CN102250404B - Packaging material - Google Patents

Abstract

The invention provides a packaging material, which comprises 80-99.5 weight percent (wt%) of ethylene-vinyl acetate copolymer; and 0.5-20 wt% of a photoluminescent polymer; wherein the ethylene-vinyl acetate copolymer is uniformly mixed with the photoluminescent polymer. The packaging material can be applied to packaging solar cells, and can reduce the damage of ultraviolet rays to ethylene-vinyl acetate copolymer and improve the light utilization rate of the solar cells.

Description

Packaging material

technical field

The invention relates to an encapsulation material, in particular to the application of the encapsulation material in a solar cell encapsulation module.

Background technique

The first solar cell was manufactured by Bell Labs in the United States in 1954 to provide power for communication systems in remote areas. However, its efficiency is too low (only 6%) and the cost is too high ($357/W), so it lacks commercial value. In order to overcome the shortcomings of low efficiency, high cost, and short service life, many researchers have proposed many solutions over the years, but most of them cannot completely solve the related problems.

In order to block the influence of air and water vapor on the solar cell, reduce environmental damage to the chip, and increase its industrial applicability, an encapsulation module can be used. The above-mentioned packaging module must have good UV resistance, thermal cracking resistance, and fast curing characteristics, so as to meet the market demand and application.

In 1970, NASA laboratories in the United States adopted ethylene-vinyl acetate copolymer (EVA) resin and polyvinyl butyral (PVB) resin as packaging modules. EVA resin has the advantages of low cost and high transparency, so it has been widely used in solar cells. However, the EVA resin has poor UV resistance and heat resistance, and it deteriorates after a period of use and cannot continue to protect the solar cell. In order to solve the above problems, US 6093757, WO06093936, JP 2000183382, US 7368655, EA0001908, and US 5447576 and other patents propose solutions. The above-mentioned solutions mainly focus on adding UV absorbers to improve the UV resistance of EVA resins, adding heat stabilizers to improve the thermal cracking resistance of EVA resins, and/or adding resin accelerators such as peroxides to make EVA resins quickly cure and does not form photoacid. Although the above solution can solve the problem of packaging materials, it still cannot further improve the light conversion efficiency.

In JP2001007377, a layer of fluorescent dye is further coated on the outside of the glass substrate to convert ultraviolet light into visible light. In addition to reducing the impact of ultraviolet rays on the packaging material, the above-mentioned method can also improve the light conversion efficiency. However, the above methods cannot improve the heat resistance of the inner packaging material, and the manufacturing process is complicated. On the other hand, the outermost fluorescent dye layer may require additional packaging material protection, which will increase the process and related costs.

To sum up, there is an urgent need for an encapsulation material that, in addition to having a long service life, can also convert ultraviolet light into visible light to improve the efficiency of solar cells.

Contents of the invention

The invention provides an encapsulation material, comprising 80 weight percent (wt%) to 99.5 weight percent (wt%) ethylene-vinyl acetate copolymer; and 0.5 weight percent (wt%) to 20 weight percent (wt%) Photoluminescent polymer; wherein the ethylene-vinyl acetate copolymer is uniformly mixed with the photoluminescent polymer; wherein the structure of the photoluminescent polymer is as follows:

Among them, D is a fluorescent group; R ₁ , R ₂ , R ₃ , and R ₄ are each independent, R ₁ , R ₂ , and R ₃ are hydrogen or C _1-6 alkyl groups optionally containing substituents, and R ₄ is any Choose a C _1-6 alkylene group containing substituents; m is a positive integer of 1-5; n is 10-10,000.

Description of drawings

FIG. 1 is a schematic diagram of a solar cell packaging module in an embodiment of the present invention.

FIG. 2 is an excitation-emission spectrum of a photoluminescent polymer containing a pyrenyl group in an embodiment of the present invention.

FIG. 3 is an excitation-emission spectrum of a photoluminescent polymer having a naphthyl group at its end in an embodiment of the present invention.

Symbol Description

10～solar battery packaging module;

11 ~ packaging materials;

13, 15 ~ substrate;

17 ~ solar battery.

