JPH0362974A - Solar cell using metal substrate - Google Patents

Abstract

PURPOSE:To enable a high voltage to be taken out by enabling at least the surface of a lower-part electrode to have a texture structure. CONSTITUTION:The title item consists of a metal substrate 1, an insulation film 2, a metal electrode 3 with a surface in texture structure, an amorphous silicon photoelectric conversion layer 4, and a transparent electrode 5. An elec trode material is coated on the insulation film by the sputtering method for forming a textured structure. Of course, it is possible to form recessed or project ing parts on the surface under proper conditions after coating the electrode material by the sputtering method, vacuum deposition method, etc. The amor phous silicon photoelectric conversion layer has a pin or nip junction and the incident light is converted into electrical energy at this layer. Optic current shows a higher value as the incident light advances longer within the cell. Namely, the more the metal electrode at the lower part is textured, the more the inciding light is scattered randomly on the electrode surface, and scattered in various directions, thus obtaining a high optic current.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a solar cell using a metal substrate, and particularly to a solar cell with improved voltage/current characteristics by utilizing a light confinement effect.

(Prior Art) In recent years, solar cells have been actively developed as devices for realizing energy savings, and are already being used in various fields.

In most cases, the photoelectric conversion function of these solar cells that have been put into practical use is performed by a silicon material such as amorphous silicon or crystalline silicon.

For example, in small electronic devices such as watches and calculators,
Amorphous silicon solar cells are the mainstream, as they have the advantages of being able to operate even with weak light such as indoor fluorescent lights, being small, lightweight, and inexpensive.

The amorphous silicon solar cell in this case usually consists of a substrate, a lower electrode, an amorphous silicon photoelectric conversion layer, an upper electrode, and a protective film.
Generally, an in junction is formed.

In addition, since the power that can be generated by a single cell is small, to improve this, a tandem type solar cell in which single cells are stacked in 2 to 4 layers, or a tandem solar cell in which 2 to 4 single cells are stacked in a flat They are often integrated solar cells arranged in series.

Among these, tandem solar cells adjust the characteristics of each single cell to ensure current matching during stacking.
This determines the voltage that can be extracted, and integrated solar cells can only extract a voltage that is an integral multiple of a single cell. In this way, whether it is a tandem type or an integrated type,
There are limits to obtaining desired voltage/current characteristics. These limitations become a major obstacle when it is required to obtain desired voltage/current characteristics in a limited area, such as in the case of small electronic devices.

On the other hand, substrates used for solar cells include glass substrates,
A metal substrate such as stainless steel or a polyimide substrate is used. In this case, it is known that by creating a textured structure on the surface of the substrate, it is possible to effectively utilize incident light and increase the photoelectric conversion efficiency. It is known that several thousand irregularities can be uniformly formed by chemical treatment or the like. For example, I
A method of forming a TO film or a SnO film to make the surface uneven (Showa No. 57-31312), a method of manufacturing a glass substrate with an uneven surface by welding flat glass and fine powder glass (Japanese Unexamined Patent Application Publication No. 1983-1982) JP-A-62-98678), a method of bringing a substance with an uneven surface into contact with glass and transferring the unevenness to the glass surface (Japanese Patent Application Laid-Open No. 62-98678), etc. have been proposed.

(Problem to be solved by the invention) On the other hand, metal substrates are durable even when made thin, have heat resistance, are flexible, and are inexpensive, so they are the most preferable substrates, especially when trying to make them thinner. However, few effective methods have been proposed because the material is hard and it is not easy to make the surface uneven. In the case of stainless steel sheets, the size of the deposited grains is slightly between 0.01 and 1.
The only methods that have been proposed include a method in which the substrate itself is textured by plating it with nickel to a thickness of 5 μm (Japanese Unexamined Patent Publication No. 143481/1981).

Therefore, the inventors of the present invention conducted intensive studies to extract a high voltage without reducing the photocurrent of a solar cell using a metal substrate, and as a result, they provided an insulating film on the metal substrate and applied a textured layer on top of the insulating film. The present inventors have discovered that photocurrent can be increased by forming a lower electrode with a structure, and therefore, even if the amorphous silicon photoelectric conversion layer is made thinner, a high voltage can be extracted without reducing the photocurrent. .

Therefore, a first object of the present invention is to provide an amorphous silicon solar cell using a gold i-substrate that can extract high voltage.

A second object of the present invention is to provide an amorphous silicon solar cell having voltage/current characteristics different from conventional ones.

