JPS6079780A - Amorphous silicon solar cell - Google Patents

Abstract

PURPOSE:To form a flexible amorphous silicon solar cell, conduction characteristics thereof are improved, by using a fiber cloth-like material, on which conductive paste is applied, as a substrate. CONSTITUTION:A fiber cloth-like material is employed as a flexible substrate 9 while conductive paste is applied on the surface of the fiber cloth-like material. Since clearances among fibers are buried by the application and the undulations of the surface of a woven fabric used appear as they are on the conductive paste side of a back electrode, the area of conduction is increased, and photoelectric conversion efficiency can be improved. Conductive paste is applied, and an amorphous silicon thin-film is shaped on the cloth substrate 9 as a photoelectric conversion element by using cluster ion beam devices 4-8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amorphous silicon solar cell that has flexibility and can significantly improve current conductivity.

In general, solar cells in which an amorphous thin film is formed on a non-flexible substrate such as a stainless steel plate or glass plate, or a solar cell in which an amorphous thin film is formed on a relatively flexible substrate such as a resin thin film such as polyimide, are well known. It is being In manufacturing amorphous solar cells, the characteristics achieved by using a flexible substrate are the required amorphous 9! j ml > continuously,
It is certain that the structure Gt80 is extremely superior to the non-flexible substrate 5 in terms of manufacturing cost and ease of manufacturing.

Furthermore, amorphous solar cells formed on flexible substrates
Unlike conventional solar cells formed on non-flexible substrates, the sheet-like structure allows the product to be shaped arbitrarily, and it is expected that the development of Imamawara's applications will expand its applications.

However, when forming such an amorphous FIN cell on a flexible substrate, according to the glow discharge method commonly used at present, when trying to obtain high quality amorphous silicon wIII, the temperature is 250°C. ~350℃ is required, and when using a polymer film, only boilimide film with excellent heat resistance is applied.The initial Young's modulus in the IS column is not very large, making it difficult to manufacture amorphous silicon. There is a problem in that the film does not have sufficient strength to withstand the thermal stress caused by heating. In other words, in the case of a substrate that does not have sufficient film strength, when an amorphous silicon thin film is provided on the substrate, heat loss due to the difference in thermal expansion coefficient between the amorphous silicon thin film and the substrate may occur. The stress exceeds the mechanical strength of the substrate, causing the substrate to curl. It has been confirmed that when the degree of curl increases, a serious defect occurs in that the efficiency as a solar cell is significantly reduced.

Conventionally, in order to realize an amorphous silicon solar cell using a flexible substrate, in addition to heat resistance of at least 250°C, it is necessary to be able to withstand thermal stress during film formation at such high temperatures. It is necessary to provide a sturdy board and get the first run.

Furthermore, providing appropriate surface roughness or unevenness to the substrate surface is also effective in improving photoelectric conversion efficiency, but regarding surface roughness or unevenness, conventional polyimide films have too smooth surfaces. The reflected light is emitted outside the solar cell without being used again, making it difficult to obtain high photoelectric conversion efficiency.

Therefore, the main object of the present invention is to use m-fiber fabric as a flexible substrate and form a conductive paste layer thereon to prevent the substrate from curling and to maintain appropriate surface roughness or The object of the present invention is to provide a solar cell that utilizes unevenness to enable multiple reflections of incident light on the surface, thereby increasing the light absorption rate and at the same time increasing the current-carrying area. Although the above-mentioned advantages are achieved in batteries, the method of simply depositing metal sole on top of the fabric when forming the lower electrode results in metal being deposited only on the surface of the fabric due to the gaps between the rIA fibers, making it difficult to conduct electricity. There was a limit to the surface area, and there was also the inherent disadvantage that metal-to-metal connections on the surface of the fabric would occur, reducing the current conduction efficiency.If such current conductivity could not be improved, solar cells with high conversion efficiency would eventually result. This means that batteries cannot be created.

The inventors lowered the substrate temperature required for forming an amorphous silicon thin film, expanded the selection range of flexible substrates, prevented curling during film formation, and created an appropriate surface roughness or unevenness. As a result of intensive study on producing an amorphous silicon solar cell on a substrate, we found that a fabric was used as a substrate for an amorphous silicon thick layer, and 1? The object of the present invention can be advantageously achieved by applying an electrically conductive paste to fill the gaps between the fabrics, and further forming an amorphous silicon thin film on the electrically conductive paste, preferably by a cluster ion beam method. I was able to achieve this.

