JP5532327B2 - Solar cell front plate member and solar cell module - Google Patents

Description

  The present invention relates to a transparent plate-like member disposed on the front surface of a solar battery cell (solar cell element) and a solar cell module using the plate-like member.

  FIG. 1 shows an example of the solar spectrum and the spectral sensitivity of a general solar cell. As can be seen from FIG. 1, solar cells usually have low sensitivity characteristics in the short wavelength band, and sunlight cannot be used effectively. For this reason, attempts have been made to improve the use efficiency of sunlight by converting light in the short wavelength band with low sensitivity characteristics into light in the long wavelength band with high sensitivity characteristics using wavelength conversion materials such as phosphors. .

  For example, in Patent Document 1 and Patent Document 2, a light guide plate is used, light is captured from the surface of the light guide plate, wavelength conversion is performed with a phosphor inside the light guide plate, and light is applied to solar cells arranged opposite to the side surface of the light guide plate. The technology to propagate is introduced. Patent Document 3 introduces a technique for arranging a fluorescent layer between a condenser lens and a solar battery cell.

JP-A-57-095675 JP-A-2-052470 JP 2003-086823 A JP-A-9-265015 Japanese Patent No. 3332922 Japanese Patent Publication No.52-5857 JP-A-6-186441 Japanese Patent Publication No.55-18882 Japanese Patent Laid-Open No. 7-27928 JP 2010-60891 A

  However, each technique has the following problems. That is, the light once absorbed by the phosphor does not preserve the traveling direction of the original light when it is emitted, and isotropically emitted, so a lot of light goes in a useless direction. As a result, the solar cell The light that does not reach the cell will increase.

  An object of the present invention is to control the direction of light that has been subjected to wavelength conversion by a phosphor, and to provide a transparent plate-like member that can more efficiently guide the wavelength-converted light to a solar cell, and the plate-like member. It is in providing the solar cell module using this.

  Thus, as a result of intensive studies, the present inventors have proceeded with the isotropically emitted light from the phosphor by dispersing the phosphor in a plate-like medium having a refractive index distribution in the thickness direction. It has been found that the direction can be controlled, and the light reaching the solar battery cell among the light isotropically emitted from the phosphor is increased.

  That is, the plate member according to the present invention is a transparent plate member, and the refractive index of one surface is higher than the refractive index of the other surface, and the refractive index is stepped along the thickness direction of the plate. It is characterized by changing continuously or continuously.

  Further, the plate-like member according to the present invention is a transparent plate-like member used for a solar cell, and contains at least one type of phosphor having different wavelengths of excitation light and emission light, and receives sunlight. A light incident surface, and an opposite surface opposite to the light incident surface in the thickness direction, the refractive index on the opposite surface side is higher than the high refractive index compared to the refractive index on the light incident surface side, The refractive index varies stepwise or continuously along the thickness direction.

  In one aspect of the present invention, the refractive index increases in a range from 1.40 to 1.70 from the light incident surface side toward the opposite surface side.

  In another aspect of the present invention, the phosphor is unevenly distributed on the opposite surface side in the thickness direction.

  Another aspect of the present invention is characterized in that, in the thickness direction, the concentration of the phosphor increases as the refractive index increases.

  Another aspect of the present invention is characterized by further containing an ultraviolet absorber, and the concentration of the ultraviolet absorber increases in the thickness direction as the refractive index decreases.

  The solar cell module according to the present invention includes the above-described plate-like member and solar cells arranged so as to face the opposite surface of the plate-like member.

  By carrying out the present invention, it is possible to obtain a transparent plate member having a refractive index distribution in which the refractive index changes stepwise or continuously along the thickness direction of the plate. In addition, it is possible to provide a solar cell module with improved utilization efficiency of sunlight.

It is a figure which shows the spectrum of sunlight, and the spectral sensitivity characteristic of a solar cell. It is a schematic cross section of a solar cell module to which a front plate according to the present invention is attached. It is a model figure of the optical simulation of the front plate concerning the present invention. It is a model figure of the optical simulation of the front plate concerning the present invention. It is the data which measured the refractive index distribution of the board produced in Example 1 with the interfaco interference microscope. 6 is a schematic view of a multilayer film produced in Example 2. FIG. It is an excitation-fluorescence spectrum of the plate produced in Example 3.

  Hereinafter, the transparent plate member according to the present invention will be described in detail with reference to the drawings, taking a front plate for a solar cell as an example. In the present specification, the term “transparent” means that light in at least a part of the wavelength band that contributes to power generation of the solar battery cell is transmitted.

  FIG. 2 is a schematic cross-sectional view of a solar cell module to which a solar cell front plate according to the present invention is attached. As shown in FIG. 2, the solar cell module is configured by arranging the front plate 10 so as to cover the entire cell surface of the solar cell 15. The front plate 10 has a refractive index distribution in which the refractive index changes stepwise or continuously along the thickness direction, and the side of the front plate where sunlight 20 enters is a low refractive index (low refractive index). Side 11), and the solar battery cell side has a high refractive index (high refractive index side 12). Further, the front plate 10 contains a phosphor 13 and emits emitted light 14 isotropically having a wavelength band different from the excitation wavelength with a predetermined wavelength band of sunlight 20 as an excitation wavelength. The thickness dimension of the front plate according to the present invention is not particularly limited, but is preferably in the range of 0.05 to 10 mm from the viewpoints of sunlight transmittance and the concentration of the phosphor to be added. When the thickness of the front plate is reduced, the sunlight transmittance tends to increase. Further, when the thickness of the front plate is increased, the amount of phosphor that can be added per area can be increased, and conversion efficiency tends to be improved. By setting the thickness of the front plate 10 to 0.05 to 10 mm, the front plate 10 can contain an amount of the phosphor 13 suitable for wavelength conversion while ensuring sunlight transparency.

