JPH0974213A - Manufacture of compound semiconductor thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to pattern by thinning a film by a method wherein an organic metal, having at least one or more metal-sulfur couplings in its molecule, is dissolved into a solvent and a solution having the viscosity of a specific range is formed. SOLUTION: An organic metal compound, having at least one or more metal- sulfur couplings in the interior is coated on a substrate using an inkjecting method, said organic metal compound is thermally decomposed on the substrate, and a metal sulfide thin film is obtained as a compound semiconductor. As the sulfide thin film can be patterned by having the viscosity of a solution of 1 to 20cp, various kinds of functions can be given to the thin film as a compound thin film. For example, when a thin film solar battery of a cadmium sulfide/cadmium telluride structure is prepared, a very thin cadmium sulfide layer 1 can be formed. As a result conrersion rate of the solar battery can be greatly improved.

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 thin film used in a photoelectric conversion element, and more particularly to a method for forming a metal sulfide thin film.

[0002]

2. Description of the Related Art Conventionally, compound semiconductors, particularly sulfide thin films such as cadmium sulfide, zinc sulfide, lead sulfide, and copper sulfide, have been widely used as photoelectric conversion element materials in the field of optoelectronics. Many of these compounds have been conventionally produced by a sputtering method, an evaporation method, a CVD method, or the like. The thin film formed by these methods has a desired film quality as a photoelectric conversion element material, but all of them require a vacuum device, so that large area uniform film formation, high-speed continuous film formation, etc. are difficult. Or, even if it is possible, there is a problem that the device becomes very expensive.

There is a solution method as a method for forming a large-area thin film at a lower cost. However, even if this method is used, the apparatus and process are certainly inexpensive, but a large-area compound semiconductor thin film is formed. However, there was a big problem in the uniformity and reproducibility of the film quality.

Therefore, a solar cell using a coating / sintering method has been proposed as a method for forming a large area of a compound semiconductor thin film with an inexpensive apparatus with good reproducibility. This is a cadmium telluride solar cell in which a fine powder dispersion paste of a compound semiconductor is screen-printed on a substrate, and a cadmium sulfide sintered film is laminated on the cadmium sulfide sintered film by a method of sintering in a continuous belt furnace by the same method. A battery is disclosed (Japanese Patent Publication No. 56-28386).

As described above, this coating / sintering method can continuously and uniformly form a large area of a compound semiconductor thin film with an inexpensive apparatus, and patterning can be performed simultaneously with the film formation. There is an extremely excellent feature. However, the coating / sintering method also has some problems. Since they have a high sintering temperature of about 700 ° C, low-priced ordinary glass cannot be used as a substrate, and they require a long-time sintering reaction of 2 hours or more, which makes them unsuitable for high-speed mass production. , An expensive sintering case made of ceramic for controlling the evaporation of the melting point depressant at the time of sintering, an inert atmosphere such as nitrogen is required at the time of sintering, the particle size of the raw material (usually 2 However, there are many voids in the sintered film and the film quality is not uniform. However, these problems are caused by applying fine powder of metal compound as a raw material. It was said that the sintering method was extremely difficult to solve.

Recently, as a method for solving these problems by taking advantage of the characteristics of the coating / sintering method, an organometallic compound layer having at least one metal-sulfur bond inside is coated on a substrate and then in an oxidizing atmosphere. It has been proposed to thermally decompose the organometallic compound to form a metal sulfide thin film (Japanese Patent Publication No. 6-99809).

[0007]

The method for forming a sulfide thin film described above has a sintering temperature of 3 while making the most of the characteristics of the coating / sintering method, which is a large area, low cost film forming method for compound semiconductor thin films.
Since it can be suppressed at 20 to 450 ° C., a low-priced ordinary glass can be used as a substrate, and since thermal decomposition is performed in an oxidizing atmosphere, carbon and hydrogen that are organic components can be completely decomposed. It is described that after pyrolysis, firing is performed in an inert atmosphere.

However, in the coating method, only the spinner was used, and the patterning, which is one of the features of using the compound semiconductor, could not be performed.
When this thin film is used as a solar cell, the film thickness is 5
Since the thickness is as thick as 00 to 5000 Å, the light transmittance is poor and the conversion efficiency is poor.

