JPH02123771A - solar cells - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention improves the reflection of the window layer by applying a specific low refractive index material to the surface of the transparent substrate, transparent electrode, or photoelectric conversion part that becomes the window layer. This invention relates to solar cells with reduced loss and increased conversion efficiency.

[Prior Art] A solar cell is usually composed of a support substrate, a transparent electrode, and a photoelectric conversion section. In order to effectively utilize incident light, it is necessary to It is important to reduce losses due to reflection and absorption of light energy by the layers and to send as much incident light as possible to the photoelectric conversion section.

Generally, in amorphous silicon or chalcogenide thin film solar cells, glass, plastic, etc. are used as the transparent support substrate, and ITO (tndium T) is used as the transparent electrode.
In Oxide), SnO2, ZnO, etc. are used. However, since these materials have large refractive indexes of approximately 1.5 and 1.9, respectively, there is a problem in that the reflection at surfaces and interfaces is large and a part of the incident light energy becomes a reflection loss, making it impossible to use it effectively. Ta. Furthermore, in crystalline solar cells (crystalline silicon, polycrystalline silicon, gallium arsenide, indium phosphide, chalcogenide, etc.) with a structure in which the surface of the photoelectric conversion part is exposed, the refractive index of the surface material is 3 to 4 or more, so one surface It is known that the reflection loss is 20 to 30%.

Conventionally, anti-reflection methods include coating the surface with a material having as low a refractive index as possible, or using a single-layer or multi-layer optical interference film corresponding to a desired wavelength range. The latter is generally formed using expensive vacuum evaporation equipment or sputtering equipment;
The former has low productivity and high cost, but the former has high productivity and low cost because it can be manufactured with inexpensive equipment such as application using a brush or roller, spraying, or immersion in a treatment liquid. Further, while the former allows reflection reduction over a wide wavelength range, the latter has theoretical restrictions on expanding the wavelength range.

Although materials with a low refractive index are effective in enhancing the antireflection effect, there are few materials with a refractive index of 1.45 or less. Inorganic materials are limited to fluorine compounds of calcium and magnesium, and these materials are generally formed into films by vapor deposition, which is difficult to achieve by coating. On the other hand, among organic materials, polycarbonate and acrylic resins are not so low at around 1.49, and fluorine-based polymers such as PFA are low at around 1.35, but they are opaque and maintain practical durability. However, it has not been possible to obtain a product with sufficient molecular weight.

[Problems to be Solved by the Invention] The present invention eliminates the drawbacks of the reflection reduction treatment method of the prior art as described above, and eliminates the problem of impairing the high transparency of the window layer material of the solar cell and the photoelectric properties of the solar cell. To provide a highly durable low-reflection finishing agent that reduces reflection loss and maintains its performance over a long period of time by using a known method such as coating, spraying, or dipping on the surface of the window layer material. The purpose is to

[Means for Solving the Problems] As a result of intensive studies based on the above-mentioned purpose, the present inventor has found that a polymer having a fluorine-containing aliphatic ring structure has high transparency and a low refractive index, and It has excellent formability and sufficient durability as a coating film on the surface of the base material, and when applied to the surface of the window layer material of solar cells, it reduces reflection loss without impairing transparency and the power generation characteristics of solar cells, and reduces the amount of light. We have newly discovered that this material is extremely useful as a material that can be used effectively.

Thus, the present invention has been completed based on the above findings, and is characterized in that a coating film with a low refractive index is formed on the light intake surface, and the low refractive index member is made of a polymer having a fluorine-containing aliphatic ring structure. The objective is to provide a new solar cell.

In the present invention, examples of the polymer having a fluorine-containing aliphatic ring structure include a wide variety of polymers, including those that are conventionally known or well-known. Therefore, in the present invention, a fluorine-containing bomber having the above-mentioned specific ring structure in its main chain is preferably employed.

For example, general formula %formula%) general formula (CFCI).

Examples include those having a ring structure as shown in the general formula. Among these,
Polymers having the following ring structures are typical. However, the content of the present invention is not limited to these only.

F2 The manufacturing method of these polymers is as follows: The following two ways It is.

Tatashi Although it is limited to the manufacturing method There is no end.

