JPH03185769A - Solar cell - Google Patents

Abstract

PURPOSE:To improve a solar cell of this design in durability by a method wherein an ethylene-tetrafluoroethylene copolymer biaxially oriented film is used as a solar cell module protective film. CONSTITUTION:A solar cell module is composed of a substrate 1 of glass, stainless steel, or the like and an amorphous silicon 2, or a solar cell element of CdS/CdTe or the like and a protective film 5 of ethylene-tetrafluoroethylene copolymer biaxially oriented film. In this case, as the protective film 5 is formed of ethylene-tetrafluoroethylene copolymer biaxially oriented film, it is needless to say that it hardly deteriorates over a long term when it is kept at normal temperature and humidity, and further it also hardly deteriorates even if it is kept at high temperature and high humidity, and as it is kept transparent, a solar cell of this design can be prevented from deteriorating in photoelectric conversion efficiency. As the surface of the protective film 5 is lubricant, foreign particles, dusts, and the like are hardly attached to it, in result it is prevented from deteriorating in light transmittance. By this setup, a solar cell of long life can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a solar cell, and particularly to a solar cell having a protective film with excellent heat resistance, moisture resistance, and weather resistance.

[Conventional technology and problems to be solved by the invention] Solar cells can be used as an energy supply means without worrying about environmental pollution like thermal power generation or nuclear power generation, and electrical energy can be easily obtained directly from clean solar energy anywhere. It is attracting attention because of this.

However, at present, the production cost of L-type solar cells is high and the conversion efficiency is not sufficient, so they have not reached the stage where they are widely used.

In order to popularize solar cells', it is necessary to improve conversion efficiency and to have long-term durability outdoors.

To increase the durability and reliability of solar cell modules,
The protective film has an important role.

Electrodes of solar cell elements are easily oxidized by moisture, so they need to be shielded from the outside with a protective film to improve moisture resistance and weather resistance.

In conventional solar cells, the protective film is polymethyl methacrylate and epoxy resin (Japanese Patent Application Laid-open No. 6O-88481).
, silicone resin (FR-2426337), polyvinyl fluoride (JP-A-6O-148175), etc. are used.

However, polymethyl methacrylate has poor moisture resistance and lacks flexibility, so it is prone to cracking, epoxy resin is prone to yellowing and deterioration at high temperatures and high humidity, and has the disadvantage of impeding light transmission. Polyvinyl fluoride is stable. However, there is a problem in that the transparency is inherently poor, which lowers the conversion efficiency. In addition, the conventionally used RTV type (room temperature vulcanization type)
Although silicone resin is an expensive material and is chemically stable, it is easy for dirt and dust to adhere to its surface.
There is a problem that it obstructs light transmission.

[Objective of the Invention] The present invention does not have the above-mentioned drawbacks, that is, the protective film itself does not deteriorate, is stable even under high temperature and high humidity, and has a long lifespan that maintains light transmittance and protective function. solar cells.

[Means and effects for solving the problems] The present invention solves the above-mentioned problems by using a biaxially stretched ethylene-tetrafluoroethylene copolymer film as a protective film in a solar cell in which a solar cell element is provided on a conductive substrate. This is what we are trying to solve by using solar cells that have the same characteristics.

That is, the solar cell of the present invention includes a substrate made of glass, stainless steel, etc., and amorphous silicon (hereinafter referred to as a-3L),
Or solar cell elements such as CdS/CdTe and ethylene-
Consists of a protective film made of biaxially stretched tetrafluoroethylene copolymer film.

Although ethylene film has good transparency, it has poor heat resistance and poor surface lubricity.

On the other hand, tetrafluoroethylene film is completely opaque, but has high heat resistance and good surface lubricity.

Ethylene-tetrafluoroethylene copolymers maintain the advantages of each, with high transparency, high heat resistance, and good surface lubricity.

However, an unstretched ethylene-tetrafluoroethylene copolymer film has a low film density and allows water vapor to pass through it, which may oxidize the internal electrodes of solar cell modules or crystallize and turn cloudy over a long period of time.

