JP2005101513A - Condensing film and solar cell unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a repairable solar cell unit in which the light utilization rate (power generation efficiency) is enhanced. <P>SOLUTION: In the condensing film having one smooth surface and the other surface covered with a multiplicity of micro protrusions, the micro protrusions have a substantially identical conical or pyramidal shape, and they have a refractive index of 1.4 or above and are transparent. On the micro protrusion side of the condensing film 1a, a multiplicity of micro recesses being bonded complementarily to the micro protrusions are formed thus obtaining a condensing film (1a+2a) superposed with a mold film (becoming a mold for forming the protrusions of the condensing film) 2a having a refractive index lower than that of the condensing film 1a. The condensing film (1a+2a) with a mold film is laminated on the light receiving surface of a solar cell while directing the condensing film 1a side toward the solar cell 3 side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a concentrating film for solar cells, a condensing film with a mold film, and a solar cell unit (also referred to as a solar cell module). More specifically, incident light is efficiently introduced into solar cells. The present invention relates to a solar cell condensing film or a condensing film with a mold film that has high power generation efficiency and can be repaired, and a solar cell unit using the condensing film.

  In recent years, research on solar cells has been actively conducted as clean and non-depleting energy. Among various types of solar cells, single crystal silicon, polycrystalline silicon, or silicon crystal solar cells in which amorphous silicon is laminated on single crystal silicon dominate in terms of power generation efficiency, and the market share gradually increases. By the way, since a silicon crystal system is more expensive than an amorphous material, cost reduction is required for further spread. At present, it is unavoidable to reduce the cost by reducing the members used in the solar cell unit and the manufacturing cost, or improve the power generation efficiency and reduce the amount of the members to be used.

  A schematic view (cross-sectional view) of a conventional silicon crystal solar cell unit is shown in FIG. The protective glass 6 on the surface is made of tempered glass in consideration of impact resistance. In order to improve the adhesion with the sealing material, one surface is provided with an uneven pattern by embossing. The uneven pattern is formed on the inner side (that is, the lower surface of the protective glass 6 in FIG. 11), and the surface of the solar cell unit is smooth. Further, a sealing material (usually a resin mainly composed of ethylene vinyl acetate copolymer) 4 and a back film are provided on the lower side of the protective glass 6 to protect and seal the solar cells 3 (non-patented). Reference 1).

  It has long been known that there is a moth-eye (insect's eye) structure as one of the methods for efficiently taking in external light from all angles including an oblique direction while reducing reflection loss. In this method, a transparent shape such as a fine cone, a triangular pyramid, or a quadrangular pyramid is formed to reduce reflection loss and efficiently take in external light.

Yasuhiro Sasakawa, “Solar Power Generation”-Latest Technology and System, 2000, CMC Corporation

  However, the above-described conventional solar battery unit has a large refractive index difference between the solar battery cell 3 and the sealing material 4, so that light reflection occurs at the interface and light cannot be used efficiently. Moreover, the light-transmitting and low-cost ethylene vinyl acetate copolymer (EVA) used as the sealing material 4 cannot be removed once the solar battery cell 3 is sealed. For example, the solar battery cell 3 Even if there is a continuity failure at the electrical connection part, the entire solar cell unit must be replaced. The present invention is intended to solve such problems, and an object thereof is to provide a solar cell unit that can be repaired while improving the light utilization rate (power generation efficiency) in the solar cell unit.

[Summary of the Invention]
Although the above-mentioned fine moth-eye structure is considered to be a very effective technique for solar cells, when it is provided in the outermost layer of the solar cell, it is exposed to the outdoors for a long period of time to reverse the dirt. There is a risk of blocking the light. Further, in order to avoid this, when the both-eye structure is provided on the light receiving surface side inside the unit, the difference in refractive index from the sealing material (resin) sealing the solar battery cell 3 is small, and therefore efficient. External light cannot be taken in and it has hardly been adopted in the past. The inventors of the present invention have made various studies on incorporating the both-eye structure into the solar cell unit and have completed the present invention.

In the present invention, first, a condensing film used for a solar cell unit, that is,
One side is smooth and the other side is a condensing film formed so as to spread many fine convex parts,
Each of the fine convex portions has a substantially identical conical shape or polygonal pyramid shape, and
The condensing film 1a is characterized in that its refractive index is 1.4 or more and is transparent.

