Solar wavelength conversion material, solar cell encapsulant comprising the solar wavelength conversion material, and solar cell comprising the solar wavelength conversion material

Abstract

A solar wavelength conversion material comprising luminescent aluminum hydroxide having ultraviolet absorption properties and photoluminescence properties in the visible light wavelength range, wherein the solar wavelength conversion material further comprises a lanthanide ion or a derivative containing the same.

Description

TECHNICAL FIELDThe present invention relates to a solar wavelength conversion material having improved efficiency, a solar cell encapsulant, and a solar cell comprising the solar wavelength conversion material.BACKGROUND ARTThe most commonly commercialized solar cells are made of a silicon material, and about 50% of the light cannot be used due to the mismatch between the natural sunlight spectrum and the band gap of the silicon-based material. That is, the natural solar spectrum has a broad distribution (280-2500 nm, 0.5-4.4 eV) of ultraviolet to infrared wavelengths, while silicon solar cells can only absorb some wavelengths of ultraviolet and visible wavelengths.In order to compensate for this, studies using a wavelength conversion solar material have recently been proposed to improve photocurrent conversion efficiencies of natural sunlight and silicon solar cells (Chem. Soc. Rev., 2013, 42, 173). That is, the studies propose to incorporate a solar wavelength conversion material (solar spectral converter) into a silicon solar cell, wherein the solar wavelength conversion material converts the light in the ultraviolet region in which silicon insufficiently absorbs the sunlight or in the infrared region in which it has lower energy than the silicon bandgap into the light in wavelength regions of the visible light or the near infrared light in which the visible or near infrared light can be well absorbed by silicon.In addition, since solar cells or solar modules mainly composed of solar cells are installed outdoors and exposed to external environments such as heat, moisture, time-of-day fluctuations or pollution sources over a long period of time, it is important to ensure long-term durability so as not to be affected by these external factors.In order to solve the above problems, a functional additive may also be dispersed in an encapsulant. For example, long-term durability can be ensured by adding a UV stabilizer, a UV absorber, or a combination of an absorber and a stabilizer, which can be added to improve resistance to UV rays, to the encapsulant.However, in the case of an ultraviolet absorber, the light near an ultraviolet region cannot be incident on a solar cell, and thus the initial total output of a solar cell module can be undesirably reduced. In addition, in order to improve insulation or to cause moisture absorption when inorganic particles such as silica or magnesium hydroxide are incorporated, the durability of the encapsulant can be more or less improved; however, light absorption of the solar cell may be disturbed due to scattering or reflection of sunlight incident on the front surface of the solar cell. When a plurality of functional additives are added to solve the above problems, the durability of the encapsulant per se may be improved, but the overall performance of a solar cell or a solar cell module may be reduced.CHEN, B. [et al.]: Single Source Precursor Chemical Vapor Decomposition Method to Fabric Stable, Bright Emissive Aluminum Hydroxide Phosphors for UV-Pumped White Light-Emitting Devices. In: Adv. Optical Mater., Vol. 6, 2018, pp. 1701115 (1-8) describes a method for producing aluminum hydroxide-based LEDs.WO 2015 / 069 384 A2 describes nanocrystals containing silicone blocking agents. Also described are dispersions which comprise the nanocrystal(s) and at least one silicone monomer, silicone prepolymer and / or silicone polymer and optionally additionally comprise a solvent. Furthermore, cured dispersions, compositions of nanocrystals and LEDs and associated structures containing the composition(s) are provided.KR 10 2016 0 144 232 A describes a transparent plate for a light module, a method for producing the same, and a light module comprising the transparent plate.DESCRIPTION OF THE EMBODIMENTS TECHNICAL PROBLEMIn order to solve the above problems, an object of the present invention is to provide a solar conversion material capable of improving the photocurrent conversion efficiency of a solar cell.Another object of the present invention is to provide a solar cell encapsulant and a solar cell having high durability and excellent photocurrent conversion efficiency.SOLUTION OF PROBLEMTo achieve an object of the present invention, the present invention provides a solar wavelength conversion material comprising an aluminum hydroxide luminescent precursor.In one embodiment, the aluminum hydroxide precursor is preferably one of the following substances: aluminum monoacetate, aluminum triacetate, aluminum diacetate, aluminum triethyl aluminum, trimethyl aluminum, aluminum alkoxide, diethyl aluminum chloride, aluminum sulfate, aluminum cyanide, aluminum nitrite, aluminum carbonate, aluminum sulfate, aluminum hydroxide, aluminum oxide, aluminum chlorate, aluminum sulfide, aluminum chromate, aluminum trichloride, aluminum perchlorate, aluminum nitrate, aluminum permanganate, aluminum hydrogen carbonate, aluminum phosphate, aluminum oxalate, aluminum hydrogen phosphate, aluminum thiosulfate, aluminum chlorite, aluminum hydrogen sulfate, aluminum dichromate, aluminum bromide, aluminum hypochlorite, aluminum chloride hexahydrate, aluminum dihydrogen phosphate, aluminum phosphite, Aluminiumkaliumsulfatdodecahydrat aluminum bromate, aluminum nitride, or derivatives thereof.In an embodiment, the solar wavelength conversion material preferably comprises an Al(OH) 3-, AlOOH, 5Al 2 O 3 ·2H 2 O-, or Al 2 O 3- structure.In one embodiment, the luminescent aluminum hydroxide preferably has a size in the range from 1 nm to 1000 μm.In one embodiment, the luminescent aluminum hydroxide preferably has a porous structure.According to the present invention, the solar wavelength conversion material preferably further comprises a lanthanide ion or a derivative containing the same.In one embodiment, the lanthanide ion is preferably capable of emitting light in a near infrared, ultraviolet or visible light wavelength range.In one embodiment, a near infrared luminescent lanthanide ion precursor is one or more of the following: Yb (ytterbium), Nd (neodymium), Er (erbium), Ho (holmium), Tm (thulium), and derivatives containing the same.In one embodiment, the lanthanide ion precursor preferably contains an element having an emission wavelength in the visible light wavelength range.In one embodiment, the lanthanide ion or the derivative containing the same is preferably contained in an amount of 0.001 to 10 parts by weight based on 100 parts by weight of the aluminum hydroxide precursor.In one embodiment, the solar wavelength conversion material preferably further comprises an aromatic ring compound or a derivative thereof.In one embodiment, the aromatic ring compound or derivative thereof is localized within 10 nm of the aluminum hydroxide precursor or aluminum hydroxide derived therefrom or is preferably formed by a covalent bond.In one embodiment, the aromatic ring compound is preferably one or more of the following: an aromatic hydrocarbon in which only carbons and hydrogens are linked to each other, an aromatic heterocyclic compound in which some of the ring-forming carbon atoms are substituted with oxygen, nitrogen or sulfur atoms not with carbon, or a derivative in which some of the hydrogens are substituted with functional groups in the aromatic hydrocarbon and aromatic heterocyclic compound molecules.In one embodiment, the aromatic ring compound is preferably one or more of the following substances: furan, benzbenzofuran, isobenzbenzofuran, pyrrole, indole, isoindole, thiophene, benzbenzothiophene, imidazole, benzimidazole, purine, pyrazole, indazole, oxazole, benzoxazole, oxazoleisoxazole, benzoxazole isoxazole, thiazole, benzbenzothiazole, benzbenzene, naphthalene, anthracene, pyridine, quinoxaline, acridine, pyrimidine, quinazoline, pyridazine, cinnoline, phthalazine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, and derivatives thereof.In one embodiment, the particle size of the solar wavelength conversion material is preferably in the range of 0.5 nm to 500 μm.In an embodiment, the maximum absorption wavelength of the solar wavelength conversion material is 200 nm to 500 nm, preferably 300 to 450 nm.In an embodiment, the maximum emission wavelength of the solar wavelength conversion material is preferably 450 nm to 1100 nm.To achieve another object of the present invention, the present invention provides a solar cell encapsulant containing