JP2017039834A - Inorganic phosphor, wavelength conversion member and photovoltaic powder device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inorganic phosphor less in refractive index difference with an encapsulation material constituting a wavelength conversion member.SOLUTION: In the inorganic phosphor, a host crystal containing a halide having refractive index of less than 1.46 and irradiating fluorescence and a refractive index adjustment material consisting an atom of an element with existing amount in a crystal lattice of the halide of less than 1 mol% or a compound having the element has a crystal structure substituted by a luminescent center and has larger refractive index than that of the halide. The halide irradiating the fluorescence preferably contains fluorine. The halide irradiating fluorescence is preferably a fluoride.SELECTED DRAWING: Figure 1

Description

  The present invention can convert ultraviolet light to visible light or infrared light at room temperature or higher, has a small difference in refractive index from the sealing material of the wavelength conversion member, and does not change the light emission characteristics even when it comes into contact with moisture, thus being reliable. It relates to a high inorganic phosphor. Moreover, it is related with the wavelength conversion member and photovoltaic apparatus containing this inorganic fluorescent substance.

  Generally, the solar cell has a lower photoelectric conversion efficiency of ultraviolet light than that of visible light. For example, a general solar cell has a low photoelectric conversion efficiency in the ultraviolet light in the wavelength range of 300 nm or more and less than 400 nm, and a photoelectric conversion efficiency in the visible light or infrared light region in the wavelength range of 400 nm or more and less than 1200 nm. high. Moreover, the ultraviolet light within the wavelength range of less than 380 nm tends to damage the solar cell. For this reason, in the conventional solar cell, for example, ultraviolet light in a wavelength range of less than 380 nm is cut by a filter.

  However, if ultraviolet light within a wavelength range of less than 380 nm can be used for power generation, improvement in photoelectric conversion efficiency of the solar cell is expected. For this reason, in recent years, in solar cells, it has been studied to convert ultraviolet light within a wavelength range of less than 380 nm into light having a long wavelength instead of simply cutting it and use it for power generation.

  For example, a technique in which a wavelength conversion layer that converts ultraviolet light into visible light or infrared light is provided on the surface of a solar battery cell has been studied. As the wavelength conversion layer, for example, a sheet in which an inorganic phosphor is dispersed in a sealing material made of a transparent resin has been studied.

  This wavelength conversion layer preferably exhibits a high light transmittance with respect to visible light and infrared light in a wavelength region where the photoelectric conversion efficiency of the solar cell is high. If the light transmittance of visible light and infrared light of the wavelength conversion layer is low, the degree of decrease in photoelectric conversion efficiency due to the decrease in light transmittance exceeds the improvement in photoelectric conversion efficiency due to the provision of the wavelength conversion layer. Because there is a fear. A wavelength conversion layer having high visible light and infrared light transmittance is presumed to be obtained by reducing the refractive index difference between the inorganic phosphor and the sealing material in which the inorganic phosphor is dispersed. . Here, the refractive index of an ethylene vinyl acetate copolymer (EVA), which is a general transparent resin constituting the sealing material, is about 1.48.

As an inorganic phosphor having a relatively small difference in refractive index from the sealing material, conventionally, Patent Document 1 describes a barium halide inorganic phosphor activated by Eu ²⁺ . Specifically, Patent Document 1, the composition formula is _{aYOF (1-a) Ba 1} -x M x FX: barium halide inorganic phosphor represented by Eu _y is described. Here, M is at least one of Be, Mg, Ca, Br, Zn, and Cd, X is at least one of Cl, Br, and I, and 0 <a ≦ 0.6 and 0 ≦ x ≦ 0. .5, 10 ⁻⁶ ≦ y ≦ 2 × 10 ⁻¹ . The refractive index of this inorganic phosphor can be controlled by changing the value of a.

JP 59-226091 A

  It is known that the inorganic phosphor described in Patent Document 1 has a refractive index of 1.47 or more and a suitable refractive index, but the temperature quenching is remarkable and hardly emits light at 25 ° C. or more. For this reason, with the inorganic phosphor described in Patent Document 1, the photoelectric conversion efficiency of the solar cell could not be sufficiently improved. Thus, heretofore, an inorganic phosphor having a favorable refractive index and fluorescent characteristics and excellent temperature characteristics has not been known.

  The present invention has been made in view of the above problems. An object of this invention is to provide the inorganic fluorescent substance with a small refractive index difference with the sealing material which comprises a wavelength conversion member. Moreover, an object of this invention is to provide the wavelength conversion member and photovoltaic device containing this inorganic fluorescent substance.

  In order to solve the above problems, an inorganic phosphor according to an aspect of the present invention is a matrix crystal including a halide having a refractive index of less than 1.46 and emitting fluorescence, and a refractive index adjusting substance. Part has a crystal structure substituted with a luminescent center. The refractive index adjusting substance is composed of an element atom having an abundance in a crystal lattice of halide of less than 1 mol% or a compound having the element. The inorganic phosphor has a higher refractive index than the halide.

  In addition, the wavelength converter according to an aspect of the present invention is obtained by dispersing the inorganic phosphor in a translucent material.

