JPH098338A - Amorphous silicon film solar cell - Google Patents

Abstract

PURPOSE: To obtain a flexible film substrate solar cell having improved environmental resistance. CONSTITUTION: The amorphous silicon film solar cell comprises a photovoltaic power element, i.e., a thin amorphous silicon layer, a surface electrode and a rear electrode provided on a flexible film substrate wherein a layer, principally composed of silicon oxide or aluminum oxide, is formed 0.005-5μm thick at least on the surface where the solar cell is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell provided with an amorphous silicon thin film as a photovoltaic element on a flexible film substrate.
The present invention relates to a flexible film solar cell having excellent weather resistance.

[0002]

2. Description of the Related Art A solar cell in which an amorphous silicon thin film is provided on a substrate such as a stainless steel plate or a glass plate is
JP-A-52-149489, JP-A-55-499
It is known from Japanese Patent Laid-Open No. 4 and Japanese Patent Laid-Open No. 55-29154. Also, those using an aramid film or a polyimide film as a substrate are disclosed in JP-A-54-1494.
89, JP-A-55-4994, JP-A-55
-29154, JP-A-55-82474,
JP-A-56-169372, JP-A-57-103
839, JP 59-34677, JP 59-88874, JP 59-108368, JP 59-158571, JP 60-.
130867, JP-A-60-257183, JP-A-61-7624, JP-A-63-236.
It is known from Japanese Patent Application Laid-Open No. 372, Japanese Patent Application Laid-Open No. 1-119072, Japanese Patent Application Laid-Open No. 1-309385.

A method of using a film as a substrate is a method in which necessary layers such as an amorphous silicon layer are continuously vacuum-deposited, sputter-deposited or plasma-glow-discharge while the film is sent out from a roll, processed, and then wound around the roll again. It can be formed by. Further, the obtained film-shaped solar cell can be freely bent unlike a conventional solar cell provided with an amorphous silicon thin film on a glass substrate or a solar cell manufactured from a single crystal silicon plate or a polycrystalline silicon plate. It is possible, and it can be expected that its application will spread.

[0004]

In practical use of the above-mentioned solar cell, each element material such as an amorphous silicon layer is deteriorated by moisture absorption, or structural destruction occurs due to a difference in dimensional change between the materials. However, the performance as a solar cell may be deteriorated, and the solar cell is usually sealed in a module that is shielded from the outside air.

However, encapsulation in a module is not preferable because the flexibility advantage of the film solar cell is lost. An object of the present invention is to provide a flexible film solar cell having excellent environment resistance.

[0006]

The present inventors have found that an indium tin oxide film, which is a transparent electrode provided on an amorphous silicon layer, may achieve the object of the present invention depending on its production conditions. Is due to the gas barrier effect of the film, and the indium tin oxide film is poor in gas barrier stability, and as a result of earnest research,
The present invention has been completed.

That is, an object of the present invention is to provide a solar cell in which an amorphous silicon thin film, a front surface electrode and a back surface electrode are provided as a photovoltaic element on a flexible film substrate, and at least the surface on which the solar cell is formed is oxidized. 0.005-5 layer mainly composed of silicon or aluminum oxide
It is achieved by a film-shaped amorphous silicon solar cell characterized by being installed in a thickness of μm.

A detailed description will be given below while showing one mode of a specific method for carrying out the present invention. To carry out the present invention, a first conductive layer is formed on the film to a thickness of 0.01 to 20 μm. For the conductive layer, stainless steel, nickel-chromium alloy, and nickel, iron, chromium, niobium, zirconium, titanium alone or their alloys, or oxides such as tin oxide, indium oxide, indium tin oxide, and cadmium oxide are deposited It can be formed by a method or a sputtering method.

Then, an amorphous silicon layer is formed by a glow discharge method, a sputtering method, an ion plating method, or the like. For example, in the case of glow discharge,
In a vacuum reactor maintained at 1 to 0.01 Torr, the film wound in a roll is pulled out, and 200 to 400 ° C.
On the heated supporting electrode. S in the vacuum reactor
A DC voltage or a high frequency voltage of 1 to several tens of MHz is applied between the electrode facing the support electrode and the iH ₄ gas while sending iH ₄ gas to cause a glow discharge, and the inside of the vacuum reactor is brought into a plasma state to thereby produce SiH _4. Decompose to form an amorphous silicon layer on the film. At this time, SiH ₄
At the same time, p-type silicon layer is formed when B ₂ H ₆ is fed by 0.5 to 5% by weight, and n-type silicon layer is formed when PH ₃ is sent together with SiH ₄ .

