JPH0669524A - Photovoltaic device - Google Patents

Abstract

PURPOSE:To provide a high-performance and low-cost photovoltaic device wherein a collector electrode which is thin and whose resistance is low is provided. CONSTITUTION:A photovoltaic device is composed of at least a photovoltaic semiconductor layer 12 and collector electrodes 11, 13. The collector electrodes are composed of gold or a conductive powder 15 containing gold and of a metal, an alloy or a mixture 17 whose melting point is lower than that of the conductive powder, and the conductive powder is fixed to the side of the semiconductor layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device,
Particularly, it relates to a photovoltaic device having a high photoelectric conversion efficiency.

[0002]

2. Description of the Related Art Conventionally, the one shown in FIG. 4 has been used as a collector electrode of a photovoltaic element. The collector electrode shown in FIG. 4 is obtained by monodispersing silver fine particles having a diameter of about 1 to 10 μm in a thermosetting resin such as polyester, polyimide, epoxy, phenol or glass frit.
Further, a conductive paste material 44 mixed with an organic solvent such as cellosolve is printed on the electrode forming surface 41 of the photovoltaic element using a stencil screen to further adjust the viscosity, and then cured by heating. The merit of this method is that it can form an electrode with a high tact on a material having an extremely large area and a high material yield, and it greatly contributes to the reduction of manufacturing cost, which is currently the biggest problem in photovoltaic devices. ing.

However, due to the recent improvement in conversion efficiency and increase in area of photovoltaic elements, a collector electrode with less loss has been demanded, and in the collector electrode composed only of a conventional conductive paste, these are required. I can no longer answer my needs. For example, the conductive paste using the thermosetting resin has a volume resistivity of 3 to 5 × 10 ⁻⁵ , and if fine printing is performed to reduce light-shielding loss caused by the electrode, printing is performed accordingly. There is a problem that unevenness increases and the film thickness decreases, and the current loss due to the resistance of the collector electrode increases significantly. In addition, these conductive pastes need to be heated for a long time for curing, and it is practically difficult to apply them thickly for overcoating.

Therefore, an electrode having a structure in which a material having a lower volume resistivity is placed on the conductive paste has been proposed. For example, FIG. 5 shows a current collecting electrode on which the conductive paste 54 is printed and then a solder material 57 having a lower volume resistivity is placed thereon, and the current collecting electrode is placed in the molten solder after firing the conductive paste. It is formed by dipping. However, also in this case, there is a problem that it becomes difficult to form a solder layer having a sufficient thickness as the electrodes become finer.

In addition to the above, as a method for forming an electrode, a method using vapor deposition or sputtering is also known, but it is rarely used in a large-area element because of its high manufacturing cost.

[0006]

In view of the above circumstances, the present invention has a thin wire and a low resistance collector electrode,
An object is to provide a low cost photovoltaic device.

[0007]

The photovoltaic device of the present invention comprises:
In a photovoltaic device including at least a semiconductor layer that generates a photovoltaic force and a collecting electrode, the collecting electrode is gold or a conductive powder containing at least gold, and a metal having a melting point lower than that of the conductive powder. It is made of an alloy or a mixture, and the conductive powder is fixed to the semiconductor layer side.

Here, it is preferable that the conductive powder is adhered and fixed to the semiconductor layer side by a conductive fixing material, and the conductive fixing material is bound to at least the conductive powder. It is preferably composed of an agent.

In a preferred form of the photovoltaic element of the present invention, the melting point of the metal, alloy or mixture having a lower melting point than the conductive powder is 100 ° C. higher than the melting point of the conductive powder.
It is lower than that.

[0010]

The gold or conductive powder particles containing at least gold have the effect of adsorbing a low melting point metal or alloy or mixture (hereinafter referred to as low melting point metal) such as a solder material. When forming the electrode layer, the conductive powder is fixed on the semiconductor layer (or the transparent conductive layer), whereby a thick layer of low melting point metal can be formed.

Therefore, the resistance of the electrode can be reduced, and as a result, the efficiency of the photovoltaic device can be increased.
Further, if the amount of decrease in resistance due to the thickening is directed to the thinning, the light-shielding loss due to the collector electrode can be further reduced, and the conversion efficiency of the photovoltaic element can be further improved.

