WO2009102094A1

WO2009102094A1 - Manufacturing method of coating composition for protecting solar cell module

Info

Publication number: WO2009102094A1
Application number: PCT/KR2008/003246
Authority: WO
Inventors: Joo-Nam Seon; Seung-Min Oh; Chang-Keun Seo
Original assignee: Dae Joo Electronic Materials Co., Ltd.
Priority date: 2008-02-12
Filing date: 2008-06-11
Publication date: 2009-08-20
Also published as: CN101543770B; CN101543770A; KR100958690B1; KR20090087256A

Abstract

The present invention relates to a manufacturing method of a coating composition for protecting solar cell module having excellent weatherability and durability, more precisely a manufacturing method of a coating composition for protecting solar cell module comprising the steps of synthesizing a compound by mixing a silicate composition prepared by hydrolyzing methyl silicate or ethyl silicate with excessive water and a titanium dioxide composition prepared by hydrothermal synthesis and aqueous synthesis; and coating solar cell module made of low iron transparent glass having excellent light transmittance and durability with the compound to increase maximum power generation of module and light transmittance, compared with the conventional low iron glass.

Description

[DESCRIPTION]

[invention Title]

MANUFACTURING METHOD OF COATING COMPOSITION FOR PROTECTING SOLAR CELL MODULE

[Technical Field]

The present invention relates to a manufacturing method of a coating composition for protecting solar cell module having excellent weatherability and durability. More precisely, the present invention relates to a manufacturing method of a coating composition for protecting solar cell module comprising the steps of synthesizing a compound by mixing a silicate composition prepared by hydrolyzing methyl silicate or ethyl silicate with excessive water and a titanium dioxide composition prepared by hydrothermal synthesis and aqueous synthesis; and coating solar cell module which is made of low iron transparent glass having excellent light transmittance and durability with the compound to increase maximum power generation of module and light transmittance, compared with the conventional low iron glass.

[Background Art] According to the recent rise of concerns on environmental problems, solar cell attracts our attention as a clean energy source.

Solar cell materials are mainly produced by using single crystal silicon substrate or poly crystal silicon substrate, so the solar cell materials are weak in physical impact resistance. Besides, solar cell set up outside needs to be protected from rain, etc. And one sheet of solar cell generates small amount of electricity, so series and parallel connection of multiple solar cells are necessary to output practical electricity. Therefore, solar cell module has been produced to connect multiple solar cell materials and seal it with a transparent board and filler.

Solar cell module is a semiconductor device that converts light energy into electric energy by using photoelectric effect. The light energy came into the spotlight because it is the pollution-free, noise-free unlimited clean energy. Kyoto Protocol took effect from February 16, 2005, which limits the output of greenhouse gas such as carbon dioxide and methane to counter the global warming. At least 80% of energy source in Korea depends on imports, so it is needless to say that solar energy is the most important alternative energy in Korea. Solar cell module generates electricity by using multiple solar cells connected by serial-parallel connection by conductive ribbons and provides electricity to a user. Then, the user can use this electricity as a commercial power source. Recently, solar cell modules are set up outside, for example on the roof of a building, on the side wall of a building, in the mountains, on the island, in the park, on the signals, on the road signs, etc., to provide electricity thereto.

It is required for the back protective sheet layered on solar cell module to have excellent mechanical strength and durability including weatherability and hydrolysis resistance to protect the back side of the solar cell module.

Module is produced by lamination method, in which transparent front substrate, filler, solar cell device, filler and back protective sheet are layered sequentially, followed by vacuum suction and hot pressing.

Solar cell is, in fact, for outdoors, so that materials consisting the solar cell module must have excellent durability. To protect the back side of the solar cell module, a protective sheet is generally used, so that this sheet is also required to have excellent mechanical strength and durability such as weatherability and hydrolysis resistance .

As for the back protective sheet of the solar cell module, plastic having excellent strength has been widely used. A metal sheet can also be used. And, a composite film comprising a fluorine-based resin film and a metal thin film has been widely used.

The composite film with the metal thin film has high barrier characteristics against steam, so that it can be very useful for protecting solar cell from steam. However, the composite film comprising the fluorine-based resin film and the metal thin film has a problem of short-circuit generated by crack or something resulted from external force. So, it needs to be improved to be used as a material for the back protective sheet for solar cell module. It also needs to be improved in its anti—short property which is one of the major characteristics ^' required for packing materials of electric device such as solar cell module using metal thin film on which comparatively high voltage is applied.

