JP2001059157A - Transparent electrically conductive film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a film exhibiting high transmissivity and low resistance by allowing the vapor of multiple oxide of indium oxide and tin oxide to act on a group IV semiconductor power generating layer together with water vapor in a temp. region which does not exert thermal damage thereon to execute film formation and forming a transparent electrically conductive film whose surface has a rugged shape. SOLUTION: A substrate (such as non-alkali glass) having a group IV semiconductor power generating layer is carried into a vacuum vessel, and the temp. of the substrate is controlled to a temp. region of <=150 deg.C in which thermal damage is not exerted on the group IV semiconductor power generating layer. Next, the vapor or sputter particles of multiple oxide of indium oxide and tin oxide to form a film material are formed in the vacuum vessel, and moreover, water vapor is introduced therein, the vapor or sputter particles of multiple oxide of indium oxide and tin oxide are deposited on the group IV semiconductor power generating layer in the coexistence of the water vapor, and a film of multiple oxide of indium oxide and tin oxide having a surface with a rugged shape is laminated and formed to obtain a transparent electrically conductive film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a transparent conductive film and a method for producing the same, and more particularly to a transparent conductive film made of indium oxide / tin oxide composite oxide (ITO) for a solar cell and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a transparent conductive film has been used as an electrode of an amorphous silicon (hereinafter abbreviated as a-Si) solar cell, for example, a kind of group IV semiconductor. FIG. 1 shows an example of such an a-Si solar cell. A transparent conductive film 2 made of tin oxide (hereinafter referred to as SnO ₂ ) is formed on a glass substrate 1 as a surface transparent electrode, and a- Si layer 3, indium oxide.
A transparent conductive film 4 made of a tin oxide composite oxide (hereinafter referred to as ITO) is laminated, and an aluminum electrode film 5 is further laminated thereon. An aluminum electrode 6 as a current collecting electrode is separately provided on the transparent conductive film 2. Substrate 1, transparent conductive film 2
Photoelectromotive force is generated by the light 7 incident on the a-Si layer 3 through the. The transparent conductive film 2 is formed by a known thermochemical vapor deposition method, has a thickness of about 1 μm, and has a surface with irregularities of 0.1 μm or less. The unevenness greatly contributes to an increase in photovoltaic power, that is, an improvement in power generation efficiency.

One of the reasons is that light incident from the side of the glass substrate 1 is hardly reflected by irregularities at the interface between the transparent conductive film 2 and the a-Si layer 3 and is effectively taken into the a-Si layer 3. Secondly, the light reflected at the interface between the transparent conductive film 4 and the aluminum electrode film is reflected on the transparent conductive film 2, a-
Although the light is returned to the interface of the Si layer 3, the incident angle at that time increases, so that the ratio of total reflection and not going outside increases. Here, similarly to the lower transparent conductive film 2, if the upper transparent conductive film 4 has irregularities on its surface, the ratio of total reflection and not going outside increases, leading to further improvement in power generation efficiency.

[0004]

As a method of manufacturing the transparent conductive film 4 made of ITO having irregularities on the surface, there is a vacuum evaporation method or the like. In the case of the vacuum evaporation method, the transparent conductive film 4 having a structure having irregularities on the surface is used. Can be manufactured, but it is necessary to heat the substrate to 350 ° C. or higher. When the transparent conductive film 4 is formed on the a-Si layer 3 at the temperature of 350 ° C. or more, a-
There is a problem that the power generation efficiency is greatly reduced due to crystallization of the Si layer 3 and diffusion of the doped impurities.
a transparent conductive film made of ITO having a concave-convex structure on the surface at a substrate temperature of about 150 ° C. or less at which the diffusion of the doped impurities does not occur and exhibiting a high transmittance and a low resistance, and the same; A manufacturing method was required.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a transparent conductive film made of ITO having high transmittance and low resistance without causing thermal damage to a group IV semiconductor power generation layer. It is an object of the present invention to provide a manufacturing method thereof.