  The phosphor 13 used in the front plate according to the present invention is not particularly limited as long as it has a function of converting light of a specific wavelength band into light of a different wavelength band, but is a material used as a normal light emitting material. Etc. can be used. The type is not particularly limited, but it is preferable to use a phosphor that uses light in a short wavelength band with low sensitivity characteristics of the solar battery cell 15 as excitation light from the viewpoint of effectively using sunlight and increasing power generation efficiency. Specifically, it is preferable to use ultraviolet light of 400 nm or less as excitation light. Further, the emitted light is preferably a phosphor that has long wavelength light with high sensitivity characteristics, and specifically, red light to infrared light of 600 nm to 1200 nm is preferably emitted light.

  Although the kind of fluorescent substance is not specifically limited, For example, a complex, an inorganic compound, a quantum dot compound, an organic compound, a high molecular compound etc. are mentioned, These may be used independently and 2 or more types are used together. May be. For example, when two types of phosphors are used in combination, the wavelength band of the emission light of one phosphor A and the wavelength band of the excitation light of the other phosphor B overlap so that the phosphor A and the fluorescence It is preferable because the excitation light of the body B can be converted into the emission light of the phosphor B, and light having a lower sensitivity characteristic in a wider range can be converted into light having a higher sensitivity characteristic.

(Inorganic phosphor)
The inorganic phosphor described here refers to a matrix crystal doped with luminescent ions as an activator. The type is not particularly limited, but the mother crystal includes elements such as Mg, K, Ca, Sr, Y, Ba, Zn, Ga, In, Al, P, S, Cl, O, La, Gd, V, and B. Inorganic phosphors in which one or more types are used and the luminescent ions as activators include one or more types of Mn, Ag, Ce, Nd, Eu, Tb, Dy, Ho, Tm, and the like. Among them, an inorganic phosphor in which an element in the mother crystal is substituted with a luminescent ion of the same family is preferable so as not to destroy the crystal structure of the mother crystal. For example, a mother material containing at least one kind of Y, La, and Sc. An inorganic phosphor in which Eu ions are doped in the crystal is more preferable. Examples of inorganic phosphors doped with Eu ions include Hikari * Color REF-10RM / RF and Hikari * Color REF-20RM / RF (distributor: TDO Graphics Co., Ltd.).

(Quantum dot phosphor)
The quantum dot described here refers to a nanoscale lump in which hundreds to thousands of atoms are collected and has a structure in which electrons are confined from all three dimensions. Quantum dots are preferable because they can give arbitrary absorption / excitation / emission light characteristics by changing the particle size, and the particle size is small and does not scatter incident light. The type is not particularly limited, but for example, a core-shell structure composed of a core layer composed of any combination of Cd, Se, Te, Pb, etc., and a shell layer composed of Zn, S, etc., Cd, Se, Te, Pb A structure made of any combination of Zn, S, etc. can be used. Examples of the quantum dot phosphor include CdSe / ZnS core shell Evi dot, PbS core Evi dot (distributor: Ocean Photonics Co., Ltd.), Qdot nanocrystal (distributor: Life Technologies Japan Co., Ltd.), and the like.

(Organic phosphor)
Although the type is not particularly limited, examples of organic fluorescent molecules include arylamine derivatives, anthracene derivatives (phenylanthracene derivatives), pentacene derivatives, azole derivatives (oxadiazole derivatives, oxazole derivatives, triazole derivatives, benzoxazole derivatives, benzoaza Triazole derivatives), thiophene derivatives (oligothiophene derivatives), carbazole derivatives, dienes (cyclopentadiene derivatives, tetraphenylbutadiene derivatives), styryl derivatives, (distyrylbenzene derivatives, distyrylpyrazine derivatives, distyrylarylene derivatives, stilbene derivatives) , Silole derivatives, spiro compounds, triphenylamine derivatives, trifumanylamine derivatives, pyrazoloquinoline derivatives, hydrazone derivatives, pyrazoles Conductor (pyrazoline derivative), pyridine ring compound, pyrrole derivative (porphyrin derivative, phthalocyanine derivative), fluorene derivative, phenanthroline derivative, pyrene derivative (phenanthrene derivative), perinone derivative, perylene derivative, phenylene compound, rhodamines, coumarin derivative, naphthalimide Examples thereof include phosphors containing one or more of derivatives, benzoxazinone derivatives, quinazolinone derivatives, quinophthalone derivatives, rubrene derivatives, and quinacridone derivatives.

