layer, the i layer, and the p layer on the stainless steel substrate, a photoelectric conversion layer composed of a single pin type amorphous silicon layer was formed on the stainless steel substrate.

Next, Z was used as a sputtering target.
By an RF-magnetron sputtering method using a sintered target of nO (relative density 95%), a ZnO layer having a thickness of 800 angstroms (refractive index 1.7) was formed on the above-mentioned pin type amorphous silicon layer (on the p layer). )
A light confinement layer consisting of was formed. At this time, a mixed gas of Ar gas and O ₂ gas (volume concentration of O ₂ gas: 3%) was used as an atmosphere gas, and the film was formed at a pressure of 0.1 Pa and a substrate temperature of 150 ° C. .

Thereafter, an oxide sintered body target composed of In ₂ O ₃ and ZnO [In / (all metal elements) = 0.7
[0, 98% relative density] was used as a sputtering target, and a high-refractive-index transparent conductive film as a transparent electrode was formed under the same film forming conditions as in Example 2. The thickness of the high refractive index transparent conductive film is 550 Å, and the atomic ratio of In / (In
+ Zn) is 0.75, the light transmittance (transmittance of light having a wavelength of 550 nm; the same applies hereinafter) is 81.5%, and the refractive index (wavelength is 55).
Refractive index of light at 0 nm. same as below. ) Was 2.45 and the specific resistance was 3.50 × 10 ⁻⁴ Ωcm.

The optical film thickness of the high refractive index transparent conductive film is
Since the film thickness is 550 angstroms and the refractive index is 2.45 as described above, it is 134.75 nm, and the high refractive index transparent conductive film corresponds to a λ / 4 film when λ is 539 nm. This high-refractive-index transparent conductive film is used as a transparent electrode also serving as an antireflection film.

Finally, an auxiliary electrode layer made of a thin line-shaped Ag layer having a line width of 30 μm and a film thickness of 0.5 μ was formed on the high refractive index transparent conductive film by a screen printing method using a silver (Ag) paste. Formed. The overall shape of the auxiliary electrode layer has a lattice shape. By forming up to the above-mentioned auxiliary electrode layer, an amorphous silicon solar cell having a photoelectric conversion layer composed of a single layer of pin type amorphous silicon was obtained. The size of this solar cell in plan view is 10 cm □.

When the characteristics of the above solar cell were measured using a transparent electrode (high refractive index transparent conductive film) as a positive electrode and a stainless steel substrate as a negative electrode, the open-circuit voltage (V _oc ) was 0.58 V, Short circuit current density ( _Ioc ) 28m
A / cm ² , fill factor (FF) 0.68, conversion efficiency 1
1.0%. In measuring these characteristics, light from a xenon lamp adjusted by a specific optical filter (a solar simulator) was used as a light source.

Example 7 In ₂ O ₃ , ZnO and G were used as sputtering targets for forming a high refractive index transparent conductive film as a transparent electrode.
a ₂ O ₃ and an oxide sintered body target [In /
(All metal elements) = 0.70, Ga / (all metal elements) =
0.03, relative density of 98%], and a solar cell was fabricated in the same manner as in Example 6. When the characteristics of the solar cell were measured in the same manner as in Example 6, the open-circuit voltage (V _oc ) was 0.59 V, and the short-circuit current density (I _oc ) was 29 mA /
cm ² , fill factor (FF) 0.65, conversion efficiency 11.1
%Met.

Embodiment 8 After forming a pin-type amorphous silicon layer (hereinafter referred to as a “first pin-type amorphous silicon layer”) in the same manner as in Example 6, an additional layer is formed on the first pin-type amorphous silicon layer. Except that a pin-type amorphous silicon layer (hereinafter, referred to as a “second pin-type amorphous silicon layer”) was formed, a solar cell including a pin-type amorphous silicon layer having a two-layer repeating photoelectric conversion layer was formed in the same manner as in Example 6. A battery was manufactured.

In the second pin type amorphous silicon layer, the n layer and the p layer are formed in the same manner as the n layer and the p layer of the first pin type amorphous silicon layer, respectively. It was formed by Si: H. Therefore, the layer configuration of the photoelectric conversion layer is n-layer-first i-layer-p-layer-n-layer-second i-layer-p-layer when viewed from the stainless steel substrate side.

When the characteristics of the solar cell were measured in the same manner as in Example 6, the open-circuit voltage (V _oc ) was 0.58 V, the short-circuit current density (I _oc ) was 31 mA / cm ² , and the fill factor (F)
F) The conversion efficiency was 0.65 and the conversion efficiency was 11.3%.

