JPH026235B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solar cell in which an amorphous semiconductor thin film mainly composed of silicon is provided as a photovoltaic element on an electrically insulating substrate. More specifically, in order to make an electrically insulating substrate conductive, a first metal layer of low resistance made of a metal with high electrical conductivity is formed on the substrate, an amorphous silicon thin film laminated thereon, and an electrically insulating substrate are formed. At least two of the second metal layers with good mechanical bonding
The present invention relates to a solar cell constructed by depositing a conductive layer consisting of layers. A solar cell in which an amorphous silicon thin film is provided on an insulating substrate is disclosed in Japanese Patent Application Laid-Open No. 52-16990 (Japanese Patent Publication No. 53-37718).
No.), JP-A-54-149489, JP-A-55-4994,
Furthermore, it is well known as described in Japanese Patent Application Laid-open No. 55-29154. Furthermore, as a feature of using a flexible organic polymer substrate when manufacturing an amorphous silicon solar cell, as disclosed in JP-A-55-4994 and JP-A-55-29154, To make it possible to manufacture an amorphous silicon solar cell in which necessary layers are provided on a substrate by a continuous method, and also to form on a flexible substrate as disclosed in Japanese Patent Application Laid-open No. 54-149489. Compared to conventional solar cells, the amorphous silicon solar cells developed are film-like, so they can be bent arbitrarily, and are said to have a wider range of applications. However, the present inventors discovered that when an amorphous silicon solar cell was manufactured by the method described in the above patent publication, a serious defect existed in the metal conductive layer on the organic polymer substrate. In other words, if metals with high electrical conductivity such as Ag, Au, Cu, Al, etc. are used in the conductive layer in order to obtain sufficient electrical conductivity as an electrode, the adhesion to the amorphous silicon film is poor and the amorphous silicon This may cause peeling of the film, alloying of the amorphous silicon and the conductive layer metal, or interdiffusion of atoms.
Solar cells with good photoelectric conversion efficiency cannot be obtained. In addition, when forming a conductive layer with sufficiently low resistance by using a stainless steel alloy or nichrome alloy for the conductive layer, it is necessary to use a conductive layer that has a sufficiently low resistance, or the flexibility of the organic polymer substrate is impaired, or the organic polymer substrate and the metal layer are It is necessary to deposit metal to such a thickness that the metal layer cracks or peels off due to the strain stress caused by the difference in the expansion rate of the organic polymer substrate. can't make it. This fact indicates that in order to fabricate an amorphous silicon solar cell that can withstand practical use on an electrically insulating substrate such as an organic polymer substrate, mechanical bonding with the electrically insulating substrate such as an organic polymer substrate is required. This shows that it is essential to develop a conductive layer that has good electrical resistance, low electrical resistance, and good electrical and mechanical bonding with amorphous silicon (hereinafter referred to as having good compatibility with amorphous silicon). There is. Here, good electrical connection means
This means providing a low-resistance non-rectifying contact with the amorphous silicon film or a suitable contact potential difference and rectifying contact with the amorphous silicon film as required for the solar cell configuration. Good mechanical contact means good adhesion to amorphous silicon. Both of the above concepts include stability with respect to temperature, humidity, changes over time, and bending during solar cell manufacturing and use. The present inventors have arrived at the present invention as a result of intensive research into a method for making an electrically insulating substrate conductive that has such required characteristics. That is, the present invention provides a solar cell comprising an electrically insulating substrate, a metal layer provided on the substrate, and a photovoltaic element formed of an amorphous semiconductor thin film containing silicon as a main component on the metal. , Ag where the metal layer is in contact with the substrate,
A first metal layer with good electrical conductivity, which is a layer of a single metal or an alloy selected from the group consisting of Au, Pt, Cu, Al and Ni, and Mo, Cr, W in contact with the photovoltaic element. , Fe, Ti, and Ta or an alloy thereof, a stainless steel alloy, or a silicon steel alloy, and a second metal layer having good electrical and mechanical bonding. This solar cell is characterized by being composed of two layers. In the present invention, the electrically insulating substrate is not particularly limited as long as it is an electrically insulating substrate, as described below, but includes an organic polymer sheet with a surface resistance of 1000 MΩ/□ or more, and a flexible organic polymer film. It is effective for organic polymer compound substrates such as , organic polymer molded products, and composite materials where the metal surface is coated with an organic polymer material. More specifically, these organic polymer materials include polyethylene terephthalate resin, polyethylene naphthalate resin, aromatic polyester resin, aromatic polyamide resin, polyarylate resin, polysulfone