阅读说明：本技术 包括铝基太阳能转换材料的太阳能电池 (Solar cell comprising an aluminum-based solar conversion material ) 是由 金基世 李度勳 张豪植 于 2019-06-24 设计创作，主要内容包括：当基于具有紫外线吸收光谱和可见光发射光谱的低成本铝材料产生的太阳波长转换材料(太阳光谱波长转换器)位于太阳能电池和太阳能光入射到的太阳能电池的前表面的密封剂之间时,可以通过同时引起下转换效应和抗反射涂覆效应来改善太阳能电池的光电流转换效率,由此增加光生成的电流。(When a solar wavelength conversion material (solar spectrum wavelength converter) produced based on a low-cost aluminum material having an ultraviolet absorption spectrum and a visible light emission spectrum is located between a solar cell and an encapsulant of a front surface of the solar cell to which solar light is incident, it is possible to improve photocurrent conversion efficiency of the solar cell by simultaneously causing a down-conversion effect and an anti-reflection coating effect, thereby increasing a light-generated current.)

1. A solar cell whose photocurrent conversion efficiency is improved by including luminescent aluminum hydroxide generated from a single aluminum precursor by a thermal decomposition synthesis method in an interface between a sealant of a front surface of the solar cell, on which sunlight is incident, and the solar cell.

2. The solar cell of claim 1, wherein the maximum absorption wavelength of the luminescent aluminum hydroxide is formed between 300nm and 450nm and the maximum emission wavelength of the luminescent aluminum hydroxide is formed between 450nm and 1100 nm.

3. The solar cell of claim 1, wherein the thermal decomposition synthesis step of the luminescent aluminum hydroxide comprises implanting any one of impurities of carbon, carbonyl radicals, oxalic acid phosphoric acid and sulfuric acid.

4. The solar cell of claim 1, wherein the luminescent aluminum hydroxide is coated on the front surface of the solar cell.

5. The solar cell of claim 1, wherein the luminescent aluminum hydroxide is coated on a surface of the encapsulant adhered to the front surface of the solar cell.

6. The solar cell according to claim 1, wherein after the film having the thickness of 100 μm or less is fabricated by dispersing luminescent aluminum hydroxide into the light-transmitting resin including the sealant, the luminescent aluminum hydroxide is positioned between the solar cell and the sealant by interposing the fabricated film between the sealant adhered to the front surface of the solar cell and the front surface of the solar cell.

7. The solar cell according to claim 4 or 5, wherein the coating method is a spray coating method.

8. The solar cell according to claim 4 or 5, wherein the coating method is a screen printing method.

9. The solar cell of claim 6, wherein the encapsulant is formed of any one selected from the group consisting of: ethylene Vinyl Acetate (EVA), polyolefin elastomers (POE), crosslinked polyolefins, Thermoplastic Polyurethanes (TPU), polyvinyl butyral (PVB), silicones, silicone/polyurethane hybrids, and ionomers.

10. The solar cell of claim 1, wherein the luminescent aluminum hydroxide has a particle size of 10 μ ι η or less.

11. The solar cell of claim 1, wherein the aluminum precursor is any one selected from the group consisting of: aluminum monoacetate, aluminum triacetate, aluminum diacetate, aluminum triethyl aluminum, trimethylaluminum, aluminum alkoxides, diethylaluminum chloride, aluminum sulfate, aluminum cyanide, aluminum nitrite, aluminum carbonate, aluminum sulfite, aluminum hydroxide, aluminum oxide, aluminum chlorate, aluminum sulfide, aluminum chromate, aluminum trichloride, aluminum perchlorate, aluminum nitrate, aluminum permanganate, aluminum bicarbonate, 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, aluminum potassium aluminum sulfate dodecahydrate, aluminum bromate, aluminum nitride, and derivatives thereof.

12. The solar cell of claim 1, wherein the luminescent aluminum hydroxide comprises Al (OH)₃、AlOOH、5Al₂O₃·2H₂O or Al₂O₃The structure of (1).

