JPS63456A - Transparent conductive film and its production - Google Patents

Abstract

PURPOSE:To decrease the reflection loss of light by a transparent conductive film consisting of a polycrystalline metal oxide and to improve transmittance by grading the <111> axis of the crystal grains on the film surface to the direction perpendicular to the substrate surface and forming rugged structure of such crystal grains at the time of forming the transparent conductive film on the substrate. CONSTITUTION:The transparent conductive film 2 consisting of the mixture composed of In2O3 and SnO3 is deposited by evaporation at 15-30Angstrom /sec on the surface of the glass substrate 1 in the production stage of a solar battery and an amorphous Si film is deposited thereon; further, an Al metallic electrode film 4 is formed thereon. The surface of the transparent conductive film in contact with the amorphous Si film 3 is so graded that the <111> axis is perpendicular to the surface of the glass substrate 1; therefore, said surface has the rugged structure and the multiple reflections by the plans parallel with the (100) face of the crystal grains are extremely accelerated when the light entered from the substrate 1 side is made to enter the amorphous Si film 3 through the transparent conductive film 2. The quantity of the light arriving at the amorphous Si film 3 is thereby considerably increased and the photoelectric conversion efficiency of the solar battery is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a transparent conductive film and a method for manufacturing the same, particularly a transparent conductive film suitable for use as a transparent electrode of a solar cell and a method for manufacturing the same.

(Prior Art) Conventionally, a transparent conductive film has been used, for example, as a window electrode of an amorphous silicon solar cell.

As this transparent conductive film, a metal oxide such as ITO13n 02 is deposited on a transparent substrate such as glass.

Such transparent conductive films are required to have high transmittance and low specific resistance. In particular, high transmittance is extremely important in improving the light conversion efficiency of solar cells. Conventionally, it has been known to reduce reflection loss of incident light by forming a transparent conductive film made of a metal oxide with rod-shaped crystal grains having an uneven structure on the surface to cause multiple reflections (1).

(Problems to be Solved by the Invention) The surface of the conventional transparent conductive film described above is formed of crystal grains oriented in the <110> axis direction, and the (100)
There are many crystal grains whose planes are parallel to the substrate surface. Therefore, much of the incident light is directly multiplexed by tJJ
Since it is reflected without being reflected, the effect of reducing reflection loss is not sufficient, and the transmittance is low.

An object of the present invention is to provide a transparent conductive film that can eliminate the above-mentioned drawbacks and sufficiently reduce reflection loss due to multiple reflections, and a method for manufacturing the same.

(Means for Solving the Problems) The present invention provides a transparent conductive film made of a polycrystalline metal oxide deposited on a substrate, in which the film surface has an uneven structure formed by crystal grains, and more than half of the crystal grains are It is characterized in that the <111> axis is substantially oriented in a direction perpendicular to the substrate surface.

Roughly speaking, the present invention forms a transparent conductive film whose surface has an uneven structure formed by crystal grains of a metal oxide, and in which the 111> axis of more than half of the crystal grains is oriented in a direction substantially perpendicular to the substrate surface. In doing so, the substrate and the metal oxide material are placed in a vacuum container, and the metal oxide material is heated and deposited onto the substrate at a deposition rate of 15 to 30 Å/sec.

(Function) In the transparent conductive film of the present invention, the columnar crystal grains of the gold FAM compound have their <111> axes strongly oriented in a direction perpendicular to the substrate surface.
) plane is parallel to the substrate. Therefore, the uneven structure on the surface of the transparent conductive film has a triangular pyramid shape as shown in FIG. 1(a), and a 7-shaped groove is formed. Therefore, the incident light undergoes multiple reflections within the V-shaped groove, and the amount of light reflected back to the incident side is significantly reduced, resulting in extremely low reflection loss.

On the other hand, in conventional transparent conductive films, the <110> axis of the crystal grains is oriented in a direction perpendicular to the substrate surface, as shown in Figure 1(b), so the (100) plane is aligned with the substrate. They are parallel. Therefore, the number of multiple reflected light rays is small and the loss due to reflection is large, so the transmittance is low.