  Furthermore, the photovoltaic device which concerns on the aspect of this invention is equipped with the said wavelength converter.

  The inorganic phosphor of the present invention has a small refractive index difference from the sealing material constituting the wavelength conversion member. Since the wavelength converter of the present invention has a small refractive index difference between the sealing material constituting the wavelength conversion member and the inorganic phosphor, the light transmittance is high. Since the photovoltaic device of this invention has the high light transmittance of a wavelength conversion member, its quantum efficiency is high.

It is sectional drawing which shows typically an example of the solar cell module which concerns on this embodiment. 3 is a graph showing emission spectra of Example 1 and Comparative Example 1.

  Hereinafter, the photovoltaic device according to the present embodiment, the wavelength conversion member constituting the photovoltaic device, and the inorganic phosphor contained in the wavelength conversion member will be described with reference to the drawings.

[Photovoltaic device]
FIG. 1 is a cross-sectional view schematically showing an example of a solar cell module as a photovoltaic device according to this embodiment. As shown in FIG. 1, the solar cell module 1 includes a solar cell 10 as a photoelectric conversion element, a wavelength conversion member 20 disposed on the light receiving surface 13 side of the solar cell 10, and a surface of the wavelength conversion member 20. And a disposed surface protective layer 30. That is, the solar cell module 1 includes a wavelength conversion member 20. Further, the solar cell module 1 is disposed on the back surface 14 of the back surface sealing member 40 disposed on the back surface 14 that is the surface opposite to the light receiving surface 13 of the surface of the solar battery cell 10. And back surface protective layer 50. That is, the solar cell module 1 has a configuration in which the surface protective layer 30, the wavelength conversion member 20, the solar cell 10, the back surface sealing member 40, and the back surface protective layer 50 are provided in this order from the top in the drawing. Yes. The solar cell module 1 is configured such that light incident from the light incident surface 33 that is the surface of the surface protective layer 30 is received by the solar cell 10 as it is or after being converted by the wavelength conversion member 20. An electromotive force is generated.

(Solar cell)
The solar battery cell 10 absorbs light incident from the light receiving surface 13 of the solar battery cell 10 and generates photovoltaic power. The solar cell 10 is formed using a semiconductor material such as crystalline silicon, gallium arsenide (GaAs), indium phosphide (InP), for example. Specifically, the solar battery cell 10 is made of, for example, a laminate of crystalline silicon and amorphous silicon. An electrode (not shown) is provided on the light receiving surface 13 of the solar battery cell 10 and the back surface 14 which is the surface opposite to the light receiving surface 13. The photovoltaic power generated in the solar battery cell 10 is supplied to the outside through the electrode.

(Wavelength conversion member)
A wavelength conversion member 20 is disposed on the light receiving surface 13 of the solar battery cell 10. As shown in FIG. 1, the wavelength conversion member 20 includes a sealing material 21 that seals the light receiving surface 13 of the solar battery cell 10 and an inorganic phosphor 25 that is dispersed in the sealing material 21. As will be described later, the sealing material 21 is usually made of a translucent material such as a transparent resin. The wavelength conversion member 20 shown in FIG. 1 is obtained by dispersing an inorganic phosphor 25 in a translucent material 21 such as a transparent resin.

  The wavelength conversion member 20 prevents the infiltration of moisture into the solar battery cell 10 by the sealing material 21 and improves the strength of the entire solar battery module 1. Moreover, the wavelength conversion member 20 converts a part of the light passing through the wavelength conversion member 20 into light on the long wavelength side by the inorganic phosphor 25. Furthermore, since the wavelength converting member 20 has the sealing material 21 and the inorganic phosphor 25 described in detail below, the light that is high in the visible light and infrared light in the wavelength region where the photoelectric conversion efficiency of the solar cell is high. The transmittance is shown. The wavelength conversion member 20 is a sheet-like body, a film-like body, or a plate-like body disposed on the surface of the solar battery cell 10. The thickness of the wavelength conversion member is not particularly limited. For example, when the thickness is 0.2 to 1 mm, the wavelength conversion member can sufficiently absorb ultraviolet light without reducing the light transmittance of visible light and infrared light. preferable. 1 shows an embodiment in which the inorganic phosphor 25 is dispersed in the sealing material 21, but the inorganic phosphor 25 of the wavelength converting member 20 is dispersed in the sealing material 21. For example, it may be unevenly distributed in the vicinity of one surface of the sealing material 21.

<Encapsulant>
As the sealing material 21, a translucent material such as transparent resin or glass is used. When the translucent material is a transparent resin, the wavelength converter 20 that is inexpensive and easy to shape is obtained. Examples of the transparent resin include ethylene vinyl acetate copolymer (EVA); polyvinyl butyral (PVB); polyimide; polyolefin such as polyethylene and polypropylene; polyethylene terephthalate (PET). The refractive index of these transparent resins is 1.41 or more and less than 1.57. Specifically, the refractive index of EVA is about 1.48, and the refractive index of polyolefin is about 1.49.

