JP3078951B2 - Photovoltaic element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device having a current-collecting electrode having excellent environmental resistance, and more particularly to a photovoltaic device having high stability to moisture and high long-term reliability, and easy production. And a method for manufacturing a photovoltaic element having a high yield.

[0002]

2. Description of the Related Art In recent years, interest in the environment and energy, such as global warming and radioactive contamination due to a nuclear power plant accident, has been greatly increased. Under such circumstances, a solar cell, which is one of the uses of a photovoltaic element, is expected from all over the world as renewable and inexhaustible clean energy.

At present, three types of solar cells are widely used, one using single crystal silicon, one using polycrystalline silicon, and one using amorphous silicon. Although the conversion efficiency of amorphous silicon-based solar cells is not as good as that of crystalline solar cells, they are easy to increase in area and have a large light absorption coefficient, so they can be used as thin-film solar cells. It has excellent features and is one of the promising solar cells. Further, when the amount of power generation reaches several hundreds of MW, it is estimated that the cost will be much lower than that of a crystalline system.

Here, an example of a conventional solar cell is shown in FIG. In FIG. 6, an amorphous silicon-based photoelectric conversion layer 103 is formed over a conductive substrate 104, and a transparent conductive layer 102 also serving as an antireflection layer is formed thereon. further,
A current collecting grid electrode 101 for efficiently collecting a current is formed on the transparent conductive layer 102. As shown in FIG. 6, when light is incident on the photoelectric conversion layer 103 from the current collecting electrode 101 side, the energy of the light is converted into a current in the photoelectric conversion layer, and is output from the current collecting electrode 101 and the conductive substrate 104 as an output. Taken out. The photoelectric conversion layer has at least one or more pin junctions.
The side acts as a cathode. In the case of a solar cell having a configuration in which a current collecting electrode is formed on a non-single-crystal semiconductor, the current collecting electrode must be formed in a large area at a temperature or the like at which the film quality of the semiconductor is not damaged. Is formed using a conductive paste.

[0005] Solar cells having an output of several watts or more are generally used outdoors. Therefore, these solar cells are required to have durability against temperature and humidity, that is, environmental resistance.

[0006] A conventional solar cell in which a current collecting electrode is formed using a conductive paste, as shown in FIG.
There are many holes / voids 105 of various sizes in one. When this is left in the air, moisture penetrates the solar cell module from the outside world and penetrates into these pores and voids, and the photovoltaic power of the solar cell itself causes the conductive substrate such as silver contained in the collecting electrode Is eluted. This eluting conductive substrate is
Diffusion growth through defect parts such as semiconductor pinholes,
There is a problem that the positive and negative electrodes of the solar cell are short-circuited, and as a result, the conversion efficiency is greatly reduced. For example, when the conductive substrate is silver, the reaction proceeds on the anode and cathode sides according to the following chemical formula, and a short circuit occurs.

Anode: Ag ₂ O + H ₂ O → 2Ag ⁺ + 2OH ⁻ (A) Cathode: Ag ⁺ + e ⁻ → Ag (dendritic crystal deposition) (B) This is shown in FIG. Ag in the anode-side current collecting electrode 101
Silver ions 605 generated by the reaction between ₂ O and water generate photoelectric conversion layer 10 by the electromotive force generated by the photovoltaic element.
3 and penetrate into the pinholes 606 and the like, and adhere to the conductive substrate 104 to form dendritic crystals 607.
When the dendritic crystal 607 grows, the current collecting electrode 101 of the photovoltaic element and the conductive substrate 104 are short-circuited, and the conversion efficiency is reduced. As the process proceeds further, the output of the solar cell cannot be taken out.

This phenomenon is called migration, and similar phenomena are observed not only in silver but also in copper, solder, gold and the like.

[0009]

[0008] The present invention has been made in view of the above circumstances, high environmental resistance, photovoltaic that neither degradation of the conversion efficiency, particularly for formation easy moisture penetration
It is intended to provide a force element .

[0010]

The photovoltaic device of the present invention comprises one electrode, a photoelectric conversion layer, and a photoelectric conversion layer sandwiched between a conductive substrate and a conductor having a curable resin. Having the other electrode opposed to the one electrode, and having a number average molecular weight of 30 for the curable resin.
It is characterized by being set to 00 or less.

