JPH09116177A - Method for forming compound semiconductor film and method for manufacturing thin film solar cell - Google Patents

Abstract

(57) Abstract: An excellent copper-indium-selenium ternary element that does not require expensive equipment such as a sputtering apparatus, has crystals developed to the end, and has no defects such as thickness unevenness or short circuit. A method for forming a compound semiconductor film made of an alloy is provided. Thin films of copper and indium are formed by a chemical plating method, respectively, and then heat treatment is performed in an atmosphere containing selenium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a compound semiconductor film used for an absorption layer of a solar cell.

[0002]

2. Description of the Related Art A solar cell is a device for converting light energy into electric energy, and initially single crystal silicon was used. However, it is difficult to make a large area solar cell with this single crystal silicon, and However, since the cost becomes high, amorphous silicon and compound semiconductors have been used recently.

Among the compound semiconductors, a copper-indium-selenium ternary alloy is considered to have excellent photoelectric conversion efficiency, and it is expected that a large-area solar cell can be realized at low cost by using it. Where copper-indium-
Regarding the selenium ternary alloy, JP-A-61-237476
Many proposals have been made such as Japanese Patent Publication No. Hei 1-231313.

In these conventional techniques, copper and indium are electrodeposited on a substrate and heat-treated in hydrogen selenide to form copper-
An indium-selenium ternary alloy layer was formed and used as a precursor. However, when such an electrodeposition method is used, it has been difficult to make the current density on the electrodeposition surface uniform. In particular, current concentration occurs at the edges of the substrate, resulting in significant thickness unevenness.

That is, FIG. 10 shows a model (cross-sectional view) showing unevenness in thickness. In this figure, reference numeral 1'is a substrate, reference numeral 2'is a conductive layer made of molybdenum, and a copper layer 3 and an indium layer 4 are formed thereon by electrodeposition, but as shown in the figure, they are formed by electrodeposition. The thickness of the end portions of the removed copper layer 3 and indium layer 4 becomes large.

When the precursor having such a large thickness unevenness is heat-treated in an atmosphere containing selenium, thickness unevenness occurs in the obtained compound semiconductor layer, which causes cracks and peeling. The composition becomes non-uniform not only in the end portion but also in the central portion, which hinders the crystal growth of the ternary alloy to lower the photoelectric conversion efficiency, or causes a short circuit, which causes a reduction in product yield.

Since these defective portions are concentrated on the edges, they may be ignored when forming a large-area single-module solar cell, but a plurality of modules are formed on a substrate of a limited size. Then, when the size of one module is reduced, for example, when these are connected in series, the influence of the defective portion relatively increases, which is a serious problem.

Further, in the case of forming a plurality of modules on one substrate as described above, in the conventional method, first, a plurality of conductive layers (molybdenum thin films in FIG. 10) corresponding to the respective modules are formed on the substrate. , Using these conductive layers as electrodes to perform electroplating on these conductive layers to sequentially form copper layers, indium layers, etc. At this time, all of the conductive layers must be connected to the power source as cathodes. . This electrical connection has a drawback in that the degree of freedom in arranging the module on the substrate, that is, the degree of freedom in designing the module is limited.

On the other hand, in vacuum application techniques such as sputtering, defects due to the thickness unevenness described above are rarely generated, but in order to perform film formation by these methods,
In addition to requiring expensive equipment such as a vacuum container, these methods have poor processing efficiency, which causes high cost.

[0010]

SUMMARY OF THE INVENTION The present invention solves the above problems of the prior art, that is, it does not require an expensive apparatus such as a sputtering apparatus, and the crystal develops to the end,
Further, there is provided a method for forming a compound semiconductor film made of an excellent copper-indium-selenium ternary alloy, which is free from defects such as thickness unevenness, short circuit, cracking, and peeling.

[0011]

According to the method of forming a compound semiconductor film of the present invention, as described in claim 1, thin films of copper and indium are respectively formed by a chemical plating method, and thereafter, in an atmosphere containing selenium. It has a configuration for performing heat treatment. The method for producing a thin-film solar cell according to the present invention is claim 2.
As described in 1), a thin film of copper and indium is formed on a conductive substrate by a chemical plating method, and then heat treatment is performed in an atmosphere containing selenium.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A precursor obtained by forming a thin film of copper and indium on a conductive substrate by chemical plating is heat-treated in an atmosphere containing selenium to form CuInS.
e ₂ Obtain a ternary alloy layer. Here, the precursor may be formed in the order of conductive substrate / copper layer / indium layer, or may be formed in the order of conductive substrate / indium layer / copper layer. Further, a copper-indium alloy may be formed on the conductive substrate.