The present invention has been made to solve the above problems, and
It is an object of the present invention to obtain a method for forming a compound semiconductor thin film having a thin film thickness and allowing patterning.

[0010]

In order to achieve the above object, the present invention comprises dissolving an organometallic compound having at least one metal-sulfur bond therein in a predetermined solvent.
A solution having a viscosity of not less than 20 centipoise and not more than 20 centipoise is applied onto a substrate by an inkjet method and thermally decomposed.

Cadmium, zinc, copper, lead or mercury is preferred as the metal that binds to sulfur. Further, as the organometallic compound having at least one metal-sulfur bond inside, a metal mercaptide, a metal thioate,
A metal dithioate, a metal thiocarbonate salt, a metal dithiocarbonate salt, a metal trithiocarbonate salt, a metal thiocarbamate or a metal dithiocarbamate is preferred.

The solvent for dissolving the organometallic compound is preferably one which dissolves at least 0.1 mol / liter and not more than 1 mol / liter of the organometallic compound. As the solvent, it is preferable to use 1-methyl-2-pyrrolidone, γ-butyrolactone, tetralin, dimethylformamide, dimethylsulfoxide, toluene, chloroform, alcohols and polyhydric alcohols such as cellosolve and carbitol, and their derivatives. . Further, in order to further improve the film quality after thermal decomposition, it is preferable to remove the residue by filtering the solution or to remove the precipitate by centrifugation.

The temperature at which an organometallic compound is thermally decomposed is 10
It is preferably 0 ° C. or higher and 500 ° C. or lower. Further, it is preferable to use a normal glass, a metal or a resin film as the substrate. When a metal sulfide thin film is formed according to the present invention, an extremely good quality compound semiconductor thin film can be obtained if the thin film has a thickness of 700 nanometers or less.

[0014]

According to the present invention, with the above structure, an organometallic compound having at least one metal-sulfur bond inside is coated on a substrate by an ink jet method, and the organometallic compound is thermally decomposed on the substrate to form a compound semiconductor. The metal sulfide thin film as described above is obtained, and patterning can be performed by setting the viscosity of the solution to 1 centipoise to 20 centipoise. Therefore, the compound thin film should have various functions (for example, a solar cell). You can That is, the thin film is an organometallic compound having at least one or more metal-sulfur bonds coated on the substrate inside, which is separated into an organic substance and a metal-sulfur by a thermal decomposition reaction, and the organic substance scatters into a molecular form at the same time. Since the separated metal sulfides can be regularly arranged on the same substrate, a functional and extremely dense thin film can be formed.

The thermal decomposition reaction is 100 ° C to 500 ° C.
Since it is completed at a temperature of 10 minutes or less, no special glass or case for the thermal decomposition reaction is required, and the thermal decomposition reaction can be carried out in the air. Of course, it may be used in an inert gas such as nitrogen.

[0016]

EXAMPLES Examples will be described below.

Example 1 Cadmium isopropylxanthogenate as an organometallic compound was used as a solvent 1-
0.2 mol / liter is dissolved in methyl-2-pyrrolidone, and then the same solution is centrifuged to remove the precipitate to prepare a solution having a viscosity of about 5 centipoise. A SnO ₂ film was formed on the surface of the same solution to a thickness of about 600 nanometers 3.
A 5 cm square glass substrate is coated using an inkjet method, and the coated substrate is dried at 110 ° C. to volatilize the solvent. After that, a thermal decomposition reaction is performed at 450 ° C. for 3 minutes in the atmosphere. It has been confirmed that the same thermal decomposition reaction can be similarly performed in an inert atmosphere such as nitrogen. In this way,
A uniform film having a film thickness of 300 nanometer was obtained. From the analysis of the measurement result of X-ray diffraction of this film, a (002) peak of hexagonal cadmium sulfide was observed. In addition, as a result of analyzing the cadmium bond of the same film by X-ray photoelectron spectroscopy, it was confirmed that the cadmium-sulfur bond was the same as the cadmium-sulfur bond of the single crystal cadmium sulfide. Furthermore, it was also confirmed from the results of the analysis that there was no significant carbon residue on the surface of the cadmium sulfide film and in the film.
Similar results were obtained even if the solution was filtered to remove the precipitate.