  Examples include Lumogen F series (manufacturer: BASF), 7-Diethylamino-4a, 8a-dihydro-chromen-2-one, 7-Diethylamino-4-trifluoro-2-chloro, 7-Diethylamino-3-phene. -Chromen-2-one, 1,4-Bis- [2- (4-fluoro-phenyl) -vinyl] -2,5-bis-octyloxy-benzene, [4- [2- (4-Fluoro-phenyl) -Vinyl] -phenyl] -diphenyl-amine, Diphenyl- (4-styryl-phenyl) -amine, 5-tert-Butyl-2- (2- (4- (2- (5- tert-butylbenzoxazol-2-yl) vinyl) vinyl) vinyl) benzoxole (Technochemical Co., Ltd.), new organic fluorescent dye series (manufacturer: Harima Kasei Co., Ltd.), Shinrohi Color Series (distributor: Shinrohi Co., Ltd.), TINOPAL OB, TINOPAL OB-one (sales agency: Ciba Japan Co., Ltd.), etc. are mentioned. Among these, Lumogen F Violet 570 and Blue650 (manufacturer: BASF) are particularly preferable because they have a wide excitation band from the ultraviolet region to the entrance of the visible region, high quantum yield, and little overlap between excitation light and emission light. . In addition, the new organic fluorescent dye Orange 600 (manufacturer: Harima Kasei Co., Ltd.) has an excitation band overlapping with the emission light of Lumogen F Violet 570 and Blue 650, has a high quantum yield, and has little overlap between the excitation light and the emission light. , Preferred as a phosphor to be combined.

(Complex phosphor)
The complex described here refers to a molecular compound formed by coordination of a ligand to one or more emission centers by coordination bond or hydrogen bond. Although not particularly limited, for example, a transition metal element, a typical element, an atypical element, or the like is used as the emission center of the complex. As the ligand, a structure that emits fluorescence may be used. These complexes may include one or more luminescent centers and may include one or more types. Complexes containing Be for typical elements, B for non-typical elements, Al, Fe, Cu, Zn, Ru, Ir, Pt, Au, Re, Os, etc. for transition metal elements exchange ligands. By doing so, it is possible to obtain desired light emission characteristics and it is preferable because it can be obtained at a relatively low cost. Furthermore, the complex containing any of the rare earth elements Gd, Yb, Y, Eu, Tb, Yb, Nd, Er, Sm, Dy, Ce, etc. in the transition metal element is obtained by the excitation light and the emission light. The overlap is small, and light emission with a narrow half-value width not strongly dependent on the ligand is preferable. In particular, the Eu complex is more preferable because of its high quantum yield. In particular, Eu (TTA) 3phen (distributor: Tokyo Kasei Kogyo Co., Ltd.) has a high quantum yield, the difference in wavelength between the excitation light and the emission light is very large and there is no overlap, and the excitation light band is wide. preferable.

(Polymer phosphor)
Polymer phosphors are those in which the above-mentioned complex phosphors, inorganic phosphors, quantum dot phosphors, and organic phosphors are introduced into the main chain or side chain in the molecule, dimers, and trimers. A polymer, a dendrimer, or the like that is continuous with the polymer, or a copolymer in which each is arbitrarily introduced may be used. Examples include polyparaphenylene vinylene derivatives, polyparaphenylene derivatives, polyvinylcarbazole derivatives, polyfluorene derivatives, polysilane derivatives, polyacetylene derivatives, polyfluorenone derivatives, polyquinoxaline derivatives, polythiophene derivatives, and copolymers thereof.

  The concentration gradient of the phosphor is preferably uniform in the plane direction, but the thickness direction may be changed continuously along the thickness direction of the plate or may be changed stepwise (layered). When a plurality of phosphors are included, the individual phosphors may have the same concentration gradient or different concentration gradients. Among these, as the refractive index increases, it is preferable to increase the concentration of the phosphor from the viewpoint of increasing the power generation efficiency.

  The optimum particle size of the quantum dot phosphor and the inorganic phosphor varies depending on the thickness of the solar cell or front plate used and the phosphor to be combined. Although not particularly limited, 0.1 to 1500 nm is preferable, and 1 to 1200 nm is particularly preferable. If it is less than 0.1 nm, both the excitation light and the emitted light may be too short because the particle size is too small, or the intensity of the emitted light may be remarkably reduced and the desired characteristics may not be satisfied. There is a possibility that light is scattered and incident on the solar cell is hindered.

The addition amount of the phosphor is not particularly limited as long as the optimum concentration changes depending on the thickness of the front plate, so long as it is within a range where it is dissolved or dispersed. preferably in the range of 1500 g / ^{m 2,} and particularly preferably in the range of 0.005~1250g / ^{m 2.} If the amount is less than 0.001 g / m ² , sufficient wavelength conversion ability may not be imparted. If the amount is more than 1500 g / m ² , saturation of fluorescence intensity and concentration quenching occur, resulting in a decrease in economic efficiency. In addition to this, it tends to cause a decrease in wavelength conversion ability.

  Here, how the emitted light 14 radiated from the phosphor 13 of the front plate 10 proceeds will be described. The front plate 10 has the lowest refractive index on the light incident surface side where the sunlight 20 enters (low refractive index side 11), and is opposite to the light incident surface in the thickness direction and faces the solar battery cell. The refractive index on the side (opposite surface side) is the highest (high refractive index side 12), and the refractive index changes continuously or stepwise (intermittently) along the thickness direction. Since the light has a property of bending toward the higher refractive index, that is, toward the higher refractive index side, the emitted light 14 isotropically emitted from the phosphor 13 inside the front plate 10 by having such a structure. Is bent toward the solar cell 15 side of the high refractive index side 12 as it advances through the front plate 10. Thereby, a lot of emitted light 14 can be taken into the solar battery cell 15.

