JP2000183376A - Insulation base material for solar cell and manufacturing method for the board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an oxide layer that is effective as an insulation layer for a substrate of a solar cell on the surface of a metal plate through a sol/gel method. SOLUTION: In a substrate for a solar cell, an insulation layer 2 with a thickness of 0.5-10 μm a is formed on the surface of a metal plate 1 as a backing material by the sol/gel method. With inorganic powder of particle diameter of 0.2-2.0 μm, a concentration with respect to insulation layer of 25-75 mass %, and a visible light reflection coefficient of 70% or higher, an optoelectric conversion efficiency can be improved. The base material can be manufactured by dissolving one or two types or more of alkoxysilane, organoalkoxysilane, aluminumalkoxide, titaniumalkoxide, alkali metal, or alkoxide of alkaline earth metal and water or a thickening agent into an organic solvent, bringing the metal plate into contact with a solution where the inorganic powder is dispersed, drying and burning the solution which is adhering to the surface of the metal plate, and forming an insulation layer on the surface of the metal plate.

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 flexibility, heat resistance, insulation, adhesion to an electrode material, and photoelectric conversion efficiency when forming the solar cell, and a method of manufacturing the same. .

[0002]

2. Description of the Related Art A glass plate or a metal plate is used as a substrate for forming a solar cell made of amorphous Si. Above all, a metal plate has been attracting attention as a substrate material utilizing flexibility that is superior to a glass plate. When a metal plate is used as a solar cell substrate, the substrate surface needs to be insulated, and a resin-based insulating film, an inorganic-based insulating film, a metal oxide film, an anodized film, and the like have been proposed. For example, in JP-A-59-47776, a liquid resin is applied to the surface of a stainless steel substrate by a spinner, spray, or immersion method, and is fired at a high temperature to form a polymer resin film having a thickness of about 2 μm. Also, Japanese Unexamined Patent Publication No. 59-477
No. 5 discloses sputtering, evaporation, ion plating, plasma CVD, pyrolysis CVD, etc., for SiO ₂ , Al ₂ O ₃ , SiNx
Etc. are formed. Further, Japanese Patent Application Laid-Open No. 2-18
In No. 0081, an insulating film is formed using a coating material containing an organic silicate containing insulating fine particles as a main component.

[0003]

SUMMARY OF THE INVENTION Resin-based insulating films are flexible and have excellent impact resistance. However, when heated during the deposition of amorphous Si that functions as a solar cell, it is likely to thermally decompose and generate gas, causing defects to be introduced into the amorphous Si layer. In addition, since moisture resistance is not sufficient, there is a problem in durability. On the other hand, in a method of providing an inorganic insulating film by sputtering, vapor deposition, ion plating, plasma CVD, thermal decomposition CVD, or the like, it takes time until the insulating film grows to a required thickness, and the manufacturing cost increases.

Further, in the process of laminating an electrode material and an amorphous Si layer on the inorganic insulating film, if a minute crack is generated in the inorganic insulating film due to a difference in thermal expansion coefficient, the solar cell may have a problem. There is a problem that a short circuit occurs. In addition, the method of using an SiO ₂ film containing insulating fine particles such as TiO ₂ as an insulating film is effective as a method of improving the photoelectric conversion efficiency when forming a solar cell, but mainly uses an organic compound of SiO _2. Since the film is formed from a bath as a component, there is a disadvantage that organic components easily remain during curing. When the electrode material is laminated on the SiO ₂ -based film in which the organic component remains, peeling occurs at the interface between the electrode material and the SiO ₂ -based film, and a favorable solar cell cannot be formed. The anchor effect due to the irregularities of the added particles is effective in improving peeling, but if the concentration of the added particles is too low, the anchor effect is reduced, so that the adhesion to the electrode material is reduced and the peeling is performed, and conversely, the amount is too large. There is a problem that the added particles aggregate and cracks occur, which lowers the photoelectric conversion efficiency, and simply defining the particle size of the added particles cannot actually improve the photoelectric conversion efficiency of the solar cell. .

