JP2001185747A - Insulation board superior in heat resistance for solar cells and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an insulation board for solar cells, having an insulation film which causes no defects such as pin-holes and never rusts, if heated at high temperatures when solar cells are formed. SOLUTION: The solar cell insulation board has a first layer of insulation film 2 made of an alkali silicate paint compounded with alumina particulates, and a second layer of insulation film 3 made of a silicone paint formed one above the other on a metal board 1, the metal board preferably uses a stainless steel plate superior in corrosion resistance, and the first layer of insulation film is preferably formed as a single or double layer of 1 μm or more, using an alkali silicate paint compounded with alumina particulates of 1 μm or less in mean grain size at a ratio of 10-30%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating substrate for a solar cell which is excellent in heat resistance such that good insulating properties are not deteriorated even by heating at a high temperature when forming a solar cell, and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a substrate for a solar cell, a glass plate, a resin film, a metal plate or the like is used. Above all, a metal substrate has advantages in that it is excellent in flexibility as compared with a glass plate and has heat resistance not found in a resin film. When solar cells are directly formed on a metal substrate, one electrode of each cell is electrically connected in parallel via the metal substrate, so that practical power cannot be obtained. The parallel connection can be avoided by separating the cells by cutting even the metal substrate, but this not only reduces the manufacturability, but also creates an extra gap between the cells when integrating a plurality of cells, and the The power generation efficiency per unit area of the battery module decreases.

Therefore, a method of insulating the surface of a metal substrate has been adopted. For example, spinner, spray,
Apply liquid resin to the surface of stainless steel plate by dipping method etc.
A method of forming a polymer resin film having a thickness of about 2 μm by high-temperature baking (Japanese Patent Laid-Open No. 59-47776), sputtering, vapor deposition, ion plating, plasma CV
D, a method of forming an inorganic insulating film such as silica, alumina, silicon nitride or the like by thermal decomposition CVD, etc.
JP-A-9-47775), a method of curing a coating material obtained by adding insulating fine particles to an organic silicate to form an inorganic / organic composite insulating film mainly composed of silica (Japanese Patent Laid-Open No. 2-18)
001 publication).

In Japanese Patent Application Laid-Open No. H11-238891, an inorganic insulating coating is formed by applying an alkali silicate (silicate) -based paint containing fine alumina particles to the surface of a stainless steel plate. However, the alkali silicate paint is usually an alkaline aqueous solution obtained by making glass obtained by melting silica sand and alkali carbonate or alkali hydroxide water-soluble. Therefore, most alkali silicate paints are water-permeable and breathable (moisture-permeable).
Is very strong and does not show waterproofness. These disadvantages are improved by the addition of silicofluoride, various mineral acids, metal powders, polyvalent metal oxides, etc.
Japanese Unexamined Patent Publication No. 2-338891) is another means for improvement.

[0005]

Among the various insulating films proposed so far, the insulating film containing a silicone resin as a main component can be formed by roll coating or the like, so that the manufacturing cost is excellent and the bonding energy is large. Since the resin skeleton has a siloxane bond as a main chain, it has excellent heat resistance. In addition, cracks due to heating during the formation of the solar cell are less likely to occur as compared with the inorganic insulating film, since they contain an organic component. However, the organic component is decomposed and disappears by heating at the time of forming the solar cell, generating fine pinholes in the insulating film, and causing a short circuit between the solar cells. When amorphous silicon is deposited by heating at low temperature, the generation of pinholes can be reduced by selecting an organic component having excellent heat resistance, but amorphous silicon can be deposited at a higher temperature or thin-film polycrystalline silicon can be deposited. In the case of depositing, for example, pinholes are likely to occur frequently due to decomposition and disappearance of organic components. When the organic component is reduced to prevent the generation of pinholes, fine cracks are generated by heating at the time of forming the solar cell, as in the case of the inorganic insulating film, which causes a short circuit between the solar cells.

