JPH081959B2 - Solar cell - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a flexibility in which a metal foil is attached to the surface of a fiber cloth, and a thin film of amorphous silicon as a photovoltaic element is formed on the metal foil. In addition, the present invention relates to a solar cell that can remarkably improve current-carrying performance.

[0002]

2. Description of the Related Art Generally, an amorphous thin film is formed on a stainless steel plate,
A solar cell provided on a non-flexible substrate such as a glass plate and a solar cell provided on a relatively flexible substrate such as a resin thin film such as polyimide are well known. When manufacturing an amorphous solar cell, the characteristics achieved by using a flexible substrate are that the required amorphous silicon can be continuously provided on the substrate, and the manufacturing cost and ease of manufacture are high. In terms of the above, it is extremely superior to the non-flexible substrate. Further, the amorphous solar cell formed on the flexible substrate is sheet-like, unlike the conventional solar cell formed on the non-flexible substrate, so that the product shape can be made arbitrary. It is possible, and it is expected that its application will be expanded by future application development.

[0003]

However, when such an amorphous solar cell is formed on a flexible substrate, a good quality amorphous silicon thin film can be obtained by the glow discharge method which is generally used at present. When trying to obtain 250 ℃ ~ 35
A high temperature of 0 ° C. is required, and when a polymer film is used, only a polyimide film having excellent heat resistance can be applied. However, the polyimide film has a problem that the initial Young's modulus at such a high temperature is not so large and the film strength is not sufficient to withstand the thermal stress at the time of producing amorphous silicon. That is, in the case of a substrate that does not have a sufficient film strength, when the amorphous silicon thin film is provided on the substrate, the thermal stress due to the difference in the thermal expansion coefficient between the amorphous silicon thin film and the substrate is This means that the substrate will curl beyond the mechanical strength of. It has been confirmed that when the degree of this curl increases, a region where the angle of the light-receiving surface with respect to the incident light beam cannot be kept in an efficient state and the efficiency of the solar cell is significantly reduced, which causes a serious defect. Has been done.

Conventionally, in order to realize an amorphous silicon solar cell using a flexible substrate, in addition to heat resistance of at least about 250 ° C., it is possible to withstand thermal stress during film formation at such a high temperature. It is necessary to provide a flexible substrate that can be used. Further, it is effective to improve the photoelectric conversion efficiency by providing an appropriate surface roughening or unevenness on the substrate surface, but as for the surface roughening unevenness, since the surface of the conventional polyimide film is too smooth, The reflected light is emitted outside the solar cell without being reused,
It was difficult to obtain high photoelectric conversion efficiency.

Therefore, the main object of the present invention is not to cause the curl deformation of the substrate, yet to realize an appropriate surface roughness or unevenness, and to enable multiple reflection of incident light on the surface, whereby the optical absorptivity is obtained. It is intended to provide a solar cell having a high conversion efficiency by increasing the energizing area, protecting the metal foil, and enhancing the electric conductivity of the solar cell. That is, although the solar cell using the cloth as the substrate has the above-described advantages, the method of simply depositing the metal on the cloth for forming the lower electrode does not deposit the metal only on the cloth surface, and the conductive area is increased. There was a limit, and there was an inconvenience that the current-carrying efficiency was reduced due to the occurrence of metal-to-metal connection on the fabric surface. If the conductivity is not improved, a solar cell with high conversion efficiency cannot be finally manufactured.

[0006]

The inventors of the present invention reduced the substrate temperature required for forming an amorphous silicon thin film, widened the selection range of flexible substrates, and prevented curl during film formation. As a result of diligent studies on producing an amorphous silicon solar cell on a substrate having an appropriate surface roughness or unevenness, a cloth was used as a substrate for the amorphous silicon solar cell, and metal vapor deposition was applied to the surface of the cloth. The object of the present invention could be advantageously achieved by laminating a metal foil and then forming an amorphous silicon thin film on the metal foil, preferably by a cluster ion beam method.