1. By cyclization polymerization CF2=CF-0-CF2-CF2-0-CF CF.

\ / CF2-CF2 F2 \ 1 0F2-CF2 (USP: 14+8303°B 110634'l) CF2-CF-CF2-CFCI-CF2-CF-CF
.

C.F.C.I. (usp Such) Ch=CF-0-CFz-CF2CF20-CF.

2. Those using cyclic monomer cusp39780:
10) In the above, polymers having a perfluoroaliphatic ring structure are exemplified, but in the present invention, polymers in which some of the fluorine atoms in the above examples are substituted with other hydrogen atoms or organic groups, or polymers that have been polymerized by metathesis polymerization are used. Examples include those having a ring structure such as those obtained.

Therefore, the polymer having a specific ring structure according to the third aspect of the present invention can be obtained smoothly and advantageously by the above-mentioned cyclization polymerization, or
In particular, by using a hexamer which has two polymerizable groups with different polymerizability in the molecule and has 2 to 7 atoms in the linear part of the connecting chain connecting these two polymerizable groups. ,
Even without employing ultra-high pressure conditions or large dilution conditions, the cyclization polymerization can proceed smoothly and advantageously by suppressing gelation by-products.

As a monomer suitable for the above-mentioned cyclization polymerization, first of all, it is desirable that the monomer has two carbon-carbon multiple bonds having different polymerizability. Usually, a carbon-carbon double bond is used, or two multiple bonds of different types or structures are used.

For example, a fluorine-containing monomer having two multiple bonds that are not bilaterally symmetrical, a vinyl group and an allyl group, a 2'nylether group and a vinyl group, a fluorine-containing multiple bond and a hydrocarbon multiple bond,
Examples include perfluorinated multiple bonds and partially fluorinated multiple bonds.

Secondly, it is desirable that the number of atoms in the linear portion of the connecting chain connecting these two carbon-carbon multiple bonds is 2 to 7. When the number of atoms in the linear portion of the connecting chain is 0 to 1, cyclization polymerization is difficult to occur, and the same applies when the number of atoms is 8 or more. Usually, the number of atoms is preferably 2 to 5. Furthermore, the connecting chain is not limited to a straight chain, and may have a side chain structure or a ring structure, and the constituent atoms are not limited to carbon atoms, but may also include heteroatoms such as O, S, and N. good. Thirdly, it is desirable that the fluorine content be 10% by weight or more. If the fluorine content is too low,
The specificity of the fluorine atom becomes difficult to demonstrate. Naturally, perfluoromonomers are preferably employed.

Specific examples of the above-mentioned specific fluorine-containing monomers include CF2-CFOCF2CF-CF, CF2-CFOC
F2CF2CF-CF2゜CF2-CFOCF20CF
2CF Snow CF.

CF21CFOCFtCFtCH zero CH,.

~4 arrangement a) CF, -CFOCF, CF2O-CL.

CF2-CFO(CF2)CF-CFCF3.

C.F.

CF2-CHoCH, Cl12CF-CF2゜CH2-
An example may be CFCOCHzC1+□cF=cF2゜υ.

In the present invention, those having one vinyl ether group, CF2-CFO-, are preferably employed in terms of polymerization reactivity, cyclization polymerizability, gelation suppression, etc., and in particular perfluoroallyl vinyl ether (CF2"CFOCF2CF")
CF2) and perfluorobutenyl vinyl ether (C
A suitable example is F2.CF (lcF2cF2cF-CF2).

The above monomer components may be used alone or in combination of two or more, and there is no problem in copolymerizing them in combination with other copolymerization components to the extent that the essence of these components is not impaired. If necessary, the polymer may be crosslinked in some way.

Other monomers to be copolymerized are not particularly limited as long as they are radically polymerizable monomers, and include a wide range of fluorine-containing monomers, hydrocarbon monomers, and others.

Of course, these other monomers may be used alone in radical copolymerization with a monomer capable of introducing the specific ring structure, or two or more appropriate types may be used in combination in the copolymerization reaction. You may also have them do this.

In the present invention, it is usually desirable to select fluorine-containing monomers such as fluoroolefins and fluorovinyl ethers as other monomers. For example, preferred examples include detrafluoroethylene, perfluoromethyl vinyl ether, perfluoroflopyr vinyl ether, and perfluorovinyl ether containing a heptafunctional group such as a carboxylic acid group or a sulfonic acid group. , vinyl fluoride, chlorotrifluoroethylene, and the like.