The fluorine-based resin film is suitable for weight- reduction which favors handling. The fluorine film itself has excellent weatherability but it allows UV to pass through, so that solar cell module components can be easily deteriorated by UV, adhesion is reduced and the strength of the structural material is decreased. In the case of using the fluorine film containing UV absorber, when a gas barrier film of PET film bass is used in surface protective sheet construct, the module was easily affected by UV and electricity power generation efficiency was reduced. Besides, the waste treatment might be a burden of environmental problem. So this film seemed not the most appropriate component for solar cell module, particularly for such clean energy.

[Disclosure]

[Technical Problem]

To overcome the above problems, the present inventors developed a coating composition for protecting solar cell module that is directly coated on a solar cell module which is made of a low iron transparent glass solar cell module having high light transmittance and durability to increase such durability and weatherability, along with light transmittance and maximum power generation, compared with the conventional low iron glass.

So, it is an object of the present invention to provide a coating composition for protecting solar cell module having excellent durability and weatherability even after long-term use, and high light transmittance and increased maximum power generation, compared with the conventional low iron glass.

[Technical Solution] To achieve the above objects, the present invention provides a manufacturing method of a coating composition for protecting solar cell module comprising the following steps: hydrolyzing a titanium compound with water and adding alcohol and acid thereto, followed by hydrothermal synthesis to grow crystals; mixing the titanium compound and an organic solvent with water and raising temperature, and adding acid thereto, followed by aqueous synthesis to improve dispersibility; mixing each compound prepared by the above hydrothermal synthesis and aqueous synthesis to give photocatalyst sol; synthesizing a water soluble silicate binder compound by hydrolyzing silicate compound with excessive water; and mixing the photocatalyst sol, the water soluble binder compound and alcohol altogether.

Herein, the alcohol is preferably methanol, ethanol or isopropyl alcohol.

The coating composition can additionally include colloidal silica particles. Particularly, the present invention provides titanium oxide sol for anatase type photocatalyst that reacts in transparent visible light region and has excellent crystallinity and high activity by taking advantage of both hydrothermal synthesis and aqueous synthesis and further provides a coating composition for protecting solar cell module prepared by mixing the synthesized water soluble methyl silicate or water soluble ethyl silicate (referred as water soluble binder hereinafter) with the photocatalyst sol, which is appropriate for direct coating on the solar cell module and has excellent durability, weatherability and super-hydrophilicity .

The titanium compound herein is a titanium dioxide compound, which, is preferably titanium (IV) isopropoxide (titanium tetraisopropanol) , titanium (IV) butoxide, titanium (IV) ethoxide (titanium tetraethanolate) , titanium (IV) methoxide, titanium (IV) stearate, titanium chloride, titanium nitrate, titanium sulfate, titanium aminooxalate or a mixture thereof. The acid herein can be an organic acid selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid, lactic acid, and citric acid and fumaric acid, or an inorganic acid selected from the group consisting of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, chlorosulfonic acid, para-toluene sulfonic acid, 3-chloroacetic acid, polyphosphoric acid, iodic acid, iodic acid anhydride and perchloric acid, and preferably such an inorganic acid as nitric acid, hydrochloric acid, hydrofluoric acid and sulfuric acid.

The silicate compound herein can be selected from the group consisting of is methyltrichlorosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriisopropoxysilane, ethyltributoxysilane, butyltrimethoxysilane, pentafluorophenyltrimethoxysilane, phenyltrimethoxysilane, nonafluorobutylethyltrimethoxysilane, trifluoromethyltrimethoxysilane, dimethyldiaminosilane, dimethyldichlorosilane, dimethyldiacetoxysilane, dimethyldimethoxysilane, diphenyldimethoxysilane, dibutyldimethoxysilane, trimethylchlorosilane, vinyltrimethoxysilane, (met) acryloxypropyltrimethoxysilane, glycidyloxytrimethoxysilane, 3- (3-methyl-3- oxetanemethoxy) propyltrimethoxysilane, oxacyclohexyltrimethoxysilane, methyltri (met) acryloxysilane, methyl [2- (met) acryloxyethoxy] silane, methyl- triglycidyloxysilane and methyltri (3-methyl-3- oxetanemethoxy) silane . These compounds can be used alone or combined at least two, and in particular, methyl silicate or ethyl silicate is preferably used.

Hereinafter, hydrothermal synthesis reaction, aqueous synthesis reaction and water soluble binder are described in detail.

1. Hydrothermal synthesis reaction

In the present invention, hydrothermal synthesis reaction growing a crystal at high temperature and high pressure was efficiently performed to give anatase-type crystals with high yield. To perform the reaction at high temperature/high pressure, a hydrothermal synthesis reactor was used. The temperature for the hydrothermal synthesis in this invention was 100-300"C, preferably 150-200^°C, and the pressure was 10τ20 a. p. and the reaction time was 2-3 hours. If the temperature and pressure are too low, hydrothermal synthesis reaction will not be induced, whereas if the temperature and pressure are too high, the reaction will be dangerous .

