JPH0294574A - Flexible solar cell sheet - Google Patents

Abstract

PURPOSE:To obtain a solar cell sheet in which the quantity of incident light is increased without loss of its flexibility by utilizing the merit of capability of winding of a flexible substrate, and employing a polymer film in which its face in contact with an air layer is roughed as a window member. CONSTITUTION:A PET film having heat resistance necessary for depositing amorphous silicon and 100mum of thickness is employed as a flexible substrate 21 to form an integrated amorphous solar cell in which three rows of cells 20a are aligned in series. Leads 29a, 29b made of copper foils are attached to both ends of the cells 20a to obtain a solar cell unit sheet 20. Then, a roughed polymer film 40 is laminated as a window member, and a solar cell sheet 20 sealed at its periphery is manufactured. The sheet 10 in which a roughed FET film with ionomer formed with an ionomer layer is laminated on the front side (on the solar cell) of the sheet 20, i.e., window is manufactured. Thus, the output of the flexible solar cell can be improved.

Description

[Detailed Description of the Invention] Field of Application] The present invention is a flexible solar cell sheet that can be rolled up and expanded, and more specifically, it is used to improve the light diffusion transmittance of a window member used to protect a window. This invention relates to a flexible solar cell sheet that increases the output of solar cells and makes it easy to carry.

[Prior Art] The output obtained from a thick IN pond largely depends on the amount of incident light, that is, the area of incidence. In other words, in order to obtain a large amount of electric power, a solar cell with a corresponding area is required. From this viewpoint, a portable solar battery power source has been proposed in Japanese Patent Application Laid-Open No. 117472/1983.

In this publication, a flexible thin film solar cell is rolled up and stored, and unfolded when used. However, the output of a solar cell is determined by the incident area when it is unfolded, but in flexible solar cells, the thickness of epoxy resin, acrylic resin, etc. is 10 to 20 μm.
Since the window member is coated with a transparent protective film having a coating thickness of about 100 m, the vertical transmittance of the window member is high. However, in the case of an amorphous solar cell, it is effective to increase the diffuse transmittance in order to lengthen the optical path length in the amorphous silicon layer. Moreover, since the vertical reflectance of the protective film is higher than the diffuse reflectance, there are drawbacks such as a decrease in the amount of incident light and a lack of mechanical buffering effect as a protective film.

On the other hand, in order to increase the amount of light incident on window members,
There is a proposal for an electrode substrate in Japanese Patent No. 2-57267.

In this publication, light reflection on the substrate surface is reduced by constructing a solar cell using a substrate on which a low-reflection layer is formed by leaching treatment on at least one of the two opposing surfaces of a glass plate. Therefore, it has high transmittance and can increase the amount of incident light. However, since it is a glass substrate, flexibility cannot be imparted to the solar cell. Further, the high transmittance disclosed in this publication is around 95% at a wavelength of 550 nm. However, in order to increase the output of solar cells, the present inventors believe that rather than forming a low reflection layer to obtain high transmittance, it is better to have the diffuse transmittance and diffuse reflectance within a certain range. It has been found that the amount of incident light can be increased.

[Objective of the Invention] The present invention was made in view of the current situation, and utilizes the advantage of being able to wind up a flexible substrate, and uses a polymer film with a roughened surface in contact with the air layer for the window member. The object of the present invention is to provide a solar cell sheet that can increase the amount of incident light without impairing its flexibility.

[Component 1 of the invention] The above objects are achieved by the invention as follows.

In other words, the present invention comprises a module sheet in which a film serving as a window is laminated on at least the light incident side of an amorphous silicon solar cell using a flexible substrate via a buffer adhesive film layer, and the window member has an air layer. The module sheet is made of a polymer film whose contact surface is roughened, the thickness of the module sheet is 1000 μm or less, and the bending rigidity of the module sheet is 100 Kg・mm2 or less in a sample of 5 bending widths. It is a flexible solar cell sheet.

As described above, the present invention forms an amorphous silicon solar cell on a flexible substrate, and furthermore, a window member made of a roughened polymer film having an uneven structure on the light incident side is coated with a thin buffer adhesive layer. The thickness of the solar cell sheet as a whole is 1000 μm or less, and the bending rigidity is 10
By stacking the layers so that it is less than 0Ky・mm2,
We have discovered that the solar cell sheet can maintain flexibility to be rolled up and unfolded, and can also increase the amount of light that enters the solar cell through the window member when unfolded.

The present invention will be explained in detail below.

The flexible film referred to in the present invention is electrically insulating.