On the other hand, in the same experiment, the viscosity of the solution in which cadmium isopropylxanthogenate was dissolved at 0.05 mol / liter was 0.8 centipoise. The same solution was applied on the substrate by the inkjet method, and then the same drying and
Pyrolysis was performed, but a uniform film could not be obtained because the viscosity of the solution was too low. Further, a similar experiment was tried using a solution in which the precipitate was not removed by centrifugation or filtration, but a uniform and good membrane was not obtained.

Similarly, the same experiment was carried out with a solution in which cadmium isopropylxanthogenate was dissolved in 0.1 mol / liter, 0.8 mol / liter, 1.0 mol / liter and 1.1 mol / liter. The viscosities of the solutions were 1, 10, 20, and 30 centipoise, respectively. Each solution was applied onto the substrate by the inkjet method, and then dried and pyrolyzed in the same manner as above, and as a result, 0.1 mol / liter,
A uniform and good film was obtained using the 0.8 mol / liter and 1.0 mol / liter solutions, but the 1.1 mol / liter solution had an excessively high viscosity. It was difficult to apply it uniformly using the method, and a uniform film could not be obtained.

The above results are summarized in Table 1.

[0021]

[Table 1]

As shown in the table, the concentration of the cadmium isopropylxanthogenate solution was 0.1 mol / liter,
0.2 mol / l, 0.8 mol / l, 1.0
In the case of mol / liter, the viscosities are 1 centipoise, 5 centipoise, 10 centipoise, and 20 centipoise, respectively, and the solution is applied onto a substrate by an inkjet method, dried and pyrolyzed to obtain a uniform film. Was given. On the other hand, when the concentration of the cadmium isopropylxanthogenate solution is 0.05 mol / liter and 1.1 mol / liter, the viscosities are 0.8 centipoise and 30 centipoise respectively, and the ink is applied onto the substrate by an inkjet method and dried. The film was pyrolyzed, but a uniform film was not obtained.

As described above, in order to obtain a uniform and high-quality film, the concentration of the solution is 0.1 mol / liter or more and 1.0 mol / liter or less, and the viscosity of the solution is 1 centipoise or more 2
It can be seen that it needs to be 0 centipoise or less.

Example 2 Cadmium dibenzyldithiocarbamate as an organometallic compound was used as a solvent 1
-Dissolved in methyl-2-pyrrolidone at 0.4 mol / l, then centrifuge the solution to remove the precipitate,
Make a solution with a viscosity of about 10 centipoise. The same solution
It is applied by flexographic printing on a 35 cm square normal glass substrate on the surface of which a SnO ₂ film is formed to a thickness of about 600 nm, and the applied substrate is dried at 150 ° C. to volatilize the solvent. After that, a thermal decomposition reaction is performed at 450 ° C. for 3 minutes in the atmosphere. It has been confirmed that the same thermal decomposition reaction can be similarly performed in an inert atmosphere such as nitrogen. In this way, a uniform film having a film thickness of 100 nanometer was obtained. X of this film
From the analysis of the measurement results of the line diffraction, the (002) peak of hexagonal cadmium sulfide was observed. In addition, as a result of analyzing the cadmium bond of the same film by X-ray photoelectron spectroscopy, it was confirmed that the cadmium-sulfur bond was the same as the cadmium-sulfur bond of the single crystal cadmium sulfide. Furthermore, it was also confirmed from the results of the analysis that there was no significant carbon residue on the surface of the cadmium sulfide film and in the film.
Similar results were obtained even if the solution was filtered to remove the precipitate. Further, a similar experiment was tried using a solution in which the precipitate was not removed by centrifugation or filtration, but a uniform and good membrane was not obtained.

On the other hand, in the same experiment, the viscosity of the solution in which 1.2 mol / l of cadmium dibenzyldithiocarbamate was dissolved was 50 centipoise, but since the viscosity of this solution was too high, it was applied uniformly by the ink jet method. It was difficult to obtain a uniform film.

