JPS6284568A - Thin-film solar cell - Google Patents

Abstract

PURPOSE:To obtain a thin-film solar cell abounding with flexibility and having excellent optical conversion efficiency by using a specific biaxially oriented polyethylene-2,6-naththalene dicarboxylate film as a flexible substrate. CONSTITUTION:In a thin-film solar cell in which a photovoltage generating layer consisting of amorphous silicon is formed onto a flexible substrate, a biaxially oriented polyethylene-2,6-naphthalene dicarboxylate film 1, a thermal shrinkage factor thereof at 200 deg.C extends over 2.0% or less in all directions-that is, 1.355-1.390g/cm<3> density, is employed as said substrate. The PEN film having such characteristics can be acquired by thermally treating a film obtained through a normal manufacturing process. 210-250 deg.C, preferably, 230-245 deg.C, are used as the temperature of heat treatment, and several sec - several min are used as the treatment time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a thin film solar cell, and more particularly to an amorphous silicon film characterized by using a specific flexible thermoplastic polymer film as a substrate. Regarding type thin film solar cells.

[Prior art]

The amorphous silicon film constituting the photovoltaic generation layer of a solar cell is disclosed in Japanese Patent Application Laid-open Nos. 52-16990 and 56-104433.
No. 1-1 and No. 56-104433.
It is formed by a plasma glow discharge method, a sputter deposition method, or an ion blating method, and the film contains a small amount of hydrogen atoms (from 10 to 30 atoms), as well as third component atoms (-1 fluorine atoms, -1 fluorine atoms, Typical examples include those containing carbon atoms, nitrogen atoms, etc. Here, the term "amorphous silicon film" refers to a film containing a particle size of approximately 100 mm.
The term is used to include silicon films made of microcrystals of A or smaller.

The above-mentioned amorphous silicon film has an absorption coefficient for visible light that is one order of magnitude larger than that of single crystal silicon yK, and therefore, the film thickness required to effectively absorb and utilize sunlight can be set to 3 μm or less. This suggests that by providing a photovoltaic power generating layer made of the amorphous silicon film on a flexible substrate, it is possible to manufacture a thin film solar cell with a wide range of applicability that can be bent at will. ing.

In fact, an amorphous silicon thin-film solar cell based on a highly flexible plastic film has already been published in Japanese Patent Application Laid-Open No. 54
-149489, 55-4994 and 55-1
It is described in No. 54726.

However, in order to form a high-quality amorphous silicon film as a solar cell, a flexible plastic film of 20
It is said that heat resistance from 0 to 300°C is required, and from this point of view it has been proposed to use a heat-resistant polyimide film as a base (although these films contain solvents and adsorbed water). Therefore, when heated to a temperature range in which amorphous silicon films are laminated, the solvent and adsorbed water are released, contaminating the formed amorphous silicon film and interfering with the formation of a high-quality amorphous silicon film. Since these films are generally colored 1-, they must be used in a manner in which light is incident from the film side, which poses problems such as limiting their application form.

Therefore, the present inventors chose a polyethylene terephthalate film as a transparent plastic film to avoid problems such as release of solvent and adsorbed water even in the temperature range in which amorphous silicon films are laminated. Attempts were made to produce solar cells, but the film did not have sufficient heat resistance at the temperature at which amorphous silicon films were laminated (e.g., around 200°C), so it contracted due to heat, and cracks appeared in the formed amorphous silicon film. , it was practically difficult to use solar cells and L°C.

[Purpose of the invention]

The purpose of the present invention is to eliminate the above-mentioned drawbacks and provide a thin film solar cell that is highly flexible and has excellent light conversion efficiency.1. This is what we are trying to do. In particular, we have discovered a new flexible material that has no problems with transparency, heat resistance, and processability (silicon film formation, etc.) to serve as a substrate for thin-film solar cells, and have developed a practical flexible material. The present invention provides a thin-film solar cell with high properties.

[Structure of the invention]

The present invention provides a thin film solar cell in which a photovoltaic power generation layer made of amorphous silicon is formed on a flexible substrate, and the thermal shrinkage rate of the substrate at 200°C is 2.0 in all directions. %
or less, if necessary, the density is 1.355 to 1.390 f
/cd(r) A thin film solar cell characterized by using a biaxially oriented polyethylene-2,6-naphthalene dicarboxylate film.