[0011]

[0012]

[0013]

[0014]

[0015]

Operation and Embodiments As described above, if there are vacancies and voids in the current collecting electrode, moisture that has permeated from the outside reacts with a conductive substrate such as silver to generate silver ions and the like. A short circuit between the electrodes occurs.

On the other hand, in the present invention, as the curable resin of the conductive paste, a resin having a number average molecular weight of 3000 or less is used. It is difficult to form voids. Therefore,
Since it is difficult for water to reach the conductive substrate, the reaction represented by the chemical formula (A) can be suppressed, and the generation of silver ions and the like can be suppressed. As a result, a short circuit between the electrodes can be prevented.

Even if silver ions are generated, if the number average molecular weight of the curable resin is 3000 or less, the resin moves greatly and the resin sinks slightly below. Can hardly reach the transparent electrode layer, and a short circuit can be prevented.

Further, since the resin is largely moved, it becomes easy to form a paste on the photoelectric conversion layer by screen printing or the like.

As described above, according to the present invention, it is possible to provide a photovoltaic element which is less likely to cause migration and has good environmental resistance. Further, since the conversion efficiency does not deteriorate, the cost of the entire photovoltaic element can be reduced.

The solar cell according to the present invention is configured as follows when using an amorphous silicon-based material deposited on a conductive substrate as a photoelectric conversion semiconductor layer.

A plasma C such as silane gas is placed on a conductive substrate.
An amorphous silicon-based layer having at least one pin junction is formed by the VD method. As the conductive substrate, stainless steel, aluminum, copper, titanium, carbon sheet or the like is preferably used. Alternatively, a substrate obtained by depositing a metal or the like on an insulating substrate such as a resin can be used as the substrate.

Subsequently, indium oxide,
A transparent conductive layer made of tin oxide or the like is formed by vapor deposition or a spray method.

Further, a conductive paste comprising a conductive substrate and a curable resin is applied on the transparent conductive layer by a screen printing method, and cured at a temperature of 125 to 250 ° C. to form a current collecting electrode.

As the conductive substrate in the conductive paste,
Silver, silver-palladium alloy, a mixture of silver and carbon, copper, nickel, aluminum, gold and the like can be used. The conductive substrate in the current collecting electrode is preferably at least 70% by weight, and more preferably 75% by weight in order to obtain a conductivity required for flowing an electric current.
The above is more preferable.

As the curable resin, a urethane resin, an epoxy resin, a polyimide resin, a polyester resin, a phenol resin, a vinyl resin, an acrylic resin or the like having a number average molecular weight of 3000 or less is used. Of these, epoxy systems are most preferred, particularly from the viewpoints of water resistance and economy. Also,
It is desirable that impurities such as chlorine and sodium contained in the conductive paste act as catalysts for the migration reaction and promote generation of metal ions, so that they are as small as possible.

In general, the holes and voids in the current collecting electrode are
Depending on the type of resin forming the collecting electrode, the temperature at the time of formation, and the time, generally, if a sufficient curing time is given at a temperature of 120 ° C. or more, the degree of crosslinking of the resin hardly changes and the pores and There is almost no change in the air gap. further,
When the paste is used as a current collecting electrode of an amorphous semiconductor photovoltaic element, the forming temperature is generally 120 ° C. to 250 ° C., depending on the type of resin. If the temperature is lower than 120 ° C., the resin crosslink in the Petos is insufficient, so that the electric conductivity and the adhesive strength are reduced. If the temperature is higher than 250 ° C., the film quality of the amorphous semiconductor is deteriorated.

[0027]

The present invention will be described below in more detail with reference to examples. In addition, the number average molecular weight of the curable resin of the present invention was measured by gel permeation chromatography (GPC). The gel permeation chromatography (GPC) used here uses the property that the adsorbent absorbs better as the sample has a lower molecular weight, and injects the measurement sample into a column (pipe-shaped adsorbent) that is kept at a constant temperature. The average molecular weight is measured from the amount and time.