Further, the present invention provides a condensing film with a mold film used for a solar cell unit, that is,
A large number of fine concave portions are formed on the light condensing film 1a and the fine convex portion side of the light condensing film so as to complement (adhere completely to the fine convex portions) and adhere, and the refractive index is condensed. There is also provided a condensing film (1a + 2a) with a mold film having a smooth appearance, in which a mold film (a mold film serving as a mold for forming convex portions of the condensing film) 2a having a smaller refractive index than the film 1a is layered.

  The present invention also provides a solar cell unit in which the condensing film (1a + 2a) with the mold film is laminated on the light receiving surface of the solar cell with the condensing film 1a side being the solar cell 3 side. (See FIG. 1).

In the present invention, the light collecting surface 1a of the present invention is laminated on the light receiving surface of the solar battery cell with the smooth surface thereof facing the solar battery cell 3, and the sealing material is further laminated thereon. A battery unit is also provided.

  In any case, the solar cell unit usually has a protective glass 6 laminated on the light-collecting film side with an adhesive layer 7 interposed therebetween, and a sealing material 4 and a back film on the lower side of the solar cell 3. 5 are laminated (see FIG. 1).

[Detailed description of the invention]
As described above, the condensing film of the present invention is a condensing film formed so that one side is smooth and the other side is regularly laid with a large number of fine convex portions, and each of the fine convex portions is provided. The condensing film 1a is characterized in that it has a conical shape or a polygonal pyramid shape having substantially the same shape, and has a refractive index of 1.4 or more and is transparent.

  In order for external light entering from all angles to be efficiently introduced into the solar battery cell with little reflection loss, the condensing film preferably has a high refractive index, usually 1.4 or more, preferably 1.5-2. 6. In addition, a condensing film also plays the role of the sealing material in the conventional solar cell unit.

The smooth surface of the condensing film is usually bonded toward the solar cell, and the mold film (described later) used on the fine convex surface of the condensing film is left without being removed or sealed. Laminate the materials. Here, the refractive index of the mold film or the sealing material must be smaller than the refractive index of the condensing film. This is because external light entering from an angle is also efficiently introduced into the solar battery cell with little reflection loss.
The convex part of the condensing film having a large refractive index is directed to the mold film (or sealing material) side having a smaller refractive index, that is, the convex part of the condensing film having a large refractive index is spread on the mold film ( Alternatively, when facing the opposite side (that is, toward the solar cell side) of the sealing material, external light entering from any angle is efficiently introduced into the solar cell with little reflection loss. The refractive index of the mold film or the sealing material is preferably 1.4 to 1.6.

  Each of the fine convex portions formed so as to be spread on one side of the light-collecting film has a fine conical shape or a fine polygonal pyramid shape, and is usually a structure called a “moth-eye structure”. In the non-reflective structure, the narrower the apex angle, the more advantageous. However, in the present invention, the condensing film is sealed in the resin and further brought close to the solar battery cell, so the situation is different. In order to efficiently introduce incident light from any angle into the solar cell, it is advantageous that the apex angle is narrow. However, since the reflection loss is large at the interface between the condensing film and the solar cell, the apex angle is If it is too narrow, the reflected light leaks to the outside again. In order to reflect the reflected light again by the light collecting film and return it to the solar battery cell well, the apex angle should be wide. In the light collecting film in the present invention, it is necessary to adjust these two contradictory properties, and in the present invention, it was possible to find a preferable apex angle range. That is, the apex angle of the conical or polygonal pyramid is preferably 150 degrees or less, and more preferably 140 to 30 degrees.

  A more preferable shape of the fine convex portion formed on one side of the light collecting film is a fine quadrangular pyramid (pyramid shape). This is because the shape of the quadrangular pyramid (pyramid shape) can be easily formed so that convex portions having a uniform size can be spread without gaps, and the light collection efficiency in the solar cell surface can be further increased. In terms of mold processing, the number of cutting operations is small, which is advantageous.

  According to the literature, eg Hiroshi Toyoda; “Non-reflective periodic structure”, Optics, Vol. 32, No. 8, page 489 (2003), the size of the base is the value obtained by dividing the shortest wavelength to be used by the refractive index of the material. For example, when the refractive index is 2, the solar cell module has a thickness of about 175 nm. However, in order to obtain such a fine structure, processing accuracy is also required. Therefore, the size of the base is preferably 0.1 μm to 8000 μm, and more preferably 1 μm to 1000 μm. 0.1 μm is the lower limit that can guarantee the processing accuracy, and 8000 μm is the upper limit that ensures effective light collection efficiency.

