JPH01205571A - Manufacture of substrate for thin-film solar cell - Google Patents

Abstract

PURPOSE:To improve heat resistance by forming an anode oxide film by performing a first-stage anode oxidation processing to an aluminum plate and by performing a second-stage anode oxidation processing by constant voltage electrolysis. CONSTITUTION:A first-stage anode oxidation processing is performed to an aluminum plate made of an aluminum based alloy containing 0.05-0.4% Cu with the remaining part being Al and unavoidable impurities in an electrolytic solution containing oxalic acid, and on the surface is formed an anode oxidation film. Following this, the voltage is abruptly dropped in the same electrolytic solution, after which a second anode oxidation processing is performed by constant-voltage electrolysis. The surface of a base aluminum-based alloy is made coarse in the interface with the film by, recovery phenomenon so internal stress within the film is reduced in the interface at the time of high-temperature heating, preventing cracks. This makes it possible to improve heat resistance of an anode oxide film.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for manufacturing a substrate for thin-film solar cells, and more specifically, to a method for manufacturing a substrate for use in series-connected thin-film solar cells suitable for extracting high voltage. It is about the method.

In this specification, "%" is by weight.

Conventional technology and its problems A series-connected thin-film solar cell is created by forming multiple solar cells on one substrate and connecting them in series.A lower electrode made of a chromium alloy or the like is formed on the substrate by electron beam evaporation. A thin film amorphous silicon (hereinafter referred to as RA-3iJ) layer is formed on each lower electrode by CVD method or the like, and each A-8i layer is covered with a transparent conductive film that becomes the upper electrode. Are there any that are connected in series? In such a solar cell, it is a matter of course that the lower electrodes must be electrically insulated from each other, and the electrical resistance value between the lower electrodes must be, for example, 20 MΩ or more. It's coming.

Conventionally, substrates for A-3I thin film solar cells have been made of: ■ glass, ■ high heat resistant resin such as polyimide resin, and ■ high heat resistant resin such as polyimide resin as an electrical insulating layer on the surface of a stainless steel plate. A film formed from

However, the above-mentioned item (1) had problems in that it had poor heat dissipation, was heavy, lacked flexibility, and was easily damaged. In addition, since polyimide resin is expensive, it is difficult to reduce the cost of solar cells manufactured using polyimide resin, and the substrate is soft and unstable. There was a problem in that noise was generated during the formation of the -8i layer. Furthermore, the above-mentioned method (1) has the problem that it is difficult to reduce the cost of the solar cell because the stainless steel plate and polyimide resin are expensive.

Therefore, as a manufacturing method for an A-8I thin film solar cell substrate that solves the above problems, the present applicant applied anodization treatment to an aluminum plate in an electrolytic solution containing oxalic acid, and the surface of the aluminum plate was anodized. A method characterized by forming an anodic oxide film with a thickness of 1 to 20 tllll (Japanese Patent Application Laid-Open No. 61-429
No. 72) and anodizing an aluminum plate in an electrolytic solution containing chromic acid to give a film thickness on the surface] ~ 201
proposed a method (Japanese Unexamined Patent Publication No. 133675/1983) characterized by forming an anodic oxide film of i m.

According to the former method, it is possible to obtain a lightweight and low-cost board with excellent insulation and heat dissipation properties, and with the latter method, it is possible to obtain a lightweight and low-cost board with excellent insulation and heat dissipation properties. It is difficult to say whether it is possible to obtain a substrate that has fewer defects and is less likely to cause cracks in the film even when heated to high temperatures, such as when forming an A-8i layer. , each had the following problems.

In other words, in the former case, sealing of the anodic oxide film is not performed in order to prevent cracks in the film when forming the a-3i layer. For example, there was a risk that the film would deteriorate over time (during the inventory period before shipping). In addition, the latter method has the problem of not only causing pollution problems due to the use of a-poisonous or romic acid but also increasing costs.

The first object of the present invention is to provide a method for manufacturing a thin film solar cell substrate that solves the problems mentioned in section 2 above.

Means for Solving the Problems The method for manufacturing a thin film solar cell substrate according to the present invention is a method for manufacturing a thin film solar cell substrate using Cu.
An aluminum plate made of an aluminum-based alloy containing 0.05-0.4% of oxalic acid, the balance being 8 ohms, and inevitable impurities is subjected to a first-stage anodizing treatment in an electrolytic solution containing oxalic acid to coat its surface. After forming an anodic oxide film and subsequently rapidly lowering the voltage in the same electrolytic solution, it is recommended that a second stage of anodizing treatment be performed by constant voltage electrolysis.