Example 3 n- as an organometallic compound
Cadmium butylxanthogenate is dissolved in a solvent, 1-methyl-2-pyrrolidone, at 0.6 mol / liter, and then the solution is centrifuged to remove precipitates to prepare a solution having a viscosity of about 10 centipoise. The solution is applied by flexographic printing on a normal glass substrate having a side of 35 cm and a SnO ₂ film having a thickness of about 600 nanometers formed on the surface by flexographic printing, and the applied substrate is dried at 100 ° C. to volatilize the solvent. After that, a thermal decomposition reaction is performed at 450 ° C. for 3 minutes in the atmosphere. It has been confirmed that the same thermal decomposition reaction can be similarly performed in an inert atmosphere such as nitrogen. Thus, a uniform film having a film thickness of 150 nanometer was obtained. X of this film
From the analysis of the measurement results of the line diffraction, the (002) peak of hexagonal cadmium sulfide was observed. In addition, as a result of analyzing the cadmium bond of the same film by X-ray photoelectron spectroscopy, it was confirmed that the cadmium-sulfur bond was the same as the cadmium-sulfur bond of the single crystal cadmium sulfide. Furthermore, it was also confirmed from the results of the analysis that there was no significant carbon residue on the surface of the cadmium sulfide film and in the film.
Similar results were obtained even if the solution was filtered to remove the precipitate. Further, a similar experiment was tried using a solution in which the precipitate was not removed by centrifugation or filtration, but a uniform and good membrane was not obtained.

Example 4 Cadmium thiobenzoate as an organometallic compound was dissolved in γ-butyrolactone as a solvent in an amount of 0.5 mol / liter, and then the solution was centrifuged to remove a precipitate, and the viscosity was increased. Make a solution of about 15 centipoise. The solution was applied by flexographic printing on a 35 cm square normal glass substrate on the surface of which an SnO ₂ film was formed to a thickness of about 600 nanometers.
Dry at 0 ° C. and evaporate the solvent. Then in the atmosphere, 4
Carry out thermal decomposition reaction at 50 ° C for 3 minutes. It has been confirmed that the same thermal decomposition reaction can be similarly performed in an inert atmosphere such as nitrogen. In this way, a uniform film having a film thickness of about 500 nanometers was obtained. From the analysis of the measurement result of X-ray diffraction of this film, a (002) peak of hexagonal cadmium sulfide was observed. In addition, as a result of analyzing the cadmium bond of the same film by X-ray photoelectron spectroscopy, it was confirmed that the cadmium-sulfur bond was the same as the cadmium-sulfur bond of the single crystal cadmium sulfide. Furthermore, it was also confirmed from the results of the analysis that there was no significant carbon residue on the surface of the cadmium sulfide film and in the film. Similar results were obtained even if the solution was filtered to remove the precipitate. Further, a similar experiment was tried using a solution in which the precipitate was not removed by centrifugation or filtration, but a uniform and good membrane was not obtained.

A thin film solar cell having a cadmium sulfide / cadmium telluride structure was produced by using the cadmium sulfide thin film produced by the method shown in Examples 1 to 4.
The proximity sublimation method was used for the production of the cadmium telluride thin film. FIG. 1 shows the cross-sectional structure of the thin-film solar cell of this example. For reference, FIG. 3 shows a cross-sectional structure of a solar cell manufactured by a conventional coating / sintering method. As is apparent from the figure, the thickness of the cadmium sulfide layer 1 of the solar cell of this example is much thinner than the thickness of the cadmium sulfide layer 7 of the solar cell prototyped by the conventional coating and sintering method. FIGS. 2 and 4 show the voltage-current characteristics of the solar cell of this example and a solar cell prototyped by the conventional coating / sintering method.
From FIG. 2, the conversion efficiency of the solar cell manufactured in this example is 1
It is 4.6% (1 cm ² ) and the open circuit voltage is 813 m.
V, short circuit current density 24.8 mA, fill factor 72.6
It turned out to be a high value of%. On the other hand, the performance of a cadmium sulfide / cadmium telluride solar cell manufactured by a conventional coating / sintering method has a conversion efficiency of 1 as shown in FIG.
1.3% (1 cm ² ) and open circuit voltage is 797 m
V, short circuit current density 21.1 mA, fill factor 67.2
%. From these, it can be seen that the conversion efficiency of the solar cell of this example is significantly improved. This is because the solar cell of the present example is a dense film having a thin cadmium sulfide layer and no voids, so that the short wavelength sensitivity is increased, and as a result, the short circuit current is increased.