Technical Field

The present disclosure relates to a solar cell (module) having improved efficiency including a low-cost aluminum-based solar (wavelength) conversion material and a method of manufacturing the same, and to a technique of improving photoelectric conversion efficiency according to an increase in short circuit current by positioning the material on an interface between a solar cell and an encapsulant of a front surface of the solar cell on which sunlight is incident, thereby simultaneously inducing a down-conversion effect and an anti-reflection coating effect.

The present disclosure relates to a solar cell, which can be applied to a material regardless of the types of an organic photovoltaic cell (OPV), a semiconductor-based solar cell based on a semiconductor including Copper Indium Gallium Selenide (CIGS), cadmium telluride (CdTe), perovskite, and the like, a silicon-based solar cell, and the like, and is characterized by improving photoelectric conversion efficiency by increasing a short-circuit current of the solar cell.

Background

Most commonly commercial solar cells are made of silicon single materials and about 50% of the light is unused due to the mismatch between the band gap of the natural solar spectrum and the silicon single material. That is, the natural solar spectrum has a wide wavelength distribution range (280 to 2500nm, 0.5 to 4.4eV) from ultraviolet to infrared, whereas the silicon solar cell can absorb only part of the wavelengths of the ultraviolet and visible wavelength regions.

For example, the entire solar spectrum is not effectively used in a silicon solar cell because of parasitic absorption due to silicon surface reflection or the like when the solar spectrum is incident on the silicon solar cell, heat loss (thermalization) in which an energy difference between solar light and silicon is emitted as heat due to the fact that the energy of the solar light band gap is larger than that of the silicon band gap and the sub-band gap transmitted as the sub-band gap is smaller than the band gap.

Recently, studies have been proposed to use solar wavelength conversion materials (solar spectrum converters) to improve the photocurrent conversion efficiency of natural sunlight and silicon solar cells by supplementing such materials (chem.soc.rev.,2013,42, 173). That is, a solar wavelength conversion material is introduced into a silicon solar cell, which converts light in an ultraviolet region where solar light absorption of silicon is insufficient or light in an infrared region where energy is smaller than a silicon band gap into light in a visible light region where silicon can absorb light well.

Solar wavelength conversion materials are largely classified into two types of down-conversion and up-conversion according to the direction of wavelength conversion. First, down-conversion is a technique of absorbing one photon of a short wavelength (e.g., a wavelength of ultraviolet rays) having energy higher than a band gap of silicon to convert the absorbed photon into one or two or more photons in a long wavelength region having low energy where silicon can absorb light well. On the other hand, upconversion is a technique of absorbing two photons of the infrared region where light is not absorbed in silicon but is transmitted through silicon because the energy of the infrared region is smaller than that of the silicon bandgap to convert the absorbed photons into one photon of the visible ray region where light is easily absorbed in silicon.

In general, an improvement in the overall power output of a solar module is caused by placing a down-conversion material on the front surface of a solar cell on which sunlight is incident and placing an up-conversion material on the rear surface of the solar cell while considering the driving principle of a solar spectrum wavelength converter, thereby minimizing the spectrum mismatch between the solar light and the silicon solar cell.

Disclosure of Invention

It is an object of the present disclosure to provide solar cells including aluminum-based solar conversion materials that increase the total power output of the solar module by supplementing the mismatch between solar irradiance spectra, as well as solar cells formed of various materials including polycrystalline and single crystalline silicon solar cells that use low-cost luminescent aluminum hydroxide materials as the material of the solar wavelength conversion material, and methods of making the same.

The present disclosure can achieve the effect of improving the total power output of a solar module by positioning a down conversion material at the interface between the solar cell and the encapsulant of the front surface of the solar cell upon which the solar spectrum is incident as a solar wavelength conversion material positioned at the interface thereby increasing the photocurrent. For example, the photocurrent conversion efficiency may be improved by absorbing ultraviolet rays of the solar spectrum, which are difficult to absorb light into silicon, into a solar wavelength conversion material and then down-converting the absorbed solar spectrum into light of visible rays, which are easy to absorb light into silicon, thereby effectively using the ultraviolet rays.

Further, when using a luminescent aluminum hydroxide made based on an aluminum material having low cost, excellent durability, and containing no heavy metal as a solar wavelength conversion material, along with the down-conversion effect, when applying the luminescent aluminum hydroxide to a commercial solar cell, the unit cost of photovoltaic power generation can be further reduced, since an anti-reflection coating effect from the interface between the sealant and the surface of the silicon solar cell can be expected.

