JP3481123B2 - Photovoltaic device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device in which a transparent conductive oxide film is interposed between a highly reflective metal and a photoelectric conversion layer to effectively use incident light.

[0002]

2. Description of the Related Art Conventionally, in a photovoltaic device using amorphous silicon or the like as a photoelectric conversion layer, an electrode made of a highly reflective metal is arranged on the back surface side to make effective use of incident light, and photoelectric conversion is performed. A structure is adopted in which light transmitted through the layer is reflected and is made incident again in the photoelectric conversion layer.

On the amorphous silicon semiconductor layer, silver (A
When a highly reflective metal such as g), aluminum (Al), or copper (Cu) is formed, the metal reacts with the amorphous silicon semiconductor layer to form an alloy at the interface, and good reflection characteristics can be obtained. Absent. Therefore, for example, Japanese Patent Publication No. 60-418
As disclosed in Japanese Patent No. 78, a diffusion barrier layer made of a transparent conductive oxide film such as indium tin oxide (ITO) is interposed between an amorphous semiconductor layer and a highly reflective metal layer to form amorphous silicon. The diffusion of the semiconductor layer is prevented.

As the diffusion prevention layer, an ITO film having a uniform composition, which is usually formed by a sputtering method, is used, and a highly reflective metal such as silver, aluminum or copper is formed on the ITO film by a sputtering method. ing.

[0005]

By the way, when a diffusion preventing layer made of a transparent conductive oxide film and a highly reflective metal layer are continuously formed by a sputtering method, when the highly reflective metal layer is formed, a transparent conductive oxide film is formed. There is a problem in that the interface with the highly reflective metal layer is damaged and the reflectance is lowered. The reason for this damage is currently unknown,
Oxygen deficiency occurs on the surface of the transparent conductive oxide film such as the ITO film due to plasma during sputtering, or the surface of the transparent conductive oxide film such as the ITO film becomes active, and a reduction reaction occurs at the interface with the highly reflective metal layer, resulting in transparency. It is considered that oxygen deficiency occurs on the surface of the conductive oxide film. If oxygen deficiency occurs in the transparent conductive oxide film, the light transmittance decreases, the amount of reflected light decreases, and effective use of light cannot be achieved.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 5-121769, an oxidation preventing metal such as steel containing chromium or platinum containing chromium is interposed between the transparent conductive oxide film and the high reflection metal layer, and the surface of the high reflection metal layer is A photovoltaic device has been proposed which prevents deterioration due to oxidation and efficiently reflects light.

However, in the above-mentioned photovoltaic device, since an anti-oxidizing metal such as steel or platinum containing chromium is interposed, light transmission is hindered by this film. That is, even if these films are formed thin, the light transmittance is lower than that of the transparent conductive oxide film, and it is undeniable that the reflection efficiency of the spectrum is lowered.

The present invention has been made in order to solve the above-mentioned problems of the prior art, prevents oxygen deficiency from occurring in the transparent conductive oxide film, prevents a decrease in light transmittance of the transparent conductive film, and improves efficiency. It is an object of the present invention to provide a photovoltaic device capable of effective light reflection.

[0009]

The present invention is a photovoltaic device in which a diffusion prevention layer made of a transparent conductive oxide film is inserted between a photoelectric conversion layer and a highly reflective metal layer, wherein the diffusion prevention layer comprises: It is characterized in that the amount of oxygen atoms in the film in the vicinity of the interface with the highly reflective metal layer is made larger than the amount of oxygen atoms in the film in other regions in order to compensate for the oxygen deficiency generated in the vicinity of the interface.

The transparent conductive oxide film is composed of an ITO thin film, and the composition ratio is changed so that the ratio of oxygen atomic weight to indium atomic weight (O / In) in the ITO thin film increases toward the highly reflective metal layer. You should let me.

The specific resistance of the ITO thin film is 10 ^-2 Ω.
cm or less, the ratio of the atomic weight of oxygen to the atomic weight of indium (O / In) in the ITO thin film may be changed between 1.5 and 4.