The ethylene-tetrafluoroethylene copolymer biaxially stretched film of the present invention has a high film density, does not allow water vapor to pass through, does not undergo crystallization, and can be used for a long period of time.

The ethylene-tetrafluoroethylene copolymer biaxially stretched film is produced by forming an ethylene-tetrafluoroethylene copolymer into a film and biaxially stretching the film.

Here, two-wheel stretching in the present invention means to orient the molecules in both the longitudinal and transverse directions, thereby balancing the strength and improving other physical properties. In the present invention,
The ethylene-tetrafluoroethylene copolymer is stretched by 150 to 500% in the longitudinal and transverse directions at a temperature above the glass transition point and below the melting point, and then formed into a film.

As the protective film, the thickness of the biaxially stretched ethylene-tetrafluoroethylene copolymer film is 10 to 200 μm, preferably 30 to 1OOLL11.

Furthermore, a transparent adhesive similar to that used in the past is used to bond the protective film and the solar cell element.

Since the protective film of the present invention is made of a biaxially stretched ethylene-tetrafluoroethylene copolymer film, it does not deteriorate over a long period of time and maintains its transparency not only at room temperature but also under high temperature and high humidity. Does not reduce the conversion efficiency from light to electrical energy.

In addition, since the surface has lubricating properties, dirt, dust, etc. are difficult to adhere to, and light transmission is not obstructed.

In addition, since the solar cell module has low water vapor permeability, the electrodes inside the solar cell module are not oxidized and can be used for a long period of time.

[Example] In order to explain the structure of the solar cell of the present invention, FIG. 1 shows a cross-sectional view of a solar cell module of an example. In Fig. 1, l is a stainless steel substrate as a base, an amorphous silicon film 2 is formed on the base, and an In*O film is formed on it.
The solar cell of the present invention is constructed by providing an s-electrode 3 and pasting a protective film 5 via an adhesive 4.

Next, an example of manufacturing an a-5L (amorphous silicon) solar cell used in the present invention will be described.

FIG. 3 is a block diagram showing the outline of the apparatus used for manufacturing the a-5L photovoltaic device, in which 31 is a reaction vessel, 32
33 is a negative electrode for discharge, 33 is a positive electrode for discharge, 34 is a heating rotary table, 35 is a substrate, 36 is a tube connected to a vacuum gauge, 37 is an exhaust gas port, 38 is a raw material gas supply tube, 39 is for evacuation Pipe to be connected, 40141.42 is gas tank, 43.44
．． 45 is a flow meter, 46 is a cold trap, 47.48
．． 49 is an open and closed valve.

Next, an example of the operation of this manufacturing apparatus will be shown. First, an exhaust pump (not shown) connected to the exhaust gas port 37 is started, and the inside of the reaction vessel 31 is heated to 1.0-'T.

After reducing the pressure to about rr, operate the heating rotary table 34,
The substrate 35 placed thereon is heated and rotated. Before and after the heating operation, the on-off valves 47 and 48 are opened, and the S i Ha / Hl mixed gas and the P Hl / Hl mixed gas are supplied to the reaction vessel 31 from the gas tanks 40 and 41, respectively.

Next, the discharge generator G is operated to apply a high-frequency electric field to the gas, and a glow discharge is generated between the discharge positive electrode 33 and the negative electrode 32. In this way, after depositing the n-type layer-Si layer on the substrate 35, the discharge is stopped, and after that, the on-off valves 47 and 48 are closed to stop the gas supply, and the reaction vessel 31 Exhaust the raw material gas remaining inside.

Next, open and close the on-off valve 47 to remove the S i from the gas tank 4o.
The H4/Hl mixed gas is supplied to the reaction vessel 31 and the glow discharge is restarted. In this way, after depositing the i-type layer-Si layer on the n-type layer, the glow discharge is stopped, and at the same time, the on-off valve 47 is closed to stop the supply of raw material gas, and the remaining raw material Exhaust the gas.