(Example 1) Thickness 8 MIL, area 16 cm
^On the stainless steel substrate No. ² , pin-type photoelectric conversion layers made of amorphous silicon were deposited in two layers by a plasma CVD method, and a transparent electrode layer made of indium oxide was deposited thereon by sputtering.

Next, a conductive paste composed of a urethane resin and silver fine particles (a conductive substrate of 70% by weight, a urethane resin having a number average molecular weight of 2010 of 20% by weight, and a solvent (methyl ethyl ketone) of 10% by weight) is desired. The shape was screen-printed and cured at a temperature of 130 ° C. for 1 hour to form a solar cell of this example. This solar cell is called a tandem type, and its optimum operating voltage is 1.2V.

The solar cell was subjected to a forward bias of 1.2 V at a high temperature of 85 ° C. and a high humidity of 85% RH and a high humidity, and the time change of the leakage current flowing in the solar cell was measured. The forward bias is for simulating an operation state. The measurement result is shown by a solid line A in FIG. The vertical axis in FIG. 2 represents the leakage current value per unit area, and the horizontal axis represents time.

(Comparative Example) For comparison, a polyimide resin (number average molecular weight: 14400) or a polyester resin (number average molecular weight: 31000) is used as the curable resin.
A solar cell was prepared in the same manner as in Example 1 except that was used, and the same measurement was performed.

FIG. 2 shows the result. In FIG. 2, results obtained when a polyimide resin (number average molecular weight: 14400) and a polyester resin (number average molecular weight: 31,000) were used are indicated by B and C, respectively.

As apparent from FIG. 2, the leakage current of the solar cell of the comparative example was 1.7 m / hour for the polyimide-based solar cell.
A / cm ² , ² mA / c per hour for polyester
m ² , whereas the solar cell of Example 1 was 0.2 mA / cm ² per hour, which was about 1/100 of the comparative example.
10, which indicates that the elution of silver is extremely small.

When the bending tests of the solar cells of Example 1 and the comparative example were performed, the current collecting electrodes of the comparative example were partially peeled, but the current collecting electrodes of the example 1 were not peeled at all. It turned out that it was excellent in adhesiveness.

Example 2 In the same manner as in Example 1, a paste composed of an epoxy resin and silver fine particles (conductive substrate 8
A tandem solar cell was produced using 0% by weight, 20% by weight of an epoxy resin having a number average molecular weight of 540, and no solvent). The curing conditions were 150 ° C. for 3 hours.

As in Example 1, a forward bias was applied at a high temperature and high humidity of 85 ° C. and 85% RH, and the increase in leakage current was examined. The result is shown in FIG. For comparison, the results of the comparative example are also shown.

In this embodiment, the increase in leakage current was as small as 0.03 mA / cm ² per hour, which was about 1/100 as compared with the comparative example. This is compared to the first embodiment.
It is almost 1/10, and it has been found that the use of the conductive paste containing a resin having a small number average molecular weight as a component can provide a still greater effect.

Example 3 A paste comprising unsaturated polyester resin having various number average molecular weights and silver fine particles (85% by weight of conductive substrate, 10% by weight of unsaturated polyester resin, 5% by weight of solvent) was used. A tandem type amorphous solar cell was produced in the same manner as in Example 1.

As in Example 1, 85 ° C., 85% R
A forward bias was applied under high temperature and high humidity of H, and the time change of the leakage current was examined. FIG. 4 shows the results. In FIG. 4, the solid line X indicates that the number average molecular weight of the unsaturated polyester resin is 29.
00 is the time change of the leakage current when the paste No. 00 is used, the dotted line Y is the time change of the leak current when the paste whose unsaturated polyester resin has a number average molecular weight of 3350, and the dashed line Z is the change over time. This is a change over time of leakage current when a paste having a number average molecular weight of 5000 of a saturated polyester resin is used.

The rate of increase of the leakage current was found to be a number average molecular weight of 290.
0.25 mA / cm when a resin paste of 0 is used.
^{2, which} is very small and migration of silver is extremely small, whereas the amount of leakage current increases when a resin paste having a molecular weight of 3350 or 5000 is used,
In particular, when a paste having a molecular weight of 5000 is used, 1.1 is used.
It can be seen that the leakage current is 4 to 5 times that in the case of using a paste having a molecular weight of 2900 mA / cm ² . This shows that although the same unsaturated polyester resin is used, the amount of silver eluted differs due to the difference in molecular weight, and shows different characteristics regarding migration resistance.