the solar wavelength conversion material according to the present invention.In one embodiment, the encapsulant is preferably in the form of a film having a thickness of 100 μm or less.In one embodiment, the encapsulant is preferably EVA (ethylene vinyl acetate), POE (polyolefin elastomer), cross-linked polyolefin (PO), TPU (thermal polyurethane), PVB (polyvinyl butyral), silicone, silicone / polyurethane hybrid, or ionomer.In one embodiment, the solar wavelength conversion material is preferably contained in an amount of 0.0001 to 10 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the resin of the encapsulant.To achieve another object of the present invention, the present invention provides a solar cell containing the solar wavelength conversion material or the solar cell encapsulant according to the present invention.In one embodiment, the solar wavelength conversion material is preferably coated on the front side of the solar cell or on the back side of the encapsulant on the front side of the solar cell.In one embodiment, the coating is preferably a spray coating or screen coating.In one embodiment, the encapsulant of the solar cell is preferably EVA (ethylene vinyl acetate), POE (polyolefin elastomer), cross-linked polyolefin (PO), TPU (thermal polyurethane), PVB (polyvinyl butyral), silicone, silicone / polyurethane hybrid or ionomer.In addition, in a preferred embodiment of the present invention, the encapsulant of the present invention is laminated on the front and back surfaces of the solar cell, glass is laminated on the front surface of the encapsulant located on the front surface of the solar cell, and a back surface film is laminated on the back surface of the encapsulant located on the back surface of the solar cell.ADVANTAGEOUS EFFECTS OF THE DISCLOSUREWhen a solar module is manufactured by uniformly dispersing a solar wavelength conversion material having ultraviolet absorption properties and visible photoluminescence properties in a resin, not only an ultraviolet blocking effect by ultraviolet absorption but also a down conversion effect of visible photoluminescence can be expected, thereby manufacturing a solar module with increased performance while keeping durability.In addition, the durability of an encapsulant can be further improved by the heat-resistant, moisture-resistant effects due to aluminum hydroxide materials capable of absorbing heat and moisture.Therefore, a solar module with an encapsulant in which a solar wavelength conversion material having such a photoluminescence property is dispersed can prevent a decrease in power due to long-term outdoor exposure by increasing the long-term durability, thus promoting generation of solar energy.In addition, the solar wavelength conversion material according to the present invention can emit one or more photons of ultraviolet light having low photocurrent conversion efficiency of a solar cell into visible and near infrared light wavelength ranges having high photocurrent conversion efficiency, thereby maximizing the efficiency of a solar cell.Moreover, the solar wavelength conversion material according to the present invention introduces an aromatic ring compound and / or a lanthanide ion into the aluminum hydroxide luminescent synthesizing step to further increase the absorption in the ultraviolet region, thereby enabling effective down conversion and, at the same time, improving the durability of the solar cell, thereby reducing the power generation cost of the solar cell and ensuring long-term performance.When the solar wavelength conversion material is applied to the front surface of the solar cell or the back surface of the encapsulant on the front surface of the solar cell, the efficiency of the solar cell can be increased. When the material is directly applied to the solar cell, down conversion is caused, thereby improving the performance.In addition, when the solar wavelength conversion material is located at the interface between the encapsulant and the solar cell, the increased photovoltaic current due to an antireflection coating effect and the anti-PID (potential-induced degradation) effect of a solar energy module due to trapping of Na+ions generated from the cured glass of the module and the anti-LeTID (light and increased temperature-induced degradation) effect due to the UV blocking and heat dissipation properties can also be expected.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a schematic cross-sectional view of an encapsulant in which aluminum hydroxide luminescent particles are dispersed, a photovoltaic (PV) solar cell including the encapsulant and a solar module. FIG. 2 is a schematic diagram showing the principle of aluminum hydroxide photoluminescence for ultraviolet absorption and visible and near infrared photoluminescence: (a) principle of visible photoluminescence; and (b) principles of photoluminescence in visible and near infrared. FIG. 3 shows absorbance and photoluminescence spectra of aluminum luminescent hydroxide: the dashed line represents absorbance; and the solid line represents photoluminescence spectrum. Figure 4 shows excitation and photoluminescence spectra of near infrared luminescent aluminum hydroxide: (a) Yb doping; (b) Ce, Yb doping; (c) Tb, Yb doping; and (d) Yb, 2-naphthoic acid doping. FIG. 5 is a spectrum showing a change in photoluminescence (PL) intensity according to the 2-naphthoic acid doping of near infrared luminescent aluminum hydroxide. FIG. 6 shows extinction and photoluminescence spectra of aluminum luminescent hydroxide containing aluminum luminescent hydroxide, an aromatic ring compound and derivatives thereof:(a) and (d) show extinction and photoluminescence spectra of luminescent aluminum hydroxide (AlOH);(b) and (e) show extinction and photoluminescence spectra of luminescent aluminum hydroxide containing 2-naphthoic acid containing (AIOH-NA); and(c) and (f) show extinction and photoluminescence spectra of aluminum luminescent hydroxide containing 1,2,3,4-tetrahydro carbazol-4-one (AlOH-CA). FIG. 7 shows time-resolved fluorescence spectra of luminescent aluminum hydroxides of (a) AIOH and (b) AIOH-NA. FIG. 8 shows the total transmission spectra of a solar encapsulant before and after the introduction of luminescent aluminum hydroxides and UV absorbers: the dash-double-dot line represents the total transmission of EVA, the dash-single-dot line represents the total transmission of EVA-AIOH 0.1, the solid line represents the total transmission of EVA-AIOH 0.5, and the dashed line represents the total transmission of EVA-C81 0.2). FIG. 9 shows total transmission spectra of encapsulants before and after incorporation of aluminum luminescent hydroxides: (a) UV aging after 2000 hours; and (b) wet heat aging after 2000 hours. FIG. 10 shows external quantum efficiency spectra of a solar cell #2 of Tables 5 and 6 and an AIOH-NA-Yb coated cell of Example 4. FIG. 11 shows spectra obtained by measuring the changes in total reflectance of a solar cell #2 of Tables 5 and 6 and an AIOH-NA-Yb coated cell of Example 4; FIG. 12 shows external quantum efficiency spectra before and after coating a silicon solar cell with luminescent aluminum hydroxide. FIG. 13 shows reflection spectra before and after coating a silicon solar cell with luminescent aluminum hydroxideBEST MODEHereinafter, the present invention will be described in more detail, but this is for explaining the present invention in more detail and is not intended to limit the scope of the present invention.According to an embodiment of the present invention, the present invention provides a solar wavelength conversion material comprising aluminum luminescent hydroxide having ultraviolet absorption properties and visible photoluminescence properties.Solar wavelength conversion materials are substantially divided into two types: down conversion and up conversion depending on the photoconversion method.First, the down conversion is divided into a down shift in which a photon of a short wavelength (e.g., ultraviolet) having a higher energy than the silicon bandgap is absorbed and then converted into a photon in the long wave region having a lower energy that can well absorb silicon; and quantum cutting in which an absorbed photon is converted into two or more photons in a low energy region having a wavelength twice as long as the absorbed wavelength.Conversely, a technology in which two photons in the infrared region having an energy lower than the band gap of silicon are absorbed and transmitted without being absorbed by silicon, and then converted into a photon in the high visible light region that can be easily absorbed by silicon is called up conversion.According to an embodiment of the present invention, there is provided a solar wavelength conversion material comprising: an aluminum hydroxide luminescent precursor; and a lanthanide ion or a derivative containing the same.