Specific Embodiments of the Invention

The invention provides an encapsulation material, which comprises 80-99.5 weight percent (wt%) ethylene-vinyl acetate copolymer (EVA) and 0.5-20 weight percent (wt%) photoluminescence polymer. If the weight ratio of EVA is too high (that is, the weight ratio of the photoluminescent polymer is too low), the ultraviolet rays in the incident light cannot be effectively converted into visible light. If the weight ratio of EVA is too low (that is, the weight ratio of the photoluminescent polymer is too high), not only the conversion rate of ultraviolet rays cannot be greatly increased, but also the cost will be greatly increased. In one embodiment of the present invention, the number average molecular weight of EVA is between 5000～100000, and the molar ratio of vinyl monomer and vinyl acetate monomer in EVA is between 60:40～80:20, The preferred ratio is between 65:35 and 75:25. If the molar ratio of vinyl monomer is too high, the light transmittance and adhesiveness of EVA will be reduced. If the molar ratio of vinyl acetate monomer is too high, the water absorption of EVA will be too high.

The above-mentioned photoluminescent polymers are uniformly mixed in the ethylene-vinyl acetate copolymer, and will not aggregate into particles or transfer to the surface of the mixture. In order to achieve a uniform mixing effect, the structure of the photoluminescent polymer is shown in Formula 1:

In Formula 1, D is a photoluminescent group; R ₁ , R ₂ , R ₃ , and R ₄ are each independently, and R ₁ , R ₂ , and R ₃ are hydrogen or C _1-6 alkyl groups optionally containing substituents , R ₄ is a C _1-6 alkylene group optionally containing substituents. m is a positive integer of 1-5, and n is 10-10,000. In Formula 1, D is a photoluminescent gene, including, for example, pyrene, anthracene, naphthalene, flavone, coumarin, perylene ), other photoluminescent groups, derivatives of the above groups, or combinations of the above groups. The function of the photoluminescent group D is to absorb ultraviolet rays with a wavelength of less than 400nm in sunlight, and convert them to emit visible light with a wavelength greater than 400nm, such as fluorescence or phosphorescence. In this way, when ambient light irradiates the packaging material, in addition to reducing the damage of ultraviolet rays to EVA, the conversion efficiency of the solar cell can also be increased.

In formula 1, the end of the photoluminescent polymer is a photoluminescent group D, its skeleton is polylactone, and its formation method is ring-opening polymerization. Monomers suitable for use in the present invention may be caprolactone, valerolactone, butyrolactone, propionolactone, lactic acid-, or acetolactone ), the carbon number of the above-mentioned monomers will determine the size of m, and the substituents of the above-mentioned monomers will determine the types of _R1 and _R2 . The catalyst for the above ring-opening polymerization can be stannous octoate (Sn(Oct) 2 ), and the weight ratio of the catalyst to the lactone will determine the degree of polymerization n (or molecular weight) of the photoluminescent polymer. In one embodiment of the present invention, the number average molecular weight (Mn) of the photoluminescent polymer is between 5,000 and 100,000. If the number average molecular weight of the photoluminescent polymer is too high or too low, it cannot be uniformly mixed in the EVA. In order to make the packaging material have higher light transmittance and lower haze, the refractive index of the photoluminescent polymer is between 1.2 and 1.7. In order to make the encapsulation material easy to process, the melting point of the photoluminescent polymer is between 50° C. and 130° C.

Although the photoluminescent polymers in the above packaging materials can reduce the damage of ultraviolet rays to EVA, they still cannot completely convert ultraviolet rays into visible light. In order to increase the lifespan of the packaging material and improve the processability of the packaging process, 0.1-5 weight percent (wt%) additives such as resin accelerators, heat stabilizers, or a combination thereof can be further added to the packaging material. Resin accelerators are generally peroxides such as benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 1,1- Di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, or a combination of the above. The above-mentioned resin accelerator can generate free radicals to cross-link EVA when heated, so that the original thermoplastic packaging material becomes thermosetting after packaging. In this way, the encapsulation material after encapsulation will not be denatured due to heat, which can effectively protect the components it encapsulates, such as solar cells, from being damaged by air or moisture. On the other hand, the above-mentioned thermal stabilizers such as dibutyl hydroxytoluene, bis(2,2,6,6-tetrabutyl-4-piperidinyl) sebacate, or the above-mentioned combination can stabilize EVA due to heat or The free radicals or photoacids produced by the bond breaking by irradiation of ultraviolet rays can prevent these free radicals or photoacids from damaging solar cell components.