Polyethylene naphthalate in the present invention refers to polyethylene-2,6-naphthalene dicarboxylate (hereinafter abbreviated as PEN) homopolymer, Ike's isomer polymer P
It refers to a copolymer or a mixture containing 70% by weight or more of EN, and also includes a low loss polyester composition that essentially has the properties of polyethylene 2,6-naphthalene dicarboxylate.

In the present invention, the substrate is a PEN film with a base and a substrate.
1. On top of that, 1 is necessary for solar cells! It may include laminated layers such as polar layers. Such an electrode layer is usually a υ metal layer.

The biaxially oriented PEN film in the present invention may be one manufactured by a known sequential biaxial stretching method (or a film manufactured by a simultaneous biaxial stretching method or a film manufactured using a simple testing device). It may be something that

A P film having such characteristics can be obtained by heat-treating a film obtained by a conventional manufacturing method at temperatures as low as K.degree. The temperature of the heat treatment (depending on the relationship with time and the method, but when it is carried out under a fixed length using a stenter) is 210°C to 250°C, preferably 230°C to 250°C.
The temperature is 45°C, and the processing time is from several seconds to several minutes.

Heat treatment can be carried out tension-free or under tension, but it is preferable to apply four-sided tension (7).On a small scale, the film can be fixed with a frame on all sides (industrially, it can be carried out using an unwinding roll, This can be achieved by applying tension in the traveling direction with a take-up roll or the like and fixing the width direction with a tenter.It is also possible to maintain a constant tension by fixing with a spring or the like.

The above PEN film can be heat treated before or after heat treatment.
Various undercoat layers can be provided on one or both sides as necessary.

The thickness of the film is preferably 25 to 500 μm for manufacturing and handling purposes.

Next, the present invention will be explained in detail with reference to the drawings.

A representative structure of a thin film solar cell obtained by the present invention using a flexible film as a substrate is shown in FIGS. 1 to 4. 1 in the figure is a PEN film.

2 is a metal layer that makes ohmic contact with the amorphous silicon film. This layer contains iron, chromium, titanium, tal/niobium, nickel, aluminum, cobalt, etc.
) Made of alloys such as gold M, nikpm, and stainless steel.

These can be applied in conjunction with the C. thin layer by physical or chemical methods. 3 and 4.5 are amorphous silicon films (as described above (including those made of microcrystals with a grain size of 100X or less). 1 should be provided. 3 is a group V atom, phosphorus (P) or arsenic (A3), at 100 ppp.
It is an n-type silicon layer containing m to 20,000 ppm, and makes ohmic contact with the metal layer 2. 5 is a group II atom such as boron (B), gallium (Ga) or aluminum (At) at 100 ppm to 20,000 ppm
It is a P-type silicon layer containing m. In FIGS. 1 and 3, the n-type silicon layer and the P-type silicon layer 5 may be exchanged.

In order to form the silicon layers 3 to 5, the glow discharge method uses silane (Si&) gas or disilane (Si, H,) as a starting material and decomposes them by glue discharge to form a film. The n-type silicon layer of No. 3 has about 1% of PI (I or A3) with respect to Si.
Glow discharge is performed using a mixed gas containing H4. In this case, it may be diluted with a gas such as Arl+H8w. On the other hand, in the case of the P-type silicon layer 5, when adding boron, for example, a glow discharge may be performed using a mixed gas of SiH and approximately 1 tB of BtHs. In this case as well, it can be diluted and used in the same manner as above. The RF power in glow discharge and the pressure during discharge are appropriately selected depending on the required silicon film, but usually 1OTo.
It can be carried out under known conditions of rr or less, preferably 5 Torr or less. The substrate temperature is 100 to 300°C, preferably 200 to 270°C, particularly preferably 230 to 26°C.
It is 0°C.

In the sputtering method and ion blating method, hydrogen gas is introduced into the atmosphere in order to contain 10 to 30 atoms of hydrogen in the film, and hydrogen atoms compensate for dangling bonds in the silicon film (-1 electrical characteristics Improve - ¥1 - Meryo5.