It has the advantages of being bendable and being rolled up into a small diameter of several centimeters or less, being easy to process, and being lightweight. A polymer film such as a film is preferably used. From the above-mentioned point of view, the thickness is usually 30 to 300 microns.

In addition, as another embodiment of the flexible film, an insulated metal film in which an insulating film of polyimide resin or the like is provided on the surface of aluminum metal or stainless steel alloy foil having a thickness of about 25 μ'TrL to 100 μm can be similarly used. can.

Next, the thin film solar cells formed on these film substrates of the present invention are amorphous silicon solar cells that are thin and will not be damaged by bending. Amorphous silicon solar cells basically have a structure in which an amorphous silicon layer is sandwiched between electrode layers.

The electrode layer must be transparent to sunlight on the light incident side, and a known transparent electrode layer such as tin oxide, indium oxide, a mixed layer of both, or cadmium stannate can be used.

On the other hand, the metal electrode layer provided on the flexible substrate is made of Hedan, AQ, Ti, Pt, Ni, or stainless steel.

Single metals such as chromium and nichrome, and alloy metals can be used. Further, in some cases, a layer of an oxide such as a transition metal, carbon, titanium oxide, or indium Mide may be provided at the interface between these metal layers and the amorphous silicon layer for the purpose of improving the bonding between both layers.

In addition, the structure of the amorphous silicon layer includes pin, pin/pin, pin/Din/pin.
In addition to a multilayer tandem structure such as, a narrow bandgap or wide bandgap amorphous silicon semiconductor layer such as amorphous silicon germanium or amorphous silicon carbide can also be used as appropriate. Among them, the following integrated amorphous solar cells are preferably used in terms of bending durability.

That is, after dividing the power generation layer of a continuous amorphous silicon solar cell of a predetermined area formed on a long film substrate of a predetermined width into cells having an appropriate area by a laser scoring method or knife cutting method, are electrically connected to obtain an integrated solar cell. The method of electrically connecting the divided cells is not particularly limited as long as the upper electrode of one cell to be connected and the lower electrode of the other cell can be electrically connected, and connection with lead wires is possible. method, vacuum evaporation.

Known methods such as forming a connection layer made of a metal thin film by physical vapor deposition such as sputtering, and forming a connection layer made of a conductive resin layer by screen printing can be applied. Among them, productivity 1. From the equipment point of view, electrical connection by screen printing is preferably applied.

Such a method provides an integrated amorphous silicon solar cell on a flexible film substrate.

Further, in the present invention, a roughened transparent polymer film having an uneven structure on the surface is provided thereon for the purpose of increasing the amount of incident sunlight in addition to the conventional purpose of improving environmental resistance. This polymer film is provided with a buffer adhesive film layer interposed therebetween to prevent damage to the solar cell during lamination, bending, etc., and to relieve internal stress of the solar cell. As the transparent polymer film, films such as polyethylene terephthalate, polyethylene naphthalate, acrylate, polysulfone, and polycarbonate are used because they are transparent in the visible light region and have good weather resistance. The thickness of these materials is preferably 30 to 200 μm from the viewpoint of handling and maintaining flexibility.

By the way, the above-mentioned roughened transparent polymer film having an uneven structure on its surface increases the amount of incident sunlight. The sum of the ratios (RD) is 85
% or more and TD is preferably 70% or more. Such a roughened structure can be formed by mechanically etching the surface of the transparent polymer film by sandblasting, chemically etching it with a solvent that can dissolve the film, or further by embossing. This processing method forms irregularities with various shapes and sizes on the surface of the transparent polymer film, and the optical properties of the film include diffuse transmittance (TD), diffuse reflectance (RD), and vertical transmittance (Tv). >, vertical reflectance (Rv)
and the light absorption rate (A[) of the polymer film. The present inventors believe that in order to increase the amount of light incident on the solar cell, the total transmittance of the film (TD + Tv
) rather than increasing the optical path length in the amorphous silicon film, the sum of the diffuse transmittance (TD) and the diffuse reflectance (RD) (TD + Ro) of the film is large;
In addition, it has been found that a film having optical properties such as a large diffuse transmittance TD is effective. In order to exhibit such an effect, TD + Ro is at least 85%, preferably 95% or more, and TD is 70% or more, more preferably 75% or more.

The rough surface that provides such optical properties consists of conical protrusions formed closely on the surface, and the protrusions have a bottom diameter of 12 to 50 μm and a height of 0.3 to 0.0 μm of the diameter.
It consists of a large protrusion that is 7 times the diameter and a small protrusion that has a bottom diameter of less than 12 μm and a height of 0.3 to 0.7 times the diameter,
An uneven structure in which the area occupied by the large protrusions is 50% or more is suitable. A roughened polymer film having such an uneven structure is prepared by applying a polyhalogenated aliphatic alcohol to the surface of a polymer film such as a polyester film having a thickness of 30 to 200 μm for several minutes to several tens of minutes at a temperature around room temperature. It can be formed by bringing them into contact.