As described above, luminescent aluminum hydroxide is used as the solar wavelength conversion material in the solar cell of the present disclosure. When the light-emitting aluminum hydroxide is applied to a solar cell, by the anti-reflection coating effect in the interface between the sealant and the surface of the silicon solar cell together with the down-conversion effect, since the current generated by light increases and the overall photoelectric conversion efficiency can be improved, the solar cell of the present disclosure can ensure competitiveness by further reducing the unit cost of photovoltaic power generation. Furthermore, the solar cell of the present disclosure may be expected to be resistant to potential induced degradation (anti-PID) effects of solar modules. It is well known that PID is due to Na generated from the glass of the module⁺Ions are generated by moving on the surface of the cell. Thus, the aluminum hydroxide on the surface of the solar cell has Na collected by⁺Ion protection of the solar cell.

Drawings

FIG. 1 is a cross-sectional view of a solar cell incorporating an aluminum-based solar wavelength conversion material;

fig. 2 is a conceptual diagram showing a light emission mechanism of an aluminum-based solar wavelength conversion material;

fig. 3 is a diagram showing an absorption spectrum and a luminescence spectrum of an aluminum-based solar wavelength converting material;

(black dotted line indicates absorption, blue dotted line indicates luminescence (case of no impurity added), red solid line indicates luminescence (case of impurity added));

fig. 4 is a graph showing External Quantum Efficiency (EQE) spectra of a silicon solar cell before coating with aluminum hydroxide (blue solid line) and after coating with aluminum hydroxide (red solid line); and

fig. 5 is a graph showing reflection spectra of a silicon solar cell before coating with aluminum hydroxide (black dotted line) and after coating with aluminum hydroxide (red solid line).

Detailed Description

Hereinafter, solar cells including aluminum-based solar wavelength converting materials according to the present disclosure are provided to improve the power output of solar modules by addressing the mismatch between the above-described solar irradiance spectrum and the absorption spectra of silicon solar cells and solar cells formed from various materials.

In the present disclosure, aluminum hydroxide having a luminescent property synthesized based on an aluminum material is used as a solar wavelength conversion material, which is a low-cost material and has excellent durability, so as to be applied to a solar module. The synthesis method of the luminous aluminum hydroxide comprises a hydrothermal method, a sol-gel method and a thermal decomposition synthesis method. In the present disclosure, although the present disclosure is more specifically described by a thermal decomposition synthesis method, the scope of the present disclosure is not limited thereto.

In the present disclosure, the aluminum precursor as the solar wavelength conversion material is an aluminum compound corresponding to any one selected from the group consisting of: aluminum monoacetate, aluminum triacetate, aluminum diacetate, aluminum triethyl aluminum, trimethylaluminum, aluminum alkoxides, diethylaluminum chloride, aluminum sulfate, aluminum cyanide, aluminum nitrite, aluminum carbonate, aluminum sulfite, aluminum hydroxide, aluminum oxide, aluminum chlorate, aluminum sulfide, aluminum chromate, aluminum trichloride, aluminum perchlorate, aluminum nitrate, aluminum permanganate, aluminum bicarbonate, 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, aluminum potassium aluminum sulfate dodecahydrate, aluminum bromate, aluminum nitride, and derivatives thereof.

When aluminum hydroxide is synthesized by the above-described thermal decomposition synthesis method, a material having a boiling point higher than the thermal decomposition temperature of the above-described single aluminum precursor may be used as the solvent. For example, a material having a high boiling point of 200 ℃ or more such as hexadecylamine, 1-eicosene, 1-octadecene, docosane, phenylene ether, benzyl ether, octyl ether, oleic acid, oleylamine, or polyisobutylene is used as the solvent.

The above solvent may be used as a solvent, and may be used to adjust light emitting characteristics or improve light emitting performance by injecting any one of impurities including carbon, carbonyl radicals, oxalic acid phosphoric acid, sulfuric acid, and the like into the solvent. Further, the alkyl group (C) may be additionally included by adding in the thermal decomposition synthesis step₁～C_n) Acetate, etc. to adjust optical characteristics such as absorption and light emission characteristics.