Furthermore, the on-off valves 47 and 49 are opened, and the S i H4/Hl mixed gas and B* are discharged from the gas tanks 40 and 42, respectively.
HII/H*l mixed gas is supplied to the reaction vessel 31,
Restart glow discharge. After depositing the p-type layer -3t on the i-type layer in this way, the glow discharge is stopped, and at the same time, the on-off valves 47 and 49 are closed to stop the supply of raw material gas, and the remaining Exhaust raw material gas. The n-type, i-type and p-type a-3i layers obtained in this way are collectively a
- Called Si unit cell.

In order to further increase the electromotive force, a-Si unit cells may be repeatedly stacked.

Furthermore, a transparent conductive layer of tin indium oxide or the like is formed on the p-type layer-Si layer of the final A-8T single cell by known electron beam evaporation, RF sputtering, or the like.

In this example, using the above-mentioned apparatus, a-
A 3i cell was manufactured.

First, the substrate 35 has a thickness of 0.5 mm and dimensions of 20×2.
Stainless steel with a mirror-polished surface of 0 mm was used.

In addition, the volume ratio of the raw material gas is S i H4/H, = 0.1,
PHs/Hz = 5 x 10-'B x Ha/H
z = 5
The ratio of mixed gases is on the order of 0.1 to 1% in all cases. The pressure of the raw material gas in the reaction vessel was set at 2 to 5 Torr, and the high frequency output of the discharge generator G was set at 50 to 500 W (4 MH
z) When the temperature of the stainless steel substrate is 250 to 350°C, the growth rate of the p-type and n-type layers-5i layer is 0.4
~1 entry/sec, growth rate of i-type layer-3i layer is 0.8~
There were 3 people/sec. The thickness of the a-Si layer can be easily adjusted to any desired thickness by adjusting the deposition time.

The layer structure of the a-3i used in the present invention is that the thickness of the n-type a-3i layer is 100 mm, and the thickness of the i-type a-3i layer is 6000 mm.
The thickness of the p-type a-Si layer was 30 people.

(Example 1) In the solar cell module shown in FIG.
), and a two-wheel stretched film (thickness lOOμm) of ethylene-tetrafluoroethylene copolymer (ethylene 20 mo1%, tetrafluoroethylene 80 mo1%) was used as a protective film to produce a solar cell module.

Using this solar cell module, a 2000 hour weather test was conducted using a xenon fade meter (FAL-25AX-HC-B-EC manufactured by Suga Test Instruments Co., Ltd.).

Figure 2 is a diagram showing the structure of the testing machine used in the weather resistance test of this example, and Figure 2 (a) is a front view of the equipment equipped with a vertical sample holder; The internal structure is also illustrated. FIG. 2(b) is a diagram showing an enlarged view when the standard type sample holder is used.

As shown in FIG. 2(a), this device has a control panel 12 on the left side of the front of the main body, and includes meters and meters necessary for operating the test machine.
Switches etc. are installed. Further, there is a test tank on the right side, a xenon lamp 10 is installed in the center, and a sample rotating frame 15 rotates around the xenon lamp 10. Further, the lower part is a machine room in which a blower 17, a transformer 18, etc. are installed. A weather resistance test was conducted using the above-mentioned apparatus as follows.

First, a test sample was set on the sample holder 19 attached to the sample rotation frame 20 shown in FIG. 2(b), and the measured value of the black panel thermometer 21 attached to the rotation frame 20 was 63±3℃. do. As a result, the temperature inside the test machine becomes approximately 45°C. Furthermore, the humidity inside the test machine is 70% RH. In addition, the measured value of the irradiance meter (not shown) installed in the test machine was 0.5 ± 0.02 W/m at 340 mm.
And so. The sample was rotated to receive light evenly, and irradiated with light for 2000 hours under the above conditions.

Thereafter, the output reduction was measured in comparison with a solar cell element without a protective film, and the state of the protective film was observed after the weather test.