According to the above structure, the amount of oxygen in the vicinity of the interface of the transparent conductive oxide film increases, oxygen deficiency of the transparent conductive oxide film can be prevented, and the reduction of the light transmittance in this portion can be prevented.
As a result, the decrease in short-circuit current is reduced, and the conversion efficiency can be improved.

Further, a transparent insulating film may be provided between the transparent conductive oxide film and the highly reflective metal layer.

By interposing the transparent insulating film, it is possible to prevent the metal reflective film from being oxidized by the reduction of the ITO film or the like when forming the highly reflective metal, so that the high reflectance can be maintained.

Further, the present invention is a photovoltaic device in which a diffusion prevention layer made of a transparent conductive oxide film is inserted between a photoelectric conversion layer and a back electrode as a highly reflective metal layer, wherein the transparent conductive oxide film is provided. Thickness of electrical conduction between the electrode and the back electrode
The transparent insulating film is provided.

The average thickness of the transparent insulating film is 5 nm or more and 5
It is preferable to set it to 0 nm or less.

By inserting the transparent insulating film, it is possible to prevent damage at the time of forming the highly reflective metal layer by the sputtering method and improve the light reflectance.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an element structure diagram for explaining a first embodiment of a photovoltaic device of the present invention.

As shown in FIG. 1, a transparent conductive film 2 made of indium tin oxide (ITO), tin oxide (SnO ₂ ), zinc oxide (ZnO) or the like is provided on a transparent insulating substrate 1 made of glass or the like. To be In this embodiment, the film thickness is 500n
m tin oxide is formed by the thermal CVD method. A photoelectric conversion layer 3 made of an amorphous silicon semiconductor is provided on the transparent conductive film 2 by a conventionally known plasma CVD method.

The photoelectric conversion layer 3 is composed of B ₂ H ₆ and Si.
A mixed gas of H ₄ , CH ₄ , and H ₂ is decomposed by glow discharge and p-type amorphous silicon carbide (a-Si) having a film thickness of about 5 nm.
C) A film made of i-type a-SiC for depositing the layer 3a, and then performing glow discharge decomposition of a mixed gas of SiH ₄ , CH ₄ , and H ₂ to prevent recombination of carriers at the p / i interface. Thickness 5nm
The i-type amorphous silicon (a-Si) layer 3c having a film thickness of about 300 nm, which is a power generation layer, is deposited by glow discharge decomposition of SiH ₄ gas.
Finally, glow discharge decomposition of a mixed gas of PH ₃ , SiH ₄ , and H ₂ was performed to perform n-type amorphous silicon (a-
It is formed by depositing a Si) layer 3d.

On the photoelectric conversion layer 3, a transparent conductive oxide film 4 having a film thickness of about 100 nm is provided as a diffusion prevention layer, which is a feature of the present invention, by a sputtering method. In this embodiment, an ITO film is used as the transparent conductive oxide film 4, and the composition ratio is changed so that the ratio of the atomic weight of oxygen and the atomic weight of indium (O / In) in the film increases toward the highly reflective metal layer. I am letting you. Then, a back electrode 5 made of a highly reflective metal layer is provided on the transparent conductive oxide film 4 by a sputtering method. In this embodiment, the back electrode 5 has a film thickness of 300.
nm Ag was formed by the sputtering method. The conditions of this sputtering method were RF power of 1000 W, target size of 6 inches Φ, Ar gas as a sputtering gas, and substrate temperature of 200 ° C. The other forming conditions described above are shown in Table 1.
Table 2 shows the conditions for forming the ITO film as the transparent conductive oxide film.
Shown in.

[0022]

[Table 1]

ITO as the transparent conductive oxide film 4 described above
The film forming conditions are RF power of 300 W, target size of 6 inches Φ, reaction pressure of 3 × 10 ⁻³ Torr, and other conditions are shown in Table 2. In addition, in Table 2, ITO
The conditions for forming a conventional ITO film that does not change the oxygen concentration in the film are also described.