In order to take advantage of the characteristics of the specific fluorine-containing alicyclic structure targeted in the present invention, the copolymer composition preferably has a cyclic structure composition of 20% or more, more preferably 4% or more.
It is desirable that it be 0% or more, but it is selected appropriately depending on the relationship between the refractive index and adhesiveness of the coating film formed as a low-reflection treated material.

Since the polymer having a specific ring structure in the present invention is soluble in fluorine-based solvents, a solution can be used to treat the transparent substrate.

The solvent to be used is not limited as long as it dissolves the above polymer, such as perfluorobenzene, "Afluto" (trade name: fluorine-based solvent manufactured by Asahi Glass Co., Ltd.), "
Fluorinert” (Product name: Perfluoro manufactured by 3M Company)
Liquids containing 2-butyltetrahydrofuran), trichlorotrifluoroethane, etc. are suitable. As a matter of course, two or more appropriate types can be used in combination as a solvent. Particularly in the case of a mixed solvent, hydrocarbons, chlorinated hydrocarbons, fluorochlorinated hydrocarbons, alcohols, and other organic solvents can also be used in combination. Solution concentration is 0.01wt%~50
wt%, preferably 0.1 wt% to 20 wt%.

There are no particular limitations on the method of processing the window layer material for solar cells, and ordinary brushing or roll coating can be used.

It is applied by spraying, dipping, spin-casting, etc.

In the present invention, a film with adhesive properties that can be used in practical use can be obtained by directly treating the window layer material for solar cells such as glass or transparent plastic or on the photoelectric conversion part, but depending on the type of window layer material, the adhesiveness If the adhesion is poor, or in order to make the adhesion even stronger, it is possible to treat the coating film that has been previously formed on the transparent substrate with a primer such as a silane coupling agent. It is also possible to copolymerize a monomer having an adhesive group to further improve adhesiveness.

When forming an anti-reflection film on the surface of a transparent substrate using the low-reflection finishing agent of the present invention, sufficient anti-reflection effect can be obtained even if a single layer of a fluorine-containing polymer coating film with a low refractive index is formed on the substrate. However, it is also possible to provide a coating film with a higher refractive index than the fluorine-containing polymer between the base material and the fluorine-containing polymer layer to form a multilayer structure, thereby increasing the antireflection performance.

The film formed by the low-reflection finishing agent of the present invention must have practical strength by itself, or if a very thin film or scratch resistance is required, it may be hardened by a crosslinking reaction. Ru.

As a method for crosslinking the fluorine-containing polymer used in the present invention, commonly used methods can be used as appropriate. For example, crosslinking can be achieved by copolymerizing a monomer having a crosslinking site, by adding a crosslinking agent, or by using radiation or the like.

The antireflection finishing agent of the present invention can be used not only for glass and transparent plastics as transparent window materials for solar cells, but also for transparent electrodes.
It is suitably used as an antireflection treatment agent for the surface of high refractive index materials such as TO, SnO□, and 2nO.

Can the coating process of the anti-reflective agent be carried out after constructing the solar cell? Since the anti-reflective agent has heat resistance up to 400°C, it is suitable for forming transparent electrodes and photoelectric conversion films of solar cells. By setting the film forming temperature at 400° C. or lower, a coating film can be formed using the antireflection treatment agent on the glass surface prior to forming transparent electrodes and solar cells. That is, when forming a solar cell, it is possible to perform antireflection treatment on the substrate glass, or it is also possible to perform antireflection treatment after forming the transparent electrode. For example, since the film forming temperature for amorphous silicon solar cells is 200 to 250°C, solar cells can be formed using a solar cell substrate with an antireflection film that has been pretreated with the antireflection agent. It is possible.

Furthermore, by molding the antireflection agent to a thickness sufficient to be used as a transparent substrate of a solar cell, it can be used as the supporting substrate itself in place of glass or plastic.

[Function] In the present invention, since the polymer having a fluorine-containing aliphatic ring structure has small crystallinity or almost no crystallinity,
Although it is a fluororesin, it exhibits high transparency and high light transmittance, and because it is a fluorine-containing polymer, it has a lower refractive index than ordinary hydrocarbon resins and has electrical insulation properties. It is considered to have high moisture resistance, weather resistance, and chemical resistance. However, it goes without saying that such explanations are provided to assist in understanding the present invention and do not limit the present invention in any way.