[0006] Even when an alkali silicate-based paint is used, an insulating film can be formed by roll coating or the like, which is excellent in manufacturing cost. In addition, since the silica network has a resin skeleton with alkali metal incorporated therein, it has excellent adhesiveness, and cracks such as those seen in inorganic insulating films occur even when heated during solar cell formation. It is hard. However, since the alkali silicate-based coating is a water-based coating, moisture tends to remain in the formed insulating film. If the heating temperature at the time of forming the solar cell is higher than the heating temperature at the time of forming the film, the remaining moisture evaporates, causing blisters on the insulating film. When the swelling grows to about several tens of μm, a fine crack is generated at the top of the swelling, which causes a short circuit between the solar cells. By increasing the heating temperature during film formation, blisters and blister growth can be prevented.
At a heating temperature exceeding 00 ° C., blisters occur after the film is formed. For this reason, an insulating film formed by an alkali silicate paint can be used when depositing amorphous silicon by heating at a low temperature, but it is possible to deposit amorphous silicon at a higher temperature, or to use thin-film polycrystalline silicon. Cannot be used as an insulating substrate for solar cells.

[0007]

SUMMARY OF THE INVENTION The present invention has been devised to solve such a problem, and combines an alkali silicate-based coating and a silicone-based coating having different forms of defects generated upon heating. The purpose of the present invention is to provide an insulating substrate for a solar cell in which the defects of the insulating films are compensated for by each other and the advantages of the alkali silicate-based paint and the silicone-based paint are utilized to improve the insulating properties under high-temperature heating. I do. In order to achieve the object, the insulating substrate for a solar cell according to the present invention comprises a first substrate made of an alkali silicate-based coating in which alumina particles are blended on the surface of a metal substrate.
The insulating film of the layer and the insulating film of the second layer made of a silicone-based paint are sequentially formed.

For the metal substrate, it is preferable to use a stainless steel plate having excellent corrosion resistance. The insulating film of the first layer may be formed as a single layer or a multilayer having a thickness of 1 μm or more using an alkali silicate paint in which alumina fine particles having an average particle diameter of 1 μm or less are blended at a ratio of 10 to 30% by mass. preferable. The second insulating film is also preferably formed with a thickness of 2 μm or more. This insulating substrate for solar cells is obtained by applying an alkali silicate-based coating compounded with alumina fine particles to the surface of a metal substrate, drying and baking to form a first insulating film. It is manufactured by applying a silicone-based paint to the resin, drying and baking to form a second insulating film.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The insulating substrate for a solar cell according to the present invention has a first insulating film 2 and a second insulating film 3 sequentially laminated on a metal substrate 1 as shown in FIG. ing.
The first insulating film 2 is formed from an alkali silicate paint containing alumina fine particles 4, and the second insulating film 3 is formed from a silicone paint. The first insulating film 2 can be provided as a multilayer structure as shown in FIG. The first insulating film 2 is an inorganic insulating film formed by applying an alkali silicate paint, and has excellent adhesiveness due to having a skeletal structure in which an alkali metal is incorporated. Thus, large cracks peculiar to the inorganic insulating film derived from the difference in thermal expansion coefficient are unlikely to occur. However, since it is a water-based paint, when it is used for a solar cell application in which cells are formed at a high temperature exceeding 400 ° C., there is a disadvantage that blisters are generated in the insulating film due to evaporation of residual moisture.

The present inventors have studied to prevent blistering of the insulating film by forming a multilayered inorganic insulating film composed of an alkali silicate paint. However, although blistering of the insulating film on the lower layer side can be prevented, blistering occurs on the insulating film on the surface layer side. It was small. In addition, in order to suppress the vapor pressure enough to cause blisters, the upper insulating film having the same composition as the lower insulating film in which blisters actually occur has insufficient pressure resistance.