According to the present invention, a cloth is used as a flexible substrate, and a metal foil on which metal vapor has been vapor-deposited is adhered to the surface of the cloth, and an amorphous silicon thin film as a photovoltaic element is further laminated on the metal foil. Preferably, it is characterized by being formed by a cluster ion beam method, but the cloth here includes a fiber cloth-like material such as woven cloth, knit, and non-woven cloth, and has a basis weight of 10 to 400 g / It is in the range of m ² . The major factors that influence the structure, texture, and appearance of the fabric include the choice of yarn, woven fabric, and knitting method. Depending on the intended fabric structure, yarn thickness, cross-sectional shape, monofilament, multifilament, etc. Is selected and an appropriate woven fabric or knit system is selected to form a substrate suitable as an amorphous solar cell. The fiber material constituting the cloth is not particularly limited, but a non-woven fabric or a woven fabric made of a heat-resistant aromatic polyamide (Nomex) is also used.

One of the characteristics of using such a cloth as a substrate for a solar cell is its excellent flexibility. Conventionally, a polyimide film has been used as a flexible substrate, but the flexibility of the film is, so to speak, unidirectional, and if it is attempted to follow a quadric surface, for example, a spherical surface, hard creases are generated. Is not preferable. That is, the wire may be electrically disconnected or the human body may feel uncomfortable. Thus, for example, a solar cell using a polyimide film as a substrate is significantly lacking in flexibility. On the other hand, a solar cell manufactured using a cloth as a substrate has a property of sufficient flexibility. Another advantage of using the cloth is that the silicon surface is protected when the silicon thin film-formed solar cell is rolled up.

On this cloth, a metal foil having metal vapor deposition is used as a lower electrode. This protects the metal foil and further enhances the electrical conductivity of the solar cell, and finally a cell having high conversion efficiency can be obtained. The vapor deposition metal used at this time includes nickel, chromium, molybdenum, tungsten, etc., and is formed as a thin film on the metal foil by a conventional vapor deposition (including sputtering, ion plating, cluster ion beam vapor deposition, vacuum vapor deposition, etc.) means.

A solar cell having an amorphous silicon thin film according to the present invention is a solar cell in which a Schottky type, pin type or tandem type element structure is formed by using a silicon type amorphous thin film. The silicon-based amorphous thin film includes a hydrogenated amorphous film or a fluorinated amorphous film made of a simple substance or a compound such as Si, Si-Ge, Si-C, and Si-N.

Next, according to the present invention, a cluster ion beam method, which is a preferable method for forming a non-crystalline silicon thin film on a cloth as a substrate, will be described. According to the cluster ion beam method, a constituent element of a substance to be formed is stored in a closed crucible having at least one injection nozzle, heated and vaporized, and the vapor has a pressure sufficiently lower than the pressure of the vapor. Of 100 to 2 due to a supercooling phenomenon caused by adiabatic expansion at the time of injection, by injecting from a spray nozzle into a high vacuum of, for example, a high vacuum having a pressure of 1/100 or less than the steam pressure in the crucible.
About 000 atoms form a so-called cluster, which is a cluster of atoms that are loosely bonded by Van der Waals forces,
Further, at least a part of this cluster is ionized and accelerated by the kinetic energy applied at the time of nozzle injection or by electrolysis given as needed to reach the surface of the substrate to form a thin film of the above-mentioned component elements on the substrate. Is what you are trying to do.

In this case, by setting the substrate temperature, the degree of vacuum in the space around the crucible, the ionization rate of the clusters, or the acceleration voltage of the cluster ions when accelerating the cluster ions, the substance to be grown on the substrate is in an amorphous state or in a large amount. A thin film of a compound can be easily formed by introducing a reactive gas into the cluster formation space, which has a characteristic that it can be arbitrarily controlled to be in a crystalline state or a single crystalline state.