resin, and polyimide resin, which are required in the solar cell manufacturing process. It is suitable because it has heat resistance of ℃ or higher. When the organic polymer material described above is used as a substrate for a solar cell, it is necessary to laminate a conductive layer with a surface resistance of at least 100 Ω/□ or less, preferably 10 Ω/□ or less. In the present invention, this conductive layer has a multilayer structure including a first metal layer with high electrical conductivity, an amorphous semiconductor layer described below, and a second metal layer with good electrical and mechanical bonding. do. For the first metal layer, a single metal selected from Ag, Au, Pt, Cu, Al, and Ni, which are known metals with high electrical conductivity, and/or an alloy thereof is used as an electrode material. The above metals not only have good mechanical bonding with organic polymer materials, but also have high thermal conductivity, so high heat dissipation can be obtained during solar cell operation. In addition, since the metal layer is highly extensible, it alleviates the stress caused by the difference in coefficient of thermal expansion and difference in hygroscopic expansion between the organic polymer substrate material and the amorphous silicon semiconductor film, thereby preventing deterioration of the photovoltaic portion. Such a metal layer is deposited on an electrically insulating substrate such as an organic polymer substrate to a thickness of 0.005 μm to 20 μm, more preferably 0.01 μm to 5 μm, by physical methods such as vapor deposition or sputtering, or chemical methods such as plating method. The conductive layer is preferably deposited by a conventional method or laminated with the metal film described above. Among these, those deposited by the above-mentioned physical methods are preferred. If the thickness of the metal layer is less than 0.005 μm, the conductivity is insufficient, and if it exceeds 20 μm, the metal layer may crack when the substrate is bent, and the flexibility of the substrate may be impaired, which is not preferable. The thickness of the metal layer is 0.01μ
Sufficient conductivity and flexibility can be obtained in the range of m to 5 μm. However, conventionally known conductive substrates with only the first metal layer laminated with highly conductive metals do not have sufficient compatibility with the amorphous silicon film, causing peeling of the amorphous silicon film and amorphous formation. Undesirable alloying and interdiffusion of atoms between the silicon film and the conductive layer metal and/or formation of unwanted current rectifying contacts with the amorphous silicon film. This difficulty is due to the following second metal layer that has good consistency with the amorphous silicon film on the first metal layer.
This can be solved by laminating more metal layers. As a result of the research conducted by the present inventors, a single metal selected from among Mo, Cr, W, Fe, Ti, and Ta is selected as a metal that has good compatibility with the amorphous silicon film that constitutes the second metal layer. It has been found that and/or alloys thereof, stainless steel alloys, and silicon steel alloys can be used. The second metal layer is required to be a continuous film with no contact portion between the first metal layer and the amorphous silicon film, whose main purpose is to provide conductivity necessary as an electrode.
Its thickness is 0.01 μm to 2.0 μm, more preferably
A range of 0.02 μm to 1 μm is suitable. layer thickness
If it is less than 0.01 μm, it is difficult to form a continuous film, or
Alternatively, seepage may occur due to diffusion of metal atoms in the first metal layer, and if the thickness exceeds 2.0 μm, the second metal layer itself may crack or peel off from the substrate. When the thickness of the second metal layer is in the range of 0.01 μm to 1 μm, sufficient flexibility and consistency with the amorphous silicon film can be obtained. According to the conventionally known method of using a single conductive layer, if a metal that provides good compatibility with the amorphous silicon film of the second metal layer is used for the conductive layer, there will be no restrictions on cracking or peeling. The resistance of the conductive layer increases, and this resistance becomes a series resistance of the current generated in the photovoltaic part, reducing the light/power conversion efficiency. If a high-quality metal is used, the compatibility with the amorphous silicon film will deteriorate. In any case, the method disclosed in the above-mentioned patent publications, etc., can produce a practical solar cell.
In particular, it is difficult to realize solar cells with a large area and high output current. However, the first of the at least two layers,
On the surface where the second metal layer is laminated on the organic polymer substrate, a non-silicon based material such as amorphous silicon, amorphous silicon carbide alloy, or amorphous silicon germanium is applied as a photovoltaic element. According to the present invention, which deposits a crystalline semiconductor thin film, a large area, high output current solar cell can be manufactured. As an example, a case will be described in which an amorphous silicon thin film is used as a photovoltaic element. Known methods such as glow discharge, sputtering, and ion plating are used to deposit the amorphous silicon thin film on the substrate. For example, in the case of glow discharge method, 10~
The substrate was heated to 100℃ in a vacuum chamber maintained at 0.1Torr.
Place it in close contact with a substrate holder heated to ~400℃.