[0036] According to an embodiment of the present invention, there is provided a solar wavelength conversion material comprising: an aluminum hydroxide luminescent precursor; and an aromatic ring compound or a derivative thereof.The present invention relates to an improved efficiency solar wavelength conversion material containing inexpensive aluminum luminescent hydroxide and a solar cell comprising the same, and relates to a technology for improving photocurrent conversion efficiency corresponding to an increase in short circuit current by causing downward conversion, an antireflection coating effect, and an improvement in durability by disposing the solar wavelength conversion material at the interface of the solar cell and the front encapsulant into which sunlight is incident or by dispersing it in the encapsulant.FIG. 1 is a schematic cross-sectional view of an encapsulant having aluminum hydroxide luminescent particles dispersed therein, a photovoltaic (PV) solar cell including the same, and a solar module.Referring to FIG. 1, a silicon solar cell module may be manufactured by laminating after glass / encapsulant layer / photovoltaic (PV) solar cell / encapsulant layer / back side are stacked in this order from the front side on which light is incident.< Wavelength Conversion Material>In order to produce a solar wavelength conversion material capable of improving the photocurrent conversion efficiency and improving the durability of an encapsulant, aluminum hydroxide luminescent, which is a low cost material and has characteristics such as excellent absorption and photoluminescence properties, heat resistance and moisture resistance, is used in the present invention.The aluminum luminescent hydroxide comprises an Al(OH) 3-, AlOOH, 5Al 2 O 3 ·2H 2 O-, or Al 2 O 3- structure, and in the present invention, this structure is hereinafter referred to as aluminum hydroxide, AlOH, or aluminum hydroxide.The aluminum hydroxide luminescent precursor is one of aluminum monoacetate, aluminum triacetate, aluminum diacetate, aluminum triethyl aluminum, trimethyl aluminum, aluminum alkoxide, diethyl aluminum chloride, aluminum sulfate, aluminum cyanide, aluminum nitrite, aluminum carbonate, aluminum sulfate, aluminum hydroxide, aluminum oxide, aluminum chlorate, aluminum sulfide, aluminum chromate, aluminum trichloride, aluminum perchlorate, aluminum nitrate, aluminum permanganate, aluminum hydrogen carbonate, aluminum phosphate, aluminum oxalate, aluminum hydrogen phosphate, aluminum thiosulfate, aluminum chlorite, aluminum hydrogen sulfate, aluminum dichromate, aluminum bromide, aluminum hypochlorite, aluminum chloride hexahydrate, aluminum dihydrogen phosphate, aluminum phosphite, Aluminiumkaliumsulfatdodecahydrat aluminum bromate, aluminum nitride, or derivatives thereof.According to one embodiment, the luminescent aluminum hydroxide preferably has a porous structure. The produced aluminum luminescent hydroxide can be synthesized to have a porosity depending on variables such as precursors, solvents, impurities, or temperature and time of the thermal decomposition reaction, and when the produced aluminum luminescent hydroxide has a porosity, its surface area increases, and thus durability such as moisture resistance and heat resistance of the encapsulant can be improved.According to an embodiment of the present invention, the solar wavelength conversion material according to the present invention preferably further contains a lanthanide ion or a derivative containing the same.In particular, when a lanthanide ion allowing near infrared photoluminescence is introduced, ultraviolet light can be absorbed and visible light and near infrared light can be emitted simultaneously, and thus a higher photocurrent conversion rate can be realized when applied to a high-efficiency solar cell having excellent power generation efficiency in the visible and near infrared wavelength ranges.In addition, when aluminum hydroxide absorbs high energy in the ultraviolet light wavelength range and transmits it to the lanthanide ion, enabling near infrared photoluminescence, two photons in the near infrared light wavelength range are emitted with low energy of a long wavelength that is more than twice the absorption wavelength, thereby maximizing the photocurrent conversion rate of a solar cell.The lanthanide ion may emit light in wavelength ranges of near infrared, ultraviolet or visible light.According to one embodiment of the present invention, some lanthanide ions may be introduced to induce near infrared photoluminescence. The near infrared luminescent lanthanide precursor capable of emitting near infrared light having a long wavelength of 800 nm or more may include Yb (ytterbium), Nd (neodymium), Er (erbium), Ho (holmium), Tm (thulium), etc., and according to the external quantum efficiency characteristics of a solar cell, ions having a photoluminescence spectrum at a wavelength having a high photocurrent conversion efficiency of the solar cell may be selected and doped into aluminum hydroxide.According to an embodiment of the present invention, a lanthanide ion is selected that allows near infrared photoluminescence, and for example, when Yb is selected, all derivatives comprising Yb may be used as precursors of Yb. Examples thereof may include ytterbium trifluoromethane sulfonate, Ytterbiumtrifluormethansulfonathydrat ytterbium chloride, ytterbium fluoride, ytterbium iodide, ytterbium chloride hydrate, ytterbium fluoride hydrate, ytterbium fluoride, ytterbium oxide, ytterbium oxide, ytterbium nitrate pentahydrate, ytterbium acetate hydrate, ytterbium acetate hydrate, ytterbium acetate hydrate, ytterbium polystyrene sulfonate, 3-hydroxy-2-naphthoic (2-hydroxylbenzylidene)hydrazide, Ytterbiumisopropoxid ytterbium bromide, tris[N,N-bis(trimethylsilyl)amide]ytterbium, and so forth.In addition, according to an embodiment of the present invention, in order to cause efficient energy transfer of aluminum luminescent hydroxide to near infrared light, a lanthanide-based ion precursor including Ce, Tb, Eu, etc. may be codoped with a photoluminescence wavelength in the visible light wavelength range.According to an embodiment of the present invention, the lanthanide ion or the derivative comprising the same may be contained in an amount of 0.001 to 10 parts by weight based on 100 parts by weight of the aluminum hydroxide precursor. When the lanthanide ion is introduced in excess outside the range of 0.001 to 10 parts by weight based on 100 parts by weight of the aluminum hydroxide precursor, the photoluminescent performance may be deteriorated by quenching due to the aggregation of lanthanide ions, and when a small amount of the lanthanide ion or the derivative containing the same is introduced, the energy transfer from the luminescent aluminum hydroxide to the lanthanide ion may be limited, and thus a down conversion effect may be difficult to expect.According to an embodiment of the present invention, when an impurity or aromatic ring compound and a derivative thereof are appropriately added, the trap state of aluminum hydroxide may be changed, and the position of the emission wavelength may also be controlled depending on the changed trap state.According to an embodiment of the present invention, the aromatic ring compound or a derivative containing the same may be contained in an amount of 0.001 to 10 parts by weight based on 100 parts by weight of the aluminum hydroxide precursor.In addition, when the light absorbed by the aromatic ring compound and its derivative is at an energy higher than the trap emission, energy transfer from the aromatic ring compound and its derivative to the trap state of aluminum hydroxide is achieved. In this case, the photoluminescence intensity of the near infrared luminescent aluminum hydroxide is enhanced by additional energy transfer. That is, the aromatic ring compound and the derivative thereof can act as an antenna that captures light in the wavelength range of the ultraviolet light and transmits the captured light to aluminum hydroxide.Therefore, in the case where the aromatic ring compound and the derivative thereof coexist, instead of the case where aluminum hydroxide alone coexists, effective ultraviolet absorption and stronger visible and near infrared photoluminescence can be realized. In addition, since the position of the trap state is decreased, the emission wavelength shifts to a longer wavelength, and the Stokes shift, which is a difference between the absorption wavelength and the emission wavelength, may increase, thereby decreasing the reabsorption of light emitted from a material.For effective energy transfer from the aromatic ring compound and the derivative thereof to aluminum hydroxide, the distance between the two materials must be within 10 nm or form a covalent bond. Therefore, the aromatic ring compound is preferably within 10 nm of the aluminum hydroxide precursor or the aluminum hydroxide derived therefrom or is in a state formed by a covalent bond.According to an embodiment of the present invention, the aromatic ring compound is preferably one or more of the following: an aromatic hydrocarbon in which only carbons and hydrogens are bonded to each other, an aromatic heterocyclic compound in which some of the carbon atoms constituting a ring are replaced with oxygen, nitrogen or sulfur atoms other than carbon, or a derivative in which some of the hydrogens are replaced with functional groups in the aromatic hydrocarbon and aromatic heterocyclic compound molecules.According to one embodiment of the present invention, the aromatic ring compound may be selected from one or more of the following substances: furan, benzbenzofuran, isobenzbenzofuran, pyrrole, indole, isoindole, thiophene, benzbenzothiophene, imidazole, benzimidazole, purine, pyrazole, indazole, oxazole, benzoxazole benzoxazole, oxazoleisoxazole, benzoxazoleisoxazole, thiazole, benzbenzothiazole, benzbenzene, naphthalene, anthracene, pyridine, quinoxaline, acridine, pyrimidine, quinazoline, pyridazine, cinnoline, phthalazine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine and derivatives thereof.The solar wavelength conversion material may be manufactured using a hydrothermal, sol-gel, thermal decomposition synthesis method, or the like. In the present invention, the present invention is described in more detail by a pyrolytic synthesis method, but the scope of the present invention is not limited thereto.In the case of synthesizing aluminum