Sim Bum Yuk

Influence of solvent and bridge structure in alkylthio-substituted triphenylamine dyes on the photovoltaic properties of dye-sensitized solar cells.

Three new triphenylamine dyes that contain alkylthio-substituted thiophenes with a low bandgap as a π-conjugated bridge unit were designed and synthesized for organic dye-sensitized solar cells (DSSCs). The effects of the structural differences in terms of the position, number, and shape of the alkylthio substituents in the thiophene bridge on the photophysical properties of the dye and the photovoltaic performance of the DSSC were investigated. The introduction of an alkylthio substituent at the 3-position of thiophene led to a decrease in the degree of redshift and the value of the molar extinction coefficient of the charge-transfer band, and the substituent with a bridged structure led to a larger redshift than that of the open-chain structure. The introduction of bulky and hydrophobic side chains decreased the short-circuit photocurrent (J(sc)), which was caused by the reduced amount of dye adsorbed on TiO(2). This resulted in a decrease in the overall conversion efficiency (η), even though it could improve the open-circuit voltage (V(oc)) due to the retardation of charge recombination. Furthermore, the change in solvents for TiO(2) sensitization had a critical effect on the performance of the resulting DSSCs due to the different amounts of dye adsorbed. Based on the optimized dye bath and molecular structure, the ethylene dithio-substituted dye (ATT3) showed a prominent solar-to-electricity conversion efficiency of 5.20%.

Synthesis and characterization of bay-substituted perylene dyes for LCD black matrix of low dielectric constant

Organic dyes with low electrical conductivity have recently been suggested as replacements for Cr/CrOx and carbon black in developing black matrices with low dielectric constants for liquid crystal displays (LCDs). Two perylene diimide dyes with broad absorption spectra were synthesized, and dye-type, hybrid-type and carbon black-type black matrices were fabricated using one of the dyes. Donating groups were substituted on the bay positions of the dyes by C–N coupling to enhance their solubility in propylene glycol methyl ether acetate, one of the most widely used industrial solvents in the LCD manufacturing processes. The thermal and spectral properties of the dyes were studied by thermogravimetric analysis and UV–Visible spectroscopy. Furthermore, the thermal, optical and dielectric properties of the black matrices were examined by color spectroscopy, optical density measurement and impedance analysis. The hybrid-type black matrix showed promising results with a low dielectric constant, low transmittance spectrum and high thermal stability.

Synthesis and characteristics of metal-phthalocyanines tetra-substituted at non-peripheral (α) or peripheral (β) positions, and their applications in LCD color filters

Four metal-phthalocyanine dyes were synthesized to evaluate the variation of their properties with both the position of the substituents and the type of metal used for coordination. The substituent, ethyl 4-hydroxy-3-methoxybenzoate, was introduced at the non-peripheral (α) or the peripheral (β) position in order to improve the solubility of the phthalocyanine. Cu and Zn were chosen as coordination metals, both to increase thermal stability and to fine-tune the color of the complex. The resulting complexes were highly soluble in a range of organic solvents as well as industrial solvents, such as di(propylene glycol) methyl ether acetate, diethylene glycol monobutyl ether acetate, and propylene glycol methyl ether acetate. The solubility of the dyes substituted at the α-position was higher than that of β-substituted dyes. Structural analyses of the substituted phthalonitriles were achieved using 1H and 13C NMR spectroscopy, and high-resolution mass spectrometry. The structures of the dyes were confirmed by MALDI-TOF spectroscopy and FT-IR spectrophotometry. The optical properties and thermal stabilities of the dyes were estimated by UV–Vis spectrophotometry and thermogravimetric analysis. The synthesized dyes were cyan in color, and thus could be successfully applied in six-primary-color (RGBCMY) liquid crystal display (LCD) color filters in order to improve the color gamut. Dye-based color filters showing adequate optical spectra for LCD cyan color filters were manufactured. Appropriate compensating dyes were also required in order to cut off undesirable transmittance peaks.

Simple modification of basic dyes with bulky & symmetric WCAs for improving their solubilities in organic solvents without color change

A simple and easy solubility enhancement of basic dyes was performed with bulky and symmetric weakly coordinating anions (WCAs). The WCAs decreased the ionic character of the dyes by broadening the partial charge distribution and causing a screening effect on the ionic bonding. This new modification with WCAs has advantages in that it has no influence on the optical properties of the dyes. The solubilities of unmodified and modified dyes were tested in several organic solvents. X-ray powder diffraction patterns of the dyes were measured. Color films were prepared with the dyes and their color loci were analyzed to evaluate the optical properties. By the modification with WCAs, commercial basic dyes showed sufficient solubilities for be applied to various applications while preserving their superior optical properties.