JP2002151708A - Photovoltaic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photovoltaic element which is easily manufactured and provides a solar cell with improved reliability. SOLUTION: The photovoltaic element is provided which is flexible and in which a power generating layer and an electrode layer are formed on a conductive material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible photovoltaic element and a solar cell using the same.

[0002]

2. Description of the Related Art As is well known, a solar cell converts light energy of sunlight into electric energy, and is expected from the viewpoint of environmentally friendly energy technology. In this solar cell, for example, when light near the semiconductor pn junction connected to a resistive load is irradiated with light having a band gap or more, the generated electron-hole pairs become n-layer (electrons).
And a p-layer (hole), and an electromotive force is generated at the pn junction, so that electric energy can be extracted through a resistance load.

Conventionally, various structures have been proposed as solar cells, and a well-known structure such as a bulk type using silicon single crystal, a thin film type using amorphous silicon (a-Si) or the like, a printing type using CdS or the like is well known. Among them, a silicon single crystal has the highest power generation efficiency, and a thin film type and a printed type are also expected from the viewpoint of manufacturing cost. In addition, various studies have been made to obtain even lower cost and higher power generation efficiency. For example, a-S
A fibrous solar cell using an i-film is known (Electronic Technology, Vol. 26, No. 2, page 56, Showa 59).
After that, various fibrous solar cells have been proposed for the purpose of weight reduction and large area (for example, JP-A-5-3).
6999, 6-283742, 6-77511). It is considered that these solar cells have achieved the purpose in a predetermined range.

[0004]

However, in the above-mentioned fibrous solar cell or the like, the joining technique between the electrodes is complicated and involves difficulties in the process, the degree of freedom in the configuration is small, and the mechanical load is locally limited. Therefore, the reliability was not always sufficient.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a photovoltaic element capable of obtaining a highly efficient solar cell which is easy to manufacture and further improved in reliability. is there. That is, the gist of the present invention resides in a photovoltaic element having a power generation layer and an electrode layer formed on a conductive material and having flexibility, and a solar cell configured using the photovoltaic element.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the photovoltaic element of the present invention, a material having excellent flexibility and conductivity is used as the conductive material, and a fibrous material is preferably selected from the viewpoint of flexibility, specific surface area, and the like.

Here, it is necessary that the flexibility does not impair the battery performance against a temperature change and a mechanical load in a use environment. The fibrous conductive material preferably has a diameter of about 1 mm or less, and may be hollow. For example, PAN-based or pitch-based carbon fibers (which may be monofilaments or bundles), carbon fibers produced by a vapor phase method or graphite fibers obtained by graphitizing them, and metal fibers such as copper, aluminum, iron, etc. Is mentioned.

These fibers are preferably used as a woven fabric, a knitted fabric, or a nonwoven fabric in order to increase the light-collecting area when a solar cell is formed as a photovoltaic element. For example, three types of fabrics are plain weave, twill weave and satin weave.
Original woven fabrics including original woven fabrics, single woven woven fabrics which are modified woven fabrics; lapping woven fabrics such as weft double woven fabric, warp double woven fabric, weft double woven fabric and multi-layer woven fabric; Weft pile weave; warp pile weave such as velvet, towel, carpet; knit pile weave; and pile fabric weave such as curl pile weave. Non-woven fabric
The fibers may be directional, random or random. From the viewpoint of improving the power generation efficiency by making the configuration of the obtained solar cell three-dimensional, the one having a pile structure on one or both sides of a cut or a ring on a cloth surface is most preferable. Such a pile structure preferably includes a cut pile, a loop pile, a tufted pile, a double-bonded knitting pile, a double-bonded woven pile, and the like.

In the photovoltaic element of the present invention, a power generation layer and an electrode layer are formed on these conductive materials. The power generation layer is preferably a photo-potential inducing layer composed of a pn junction or a Schottky junction. Irradiation with light produces electrons and holes, which then move in different directions along the potential gradient of the semiconductor band structure at the junction. For example, electrons move to n-type and holes move to p-type due to the electric field gradient due to the difference in energy level.

Materials constituting such a power generation layer include silicon, III-V semiconductors (GaAs, AlGa).
The as, InP, etc.), II-VI group semiconductor (CdS, CdTe, Cu ₂ S
Etc.), a conductive organic compound, a carbon allotrope, etc., but from the viewpoint of cost and environmental requirements, it is preferable to use a material containing carbon. For example, carbon allotrope-silicon, carbon allotrope-organic compound and the like can be mentioned. Examples of carbon allotropes include fullerene (C ₆₀ , C _{70 and the} like), carbon nanotubes, and diamond-like carbon, and examples of silicon include amorphous silicon and silicon fine particles.