After dispersing a single aluminum precursor into the above solvent to produce a luminescent aluminum hydroxide, a reaction is performed at a thermal decomposition temperature of the aluminum precursor. When the reaction is complete, the final luminescent aluminum hydroxide can be obtained by isolating and purifying the product of the reaction.

The aluminum hydroxide ultimately produced may include Al (OH)₃、AlOOH、5Al₂O₃·2H₂O or Al₂O₃Etc., and may be labeled as aluminum hydroxide, AlOH, or aluminum oxyhydroxide hereinafter in this disclosure. The reason why aluminum hydroxide produced by the thermal decomposition synthesis method exhibits luminescence characteristics is trap emission caused by defects in the metal oxide. Fig. 2 shows a conceptual diagram of trap emission. When a defect of the material exists, another energy level is formed at an energy level lower than the conduction band, an electron in the conduction band transferred from the valence band to the conduction band by external energy is stabilized and moved to the lower energy level due to the defect, and the electron in the conduction band emits light when the electron is transferred to the valence band. Various impurities are added in the thermal decomposition synthesis step so that the energy level below the conduction band can be adjusted and the emission wavelength can also be controlled accordingly.

Since the finally synthesized luminescent aluminum hydroxide exhibits luminescence characteristics using only a single material of the above aluminum precursor even without including expensive lanthanide ions or organic phosphorus having luminescence characteristics, the finally synthesized luminescent aluminum hydroxide can further reduce the power generation cost of the photovoltaic module by increasing the efficiency of the solar cell.

In order to apply the solar wavelength conversion material to a silicon solar cell, the solar wavelength conversion material allows an absorption process to be performed in an ultraviolet wavelength and should have a light emitting characteristic in a visible wavelength. Specifically, it is preferable to form an absorption wavelength in the range of 300 to 450 nm. In addition, it is preferable to form an emission wavelength in the range of 450 to 1100 nm.

In particular, it is preferred that the absorption wavelength and the emission wavelength do not overlap with each other in the solar wavelength converting material. The reason is that the re-absorption of light emitted from the material, which is absorbed again when the absorption wavelength and the emission wavelength overlap each other, acts as a loss.

Furthermore, since the solar wavelength conversion material capable of performing down-conversion is located on the front surface of the solar cell, it is advantageous to have particles having a wavelength size smaller than the wavelength size of the solar light incident on the solar cell. If the solar conversion material has a particle size similar to or larger than the wavelength of sunlight, the overall efficiency of the solar cell may be reduced more or less when sunlight incident on the solar cell is scattered or reflected. Therefore, the solar spectrum wavelength converter preferably has a particle size range of 5nm or more and 10 μm or less.

Fig. 3 shows an absorption spectrum and a luminescence spectrum of aluminum hydroxide produced by a thermal decomposition synthesis method. More specifically, as the absorption spectrum of aluminum hydroxide, the black dashed line shows strong absorption in the ultraviolet region by starting absorption at 450 nm. Further, as the aluminum hydroxide emission spectrum, the blue dotted line shows the maximum emission peak at 456 nm. Meanwhile, when impurities were added to aluminum hydroxide, the emission spectrum of a red solid line was shown, and in this case, the maximum emission peak was shown at 526 nm. That is, when impurities are added to aluminum hydroxide, loss due to reabsorption may be minimized by shifting the emission spectrum to a long wavelength of 70nm to reduce the overlapping degree of the emission spectrum and the absorption spectrum, as compared to when no impurities are added to aluminum hydroxide.

Further, the aluminum hydroxide produced in this manner has an absolute luminous efficiency (absolute quantum yield) value of 60% or more.

In the present disclosure, a 6-inch polycrystalline silicon solar cell is used as the solar cell, and the type and size of the material constituting the solar cell are not limited thereto.

The method of introducing the above-described synthetic aluminum hydroxide into the solar cell may include a method of making aluminum hydroxide dispersed on a sealant into a sheet shape by dispersing the aluminum hydroxide on the sealant functioning to protect the silicon solar cell, a method of applying the aluminum hydroxide directly to the front surface of the silicon solar cell, a method of applying the aluminum hydroxide to the surface of the sealant bonded to the front surface of the solar cell, and the like, depending on the position of the introduction material of the solar cell.