In one embodiment of the present invention, after the above mixed encapsulation material 11 is formed on the substrates 13 and 15, the solar cell 17 is placed between the encapsulation materials 11 of the two substrates 13 and 15, heated and pressed together to form the solar cell. The packaging module 10 is shown in FIG. 1 . The substrate 13 can be made of transparent material such as glass, plastic, or resin. The substrate 15 can be a reflective material such as metal. The solar cell 17 may be a solar cell chip mainly based on a silicon substrate.

Compared with the known encapsulation material EVA, the mixture containing photoluminescent polymers of the present invention can convert ultraviolet rays into visible light, which not only improves the light utilization rate of solar cells encapsulated by it, but also reduces the damage of ultraviolet rays to EVA and increases the life of components. On the other hand, the present invention grafts the photoluminescent group to the end of the polylactone that can be uniformly mixed with EVA, instead of directly mixing photoluminescent small molecules into EVA. Experiments have proved that other polymers such as polystyrene cannot be uniformly mixed in EVA, which will increase the haze of the mixture and reduce the light transmittance of the mixture. In addition, if the photoluminescent small molecules are directly mixed in EVA, since the photoluminescent small molecules cannot be dissolved in the EVA resin, they can only exist in the EVA resin in a dispersed manner, which will cause the small molecules to aggregate or even migrate. ) to the surface of the mixture, which instead deteriorates the properties of the encapsulation material and reduces the life of the component.

In order to make the above and other objects, features, and advantages of the present invention more comprehensible, a number of embodiments are listed below and described in detail with reference to the accompanying drawings.

Example

Example 1

Get 80,90,98, and 99 weight percent (wt%) ethylene-vinyl acetate copolymer (DupontD150, VA content: 32%) and 20, 10, 2, and 1 weight percent (wt%) respectively Caprolactone (source as shown in Preparation Example 1B) was mixed with toluene (Tedia, 99%) as a solvent, and then made into a film on glass by spin coating (Spin coating), and its haze and transmittance were measured respectively As shown in Table 1. It can be seen from Table 1 that even if the amount of polycaprolactone is increased to 10wt%, the film still has high transmittance and low haze, indicating that polycaprolactone can be effectively dispersed in ethylene-vinyl acetate copolymer.

Table 1

Example 1a Example 1b Example 1c Example 1d EVA weight ratio 99 98 90 80 PCL weight ratio 1 2 10 20 Transmittance(%) 91.29 91.81 91.74 91.14 Haze (%) 1.28 0.82 0.86 0.36

Comparative example 1

Get 90, 98, and 99 weight percent (wt%) ethylene-vinyl acetate copolymer (DupontD150) and 10, 2, and 1 weight percent (wt%) polystyrene (Acros MW=250000) to mix respectively , after making a thin film on glass by spin coating, the haze and transmittance were measured respectively, as shown in Table 2. It can be seen from Table 2 that when the amount of polystyrene is increased to 10wt%, the haze of the film will be greatly increased, indicating that polystyrene cannot be effectively dispersed in the ethylene-vinyl acetate copolymer.

Comparing Example 1 and Comparative Example 1, it can be seen that not all polymers can be effectively dispersed in ethylene-vinyl acetate copolymer like polylactone. Based on the above comparison, the present invention uses polylactone as the skeleton of the photoluminescent polymer, and further grafts photoluminescent groups.