  When the translucent material 21 is a transparent resin, if the melting point or glass transition temperature of the transparent resin is outside the temperature range of −40 ° C. or more and less than 90 ° C., which is the operating temperature range of the solar cell module 1, This is preferable because the light transmittance of the wavelength conversion member 20 is unlikely to decrease during use. Specifically, the melting point and glass transition temperature of the transparent resin 21 are preferably 90 ° C. or higher. The refractive index of the transparent resin 21 changes greatly in the vicinity of the melting point and glass transition temperature of the transparent resin 21 and the refractive index difference from the inorganic phosphor 25 increases. For this reason, when the solar cell module 1 is used in the vicinity of the melting point or glass transition temperature of the transparent resin 21, the refractive index difference between the transparent resin 21 and the inorganic phosphor 25 becomes large, and visible light or The light transmittance of infrared light tends to decrease. On the other hand, when the melting point and the glass transition temperature of the transparent resin 21 are 90 ° C. or higher, and within the temperature range other than −40 ° C. or higher and lower than 90 ° C., which is the operating temperature range of the solar cell module 1, the wavelength conversion member. A decrease in the light transmittance of the entire 20 can be avoided.

<Inorganic phosphor>
The inorganic phosphor 25 generally has a crystal structure in which a part of atoms constituting a host crystal made of an inorganic compound is partially substituted with a luminescence center that emits fluorescence.

  The inorganic phosphor 25 used in this embodiment includes a halide having a refractive index of less than 1.46 and emitting fluorescence, and atoms of elements having an abundance in the crystal lattice of the halide of less than 1 mol%. Alternatively, a host crystal including a refractive index adjusting substance made of a compound containing the element is included. Here, the refractive index adjusting substance is a substance having a higher refractive index than a halide emitting fluorescence. In addition, the inorganic phosphor 25 used in the present embodiment has a crystal structure in which a part of the host crystal is replaced with a light emission center. Furthermore, the inorganic phosphor used in the present embodiment has a higher refractive index than the halide that emits the fluorescence. Hereinafter, the inorganic phosphor 25 will be described in detail.

[Fluoride emitting halides]
The halide that emits fluorescence and constitutes the base crystal of the inorganic phosphor has a refractive index of less than 1.46. As such a halide, for example, CaF ₂ and SrF ₂ are used. The refractive index of CaF ₂ is 1.44. The refractive index of SrF ₂ is 1.44. The halide that emits fluorescence is usually polycrystalline.

  The halide that emits fluorescence is preferably one containing fluorine because the refractive index of the inorganic phosphor 25 containing the halide, the refractive index adjusting substance, and the emission center can be made relatively small. Since fluorine is an element having a low polarizability, the refractive index of the inorganic phosphor 25 is relatively small.

  If the halide that emits fluorescence is a fluoride, the refractive index of the inorganic phosphor 25 including the halide, the refractive index adjusting substance, and the emission center is compared with the case where the inorganic phosphor is made of an oxide. Since it can be made small, it is preferable. Since fluorine is an element having a low polarizability, the inorganic phosphor 25 in which the halide that emits fluorescence is made of fluoride has a smaller refractive index than the inorganic phosphor in which the halide that emits fluorescence is an oxide. Become.

  When the halide that emits fluorescence contains an alkaline earth metal element, it is easy to contain a large amount of rare earth ions that function as the emission center in the crystal structure of the halide that emits fluorescence, and the resulting inorganic phosphor 25 can sufficiently absorb ultraviolet light. Here, the alkaline earth metal element means one or more elements selected from the group consisting of Ca, Sr and Ba. The alkaline earth metal element in the halide that emits fluorescence has an ionic radius close to that of a rare earth ion that functions as an emission center. Therefore, when the halide that emits fluorescence contains an alkaline earth metal element, the inorganic phosphor 25 containing a large amount of rare earth ions functioning as the emission center is obtained by substituting the alkaline earth metal element with the rare earth ions. It is done.

When the halide that emits fluorescence contains a rare earth element, this rare earth element functions as a luminescence center, or the rare earth element contained in the halide that emits fluorescence is replaced with a rare earth ion that functions as a luminescence center. Can do. Here, the rare earth element is one selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y. The above elements are meant. That is, in this specification, the rare earth element means 17 elements obtained by adding Sc and Y to 15 lanthanoid elements from La to Lu. Rare earth elements in halides that emit fluorescence are easily replaced by emission centers such as Ce ³⁺ and Eu ²⁺ . Therefore, when the halide that emits fluorescence contains a rare earth element, an inorganic phosphor 25 in which a large amount of Ce ³⁺ and Eu ²⁺ are contained in the crystal structure of the halide that emits fluorescence is obtained. The absorption rate of the ultraviolet light of the body 25 is increased.

  Halides having a fluorite structure are naturally occurring compounds. For this reason, when the halide that emits fluorescence has a fluorite structure, the obtained inorganic phosphor 25 is chemically stable, and the inorganic phosphor 25 can be manufactured relatively easily.

[Refractive index adjusting substance]
As described above, the refractive index adjusting substance is a substance having a higher refractive index than the halide that emits fluorescence. The inorganic phosphor 25 according to the present embodiment includes a refractive index adjusting substance that constitutes the base crystal of the inorganic phosphor together with a halide that emits fluorescence, thereby forming a halide that emits fluorescence that does not contain the refractive index adjusting substance. In comparison, the refractive index is increased.