[0024]

[Table 2]

The specific resistances of the ITO film of the present invention and the conventional ITO film formed under the above conditions are 1 × 10 ⁻³ Ωcm in the present invention and 5 × 10 ⁻⁴ Ωcm in the conventional example, which are very good. Various characteristics were obtained. Further, the high resistivity of the thin film prepared in the present invention, the transmittance is improved with an increase in the amount of oxygen,
This is probably because the carrier density is decreasing.

The amounts of oxygen and indium in the ITO film prepared under the above conditions were measured by SIMS, and the ratio (O / In) of the atomic weight of oxygen to the atomic weight of indium in the ITO thin film was determined. The results are shown in FIG. The thickness of the ITO thin film is 1000 angstroms. In the conventional example, (O / In) is 1.5
However, in the present invention, (O / In) is 1.5 to
It turned out that it increased to nearly four. That is, the ratio of the atomic weight of oxygen increases from the photoelectric conversion layer 3 side toward the back electrode 4 side.

Next, as an anti-diffusion layer, the above-mentioned ITO thin film according to the present invention and a conventional ITO thin film were used, and the photovoltaic characteristics were obtained when the ITO thin film and the back electrode 5 made of Ag were continuously formed by the sputtering method. Table 3 shows the measured results.
Both samples were prepared under the same conditions except that the ITO film was different.

[0028]

[Table 3]

In the conventional photovoltaic device, IT is used by sputtering.
When the O thin film and the back electrode are continuously formed, the surface of the ITO thin film is damaged, oxygen deficiency occurs on the surface of the ITO thin film, and the short circuit current is reduced due to the reduction of the light transmittance in this portion. Was there. On the other hand, like the present invention,
By increasing the amount of oxygen near the interface, oxygen vacancies could be prevented, the decrease in light transmittance at this part was prevented, the decrease in short-circuit current was reduced, and the conversion efficiency was improved.

In the above-described embodiment, the amount of oxygen atoms in the transparent conductive oxide film is changed so as to be gradually increased toward the highly reflective metal layer. The same effect can be obtained by using a laminated film in which the composition in the film is increased and the other regions are left as they are.

In the first embodiment described above, a photovoltaic device having a structure in which light enters from the substrate side, that is, a so-called forward type photovoltaic device has been described. However, a metal electrode is formed on a non-translucent substrate. Then, the semiconductor layer and the translucent electrode are sequentially formed,
The present invention can be applied to a photovoltaic device having a structure in which light is incident from the transparent electrode side, that is, a so-called reverse type photovoltaic element. FIG. 3 is a sectional view showing an element structure in which the present invention is applied to a so-called reverse type photovoltaic device.

As shown in FIG. 3, a back electrode 12 made of a highly reflective metal such as Ag is provided on a non-translucent substrate 11 such as a stainless substrate. A transparent conductive oxide film 13 as a diffusion preventing layer is provided on this back electrode 12. In this embodiment, Z is used as the transparent conductive oxide film 13.
nO was used. The composition ratio of Zn and O in the transparent conductive oxide film 13 is changed from the back electrode 12 side to the photoelectric conversion layer 14 side so that the atomic weight of oxygen decreases. That is, the amount of oxygen atoms near the back electrode 12 is increased.
Then, a conventionally well-known plasma CVD is performed on the diffusion prevention layer 13.
The photoelectric conversion layer 14 made of an amorphous silicon semiconductor is provided by the method. The photoelectric conversion layer 14 is an n-type a-Si layer 1
4a, an i-type a-Si layer 14b that is a power generation layer, and p / i
In order to prevent recombination of carriers at the interface, i-type a-SiC
Interface i layer 14c composed of and p-type a-SiC layer 14d
And are sequentially deposited to be formed. The conditions for forming these films are the same as those in the above-described first embodiment.

Then, ITO is formed on the p-type a-SiC 14d.
A transparent electrode 15 made of a film is provided, and a collector electrode 16 made of Ag is provided thereon.