In a preferred embodiment of the present invention, this cluster ion beam evaporation method is used to form an amorphous silicon thin film as a photoelectric conversion element. The present inventors have conducted various studies on a method of producing an amorphous silicon thin film as a photoelectric conversion element using this cluster ion beam deposition method.
It was confirmed that an extremely good quality amorphous silicon thin film can be obtained even at the following substrate temperatures. The conventional glow discharge method requires a substrate temperature of at least 250 ° C. or more to obtain a good quality amorphous silicon thin film, so that the selection range of the flexible substrate material is extremely narrow. On the other hand, if the cluster ion beam evaporation method is used,
It was confirmed that the substrate temperature may be 200 ° C. or lower, and specifically, a good quality amorphous silicon thin film can be obtained even at about 180 ° C. Therefore, polyester, rayon,
It has been found that fabrics made from very commonly fibrous materials such as polynosic fibers can also serve as substrates for amorphous silicon solar cells. The fiber material that can be used for forming the fabric of the present invention is not limited to the organic material as described above, and in addition to the aromatic polyamide fiber described above, it may be an inorganic material such as glass fiber or steel fiber, In short, any fiber material capable of forming a cloth may be used. In addition, the cluster ion beam method is excellent in step covering property, and it is possible to form a thin film having excellent uniformity even on a cloth substrate used in the present invention having a step. Furthermore, step covering property arranges plural crucibles appropriately,
It can also be improved by simultaneously using them to form a film.

Regarding the heat resistance of the substrate, it was confirmed that a good quality amorphous silicon thin film can be obtained even at about 180 ° C. by the cluster ion beam method as described above. The rough surface or the unevenness can be arbitrarily set by appropriately selecting the structure of the cloth, the structure of the thread, etc., so that it is possible to prevent curling during the film formation of the amorphous silicon thin film and a suitable surface as a substrate for a solar cell. It is also possible to provide rough or unevenness.

In the present invention, since the cloth is used as the substrate of the solar cell, it is necessary to bond the metal foil to the surface of the cloth substrate to form the electrode. The metal foil is not particularly limited, and metal foils such as aluminum, iron, stainless steel, nickel, tungsten, copper, gold, and silver are used, which are laminated with a heat-resistant adhesive to form the lower electrode. To do. By laminating the metal foil on the cloth in this manner, the energized area can be increased and a solar cell with good conversion efficiency can be manufactured. The heat-resistant adhesive is
It is desirable to use a material that does not generate decomposition gas (gas must not diffuse through the metal foil to the silicon thin film side) and further does not reduce flexibility. Specifically, a polyimide adhesive or an epoxy adhesive is preferably used.

The laminate is formed by pressing a cloth and a predetermined metal foil with an adhesive if necessary and pressing them with a press roller, for example.

It has already been described that the cluster ion beam method is preferably used to form the amorphous silicon thin film as the photoelectric conversion element on the electrode-formed fabric substrate. The drawings are views showing an example of an apparatus used for forming an amorphous silicon thin film according to the present invention. Referring to the drawings, a crucible 4 having a nozzle 5 having a hole diameter of about 0.5 to 2.0 mm is provided. The crucible 4 is filled with silicon crushed to an appropriate size. A cloth (metal foil laminated) as a substrate 9 is placed in front of the nozzle 5, an accelerating electrode 8 is arranged in the middle thereof, and an ionizing electrode 7 is arranged between the nozzle 5 and the accelerating electrode 8.
A gas introduction pipe 6 is provided on the side of the ionization electrode toward the ionization electrode 7. Each of these members in the drawing is arranged in a vacuum container (not shown) supported by an appropriate supporting member, and the vacuum container is evacuated to a high vacuum atmosphere of at least 10 ⁻⁵ Torr or less.

Then, hydrogen, phosphine and diborane are supplied into the vacuum container through the gas introduction pipe 6 to maintain the pressure in the vacuum container at 10 ^-6 to 10 ^-3 Torr. The substrate 9 is also heated to an appropriate temperature.

Next, the crucible 4 is heated to heat and melt the silicon filled in the crucible 4 to generate vapor of silicon. In this case, the heating temperature of silicon is
It is set according to the pressure in the space around the crucible 4, that is, the pressure in the vacuum container. When the pressure in the crucible 4 is P and the pressure in the vacuum container is PO, P / PO ≧ 10 ² , preferably Set so that P / PO ≧ 10 ⁴ . Actually, the heating temperature is set in the range of about 1400 to 2300 ° C. However, due to this pressure difference, silicon vapor is ejected from the nozzle 5 to the outside of the crucible 4, and at this time, due to the supercooling phenomenon due to adiabatic expansion, a cluster of vapor-like silicon atoms and molecules loosely bound by the Van der Waals force is formed. It is formed.