In addition, as in the manufacturing method of the present invention, the deposition rate is 15 to 30 Å.
/second, more than half of the grains are
The Nl> axis is oriented in a direction perpendicular to the substrate surface, and a transparent conductive film with high transmittance can be obtained.
In particular, by setting the deposition rate to 20 to 25 Å/sec,
It was confirmed that the crystal grains of ~80% or more have their 111> axes oriented in a direction perpendicular to the substrate surface, and the transmittance improvement effect becomes particularly remarkable.

(Example) In one embodiment of the method for manufacturing a transparent conductive film according to the present invention, a vacuum evaporation apparatus using electron beam heating is used, and this apparatus is provided with an ionization apparatus using DC arc discharge. Attach a substrate such as soda glass to the holder of a vacuum thermal bonding device and reduce the pressure in the vacuum chamber to 5 x 1Q-6 Torr or less. In addition, the substrate is heated to 200 to 500°C, preferably 300 to 400°C by a heater provided adjacent to the substrate holder.
Keep at temperature of °C. In addition, inside the evaporation pot, for example, IT
A sintered body of O is stored and irradiated with an electron beam to deposit ITO on the substrate. At this time, the deposition rate and film thickness are monitored by changes in the oscillation frequency of the crystal resonator. In the present invention, the intensity of the electron beam is controlled so that the deposition rate is 15 to 30 Å/sec, preferably 20 to 25 Å/sec. At this time, in normal oxygen atmosphere evaporation, I
TO is reduced and metallic indium and tin become deposited. Therefore, ionization is performed by arc discharge. Indium and tin reduced with ionization power of 80 W (40 V x 2 A) are oxidized again, and an ITO film is deposited on the substrate.

The film thickness is 600 to 10,000, preferably 2000 to 10,000.
Once the number of participants reaches 3,000, the deposition will be completed. In this way, a transparent conductive film made of a mixture of in203 and SnO2 is obtained. The resistivity of the film thus obtained is approximately 2×10 −4 Ω−, which is equivalent to the resistivity of conventionally produced ITO films.

Figure 2 (a) shows a 20,000x micrograph taken with a scanning frost microscope of the transparent conductive film of the present invention formed as described above, showing that many triangular columnar crystal grains are formed. Furthermore, Fig. 2(b) shows a micrograph of a conventional transparent conductive film having an uneven structure, and it can be seen that a large number of square columnar crystal grains are formed. In the photographs in (a) and (b), the length of the lower white frame is 1 μm.In contrast to this conventional transparent conductive film, the (100) plane is oriented parallel to the substrate surface. , in the transparent conductor Tt, Mu of the present invention (2
22) It is parallel to the substrate surface, that is, the <111> axis is perpendicular to the substrate surface.

In order to further confirm this, the atomic planes (222), (440), (400) of the transparent conductive film of the present invention
) and (211), the results of determining the relative intensity ratio of the X-ray diffraction peaks are shown in FIG. As is clear from this graph, in the transparent conductive film of the present invention, the (222) plane is parallel to the substrate surface, and the <111> axis is markedly inclined to be perpendicular to the substrate surface. .

FIG. 4 shows a 11-inch model equipped with the transparent conductive film of the present invention! FIG. 2 is a cross-sectional view showing the configuration of an example of an m-cell, in which a transparent conductive g! 2, an amorphous silicon film 3 is deposited thereon, and an aluminum metal electrode film 4 is further formed thereon.

Light incident from the glass substrate 1 side passes through the transparent conductive film 2 and enters the amorphous silicon film 3, but the surface of the transparent conductive film 2 that comes into contact with the amorphous silicon film 3 has a <111> axis. Since it is oriented perpendicularly to the surface of the glass substrate 1 and has an uneven structure, multiple reflections due to planes parallel to the (1oo) plane of the crystal grains become noticeable, and the light incident on the amorphous silicon film 3 This results in a significant increase in the amount of light.

FIG. 5 shows the reflectance of light incident on the transparent conductive film 2 from the glass substrate 1, where curve A shows the one according to the present invention and curve B shows the one having a conventional uneven structure. As is clear from these curves, it can be seen that the transparent conductive film of the present invention has a lower reflectance than the conventional film over almost the entire wavelength range. In particular, the decrease in reflectance in the wavelength range of 600 to 800 nm is noticeable.

