JPH0518269B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to improvements in solar cells, and particularly to solar cells in which an amorphous silicon thin film is provided as a photovoltaic force generating element on a specific flexible substrate. Solar cells in which an amorphous silicon thin film is provided on a non-flexible substrate such as a stainless steel plate or a glass plate are well known, and solar cells in which an amorphous silicon thin film is provided on a flexible substrate made of a resin thin film such as polyimide are well known. Solar cells are also well known. A feature of manufacturing an amorphous solar cell using a flexible substrate is that the necessary amorphous silicon layer can be continuously provided on the substrate, which is non-trivial in terms of manufacturing cost and ease of manufacturing. This is extremely advantageous compared to the case where a flexible substrate is used. Furthermore, unlike conventional solar cells that have an amorphous silicon thin film on a non-flexible substrate, amorphous solar cells that have an amorphous silicon thin film on a flexible substrate are sheet-shaped, so the product The shape can be made arbitrary, and it is expected that its applications will expand with future application development. As mentioned above, in the conventionally developed solar cells in which an amorphous silicon thin film is provided on a flexible substrate, a polyimide film is used for the flexible substrate. However, in solar cells in which an amorphous silicon thin film is provided on a polyimide film, depending on the type of polyimide, the lower electrode (also called the back electrode) of the solar cell may corrode or the substrate, that is, the film and the lower electrode, may corrode. may peel off,
This poses a serious practical problem, as it may lead to a decrease in the output of the solar cell. In order to create an amorphous silicon solar cell by providing an amorphous silicon thin film on a flexible substrate, the flexible substrate needs to be heat resistant to at least 250°C, and it is also difficult to separate it from the bottom electrode. It is necessary to use a substrate that does not cause corrosion of the lower electrode or the lower electrode. At present, most such amorphous silicon solar cells are realized by forming an amorphous silicon thin film using a glow discharge method, so when selecting the material for the substrate of such a solar cell, the aforementioned As shown in Figure 2, heat resistance of 250℃ or higher is required, and the range of substrate material selection is becoming extremely narrow. Therefore, an object of the present invention is to form an amorphous silicon thin film on a flexible substrate by forming the amorphous silicon thin film while keeping the temperature of the substrate relatively low. An object of the present invention is to provide an amorphous silicon thin film solar cell in which the stability of solar cell characteristics over time is improved by appropriately selecting materials. To summarize, the method for manufacturing an amorphous silicon thin film solar cell of the present invention is characterized by forming an amorphous silicon thin film on a flexible substrate of polyethersulfone film by a cluster ion beam method. The polyether sulfo film used in the flexible substrate of this invention is represented by the following formula. This kind of polyether sulfone film is
According to the present invention, when an amorphous silicon thin film is formed thereon, it exhibits excellent dimensional stability with a thermal shrinkage rate of 0.15% or less at a substrate temperature of about 200°C, and furthermore, it has been obtained. The amorphous silicon thin film solar cell of the present invention does not cause corrosion or peeling of the lower electrode. In this way, polyether sulfone film has extremely excellent properties as a substrate for amorphous silicon thin film solar cells. Furthermore, the polyether sulfone film substrate has extremely excellent electrical properties such as dielectric breakdown resistance, dielectric constant, and volume resistivity. As described above, when a polyether sulfone film is used as a substrate for the amorphous solar cell of the present invention, the thickness of the film is preferably 10 to 500μ from the viewpoint of flexibility.
If the thickness exceeds 500μ, it will not be flexible, which is one of the advantages of using a flexible polymer film as a substrate.
It becomes difficult to adopt the to roll method. On the other hand, if the thickness of the film becomes less than 10 μm, the thermal stress during the formation of the amorphous silicon thin film may not be fully alleviated and the substrate may deform, so it is not preferable to reduce the thickness of the substrate too much. A polyether sulfone film is produced by melt film forming, and the film having a thickness of 10 to 500 μm as described above can be easily obtained. Next, the cluster ion beam method will be mentioned. In the cluster ion beam method, the constituent elements of the substance to be formed are stored in a closed crucible with at least one injection nozzle, heated and vaporized, and the vapor is heated to a high pressure sufficiently lower than the vapor pressure. Usually, about 100 to 2000 atoms are injected from an injection nozzle into a vacuum, for example, into a high vacuum with a pressure less than 1/100 of the vapor pressure in the crucible, and a supercooling phenomenon based on adiabatic expansion during injection occurs. forms a loosely bound mass of atoms, a so-called cluster, due to Van der Waals forces, and further ionizes at least a portion of this cluster,
The purpose is to form a thin film of the component elements on the substrate by accelerating them to the substrate surface using kinetic energy applied during nozzle injection or, if necessary, an electric field. In this case, by setting various parameters such as the temperature of the substrate, the degree of vacuum in the space around the crucible, the ionization rate of clusters, or the acceleration voltage when accelerating cluster ions, the material to be grown on the substrate can be changed to an amorphous state or a polymorphous state. It has the characteristic that it can be arbitrarily controlled to a crystalline state or a single crystalline state, and a thin film of the compound can be easily formed by introducing a reactive gas into the cluster formation space. 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. As a result of various studies on how to form an amorphous silicon thin film as a photoelectric conversion element using this cluster ion beam evaporation method, we found that by appropriately selecting the conditions, the quality is extremely high even at substrate temperatures below 200℃. We were able to obtain a thin amorphous silicon film. In the conventional glow discharge method,
In order to obtain a high-quality amorphous silicon thin film, a substrate temperature of at least 250°C is required.
