Coating compositions comprising polyorgano-silsesquioxane and a wavelength converting agent, and a wavelength converting sheet using the same

Abstract

The present invention relates to a coating composition having excellent wavelength conversion efficiency and a wavelength converting thin film/sheet prepared using the same. The coating composition of the present disclosure includes 1 to 60 wt % of polyorgano-silsesquioxane, 0.0001 to 30.0 wt % of a wavelength converting agent, and a solvent, and exhibits a transmittance of 70% or more as compared to that of an aqueous solution. A wavelength converting thin film/sheet prepared by using the coating composition has not only excellent photoluminescence, thermal resistance, and light-fastness, but also moisture and oxygen permeability is low, and the visible light transmittance thereof is 70% or more as compared to that of the air, and when patterning is added, the photoluminescence intensity of sheet is at least two-fold higher than that of a non-patterned sheet. Therefore, the coating composition of the present invention may be conveniently used in the preparation of a wavelength converting thin film/sheet, and feasibly applied to the preparation of a solar cell in an efficient manner.

Claims

1. A method for preparing a wavelength converting sheet, comprising the steps of: (a) applying the following coating composition on a substrate, wherein the coating composition comprises 1.0 to 60 wt % of polyorgano-silsesquioxane represented by the following Formula 1, 0.0001 to 30 wt % of a wavelength converting agent, and a solvent: ##STR00007## wherein in the Formula 1, R.sub.1 and R.sub.2 are independently selected from the group consisting of a C.sub.1-C.sub.10 straight chain or branched chain alkyl group, a vinyl group, a C.sub.6-C.sub.10 aryl group, a C.sub.7-C.sub.16 aralkyl group, a C.sub.7-C.sub.16 alkaryl group, a C.sub.3-C.sub.15 cycloalkyl group, a C.sub.4-C.sub.20 alkylcycloalkyl group, a methacrylate group, an acrylate group and an epoxy group, wherein the polyorgano-silsesquioxane has a number average molecular weight in a range of 10.sup.2 to 10.sup.6, and wherein the ratio of m to n is in a range of 6:4, and m and n are an integer of 1 to 10,000; and (b) curing the applied substrate; and (c) applying a polyorgano-silsesquioxane protective layer.

2. The method of claim 1, wherein the substrate comprises plastic, stainless steel, aluminum, glass, quartz, a solar cell, an LED chip or a fiber.

3. The method of claim 1, wherein the sheet has a visible light transmittance of 70% or more compared to that of the air.

4. The method of claim 1, further comprising patterning a surface of the prepared sheet.

5. A wavelength converting sheet prepared according to the method of claim 1.

6. The sheet of claim 5, wherein the sheet is a patterned sheet and has at least two-fold higher photoluminescence intensity as compared to that of a non-patterned sheet.

7. A solar cell comprising the wavelength converting sheet of claim 5.

8. A method for preparing a solar cell, comprising the steps of: (a) preparing a solar cell; and (b) applying the wavelength converting sheet of claim 5 on at least one surface of the solar cell to form a wavelength converting layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view illustrating a manner in which a wavelength converting agent (M) is coordinated to a ladder-like polyorgano-silsesquioxane. Upper panel, a coordinate bond through an end silica SiOH group; and lower panel, a coordinate bond through functional groups (R).

(2) FIG. 2 is a schematic view illustrating a preparation method of a wavelength converting sheet (thin film) according to the present invention.

(3) FIGS. 3a to 3f are each result showing photoluminescence spectra of the coating compositions prepared in Examples 1 to 20 of the present invention.

(4) FIG. 4 is a result showing (a) a photograph of a coating composition in Example 5, and (b) a photograph of a wavelength converting sheet prepared using the same under ultraviolet (UV) light.

(5) FIG. 5 represents (a) a photograph of a pattern-less wavelength converting sheet in Example 21 and (b) a photograph of a patterned wavelength converting sheet in Example 22 under UV light, and is (c) a result measuring the photoluminescence spectra thereof.

(6) FIG. 6 is a SEM photograph of each lateral face of (a) a pattern-less wavelength converting sheet in Example 21 and (b) a patterned wavelength converting sheet in Example 22. Scale bar=500 nm.