Next, the material used for manufacture of the condensing film of this invention is demonstrated.
As the resin having a large refractive index used for the light collecting film, a resin that easily imparts a fine concavo-convex shape is preferably used. As such a resin, in addition to a UV curable resin (described later) used for a mold film, A thermoplastic resin that flows by heating or pressurization can be used. For example, natural rubber (refractive index (hereinafter also referred to as n) = 1.52), polyisoprene (n = 1.521), poly-1,2-butadiene (n = 1.50), polyisobutene (n = 1) .505 to 1.51), polybutene (n = 1.513), poly-2-heptyl-1,3-butadiene (n = 1.50), poly-2-t-butyl-1,3-butadiene ( n = 1.506), (di) enes such as poly-1,3-butadiene (n = 1.515),

Polyoxyethylene (n = 1.456), polyoxypropylene (n = 1.450), polyvinyl ethyl ether (n = 1.454), polyvinyl hexyl ether (n = 1.659), polyvinyl butyl ether (n = 1) .456) and the like,
Polyesters such as polyvinyl acetate (n = 1.467) and polyvinyl propionate (n = 1.467);

  Polyurethane (n = 1.5-1.6), ethyl cellulose (n = 1.479), polyvinyl chloride (n = 1.54-1.55), polyacrylonitrile (n = 1.52), polymethacrylo Nitrile (n = 1.52), polysulfone (n = 1.633), polysulfide (n = 1.6), phenoxy resin (n = 1.5-1.6), polyethyl acrylate (n = 1.469) ), Polybutyl acrylate (n = 1.466), poly-2-ethylhexyl acrylate (n = 1.463), poly-t-butyl acrylate (n = 1.464), poly-3-ethoxypropyl acrylate (n = 1.465), polyoxycarbonyltetramethacrylate (n = 1.465), polymethyl acrylate (n = 1.472-1.480), polyisopropyl Methacrylate (n = 1.473), polydodecyl methacrylate (n = 1.474), polytetradecyl methacrylate (n = 1.475), poly-n-propyl methacrylate (n = 1.484), poly-3, 3,5-trimethylcyclohexyl methacrylate (n = 1.484), polyethyl methacrylate (n = 1.485), poly-2-nitro-2-methylpropyl methacrylate (n = 1.487), poly-1,1 -Poly (meth) acrylic acid esters such as diethylpropyl methacrylate (n = 1.490) and polymethyl methacrylate (n = 1.490) can be used.

  Two or more kinds of these acrylic polymers may be copolymerized as needed, or two or more kinds may be blended and used.

  Furthermore, as copolymer resins of acrylic and other than acrylic, epoxy acrylate (n = 1.48 to 1.60), urethane acrylate (n = 1.5 to 1.6), polyether acrylate (n = 1.48) To 1.49), polyester acrylate (n = 1.48 to 1.54), and the like can also be used. In particular, urethane acrylate, epoxy acrylate, and polyether acrylate are excellent from the viewpoint of adhesiveness.

As epoxy acrylate, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, allyl alcohol diglycidyl ether, resorcinol diglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, polyethylene glycol diglycidyl ether And (meth) acrylic acid adducts such as trimethylolpropane triglycidyl ether, glycerin triglycidyl ether, pentaerythritol tetraglycidyl ether, and sorbitol tetraglycidyl ether.
A polymer having a hydroxyl group in the molecule such as epoxy acrylate is effective for improving the adhesion. These copolymer resins can be used in combination of two or more as required. The softening temperature of these resins is preferably 200 ° C. or less, and more preferably 150 ° C. or less from the viewpoint of handleability. Considering that the use environment temperature of the solar cell unit is usually 80 ° C. or lower and workability, the softening temperature of the resin is particularly preferably 80 to 120 ° C.

  In addition, it is preferable to use a resin having a weight average molecular weight of 500 or more for the condensing film. This is because when the molecular weight is 500 or less, the cohesive force of the resin composition is too low, and the adhesion to the adherend is reduced. You may mix | blend additives, such as a diluent, a plasticizer, antioxidant, a filler, a ultraviolet absorber, a tackifier, with the resin composition to be used as needed.