Further, examples of the organic compound include polyacetylenes, polythiophenes, polypyrroles,
Examples of the conductive polymer include poly (p-phenylenes) and poly (p-phenylenevinylenes), and a polyphenylenevinylene-based polymer such as MEH-PPV / PCBM is particularly preferable. Such a power generation layer can be formed by a conventional method, for example, plasma CVD (chemical deposition), dip coating, sputtering and the like.

The formation of a pn junction or a Schottky junction in these power generation layers can be performed by a conventional method.
That is, the former is formed by introducing (doping) various impurities into the above-mentioned material, and the latter is formed by contact between the above-mentioned material and an electrode metal described later. For example, impurities during the formation of a pn junction include:
B is generally used as the p-type, and P, As or Sb is generally used as the n-type, and is usually introduced by a thermal diffusion method or an ion implantation method. When using only carbon allotropes, MIS
It is common to use a Schottky junction of the molds.

Further, as the electrode layer, a metal ultrathin film or a transparent electrode is usually used. For example, transparent electrodes such as ITO and SnO ₂ used on the light incident side are formed by CVD,
It is formed by a sputtering method, a vapor deposition method, or the like, and an extremely thin metal film of aluminum, silver, or the like is formed by a vapor deposition method, a printing method, or the like. The electrons and holes separated in the power generation layer as described above are recombined in an external circuit connected through terminals of the electrode layer.

Further, in the photovoltaic device of the present invention,
Preferably, a protective layer can be provided on the surface of the power generation layer and the electrode layer. This protective layer is intended to prevent reflection, improve environmental resistance, and the like, and is not particularly limited as long as the power generation performance is not significantly deteriorated, and is preferably a fluorine-based compound, such as a fluorine-based transparent polymer film. Is selected. The thickness of these protective layers is usually selected from about 150 μm or less.

The formation of the protective layer can be carried out by a conventional method. 1a and 1b schematically show a preferred example of the photovoltaic device of the present invention (FIG. 1a is a perspective view, and FIG. 1b is a cross-sectional view), which is flexible and functions as a back electrode. A power generation layer (2) (up to 5 μm) on a fibrous conductive material (1) (up to 300 μm) having the following characteristics, and a transparent electrode (3) (up to 5 μm) and a ribbon-shaped collector electrode (4) as electrodes (〜100 μm), and then a surface protective layer (5) (〜150 μm) is formed.

The photovoltaic device thus obtained is
In particular, in the case of a fibrous form, a flexible non-film type solar cell which can be easily manufactured, has a large surface area, and can be formed into a free shape can be obtained. That is, in the present invention, using such a photovoltaic element, a solar cell having a condensing area preferably 1.6 times or more the planar structure can be formed. For example, when the fibrous photovoltaic element shown in FIG. 1 is woven into a pile structure in FIGS. 2 and 3, the surface area is about 1.6 times and about 2.0 times the plane structure, that is, the light-collecting area, respectively. Can be obtained.

In manufacturing a solar cell, it is necessary to have a structure having sufficient mechanical strength and weather resistance for outdoor installation and power generation. For this reason, a structure called a module is adopted. In general, the elements are electrically connected in series and arranged on the back surface of a glass plate in a size suitable for carrying for outdoor installation. A frame made of aluminum or the like is provided in a peripheral portion thereof to increase the strength of the module, and furthermore, becomes a place to be attached to a gantry in the case of outdoor installation. In designing such a module, the number of series elements and the size of the elements are determined on the premise of the environment of the equipment used, the specifications of the equipment used, the necessity of a secondary battery, and the like. For example, (1) In the case where only a solar cell is used as a power supply: A voltage control diode and a voltage stabilizing circuit are used to stabilize the output voltage of the solar cell with respect to a change in illuminance of incident sunlight. Although connected to an external load to extract power, the operating point of the solar cell is the intersection of the voltage-current characteristics of this load. The optimum operating current of the module required to obtain the required output current is determined from the optimum operating point of the output characteristics. Normally, the operating point is set to the point where the output becomes maximum. Next, the light receiving area necessary for obtaining the optimum operating current is obtained, and the size of the element is determined from this. (2) When a secondary battery is added to the solar battery: a secondary battery; a backflow prevention diode for preventing current from flowing backward from the secondary battery to the solar battery; and reducing the charging current to the secondary battery to a limited current value. The voltage control circuit controls the voltage to prevent overcharge of the secondary battery or the current limiting resistor. In this case, the operating point of the solar cell is a point where the voltage is equal to or higher than the voltage of the secondary battery. A predetermined current consumption, determine the charging current of the secondary battery required to operate the used device having a charging / discharging time for a predetermined time,
From this, the size of the element is similarly determined.