luminescent hydroxide by the thermal decomposition synthesis method, a material having a boiling point higher than the thermal decomposition temperature of the aluminum precursor may be used as the solvent. For example, a material having a high boiling point of 200° C. or higher, such as hexadecylamine, 1-eicosane, 1-octadecene, docosane, phenyl ether, benzyl ether, octyl ether, oleic acid, oleylamine, polyisobutylene, etc., is used as the solvent.The solvent may act as a solvent and provide impurities such as carbon, carbonyl radical, oxaliphic acid radical, sulfuric acid, etc., and thus may control the photoluminescence properties or may serve to further improve the luminous performance. In addition, in the pyrolysis synthesis step, by adding impurities such as alkyl (alkyl))(C 1 to C n) acetate, thus, the absorption and photoluminescence properties can be controlled.In addition, in the pyrolysis synthesis step, particularly absorption of near infrared luminescent aluminum hydroxide, when an aromatic ring compound having a high extinction coefficient in the wavelength range of ultraviolet light and a derivative thereof are appropriately added, increased photoluminescence, large Stokes shift, etc. can be caused. Therefore, in the pyrolytic synthesis step, the aromatic ring compound is added together with the aluminum hydroxide precursors and lanthanide ions.One or more of the aluminum precursors, one or more of the lanthanide ions, and one of the aromatic ring compound and its derivative are dispersed in the solvent and then reacted at the pyrolysis temperature of the aluminum precursor. When the reaction is complete, the product can be isolated and purified to obtain a final aluminum luminescent hydroxide (solar conversion material).The reason why the aluminum hydroxide produced by pyrolysis synthesis exhibits photoluminescence properties is the trap emission from defects in the metal oxide. In the case of the trap emission, a trap state representing a different energy level is formed between the ground state and the excited state when defects are present in the material, and electrons transferred from the ground state to the excited state by external energy are stabilized and transferred to a lower energy level generated due to defects, and emit light while being transferred to the final ground state (FIG. 2( a)). In this case, when a small amount of one or more of the lanthanide ions that allow the near-infrared photoluminescence is doped, energy transfer from the aluminum hydroxide to the lanthanide-based ion occurs, and the near-infrared photoluminescence occurs at low energy at a wavelength that is more than twice the photoluminescence wavelength of aluminum hydroxide. In particular, two or more photons in the near infrared light wavelength range may be emitted (FIG. 2( b)).Since the solar wavelength conversion material is located in the front part of a solar cell, particles smaller in size than the wavelength of sunlight incident on the solar cell are advantageously used. When the particle size is similar to or larger than the wavelength of the incident sunlight, the incident sunlight may be scattered or reflected, and thus the efficiency of the entire solar cell may be reduced. Accordingly, the particle size of the solar wavelength conversion material may be in the range of 0.5 nm to 500 μm, preferably 1 nm to 100 μm or less.The aluminum luminescent hydroxide according to the present invention preferably has an absolute quantum yield of 40% or more.Fig. 3 shows absorption and photoluminescence spectra of luminescent aluminum hydroxide produced by a pyrolysis synthesis process. More specifically, the broken line represents the absorption spectrum of aluminum hydroxide that starts absorption at 450 nm and exhibits strong absorption in the ultraviolet region; and the solid line represents the photoluminescence spectrum that exhibits the maximum emission peak at 526 nm.In order to apply the solar wavelength conversion material to a silicon solar cell, the solar wavelength conversion material should have an absorbance in the ultraviolet light wavelength range and photoluminescence properties in the visible and near infrared light wavelength range. In particular, the absorption wavelength range of the solar wavelength conversion material is preferably formed at 200 to 500 nm. In addition, the photoluminescence wavelength range is preferably formed at 450 nm or more, preferably 450 nm to 1100 nm.In particular, in terms of the solar wavelength conversion material, it is preferable that the absorption wavelength and the photoluminescence wavelength range do not overlap, and a material having a large Stokes shift is advantageously used because, when the absorption wavelength and photoluminescence wavelength ranges overlap each other, reabsorption in which the light emitted from the material is reabsorbed may act as a loss.The produced aluminum luminescent hydroxide can be synthesized to have porosity depending on variables such as precursors, solvents, impurities, or temperature and time of thermal decomposition reaction; and when the aluminum luminescent hydroxide has porosity, the surface area increases, and the durability of the solar module such as moisture resistance and heat resistance can be improved.The characteristics required for a solar wavelength conversion material, particularly a down conversion material, include a high luminous efficiency, a high extinction coefficient, high light safety, UV absorption, photoluminescence below the wavelength of visible light, and a large Stokes shift (a wavelength difference between the maximum absorption wavelength and the maximum photoluminescence wavelength (Δλ=λ em- λ ab)), etc.In order to apply the down conversion material to a solar cell, the required characteristics must be appropriately satisfied. Otherwise, the efficiency of the solar cell can be reduced. For example, when a material having low light efficiency is introduced into the front part of a solar cell, sunlight may be absorbed but not converted into visible light, and thus solar absorption of the solar cell may be more likely to be obstructed.In addition, a down conversion effect is difficult to expect with a material having a low extinction coefficient because the absorption efficiency of the material is low even when the light efficiency is high. In the case of materials having an absorption in the wavelength range of visible light below the wavelength range of ultraviolet light, no additional downconversion effect can be expected for commercially available silicon solar cells, since the photocurrent conversion efficiency in the wavelength range of visible light is already at high 90%. Moreover, a material having a small Stokes shift has a large degree of overlap between the absorption wavelength and the photoluminescence wavelength, and thus loss due to reabsorption of the emitted light may occur, making it difficult to expect effective down conversion.Meanwhile, when quantum cutting is caused, short wavelength photons that cannot be absorbed by a solar cell are emitted as two or more long wavelength photons in which the conversion efficiency of a solar cell is high, thereby dramatically improving the efficiency of the solar cell.According to an embodiment, the solar wavelength conversion material is preferably used in the form of a film having a thickness of 100 μm or less prepared by dispersing in a light transmissive resin.Hereinafter, the present invention will be described with reference to the drawings to prove that the solar wavelength conversion material manufactured according to the present invention is an excellent solar wavelength conversion material capable of improving the efficiency of a solar cell.Fig. 4 shows excitation and photoluminescence spectra of the thus prepared near infrared luminescent aluminum hydroxide. Fig. 4(a) shows excitation and photoluminescence spectra of the near infrared luminescent aluminum hydroxide doped only with Yb. When ultraviolet light of 350 nm is irradiated using a Xe lamp as an excitation light source, blue light emission near 450 nm (dot-and-dash line) and near infrared light emission near 1000 nm (broken line) occur simultaneously. To determine in which wavelength range the visible light and near infrared photoluminescence of aluminum hydroxide was absorbed and expressed, the excitation spectrum was analyzed.In FIG. In 4(a), the dot-and-dash line represents an excitation spectrum of 450 nm photoluminescence, and the dotted line represents an excitation spectrum of 1000 nm photoluminescence. That is, it was confirmed that both visible photoluminescence and near infrared photoluminescence occurred by absorption of a wavelength in the ultraviolet range in the range of 300 nm to 500 nm. In addition, in FIGS. 4( b) and 4( c), even when Ce and Tb are additionally introduced, no Ce and Tb photoluminescence peaks are observed, but only alumina and Yb photoluminescence peaks, confirming that effective energy transfer occurs in the order of aluminum hydroxide, Ce (or Tb), and Yb.Meanwhile, FIG. 4( d) shows the excitation and photoluminescence spectra of near infrared luminescent aluminum hydroxide prepared by introducing 2-naphthoic acid together with Yb as one of the aromatic ring compounds and a derivative thereof. In FIG. 4( d), the dashed double-dotted line and the dashed line indicate the maximum emission peaks in the vicinity of 500 nm and 1000 nm, respectively, in the photoluminescence spectrum. When 2-naphthoic acid is added, it can be seen that the maximum emission peak shifts by about 50 nm to a longer wavelength as compared with FIG. 4( a), which means that the trap state is changed by the incorporation of 2-naphthoic acid as described above, and which also means that the reabsorption loss is reduced due to the long-wavelength shift of the photoluminescence spectrum. In addition, since the emission peak of Yb was observed in the near infrared wavelength region, it was confirmed that effective energy transfer was realized in the order of 2-naphthoic acid, aluminum hydroxide, and Yb. As described with reference to Figs. 4(a) to 4(c), it was confirmed by the observation of the excitation spectrum that visible light and near infrared light emitted around 500 nm and 1000 nm were all absorbed by the wavelength of the ultraviolet region in the range of 300 nm to 500 nm (Fig. 4(d)).Fig. 5 shows the photoluminescence spectrum of near infrared luminescent aluminum hydroxide