By the way, the vapor flow, which has obtained kinetic energy by being jetted out of the crucible 4, enters the ionization chamber, where at least a part thereof is ionized and so-called cluster ions are formed.

An appropriate accelerating voltage is applied to the accelerating electrode 8 to accelerate the cluster ions and cause them to strike the substrate 9. that time,
The cluster is separated into individual atoms by the impact at the time of collision in the vacuum layer and moves on the surface of the substrate 9 in an atomic state, so-called surface migration effect and the ionization effect produced by partially ionized silicon ions. , Silicon operation coupling is promoted. On the other hand, a part of H ₂ introduced into the vacuum container is ionized by electron bombardment or becomes a single atom, bombards the substrate 9 together with the ion vapor flow, and moves on the surface. This means that H is bonded to the unbonded portion of silicon which is bonded while moving through the substrate 9, and an amorphous silicon thin film having a structure in which dangling bonds are closed by H is formed.

More specifically, in order to form an i-type amorphous silicon thin film, only H ₂ gas is used as an introduction gas, and to form a P-type silicon thin film, H ₂ gas and diborane gas ( B ₂ H ₅ )
Moreover, H is used as an introduction gas to form an N-type silicon thin film.
₂ gas and phosphine gas (PH ₃ ) are used. Therefore, as the amorphous silicon layer as the photoelectric conversion element, the n layer, then the i layer, and finally the p layer are sequentially formed on the fabric substrate 9 on which the back electrode is formed. Next, in order to use this amorphous silicon thin film as a solar cell device, a fabric substrate in which an n layer, an i layer, and ap layer are laminated is mounted in a vacuum layer. For example, in the case of a Schottky junction cell, As the Schottky barrier metal, platinum, gold, palladium or the like is formed by a sputtering method, a vacuum deposition method, an ion plating method (including a cluster ion beam method), or the like.
Deposit with a film thickness of approximately Å. In the case of a hetero-face junction cell, a film of indium oxide, tin oxide, tin oxide-indium oxide or the like is formed by a sputtering method, a vacuum deposition method, an ion plating method (cluster method) so as to have a film thickness of about 200 to 5000 Å. (Including an ion beam method) to form a surface electrode. Next, a collecting electrode is provided on the surface of the Schottky barrier metal, heteroface electrode to complete the amorphous silicon solar cell device. According to the present invention, an amorphous silicon solar cell has a back electrode made of a metal foil formed on a cloth substrate, and an n-layer, i-layer, and p-layer amorphous silicon film is formed on the metal by a cluster ion beam method. It has a basic structure in which a Schottky barrier metal or a hetero (face) electrode is sequentially provided, and a collecting electrode is further provided thereon.

[0023]

As described above, in the solar cell of the present invention, the cloth is used as the substrate, the metal foil on which the metal is vapor-deposited is laminated on the surface of the cloth, and the amorphous silicon thin film is formed thereon. It is characterized by As a result, it was possible to manufacture a solar cell with a metal foil that can be protected, a large current-carrying area, high current-carrying performance, and high conversion efficiency. Furthermore, since an appropriate surface roughness or unevenness is realized on the metal foil side, the incident light entering the solar cell is multiple-reflected, and the light absorption rate is improved. can get. Good flexibility is achieved by using a cloth as the substrate, and as a result, the application of the solar cell of the present invention is widened, and it is considered that the product can be easily applied to, for example, tents and sails of yachts. The disconnection is reduced, and when the solar cell of the present invention is used for clothes or the like, the discomfort to the human body is reduced.