This invention uses a vAN fabric as a flexible substrate, coats a conductive paste on this fabric, and further coats an amorphous silicon thin film as a photovoltaic element thereon, preferably by cluster ion beam method. This includes fabrics and fabrics such as banyo-woven fabrics, knits, and non-woven fabrics, and the dates range from 10 to 400Q/Ill'. be.

The major factors that influence the composition, organization, and appearance of a fabric include the selection of yarn, woven fabric, and knitting method, but there are also various factors such as the desired fabric structure, thread thickness, cross-sectional shape, monofilament, multifilament, etc. A suitable woven fabric or knitting method is selected to form a substrate suitable for an amorphous solar cell. Although there are no particular restrictions on the au material constituting the fabric, for example, non-woven fabrics or woven fabrics made of heat-resistant aromatic polyamide (Nomex) may also be used.

One of the characteristics of using such fiber fabrics as substrates for solar cells is their good flexibility.

Conventionally, polyimide film has been used as a flexible substrate, but the flexibility of the film is, so to speak, unidirectional, and if you try to make it conform to a quadratic curved surface, such as a spherical surface, hard folds and wrinkles will occur. I don't like it. That is, electrically l! FiIi! It may cause discomfort or cause discomfort to the human body. Thus, for example, a thick III battery using a polyimide film as a substrate is significantly lacking in flexibility. On the other hand, solar cells fabricated using fabric as a substrate have sufficient flexibility. Another advantage of using cloth is that it protects the silicon surface when the silicon thin film formed solar cell is rolled up.

Further, the solar cell having an amorphous silicon thin film according to the present invention is a solar cell in which a Schottky type, PLN type, or tandem type element structure is formed using a silicon-based amorphous WI film. Note that the silicon-based amorphous thin film includes a hydrogenated amorphous film or a fluorinated amorphous film made of a single substance or a compound such as 81.8l-GetSl-C or St-N.

Next, a cluster ion beam method will be described which is a preferred method of forming the above-mentioned amorphous silicon thin film thereon using a fabric as a substrate according to the present invention. In the cluster ion beam method, the constituent elements of the substance to be formed are stored in a closed crucible with an injection nozzle of at least 1aI, heated and vaporized, and the vapor is heated to a pressure sufficiently lower than that of the vapor. It is injected from an injection nozzle into a high vacuum, for example, in a high vacuum with a pressure less than 1/100 of the vapor pressure in the crucible, and usually about 100 to 2000 pieces are produced due to the supercooling phenomenon based on adiabatic expansion during injection. atoms form a mass of atomic agglomerates, so-called clusters, which are loosely bound together by van der Waals forces, and further ionize at least a portion of this cluster and ionize it by the kinetic energy imparted during the nozzle jet or as required. The electrolysis caused by the electrolysis causes it to accelerate and reach the substrate surface.
The purpose is to form a thin film of the component elements on a substrate.

In this case, the material to be grown on the substrate can be made into an amorphous state, a polycrystalline state, or It has the characteristic that it can be arbitrarily controlled as a single crystal state,
and by introducing a reactive gas into the cluster formation space, the rIIl! W can also be easily formed.

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 inventors have conducted various studies on the method of manufacturing an amorphous silicon thin film as a photoelectric conversion element using this cluster ion beam evaporation method. It was confirmed that an extremely high quality amorphous silicon WI film could be obtained even at the substrate temperature. In the conventional glow discharge method, in order to obtain a high-quality amorphous silicon thin film, a substrate humidity of at least 250° C. or higher is required, so the range of options for flexible substrate materials is extremely narrow. On the other hand, it has been confirmed that when cluster ion beam evaporation is used, a high-quality amorphous silicon thin film can be obtained even at a substrate temperature of 200° C. or lower, and specifically at about 180° C.

Therefore, it has been found that fabrics made from very common mi materials such as polyester, rayon, polynosic fibers can also serve as substrates for amorphous silicon solar cells. The 1 liter material that can be used to form the fabric of the present invention is not limited to the above-mentioned organic materials, but may also be inorganic materials such as glass fibers and steel fibers in addition to the aromatic polyamide fibers described above. ,in short,
Any material that can be used to form a cloth may be used. In addition, the cluster ion beam method has excellent step covering properties, and can form a thin film with excellent uniformity even on a substrate with steps, such as the fabric substrate used in this invention. Further, the step covering property can be improved by appropriately arranging a plurality of crucibles and simultaneously using them to form a film.