The reason why an aluminum-based alloy containing Cu is used in Section 2 is because it is suitable for causing the recovery phenomenon described below, and the reason why the amount of Cu is limited to 0.05 to 0.4% is because
This is because if the lower limit value is exceeded, no recovery phenomenon will occur, whereas if the upper limit value is exceeded, the insulation properties of the formed anodic oxide film may deteriorate. In other words, ρ of aluminum-based alloy
It is preferable that the purity is 99.7% or higher. If the purity is less than 99.7%, the content of Si and Fe, which are unavoidable impurities during production, inevitably increases. In that case, the crystallized products of Sl and Fe are exposed on the surface of the aluminum plate, and defects may occur in the anodic oxide film in this area, which may deteriorate the insulation properties of the film.

In the above, the reason why the anodic oxidation treatment is performed in an electrolytic solution containing oxalic acid is as follows. In other words, an anodized film formed by anodizing in an electrolytic solution containing oxalic acid contains electrolyte anions with a large dissociation constant, and also has a very small amount of water adsorption, so its electricity is This is because the insulation properties are better.

Electrolytes for anodizing include those containing oxalic acid, sulfuric acid, phosphoric acid, and chromic acid. However, the anodic oxide film formed by anodizing in an electrolytic solution containing sulfuric acid has poor insulation properties because it contains a large amount of sulfate anions with a large dissociation constant and adsorbed water. In addition, when anodizing is performed using an RR solution containing phosphoric acid, the thickness of the anodic oxide film on the film surface (because it is thin, it must be handled carefully when used as a substrate for solar cells). In addition, anodizing in an electrolytic LTK containing chromic acid may cause pollution problems due to intoxication or the use of chromic acid, and is expensive.

The surface roughness of the aluminum plate before the first stage anodizing treatment in an electrolytic solution containing oxalic acid is aluminum + IM.
It is preferable that the maximum height (Rmax) is set to 03μ[]1 or less so that a film is formed smoothly on the surface of the film. As a method for reducing the IRmrtx to 0.3 μll or less, there is a method of performing nof polishing and chemical polishing in this order. Moreover, instead of performing such polishing, a glossy rolled plate may be used as the aluminum plate.

The first stage of anodizing treatment is to electrolyze the above aluminum-based alloy in an oxalic acid electrolyte using alternating current, direct current, or a superimposed flow of alternating current and direct current until a thin film is obtained. . Here, the concentration of oxalic acid is preferably 1 to
5%, particularly preferably 2-3%. This electrolysis may be constant current electrolysis or constant voltage electrolysis.

In the second stage anodizing treatment, the voltage is rapidly lowered from the voltage in the first stage to a predetermined value, and then the product treated in the first stage is subjected to constant voltage electrolysis treatment. In this way, when constant voltage electrolysis is performed after the voltage has been rapidly lowered, the current does not flow quickly, but gradually begins to flow after several seconds to several minutes, and reaches a steady state after a while. This phenomenon is called a recovery phenomenon. Due to this recovery phenomenon, the anodic oxide film grows, and the surface of the underlying aluminum-based alloy surface of the film is uniformly roughened at the interface with the film.

Here, the voltage drop from the voltage in the first stage to the voltage in the second stage occurs rapidly, but in actual operation, the energization in the first stage is temporarily stopped and the voltage in the second stage is dropped rapidly.
It is preferable to adopt a method of applying a predetermined voltage of 1-1f at the beginning of the stage.

If the voltage in the second stage is less than 5V, the above-mentioned recovery effect will be small and the roughening of the underlying surface will not proceed.On the other hand, if it exceeds 35V, the oxide film will grow rapidly and the roughening of the underlying surface will disappear. It is preferable to set it in the range of 5 to 35 cm.

A particularly preferred voltage range is 15-20V. Further, the current in this second stage may be either an alternating current, a direct current, or a superimposed flow of alternating current and direct current.

The second stage electrolytic treatment time is not particularly limited, or if 5 minutes is left unused, the surface roughening of the underlying aluminum-based alloy will not proceed.
On the other hand, if it exceeds 25 minutes, the rough surface of the base tends to disappear, so 5 to 25 minutes, particularly 10 to 20 minutes, is preferable.

The thickness of the anodic oxide film formed by performing two-stage anodic oxidation treatment in an electrolytic solution containing oxalic acid is preferably 1 to 2 OAtm. If it is less than the lower limit, there is a risk of dielectric breakdown due to handling scratches when used as a solar cell substrate, and if it exceeds the upper limit, film cracks may occur due to the rise in substrate temperature during CVD, resulting in dielectric breakdown. This is because the risk of oxidation only increases, and it does not contribute much to improving insulation. A more preferable film thickness is around 10 μm.

In the substrate manufactured by the above method, the anodic oxide film
2. Form a plurality of lower electrodes on each lower electrode, and form a-8 on each lower electrode.
An i layer is formed and the a-3i layer is covered with a transparent conductive film serving as an upper electrode to form a series-connected a-81 thin film solar cell.