In order to increase the refractive index of the light collecting film, an inorganic material (inorganic fine particles) having a high refractive index can be dispersed in the resin composition. However, if the size of the inorganic fine particles dispersed in the resin is larger than the wavelength, light is scattered, which is counterproductive.
Examples of such inorganic fine particles include titanium oxide, zirconium oxide, zinc oxide, tin oxide, cerium oxide, antimony oxide, indium tin mixed oxide, antimony tin mixed oxide, and the like. Surface treatment may be performed with silica, zirconium oxide, higher fatty acid or the like.

  Further, in order to disperse these inorganic fine particles in the resin, a dispersant, titanate-based, aluminum-based, or silicon-based coupling agent may be used. Dispersants include, for example, Disperbyk-111, Disperbyk-110, Disperbyk-116, Disperbyk-140, Disperbyk-161, Disperbyk-162, Disperbyk-163, products supplied under the trade name of Disperbic of Big Chemie Japan. Disperbyk-164, Disperbyk-170, Disperbyk-171, Disperbyk-174, Disperbyk-180, Disperbyk-182, etc.

Kao's Acetamine 24, Acetamine 86, Cotamin 24P, Cotamin 86PW, Cotamin 60W, Cotamin D86P, Farmin CS, Farmin 08D, Farmin 20D, Farmin 80, Farmin 86T, Farmin O, Farmin T, Farmin D86, Farmin DM24C, Farmin DM0898, Farmin DM 1098, Farmin DM 2098, Farmin DM 2465, Farmin DM 2463, Farmin DM 2458, Farmin DM 4098, Farmin DM 4662, Farmin DM 6098, Farmin DM 6875, Farmin DM 8680, Farmin DM 8098, Farmin DM 2285, and the like.

  In addition, as titanate coupling agents, products provided by Ajinomoto Co. under the trade name Plenact, KR-TTS, KR-46B, KR-55, KR-41B, KR-38S, KR-138S, KR-238S, 338X, KR-44, KR-9SA and the like. Examples of the aluminum coupling agent include Plenact AL-M manufactured by the same company.

As described above, in addition to increasing the refractive index of the light collecting film by dispersing inorganic fine particles, an organic / inorganic hybrid material can also be obtained by using a sol-gel method. What is used in the sol-gel method is a metal alkoxide, water added if necessary, and an acid (or alkali) catalyst. The metal alkoxide is represented by the following general formula.
(R ¹ ) n-M- (OR ² ) m
Here, M is a metal selected from Ti, Zn, Zr, Al, Si, Sb, Be, Cd, Cr, Sn, Cu, Ga, Mn, Fe, Mo, V, W and Ce, preferably Ti , Zn or Zr. R ¹ is an organic group having 1 to 10 carbon atoms. R ² is an organic group having 1 to 10 carbon atoms. A plurality of R ¹ and R ² are bonded to M, but each may be the same or different. n is an integer of 0 or more, m is an integer of 1 or more, and n + m is equal to the valence of M. When obtaining an organic / inorganic hybrid material by the sol-gel method, the metal alkoxide used may be one kind or plural kinds.

In order to obtain an organic / inorganic hybrid material using the sol-gel method, a metal alkoxide, water, and an acid (or alkali) catalyst are added to a resin composition in a solution state, applied to a substrate, and the solvent is blown off. Obtained by heating. However, depending on the reactivity of the metal alkoxide chosen, water and / or acid (or alkali) catalysts may not be required. The heating temperature also depends on the reactivity of the metal alkoxide. A highly reactive material such as Ti requires neither water nor a catalyst, and the heating temperature may be about 100 ° C. In the present invention, (-MO-) three-dimensional crosslinking is not necessarily required, as long as a high refractive index can be realized.

Next, materials used for the mold film will be described.
The resin of the mold film used in the present invention is not particularly limited as long as it is transparent and has a refractive index smaller than that of the resin in the light collecting film, but a UV curable resin is preferable. The resin composition of the UV curable resin and the UV curing method are not particularly selected.

For example, in the curing method using a photoradical initiator, the resin composition comprises (A) a binder resin, (B) a crosslinkable monomer, and (C) a photoinitiator that generates free radicals by light.
Here, as the binder polymer of the component (A), a copolymer obtained by copolymerizing acrylic acid or methacrylic acid and their alkyl ester and other vinyl monomers copolymerizable therewith as a constituent monomer is used. These copolymers can be used alone or in combination of two or more. Examples of the alkyl acrylate ester or alkyl methacrylate ester include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and the like. Acrylic acid unsubstituted alkyl ester or methacrylic acid unsubstituted alkyl ester, acrylic acid substituted alkyl ester or methacrylic acid substituted alkyl ester in which a hydroxyl group, an epoxy group, a halogen group or the like is substituted on these alkyl groups.