only with Yb or with Yb added with 2-naphthoic acid. The dotted line represents the photoluminescence spectrum in which only Yb is doped, and the solid line represents the photoluminescence spectrum in which Yb and 2-naphthoic acid were introduced together. It was confirmed that when 2-naphthoic acid was added, photoluminescence enhancement of aluminum hydroxide and effective energy transfer to Yb were achieved with increasing ultraviolet absorption and thus photoluminescence intensity of Yb was increased.Figure 6 shows absorbance and photoluminescence spectra of aluminum hydroxide luminescent complexes. Specifically, Figs. 6(a) and 6(d) show absorbance and photoluminescence spectra of aluminum hydroxide alone (AlOH), respectively, wherein the absorbance starts at 450 nm and the absorbance is shown in the ultraviolet region. In addition, characteristic peaks of photoluminescence at 390 nm, 465 nm and 514 nm are shown and the maximum emission wavelength is 465 nm. Figs. 6(b) and 6(e) show extinction and photoluminescence spectra of aluminum luminescent hydroxide (AlOH-NA) prepared by incorporating 2-naphthoic acid together with an aluminum precursor in the synthesis step. Similarly to the case of aluminum hydroxide alone, AlOH starts absorption at 450 nm and strong absorption is shown in the wavelength range of 380 nm. Meanwhile, the maximum emission wavelength was 520 nm, which was shifted by about 55 nm from a longer wavelength compared to AlOH. Figs. 6(c) and 6(f) show absorbance and photoluminescence spectra of aluminum luminescent hydroxide (AlOH-CA) prepared by incorporating 1,2,3,4-tetrahydro carbazol-4-ones together with an aluminum precursor in the synthesis step, starting absorption at 450 nm and showing strong absorption in the wavelength range of 370 nm. Meanwhile, the maximum emission wavelength was 530 nm, which was shifted by about 65 nm from a longer wavelength compared to AlOH. As the results of FIG. 6 confirm, when the aromatic ring compound is introduced in the pyrolysis synthesis step, the absorption in the ultraviolet region is improved and a difference between the maximum absorption wavelength and the photoluminescence wavelength is further increased, thereby minimizing a loss due to reabsorption.The change of photoluminescence properties of aluminum luminescent hydroxide by the addition of the aromatic ring compound and the derivative thereof and the energy transfer effect by the aromatic ring compound and the derivative thereof can be more clearly understood by time-resolved fluorescence (TRF).FIGS. 7( a) and 7( b) show TRF spectra of AIOH and AIOH-NA, and an average lifetime (τ ave) can be calculated from these spectra. Fig. 7(a) shows AIOH emission wavelengths observed at 400 nm, 450 nm and 500 nm, respectively, and the average lifetime values (τ ave) were 1.07 ns, 2.19 ns and 3.39 ns, respectively. Meanwhile, FIG. 7( b) shows that the emission wavelengths of AIOH-NA were observed at 400 nm, 450 nm, 500 nm, and 520 nm, respectively, and it is seen that the average lifetime of AIOH-NA for each wavelength is larger than that of AIOH, and the average lifetime values (τ ave) calculated based on this graph were 1.21 ns, 8.18 ns, 11.25 ns, and 11.84 ns, respectively. That is, the average lifetime according to the emission of AIOH was generally delayed due to the energy transfer of the ultraviolet light absorbed by NA to AIOH. That is, when the aromatic ring compound or the derivative thereof is introduced together in the synthesis step, it is seen that strong absorption of light in the ultraviolet region and effective energy transfer are realized. This means that effective downconversion is achieved.Methods for introducing the synthesized material for converting solar wavelengths into a solar cell may include, depending on the location where the material is introduced, a method for manufacturing a silicon solar cell in the form of a film by dispersing the material in an encapsulant for protecting the silicon solar cell, a method for directly applying the material to the entire surface of the silicon solar cell, a method for applying the material to the surface of an encapsulant connected to the front surface of the solar cell, and so on.< Solarzellen Encapsulant>The solar wavelength conversion material is dispersed in a resin to form a sheet, and is used in manufacturing a photovoltaic solar module.First, as an encapsulant of a solar cell, a material such as ethylene vinyl acetate (EVA), polyolefin elastomer (POE), cross-linked polyolefin, thermal polyurethane (TPU), polyvinyl butyral (PVB), silicone, silicone / polyurethane hybrid, ionomer, etc. is used, and EVA or POE is most commonly used.In general, a number of methods for manufacturing a solar cell module by thermal lamination are reported after incorporating a solar wavelength conversion material into an encapsulant and placing it on the front side of the solar cell, and there are cases where the reported methods are applied to commercial production.In this case, however, the light emitted from the solar wavelength conversion material inside the encapsulant travels not to the solar cell but to the side of an encapsulating film due to a large difference between the refractive index (n∼ 1.4) of a polymer such as EVA or POE constituting the encapsulant and the refractive index (n∼ 2.5) of SiNxon the surface of the silicon solar cell, because the waveguide phenomenon predominates due to total internal reflection inside the encapsulant. This phenomenon may act as light loss from the solar cell side.< To Surface of Solar Cell>Conversely, when applied to the surface of a solar cell or the surface of an encapsulant, the solar wavelength conversion material is at the interface between the encapsulant and the solar cell, and due to the silicon texturing structure, from several micrometers (μm) to several tens of micrometers (μm), the light cannot travel laterally but travels inside the solar cell. In addition, when the solar wavelength conversion material can be set to have a value between the refractive index of the encapsulant (n∼1.4) and the refractive index of the solar cell surface (n∼2.5), light entrance toward the encapsulant, the solar wavelength conversion material, and the solar cell can become highly advantageous according to Snell's law, and thus the light from the solar cell side can be more utilized, thereby improving photocurrent conversion efficiency. That is, both the down conversion effect of the solar wavelength conversion material and the antireflection coating effect can be expected.When dispersed in a solvent, the solar wavelength conversion material may be applied to the surface of a solar cell. The methods for applying the solar cell surface may include spin coating, bar coating, spray coating, dip coating, screen printing, and the like. In addition, in applying to the encapsulant, any of methods other than spin coating may be used.< Cell Module / Solar Cell>According to an embodiment of the present invention, in the case of a silicon solar module, as shown in the schematic diagram of FIG. 1, glass / encapsulant layer / photovoltaic (PV) cell / encapsulant layer / back side are stacked in this order from the front side on which light is incident, and the silicon solar cell module may then be manufactured by laminating, wherein the aluminum luminescent hydroxide may be dispersed in the front side encapsulant or both the front side encapsulant and the back side encapsulant.According to an embodiment of the present invention, the type and size of the material constituting the solar cell are not limited thereto. The present invention relates, for example, to a solar cell that can be applied regardless of the type of material including an organic photovoltaic (OPV) cell, a semiconductor-based solar cell such as copper indium gallium selenide (CIGS), cadmium telluride (CdTe), perovskite, etc., a silicon-based solar cell, and a semiconductor-silicon tandem structure-based solar cell, whereby photocurrent conversion efficiency of the solar cell is improved.However, a 6-inch polycrystalline silicon solar cell has been used and described to illustrate the invention.In the present invention, a spray coating method is used by which rapid and uniform coating is achieved with respect to a commercial production application, but is not limited thereto.DISCLOSURE MODEHereinafter, preferred embodiments of the present invention will be described in detail, but the following examples are presented only for better understanding of the present invention, and the scope of the present invention is not limited to the following examples.Production Example 1: Production of a solar wavelength conversion material (aluminum hydroxide precursor)10 g of aluminum acetate was mixed with 100 ml of 1-octadecene solvent, and then the thermal decomposition reaction was carried out at 300°C with stirring for 30 minutes. After completion of the reaction, aluminum hydroxide was separated by centrifugation and redispersed in 10 ml of toluene solvent. Fig. 3 shows the UV-Vis spectrum and the photoluminescence spectrum of the thus prepared aluminum hydroxide luminescent solution, wherein the dotted line represents the absorption and the solid line represents the photoluminescence spectra. Examples based on the contents of aluminum hydroxide were used in Examples 1 and 2, respectively.Production Example 2: Production of a solar wavelength conversion material (aluminum hydroxide precursor + lanthanide ion)10 Aluminium acetate was mixed with 10 ml of 1-octadecene solvent. To this mixed solution, Ytterbium(III)acetathydrat among the above-mentioned near infrared luminescent lanthanide ions was added in an amount of 0.2 wt % as compared with the aluminum precursor, and then the thermal decomposition reaction was carried out at 300° C. with stirring for 30 minutes. After completion of the reaction, aluminum hydroxide was separated by centrifugation and redispersed in 10 ml of toluene solvent. The solar wavelength conversion material thus synthesized was used in Example 3, and the solar wavelength conversion material synthesized without adding ytterbium (III) acetate hydrate was used in Comparative Example 5.Preparation Example 3: Preparation of solar wavelength conversion material (aluminum hydroxide + aromatic ring compound)10 g of aluminum acetate was mixed with 100 ml of 1-octadecene solvent, and then the thermal decomposition reaction was carried out at 300°C with stirring for 30 minutes. After