[0005] The present invention has been devised to solve such a problem. A metal plate is brought into contact with a sol-gel bath containing an inorganic powder having a prescribed particle size, additive concentration and visible light reflectance. Forming an insulating layer on the surface of the metal plate, controlling the surface roughness of the insulating layer, the height of the inorganic powder protruding from the surface of the insulating layer, and the distance between adjacent ones, suppressing the occurrence of cracks even in a thick film, An object of the present invention is to provide a solar cell substrate having an inorganic insulating layer formed on a metal plate surface, which has good adhesion, does not peel off, and improves photoelectric conversion efficiency by a texture effect.

[0006]

In order to achieve the object, an insulating substrate for a solar cell according to the present invention comprises a metal plate as a substrate,
An insulating layer containing an inorganic powder is formed on a surface of a metal plate by a sol-gel method.

The insulating layer is an oxide layer having a thickness of 0.5 to 10 μm, in which inorganic powder is dispersed. The inorganic powder to be added is an insulating inorganic powder such as an inorganic compound having a visible light reflectance of 70% or more,
The particle size can be 0.2 μm or more and 2.0 μm or less and can be dispersed in the insulating layer at a rate of 25 to 75 mass%. The surface roughness of the insulating layer is in the range of 0.2 to 0.4 μm in Ra and 0.8 to 2.0 μm in Rmax, the height of the inorganic powder protruding on the surface of the insulating layer is 0.2 to 2.0 μm, and the adjacent space is 0.2 to 2.0 μm. It is desirable to control.

The insulating substrate for a solar cell includes an alkoxysilane, an organoalkoxysilane having a structure of the formula (1), an aluminum alkoxide, a titanium alkoxide,
Alkoxides of alkali metals or alkaline earth metals
Kind or two or more, water and a thickener are dissolved in an organic solvent, and a metal plate is immersed in a sol-gel solution in which an inorganic powder is dispersed, contacted by coating, spraying, etc., and adhered to the surface of the metal plate. It is formed by drying and baking the solution.

[0009]

(Equation 1) X: vinyl group, epoxy group, amino group, methacryloxy group or mercapto group R: alkyl group

[0010]

The sol-gel method has been conventionally used as a method for forming an oxide layer on the surface of a metal plate, and has an advantage that an oxide layer can be formed at a relatively low temperature. However, according to the conventional sol-gel method, only a thin film having a thickness of 1 μm or less can be obtained. Such a film cannot be used as an insulating layer of a solar cell substrate because of insufficient insulation.
By the way, the present inventors have found that a relatively thick oxide layer is formed when a coating solution in which an organoalkoxysilane is used as a film strengthening agent and hydroxyalkyl cellulose is added to an alkoxide as a thickening agent is used. And Japanese Patent Application No. 8-40558.

The basic sol-gel bath includes an alkoxide containing one or more of aluminum alkoxide, titanium alkoxide, alkoxysilane, organoalkoxysilane, alkali metal and / or alkaline earth metal, alcohol amine, water And an alcohol-based solvent for dissolving each alkoxide. Alkoxides dissolved in alcohol solvents,
Hydrolyzes by addition of water to form hydroxide. But,
Since a precipitate is generated by rapid hydrolysis, the reaction rate of the hydrolysis is adjusted by adding alcohol amine.

This sol-gel bath is immersed in a metal plate, coated,
When coated with a spray or the like, a hydrolyzed hydroxide such as an aluminum alkoxide, a titanium alkoxide, an alkoxysilane, an alkoxide of an alkali metal or an alkaline earth metal adheres. When the metal plate is heated in this state, the synthesis reaction proceeds, and an oxide layer is formed on the surface of the metal plate. The heating at this time is about 100 to 600 ° C., which is much lower than the temperature at which conventional inorganic oxides are baked. For this reason, the insulating layer does not adversely affect the metal plate thermally and exhibits excellent insulating properties inherent to the oxide.

The formed insulating layer is different from the oxide layer formed by the conventional sol-gel method in that the bonding of the silica network structure is strengthened by the addition of the organoalkoxysilane, and the cracks accompanying the rapid evaporation of the solvent are caused by the addition of the hydroxyalkyl cellulose. And the adhesion to the metal plate is good.