Although the range of material selection for the flexible substrate was extremely limited, by using the cluster ion beam evaporation method, it was possible to obtain a high-quality amorphous silicon thin film even at a substrate temperature of 200°C or less, specifically around 180°C. I confirmed that it is possible. When a polymer film is used as a substrate for a solar cell having an amorphous silicon thin film, there is a problem in that the gas released from the substrate has an adverse effect on the amorphous silicon thin film itself as a photoelectric conversion element. By employing the cluster ion beam method, the required substrate temperature can be lowered and problems associated with outgassing can also be resolved. In other words, with the conventional glow discharge method, a high temperature of 250°C or higher is required to obtain a high-quality amorphous silicon thin film, but by adopting the cluster ion beam method, the required substrate temperature can be lowered. is possible,
For the first time, it has become possible to use polyethersulfone film as a substrate for solar cells with amorphous silicon thin films. Polyether sulfone film can be used without problems up to substrate temperatures of around 230°C. When a polyether sulfone film is used as a substrate for a solar cell having an amorphous silicon thin film, an electrode is formed on the surface of the film, but the material for the electrode is not limited and may include aluminum, iron, stainless steel, nickel, etc. A thin film of tungsten or the like may be formed on the substrate by methods such as vapor deposition, sputtering, or ion plating (including cluster ion deposition), or it may be laminated with aluminum foil, stainless steel foil, etc. via a heat-resistant adhesive. The electrode may also be formed by A cluster ion beam method is used to form an amorphous silicon thin film as a photoelectric conversion element on a polyether sulfone film substrate on which electrodes are formed. The figure shows an example of an apparatus used for forming an amorphous silicon thin film according to the present invention. Referring to the figure, a crucible 1 having a nozzle 2 with a hole diameter of about 0.5 to 2.0 mm is provided in a vacuum container (not shown) supported by an appropriate support member, and the vacuum container has a pressure of at least 10 ^-5 Torr or less. is evacuated to a high vacuum atmosphere. Crucible 1 is filled with silicon crushed to an appropriate size. Next, a gas introduction pipe 3 is provided to the vacuum container, and hydrogen, phosphine, and diborane are supplied from this gas introduction pipe 3 into the vacuum container to increase the pressure in the vacuum container to 10 ^-6 to 10 ^- Maintain at ³ Torr. A substrate 6 is provided in front of the nozzle 2 of the crucible 1 in the vacuum vessel, and this substrate 6 is also heated to an appropriate temperature. Next, the crucible 1 is heated to melt the silicon filled in the crucible 1 and generate silicon vapor. in this case,
The heating temperature of silicon is limited according to the surrounding space of the crucible 1, that is, the pressure inside the vacuum container.If the pressure inside the crucible 1 is P and the pressure inside the vacuum container is P ₀ , then P/P ₀ ≧10 ² , preferably P/P ₀ ≧10 ⁴ . Actually, the heating temperature is
A range of about 1400 to 2300°C is selected. Due to this pressure difference, silicon vapor is ejected from the nozzle 2 to the outside of the crucible 1, and at this time, a supercooling phenomenon based on adiabatic expansion forms clusters in which vaporized silicon atoms and molecules are loosely bonded by Van der Waals forces. be done. By the way, the vapor flow of silicon atoms and molecules that have gained kinetic energy by being ejected out of the crucible 1 enters the ionization chamber, where at least a portion of them is ionized, forming so-called cluster ions. An accelerating electrode 5 is provided between the crucible 1 and the substrate 6 in the vacuum container, and an appropriate accelerating voltage is applied to the accelerating electrode 5, so that the cluster ions are accelerated and bombarded with the substrate 6. . At this time, the cluster ions are separated into individual atoms in the vacuum container due to the impact of the bombardment and move on the surface of the substrate in an atomic state, resulting in the so-called surface migration effect and the ionization created by partially ionized silicon ions. This effect promotes bonding between silicones. On the other hand, some of the H ₂ introduced into the vacuum container is ionized by the bombardment of atoms, or becomes a single atom H, hits the substrate 6 together with the silicon vapor flow mentioned above, and moves on the surface. do. H is applied to the unbonded portion of the silicon that is bonded while moving the substrate 6.