The polyhalogenated aliphatic alcohol has 3 carbon atoms
-7 aliphatic alcohols having 3 to 10 halogen atoms, and monohydric alcohols are particularly preferred.

Examples of the halogen atom include F and Cf, with F being particularly preferred.

Further, a known thermoplastic resin or the like is used as a buffer adhesive layer for bonding the roughened polymer film having the uneven shape and the amorphous silicon solar cell element on the flexible substrate. From the viewpoint of transparency, weather resistance, softening point, etc., such thermoplastic resins include ethylene/vinyl acetate copolymers,
Polyvinyl butyral, ionomer, and polyethylene resin are used singly or in combination. The thickness of this film is preferably thicker from the viewpoint of the above-mentioned function, utility, and durability, but thinner is preferred from the viewpoint of flexibility, and 20 to 300 μm is suitably used. These buffer adhesive film layer and polymer film layer are laminated by a so-called lamination method, etc., by passing the amorphous silicon solar cell of the above-mentioned film substrate between heating rolls to produce a desired solar cell sheet.

In addition, if necessary, on the opposite side of the flexible substrate, a moisture-proof film made by laminating a polymer film such as a polyester film or a corrosion-resistant aluminum metal foil with a polyester film as a back protective film layer. It may be provided for the purpose of improving environmental resistance. These are laminated by a laminating method or the like via the buffer adhesive layer made of thermoplastic resin, similar to the polymer film layer on the front side.

By laminating both the front and back film layers so that they are larger than the amorphous silicon solar cell, it is possible to seal the edges of the amorphous solar cell, which is preferable because the durability is further improved.

Next, bending rigidity, which is a physical property value representing flexibility used in the present invention, will be explained. Bending stiffness (S) is Young's modulus (E)
It is the product of the moment of inertia of area (Iz), and by using the beam method with both ends supported, a load is placed at the center of the beam! The following relationship holds true with the deflection (y) when (P) is applied.

S=E Iz=PJl13/48y Here is the distance between the supporting points at both ends.

In other words, the bending rigidity (S) can be determined by measuring the deflection at the center of the beam when a load is applied thereto.

The present invention is characterized in that the solar cell characteristics and appearance do not change even when rolled up or unfolded, and for this purpose, the bending rigidity of the 5M wide module must be 100 Kg・mm2 or less,
Preferably, it needs to be 10 kg/mm2 or less.

The solar cell sheet of the present invention comprises a flexible film substrate, a thin film solar cell formed thereon, a roughened polymer film layer having an uneven structure on the surface of a buffer adhesive film layer 1, and in some cases a back protective film layer. However, the thicker each layer is, the greater the bending rigidity becomes. Separate mechanical η properties such as Young's modulus differ depending on the material, and it is not possible to unambiguously determine the thickness of each layer, but in order to roll it up to a small diameter on the order of several crrr without any problems, the bending rigidity of the module as a whole must be 100 Kg・mm2 or less. Therefore, the film thickness of the entire module must be 1000 μm or less, and more preferably the film thickness is 400 μm or less.

A roughened polymer film with a buffer adhesive film layer is preferably used for covering the roughened polymer film layer, and a roughened polyester film with an adhesive will be described as an example thereof. Various thicknesses can be considered for both film thicknesses, but for example, polyethylene terephthalate (
Roughened PET (50μm>
/Adhesive (50μTrL), roughened PET (100μ
m)/adhesive (200 μm) is used.

As mentioned above, the roughened PET film plays the role of a protective film layer against the environment and also increases the amount of incident light and increases the output of the solar cell, and the adhesive acts as a buffer adhesive film layer. At the same time, it serves as an adhesive layer for thermocompression bonding the film layer to the solar cell, and at the same time, the current extraction electrode and the outermost layer of the solar cell that are present on the surface of the solar cell are not destroyed during thermocompression bonding. It also plays the role of a buffer layer to relieve stress.

The thickness of each layer is selected based on these effects, depending on the degree of bending rigidity and the degree of resistance to environmental changes, and is appropriately selected depending on the intended use and location.

The flexible module thus obtained may be laminated onto a flexible base material such as cloth or metal foil, if necessary. For example, when used as a flexible blind, rolled up when not generating electricity, and unfolded when generating electricity, by laminating it on fabric, people in the room can only see the fabric surface, creating a natural environment. be able to.