In the present invention, as shown in FIG. 1 (a), a film is formed on a surface of a metal plate 1 by using a sol-gel bath in which inorganic powders such as oxides, nitrides and carbides are dispersed. When an oxide layer having a thickness of 0.5 μm or more is formed, an oxide layer 2 in which the inorganic powder 3 is dispersed is obtained. The inorganic powder 3 suppresses the occurrence of cracks in the oxide layer 2 and can relatively easily increase the thickness of the oxide layer 2, so that sufficient insulating properties are exhibited as an insulating layer for a solar cell. However, if the thickness of the oxide layer 2 is too large, a large number of wide cracks will occur and insulation failure will occur. Therefore, it is desirable to adjust the thickness of the oxide layer 2 to 10 μm or less. If the particle size of the inorganic powder 3 to be added is too small, the diffusion of the reflected light becomes insufficient, and the texture effect is reduced, so that the photoelectric conversion efficiency is reduced. More likely to occur. On the other hand, if the particle size of the inorganic powder 3 to be added is too large, the inorganic powder 3 is likely to agglomerate, cracks are generated in the agglomerated portion by heating and physical impact, and short-circuiting occurs through the electrode material that is surface-diffused along the cracks. Occurs, and the photoelectric conversion efficiency decreases.
Therefore, it is desirable that the particle diameter of the inorganic powder 3 be 0.2 to 2.0 μm. If the concentration of the inorganic powder 3 to be added is too low, the diffusion of the reflected light becomes insufficient, and the texture effect is reduced, so that the photoelectric conversion efficiency is reduced. More likely to occur. In addition, due to the decrease in the anchor effect, the adhesion to the electrode formed on the upper layer is also reduced, and peeling occurs. Conversely, if the concentration of the inorganic powder 3 to be added is too high, the inorganic powder 3 tends to agglomerate, cracks occur in the agglomerated portion due to heating and physical impact, and short-circuiting occurs via the electrode material whose surface has diffused along the cracks. Occasionally, the photoelectric conversion efficiency decreases. Therefore, the concentration of the inorganic powder 3 is desirably 25 to 75 mass% with respect to the oxide layer 2. The surface roughness of the insulating layer is Ra <0.2μm, Rmax <
At 0.8 μm, the diffusion of the reflected light becomes insufficient and the texture effect is reduced, so that the photoelectric conversion efficiency is reduced, and the adhesion to the electrode formed on the upper layer is also reduced due to the reduced anchor effect, and peeling is caused. Conversely, if the surface roughness of the insulating layer is Ra
If> 0.4 μm and Rmax> 2.0 μm, cracks and the like may occur in the electrode material and the amorphous semiconductor layer formed on the surface of the insulating layer. The surface roughness of the insulating layer is 0.2 to 0.4 μm in Ra, and
A range of 0.8 to 2.0 μm is desirable.

As shown in FIG. 1B, when the height of the inorganic powder protruding from the surface of the insulating layer and the interval between adjacent inorganic powders are both less than 1 μm, the improvement in photoelectric conversion efficiency due to the texture effect is maximized. The height of the inorganic powder protruding from the insulating layer surface is 0.2
Even when the thickness is up to 2.0 μm, the improvement of the photoelectric conversion efficiency is remarkable, but outside the range, the degree of improvement is small. Even if the interval between adjacent inorganic powders protruding from the surface of the insulating layer is 0.2 to 2.0 μm, the improvement in photoelectric conversion efficiency is remarkable, but outside the range, the degree of improvement is small. Therefore, the height of the inorganic powder protruding from the surface of the insulating layer and the interval between adjacent inorganic powders are desirably 0.2 to 2.0 μm. Powders with high visible light reflection characteristics were converted to inorganic powder 3
When it is used, multiple reflection of incident light inside the insulating layer when a solar cell is formed is promoted, and the photoelectric conversion efficiency is improved. Al ₂ O ₃ , S
iO ₂ , TiO ₂ , ZnO, MgO, CaCO ₃ , MgCO _{3 and the} like are used.

[0016]

[Example 1] [Example 1] 1.0 mol of aluminum isopropoxide, 2.5 mol of tetraethyl orthosilicate, 1.0 mol of sodium methoxide, 4.0 mol of triisopropanolamine and 7.0 mol of water: butyl cellosolve:
Dissolved in 15 mol, added Al ₂ O ₃ with a particle size of 0.3 μm: 30 mass%,
The mixture was stirred for 24 hours to prepare a sol-gel bath for the zeolite-based membrane. The resulting sol-gel bath was white, and was stable even after stirring for 100 hours.