Therefore, in order to prevent blisters, which tend to occur on the inorganic insulating film made of an alkali silicate paint, by using an upper insulating film to prevent the blisters, the second insulating film 3 is made of a system free of blisters. It was considered necessary to form an insulating film having a stronger skeletal structure than the first insulating film 2 made of an alkali silicate paint. On such a premise, when the second layer insulating film 3 is formed using a silicone-based paint having a siloxane bond as a main chain, the insulating film 3 having a strong skeleton structure is formed on the upper layer, and as a result, It has been found that blisters generated in the first insulating film 2 can be suppressed. Further, after the heat test by heating at a high temperature, cracks due to the decomposition and shrinkage of the resin are detected in the second insulating film 3, but no blisters starting from the first insulating film 2 are observed. Moreover, even if pinholes are formed in the silicone-based insulating film 3 due to heating during the formation of the solar cell, conduction of the solar cell to the metal substrate 1 via the pinhole is prevented by the first-layer insulating film 2. Is done.

Examples of the alkali silicate paint used for forming the first insulating film 2 include a sodium silicate paint, a potassium silicate paint, a lithium silicate paint and a composite thereof. Examples of the silicone paint used to form the second insulating film 3 include pure silicone such as methyl silicone and methyl phenyl silicone, and alkyd-modified and polyester-modified silicone. It is preferable that alumina fine particles 4 having an average particle diameter of 1 μm or less are dispersed and blended in the first insulating film 2 at a ratio of 10 to 30% by mass. When an alkali silicate-based film having poor water resistance is used for the insulating film, a short circuit due to moisture absorbed by the film is concerned. In this regard, when the alumina fine particles are dispersed and blended in the alkali silicate coating, the passage of moisture through the coating is prevented by the alumina fine particles, and the water resistance is improved.

When the average particle size of the alumina fine particles 4 exceeds 1 μm, the insulating film has a surface roughness of the order of several μm at Rmax, and the power generation layer of a solar cell formed of a thin film of 1 μm or less is cut off. Short circuits are likely to occur. If the amount of the alumina fine particles 4 is less than 10% by mass as the solid content ratio in the first insulating film 2, the durability such as water resistance, corrosion resistance, weather resistance and the like is likely to deteriorate. On the other hand, when the amount is more than 30% by mass, the alumina fine particles 4 are liable to secondary aggregation,
The storage stability of the alkali silicate paint deteriorates. The first insulating film 2 is preferably formed with a thickness of 1 μm or more. If the film thickness is less than 1 μm, defects such as tearing are likely to occur in the first insulating film 2 due to unevenness of the metal substrate 1 and sufficient insulating properties cannot be obtained. The second layer insulating film 3 is also preferably formed with a film thickness of 1 μm or more in order to provide a film strength effective for suppressing blistering of the first layer insulating film 2.

The first insulating film 2 has a thickness of 95 × 10 ⁻⁷ / ° C.
It has a degree of thermal expansion coefficient. In order to prevent the occurrence of cracks due to the difference in thermal expansion coefficient, it is preferable to use a metal substrate 1 having a thermal expansion coefficient close to that of the first insulating film 2. In this respect, stainless steel plate is about 10
It is 4 × 10 ⁻⁷ / ° C., which is suitable as a substrate material for solar cells. In addition, when the first-layer insulating film 2 is provided in a multilayer structure, the generation of cracks due to the difference in thermal expansion coefficient is reduced, and the insulation stability is improved.

[0015]

EXAMPLES deposition method Film Formation Example 1 (Embodiment): As the insulating film 2 for forming an alkali silicate coating of the first layer, the solid content ratio of sodium silicate in the coating (SiO _2: 58-61 wt %, Na
₂ O: 19 to 21 wt%) 50 wt%, potassium silicate (SiO _2: 19 to 21 wt%, K ₂ O: 8 to 10 wt%) were blended so that 35 wt%, average particle diameter 0 .2μ
m of alumina fine particles were blended at a ratio of 15% by mass. As the silicone-based paint for the second insulating film 3, Pyrotherm # 0400P (produced by Nippon Grebekashu Co., Ltd.) was used. This paint is made of a silicone resin in which a methyl group or the like is added to the side chain of Si—O, and contains a metal oxide as a pigment. SUS with a thickness of 0.15 mm and a width of 300 mm, which has been degreased with alkali, as the metal substrate 1
A 430 stainless steel plate was used. After applying the alkali silicate paint to the stainless steel strip with a roll coater,
Baking was performed at 300 ° C. for 1 minute to form a first-layer insulating film 2 having a thickness of 4 μm. Further, a silicone-based paint is applied on the first insulating film 2 and baked at 350 ° C. for 2 minutes.
A second insulating film 3 having a thickness of 15 μm was formed.