Next, the present invention will be explained by examples. The bending rigidity was measured using a 5 s wide module using a beam method with both ends supported at 21 m+ intervals.

Examples 1-3. Comparative Example 1 FIG. 1 shows a side sectional view of the solar cell unit sheet used in the example. Although a polymer film is used as the flexible substrate 21 shown in the figure, any polymer film having the heat resistance necessary for amorphous silicon deposition may be used, but polyethylene terephthalate (PET) is preferable. Film, polyimide film, etc. are used.

In this example and the comparative example, a PET film with a thickness of 100 μm is used.

As the metal electrode layer 22, an An/SUS laminate was used, in which an approximately 0.5 μm thick layer and a stainless steel (SLJS) layer of approximately 30 layers were sequentially deposited on the substrate 21 using a sputtering method.

The amorphous silicon semiconductor layer 23 of the photovoltaic layer is a well-known Pi
An n-type structure was adopted and deposited on the stainless steel layer of the metal electrode layer 22 using a glow discharge decomposition method using silane gas or the like similar to that disclosed in JP-A-59-34668.

Next, the cells 2 are marked with a predetermined pattern using the laser scribing method.
The amorphous silicon semiconductor layer 23 is used as an electrically insulating patterned insulating resin layer 25 provided at the interface between the amorphous silicon semiconductor layer 23 and the transparent electrode layer 24 to prevent short circuit between electrodes when dividing into 0a. Epoxy resin was previously applied on the groove portions to be divided into cells 20a using a laser using a screen printing method.

Next, indium oxide (ITD) is used as the transparent electrode layer 24.
Approximately 600 pieces of 11 were deposited by sputtering, and P E T // A u / S LJ S /l
A large area amorphous M film solar cell having an amorphous silicon pin patterned epoxy resin layer/ITO structure was obtained.

Next, this PET//l/5LIS/amorphous silicon pin/patterned epoxy resin layer/■ TO structure amorphous solar cell with a 103 x 10 (:II square) cell was heated with a YAG laser using an epoxy resin rfill. The above-mentioned insulating resin layer 25 consisting of is scanned, and one part of the parallel insulating resin layer is melted and evaporated to remove only the metal electrode layer 22 and the other part is the transparent electrode layer 24. A dividing groove was formed to divide the cells 20a into three approximately 3cIR x 10α square cells 20a.In order to connect these three divided cells 20a in series, a part of the bus bar and a finger were connected as is known. A collecting electrode 21 made of a comb-shaped conductive ink having a section was provided on the cell 2Oa using a screen printing method.Then, a laser beam was irradiated to the connection point 28 of one part of the bus bar to separate the adjacent cells 20a. The collector electrode 27, that is, the transparent electrode 24, and one metal electrode layer 22 were fused and connected to establish an electrical connection, and an integrated amorphous solar cell with three cells 20a connected in series was fabricated.
Leads 29a and 29b made of copper foil were attached to both sides of the solar cell unit sheet 20 to obtain a solar cell unit sheet 20.

Subsequently, a roughened polymer film layer 40 is laminated as a window member through the buffer adhesive film layer 30 below so that the surface in contact with the air becomes a rough surface, and the surrounding sealed solar panel shown in FIG. A battery sheet 10 was manufactured and evaluated. That is, in Example 1, a 50 μm thick PET film roughened by sandblasting was used as the roughened polymer film 40, and a 50 μm thick ionomer layer was formed as the buffer adhesive film layer 30 on the smooth side of the ionomer film. In Comparative Example 1, a roughened PET film was coated on the front side (on the solar cell) of the unit sheet 20, that is, on the window part.
A solar cell sheet 10 was manufactured by laminating the same smooth PET with ionomer on the front side of the unit sheet 20 using μ-thick PET without roughening. In addition, as Example 2, PE with a thickness of 150 μm is placed on the front side of the unit sheet 20.
The T film was etched by contacting the surface with hexafluoroisopropanol for 3 minutes or more, and the roughened PET was used as the protective film layer 40, and EVA (ethylene-vinyl acetate copolymer) with a thickness of 150 μm was formed. A solar cell sheet 10 was manufactured by laminating the solar cell sheet 10 with a buffer adhesive film layer 30 formed of the following. Furthermore, as Example 3, a moisture-proof film was prepared by laminating an aluminum foil with a thickness of 25 μm on a commercially available PET film with a thickness of 50 μm, with an EVA buffer adhesive film layer 30 having a thickness of 250 μm interposed on the back side of the solar cell sheet of Example 2. We produced a solar cell sheet laminated with the following as a back protective film layer.