1. Fluorine atom and third component atom. When introducing fluorine gas or silane trifluoride (SiF) gas: When introducing carbon atoms, use hydrocarbon molecules with 1 to 2 carbon atoms such as methane, ethylene, and ethane: Nitrogen atoms. When introducing, drilling gas or ammonia gas may be mixed with silane gas or hydrogen gas and deposited.

6 in the figure is the potential V! , is a wall-forming layer and has a thickness of 10 to 20
It is a metal thin film of 0x gold, -platinum, palladium, etc., or a 100-5000x thick transparent conductive film of tin oxide, indium oxide, cadmium stannate, etc. These potential barrier forming layers are preferably layers that transmit incident light easily and have a small surface resistance, such as a gold or platinum layer with a thickness of 50-150 K or a tin-topped indium oxide layer with a thickness of 300-1500 K. Preference 1. Yes.

7 in the figure is the collecting electrode, which can be used by vapor deposition method, spanner method, printing method, etc.
Various methods such as plating can be used.

In the figure, reference numeral 8 denotes a non-reflective coating layer, and an inorganic layer such as silicon oxide, titanium oxide, Kungesten oxide, etc. or a suitable organic layer can be used.

〔Effect of the invention〕

Since the thin film solar cell of the present invention uses a biaxially oriented P group film, there is no solvent or adsorbed water in the film, and unlike polyethylene terephthalate film, there are far fewer residual gases and oligomers. The amorphous silicon film is not contaminated over time after the thin film is formed.

In addition, the thermal shrinkage rate measured when left at 200°C for 1 hour is as low as 2.0% or less, and there is little dimensional change and no cranking occurs in the amorphous silicon film.
It can exhibit the characteristics of thin-film solar cells, which are highly flexible and have excellent light conversion efficiency.

In addition, since the substrate temperature during silicon film formation can be raised to around 250°C, the range of film formation conditions that can be selected is expanded when using a curved thermoplastic polymer film as the base material, and high conversion efficiency can be achieved. A layered solar cell is obtained.

〔Example〕

The present invention will be described below based on Examples.

In addition, the heat shrinkage rate and density in this invention are measured by 1- as follows.

(1+ heat shrinkage rate tension II- means the rate of length reduction when held at 200℃ for 1 hour12, for example, in the length direction (MD) and width direction (TD) of the film, the length is Prepare samples 1-1 Hold one side of each sample with a clip, etc.
Hold at 200℃ for 1 hour in a tension-free state 1-,
Measure the length before and after the test to determine the shrinkage rate. When the length before the test is calculated and the length after the test is L, the shrinkage rate is calculated as m L Shrinkage rate (%) = -X 100 L.

(2) Density Measured at 25°C using a mixed solution of heptane and carbon tetrachloride using a density gradient tube method.

The unit is [t/dl].

Example 1. Comparative Example 1 Pellets of polyethylene 2.6 naphthalene dicarpoxylate (homopolymer) with an intrinsic viscosity of 0.65 were heated at 170°C.
The solid pellets were melt-extruded at 300°C using a T-shaped die according to a conventional method, and then stretched 3.7 times in the machine direction at 130°C and 3.7 times in the transverse direction by a known sequential biaxial stretching method. 3.9 times elongation at 135℃ 12.Furthermore, 3 times elongation at 240℃
Heat set for 0 seconds to a thickness of 100μm O) PEN
A biaxially oriented film was obtained. A portion of this film was cut out, kept in a dryer at 200°C for 1 hour, and its heat shrinkage rate was measured.The shrinkage rate in the longitudinal direction (MD) of the film was 1. s%, shrinkage rate in film width direction (TD) is 1
．． It was 3 yen. Moreover, the density was 1.359 f/cn. Stainless steel (SUS 304) with a thickness of about 40 f) was provided as one metal electrode on the remaining σ) PF2N film by sputtering.