Table 2

Comparative Example 1a Comparative Example 1b Comparative Example 1c EVA weight ratio 99 98 90 PS weight ratio 1 2 10 Transmittance(%) 91.27 91.02 91.55 Haze (%) 2.5 2.82 9.5

Preparation Example 1A

Get 0.09g of 1-pyrene butanol (1-pyrenebutanol, Aldrich), 18g of caprolactone (Tokyo Chemical TCI purity 98%) and 0.1g of stannous octoate (Aldrich) dissolved in 20mL toluene (Tedia, 99% ), heated to 130°C for ring-opening polymerization for 8 hours as shown in Formula 2, 7g of photoluminescent polymers (yield 70%) were formed, the number average molecular weight was 8139 as measured by GPC, and its melting point was between 55°C Its refractive index is between 1.52 and 1.48, and its film absorption spectrum and fluorescence emission spectrum obtained with a central wavelength of 340nm as the excitation light source are shown in Figure 2.

Preparation Example 1B

Get 18g of caprolactone (TCI) and 0.1g of stannous octoate (Aldrich) and be dissolved in 20mL toluene, be heated to 130 ℃ and carry out ring-opening polymerization reaction and promptly form 15g polycaprolactone polymer (productive rate 83% ), its number average molecular weight measured by GPC is 8500, and its melting point is between 55°C and 60°C.

Preparation example 2

Take 0.1g of naphthyl derivatives (structure as shown in compound B in formula 3), 10g of caprolactone and 0.1g of stannous octoate were dissolved in 20mL of toluene, heated to 130 ° C for 8 hours of ring-opening polymerization reaction as Formula 3, namely the formation of 6.5g photoluminescent polymer (yield 65%), its number average molecular weight measured by GPC is 7140, its melting point is between 55°C and 60°C, and its refractive index is between 1.51 and 1.48 Between, and its thin film absorption spectrum and the fluorescence emission spectrum obtained with the central wavelength of 340nm as the excitation light source are shown in Figure 3.

Example 2

According to the percentage by weight of Table 3, get respectively the ethylene-vinyl acetate copolymer (Dupont D150) of 90, 98, and 99 weight percent (wt %) and mix respectively with 10, 2 and 1 weight percent (wt %) Preparation Example 1A The product of formula 2 was dissolved in toluene and mixed, then spin coated (spin coating) to form a film on glass, and then its haze and transmittance were measured respectively, as shown in Table 3. It can be seen from Table 3 that even if the amount of the product of Formula 2 in Preparation Example 1A is increased to 10 wt%, the film still has high transmittance and low haze, indicating that the product of Formula 2 in Preparation Example 1A can be effectively dispersed in ethylene-vinyl acetate copolymer middle.

table 3

Comparative Example 2a Comparative example 2b Comparative example 2c EVA weight ratio 99 98 90 The weight ratio of formula 2 product 1 2 10 Transmittance(%) 91.34 91.71 91.63 Haze (%) 0.81 0.81 0.51

Comparative example 2

Get 90 weight percent (wt%) ethylene-vinyl acetate copolymer (Dupont D150) and 10 weight percent (wt%) 3-hydroxyflavone (Aldrich 3-Hydroxyflavone) to mix, spin coating (spin coating) on After the film was formed on the glass, its haze and transmittance were measured respectively, as shown in Table 4. From Table 3 (Example 2c) and Table 4 (Comparative Example 2), it can be seen that even if the amount of 3-hydroxyflavone and the product of formula 2 are the same, the small molecule 3-hydroxyflavone still cannot be effectively dispersed in the product like formula 2. Among ethylene-vinyl acetate copolymers. As a result, the film containing fluorescent small molecules will be greatly atomized and not suitable for encapsulating solar cells.

