JPH08264818A - Amorphous silicon film solar cell - Google Patents

Abstract

PURPOSE: To provide a film solar cell excellent in flexibility and photoelectric conversion efficiency. CONSTITUTION: Within the solar cell wherein amorphous silicon thin film is provided as a photovoltaic element on a flexible film substrate, as for a film substrate, a thermal resistant synthetic resin film in thermal contraction coefficient at 200 deg.C not exceeding 2% wherein fine protrusions in level of 0.05-0.4μm exist at density of 50-1000pieces/μm<2> is adopted. Through these procedures, the flexible film solar cell in high utilization factor of incident light can be provided.

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 film solar cell with improved photoelectric conversion efficiency.

[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
No. 4, JP-A-55-29154, and the like. Also, those using an aromatic polyamide (hereinafter referred to as aramid) film or a polyimide film as a substrate are disclosed in JP-A-54-149489, JP-A-55-4994, JP-A-55-29154, JP-A-55-82474, JP-A-56-16
9372, JP-A-57-103839, JP-A-59-34677, and JP-A-59-88874.
JP-A-59-108368, JP-A-59-108368
-158571, JP-A-60-130867, JP-A-60-257183, and JP-A-61-1.
It is known from JP-A No. 624, JP-A No. 63-236372, JP-A No. 1-119072, and JP-A No. 1-309385.

When these films are used as a substrate, each of the necessary layers such as an amorphous silicon layer is continuously vacuum-deposited, sputter-deposited or plasma-glow-discharge while the film is sent out from a roll, processed, and then rewound on the roll. There is an advantage that it can be formed by. Further, unlike the conventional solar cell using a glass substrate, the obtained film-shaped solar cell can be freely bent, and its application can be expected to expand.

By the way, as a general problem of solar cells, there is an improvement in photoelectric conversion efficiency. One of the factors that lowers the photoelectric conversion efficiency is light absorption loss due to reflection of light on the silicon semiconductor surface. As a device to solve this,
There has already been proposed a solar cell in which an amorphous silicon layer is provided on a substrate having an uneven surface that reflects light repeatedly. For example, US Pat. No. 4,376,228
The use of a film with a parabolic cross-section is proposed in U.S. Pat. However, in this case, it is difficult to form the heat resistant film. In addition, JP-A-59
In Japanese Patent No. 14682, use of a chemically etched metal substrate is proposed, but it has not been practically used as a film. In addition, JP-A-60-201668
In the publication, use of a film formed in a corrugated shape with a sinusoidal cross section is proposed, but such a simple concavo-convex surface can be expected to provide unsatisfactory results from the viewpoint of multiple reflection of light.

The idea of providing a solar cell by providing an amorphous silicon layer on the above-mentioned substrate having an uneven surface is as follows.
As a reason for not being put to practical use in a film-shaped solar cell, it was difficult to form preferable unevenness in a film shape, and when an amorphous silicon layer was formed on the uneven surface, the silicon layer was easily peeled from the film, so that the solar cell There are problems such as a low yield and a large decrease in performance during use.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a film type solar cell having excellent flexibility and photoelectric conversion efficiency.

[0007]

The inventor of the present invention has been able to solve the above-mentioned problems.
The present invention has been reached as a result of intensive studies to overcome the drawbacks of the technology.
did. That is, the present invention is a photovoltaic device on a flexible film substrate.
Solar cell with amorphous silicon thin film as an element
Shrinkage as a film substrate at 200 ℃
The rate is 2% or less, and an amorphous silicon thin film is provided.
On the side of the film that has a height of 0.05 to 0.4 μm
50-1000 fine projections / μm ²Present in the density of
Characterized by using a heat-resistant synthetic resin film
It is a film-shaped amorphous silicon solar cell.

What is important in carrying out the present invention is to use a film having fine projections formed on the surface of the film on which the amorphous silicon thin film for forming a solar cell is provided (hereinafter referred to as a fine projection film). The fine protrusions have a height of 0.05 to 0.4 μm,
The density is more preferably 0.1 to 0.3 μm, and the density thereof is 50 to 1000 pieces / μm ² , and further preferably 10
The number is preferably 0 to 500 pieces / μm ² . Since the solar cell formed on this film has a thin amorphous silicon layer, etc., it shows a surface shape that is almost in line with the shape of the film surface. While complex multiple reflections on the solar cell surface,
It is absorbed by solar cells and can realize high conversion efficiency.