  The refractive index adjusting substance is composed of an element atom having an abundance in the crystal lattice of the halide emitting the fluorescence of less than 1 mol% or a compound having the element. As the refractive index adjusting substance, for example, an oxygen atom or an inorganic compound containing oxygen is used.

  When the refractive index adjusting substance is an oxygen atom, the refractive index adjusting substance is contained in the crystal grains of the halide that emits fluorescence or in the crystal grain boundaries. That is, when the refractive index adjusting substance is an oxygen atom, the base crystal of the inorganic phosphor usually emits a halide that emits fluorescence containing oxygen atoms in crystal grains, or fluorescence that contains oxygen atoms in crystal grain boundaries. It becomes a halide.

  When the refractive index adjusting substance is an oxygen atom, the refractive index of the obtained inorganic phosphor becomes larger than that when the refractive index adjusting substance is not included. Specifically, the refractive index adjusting substance is intermediate between the halide that emits fluorescence and the oxide. Is the refractive index. More specifically, the refractive index of the obtained inorganic phosphor is larger than the refractive index of fluoride and smaller than the refractive index of oxide, and is close to the transparent resin constituting the encapsulant 21. When the refractive index adjusting substance is an oxygen atom, the refractive index adjusting substance is usually contained in an amount of 0.1 to 50 mol%, preferably 1 to 30 mol% with respect to 100 mol% of the halide. It is preferable that the content of the refractive index adjusting substance is within the above range because the refractive index of the inorganic phosphor 25 can be made close to the refractive index of the transparent resin constituting the sealing material 21.

Further, when the refractive index adjusting substance is an inorganic compound containing oxygen, examples of the inorganic compound containing oxygen include oxides, oxyfluorides, heavy element fluorides, and the like. Examples of the oxide include MgO, CaO, SrO, BaO, Al ₂ O _{3 and the} like. Examples of the acid fluoride include ScOF and YOF. Examples of heavy element fluorides include LaF ₃ , TbF ₃ , LuF ₃ , and GdF ₃ . When the refractive index adjusting substance is an oxyfluoride among inorganic compounds containing oxygen, it is preferable because the refractive index of the inorganic phosphor 25 having a fluoride structure can be easily realized.

  In addition, when the refractive index adjusting substance is an inorganic compound containing oxygen, the inorganic compound containing oxygen usually forms crystal grains in the base crystal of the inorganic phosphor, similarly to the halide that emits fluorescence. The crystal grains of the refractive index adjusting substance are in solid solution with the halide crystal grains that emit fluorescence in the base crystal of the inorganic phosphor. That is, when the refractive index adjusting substance is an inorganic compound containing oxygen, the base crystal of the inorganic phosphor is usually a solid solution of the crystal grains of the halide that emits fluorescence and the crystal grains of the refractive index adjusting substance. . When the base crystal of the inorganic phosphor is a solid solution of halide crystal grains that emit fluorescence and crystal grains of the refractive index adjusting substance, the refractive index control of the inorganic phosphor becomes relatively easy.

  When the refractive index adjusting substance is an inorganic compound containing oxygen, the refractive index of the inorganic phosphor is higher than when the refractive index adjusting substance is not included, and approaches the refractive index of the transparent resin constituting the sealing material 21. be able to. When the refractive index adjusting substance is an inorganic compound containing oxygen, the refractive index adjusting substance is usually contained in an amount of 0.1 to 50 mol%, preferably 1 to 30 mol% with respect to 100 mol% of the halide. When the content of the refractive index adjusting substance is within the above range, it is preferable because the refractive index of the inorganic phosphor 25 can be made close to the refractive index of the transparent resin constituting the sealing material 21.

[Parent Crystal Containing Fluoride-Emitting Halide and Refractive Index Adjusting Substance]
The inorganic phosphor 25 used in the present embodiment has a host crystal containing the halide that emits the fluorescence and the refractive index adjusting substance, and a part of the atoms constituting the host crystal is partially the emission center. Has a substituted crystal structure.

  The base crystal of the inorganic phosphor 25 contains a refractive index adjusting substance in the crystal lattice of the halide that emits fluorescence, so that the crystal structure does not change as compared with the halide that emits fluorescence. There is. The crystal structure of the inorganic phosphor 25 is such that part of the atoms constituting the host crystal is partially substituted with the emission center, and even if it is replaced with the emission center, it is usually different from the crystal structure of the host crystal. do not do. For this reason, the presence or absence of a change in the host crystal due to the inclusion of the refractive index adjusting substance is substantially synonymous with the presence or absence of a change in the crystal structure of the inorganic phosphor 25.

  If the crystal structure of the host crystal does not change from the halide that emits fluorescence even if the refractive index adjusting substance is included, the inorganic phosphor 25 has the same fluorescence as the halide that emits fluorescence even if it contains the refractive index adjusting substance. It is preferable at the point which can show a characteristic. Further, when the crystal structure of the host crystal changes due to the inclusion of the refractive index adjusting substance, it is preferable in that the fluorescent characteristic of the inorganic phosphor 25 can be controlled by including the refractive index adjusting substance.