The matrix resin constituting the front plate 10 is not particularly limited, but it is preferable to use an acrylic or vinyl resin from the viewpoints of transparency and weather resistance.
The component on the high refractive index side 12 is not particularly limited, but a polymer such as benzyl methacrylate, phenyl methacrylate, methyl methacrylate, phenyl ethyl methacrylate, benzyl acrylate, vinyl benzoate, orthochlorostyrene, parafluorostyrene or paraisopropylstyrene is preferable. Used.
Further, the component on the low refractive index side 11 is not particularly limited, but methyl methacrylate, 2,2,2, -trifluoroethyl (meth) acrylate, 2,2,3,3,4,4,5,5-tetra Fluoroethyl (meth) acrylate, 2,2,3,3,4,4,5,5-octafluoropentyl acrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, fluorine Polymers such as vinylidene chloride are preferably used.
Moreover, these may be used as a homopolymer or may be used as a copolymer in which a plurality of types are combined.

  When the front plate 10 according to the present invention is used as a front plate for a solar cell, the front plate 10 is exposed to sunlight for a long period of time. Therefore, an ultraviolet absorber and a light stabilizer that are weathering stabilizers, particularly an ultraviolet absorber. It is preferable to improve weather resistance by adding. Further, at this time, in the thickness direction, when a large amount of the ultraviolet absorber is distributed on the low refractive index side 11, that is, the side closer to the sun so that the concentration of the ultraviolet absorber increases as the refractive index decreases, It is more preferable because the lifetime tends to be extended.

As a UV absorber,
Salicylic acid series such as phenyl salicylate, p-tert-butylphenyl salicylate,
Benzophenone series such as 2-4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-dodecyloxybenzophenone,
2- (2′-hydroxy-5′-tert-butylphenyl) benzotriazole, 2- (2′hydroxy-3 ′, 5′-di-tert-butylphenyl) benzotriazole, 2- (2′-hydroxy-3) '-Tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'hydroxy-3', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole, etc. Benzotriazole,
Cyanoacrylate systems such as 2-ethylhexyl-2-cyano-3,3′-diphenylacrylate, ethyl-2-cyano-3,3′-diphenylacrylate,
Examples thereof include nickel bis (octylphenyl) sulfide, (2,2′-thiobis (4-tert-octylphenolate) -n-butylamine nickel, etc. Examples of the light stabilizer include bis (2,2,6,6- Hindered amine light stabilizers such as tetramethyl-4-piperidyl) sebacate, etc. These ultraviolet absorbers and light stabilizers can be used alone or in admixture of two or more. .

  The added amount of the weather stabilizer, particularly the ultraviolet absorber, is preferably 0.001 to 10 parts by weight, particularly preferably 0.005 to 5 parts by weight, based on 100 parts by weight of the matrix resin. If it is less than 0.001 part by weight, sufficient weather resistance may not be imparted. Even if it is added in an amount of more than 10 parts by weight, the UV shielding ability is saturated, and not only the economical efficiency is lowered, but also the front plate. In the manufacturing process, the appearance of the product is likely to deteriorate due to bleeding out of the ultraviolet absorber. Therefore, from the viewpoint of preventing bleed-out, it is desirable to suppress to the minimum addition amount for satisfying the performance.

  The method for imparting the refractive index distribution to the front plate according to the present invention is not particularly limited. These methods are shown below.

  Two types of high-viscosity blends with different refractive indexes mixed with a polymer and a polymerizable compound are prepared, and these layers are layered and cured while mutually diffusing monomers to give a refractive index distribution The manufactured front plate may be manufactured.

  In Patent Document 4, a plurality of polymers and polymerizable compounds having different refractive indexes are discharged into a concentric stack using a multi-layer composite nozzle and polymerized and cured, whereby the refractive index distribution in the circumferential direction is increased. A method for producing a plastic optical fiber is disclosed, and this method can be applied.

  The polymer and polymerizable compound to be used are not particularly limited, but benzyl methacrylate, phenyl methacrylate, methyl methacrylate, phenyl ethyl methacrylate, benzyl acrylate, vinyl benzoate, orthochlorostyrene, parafluorostyrene, paraisopropylstyrene, 2 , 2,2, -trifluoroethyl (meth) acrylate, 2,2,3,3,4,4,5,5-tetrafluoroethyl (meth) acrylate, 2,2,3,3,4,4 , 5,5-octafluoropentyl acrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, vinylidene fluoride and the like are preferably used. These can be used alone or in any combination of two or more.

  Further, a refractive index distribution in which the refractive index continuously changes may be created by diffusing low molecular additives having different refractive indexes during the polymerization of the matrix resin constituting the front plate.

  As one of the methods, interfacial gel polymerization can be mentioned as a method of creating a continuous refractive index distribution by diffusing low molecular additives having different refractive indices during polymerization of a resin and then polymerizing the same (Patent Document 5). According to that method, a cylindrical tube made of a polymer such as polymethyl methacrylate is first prepared. The cylindrical tube becomes a clad portion. Next, interfacial gel polymerization is performed inside the cylindrical tube by injecting a monomer such as methyl methacrylate, a polymerization initiator, a chain transfer agent, a refractive index adjusting agent, etc., which is a raw material of the core portion, into the hollow portion of the cylindrical tube. Then, a core part is formed to obtain a preform. The core portion formed by interfacial gel polymerization has a concentration distribution of the refractive index adjusting agent and the like contained therein, and a refractive index distribution is formed in the core portion based on the concentration distribution. The preform thus obtained is heated and stretched in an atmosphere of about 180 ° C. to 250 ° C. to obtain a gradient index plastic optical fiber.