Next, in the case of a Schottky junction cell, for example, platinum, gold, palladium or the like is formed as a Schottky barrier electrode by sputtering or vacuum evaporation to a thickness of about 100 Å. In the case of a hetero-coupled cell, an indium oxide, tin oxide, indium tin oxide, and cadmium oxide layer is formed to a thickness of about 200 to 3000 angstroms by a sputtering method or a vacuum evaporation method.

Next, a collecting electrode is provided on the Schottky barrier metal / hetero electrode to complete the amorphous silicon solar cell. Then, on the thus-formed film-shaped solar cell, more preferably on the back surface of the base film, a layer mainly composed of silicon oxide or aluminum oxide (hereinafter referred to as a barrier layer), which is a feature of the present invention, will be described. To form. As a barrier layer, it is also a preferable embodiment that a layer mainly containing silicon oxide and a layer mainly containing aluminum oxide are laminated and provided.

In order to improve the environmental resistance of the solar cell,
Although the effect of the present invention is often obtained only by providing a barrier layer on the solar cell surface, it is a preferred embodiment to provide a barrier layer on the back surface of the solar cell (substrate film surface) depending on the substrate film used. The barrier layer provided at this time may be the same as or different from that provided on the solar cell surface, and in addition to those mainly containing silicon oxide or aluminum oxide, metal aluminum, nickel, chromium, Titanium and alloys based on them,
A synthetic resin having a small gas permeability such as vinylidene chloride or vinylidene fluoride is also preferably used.

Silicon oxide and aluminum oxide include metals other than these (for example, boron, magnesium, lead,
The inclusion of oxides such as zinc) is also permitted as long as it does not impair the effects of the present invention. As a method for forming the barrier layer, a sputtering method, a vacuum vapor deposition method or the like may be arbitrarily used.

The thickness of the barrier layer is 0.005-5.
[mu] m, preferably 0.01 to 2 [mu] m, more preferably 0.04 to 0.5 [mu] m. Below this range, the barrier effect may be insufficient due to pinholes during barrier layer formation. There is. If the thickness is larger than this, the barrier layer may be destroyed when the film solar cell is bent, and the barrier effect may be lost.

The processes such as the vacuum deposition process, the sputtering process and the glow discharge process are carried out while the film is continuously moved from roll to roll, or the film having a certain size is batchwise processed. Either method may be used. The mechanical properties of the film used in the present invention are, in processing or handling the film-shaped solar cell, preventing unnecessary deformation due to the force applied to the solar cell, and preventing the destruction of the amorphous silicon layer, and the strength is 18 kg / mm
² or more, preferably 25 kg / mm ² or more, elastic modulus of 30
It is recommended to use 0 kg / mm ² or more, preferably 600 kg / mm ² or more. Further elongation is 10 to 1
Preferably, it is 00%. The characteristics of these films should be satisfied in both the longitudinal direction and the width direction, but they do not necessarily have to be the same,
It may be a so-called balanced type or a uniaxial tension type.

As the film used in the present invention, polyethylene terephthalate, polyethylene naphthalate, etc. which have been conventionally used are used as inexpensive materials, and more preferably, a material having heat resistance to withstand the high temperature received when forming an amorphous silicon layer. Is recommended. As a measure of the heat resistance, the heat shrinkage at 200 ° C. is 2% or less.

Further, when the film used in the present invention has a large coefficient of thermal expansion, the formed amorphous silicon layer is exposed to the temperature difference between when it is cooled to room temperature and when it is heated and cooled by sunlight during use. When this occurs, strain stress may occur due to the dimensional difference from the film substrate and peel off, and the thermal expansion coefficient of the film is 15 × 10 ⁻⁶ , and further 10 × 10
^-6, -2 × 10 ^-6 or more, further preferably greater than or equal to zero. Here, the coefficient of thermal expansion is from room temperature to 3
It shall be expressed as an average value between 00 ° C.

As the film satisfying these characteristics, a part of the film made of aramid resin or polyimide resin can be used. The aramid resin used in the present invention is substantially composed of units selected from the group consisting of the following structural units. —NH—Ar ₁ —NH— (A) —CO—Ar ₂ —CO— (B) —NH—Ar ₃ —CO— (C) where Ar ₁ , Ar ₂ and Ar ₃ are at least one aromatic ring. And may be the same or different, and typical examples thereof include those represented by the following general formula.