In this embodiment, the ratio of the atomic weight of oxygen to the atomic weight of zinc in the ZnO film (O / Zn) is 12
Then, the photoelectric conversion layer 14 is increased in number so that oxygen deficiency does not occur.
The composition ratio is changed so as to decrease toward.

When the back electrode 12 and the transparent conductive oxide film 13 are continuously formed, even if oxygen is reduced by the reduction reaction at the interface between the transparent conductive oxide film 13 and the back metal 12, many oxygen atoms are already present in this portion. Since it is contained, oxygen deficiency does not occur, and deterioration of the light transmittance in this portion can be prevented. In this way, by increasing the amount of oxygen near the interface,
Oxygen deficiency can be prevented, a decrease in light transmittance at this portion is prevented, a decrease in short circuit current is reduced, and conversion efficiency is improved.

Next, a third embodiment of the present invention will be described. In the first and second embodiments described above,
The oxygen deficiency of the transparent conductive oxide film in the continuous formation of the transparent conductive oxide film and the highly reflective metal layer is compensated for in advance by increasing the number of oxygen atoms in the transparent conductive oxide film in this region. In the third and fourth embodiments, the amount of oxygen atoms in the transparent conductive oxide film is the same as the conventional one, and oxygen deficiency does not occur in this film.

First, the third embodiment will be described with reference to FIG. FIG. 4 is a sectional view of an element structure of a so-called forward type photovoltaic device.

On a transparent insulating substrate 1 made of a glass substrate having a thickness of 4 mm, a transparent electrode film 2 made of tin oxide and having a thickness of about 500 nm and having a concavo-convex surface for confining light formed on the surface is deposited. A photoelectric conversion layer 3 made of an amorphous silicon semiconductor is provided by a conventionally known plasma CVD method. This photoelectric conversion layer 3 has a p-type structure similar to that of the first embodiment.
The i-type a-SiC layer 3a and the interface i-layer 3b made of i-type a-SiC to prevent recombination of carriers at the p / i interface.
Then, the i-type a-Si 3c and the n-type a-Si layer 3d are sequentially formed.

A transparent conductive oxide film 4 is provided on the photoelectric conversion layer 3 by a sputtering method. In this embodiment, an ITO film is used as the transparent conductive oxide film, and the ratio of oxygen atom weight to indium atom weight (O / In) in the film is formed in the same manner as in the conventional example shown in Table 2, and the concentration in the film is It is constant.

A transparent insulating film 6 is formed on the transparent conductive oxide film 4. In this embodiment, S having a thickness of 3 to 100 nm is used.
An iO ₂ film was formed. Then, the back surface electrode 5 as a highly reflective metal layer made of Ag is provided on the transparent insulating film 6 by a sputtering method. The above-mentioned SiO ₂ film was formed by a sputtering method, using Ar gas as a sputtering gas, RF power of 1000 W, target size of 6 inches Φ, and substrate temperature of 200 ° C. A conventional photovoltaic device having no transparent insulating film 4 in Table 4 and the transparent insulating film 4
The results of measuring the photovoltaic characteristics of the photovoltaic device of the present invention in which the film thickness of the film is variously changed are shown.

[0041]

[Table 4]

As shown in Table 4, when the ITO film and the back electrode are continuously formed by the conventional sputtering method, the short circuit current is reduced due to the damage of the ITO thin film and the metal interface. The reduction reaction between the highly reflective metal layer and the transparent conductive oxide film due to is prevented, and as a result,
The short-circuit current increased and the conversion efficiency increased. In this embodiment, the conversion efficiency was increased when the thickness of the transparent insulating film 6 was in the range of 5 to 50 nm.

It is considered that the provision of the transparent insulating film 6 suppresses the oxygen deficiency due to the reduction of the transparent conductive oxide film when the back surface metal 5 is formed by the sputtering method, and prevents the reduction of the light transmittance. .