The film used in the present invention is required to have heat resistance to withstand the high temperature received during the formation of the amorphous silicon layer. As a measure of the heat resistance, if the heat shrinkage at 200 ° C. is 2% or less, The object of the present invention is achieved. In forming an amorphous silicon layer on the fine projection film of the present invention, the thermal expansion coefficient of the film is 10 × 10 ⁻⁶ or less, −2 × 10 ⁻⁶ or more, more preferably 7 × 10 ⁻⁶ or less, 0 or more. Is preferred. Here, the coefficient of thermal expansion is represented by an average value between room temperature and 300 ° C. If the coefficient of thermal expansion deviates from these ranges,
In the production of solar cells, when the formed amorphous silicon layer is cooled to room temperature, the dimensional difference from the film substrate becomes large and strain stress occurs, so peeling is likely to occur, and when used as a solar cell In addition, peeling may occur similarly due to repeated temperature fluctuations.

Further, the strength of the film used in the present invention is preferably 20 kg / mm ² or more, more preferably 25 kg / mm ² or more, and it is handled in processing or using the film-shaped solar cell. It is suitable for preventing damage at the time. The elastic modulus of the film is also 600 kg / mm ² or more, preferably from the viewpoint of preventing unnecessary deformation due to the force applied to the solar cell when processing or handling the film solar cell and preventing the destruction of the amorphous silicon layer. 8
It is preferable to use a material of 00 kg / mm ² or more.

The characteristics of these films should be satisfied in both the lengthwise direction and the widthwise direction, but they do not necessarily have to be the same, and may be so-called balanced type or uniaxial tension type. Good. As a 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 a unit selected from the group consisting of the following constitutional units. —NH—Ar ₁ —NH— (1) —CO—Ar ₂ —CO— (2) —NH—Ar ₃ —CO— (3) 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 the following.

[0013]

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In addition, some of the hydrogen atoms on the rings of 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 for producing the film used in the present invention.

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.

[0016]

Embedded image

Here, Ar ₄ and Ar ₆ in the above (1) and (2) contain at least one aromatic ring, and two carbonyl groups forming an imide ring are bonded to adjacent carbon atoms on the aromatic ring. are doing. This Ar ₄ is derived from an aromatic tetracarboxylic acid or its anhydride. The following are typical examples.

[0018]

Embedded image

Here, Y is --O--, --CO--, --CH ₂
-, - S -, - SO 2 - and the like. Ar ₆ is derived from tricarboxylic acid anhydride or its halide. Ar ₅ and Ar ₇ in the above (1) and (2) include at least one aromatic ring and are derived from aromatic diamine and aromatic isocyanate. The following are typical examples of Ar ₅ or Ar ₇ .

[0020]

[Chemical 4]

Here, one of the hydrogens on 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
In addition, Ar of the above (1) and (2)_Five, Ar₇More than 80%
Is a polyimide resin that is an aromatic ring bonded in the para position,
It is preferable for producing the film used in the present invention.

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 production method of the film of the present invention is not particularly limited, and a production method suitable for each resin may be adopted.

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, a tetracarboxylic acid anhydride and an aromatic diamine are reacted in an organic solvent to give a polyamic acid, and this solution is directly or once subjected to a ring-closing treatment to give a polyimide, which is again used as a 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 and cast onto a support such as a metal drum or 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 manufactured by washing the solvent, inorganic salt and the like in the film, subjecting them to treatments such as stretching, drying and heat treatment and winding them into a roll.

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. Further, the film may contain a lubricant, a colorant such as a dye or a pigment, a flame retardant, an antistatic agent, an antioxidant, and other modifiers, as long as they do not violate the object of the present invention. Good.

The method for producing the fine projection film of the present invention is, for example, a method of treating the film surface with low temperature plasma by glow discharge and etching, and as a more preferable example, the ions in the plasma generated by glow discharge are applied by a direct current high electric field. Examples thereof include, but are not limited to, a method of treating the film surface by a sputtering method of accelerating and colliding with an object (these are collectively referred to as a sputter etching method). Further, in these treatments, it is also a preferred embodiment that active molecules such as oxygen and water are allowed to coexist within a range that does not hinder glow discharge to promote decomposition of synthetic resin molecules on the film surface.

In practicing the present invention, after being processed by the sputter etching method, the film may be washed again if necessary. It is also one of the embodiments of the present invention that, following the sputter etching method for producing the fine projection film, the amorphous silicon solar cell described below is directly built on the film.

