JPH059947B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solar cell in which an amorphous silicon thin film is provided as a photovoltaic force generating element on a flexible substrate. More specifically, the present invention relates to a solar cell using a paper-like or cloth-like ceramic material as the substrate for the solar cell. Solar cells are well known in which an amorphous thin film is provided on a non-flexible substrate such as a stainless steel or glass plate, or a resin thin film such as polyimide is used as a flexible substrate. The advantage of using a flexible film substrate when manufacturing amorphous solar cells is that the necessary amorphous silicon layer can be continuously provided on the substrate, which is an advantage in terms of manufacturing cost and ease of manufacturing. This gives it an extremely advantageous advantage over flexible substrates. Furthermore, unlike solar cells formed on conventional non-flexible substrates, amorphous solar cells formed on flexible substrates are film-like, so the product shape can be arbitrary, such as curved surfaces. It can be used in any state, and its applications are expected to expand. However, when forming such an amorphous solar cell on a flexible substrate, a high temperature of at least 250 to 350°C is desirable as the amorphous silicon formation temperature.
When using a polymer film, only polyimide film can be used due to its excellent heat resistance. However, the polyimide film has a problem in that its initial Young's modulus at such high temperatures is not very large and the film does not have sufficient film strength to withstand the thermal stress during the formation of an amorphous silicon film. In other words, in the case of a substrate that does not have sufficient film strength, when an amorphous thin film is provided on the substrate, thermal stress due to the difference in thermal expansion coefficient between the amorphous silicon thin film and the substrate may occur. exceeds the mechanical strength of the substrate, resulting in the substrate curling. It has been confirmed that when the degree of curl increases, a serious defect occurs in that the efficiency as a solar cell is significantly reduced. Furthermore, since the surface of conventional polyimide films is too smooth, it is difficult to obtain high photoelectric conversion efficiency. Therefore, in order to realize an amorphous silicon solar cell using a flexible substrate, in addition to heat resistance of at least 250°C, it must also have sufficient strength to withstand the thermal stress during film formation at such high temperatures. and a substrate with appropriate surface roughness must be provided. One of the purposes of the present invention is to prevent curling during film formation, but another purpose is to prevent surface roughness of the substrate, which has a large effect on photoelectric conversion efficiency. An object of the present invention is to provide a substrate having an appropriately rough surface that makes it possible to obtain high photoelectric conversion efficiency in a solar cell on which a crystalline silicon thin film is formed. Regarding the relationship between the surface roughness of the substrate and the conversion efficiency of solar cells, in order to improve the conversion efficiency, it is important to prevent the reflection of sunlight on the surface of the solar cell, that is, to reduce the reflectance of sunlight. . However, if the surface is roughened too much, it will cause the formation of pores in the amorphous silicon thin film and many short circuits of the electromotive force elements, which will deteriorate the characteristics of the solar cell itself. It deviates from its original purpose. Therefore, the substrate needs to have an appropriate surface roughness in order to prevent reflection and maintain battery characteristics. The present inventor has developed a thin film solar cell using an amorphous silicon thin film as a photovoltaic element, which can sufficiently withstand thermal stress when forming an amorphous silicon thin film on a substrate, thereby preventing curling. As a result of our earnest efforts, we have succeeded in achieving the objective of improving battery characteristics by obtaining a suitable surface roughness, and as a result, we have succeeded in using ceramic paper-like or cloth-like materials as substrates for amorphous silicon thin-film solar cells. By using the present invention, the object of the present invention can be achieved and the present invention has been achieved. As mentioned above, the present invention uses a flexible ceramic paper-like or cloth-like material having a moderately rough surface as a substrate in a solar cell in which an amorphous silicon thin film is provided as a photovoltaic element on a flexible substrate. The ceramic paper/cloth material used in the present invention will be described below. The ceramic paper/cloth-like material according to the present invention is not particularly limited in the type of ceramic as long as it can be molded into the shape. A flexible mica paper/cloth will be mentioned as a preferred example of the ceramic paper/cloth. Mica such as _M.7 (MG _{2.3 Li.7} )
It has the composition formula Si ₄ O ₁₀ F ₂ .nH ₂ O, and M is Li or K.