First, a sealant including Ethylene Vinyl Acetate (EVA), polyolefin elastomer (POE), cross-linked polyolefin, thermoplastic polyurethane (TPU, thermal polyurethane), polyvinyl butyral (PVB), silicone/polyurethane hybrid, ionomer, and the like is used in the solar cell, and EVA and POE are most widely used in the sealant for the solar cell.

In general, there have been many reports on a method of manufacturing a solar cell module by thermal bonding (thermal lamination) after positioning a solar spectrum wavelength converter on the front surface of a solar cell by introducing the solar spectrum wavelength converter inside an encapsulant, and there are some cases where the method is applied to commercial production.

However, in this case, since the light emitted from the light conversion material within the encapsulant is due to the refractive index (n-1.4) of the polymer such as EVA or POE constituting the encapsulant and SiN in the surface of the solar cell_xIs not directed to the solar cell, light is directed to the side of the encapsulant sheet, and the optical waveguide phenomenon caused by total internal reflection inside the encapsulant is dominant. This phenomenon may act as a light loss on the side of the solar cell.

In contrast, when the solar conversion material is applied to the surface of the solar cell or the surface of the encapsulant, since the solar conversion material is positioned on the interface between the encapsulant and the solar cell, light is not directed to the side of the solar cell but is directed to the inside of the solar cell through the silicon textured structure of several μm (micrometers) to several tens of μm (micrometers). Further, according to Snell's law, since the direction in which light enters the encapsulant, the light conversion material, and the solar cell becomes very advantageous, the photoelectric conversion efficiency can be improved, thereby enabling light to be further used on the side surface of the solar cell if the solar conversion material can be adjusted to have a refractive index value between the refractive index (n-1.4) of the encapsulant and the refractive index (n-2.5) of the surface of the solar cell. In other words, both the down-conversion effect and the anti-reflection coating effect of the solar energy conversion material can be expected (fig. 1).

When the solar wavelength conversion material is dispersed in a solvent, the solar wavelength conversion material dispersed in the solvent may be applied to the surface of the solar cell, and the method of applying the solar wavelength conversion material dispersed in the solvent to the surface of the solar cell may include a spin coating method, a bar coating method, a spray coating method, a dip coating method, a screen printing method, and the like. Further, even when the solar wavelength conversion material dispersed in a solvent is applied to the sealant, all methods other than the spin coating method may be applied.

Although commercial production applications of solar wavelength conversion materials are contemplated in the present disclosure using spray coating methods that enable rapid and uniform application, the present disclosure is not so limited.

Hereinafter, preferred examples of the present disclosure will be described in detail with reference to examples, but the following examples are provided only to help us understand the present disclosure, and do not limit the scope of the present disclosure.

[ examples ]

EXAMPLE 1 Generation of luminescent aluminum hydroxide

After mixing 1 to 20 wt% of one of the above suggested aluminum precursors with 1-octadecene or oleic acid solvent, thermal decomposition reaction was performed at 200 to 300 ℃ for 30 minutes in a stirred state. After completion of the reaction, the aluminum hydroxide is separated from the stirred mixture by centrifugal separation to redisperse the separated aluminum hydroxide in a nonpolar solvent such as toluene, chloroform, or hexane. When a process of controlling the emission wavelength is additionally performed, after 0.1 to 10 wt% of one of the above-suggested impurities is added to the solvent with respect to the weight of the aluminum precursor to perform a thermal decomposition reaction in the same method as above in a state of stirring a mixture of the aluminum precursor, the impurities and the solvent, a separation and purification process is performed on the stirred mixture to produce a luminescent aluminum hydroxide solution. Fig. 3 shows the UV-visible spectrum and photoluminescence spectrum of the resulting luminescent aluminum hydroxide solution, and the dark dotted line means the absorption spectrum, the blue dotted line means the luminescence spectrum (case where no impurities are added), and the red solid line means the luminescence spectrum (case where impurities are added).