completion of the reaction, aluminum hydroxide was separated by centrifugation and redispersed in 10 ml of toluene.In order to adjust the photoluminescence properties, 3-hydroxyl-2-naphthoic acid as an aromatic ring compound was added in an amount of 5 wt % compared to aluminum acetate which is an aluminum precursor, and a thermal decomposition reaction was carried out at 300° C. for 30 minutes with stirring, followed by separation and purification.Production Example 4: Production of a solar wavelength conversion material (aluminum hydroxide + lanthanide ion + aromatic ring compound)A solar wavelength conversion material was prepared in the same manner as in Preparation Example 2 except that, for further enhancing UV absorption and adjusting photoluminescence properties, 3-hydroxy-2-naphthoic acid, which is one of aromatic ring compound derivatives, was added in an amount of 0.2 wt% as compared to the aluminum precursor, and the thermal decomposition reaction was carried out in the same manner as above with stirring, followed by separation and purification. The solar wavelength conversion material thus synthesized was used in Example 4, and a solar wavelength conversion material synthesized without adding ytterbium (III) acetate hydrate was used in Comparative Example 6.Examples 1 and 2: Preparation of encapsulating sheet containing solar wavelength conversion materialThe solar wavelength conversion material prepared in Preparation Example 1 was added to an encapsulating resin in an encapsulating film preparation step to then prepare an encapsulating film in which the solar wavelength conversion material was dispersed by extrusion. As the encapsulating resin, an ethylene-vinyl acetate copolymer (manufactured by Hanwha Total Petrochemical Co., Ltd.) having a melt index of 15 g / 10 min and a vinyl acetate content of 28 wt% was used. 1 part by weight of Luperox TBEC (tert-butyl-2-ethylhexyl monoperoxycarbonate) from Fa. Alkemas, 0.5 part by weight of TAICROS (triallyl isocyanurate) from Fa. Evonik as a crosslinking aid, 0.1 part by weight of Tinuvin 770 (bis-2,2,6,6,-tetramethyl-4-piperidinyl sebacate) manufactured by Ciba as a UV stabilizer, and 0.3 part by weight of OFS-6030 (methacryloxypropyltrimethoxysilane) manufactured by Dow Corning as a silane coupling agent were added to 100 parts by weight of EVA and mixed. Thereafter, EVA films were produced by an extruder, the extruder temperature was maintained at 100° C., the T die temperature (T die temperature) was maintained at 100° C., and the thicknesses of the produced films were 0.5 mm. Hereinafter, each of the sheets thus produced is referred to as "EVA".For comparative evaluation of durability, films were produced in the same manner as in the above-described production method of EVA film except that 0.1 or 0.5 part by weight of aluminum luminescent hydroxide was added in addition to 100 parts by weight of EVA in the production method of EVA film, and the produced sheets were referred to as "EVA-AIOH 0.1" and "EVA-AIOH 0.5", and were used in Examples 1 and 2, respectively.For comparative evaluation, in Comparative Example 1, a film prepared in the same manner as in Example 1 except that no aluminum luminescent hydroxide was used (hereinafter referred to as "EVA" film) was used, and the film was prepared in the same manner except that 0.1, 0.2 and 0.5 parts by weight of Chimassorb 81 (2-hydroxy-4-octyloxybenzophenone) produced by Ciba were additionally added as the UV absorber and referred to as "EVA-C81 0.1", "EVA-C81 0.2" and "EVA-C81 0.5", respectively, used in Comparative Examples 2 to 4.Examples and comparative examples are listed in Table 1 below corresponding to incorporation of the aluminum luminescent hydroxide (AlOH) and the ultraviolet absorber (C81), as well as their contents. [Table 1] Table 1] [Table 1] Table 1]Added AIOH (wt %)0.10.5----Added C81 (wt %)---0.10.20.5<Production of Solar Module Comprising Encapsulant Having Aluminum Luminescent Hydroxide Dispersed therein>Each of the sealing films prepared in Examples 1 and 2 and Comparative Examples 1 to 4 was stacked in the order of glass (200 mm×200 mm), a sealing agent layer, a 6-inch polycrystalline solar cell manufactured by GINTECH, a sealing agent layer, and a PVDF-based back sheet (polyvinylidene fluoride) manufactured by SFC, and mini-modules were prepared by thermal lamination. In the thermal lamination method, after a vacuum step at 150° C. for 6 minutes, crosslinking was performed by keeping a difference between the upper and lower pressures of a laminator at 0.4 MPa for 11 minutes.Experimental Example 1: Evaluation of encapsulant durabilityTo evaluate the durability of the encapsulant according to the incorporation of aluminum luminescent hydroxide, an accelerated weathering test was performed on a sample with the encapsulant between the mini-solar module manufactured and two glass sheets. In a UV aging experiment, changes in total transmission properties (of glass samples) and solar cell efficiency (of solar minimodule samples) over time were observed by exposing the sample to an ultraviolet lamp (340 nm, 0.9 W / m 2) at a temperature of 63 °C. In a wet heat aging experiment in which the sample was exposed to a temperature of 85° C. and a humidity of 85%, the change in the total transmission characteristics (of glass samples) and the solar cell efficiency (of solar minimodule samples) over time was observed. A solar simulator (WXS-156S-10) manufactured by WACOM was used for analysis of solar cell efficiency, and an UltraScan PRO spectrometer (HunterLab) was used for analysis of transmission characteristics.FIG. 8 shows the total transmittance of the samples subjected to thermal lamination by placing the encapsulants of Examples 1 and 2 and Comparative Examples 1 and 3 between two glass substrates. The dash-double-dotted line represents the total transmission of an EVA sample (Comparative Example 1) and shows a high transmission of 90% in the entire wavelength range, the EVA-AIOH 0.1 and EVA-AIOH 0.5 samples (Examples 1 and 2) show absorption peaks by AIOH (aluminum hydroxide) in the ultraviolet range 450 nm or more and high transmission of 90% in the visible range, similarly to the EVA sample (Comparative Example 1). Meanwhile, it is seen that EVA-C81 (Comparative Example 3) has a large decrease in transmission in the ultraviolet region of 400 nm or more. That is, as described above, when a UV absorber is used, the durability of the encapsulant can be improved by a UV blocking effect. However, ultraviolet rays of 400 nm or less cannot be absorbed by a solar cell and not converted into electricity, so that the initial power is undesirably lowered.FIG. 9 shows the total transmission of samples subjected to thermal lamination by disposing an encapsulant before and after the introduction of aluminum luminescent hydroxide between two glass substrates after UV aging and wet heat aging tests for 2000 hours. Fig. 9(a) shows the results of the UV aging test, and it was confirmed that the encapsulants of Example 1 (EVA-AIOH 0.1, dotted line) and Example 2 (EVA-AIOH 0.5, dash-double-dot line) in which aluminum hydroxide was incorporated maintained the same transmission levels as before the accelerated test of Fig. 3; however, EVA had a reduced transmission in the ultraviolet region of 400 nm or more. In addition, FIG. 9( b) shows the results of wet heat aging tests, and it was confirmed that the encapsulants of Example 1 (EVA-AIOH 0.1, dotted line) and Example 2 (EVA-AIOH 0.5, dash-double-dot line) in which aluminum hydroxide was introduced maintained the same transmission levels as those of the accelerated test of FIG. 8, similar to the UV aging test of FIG. 9( a); however, EVA of Comparative Example 1 had greatly reduced transmission in the ultraviolet range of 400 nm or more, which means that the light in the ultraviolet range of 400 nm or more cannot pass through the encapsulant and thus cannot reach the solar cell, indicating that the solar cell cannot convert so much light into current.Tables 2 to 4 show open-circuit voltage (V oc), short-circuit current density (J sc), fill factor (FF), and efficiency values determined by current-voltage curve (IV curve) analysis of mini-isolar modules before and after the durability evaluation corresponding to the respective incorporation of luminescent aluminum hydroxide. [Table 2] [Table 2]V ocJsc (mA / cm 2)FF (%)Efficiency (%)Efficiency (%)Example 10.62235.720.7917.552.33Example 20.62135.890.7917.612.68Comparative Example 10.62035.010.7917.15ReferenceComparative Example 20.62134.810.7917.08- 0.41Comparative Example 30.62234.610.7917.01- 0.81Comparative Example 40.62134.100.7916.83- 2.45In Table 2, the solar modules using the encapsulant (EVA-AIOH 0.1) of Example 1 and the encapsulant (EVA-AIOH 0.5) of Example 2 into which aluminum luminescent hydroxide was introduced into which aluminum luminescent hydroxide was introduced exhibited, before deterioration due to weathering, 2.33 and 2.68% improvement in relative efficiency as compared with the module using the encapsulant using only EVA. That is, it is seen that by introducing aluminum luminescent hydroxide, the initial efficiency of a solar module increases according to the increase in short-circuit current density by down-converting ultraviolet absorption and visible photoluminescence. [Table 3] [Table 3]V ocJsc (mA / cm 2)FF (%)Efficiency (%)Efficiency (%)Example 10.62135.690.7817.293.35Example 20.62135.820.7817.333.59Comparative Example 10.62134.540.7816.73- ReferenceComparative Example 20.6234.590.7816.720.12Comparative Example 30.62134.480.7816.70- 0.18Comparative Example 40.62134.050.7816.49- 1.43Moreover, as shown in Table 3, regarding the changes in the efficiency after the samples were subjected to the UV aging test for 2000 hours, the solar modules including the encapsulant (EVA-AIOH 0.1) of Example 1 and the encapsulant (EVA-AIOH 0.5) of Example 2 in which aluminum luminescent hydroxide was incorporated exhibited an improvement in the relative efficiency by 3.35 and 3.59% as compared with the module using the encapsulant in which only EVA was used. That is, as described above with reference to FIG. 9, in the case of the encapsulant only with EVA (Comparative Example 1), the transmittance of the EVA encapsulant layer decreases according to the UV aging, and thus the photocurrent conversion efficiency of the solar cell under the encapsulant is lowered, while in the case of the encapsulants EVA-AIOH 0.1 and