can be easily molded into paper-like or cloth-like materials. When molding into the shape, it is also possible to mold a material having the above composition formula alone. The surface of the product formed in this manner has a suitable roughness. Even if glass fiber is mixed in, it can be sufficiently molded, so it is extremely effective for further improving the strength. When mica is molded into paper or cloth, it can be made to a thickness of about 50 to 300 μm, and the weight per unit area is in the range of 50 to 250 g/m ² . Moreover, the apparent packing density was 600 to 1400 Kg/m ³ . The electrical properties of the produced film, such as dielectric breakdown resistance, dielectric constant, and specific resistance, were extremely excellent. Furthermore, regarding strength, rigidity, and heat resistance, especially rigidity,
In terms of heat resistance, since it is made of ceramics, it exhibits extremely superior properties compared to polymer films, which are commonly used as flexible substrates for solar cells. There is no problem with heat resistance even when heated to around 400℃.
This is extremely advantageous for producing high-quality amorphous silicon thin films. As for rigidity, as well as heat resistance, since it is made of ceramics, it is stiff when molded into a paper-like or cloth-like material, and can sufficiently withstand stress during the formation of an amorphous silicon film. In order to use a flexible mica paper/cloth material as a substrate for a solar cell, electrodes are created on the surface of the substrate. The electrode is not particularly limited, and a thin film of aluminum, iron, stainless steel, nickel, tungsten, or the like is formed on a substrate by vapor deposition, sputtering, ion plating, or the like. In order to form an amorphous silicon thin film on a flexible substrate, a known method such as a glow discharge method, a sputtering method, an ion plating method, or a pyrolysis method is used.
For example, in the case of the glow discharge method, a flexible substrate is rolled up in a vacuum chamber maintained at 0.1 to 10 torr, and then the substrate is pulled out and brought into close contact with a substrate holder heated to 200 to 350°C. This substrate holder is used as one electrode, and high frequency power of, for example, 13.56 MHz is supplied between this and the opposing electrode. Silane gas (SiH ₄ ), diborane gas (B ₂ H ₆ ), phosphine gas (PH ₃ ), and hydrogen gas (H ₂ ) are introduced into the vacuum chamber to cause glow discharge, and the raw material gas is fed until a predetermined film thickness is achieved. and forms an amorphous silicon thin film, which is an element of photovoltaic power. More specifically, in order to create an i-type silicon thin film, silane gas and H ₂ gas are supplied to form the film, and P
To create a silicon thin film, silane gas, hydrogen gas, and diborane gas are supplied to form the film.
Further, the n-type silicon thin film is formed by supplying silane gas, hydrogen gas, and phosphine gas. Next, in order to use the amorphous silicon thin film as a solar cell device, a back electrode is formed, and then a P layer, an i
For example, in the case of a Schottky junction cell, a flexible substrate with laminated layers and n layers is mounted in a vacuum chamber.
As a Schottky barrier metal, platinum, gold, palladium, etc. are deposited to a film thickness of about 100 Å by sputtering, vacuum evaporation, ion plating, etc.
In the case of a heterojunction cell, indium oxide, tin oxide, and tin oxide-indium oxide films are deposited to a thickness of approximately 200 to 5000 Å using sputtering, vacuum evaporation, ion plating, etc. to form a surface electrode. A collection electrode is then provided on the Schottky barrier metal, heteroface electrode surface to form an amorphous silicon solar cell device. In the amorphous silicon solar cell of the present invention, a back electrode is formed on a flexible ceramic paper/cloth substrate, a multilayer amorphous silicon film is provided on the electrode, and a multilayer amorphous silicon film is provided on the back electrode. It has a basic structure in which a Schottky barrier metal or heteroface electrode is provided, and a collector electrode is further provided on top of the Schottky barrier metal or heteroface electrode. The amorphous silicon solar cell of the present invention has a major feature in that a paper-like or cloth-like ceramic material is used as a flexible substrate. It has the following characteristics. It has high rigidity and can withstand thermal stress during film formation. It has excellent heat resistance, that is, there is no problem even when heated to 400°C. It also has excellent strength, but it can be made even stronger by incorporating glass fiber. Since it has an appropriate surface roughness, it is possible to obtain excellent photoelectric conversion efficiency as shown in Examples described later. In this way, by using ceramic paper/cloth as a flexible substrate, it is possible to manufacture continuous solar cells in roll form, and it also has the rigidity to withstand thermal stress during film formation. For the first time, it has become possible to realize a solar cell with excellent photoelectric conversion efficiency, which is attributable to the fact that it has a suitable surface roughness. The present invention will be explained below with reference to Examples. Example 1 Mica having the compositional formula Li _.7 (MG _2.3 Li _.7 ) Si ₄ O ₁₀ F ₂ .nH ₂ O was molded into a paper shape to obtain a flexible mica paper with a thickness of 130 μm. This mica paper was heated at 150℃ under a vacuum of 10 ^-2 torr.