Regarding the heat resistance of the substrate, as mentioned above, it was confirmed that good quality amorphous silicon WIrM can be obtained even at around 180°C using the cluster ion beam method, but the strength, rigidity, and surface roughness of the substrate are As for the unevenness, it can be set arbitrarily by appropriately selecting the structure of the fabric, the structure of the thread, etc., so it is possible to prevent curling during production of the amorphous silicon thin film, and it is possible to prevent surface roughness as appropriate for use as a substrate for solar cells. It is also possible to provide unevenness.

In this invention, since the fabric is used as a substrate for solar cells,
It is necessary to form electrodes on the surface of the fabric substrate. In this invention, the formation of such electrodes is important. That is,
A lower electrode with low electrical resistance is formed by applying a conductive paste to the m-fiber fabric. The conductive base is amorphous silicon WI! l! Metal powder is mixed into a resin that can withstand the temperatures required during production,
It is plasticized. Examples of the resin include polyesterimide, polyimideamide, etc., and examples of the metal powder include Δ9. CO, AA, Sn, etc. can be used. The conductive paste layer at this time has a thickness of about 0.1 to 10 μm.

In this way, by applying a conductive paste to the mi fabric, the gaps between the m fibers are filled, and the surface undulations of the used woven fabric appear as they are on the conductive paste side of the back electrode, thereby increasing the current carrying area. can be significantly increased, and solar cells with high conversion efficiency can be produced.

It has already been mentioned that the cluster ion beam method is preferably used to form an amorphous silicon thin film as a photoelectric variable element on a fabric substrate on which electrodes are formed. The drawing shows an example of an apparatus used for forming amorphous silicon ions into a film according to the present invention. Referring to the drawing, 0
．． A crucible 4 having a nozzle 5 with a hole diameter of about 5 to 2.0111111 is provided. 1 in this crucible 4. Fill with silicon crushed to a size of 11 layers. In front of the nozzle 5, a cloth (coated with y# electrical paste material) as a W plate 9 is placed, an accelerating electrode 8 is placed in the middle of the cloth, and an ionizing electrode is placed between the nozzle 5 and the accelerating electrode 8. 7 is placed. A gas inlet pipe 6 is provided on the side of the ionization electrode toward the ionization electrode 7 . Each of these members in the drawings is disposed in a vacuum container (not shown) supported by a suitable support member, and this vacuum container has at least 'I O
-'T' orr or less is evacuated to a high vacuum atmosphere.

Next, water death gas 12), phosphine gas (PI-1,), and diborane gas (8286) were supplied into the vacuum container through the gas introduction vibro, and the pressure inside the vacuum container was increased to 10-G.
The substrate 9 is also heated to an appropriate degree.

Next, the crucible 4 is heated to melt the silicon filled in the crucible 4 and generate silicon vapor. In this case, the heating humidity of the silicon is set according to the pressure in the surrounding space of the crucible 4, that is, the vacuum container.If the pressure in the crucible 4 is P, and the pressure in the vacuum container is PO, P/PO≧102, preferably P/PO
Set so that PO≧104. Actually, the heating temperature is set in a 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 based on adiabatic expansion, clusters of vaporized silicon atoms and molecules are loosely bonded by van der Waals forces. It is formed.

By the way, the vapor flow that has gained kinetic energy by being ejected out of the crucible 4 enters the ionization chamber, where at least a portion thereof is ionized to form so-called cluster ions.

An appropriate accelerating voltage is applied to the 31iTi electrode 8 to accelerate the cluster ions and cause them to collide with the substrate 9. At this time, the cluster is separated into individual atoms due to the impact during the collision within the vacuum layer, and the clusters move on the surface of the substrate 9 in an atomic state, resulting in the so-called surface migration effect and the formation of partially ionized silicon ions. Ionization effects facilitate silicon operation. On the other hand, a part of the hydrogen gas (12) introduced into the vacuum container is ionized by electron bombardment, or becomes a single atom, and hits the substrate 9 together with the silicon airflow, and the surface H is bonded to the unbonded portion of the silicon that is bonded while moving the substrate 9, and an amorphous silicon thin film !Iv having a structure in which the dangling bonds are closed by 11 is formed.