[0006]

The transparent conductive film according to the present invention is a transparent conductive film laminated on a group IV semiconductor power generation layer, and does not thermally damage the group IV semiconductor power generation layer.
In a temperature range of 50 ° C. or lower, the film is formed by applying steam together with the vapor of the indium oxide / tin oxide composite oxide, and has a surface with an uneven shape.

Further, the transparent conductive film is made of indium oxide.
The film is preferably formed by the action of oxygen together with the vapor of tin oxide composite oxide and water vapor. In the case of forming a film using a sputtering method, an argon gas is used in an amount of 50 to 9%.
It is desirable to apply a mixed gas containing 9.99% by volume, 50 to 0.01% by volume of water vapor, and 0 to 1% by volume of oxygen gas. If the amount of added steam is less than 0.01% by volume, no irregularities appear on the surface of the formed transparent conductive film, so the lower limit of the amount of added steam is set to 0.01% by volume. On the other hand, if the amount of added steam exceeds 50% by volume, the resistivity of the film increases (for example, the resistivity exceeds 1 × 10 ⁻³ Ω · cm), resulting in a film having poor electrical performance. The value is 50% by volume.

When a film is formed by a vacuum evaporation method, oxygen gas is 50 to 99.99% by volume and water vapor is 50 to 0.0
It is desirable to cause a mixed gas containing 1% by volume to act. The reason for limiting the numerical value of the amount of added steam is the same as described above.

Further, the transparent conductive film may have an irregular shape on the surface by arranging a large number of triangular crystal grains shown in FIG. 3A or hemispherical crystal grains shown in FIG. preferable.

It is desirable that the film thickness be in the range of 50 to 1000 nm.

The method for producing a transparent conductive film according to the present invention comprises the steps of:
In the method for producing a transparent conductive film laminated on a group IV semiconductor power generation layer, (a) carrying a substrate having a group IV semiconductor power generation layer into a vacuum vessel; (C) adjusting the temperature of the substrate to a temperature range of 150 ° C. or less without causing damage;
While producing vapor or sputtered particles of the tin oxide composite oxide in the vacuum vessel, introducing steam into the vacuum vessel, and producing vapor or sputtered particles of indium oxide / tin oxide composite oxide in the presence of water vapor. Depositing on the group IV semiconductor power generation layer, and laminating a film of indium oxide / tin oxide composite oxide having an uneven surface,
It is characterized by having.

In the step (c), it is preferable that oxygen gas is further introduced into the vacuum vessel. When forming a film by the sputtering method, argon gas, water vapor, and oxygen gas are introduced into a vacuum vessel, and a high frequency is applied between a substrate of indium oxide / tin oxide composite oxide as a film material and a substrate to discharge. By causing sputtered particles of indium oxide / tin oxide composite oxide to fly out of the target surface in the presence of water vapor and oxygen gas,
It is desirable that a film of indium oxide / tin oxide composite oxide having an uneven surface is laminated on the group IV semiconductor power generation layer. In this case, 50 to 99.9 of argon gas is used.
It is desirable to use a mixed gas containing 9% by volume, 50 to 0.01% by volume of steam, and 0 to 1% by volume of oxygen gas.