  Examples of other vinyl monomers that can be copolymerized with acrylic acid, methacrylic acid, alkyl acrylate ester, or alkyl methacrylate ester include acrylamide, acrylonitrile, diacetone acrylamide, styrene, vinyl toluene, and the like. These vinyl monomers can be used alone or in combination of two or more. Moreover, it is preferable that the weight average molecular weight of the binder polymer of (A) component is 10,000-300,000 from the point of coating-film property, coating-film strength, and developability.

  As the component (B), for example, dicyclopentenyl (meth) acrylate; tetrahydrofurfuryl (meth) acrylate; benzyl (meth) acrylate; a compound obtained by reacting a polyhydric alcohol with an α, β-unsaturated carboxylic acid (For example, polyethylene glycol di (meth) acrylate (having 2 to 14 ethylene groups), trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane ethoxytri (meth) acrylate , Trimethylolpropane propoxytri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, tetramethylolmethanetetra (meth) acrylate, polypropylene glycol di (meth) acrylate (number of propylene groups 2-14), dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, bisphenol A polyoxyethylene di (meth) acrylate, bisphenol A dioxyethylene di (meth) acrylate, bisphenol A Trioxyethylene di (meth) acrylate, bisphenol A decaoxyethylene di (meth) acrylate, etc.);

Compounds obtained by adding an α, β-unsaturated carboxylic acid to a glycidyl group-containing compound (for example, trimethylolpropane triglycidyl ether triacrylate, bisphenol A diglycidyl ether diacrylate, etc.); a polyvalent carboxylic acid (for example, anhydrous Phthalic acid) and an esterified product of a substance having a hydroxyl group and an ethylenically unsaturated group (for example, β-hydroxyethyl (meth) acrylate); an alkyl ester of acrylic acid or methacrylic acid (for example, (meth) acrylic acid methyl ester, (Meth) acrylic acid ethyl ester, (meth) acrylic acid butyl ester, (meth) acrylic acid 2-ethylhexyl ester); urethane (meth) acrylate (for example, tolylene diisocyanate and 2-hydroxyethyl (meth) acrylic ester) Reactant, a reaction product of trimethylhexamethylene diisocyanate and cyclohexanedimethanol and 2-hydroxyethyl (meth) acrylate and the like) can be mentioned of.

Particularly preferred components (B) include trimethylolpropane tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and bisphenol A polyoxyethylene dimethacrylate. In addition, the said compound is used individually or in combination of 2 or more types.
In particular, in the light collecting film, it is necessary to increase the refractive index. To this end, it is advantageous that the component (A) and / or the component (B) contain bromine and sulfur atoms. Examples of the bromine-containing monomer include New Frontier BR-31, New Frontier BR-30, and New Frontier BR-42M manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Examples of the sulfur-containing monomer composition include IU-L2000, IU-L3000, and IU-MS1010 manufactured by Mitsubishi Gas Chemical Company. However, the bromine and sulfur atom-containing monomers (polymers containing them) used in the present invention are not limited to those listed here.

  As the component (C), a photoinitiator that generates a free radical by ultraviolet light or visible light is preferable. For example, benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isobutyl ether, benzoin phenyl ether, Benzophenones such as benzophenone, N, N'-tetramethyl-4,4'-diaminobenzophenone (Michler ketone), N, N'-tetraethyl-4,4'-diaminobenzophenone, benzyldimethyl ketal (Ciba Specialty Chemicals) Irgacure 651), benzyl ketals such as benzyl diethyl ketal, 2,2-dimethoxy-2-phenylacetophenone, p-tert-butyldichloroacetophenone, p-dimethyla Acetophenones such as noacetophenone, xanthones such as 2,4-dimethylthioxanthone and 2,4-diisopropylthioxanthone, or hydroxycyclohexyl phenyl ketone (Ciba Specialty Chemicals, Irgacure 184), 1- (4-isopropylphenyl) ) -2-vitroxy-2-methylpropan-1-one (Merck, Darocur 1116), 2-hydroxy-2-methyl-1-phenylpropan-1-one (Merck, Darocur 1173) and the like. These are used alone or in combination of two or more.