This means that an amorphous silicon thin film having a structure in which the 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 introduced as the introduced gas, and in order to form a p-type amorphous silicon thin film, H ₂ gas and diborane gas (B ₂ H ₆ ) and to form an n-type amorphous silicon thin film.
Introduce _H2 gas and phosphine gas ( _PH8 ). Therefore, as an amorphous silicon layer serving as a photoelectric conversion element, an n layer, an i layer, and a p layer are appropriately formed on a polyether sulfone film substrate on which a back electrode is formed. In the case of shot cell, a polyether sulfone substrate on which an n-layer and an i-layer are laminated is placed in a vacuum container, and platinum, gold, palladium, etc. are deposited as a shot barrier metal by sputtering, vacuum evaporation, or ion plating (cluster). (including ion beam method), etc.
Deposit to a film thickness of approximately 100 Å. In the case of a hetero (face) junction cell, indium oxide, tin oxide, or tin oxide-
A surface electrode is formed by depositing an indium oxide film to a thickness of about 200 to 5000 Å using a sputtering method, a vacuum evaporation method, an ion plating method (including a cluster ion beam method), or the like. A collection electrode is then provided on the shot barrier metal, heteroface surface to complete the amorphous silicon solar cell device. As described above, the method for manufacturing an amorphous silicon solar cell according to the present invention involves forming a back electrode on a polyether sulfone film substrate, and depositing amorphous silicon on this back electrode using an ion cluster beam method. The method includes the steps of providing a membrane, providing a shot barrier metal or hetero (face) electrode thereon, and providing a collector electrode thereon. In manufacturing the amorphous silicon solar cell of the present invention, the cluster ion beam method is used as a method for forming an amorphous silicon thin film on a polyether sulfone film, thereby providing the following advantages. (1) By using the cluster ion beam method, extremely high-quality amorphous silicon thin films can be formed even at substrate temperatures of 200°C or lower, specifically 180°C. (2) Since the required substrate temperature is significantly lowered, the selection range of substrate materials is expanded, and polyether sulfone films, which cannot be used with the glow discharge method, can now be used. (3) By using the cluster ion beam method, an amorphous silicon thin film with excellent adhesion to the substrate can be obtained. As described above, according to the present invention, since an amorphous silicon thin film is formed on a polyethersulfone film using the cluster ion beam method, the dimensional stability of the substrate is excellent, and furthermore, the lower electrode of the substrate A solar cell substrate that does not cause peeling or corrosion of the lower electrode can be realized, and a solar cell that provides stable electrical output over a long period of time can be provided. Naturally, solar cells are placed in harsh natural environments where they are exposed to direct sunlight and exposed to wind and rain. Therefore, the above-mentioned excellent dimensional stability under high temperature and high humidity conditions and no deterioration in the performance of the lower electrode can be said to be a great advantage as a substrate for solar cells. Thus, in this invention, by using a polyether sulfone film as a solar cell substrate, it has become possible to realize a highly practical solar cell. Examples of the present invention will be described below. Examples and Comparative Examples First, the production of polyether sulfone film will be described. Polyether sulfone resin (200P) manufactured by ICI was heated at 150℃ under a vacuum of 10 ^-2 Torr.
Dry for 24 hours. The dried resin was extruded through a T-die having a slit of 0.6 mm in width and 150 mm in length at a cylinder temperature of 340° C. to obtain an unstretched film. Next, this unstretched film was stretched in the MD direction (machine width direction), then in the TD direction (direction orthogonal to the machine axis), and finally heat-set at 320°C for 1 minute to form a polyether sulfone film with a thickness of 75μ. I got it. The heat shrinkage rate of the obtained film at 200°C was 0.15% or less. Next, the production of a solar cell using the aforementioned polyether sulfone film will be described. The polyether sulfone film with a thickness of 75μ obtained as described above was heated at 150°C under a vacuum of 10 ^-2 Torr for 2 hours.
Drying was carried out for a period of time. This dried substrate was mounted on a sputtering device, and a 1.5 μm thick tungsten thin film was formed as a back electrode using tungsten as a target. The substrate on which the back electrode was formed was then set under tension on a substrate support stand of a cluster ion beam device, and heated to 200° C. while exhausting to 5×10 ⁻⁷ Torr. 5×
Once the vacuum level reaches 10 ^-7 Torr, H ₂ will be present in the vacuum container.