[0019]

Embedded image

In addition, some of the hydrogen atoms on these aromatic rings are substituted with a halogen group, a nitro group, an alkyl group, an alkoxy group or the like. Also, X is -O-,
_{-CH 2 -, - SO 2 -} , - S -, - CO- , and the like.
In particular, an aramid resin in which 80 mol% or more of all aromatic rings are bonded in the para position is preferable because it is easy to produce a film having a small thermal expansion coefficient.

The polyimide resin used in the present invention contains at least one aromatic ring and one imide group in the repeating unit of the polymer, and is represented by the following general formula (1) or (2). Is.

[0022]

Embedded image

Here, Ar ₄ and Ar ₆ contain at least one aromatic ring, and two carbonyl groups forming an imide ring are bonded to adjacent carbon atoms on the aromatic ring. This A
r ₄ is derived from an aromatic tetracarboxylic acid or its anhydride. A typical example is one represented by the following general formula.

[0024]

Embedded image

Here, Y is --O--, --CO--, --CH ₂
-, - S -, - SO 2 - and the like. The above (2)
Ar ₆ is derived from tricarboxylic acid anhydride or its halide. Ar ₅ and Ar ₇ in the above (1) and (2) are
It contains at least one aromatic ring and is derived from aromatic diamines and aromatic isocyanates. Representative examples of Ar ₅ or Ar ₇ include those represented by the following general formula.

[0026]

Embedded image

Here, one of the hydrogens on the ring of these aromatic rings is
Part is halogen group, nitro group, alkyl group, alkoxy
It also includes those substituted with a group. Z is -O-,-
CH ₂-, -S-, -SO₂-, -CO- and the like. Special
, Ar_Five, Ar₇More than 80% of the
Polyimide resin, which is an aromatic ring, has a small coefficient of thermal expansion.
It is preferable because rum is easy to manufacture.

Further, the aramid resin or polyimide resin of the present invention contains a lubricant, an antioxidant, other additives, and other polymers as long as the physical properties of the film are not impaired and the object of the present invention is not impaired. It may be. The method for producing the film of the present invention is not particularly limited, and a production method suitable for each resin may be employed.

As for the aramid resin, if it is soluble in an organic solvent, it is polymerized directly in a solvent, or once the polymer is isolated and then redissolved to prepare a solution, which is then prepared by a dry method or a wet method. Films that are hardly soluble in an organic solvent such as polyparaphenylene terephthalamide (PPTA) are dissolved in concentrated sulfuric acid to form a solution, and then formed into a film by a dry method or a wet method.

On the other hand, regarding the polyimide resin, tetracarboxylic acid anhydride and aromatic diamine are reacted in an organic solvent to form a polyamic acid, and this solution is directly or once subjected to a ring-closing treatment to form a polyimide, which is then re-solvent. A solution is obtained by dissolving them, and they are formed into a film by a dry method or a wet method. In the dry method, the solution is extruded from a die, cast on a support such as a metal drum or an endless belt, and the drying or imidization reaction proceeds until the cast solution forms a self-supporting film.

In the wet method, the solution is extruded directly from a die into a coagulating liquid, or is cast on a metal drum or an endless belt as in the dry method and then introduced into the coagulating liquid to be solidified. Next, these films are washed with solvents and inorganic salts in the films and subjected to processes such as stretching, drying and heat treatment.

Fine particles may be mixed for the purpose of imparting slipperiness to the film. As fine particles,
There are organic compounds and inorganic compounds, but usually, for example, Si
O ₂ , TiO ₂ , ZnO, Al ₂ O ₃ , CaSO ₄ , BaS
Inorganic compounds such as O ₄ , CaCO ₃ , carbon black, zeolite and other metal powders are used. The particle size is 0.005 to 2 μm, the addition amount is 0.03% by weight or more,
It is often chosen to be less than 5% by weight.

The thickness of the film used in the present invention is not particularly limited and is usually 5 μm or more and 150 μm.
The following is preferably selected to be 12 μm or more and 100 μm or less. Also, on the film, coloring agents such as dyes and pigments,
Flame retardants, antistatic agents, antioxidants, and other modifiers may also be included as long as they do not violate the object of the present invention.