  Examples of the photoinitiator that can be used as the component (C) include 2,4,5-triallylimidazole dimer, 2-mercaptobenzoxazole, leucocrystal violet, and tris (4-diethylamino-2-methyl). Combinations with phenyl) methane and the like can also be mentioned. In addition, although there is no photoinitiation by itself, an additive that can be used as a sensitizer system with a better photoinitiation performance as a whole when used in combination with the above substances, such as triethanolamine for benzophenone, etc. Secondary amines can be used.

  A mold film (a mold film serving as a mold for forming convex portions of the light-collecting film) can be produced by the method described in JP-A-2002-225133. A specific manufacturing example will be described later (see FIG. 2).

  The light collecting film of the present invention is novel. Further, by applying the light collecting film of the present invention to a solar cell unit, it is possible to improve the light utilization rate (power generation efficiency) in the solar cell unit and provide a repairable solar cell unit.

  Hereinafter, the present invention will be described more specifically with reference to the accompanying drawings.

(Example 1)
1. Preparation of photosensitive resin composition for mold film Hitaroid HA7885 (manufactured by Hitachi Chemical Co., Ltd.) as binder resin (component A): 50 parts by weight
FANCLIL FA-321M (manufactured by Hitachi Chemical Co., Ltd.) as a crosslinkable monomer (component B): 50 parts by weight, and IRGACURE 184 (manufactured by Ciba Specialty Chemicals) as a photoinitiator (component C): 3.0 A part by weight was dissolved in methyl ethyl ketone as an organic solvent to obtain a varnish (photosensitive resin composition). A film of this varnish was formed on a silicon wafer so as to have a thickness of about 5000 mm, and the refractive index was measured with an ellipsometer to be 1.48.

2. Production of Mold Film FIG. 2 shows a method for preparing a mold film. The previously prepared photosensitive resin composition was uniformly coated on a 25 μm thick polyethylene terephthalate (PET) film 8 and dried by a hot air convection dryer at 80 to 100 ° C. for about 10 minutes. To this, a mold having a shape in which a large number of fine pyramid-shaped protrusions having a base length of 50 μm and an apex angle of 120 ° can be spread on one surface is pressed, and ultraviolet rays are irradiated from the back side of the PET film, thereby forming a photosensitive resin composition After curing, the mold was peeled off. On the PET film 8, a mold film 2a obtained by copying the fine pyramidal protrusions of the mold was obtained.

3. Preparation of highly refractive resin composition for light collecting film Titanium oxide fine particles TTO-S-2 (manufactured by Ishihara Techno): 100 parts by weight, Farmin DM2465 (manufactured by Kao): 20 parts by weight, and butyl acetate: 76 parts by weight Then, it was mixed using a bead mill to obtain a dispersion. To 196 parts by weight of this titanium oxide fine particle dispersion, 714 parts by weight of Tuffy TF-4200 (manufactured by Hitachi Chemical Co., Ltd.) was added and stirred to obtain a highly refractive resin composition (thermoplastic resin) for a light collecting film. A film of this resin composition was formed on a silicon wafer so as to have a thickness of about 5000 mm, and the refractive index measured by an ellipsometer was 1.7.

4). Production of light collecting film FIG. 3 shows a method for preparing a light collecting film. On the PET film (base material) 8 is formed a mold film 2a having a concave portion obtained by copying the fine pyramid-shaped convex portion of the mold, and on the concave pattern, the highly refractive resin composition (heat (Plastic resin) was applied, passed through a hot air convection dryer at 80 to 100 ° C., and dried for about 10 minutes. The condensing film 1a was obtained on the mold film 2a on the PET film (base material) 8. From this, if only the base material 8 is peeled and removed, a condensing film with a mold film (1a + 2a) is obtained, and if the base material 8 and the mold film 2a are peeled and removed, the condensing film 1a is obtained.

  In addition, UV curable resin can also be used for a condensing film. FIG. 4 shows a method for preparing a light condensing film when a UV curable resin is used. A UV curable high refractive resin composition for a condensing film is directly applied onto the solar battery cell 3, and a mold film 2a (integrated laminate) formed on the PET film 8 is pressed from the UV curable high refractive resin composition. The resin is cured by irradiating ultraviolet rays from the film 8 side. On the photovoltaic cell 3, the condensing film 1a, the type | mold film 2a, and PET film 8 are laminated | stacked in order.

5). Preparation of measurement sample A condensing film side of the film-equipped condensing film (1a + 2a) was thermocompression bonded so as to face a glass plate previously heated to 90 ° C. to obtain a measurement sample.