As described above, by inserting the transparent insulating film 6 having a film thickness of 5 nm or more between the transparent conductive oxide film 4 and the back surface electrode 5, damage caused when the highly reflective metal layer is formed by the sputtering method. Can be prevented and the light reflectance can be improved. The details of the damage are not clear at present, but IT
It is expected that oxygen deficiency occurs due to the reduction of the ITO film at the O film / metal interface and the light transmittance of the ITO decreases, resulting in a decrease in the light reflectance of the back electrode. If the thickness of the transparent insulating film 6 is set to 50 nm or less, the transparent conductive oxide film 4 and the back surface electrode 5 are electrically connected to each other through a pinhole or the like of the insulator. There is no adverse effect of loss. In particular, if there are irregularities, the thin insulating film causes more leakage.

In this embodiment, the SiO ₂ film is used as the transparent insulating film 6, but another insulating material such as S is used.
It is also possible to use a metal / semiconductor oxide film such as i ₃ N ₄ , Al ₂ O ₃ , AlN, TiN, and TiO ₂ and a nitride film. In addition to tin oxide, zinc oxide, copper oxide, a copper oxide-aluminum oxide compound or the like can be used as the transparent electrode.

FIG. 5 shows a photovoltaic device according to a fourth embodiment of the present invention, in which a stainless substrate 11 having a thickness of 0.55 mm is provided with unevenness on its surface and is made of aluminum having a thickness of 500 nm. The reflective metal layer 12 is formed. On this, a SiO ₂ film having a thickness of 50 nm is provided as a transparent insulating film 17. 50 nm thick as a diffusion prevention layer on top of this
A transparent conductive oxide film 13 made of ZnO is provided. A photoelectric conversion layer 14 made of an amorphous silicon semiconductor is provided on the transparent conductive oxide film 13 by a conventionally known plasma CVD method. This photoelectric conversion layer 14 is an n-type a-Si 14a.
The i-type a-Si layer 14b, the interface i-layer 14c made of i-type a-SiC in order to prevent carrier recombination at the p / i interface, and the p-type a-SiC layer 14d are the same as those described above. It is sequentially formed in the same manner as the above.

A transparent electrode 15 made of ITO is provided on the p-type a-SiC. Also in this embodiment, the conversion efficiency is increased when the film thickness of the transparent insulating film 17 is in the range of 5 to 50 nm.

By the way, in the above-described first and second embodiments, a transparent conductive oxide film such as ITO is interposed as a diffusion preventing layer between the highly reflective metal film such as silver and aluminum and the photoelectric conversion layer. However, a highly reflective metal film such as silver or aluminum may be oxidized by oxygen in the transparent conductive oxide film. Therefore, in order to prevent the oxidation of the highly reflective metal film, steel or platinum containing chromium in a film having a film thickness of about 10 angstroms to 100 angstroms is interposed between the diffusion prevention layer and the highly reflective metal film. Good. However, it is undeniable that the presence of chromium-containing steel or platinum in the film causes light to be absorbed by this film, resulting in a slight decrease in reflection efficiency. Therefore, in the present invention, the transparent insulating film used in the third and fourth embodiments is interposed between the transparent conductive oxide film serving as the diffusion prevention layer and the highly reflective metal layer.
As the transparent insulating film to be interposed, SiO ₂ , Si ₃ N ₄ ,
The film is made of Al ₂ O ₃ or the like and has a film thickness of 50 nm or less. By interposing a transparent insulating film, when forming a highly reflective metal, I
Due to the reduction of the TO film or the like, the metal reflection film is not oxidized and high reflectance can be maintained. Further, since the intervening film is a transparent insulating film, there is almost no absorption of light in this portion, and the reflectance between the transparent insulating film and the metal interface is as high as 95% or more, and the reflectance is improved. Since this thin insulator conducts electricity due to leakage, its resistance component is small.