Table 4

Comparative example 2 EVA weight ratio 90 3-Hydroxy brass weight ratio 10 Transmittance(%) 91.25 Haze (%) 4

Embodiment 3 (preparation of encapsulation film for solar cell and module encapsulation)

Take 90 grams of EVA resin granules and 10 grams of photoluminescent polymers (such as formula 2) and first blend them with a single-screw mixer (Star Metal Co., Ltd., L/D ratio 20) at 80 ° C, and then take 50 A gram of the mixed resin was pressed into a film by a press machine to obtain a packaging film of 200mm×200mm×0.65mm. In addition, the EVA packaging film (purchased from Mitsui, Japan) and the MCLA2D prepared by the laboratory were used as the packaging film for comparison, and their thicknesses were both 0.6 mm to 1 mm. The composition of MCLA2D contains 100g of EVA (purchased from Dupont) and 3.95g of resin accelerator, and the resin accelerator contains 0.6g of 2-hydroxyl-4-n-octyloxybenzophenone (purchased from Acros), 0.6 g of bis(2,2,6,6-tetrabutyl-4-piperidine) sebacate (purchased from Acros), 0.8 g of 2,5-dimethyl-2,5-di(tert-butyl peroxy)hexane (available from ACROS), and 1.95 g of triallyl isocyanate (available from Acros).

After the above packaging material (11 in Figure 1) is formed on the substrate (13 and 15 in Figure 1), the solar cell module (17 in Figure 1) is placed in a vacuum pressing device for heating and pressing to complete Package structure module. The above-mentioned encapsulated solar cell module was subjected to circuit measurement, and the measured component performance is shown in Table 5.

table 5

It can be seen from Table 5 that the photoluminescent polymer mixed with EVA can not only increase its light transmittance, but also further improve the light conversion efficiency.

Although the present invention has disclosed several preferred embodiments as above, these embodiments are not intended to limit the present invention, and anyone skilled in the art can make any changes and modifications without departing from the spirit and scope of the present invention. Therefore The protection scope of the present invention should be determined by the scope defined by the appended claims.

Claims (12)

1. A packaging material, comprising: 80-99.5% by weight of ethylene-vinyl acetate copolymer; and 0.5-20% by weight of photoluminescent polymer; Wherein, the ethylene-vinyl acetate copolymer is uniformly mixed with the photoluminescent polymer; Wherein the structure of the photoluminescent polymer is as follows: Wherein D is a photoluminescent group; R ₁ , R ₂ , R ₃ , and R ₄ are each independently, R ₁ and R ₂ are hydrogen, and R ₃ is hydrogen or a C 1-6 alkyl group optionally containing a substituent, and R ₄ is a C _1-6 alkyl group optionally containing a substituent C _1-6 alkylene; m is a positive integer 1-5; and n is 10 to 10,000, Wherein, the photoluminescent group is pyrenyl, anthracenyl, naphthyl, flavonyl, coumarinyl, perylenyl, derivatives of the above groups, or a combination of the above groups. 2. The packaging material according to claim 1, wherein the number average molecular weight of the ethylene-vinyl acetate copolymer is 5,000-100,000. 3. The packaging material according to claim 1, wherein the photoluminescent group of the photoluminescent polymer absorbs ultraviolet rays with a wavelength less than 400nm, and emits visible light with a wavelength greater than 400nm; wherein the visible light is produced by fluorescence (Fluorescence) Or phosphorescence (Phosphorescence) composition. 4. The packaging material according to claim 1, wherein the number average molecular weight of the photoluminescent polymer is 5000-100000. 5. The packaging material according to claim 1, wherein the refractive index of the photoluminescent polymer is 1.2˜1.7. 6. The packaging material according to claim 1, wherein the melting point of the photoluminescent polymer is 50°C-130°C. 7. The packaging material according to claim 1, wherein in the ethylene-vinyl acetate copolymer, the molar ratio of ethylene monomer to vinyl acetate monomer is 60:40˜80:20. 8. The packaging material according to claim 1, further comprising 0.1-5% by weight of additives. 9. The packaging material according to claim 8, wherein the additive comprises a resin accelerator, a thermal stabilizer, or a combination thereof. 10. The packaging material according to claim 9, wherein the resin accelerator comprises benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxide) oxy)hexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, or a combination of the above. 11. The packaging material according to claim 9, wherein the thermal stabilizer comprises dibutyl hydroxytoluene, bis(2,2,6,6-tetrabutyl-4-piperidinyl) sebacate, or a combination of the above. 12. The encapsulation material according to claim 1, which is used for encapsulating solar cells.

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