A third object of the present invention is to provide a method that can reduce the thickness of an amorphous silicon photoelectric conversion layer without reducing the photocurrent of a solar cell using a metal substrate.

(Means for Solving the Problems) The above aspects of the present invention provide a solar cell having a metal substrate, an insulating film, a lower electrode, an amorphous silicon photoelectric conversion layer, and a transparent electrode, in which at least the surface of the lower electrode is This was achieved by a solar cell characterized by having a textured structure.

Next, the solar cell of the present invention will be explained using the drawings.

Figure 1 shows a solar cell constructed of a metal substrate (1), an insulating film (2), a metal electrode with a textured surface (3), an amorphous silicon photoelectric conversion N (4), and a transparent electrode (5). This shows the battery.

Examples of the metal substrate include stainless steel and aluminum. 511F1 or less, preferably about 0.3
A thin plate-like substrate with a thickness of mm or less is employed.

Examples of the insulating film include diamond, silicon nitride, aluminum carbide, and boron nitride. Film thickness is approximately 1,000
Preferably, the number is 0 to 10,000 people.

The substrate surface and the insulating film surface may be smooth, but it is more suitable if they have many small protrusions (about several tens of holes).

As the metal electrode provided on the insulating film, materials with excellent conductivity such as chromium, titanium, aluminum, SUS, and I are used. The thickness of the film is preferably about 5,000 to 8,000 mm, and the surface has irregularities of 2,000 to 5,000 mm by the following method.

That is, an electrode material is coated on the insulating film by sputtering or the like to form a texture. Of course, after coating the electrode material by sputtering, vacuum evaporation, or the like, the surface may be roughened under appropriate conditions. For example, when forming a textured chromium electrode by sputtering, the substrate temperature is
The temperature condition is between 00 and 500"C. Below 100°C, the surface unevenness is too small to form an effective unevenness;
If it exceeds 0''C, it is unfavorable in terms of the performance of the reactor.

The amorphous silicon photoelectric conversion layer is pin or nip
The incoming light is converted into electrical energy in this layer.

The photocurrent exhibits a higher value as the incident light travels longer within the cell. In other words, the more textured the lower metal electrode is, the more diffusely the incident light is reflected on the electrode surface and scattered in multiple directions, making it possible to obtain a higher photocurrent. The thickness of the conversion layer can be reduced. That is, in the case of the present invention, the thickness of the photoelectric conversion layer can be set to 200 to 2,000 layers, and further can be set to 300 to 1,000 layers.

As the transparent electrode, tin oxide, indium oxide, or I
TO etc. will be adopted. The film thickness is preferably 500 to 1000 thick.

Although FIG. 1 shows a single cell structure, two or more cells can also be integrated, and the present invention encompasses such integrated solar cells.

A protective film is formed on the transparent electrode as necessary.

The amorphous silicon photoelectric conversion layer is made of known plasma C
It can be formed by turning a raw material containing silicon atoms into plasma using a VD device. The raw material containing silicon atoms is silane ((S i ) n
Hzn+z: n is an integer) and/or general formula S i
It means any of the halogenated silanes represented by HO-3X4-1 (X' halogen atom), or a mixed gas of two or more of these, and among them, silane S
A halogenated silanga in which iH4 and/or X is chlorine or fluorine is preferred, and SiH and/or SiF4 are particularly preferred.

When the photoelectric conversion layer is made to be p-type or n-type, a dopant is used as is known in the art. The dopant is an element of group Ⅰ of the periodic table of elements when making a p-type semiconductor, and an element of group V when making an n-type semiconductor. In the present invention, these dopants are mixed in the raw material gas as a dopant gas in the form of a single vapor and/or a gaseous compound.

These dopant gases include, for example, BZ H&,
Examples include BF3, PH3, PF3 and the like.

The dopant gas is mixed in a gas ratio of 10-5% to 1% by volume with respect to the raw material containing silicon atoms.

Also, the plasma in the plasma CVD method refers to a reactive gas! This refers to a plasma state caused by discharge in a magnetic field.

As the raw material gas used during discharge, it is preferable to use a raw material gas diluted with hydrogen and/or a rare gas rather than simply using a raw material gas containing silicon atoms.

Amorphous silicon pin junction has a substrate temperature of 100
~300°C1 and reaction pressure 10mTorr~10To
It can be formed by adopting the conditions of rr and power density of 0.01 to 0.05 w/cm. Note that although iN usually does not contain a dopant, a pin junction can be formed so that the dopant concentration changes continuously.