(7) FIG. 7 is a front SEM photograph of the photonic crystallized wavelength converting sheet in Example 23. Scale bar=500 nm.

(8) FIG. 8 is a result of photoluminescence spectra comparing a light emission between the wavelength converting sheets formed with the coating compositions of Examples 9 and 16 and those prepared in Comparative Examples 1 and 2.

(9) FIG. 9 is a result of photoluminescence spectra comparing a light emission between the wavelength converting sheet in Example 5 and the wavelength converting sheets prepared in Comparative Examples 3 and 4.

(10) FIG. 10 is a .sup.1H-NMR analysis result using the coating composition of polyorgano-silsesquioxane (a), the coating composition prepared in Example 14(b) or Example 13(c).

DETAILED DESCRIPTION OF THE DISCLOSURE

(11) Hereinafter, the present invention will now be described in further detail by examples. It would be obvious to those skilled in the art that these examples are intended to be more concretely illustrative and the scope of the present invention as set forth in the appended claims is not limited to or by the examples.

EXAMPLE

Examples 1 to 20

Preparation of Coating Composition

(12) After 0.8 g of polyorgano-silsesquioxane was added to a glass container, and a wavelength converting agent, an additive, and a solvent (hexane, tetrahydrofuran (referred to as THF), chloroform, or toluene) were introduced into the container as in the composition shown in Table 1, the container was sealed and subjected to ultrasonic treatment in an ultrasonic bath until a uniform solution was obtained, resulting in a coating composition.

(13) TABLE-US-00001 TABLE 1 Composition of Coating Solution Transmittance (%) of Coating Wavelength Wavelength Solution converting converting (Visible light agent 1 agent 2 Additive (g) Solvent region) Example 1 0.0005 g of 3.2 g of THF 98.8 Coumarin 6 Example 2 0.001 g of BASF 3.2 g of THF 99.0 Lumogen V570 Example 3 0.001 g of Poly 3.2 g of THF 92.2 Coumarin Example 4 0.0005 g of 0.001 g of BASF 3.2 g of THF 99.0 Coumarin 6 Lumogen V570 Example 5 0.001 g of CdSe 3.2 g of THF 99.8 490 nm and 0.1 g of semiconductor Chloroform nanocrystals Example 6 0.001 g of CdSe 3.2 g of THF 99.7 620 nm and 0.1 g of semiconductor Hexane nanocrystals Example 7 0.001 g of 3.2 g of THF 99.7 CuInS/ZnS 570 nm semiconductor nanocrystals Example 8 0.0005 g of 0.001 g of CdSe 3.2 g of THF 99.0 Coumarin 6 490 nm and 0.1 g of semiconductor Chloroform nanocrystals Example 9 0.05 g of 3.2 g of THF 98.9 Eu(NO.sub.3).sub.35H.sub.2O Example 0.05 g of 3.2 g of THF 98.7 10 Tb(NO.sub.3).sub.36H.sub.2O Example 0.05 g of 0.05 g of 3.2 g of THF 99.4 11 Tb(NO.sub.3).sub.36H.sub.2O Eu(NO.sub.3).sub.35H.sub.2O and 0.600 g of Toluene Example 0.01 g of 3.2 g of THF 99.9 12 Zn(OAc).sub.2 Example 0.05 g of EuFOD 3.2 g of THF 99.5 13 Example 0.05 g of Tb(thd).sub.3 3.2 g of THF 99.4 14 Example 0.05 g of 0.0005 g of 3.2 g of THF 99.3 15 Eu(NO.sub.3).sub.35H.sub.2O Coumarin 6 Example 0.05 g of 0.001 g of BASF 3.2 g of THF 98.7 16 Eu(NO.sub.3).sub.35H.sub.2O Igracure Example 0.05 g of 0.01 g of gold 3.2 g of THF 98.5 17 Eu(NO.sub.3).sub.35H.sub.2O nanoparticles (10 nm) Example 0.05 g of Silica spherical 3.2 g of THF 93.4 18 Eu(NO.sub.3).sub.35H.sub.2O particles (100 nm) Example 0.05 g of 1.2 g of THF 98.1 19 Eu(NO.sub.3).sub.35H.sub.2O Example 0.05 g of 6.2 g of THF 99.3 20 Eu(NO.sub.3).sub.35H.sub.2O

(14) Each material used in Examples 1 to 20 is as follows:

(15) As polyorgano-silsesquioxane, a copolymer having a structure of the following Formula 2 (m:n=6:4) was synthesized as follows and used.