Embodiment 9 After forming a pin-type amorphous silicon layer (hereinafter, referred to as a “first pin-type amorphous silicon layer”) in the same manner as in Example 6, other layers are formed on the first pin-type amorphous silicon layer. (Hereinafter referred to as “second pin-type amorphous silicon layer”), and another pin-type amorphous silicon layer (hereinafter “third-type amorphous silicon layer”) is formed on the second pin-type amorphous silicon layer. In the same manner as in Example 6, except that a pin-type amorphous silicon layer was formed, a photovoltaic layer was formed of a pin-type amorphous silicon layer having a three-layer repeating structure.

The n and p layers of the second and third pin type amorphous silicon layers are formed in the same manner as the n and p layers of the first pin type amorphous silicon layer, respectively. The i-layer in the amorphous silicon layer is made of a-Si: H, and the third pi
The i-layer in the n-type amorphous silicon layer is a-Si
C: formed by H respectively. Therefore, when viewed from the stainless steel substrate side, the layer configuration of the photoelectric conversion layer is n-layer-first
Layer, p layer, n layer, second i layer, p layer, n layer, third i layer, and p layer.

When the characteristics of the solar cell were measured in the same manner as in Example 6, the open-circuit voltage (V _oc ) was 0.57 V, the short-circuit current density (I _oc ) was 31 mA / cm ² , and the fill factor (F)
F) The conversion efficiency was 0.65 and the conversion efficiency was 11.5%.

Example 10 An alkali-free glass substrate having a surface roughness (R _max ) of 50 μm was used as a substrate. An Al film having a thickness of 0.3 μm and a TiN film having a thickness of 0.1 μm were formed on the alkali-free glass substrate. Are sequentially formed by vacuum evaporation to form a back electrode having a two-layer structure, and then an amorphous silicon layer (photoelectric conversion layer) and Zn are formed on the back electrode in the same manner as in Example 6.
A solar cell was manufactured by sequentially forming an O layer (light confinement layer), a high refractive index transparent conductive film (a transparent electrode also serving as an antireflection film), and an auxiliary electrode layer. When the characteristics were measured using the high refractive index transparent conductive film in the above solar cell as a positive electrode and the back electrode as a negative electrode, the open voltage (V _oc ) was 0.58 V and the short circuit current density (I _oc ) was 27 m.
A / cm ² , fill factor (FF) 0.66, conversion efficiency 1
0.3%.

Example 11 The surface roughness (R _max ) was changed to 5 in place of the alkali-free glass substrate.
A solar cell was fabricated in the same manner as in Example 10, except that a 0 μm polyimide resin substrate (125 μm in thickness) was used.
When the characteristics of the above solar cell were measured in the same manner as in Example 10, the open-circuit voltage (V _oc ) was 0.59 V, the short-circuit current density (I _oc ) was 26 mA / cm ² , and the fill factor (FF) was 0. 67, the conversion efficiency was 10.3%.

Comparative Example 3 A solar cell was produced in the same manner as in Example 6, except that a transparent electrode (ITO film) was formed in the same manner as in Comparative Example 1. When the characteristics of the above solar cell were measured in the same manner as in Example 6, the open-circuit voltage (V _oc ) was 0.57 V, the short-circuit current density (I _oc ) was 16 mA / cm ² , and the fill factor (FF) was 0.
68, and the conversion efficiency was as low as 6.2%.

The low conversion efficiency of this solar cell is as follows.
The transparent electrode (actual film thickness of 600 Å, refractive index 1.83) has a peak wavelength of about 439 nm which can function as an anti-reflection film, whereas the photoelectric conversion layer (pin type amorphous silicon layer) has the highest efficiency. Since the wavelength of the light to be photoelectrically converted is about 550 nm, it is presumed that the reason is that the antireflection ability of the transparent electrode did not significantly contribute to the improvement of the conversion efficiency of the solar cell.

By setting the thickness of the transparent electrode film to about 751 Å, the peak wavelength at which the transparent electrode can function as an anti-reflection film is approximately 550 n.
m, it seems at first glance that the conversion efficiency of the solar cell is improved. However, when the thickness of the transparent electrode is as large as about 751 Å, the light transmittance is reduced. It is presumed that the conversion efficiency cannot be improved so much.