After providing the pin junction to the substrate as described above, a transparent conductive film is formed. The transparent conductive film is formed as a bottom film by a spray method or a sputtering method.

(Function) In the solar cell of the present invention using a metal substrate obtained as described above, the lower electrode is textured and the amorphous silicon photoelectric conversion layer has a light confinement effect, so the voltage/current characteristics are different from those of the conventional solar cell. However, when the thickness of the amorphous photoelectric conversion layer is the same as that of the conventional one,
A larger photocurrent than before can be obtained (Figure 2)
.

Therefore, in the case of the present invention, the film thickness of the amorphous silicon photoelectric conversion layer can be reduced in order to obtain the same photocurrent as the conventional one.

On the other hand, since there is a relationship as shown in Figure 3 between the film thickness and release voltage of an amorphous silicon solar cell, the output voltage of the solar cell of the present invention with a thin film thickness is higher than that of a conventional solar cell. . That is, when compared with the same area and the same photocurrent, the solar cell of the present invention can obtain a higher voltage than the conventional solar cell.

(Effects of the Invention) As detailed above, the solar cell of the present invention can obtain a higher voltage than the conventional one, so when obtaining the desired voltage through integration, the number of single cells can be reduced compared to the conventional one. Therefore, the area of each cell increases, and the current that can be taken out also increases, making it possible to obtain an extremely high-performance battery.

Therefore, the solar cell of the present invention is particularly suitable for IC cards and the like that require small size, light weight, and high performance current characteristics.

(Example) Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 A diamond film having a thickness of 1,000 mm and a surface roughness of about 20 mm was formed on a stainless steel substrate with a thickness of 0.1 mm using a plasma CVD apparatus.

Next, a film of metallic chromium was formed to a thickness of about 6,000 mm using a sputtering method under conditions of 300''C. The unevenness of this chromium electrode was about 3,000 mm. A thin film was formed, and then a stainless steel/nip/ITO type solar cell was produced according to a known method.

n layer; PH3:SiH4:Hz =0.01:1
A mixed gas of 100 mTorr and 203 CCM was flowed into the reaction tank at a flow rate of 203 CCM and discharged at a power density of 100 W/cI11 to form about 200 phosphorus-doped amorphous silicon layers on the above substrate at 250°C. .

1 layer; SiH, gas at 200mTorr, 30SC
A flow rate of CM was flowed into the reaction tank, the substrate temperature was set to 250°C, and discharge was performed at a power density of 25 W/c'IIT to form an amorphous silicon layer of about 1,000 layers on the n-layer.

9 layers; B, H,:SiH,:Hz -0,005
: 1:100 mixed gas at 100 mTorr.

Flowed into the reaction tank at a flow rate of 203CCM, and the substrate temperature was adjusted to 200CCM.
°C and discharged at a power density of 100 W/bo,
About 100 people formed an amorphous silicon layer doped with boron on the layer.

Furthermore, about 700 layers of ITO were laminated on top of the above nine layers by sputtering to form a transparent electrode.

As a result of current-voltage measurement of the solar cell obtained as described above using a 1,000 lux fluorescent lamp, the Voc was 0. 9 volts, Jsc was 84.4 μA/d.

Furthermore, when the surface reflection characteristics of this solar cell were measured, the reflectance was reduced over the entire wavelength range, demonstrating that optical confinement was achieved.

Comparative Example 1 A solar cell was produced in the same manner as in Example 1 except that a conventional chromium electrode with a flat surface (less than 30 irregularities) was used as the lower electrode, and the Voc was 0.84 volts.
Jsc was 78.9, 1/A/cell. The results of Example 1 and Comparative Example 1 demonstrate that the solar cell using the textured insulating film of the present invention is extremely effective.

[Brief explanation of drawings]

FIG. 1 shows a solar cell using the metal substrate of the present invention. In the figure, symbol I is a substrate, 2 is an insulating film, 3 is a metal electrode, 4 is an a-3i layer, and 5 is a transparent conductive film. FIG. 2 shows the relationship between the photocurrent and the film thickness of the amorphous silicon photoelectric conversion layer in the solar cell of the present invention and the conventional amorphous silicon solar cell. Figure 3 shows the relationship between the output pressure of an amorphous silicon solar cell and the thickness of the amorphous photoelectric conversion layer.

Claims (1)

[Claims] 1) A solar cell comprising a metal substrate, an insulating film, a lower electrode, an amorphous silicon photoelectric conversion layer, and a transparent electrode, characterized in that at least the surface of the lower electrode has a textured structure.