  The interfacial gel polymerization is preferably used in producing a plate-like member whose refractive index, which is also a feature of the present invention, changes stepwise or continuously along the thickness direction of the plate. In order to produce a plate-like member using interfacial gel polymerization, a matrix resin containing an additive such as another resin or a refractive index adjusting agent for changing the refractive index on a matrix made of a matrix resin. By filling the matrix resin, the matrix resin gradually undergoes interfacial gel polymerization on the matrix. In the present invention, the refractive index is distributed so that the matrix has a low refractive index. In the additive contained in the present invention, since the fluorescent agent has a higher molecular weight than the matrix resin, the fluorescent agent is slow to be taken in at the time of polymerization, the concentration is increased on the high refractive index side, and the ultraviolet absorber has a low molecular weight. It is rapidly taken in during polymerization, and the concentration increases on the low refractive index side.

  Further, Patent Document 6 discloses a method in which a gel is produced with a monomer, another type of monomer is injected and diffused therein, and then completely polymerized. First, a polymer precursor having a transparent three-dimensional cross-linked structure is produced, and after a monomer that forms a polymer having a different refractive index is diffused from the periphery, this is completely processed by post-treatment. A method of obtaining a refractive index distribution type optical transmission body by polymerizing and solidifying is proposed.

  Alternatively, a molded product of the transparent polymer A is converted into a transparent non-polymerizable compound B having compatibility with the polymer A and having a different refractive index, or a molten polymer C containing the non-polymerizable compound B. The non-polymerizable compound B may be diffused into the inside from the surface of the molded product of the polymer A by dipping in.

  In the former, by using a polymer as a polymerization vessel, a gel layer is formed on the surface of the vessel in the initial stage of polymerization, so that polymerization in the vicinity of the interface is promoted. At this time, two types having different diffusion coefficients to the gel layer are used. There is a method of forming a refractive index distribution by using the above compounds in combination. For example, as a method for producing a resin rod having a refractive index distribution in the circumferential direction, a high refractive index non-polymerizable compound is unevenly distributed in the center by polymerization or spinning at the time of forming the rod, thereby making the refractive index in the circumferential direction. A method for imparting a distribution has been known (Patent Document 7). As an example of the latter, there is a method in which a non-polymerizable compound having a low refractive index or a high refractive index is used and the low-refractive index non-polymerizable compound is diffused from the outer periphery to the inside of the rod (Patent Document 8 and Patent Document 9).

The type of polymer is not particularly limited, but for example,
Methyl methacrylate, ethyl methacrylate, (n-, i-) propyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, phenyl methacrylate, n-bornyl methacrylate, isobornyl methacrylate, adamantyl methacrylate , 2-hydroxyethyl methacrylate,
2,2,2-trifluoroethyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,4,4,5,5-octafluoropropyl, 2,2,3,4, 4,4-hexafluoropropyl,
α-methyl fluoroacrylate, ethyl α-fluoroacrylate, isopropyl α-fluoroacrylate, α-fluoroacrylic acid 2,2,2-trifluoroethyl, α-fluoroacrylic acid 2,2,3,3-tetra Fluoropropyl, α-fluoroacrylic acid 2,2,3,3,4,4,5,5-octafluoropropyl, α-fluoroacrylic acid 2,2,3,4,4,4-hexafluoropropyl,
n-methylmaleimide, n-ethylmaleimide, n-isopropylmaleimide, n-isobutylmaleimide, n-secondary butylmaleimide, nt-butylmaleimide n-2,2-dimethylpropylmaleimide, n-cyclohexylmaleimide,
Examples of the polymer include styrene, methylstyrene, dimethylstyrene, t-butylstyrene, chlorostyrene, dichlorostyrene, bromostyrene, fluorostyrene, and phenylstyrene. These can be used alone or in any combination of two or more.

  The high refractive index non-polymerizable compound is not particularly limited, and examples thereof include benzyl n-butyl phthalate, dimethyl phthalate, diallyl phthalate, dioctyl phthalate, dipropylene glycol dibenzoate, diethylene glycol dibenzoate, and triphenyl phosphate. .

  Although it is not particularly limited as a low refractive index or a high refractive index non-polymerizable compound, in the case of a polymer mainly composed of methacrylic acid esters and styrenes, dihexyl adipate, dicapryl adipate, diisooctyl adipate, Examples include dibutyl sebacate, di-2-ethylhexyl sebacate, tributyl phosphate, glycerol triacetate, butyl benzyl phthalate, dibutyl phthalate, fluorinated alkyl methacrylate, and alkyl α-fluoroacrylate. In the case of polymers mainly composed of fluorinated alkyl α-fluoroacrylate, etc., dihexyl adipate, dicapryl adipate, diisooctyl adipate, dibutyl sebacate, di-2-ethylhexyl sebacate, tributyl phosphate, glycerol Examples include triacetate, butylbenzyl phthalate, dibutyl phthalate, and fluorinated compounds thereof.

  Moreover, you may manufacture the front board from which a refractive index changes in steps by laminating | stacking several layers from which refractive indexes differ little by little. For example, in Patent Document 10, a binder polymer, a photosensitive monomer, a photopolymerization initiator, and a wavelength conversion phosphor dissolved in a solvent on a protective film are applied and dried, then laminated on a support film, and activated. A method is disclosed in which a laminate of a support film and a resin copolymer is formed by photocuring by irradiating light and then peeling off the protective film. By using this method, the combination of the binder polymer and the photosensitive monomer is changed, and a plurality of resin layers are stacked on the support film and the resin copolymer in the same manner several times. It is possible to produce a laminate.