[Examples] Next, Examples of the present invention will be described in more detail, and it goes without saying that this description does not limit the present invention.

Synthesis Example 1 35 g of perfluoroallyl vinyl ether, 5 g of trichlorotrifluoroethane (hereinafter abbreviated as R-1, 13), 150 g of ion exchange water, and 35 mg of (CsF7CO)t as a polymerization initiator. ,
It was placed in a pressure-resistant glass autoclave with an internal volume of 2,001 cm. After purging the system with nitrogen three times, suspension polymerization was carried out at 26°C for 23 hours. As a result, 28 g of polymer was obtained.

When we measured the infrared absorption spectrum of this polymer, we found that
186 (1cm-
', There was no absorption near 1840 cm-'.

In addition, this polymer was dissolved in perfluorobenzene.
When the IIMR spectrum of 9F was measured, a spectrum showing the following repeating structure was obtained.

0-CF.

The intrinsic viscosity [η] of this polymer is “Florinert” F
(Knee 75 (Product name: Perfluoro (2) manufactured by 3M Company)
-butyltetrahydrofuran) (hereinafter abbreviated as FC-75) at 30°C. The glass transition point of the polymer is 69°C, and it is a tough, transparent glass-like polymer at room temperature. In addition, the 1O% thermal decomposition temperature is 462°C, and this polymer is colorless and transparent, has a low refractive index of 1.34, and has a light transmittance of 95%.
It was expensive.

Example 1 The fluorine-containing polymer obtained in Synthesis Example 1 was used as Fluorinert F.
It was dissolved in C-75 to prepare a 2 wt % solution and used as an antireflection finishing agent. A crystalline silicon solar cell was immersed in this coating composition, pulled up at a speed of 20 cm/win, left to dry at room temperature for 10 minutes, and then heated at 1 torr, 2
A coating film was formed by drying under reduced pressure for 0 minutes. The thickness of the film formed was approximately 0.2 mm. Regarding the output characteristics of this solar cell,
A comparison was made before and after the coating film was formed under irradiation, and the results shown in Table 1 below were obtained.In addition, the average reflectance of the solar cell surface (light incident side) was measured using a self-recording spectrophotometer U-3 manufactured by Hitachi, Ltd.
Using the 400 type integrating sphere attachment, wavelength 4DOnrs~5
When measured at an incident angle of 5'' at 0 hm, it was 17.4% before coating and 12.6% after coating.

Table 1 Example 2 An amorphous silicon solar cell was immersed in a synthetic fil solution, pulled up at a rate of 5 cm/sin, left to dry at room temperature for 5 minutes, and then dried under reduced pressure at l torr for 20 minutes. A coating film was formed. The thickness of the formed film was 0.08 μm. The output characteristics of this solar cell were compared in the same manner as in Example 1, and the results shown in Table 2 below were obtained. In addition, the average reflectance of the solar cell surface (light incident side) was measured using a self-recording spectrophotometer U-3 manufactured by Hitachi.
Wave & 400mm ~ 80mm using 400 type integrating sphere attachment device
When measured with 011111, it was 11.2% before application,
After coating, it was 8.61%.

Table 2 For reference, the coating film of Synthesis Example 1 was formed on a glass plate and a polycarbonate plate, and the average reflectance was measured. The results are shown in Table 3 below.

Table 3 [Effects of the Invention] By employing a polymer having a fluorine-containing aliphatic ring structure as a low-reflection finishing agent, it is possible to form a film with a low refractive index on the surface of the window layer material of a solar cell. , it is possible to significantly reduce the light reflectance of the window layer material of solar cells.

Claims (1)

[Scope of Claims] 1. A solar cell characterized in that a coating film with a low refractive index is formed on a light intake surface, and the low refractive index member is made of a polymer having a fluorine-containing aliphatic ring structure. 2. The solar cell according to claim 1, which is a thin film solar cell using glass or transparent plastic as a support substrate. 3. The solar cell according to claim 1, wherein the support substrate constitutes a photoelectric conversion section, and the solar cell has a structure in which the photoelectric conversion section is exposed.