Example 2 fabrication of solar cells comprising luminescent aluminum hydroxide

In order to position the above-generated aluminum hydroxide particles on the interface between the silicon cell and the sealant, the aluminum hydroxide particles may be applied to the front surface of the silicon cell or to the rear surface of the upper sealant to which the light receiver of the silicon cell and the sealant adhere, by using a spray coating method. As another method of introducing aluminum hydroxide, a sheet having a thickness of 100 μm or less is manufactured by dispersing aluminum hydroxide into a light-transmitting resin including a sealant, and then the aluminum hydroxide is inserted into the light-transmitting resin in a lamination step for manufacturing a solar cell module. As shown in the diagram of fig. 1, a silicon solar cell module is manufactured by lamination after sequentially stacking glass, a sealant, aluminum hydroxide, a solar cell, a sealant, and a rear sheet from a front surface of the solar cell to which light is incident. Aluminum hydroxide is located at the interface between the encapsulant and the solar cell in the solar cell module manufactured in this manner.

Experimental example 1: performance evaluation of solar cells comprising luminescent aluminum hydroxide

In order to confirm the power output of the solar cell from the introduction of the luminescent aluminum hydroxide, a solar simulator (WXS-156S-10) of Wacom co. Further, in order to analyze external quantum efficiency by wavelength, IPCE (QEX10) equipment of PV Measurements, inc., was used, and changes in conversion efficiency before and after coating with aluminum hydroxide were observed. To measure the total reflectance from the coating of aluminum hydroxide additionally, UV-3600nir (with MPC-3100) from Shimadzu Corporation was used, and the efficiency change of the solar cell before and after the coating of aluminum hydroxide was analyzed.

Table 1 shows the efficiency measurements of a 6 inch polycrystalline silicon solar cell to which the luminescent aluminum hydroxide was applied. After measuring all the efficiencies of the solar cells before applying aluminum hydroxide to the solar cells to improve the accuracy of the measured efficiencies, their efficiency measurement results are compared with the results after applying aluminum hydroxide to the solar cells.

[ Table 1]

Table 1 shows that both the short-circuit current and the efficiency are increased more in the case where aluminum hydroxide is coated on the solar cell than in the case where aluminum hydroxide is not coated on the solar cell. To verify this increase in efficiency, the photocurrent conversion efficiency (IPCE, efficiency of incident photons to current) before and after coating aluminum hydroxide was measured, and fig. 4 shows the photocurrent conversion efficiency according to wavelength, i.e., External Quantum Efficiency (EQE) spectrum, as the IPCE measurement result.

Fig. 4 shows the results of the solar cell #4 in table 1, in which the blue solid line is the EQE spectrum before coating with aluminum hydroxide and the red solid line is the EQE spectrum after coating with aluminum hydroxide. That is, as can be seen from the results of fig. 4, the conversion efficiency increases in the wavelength range from 300nm to nearly 500nm by down-conversion of aluminum hydroxide. Further, fig. 5 is a result of measuring a change in reflectance before and after coating aluminum hydroxide on the solar cell #4 in table 1, in which a black dotted line is a total reflectance before coating aluminum hydroxide on the solar cell #4, and a red solid line is a reflectance spectrum after coating aluminum hydroxide on the solar cell # 4. It can be seen that the reflectance values are more reduced in the spectral region ranges of 300 to 500nm and 800 to 1100nm after the coating process is performed.

That is, aluminum hydroxide is coated on the surface of the silicon solar cell, so that the short circuit current of the silicon solar cell is increased and the total efficiency thereof is increased by a down-conversion effect due to absorption of ultraviolet light and emission of visible light and an anti-reflection coating effect in which the refractive index due to the aluminum hydroxide has a value between the refractive index of the surface of the silicon solar cell and the refractive index of the sealant (1.5)<n_{Aluminum hydroxide}<2.5), light easily enters the interior of the silicon solar cell.

Table 2 shows the efficiency change before and after the introduction of aluminum hydroxide to the silicon solar cell micromodule fabricated in example 2.

[ Table 2]

It was confirmed that even with the module formed similarly to the results of table 1, both the short-circuit current and the efficiency in the solar cell into which aluminum hydroxide was introduced were increased more than those in the solar cell into which aluminum hydroxide was not introduced.