(16) (a) 3-Glycidoxypropyltrimethoxysilane (0.24 mol) and phenyltrimethoxysilane (0.16 mol) were mixed to prepare a monomer mixture. Additionally, an aqueous solution prepared by dissolving potassium carbonate (0.2 g) in distilled water (24 g) was mixed with HPLC-grade tetrahydrofuran (40 g) to prepared a water-containing mixture solvent.

(17) (b) A polymerization reaction was performed by adding the aforementioned mixture monomer solution to the water-containing mixture solvent in a dropwise manner while stirring, and terminated after the reaction was carried out at 25 C. for 14 days. In order to recover the polyorgano-silsesquioxane copolymer produced, extraction was performed by using a solvent, such as chloroform, methylene chloride, toluene, and xylene, which is capable of dissolving a polymer while not being mixed with water, and a purified copolymer was collected by drying the solvent from the extracted solution.

(18) ##STR00005##

(19) Coumarin 6 (product No. 442631; Aldrich) and Lumogen V570 (BASF) as an organic dye were purchased and used, and a polymer having a structure of the following Formula 3 as a poly coumarin was directly synthesized through an azide-alkyne click reaction to react a coumarin 6 with an alkyne group and a polystyrene with an azide in a DMF solvent using a Cu catalyst and a PMEDTA ligand, and used.

(20) ##STR00006##

(21) CdSe nanoparticles or CuInS/ZnS 570 nm luminescent nanoparticles were used as a semiconductor nanocrystal (or quantum dot), and the CdSe nanoparticles were purchased from Nanosquare INC. and used, and the CuInS/ZnS nanoparticles were directly synthesized and used.

(22) Terbium (III) tris(2,2,6,6-tetramethyl-3,5-heptanedionate (product No., 434051; Aldrich; hereinafter, referred to as Tb(thd).sub.3) and terbium (III) nitrate hydrate (product No., 74103; Alfa Aesar) were used as a supply source of terbium ions (Tb.sup.3+). Tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium (III) (product No., 33541; Alfa Aesar; hereinafter, referred to as Eu(FOD).sub.3) was used as a supply source of europium ions (Eu.sup.3+). Acetyl zinc (Zn(COOCH.sub.3).sub.2, Zn(OAc).sub.2) (Aldrich) was used as a supply source of zinc ions (Zn.sup.2+).

(23) Products having a purity of 99% or more from Daejung Chemical & Metals Co., Ltd. were used as hexane, tetrahydrofuran (THF), chloroform, and toluene.

(24) A photocurable agent Igracure (BASF) was used as an additive, and a nanoparticle colloidal solution having a particle diameter of 10 nm (product No., G1527; Sigma) was purchased as a metal particle additive, and used by substituting the solvent with hexane. One wt % of silica aqueous solution having a particle size of 100 nm was purchased from Polysciences, INC. as a spherical silica particle, and used by exchanging the solvent with ethanol.

(25) The photoluminescence spectra measured from the coating solution in Examples 1 to 18 were illustrated in FIGS. 3a to 3e. In the case of the coating solutions in Examples 19 and 20, photoluminescence spectra are measured as same as in Example 9, but a change in photoluminescence intensity was observed by varying the amount of solvent added (FIG. 3f).

Example 21

Preparation of Wavelength Converting Sheet

(26) A scotch tape (product No., 122A; 3M) was adhered to the edge of a glass substrate (a thickness of 1.0 mm; product manufactured by Knittel Glaser Inc.) with a size of 1 cm1 cm, and 200 l of the coating solution in Table 1 was dropped onto the glass substrate, and then uniformly applied using a blade (Dorco Corporation Ltd.). In order to remove the solvent from the coating solution, the thin film was disposed in a hood for 1 hour. The prepared transparent sheet was subjected to heat treatment at 150 C. in an oven for 1 hour to prepare a transparent sheet which had been completely cured. At this time, the curing of coating solution used with the BASF Igracure additive as in Example 16 could be facilitated within 10 min at room temperature under UV light using photocuring instead of thermal curing.