Film forming example 2 (Example of the present invention): heat-resistant paint Okitsumo 6831 (manufactured by Okitsumo Co., Ltd .: same silicone paint as in film forming example 1) is used as the silicone-based paint.
An insulating film was formed in the same manner as in Film-forming Example 1. The thickness of the obtained insulating film was 6 μm for the first insulating film 2 and 14 μm for the second insulating film 3. Film-forming Example 3 (Example of the present invention): An insulating film was formed in the same manner as in Film-forming Example 1, except that the average particle diameter of the alumina fine particles added to the alkali silicate-based paint was 1 μm. The thickness of the obtained insulating film was 5 μm for the first insulating film 2 and 13 μm for the second insulating film 3.

Film forming example 4 (Example of the present invention): Film forming example 1 except that the concentration of the alumina fine particles added to the alkali silicate paint was set to 10% by mass as the solid content ratio in the first insulating film 2. An insulating film was formed in the same manner as described above. The thickness of the obtained insulating film was 5 μm for the first insulating film 2 and 15 μm for the second insulating film 3. Film-forming Example 5 (Example of the present invention): Same as Film-forming Example 1 except that the concentration of the alumina fine particles added to the alkali silicate-based coating material is 30% by mass as the solid content ratio in the first-layer insulating film 2. An insulating film was formed. The thickness of the obtained insulating film is 6 μm for the first insulating film 2 and 3 μm for the second insulating film 3.
Was 14 μm. Film-forming example 6 (Example of the present invention): The same as the film-forming example 1 except that the peripheral speed of the applicator roll is reduced when the alkali silicate paint for the first insulating film 2 is roll-coated. Was formed. The thickness of the obtained insulating film was 1 μm for the first insulating film 2 and 13 μm for the second insulating film 3.
Met.

Film-forming example 7 (Example of the present invention): Same as film-forming example 1 except that the peripheral speed of the applicator roll is reduced when the silicone-based paint for the second insulating film 3 is roll-coated. An insulating film was formed. The thickness of the obtained insulating film was 5 μm for the first insulating film 2 and 1 μm for the second insulating film 3.
m. Film forming example 8 (example of the present invention): the same conditions as the first layer as an intermediate layer between the first layer insulating film 2 made of an alkali silicate paint and the second layer insulating film 3 made of a silicone paint. An insulating film was formed in the same manner as in Film-forming Example 1 except that the insulating film was formed in Step 1. The thickness of the obtained insulating film was 5 μm for the first insulating film 2, 5 μm for the intermediate insulating film, and 10 μm for the second insulating film 3.

Film forming example 9 (comparative example): Only the first insulating film 2 having a thickness of 6 μm was formed under the same conditions as in film forming example 1. Film forming example 10 (comparative example): film thickness 1 under the same conditions as film forming example 1
Only a 6 μm second insulating film 3 was formed. Film forming example 11 (comparative example): film thickness 1 under the same conditions as film forming example 2
Only the second insulating film 3 having a thickness of 5 μm was formed. Film-forming Example 12 (Comparative Example): An insulating film was formed in the same manner as in Film-forming Example 1, except that alumina fine particles having an average particle size of 5 μm were added to the alkali silicate paint. The thickness of the obtained insulating film was 6 μm for the first insulating film 2 and 15 μm for the second insulating film 3.

Film-forming Example 13 (Comparative Example): An insulating film was formed in the same manner as in Film-forming Example 1, except that alumina fine particles having a solid content ratio of 70% by mass in the film were mixed with the alkali silicate paint. The thickness of the obtained insulating film was 6 μm for the first insulating film 2 and 15 μm for the second insulating film 3.