In the present invention, for example, FIGS.
When a solar cell having the above configuration is formed, for example, the necessary circuits and the like can be formed on the back surface of an epoxy resin substrate.

[0019]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Example 1 A PAN-based graphite fiber having a diameter of 0.015 mm was used as a conductive material, and diamond-like carbon-silicon was deposited thereon as a power generation layer to a thickness of 1 μm-1 μm by a CVD method. Formed. The electrodes were formed by a CVD method and a sputtering method (transparent electrode ITO: 2 μm, collector electrode was aluminum ribbon,
10 μm). The obtained fibrous photovoltaic element has the structure shown in FIG.

These were arranged in a single pile shape as shown in FIG. 2 to produce a solar cell. When this was irradiated with sunlight. An electromotive force (open circuit voltage) of 0.55 V was generated. The short circuit current was 700 mA. Example 2 Using a hollow copper wire having a diameter of 0.15 mm as a conductive material, a fibrous photovoltaic element was obtained in the same manner as in Example 1, and a solar cell was further produced. The electromotive force was 0.5 V and the short-circuit current was 800 mA. Example 3 An aluminum thin film (10 n) was formed on a power generation layer formed using only amorphous carbon (5 μm) in Example 1.
A solar cell was produced in the same manner as in m) except that electrodes were formed by vapor deposition to form MIS type Schottky junctions. The electromotive force was 0.2 V and the short-circuit current was 1 μA.

[0021]

According to the present invention, a highly reliable flexible solar cell can be constructed. Particularly, when a fibrous or spherical photovoltaic element is used, the surface area is large, the weight is small, and the structural load is small. Has the advantage that it can be easily processed into a free shape. Therefore, sunlight can be efficiently absorbed, and a large area or a complicated shape can be easily formed. Furthermore, a multi-parallel circuit is formed as a whole, and a large current can be taken out even in a power generation layer having a large volume specific resistance, and even if one of the electrode wires is broken, the fail-safe property has almost no effect on the entire current. Also have.
As described above, the photovoltaic device of the present invention can be applied to a wider range of uses than conventional ones, including everyday uses.

[Brief description of the drawings]

FIG. 1a is a perspective view schematically showing one example of a photovoltaic element of the present invention. b is a cross-sectional view schematically illustrating one example of the photovoltaic element of the present invention.

FIG. 2 is a view schematically showing one example of the solar cell of the present invention.

FIG. 3 is a diagram schematically showing one example of a solar cell of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fibrous conductive material 2 ... Power generation layer 3 ... Transparent electrode 4 ... Collector electrode 5 ... Surface protective layer

Continued on front page (72) Inventor Masamichi Ishikawa 2-3-6 Otemachi, Chiyoda-ku, Tokyo Inside Mitsubishi Research Institute, Inc. (72) Inventor Katsuya Honda 2-3-6, Otemachi, Chiyoda-ku, Tokyo Stock Association F-term in Mitsubishi Research Institute, Inc. (reference) 5F051 AA01 BA15 DA01 DA20 FA14 GA02 GA05 GA11

Claims (8)

[Claims] 1. A flexible photovoltaic element comprising a power generation layer and an electrode layer formed on a conductive material and having flexibility. 2. The photovoltaic device according to claim 1, wherein the conductive material is fibrous. 3. The photovoltaic device according to claim 2, wherein the fibrous conductive material is a graphite fiber or a metal fiber. 4. The photovoltaic device according to claim 1, wherein the power generation layer is made of a material containing carbon. 5. The photovoltaic device according to claim 5, wherein the material containing carbon is carbon allotrope-silicon or carbon allotrope-organic compound. 6. The photovoltaic device according to claim 1, further comprising a surface protective layer formed on the surfaces of the power generation layer and the electrode layer. 7. A solar cell using the photovoltaic element according to claim 1. 8. The solar cell according to claim 7, wherein the structure using the photovoltaic element has a light-collecting area 1.6 times or more the planar structure.