[Light emission center]
The emission center of the inorganic phosphor 25 used in the present embodiment is not particularly limited, but a known emission center can be used. Examples of the emission center include rare earth ions. Here, the rare earth ions are ions of rare earth elements. The rare earth element is one or more selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y. Means the element. When rare earth ions are used as the emission center, an inorganic phosphor 25 with high emission efficiency can be obtained. In particular, when an emission center is an ion of one or more elements selected from the group consisting of Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb, the inorganic phosphor 25 having high emission efficiency. Is obtained. In addition, transition metal ions such as Mn, Sb, Cu, Fe, and Ag are also used as the emission center.

The rare earth ions used for the luminescent center are preferably of a parity acceptable transition type. For example, Ce ³⁺ , Eu ^{2+ and the} like are used as the parity-allowable transition type rare earth ions. When a parity-allowed transition type rare earth ion is used for the emission center, light in a wide wavelength range in the near ultraviolet region can be absorbed. In addition, when a parity-allowed transition type rare earth ion is used for the emission center, the energy difference between light absorption and emission by the rare earth ion is small, so for example, an inorganic phosphor that can easily convert the wavelength of near-ultraviolet light into visible light. 25 is obtained. On the other hand, when a rare earth ion other than the parity-allowable transition type is used for the emission center, the light absorption of the rare earth ion of the inorganic phosphor is a narrow linear absorption, and therefore the inorganic phosphor cannot sufficiently absorb ultraviolet light. There is a fear.

Moreover, one kind or two or more kinds of parity-allowable transition type rare earth ions such as Ce ³⁺ and Eu ²⁺ may be used in combination. Among the parity-allowable transition type rare earth ions, Ce ³⁺ and Eu ²⁺ can adjust the absorption wavelength and emission wavelength by adjusting the composition of the host crystal, and are 350 nm or more and less than 380 nm. It is preferable because it is easy to absorb light. For this reason, it is preferable that the inorganic phosphor 25 includes, for example, at least one of Ce ³⁺ and Eu ²⁺ . The inorganic phosphor 25 may include a plurality of emission centers. In this case, it is possible to control the emission wavelength using energy transfer.

[Particle properties of inorganic phosphor]
The inorganic phosphor 25 used in the present embodiment is usually in the form of particles. The inorganic phosphor 25 is preferably a particle group having a central particle size (D ₅₀ ) of 1 μm or more and 100 μm or less because of high luminous efficiency. Here, the central particle size (D ₅₀ ) can be measured by, for example, a laser diffraction / scattering particle size distribution measuring apparatus. Incidentally, the mean particle size of the inorganic phosphor 25 (D ₅₀₎ is less than 1 [mu] m, the emission efficiency tends to be low. On the other hand, if the center particle diameter (D ₅₀ ) of the inorganic phosphor 25 exceeds 100 μm, the probability that ultraviolet light will pass through without passing through the inorganic phosphor increases, so it is necessary to increase the amount of inorganic phosphor added. . The particle group is preferably made of monodispersed particles because light scattering by the inorganic phosphor 25 is suppressed. Further, it is preferable that the monodisperse particles have no crushing surface because a highly efficient inorganic phosphor with few crystal defects can be obtained and an inorganic phosphor with small light scattering can be obtained. The inorganic phosphor 25 preferably has an average particle size of 1 μm or more and less than 100 μm. In this specification, the average particle diameter of the inorganic phosphor is defined as an average value of the longest axis length of any 20 or more phosphor particles observed with a scanning electron microscope. When the average particle diameter of the inorganic phosphor 25 is within the above range, it is possible to obtain a wavelength conversion member that sufficiently absorbs ultraviolet light in sunlight and suppresses the decrease in transmittance of visible light and infrared light. It becomes possible.

[Refractive index of inorganic phosphor]
The inorganic phosphor 25 has a refractive index of light at 25 ° C. and a wavelength of 590 nm of 1.41 or more and less than 1.57, preferably 1.45 or more and less than 1.57, more preferably 1.46 or more and less than 1.52. . When the refractive index of the inorganic phosphor is within the above range, an inorganic phosphor having a low refractive index close to that of the transparent resin constituting the sealing material 21 can be obtained. For this reason, the fall of the light transmittance of visible light of the wavelength conversion member 20 at the time of disperse | distributing this low-refractive-index inorganic fluorescent substance to the sealing material 21 can be suppressed.

[Light absorption characteristics of inorganic phosphors]
It is preferable for the inorganic phosphor 25 to absorb light in a wavelength region of 350 nm or more and less than 380 nm because it functions as an absorber of near ultraviolet rays and is expected to improve the photoelectric conversion efficiency of the solar cell.

[Light emission characteristics of inorganic phosphors]
When the inorganic phosphor 25 emits fluorescence having an emission peak in a wavelength region of 400 nm or more and less than 1200 nm, light having a wavelength that can be used by the solar cell is emitted, and the output of the solar cell can be improved. Therefore, it is preferable.