Examples of the atmosphere containing selenium include hydrogen selenide and an inert gas containing selenium vapor. However, since hydrogen selenide is extremely toxic, it is desirable to use selenium vapor. Selenium vapor can be obtained by simultaneously encapsulating solid selenium in a vessel for heat treating the precursor. On the other hand, heat treatment is 350-50
It can be carried out at 0 ° C. Here, 400 ° C or more and 500 ° C
It is desirable to perform the heat treatment at the following temperature because a highly efficient solar cell can be obtained.

[0014]

【Example】

[Example 1] [Preparation of copper plating solution] First, a plating solution was prepared.
Table 1 shows the composition of the copper plating solution. That is, each chemical shown in Table 1 was dissolved and sodium hydroxide was added to adjust the pH to 12.6 to obtain a plating solution. The liquid temperature was kept at 69 ° C. during use.

[0015]

[Table 1]

[Preparation of Indium Plating Solution] On the other hand, Table 2 shows the composition of the indium plating solution. That is, each drug was dissolved to have such a composition, and sodium hydroxide was added thereto to adjust the pH to 10.0. The liquid temperature of the indium plating solution was kept at 80 ° C. during use.

[0017]

[Table 2]

[Preparation of Precursor] A 2 μm molybdenum layer was formed as a conductive layer on soda lime glass by a sputtering method to obtain a conductive substrate. When this conductive substrate was dipped in the above copper plating solution for 12 minutes, a copper layer on the molybdenum layer was 0.3 μm in both the central portion and the end portion.
Formed to a thickness of No plating layer was formed on the portion without the molybdenum layer (soda lime glass portion).

Then, indium plating was performed. When the copper-plated conductive substrate was immersed in the indium plating solution described above for 20 minutes, the central portion had a thickness of 0.67 μm.
An indium layer having a thickness of 0.65 μm (according to a fluorescent X-ray film thickness meter) was formed at the edge (hereinafter referred to as “precursor A”). At this time, no plating layer was formed on the soda lime glass portion. From the weight change before and after the plating process, it was found that the amount of copper element and the amount of indium element in each plating layer were 1.01: 1.

[Heat Treatment] The precursor A was enclosed in a closed container together with selenium powder, heated to 450 ° C. at a heating rate of 25 ° C./min, and kept for 1 hour. Then, it was naturally cooled to room temperature to obtain a copper-selenium-indium ternary alloy layer. The appearance of this alloy layer was good on the whole, and there were no defects such as thickness unevenness, cracks or peeling. When X-ray diffraction analysis was performed on the edge portion and the center portion of the alloy layer, it was confirmed that there existed well-developed and oriented CuInSe ₂ chalcopyrite type crystals.

COMPARATIVE EXAMPLE A soda lime glass having a molybdenum film similar to that used in Example 1 was used as a positive electrode and a platinum plate as a cathode, and a sulfuric acid-acidified copper sulfate aqueous solution (0.5 mol / l) was used. ) Was used for electroplating. At this time, the thickness of the obtained copper layer is 0.31 μm at the central portion.
The edge was 0.78 μm.

Next, indium plating was performed on this copper film using an indium sulfamate aqueous solution. The thickness of the obtained indium layer was 0.67 μm at the center and 1.41 μm at the edges (this is hereinafter referred to as “precursor B”). This precursor B was heat-treated in the same selenium atmosphere as in Example 1.

There were many small cracks at the end of the obtained ternary alloy layer, and there was a part where it was peeled off. Also,
As a result of X-ray diffraction analysis, it was confirmed that good CuInSe ₂ crystals were present in the central portion as in Example 1, but the diffraction intensity at the end portions was 60 at the central portion.
%, Which was found to be unsatisfactory.

[Embodiment 2] As Embodiment 2, a process of forming a plurality of modules on one substrate will be described with reference to the model diagrams of FIGS. 1 to 9. FIG. 1 is a cross-sectional view of soda lime glass (reference numeral 1 in the figure) on which a 2 μm molybdenum layer (reference numeral 2 in the figure) is formed.

As shown in FIG. 2, the molybdenum layer 2 was patterned by a laser scribing method to divide it into strip-shaped metal electrodes 2a and 2b. Then, in the same manner as in Example 1, copper plating and indium plating are performed to form copper layers 3a and 3b and indium layers 4a and 4a.
b was formed to obtain a precursor C as shown in FIG. In addition, the thickness unevenness of the plating layer in each plating step was investigated in the same manner as in Example 1, but it was found that there was no thickness unevenness between the central portion and the end portion, and the plating layer was good.