[0021]Evaluation of coating film performance Heat resistance test: Each stainless steel sheet with insulating film formed
Cut out a test piece of 300 mm x 300 mm from
Tested. In the heat resistance test, 50 mm in diameter was
Al electrodes at 60 mm intervals in both the width and length directions
A total of 25 pieces are formed, and a vacuum annealing furnace (attained vacuum degree: 1-3 × 1)
0^-2Pa) and kept at 500 ° C. for 90 minutes,
Apply a voltage of 1 V between the electrode surface and the back of the test piece,
Product resistance is 1MΩcm ^TwoCount the number of electrodes
I did it. 1MΩ · cm^TwoThe number of the above electrodes is 25
サ ン プ ル, 23 or more samples as ，, 22 or less samples as ×
The heat resistance was evaluated. Paint stability: Each paint prepared in film forming examples 1 to 13 was heated to 40 ° C.
After one month, the average particle size of the fine particles in the paint
It was measured with a distribution meter and the degree of secondary aggregation was investigated. Average grain
◎: 1 μm or less, ○: 2 μm or less, more than 2 μm
The coating stability was evaluated as “×”.

As can be seen from the investigation results in Table 1, all of the insulating films of Film-forming Examples 1 to 8 (Examples of the present invention) exhibit excellent heat resistance and are exposed to the heating atmosphere at the time of forming the solar cell. It can be seen that no defects such as pinholes occur. The used paint also has excellent storage stability and is used for forming an insulating film whose quality is stable over a long period of time. On the other hand, in film-forming examples 9 to 11 in which only an insulating film made of an alkali silicate paint or a silicone paint was formed. The paint stability was excellent, but the heat resistance was poor. Even when a coating film having a multilayer structure was formed, in a film forming example in which alumina fine particles 4 having a large average particle size were dispersed in the insulating film 2 of the first layer, the coating stability was poor although the heat resistance was excellent. Film forming example 13 in which excessive alumina fine particles 4 are dispersed in first insulating film 2
Was inferior in both heat resistance and paint stability. As is clear from this comparison, when the silicone-based insulating film 3 is formed on the alkali-silicate-based insulating film 2 in which the alumina fine particles 4 are dispersed, an insulating film having excellent heat resistance is obtained, and the The present invention provides an insulating substrate for a solar cell which is excellent in heat resistance and free from defects such as pinholes which may cause a short circuit even by heating.

[0023]

[0024]

As described above, the insulating substrate for a solar cell according to the present invention has an alkali silicate insulating film and a silicon insulating film in which alumina fine particles are dispersed on a metal substrate in order. In addition, the defects of each film are compensated for by the other film, and the insulating property does not decrease even if the film is heated at a high temperature during the formation of the solar cell. In addition, when adjusting the particle size and the amount of dispersion of the alumina fine particles to be added to the alkali silicate paint, heat resistance, durability and paint stability are improved, and a high-quality insulating substrate for a solar cell can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a solar cell insulating substrate in which an alumina silicate-based insulating film (first layer) and a silicone-based insulating film (second layer) are sequentially laminated on a metal substrate surface.

FIG. 2 is a cross-sectional view of an insulating substrate for a solar cell in which a first layer has a plurality of layers and a silicone-based insulating film (second layer) is formed thereon.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Jun Kajimoto 7-1 Takaya Shinmachi, Ichikawa-shi, Chiba F-term in Nisshin Steel R & D Co., Ltd. F-term (reference) 5F051 AA03 AA05 BA17 BA18 GA02 GA06 GA20

Claims (3)

[Claims] 1. An alumina fine particle having an average particle diameter of 1 μm or less as a solid content ratio of 10 to 30% by mass on a surface of a metal substrate.
An insulating substrate for a solar cell having excellent heat resistance in which a first layer insulating film made of an alkali silicate paint and a second layer insulating film made of a silicone paint are sequentially formed. 2. The solar cell insulating substrate according to claim 1, wherein a stainless steel plate is used as the metal substrate. 3. An alkali silicate-based coating compounded with alumina fine particles is applied to the surface of a metal substrate, dried and fired to form a first-layer insulating film, and then a silicone-based coating is formed on the first-layer insulating film. A method for producing an insulating substrate for a solar cell, comprising applying a paint, drying and firing to form a second insulating film.