[Inorganic phosphor manufacturing method]
The inorganic phosphor 25 can be manufactured, for example, by mixing and firing a halide that emits fluorescence, a refractive index adjusting substance, and a raw material of the emission center. Specifically, CaF ₂ as a halide that emits fluorescence, ScOF as a refractive index adjusting substance, and EuF ₃ as a raw material of the emission center Eu ²⁺ can be mixed and fired. . Examples of the firing atmosphere include a reducing atmosphere. Although it does not specifically limit as a calcination temperature, Usually, 1000-1400 degreeC, Preferably you may be 1100-1300 degreeC.

[Effect of inorganic phosphor]
The inorganic phosphor 25 used in the present embodiment has a small refractive index difference from the sealing material 21 constituting the wavelength conversion member 20. For this reason, the inorganic phosphor 25 used in the present embodiment is suitable for the wavelength conversion member 20 of the solar cell module 1.

<Combination ratio of sealing material and inorganic phosphor in wavelength conversion member>
The wavelength conversion member 20 contains the inorganic phosphor 25 in an amount of usually 0.1 vol% or more and less than 15 vol%, preferably 1 vol% or more and less than 10 vol%, when the wavelength conversion member 20 is 100 vol%. When the content of the inorganic phosphor is within the above range, it is possible to obtain the wavelength conversion member 20 that sufficiently absorbs ultraviolet light and suppresses a decrease in light transmittance of visible light and infrared light.

<Characteristics of wavelength conversion member>
If the refractive index difference between the inorganic phosphor 25 and the light-transmissive material 21 at 25 ° C. and the wavelength of 590 nm in the wavelength conversion member 20 is 0.03 or less, the light transmittance of the wavelength conversion member 20 is high. preferable. A high light transmittance is suitable as the wavelength conversion member 20 for the solar cell module 1.

  In the wavelength conversion member 20, a decrease in light transmittance at 25 ° C. and a wavelength of 590 nm of the translucent material 21 accompanying dispersion of the inorganic phosphor 25 is preferably 3 points or less because light transmission loss is small. When the light transmission loss is small, it is suitable as the wavelength conversion member 20 for the solar cell module 1.

  The light transmittance of the wavelength conversion member 20 at a wavelength of 590 nm is preferably more than 85%, and more preferably more than 88%. When the light transmittance is within the above range, a highly transparent wavelength converter 20 is obtained. When the transparency is high, the wavelength conversion member 20 for the solar cell module 1 is suitable.

  By the way, generally, the refractive index of a material changes with temperature. This property that the refractive index changes with temperature is called temperature dependency of the refractive index. The refractive index of the material usually decreases with increasing temperature. In the present embodiment, it is preferable that the temperature-dependent characteristics of the refractive indexes of the translucent material 21 and the inorganic phosphor 25 constituting the wavelength conversion member 20 are similar. When the temperature dependence of the refractive index of the translucent material 21 and the phosphor 25 is similar, a high light transmittance can be maintained even when the temperature of the wavelength conversion member 20 changes during use.

<Method for producing wavelength conversion member>
The wavelength conversion member 20 is, for example, mixed with an inorganic phosphor 25 and a translucent material constituting the sealing material 21 to disperse the inorganic phosphor 25 in the translucent material, and is in the form of a sheet, film, or plate. It can produce by shape | molding in the form of these.

<Operation of wavelength conversion member>
The operation of the wavelength conversion member 20 will be described with reference to FIG. When the solar cell module 1 is irradiated with sunlight including ultraviolet light 70 and visible light and infrared light 80, the ultraviolet light 70 and visible light and infrared light 80 are transmitted through the surface protective layer 30. The light enters the wavelength conversion member 20. Visible light and infrared light 80 incident on the wavelength conversion member 20 pass through the wavelength conversion member 20 as they are without being substantially converted by the inorganic phosphor 25 and are irradiated to the solar cells 10. On the other hand, the ultraviolet light 70 incident on the wavelength conversion member 20 is converted into visible light and infrared light 80 which are light on the long wavelength side by the inorganic phosphor 25, and then irradiated to the solar battery cell 10. The photovoltaic cell 10 generates a photovoltaic power 90 by the irradiated visible light and infrared light 80, and the photovoltaic power 90 is supplied to the outside of the solar battery module 1 through a terminal (not shown).

In the wavelength conversion member 20, the translucent material constituting the sealing material 21 and the inorganic phosphor 25 take values with similar refractive indexes. Specifically, when the translucent material is EVA and the inorganic phosphor 25 is CaF ₂ —ScOF: Eu ²⁺ , the refractive index of light at 25 ° C. and a wavelength of 590 nm is EVA and CaF ₂ —ScOF: Eu ²⁺ . Both are about 1.48. For this reason, the incident light to the wavelength conversion member 20 does not reflect in the wavelength conversion member 20 due to the difference in refractive index between the inorganic phosphor 25 and the translucent material 21, and travels substantially straight from the wavelength conversion member 20. Since it is emitted, the light transmittance of the wavelength conversion member 20 is high.