6). Measurement of transmission and reflection spectra The transmission and reflection spectra were measured using a spectrophotometer V-570 (manufactured by JASCO Corporation) equipped with an integrating sphere as an attachment. Light was incident from the front side (light collecting film side) and the back side (glass side), and the transmission spectrum and reflection spectrum transmission were measured. FIG. 5 is a schematic diagram of the used transmission spectrum measuring apparatus, and FIG. 6 is a schematic diagram of the used reflection spectrum measuring apparatus. FIG. 7 shows the transmission spectrum of the measurement sample, and FIG. 8 shows the reflection spectrum of the measurement sample. Table 1 below shows the transmittance and reflectance at a wavelength of 580 nm.
The transmittance at a wavelength of 580 nm is 131.9% when the front surface (condensing film side) is the incident surface, and 76.8% when the rear surface (glass plate side) is the incident surface, and the wavelength is 580 nm. The reflectance in the film was 3.3% when the front surface (condensing film side) was the incident surface and 39.7% when the rear surface (glass plate side) was the incident surface (Table 1). .

7). FIG. 9 shows a condensing film (1a + 2a) with a mold film thermocompression-bonded to a glass plate 16 on a rotating stage that can be rotated around one point of a sample placed and fixed. The glass plate side was fixed so as to fit the detector. Further, the light from the halogen lamp (light source) was converted into parallel light using a lens, and a slit was provided so that the beam diameter was 2 mm. Assuming that the amount of received light at normal incidence in the absence of the sample is 100, the intensity of emission from the sample while changing the incident angle was 84% when the incident angle was 40 °.

8). Evaluation of repairability A condensing film with a mold film (1a + 2a) thermocompression-bonded to a glass plate 16 is immersed in acetone as it is, left at room temperature for 1 hour, and then the condensing film is peeled off. Without remaining, the condensing film could be peeled cleanly from the glass plate.
Further, a solar battery is formed by bringing an integral laminate of PET (base material), a condensing film with a mold film (1a + 2a + 8), an adhesive layer 7 and a protective glass 6 so that the condensing film surface side is in contact with the solar cell 3. Even when thermocompression bonding was performed on the cell 3, it was possible to exfoliate cleanly without remaining resin on the solar cell 3 under the above-described delamination conditions.

(Example 2)
Samples for measurement were prepared in the same manner as in Example 1 except that a mold having a shape capable of laying a large number of fine pyramid-shaped protrusions with a base of 30 μm and an apex angle of 90 ° on one surface was used at the time of mold film production. Then, when the output intensity dependency on the incident angle was measured, the output intensity was 84% when the incident angle was 40 °.

(Example 3)
A sample for measurement was prepared in the same manner as in Example 1 except that a mold having a shape capable of spreading a large number of fine pyramid-shaped protrusions with a base of 20 μm and an apex angle of 60 ° on one surface was used at the time of mold film production. Then, when the output intensity dependency on the incident angle was measured, the output intensity was 85% when the incident angle was 40 °.

Example 4
Samples for measurement were prepared in the same manner as in Example 1 except that a mold having a shape capable of laying a large number of fine pyramid-shaped protrusions having a base of 10 μm and an apex angle of 40 ° on one side was used at the time of mold film production. Then, when the output intensity dependency on the incident angle was measured, the output intensity was 85% when the incident angle was 40 °.

(Example 5)
For measurement by the same method as in Example 1 except that 98 parts by weight of the titanium oxide fine particle dispersion and 714 parts by weight of Tuffy TF-4200 (manufactured by Hitachi Chemical Co., Ltd.) were used at the time of preparing the high refractive resin composition. When a sample was produced and the output intensity dependency on the incident angle was measured, the output intensity was 84% when the incident angle was 40 °. A film of this resin composition was formed on a silicon wafer so as to have a thickness of about 5000 mm, and the refractive index was measured with an ellipsometer to be 1.6.

(Example 6)
For the measurement by the same method as in Example 1, except that 20 parts by weight of the titanium oxide fine particle dispersion and 714 parts by weight of Toffy TF-4200 (manufactured by Hitachi Chemical Co., Ltd.) were used at the time of preparing the high refractive resin composition. When a sample was prepared and the output intensity dependency on the incident angle was measured, the output intensity was 81% when the incident angle was 40 °. A film of this resin composition was formed on a silicon wafer so as to have a thickness of about 5000 mm, and the refractive index was measured with an ellipsometer to be 1.5.