When a film is formed by a vacuum evaporation method, indium oxide / tin oxide composite oxide, which is a film material, is heated by an evaporation source to evaporate to generate steam, and water vapor and oxygen gas are supplied into the vacuum vessel. To generate a discharge in a region sandwiched between the evaporation source and the substrate, and convert the indium oxide / tin oxide composite oxide vapor, water vapor, and oxygen gas into plasma, thereby oxidizing the surface having an uneven surface. It is desirable to form a layer of an indium / tin oxide composite oxide on the group IV semiconductor power generation layer. In this case, it is desirable that the oxygen gas is 50 to 99.99% by volume and the water vapor is 50 to 0.01% by volume. If the amount of added steam is less than 0.01% by volume, no irregularities appear on the surface of the formed transparent conductive film, so the lower limit of the amount of added steam is set to 0.01% by volume. On the other hand, if the amount of added steam exceeds 50% by volume, the resistivity of the film exceeds 1 × 10 ⁻³ Ω · cm, resulting in a film having poor electrical performance.
% By volume.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) FIG. 2 is a schematic configuration diagram showing an apparatus used for manufacturing a transparent conductive film according to a first embodiment of the present invention. In the first embodiment, an ITO transparent conductive film is formed on a glass substrate by using a sputtering apparatus 10. The sputtering device 10 includes a vacuum vessel 11 that is evacuated by a vacuum exhaust device (not shown). The sputtering source 12 includes a target 13 made of ITO, a magnet 14 for generating a magnetic field, a target holder electrode 15 having a water cooling function, a shield 16, and an insulator 17 having a vacuum sealing function. A high-frequency power supply 19 is connected to the target holder electrode 15 via a matching unit 18.

A heater 21 is provided at a portion facing the target 13.
Is provided, and the substrate 20 is mounted and held on the lower surface thereof. In addition, a gas inlet 25a of a gas supply pipe 25 communicating with a gas flow controller (not shown) is disposed near the target 13.

In the above-described apparatus, first, the substrate 20 made of non-alkali glass or the like is subjected to ultrasonic cleaning with an organic solvent (for example, acetone), and then attached to the substrate holder electrode 22 in the vacuum vessel 11 to obtain 2 × 10 ^−. Pre-evacuate to ⁶ Torr or less. The substrate 20 is heated to about 150 ° C. by the heater 21.

Further, a gas inlet 25 is provided in the vacuum vessel 11.
A process gas is introduced via a. This process gas is obtained by adding 10% by volume water vapor (H ₂ O) to 90% by volume of argon gas (Ar). The amount of exhaust by the vacuum pump and the amount of gas introduced by the gas supply device are controlled, and the internal pressure of the vacuum vessel 11 is adjusted to 5 × 10 ⁻³ Torr.

Next, the high-frequency power supply 1
When a high-frequency power is applied to the target holder electrode 15 from FIG. 9, a discharge is generated between the electrodes 15 and 22, and argon ions generated by the discharge collide with the surface of the target 13, and the sputtered particles are directed toward the substrate 20. Jump out. As a result, ITO sputter particles are deposited on the substrate 20, and the ITO film 24 is formed. Obtained ITO film 2
No. 4 has a film thickness of 50 to 1000 nm (0.05 to 1 μm)
And the resistivity was 5 × 10 ⁻⁴ Ω · cm. This value of the resistivity is substantially equal to that of the film formed by the conventional method.

FIG. 3A is a micrograph of the transparent conductive film according to the first embodiment of the present invention formed as described above, which is observed and photographed with a scanning electron microscope (SEM). Thus, it was found that a large number of triangular crystal grains were formed, and the surface of the transparent conductive film had an uneven shape.
On the other hand, FIG. 3B shows a microscope in which a transparent conductive film formed by introducing only 100% by volume of argon gas without water vapor from the gas inlet 25a (the other conditions are the same) was observed and photographed by SEM. It is a photograph. As described above, the surface of the conventional film is smooth and has no uneven shape. From the comparison between the two, when the film is formed by adding water vapor to the process gas, the surface of the transparent conductive film becomes uneven, and the proportion of incident light that is totally reflected and does not go outside increases, resulting in power generation efficiency. Was found to improve.

In this case, if the amount of added steam is less than 0.01% by volume, no irregularities appear on the surface of the formed transparent conductive film. Therefore, the lower limit of the amount of added steam is set to 0.01% by volume. On the other hand, if the amount of added steam exceeds 50% by volume, the resistivity of the film exceeds 1 × 10 ⁻³ Ω · cm, resulting in a film having poor electrical performance.
% By volume.

When oxygen is further added simultaneously with the addition of steam, the transmittance is further improved. However, if oxygen is added in an amount of 1% by volume or more, the resistivity of the film decreases, which is not preferable.