These results are shown in Table 1.

(Example 2) In the solar cell module shown in Fig. 1, an ethylene-vinyl acetate hot melt sheet (film thickness 50 μm) was used as the adhesive, and an ethylene-tetrafluoroethylene copolymer (ethylene 50 mo1%, tetrafluoroethylene copolymer) was used as the protective film. ethylene 50
A solar cell module was manufactured using a biaxially stretched film (film thickness: 501LI11). Using this solar cell module, the same measurements as in Example 1 were carried out.
．． The results are shown in Table 1.

(Example 3) In the solar cell module shown in Fig. 1, an ethylene-vinyl acetate hot melt sheet (film thickness 50 μm) was used as the adhesive, and an ethylene-tetrafluoroethylene copolymer (ethylene 70 mo1%, tetrafluoroethylene copolymer) was used as the protective film. ethylene 30
A solar cell module was manufactured using a biaxially stretched film (film thickness: 80 μI) and the same measurements as in Example 1 were performed, and the results are shown in Table 1.

(Comparative Example 1) In the solar cell module shown in Fig. 1, an ethylene-vinyl acetate hot melt sheet (film thickness 50 μm) was used as the adhesive, and an ethylene-tetrafluoroethylene copolymer (ethylene 20 mo1%, tetrafluoroethylene copolymer) was used as the protective film. ethylene 80
A solar cell module was manufactured using an unstretched film (film thickness: 80 gm+) (mo1%). Measurements were carried out in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 2) In the solar cell module shown in Fig. 1, an ethylene-vinyl acetate hot melt sheet (thickness: 50 um) was used as the adhesive, and a conventional polyvinyl fluoride film (thickness: 100 gm) was used as the protective film. A solar cell module was manufactured. Measurements were carried out in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 3) In the solar cell module shown in Fig. 1,
A solar cell module was manufactured using an ethylene-vinyl acetate hot melt sheet (thickness: 50 μm!+) as an adhesive and a conventional polymethyl methacrylate film (thickness: 100 μm) as a protective film. Measurements were carried out in the same manner as in Example 1, and the results are shown in Table 1.

As shown in Table 1, in Examples 1 and 2.3, in which the ethylene-tetrafluoroethylene copolymer two-wheel stretched film was used as the protective film, there were some differences depending on the film thickness, but both , the initial output efficiency ratio of 92-94% was reduced to 91-92% after the test, resulting in only a 1-2% decrease in the output efficiency ratio, and the surface of the protective film did not change. however,
In Comparative Example 1 using an ethylene-tetrafluoroethylene copolymer unstretched film, the initial efficiency ratio was as low as 86%.
After the test, it decreased to 80%, 6% deterioration occurred, and the protective film itself peeled off.

Also, in Comparative Example 2゜3 using a protective film made of a conventional material,
In some cases, the initial efficiency ratio was low, the efficiency decreased by 4% to 34% after the test, and the protective film was cracked.

Table 1 [Effects of the invention] As explained above, by using the ethylene-tetrafluoroethylene copolymer biaxially stretched film as the protective film of the solar cell module, it has good transparency, high output efficiency from the beginning, In addition, it is possible to obtain long-term durability such as good transparency, stable output efficiency, and no deterioration of the protective film itself, and also to avoid the adhesion of dirt, dust, etc.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an example of the solar cell module of the present invention. FIG. 2 is a structural diagram of the test equipment used in the weather resistance test conducted in the example. FIG. 3 is a block diagram showing an outline of an apparatus used for manufacturing a photovoltaic element. 1, stainless steel substrate 2, amorphous silicon 3, 1nn's electrode 4, adhesive 5, protective film 31, reaction vessel 32, negative electrode for discharge 33, positive electrode for discharge 34, heating rotary table 35, substrate

Claims (1)

[Claims] A solar cell in which a solar cell element is provided on a conductive substrate, the solar cell having an ethylene-tetrafluoroethylene copolymer biaxially stretched film as a protective film.