The film-shaped solar cell of the present invention may be used alone to make the most of its flexibility, or may be used by being laminated and fixed on any support, or may be used by being incorporated as a module. May be. (Method of measuring characteristics) The method of measuring characteristic values according to the present invention is as follows. (1) Method for measuring film thickness, strength, elongation and elastic modulus The film thickness is measured with a dial gauge having a measuring surface with a diameter of 2 mm.

The strength, elongation and elastic modulus were measured using a constant speed elongation type strong elongation measuring machine, measuring length 100 mm, pulling speed 50 m.
It is measured in m / min. (2) Method of measuring heat shrinkage A sample piece of 2 cm × 5 cm is cut out from a film and 4c
The mark is made by making a mark with a knife at intervals of m.
After leaving for 72 hours in an atmosphere of 5% RH, the distance between the labels was read and measured with a microscope, and then left in a hot air oven at 200 ° C. for 2 hours without restraining, then again at 23 ° C. and 55% RH. After leaving for 72 hours in the atmosphere of
The distance between the labels was read and measured with a microscope. (3) Measurement method of thermal expansion coefficient Thermodynamic property measuring device (TMA, TM7 manufactured by Vacuum Riko Co., Ltd.)
A sample with a width of 5 mm is attached to the (000 type) and the load is 0.
After removing the residual strain of the sample by raising the temperature once to 300 ° C. under 3 g, the sample was cooled under a nitrogen stream, and the temperature was lowered from 300 ° C. to 30 ° C.
The dimensional change of the film up to ° C. is measured, and the coefficient of thermal expansion during this period is determined as an average value. (4) Photoelectric conversion characteristics The photoelectric conversion characteristics were measured with a solar simulator manufactured by Oriel Co., Ltd., whose conversion efficiency was adjusted to AM = 1.

[0036]

【Example】

[0037]

Example 1 Polyparaphenylene terephthalamide (P
PTA) in 99.8% concentrated sulfuric acid with a polymer concentration of 12%
It was melted so as to become and was cast from the die onto an endless belt. After heating and moisture absorption on the belt, the dope was changed from the liquid crystal phase to the isotropic phase, and then the temperature was 45% at 0 ° C.
Coagulate in sulfuric acid, neutralize, wash with water, and measure 1.1
After stretching twice, it is dried with hot air using a clip tenter while maintaining a constant length, then heat treated at 400 ° C for tension, 3
After free heat treatment at 50 ° C., it was wound up.

The PPTA film obtained had a thickness of 50 μm and had strengths of 35 and 3 in the longitudinal direction and the width direction, respectively.
7 kg / mm ² , elongation 40, 37%, elastic modulus 950, 9
80 kg / mm ² , 200 ° C heat shrinkage rate 0.06, 0.0
The thermal expansion coefficient was 5% and the thermal expansion coefficient was 4.2 × 10 ⁻⁶ and 4.0 × 10 ⁻⁶ . A 1000 angstrom thick stainless steel layer was formed on the film from a stainless steel target using a sputtering apparatus.

Next, the above-mentioned treated film was placed on the supporting electrode in the vacuum reactor, and the inside of the reactor was once maintained at 10-5 Torr.
After evacuating to r and raising the temperature of the supporting electrode to 300 ° C., argon gas was introduced into the vessel while applying a high frequency voltage of 30 W at 13.56 MHz to the counter electrode and the supporting electrode, and 1 To was obtained.
Pre-sputtering in rr argon atmosphere, then 1% with hydrogen gas as well as SiH ₄ diluted to 10% with hydrogen gas
A diluted PH ₃ gas is introduced, and a 200 Å n-type amorphous silicon layer is formed on the film in an atmosphere of 0.8 Torr. Subsequently, only SiH ₄ was introduced, an i-type amorphous silicon layer having a thickness of 6000 angstrom was laminated, and SiH ₄ gas containing 1% of B ₂ H ₆ was further introduced to obtain a p-type film having a thickness of 200 angstrom. A type amorphous silicon layer was formed.

Next, the film on which the pin type amorphous silicon semiconductor layer was formed was placed in a vacuum vapor deposition apparatus, and an indium tin oxide layer having a thickness of 1000 angstrom was vapor deposited by an electron beam method to form a heteroface layer. Finally, a 1000 Å-thick palladium layer was vacuum-deposited thereon in a comb shape to form a film-shaped solar cell.