Next, a method for constructing an amorphous silicon solar cell on the above substrate film will be described. In order to obtain the amorphous silicon solar cell of the present invention,
First, the first conductive layer is formed on the film by 0.01 to 20 μm.
It is formed with the thickness of. As 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 sputtering method or a sputtering method.

After that, 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, pull out the film wound into a roll, and 200 to 400 ° C.
It is made to run on the support electrode heated to the above. S in the vacuum reactor
iH ₄ by applying a DC voltage or to several 10MHz high frequency voltage between the electrodes against the support electrode while feeding a gas, causing a glow discharge, is SiH ₄ by the vacuum reactor and a plasma state Decomposes to form an amorphous silicon layer on the film. At this time, SiH ₄
If B ₂ H ₆ is sent together with 0.5 to 5% by weight, a p-type silicon layer is formed, and if PH ₃ is sent together with SiH ₄ , an n-type silicon layer is formed.

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 heterojunction cell, indium oxide, tin oxide, indium tin oxide, and cadmium oxide layers are formed by sputtering or vacuum evaporation to a thickness of about 200 to 3000 angstroms.

Further, a collecting electrode is provided on the Schottky barrier metal / hetero electrode to complete the amorphous silicon solar cell. These vacuum deposition treatment, sputtering treatment, glow discharge treatment and the like can be carried out while continuously moving the film from roll to roll, or even if the film having a certain size is treated batchwise. May be

[0033]

EXAMPLES Examples of the present invention will be shown below, but it goes without saying that the present invention is not limited thereto. (Characteristic Measuring Method) The characteristic value measuring method of 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 by a constant speed elongation type strong elongation measuring machine (DSS-500 manufactured by Shimadzu Corporation) at a measuring length of 100 mm and a pulling speed of 50 mm / min. (2) Method of measuring heat shrinkage A sample piece of 2 cm × 5 cm was cut out from the film, 4c
Mark with scratches at m intervals with a knife and pre-set at 23 ° C, 5
After leaving in the atmosphere of 5% RH for 72 hours, the distance between the markers was read and measured with a microscope, and then left in a hot air oven at 200 ° C for 2 hours without being restrained, and then again at 23 ° C and 55% RH. After leaving it in the atmosphere for 72 hours,
The distance between the markers was determined by reading with a microscope. (3) Measuring method of thermal expansion coefficient Thermodynamic characteristic measuring machine (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.
Under 3 g, the temperature was once raised to 300 ° C. to remove the residual strain of the sample, and then cooled under a nitrogen stream, and the temperature was changed 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) Method for observing fine projections Gold having a thickness of 400 to 500 angstrom was vapor-deposited on the film surface to be observed, and the sample was set at a scanning electron microscope with an inclination of 45 degrees, and the acceleration voltage was 15 kV and the magnification was 40,000 times. Taken at, and measured from the photo. (5) Photoelectric conversion characteristic The photoelectric conversion characteristic was measured by a solar simulator manufactured by Oriel Co., Ltd., whose conversion efficiency was adjusted to AM = 1.

[0035]

Example 1 Polyparaphenylene terephthalamide (P
PTA) with 0.04 μm silica particles in advance in PPTA
In contrast, it was dissolved in 99.8% concentrated sulfuric acid dispersed by an ultrasonic stirrer so as to have a concentration of 0.3% by weight so that the polymer concentration became 12%, and cast from a die onto an endless belt. After heating and absorbing moisture on the belt at the same time, the dope is phase-converted from a liquid crystal phase to an isotropic phase, and then solidified in 45% sulfuric acid at 0 ° C., neutralized, washed with water, and 1.1 times the length and width. After stretching, it is dried with hot air using a clip tenter while maintaining a constant length, and then heat treated at 400 ° C. for tension, 350
It was wound up after free heat treatment at ℃.

The obtained PPTA film has a thickness of 50 μm and has 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 . When the presence or absence of fine protrusions was observed under the above conditions for this film, no fine protrusion was found.