(27) All of the prepared sheets exhibited transparency, and as a representative example among them, photographs of a coating solution containing CdSe semiconductor quantum crystals in Example 5 and a transparent sheet prepared from the solution under UV light (UV lamp (Vilerber Lourmat Inc.), 365 nm) are illustrated in FIG. 4 (FIG. 4(a): the coating solution, FIG. 4(b): the wavelength converting sheet under UV light).

(28) In the case of the sheets prepared from the coating solutions in Examples 1 to 18, their thickness were about 300 to 500 m; in the case of the sheet prepared from the coating solution in Example 19, the thickness was about 600 to 1,000 m; and in the case of the sheet prepared from the coating solution in Example 20, the thickness was about 50 to 150 m.

Example 22

Surface-Patterning Process for Enhancing Light Emission of Wavelength Converting Sheet

(29) A scotch tape (product No., 122A; 3M) was adhered to the edge of a glass substrate (a thickness of 1.0 mm) with a size of 1 cm1 cm, and 200 l of the coating solution containing Eu(NO.sub.3).sub.3.5H.sub.2O in Example 9 among the coating solutions in Table 1 was dropped onto the glass substrate, and then uniformly applied using a blade. In order to remove the solvent from the coating solution, the thin film was disposed in a hood for 1 hour. A 1 cm1 cm PDMS stamp having a nanopattern was placed on the coating solution-applied surface and then the glass substrate was pressed with a mounting press so as to have a pressure of 510.sup.2 Pa, and subjected to heat treatment at 150 C. for 1 hour. After cooled to room temperature, the PDMS stamp was removed to obtain a patterned wavelength converting sheet. The coating agent in Example 9 was used to prepare the pattern-less wavelength converting sheet (a) in Example 21 and the patterned wavelength converting sheet in Example 22, and then these sheets were compared by illustrating the photographs thereof under UV light (UV lamp (Vilerber Lourmat Inc.), 365 nm) in FIGS. 5(a) and 5(b), respectively, and the photoluminescence spectra of these sheets are shown in FIG. 5(c). It was confirmed that the patterned wavelength converting sheet exhibited much more intense light emission than the pattern-less wavelength converting sheet as in FIG. 5(b). According to FIG. 5(c), the patterned sheet increased light emission at least 2.5-fold higher than the pattern-less sheet. An SEM image of the patterned wavelength converting sheet in Example 22 is represented in FIG. 6.

Example 23

Process of Forming Photonic Crystals for Enhancing Light Emission of Wavelength Converting Sheet

(30) In the same manner as in Example 18, 0.1 mL of a colloidal solution containing silica spherical particles (diameter of 100 nm, a 1 wt % ethanol solution; Polysciences INC.) was mixed with 4 mL of a coating solution including Eu(NO.sub.3).sub.3.5H.sub.2O, and the mixture was subjected to ultrasonic treatment. A scotch tape (Cat 122A) was adhered to the edge of a glass substrate (a thickness of 1.0 mm) with a size of 1 cm1 cm, and 200 l of the colloidal coating solution was dropped onto the glass substrate, and then naturally dried in a hood for 1 hour. In order to remove the solvent from the coating solution, the thin film was stored in a hood for 1 hour. The dried sheet was subjected to heat treatment at 150 C. in an oven for 1 hour to prepare a transparent photonic crystal sheet which had been completely cured. An SEM image of the photonic-crystallized wavelength converting sheet in Example 23 is illustrated in FIG. 7.