2. Aqueous synthesis reaction

Aqueous synthesis was performed at 80-90^°C for 2 hours, followed by stirring for 12 hour and passive-cooling.

The composition prepared by mixing each compound resulted from the hydrothermal synthesis and the aqueous synthesis contains titanium oxide preferably by 0.5-5 weight%.

To improve coating property, a polar solvent such as alcohol was added to the hydrothermal synthesis process to give photocatalyst sol. Preferably, the polar solvent is ethyl alcohol, isopropyl alcohol or methyl alcohol.

To maintain the dispersibility of the prepared photocatalyst, the amount of water added thereto was preferably 5-20 weight% .

3. Synthesis of water soluble binder compound

Water soluble methyl silicate or water soluble ethyl silicate was necessarily obtained by hydrolysis with excessive water. This was because the ethyl silicate or methyl silicate^' generated by the general hydrolysis was so unstable at room temperature that it was turned into gel. So, to stabilize these compounds, ethyl alcohol or methyl alcohol was necessarily added rightly to dilute these compounds at the concentration of up to 20%.

The amount of water added for the hydrolysis to synthesize the binder compound was preferably 50-70weight% .

The solid content of the water soluble silicate compound in the total weight of the composition was preferably 5-20 weight%.

The hydrolysate is insoluble in water and the dried membrane coated on the substrate does not form a hydrophilic coat (water drop contact angle thereon was 60°). But, the methyl silicate or ethyl silicate obtained from the hydrolysis with excessive water is water-soluble and stable and the dried membrane coated on the substrate has water drop contact angle of up to 10°, exhibiting super-hydrophilicity.

[Advantageous Effect]

The method of the present invention is improved from the conventional sol-gel method-based hydrolysis, which is expected to be efficiently applied in protecting solar cell module and its related field because, according to this method, excellent photoactivity, stability and dispersing power in addition to the excellent coating capacity and organism decomposing capacity are expected by using the photocatalyst prepared by hydrothermal and aqueous synthesis with titanium compound and by using water soluble binder.

[Description of Drawings] The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which: Fig. 1 is a photograph illustrating the result of FE- SEM of the composition of the present invention.

Fig. 2 is a graph illustrating the result of X-ray diffraction (XRD) analysis of the composition of the present invention.

Fig. 3 is a graph illustrating the result of particle size analysis (PSA) of the composition of the present invention. Fig. 4 is a photograph illustrating the thickness of a coating layer of the composition of the present invention.

Fig. 5 is a set of photographs illustrating the primary contact angle and the contact angle after 2000 hours of accelerated weathering test with the composition of the present invention.

Fig. 6 is a graph illustrating the maximum output power of the solar cell module coated with the composition of the present invention.

Fig. 7 is a graph illustrating the light transmittance of the solar cell module protecting glass coated with the composition of the present invention.

[Best Mode]

Practical and presently preferred embodiments of the present invention are illustrative as shown in the following Examples.

However, it will be appreciated that those skilled in the art, on consideration of this disclosure, may make modifications and improvements within the spirit and scope of the present invention.

Example 1: Hydrothermal synthesis

63 g of pure water was added to 400 g of tetratitanium isopropoxide (TTIP) , one of the titanium compounds, followed by hydrolysis. 6 L of 95% ethylalcohol and 25 g of HNO₃

(67%) were added thereto, and rpm of the stirrer was set at

1000 and the temperature was regulated as follows.

The temperature was raised to 150^°C for one hour and hydrothermal synthesis was performed at 150^°C for 2 hours.

Then, the temperature was lowered to room temperature and 1% white titanium oxide dispersion sol was obtained through an outlet. The pre'ssure in the vessel at 150^°C was 10 - 15 a. p.

Example 2: Aqueous synthesis

To synthesize aqueous sol, 2 Kg of pure water, 200 g of TTIP, one of the titanium compounds, and 65 g of acetyl acetone were added into a 5 L reactor, followed by reaction for 30 minutes with stirring. Temperature was raised to 90°C by using heating mantle and hot plate. The temperature was maintained at 90 ^°C for 2 hours and then 9.8 g of HNO₃ was added, followed by stirring for 2 hours. The reactant was passive-cooled for 12 hours with stirring to give yellow aqueous sol .

Example 3: Hydrothermal synthesis + aqueous synthesis

The compounds obtained in Example 1 and Example 2 were mixed at the ratio of 50:50 (weight ratio) to give the photocatalyst sol of the present invention.