<Effect of wavelength conversion member>
The wavelength conversion member 20 used in the present embodiment has a high light transmittance because the difference in refractive index between the sealing material 21 and the inorganic phosphor 25 constituting the wavelength conversion member 20 is small. For this reason, the wavelength conversion member 20 used in this embodiment has high quantum efficiency and is suitable for the solar cell module 1.

(Surface protective layer)
The surface protective layer 30 disposed on the surface of the wavelength conversion member 20 protects the wavelength conversion member 20 and the solar battery cell 10 from the external environment of the solar battery module 1. Moreover, the surface protective layer 30 may be provided with a filter function that does not transmit light in a specific wavelength region, if necessary. The surface protective layer 30 is made of, for example, a glass substrate, polycarbonate, acrylic, polyester, fluorinated polyethylene, or the like.

(Back side sealing member)
The back surface sealing member 40 disposed on the back surface 14 of the solar battery cell 10 prevents moisture from entering the solar battery cell 10 and improves the overall strength of the solar battery module 1. The back surface sealing member 40 consists of the same material as the material which can be used with the sealing material 21 of the wavelength conversion member 20, for example. The material of the back surface sealing member 40 may be the same as or different from the material of the sealing material 21 of the wavelength conversion member 20.

(Back protection layer)
The back surface protective layer 50 disposed on the back surface of the back surface sealing member 40 protects the back surface sealing member 40 and the solar battery cell 10 from the external environment of the solar cell module 1. The back surface protective layer 50 is made of, for example, the same material that can be used for the surface protective layer 30. The material of the back surface protective layer 50 may be the same as or different from the material of the front surface protective layer 30.

(Operation of solar cell module)
Since the operation of the solar cell module 1 has been described together in the section of the operation of the wavelength conversion member 20, the description thereof is omitted here.

(Effect of solar cell module as photovoltaic device)
Since the solar cell module 1 as the photovoltaic device according to the present embodiment uses the wavelength conversion member 20 that has a small refractive index difference between the sealing material 21 and the inorganic phosphor 25 and a high light transmittance, the quantum efficiency is high. .

  Hereinafter, the present embodiment will be described in more detail by way of examples, but the present embodiment is not limited to these examples.

The fluoride inorganic phosphors of Example 1 and Comparative Example 1 were synthesized using an adjustment method utilizing a solid phase reaction, and the characteristics thereof were evaluated. In the examples and comparative examples, the following compound powders were used as raw materials.
Calcium fluoride (CaF ₂ ): purity 3N, manufactured by High Purity Chemical Laboratory Co., Ltd. Scandium fluoride (ScF ₃ ): purity 97%, manufactured by Wako Pure Chemical Industries, Ltd. scandium oxide (Sc ₂ O ₃ ): purity 3N, Europium fluoride (EuF ₃ ) manufactured by Shin-Etsu Chemical Co., Ltd .: purity 3N, manufactured by Wako Pure Chemical Industries, Ltd.

[Example 1]
First, 0.4248 g of ScF ₃ and 0.5781 g of Sc ₂ O ₃ as raw materials were weighed. Next, the raw materials were sufficiently dry-mixed using a magnetic mortar and a magnetic pestle to obtain a fired raw material. Thereafter, the firing raw material was transferred to an alumina crucible and fired at a temperature of 1000 ° C. for 2 hours in a reducing atmosphere using a tubular atmosphere furnace. Then, ScOF was obtained by crushing the fired product using an alumina mortar and an alumina pestle.
Next, the obtained ScOF, CaF ₂ , and EuF ₃ were weighed 0.1599 g, 1.4006 g, and 0.0125 g, respectively. Next, the raw materials were sufficiently dry-mixed using a magnetic mortar and a magnetic pestle to obtain a fired raw material. Thereafter, the firing raw material was transferred to an alumina crucible and fired at a temperature of 1200 ° C. for 2 hours in a reducing atmosphere using a tubular atmosphere furnace. Then, the inorganic phosphor of Example 1 was obtained by crushing the fired product using an alumina mortar and an alumina pestle. The composition of the inorganic phosphor was Ca _0.897 Sc _0.1 Eu _0.03 F _1.9 O _0.1 .
When the obtained inorganic phosphor of Example 1 was irradiated with ultraviolet rays (wavelength 365 nm), blue fluorescence was visually observed.

[Comparative Example 1]
As raw materials, 1.5567 g of CaF ₂ and 0.0125 g of EuF ₃ were weighed. Next, the raw materials were sufficiently dry-mixed using a magnetic mortar and a magnetic pestle to obtain a fired raw material. Thereafter, the firing raw material was transferred to an alumina crucible and fired at a temperature of 1000 ° C. for 2 hours using a tubular atmosphere furnace. Thereafter, the fired product was pulverized using an alumina mortar and an alumina pestle to obtain an inorganic phosphor of Comparative Example 1. The composition of the inorganic phosphor was Ca _0.997 Eu _0.03 F ₂ .
When the obtained inorganic phosphor of Comparative Example 1 was irradiated with ultraviolet rays (wavelength 365 nm), blue fluorescence was visually observed.