By providing a conductive fixing material for fixing the conductive powder between the semiconductor layer (or the transparent conductive layer) and the low melting point metal, the semiconductor layer (or the transparent conductive layer) and the conductive powder and The bond of the low melting point metal is strengthened, and the output stability over time can be improved over a long period of time.

The structure of the photovoltaic element of the present invention is shown in FIGS.
Will be described in detail.

In FIG. 1, 11 is a transparent conductive film, 12 is a semiconductor layer, 13 is a substrate, 14 is a conductive fixing material for fixing gold or a conductor powder 15 containing gold, and 17 is a low melting point metal. is there.

As the low melting point metal of the present invention, any metal or alloy can be used as long as it has a melting point lower than that of the conductive powder, but the difference in melting point from the conductive powder is 100.
A material having a temperature of not less than 0 ° C. is more preferable because a thicker electrode layer can be formed. A specific example of the low melting point metal is solder. The solder material is, for example, Sn
Examples include -Pb type, Sn-Ag type, Pb group and In group. It is also possible to use cream solder, which is more preferable because it has the advantage of controlling the amount of solder.

The shape of the conductive powder particles is not limited to a sphere, and for example, a flaky shape or a needle shape can be used.
The size varies depending on the width of the collecting electrode to be formed, but a size of about 0.1 to 100 μm is usually used.

The conductive fixing material of the present invention is made of a material having a low melting point metal and high wettability. For example, metal particles such as gold, silver, copper, nickel and iron are mixed with an epoxy resin, a phenol resin or a polyester resin. A conductive paste dispersed in a binder such as an organic resin such as a polyimide resin is preferably used. When relatively high temperature treatment is allowed, a firing paste or the like in which the above metal material and glass frit are mixed can be used.

[0018]

The present invention will be described in detail below with reference to examples, but it goes without saying that the present invention is not limited to these examples.

(Example 1) FIG. 2 shows a manufacturing process of the photovoltaic device having the structure shown in FIG.

FIG. 2A shows an amorphous solar cell as an electrode forming surface, in which an amorphous silicon layer 22 and a transparent conductive film 21 are formed on a stainless steel substrate 23. The transparent conductive film of this example is ITO having a thickness of 64 nm.

ITO has a specific resistance of 1 × 10 ⁻³ Ω as compared with metal.
Since it is as high as about cm, a collector electrode is formed on it by using a silver polymer paste material having a low specific resistance value.

As shown in FIG. 2B, the transparent conductive layer 21
Polymer paste 2 containing silver particles having a particle size of 1 to 5 μm on the top
The pattern 4 was formed by screen printing using a stainless steel mesh 400 mesh and a printing plate having an emulsion thickness of 10 μm. Under these conditions, a pattern having a line width of 100 μm and a thickness of about 30 μm could be formed. The thickness after heat curing is about 20 μm.

Next, a grain size of 0.
The metal particles 25 containing gold of about 1 to 100 μm were sprayed. This is shown in FIG. 2 (c). Since the sprayed metal particles 25 adhere not only on the polymer paste 24 but also on the transparent conductive film 21, an air flow was sprayed and the metal particles not on the polymer paste were blown away. Then, heat drying was performed in air at 160 ° C. The polymer paste was shrunk and hardened by incorporating metal particles. This is shown in FIG. 2 (d).

Next, the flux 26 was applied to the entire electrode formation surface (FIG. 2 (e)).

Further, the electrode forming surface coated with the flux is gradually heated while being dipped into the molten solder bath,
After soaking for 30 seconds, the material is slowly pulled up while heating and then cooled to form a solder layer on the polymer paste.
By applying the flux, it is possible to promote the wetting of the solder with the polymer paste and the metal particles, and it is possible to more completely prevent the adhesion of the solder to the electrode forming surface without the polymer paste.

FIG. 2 (f) shows an electrode forming surface after dipping into a solder bath. In this state, a solder layer 27 is formed on the polymer paste 24, and a large amount of flux 26 remains on the electrode forming surface. The residual flux was washed off with a shower of warm water. After the completion of washing, it was dried to complete the production of the collecting electrode (FIG. 2 (g)).