After fixing this film to a metal frame made of SUS 304 on all four sides, it was set in a glow discharge reactor and heated with argon yjl at a closing plate temperature of 200°C and a pressure of 0.6 Torr.
12! ! 13.56MH2C1) in air for 15 minutes
Cleaning was carried out by high frequency discharge. Then 10-” Tor
After evacuation to r, 10% silane gas diluted with hydrogen (S
ilL) and 2% boss' in gas (Ple) (SiH4 with 1% C1% PI(,);
r, high-frequency decentering was performed at a substrate temperature of 200° C., and an n-type silicon layer with a thickness of about 350° C. was provided on the stainless steel layer.

Next, the inside of the apparatus was evacuated, and only silane gas diluted with hydrogen was supplied to form a silicon layer of approximately 0.5 μm (1).

Furthermore, about 0.5-
A P-type silicon layer of about 150× was formed using high-frequency discharge at 1° C. and introduced into the reactor.

Next, indium oxide with a thickness of approximately 700× was provided on this P-type silicon layer by reactive vapor deposition. Further, silver was deposited in a comb shape on the indium oxide film to form a collecting TL electrode.

For comparison purposes, a polyethylene terephthalate (homopolymer) (abbreviated as PET) vent having an intrinsic viscosity of 0.65 was used, and the temperature conditions were appropriately changed to obtain a biaxially oriented polyethylene terephthalate film with a thickness of 100 μm. However, the heat setting temperature was 210°C.

In this case, the amount of heat shrinkage of the PET film at 200°C for 1 hour is 6.3% in the film length direction (MD).

The width direction (TD) was 5.9%. Also, the density is 1.3
At 96P/i, many cracks were observed on the film surface after the amorphous silicon layer was provided.

When forming the indium oxide layer, use a mask to
300 3 m square cells were placed on the same film, and the cells with the maximum conversion efficiency of 85 cm were considered as viable cells (
-I counted. Table 1 shows the number of survivors with and without heat treatment.

Table-1 Example 2. Comparative Example 2 The biaxially oriented PEN film of Example 1 with a thickness of 100 μm was cut into squares, the four sides were fixed and heat treated at 245° C. for 3 minutes, and a portion was cut to measure the heat shrinkage rate and density. Film Q heat shrinkage rate is 1 in both length and width directions.
．． At 0%.

The density was 1.37 Sl/m.

Similarly 1. Comparative Example 10 PET film at 240℃
After heat treatment for 1 minute, the heat shrinkage rate in the length direction is 1.4%.

A film having a width of 1.6% and a density of 1.402 t/- was obtained.

For these two types of films, the temperature of the substrate during silicon layer formation was changed to 200°C and 240°C, respectively, and the temperature was 1t! ! A solar cell was manufactured under the same conditions as in Example 1, and its cell characteristics were measured. 100 cell plates of 3 Pm square Q) The survival rate and the average conversion rate of 5 living cells are shown in Table 2.

Table 2 By using a PEN film as a substrate, the selection range of film forming conditions is expanded, and the conversion efficiency can be reduced.

Example 4 and Comparative Example 4 Heat setting was carried out by changing the heat setting temperature in Example 1, and samples were prepared in the same manner as in Example 1 and evaluated in the same manner as in 1-1. The results are shown in Table-3.

Table-3

[Brief explanation of drawings]

FIGS. 1 to 4 show structural examples of thin film solar cells obtained by the present invention. In the figure, 0) is a polyethylene-2,6-naphthalene dicarboxylate film, (2) is a metal layer, +31° +41
．． (51 is an amorphous silicon layer, (6) is a potential barrier forming layer, (7) is a collection electrode, and (8) is an anti-reflection coating layer.)

Claims (2)

[Claims] (1) In a thin film solar cell in which a photovoltaic generation layer made of amorphous silicon is formed on a substrate made of a flexible thermoplastic polymer film, the flexible substrate is heated at 200°C for 1
1. A thin film solar cell characterized by using a biaxially oriented polyethylene-2,6-naphthalene dicarboxylate film having a thermal shrinkage rate measured over time of 2.0% or less in all directions. (2) The density of the biaxially oriented polyethylene-2,6-naphthalene dicarboxylate film is 1.355 to 1.39.
The thin film solar cell according to claim 1, which has a thickness in the range of 0 g/cm^3.