This substrate holder is used as one electrode, and 13.56 MHz high-frequency power is supplied between it and the opposing electrode. Silane (SiH ₄ ), diborane (B ₂ H ₆ ), and phosphine (PH ₃ ) gases are introduced into the vacuum chamber to cause a glow discharge, and the decomposition products of the gases are deposited in a predetermined structure, which is then exposed to light. An amorphous silicon thin film is provided as an electromotive force element. For example, in the case of a Schottky junction cell, platinum, gold, palladium, or the like is deposited as a Schottky barrier metal to a thickness of about 100 Å by sputtering or vacuum evaporation. In addition, in the case of a hetero (face) junction cell, indium oxide,
A thin film of tin oxide or cadmium stannate is deposited to a thickness of approximately 200 to 3000 Å by sputtering or vacuum evaporation to form a surface electrode. A collection electrode is then provided on the Schottky barrier metal, hetero (face) electrode surface to form an amorphous silicon solar cell device. Typical examples of the amorphous silicon solar cell of the present invention include an organic polymer sheet or flexible organic polymer film as a substrate; 1
and a second metal layer having good matching with the amorphous silicon film; and an amorphous silicon film provided thereon, a Schottky barrier metal or a hetero (face) electrode, and a photovoltaic element consisting of a current collecting electrode. In a preferred example of the amorphous silicon solar cell of the present invention, an insulating organic polymer material substrate is formed, which has low electrical resistance and has the effect of relieving the strain stress generated between the substrate and the amorphous silicon thin film. 1st
A major feature is that a multilayer plate made of at least two metal layers laminated with a metal layer and a second metal layer that has good consistency with amorphous silicon is used as a support plate for a photovoltaic element. ing. The conductive support plate with this structure has a conductive layer that has good compatibility with amorphous silicon, and is thin and has low internal stress and does not cause cracks, making it suitable for flexible organic polymer substrates. This makes it possible to create a revolutionary solar cell that has high light/power conversion efficiency, is highly durable, and can withstand bending without sacrificing the advantage of being lightweight. Of course, the above-mentioned method for making an insulating material conductive can also be applied to the case where an insulating material other than an organic polymer material such as a glass plate, a ceramic plate, or a flexible ceramic sheet is used as a substrate for a solar cell. When the solar cell of the present invention is put to practical use, it is usually provided with a solar cell surface protective layer that can withstand harsh environmental conditions, as is well known. In the case of a flexible solar cell, the surface protective layer is usually an organic resin film that is flexible and has excellent weather resistance, such as a fluororesin film, so as not to impair its flexibility. . The present invention will be explained below with reference to Examples. Example 1 An organic polymer film, specifically a polyimide resin film with a thickness of 125 μm, was used as an electrically insulating and flexible substrate. Stainless steel alloy (SUS304) is coated on this substrate by RF sputtering method as a conductive layer.
The alloys were deposited to various thicknesses using as a target, and the surface resistance at room temperature was measured. Sputtering was performed in an atmosphere of Ar pressure of 0.5 millimeters (mTorr) with RF power of 500 W applied. The relationship between the surface resistance of such a conductive organic polymer film and the thickness of the conductive layer is shown as curve 1 in FIG. In addition, using the same method as above, aluminum and stainless steel alloy targets were used as the conductive layer on the same organic polymer film, and various thicknesses were formed as the first metal layer.
A conductive film was prepared by depositing an Al film and laminating a stainless steel alloy film with a thickness of 0.05 μm on top of it as a second metal layer.The relationship between the surface resistance at room temperature and the thickness of the entire conductive layer was measured. The results shown as curve 2 in Figure 1 were obtained. As is clear from curves 1 and 2 in FIG. 1, a multilayer conductive layer made of Al as the first metal layer has much higher conductivity than a conductive layer made only of stainless steel alloy. For example, when trying to achieve a surface resistance of about 1Ω/□, in a multilayer conductive layer in which Al is used as the first metal layer and a stainless steel alloy is laminated on top of it as the second metal layer, the thickness of the metal layer is 0.1 μm was sufficient, and the flexibility of the substrate was not impaired. On the other hand, a conductive layer made only of stainless steel requires a thickness exceeding 1 μm. Substrates coated with such thick conductive layers often suffer from cracks or delaminations in the conductive layer. For more details 10×10
When a conductive layer consisting only of a stainless steel alloy layer is deposited on the organic polymer film of ^cm2 , the layer thickness is 2μ.