The flux also contains residual metal particles that cannot be completely removed by the air flow. Since the flux is acidic or alkaline, it may erode the transparent conductive film or block incident light if left unattended. Therefore, it is necessary to perform cleaning.

As described above, it was confirmed that it is possible to accurately manufacture a low resistance collector electrode having a thickness of 40 μm even though it is a fine wire of 100 μm.

(Embodiment 2) A second embodiment of the present invention is shown in FIG.
Will be explained.

FIG. 3 shows an electrode forming process using cream solder. In FIG. 3A, 34 is a pattern formed by using a copper paste in which copper particles having a particle size of 5 to 20 μm are monodispersed in a phenol resin. Reference numeral 31 is a transparent conductive film ITO, and 32 is an amorphous silicon layer which is a photovoltaic layer. Here, the electrode formation surface is the surface of the ITO film 31.

On the well-washed and dried surface, a wire having a line width of about 100 μm was first formed with a copper paste by a screen printer.

Next, as shown in FIG. 3B, gold particles 35 were sprayed on the electrode formation surface. The gold particles were sprayed in a scattered state on the entire electrode formation surface.

An air stream was made to flow horizontally with respect to the scattered electrode forming surface to remove the gold particles other than those on the polymer paste, leaving the gold particles on the polymer paste. Figure 3 (c)
Indicates this state.

Then, it was heated in a heat drying furnace. The copper paste shrank and hardened with the gold particles encased. Here, the curing conditions were 160 ° C. and 30 minutes. The state after curing is shown in FIG.

Thus, the cream solder 37 'was adhered by screen printing on the current collecting electrode in which the gold particles were studded (FIG. 3 (e)).

The cream solder 37 'also contains the flux 36, and since ITO, which is the electrode forming surface, has poor wettability with the solder, it is left at 220 ° C. in an infrared heating furnace or the like as it is.
When heated to, as shown in FIG. 3 (f), the solder gathers on the side of the conductive paste having good solder wettability, and the gold particles on the conductive paste adsorb the solder material and rise up on the conductive paste. It became a state of

Finally, the bleeding flux 36 was washed by washing with warm water and dried, and the process was completed (FIG. 3 (g)).

As described above, 100 μm width, 40 μm
It was confirmed that the m-thick current collecting electrode can be accurately manufactured. Further, by using the cream solder, the uniformity of the thickness of the solder layer was further increased.

[0039]

According to the present invention, it is possible to form a thick collecting electrode even though it is a thin wire. As a result, the resistance of the collecting electrode can be significantly reduced, and the photovoltaic power generation with high photoelectric conversion efficiency can be achieved. It is possible to provide the element at low cost.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a photovoltaic device of the present invention.

FIG. 2 is a conceptual diagram illustrating a manufacturing process of the photovoltaic device of Example 1 of the present invention.

FIG. 3 is a conceptual diagram illustrating a manufacturing process of the photovoltaic device of Example 2 of the present invention.

FIG. 4 is a conceptual diagram showing an example of a conventional photovoltaic device.

FIG. 5 is a conceptual diagram showing another example of a conventional photovoltaic device.

[Explanation of symbols]

 11, 21, 31, 41, 51 transparent conductive film, 12, 22, 32 amorphous silicon layer, 13, 23 stainless steel substrate, 14, 24, 34, 44, 54 polymer paste, 15, 25, 35 conductive particles, 17 , 27, 37, 57 solder, 26 flux, 37 'cream solder.

Claims (4)

[Claims] 1. A photovoltaic element comprising at least a semiconductor layer for generating a photovoltaic power and a collector electrode, wherein the collector electrode is gold or a conductive powder containing at least gold, and more than the conductive powder. A photovoltaic element, comprising a metal or alloy or mixture having a low melting point, wherein the conductive powder is fixed to the semiconductor layer side. 2. The photovoltaic element according to claim 1, wherein the conductive powder is closely fixed to the semiconductor layer side by a conductive fixing material. 3. The electrically conductive fixing material comprises at least electrically conductive powder and a binder.
Alternatively, the photovoltaic element according to item 2. 4. The light according to claim 1, wherein the low melting point metal or alloy or mixture has a melting point lower than the melting point of the conductive powder by 100 ° C. or more. Power generation element