Comparative Example 1

Preparation of Dimethyl Silicone-Based Polymer (PDMS) Sheet Containing Eu(NO3)3.5H2O Wavelength Converting Agent

(31) A scotch tape (Cat 122A) was adhered to the edge of a glass substrate (a thickness of 1.0 mm) with a size of 1 cm1 cm, and 200 l of a coating solution mixing 16 g of a THF solvent, 4.0 g of a PDMS resin (Sylgard 184; Dow Corning Corporation), and 0.05 g of Eu(NO.sub.3).sub.3.5H.sub.2O was dropped onto the glass substrate, and then uniformly applied using a blade. The prepared transparent sheet was subjected to heat treatment at 150 C. in an oven for 1 hour to prepare a cured polymer wavelength converting sheet. The light emission of the prepared polymer sheet was compared to that of the wavelength converting sheet formed through thermal curing in Example 9 and the wavelength converting sheet formed through photo curing in Example 16, and the result was illustrated in FIG. 8.

Comparative Example 2

Preparation of Silica (SiO2) Sheet Containing Eu(NO3)3.5H2O Wavelength Converting Agent

(32) A scotch tape (Cat 122A) was adhered to the edge of a glass substrate (a thickness of 1.0 mm) with a size of 1 cm1 cm, and 200 l of a polysilazane coating solution mixing 16 g of a dibutyl ether solvent, 4.0 g of polysilazane (DNF Co., Ltd.), and 0.05 g of Eu(NO.sub.3).sub.3.5H.sub.2O was dropped onto the glass substrate, and then uniformly applied using a blade. The prepared transparent sheet was subjected to heat treatment at 150 C. in an oven for 1 hour to prepare a cured silica (SiO.sub.2) wavelength converting sheet. The light emission of the prepared silica sheet was compared to that of the wavelength converting sheet formed by Example 9, and the result was shown in FIG. 8. As illustrated in FIG. 8, it could be confirmed that a thin film formed by photocuring in Example 16 was excellent, and a thin film formed by thermal curing in Example 9 was far excellent as compared to those in Comparative Examples 1 and 2.

Comparative Example 3

Preparation of Dimethyl Silicone-Based Polymer (PDMS) Sheet Containing CdSe 490 nm Luminescent Nanoparticle Wavelength Converting Agent

(33) A scotch tape (Cat 122A) was adhered to the edge of a glass substrate (a thickness of 1.0 mm) with a size of 1 cm1 cm, and 200 l of a silicone-based polymer (PDMS) coating solution mixing 16 g of a THF solvent, 4.0 g of a PDMS resin (Sylgard 184; Dow Corning Corporation), and 0.001 g of CdSe luminescent nanoparticles (Nanosquare INC.) was dropped onto the glass substrate, and then uniformly applied using a blade. The prepared transparent sheet was subjected to heat treatment at 150 C. in an oven for 1 hour to prepare a cured polymer wavelength converting sheet. The light emission of the prepared polymer sheet of comparative Example 3 was compared to that of the wavelength converting sheet formed by Example 5, and then illustrated in FIG. 9.

Comparative Example 4

Preparation of Silica (SiO2) Sheet Containing CdSe 490 nm Luminescent Nanoparticle Wavelength Converting Agent

(34) A scotch tape (Cat 122A) was adhered to the edge of a glass substrate (a thickness of 1.0 mm) with a size of 1 cm1 cm, and 200 l of a silica coating solution mixing 16 g of a dibutyl ether solvent, 4.0 g of polysilazane (DNF Co., Ltd.), and 0.001 g of CdSe luminescent nanoparticles (Nanosquare INC.) was dropped onto the glass substrate, and then uniformly applied using a blade. The prepared transparent sheet was subjected to heat treatment at 150 C. in an oven for 1 hour to prepare a cured silica (SiO.sub.2) wavelength converting sheet. The light emission of the prepared silica sheet was compared to that of the wavelength converting sheet formed by Example 5, and illustrated in FIG. 9. As confirmed in FIG. 9, it could be seen that light emission of Example 5 was far excellent as compared to those of Comparative Examples 3 and 4.

