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액정 디스플레이 블랙 매트릭스 용 프탈로시아닌 염료 및

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Authors
이우성
Advisor
김재필
Major
공과대학 재료공학부
Issue Date
2014-02
Publisher
서울대학교 대학원
Keywords
Liquid crystal displayBlack MatrixdyesPhthalocyanineDielectric constantLight absorptionSolubilityThermal stabilityLight AbsorptionDye-sensitized solar cellsPhenoxazine dyesFive-membered heterocyclic bridgesEthoxyphenyl substitutionDihedral angleDye adsorptionDi-anchorN-substituentDihedral angleDye adsorption
Description
학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2014. 2. 김재필.
Abstract
The most frequently used material for black matrix is carbon black, which has advantages of high thermal stability and high light absorption. However, black matrices fabricated with carbon black have high dielectric constants, causing electrical signal transduction errors on thin film transistors. To avoid this problem, organic pigment BMs with a low dielectric constant can be used, but their low spectral properties due to the lower molar extinction coefficient of organic pigments have limited their applications.
In general, dyes have much lower dielectric constants compared with carbon black, and show much higher light absorption properties than organic pigments. Thus, if dyes are used for the manufacture of the black matrix, the high dielectric constant and low light absorption of conventional black matrices can be overcome. On the other hand, dyes generally have low thermal stability compared to carbon black and organic pigments. Therefore, the dyes for black matrix need to be structurally stable. They also should have good solubility in industrial solvents, such as propylene glycol methyl ether acetate and cyclohexanone. In addition, as dyes generally have sharp absorption ranges, dye-based black matrices need to be fabricated by mixing red, green and blue dyes, or cyan, magenta and yellow dyes, as well as by mixing dyes and carbon black..
In this study, green metal-free phthalocyanine dyes with high thermal stability and high solubility were designed. Three phthalocyanine dyes were synthesized by introducing substituents including alkyl or alkoxy groups to the peripheral position of the phthalocyanine rings, and their spectral properties, solubilities and thermal stabilities were measured. In addition, dye-based black matrices were fabricated and their optical and dielectric properties were examined.
The metal-free phthalocyanine dyes showed the increase in solubility due to bulky functional substituents at the peripheral positions of them. In addition, the dyes including terminal alkoxy groups showed suitable thermal stability for commercial use due to terminal alkoxy groups are stable at postbaking temperature. Since all dyes had high molar extinction coefficients, dye-based black matrices absorbed light in the visible region with the small amounts of the dyes. The dielectric constants of the black matrices containing more than 30wt% of dyes were significantly lower than that of the black matrix prepared with carbon black only.
Furthermore, greenish zinc phthalocyanine dyes and reddish perylene dyes were synthesized and employed to fabricate black matrices with low dielectric constant and light absorption in the whole visible region. The spectral and thermal properties and solubility of the prepared dyes were investigated, and optical, thermal and dielectric properties of the dye-based black matrices were examined. For further investigation of surface morphology of the black matrix films, dye-based black matrices were probed by field emission scanning electron microscopy and atomic force microscopy.
The dye-based black matrix showed the high thermal stability due to the rigid molecular structures of the dyes. In addition, due to the low dielectric characteristics of the dye, the dielectric constants of the dye-based black matrices were significantly lower than that of the black matrix prepared with carbon black only. However, the low solubility of the dyes in industrial solvents and dye aggregations in the baking process limited the input of the dye in the black matrix resist, resulting in low light absorption of the dye-based black matrix.
Dye-sensitized solar cells have attracted considerable attention as promising solar devices and the Ru complex dyes typical used as sensitizers in dye-sensitized solar cells have shown high electronic conversion efficiencies of over 11% with good stability. However, high production cost and difficulties in purification of Ru complex dyes have limited their development for large-scale applications. Recently, more attention has been paid to sensitizers without Ru (metal-free organic dyes and organometallic dyes) due to their lower cost, easier modification and purification, high molar extinction coefficient, and environmental friendliness.
Phenoxazine-based sensitizers have exhibited higher conversion efficiencies than triphenylamine and phenothiazine-based sensitizers, which are structurally similar. This is because phenoxazine-based sensitizers, with electron-rich nitrogen and oxygen heteroatoms, have stronger electron-donating ability than triphenylamine and phenothiazine-based sensitizers. phenoxazine-based sensitizers also show sufficient electrochemical properties for use in dye-sensitized solar cells. However, despite their potential for application to dye-sensitized solar cells, phenoxazine-based sensitizers have not been studied extensively.
In this research, to study effects of conjugated bridges with a phenoxazine moiety on photovoltaic performance, five-membered heterocyclic rings were introduced as a conjugated bridge unit to phenoxazine molecules. Furthermore, to improve the donating power and molar extinction coefficient, an ethoxy phenyl ring was substituted in the 7 position of the phenoxazine -furan dye as an additional donor. Based on these strategies, three organic dyes were synthesized and the photophysical, electrochemical, and photovoltaic properties of the solar cells based on these dyes were investigated.
The introduced heterocyclic bridge units furan and thiophene improved the short-circuit current due to the red-shifted absorption spectra of the dyes. The ethoxyphenyl ring introduced to the phenoxazine moiety as an additional donor broadened the spectrum of the dye, while the reduced adsorption of the dye caused by its non-planar structure limited the enhancement of the short-circuit current. As a result, among the synthesized dyes, the one with furan as a bridge unit showed the best overall conversion efficiency of 5.26%.
In addition, to study the effects of the number of anchoring groups and N-substitution on the performance of phenoxazine dyes in dye-sensitized solar cells, cyanoacrylic acid as an additional anchoring group was introduced to the phenoxazine for efficient electron extraction from the donor part, and an N-methoxyphenyl unit was added to suppress dye aggregation. Based on these strategies, four phenoxazine derivatives were synthesized and the photophysical, electrochemical and photovoltaic properties of the solar cells based on these dyes were investigated.
The additional cyanoacrylic acid acceptor improved the short-circuit current because it widened the absorption ranges of the dyes, although it also increased the recombination rate. The N-methoxyphenyl unit decrease charge recombinations, resulting in higher open-circuit voltage. However, the bulky substituent decreased the amount of dye absorbed on the TiO2. As a result, the fabricated cells with the four dyes exhibited similar overall conversion efficiencies and, of these cells, the solar cell based on the N-4-methoxyphenyl mono-cyanoacrylate substituted dye showed the highest conversion efficiency of 5.09%.
Language
Korean
URI
https://hdl.handle.net/10371/117941
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Materials Science and Engineering (재료공학부)Theses (Ph.D. / Sc.D._재료공학부)
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