In addition, among the cadmium sulfide thin films prepared by the method shown in Example 1, a cadmium sulfide thin film made nonuniform in Table 1 was used to try to prepare a thin film solar cell having a cadmium sulfide / cadmium telluride structure. . FIG. 5 shows the voltage-current characteristics of the solar cell. It can be seen from comparison with the characteristics of FIG. 2 that only inferior characteristic values are obtained for all parameters.

[0030]

As described above, a solution in which an organometallic compound having at least one metal-sulfur bond inside is dissolved in a predetermined solvent is applied on a substrate by an ink jet method and thermally decomposed. This makes it possible to extremely easily form a high-quality metal sulfide thin film as a functional compound semiconductor.

Furthermore, if it is 700 nanometers or less,
By changing the coating thickness or the concentration of the solution, etc.
It is possible to obtain desired high quality compound semiconductor thin films made of metal sulfides of arbitrary thickness without voids, and when applied to the fabrication of thin film solar cells with a cadmium sulfide / cadmium telluride structure, conventional coating / baking The conversion efficiency of the solar cell of the same structure manufactured by the binding method is 11.3% (1 cm ² ), whereas the conversion efficiency of the solar cell manufactured by the film forming method of the present invention is 14.6% (1 cm ^2). ), It was confirmed that the characteristics were significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a cadmium sulfide / cadmium telluride thin film solar cell prepared according to an example of the present invention.

FIG. 2 is a diagram showing voltage-current characteristics of a cadmium sulfide / cadmium telluride thin film solar cell prepared according to an example of the present invention.

FIG. 3 is a schematic cross-sectional view of a cadmium sulfide / cadmium telluride solar cell prepared by a conventional coating / sintering method.

FIG. 4 is a diagram showing voltage-current characteristics of a cadmium sulfide / cadmium telluride solar cell prepared by a conventional coating / sintering method.

FIG. 5 is a diagram showing voltage-current characteristics of a cadmium sulfide / cadmium telluride solar cell prepared as a comparative example.

[Explanation of symbols]

 1 Cadmium Sulfide 2 Cadmium Telluride 3 Carbon Electrode 4 AgIn Electrode 5 Glass Substrate 6 Transparent Conductive Film 7 Cadmium Sulfide 8 Cadmium Telluride 9 Carbon Electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mikio Murozono 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (9)

[Claims] 1. An organometallic compound having at least one metal-sulfur bond inside is dissolved in a solvent to form a solution having a viscosity of 1 centipoise or more and 20 centipoise or less, and the solution is applied onto a substrate by an inkjet method. A method for forming a compound semiconductor thin film, which comprises decomposing and thermally decomposing. 2. The method for forming a compound semiconductor thin film according to claim 1, wherein the metal forming the metal-sulfur bond is cadmium, zinc, copper, lead or mercury. 3. The organometallic compound is a metal mercaptide, a metal thioate, a metal dithioate, a metal thiocarbonate salt, a metal dithiocarbonate salt, a metal trithiocarbonate salt, or a metal thiocarbonate. 2. The method for forming a compound semiconductor thin film according to claim 1, which is a carbamate or a metal dithiocarbamate. 4. The solvent is 1-methyl-2-pyrrolidone, γ
-Butyrolactone, tetralin, dimethylformamide, dimethylsulfoxide, toluene, chloroform,
The method for forming a compound semiconductor thin film according to claim 1, wherein the compound semiconductor thin film is an alcohol and a polyhydric alcohol such as a cellosolve-based or carbitol-based alcohol and a derivative thereof. 5. The concentration of the solution is 0.1 mol / liter or more and 1 mol / liter or less.
A method for forming a compound semiconductor thin film as described above. 6. The method for forming a compound semiconductor thin film according to claim 1, wherein the organometallic compound is dissolved in a solvent and then the residue is removed by filtration or the precipitate is removed by centrifugation. . 7. A temperature at which an organometallic compound is thermally decomposed is 100.
The method for forming a compound semiconductor thin film according to claim 1, wherein the temperature is not lower than 500 ° C and not higher than 500 ° C. 8. The method for forming a compound semiconductor thin film according to claim 1, wherein the substrate is a glass, metal, ceramic or resin film. 9. The method for forming a compound semiconductor thin film according to claim 1, wherein the film thickness of the metal sulfide thin film obtained by thermal decomposition is 700 nanometers or less.