This film was treated with an ion sputtering apparatus having electrodes having a diameter of 80 mm and an electrode distance of 45 mm under an argon gas atmosphere at a current of 10 mA and a vacuum degree of 0.1 Torr for 10 minutes. The obtained film was formed with fine projections having a height of 0.11 μm and a density of 340 / μm ² , and the mechanical properties of the film were that the strength was 32 and 33 kg / in the longitudinal direction and the width direction, respectively. mm
² , elongation 35, 33%, elastic modulus 933, 960 kg / m
m ² , 200 ° C., thermal shrinkage rate was 0.05, 0.05%, and thermal expansion coefficient was 4.1 × 10 ⁻⁶ and 4.0 × 10 ⁻⁶ .

This film was sputtered with a sputtering device.
Ten-less steel target with a thickness of 10 on the film
Forming a 00 angstrom layer of stainless steel
Was. Then, the above-mentioned treatment film is placed on a supporting electrode in a vacuum reactor.
Install the rum and once in the reactor 10^-FiveExhaust to Torr
Then, after raising the temperature of the supporting electrode to 300 ° C,
Apply 30W 13.56MHz high frequency voltage to the supporting electrode.
Argon gas was introduced into the vessel while adding, and the pressure was 1 Torr.
Pre-sputter in a Rugong atmosphere, then with hydrogen gas 1
SiH diluted to 0%_FourSimilarly, dilute to 1% with hydrogen gas
PH₃Introduce gas and make the atmosphere of 0.8 Torr.
200 angstrom n-type amorphous film on film
Form a silicon layer. Continuously, SiH_FourIntroduced only
And i-type amorphous with a thickness of 6000 angstroms
Laminate a silicon layer and further SiH _Four1% B in gas₂
H₆With a thickness of 200 angstroms
A p-type amorphous silicon layer of a membrane was formed.

Next, the film having the pin type amorphous silicon semiconductor layer formed thereon 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.

The photoelectric conversion efficiency of the obtained solar cell was 8.2.
%Met.

[0041]

Comparative Example 1 For comparison, Example 1 was carried out in exactly the same manner as Example 1 except that the PPTA film without fine projections before the sputter etching method was used. The photoelectric conversion efficiency of the obtained solar cell was 6.5%.

[0042]

Example 2 Kapton (trademark of Toray DuPont Co., Ltd.), which is a commercially available polyimide film, 200 V (thickness: 50 μm)
Using m), a sputter etching process was performed in the same manner as in Example 1 to manufacture a solar cell. Length direction of the film used,
Strength in each width direction is 18.5, 17.4 kg / mm
² , elongation 45.4, 47.9%, elastic modulus 390, 430
kg / mm ² , coefficient of thermal expansion 23 × 10 ^-6 , 20 × 10 ^-6
The same surface structure as in Example 1 was observed, and fine protrusions having a height of 0.09 μm and a density of 315 / μm ² were formed. When a solar cell was manufactured using this film, the solar cell obtained had a photoelectric conversion efficiency of 6.7%.
Met.

[0043]

[Comparative Example 2] For comparison, a solar cell was manufactured in the same manner as in Example 2 except that a polyimide film having no fine protrusions before the sputter etching method of Example 2 was used. The photoelectric conversion efficiency of the obtained solar cell was 4%.

[0044]

According to the present invention, since incident light can be efficiently absorbed on the surface of the solar cell, a solar cell having high photoelectric conversion performance can be provided. In addition, it is possible to avoid manufacturing yield defects due to peeling between the film substrate and the amorphous silicon layer, which also contributes to cost reduction, and there is no peeling due to repeated temperature changes during use, and stable performance is demonstrated for a long time. it can. Therefore, it can withstand long-term use in an outdoor environment and is effective for practical use of solar power generation. Further, the flexibility of the film solar cell can be combined with the application range of the solar cell.

Claims (3)

[Claims] 1. A solar cell in which an amorphous silicon thin film is provided as a photovoltaic element on a flexible film substrate, and the film substrate has a heat shrinkage factor of 2 at 200 ° C.
% Or less, and a heat-resistant synthetic resin film in which fine projections having a height of 0.05 to 0.4 μm are present at a density of 50 to 1000 pieces / μm ² on the film surface on the side where the amorphous silicon thin film is provided. A film type amorphous silicon solar cell characterized by being used. 2. The film-form amorphous silicon solar cell according to claim 1, wherein the fine projections of the heat-resistant synthetic resin film are formed by a sputter etching method. 3. The film-like amorphous silicon solar cell according to claim 1, wherein the heat-resistant synthetic resin film has a coefficient of thermal expansion of 10 × 10 ⁻⁶ or less and −2 × 10 ⁻⁶ or more.