EVA-AIOH 0.5, the same transmittances as before the UV aging were maintained, thereby preventing deterioration of the performance of the solar cell. In addition, in Comparative Examples 2 to 4, Chimassorb 81 (2-hydroxy-4-octyloxybenzophenone) produced by Ciba was added as the ultraviolet absorber to EVA, respectively, but the efficiencies of EVA-C81 were 0.1, 0.2 and 0.5, respectively, 0.12%, -0.18% and -1.43% as compared with the encapsulant only with EVA (Comparative Example 1), indicating that adverse results were obtained as compared with the Examples. It is also seen that undesirable results were obtained when the encapsulants of Comparative Examples 2 and 4 having the same content as the aluminum luminescent hydroxide were used in Examples 1 and 2 of the present invention. [Table 4] [Table 4]V ocJsc (mA / cm 2)FF (%)Efficiency (%)Efficiency (%)Example 10.61935.570.7516.515.43Example 20.61935.720.7516.585.87Comparative Example 10.61834.250.7415.66ReferenceComparative Example 20.61934.180.7415.65- 0.06Comparative Example 30.61934.010.7415.58- 0.51Comparative Example 40.61933.950.7415.55- 0.70In addition, as is apparent from Table 4, regarding the changes in the efficiency after the samples were subjected to the wet heat aging test for 2000 hours, the solar modules using the encapsulant (EVA-AIOH 0.1) of Example 1 and the encapsulant (EVA-AIOH 0.5) of Example 2 into which aluminum luminescent hydroxide was introduced exhibited an improvement in the relative efficiency by 5.43 and 5.87% as compared with the module using the encapsulant in which only EVA was used. The relative efficiency values after incorporation of the aluminum luminescent hydroxide showed larger differences in the results of the moisture-heat aging test than in the UV aging test because the EVA encapsulant showed more deterioration in the moisture-heat aging test than in the UV aging test, and the transmission of the encapsulating layer could be maintained by preventing deterioration by incorporation of aluminum luminescent hydroxide. As described above, the present invention provides a technology in which, when a solar cell and a solar module are formed by dispersing aluminum luminescent hydroxide in a solar encapsulant, transmission of an encapsulant layer is maintained by improving durability of the encapsulant, thereby improving long-term durability of the solar cell and the solar module and securing the amount of power generation by minimizing a power decrease over time.Examples 3-6: Preparation of encapsulating sheet containing solar wavelength conversion materialEach of the aluminum hydroxide solutions prepared in Preparation Examples 2 and 4 (Examples 3 and 4) and the aluminum hydroxide solutions prepared in Preparation Examples 1 and 3 (Examples 5 and 6) was applied to the surface of a 6-inch polycrystalline solar cell using a spray coating method so as to be located at the interface between the silicon cell and the encapsulant. Glass / sealing layer / photovoltaic (PV) cell / sealing layer / back side were stacked in this order from the front side on which light is incident, and the silicon solar cell module may then be manufactured by lamination. In the manufactured solar cell module, near infrared luminescent aluminum hydroxide is placed at the interface between the encapsulant and the solar cell. The compositions of the solar wavelength conversion materials constituting the solar cell are shown in Table 5, and 50 mg each was included.Comparative Example 5: Production of a solar cell containing luminescent aluminum hydroxideFor comparison, a simple mixed solution of 50 mg of aluminum hydroxide luminescent prepared alone as an aluminum hydroxide precursor and 0.1 mg of lanthanide ion Ytterbium(III)acetathydrat was spray coated on the surface of a silicon cell. A solar cell was produced in the same manner as in Example 3 except that a simple mixed solution of aluminum luminescent hydroxide and ytterbium (III) acetate hydrate was prepared. [Table 5] (unit: mg / ml) [Table 5] (unit: mg / ml)Solar Wavelength Conversion MaterialAIOH-YbAIOH-NA-YbAIOHAIOH-NAAIOH, ytterbium (III) acetate hydrateExperimental Example 2: Performance evaluation of a solar cell containing a solar wavelength conversion materialIn order to analyze the change in solar cell efficiency according to the incorporation of aluminum luminescent hydroxide, a solar simulator (WXS-156S-10) manufactured by WACOM was used. In addition, in order to measure the total reflectance according to the aluminum hydroxide coating, UV-3600 NIR (with MPC-3100) manufactured by Shimadzu was used, and the change before and after the coating was analyzed.Table 6 shows the results of measuring the efficiency of a 6-inch polycrystalline silicon solar cell coated with aluminum hydroxide luminescent. In order to enhance the accuracy of the efficiency measurement, all solar cell efficiencies were measured before the application of the aluminum hydroxide and then compared with the results after the application of the aluminum hydroxide. The following solar cells 1 to 5 are solar cells manufactured under the same conditions as the solar cells of the respective Examples and Comparative Examples without including the solar wavelength conversion material. [Table 6] [Table 6]Solar Cell #10.62034.7078.984.15517.07-Example 30.62435.8479.034.30117.67+0.60 (3.51%)Solar Cell #20.62434.5978.964.14717.04-Example 40.62436.3179.014.35617.90+0.86 (5.04%)Solar Cell #30.62035.0379.264.18917.21-Example 50.62035.4579.354.24517.44+0.23 (1.33%)Solar Cell #40.62234.8179.164.17117.14-Example 60.62235.5979.184.26617.53+0.39 (2.27%)Solar Cell #50.62034.8679.254.16817.12-Comparative Example 50.62035.3179.24.21117.34+0.22 (1.29%)In Table 6, both the short circuit current density and the efficiency were increased compared to uncoated silicon solar cells when luminescent aluminum hydroxides AIOH, AIOH-NA, AIOH-Yb and AIOH-NA-Yb were applied. The relative efficiency changes for AlOH, AIOH-NA, AIOH-Yb and AlOH-NA-Yb were 1.33%, 2.27%, 3.51% and 5.04%, respectively, which was better than the values for AlOH and AlOH-NA doped with Yb to allow near infrared photoluminescence. In particular, it was confirmed that when 2-naphthoic acid was codoped with Yb, the relative efficiency increased more significantly than when only Yb was doped.In addition, in Comparative Example 5, it was confirmed that when a solar cell was produced by spray coating a mixed solution of aluminum hydroxide luminescent (AlOH) and lanthanide ion Ytterbium(III)acetathydrat synthesized with a single aluminum hydroxide precursor on the surface of a silicon cell, the relative efficiency increased by 1.29%, which is similar to the result of Comparative Example 5 in which only aluminum hydroxide luminescent was applied. This is because there was no effective energy transfer from aluminum luminescent hydroxide to Yb ions and thus only the down conversion effect of aluminum luminescent hydroxide was realized, thereby clearly confirming the light conversion effect of the aluminum luminescent hydroxide according to the present invention.In order to verify such efficiency increases, photocurrent conversion efficiencies (or external quantum efficiency) before and after the aluminum hydroxide luminescent coating were measured, and FIG. 10 shows the result of measuring the external quantum efficiency changes of a solar cell #2 of Table 6 and an AIOH-NA-Yb coated cell of Example 4.In FIG. 10, the dotted line represents the external quantum efficiency spectrum of the solar cell #2 of Table 6, and the solid line represents the external quantum efficiency spectrum of the AlOH-NA-Yb-coated cell of Example 4.FIG. 11 shows the result of measuring the change in the total reflectance of the solar cell #2 of Table 6 and the AIOH-NA-Yb-coated cell of Example 4. the dotted line represents the total reflectance before the application of near infrared photoluminescent aluminum hydroxide, and the solid line represents the reflectance spectrum after the coating of AIOH-NA-Yb. It can be seen that after the coating, the reflectivity decreases more in the ranges 300 to 500 nm and 800 to 1100 nm and that the reflectivity is low, which is more advantageous for solar cells. That is, by coating near infrared luminescent aluminum hydroxide on the surface of a silicon solar cell, the short-circuit current of the silicon solar cell is increased and thus the overall efficiency is increased by the downconversion effect by ultraviolet absorption and visible and near infrared photoluminescence and the antireflection coating effect in which the refractive index of the near infrared luminescent aluminum hydroxide has a value between the refractive index of the silicon solar cell surface and the refractive index of the encapsulant (1.5<naluminium hydroxide<2.5), and thus light entrance into the silicon solar cell is facilitated.The present invention provides a technology in which, when a solar cell and a solar module are formed by dispersing aluminum luminescent hydroxide in a solar encapsulant, transmission of an encapsulant layer is maintained by improving durability of the encapsulant, thereby improving durability of the solar cell and the solar module and ensuring the amount of power generation by minimizing a power decrease over time.Examples 7-12: Preparation of encapsulating sheet containing solar wavelength conversion materialA 6-inch polycrystalline silicon solar cell was used.The solar wavelength conversion material solution prepared according to Production Example 3 was applied to the surface of the 6-inch silicon cell using a spray coating method to be disposed at the interface between the silicon solar cell and the encapsulant.Glass / sealing layer / solar wavelength conversion material / solar cell e / sealing layer / back side were stacked in this order from the front side on which light is incident, and the silicon solar cell module can then be manufactured by lamination. In the manufactured solar cell module, aluminum luminescent hydroxide was placed at the interface between the encapsulant and the solar cell. As the composition of the solar wavelength conversion material constituting the solar cell, aluminum luminescent hydroxide prepared by the above-described method was used, and in these Examples, the solar wavelength conversion material prepared by adding an aromatic ring component was used, and in Examples 10 to 12, solar cells were each prepared in the same manner as in Examples 7 to 9 except that only