More specifically, in order to make an i-type amorphous silicon thin film, only water-dead gas is used as the introduced gas, and in order to form an n-type silicon thin film, hydrogen gas and diborane gas are used as the IJ injected gas. (B2) 16), and hydrogen gas and phosphine gas (pHa) are used as introduced gases to form an n-type silicon thin film.Therefore, photoelectric conversion; M-R.

From the fabric substrate 9 on which the rear N pole was formed, first the 0 layer, then the IB layer, and finally the 1 layer are sequentially formed.Next, this amorphous silicon thin film In order to connect the thick P4 battery to the base, we placed a fabric substrate with laminated layers of N, I, and P in a vacuum layer.
For example, in the case of a Schott I main junction cell, platinum, gold, palladium, etc. are used as the Schottky barrier metal by sputtering, vacuum evaporation, ion blating (including cluster ion beam method), etc. to 100A11! i! It is deposited with a film thickness of about 1000 ml.

In addition, in the case of a heteroface junction cell, a film of indium oxide, tin oxide, tin oxide-indium oxide, etc.
A surface electrode is formed by depositing the film to a thickness of about 5000 Å by sputtering, vacuum evaporation, ion blating (including cluster ion beam), or the like.

Next, a collection electrode is provided on the surface of the Schottky barrier metal and heteroface electrode to complete the amorphous silicon thick battery device. According to this invention, an amorphous silicon six-barrel battery is manufactured by forming a back electrode made of a conductive paste on a fabric substrate, and applying a cluster ion beam method to the back electrode of n111, 1 lil, I) 1 m amorphous silicon. A silicon film is sequentially formed, and a Schottky barrier metal or hetero (
It has a basic 411 structure with a face electrode 1 and a collecting electrode further provided thereon.

As described above, the solar cell of the present invention is characterized in that a fabric is used as a substrate, a wm base is applied to the fabric, and an amorphous silicon thin film is formed on the fabric.

As a result, we were able to fabricate a solar cell with a large current-carrying area, improved current-carrying performance, and high conversion efficiency. Furthermore, since appropriate surface roughness or unevenness is achieved on the paste-like material side, the incident light entering the solar cell is multi-reflected, which improves the light absorption rate and improves the conversion efficiency. ＾You can get a solar cell. In addition, good flexibility is achieved by using fabric as a substrate, and as a result, the applications of the Taiko battery of this invention are expanded, and for example, it can be easily used for displaying products such as tents and yacht sails. This eliminates electrical disconnection and reduces the discomfort felt by the human body when this solar cell is used in clothing, etc.

In a preferred embodiment of the present invention, a cluster ion beam method is used as a method for forming the amorphous silicon thin film. By using this cluster ion beam method, even at a substrate temperature of 200°C or less, specifically 180°C,
Extremely high quality amorphous silicon R[ can be obtained.

In this way, the required substrate temperature is significantly lowered,
The range of substrate selection has expanded, and aromatic polyamide (N
Of course, glass fiber can be used, but general IM fiber materials such as polyester, rayon, and Borinojita can also be used. In addition, arbitrary surface roughness or unevenness, strength, and rigidity can be set by appropriately selecting thread thickness, material, cross-sectional shape, multifilament, monofilament, etc., and vA wear, basis weight, etc. of the fabric. be able to.

As a result, it is possible to prevent curling during film formation, and as described above, it is possible to achieve appropriate surface roughness or unevenness, resulting in excellent Kyuden conversion efficiency, as shown in the examples below. can be achieved. Furthermore, by adopting the cluster ion beam method for forming an amorphous silicon thin film and using fabric as a substrate, it is possible to realize a solar cell with rigidity that can withstand thermal stress during film formation.

Examples of this disclosure will be described below.

Example 1 Warp 75 denier, weft 75 denier, mesh f 60 g/
A conductive paste made of polyimide amide resin mixed with silver powder is applied to a polyester plain weave fabric of I12.
It was dried at ℃ for 5 minutes to form the back side N41i. On the paste side of this back electrode, the surface undulations of the woven fabric used appeared as they were. The woven fabric substrate on which the back electrode was formed was heated at 150°C x 21-1r under vacuum at
was dried. This dried substrate was set under tension on a substrate support stand for cluster ion beam method.
The substrate was heated to 180° C. while being evacuated to Torr. When a vacuum of 5X 10-' Torr was reached, hydrogen gas and phosphine gas (PH,) diluted to 1% with hydrogen gas were introduced into the vacuum layer at a flow rate of 5:1, and the vacuum layer was heated to 1X10- 'Torr maintained.