Here, in these plating processes, a plating layer is not usually formed on soda lime glass,
When a plating layer is likely to be formed, for example, when the glass surface has a large number of irregularities, measures such as preventing the plating layer from being formed by adhering silicon rubber or the like to places where plating is unnecessary are taken.

Precursor C obtained as described above
Was selenized in the same manner as in Example 1 to obtain copper-indium-selenium ternary alloy layers 5a and 5b (see FIG. 4).
This ternary alloy layer was good, free from cracks, peeling, and the like, and the X-ray diffraction results at the central portion and the end portion were both satisfactory.

On the ternary alloy layer which is a p-type semiconductor, a cadmium sulfide layer which is an n-type semiconductor (reference numerals 6a and 6 in FIG. 5).
b) was formed by liquid phase epitaxy. That is, the soda lime glass having the thin film layer formed thereon was dipped in a 0.01 mol / l aqueous solution of cadmium sulfate (CdSO ₄ ) at 70 ° C. (pH adjusted to 8.5 with ammonia water) for 5 minutes, and then, An aqueous solution of 0.01 mol / l thiourea was added and kept for 5 minutes to grow cadmium sulfide layers 6a and 6b. At this time, silicon rubber was adhered to unnecessary portions to prevent the formation of the cadmium sulfide layer.

Then, while adjusting the beam intensity by applying the laser scribing method, the cadmium sulfide layer and a part of the ternary alloy layer were removed as shown in FIG. Then, a 2 μm thick thin film of zinc oxide doped with 2% by weight of aluminum was formed by sputtering as a transparent electrode layer (reference numeral 7 in FIG. 7), and then the beam intensity was adjusted again and a laser scribing method was performed as shown in FIG. As shown in FIG. 5, a part of this zinc oxide layer was removed, and finally a lead wire 8 was attached as shown in FIG. 9 to obtain a solar cell unit composed of a plurality of modules connected in series.

As described above, according to the method for manufacturing a thin-film solar cell of the present invention, it is not necessary to electrically connect the conductive layers in the plating process as is apparent from the second embodiment. It is understood that, when forming a plurality of solar cell modules, the degree of freedom in arranging the modules is very high.

[0031]

As is apparent from the above-mentioned examples and comparative examples, according to the present invention, a good copper-indium-selenium ternary material is obtained, which is uniform and not only in the central portion but also in the end portions without requiring an expensive device. The alloy layer can be efficiently obtained. Also, 1
The flexibility of design is extremely high when a plurality of solar cell modules are formed on one substrate.

[Brief description of the drawings]

FIG. 1 is a diagram showing an intermediate step of manufacturing a solar cell unit (a state in which a molybdenum layer is formed on soda lime glass).

FIG. 2 is a diagram illustrating an intermediate step of manufacturing a solar cell unit (a state in which a molybdenum layer is cut into strips).

FIG. 3 is a diagram illustrating an intermediate step of manufacturing a solar cell unit (a state in which a copper layer and an indium layer are formed on a molybdenum layer (precursor C)).

FIG. 4 is a diagram illustrating an intermediate step of manufacturing a solar cell unit (a state in which a copper-indium-selenium ternary alloy layer is formed).

FIG. 5 is a diagram illustrating an intermediate step (a state in which a cadmium sulfide layer is formed) for manufacturing a solar cell unit.

FIG. 6 is a diagram showing an intermediate step of manufacturing a solar cell unit (a state in which a part of a cadmium sulfide layer and a ternary alloy layer are patterned).

FIG. 7 is a diagram illustrating an intermediate step (a state in which a zinc oxide layer is formed) for manufacturing a solar cell unit.

FIG. 8 is a diagram illustrating an intermediate step of manufacturing a solar cell unit (a state in which a part of a zinc oxide phase is patterned).

FIG. 9 is a diagram illustrating an intermediate step (a state in which lead wires are connected) for manufacturing a solar cell unit.

FIG. 10 is a cross-sectional view schematically showing a state of a copper layer and an indium layer formed on a conductive layer of a substrate by a conventional technique.

[Explanation of symbols]

 1 Soda lime glass 2 Molybdenum layer 2a, 2b Strip-shaped molybdenum layer 3a, 3b Copper layer 4a, 4b Indium layer 5a, 5b Copper-indium-selenium ternary alloy layer 6a, 6b Cadmium sulfide layer 7 Zinc oxide layer 8 Lead wire

Claims (2)

[Claims] 1. A method for forming a compound semiconductor film, which comprises forming thin films of copper and indium by a chemical plating method and then performing heat treatment in an atmosphere containing selenium. 2. A method for manufacturing a thin film solar cell, which comprises forming a thin film of copper and indium on a conductive substrate by a chemical plating method, and then performing a heat treatment in an atmosphere containing selenium.