Example 4 : Synthesis of water soluble binder

To synthesize a water soluble binder, 1.2 kg of pure water (pH was regulated as 4 by using nitric acid) was added into a 5 L reactor and 0.3 kg of a silicate compound

(tetramethylorthosilicate, TMOS) was dropped thereto, followed by stirring for 30 minutes. Then, 0.5 kg of 2- butoxyethanol was added thereto, which was stirred at 500 rpm for 2 hours at 70^°C to synthesize the sol of the present invention.

Example 5: Synthesis of a solution for protecting solar cell module

The compound of Example 3, the compound of Example 4 and ethyl alcohol were mixed at the ratio of 20:20:60 (weight ratio) to give the composition of the present invention. The physical properties of the composition were tested as follows.

[Physical property test]

The primary diameter of the composition was measured by scanning electron microscopy (SEM) . Fig. 1 is a photograph illustrating the result of SEM of the composition of the present invention. As a result, the primary diameter was confirmed to be 10 - 20 nm.

X-ray diffractometer (XRD) was used to investigate crystallinity and granularity, and the results are shown in Fig. 2.

The secondary diameter was measured by particle size analyzer (PSA) and the results are shown in Fig. 3. As a result, the secondary diameter was confirmed to be 150 nm.

The composition of the present invention was spray- coated on the solar cell module, and then the thickness was measured by FE-SEM. The results are shown in Fig. 4.

[Accelerated weathering test]

After coating the solar cell module with the composition of the present invention, indoor accelerated test using QUV (Accelerated weathering meter, Q-Panel, USA) was performed for 2000 hours, in addition to outdoor exposure test.

As a result, even after 2000 hours, peeling or blistering was not observed on the surface and hydrophilicity was still excellent. Fig. 5 is a set of photographs showing the contact angles measured 2000 hours later (right: primary contact angle, left: contact angle after 2000 hours).

[Field test] In the present invention, electrical and optical characteristics of the solar cell module coated with the composition of the present invention were investigated according to environmental changes. The solar cell module was exposed outside and maximum output power over the environmental changes was investigated.

Solar cell module was exposed outside for 100 days. During the period, maximum output power of the module was measured for 4 times. When the conventional glass was used, output power reduction was observed over the time, and the final output power was 4.5% decreased from the early output power. When the module was coated with the composition of the present invention, the output power was decreased 0.4% at average. And the results are shown in Fig. 6.

Contamination on the surface of the solar cell module was investigated by the naked eye and light transmittance test. When the conventional glass was used, high density of contaminants and dense coagulation were observed. In addition, when the conventional glass was used, light transmittance was 3.5% reduced from the primary light transmittance. In the meantime, when the glass coated with the composition of the present invention was used, the decrease rate was approximately 0.8%, which was 1/4 of the decrease rate of when the conventional glass was used. The results are shown in Fig. 7.

From the above physical property test and field test, the composition sol of the present invention prepared by mixing the compounds obtained from hydrothermal synthesis and aqueous synthesis and a water-soluble binder was confirmed to have excellent crystallinity and photocatalytic activity. Moreover, the composition sol of the present invention had so excellent dispersibility that it can be effectively layered on a substrate for coating.

Claims

[CLAIMS]

[Claim l]

A manufacturing method of a composition for protecting solar cell module comprising the following steps: hydrolyzing a titanium compound with water and adding alcohol and acid thereto, followed by hydrothermal synthesis to grow crystals; mixing the titanium compound and an organic solvent with water and raising temperature, and adding acid thereto, followed by aqueous synthesis to improve dispersibility; mixing each compound prepared by the above hydrothermal synthesis and aqueous synthesis to give photocatalyst sol; synthesizing a water soluble silicate binder compound by hydrolyzing silicate compound with excessive water; and mixing the photocatalyst sol, the water soluble binder compound and alcohol altogether.

[Claim 2]

The manufacturing method of a composition for protecting solar cell module according to claim 1, wherein the titanium compound is selected from the group consisting of tetratitanium isopropoxide, titanium alkoxide, titanium chloride, titanium nitrate, titanium sulfate and titanium aminooxalate .

[Claim 3]

The manufacturing method of a composition for protecting solar cell module according to claim 1, wherein the alcohol is methanol, ethanol or isopropyl alcohol, and the silicate compound is methyl silicate or ethyl silicate.

[Claim 4] The manufacturing method of a composition for protecting solar cell module according to claim 1, wherein the amount of water added for the hydrolysis of the binder compound is 50 - 70 weight%.

[Claim 5]

The manufacturing method of a composition for protecting solar cell module according to claim 1, wherein the content of the titanium oxide in the composition of the present invention is 0.5 - 5 weight% .

[Claim 6]

The manufacturing method of a composition for protecting solar cell module according to claim 1, wherein the solid content of the water-soluble silicate compound in the composition of the present invention is 5 - 20 weight% .