Comparative Example 4 A solar cell was fabricated in the same manner as in Example 6 except that a transparent electrode (an In-Zn-O-based amorphous oxide film having a low refractive index) was formed in the same manner as in Comparative Example 2. did. When the characteristics of the above solar cell were measured in the same manner as in Example 6, the open-circuit voltage (V _oc ) was 0.58 V, and the short-circuit current density (I _oc ) was 18 m.
A / cm ² , fill factor (FF) was 0.66, and conversion efficiency was as low as 6.9%.

The low conversion efficiency of this solar cell is as follows.
As in Comparative Example 3, the above transparent electrode (actual film thickness 600
This is presumed to be due to the fact that the antireflection ability of Angstroms and the refractive index of 1.85) did not significantly contribute to the improvement of the conversion efficiency of the solar cell. Even if the peak wavelength at which the transparent electrode can function as an anti-reflection film is set to 550 nm by setting the thickness of the transparent electrode film to about 743 angstroms, for the same reason as in Comparative Example 3, the solar cell It is presumed that the improvement of the conversion efficiency cannot be expected so much.

[0090]

As described above, the high-refractive-index transparent conductive film of the present invention has a high refractive index of 2.2 to 2.5 and a low specific resistance of 5 × 10 ⁻⁴ Ωcm. It becomes easy to form a thin transparent electrode that also serves as a film. Therefore, by using the high refractive index transparent conductive film of the present invention,
For example, the solar cell can be manufactured at lower cost without lowering the conversion efficiency of the solar cell.

Further, in the solar cell of the present invention, the transparent electrode can also serve as an anti-reflection film (an anti-reflection film having a design wavelength at or near the wavelength of light to be photoelectrically converted with high efficiency ). The conversion efficiency when the electrode also serves as the antireflection film does not substantially decrease as compared with a conventional solar cell having the same structure except that the transparent electrode also does not serve as the antireflection film. Therefore, by using the solar cell of the present invention, it becomes easy to provide an inexpensive solar cell without lowering the conversion efficiency.

Claims (16)

[Claims] 1. A refraction index of 2.2 to 2.5 and a specific resistance of 5
A high-refractive-index transparent conductive film comprising an oxide having a density of ^10-4 Ωcm or less. 2. The high refractive index transparent conductive film according to claim 1, wherein indium (In), zinc (Zn) and oxygen (O) are main constituent elements. 3. The high refractive index transparent conductive film according to claim 1, wherein gallium (Ga) is contained as a constituent element. 4. The atomic ratio In / (all metal elements) of indium (In) is 0.5 to 0.9, and the atomic ratio Ga / (all metal elements) of gallium (Ga) is 0.04 or less. The high refractive index transparent conductive film according to any one of claims 1 to 3. 5. A photoelectric conversion layer that generates an electromotive force by light irradiation, and a pair of positive and negative electrodes electrically connected to the photoelectric conversion layer, at least one of the pair of electrodes being a light incident surface. And the electrode formed on the light incident surface side is a transparent electrode made of the high refractive index transparent conductive film according to any one of claims 1 to 4. Solar cell. 6. The solar cell according to claim 5, wherein a transparent electrode made of a high refractive index transparent conductive film functions as an antireflection film. 7. The solar cell according to claim 5, wherein a photoelectric conversion layer made of an amorphous silicon layer and a transparent electrode made of a high-refractive-index transparent conductive film are laminated in this order on a substrate. 8. The solar cell according to claim 7, wherein the substrate is a glass substrate. 9. The solar cell according to claim 7, wherein the substrate is a metal substrate. 10. The solar cell according to claim 7, wherein the substrate is a heat-resistant resin substrate. 11. The solar cell according to claim 7, further comprising a back electrode layer between the substrate and the amorphous silicon layer. 12. The substrate according to claim 7, wherein a surface of the substrate on which the amorphous silicon layer is provided is provided with irregularities having a surface roughness of 1 μm or more. Solar cell. 13. The amorphous silicon layer has a two-layer repeating structure, and each layer having the two-layer repeating structure is made of pin-type amorphous silicon.
The solar cell according to claim 12. 14. The amorphous silicon layer has a three-layer repeating structure, and each layer having the three-layer repeating structure is made of pin-type amorphous silicon.
The solar cell according to claim 12. 15. The solar cell according to claim 7, further comprising a light confinement layer between the amorphous silicon layer and a transparent electrode made of a high refractive index transparent conductive film. 16. The solar cell according to claim 5, having an auxiliary electrode layer as an uppermost layer on the light incident surface side.