In the preferred embodiment of the present invention, the cluster ion beam method is used as the method for forming the amorphous silicon thin film. By using this cluster ion beam method, the substrate temperature is 200 ° C. or lower, specifically, 1
Even at 80 ° C., an extremely good quality amorphous silicon thin film can be obtained. As described above, since the required substrate temperature is significantly lowered, the selection range of the substrate is widened, and aromatic polyamide fiber (Nomex) and glass fiber can be used, but general polyester, rayon, polynosic, etc. Textile materials can also be used. Also, by selecting the thickness, material, cross-sectional shape, multifilament, monofilament, etc. of the thread and the texture of the cloth, the basis weight, etc., it is possible to set the desired roughness and strength and rigidity of the surface. You can As a result, it is possible to prevent curling at the time of film formation, and it is possible to realize appropriate surface roughening or unevenness as described above, so that excellent photoelectric conversion efficiency can be achieved as shown in Examples described later. can do. Further, since the cluster ion beam method is adopted for the amorphous silicon thin film forming method and the cloth is used as the substrate, it is possible to realize a solar cell having rigidity that can withstand thermal stress during film formation.

[0025]

EXAMPLES Reference examples and examples of the present invention will be described below. First, a reference example will be described.

Reference Example 75 denier warp yarn, 75 denier weft yarn, and basis weight 60 g / m
An aluminum foil having a thickness of 10 μm was bonded to the aromatic polyamide (Nomex) plain weave woven fabric of No. ² through a polyimide adhesive with a press roller to form a back electrode. The woven fabric substrate having the back electrode formed thereon was dried at 150 ° C. for 2 hours under a vacuum of 1 × 10 ⁻² Torr. This dried substrate was set on a substrate support of the cluster ion beam method under tension and evacuated to 5 × 10 ⁻⁵ Torr while
The substrate was heated to 80 ° C. When a vacuum of 5 × 10 ^-7 Torr is reached, H ₂ gas and hydrogen gas are added to the vacuum layer,
Phosphine gas (PH ₃ ) diluted to 5% was introduced at a flow rate ratio of 5: 1 to maintain the inside of the vacuum layer at 1 × 10 ⁻⁴ Torr. An n-type amorphous silicon thin film was formed to a thickness of 200 Å under the conditions of a crucible heating temperature of 2000 to 2200 ° C., an ionization current of 200 mA (300 V), and a substrate temperature of 180 ° C.

Then, an i-type amorphous silicon thin film having a thickness of 3000 Å was formed on the n-type amorphous silicon thin film with the introduction gas of only hydrogen gas in the same manner as described above.
Then, hydrogen gas and 1% diborane gas diluted with hydrogen gas are introduced into the vacuum container to form a p-type amorphous silicon thin film with a thickness of 100Å, and a pin-type amorphous silicon thin film is formed on the fabric substrate. Was set up. The pin type amorphous silicon thin film thus obtained was mounted on a sputtering device,
A tin oxide-indium oxide thin film was deposited to 100 Å to form a heteroface layer.

Finally, as a collecting electrode, palladium was deposited in a comb shape on the heteroface layer in a thickness of 1000 L to realize a pin heteroface type solar cell device on the fabric substrate. The performance of this solar cell device is shown in Table 1.
Shown in

Next, examples will be described. Example 1 Polydensic fiber having 75 denier of raw yarn used, weight of 80 g
A copper foil having a thickness of 10 μm was laminated on a knitted fabric of / m ² via a polyimide adhesive with a press roller to form a back electrode. The knit fabric on which the back surface electrode has been formed is subjected to a vacuum of 1 × 10 ^-2 Torr at 150 ° C. for 2
The Hrs was dried. This dried fabric substrate was mounted on a sputtering device, and a tungsten thin film having a thickness of 1.5 μm was formed on the copper foil by using tungsten as a target. The pin hetero face type solar cell device was manufactured under the same conditions as in the reference example. The battery performance of this device is shown in Table 1.

Example 2 An aluminum foil having a thickness of 10 μm was set in a sputter deposition apparatus in a tensioned state, heated to 180 ° C. by a substrate heating apparatus, Ar gas was introduced, and a thin film of 1 μm was formed with nichrome as a target. Formed. 75 denier warp, 75 weft
This metal foil was attached to a polyester plain weave woven fabric having a denier and a basis weight of 60 g / m ² with a press roller to form a back electrode. At this time, the surface undulation of the woven fabric was reflected on the metal foil side of the back electrode, and the nichrome thin film did not crack.