FIG. 4 is a graph showing a comparison of short-circuit current between the transparent conductive film according to the first embodiment and a solar cell having a conventional transparent conductive film. The configuration of the solar cell was as shown in FIG. As a comparative example, assuming that the short-circuit current of the solar cell using the transparent conductive film without adding water vapor is 1, the short-circuit current Isc of the solar cell using the transparent conductive film manufactured in this study is significantly increased to 1.50. Thus, it was found to have a large photoelectric conversion efficiency.

(Second Embodiment) FIG. 5 is a schematic structural view showing an apparatus used for manufacturing a transparent conductive film according to a second embodiment of the present invention. In the second embodiment, the vacuum deposition device 3
Using 0, an ITO transparent conductive film is formed on a glass substrate. The vacuum vapor deposition device 30 includes a vacuum vessel 31 that is evacuated by a vacuum exhaust device (not shown). The evaporation source 32 is provided with an evaporation material 33 composed of ITO. Here, the evaporation source 32 may be of any heating method such as an electron beam heating method, a resistance heating method, or a laser heating method. A gas supply pipe 38 is introduced through the side wall of the vacuum vessel 31, and a gas inlet 38 a is opened in the vacuum vessel 31. The gas supply pipe 38 communicates with a gas flow control device (not shown) including a process gas supply source.

A high-frequency coil 34 for generating electric discharge is fixed above the evaporation source 32 through an insulator 35 having a vacuum sealing function. The high-frequency coil 34 has a matching device 36
The high frequency power supply 37 is connected via the. Further, a substrate holder electrode 39 having a heater 40 is provided above the high-frequency coil 34. A substrate 41 is attached and held on the lower surface of the substrate holder electrode 39.

In the above apparatus, first, the substrate 41 made of non-alkali glass or the like is subjected to ultrasonic cleaning with an organic solvent (for example, acetone), and then attached to the substrate holder electrode 39. The substrate 41 is kept at 2 × 10 ⁻⁶ Torr or less. Exhaust. Heater 4
0 heats the substrate 41 to about 150 ° C.

Further, a gas inlet 38 is provided in the vacuum vessel 31.
A process gas is introduced via a. This process gas is obtained by adding 10% by volume of steam (H ₂ O) to 90% by volume of oxygen gas (O ₂ ). Controlling the amount of exhaust by the vacuum pump and the amount of gas introduced by the gas supply device,
The internal pressure of the vacuum vessel 31 is adjusted to 8 × 10 ⁻⁴ Torr.

Next, the evaporating material 33 composed of ITO is heated and evaporated by the evaporating source 32, and at the same time, a high frequency is applied to the coil 34 from the high frequency power source 37 through the matching unit 36, and the discharge plasma 43 is generated. Then, the film forming components are deposited on the substrate 41. Thus, an ITO film 42 as a transparent conductive film is formed on the substrate 41. The obtained ITO film 42 has a thickness of 50 to 1000 nm (0.05
１1 μm), and its resistivity is 6 × 10 ⁻⁴ Ω ·
cm. This value of the resistivity is substantially equal to that of the film formed by the conventional method.

FIG. 6 (a) is a photomicrograph of the transparent conductive film according to the second embodiment of the present invention formed as described above, observed and photographed by a scanning electron microscope (SEM). Thus, it was found that a large number of hemispherical crystal grains were formed, and that the surface of the transparent conductive film had an uneven shape.
On the other hand, FIG. 6B shows a microscope in which a transparent conductive film formed by introducing only 100% by volume of oxygen gas without water vapor from the gas inlet 38a (other conditions are the same) was observed and photographed by SEM. It is a photograph. As described above, the surface of the conventional film is smooth and has no uneven shape. From the comparison between the two, when the film is formed by adding water vapor to the process gas, the surface of the transparent conductive film becomes uneven, and the proportion of incident light that is totally reflected and does not go outside increases, resulting in power generation efficiency. Was found to improve.