Table 1 and FIG. 5 summarize the results of Examples 1 to 3 and Comparative Example.

[0042]

[Table 1] As can be seen from Table 1 and FIG. 5, the number average molecular weight is 3000.
There is a clear difference in the increase rate of leakage current between the paste using the following resin and the paste using a resin having a number average molecular weight of 3,000 or more, and the paste having a number average molecular weight of 3,000 or less is excellent in migration resistance. Is shown. Also, it can be seen that the smaller the number average molecular weight, the greater the effect.

According to the present invention, that is, when the number average molecular weight is 30
By forming the current collecting electrode using a conductive paste containing a curable resin of not more than 00, short circuit between the electrodes of the photovoltaic element due to moisture permeation or the like can be prevented. It is possible to provide a solar cell having excellent environmental properties.

Further, since a mixture of a resin and a conductive substrate is used for the current collecting electrode, the current collecting electrode can be formed at a low temperature.
A solar cell having characteristics can be manufactured at low cost.

Furthermore, since the current collecting electrode containing the resin of the present invention is flexible and resistant to mechanical shock, a flexible and robust photovoltaic element can be provided.

As described above, according to the present invention, a photovoltaic element having excellent environmental resistance can be supplied at a low cost, so that its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a photovoltaic device of the present invention.

FIG. 2 is a graph showing a temporal change of a leakage current of the photovoltaic devices of Example 1 and Comparative Example.

FIG. 3 is a graph showing a temporal change of a leakage current of the photovoltaic devices of Example 2 and Comparative Example.

FIG. 4 is a graph showing a temporal change of a leakage current of the photovoltaic device of Example 3.

FIG. 5 is a graph showing the relationship between the number average molecular weight of a curable resin and the leakage current of a photovoltaic element.

FIG. 6 is a schematic sectional view showing a conventional photovoltaic element.

FIG. 7 is a diagram for explaining a cause of deterioration of a conventional photovoltaic element.

[Explanation of symbols]

 101 collector grid electrode, 102 transparent conductive layer, 103 photoelectric conversion layer, 104 conductive substrate, 105 void, 605 silver ion, 606 pinhole, 607 dendritic crystal.

Claims (9)

(57) [Claims] 1. An electrode formed by a conductor having a conductive substrate and a curable resin, a photoelectric conversion layer, and
A photovoltaic device having another electrode disposed opposite to the one electrode with the photoelectric conversion layer interposed therebetween, wherein the number average molecular weight of the curable resin is set to 3000 or less. element. Wherein said conductive substrate has a particle shape, and the content of its conductor, photovoltaic device according to claim 1, wherein a is 70 wt% or more. Wherein the conductive substrate has a particle shape, and the content of its conductor, photovoltaic device according to claim 1, characterized in that 75% by weight or more. 4. The method according to claim 1, wherein the conductive substrate is made of silver or silver palladium.
Gold, silver and carbon mixture , copper, nickel, aluminum
The photovoltaic device according to any one of claims 1 to 3 is at least one selected from the group consisting of beam及 beauty gold. 5. The method according to claim 1, wherein the space between the one electrode and the photoelectric conversion layer is
The transparent conductive layer is uniformly disposed on the photoelectric conversion layer, and the one electrode is disposed on a part of the photoelectric conversion layer.
3. The photovoltaic device according to claim 1. 6. A space between the one electrode and the photoelectric conversion layer,
The transparent conductive layer is uniformly disposed on the photoelectric conversion layer, the one electrode is disposed on a part of the photoelectric conversion layer, and the surface of the other electrode forms a surface of the conductive substrate. Photovoltaic element. 7. The photovoltaic device according to claim 1, wherein the photoelectric conversion layer is a layer having an amorphous semiconductor. 8. The photovoltaic device according to claim 1, wherein the photoelectric conversion layer is a layer having a pin junction amorphous semiconductor. 9. The photovoltaic device according to claim 1, wherein said photoelectric conversion layer is a layer having at least two pin junction amorphous semiconductors.