A-M (AirM ass) of the solar cell shown in Fig. 4
) I at 1.5 (100mW/+j)
-V characteristics are shown by curve A in FIG. Further, curve B in FIG. 6 shows the I-V characteristics of a solar cell having a conventional transparent conductive film having an uneven structure, and curve C shows the I-V characteristic of a solar cell having a conventional non-gradient transparent conductive film. It shows the characteristics. As is clear from these curves, the short circuit current of the solar cell having the transparent conductive film according to the present invention is 20 m
A/c7 with conventional uneven structure (181
nA/cze) and one with a non-gradient structure (16m
A/cffl), the photoelectric conversion efficiency is increased by 13% and 25%, respectively, and has a large photoelectric conversion efficiency.

The present invention is not limited to the embodiments described above, but can be modified in many ways. For example, in the above example, the transparent conductive film was formed using ITO, but it can also be formed using 3n02. Furthermore, although the ITO sintered body was heated by an electron beam in the above-described embodiment, it can also be heated by other means, such as a rape beam.

Furthermore, in the solar cell shown in FIG. 4, a transparent conductive film was formed on the glass substrate, but as shown in FIG.
An n-type single crystal silicon layer 1 is formed on a type silicon wafer 11.
2, and then the transparent 54-electrode film 13 of the present invention can be formed thereon.

(Effect of the invention) As described above, according to the transparent conductive film of the present invention, < 1
Since the 11> axis is oriented in a direction perpendicular to the substrate surface, the incident light is subjected to multiple reflections, and loss due to reflection can be significantly reduced. Therefore, a solar cell with such a transparent conductive film can obtain a large short circuit current,
Photoelectric conversion efficiency improves dramatically. Furthermore, according to the method of the present invention, more than half of the columnar crystal grains are formed in a direction in which the <111> axis is perpendicular to the substrate surface by a #I process in which the deposition rate is set in the range of 15 to 30 Å/sec. A transparent conductive film having a high transmittance can be formed using conventional manufacturing equipment almost as is.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are cross-sectional views schematically showing the uneven structure of the surface of the transparent conductive film of the present invention and a conventional transparent conductive film, and FIGS. 2(a) and (b) are the A photomicrograph of a transparent conductive film and a conventional transparent conductive film, FIG. 3 is a graph showing the relative intensity ratio of the X-ray diffraction peaks of the transparent conductive film according to the present invention, and FIG. 4 is a solar cell having the transparent conductive film according to the present invention. FIG. 5 is a graph showing the spectral reflectance of the transparent conductive film according to the present invention and the conventional transparent conductive film. FIG. 6 is a cross-sectional view showing the structure of an example of the transparent conductive film according to the present invention and the conventional transparent conductive film. FIG. 7 is a cross-sectional view showing the structure of another example of the solar cell having a transparent conductive film according to the present invention. 1...Glass substrate 2...Transparent conductive film 3...
・Amorphous silicon film 4...Metal electrode film 11...ρ type silicon wafer? 12...n-type silicon layer 13...Transparent conductive film patent applicant TDC Co., Ltd. (a) (b) Figure 3 Figure 4 Figure 5 Figure 6 Voltage (V) Procedural amendment ( Method) September 9, 1985 1, Display of the case 1986 Patent Application No. 142966 Z Name of the invention Transparent conductive film and its manufacturing method 3 Person making the amendment Relationship with the case Patent applicant TDC Co., Ltd. August 26, 1986 a Correction: False 1 of "Brief explanation of drawings" in the specification, "Microphotograph of transparent conductive film" on page 11, line 5 of the specification was changed to "transparent conductive film" Photomicrograph of particle groove structure, corrected to j.

Claims (1)

[Claims] 1. In a transparent conductive film made of a polycrystalline metal oxide deposited on a substrate, the film surface has an uneven structure due to crystal grains, and the <111> axis of more than half of the crystal grains is aligned with the substrate. A transparent conductive film characterized by being oriented substantially perpendicular to the surface. 2. The polycrystalline metal oxide film is In_2O_3 and SnO_
2. The transparent conductive film according to claim 1, wherein the transparent conductive film is made of a mixture of 2 and 2. 3. In forming a transparent conductive film in which the film surface has an uneven structure due to metal oxide crystal grains and the <111> axis of more than half of the crystal grains is oriented in a direction substantially perpendicular to the substrate surface, A method for forming a transparent conductive film, comprising placing a substrate and a metal oxide material in a vacuum container, heating the metal oxide material, and depositing the metal oxide material onto the substrate at a deposition rate of 15 to 30 Å/sec.