aluminum luminescent hydroxide without including an aromatic ring component was used. The content of the solar wavelength conversion material is shown below in Table 7. [Table 7] (unit: mg / ml) [Table 7] (unit: mg / ml)Solar Wavelength Conversion Material8.316.6208.316.620Comparative Example 6A solar cell was produced in the same manner as in Example 7 except that a coating composition was prepared by simply mixing and dispersing an aluminum hydroxide precursor (20 mg / ml) and an aromatic ring compound 3-hydroxyl-2-naphthoic acid (2 mg / ml) in the same amount as in Example 7, and then placed on the light receiving side of a solar cell material.Experimental Example 3: Performance evaluation of a solar cell containing a solar wavelength conversion materialIn order to analyze the change in solar cell efficiency according to the incorporation of aluminum luminescent hydroxide, a solar simulator (WXS-156S-10) manufactured by WACOM was used; changes in efficiency before and after the coating of aluminum hydroxide and before and after the thermal lamination were all measured. In addition, in order to analyze the external quantum efficiency for each wavelength, IPCE (QEX10) equipment manufactured by PV Measurement was used, and the changes in conversion efficiency before and after the application of aluminum hydroxide were observed. In addition, UV-3600 NIR (with MPC-3100) manufactured by Shimadzu was used for measuring the total reflectance according to the aluminum hydroxide coating, and the changes before and after the coating were analyzed.Table 8 shows the results of measuring the efficiency of a 6-inch polycrystalline silicon solar cell coated with aluminum hydroxide luminescent. In order to enhance the accuracy of the efficiency measurement, all solar cell efficiencies were measured before the application of the aluminum hydroxide and then compared with the results after the application of the aluminum hydroxide. The following solar cells 5 to 11 are solar cells manufactured under the same conditions as the solar cells of the respective examples and comparative examples, each without including the solar wavelength conversion material. [Table 8] [Table 8]Solar Cell #50.62234.8179.164.17117.14Example 70.62235.59 (2.24%↑)79.184.26617.53+0.39 (2.27%)Solar Cell #60.62234.6479.244.15517.07Example 80.62235.53 (2.57%↑)79.284.26417.52+0.45 (2.63%)Solar Cell #70.62434.5978.964.14717.04Example 90.62435.48 (2.57%↑)79.084.26117.51+0.47 (2.76%)Solar Cell #80.62035.0379.264.18917.21Example 100.62035.45 (1.2%↑)79.354.24517.44+0.23 (1.33%)Solar Cell #90.62234.8379.714.20317.27Example 110.62235.32 (1.41%↑)79.854.26917.45+0.17 (0.98%)Solar Cell #100.62234.8179.604.19517.24Example 120.62235.54 (2.10%↑)79.274.26417.52+0.28 (1.62%)Solar Cell #110.62234.9279.214.18717.20Comparative Example 60.62235.3579.254.24017.43+0.23 (1.34%)In Table 8, both the short circuit current density and the efficiency were increased compared to an uncoated silicon solar cell when the luminescent aluminum hydroxide AIOH or AIOH-NA was applied. Especially when using AlOH-NA, the short circuit current density and the efficiency were better than when using AlOH.In addition, when a solar cell was manufactured by separately adding AIOH and NA, mixing, and coating (Comparative Example 6), effective energy transfer from NA to AIOH became impossible, and thus the desired result was not obtained.In order to verify such efficiency increases, the incident photon current efficiency (IPCE) before and after the aluminum hydroxide coating was measured, and FIG. 12 shows the photocurrent conversion efficiency according to the wavelength as a result of an IPCE measurement, i.e., an external quantum efficiency (EQE) spectrum.FIG. 12 shows the results of solar cells #10 (Example 12) and #7 (Example 9) in Table 8, the dotted line represents the EQE spectrum before coating, the dashed-double-dotted line represents the EQE spectrum when coating AIOH (Example 12), and the solid line represents the EQE spectrum after coating AIOH-NA (Example 9). From the result of FIG. From FIG. 12, it can be seen that when the aluminum luminescent hydroxide was coated, conversion efficiency was increased by downconversion from 300 nm to about 500 nm, and more effective downconversion can be achieved when coating with AlOH-NA than when coating with AlOH.In addition, FIG. 13 shows the results of measurement of the reflection changes of solar cells #10 (Example 12) and #7 (Example 9) in Table 8 according to the aluminum hydroxide luminescent coating. The solid line represents the total reflectance before application of aluminum hydroxide, the dash-double-dotted line represents the reflectance spectrum when applying AIOH, and the broken line represents after application of AIOH-NA. After coating, it is seen that the reflectance decreases more in the ranges 300 to 500 nm and 800 to 1100 nm. Similar to the EQE spectrum, AIOH-NA has a lower reflection in the ultraviolet wavelength range than AIOH, which is advantageous for solar cells. That is, by coating the surface of a silicon solar cell with aluminum hydroxide luminescent, the short-circuit current of the silicon solar cell increases and the overall efficiency accordingly increases by the downconversion effect by ultraviolet absorption and visible photoluminescence and the antireflection coating effect in which the refractive index of the near infrared luminescent aluminum hydroxide has a value between the refractive index of the silicon solar cell surface and the refractive index of the encapsulant (1.5<nalumum hydroxide<2.5), and thus the introduction of light into the silicon solar cell is facilitated.The present invention provides a technology in which, when a solar cell and a solar module are formed by dispersing aluminum luminescent hydroxide in a solar encapsulant, transmission of an encapsulant layer is maintained by improving durability of the encapsulant, thereby improving durability of the solar cell and the solar module and ensuring the amount of power generation by minimizing a power decrease over time.

Claims

A solar wavelength conversion material comprising aluminum hydroxide luminescent having ultraviolet absorption properties and photoluminescence properties in the visible light wavelength region, wherein the solar wavelength conversion material further comprises a lanthanide ion or a derivative containing the same.The solar wavelength conversion material according to claim 1, wherein the solar wavelength conversion material comprises an Al(OH) 3-, AlOOH, 5Al 2 O 3 ·2H 2 O-, or Al 2 O 3- structure.The solar wavelength conversion material according to claim 1, wherein the aluminum luminescent hydroxide has a porous structure.The solar wavelength conversion material according to claim 1, further comprising an aromatic ring compound or a derivative thereof.The solar wavelength conversion material according to claim 4, wherein the aromatic ring compound is one or more of an aromatic hydrocarbon in which only carbons and hydrogens are bonded to each other, an aromatic heterocyclic compound in which some of the ring-forming carbon atoms are substituted with oxygen, nitrogen or sulfur atoms not with carbon, or a derivative in which some of the hydrogens are substituted with functional groups in the aromatic hydrocarbon and aromatic heterocyclic compound molecules.The solar wavelength conversion material according to claim 4, wherein the aromatic ring compound is one or more of furan, benzbenzofuran, isobenzbenzofuran, pyrrole, indole, isoindole, thiophene, benzbenzothiophene, imidazole, benzimidazole, purine, pyrazole, indazole, oxazole, benzoxazole, oxazole-isoxazole, benzoxazole-isoxazole, thiazole, benzbenzothiazole, benzbenzene, naphthalene, anthracene, pyridine, quinoxaline, acridine, pyrimidine, quinazoline, pyridazine, cinnoline, phthalazine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, and derivatives thereof.The solar wavelength conversion material according to claim 1, wherein the particle size of the solar wavelength conversion material is 0.5 nm to 500 μm.The solar wavelength conversion material according to claim 1, wherein the maximum absorption wavelength of the solar wavelength conversion material is 200 nm to 500 nm.The solar wavelength conversion material according to claim 1, wherein the maximum emission wavelength of the solar wavelength conversion material is 450 nm to 1100 nm.A solar cell encapsulant comprising a resin having a solar wavelength conversion material dispersed therein, wherein the solar wavelength conversion material is the solar wavelength conversion material according to any one of claims 1 to 9.The solar cell encapsulant according to claim 10, wherein the solar cell encapsulant is in the form of a film having a thickness of 100 μm or less.The solar cell encapsulant of claim 10, wherein the solar cell encapsulant is EVA (ethylene vinyl acetate), POE (polyolefin elastomer), cross-linked polyolefin (PO), TPU (thermal polyurethane), PVB (polyvinyl butyral), silicone, silicone / polyurethane hybrid or ionomer.The solar cell encapsulant according to claim 10, wherein the solar wavelength conversion material is contained in an amount of 0.0001 to 10 parts by weight based on 100 parts by weight of the resin of the solar cell encapsulant.A solar cell comprising a solar wavelength conversion material located between a solar cell encapsulant on a front surface of the solar cell where sunlight is incident and an interface of the solar cell, wherein the solar wavelength conversion material is the solar wavelength conversion material according to any one of claims 1 to 9.The solar cell according to claim 14, wherein the solar wavelength conversion material is coated on the front surface of the solar cell or on the back surface of the solar cell encapsulant on the front surface of the solar cell.The solar cell of claim 14, wherein the solar cell encapsulant of the solar cell is EVA (ethylene vinyl acetate), POE (polyolefin elastomer), cross-linked polyolefin (PO), TPU (thermal polyurethane), PVB (polyvinyl butyral), silicone, silicone / polyurethane hybrid or ionomer.A solar cell, wherein the solar cell encapsulant according to claim 10 is laminated on front and back sides of the solar cell, glass is laminated on the front side of the solar cell encapsulant located on the front side of the solar cell, and a back sheet is laminated on the back side of the solar cell encapsulant located on the back side of the solar cell.

Images