A stainless steel plate having a thickness of 0.15 mm was degreased, coated with a sol-gel solution using a roll coater, and fired at 400 ° C. for 1 minute to form an oxide layer. The resulting oxide film was a white film having a uniform and dense structure with a thickness of 1.3 μm, and had surface roughnesses of Ra 0.22 μm and Rmax 1.44 μm.

Example 2 A hot-dip Al (55%)-Zn plated steel sheet was used as a substrate and coated under the same conditions as in Example 1. The obtained oxide film is a white film having a uniform and dense structure with a thickness of 1.4 μm, the surface roughness is Ra 0.24 μm,
Rmax was 1.51 μm.

Example 3 A stainless steel plate was used as a substrate,
1.8μm particle size Al powder _TwoO_Three:Five
Coating was performed under the same conditions as in Example 1 except that it was set to 0 mass%.
I did it. The resulting oxide film has a uniform thickness of 1.3 μm and
A white film with a dense structure that protrudes from the surface of the insulating layer.
The height of the inorganic powder is 0.9 μm and the distance between adjacent
Was being controlled. The surface roughness is Ra 0.28 μm, Rmax 1.7
It was 7 μm.

[Comparative Example 1] Methylethoxysilane: 1.0 mol, phosphoric acid: 0.05 mol, water: 4.0 mol, butanol: 7.0
After dissolving in a mole, 1 mass% of hydroxypropylcellulose and 0.2 μm of TiO ₂ having a particle size of ₂₀ mass% were added and stirred for 24 hours to prepare a sol-gel bath for a silica-based film. The resulting sol-gel bath was white, and was stable even after stirring for 100 hours.

Coating was performed under the same conditions as in Example 1 except that a sol-gel bath for a silica-based membrane was used instead of the zeolite-based membrane. The resulting oxide film is a white film having a uniform and dense structure with a thickness of 1.2 μm and a surface roughness of
Ra 0.20 μm and Rmax 1.21 μm.

Comparative Example 2 Coating was performed under the same conditions as in Example 1 except that the particle size of the inorganic powder was 0.2 μm. The obtained oxide film was a white film having a uniform and dense structure with a thickness of 1.2 μm, and the surface roughness was Ra = 0.21 μm, Rmax 1.38.
μm.

Comparative Example 3 The additive concentration of the inorganic powder was 80 mass%.
Coating was performed under the same conditions as in Example 3 except that The resulting oxide film is a white film having a uniform and dense structure with a thickness of 1.4 μm, the surface roughness is Ra 0.35 μm,
Rmax was 2.25 μm.

Comparative Example 4 Coating was performed under the same conditions as in Example 3 except that the particle size of the inorganic powder was 2.7 μm. The resulting oxide film is a white film having a uniform and dense structure with a thickness of 1.4 μm, the surface roughness is Ra 0.32 μm, Rmax 1.90
μm.

Comparative Example 5 Coating was carried out under the same conditions as in Example 3 except that a sol-gel bath containing CuO was used instead of Al ₂ O ₃ . The resulting oxide film is a gray film having a uniform and dense structure with a thickness of 1.4 μm and a surface roughness of Ra.
0.30 μm and Rmax 1.89 μm.

The metal plates on which the oxide layers were formed in Examples 1 to 3 and Comparative Examples 1 to 5 were used as solar cell substrates,
A solar cell was formed in the following manner according to a conventional method.

First, a mixture of indium oxide and tin oxide was deposited on the heated substrate surface to form lower electrodes at predetermined intervals. Then, an amorphous Si film is formed on the lower electrode by plasma CV.
An indium oxide film was formed on the amorphous Si film by a sputtering method as a light-transmitting upper electrode corresponding to the lower electrode by the D method. Further, a high-molecular resin was uniformly applied on the light-transmitting upper electrode and baked to form a light-transmitting passivation film.