A pin heteroface type solar cell device was produced on this substrate under the same conditions as in the reference example. However, at the time of forming the p layer, C ₂ H ₂ together with H ₂ and B ₂ H ₅ are formed.
Gas was introduced to form a-SiC: H. The flow rate of C ₂ H ₂ was set to 1/10 of the flow rate of H ₂ . This device exhibited the battery performance shown in Table 1.

COMPARATIVE EXAMPLE A polyimide film having a thickness of 125 μm was selected as a substrate, and this film was subjected to 150 × 10 ⁻² Torr under vacuum.
C., and dried for 2 hours. This dried polyimide film was attached to a sputtering apparatus, and a tungsten thin film having a thickness of 1.5 μm was formed as a back electrode by using tungsten as a target. For the amorphous silicon thin film, a capacitively coupled high frequency (13.56 MHz) glow discharge device was used, and the substrate on which the back electrode was formed was placed under tension on the electrode on the anode side of the glow discharge device.
The substrate was heated to 250 ° C. while being placed at 10 ⁻⁶ Torr. Then, N ₂ gas was introduced at 500 ml / min, high-frequency power of 200 W was applied in a 1.0 Torr N ₂ gas atmosphere, and ion bombardment of the substrate was performed for 20 minutes to clean the substrate. Next, 10% silane gas diluted with hydrogen gas and phosphine gas diluted with hydrogen gas to 0.1% were introduced into the glow discharge device to obtain 6 × 10 6.
A high frequency power of 100 W was applied in this gas atmosphere of ⁻¹ Torr to form a 200 Å n-type amorphous silicon thin film. Then, with hydrogen gas and silane gas in the same manner as described above,
An i-type amorphous thin film is formed on the n-type amorphous silicon thin film.
It was formed to a thickness of 00Å. Then 10% with hydrogen gas
Diborane gas diluted to 0.1% with silane gas and hydrogen gas was introduced into the glow discharge device to form a 300Å p-type amorphous silicon thin film on the i-type amorphous silicon thin film, and the pin was placed on the fabric substrate. A type amorphous silicon thin film was provided. The pin-type amorphous silicon thin film thus obtained was mounted in a sputtering apparatus, and a tin oxide-indium oxide thin film was deposited by 1000 Å to form a heteroface layer. Finally, palladium was deposited as a collecting electrode on this heteroface layer in a 1000 l comb shape to obtain a pin heteroface type solar cell device on a flexible polyimide film substrate.

The initial characteristics of the solar cell device of Reference Example and Example 2 and the initial characteristics of the solar cell device of Comparative Example were measured by a solar simulator manufactured by Oriel Co. adjusted to AM = 1. In addition, at the time of this measurement, the sample was used as a measurement sample without releasing the tension of the sample even once through the solar cell device forming step.

Example 3 The initial characteristics of the solar cell devices in Reference Example and Examples 1 and 2 are the results measured under the condition that the tension state was never released. In this Example, the tension state of each sample is shown. The results of measurement under the condition that is once solved are shown. Regarding the samples of Reference Examples and Examples 1 and 2, there was almost no curl even when the tension was released, and the battery characteristics were almost the same as those before the tension was released. Before the solution, the conversion efficiency was 3.2%, but it decreased to 2.4%.

[0035]

[Table 1]

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a basic structure of a cluster ion beam device.

[Explanation of symbols]

 4 crucible 5 nozzle 6 gas introduction tube 7 ionization electrode 8 acceleration electrode 9 substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Setsu Akiyama 280-8 Harimata-cho, Moriyama-shi, Shiga (56) References Japanese Patent Publication 5-50150 (JP, B2)

Claims (1)

[Claims] 1. A solar cell having an amorphous silicon thin film formed by laminating a metal foil on which a metal vapor has been deposited on a surface of a fiber cloth substrate, and further forming an amorphous silicon thin film on the metal foil.