In this case, if the amount of steam addition is less than 0.01% by volume, no irregularities appear on the surface of the formed transparent conductive film, so the lower limit of the amount of steam addition is 0.01% by volume. On the other hand, if the amount of added steam exceeds 50% by volume, the resistivity of the film exceeds 1 × 10 ⁻³ Ω · cm, resulting in a film having poor electrical performance.
% By volume.

FIG. 7 is a graph showing a comparison of the short-circuit current of the solar cell having the transparent conductive film according to the second embodiment and a conventional transparent conductive film. The configuration of the solar cell was as shown in FIG. As a comparative example, assuming that the short-circuit current of a solar cell using a transparent conductive film to which water vapor is not added is 1, the short-circuit current Isc of the solar cell using the transparent conductive film manufactured in this study is significantly increased to 1.45. Thus, it was found to have a large photoelectric conversion efficiency.

[0032]

As described above, according to the present invention, 150
A transparent conductive film having a concavo-convex structure on the surface can be formed at a substrate temperature of not more than ℃, without causing thermal damage to the group IV semiconductor power generation layer, the obtained transparent conductive film shows high transmittance,
And low resistance. Such a solar cell using the transparent conductive film of the present invention can obtain a large short-circuit current Isc and significantly improve photoelectric conversion efficiency.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a structure of a group IV semiconductor solar cell.

FIG. 2 is a schematic configuration diagram showing a sputtering apparatus used for manufacturing a transparent conductive film according to the first embodiment of the present invention.

3A is a micrograph showing a transparent conductive film according to the first embodiment of the present invention, and FIG. 3B is a micrograph showing a conventional transparent conductive film.

FIG. 4 is a graph showing a comparison between short-circuit currents of a solar cell including the transparent conductive film according to the first embodiment and a solar cell including a conventional transparent conductive film.

FIG. 5 is a schematic configuration diagram showing a vacuum evaporation apparatus used for manufacturing a transparent conductive film according to a second embodiment of the present invention.

FIG. 6A is a micrograph showing a transparent conductive film according to a second embodiment of the present invention, and FIG. 6B is a micrograph showing a conventional transparent conductive film.

FIG. 7 is a graph showing a comparison between short-circuit currents of a solar cell including a transparent conductive film according to the second embodiment and a solar cell including a conventional transparent conductive film.

[Explanation of symbols]

1 ... substrate, 2 ... SnO ₂ transparent conductive film, 3 ... IV group semiconductor power layer (a-Si layer), 4 ... ITO transparent conductive film, 5 ... aluminum electrode film, 6 ... aluminum electrode (collecting electrode),
DESCRIPTION OF SYMBOLS 10 ... Sputtering apparatus, 11 ... Vacuum container, 12 ... Sputter source, 13 ... Target, 14 ... Magnet, 15 ... Target holder electrode, 16 ... Shield, 17 ... Insulator, 1
8 Matching device 19 High frequency power supply 20 Substrate 21 Heater 22 Substrate holder electrode 23 Insulator 24 I
TO transparent conductive film, 25 gas supply pipe, 25a gas inlet, 26 exhaust port, 30 vacuum evaporation device, 31 vacuum container, 32 evaporation source, 33 evaporation material, 34 high frequency coil, 35 Insulator, 36 matching device, 37 high frequency power supply,
38: gas supply pipe, 38a: gas inlet, 39: substrate holder electrode, 40: heater, 41: substrate, 42: ITO transparent conductive film, 43: plasma, 46: exhaust port.