Next, this film-shaped solar cell was installed in a vacuum vapor deposition apparatus, and 0.1% of aluminum oxide was sputtered on the surface of the solar cell and then on the back surface of the film.
It was laminated to a thickness of μm. The photoelectric conversion characteristic of this film solar cell was 6.5%. This film solar cell was immersed in water at room temperature for one day and no special change in appearance was observed. After that, the product was taken out from water and dried in a hot air dryer at 80 ° C., and the photoelectric conversion characteristics were measured. As a result, it showed 6.5%, and no deterioration in performance due to immersion in water was observed.

[0042]

Comparative Example 1 For comparison, a film solar cell obtained in Example 1 before being sputtered with aluminum oxide was immersed in water in the same manner as in Example 1. The battery is warped. Further, the photoelectric conversion characteristics of the film-shaped solar cell taken out from water and dried are 6.5% to 5. 5% before being immersed in water.
It fell to 0%.

[0043]

Example 2 A solar cell was constructed in the same manner as in Example 1 except that Kapton (trademark of Toray DuPont Co., Ltd.) 200V which was a commercially available polyimide film was used. The strength of the film used in the long and width directions is 22.5 and 2 respectively.
3.5 kg / mm ^2, elongation 61.4,61.9%, elastic modulus 386,422kg / mm ^2, a thermal expansion coefficient 23 × 10
^-6 and 20 x 10 ^-6 .

Next, silicon oxide was applied on both surfaces of 0.12 μm.
The thickness of m was laminated by the sputter method. The photoelectric conversion characteristic of the obtained film solar cell is 5.8%,
After being left in an atmosphere of 95% RH for 1 week and then taken out and dried, the photoelectric conversion characteristic was 5.8%.

[0045]

Comparative Example 2 When the film-form solar cell obtained in Example 2 before being laminated with silicon oxide was exposed to the same moist heat atmosphere, the photoelectric conversion characteristics decreased from 5.8% to 4.0%. did.

[0046]

Example 3 Using a commercially available polyethylene naphthalate having a thickness of 75 μm, a film type solar cell was manufactured in the same manner as in Example 1, and an aluminum oxide layer was laminated only on the solar cell surface in the same manner as in Example. . This photoelectric conversion characteristic is 6.
A 1% film type solar cell is attached to a stainless steel plate with epoxy resin, and water at room temperature is applied to the solar cell surface for 5 hours.
Poured over time. The photoelectric characteristics of the film which was air dried thereafter was 6.1%.

[0047]

COMPARATIVE EXAMPLE 3 A completely similar test was carried out except that the aluminum oxide layer was not laminated in Example 3, and the photoelectric conversion characteristic was lowered from 6.1% to 3.2%.

[0048]

Industrial Applicability According to the present invention, it is possible to provide a flexible film-shaped solar cell having excellent environmental resistance, which is less likely to deteriorate in characteristics due to moisture absorption in practical use. Therefore, it is not necessary to perform processing such as encapsulation as a module as in the conventional solar cell, which is advantageous in terms of cost and flexibility is not lost.

According to the present invention, it can be expected that a new solar cell utilization method utilizing the flexibility and environment resistance can be developed. As a specific practical advantage, for example, it is used for leisure or emergency solar power generation because it is lightweight and easy to carry by means such as winding.

Claims (4)

[Claims] 1. A solar cell in which an amorphous silicon thin film and a front surface electrode and a back surface electrode are provided as a photovoltaic element on a flexible film substrate, and silicon oxide or aluminum oxide is mainly used on at least the surface on which the solar cell is formed. A film-like amorphous silicon solar cell, characterized in that the layer is set to a thickness of 0.005 to 5 μm. 2. A film substrate having a strength of 18 kg /
The film-form amorphous silicon solar cell according to claim 1, wherein a synthetic resin film having a modulus of ² or more and an elastic modulus of 300 kg / mm ² or more is used. 3. A film substrate having a strength of 18 kg /
mm ² or more, elastic modulus 300 kg / mm ² or more, 200 ° C.
The film-form amorphous silicon solar cell according to claim 1, wherein the heat-resistant synthetic resin film having a heat shrinkage ratio of 2% or less is used. 4. The strength as a film substrate is 18 kg / m.
m ² or more, elastic modulus is 300 kg / mm ² or more, thermal shrinkage at 200 ° C. is 2% or less, and thermal expansion coefficient is 15 ×
10 ^-6, the film-like amorphous silicon solar cell according to claim 1 using a heat-resistant synthetic resin film is -2 × 10 ^-6 or more.