  The binder polymer is not particularly limited, and examples thereof include acrylic acid, methacrylic acid or derivatives thereof, styrene, styrene derivatives, and the like. Examples of the photosensitive monomer include a compound obtained by reacting a polyhydric alcohol with an α, β-unsaturated carboxylic acid, a bisphenol A-based (meth) acrylate compound, and a glycidyl group-containing compound with an α, β-unsaturated carboxylic acid. Examples include compounds obtained by reaction, urethane monomers such as (meth) acrylate compounds having a urethane bond in the molecule, nonylphenoxypolyethyleneoxyacrylate, phthalic acid compounds, and (meth) acrylic acid alkyl esters. These can be used alone or in any combination of two or more.

As the photopolymerization initiator, for example,
4,4′-bis (diethylamino) benzophenone, benzophenone, 2-benzyldimethylamino-1- (4-morpholinophenyl) -butanone-1,2-methyl-1- [4- (methylthio) phenyl] -2-morpholino -Aromatic ketones such as propanone-1;
Quinones such as alkylanthraquinone,
Benzoin ether compounds such as benzoin alkyl ether,
Benzoin compounds such as benzoin and alkylbenzoin,
Benzyl derivatives such as benzyldimethyl ketal,
2- (o-chlorophenyl) -4,5-diphenylimidazole dimer, 2- (o-chlorophenyl) -4,5-di (methoxyphenyl) imidazole dimer, 2- (o-fluorophenyl) -4 2,5-diphenylimidazole dimer, 2- (o-methoxyphenyl) -4,5-diphenylimidazole dimer, 2- (p-methoxyphenyl) -4,5-diphenylimidazole dimer, etc. 4,5-triarylimidazole dimer,
Examples include acridine derivatives such as 9-phenylacridine and 1,7-bis (9,9′-acridinyl) heptane.

  In addition, as other methods, a method of recoating a solution of polymers having different refractive indexes, a method of thermally laminating a plurality of polymer films, or applying a polymerizable compound and performing polymerization by heat or active light The method of obtaining a multilayer laminated body by repeating is considered.

  The front plate 10 may form a hard coat film on the surface as necessary. Conventionally known methods and materials may be used for the hard coat treatment for forming the hard coat film, but from the viewpoint of further improving the strength and weather resistance, an alkoxysilane composition, organoalkoxysilane and colloidal silica are used. It is preferable to apply a composition containing a curing catalyst and a solvent as a main component to the low refractive index side 11 of the front plate 10 and dry it to obtain a hard coat film. The composition used for the hard coat treatment is, for example, “KP-851”, “X-12-2206” manufactured by Shin-Etsu Chemical Co., Ltd., “Tosguard 510” manufactured by Toshiba Silicone Co., Ltd., Nippon Dacro Shamrock Co., Ltd. “Solgard NP-720” and “Solgard NP-730” can be used. Examples of a method for applying such a composition include known methods such as spraying, dipping, flow, roll coating, die coating, and gravure coating. Further, a film or the like on which a hard coat film is formed may be attached to the front plate 10.

  The thickness of the hard coat film can be selected as appropriate, but is preferably in the range of 2 to 10 μm, particularly preferably in the range of 2 to 5 μm. If the thickness of the hard coat film is less than 2 μm, sufficient surface hardness cannot be obtained, and if it is greater than 10 μm, the flexibility of the coating film may be reduced and cracks may occur. Further, in order to improve the adhesion between the hard coat film and the front plate 10, a primer layer may be provided between the front plate 10 and the hard coat film as necessary. For the primer layer, various engineering plastics such as polycarbonate resin, thermoplastic resins such as acrylic resin, ABS resin, polystyrene resin, and vinyl chloride resin, and mixtures thereof may be used.

  Next, the results of optical simulation will be described. A model as shown in FIG. 3 was created using computer software for optical simulation (LightTools Ver. 5.5, manufactured by ORA), and ray tracing simulation was performed under the following conditions.

  The size of the front plate was a rectangle with a thickness of 3 mm and a side of 100 mm. The front plate has a refractive index distribution of 50 layers having different refractive indexes in the thickness direction. In the refractive index distribution, the refractive index of each layer is uniformly changed so that the refractive index difference between the low refractive index side (first layer) and the high refractive index side (50th layer) is divided by 50, and the thickness of the front plate is changed. A structure in which the refractive index changes stepwise along the vertical direction was adopted. The side receiving sunlight is the first layer, the side facing the solar battery cell is the 50th layer, and the 50th layer and the solar battery cell are in an optically close contact state.

  The optical simulation does not consider the amount of sunlight that passes through the front plate and reaches the solar cells directly, and focuses on only the light emitted from the phosphor that received sunlight (5 million light beams). Went.

  In the present invention, the phosphor should be evenly distributed at least in the plane direction, but in order to simplify the calculation within a range not losing validity, only the central portion in the plane direction and the thickness direction in the thickness direction. A central 25th layer and every 10 layers above and below it were placed (that is, phosphors were placed on the 5th, 15th, 25th, 35th, and 45th layers). Each phosphor was set as a minute light source that isotropically emits light (see FIG. 4). It was assumed that there was a Fresnel loss between the layers, the refractive index of the solar battery cell was 4.0, and all the light incident on the solar battery cell was absorbed. Table 1 shows the optical simulation results.