Continued on the front page (72) Inventor Shoji Morita 1-8-1 Koura, Kanazawa-ku, Yokohama-shi Inside the Basic Technology Research Laboratory Mitsubishi Heavy Industries, Ltd. (72) Inventor Akemi Takano 5-717-1 Fukahori-cho, Nagasaki-shi, Nagasaki Prefecture No. F-term (reference) in Nagasaki Research Laboratory, Nagasaki R & D Co., Ltd. 4K029 AA06 AA09 BA45 BA47 BA50 BB01 BB02 BC09 BD00 CA01 CA05 DB18 DB20 DB21 DC05 EA01 EA05 EA08 FA06 5G307 FA01 FA03 FB01 FC09 FC10 5G323 BA02 BB05

Claims (13)

[Claims] 1. A transparent conductive film laminated on a group IV semiconductor power generation layer, wherein the indium oxide / tin oxide composite is used in a temperature range of 150 ° C. or less so as not to thermally damage the group IV semiconductor power generation layer. A transparent conductive film, which is formed by applying water vapor together with the vapor of an oxide to form a film and has an uneven surface. 2. The transparent conductive film according to claim 1, further comprising a film formed by applying oxygen together with vapor and water vapor of the indium oxide / tin oxide composite oxide. 3. An amount of 50 to 99.99% by volume of argon gas, 50 to 0.01% by volume of water vapor and 0 to 1% by volume of oxygen gas.
The transparent conductive film according to claim 1, wherein the film is formed by applying a mixed gas containing each volume%. 4. The transparent conductive film according to claim 2, wherein a film is formed by applying a mixed gas containing 50 to 99.99% by volume of oxygen gas and 50 to 0.01% by volume of water vapor. film. 5. The surface irregularities formed by arranging a large number of triangular crystal grains.
The transparent conductive film according to the above. 6. A surface irregularity formed by arranging a large number of hemispherical crystal grains.
The transparent conductive film according to the above. 7. The transparent conductive film according to claim 1, wherein the thickness is in the range of 50 to 1000 nm. 8. A method for producing a transparent conductive film laminated on a group IV semiconductor power generation layer, comprising: (a) carrying a substrate having a group IV semiconductor power generation layer into a vacuum vessel; 150 that does not thermally damage the semiconductor power generation layer
(C) generating vapor or sputtered particles of indium oxide / tin oxide composite oxide as a film material in the vacuum vessel, and distributing water vapor in the vacuum vessel. And vapor or sputtered particles of indium oxide / tin oxide composite oxide are deposited on the group IV semiconductor power generation layer in the presence of water vapor to form an indium oxide / tin oxide composite oxide having an uneven surface. A method of manufacturing a transparent conductive film, comprising: forming a film by lamination. 9. The method according to claim 8, wherein in the step (c), an oxygen gas is further introduced into the vacuum vessel. 10. In the step (c), an argon gas, water vapor and an oxygen gas are introduced into a vacuum vessel, and a high frequency is applied between an indium oxide / tin oxide composite oxide target to be a film material and the substrate. Discharge, and sputter particles of indium oxide / tin oxide composite oxide fly out of the target surface in the coexistence of water vapor and oxygen gas, thereby forming an indium oxide / tin oxide composite oxide having an uneven surface. The method for producing a transparent conductive film according to claim 8, wherein the film is formed on the group IV semiconductor power generation layer. 11. An argon gas of 50 to 99.99% by volume, a water vapor of 50 to 0.01% by volume, and an oxygen gas of 0 to 1%.
The method for producing a transparent conductive film according to any one of claims 8 to 10, wherein a mixed gas containing each volume% is applied. 12. In the step (c), indium oxide / tin oxide composite oxide serving as a film material is heated by an evaporation source and evaporated to generate steam, and steam and oxygen gas are further introduced into the vacuum vessel. Introduced, a discharge is generated in a region sandwiched between the evaporation source and the substrate, and the indium oxide / tin oxide composite oxide vapor, water vapor, and oxygen gas are turned into plasma, thereby forming an indium oxide having an uneven surface. 9. The method for producing a transparent conductive film according to claim 8, wherein a film of a tin oxide composite oxide is laminated on the group IV semiconductor power generation layer. 13. An oxygen gas comprising 50 to 99.99% by volume,
The method for producing a transparent conductive film according to claim 12, wherein the water vapor is 50 to 0.01% by volume.