Drying was performed for 2 hours. This dried mica paper was attached to a sputtering device, and a 1.5 μm thick tungsten thin film was formed as a back electrode using tungsten as a target. The amorphous silicon thin film was prepared using a capacitively coupled high frequency (13.56 MHz) glow discharge device, and the substrate on which the back electrode was formed was mounted under tension on the anode electrode of the glow discharge device to form an 8×10 ^- Heat the substrate to 300° C. while evacuating to ₆ torr. Then add _N2 gas at 500c.c./min
ion bombardment of the substrate for 20 minutes by applying 200W of high frequency power in a 1.0torr N ₂ gas atmosphere, cleaning the substrate, then 10% silane gas (SiH ₄ ) diluted with hydrogen gas and hydrogen gas in
Phosphine gas diluted to 0.1% is introduced into a glow discharge device, and a high frequency power of 100 W is applied in the gas atmosphere of 0.6 torr to form an n-type amorphous silicon thin film of 200 Å. Next, an i
Form an amorphous thin film with a thickness of 3000 Å. Next, 10% silane gas (SiH ₄ ) diluted with hydrogen gas and diborane gas diluted to 0.1% with hydrogen gas were introduced into the glow discharge device to form a 300 Å P-type amorphous silicon thin film on the i-type amorphous silicon thin film. to form;
A pin-shaped amorphous silicon thin film is provided on flexible mica paper. The pin-type amorphous silicon thin film obtained in this way was mounted on a sputtering device and exposed to tin oxide.
An indium oxide thin film was deposited to a thickness of 1000 Å to form a heteroface layer. Finally, palladium was deposited in a 1000 Å comb shape as a collection electrode on this heteroface layer to obtain a Pin heteroface type solar cell device on a flexible mica paper substrate. Example 2 A mica paper having the compositional formula _K.7 MG _2.3 Li _.7 ) Si ₄ O ₁₀ F ₂ .nH ₂ O was molded to obtain a flexible mica paper having a thickness of 130 μm. A Pin heteroface type solar cell device was produced under the same conditions as in Example 1. Example 3 Li _.7 (MG _2.3 Li _.7 ) Si ₄ O ₁₀ F ₂ .nH ₂ O mica was mixed with 20 wt% of glass fiber based on the mica and formed into a paper shape, and a glass-reinforced mica paper with a thickness of 130μ was made. Obtained. A Pin heteroface type solar cell was produced under the same conditions as in Example 1. Example 4 Initial characteristics of the solar cell devices of Examples 1 to 3
Measurement was performed using a solar simulator manufactured by Oriel Co., Ltd. adjusted to AM=1. A polyimide film was selected as a comparative example, and a pin-type solar cell device was formed on this film in the same manner as in Example 1. In this measurement, the sample was used as a measurement sample without once releasing the sample from its tensile state throughout the solar cell device forming process. The results are shown in Table 1.

[Table] Example 5 Example 4 showed the results of measuring the initial characteristics of a solar cell device under conditions where the tension state was never resolved, but in this example, the tension state of each sample was resolved once. The results are shown below. For the samples of Examples 1 to 3, there was almost no curling even after the tension was released, and the battery properties were almost the same as before the tension was released, but the polyimide film curled significantly and the battery properties also showed poor results.
Before the tension was released, the conversion efficiency was 3.2%, but now it is 2.5.
%.

Claims (1)

[Claims] 1. Ceramic paper or cloth having a thickness of 50 to 300 μm and a weight per unit area of 50 to 250 g/m ² in a solar cell having an amorphous silicon thin film on a flexible substrate. An amorphous silicon thin film solar cell characterized by using as a substrate. 2. The solar cell according to claim 1, wherein the paper-like or cloth-like ceramic material is obtained by processing mica into a paper-like or cloth-like material. 3. The solar cell according to claim 1, wherein the paper-like or cloth-like ceramic material is made by mixing ceramics with glass fibers and processing them into a paper-like or cloth-like material.