(Example 7) Preparation of highly refractive resin composition for condensing film using sol-gel method 5 Irgacure 187 (manufactured by Ciba-Geigy Corporation) with respect to 100 parts by weight of polyset DH-75C-2 (manufactured by Hitachi Chemical Co., Ltd.) Part by weight and 100 parts by weight of titanium tetraisopropoxide were added and stirred for 1 hour. When this was coated on a silicon wafer and exposed at 1000 mJ / cm ² using a high-pressure mercury lamp, the refractive index was measured using an ellipsometer and found to be 2.2.
A sample for measurement was produced from this resin composition in the same manner as in Example 1 and the dependency of the emission intensity on the incident angle was measured. When the incident angle was 40 °, the emission intensity was 87%.

(Comparative Example 1)
The transmission and reflection spectra were measured using the glasses used in Examples 1-6 as they were. The transmittance and reflectance at a wavelength of 580 nm were 91.4% and 8.6%, respectively (see Table 1).

(Comparative Example 2)
A sample for measurement was prepared by the same method as in Example 1 except that a mold was not used at the time of forming the mold film, and the dependency of the emission intensity on the incident angle was measured. When the incident angle was 40 °, The emission intensity was 75%. Table 2 summarizes these results.

(Comparative Example 3)
Glasses were thermocompression bonded at 150 ° C. and 1 MPa using EVA as a filler for solar cells. Although this was immersed in acetone, glass was not able to be peeled off. In addition, it was immersed in toluene, xylene, n-methylpyrrolidone and dimethylacetamide in the same manner, but none of them could be peeled off.

1 is a schematic view (cross-sectional view) of a solar cell unit according to an embodiment of the present invention. Process drawing which manufactures a mold film. Process drawing which manufactures a condensing film. The another manufacturing process figure of the solar cell unit which formed the condensing film on the light-receiving surface. Schematic of a transmission spectrum measuring apparatus. Schematic of a reflection spectrum measuring apparatus. The transmission spectrum of the condensing film of Example 1. FIG. The reflection spectrum of the condensing film of Example 1. Schematic of the measuring apparatus of output intensity incident angle dependence. The graph which shows the output intensity incident angle dependence of Examples 1-6 and Comparative Example 2. FIG. Schematic (cross-sectional view) of a conventional solar cell unit.

Explanation of symbols

1: High refractive index resin 1a for condensing film: Condensing film (high refractive index resin; after solidification or curing)
2: Resin for mold film 2a: Mold film (after solidification or curing)
3: Solar cell 4: Sealing material (filler)
5: Back film 6: Protective glass 7: Adhesive layer 8: Base material (PET) film 9: Mold 10: Sample 11: Detector 12: Integrating sphere 13: Lens 14: Slit 15: Rotating stage 16: Glass plate

Claims (10)

One side is smooth, and the other side is a condensing film formed so as to spread many fine protrusions,
Each of the fine convex portions has a substantially identical conical shape or polygonal pyramid shape, and
A condensing film having a refractive index of 1.4 or more and being transparent. The condensing film according to claim 1, wherein the apex angle of the conical or polygonal pyramid is smaller than 150 degrees. The condensing film of Claim 1 or 2 whose shape of a fine convex part is a square pyramid. The condensing film in any one of Claims 1-3 whose length of the base of a square pyramid is 0.1 micrometer or more and 8000 micrometers or less. The light-collecting film according to claim 1, wherein the film material comprises a composite of a resin and an inorganic material having a high refractive index. The light-collecting film according to claim 1, wherein the composite of the resin and the inorganic material having a high refractive index is a composite obtained by causing a sol-gel reaction in the resin. The light collecting film according to any one of claims 1 to 6,
On the fine convex portion side of the condensing film, a large number of fine concave portions that are bonded in a complementary manner to the fine convex portion are formed, and a mold film whose refractive index is smaller than the refractive index of the condensing film is overlaid. Condensing film with mold film. The solar cell unit by which the condensing film with a type | mold film of Claim 7 is laminated | stacked by making the condensing film side into the solar cell side on the light-receiving surface of a photovoltaic cell. A solar cell unit in which the light-collecting film according to any one of claims 1 to 6 is laminated on the light-receiving surface of the solar cell with the smooth surface thereof facing the solar cell, and a sealing material is further laminated thereon. . The solar cell unit according to claim 8 or 9, wherein
A protective glass is further laminated on the light collecting film side,
A solar cell unit in which a sealing material and a back film are further laminated below the solar cell.

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