When the thickness of the conductive layer was 3 μm, there was a probability of about 40%, and when the thickness of the layer was 3 μm, there was a probability of more than 90% that cracks or peeling occurred on part or the entire surface of the conductive layer. Example 2 As in Example 1, a polyimide resin film with a thickness of 125 μm was used as an electrically insulating and flexible substrate, and a conductive layer on the film with a thickness of
Substrate coated with 0.4μm stainless steel alloy,
A substrate in which a second metal layer of stainless steel alloy with a thickness of 0.1 μm is laminated on a first metal layer of Al with a thickness of 0.05 μm, and a first metal layer of Ni with a thickness of 0.05 μm is laminated. A substrate on which a second metal layer of stainless steel alloy with a thickness of 0.1 μm was laminated was fabricated by sputtering. Sputtering is performed by applying RF power of 500 W in an Ar pressure of 0.5 mm (mTorr) to target Al, stainless steel alloy (SUS304), and Ni.
It was carried out using On this conductive film substrate, an amorphous silicon thin film was deposited under the same conditions by the RF glow discharge method using silane, diborane, and phosphine gases, and a transparent electrode of In and Sn oxides and a Pd comb were deposited on top of the amorphous silicon thin film. A solar cell having a substrate/nip (amorphous silicon)/transparent electrode configuration was fabricated by vapor-depositing a type collecting electrode, and the moisture resistance of the cell was examined. The humidity resistance test was conducted by leaving the solar cell in an atmosphere with a relative humidity of 80% for 24 hours, then transferring it to an atmosphere with a relative humidity of 30%, and then exposing it to an atmosphere with a relative humidity of 80% again after 48 hours. This was done by measuring the deterioration of power conversion efficiency. The results are shown in Figure 2. As is clear from Figure 2, a solar cell on a substrate made of only stainless steel layered on a polyimide film is
Compared to solar cells on substrates with a stainless steel alloy layered on top of a Ni layer or Ni layer, the light/power conversion efficiency deteriorated much more rapidly. Such deterioration is thought to be mainly due to minute cracks in the metal layer caused by strain stress caused by the difference in hygroscopic expansion coefficient between the organic polymer film and the stainless steel alloy or amorphous silicon thin film. It can be seen that Al and Ni in the first metal layer have the effect of alleviating these deterioration factors. Example 3 In order to select a metal for the second metal layer that has good electrical contact with the amorphous silicon photovoltaic layer, Au, Ag,
A polyimide resin film with a thickness of 125 μm was created using sputtering method targeting Cu, Mo, Cr, Ti, W, Fe, Ta, stainless steel alloy (SUS), and silicon steel metal plates in an Ar atmosphere of 10 ^-4 Torr. Substrates were prepared on which each metal layer was deposited to a thickness of about 0.1 μm, and solar cells were formed on these substrates in the following manner, and the effects on the solar cell characteristics were investigated. For the solar cell, an nip type amorphous silicon film was deposited by the RF glow discharge method as in Example 2. Furthermore, an indium oxide electrode was deposited as a transparent electrode using the EB evaporation method. As an indicator of the quality of the bond between these metal layers and the amorphous silicon layer, the fill factor, which is said to indicate the quality of electrical bond among solar cell characteristics, was measured and evaluated. The results are shown in Table 1.

【table】

[Table] The metals of the second metal layer of the present invention excluding Au, Ag, and Cu of the comparative example have a fill factor of 50% or more, and a good bond that can be used practically as a solar cell is obtained. The effects of the present invention are obvious.

[Brief explanation of drawings]

Figure 1 shows the relationship between the layer thickness and surface resistance of the SUS conductive layer and Al/SUS conductive layer of Example 1,
FIG. 2 shows the durability of the solar cell using the SUS conductive layer, Al/SUS conductive layer, and Ni/SUS conductive layer of Example 2.

Claims (1)

[Scope of Claims] 1. A solar cell consisting of an electrically insulating substrate, a metal layer provided on the substrate, and a photovoltaic element made of an amorphous semiconductor thin film mainly composed of silicon on the metal. The metal layer is a first metal with good electrical conductivity, which is a layer of a single metal or an alloy selected from the group consisting of Ag, Au, Pt, Cu, Al, and Ni, in contact with the substrate. Mo, Cr, W, Fe, Ti and in contact with the layer and the photovoltaic element.
Consisting of at least two layers: a semiconductor thin film, which is a layer of a single metal selected from the group consisting of Ta or its alloy, stainless steel alloy, or silicon steel alloy, and a second metal layer with good electrical and mechanical bonding. A solar cell featuring: 2. The solar cell according to claim 1, wherein the substrate is an organic polymer compound. 3. The solar cell according to claim 2, wherein the substrate has flexibility.