  The number of incident light rays in the cell 1 in the table indicates the ratio (%) of light reaching the solar battery cell out of 5 million light rays (see FIG. 4). The number of light beams emitted from the upper surface indicates the ratio (%) of light emitted from the low refractive index side 11 (that is, the upper surface) of the front plate (see FIG. 4). The number of rays reaching the side surface indicates the ratio (%) of light that has reached the side surface before reaching the solar battery cell (see FIG. 4). According to this, when the refractive index difference of the front plate is large, the amount of light passing through the side surface tends to be small, and when the refractive index on the low refractive index side is high, the amount of light passing through the top surface is small. There is a tendency. That is, if the difference in refractive index is large, light is strongly bent toward the high refractive index side, so that even if the size of the front plate is small, there is a tendency for the solar cell taking-in efficiency to improve, which is preferable. Specifically, the refractive index difference is preferably 0.005 or more, and more preferably 0.02 or more.

  Also, if the refractive index on the low refractive index side of the front plate is higher, the amount of light emitted from the upper surface is reduced and the light confinement efficiency is improved, so the amount of light finally taken into the solar cell tends to be improved. And preferred.

  The refractive index of the front plate is from the low refractive index side to the high refractive index side, that is, from the light incident surface side where sunlight enters, toward the opposite surface side opposite to the light incident side in the thickness direction. It is preferable from the viewpoint of improvement in sunlight capturing efficiency that the refractive index is increased within the range of 40 or more and 1.70 or less. The refractive index on the low refractive index side 11 of the front plate is not particularly limited, but specifically, it preferably has a refractive index of 1.40 or higher, more preferably 1.42 or higher. More preferably, it has a refractive index of .45 or more.

  Next, when the refractive index of the first layer is set to 1.42 and the refractive index of the 50th layer is set to 1.58, the fifth layer, the 15th layer, the 25th layer, the 35th layer, the 45th layer For each of the light beams emitted from the phosphors arranged in FIG. 2, the ratios of the cell incident light beam, the side surface light beam, and the upper surface light beam are calculated by simulation, and the results are shown in Table 2.

  According to the optical simulation result (Table 2), it can be seen that the light emitted from the phosphor disposed on the high refractive index side has a larger number of light rays incident on the cell. From this, the phosphor is unevenly distributed on the high refractive index side so that the concentration of the phosphor becomes higher as the refractive index becomes higher, so that the emitted light from the phosphor can be led to the solar cell more efficiently. it can. This is because the higher the refractive index around the phosphor, the higher the confinement effect of the light emitted from the phosphor.

  Moreover, it is good also as a structure which arrange | positions a reflection member etc. in the side surface of the front plate 10, and reflects a side surface arrival light toward the inside of a front plate. With this configuration, more emitted light can be guided to the solar battery cell.

  The present invention is specifically illustrated by the following examples.

(Example 1) Production 1 of a plate member having a refractive index
When casting between 300 mm square glass plates in a cast plate, a polymethyl methacrylate plate (Mitsubishi Rayon Co., Ltd., EX # 000, plate thickness: 3.0 mm) is adhered to one side and sandwiched between them Among them, 240 g of polymethyl methacrylate having a conversion rate of 20%, 60 g of benzyl methacrylate, 1900 ppm of a polymerization initiator benzyl peroxide, 43 ppm of a polymerization inhibitor, 50 ppm of a release agent, and Lumogen F Violet 570 (BASF) Manufactured) Filled with 1000ppm and polymerized at 75 ° C for 10 hours (interfacial gel polymerization), there is a continuous refractive index distribution along the thickness direction (thickness 3mm) of the plate composed of the copolymer A plate-like member was obtained.

  FIG. 5 shows data obtained by measuring the refractive index distribution of the produced plate with an interfaco interference microscope.

(Example 2) Production of a refractive index imparting plate member 2
40% by weight styrene-acrylic resin (Dainal BR-50, manufactured by Mitsubishi Rayon Co., Ltd.) dissolved in toluene and EO-modified bisphenol A diacrylate (BPE4) are mixed at a certain ratio, and Irgacure 184 3 is used as a photocuring agent. A solution in which wt% was well mixed was applied onto a PET film with a bar coater, dried at room temperature for 30 minutes, and then dried at 80 ° C. for 10 minutes to completely volatilize the toluene solvent. Then, after closely attaching the thin film coated on the PET film on the polymethyl methacrylate plate, the refractive index distribution is stepwise along the thickness direction by transferring the copolymer thin film onto the polymethyl methacrylate plate by ultraviolet irradiation. A plate-like member in which is present was obtained.

  Optical simulation data on the multilayer film produced in Example 2 and the polymethyl methacrylate single layer plate, the refractive index of the polymethyl methacrylate plate is 1.49, and the refractive index of the copolymer thin film of BR-50 and BPE4 is 1. .57 is shown in FIG.