For each of the obtained solar cells, the photoelectric conversion efficiency was measured using a solar simulator manufactured by Yamashita Denso Co., Ltd. The solar cells using the substrates of Examples 1 and 2 exhibited a photoelectric conversion efficiency of 10%. In addition, the height of the inorganic powder protruding from the surface of the insulating layer and the interval between adjacent inorganic powders are both 1
In Example 3, in which the control was made to be slightly less than μm, a high photoelectric conversion efficiency of 11% was obtained. On the other hand, when the substrate of Comparative Example 1 was used, a solar cell could not be formed because the interface between the metallic electrode and the insulating film was peeled off. In the solar cell using the substrate of Comparative Example 2, the photoelectric conversion efficiency was as low as 9% because the texture effect was small. In the solar cell using the substrate of Comparative Example 3, the added inorganic powder agglomerated to make the roughness coarse, and the agglomerate was used as a starting point to cause cracks. Therefore, the photoelectric conversion efficiency was also 0 to 6%. It varied in the low range. In the solar cell using the substrate of Comparative Example 4, as in the case of Comparative Example 3, the added inorganic powder was aggregated to make the roughness coarse, and a crack was generated from the aggregate as a starting point. The conversion efficiency also varied in a low range of 1 to 7%. In the solar cell using the substrate of Comparative Example 5, it was added.
Since the visible light reflectance of CuO was low, the photoelectric conversion efficiency also showed a low value of 6%.

As is apparent from this comparison, Examples 1 to 3 were used.
It can be seen that any of the metal plates on which the insulating layer is formed is used as a high-performance solar cell substrate.

[0030]

As described above, in the solar cell substrate of the present invention, an oxide layer effective as an insulating layer is formed on the surface of a metal plate by a sol-gel method. It is superior in heat resistance and moisture resistance as compared with the insulating layer, does not generate gas when depositing amorphous Si, and can form a metal electrode with excellent adhesion. An oxide layer formed by a sol-gel method is formed by a very simple method as compared with a conventional inorganic insulating layer, and becomes an insulating layer having excellent insulating properties. In addition, inorganic powder is dispersed in the insulating film, and photoelectric conversion efficiency is improved by a texture effect in which light is diffusely reflected on the surface and inside of the insulating layer. In particular, the height of the inorganic powder protruding from the surface of the insulating layer and the interval between adjacent inorganic powders are both set to 0.2.
~ 2.0μm, and the surface roughness of the insulation layer is Ra 0.2 ~ 0.4μ
When m and Rnax are controlled to 0.8 to 2.0 μm, the texture effect becomes large, and it is used as a substrate for a solar cell having high photoelectric conversion efficiency.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an oxide layer containing an inorganic powder formed on a metal plate surface by a sol-gel method. (A) Cross-sectional view of an oxide layer containing an inorganic powder. (B) A cross-sectional view of the oxide layer in which the height of the inorganic powder protruding from the surface of the insulating layer and the distance between adjacent inorganic powders are both controlled to be less than 1 μm.

[Explanation of symbols]

 Reference Signs List 1 metal plate 2 oxide layer by sol-gel method 3 inorganic powder

Claims (5)

[Claims] An insulating layer is formed on a surface of the substrate by a sol-gel method using a metal plate as a base material and a bath containing a metal alkoxide as a main component, and the insulating inorganic powder having a particle size of 0.2 to 2.0 μm is formed. An insulating substrate for a solar cell having improved insulation reliability and photoelectric conversion efficiency by being dispersed in the insulating layer at a ratio of 25 to 75 mass%. 2. An insulating layer having a surface roughness Ra of 0.2 to 0.4 μm,
The solar cell insulation according to claim 1, wherein the maximum is in the range of 0.8 to 2.0 µm, the height of the insulating inorganic powder protruding from the surface of the insulating layer is 0.2 to 2.0 µm, and the interval between adjacent ones is 0.2 to 2.0 µm. substrate. 3. The insulating substrate for a solar cell according to claim 1, wherein the insulating layer is an oxide layer having a thickness of 0.5 to 10 μm. 4. The insulating substrate for a solar cell according to claim 3, wherein the inorganic powder is an inorganic compound having a visible light reflectance of 70% or more. 5. An alkoxysilane, one or more of an organoalkoxysilane having the structure of the formula (1), an aluminum alkoxide, a titanium alkoxide, an alkoxide of an alkali metal or an alkaline earth metal, water and a thickener. The metal plate is brought into contact with the solution in which the inorganic powder is dispersed by dissolving in an organic solvent, and the solution adhering to the metal plate is dried.
A method for manufacturing an insulating substrate for a solar cell, comprising sintering to form an insulating layer. (Equation 1) X: vinyl group, epoxy group, amino group, methacryloxy group or mercapto group R: alkyl group