(Evaluation)
<Refractive index>
The refractive index of the inorganic phosphors of Example 1 and Comparative Example 1 was measured. The refractive index of the inorganic phosphor was measured by the Becke line method (based on JIS K7142 B method) using an Abbe refractive index system NAR-2T manufactured by Atago Co., Ltd. and a polarizing microscope BH-2 manufactured by Olympus Corporation. The measurement conditions are as follows.
Immersion: Propylene carbonate (nD ²³ : 1.420)
Butyl phthalate (nD ²³ : 1.491)
Temperature: 23 ° C
Light source: Na (D line / 589 nm)

  As a result of the measurement, the refractive index of the inorganic phosphor of Example 1 is 1.441 to 1.490, the average value is 1.453, and the refractive index of the inorganic phosphor of Comparative Example 1 is 1.439 to 1.444. The average value was 1.442. As described above, the refractive index of the inorganic phosphor of Example 1 was higher than that of the inorganic phosphor of Comparative Example 2.

  In addition, the wavelength conversion member 20 will be obtained if an inorganic fluorescent substance is disperse | distributed in the sealing material 21 which consists of translucent materials, such as a translucent resin base material. In the solar cell module 1, a transparent resin such as ethylene vinyl acetate copolymer (EVA), polyvinyl butyral (PVB), polyimide, polyethylene, polypropylene, polyethylene terephthalate (PET) is usually used as the sealing material 21. The refractive index of ethylene vinyl acetate copolymer (EVA) is 1.48, and the refractive index of polyolefin-based transparent resins such as polyethylene and polypropylene is 1.49. Thus, since the refractive index of the inorganic phosphor of Example 1 is close to the refractive index of ethylene vinyl acetate copolymer (EVA) or polyolefin-based transparent resin, the inorganic phosphor 25 is dispersed in the sealing material 21. However, the wavelength conversion member 20 in which the light transmittance does not decrease is obtained.

<Emission spectrum>
The emission spectra of the inorganic phosphors obtained in Example 1 and Comparative Example 1 were measured. The emission spectrum of the inorganic phosphor was measured using a quantum efficiency measurement system QE-1100 manufactured by Otsuka Electronics Co., Ltd. The measurement conditions are as follows.
Excitation wavelength: 350 nm
Integration count: 30 times Exposure time: 5000 ms

  FIG. 2 is a graph showing emission spectra of Example 1 and Comparative Example 1. Each graph was standardized so that the intensity of the emission peak was 1. As shown in FIG. 2, Example 1 and Comparative Example 1 showed the same emission spectrum. Both emission peak wavelengths were about 425 nm.

  From the results of Example 1 and Comparative Example 1, it was found that the inorganic phosphor of Example 1 exhibited the same emission spectrum as the inorganic phosphor of Comparative Example 1. In addition, the refractive index of the inorganic phosphor of Example 1 is larger than the refractive index of the inorganic phosphor of Comparative Example 1, and is close to 1.48 to 1.49 which is the refractive index of EVA or polyolefin-based transparent resin. I understood.

  As described above, the contents of the present embodiment have been described according to the examples. However, the present embodiment is not limited to these descriptions, and it is obvious to those skilled in the art that various modifications and improvements are possible. is there.

1 Solar cell module (photovoltaic device)
20 Wavelength conversion member 21 Sealing material (translucent material, transparent resin)
25 Inorganic phosphor

Claims (14)

Refractive index adjusting material comprising a halide having a refractive index of less than 1.46 and emitting fluorescence and an element atom having an abundance of less than 1 mol% in the crystal lattice of the halide or a compound having the element And a part of the host crystal including a crystal structure in which a luminescent center is substituted,
An inorganic phosphor having a refractive index greater than that of the halide.   The inorganic phosphor according to claim 1, wherein the halide that emits fluorescence contains fluorine.   The inorganic phosphor according to claim 2, wherein the halide that emits fluorescence is a fluoride.   The inorganic phosphor according to claim 1, wherein the refractive index adjusting substance is an oxygen atom or an inorganic compound containing oxygen.   The inorganic phosphor according to claim 1, wherein the host crystal is a solid solution of a halide that emits the fluorescence and the refractive index adjusting substance.   The inorganic phosphor according to claim 4, wherein the inorganic compound containing oxygen is an oxyfluoride.   The inorganic phosphor according to claim 1, wherein the halide that emits fluorescence includes an alkaline earth metal.   The inorganic phosphor according to claim 7, wherein the halide that emits fluorescence contains a rare earth element.   The inorganic phosphor according to claim 7, wherein the halide that emits fluorescence has a fluorite structure.   The inorganic phosphor according to claim 1, which absorbs light in a wavelength region of 350 nm or more and less than 380 nm.   2. The inorganic phosphor according to claim 1, which emits fluorescence having an emission peak in a wavelength region of 400 nm or more and less than 1200 nm.   The inorganic phosphor according to claim 1, wherein the refractive index of light at a wavelength of 590 nm is 1.41 or more and less than 1.57.   A wavelength converter obtained by dispersing the inorganic phosphor according to any one of claims 1 to 12 in a translucent material. A photovoltaic device comprising the wavelength converter according to claim 13.

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