Phosphine gas (PH ₈ ) diluted to 1% with gas and hydrogen gas was introduced at a flow rate ratio of 5:1, and the inside of the vacuum vessel was maintained at 1×10 ⁻⁴ Torr. The heating temperature of the crucible is 2000 to 2200℃, and the ionization current is 100m.
A (150V) and the acceleration voltage is 3kV.
An n-type amorphous silicon thin film was formed to a thickness of 200 Å. Next, by introducing only hydrogen gas, an i-type amorphous silicon thin film with a thickness of 3000 Å was formed on the n-type amorphous silicon thin film in the same manner as described above. Next, 1% diluted with hydrogen gas and hydrogen gas
diborane gas was introduced into a vacuum container to form a p-type amorphous silicon thin film with a thickness of 100 Å, and the pin-type amorphous silicon film was laminated on a polyethersulfone film substrate. I got it like this
A pin-type amorphous silicon thin film was attached to a sputtering device, and a tin oxide-indium oxide thin film was deposited to a thickness of 1000 Å to form a heteroface layer. lastly,
1000% palladium is added on top of this heterophase layer.
A pin heteroface type solar cell device was realized on a polyether sulfone film substrate by depositing it in a comb shape with a thickness of 1.5 Å. Next, a comparative example will be described. As the substrate, thickness
A 125μ polyimide film was selected and dried under a vacuum of 10 ⁻² Torr at a temperature of 150° C. for 2 hours. This dried polyimide film was mounted on a sputtering device, and a 1.5 μm thick tungsten thin film was formed as a back electrode using tungsten as a target. The amorphous silicon thin film was produced using a capacitively coupled high frequency (13.56 MHz) glow discharge device. The substrate was heated to 300°C while being evacuated to 10 ^-6 Torr.N2 gas was then introduced at 500c.c./min _, and 200W of high frequency power was applied in a 1.0Torr _N2 gas atmosphere to heat the substrate. Ion bombardment 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, and 100W was generated in this gas atmosphere of 0.6 Torr. high frequency power was applied to form a 200 Å n-type amorphous silicon thin film.Next, an i-type amorphous silicon film was formed on the n-type amorphous silicon thin film using hydrogen gas and silane gas in the same manner as above. thin film
It was formed with a thickness of 3000 Å. Then with hydrogen gas 10
% silane gas and diborane gas diluted to 0.1% with hydrogen gas are introduced into the glow discharge device to form a 300 Å p-type amorphous silicon thin film on the i-type amorphous silicon thin film, and then to form a 300 Å p-type amorphous silicon thin film on the polyimide film.
A pin-type amorphous silicon thin film was provided. The pin-type amorphous silicon thin film obtained in this way was attached to a sputtering device, and a tin oxide-indium oxide thin film was formed.
It was deposited to a thickness of 1000 Å to form a heterophasic layer. Finally, palladium was deposited in the shape of a comb to a thickness of 1000 Å on top of this heteroface layer as a collecting electrode, and a pin heteroface type solar cell device was realized on a polyimide film substrate. Next, a comparison between an example of the present invention and a comparative example will be described. The initial characteristics of the solar cell device of the example of this invention and the initial characteristics of the solar cell device of the comparative example were measured using a solar simulator manufactured by Oriel Co., Ltd. adjusted to AM=1. The results are shown in Table 1.

[Table] Next, comparisons at specific temperatures and temperatures will be described. The solar cells whose initial characteristics were measured in the above comparison were placed in a room with humidity and temperature controlled at 20℃ and 75% RH for 30 minutes.
The conversion efficiency was measured after being left in the sun. Second result
Shown in the table.

[Table] As described above, according to the present invention, using a polyether sulfone film as a solar cell substrate,
It can be seen that when an amorphous silicon thin film is formed on the substrate by the cluster ion beam method, a solar cell with extremely excellent practical performance can be obtained.

[Brief explanation of the drawing]

The figure is a diagram showing the basic configuration of a cluster ion beam apparatus used for manufacturing the solar cell of the present invention. In the figure, 1 is a crucible, 2 is a nozzle, 3 is a gas introduction tube, 4 is an ionization electrode, 5 is an acceleration electrode, and 6
is the substrate.

Claims (1)

[Claims] 1. In a method for manufacturing a solar cell having an amorphous silicon thin film on a flexible substrate, a polyether sulfone film is used as the substrate, and a cluster ion beam method is used as a means for forming the amorphous silicon thin film. Characteristic solar cell manufacturing method.