In addition, as Comparative Example 2, in Example 1, the protective film layer 40 of the window portion was replaced with a roughened PET film of 1aa+
We manufactured a solar cell module using thick polycarbonate plates.

In addition, lamination was performed by passing between heated rolls at 130°C. Table 1 shows the measurement results of the total thickness 2 bending rigidity, optical properties at a wavelength of 550 nm, and short circuit current of each of these samples. Note that the total thickness is an approximate average value. The optical property is diffuse transmittance T.

and the sum of the diffuse transmittance TD and the diffuse reflectance Ro (T.

+Ro). The short-circuit current was expressed as a relative value with Comparative Example 1, which is a typical example of the conventional example, as 1.

Moreover, the rough surface of the window portion of each sample is as follows.

The roughened PET surface of sandblasting in Example 1 was several μm.
The rough surface had an irregular scale-like uneven structure of various sizes as shown below. The roughened PET obtained by etching the hexafluoroisobutylene panol of Examples 2 and 3 has an uneven structure consisting of densely formed conical protrusions, and the protrusions have a diameter of 12 μm to 4 μm.
With a bottom diameter of 0 μm, the height is 0.3 to 0.0 μm of this bottom diameter.
It was a rough surface consisting of 7 times larger protrusions and smaller protrusions, with the large protrusions occupying 50% or more of the area.

Table 1 The samples of Example 1.2 and Comparative Example 1 were wound around a paper tube having a diameter of 4α, and after being left for one day, the cell properties were measured, and no change was observed in the cell properties or appearance. In addition, in Example 3, it was difficult to wrap around a paper tube with a diameter of 4 cm, but it was easy to wrap around a paper tube with a diameter of 8 G.
Similarly, no changes in cell characteristics were observed.

In the module of Comparative Example 2, it was impossible to wrap it around a paper tube having a diameter of 10 cm.

Furthermore, the conversion efficiency as a flexible solar cell relates to the effective utilization rate of incident light. The improvement in the effective utilization rate results in an increase in the short-circuit current of the solar cell. Therefore, the effect of the window member having a roughened surface according to the present invention was evaluated using short circuit current. Comparative Example 1 is a typical example of the prior art, which uses a PET film with a smooth surface, has a total light transmittance (TD + TV ) of 91%, and has a short circuit current of 1 under a predetermined light irradiation. In Example 1, a PET film roughened by sandblasting as described above was used as a protective film for the window member, and although the total light transmittance (TD + Tv > was as low as 78%), the TD
+Ro = 87% and TO = 70%, which are large, resulting in an increase in the amount of incident light and a 4% increase in short circuit current. In addition, in Example 2.3, a PET film roughened by chemical etching was used as a protective film for the window member, and the total light transmittance (TD + Tv) was as low as 80%.
+Ro = 98% and TD = 78%, which is large, and the effective utilization rate of the incident light amount further increases, and the short circuit current increases by 8%.
The effectiveness of the window member of the present invention was demonstrated. As a result, we were able to improve the output of flexible solar cells.

[Brief explanation of drawings]

FIG. 1 is a side cross-sectional view showing the cross-sectional structure of a unit sheet of an amorphous silicon solar cell according to an example. 21: Polyethylene terephthalate film 22 Nialuminum/stainless steel layer 23: Amorphous silicon layer 24: Transparent electrode layer 25: Insulating resin layer 27: Collection electrode layer FIG. 2 shows Example 1
FIG. 20: Unit sheet 30: Buffer adhesive film layer 40: Protective film layer

Claims (1)

[Scope of Claims] 1. Consisting of a module sheet in which a film serving as a window is laminated on at least the light incident side of an amorphous silicon solar cell using a flexible substrate with a buffer adhesive film layer interposed therebetween; is a polymer film whose surface in contact with the air layer is roughened, and the thickness of the module sheet is 1
A flexible solar cell sheet having a thickness of 000 μm or less and a bending rigidity of 100 kg·mm^2 or less in a 5 mm wide sample. 2. The polymer film has a sum of diffuse transmittance (T_D) and diffuse reflectance (R_D) at a wavelength of 550 nm of 85% or more, T_D is 70% or more, and has a thickness of 30 μm.
2. The flexible solar cell sheet according to claim 1, which is a polymer film with a diameter of 5 m or more and 200 μm or less. 3. The polymer film consists of conical protrusions whose rough surfaces are closely formed, and the protrusions have a bottom diameter of 12
~50 μm, the polyester film mainly consists of large protrusions whose height is in the range of 0.3 to 0.7 times the diameter and small protrusions with a bottom diameter of less than 12 μm, and the area occupied by the large protrusions is 50% or more. The flexible solar cell sheet according to claim 2.