(Example 3) Production of refractive index imparting plate member 3
When casting between 300 mm square glass plates in a cast plate, first, 92% by weight of polymethyl methacrylate syrup having a conversion rate of 20% is placed in a 1.5 mm thickness gasket sandwiched between the glass plates, methyl methacrylate. A monomer was charged at 8% by weight, a polymerization initiator perhexyl PV of 1900 ppm, a polymerization inhibitor of 43 ppm, and a release agent of 50 ppm, and a polymerization reaction was carried out at 80 ° C. for 21 minutes. After the polymerization reaction, the glass plate was quickly cooled with ice water. Thereafter, only the glass plate on one side was peeled off, and a 3.0 mm thick gasket was placed around the acrylic plate so as to cover the 1.5 mm thick acrylic plate. A 3.0 mm-thick gasket is sandwiched between glass plates, and 60% by weight of polymethyl methacrylate syrup with a conversion rate of 20%, benzil methacrylate 25% by weight, methyl methacrylate monomer 15% by weight, polymerization start The agent was charged with 1900 ppm of perhexyl PV, 43 ppm of polymerization inhibitor, 50 ppm of release agent and 1000 ppm of Lumogen F Violet 570 (manufactured by BASF) as a wavelength converting fluorescent agent, and reacted at 60 ° C. for 300 minutes (interfacial gel polymerization). Thereafter, a plate-like member having a continuous refractive index distribution along the thickness direction (thickness 3 mm) was obtained by performing a polymerization reaction at 130 ° C. for 30 minutes.

  The excitation-fluorescence spectrum of the obtained plate is shown in FIG.

<Production of solar cell module>
Next, a production example of a 180 mm square single cell module using the obtained copolymer as a front plate of a solar cell is shown.

  The high refractive index side is arranged on the solar cell side so that the low refractive index side of the plate obtained in the plate-shaped member production 3 is the light incident surface side, and an ethylene-vinyl acetate copolymer (fast Polycrystalline silicon cell (made by Zintech Energy), EVA, PMMA plate (Mitsubishi Rayon Co., Ltd., MR200, plate thickness 1.5 mm) wired with a cure type, made by Sanvic, hereinafter referred to as EVA) The solar cell module was obtained by stacking and vacuum pressing at 135 ° C. and 101.3 kPa using a vacuum laminator (MP50, manufactured by NPC).

<Evaluation of power generation characteristics of solar cell module>
The power generation characteristics of the obtained solar cell module were measured using a solar simulator SPI-SUN SIMULATOR 1116N (manufactured by SPIRE). The obtained short-circuit current value was used as an evaluation value of characteristics. The comparison of the power generation characteristics is shown in Table 4 with the change rate of the short circuit current (Isc) as 100% as the value of the comparative example 1 for the purpose of measuring the light capturing performance.

(Comparative example 1) Solar cell module which arranges a PMMA board in the light-incidence side The acrylic board which does not have refractive index distribution and a wavelength conversion fluorescent agent was manufactured with the following method.

  When casting between 300 mm square glass plates in a cast plate, 92% by weight of polymethyl methacrylate syrup with a conversion rate of 20% in a gasket for 3.0 mm thickness, 8% by weight of methyl methacrylate monomer, polymerization started The agent was charged with 1900 ppm of perhexyl PV, 43 ppm of a polymerization inhibitor, and 50 ppm of a release agent, and a polymerization reaction was carried out at 80 ° C. for 30 minutes. Thereafter, a plate-like member was obtained by further polymerization reaction at 130 ° C. for 30 minutes. Using the obtained plate-like member, a solar cell module was obtained in the same manner as in Example 3, and the power generation characteristics were evaluated in the same manner as in Example 3.

(Comparative example 2) Solar cell module which arrange | positions the board | substrate with a wavelength conversion fluorescent agent on the light-incidence side The board which does not have refractive index distribution but has only a wavelength conversion fluorescent agent was manufactured with the following method.

  When casting between 300 mm square glass plates in a cast plate, 92% by weight of polymethyl methacrylate syrup with a conversion rate of 20% in a gasket for 3.0 mm thickness, 8% by weight of methyl methacrylate monomer, polymerization started The agent was charged with 1900 ppm of perhexyl PV, 43 ppm of polymerization inhibitor, 50 ppm of release agent, and 1000 ppm of Lumogen F Violet 570 (manufactured by BASF) as a wavelength conversion fluorescent agent, and a polymerization reaction was carried out at 80 ° C. for 30 minutes. Thereafter, an acrylic resin plate containing a wavelength-converting fluorescent agent was obtained by further polymerization at 130 ° C. for 30 minutes. Using the obtained plate-like member, a solar cell module was obtained in the same manner as in Example 3, and the power generation characteristics were evaluated in the same manner as in Example 3.

  The present invention is not limited to the above description, and various changes and the like may be added without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 10 Front plate 11 Low refractive index side 12 High refractive index side 13 Phosphor 14 Emission light 15 Solar cell 20 Sunlight

Claims (6)

A transparent plate member used for solar cells,
Containing one or more phosphors having different wavelengths of excitation light and emission light,
A light incident surface on which sunlight enters, and an opposite surface opposite to the light incident surface in the thickness direction;
A plate-like member, wherein a refractive index on the opposite surface side is higher than a refractive index on the light incident surface side, and the refractive index changes stepwise or continuously along the thickness direction. 2. The plate-like member according to claim 1 , wherein the refractive index increases in a range of 1.40 to 1.70 from the light incident surface side toward the opposite surface side. The plate member according to claim 1 or 2 , wherein the phosphor is unevenly distributed on the opposite surface side in the thickness direction. The plate-like member according to claim 3 , wherein in the thickness direction, the concentration of the phosphor increases as the refractive index increases. Furthermore it contains the ultraviolet absorber, the in the thickness direction, the refractive index, characterized in that the concentration of the ultraviolet absorbent becomes higher as lower, according to any one of claims 1 to 4 Plate-like member. A plate-like member according to any one of claims 1 to 5 ,
A solar cell module comprising: solar cells arranged to face the opposite surface of the plate-like member.