Although amorphous silicon is used for the power generation layer in the above-described embodiments, microcrystalline silicon or thin film polycrystalline silicon may be used instead. Also,
Thin film compound semiconductors such as CdTe, GaAs, and CuInSe ₂ can also be used. Furthermore, a-Si / a-Si
Ge, a-Si / a-SiGe / a-SiGe, a-S
A laminated structure such as i / microcrystalline Si or a-Si / thin film polycrystalline Si may be used.

[0050]

According to the above structure, the amount of oxygen near the interface of the transparent conductive oxide film is increased, oxygen deficiency of the transparent conductive oxide film can be prevented, and the reduction of the light transmittance in this portion can be prevented. As a result, the decrease in short-circuit current is reduced, and the conversion efficiency can be improved.

Further, according to the present invention, by inserting the transparent insulating film 6 having a film thickness of 5 nm or more between the transparent conductive oxide film and the back electrode, damage caused when the highly reflective metal layer is formed by the sputtering method. It can prevent and improve the light reflectance.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an element structure for explaining a first embodiment of a photovoltaic device of the present invention.

FIG. 2 is a diagram showing a result of measuring oxygen and indium contents of an ITO film by SIMS and obtaining a ratio (O / In) of the atomic weight of oxygen and the amount of indium in the ITO thin film.

FIG. 3 is a sectional view of an element structure for explaining a second embodiment of a photovoltaic device according to the present invention.

FIG. 4 is an element structure cross-sectional view for explaining a third embodiment of the photovoltaic device of the present invention.

FIG. 5 is a sectional view of an element structure for explaining the fourth embodiment of the photovoltaic device according to the present invention.

[Explanation of symbols]

1 Translucent insulating substrate 2 Transparent conductive film 3 Photoelectric conversion layer 4 Transparent conductive oxide film (diffusion prevention layer) 5 Back electrode

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-5-13790 (JP, A) JP-A-58-215083 (JP, A) JP-A-9-57892 (JP, A) JP-A-58- 111379 (JP, A) JP-A-5-145095 (JP, A) JP-A-5-110125 (JP, A) JP-A-6-314804 (JP, A) JP-A-6-204527 (JP, A) JP-A-8-213644 (JP, A) JP-A-6-338623 (JP, A) JP-A-5-121769 (JP, A) JP-A-58-78474 (JP, A) Actual exploitation 63-98667 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (7)

(57) [Claims] 1. A photovoltaic device in which a diffusion prevention layer made of a transparent conductive oxide film is inserted between a photoelectric conversion layer and a highly reflective metal layer, wherein the diffusion prevention layer is near an interface with the highly reflective metal layer. oxygen deficiency of the membrane oxygen atomic weight, resulting in the interface vicinity
A photovoltaic device characterized in that the amount of oxygen atoms in the film in other regions is made larger to compensate for the loss . 2. The transparent conductive oxide film is composed of an ITO thin film, and the composition ratio is such that the ratio of oxygen atomic weight to indium atomic weight (O / In) in the ITO thin film increases toward the highly reflective metal layer. 2. The photovoltaic device according to claim 1, characterized in that 3. The specific resistance of the ITO thin film is 10 ⁻² Ωc.
The photovoltaic device according to claim 2, wherein the photovoltaic device is m or less. 4. The photovoltaic power according to claim 2 or 3, wherein the ratio of the atomic weight of oxygen to the atomic weight of indium (O / In) in the ITO thin film changes between 1.5 and 4. apparatus. 5. The photovoltaic device according to claim 1, further comprising a transparent insulating film provided between the transparent conductive oxide film and the highly reflective metal layer. 6. A back surface as a photoelectric conversion layer and a highly reflective metal layer
A photovoltaic device in which a diffusion prevention layer made of a transparent conductive oxide film is inserted between an electrode and the transparent conductive oxide film and the back surface.
A photovoltaic device comprising a transparent insulating film having a thickness electrically connected to an electrode . 7. The photovoltaic device according to claim 6, wherein the average film thickness of the transparent insulating film is 5 nm or more and 50 nm or less.