Crucible heating temperature 2000-2200℃, ionization current 2
An n-type amorphous silicon thin film was formed to a thickness of 200 Å under conditions of 00 mA (300 V), substrate temperature and 180° C.

Next, using only hydrogen gas as the introduced gas, type 1 amorphous silicon ? A film was formed with a thickness of 3000Δ. Next, hydrogen gas and diborane gas (Bz
Hs) was introduced into a vacuum vessel to form a p-type amorphous silicon thin film with a thickness of 100A, and a pin-type amorphous silicon thin film was provided on the fabric substrate. The thus obtained pjn type amorphous silicon SS was mounted on a sputtering device, and a tin oxide-indium oxide thin film was formed at 1001 tf* to form a hair loss f layer.

Finally, palladium was deposited in a comb shape with a thickness of 100 OA as a collecting N pole on this heteroface 1, and a p I n heteroface type Taiyan 1-ike device was realized on the fabric substrate. The performance of this solar cell device is shown in Table 1.

Example 2 The fabric substrate (after forming the back electrode) in Example 1 was attached to a sputtering device, and a 1.5 μm thick tungsten thin film was further formed on the back electrode using tungsten as a target layer. The surface irregularities of the woven fabric still appeared in this tungsten thin film. A p1n hederoface type solar cell device was produced under the same conditions as in Example 1. Its performance is shown in Table 1.

A polyimide film with a thickness of 1125 μm was selected as a comparative example substrate, and this film was exposed to
Dry at 50℃ for 2 hours! I did this. This dried boilimide 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 S film was made using a capacitively coupled high frequency (13,56M1-1z) glow discharge N-device, and the substrate on which the back surface N pole was formed was connected to W! on the 7th node side of the glow discharge device. Attach the counter electrode with tension on the top and place it at 8 X i O"6 orr while
The substrate was heated to 0°C. Then nitrogen gas (N2)
500 mQ, 'n+in Q and 1.0 pieces Qr
A high frequency power of 200 W was applied in a nitrogen gas atmosphere to ion bombard the substrate for 20 minutes, and the substrate was cleaned. Next, add silane gas diluted to 10% with hydrogen gas and small snow carbon gas diluted to 0.1% with hydrogen scum. , introduced into the electric generator, 6xlO-'1
A high frequency power of 100 W was applied in a gas atmosphere of -orr to form an 11-type amorphous silicon iW film of 200 Δ. Next, an i-type amorphous thin film with a thickness of 3000 Å was formed on the n-type amorphous silicon thin film using hydrogen gas and silane gas in the same manner as described above.

Next, 1096 silane gas diluted with hydrogen gas and diborane gas diluted to 0.1% with hydrogen gas were introduced into the glow emission device, and 300Δ ;) type amorphous silicon was deposited on the 1 type amorphous silicon thin film. A thin film was formed, and a pin-type amorphous silicon thin film was deposited on the fabric substrate. The pin-type amorphous silicon thin film thus removed was mounted on a sputtering device, and 1,000 ml of tin oxide-indium oxide was deposited on it to form a heteroface spacing. Finally, on this heteroface layer, palladium was combed in the shape of 1000 combs with a collecting electrode, and then a flexible polyimide film substrate was deposited on the second layer.
I have 1 hetero face type humanoid battery device.

The performance of this device is also listed in Table 1.

[Brief explanation of the drawing]

The drawing is an explanatory diagram of the basic configuration of a cluster ion beam device. In the figure, 4 is a crucible, 5 is a nostle, 6 is a waste introduction tube, 7 is an ion f electrode, 8 is an acceleration electrode, and 9 is a substrate.
be. 'ii Applicant: Toyobosei Co., Ltd. (and 2 others)

Claims (2)

[Claims] (1) In a solar cell having an amorphous silicon thin film on a flexible substrate, the substrate is a fiber fabric, and the fabric is coated with a conductive paste. pond. (2) The solar cell according to claim 1, wherein the amorphous silicon thin film is formed by a cluster ion beam method.