(35) Experimental Result

(36) 1. Characteristics Evaluation of Coating Solution

(37) Hydrogen-Nuclear Magnetic Resonance (H-NMR) Spectrum of Coating Solution

(38) In order to investigate characteristics of a coating solution mixture, a coating solution (50 l) was mixed with a CDCl.sub.3 (99.80% D) NMR solvent (0.4 ml, Euriso top), and a hydrogen nuclear magnetic resonance (H-NMR) spectrum analysis was performed with a 400 MHz NMR device (Bruker Corporation). Representatively, the analysis results of the coating solutions in Examples 13 and 14 were compared to the analysis result of polyorgano-silsesquioxane such as Formula 2, and are illustrated in FIG. 10. Referring to FIG. 10(a), it could be seen that the epoxy functional group of Formula 2 appeared at 2.5 to 4.0 ppm, the alkyl group and the hydroxyl end group appeared at 0 to 2.0 ppm, and the phenyl functional group appeared at 7.0 to 8.0 ppm. In the case of the coating solutions in Examples 14 and 13, in which the Tb(thd).sub.3 wavelength converting agent and the EuFOD wavelength converting agent were mixed, respectively, as illustrated in FIGS. 10(b) and 10(c), it can be confirmed that the hydrogen-spectrum corresponding to polyorgano-silsesquioxane and the hydrogen spectrum corresponding to each wavelength converting agent appeared to be overlapped with each other (FIGS. 10(b) and (c)). In particular, it can be confirmed that an epoxy group of polyorgano-silsesquioxane corresponding to 2.5 to 4.0 ppm has a peak broadening phenomenon due to the interaction between the wavelength converting agents.

(39) Photoluminescence Spectrum of Coating Solution

(40) In order to confirm photoluminescence characteristics of a coating solution, the coating solution was placed into a 10 mm10 mm quartz cell, and a photoluminescence spectrum analysis was performed using a photoluminescence spectrometer (model No. LS50B; Perkin Elmer, Inc.). The analysis results of the coating solutions in Examples 1 to 20 were illustrated in corresponding order in FIG. 3 (FIGS. 3(a) to 3(f), respectively). At this time, an excitation light source in a region of 350 to 480 nm was used as a light source. From these results, it can be confirmed that different light emission spectra are obtained depending on the light emission characteristics of the contained wavelength converting agent.

(41) Transmittance of Coating Solution

(42) In order to analyze the transmittance of a coating solution, the coating solution was placed into a 10 mm10 mm quartz cell, and a transmission spectrum analysis was performed in a region of 500 to 700 nm using an UV-Vis spectrometer (model name, Cary 100; Varian, Inc.). The light transmittance result of the coating solution is illustrated in Table 1. The transmittance was expressed as a relative value based on a value of an aqueous solution (100% transmittance). Referring to Table 1, it can be confirmed that all the coating solutions according to Examples of the present invention have a transmittance of 90% or more in a visible light region of 500 to 700 nm. Representatively, a photograph of the transparent coating solution of Example 5 and a photograph of a transparent thin film forming a wavelength converting thin film from the coating solution of Example 5 according to Example 19 are illustrated in FIGS. 4(a) and 4(b), respectively.

(43) 2. Evaluation of Characteristics of Sheets

(44) Scanning Electron Microscope Images of Sheets

(45) SEM (Nova FE-SEM, 10 kV) images of the wavelength converting sheets formed according to Examples 21 to 23 are illustrated in FIGS. 6(a), 6(b), and 7, respectively.

(46) Photoluminescence Characteristics of Sheets

(47) In order to measure photoluminescence characteristics of a wavelength converting sheet, a thin film formed on a glass substrate with a size of 1 cm1 cm was placed into a solid sample holder of a photoluminescence spectrometer (Perkin Elmer, Inc., model name LS50B) to measure the photoluminescence spectrum. At this time, an excitation light source in a region of 350 to 480 nm was used as a light source. Representatively, FIG. 8 represents a comparison between photoluminescence characteristics of the wavelength converting sheets prepared from the coating solutions in Examples 9 and 16 and those of the sheets prepared by Comparative Examples 1 and 2, and FIG. 9 comparatively illustrates photoluminescence characteristics of the wavelength converting sheet prepared from the coating solution in Example 5, and the sheets in Comparative Examples 3 and 4.

(48) Although the specific part of the present disclosure has been described in detail, it is obvious to those skilled in the art that such a specific description is just a preferred embodiment and the scope of the present invention is not limited thereby. Therefore, the substantial scope of the present disclosure will be defined by the appended claims and equivalents thereof.