It is presumed that the heat resistance of the anodic oxide film is improved by performing the two-step anodizing treatment for the following reason. In other words, cracks occur in the anodic oxide film during high-temperature heating due to the difference in thermal expansion coefficient between the base aluminum-based alloy and the film, but as mentioned above, the recovery phenomenon causes the surface of the base aluminum-based alloy to Since the surface is roughened at the interface with the film, internal stress in the film is reduced at the interface when heated at high temperatures, preventing cracks from occurring and improving heat resistance.

EXAMPLES AND COMPARATIVE EXAMPLES Two examples of the present invention will now be described together with two comparative examples.

The sample was made of an aluminum-based alloy with 0.1% Cu, the balance Aρ, and unavoidable impurities.
Forty-eight aluminum plates measuring 100 mm and 0.5 mm were prepared. All of these surface roughnesses are 0.37zm Rma
x and below are bound-C. Then, each aluminum plate was subjected to a non-erosive degreasing treatment using a surfactant, and then divided into four groups of 12 sheets each, and each group was used for an example and a comparative example.

Example 1 Each of 12 aluminum plates was coated with 3% (COOH
2) In an electrolytic solution consisting of an aqueous solution, the liquid temperature is maintained at 35 ± 2 ° C and the current density is 3 A/dm2, and the first stage anodization treatment is performed for a predetermined time for a predetermined time to form a predetermined film thickness. An anodic oxide film was formed. After turning off the -11 power,
The aluminum plate was subjected to constant DC voltage electrolysis at a voltage of 20 V for a predetermined period of time in the same electrolytic solution, thereby performing a second-stage anodizing treatment. Then, an A-8J thin film solar cell substrate was manufactured without performing any sealing treatment on the oxide film.

Three types of film thicknesses (6 μm
, 10 μm, and 201 zm), each substrate was heated at a predetermined temperature of 250 to 400° C., and then the appearance of cracks in the film was visually observed. The results are shown in Table 1.

Example 2 Each aluminum plate was subjected to two-stage anodizing treatment under the same conditions as in Example 1. After that, these aluminum plates were sealed in boiling pure water for 20 minutes, and the a-81
A thin film solar cell substrate was manufactured. Then, the same heat resistance test as in Example 1 was conducted on these substrates. The results are shown in Table 1.

Comparative Example 1 Each aluminum plate was heated with a current density of 1.3 in an electrolytic solution consisting of a 15% H2SO4 aqueous solution while keeping the liquid temperature at 20 ± 1°C.
An anodic oxidation treatment was performed for a predetermined time by direct current electrolysis at A/c 1 m<2> to form an anodic oxide film having a predetermined thickness. These aluminum plates were then subjected to a sealing treatment under the same conditions as in Example 2 to produce a group 1-1a-3i thin film solar cell substrate. Thereafter, the same heat resistance test as in Example 1 was conducted on these substrates. The results are shown in Table 1.

Comparative Example 2 The electrolyte solution for anodizing treatment applied to each aluminum plate was 3% (
COOH) 2 aqueous solution and the temperature of the electrolyte 3
An a-81 thin film solar cell substrate was manufactured under the same conditions as Comparative Example 1 except that the temperature was maintained at 5±2°C. Thereafter, these substrates were subjected to the same heat resistance test as in Example].

The results are shown in Table 1.

Table 1 ○... No cracks ×... Cracks Effects of the Invention Since the method for manufacturing a thin film solar cell substrate according to the present invention is configured as described above, the substrate manufactured by this method is different from the conventional substrate. It has similar advantages compared to .

That is, it is lighter than conventional glass products, has good heat dissipation properties, has good flexibility, and is free from damage when handled. Furthermore, compared to conventional materials made of highly heat-resistant resins such as polyimide resins, they are less expensive, not too soft, and do not generate scum when forming the a-3i layer. Furthermore, it is cheaper and lighter than the conventional one in which a highly heat-resistant resin film such as polyimide resin is formed on the surface of a stainless steel plate.

Furthermore, compared to the conventional method of anodizing an aluminum plate in an electrolyte containing oxidized acid to form an anodized film on its surface, the anodized film is sealed. Even in cases where the coating is not anodized, the film does not deteriorate over time after the anodizing treatment until the formation of the A-81 layer, and has extremely high heat resistance.

In addition, compared to the conventional method of anodizing an aluminum plate in an electrolytic solution containing chromic acid to form an anodized film on the surface, the manufacturing process
It has the advantage of not causing any pollution problems due to the use of harmful romic acid, and is low in cost.

-4- Patent applicant: Showa Aluminum Co., Ltd.
Person Einosuke Kishimoto (4 others) -1
6 =

Claims (1)

[Claims] An aluminum plate made of an aluminum-based alloy containing 0.05 to 0.4% Cu and the remainder being Al and unavoidable impurities is subjected to a first-stage anodizing treatment in an electrolytic solution containing oxalic acid to coat its surface. A method for producing a thin-film solar cell substrate, which comprises forming an anodized film, then rapidly lowering the voltage in the same electrolytic solution, and then performing a second-stage anodic oxidation treatment by constant voltage electrolysis. .